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  • General Chemistry  (77,717)
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  • 101
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    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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  • 102
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    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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  • 103
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    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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  • 104
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 103-112 
    ISSN: 1434-1948
    Keywords: Ab initio calculations ; Ionization potentials ; Phosphorus ; Heterocycles ; Small ring systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio quantum chemical calculations have been used to explore the P3H3 potential energy surface focussing on the ring-chain rearrangements of the three-membered ring in (PH)3 (1), the parent triphosphirane. Relative energies between stationary points were estimated using the QCISD(T)/6-311G(d,p) method based on MP2/6-31G(d,p) geometries and corrected for zero-point contributions. Ring strain, proton affinities, ionization and excitation energies and heats of formation have been evaluated using larger basis sets, e.g. 6-311++G(3df,2p). The cyclic trans-triphosphirane (1a) is the most stable P3H3 isomer and lies about 40 kJ/mol below the open-chain phosphanyldi-phosphene (H2P-P=PH). The decrease of ring strain in three-membered rings when CH2 is replaced by PH is confirmed. Triphosphirane 1a is a virtually strain-free ring and even gains some stabilization relative to three separate P-P single bonds. The reduced ring strain also helps diminish the phosphorus inversion barrier to 224 kJ/mol compared to the monocyclic isomers of (CH2)(PH)2 and (CH2)2(PH). Compound 1a follows a pure ring-opening or a 1,2-hydrogen shift rather than a combined motion pathway, in fundamental contrast with corresponding processes of diphosphirane and phosphirane. This is due to the existence of an open-chain P3H3 phosphorane intermediate stabilized by allylic conjugation. The pericyclic ring-opening of 1a is the most favored process but the energy barrier in the gas phase is about 180 kJ/mol high. Electron density is largely delocalized within the three-membered P3 ring not only in the C3v-symmetric 1b (all-cis) but also in 1a (Cs). The proton affinity of 1a is similar to that of PH3. The proton affinities decrease with n in cyclo-(CH3)3 -n(PH)n and their values were obtained: PA(1a) = 777 ±10, PA(diphosphirane) = 799 ±10 and PA(phosphirane) = 802 ±10 kJ/mol. Heats of formation are evaluated as follows (ΔH°f0 at 0 K in kJ/mol): 1a, 70 ±10; cyclo-(PH)2(PH2)+ (protonated 1a), 821 ±10; diphosphirane, 85 ±10; cyclo-(CH2)(PH)(PH2)+ (protonated diphosphirane), 814 ±10; phosphirane, 86 ±10; and protonated phosphirane, 812 ±10 kJ/mol. All P rings remain cyclic following ionization to the radical cations. Adiabatic ionization energies (IEa) are estimated as: 1a and diphosphirane, 9.3 ±0.3 eV and phosphirane 9.5 ±0.3 eV. The first UV absorption band shifts toward the longer wavelength region on going from phosphirane to 1a. The GIAO/B3LYP computed magnetic shieldings for 1a and related molecules reveal a clear relationship between the narrow bond angles in the rings and their unusually strong magnetic shielding. The similarity of the predicted 31P-NMR signals in 1a and its heteroanalog diphosphirane, (CH2)(PH)2, can be rationalized in terms of a compensation of the carbon-substituent effect (downfield shift) and the bond-bending effect imposed by the ring (upfield shift).
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  • 105
    ISSN: 1434-1948
    Keywords: Coordination chemistry ; Inorganic rings ; O ligands ; Structure elucidation ; Tin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of cupferron [NH4L, L = PhN(O)NO-] with tin(IV), diphenyltin(IV) and dimethyltin(IV) halides yields the cupferronato complexes SnL4 (1), Ph2SnL2 (2) and [Me2SnL2]2 (3). All were characterized by FT-IR, FT-Raman, NMR (1H, 13C and 119Sn) spectroscopic methods and X-ray structural analysis. An almost ideal, very rare dodecahedral geometry is found in the structure of 1. The hexacoordinated tin center exhibits a bicapped tetrahedral geometry in complex 2. The tin centers are heptacoordinated in a pentagonal bipyramidal geometry in the dimeric complex 3. These complexes incorporate five-membered SnO2N2 and four-membered Sn2O2 inorganic rings. Vibrational spectral data are consistent with the structures determined. The 119Sn NMR spectra indicate that in solution 1 retains its octacoordinated nature; in compound 2 the tin atom is hexacoordinated, while in 3 the tin atom is pentacoordinated.
