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  • General Chemistry  (19,432)
  • 1995-1999  (6,850)
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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2147-2156 
    ISSN: 1434-1948
    Keywords: Tetrapodal pentadentate ligand ; Ligand periphery ; Polydentate amine complex ; Nickel ; Podand ; Schiff base ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tetrapodal pentaamine ligand 2,6-bis(1′,3′-diamino-2′-methylprop-2′-yl)pyridine (1), which contains four equivalent primary amino groups, can be derivatised partly or completely by Schiff base condensation with suitable carbonyl compounds. The new ligands thus obtained are mononucleating, as shown by the X-ray crystal structures of their respective nickel(II) complexes. Reaction of 1 with 1 equiv. of salicylaldehyde and subsequent reduction allows the selective modification of one of the four sidearms. The resulting ligand 2 is hexadentate and uninegative in its nickel(II) complex {[(2)Ni]PF6} (3) with both the secondary amine and the phenoxide functionalities coordinated to the metal centre. The unreduced Schiff base form of the ligand, 4, does not form a complex with nickel(II) as readily, and only a small quantity of the mixed salt {[(4)Ni][(1)Ni(H2O)](Br)2(PF6)} (5)has been obtained. While the overall coordination of 4 resembles that of 2, there is considerably more strain in the appended chelate ring, due to the presence of the C=N double bond. Modification of one arm in 1 can also be achieved by condensation with 1 equiv. of acetylacetone, to give the new ligand 6 which, likewise, is hexadentate in its NiII complex {[(6)Ni](PF6)2} (7). In this case, however, the N/O-functional sidearm is not deprotonated. Rather, it is coordinated as the keto-imine tautomer, making 7 a rare example of a metal complex containing this structural fragment. Two-fold functionalisation of 1 is observed upon reaction with acetone, regardless of whether the ketone is present in stoichiometric amounts or in excess, to give the pentadentate ligand 8with two diagonally juxtaposed isopropylidene-imine units. The complex isolated with this ligand {[(8)Ni](PF6)2} (9) contains pentacoordinate NiII, the sixth coordination site being blocked by the rigidly positioned isopropylidene groups. When reacted with 4 equiv. of trans-cinnamaldehyde, all the primary amino groups in 1 condense to give the four-fold Schiff base 10, which acts as a pentadentate podand towards nickel(II). In this complex, {[(10)Ni(OH2)]Br2} (11), an aqua ligand completes the coordination octahedron. All ligands are stable towards hydrolysis when coordinated to the metal, despite the presence of alkyl-imine groups in some cases.
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2157-2166 
    ISSN: 1434-1948
    Keywords: Septadentate N5S2-ligand ; Dinuclear complexes ; Nickel ; Reactivity ; Redox chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coordination chemistry of a series of dinickel complexes of the new septadentate amine-thiolate ligand N,N′-bis[2-thio-3-aminomethyl-5-tert-butylbenzyl]diethylenetriamine, H29, has been investigated in the context of ligand binding and oxidation state changes. The complexes [Ni2(9)(L)][ClO4]2 (10), [Ni2(9)(Cl)][Cl] (11), [Ni2(9)(L)][BPh4]2 (12), and [Ni2(9)(NCS)][OH·OH2] (13) have central N2Ni(μ-SR)2NiN′3L cores [L = labile solvent molecule (10, 12), Cl- (11), and NCS- (13)] composed of dithiolate bridged planar NiN2S2 and six-coordinate NiN′3S2L units. This is demonstrated for 11 and 13 by crystal structure determinations and for 10 and 12 by UV/Vis spectroscopy and room temperature magnetic susceptibility measurements. Complexes 10, 11, or 12 readily add other co-ligands at the NiN′3S2L fragment by substitution of the solvent molecule L (10, 12) or the chloride substituent (11). The overall structure of the parent complexes is not affected by the substitution reactions. An electrochemical study has shown that complex 10 undergoes two successive one-electron oxidations at +0.88 and +0.41 V vs SCE. The oxidized species are not thermally stable, but electronic absorption spectra and EPR spectra are indicative of the presence of NiIII species.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2167-2172 
    ISSN: 1434-1948
    Keywords: Macrocyclic compounds ; Amine-Thiolate Donors ; Polynuclear Complexes ; Nickel ; Condensation reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel route to macrocyclic amine-thiophenolate ligands is described. The new, air-stable thiophenolate precursor 1,2-bis(4-tert-butyl-2,6-diformyl-phenylsulfanyl)ethane (4) is readily condensed with two equivalents of 1,2-ethanediamine or 1,3-propanediamine under medium to high dilution conditions to give 2 × 4 condensation products. The smaller 1 × 2 macrocyclic compounds are not produced under these conditions. Subsequent reduction with NaBH4 (reduction of imine groups) and Na/NH3 (reductive cleavage of aryl-alkylsulfides) provides the 36- and 40-membered amine-thiophenolate ligands H46a and H46b. The macrocyclic compounds are versatile ligands for the preparation of polynuclear transition metal complexes. With divalent nickel H46a forms the di- and tetranuclear complexes [Ni2(6a)] (7) and [Ni4(6a)][ClO4]4 (8). Reaction of 8 with four equivalents of NH4SCN yields the novel isothiocyanate complex [Ni4II(6a)(NCS)4]·10MeCN (9). The structure consists of well-separated molecules of the tetranuclear complex [NiII4(6a)(NCS)4] (Ci symmetry). Two symmetry-related binuclear [N2Ni(μ2-SR)2NiN4] fragments composed of thiolate-bridged distorted planar {N2S2Ni}- and distorted cis-octahedral {(SCN)2N2S2Ni} units reside within the cavity of the macrocycle. The intramolecular distance between the two binuclear units is 6.144(1) Å.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2173-2185 
    ISSN: 1434-1948
    Keywords: EPR spectroscopy ; Metallocenylboranes ; Organovanadium radicals ; Redox chemistry (CV) ; X-ray diffraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The paramagnetic complexes di(mesityl)([5]trovacenyl)borane (5·), (mesityl)di([5]trovacenyl)borane (6··), and tri([5]trovacenyl)borane (7···) were prepared from [5]trovacenyllithium, (η5-C7H7)V(η5-C5H4Li), and (Mes)2BF, (Mes)BF2, and BF3, respectively. The propeller-shaped species 5·, 6··, and 7··· were subjected to X-ray diffraction with the aim of possibly correlating the twist angles with intramolecular intermetallic communication. Cyclic voltammetry points to successive vanadium-centered oxidation processes and boron-centered reduction, a small redox splitting δE1/2[(2+/+), (+/0)] being observed for 6··. According to EPR spectroscopy, performed in fluid solution, the exchange interaction J in the diradical 6·· approaches the fast-exchange region and is attenuated significantly by quaternization at boron in [6··-nBu]-. Although EPR spectroscopy of the triradical 7··· also indicates an extensive exchange interaction, the exchange parameters, derived from spectral simulation, follow the gradation J(7···) ≈ 1/3 J(6··). The magnetic susceptibility of 6·· and 7··· follows the same trend. As expected, compound 7··· exhibits spin frustration because it contains three antiferromagnetically coupled S = 1/2 systems that are arranged in an equilateral triangle.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2187-2199 
    ISSN: 1434-1948
    Keywords: Ansa compounds ; Cp-derived chelate ligands ; Neopentane chemistry ; Spiro compounds ; Tripodal ligands ; Cyclopentadienyl compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The neopentane-derived functionalized oxetane O(CH2)2C(CH3)(CH2OMs), 1, reacts with indenyllithium (LiInd) or fluorenyllithium (LiFlu) to produce the derivatives O(CH2)2C(CH3)(CH2R) (R = indenyl, fluorenyl), 2. The oxetane ring of 2 undergoes nucleophilic ring-opening by reaction with LiPR′2 to give the chiral chelate ligands (HOCH2)(CH3)C(CH2R)(CH2PR′2) (R = indenyl, fluorenyl), 5. Nucleophilic ring-opening by LiInd or LiFlu is possible too, resulting in the functionalized ansa-Cp ligands (HOCH2)(CH3)C(CH2R)(CH2R′) (R, R′ = indenyl, fluorenyl), 12. Electrophilic ring-opening of 2 with HBr to give (HOCH2)(CH3)C(CH2R)(CH2Br) (R = indenyl, fluorenyl), 3, is also possible. The alcohol function of 3 may be activated directly, whereas activation of this group in 5 is only possible after BH3 protection of the phosphane function. The mesylates (MsOCH2)(CH3)C(CH2R)(CH2Br) (R = indenyl, fluorenyl), 4, undergo, under basic conditions, spiro cyclization to produce spirocyclobutane derivatives 9 with the α-carbons of the five-membered cycles acting as the spiro centres. Substitution of the mesylate group of 4 by PR2 nucleophiles is therefore not possible. Ansa-Cp derivative (MsOCH2)(CH3)C(CH2Ind)(CH2Flu), 12c also reacts with LiPPh2 with spiro cyclization to produce 9d, instead of giving the substitution product. Tripodal ligands (CH3)C(CH2R)(CHPPh2)2 (R = indenyl, fluorenyl), 11, are accessible by the reaction of (MsOCH2)(CH3)C(CH2PPh2)2 with LiInd or LiFlu. All compounds are fully characterized by the usual spectroscopic and analytical techniques including single-crystal X-ray analyses in several cases.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2201-2207 
    ISSN: 1434-1948
    Keywords: Carboxylate syn-anti ; N-centered tripodal ligand ; Manganese ; Imidazole ; Helicoïdal inorganic chiral chain ; Magnetism ; π-π interaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of an infinite inorganic chain consisting of MnII and an N-centered tripodal ligand N,N-(2-pyridylmethyl)[(1-methylimidazol-2-yl)-methyl]glycinate is presented. It exhibits a chiral helical structure with a pitch of two monomeric units (each monomeric unit containing one Mn atom). Each manganese is connected to its neighbor through a carboxylate bridge in a syn-anti geometry. Around each manganese center, two carboxylates bind in a cis geometry. This peculiar bridging geometry (syn-anticis) provides a broken-line chain, running in a zig-zag manner along the b axis of the P21 space group. The magnetic properties have been investigated. They show a pseudo-2D magnetic structure, with one major pathway along the chain and an inter-chain minor one. The intrachain coupling is a weak antiferromagnetic interaction (J/k = -0.25). This low value is entirely consistent with the geometry of the bridge. The interchain coupling is a weaker antiferromagnetic coupling (J′/k = -0.11) and could be mediated through π-π interactions between pyridine and imidazole from two adjacent helixes.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2221-2231 
    ISSN: 1434-1948
    Keywords: Calixarenes ; Inclusion compounds ; Imido Complexes ; Molybdenum ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses, spectroscopic properties, molecular structures, and bonding of novel calix[4]arene imido compounds are described. Treatment of M(NtBu)2(NHtBu)2Ia (M = Mo), Ib (M = W) or M(NMes)2Cl2(dme) IIa (M = Mo), IIb (M = W) (Mes = 2,4,6-Me3-C6H2) with p-tBu-calix[4]arene LH4 affords calix[4]arene metal complexes LM(NR) 1a, b (M = Mo, W; R = tBu) and 2a, b (M = Mo, W; R = Mes). Analytical and spectroscopic data are consistent with monomeric structures for 1 and 2, retaining a local C4v symmetry for the calix[4]arene metal fragment. These complexes are well-suited to bind small molecules like acetonitrile, tBu-isonitrile, or water within their macrocyclic pockets. The spectroscopic data of some inclusion compounds and the crystal structures of LMo(NtBu)(NCMe) 1a(NCMe), LW(NtBu)(OH2) 1b(OH2), LW(NtBu)(CNtBu) 1b(CNt Bu), LMo(NMes)(NCMe) 2a(NCMe), and LW(NMes)(NCMe) 2b(NCMe) are reported. All complexes contain a group VI metal imido [M=NR] moiety mounted on the phenoxide rim of the calix[4]arene ligand as well as an incorporated guest molecule within the cavity. Some insights into the structures of complexes of the type L′W(NR′) (L′ = p-H-calix[4]arene; R′ = H, Me) and into bonding in these compounds are provided by density functional theory, applying the B-P86 density functional and an all SVP basis set within the RI-J-DFT approximation. At least one π bond is of importance for calix[4]arene-metal bonding in these compounds. The metal-imido bond can be described as a triple bond. A geometrically optimized minimum structure of L′W(NMe) 4 shows a calix[4]arene ligand only slightly distorted from a local C4v symmetry and an almost linear tungsten-imido moiety.
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  • 8
    ISSN: 1434-1948
    Keywords: Arsonium salts ; Superacidic systems ; Structure elicidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of trimethylarsane in the superacidic systems hydrogen/fluoride antimony pentafluoride and hydrogen fluoride/arsenic pentafluoride leads to trimethylarsonium fluorometallates. These salts are stable up to 60 °C and 5 °C, respectively. Structures were successfully elucidated in the cases of trimethylarsonium undecafluorodiarsenate and trimethylarsonium hexafluoroantimonate. (CH3)3AsH+As2F11- crystallizes in the monoclinic space group P21/n with four formula units per unit cell with the dimensions a = 7.362(1), b = 12.589(1), c = 13.598(1) Å and β = 95.37(1)°. (CH3)3AsH+SbF6- crystallizes in the monoclinic space group P21/m with four formula units per unit cell with the dimensions a = 8.313(1), b = 8.855(1), c = 13.285(1) Å and β = 94.358(1)°.
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  • 9
    ISSN: 1434-1948
    Keywords: Molybdenum ; μ-Oxo ; Conformational equilibrium ; X-ray diffraction ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new thiocyanatomolybdenum(VI) dioxo-μ-oxo complex dimer bearing a 4,4′-di-tert-butyl-2,2′-bipyridine ligand (2) is shown to exist in the crystal cell unit as a meso (Mo-O-Mo angle of 180°) and d,l, pair (Mo-O-Mo angle of 155.7°). These conformers are in equilibrium in solution and have been observed clearly by 1H NMR spectroscopy.
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  • 10
    ISSN: 1434-1948
    Keywords: Macrocycles ; Lithium ; Fluorescence ; Cryptands ; Coordination ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three aza-cages with the anthracene-containing photoactive groups L1, L2, and L3 have been synthesized. All compounds are able to selectively encapsulate a lithium ion and solid complexes have been isolated. The formation equilibria have been investigated by UV/Vis and 1H, 13C and 7Li NMR spectroscopic techniques. The fluorescence emission of both free ligands and lithium complexes have been investigated. Results indicate that the CHEF (chelation enhancement of the fluorescence) effect obtained by lithium coordination exits although lower than that occurring upon full protonation.