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  • 106
    ISSN: 1434-1948
    Keywords: Copper ; Oxygenase ; Copper-oxygen radical species ; RPY2 ligand ; Oxygenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe the reactivity of new copper AlkylPY2 type complexes which react with dioxygen and thus hydroxylate an aliphatic C-H bond of the ligand in the same manner as copper-containing monooxygenases.
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  • 107
    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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  • 108
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    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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  • 109
    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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  • 110
    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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  • 111
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    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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  • 112
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    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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  • 113
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    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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  • 114
    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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  • 115
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    Weinheim : Wiley-Blackwell
    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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  • 116
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    Weinheim : Wiley-Blackwell
    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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  • 117
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    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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  • 118
    ISSN: 1434-1948
    Keywords: Thiolato-bridged complexes ; Iron ; Ruthenium ; Mixed-valent compounds ; Mössbauer spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [FeIIIL] with [RuIICl2(dmso)4] in methanol under argon, affords, upon addition of NaPF6, brown crystals of [LFeRuFeL](PF6)2· 3 CH3OH (1). Its one-electron oxidation product [LFeRuFeL](PF6)3 (2) [L = 1,4,7-(4-tert-butyl-2-mercaptobenzyl)-1,4,7-triazacyclononane] was generated by using one equivalent of [NO]BF4. The crystal structure determination of [LFeRuFeL](BPh4)2· CH3CN · 3 (CH3)2CO shows that 1 contains a trinuclear, face-sharing thiolato-bridged dication. Mössbauer spectroscopy established that the oxidation state distribution of 1 can best be described by Fe2.5RuIIIFe2.5 and 2 by FeIIIRuIIIFeIII. Complex 1 possesses a diamagnetic (St = 0) and 2 an St = 1/2 ground state. The electronic structures of 1 and 2 are rationalized by an MO picture involving Fe-Ru metal-metal bonds of bond order 0.5 in both species. Complex 1 is formally a mixed valence compound with complete delocalization of the “excess electron” (class III).
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  • 119
    ISSN: 1434-1948
    Keywords: Platinum ; Uracil ; Nucleobase ; Host-guest chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The open “molecular box” [(en)Pt(U-N1,N3)]4 (1) (where en = ethylenediamine, U = uracil dianion) is able to act as an efficient ligand for additional metal ions. Reactions of the 1,3-alternate conformer of 1 with divalent metal ions result in the formation of octanuclear compounds of the general formula [(en)Pt(U-N1,N3,O2,O4)M]4X8 [M = Cu2+, X = Cl (2a), X = (SO4)0.5 (2b), and M = Co2+ (3), Ni2+ (4), Zn2+ (5) with X = (SO4)0.5], in which the heterometals are bound at the exocyclic oxygen atoms of the uracil nucleobases. The structurally characterized heteronuclear compounds show a 1,3-alternate arrangement of the uracil nucleobases. Pt-M contacts are in the range 2.743(2)-2.804(2) Å; the Pt atoms act as weak σ donors to the heterometals. In spite of the high degree of positive charge associated with compounds 2a-5, they do not behave as hosts for anions. This is a consequence of the orientation of the four nucleobases which, in contrast to a cone arrangement, does not produce a sufficiently large cavity for the incorporation of anions.
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  • 120
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 351-358 
    ISSN: 1434-1948
    Keywords: Aminophosphanes ; Palladium ; Alkylations ; Enantioselectivity ; Theoretical study ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various 4-(diphenylphosphanyl)-1-(dialkylamino)butane ligands were prepared from commercial (2S,3S)-2,3-O-isopropylidene-D-threitol. These ligands, associated with Pd2(dba)3, gave enantioselectivities of up to 75% in the alkylation of racemic 1,3-diphenylprop-2-enyl acetate with dimethyl malonate anion. A theoretical study shows the important role played by two factors in the alkylation reaction: steric control, leading to the formation of a unique diastereoisomer of the π-allylpalladium complex, and orbital control, which orients the attack of the nucleophile trans to the phosphorus atom.