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  • 11
    ISSN: 1434-1948
    Keywords: Copper ; Trinuclear complexes ; Formamidines ; Magnetism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three new copper(II) linear trinuclear compounds are reported, all of which were synthesized in-situ, with the general formula [Cu3(L)4](CF3SO3)2(Y)x, where L is the dehydronated ligand: N,N′-bis(pyridine-2-yl)formamidine (abbreviated as Hpdf), N,N′-bis(pyrimidine-2-yl)formamidine (abbreviated as Hpmf) and N,N′-bis(5-methylpyridine-2-yl)formamidine (abbreviated as Hmpdf), Y = EtOH or H2O and x = 0.5-1.5. The compounds were characterized by X-ray diffraction, IR, LF, and EPR spectroscopy and by magnetic susceptibility down to 4 K. The structure of the compound [Cu3(pmf)4](CF3SO3)2(H2O)1/2 was determined by X-ray crystallography; it was found to crystallise in the triclinic space group P-1 with a = 8.529(5), b = 15.760(5), c = 19.639(5) Å, α = 101.793(5), β = 101.263(5), γ = 102.389(5)°, Z = 2. The structure [Cu-Cu-Cu angle 174.96(11)°] consists of four nearly flat molecules of the ligand, which contribute to the propeller-type structure around the Cu-Cu-Cu axis. A strong antiferromagnetic interaction between the CuII ions is observed with calculated J values, based on the Hamiltonian H = -2J(S1·S2 + S2·S3) - 2J′·S1·S3, of -174(1) cm-1, -120(1) cm-1, and -167(1) cm-1 for the compounds studied with L = pdf, pmf, and mpdf, respectively. These values are in agreement with an S = 1/2 ground state below temperatures of 120-160 K.
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2277-2281 
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Nickel ; Carbyne complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The μ3-boryloxycarbyne complexes [{Fe(CO)3}3{μ3-COBCl{NtBu(SiMe3)}}2] (1) and [{(η5-C5H5)Ni}3{μ3-COBX(NR2)}μ3-CO] (2a: NR2 = NtBu(SiMe3), × = Cl; 2b: NR2 = N(SiMe3)2, × = Cl; 2c: NR2 = NMe2, × = BNMe2Cl) were obtained by reaction of the anionic complexes K2[{Fe(CO)3}3{μ3-CO}2] and K[{(η5-C5H5)Ni(CO)] with the corresponding chloroboranes Cl2BNR2 {NR2 = NtBu(SiMe3), N(SiMe3)2}, or 1,2-dichlorodiboranes(4) B2(NMe2)2Cl2, respectively. The products are formed by a nucleophilic attack of the CO oxygen atom at the boron centres with subsequent salt elimination. All compounds were characterized by IR and multinuclear NMR spectroscopy, and the structures of 1 and 2c in the solid state were determined by single-crystal X-ray diffraction studies.
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  • 13
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1271-1279 
    ISSN: 1434-1948
    Keywords: Chirality ; Dinuclear complexes ; Rhodium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dinuclear and polynuclear metal complexes with octahedral centers coordinated to di- or polydentate ligands are often obtained as complicated mixtures of various stereoisomers. Stereospecific synthesis of such species is therefore of high current interest. Chiral derivatives of pyridine can be used for this purpose. Dinuclear μ-chloro-bridged RhIII complexes with two didentate, cyclometalated thienylpyridine-type ligands at each metal center are formed stereoselectively when pinene groups are fused to the pyridine rings. The two octahedral RhIII centers have homochiral configurations, ΔΔ and ΛΛ. The heterochiral diastereomer ΔΛ is not observed. With (8R,10R)-2-(2′-thienyl)-4,5-pinenopyridine [Hth4,5-(R,R)ppy] the ΔΔ to ΛΛ ratio is 9:1 when the separation eluent contains NaCl. Modeling the ΛΛ and the ΔΛ isomers of the dinuclear species shows crowding of the pinene groups in both cases; however, the strain can be released by relatively small distortions only in the case of the ΛΛ isomer. NO3- cleaves the dichloro bridge, yielding the mononuclear species Δ[Rh(L2)2(NO3)] (2) in a completely stereoselective manner when NaCl is replaced by KNO3 in the eluent mixture. The molecular structure has been determined by X-ray structure analysis for both the ΔΔ and the mononuclear complex Δ[Rh(L2)2(NO3)] (2) in order to confirm the configuration at the metal center. 1H-NMR, 13C-NMR and CD spectra were measured and the latter shows that the CD activity is solely due to the chirality at the metal center.
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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1281-1289 
    ISSN: 1434-1948
    Keywords: Phosphaalkynes ; Dimerization mechanism ; Diphosphacyclobutenes ; Density functional theory ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dimerization of phosphaalkynes (R-C≡P, R = H, Me, tBu) without and with the presence of transition metal fragments, including CpCo (Cp = cyclopentadienyl) and COT-Ti (COT = cyclooctatetraene), has been probed using density functional theory calculations (B3LYP with different basis sets). MP2 and CCSD(T) calculations were also performed for the [H2C2P2] systems. In an attempt to address the exciting controversy and uncertainty about phosphaalkyne dimerization, a number of dimer formation mechanisms proposed in the literature have been examined. Some new and plausible intermediates have also been identified.
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  • 15
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1315-1324 
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; EHMO ; Vinylidene complexes ; Cobalt ; Rhodium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transformation of acetylene into vinylidene, as promoted by the metal fragment [(pp3)Co]+ [pp3 = P(CH2CH2PPh2)3], is unimolecular and features the hydride-acetylide species as an intermediate. The paper describes a detailed ab initio study of the reaction, in particular with regard to the step involving 1,3-H shift. The best computational results are obtained by mimicking the pp3 ligand with actual ethylenic chains rather than with single PH3 molecules. The keypoints along the two-step reaction path (π-acetylene, hydride-acetylide, and vinylidene complexes, as well as intermediate transition states) have been optimized for CoI and RhI derivatives at the MP2 level. For the fragment [(pp3)Co]+, the barrier associated with transformation of the hydride-acetylide intermediate to vinylidene (20.6 kcal/mol) is easier to surmount compared to that for reversion to the reactants (28.6 kcal/mol). The situation is reversed for the analogous RhI system, with the initial π-acetylene adduct being slightly more stable. Although higher in energy, the hydride-acetylide species is the experimentally detected product of the reaction of acetylene with the fragment [(pp3)Rh]+. The salient chemical aspects of the 1,3-H shift are discussed in terms of perturbation theory arguments. Parallel EHMO calculations, which have provided a relatively good consistency with the ab initio results, allow the proposal of an orbital rationale for the mode of migration of the hydride ligand along the substantially linear Co-Cα-Cβ grouping.
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  • 16
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1335-1342 
    ISSN: 1434-1948
    Keywords: Photolysis ; Alkynes ; Matrix isolation ; DFT ; Oxygenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photolytically-induced reactions of chromyl chloride with acetylene and but-2-yne (dimethylacetylene) in low-temperature argon matrices yield end-on ketene and dimethylketene complexes of O=CrCl2, respectively. The product formation probably results from an electrophilic attack of a Cr=O linkage on the C≡C triple bonds, leading to radical-like transition states or intermediates, which subsequently rearrange through 1,2-H or 1,2-methyl shifts. Consequently, allene is attacked at its central carbon and the allyl radical thus generated undergoes subsequent ring-closure to give a cyclopropanone complex of O=CrCl2.
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  • 17
    ISSN: 1434-1948
    Keywords: Copper chelates ; EPR spectroscopy ; Electronic structure ; Schiff base ligands ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of tetrahedrally distorted copper(II) complexes with thiolate and imine coordination were synthesized. Schiff bases derived from 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-thione and various diamines were used as tetradentate ligands to obtain tetrahedrally distorted metal chelates with [CuN2S2] complex units. Crystal structures of the complexes 1, 2, 5 and 6 and of ligand H25 have been determined by means of single-crystal X-ray structure analysis. The structure data show a strong influence of the diamine building blocks on the tetrahedral distortion of the copper(II) complexes. Results of Extended Hückel LCAO calculations correlate strongly with structural, electrochemical, UV/Vis- and EPR-spectroscopic features obtained experimentally. The calculations confirm for the whole complex series a strong delocalization of the frontier orbitals. The highest fully occupied molecular orbital shows a weak contribution, resulting from thiolate donor atoms, whereas the antibonding singly occupied molecular orbitals (SOMOs) are distributed between the copper(II) centre (ca. 35-40%) and the N2S2 donor set. The SOMO energy significantly lowers with increasing tetrahedral distortion of the coordination sphere. The influence of the tetrahedral distortion of copper(II) complexes on redox potentials, UV/Vis and EPR spectra is discussed.
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  • 18
    ISSN: 1434-1948
    Keywords: Half-sandwich complexes ; Molybdenum ; Optically active complexes ; Rhenium ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of (η5-PinCp*)Re(CO)3 [PinCp* = tetramethyl(pinanyl)cyclopentadienyl] is described. Successive substitution of two CO ligands by NO+ and PPh3 generates a 1:1 diastereomeric mixture of chiral-at-metal [(SRe)/(RRe)-(PinCp*)Re(CO)(NO)(PPh3)]BF4. The diastereomers are converted with sodium methoxide into the derivative “esters” (SRe)/(RRe)-(PinCp*)Re(COOCH3)(NO)(PPh3), and then with (+)-(R)-(1-naphthylethyl)amine to the “amides” (SRe)/(RRe)-(PinCp*)Re(NO)(PPh3)[CONHCH(CH3)C10H7] [(SRe)/(RRe) = 1:1]. Fractional crystallisation separates the (SRe) isomer with an optical purity of 〉 98%. The latter compound has been characterized by X-ray structure analysis. By treating the (SRe)-amide with CF3CO2H and NaBF4, (SRe)-(PinCp*)Re(CH3)(NO)(PPh3) can be generated. Protolysis of this compound with HBF4/Et2O in CD2Cl2 at -78 °C leads to the solvent-stabilized complex (SRe)-[(PinCp*)Re(NO)(PPh3)(ClCD2Cl)]+BF4-. The thermal and configurational stability of this chiral Lewis acid is investigated at various temperatures. The syntheses of [PinCp*RhCl2]2, PinCp*TiCl3 and PinCp*M(CO)2(NO) (M = Mo, W) are also described. Starting with PinCp*M(CO)2(NO), the relatively stable 16-VE complexes PinCp*MCl2(NO) and PinCp*W(CH2SiMe3)2(NO) are synthesized.
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  • 19
    ISSN: 1434-1948
    Keywords: 2,2′-Bipyridines ; Chelate complexes ; Hydrogen bonding ; π-π stacking ; Crystal structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new synthetic route for the synthesis of 5,5′-diamino-2,2-bipyridine (5) based on the coupling of 2-chloro-5-aminopyridine in the presence of NiCl2 × 6 H2O/PPh3/Zn in dimethylformamide is described. The reactions of the potentially ambidentate ligand 5 with salts of the transition metals Mn, Fe, Ni, Cu, Zn, Ag, and Cd gave a variety of 13 metal-ligand complexes depending on the anion, the crystallization conditions and the metal-to-ligand ratio. The complexes obtained were characterized by thermal analyses, NMR including 113Cd-NMR, IR, and for the iron complex 57Fe-Mößbauer spectroscopy. The structure of eight of the compounds was elucidated by X-ray crystallography. All of these metal complexes show a bipyridine-metal coordination. The amino functionality was never involved in metal coordination. The intermolecular arrangement is dictated by hydrogen bonding from the amino functionality and by π-π stacking of the bipyridine rings.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99078_s.pdf or from the author.
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  • 20
    ISSN: 1434-1948
    Keywords: Iron(III) ; Peroxo Complexes ; Kinetics ; Hydrogen Peroxide ; Catalase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new diiron complex [Fe2(tbpo){O2As(CH3)2}(CH3O)(CH3OH)](ClO4)3 · 5 CH3OH · 2 H2O (1) containing a (μ-alkoxo)(μ-dimethylarsinato)diiron(III) core was synthesized using the heptadentate ligand N,N,N′,N′-Tetrakis(2-benzimidazolylmethyl)-1,3-diamino-2-propanol (Htbpo). The complex was characterized structurally by X-ray crystallography. 1reproduces the coordination mode and the stoichiometry of the proposed purple acid phosphatase-arsenate inhibitor complex. More importantly, 1 is a good functional model for the activation of small molecules, since the solvent molecule in the coordination sphere of each iron ion can be substituted very easily by a small substrate molecule. This is confirmed by the comparatively high pH-dependent catalase-like activity of 1. In order to study the influence of the cacodylate bridge on the formation of the metastable adduct with hydrogen peroxide, the analogous hydroxo-bridged complex [Fe2(tbpo)(OH)(NO3)2](NO3)2 · CH3OH · 2 H2O (2) was employed. The reactions of 1and 2 with H2O2 were studied as a function of [H2O2], pH, temperature, and pressure, and the kinetic results including the activation parameters are reported. In the case of compound 2 the reaction proceeds in one step, and the observed first order rate constant, kobs, shows a linear dependence on the hydrogen peroxide concentration with a zero intercept. For complex 1 the kinetic traces could be fitted to two exponential functions. One of the observed pseudo-first-order rate constants, kobs1, exhibits a linear dependence on the hydrogen peroxide concentration with a zero intercept, whereas the other rate constant, kobs2, was independent of the hydrogen peroxide concentration. A mechanistic interpretation is presented.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99068_s.pdf or from the author.
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  • 21
    ISSN: 1434-1948
    Keywords: Ruthenium ; Coordination chemistry ; Paramagnetic complexes ; Magnetic properties ; Ion exchange ; Antitumor agents ; Colon tumors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Indazolium trans-tetrachlorobis(indazole)ruthenate(III) exhibits excellent results against different tumor models in vitro and in vivo. To improve the water solubility necessary for the introduction of this tumor-inhibiting compound into clinical trials, we synthesized the corresponding sodium salt in a two-step ion exchange via the tetramethylammonium salt. The sodium salt shows a 35-fold higher solubility in water relative to the indazolium salt. We also synthesized the n-butylammonium, n-octylammonium, and tetraphenylphosphonium salts, all of which showed improved solubility in organic solvents. The X-ray crystal structure of the latter could be solved, proving the trans configuration of the complex anion. In spite of the paramagnetic RuIII center an assignement of the coordinated indazole protons could be made with the help of a COSY experiment.
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  • 22
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2355-2368 
    ISSN: 1434-1948
    Keywords: Phosphane complexes ; Lithium ; Aminophosphanes ; Hydrazides ; (N-lithioamino)diorganophosphanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Butyllithium (nBuLi) deprotonates Ph2P-NHtBu in ether to give (Ph2P-NLitBu)2·OEt2. There is no Li···P interaction in this molecule. Three compounds of the type R′P(NLiR)2 have been obtained by lithiation of R′P(NHR)2, isolated as [BuP(NLitBu)2·OEt2]2, [PhP(NLiPh)2·OEt2]2 and [PhP(NLiPh)2]2. Reaction of nBuLi with MeP(NHiPr)2 in hexane/THF leads to [MeP{N(Li)iPr]2·THF}4 with an asymmetric cluster structure comprising one LiP3, three LiPN2, three LiP2N and one LiN3 cluster units. The molecular structures of these compounds as determined by X-ray structure analysis show that they are best depicted as N-lithioaminophosphanes and not as the isomeric P-lithioiminophosphoranes.
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  • 23
    ISSN: 1434-1948
    Keywords: Alkylation ; Carbonyl complexes ; Lewis acids ; Phosphaalkenes ; Protonation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of the carbonyl-functionalized phosphaalkenes RC(O)P=C(NMe2)2 [R = tBu (2a), Ph (2b)] with protic acids and alkylating reagents occurred at the two-coordinate phosphorus atom to give the phosphanyl-substituted carbocations 3a,b and 4a,b. In contrast, treatment with Me3SiOSO2CF3 resulted in attack at the oxygen atom by the silyl group, and the formation of [RC(OSiMe3)=PC(NMe2)2]SO3CF3 (5a,b). Similarly, the Lewis acids B(C6F5)3, Al(tBu)2Cl and AlMe3 were ligated to the oxygen atom of the carbonyl group. Two equivalents of GaMe3 were added to the oxygen and phosphorus atom of the phosphaalkene to yield the thermolabile complexes [RC(OGaMe3)=P(GaMe3)C(NMe2)2] (10a,b). In contrast, one molecule of InMe3 was bound to the phosphorus center of the phosphorus compound. Reaction of the phosphaalkenes with [Ni(CO)4], [Fe2(CO)9] or [{(Z)-cyclooctene}Cr(CO)5] also took place at the pnictogen atom, resulting in complexes of the type [RC(O)P{M(CO)n}C(NMe2)2] (R = tBu, Ph; M = Ni, n = 3; Fe, n = 4; Cr, n = 5). The chemical transformations reported here underline the versatile chemistry of phosphaalkenes and emphasize a relationship between carbonyl-functionalized phosphaalkenes and the well-investigated class of phosphorus ylides. X-ray structures of compounds 6b, 7b*, 10a, 11a and 12a are reported.
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  • 24
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2127-2134 
    ISSN: 1434-1948
    Keywords: Gallium ; Azides ; Chemical vapour deposition ; Gallium nitride ; Single source precursors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, properties and X-ray single crystal structure analysis of the intramolecularly adduct-stabilised organogallium bisazide (N3)2Ga[(CH2)3NMe2] (1), the mono azide (N3)Ga[(CH2)3NMe2]2 (2) and the trialkylamine adducts of triazidogallium of the type (N3)3Ga(NR3) (3a-d; R = alkyl) are reported. An unusual isomer 1b of compound 1 is described, which was obtained by slow cooling of the analytically pure neat liquid compound 1 to 0 °C. The new and unusual structure 1b can be regarded as a weak associate of dimers linked together by head-to-tail azide bridges. In contrast, compounds 2 and 3a-b (R = CH3, C2H5) are monomeric in the solid state. The suitability of the volatile compounds 1 and 2 as single source precursors to grow GaN thin films by chemical vapour deposition is compared, showing that preferentially oriented crystalline films can be obtained from compound 2 on sapphire substrates at 600-700 °C in vacuo (0.1 Pa). However the films have a grey rather than a transparent appearance, which is presumably due to N-deficiency owing to the lower N-content of the single molecule precursor 2 relative to 1.
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  • 25
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2135-2145 
    ISSN: 1434-1948
    Keywords: Density functional calculations ; Epoxidation ; Peroxo complexes ; Titanium ; Transition states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Epoxidation of olefins by TiIV peroxo and hydroperoxo (alkylperoxo) complexes was investigated using a hybrid DFT method (B3LYP). Reaction energies and activation barriers for direct oxygen transfer to ethylene as a model olefin were computed for various model complexes to compare the epoxidation activity of Ti(η2-O2) and TiOOR (R = H, CH3) moieties. The activity of complexes with a Ti(O2) peroxo group is shown to be essentially quenched when the coordination sphere of the complex is saturated by strongly basic (σ-donor) ligands. In contrast, the activity of a TiOOH functional group depends only weakly on the saturation of the coordination sphere of the Ti center. Substitution of methyl for hydrogen in a TiOOH group is found to slightly increase the activation barrier of epoxidation. The computational results give preference to reaction paths that involve TiOOR species. The factors governing the activity of Ti(O2) and TiOOR groups, in particular the effects of donor ligands, are discussed on the basis of a molecular orbital analysis.
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  • 26
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2289-2294 
    ISSN: 1434-1948
    Keywords: Intercalations ; Vanadyl phosphate ; Ethanol ; Hydration ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The course of the replacement of ethanol by water molecules in the VOPO4·2C2H5OH intercalate, and of water by ethanol in VOPO4·2H2O has been studied by X-ray diffraction and infrared and Raman spectroscopy. Formation of mixed phase VOPO4·C2H5OH·H2O was not observed. The shape of the kinetics curves indicates a transition of at least one reaction zone through the crystal. A delay in formation of the product in comparison with the decrease in the amount of starting material can be explained by the existence of non-diffracting advancing phase boundary. In a VOPO4/ethanol/water system, VOPO4·2C2H5OH is formed as the only product when the system contained more than 96 vol% of ethanol, whereas in the system with less than 94 vol% of ethanol only VOPO4·2H2O is present.
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  • 27
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2295-2299 
    ISSN: 1434-1948
    Keywords: Lewis acids ; Bismuth ; Aluminum ; Phosphorus ; Tin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dilithium salts of N-methyl-N′,N′′-bis(diisopropyl)- and -(trimethylsilyl)-diethylenetriamine 1a,b react with SnCl2 affording the corresponding stannylenes 2a,b in 60 and 80% yield, respectively. Compound 1b also reacts with BiCl3 to give the bismuth chloride 5 (90% yield). Derivatives 2b and 5 have a symmetrical bicyclic structure and are monomeric both in solution and in the solid state. When 2b is treated with BiCl3 or PCl3, an oxidation reaction leads to the hypercoordinated tin(IV) dichloride 3 (58% yield), or a transmetallation gives rise to the oniophosphane 4 (95% yield), respectively. Transmetalation reactions also occurred when 5 was treated with AlCl3, GaCl3 or SnCl2 affording the corresponding aluminum chloride 6 (81% yield), gallium chloride 7 (38% yield) or tin dichloride 3 (38% yield). The observed reactivity for 2 and 5 is compared to that reported for Veith's stannylene or bismuth chloride.
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  • 28
    ISSN: 1434-1948
    Keywords: Ruthenium ; Triazole ; Titanium ; Electron Transfer ; Sensitizers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes [Ru(dcb)2(L)] {L = 3-(2-hydroxyphenyl)-5-(pyridin-2-yl)-1,2,4-triazole (2-ppt), 3-(4-hydroxyphenyl)-5-(pyridin-2-yl)-1,2,4-triazole (4-ppt), 3,5-bis(pyrazin-2-yl)-1,2,4-triazole (bpzt), 3-(2-hydroxyphenyl)-5-(pyrazin-2-yl)-1,2,4-triazole (2-ppzt) and dcb = 4,4′-(CO2H)2-2,2′-bipyridine} have been synthesized, spectroscopically characterized and anchored to nanocrystalline TiO2 electrodes for the conversion of light into electricity in regenerative solar cells. The different efficiencies observed have been rationalized on the basis of an analytical expression relating the incident photon-to-current conversion efficiency (IPCE) to the kinetic parameters of the relevant electron transfer processes involved in the solar cell.
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  • 29
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1295-1299 
    ISSN: 1434-1948
    Keywords: Solid-state chemistry ; Structure elucidation ; Reactive flux syntheses ; Oxysulfides ; Niobium chalcogenides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new compounds K4Nb2S10O and Rb4Nb2S10O have been synthesized by the reaction of potassium or rubidium alkaline polychalcogenides with NbO2, Nb2O5, or mixtures of Nb and NbO. Their structures consist of discrete [Nb2Q11]4- anions (Q = O, S) built up of two face-sharing pentagonal bipyramids, which are connected via the alkali metal cations.
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  • 30
    ISSN: 1434-1948
    Keywords: Pyrazolato ligands ; Rhenium ; Group-11 metals ; Heterometallic complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By treating [(CO)3Re(Hpz)2(pz)] (Hpz = pyrazole) with [Cu(CH3CN)4]BF4, AgNO3, or [Au(tht)Cl] (tht = tetrahydrothiophene) in acetonitrile in the presence of Et3N, the corresponding trinuclear complexes {(CO)3Re(pz)3[M(CH3CN)]2} (1a-c) have been obtained. Treatment of complexes 1a-c with cyclohexyl isocyanide (c-C6H11NC) afforded the derivatives {(CO)3Re(pz)3[M(c-C6H11NC)]2} (2a-c). Complexes 2a-c have been characterized in solution by 1H-NMR spectroscopy and in the solid state by single-crystal X-ray diffraction analysis.
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  • 31
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1309-1313 
    ISSN: 1434-1948
    Keywords: Phthalocyanines ; Rhenium ; Nitrido(octa-n-alkylphthalocyaninato)rhenium compounds ; Nucleophilic additions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of nitrido(tetra-tert-butylphthalocyaninato)rhenium (1) with boron tribromide leading to (tBu4Pc)ReNBBr3 (4) and with acetone to give the imido complex (tBu4Pc)Re[NC(CH3)2CH2C(O)CH3]OH (2b) and its μ-oxo dimer 3 are reported. Starting from the corresponding 4,5-di-n-alkylphthalonitriles and ammonium perrhenate four soluble nitrido(octa-n-alkylphthalocyaninato)rhenium complexes 5-8 were synthesized. Nitrido(octa-n-pentylphthalocyaninato)rhenium (6) was treated with boron tribromide to afford [(C5H11)8Pc]ReNBBr3 (9).
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  • 32
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1325-1333 
    ISSN: 1434-1948
    Keywords: Platinum ; Palladium ; Platinum blues ; Naphthyridine complexes ; Trinuclear complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All three dinuclear complexes [Pd2(donp)2(bpy)2] (1) (H2donp = 1,8-naphthyridin-2,7-dione), [Pd2(H2nonp)2(bpy)2](ClO4)2 (2), and [Pt2(H2nonp)2(bpy)2](PF6)2 (3) (H3nonp = 7-amino-1,8-naphthyridin-2-one) exhibit the μ-1ĸN1:2ĸN8 bridging mode for their head/tail orientated naphthyridine ligands. Whereas 1 and 3 may be prepared by direct reaction of the dinucleating ligand with [MCl2(bpy)], formation of competing tripalladium(II) complexes must be avoided for 2 by employment of the precursor H2acnonp (7-acetamido-1,8-naphthyridin-2-one), which affords [H2nonp]- on cleavage of its original acetyl group. A mixture of the head/tail (4a) and head/head (4b) isomers of [Pd3(Hnonp)2(bpy)3](ClO4)2 is obtained when H3nonp is treated with [PdCl2(bpy)] and LiOH at room temperature for 2 d, followed by precipitation with LiClO4. Contrastingly exclusive formation of 4a is observed upon refluxing this reaction mixture for 3 d in aqueous solution. The [Hnonp]2- ligands exhibit a μ3-1ĸN1:2ĸN8:3ĸN7 bridging mode that leads to short Pd···Pd interactions of 2.781(2) and 2.775(2) Å. Similar metal-metal distances of 2.771(3) and 2.816(3) Å are observed in head/head-[Pt3(acnonp)(Hnonp)(bpy)3]Cl2 (5). An in situ 2e--oxidation (Ag+/Ag) of the [Pt3]6+ core in triplatinum(II) species such as 5 formed by the reaction of [PtCl2(bpy)] with H2acnonp allows the isolation of diamagnetic dark-brown head/head-[Pt3(Hnonp)2(NO3)(bpy)3](ClO4)2(NO3) (6) with an average oxidation state of Pt (2.67+). The Pt-Pt distances of 2.723(2) and 2.670(2) Å are markedly shorter than in 5.
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  • 33
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1343-1350 
    ISSN: 1434-1948
    Keywords: Indium ; O ligands ; N ligands ; C ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New heteroleptic indium compounds have been synthesized starting from indium(III) halides and hexamethyldisilazyllithium to form MeXInN(SiMe3)2 [X = Cl (1), Br (2)], and then subsequent alcoholysis to afford the molecules [ClMeIn(OtBu)]2 (3), [BrMeIn(OtBu)]2 (4), {ClMeIn[O(C6H4)OMe]}2 (5), {[(SiMe3)2N]MeIn(OtBu)}2 (6) and [MeIn(OtBu)2]2 (7). The molecular structures of molecules 3-7 have been obtained by single crystal X-ray diffraction studies. The structures of the compounds 3-7 are almost identical: 3-5 crystallize in the monoclinic crystal system with two dimeric molecules per unit cell in the space group P21/c, 6 crystallizes in the monoclinic space group C2/c with four molecules per unit cell, and compound 7 crystallizes in the triclinic crystal system with one dimeric molecule per unit cell in the space group P-1. The central centrosymmetric In2O2 ring, common to all the compounds, is achieved by two bridging oxygen atoms. Due to the additional coordination by an oxygen atom of the methoxy group, the coordination number of the metal center rises from 4 to “4+1” if the OtBu ligand (compounds 3, 4, 6, and 7) is exchanged for a methoxyphenol ligand (compound 5). In addition to the In2O2 ring the compound 5 possesses two annealed five-membered InO2C2 rings. The common indium methyl group of all compounds, which is transfered by an original route from the silicon to the indium atom, is used to compare structural and spectroscopic properties of the molecules, as there is a correlation between the In-C bond length and the chemical shift of the methyl group which depends on the ligand system used.
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  • 34
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1359-1366 
    ISSN: 1434-1948
    Keywords: Selenium ; Fluorine ; Multinuclear NMR ; Raman spectroscopy ; X-ray crystallography ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of perfluoroaryllithium RC6F4Li, where R = F or 4-CF3C6F4O, respectively, with selenium gives the known diselanes (RC6F4Se)2 (1a, 1b). Redox reactions of 1 with hydrogen peroxide result in the formation of the seleninic acids RC6F4SeOOH which crystallize as hydrates (2a, 2b); with mercury give the bis(arylseleno)mercuries (RC6F4Se)2Hg (3a, 3b); with sulfuryl chloride or bromine give the selenenyl chlorides (4a, 4b) or selenenyl bromides (5a, 5b). Selenenyl chlorides (4a, 4b) react with a variety of trimethylsilyl reagents Me3SiX (X = Br, CN, NMe2, NEt2) to form 5a, 5b; selenocyanates RC6F4SeCN (6a, 6b); selenenyl amides RC6F4SeNMe2 (7a, 7b) and RC6F4SeNEt2 (8a, 8b). A new synthetic route to diorgano selanes is developed by reaction of 4a, 4b with perfluoroaryllithium to give the symmetric (RC6F4)2Se (9a, 9b). All derivatives are thoroughly characterized and in addition the molecular structures of 2a, 6a, and 9a are established by X-ray crystallography.