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  • 121
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 375-381 
    ISSN: 1434-1948
    Keywords: Fluorine ; Silicon ; Ab initio calculations ; Donor-acceptor systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum chemical calculations at the ab initio level indicate that Lewis donors such as amine or water form weak donor-acceptor complexes with fluoro-substituted silanes. The strength of the donor-acceptor formation increases with increasing degree of fluorine substitution. Amine and water form strong adducts only for tetrafluorosilane. The higher element homologues of Lewis donors, such as phosphane and sulfur dihydride, do not in essence coordinate. A considerable role in donor-acceptor formation is exerted by chelation effects which impose intramolecular interactions on functionalized ligands. The corresponding structures are explored.
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  • 122
    ISSN: 1434-1948
    Keywords: Functionalized zirconocenes ; Half-sandwich complexes ; Hydroboration ; Propene polymerization/Homogeneous catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 6-Amino-6-methylfulvene has been coupled with benzoic acid by treatment with 7-azahydroxybenzotriazole and DCC. Subsequent two-fold deprotonation, at the NH and 6-methyl groups, generated the vinylidene-bridged Cp/benzoylamido ligand 5. Treatment of 5 with ZrCl4(THF)2 gave the spiro-metallocene complex 3a (characterized by X-ray crystal structure analysis), while reaction of 5 with (Et2N)2ZrCl2(THF)2 yielded the bridged half-sandwich complex 3b. Treatment of 3a with two molar equivalents of the strongly electrophilic borane HB(C6F5)2 resulted in hydroboration of the exocyclic C=C double bond with concomitant intramolecular N-B adduct formation to yield the azaboretidine-type systems 7 (three diastereoisomers, one of which has been characterized by X-ray diffraction analysis). Similarly, hydroboration of 3b with HB(C6F5)2 yielded the azaboretidine derivative 9. Activation of the complexes 7 and 9 with methylalumoxane led to active homogeneous Ziegler-type propene polymerization catalysts.
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  • 123
    ISSN: 1434-1948
    Keywords: Ruthenium ; Sulfur ligands ; Exchange reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a quest for ruthenium complexes having [RuNS4] cores, a non-fluxional configuration, trans-thiolate donors, and exchangeable coligands L, [Ru(L)(‘pyS4’)] complexes have been synthesized [‘pyS4’2- = 2,6-bis(2-mercaptophenylthio)dimethylpyridine(2-)]. Treatment of [RuCl2(PPh3)3] with ‘pyS4’2- gave [Ru(PPh3)(‘pyS4’)] (1). Alkylation of 1 with excess MeI yielded [Ru(PPh3)(‘pyS4’-Me2)]I2 (2). [Ru(DMSO)(‘pyS4’)] (3) was obtained from [RuCl2(DMSO)4] and ‘pyS4’2-. The PPh3 or DMSO coligands in 1, 2, and 3 proved to be very inert to substitution. Only the DMSO could be displaced by CO under drastic conditions yielding [Ru(CO)(‘pyS4’)] (4). Treatment of [RuCl2(CH3CN)4] with ‘pyS4’2- yielded [Ru(‘pyS4’)]2 (5); in the presence of PEt3 or N2H4 mononuclear [Ru(PEt3)(‘pyS4’)] (6) and [Ru(N2H4)(‘pyS4’)] (7) were formed. Template alkylation of NBu4[Ru(NO)(S2C6H4)2] with 2,6-bis(tosyloxymethyl)pyridine gave [Ru(NO)(‘pyS4’)]Tos (8). Complex 8 proved to be the best suited precursor for L exchange reactions. Under reducing conditions, 8 releases its NO ligand and the resulting [Ru(‘pyS4’)] fragments can combine either with each other to give 5, or with PEt3 and N2H4 to yield 6 and 7, respectively. All complexes have been characterized by spectroscopic methods and elemental analysis; 1, 2, 3, and 4 have also been submitted to X-ray structure analysis.
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  • 124
    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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  • 125
    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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  • 126
    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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  • 127
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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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  • 128
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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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  • 129
    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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  • 130
    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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  • 131
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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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  • 132
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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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  • 133
    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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    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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  • 135
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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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  • 136
    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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  • 137
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 13-16 
    ISSN: 1434-1948
    Keywords: Pyrazole ; Titanium ; Redox reaction ; Mercury ; Amalgams ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of [L2TiCl2] (1) (L = 3,5-tert-butylpyrazolate) with 1% Na/Hg in tetrahydrofuran (THF) affords the complex [L2TiCl(THF)2] (2), which crystallizes from hexane in moderate yield. The analogous reduction carried out in toluene gives dimeric [(L2TiCl)2] (3) in high yield. If the reduction time is extended to 3 days, the complex [L3Ti] (4) is isolated as light blue crystals in low yield. An alternative procedure for preparing compound 4 requires mixing [TiCl3(THF)3] with 3 equivalents of potassium 3,5-tert-butylpyrazolate in toluene. Crystallization from hexane affords 4 in high yield. Crystallographic data for 2, 3 and 4 are presented.