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  • 35
    ISSN: 1434-1948
    Keywords: Metallomesogens ; Nickel ; Salicylidenediamines ; Azo compounds ; (E)/(Z) photoisomerization ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bis[4-(n-CmH2m+1O)-5-(p-C14H29C6H4N=N)]-substituted N,N′-salicylidenediamines H2[LN(m,14)] (N = 1: 1,2-diaminoethane; N = 2: 1,3-diaminopropane; N = 3: 1,3-diamino-2,2-dimethylpropane; m = 6 or 18) have been synthesized. Both the N = 2 and 3 series of compounds display a smectic C (SmC) mesophase, with clearing points well below 100 °C. By treating the H2[LN(m,14)] ligands with an NiII salt, liquid crystalline mononuclear complexes with “unconventional” (lateral-tailed) molecular shape form. These Ni[LN(m,14)] complexes, showing nematic and smectic disordered phases, are stable over a quite large temperature range and have been characterized by different spectroscopic techniques. The newly synthesized mesogens exhibit lower transition temperatures and higher thermal stability than homologous complexes Ni[LN(14)] with a “conventional” rod-like molecular geometry.
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  • 36
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1467-1477 
    ISSN: 1434-1948
    Keywords: Oxidations ; Tertiary alcohol ; Porphyrins ; Neophyl rearrangement ; Cleavage reactions ; β-Scission ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of 4-(1-hydroxy-1-phenylethyl)benzoic acid HPEBA with a water-soluble metalloporphyrin as catalyst and KHSO5 as oxygen atom donor gives the major products, acetophenone AC and acetylbenzoic acid ABA, by a Caliph-CAr bond cleavage, but a minor product, benzoyloxybenzoic acid BOBA, requires the insertion of an oxygen atom to form the ester. This compound becomes the main oxidation product on increasing the amount of acetonitrile in the reaction medium, and its formation is oxygen-dependent. The conversion is drastically lowered by using D2O instead of H2O, suggesting that an alkoxyl radical is formed in the rate-determining step. Labeling experiments using 18O2 or H218O under different reaction conditions show that the carbonyl oxygen atoms of AC and ABA originate either from substrate, water or dioxygen. However, the carbonyl oxygen atom in the ester group of BOBA originates from dioxygen while the other oxygen atom of the ester remains unlabeled. These results can be explained by an O-neophyl rearrangement of the initial alkoxyl radical to afford a carbon-based radical which then reacts with dioxygen or MnIV-OH/water. In a competitive reaction pathway, direct β-scission of the alkoxyl radical leads to unlabeled products. The oxidation of other tertiary diaryl alcohols is also discussed.
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  • 37
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1489-1495 
    ISSN: 1434-1948
    Keywords: Peroxo complexes ; Vanadium ; Mass spectrometry ; 51V-NMR spectroscopy ; Vanadium dependent bromoperoxidases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ESI mass spectrometry and 51V-NMR spectroscopy have been used to study the reactions occurring between bisperoxo vanadates and a number of histidine and histidine-like ligands, in aqueous alcoholic solutions. Coordination of one and two molecules of ligand is observed with all the compounds investigated affording [VO5L]- and [VO52L]-, respectively. Characterization of these species has been achieved by MSn experiments, which have allowed specific fragmentations of the peroxidic moiety to be distinguished. In particular, with [VO52L]-, two distinct modes of decomposition were observed, depending on the presence in the ligand of a free carboxylic function. - Possible biochemical implications related to vanadium haloperoxidase enzymes are discussed.
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  • 38
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1479-1488 
    ISSN: 1434-1948
    Keywords: Phosphorus heterocycles ; Cations ; Tungsten complexes ; Coordination modes ; Phosphaalkenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1,1,3-tris(diisopropylamino)diphosphirenium salt 1 reacts with lithium aluminium hydride leading to the P-hydrogeno-C-phosphinophosphaalkenes 2, which on treatment with a catalytic amount of BF3·OEt2 afford the 1,3-bis(diisopropylamino)-1H-diphosphirene 3. The corresponding η1-coordinated 1H-diphosphirene 6 can be prepared by treatment of 2 or 3 with one equivalent of [W(CO)5(thf)]. Alternatively, the diphosphirenium salt 1 reacts with an excess of [W(CO)5(thf)], affording the corresponding η1-coordinated diphosphirenium salt complex 4, which is converted into the P-hydrogenophosphaalkene complex 5 with lithium aluminium hydride. The dinuclear tungsten complexes 7 and 8 are obtained by treatment of the free 1H-diphosphirene 3 with two equivalents of [W(CO)5(thf)] or one equivalent of [W(CO)4(thf)2], respectively. Compound 6 reacts with two equivalents of hydrogen chloride, giving the 1-chloro-3-diisopropylamino-1H-diphosphirene 9, which can be subsequently converted into the 1-diisopropylamino-, 1-azido, or 1-phenyl-3-diisopropylamino-1H-diphosphirenes 6, 10 and 11 by nucleophilic substitution with diisopropylamine, azidotrimethylsilane or sodium tetraphenylborate, respectively. The [η2-(3-diisopropylaminodiphosphirenylium salt)·W(CO)5] complexes 12a-c can be prepared by reaction of 9 with silver trifluoromethanesulfonate, aluminium or gallium trichloride or, alternatively, by treatment of 6 with two equivalents of trifluoromethanesulfonic acid. Reaction of 12a with diisopropylamine, water, bis(triphenylphosphoranylidene)ammonium chloride or tetrabutylammonium fluoride gives the corresponding 1H-diphosphirene complexes 6, 13, 9, or 14, respectively. Compound 12a also reacts with one or two equivalents of [W(CO)5(thf)], leading to the di- and tri-nuclear complexes 15and 16, respectively.
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  • 39
    ISSN: 1434-1948
    Keywords: Phosphane ligands ; 31P-NMR spectrometry ; Substituent increments ; Electronic and steric properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses and spectroscopic parameters of the new tertiary phosphane ligands (p-MeOC6H4)(o-MeOC6H4)2P (1), (p-MeOC6H4)(o-MeSC6H4)2P (2), (p-MeSC6H4)(o-MeSC6H4)2P (3), (p-MeSC6H4)(o-MeOC6H4)2P (4), (p-MeOC6H4)(o-NC5H4)2P (5), and (p-MeSC6H4)(o-NC5H4)2P (6) are reported. Single-crystal X-ray structures of all the compounds (1-6) have been determined. The dependence of the 31P-NMR chemical shifts on the substituent groups of the phosphanes is discussed.
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  • 40
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1373-1379 
    ISSN: 1434-1948
    Keywords: Sodium bis(borane)dimethylamide solvates ; X-ray structure ; Reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of sodium metal with dimethylamine-borane in THF yields Na[(H3B)2NMe2] (1) which can be isolated as {Na[(H3B)2NMe2]}5·THF or as Na[(H3B)2NMe2]·15-crown-5 (2) and Na[(H3B)2NMe2]·benzo-15-crown-5 (3) after addition of the appropriate crown ether to the THF solution of 1. Reaction of 1 with ZrCl4 yields Me2HN-BH2-NMe2-BH3 (4), the structure of which has been determined. In THF solution, 1 reduces aldehydes, ketones, acyl chlorides, and esters to the corresponding alcohols. It also reacts slowly with nitriles and allylbenzene. Compound (1)5·THF crystallizes in an extended three-dimensional lattice, in which the Na atoms are coordinated by 6-9 hydridic H atoms, while 3 is a molecular compound in the solid state. Only one hydrogen atom of each BH3 group coordinates to the sodium center. On the other hand, 4 forms dimeric associates in the solid state through N-H···H-B interactions.
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  • 41
    ISSN: 1434-1948
    Keywords: Haloalkyl complexes ; Five-coordinate platinum complexes ; Alkene complexes ; Olefin halogenation ; Oxidative addition ; Platinum ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Five-coordinate complexes [PtX2(olefin)(2,9-Me2-phen)] (1; 2,9-Me2-phen = 2,9-dimethyl-1,10-phenanthroline; olefin = ethene denoted by a, propene by b, 1-butene by c; × = Cl denoted by x, Br by y) undergo photoactivated reactions with Cl2 and Br2 to give the (β-haloalkyl)platinum(IV) complexes [Pt(CH2CHRX)(2,9-Me2-phen)X3] (2). Bromination of the chloro species 1ax leads to the formation of the PtIV species 2axy containing the bromide, the bromoalkyl, and the phenanthroline ligands in the equatorial plane and two chloride ions in axial positions. The iodo complexes 1(a-c)z are not oxidized by iodine even under UV irradiation but react readily with Cl2 or Br2 to give 2(a-c)x and 2(a-c)y. The structure of 2ay, the first structurally characterized (β-haloalkyl)platinum complex, has been determined by X-ray diffraction methods. The stereochemistry of the (β-haloalkyl)platinum(IV) complexes is in accord with a simultaneous addition of two halogen atoms to the coordinated olefin and to the metal center.
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  • 42
    ISSN: 1434-1948
    Keywords: Phosphanes ; Disilanes ; Disilanylamines ; Germanes ; Stannanes ; Stannanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of dialkyl(trimethylsilyl)phosphanes RR′PSiMe3 (1:R, R′ = tBu; 3: R, R′ = iPr; 5: R = iPr, R′ = tBu) with Si2Cl6 provide stable trichlorosilylphosphanes RR′PSiCl3 (2, 4, 6); the reactions of silyl- and stannylamines of iPr2NMMe3 (M = Si: 11; M = Sn: 12) with Si2Cl6, however, provide the stable pentachlorodisilanylamine iPr2NSi2Cl5 (13). Heating of 1 with the technical mixture Me2(Cl)SiSiCl2Me/(MeCl2Si)2 yields the stable silylphosphane tBu2PSiMe2Cl (8) and the disilanylphosphane tBu2PSi(Me)(Cl)Si(Me)Cl2 (9). Methylation of 9 with MeLi gave tBu2PSi2Me510, which was isolated in a pure state. Reactions of tBu(iPr)PSiMe3 (5) and of organometal phosphanes tBu(iPr)PMR3 (14: M = Ge, R = Me; 17a-c: M = Sn; R = Me, Et, nBu) with Si2Cl6 were monitored by 31P, 29Si, and 119Sn NMR. - In the first step of these reactions, new tBu(iPr)PSi2Cl5 (7) is formed. 7 is accompanied by increasing amounts of tBu(iPr)PSiCl3 (6) and Me3GeSiCl3 (15)/(Me3Ge)2Si(SiCl3)2 (16) or traces of compounds R3SnSiCl3 (19a-c) that decompose providing (R3Sn)2Si(SiCl3)2 (18a-c) and nBu3SnSi(SiCl3)3 (20c). Subsequently, compounds 19a-c decompose providing increasing amounts of 18a-c. Stannylphosphane 17bis also cleaved by SiCl4 leading to 6 with liberation of Et3SnCl, whereas 17bis formedfrom the reaction of 5 with Et3SnCl under liberation of Me3SiCl. The suggestion of an extra stabilisation of P-Si bonds of trichlorosilylphosphanes was subjected to direct evidence through the structure determination of the trichlorosilylphosphane tBu2PSiCl3 (2) in the gas phase by electron diffraction. This crowded molecule has a “normal” P-Si bond length of 225.0(12) pm; its C1 symmetric conformation with both tBu groups and the SiCl3 group twisted about 17° from the perfectly staggered positions, and with each of the three groups tilted about 6° away from each other, allows to reduce steric strain.
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  • 43
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1421-1428 
    ISSN: 1434-1948
    Keywords: Grid complexes ; Self-assembly ; Co ; Zn ; Coordination chemistry ; Bis(tridentate) ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tretrametallic [2 × 2] grid-type complexes 1-4 are formed by self-assembly of the bis(tridentate) ligands 5 and 6 with ZnII and CoII cations. They have been characterized by spectroscopic studies in solution as well as by crystal structure determination. The substituents in the central pyrimidine ring play an important role in terms of geometry and physical properties of the complexes. They induce an orthogonal orientation of the ligand in the complexes which is critical for the formation of ordered monolayers and extended self-organized arrays of grids. The physical properties of the complexes such as metal-metal interaction and π-π* stacking between the ligands may be modulated by changing these substituents.
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  • 44
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1429-1433 
    ISSN: 1434-1948
    Keywords: Antitumor drugs ; Platinum ; DNA ; Dendrimers ; L1210 Mouse leukemia ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and characterisation of the first generation of a poly(propyleneimine) dendrimer DAB(PA)4, substituted with four trans-diamminechloroplatinum moieties is reported. The compound DAB(PA-tPt-Cl)4 was designed to overcome two problems often associated with cisplatin resistance in cancer cells: (i) deactivation of the platinum species by intracellular thiolates and (ii) improved repair of crosslinks with DNA. The four-armed molecule can be expected to form crosslinks with DNA that are very different from the adducts formed by cisplatin. Also, the tetranuclear compound has four leaving groups, while cisplatin has only two. Therefore, DAB(PA-tPt-Cl)4 would be less susceptible towards inactivation by reaction with intracellular thiolates. A reaction with an excess of the model nucleobase guanosine 5′-monophosphate (GMP) confirmed that the tetranuclear compound is capable of binding a maximum of four nucleobases. Therefore, the inactivation of one or two arms would still leave the molecule with enough reactivity to form crosslinks with DNA. Cytotoxicity tests were performed on two mouse leukemia L1210 cell lines, both sensitive and resistant towards cisplatin, and in seven human tumor cell lines. In all cell lines, the tetranuclear compound showed a low cytotoxicity. It is suggested that the low activity is related to the structure of the compound. Probably the high charge (+6) at physiological pH and its branched structure hamper the molecule in crossing the cell membranes.
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  • 45
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1453-1459 
    ISSN: 1434-1948
    Keywords: Group-5 bent metallocene cation complexes ; (Butadiene)tantalocene cation ; (s-trans-η4-Butadiene)metal complex ; Ethene polymerization ; Metallocenes ; Homogeneous catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (Butadiene)TaCp*Cl2 (6) was treated with CpNa to yield (η2-butadiene)TaCp*CpCl (7). Subsequent reaction with [Cp2ZrCH3+][CH3B(C6F5)3-] resulted in transfer of the chloride ligand from tantalum to zirconium with formation of the [(s-trans-η4-butadiene)TaCp*Cp]+ cation [8, with CH3B(C6F5)3- anion]. Complex 8 was characterized spectroscopically and by an X-ray crystal structure analysis. The group-5 [(s-trans-η4-C4H6)TaCp*Cp]+ bent metallocene cation complex 8 reacts with ketones (acetone, adamantanone) to yield the corresponding seven-membered 2-tantalatetrahydrooxepine cation complexes (9, 10). 1-Cyanoadamantane reacts with 8 to yield the 2-tantala-3,6-dihydro-2H-azepine cation system 11. Activation of 8 with methylalumoxane gives an active ethene polymerization catalyst.
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  • 46
    ISSN: 1434-1948
    Keywords: Metallacycles ; Solid-state structures ; Heterocycles ; Oxidations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct oxidation of PhC(O)NHPPh2, H2NC(S)NHPPh2, (C5H4N)C(S)NHPPh2 with O2, S8, or Se gives [PhC(O)NHP(O)Ph2] (1), [H2NC(S)NHP(S)Ph2] (2), [H2NC(O)NHP-(S)Ph2] (3), [PhC(O)NHP(S)Ph2] (4), [(C5H4N)C(S)NHP(S)Ph2] (5), and [H2NC(S)NHP(Se)Ph2] (6). Deprotonation of 1, 2, 4-6 with potassium tert-butoxide gives K[PhC(O)NP(O)Ph2] (7), K[H2NC(S)NP(S)Ph2] (8), K[PhC(O)NP(S)Ph2] (9), K[(C5H4N)C(S)NP(S)Ph2] (10), and K[H2NC(S)NP(Se)Ph2] (11). Reaction of 4with KOBu and [Cu(Ph3P)2][NO3] gives [Cu(Ph3P)(PhC(O)NP(S)Ph2)] (12) which is the first crystallographically characterised example of a non-ionic six-membered “true” heterocycle (i.e. a ring in which every heterocatom is different). 9 and 10 were treated with [PdCl2(COD)] to give [Pd{PhC(O)NP(S)Ph2}2] (13) and [Pd{(C5H4N)C(O)NP(S)Ph2}2] (14), respectively The anion of 8 coordinates to zinc forming [Zn{H2NC(S)NP(S)Ph2}2] (15). Treatment of 2 or 8 with [PtCl2(COD)] gives [Pt{H2NC(S)NP(S)Ph2}{H2NC(S)NHP(S)Ph2}]+Cl- (16) and [Pt{H2NC(S)NP(S)Ph2}2] (17), respectively. The X-ray structures of 12, 15-17are reported.
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  • 47
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1523-1529 
    ISSN: 1434-1948
    Keywords: Boron ; Iron ; Ruthenium ; Boryl Complexes ; Borylene Complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactivity of aminodihaloboranes R2NBX2 (R = Me, SiMe3; × = Cl, Br) towards transition metal complexes of the type Na[(η5-C5R′5)M(CO)2)] (M = Fe, Ru; R′ = H, Me) was investigated. In the case of Me2NBBr2 and M = Fe the borylcomplexes [(η5-C5R′5)(CO)2Fe{BBr(NMe2)}] (C5R′5 = C5H59a; C5R′5 = C5H4Me 9b; C5R′5 = C5Me510) were obtained. The compounds 9aand 9bwere formed together with the corresponding bridged borylene complexes [μ-BNMe2(μ-CO){(η5-C5R′5)Fe(CO)}2] (C5R′5 = C5H511a; C5R′5 = C5H4Me 11b) in a 1:1 ratio, the latter, however, could be isolated from these mixtures as pure materials. In addition the novel boryl and borylene ruthenium complexes [(η5-C5H5)(CO)2Ru{BX(NMe2)}] (X = Cl 12a; × = Br 12b), [(η5-C5H5)(CO)2Ru{BCl{NSiMe3{BClN(SiMe3)2}}}] (13) and [μ-BN(SiMe3)2(μ-CO){(η5-C5H5)Ru(CO)}2] (14) were obtained by similar methods. All compounds were characterized by multinuclear NMR and IR spectroscopy. The structure of 13 in the solid state was determined by a single-crystal X-ray diffraction study.
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  • 48
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1531-1535 
    ISSN: 1434-1948
    Keywords: SiCl4 Combustion ; OSiCl2 ; Matrix isolation ; Thermodynamic data ; DFT calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: During the technical important combustion of SiCl4 with oxygen [SiCl4(g) + O2(g) = SiO2(s) + 2·Cl2(g)] many intermediates have been detected in the past. However, the presence of the primary species O=SiCl2 has been discussed controversially until today. With the help of matrix isolation technique we have now been successful to monitor O=SiCl2 via its IR spectrum. With the help of quantum chemical calculations the thermodynamic data have been calculated first. On this basis it was possible to find the optimal conditions to trap OSiCl2 from the high-temperature equilibrium. Furthermore it could be shown via IR spectroscopy and quantum chemical calculations, that the radical OSiCl does not play a significant role within this combustion process.
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  • 49
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1545-1550 
    ISSN: 1434-1948
    Keywords: Phosphates ; Structure ; IR spectroscopy ; Raman spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The low-temperature form of K3Sm(PO4)2 crystallizes in the monoclinic system [a = 7.4347(5) Å, b = 5.6270(5) Å, c = 9.4919(5) Å, β = 90.870(6)°, Z = 2, space group P21/m]. The structure has been determined using 1263 independent reflections (R = 0.045, Rw = 0.11) and is found to be of the glaserite type. The Raman and infrared spectra have been investigated: they are consistent with the proposed space group and an assignment of the observed frequencies is given.
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  • 50
    ISSN: 1434-1948
    Keywords: Palladium ; Phosphane ligands ; Bite angle ; Allylic alkylation ; Molecular modelling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The natural bite angle of bidentate phosphane ligands influences the isomer distribution (syn and anti) in (1-methylallyl)(bisphosphane)Pd OTf complexes. It was found (31P- and 1H-NMR studies) that the syn/anti ratio changes from 12 (dppp) to 1.3 (sixantphos). Molecular orbital calculations [PM3(tm) level] indicate that for ligands inducing a large bite angle, the phenyl rings of the ligand embrace the allyl moiety, thus influencing the syn/anti ratio. This bite-angle effect on the syn/anti ratio is transferred to the regioselectivity in stoichiometric allylic alkylation. Ligands inducing large bite angles direct the regioselectivity towards the formation of the branched product 2. Catalytic alkylation of (E)-2-butenyl acetate showed that for ligands with a small bite angle the regioselectivity of the catalytic and stoichiometric alkylation are in good agreement. This correspondence is worse for ligands with a larger bite angle, which is rationalised in terms of the relative rates of syn/anti isomerisation and alkylation. The ligand with the largest bite angle (sixantphos) gives the most active catalytic species.
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  • 51
    ISSN: 1434-1948
    Keywords: Metal string complexes ; Multicentered metal-metal multiple bond ; Quadruple bonds ; Metal-metal interactions ; Chromium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The linear pentanuclear chromium complexes [CrII5(μ5-tpda)4Cl2] (1), [CrII5(μ5-tpda)4(NCS)2] (2), [CrIIICrII4(μ5-tpda)4F2](BF4) (3), and [CrIIICrII4(μ5-tpda)4F(OTf)](OTf) (4), with four all-syn tri(α-pyridyl)diamido dianion (tpda2-) ligands, have been prepared and structurally characterized. Compounds 1 and 2 possess a delocalized Cr(II)-Cr(II)-Cr(II)-Cr(II)-Cr(II) five-centred metal-metal bond of order 1.5. In both 1 and 2 two values for CrII-CrII bond lengths are found both; the outer ones connected with axial ligands are 2.284(1) and 2.285(2) Å, and the inner ones are 2.2405(8) and 2.246(1) Å, for 1 and 2, respectively. When compound 1 reacts with 2 equiv. of AgBF4 or Ag(OTf), a oxidation reaction takes place and one of the terminal chromium(II) ions is oxidized to produce [CrIIICrII4(μ5-tpda)4F2]BF4 (3) or [CrIIICrII4(μ5-tpda)4F(OTf)](OTf) (4). Two short Cr-Cr distances [1.969(2) and 2.138(2) Å for 3, 1.846(1) and 1.922(1) Å for 4] are found, with the presence of two quadruple bonds among four adjacent CrII ions. The fifth CrIII ion, which is separated from the neighboring CrII ion by 2.487(2) Å for 3 and 2.610(1) Å for 4, is simply a square pyramidal unit with no metal-metal bonding interaction.
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  • 52
    ISSN: 1434-1948
    Keywords: Aluminium ; Amides ; Calcium ; Metallacycles ; Phosphorus ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of calcium bis[bis(trimethylsilyl)amide] with two equivalents of tris(trimethylsilylmethyl)alane yields (Me3SiCH2)2Al-N(SiMe3)2 (1) and the dimer [(Me3Si)2N-Ca(μ-CH2SiMe3)2Al(CH2SiMe3)2]2 (2). The five-coordinate bridging carbon atoms show Ca-C bond lengths of 264 and 268 pm. A similar reaction with calcium bis[bis(trimethylsilyl)phosphanide] gives the dimer [(Me3SiCH2)2Al-P(SiMe3)2]2 (3) with crystallographic C2 symmetry. A calcium-containing species is not isolable, however, in the presence of DME - ether cleavage reactions and the formation of the centrosymmetric dimer [(Me3SiCH2)2Al-OCH2CH2OMe]2 (4) are observed. The central moiety is an Al2O2 cycle with fivefold coordinated aluminium centers.
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  • 53
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2215-2220 
    ISSN: 1434-1948
    Keywords: Magnesium ; Metalation ; Phosphorus ; Polyhedra ; X-ray structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The magnesiation of triisopropylsilylphosphane with dibutylmagnesium in toluene yields the octanuclear complex [Mg8(PSiiPr3)6{P(H)SiiPr3}4] (1) which consists of MgPSiiPr3 units forming a hexagonal Mg6P6 prism, with two opposite Mg2P2 moieties capped by additional Mg[P(H)SiiPr3]2 groups. If a small amount of THF is present during the metalation reaction [(THF)4Mg6(PSiiPr3)6] (2) also containing a hexagonal Mg6P6 prism can be isolated. The magnesiation of H2P-SiiPr3 in tetrahydrofuran leads to the formation of the tetrameric complex [(THF)MgPSiiPr3]4(3) with a slightly distorted Mg4P4 cubane-like structure.The structures depend strongly on the steric strain caused by the trialkylsilyl substituents and the neutral coligands at the magnesium center. The highest steric strain, which is induced by coordination to every magnesium atom, leads to the smallest MgnPn polyhedron - the central Mg4P4 heterocubane moiety. In compounds 1 and 2 the hexagonal Mg6P6 prism is formed, however, with reduced steric strain as observed for 2 where the Mg-P bond lengths become more similar.
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  • 54
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2233-2241 
    ISSN: 1434-1948
    Keywords: Phosphorus ; Heterocycles ; Phosphinines ; Gold ; Cycloadditions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coordination behaviour of 2,6-disilyl-substituted phosphinines towards gold(I) has been examined. The reaction of the bis(trimethylsilyl)phosphinine 1 with [AuCl(SMe2)] gives the corresponding AuCl derivative 2. X-ray crystal structure analysis reveals that the aromaticity of the phosphinine ring is slightly reduced as a result of the poor π-back bonding ability of the AuCl fragment. The same phenomenon is observed in the cationic complex [Au(1)2][GaCl4] (3) which was readily prepared by reaction of two equivalents of 1 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. Reaction of 2,6-bis(phenylethynyldimethylsilyl)phosphinine (4) with the same precursor leads similarly to the complex [AuCl(4)] (5). Interestingly, this complex dimerizes upon crystallization to give the bis(phosphabarrelene) complex 6, also structurally characterized. The formation of 6 results from a [4 + 2] cycloaddition between one alkynyl group of each phosphinine with the other phosphinine subunit. The formation of the cationic complex [Au(4)][GaCl4] (8) occurs under classical conditions but it disproportionates to give the cationic complex [Au(4)2][GaCl4] (9) and colloidal gold deposition. The formation of 9 has been ascertained by treating 8 with one equivalent of ligand 4. Additionally, 9 can also be obtained in a straightforward fashion by treating two equivalents of 4 with [AuCl(SMe2)] followed by treatment with GaCl3 at low temperature. The structure of 9 has been elucidated. Despite a particular arrangement of the alkyne groups which encapsulate the gold coordination sphere, no gold-alkyne interactions are visible.
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  • 55
    ISSN: 1434-1948
    Keywords: Metallaoxirane ; HBR2 addition ; (Formaldehyde)zirconocene ; (Butadiene)zirconocene ; Heterocycles ; Boron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (η2-Formaldehyde)zirconocene dimer (8) cleanly adds one or two molar equivalents of the borane HB(C6F5)2 by insertion of the H-[B] unit into the zirconium-carbon bond of the metallaoxirane moieties to form the mono- and bis-insertion products 16 and 17, respectively. These systems contain five-membered heterocyclic rings that are built up by connecting five different elements, namely H, B, C, O, and Zr. The bis(borane) insertion product 17 was characterized by an X-ray crystal structure analysis. (Butadiene)zirconocene reacts with HB(C6F5)2 in a similar way by insertion of the H-[B] unit into the (butadiene)C4-Zr linkage to form the metallacycle 18.
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  • 56
    ISSN: 1434-1948
    Keywords: N-ligands ; Yttrium ; Samarium ; Ring-opening polymerization ; Lactones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of one equivalent of dilithiated O(SiMe2-Ap-H)2 [Ap-H = -N(2-amino-4-methylpyridine)] (1), generated in situ, with LnCl3 (Ln = Y, Sm) in THF affords O(SiMe2-Ap)2YCl(THF)2 (2) or O(SiMe2-Ap)2SmCl(THF)3 (3). In contrast, the reaction of one or two equivalents of dilithiated 1, again generated in situ, with LaBr3 in THF affords O(SiMe2-Ap)2)2LaLi(THF)3 (4). An X-ray structural analysis of 2 and 3 reveal the O(SiMe2-Ap)2- ligand to bind in a planar tetradentate manner. Equivalent Sm-N distances in 3 indicate a delocalized binding mode. Compound 2 reacts with Bu4NBH4, NaBH4 or LiCH(SiMe3)2 to give the corresponding “ate” complexes O(SiMe2-Ap)2Y(BH4)Cl(THF) Bu4N (5), O(SiMe2-Ap)2Y(BH4)2Na(THF)2 (6) and O(SiMe2-Ap)2Y(CH(TMS)2)2Li(THF)3 (7), respectively. The steric demand of the O(SiMe2-Ap)2- ligand is not large enough to stabilize monoalkyl or monoborohydride complexes. Complex 4 has been used as an initiator for the ring-opening polymerization of ε-caprolactone or δ-valerolactone. In both cases an almost linear relation between the monomer-to-initiator ratio and the molecular weight of the obtained polyester is observed. By conducting the polymerization in neat ε-caprolactone at room temperature a solid polyester block is formed after 3 min (300000 g·mol-1, Mw/Mn 2.3).