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  • 138
    ISSN: 1434-1948
    Keywords: Polyoxometalates ; Ruthenium ; Homogeneous catalysis ; Oxidations ; Microwaves ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Microwave irradiation for 15 minutes allowed the highly selective hydrothermal synthesis of the diamagnetic, air-stable oxidation catalyst [PW11O39RuII(DMSO)]5-, as confirmed by 1H, 31P, 99Ru and 183W NMR techniques.
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  • 139
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1025-1030 
    ISSN: 1434-1948
    Keywords: Phthalocyanines ; Nitrides ; Oxo complexes ; Rhenium ; Molybdenum ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of new nitrido(phthalocyaninato)molybdenum (1-4) and -tungsten complexes (5-7) starting from the corresponding phthalonitriles and MNCl3 (M = Mo, W) is reported. In addition, the reaction of (tBu4Pc)WN (6) with PPh3 leading, after several steps, to the diamagnetic compound (tBu4Pc)WO (7) is described. The reaction of (tBu4Pc)ReN (9) with PPh3 leads to [(tBu4Pc)ReO]2 (12), and of [(C5H11)8Pc]ReN (10) with PPh3 leads, under different conditions, to {[(C5H11)8Pc]ReO}2O (11).
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  • 140
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1039-1043 
    ISSN: 1434-1948
    Keywords: Iridium ; Amphiphiles ; N ligands ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 4′-functionalized 6′-phenyl-2,2′-bipyridine ligands (L-n) with the dimer [(ppy)2IrCl]2 (ppy = 2-phenylpyridine anion) and subsequent counterion exchange affords a new series of cationic orthometallated iridium(III) complexes, [(ppy)2Ir(L-n)][PF6] (1-5), which have been characterized by spectroscopic methods. These complexes have a large shape anisotropy and significant amphiphilic character. The crystal structure of 4 has been determined by X-ray diffraction.
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  • 141
    ISSN: 1434-1948
    Keywords: Carbon dioxide fixation ; Magnesium ; N ligands ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of oxalic amidines R1-N=C(NHR2)-C(NHR2)=N-R1 with CH3MgX followed by uptake of CO2 results in the formation of the trimeric carbamato complexes [R1-N=C(NR2-COO)-C(NR2COO)=N-R1]3Mg3(THF)6 (2a: R1 = R2 = Ph; 2b: R1 = R2 = p-tolyl) as the thermodynamically stable final products of the reaction. Their X-ray crystal structures show that the three metal centres are in a linear arrangement. The central magnesium ion is octahedrally surrounded by six O-donor atoms of the μ2-carbamato bridges, while both peripheral magnesium ions are facially coordinated by three O-donor atoms of the carbamato groups and three THF molecules. This coordination sphere can be considered as a structural model for the active centre in the ribulose-1,5-bisphosphate carboxylase/oxygenase enzyme. Compound 2a reacts with ZnCl2 or CoBr2, with CO2 elimination, to form dimeric complexes of the type [X2M(oxalamidinato)MX2][Mg(DMF)6] (M = Zn, Co; X = Cl, Br). X-ray crystal structure analyses show that the d-metals are tetrahedrally coordinated. The magnesium-bromide-containing intermediates in the formation of 2a and 2b are able to transfer CO2 to acetophenone, thus simulating the CO2 activation step in enzymatic biotin-dependent carboxylation reactions.
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  • 142
    ISSN: 1434-1948
    Keywords: Carbene complexes ; Carboxylato complexes ; Density functional calculations ; Palladium ; Rhodium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures of several complexes arising from the interaction between methylene and palladium and rhodium diformates were optimized through density functional calculations. For palladium, mono-, di-, and trimeric complexes were considered. The results obtained show that in all cases the most stable structures correspond to complexes in which methylene has inserted in one of the M-O bonds, while metal-carbene complexes are energy minima only for monomeric palladium diformate and for rhodium diformate. Trimeric palladium formate is thermodynamically stable upon fragmentation. However, when it reacts with methylene, fragmentation becomes favorable. The role of the resulting monomeric complex in the olefin cyclopropanation mechanism catalyzed by palladium dicarboxylates is discussed.
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  • 143
    ISSN: 1434-1948
    Keywords: Cadmium(II) pyrazolonates ; Thiosemicarbazones ; Cyclizations ; 2-[Amino(thioxo)methyl]-3-pyrazolone ; 1H-, 13C-, 113Cd-NMR spectra ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acetoacetanilide- and methylacetoacetate thiosemicarbazones (HTSC1 and HTSC2, respectively) react with cadmium(II) acetate in methanol, giving complexes containing the ligand 2-[amino(thioxo)methyl]-5-methyl-2,3-dihydro-1H-3-pyrazolonate (L-). An X-ray diffraction study of the structures of HTSC1, HTSC2, HL, and [CdL2Py], identified the main structural changes in the cyclization process. Additionally, the coordination of the metal in the complexes [CdL(AcO)] · 2 MeOH and [CdL2] · 3 H2O was analyzed using IR spectroscopy in the solid state and 1H-, 13C-, and 113Cd-NMR spectroscopy in solution. On reaction with aqueous trifluoroacetic acid, both complexes releases the free pyrazolone, which can be easily isolated.
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  • 144
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 97-102 
    ISSN: 1434-1948
    Keywords: Mesoporous materials ; MCM-48 ; Immobilization ; (1,1′-Ferrocenediyl)dimethylsilane ; 13C and 29Si solid-state NMR ; Sandwich-complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The walls of the cubic mesoporous silicate MCM-48 have been grafted with ferrocenyl end groups by a ring-opening reaction of the ansa-bridged ferrocene [Fe{(η-C5H4)2SiMe2}], carried out in a pentane solution at room temperature. The orange product has been characterized by elemental analysis, powder X-ray diffraction, 13C and 29Si solid-state NMR, N2 adsorption measurements, and Fe K-edge EXAFS. A high loading has been obtained (8.18 mass % Fe) and, as a result of the inclusion of the organometallic moiety, the N2 adsorption isotherm exhibits a lower uptake. Direct structural evidence for the surface attachment of both single ferrocenyl and short chain oligo(ferrocenyl) fragments has been obtained.
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  • 145
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 153-157 
    ISSN: 1434-1948
    Keywords: Aluminum ; Ab initio calculations ; Isomers ; Intramolecular donor-acceptor systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three aluminum compounds Ar*AlBr2 (1), Ar*AlBrtBu (2), and Ar*2AlBr (3), incorporating the chiral ligand Ar* = 2-[1-(S)-Me2NCH(Me)]C6H4, have been synthesized by salt metathesis reactions and have been characterized by multinuclear NMR (1H, 13C, and 27Al), mass spectrometry, and elemental analysis. The molecular structure of compound 3 has been determined by a single-crystal X-ray analysis (space group P212121). Alane 2 exists as a temperature-independent equilibrium mixture of two diastereomers in solution (ratio 45:55); results of NOE experiments on 2 are discussed. Only one isomer was found for compound 3 in solution and its dynamic behavior has been investigated by variable-temperature NMR methods; a ΔH of 56.6(4) kJ mol-1 and a ΔS of -0.79(1) J K-1mol-1 were deduced from band-shape analysis of the 1H-NMR signals of the N-bound methyl groups.
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  • 146
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 165-168 
    ISSN: 1434-1948
    Keywords: Arsenic ; Imino compound ; Hydrazinoiminoarsane ; Aminoiminoarsane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dehydrohalogenation of (2,4,6-tri-tert-butylphenylamino)chloro[tris(trimethylsilyl)hydrazino]arsane (3) or [tert-butyl(trimethylsilyl)amino]chloro(2,4,6-tri-tert-butylphenylamino)arsane (4) with DBU yields novel stable compounds containing an As-N double bond, (2,4,6-tri-tert-butylphenylimino)[tris(trimethylsilylhydrazino]arsane) (5) and [tert-butyl(trimethylsilyl)amino](2,4,6-tri-tert-butylphenylimino)arsane (6). The structure of 5 was confirmed by an X-ray structure determination.