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  • 57
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2301-2307 
    ISSN: 1434-1948
    Keywords: Multiple bonds ; Silicon ; Silylene ; Cycloadditions ; Insertions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Di-tert-butylsilylene, generated by photolysis of hexa-tert-butylcyclotrisilane 1 or 1,1-di-tert-butyl-trans-2,3-dimethyl-silirane (2), reacts with the 1,3-diyne (tBu-C≡C-)29 to furnish the dialkynylsilane 11 via the isolable alkynylsilirene 10. Photolysis of excess 1 in the presence of 9 furnishes the C-C linked 2,2′-disilirene 12 which, upon prolonged irradiation, rearranges to the 2,5-disilabicyclo[2.2.0]hexa-1(6),3-diene (13). Treatment of 9 with diarylsilylenes, formed by irradiation of hexamethyl-2,2-dimesityltrisilane (3) or hexamethyl-2,2-bis(2,4,6-triisopropylphenyl)trisilane (4), gives the corresponding alkynylsilirenes 14 and 15, respectively. Photolysis of 1 or 2 in the presence of (Me3Si-C≡C-)216 yields the dialkynylsilane 17 which, on further reaction with 2, yields the 2,5-disilabicyclo[2.2.0]hexa-1(6),3-diene (18). Irradiation of 3 in the presence of 16 affords the cis- and trans-isomeric 1,3-dimethylene-2,4-disila-cyclobutane derivatives cis-21 and trans-21, presumably via a 1-silaallene intermediate. The structures of 12, 15, 18, cis-21, and trans-21 have been determined by X-ray crystallography.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2319-2325 
    ISSN: 1434-1948
    Keywords: Dichloroanilines ; Propanil ; Iron(III) tetrasulfonatophthalocyanine ; Oxidations ; Catalysts ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We investigated the degradation of polychlorinated pollutants, such as dichloroanilines and related anilides, catalyzed by iron(III) tetrasulfonatophthalocyanine (FePcS) with potassium monopersulfate or hydrogen peroxide as oxidant. The reaction is influenced by the positions of the two chloro-substituents and by the nature of the oxidant. The FePcS-catalyzed oxidation of 3,5-dichloroaniline with potassium monopersulfate leads to the formation of more biodegradable products (carboxylic acids) and to potentially toxic dimers (azo and azoxy compounds). The oxidation of 3,4-dichloroaniline by FePcS/H2O2 converts this pollutant into coupling products. The formation of dimers in the catalytic oxidation of dichloroanilines can be avoided by acylation of the amine function.
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  • 59
    ISSN: 1434-1948
    Keywords: Asymmetric catalysis ; Transfer hydrogenation ; Ruthenium ; Amino alcohol ligands ; X-ray structure ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nature of ruthenium-amino alcohol precursors in the catalytic cycle of asymmetric hydrogen transfer reactions was studied using two C2-symmetrical tetradentate ligands (1 and 2) that were synthesised from (nor)ephedrine. The structure of the catalyst precursor was examined through catalysis and NMR experiments. It was shown that the active catalyst contains one ligand per metal, which coordinates in a didentate N,O fashion (9). In addition, a RuIICl2 complex, in which N,N′-bis(2-hydroxy-1-methyl-2-phenylethyl)-1,2-diaminoethane (1) coordinates through two nitrogen atoms, was structurally characterised by X-ray diffraction (8). - Based on the results of this study a series of new amino alcohol ligands was synthesised from easily available starting materials. Optimisation of the amino alcohol ligand structure resulted in the most effective chiral amino alcohol ligand (5) so far that is capable of reducing acetophenone at 0 °C with up to 97% ee in the RuII-catalysed transfer hydrogenation.
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  • 60
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2327-2333 
    ISSN: 1434-1948
    Keywords: Heterocycles ; Organo-phosphorus compounds ; Dithiadiphosphetane disulfides ; Phosphonates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New salts of thionated (naphthalene-1,8-diyl)bis(phosphonic) acid monoanhydrides [PPh4+]2[C10H6PS2(μ-S)PS22-] (2) and [K+]2[C10H6PS2(μ-S)POS2-]·H2O (3) both containing the C3P2S ring, were prepared in high yields by the reaction of 2,4-(naphthalene-1,8-diyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide (1) with NaHS and PPh4Cl, or KOH, respectively, in water. The derivative 3, containing a P=O terminal bond as well as P-S-P bridge, undergoes, in acid conditions, a rearrangement reaction leading to the O,S-symmetrically substituted derivative [K+]2[C10H6PS2(μ-O)PS22-] (4) containing a C3P2O heterocycle. Dipotassium salt 4 was converted into the bis(tetraphenylphosphonium) salt 5 by the treating with PPh4Cl. Hydrolysis of [PyH+][C10H6P(S)(NHMe)(μ-S)PS22-] (15) led to [CH3NH3+][PyH+][C10H6POS(μ-O)POS2-]·1.5 Py (6). New compounds were characterised by 31P{1H}-, 1H- and 13C{1H}-NMR, FT-IR, ES-MS and in the cases 2-6 by X-ray structure determination. The 31P{1H}-NMR spectra of these mixed O,S-derivatives are briefly discussed.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 2343-2346 
    ISSN: 1434-1948
    Keywords: Chromium ; Cyanides ; Density-functional calculation ; Electronic structure ; Spin state ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The steric and electronic factors responsible for the reactivity differences between CN and Cl complexes of CpCrIII were examined by DFT/B3LYP computational techniques. The energy difference between quadruplet and doublet [CpCr(CN)2(PH3)], ΔED-Q, was calculated to be 21.2 kcal mol-1 with the LanL2DZ basis set. Although the high-spin configuration is still the ground state for the cyanide complex, the energy gap is 8.7 kcal mol-1 less than that found for the corresponding chloride species. The difference between quadruplet [CpCr(CN)2(PH3)] and doublet [CpCr(CN)2(PH3)2] less free PH3, ΔECr-P, is also smaller than for the Cl system. The components of ΔECr-P for CN and Cl were analyzed by calculating energies at fixed geometries in both spin states, which indicated that the influence of the cyanide group on the pairing energy was more important than changes in Cr-PH3 bond strength or steric effects.
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  • 62
    ISSN: 1434-1948
    Keywords: Cyclopropanation ; Copper ; N ligands ; Macrocycles ; Supported catalysts ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CuI and CuII complexes of cyclic and open-chain polyaza compounds have been tested as catalysts in the benchmark cyclopropanation reaction of styrene with ethyl diazoacetate. In general, only small amounts of copper are needed to promote the reaction. The catalytic activity depends on the structure of the ligand, e.g. amine-amides are more efficient than polyamines, and on the oxidation state of copper, CuII being more active than CuI. Given that CuI is the active species, these changes of behavior must be related to the stabilities of the complexes. The nature of the counterion also has a noticeable influence on the catalytic activity, the role of which is discussed. XAS measurements suggest the formation of oligomeric species. Some of the chiral ligands lead to small enantiomeric excesses. Open-chain ligands can easily be supported on organic polymers and their complexes can be used as catalysts. Furthermore, cyclic and acyclic complexes can be supported on clays by cation exchange and the solids obtained tend to promote the reaction with a decrease in the trans/cis ratio.
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    Berichte der deutschen chemischen Gesellschaft 2000 (1999), S. 455-461 
    ISSN: 1434-1948
    Keywords: Aluminium ; Gallium ; Indium ; Azide ; Rietveld ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new tetraazido complexes of aluminium, gallium, and indium [thf2Na][thf2Al(N3)4] (1), [py2Na][py2In(N3)4] (2), and Na[Ga(N3)4] (3) have been synthesized from MCl3 and NaN3 by salt metatheses and characterized by X-ray diffraction analysis. In compounds 1 and 2, the Group 13 metal atom and the sodium atom are each hexacoordinated by four azido groups and two additional solvent molecules. The azido groups act as μ(1,3)-bridging ligands between the Group 13 metal and sodium, thereby forming network structures. In contrast, complex 3 is solvent-free and exhibits a tetracoordinated gallium centre and a heptacoordinated sodium atom. The structure of 3 has also been investigated by means of X-ray powder data and the Rietveld method and the results are compared with the single-crystal data.
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  • 64
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1259-1269 
    ISSN: 1434-1948
    Keywords: Metal dithiolenes ; Charge-transfer complexes ; Azo compounds ; Electrical conductivity ; High-resolution X-ray powder diffractometry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Combination of the planar redox-active ions [ML2]2- (L = mnt2- = maleonitrile-1,2- dithiolate; M = Ni (1), Pd (2), Pt (3); dmit2- = 2-thioxo-1,3-dithiol-4,5-dithiolate: M = Ni (4), Pd (5) and trans-4,4′-azobis(1-methyl-pyridinium), (a2+) affords 1:1 ion pairs exhibiting partial and complete electron transfer as evidenced by UV-Vis and EPR spectra. Replacement of planar a2+ by a non-planar dipyridinium ketone b2+ leads to the complexes 1b and 4b. 1a, 2a, and 3a are predominantly composed of dications and dianions while 4a, 5a, and 4b are rare examples of ion pairs consisting of two radical ions. Single crystal X-ray structural analyses was performed on 4a, a(PF6)2, and a(MeSO4)2 while the structure of 1a was resolved by powder X-ray diffractometry. The latter consists of mixed stacks of planar dianions and dications forming a slipped arrangement with the centers of the two ions displaced relative to each other by 250 pm. The short interplanar distances of 340 pm are in agreement with the presence of a weak charge-transfer interaction as indicated by the corresponding absorption band at about 1400 nm. A mean reorganization energy of 0.85 ±0.04 eV is calculated from the Hush equation for complexes 1a, 2a, and 3a. No ion pair charge-transfer band is observable for 4a, 5a, and 4b. Surprisingly, in the solid state structure of 4a the [Ni(dmit)2]- monoanions do not form segregated columns as found in the many ion pairs with redox inert counterions, but prefer a mixed stack arrangement as observed also for 1a.The specific electrical conductivity of pressed powder pellets of complexes exhibiting a charge-transfer band is in the range of 2 × 10-7 to 1 × 10-5 Ω-1cm-1, increasing with increasing driving force of electron transfer in accordance with previous results. Different to that, the conductivity of the other complexes does not depend on driving force and is much higher (2 × 10-4 to 4 × 10-4 Ω-1cm-1).
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1291-1293 
    ISSN: 1434-1948
    Keywords: Aluminum ; Lead ; O ligands ; Alkoxy carboxylates ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel heterometallic aggregate Pb2Al5(μ3-O)(μ4-O)(μ-OiPr)9(OiPr)3(μ-OAc)3 obtained from the interaction of Pb(OAc)2 and Al(O-iPr)3 is the first structurally characterized example based on lead and aluminum. This compound has been isolated in high yield and examined by 1H-, 13C-, and 27Al NMR, and in the solid state by X-ray crystallography.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1405-1407 
    ISSN: 1434-1948
    Keywords: Agostic interactions ; Samarium ; Silylamide ; Transsilylamination ; Trinuclear complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sm[N(SiMe3)2]2(thf)2 reacts with 1,1,3,3-tetramethyldisilazane by a transsilylamination reaction to form the hexane-soluble Sm[N(SiHMe2)2]2(thf)x in high yield. An X-ray diffraction study reveals a novel trinuclear complex of composition Sm{[μ-N(SiHMe2)2]2Sm[N(SiHMe2)2](thf)}2 featuring a bent array of metal centers. Multiple metal···SiH β-agostic interactions sterically and electronically saturate the samarium(II) centers implying a new coordination mode of the bridging amide ligands.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1409-1414 
    ISSN: 1434-1948
    Keywords: Ruthenium complexes ; Luminescence ; Bridging ligands ; Terpyridine ligands ; Polynuclear metal complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The absorption spectra and the luminescence properties of three dinuclear RuII complexes and one trinuclear RuII complex have been investigated. All the complexes have rack-type structures. The dinuclear complexes 1, 2, and 3 incorporate a bis-tridentate bridging ligand made up of a pyrimidine and four pyridine moieties, as well as two 2,2′:6′,2′-terpyridyl (tpy) ligands. The trinuclear complex 4 incorporates a tris-tridentate bridging ligand made up of two pyrimidine and five pyridine moieties, as well as three tpy ligands. The absorption spectra of the complexes show a large number of ligand-centered (LC) and metal-to-ligand charge-transfer (MLCT) bands. All the complexes exhibit emission from a triplet MLCT state, with maxima in the spectral range 840-950 nm (lifetimes between 40 and 80 ns) at 298 K in fluid solution, and in the spectral range 760-810 nm (lifetimes between 2 and 3 μs) at 77 K in rigid matrices. A fine tuning of the absorption and luminescence properties of complexes 1-3can be achieved by changing the substituents on the pyrimidine ring of the bridging ligand. Efficient energy transfer within the rack structure 4 occurs from the (upper-lying) central metal-based chromophore to the (lower-lying) peripheral ones.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1415-1420 
    ISSN: 1434-1948
    Keywords: Combinatorial chemistry ; Molecular recognition ; Functionalized bipyridine metal complexes ; Janus molecules ; Hydrogen bonding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The functionalized ligands 1 and 2 bearing hydrogen-bonding recognition groups have been synthesized. Their assembly by metal ions such as CuI and PdII having different coordination geometries generates different receptor architectures for the binding of suitable substrates. Addition of the complementary bis(imide) Janus molecules (4-7) to [1a, 2a, CuTf] or to [1b, 2b, Pd(BF4)2] mixtures leads to a moderate selective increase of the fraction of the [(1a)2Cu]+ or [(1b)2Pd]2+ complex depending on the Janus substrate used. Largest enhancements are observed for those Janus substrates that may be expected to display highest geometrical complementarity with the two complexes. These results represent a process directed by target binding based on dynamic combinatorial chemistry.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1435-1443 
    ISSN: 1434-1948
    Keywords: Captopril ; Cysteine ; Rhenium ; S ligands ; Thioaldehydes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral racemic rhenium thioaldehyde complexes [CpRe(NO)(PPh3)(η2-S=CHR)]PF6 (2a-g) bearing functionalized aliphatic groups R [R = CH2Ph (a), COOEt (b), CH2COOMe (c), CH2C(O)NHCH2Ph (d), (R)-CH(NC8H4O2)COOMe (e), (S,S)-CH(Me)C(O)NC4H7COOMe (f), C4H3O (g)] have been obtained by hydride abstraction from the corresponding thiolate complexes [CpRe(NO)(PPh3)(SCH2R)] (1a-g). With the exception of 2b, only single stereoisomers with like configurations at rhenium and the thioaldehyde carbon atom were obtained. In some cases, the corresponding sulfinate complexes [CpRe(NO)(PPh3)(SO2CH2R)] (3d-f) were formed as by-products. The analogous toluenesulfinate complex [CpRe(NO)(PPh3){SO2(4-C6H4CH3)}] (3a) has been prepared from [CpRe(NO)(PPh3)(THF)]BF4 (8), and the structure of 3e has been determined by X-ray crystallography. The use of phosphorus ligands other than PPh3 was briefly explored with the synthesis of [CpRe(NO)(PR′3)(η2-S=CHR)]PF6 (5a-d) [R′ = OPh, R = Ph (a), 4-C6H4Cl (b), R′ = iPr, R = Ph (c), H (d)]. Nucleophilic addition of NaSMe to [CpRe(NO)(PPh3){η2-S=CH(4-C6H4OMe)}]PF6 (5e) gave the dithioacetal complex [CpRe(NO)(PPh3){SCH(SMe)(4-C6H4OMe)}] (9) in high yield and with low diastereoselectivity. Diels-Alder additions of 5a, e with 2,3-dimethylbutadiene and 2,3-dimethoxy-butadiene gave complexes of cyclic thioethers (10a-c). From the relative rates of reaction (5a 〉〉 5e) and the low diastereoselectivity, it was concluded that the cycloadditions as well as the nucleophilic addition proceed via the linkage isomers [CpRe(NO)(PR′3)(η1-S=CHR)]PF6.