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  • 147
    ISSN: 1434-1948
    Keywords: Pyrazolato ligands ; Rhenium ; Manganese ; Crystal structure ; Heterometallic complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By reacting [Re(CO)3(Hpz)2(pz)] (Hpz = pyrazole) with [Mn(CO)5Br] in toluene in the presence of Et3N, the dinuclear complex [(CO)3Re(pz)3Mn(CO)3](Et3NH) (1) was obtained. The reaction of 1 with molecular oxygen affords the tetranuclear compound [(CO)3Re(pz)3Mn(O)3Mn(pz)3Re(CO)3](Et3NH)2 (3) or the trinuclear compound [(CO)3Re(pz)3Mn(pz)3Re(CO)3](Et3NH)2 (5) depending on the experimental conditions. Complexes 1, 3 and 5 were characterized in the solid state by single crystal X-ray diffraction analysis and were showed to contain Re···Mn interactions linked by and tris-μ2-pyrazolato bridges. In 5, a short [2.397(4) Å] tris(μ2-oxo)bridged MnIV-MnIV contact is found, leading to strong antiferromagnetic coupling of the d3 ions. The homometallic species [(CO)3Mn(pz)3Mn(CO)3](Et3NH) (2) was also prepared and found to be isostructural with 1.
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  • 148
    ISSN: 1434-1948
    Keywords: Cobalt(III) ; Dithionate ; Trithionate ; Sulfato ligand ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crystal structures of amminehalocobalt(III) compounds with di- or trithionate anions have been determined in order to know whether they interact to adopt specific molecular packing patterns and whether di- and trithionate anions undergo the S-S bond cleavage reactions as has been found for the S4O62- ion. In the structures of p-[Co(tren)(NH3)Cl]S2O6·H2O (1) and t-[Co(tren)(NH3)Cl]S2O6 (2), the configurational differences in the cations dictate the hydrogen-bonding pattern with the dithionate anion to lead to racemic structures. cis-[Co(en)2(NH3)Br]S3O6 (3) also crystallizes in a racemic space group P21/c in which the ions form a macrocyclic hydrogen-bonded network. Aqueous solutions of S3O62- and p-[Co(tren)(NH3)Cl]2+ produce p-[Co(tren)(NH3)(OSO3)]ClO4 (4) which is believed to be derived from the hydrolytic cleavage of S-S bond in the trithionate anion. These results reinforce our previous observation of the S-S cleavage reactions for the tetrathionate anion.
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  • 149
    ISSN: 1434-1948
    Keywords: Thiophosphites ; X-ray diffraction ; Manganese ; Iron ; Phosphorus ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thioesters of the phosphorous acid containing cymantrenyl and ferrocenyl substituents at sulfur were obtained for the first time from the reaction of organometallic disulfides with white phosphorus. According to an X-ray diffraction study tricymantrenyl trithiophosphite adopts an unusual asymmetric cis, gauche, trans conformation along the P-S bonds with respect to the phosphorus lone electron pair. Triferrocenyl trithiophosphate possesses a classical propeller-like structure in the solid state which is different from its oxygen analogue.
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  • 150
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 265-270 
    ISSN: 1434-1948
    Keywords: Host-guest compounds ; Tin ; Mercury ; Pnictide halides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel host-guest compound [Hg7As4I3](SnI3) has been prepared by a standard ampoule technique and its crystal structure was determined. It crystallizes in a cubic system [space group P213, a = 13.110(1) Å, Z = 4] with a unique structure type. The crystal structure comprises two parts: the three-dimensional [Hg7As4I3]1+ host network, and the SnI31- guest anions encapsulated in the cavities of the network. The network is built from the As2Hg7 bitetrahedra and As2Hg6 octahedra, which share corners, and contains an additional iodine atom connected to one of the mercury vertices. The SnI31- anion has the shape of a pyramid with the tin atom in a vertex. According to the quantum-chemistry calculations, the geometry of the anion deviates substantially from the equilibrium one, and is influenced by the distant mercury atoms of the host network.