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  • 70
    ISSN: 1434-1948
    Keywords: Diene complexes ; η3-Cyclooctatetraene metal complex ; B(C6F5)3 addition ; Tantalum ; Bicyclo[5.1.0]octadienyl metal complex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [(η4-diene)(η5-RCp)TaCl2] complexes 6a-e (diene = butadiene, isoprene or 2,3-dimethylbutadiene; RCp = pentamethylcyclopentadienyl, methylcyclopentadienyl or cyclopentadienyl) react with cyclooctatetraene dianion (employed as [(cot)Li2]) to yield the (η4-diene)(η3-cyclooctatetraene)(η5-RCp)tantalum complexes 7. The η3-cot coordination was confirmed by an X-ray crystal structure analysis of the compound [(supine-s-cis-η4-C4H6)(η3-cot)(η5-Cp*)Ta] 7a. In solution, the cot ligand of all the complexes 7 is fluxional. Two isomers [supine and proneorientation of the (diene)CpTa subunit] were found for the (η4-butadiene)(η3-cot)CpTa system (7e/7e′ = 95:5). Complex 7e cleanly adds the organometallic Lewis acid B(C6F5)3 to yield the betaine system [(η4-C4H6){C8H8B(C6F5)3}Cp*Ta] 8, which contains a substituted bicyclo[5.1.0]octadienyl ligand.
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    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1557-1562 
    ISSN: 1434-1948
    Keywords: Calixarenes ; Macrocycles ; Silver ; Radiotracer technique ; Metal-ion extraction ; Radiochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calixareneglycine ester acetamides 4a-c have been synthesized from calixareneacetyl chlorides 5a-c and glycine ethyl ester (6). Their ion-binding properties have been investigated by liquid-liquid extraction with radiotracer techniques. The experiments reveal a moderate affinity towards silver(I) ions, which increases with calixarene ring size.
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    Chemistry - A European Journal 1 (1995), S. cpi 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
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    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
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    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
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    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 3-3 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 76
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    Chemistry - A European Journal 1 (1995), S. 7-11 
    ISSN: 0947-6539
    Keywords: density-functional calculations ; ion-molecule reactions ; relativistic effects ; thermochemistry ; uranium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nitridooxouranium cation NUO+ has been prepared as a new isoelectronic homologue to the uranyl dication UO22+ by a sequence of ionmolecule reactions starting from the atomic uranium cation U+. Collision-induced dissociation experiments and ligand-exchange reactions serve to unambiguously identify the ion as a species in which the uranium cation is formally inserted in the NO molecule. New thermochemical data for NUO+ and UN+ are given, and the stability of NUO+ with respect to UO22+ is investigated by means of quasi-relativistic density-functional calculations.
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  • 77
    ISSN: 0947-6539
    Keywords: asymmetric catalysis ; aziridines ; chiral ligands ; palladium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral palladium π-allyl intermediate for the catalytic asymmetric synthesis shown in Scheme 1 has been isolated as the PF-6 salt. MM 2 calculations have been performed and the structure of the palladium complex in solution has also been investigated by means of NMR spectroscopy. Both the computational and spectroscopic results suggest that in the complex the bidentate bis(aziridine) ligand adopts a conformation that forces the π-allyl moiety out of the normally preferred square-planar geometry. This nicely explains the very high enantioselectivity observed in the title reaction.
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  • 78
    ISSN: 0947-6539
    Keywords: chlorine complexes ; ethene complexes ; intermediates ; rotational spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complex of ethene and Cl2 has been characterised in the gas phase. Rotational spectra of the isotopomers C2H4…35Cl2, C2H4…35Cl37Cl and C2H4…37Cl35Cl were recorded by using a fast-mixing nozzle in an FT microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl nuclear quadrupole coupling constants. χgg (Cl) are reported in each case. The complex is of the π-donor-acceptor type and has a C2v geometry in which Cl2 lies along the C2 axis perpendicular to the plane of the C2H4 nuclei. The binding is weak, and only small changes in the χgg (Cl) attend complex formation. A simple model attributes these changes to a transfer of around 0.02e from the inner to the outer Cl nucleus, thus confirming that the complex is of the Mulliken outer type. Similarities in the properties of C2H4… Cl2 and C2H4… HCl indicate that the angular geometry is in both cases determined mainly by the electrostatic part of the interaction. The distance from the π-bond midpoint to Cl decreases from C2H4… HCl to C2H4… Cl2; this suggests that Cl2 is “snub-nosed”.
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  • 79
    ISSN: 0947-6539
    Keywords: alkoxides ; clusters ; Group 15 complexes ; Lewis acids ; oxygen bridges ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As(OtBu)3 does not form adducts with alkali metal tert-butoxides MOtBu (M = Li, Na, K, Rb and Cs), whereas the corresponding Sb(OtBu)3 (2) and Bi(OtBu)3 (3) react with MOtBu (M = K, Rb, Cs) to yield M(OtBu)4Sb (M = K (6), Rb (7), Cs (8)) and M(O-tBu)4Bi (M = 9), respectively. X-ray structure determinations for 6 and 9 show them to be one-dimensional coordination polymers composed of E(OtBu)4 (E = Sb, Bi) units linked through potassium atoms. These E(OtBu)4 units display a ψ-trigonal-bipyramidal coordination around the metal atom (Sb—O = 1.971(2) and 2.181(2) Å, Bi—O = 2.068(8) and 2.275(8) Å). Both the structures exhibit a planar four-coordinate environment of oxygen around the potassium atoms (K—O = 2.650(2)-2.967(2) Å in 6, 2.53(1)-3.15(1) Å in 9). Compound 2 reacts with two equivalents of KOtBu to afford K2Sb(OtBu)5 · dioxane (10), which contains Sb2K2O5 cage units and can be described as an O5 trigonal bipyramid with metal atoms inserted in the equatorial edges. Each metal atom is tetracoordinated by oxygen atoms of the cage (Sb—O = 1.979(3)-2.144(3) Å. K—O = 2.592(3)-2.778(2) Å). The dioxane molecules increase the coordination number at each potassium atom to five by forming bridges between the molecules through K—O bonds. Reaction of 2 and 3 with NaOtBu produce the cluster compounds Na4Sb2O(OtBu)8 (4) and Na4Bi2O-(OtBu)8 (5) in high yields. K4Sb2O-(OtBu)8 (11) is obtained in almost quantitative yield by heating KSb(OtBu)4 in benzene for 24 h. Compounds 4, 5 and 11 crystallise in rhombohedral lattices; the crystal structure analyses show a superposition of molecules. With an isotropic oxygen-centred M6 octahedron. The formation of these oxo-tert-butoxides is accompanied by evolution of isobutene. Addition of four equivalents of THF to 11 gives K4Sb2O(OtBu)8 · 4 THF (12). X-ray diffraction studies reveal a cis arrangement of the Sb atoms in the central OSb2K4 unit. K4Sb2O2(OiPr)12 (13) is obtained as the major product on heating KSb(OtBu)4 and subsequent reaction with isopropyl alcohol. In the crystal structure, two oxygen-centred Sb2K2 tetrahedra (K—O 2.693(4) Å, Sb—O = 1.982(5) Å) linked through iPrO—K bonds (2.726(7)-2.738(7) Å) are observed. In the reactions of KSb(OtBu)4 (6) with the metal halides CaCl2, TlCl and CuI, a halide ion is transferred to potassium; this results in formation of potassium halide, the corresponding alkoxide and Sb(OtBu)3.
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  • 80
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    Chemistry - A European Journal 1 (1995), S. 56-67 
    ISSN: 0947-6539
    Keywords: amethyrin ; orangarin ; porphyrinoids ; terpyrroles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new, general synthesis of the first β-substituted tetra- and hexaalkyl terpyrroles is described. Also described are two new classes of expanded porphyrins derived from the hexaalkyl terpyrrole. The key step in the terpyrrole formation is the copper(II)-mediated oxidative coupling of the LDA-derived enolates of α-keto pyrroles. The first new expanded porphyrin reported here, the so-called “orangarin”, contains five pyrrolic subunits and two bridging carbon atoms, and is formally a 20π-electron nonaromatic macrocycle. The second new class of expanded porphyrins, the “amethyrins”, are 24π-electron nonaromatic macrocycles containing six pyrrole units. Both of these new macrocycles, as well as one of the new terpyrrolic precursors have been structurally characterized by single crystal X-ray diffraction analysis.
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  • 81
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    Chemistry - A European Journal 1 (1995), S. 68-73 
    ISSN: 0947-6539
    Keywords: porphyrinoids ; Rothemund synthesis ; sapphyrin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Rothemund-type condensation of pyrrole and benzaldehyde yields, apart from 5,10,15,20-tetraphenylporphyrin (TPPH2) and inverted tetraphenylporphyrin 2-aza-21-carba-5,10,15,20-tetraphenylporphyrin (CTPPH2), a unique pentapyrrolic macrocyclic molecule with the aromatic nucleus of sapphyrin, namely, 5,10,15,20-tetraphenylsapphyrin (TPSH3). Its unorthodox structural skeleton with an inverted pyrrole ring lying opposite to the bipyrrole unit accounts for the spectroscopic properties of the novel sapphyrin. The diprotonation of TPSH3 acts as a trigger for a structural transformation involving a flip of the pyrrole units, which relocates the 27-NH pyrrolic nitrogen from the periphery into the center of the macrocycle. The formation of 5,10,15,20-tetraphenylsapphyrin proves that the pentapyrrolic product is accessible by the mechanism of the Rothemund synthesis.
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  • 82
    ISSN: 0947-6539
    Keywords: catenanes ; cyclodextrins ; macrocycles ; orientational isomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel synthetic approach is described for the construction of catenanes in aqueous solution from a partially methylated cyclodextrin (CD)-namely, heptakis(2,6-di-O-methyl-β-cyclodextrin) (DM-β-CD)-and a range of substrate molecules that contain a hydrophobic central core in the form of a 4,4′-disubstituted biphenyl unit (usually bitolyl) carrying two hydrophilic polyether side chains terminated by primary amine functions. In water, the amphiphilic catenane precursors form 1:1 complexes with β-CD and DM-β-CD and 2:1 (guest: host) complexes with the larger γ-CD. Macrocyclizations of the biphenyl-containing substrates with aromatic diacid chlorides in aqueous solution and in the presence of DM-β-CD under Schotten-Baumann conditions afforded-in low yields-a range of [2]- and [3]catenanes. When a consitutionally asymmetrical diamine was employed as the substrate, orientational isomers of a [2]catenane were obtained. A [3]catenene incorporating a macrocyclic tetralactam was found to exist as a mixture of head-to-head and head-to-tail isomers, which could be separated by high pressure liquid chromatography and identified unambiguously by nuclear magnetic resonance spectroscopy. One of the [2]catenanes afforded good single crystals from which the solid state structure was determined by X-ray crystallography. Other techniques which aided the characterization of these novel compounds included ultraviolet/visible and luminescence spectroscopy, dynamic nuclear magnetic resonance spectroscopy and fast atom bombardment mass spectrometry. Generally speaking, the catenated cyclodextrins are soluble in halogenated and aromatic hydrocarbons as well as in hydroxylic solvents. The existence of these new compounds gives us a unique insight into the nature of the noncovalent bonding interactions that cyclodextrins employ in binding substrate molecules.
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  • 83
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    Chemistry - A European Journal 1 (1995), S. 100-100 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 84
    ISSN: 0947-6539
    Keywords: chiral phenols ; facial selectivity ; photooxidations ; quinols ; singlet oxygen ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three of the four possible isomeric para-substituted hydroxyethyl-methylphenols were prepared from readily available starting materials and submitted to photooxygenation. In the case of 3-hydroxy-α,6-dimethylbenzenemethanol (1 a) and 2-hydroxy-α,5-dimethylbenzene-methanol (1 b) the corresponding 4-hydroperoxy-3,5-cyclohexadienones were obtained as oxy-functionalized products (≥90%, d.r. 85:15 and 75:15). The stereochemistry of the products was assigned after reduction to the corresponding p-quinols. The ready cleavage of the initial oxygenated product, which can be observed at low temperature as a single diastereomer, prevented rigorous assignment of the π-facial selectivity of the singlet oxygen attack for the derivative 4-hydroxy-α,2-dimethylbenzenemethanol (1 c). The present stereochemical results indicate that the hydroxyl group directing effect, that is, coordination of the incoming singlet oxygen dienophile with the hydroxyl group, is also operating in the photooxygenation of the chiral phenols 1 a-c. However, in the case of the derivative 1 b, hydrogen bonding in the starting material leads to an opposite stereochemical outcome. This conclusion is further substantiated by solvent effects and the fact that the methyl ether 1 d of alcohol 1 c displays a significant lower diastereoselectivity.
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  • 85
    ISSN: 0947-6539
    Keywords: chelate ligands ; hydrogen bonds ; ligand design ; mass spectrometry ; stability constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of compounds containing the mononuclear complexes [M(tdci)2]3+ (tdci = 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol, M = Al, Fe, Ga, In) and [M(tdci)2]4+ (M = Ti, Ge, Sn) was prepared and characterized by elemental analysis, NMR spectroscopy, and FAB mass spectrometry. Characteristic fragmentation reactions in the mass spectra were elucidated. X-ray analysis of the AlIII, FeIII, GaIII, and InIII complexes revealed that two neutral, zwitterionic tdci ligands coordinate to the metal cation exclusively through deprotonated alkoxo groups. The six coordinated oxygen donors and the six N—H protons form a hydrophilic pocket, whereas the two cyclohexane rings and the twelve methyl groups form two hydrophobic shells. The hydrophilic pocket is filled with twelve water molecules, which are arranged as a second and a third coordination sphere around the metal cation. The reactivity in aqueous solution was investigated by potentiometric measurements. The bis complexes proved to be stable at pH 7. The evaluated formation constants show an increase of stability in the order AlIII〈InIII〈GaIII〈FeIII. The measurements established that tdci is one of the most effective tridentate ligands for small (r ≤ 0.8Å) and highly charged cations. The different chelating properties of tdci and of the unmethylated 1,3,5-triamino- 1,3,5-trideoxy-cis-inositol are discussed in terms of different steric requirements and different types of solvation of the corresponding complexes in aqueous solution.
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  • 86
    ISSN: 0947-6539
    Keywords: charge transfer ; EPR spectroscopy ; organometallic compounds ; platinum compounds ; spectroelectrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In spite of their very similar cyclic voltammograms, absorption spectra, and solvatochromic behavior, the two 1,4-diazabutadiene title complexes exhibit markedly different photoreactivities and underlying electronic structures, as evident from absorption and EPR spectra of the persistent anion radical forms. The lowest excited state of the nonphotoreactive PtII system [(CyN=CH—CH=NCy)-PtMe2] has MLCT (metal-to-ligand charge-transfer, 5d → π*) character, and the EPR spectrum of the corresponding anion radical at 〈g〉 = 2.016 exhibits sizable metal/ligand orbital mixing. On the other hand, the structurally characterized PtIV complex [(CyN=CH—CH=NCy)-PtMe4] (C2/c; a = 2021.6(2), b = 805.3(1), c = 1254.2(1) pm; β = 111.05(1)°; V = 1905.7(4) × 106 pm3; Z = 4) has a lowlying photoreactive LLCT (ligand-to-ligand charge-transfer, σPt—C → π*) excited state in which the axial Pt—C bonds are activated, as already suggested by the longer Pt—C(ax) bonds (214.0(8) pm) relative to Pt—C(eq) in the ground state (204.5(5) pm). The anion radical of the PtIV complex has lost the long-wavelength absorption band in the visible; it shows a well-resolved EPR spectrum at 〈g〉 = 1.9945 with π-ligand and 195Pt hyperfine structure and a small g anisotropy. A qualitative MO scheme is presented to account for the similar frontier-orbital energy differences despite dissimilar underlying electronic structures.
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  • 87
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    Chemistry - A European Journal 1 (1995), S. cpi 
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    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 88
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    Chemistry - A European Journal 1 (1995) 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 89
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    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 90
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    Chemistry - A European Journal 1 (1995), S. 111-117 
    ISSN: 0947-6539
    Keywords: alkyne complexes ; carbon networks ; macrocycles ; platinum compounds ; tetraethynylethene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of the first organometallic mono- and dinuclear platinum complexes bearing the tetraethynylethene unit as an η1-ligand are reported. Structural characterization of two of the trans σ-bis(acetylide) derivatives by X-ray crystallography reveals coplanarity of the acetylenic π-ligands and indicates possible electronic delocalization across the metal center. This notion is further supported by comparing the electronic absorption spectra of the platinum-containing compounds with those of related tetraethynylethene derivatives without metals. The solidstate structure of a dinuclear complex with two iodoplatinum fragments attached to one set of geminal acetylenes of tetraethynylethene was also investigated by X-ray diffraction. Hay coupling of a mononuclear species leads to the incorporation of the σ-bis(acetylide) moiety into a diplatinated metallacycle. This macrocyclic compound represents a novel structural motif in the design of a transition metal linked carbon network based on tetraethynylethene.
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  • 91
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    Chemistry - A European Journal 1 (1995), S. 118-123 
    ISSN: 0947-6539
    Keywords: antiferromagnetic exchange ; crystal structure ; indium compounds ; Jahn-Teller distortion ; titanium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dark green crystals of In3Ti2Br9 have been synthesized from elemental Ti and molten InBr3 at 450°C. The X-ray diffractional characterization by means of single-crystal and powder Rietveld refinement reveals a hexagonal crystal structure (a = 738.2(2), c = 1813.9(3) pm; P63/mmc, Z = 2) of Cs3Cr2Cl9 type, containing Ti2Br3-9 dimers and univalent indium cations. Self-consistent, semiempirical band structure calculations show the structural distortions of the two monovalent indium cations to arise from a second-order Jahn-Teller instability. The new compound's magnetic susceptibility and microscopic antiferromagnetic exchange are analyzed by using a Bleaney-Bowers ansatz.
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  • 92
    ISSN: 0947-6539
    Keywords: calixarenes ; cavitands ; molecular modeling ; resorcinarenes ; supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Coupling reactions of calix[4]arenes and modified resorcin[4]arenes have been investigated. Reaction of mono(chloroacetamido)calix[4]arene 4 with tetrahydroxycavitand 9 gave the 1:1 coupled product 13 in 61% yield. Combination of upper-rim 1,3-difunctionalized calix[4]arene 5 with 9 afforded predominantly the 2:1 calix-resorcinarene 18 in 47% yield. Reaction of 1,2-difunctionalized calix[4]arene 6 with 9 gave five products, namely, endo 1:1 (19), exo 1:1 (20), endo-endo 2:1 (21), endo-exo 2:1 (22), and exo-exo 2:1 (23) in ratios that depend on the reaction conditions. The stereochemistry of the different products was determined with NOESY experiments. The structures of 21 a and 23 b were calculated by using molecular mechanics, which revealed that intramolecular hydrogen bonds are only present in the former. Reaction of 1,2-bis(chloroacetamido)calix[4]arene 26, which has two additional nitro groups at the remaining aromatic rings, with 9 yielded three different products, namely, endo 1:1 (28), endo-endo 2:1 (30), and endo-exo 2:1 (32) in ratios that depend on the reaction conditions. There is a preference for the endo orientation in the formation of the 1:1 coupled product, probably owing to an interaction of the nitro groups with the cavitand in the transition state. After conversion of the nitro groups in 28 into chloroacetamido moieties, reaction with Cs2CO3 in DMF under high-dilution conditions afforded holand 33 in 26% yield together with calix[4]arene-based carceplex 34 with an encapsulated DMF molecule (27% yield). Holand 33 was obtained in 33% yield by reaction of the tetrakis(chloroacetamide) endo-endo 2:1 isomer 31 with tetrahydroxycavitand 9. Holand 33 contains a cavity of nanosize dimensions. Molecular mechanics simulations indicate that holand 33 adopts a conformation with eight hydrogen bonds and a large, preorganized cavity with two entrances of smaller dimensions. Molecular dynamics simulations of holand 33 in both CHCl3 and THF showed that four solvent molecules can be accommodated in the cavity at well-defined positions.
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  • 93
    ISSN: 0947-6539
    Keywords: alkynes ; coupling reactions ; cyclopropanes ; macrocycles ; oligoalkadiynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general approach to the family of completely spirocyclopropanated macrocyclic polydiacetylenes, that is, cyclic dehydrooligomers of 1,1-diethynylcyclopropane 4, is reported. The characterized examples of these “exploding” [n]rotanes are for n = 5, 6, 7, 8, 9, 10, and 12. X-ray crystal structure analyses for the hydrocarbons with n = 5, 6, 7, and 8 disclose a strong electronic interaction between the cyclopropane and the acetylene units leading to a significant shortening of the distal and lengthening of the proximal cyclopropane bonds. While the five-sided compound 18 can occur as a planar or envelope-shaped molecule, depending on the solvent from which crystals are grown, the six- (19), seven- (20), and eight-sided (21) molecules all have chair conformations. While the butadiyne units in 18 and 19 are bent slightly outwards, those in the seven- and eight-sided molecules 20 and 21, respectively, are bent distinctly inward. All these compounds are extremely high-energy molecules: when struck with a spatula or a pestle, they go off with a puff to yield black soot.
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  • 94
    ISSN: 0947-6539
    Keywords: alcohols ; cracking ; dehydrations ; isomerizations ; NMR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrocarbon products that are formed upon dehydration at 296-673 K of tert-butyl alcohol (tBuOH), adsorbed on H-ZSM-5 zeolite in concentrations equal to that to active Al—OH—Si sites in the catalyst, have been analyzed by 13C solid-state MAS NMR and GC-MS. To facilitate 13C NMR analysis, the alcohol selectively labeled with 13C isotope in the COH group was used. It was found that tBuOH transforms to the adsorbed C8 butene dimers plus a trace amount of alkanes at 296 K. Butene dimers exist inside H—ZSM-5 pores in the form of interconverting adsorbed octene, octyl silyl ether, and octyl carbenium ion; octyl silyl ether is the main adsorption state. Fluxionality of the carbenium ion form provides a pathway for isomerization of the highly branched hydrocarbon skeleton of the intial alcohol to the predominantly linear one in the adsorbed butene dimer. The driving force for the isomerization into the linear structure is the shape selectivity induced by the small size of the zeolite channels. At 373 K the adsorbed butene dimers further crack into species that contain an average of about 6.5 carbon atoms, in addition to further alkanes. At 448 K the adsorbed C3-C7+ paraffins become the predominant hydrocarbon products observed with both in situ 13C NMR and ex situ GC-MS. Simultaneously, a mixture of adsorbed polyenes is formed. According to 13C CP/MAS NMR, polyenes exist in the zeolite pores in the form of rather stable cyclopentenyl cations. At 573-673 K adsorbed cyclopentenyl cations further transform into a mixture of condensed and simple aromatics and then into xylenes and toluene. Simultaneously, paraffins crack further to give mainly C3-C4 paraffinic species at 573 K and propane at 673 K.
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  • 95
    ISSN: 0947-6539
    Keywords: catalysis ; crystal structure ; oxidations ; rhenium peroxo complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rhenium oxides Re2O7 and ReO3 react with hydrogen peroxide solutions yielding peroxo complexes that efficiently catalyze the oxidation of olefins, aromatics, and certain organometallic compounds. In contrast, related oxides of molybdenum (MoO3) and vanadium (V2O5) do not activate H2O2 under comparable conditions. The active rhenium peroxo complex was isolated from the system Re2O7/H2O2: the crystalline red-orange, explosive compound of formula H4Re2O13 is the most oxygen rich rhenium compound isolated to date. Its structure resembles a “peroxo perrhenic acid”. The binuclear compound could be isolated in the form of a diglyme adduct, structurally defined as two corner-sharing pentagonal bipyramids with apical oxo and aquo ligands; the equatorial positions are occupied by the bridging oxygen and by n2-peroxo groups (two [O2]2- ligands per rhenium). In contrast to the known complex [CH3ReO(O2)2].H2O, the new peroxo species [O{ReO(O2)2.H2O}2] decomposes hydrolytically during the catalytic cycle and can thus not compete in terms of catalytic activity in oxidation reactions involving H2O2. Hydrolysis yields “perrhenic acid” Re2O7.2H2O, the diglyme adduct of which compound was also characterized by means of an X-ray diffraction analysis.
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  • 96
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    Chemistry - A European Journal 2 (1996), S. 196-207 
    ISSN: 0947-6539
    Keywords: eliminations ; orbital interactions ; solvent effects ; substitutions ; theoretical chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The model reaction system F- +C2H5F + nHF (n = 0-4) has been investigated by use of a density-functional method, in order to achieve a qualitative understanding of the effect of solvation on the E2 and SN2 reactions. Two characteristic effects already occur upon monosolvation: a) the activation energies of the E2 and SN2 pathways increase significantly and even become positive, because reactants are more strongly solvated than transition states; b) the SN2 transition state is stabilized much more and becomes lower in energy than the anti-E2 transition state. This agrees with general experience from gas- and condensed-phase experiments. The solvation is analyzed from two complementary viewpoints: a) as an interaction between solvent molecules and the F-/C2H5F reaction system; b) as an interaction between the [F-, nHF] solvated base and the C2H5F substrate. The extent to which condensed-phase characteristics can be modeled by this microsolvation approach is discussed.
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  • 97
    ISSN: 0947-6539
    Keywords: heterocycles ; insertion reactions ; phosphaalkynes ; phosphorus ylides ; triphosphetenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hitherto unknown 1,2,3-triphosphetenes RC=P—PCF3—PCF3 (3a-d) are formed as main products in reactions of phosphaalkynes R—C≡P [R = iPr2N (1a), tBu (1b), Me2EtC (1c), 1-methylcyclohexyl (1d)] with the cyclotetraphosphane (PCF3)4 (2). According to NMR results the CF3 groups in 3a-d have a trans disposition; an X-ray diffraction study of 3a confirms this structure. The P—P bond lengths in 3a are equal [2.201 (2) and 2.204 (2) Å] and correspond to single bonds. A considerable shortening is observed for the sp2-C-N bond (1.336 Å) which, together with the elongation of the P=C bond (1.746 Å), indicates effective π donation of the lone pair on nitrogen. Surprisingly, 3a can be prepared in quantitative yields by reaction of the PP ylide Me3P=PCF3 (6) with 1 a (molar ratio: 2:1). In contrast, the corresponding reactions of 6 with the alkyl-substituted phosphaalkynes 1b-d lead to the novel phosphorus ylides Me3P=C(R)—P—PCF3—PCF3PCF3 [R = tBu (10a), Me2EtC (10b), 1-methylcyclohexyl (10c)] in good yields. In their molecular groundstate structures, determined by X-ray diffraction, the lone pair on the phosphano P atom prefers the syn position with respect to the ylidic P=C bond. An unusual lengthening of the sp2-C-C bond [1.553 (4) (10a), 1.543 (6) (10b), 1.551 (4) Å (10c)] to values typical for sp3-C/sp3-C distances is observed.
    Additional Material: 3 Ill.
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  • 98
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 251-254 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 99
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 265-270 
    ISSN: 0947-6539
    Keywords: cyclic compounds ; medium-sized ; rings ; tetraketones ; transannular interactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By using a fast-mixing nozzle in a Fourier transform microwave spectrometer, any chemical reaction accompanying mixing of H2S and BrCl was prevented, thus allowing the observation of the pre-reactive complex H2S ··· BrCl. The rotational spectra of eight isotopomers of the complex were recorded. The analysis of the determined spectroscopic constants shows that the atoms S ··· Br—Cl are collinear or nearly so and that the H2S plane is approximately perpendicular to the S ··· Br—Cl axis with r(S ··· Br) = 3.094 (7) Å. This geometry is in agreement with previously stated rules for B ··· XY complexes, where B is a Lewis base and XY is an (inter)halogen molecule. The intermolecular interaction is shown to be relatively weak, both in terms of the intermolecular stretching force constant kσ and the intramolecular electric change redistribution δ within the BrCl subunit that accompanies formation of H2S ··· BrCl.
    Additional Material: 3 Ill.
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  • 100
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 295-302 
    ISSN: 0947-6539
    Keywords: conformational analysis ; galabioside ; hydrogen bonds ; protein recognition ; thioglycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two thio analogues (2 and 3) of TMSEt galabioside [2-(trimethylsilyl)ethyl 4-O-(α-D-galactopyranosyl)-β-D-galactopyranoside, 1], having anomeric sulfur instead of anomeric oxygen atoms, were synthesized and their conformations investigated by NMR and computational (MM 3) methods. A spacer galabioside was covalently coupled to aminated microtiter plates, and binding of a bacterial pilus adhesin (PapG) to the plates was inhibited by the soluble ligands 1, 2 and 3. The ligand 2, which has an intersaccharidic sulfur linkage, was a much less efficient inhibitor than 1, which has the natural oxygen linkage. The inhibitory power of ligand 3 was only slightly less than that of 1. An NMR experiment with 1 and 2, in which hydroxyl-group hydrogens had been partially (50%) substituted by deuterium, demonstrated the presence (in 1) and absence (in 2) of an intramolecular (HO 2′ - HO 6) hydrogen bond. This result indicates that the conformations of 1 and 2 are different and that the difference is sufficient to cause the observed (≈ 30 times) reduction of the saccharide-protein binding strength.
    Additional Material: 8 Ill.
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