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  • 151
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 271-279 
    ISSN: 1434-1948
    Keywords: Nickel complexes ; Palladium complexes ; S ligands ; Exchange reactions ; Azide ; Sulfinylimide ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to obtain suitable precursors for nickel and palladium complexes that model the reactivity of the active sites of hydrogenases and CO dehydrogenases, a series of [M(L)(‘S3’)] complexes has been synthesized [M = NiII, PdII; ‘S3’2- = bis(2-mercaptophenyl)sulfide(2-)]. X-ray structure determinations of [Ni(‘S3’)]3 (1) and [Pd(‘S3’)]3 (2) have revealed that the [M(‘S3’)] fragments trimerize to give six-membered [MS]3 rings, which exhibit chair conformations with alternating MII centers and thiolate bridging atoms. Reactions of the parent complex [Ni(‘S3’)]3 (1) with nucleophiles L, such as thiolates SR- (R = tBu, Cy, Me, Ph), phosphanes PR3 (R = Cy, Ph), chloride, or azide, have been found to yield the corresponding anionic or neutral [Ni(L)(‘S3’)] complexes, which were isolated as (NBu4)[Ni(SR)(‘S3’)] [R = tBu (3), Cy (4), Me (5), Ph (6)], [Ni(PR3)(‘S3’)] [R = Cy (7), Ph (8)], (NBu4)[Ni(Cl)(‘S3’)] (9), and (NBu4)[Ni(N3)(‘S3’)] (10). When treated with Me3SiX, the StBu- ligand in (NBu4)[Ni(StBu)(‘S3’)] (3) was exchanged to give (NBu4)[Ni(X)(‘S3’)] [X = Cl- (9), N3- (10), NCS- (11), NSO- (12)]. The palladium complex [Pd(‘S3’)]3 (2) could also be cleaved with StBu-, but the resulting (NBu4)[Pd(StBu)(‘S3’)] (13) proved inert towards exchange reactions with Me3SiX. All the mononuclear complexes have been characterized by standard spectroscopic techniques and by elemental analysis. The molecular structures of 3, 4, 6, 7, 8, 9, and 13 have been determined by X-ray crystallography. The [MS3L] core geometries of all the complexes are non-planar, exhibiting a considerable tetrahedral distortion.
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  • 152
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 417-421 
    ISSN: 1434-1948
    Keywords: Phosphorus ; Benzynezirconocenes ; Azazirconacyclopentenes ; Exchange reactions ; 1,2-Azaphosphindole ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first 1,2-azaphosphindoles 14a,b, 15a,b were obtained in a straightforward manner upon heating diphenylzirconocene in the presence of a cyanophosphane, which afforded azazirconacyclopentenes 11a,b which can be reacted with various dichlorophosphanes. The use of the tetrachlorodiphosphane Cl2P(CH2)2PCl2 instead of a dichlorophosphane allowed the preparation of the bis(1,2-azaphosphindoles) 19, 19′. The monosulfur adduct of the azaphosphindole 14a, i.e. 16a, was characterized by X-ray structure analysis. Alkylation of 14a or 16a with methyltrifluoromethane sulfonate occurred selectively on the intracyclic phosphorus atom or on the sulfur atom, giving the salts 20 or 21, respectively.
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  • 153
    ISSN: 1434-1948
    Keywords: Methylnickel complexes ; 2-Phosphanylphenolate ; Chelates ; Homogeneous catalysis ; Oligomerization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of various substituted 2-phosphanylphenols 1a-f with half-molar amounts of cis-[MeNi(μ-OMe)(PMe3)]2 have been found to yield square-planar methyl(2-phosphanylphenolato)(trimethylphosphane)nickel(II) complexes 2a-f. 2JPP coupling constants of 305-316 Hz at low temperature indicate a trans-configuration for the products, while broad 31P-NMR signals at room temperature can be attributed to rapid dissociation of PMe3. Reaction with excess 1 gave rigid bis(2-phosphanylphenolato)nickel(II) complexes as exemplified by 3e, whereas addition of PMe3 to 2a led to the pentacoordinate methyl(2-phosphanylphenolato)bis(trimethylphosphane)nickel(II) complex 4a. Higher yields of 4a and 4d were obtained by reactions of 1a and 1d with Me2Ni(PMe3)3. Single-crystal X-ray diffraction analyses of 3e and 4a have revealed the structures as square-planar trans-bis- and trigonal-bipyramidal mono(2-phosphanylphenolato)nickel(II) P1O-chelate complexes, respectively. The methylnickel complexes 2 and 4 have been found to be effective one-component catalysts for the oligomerization of ethene. High conversions (〉 96%) were achieved with the P-basic derivatives 2e, 2f, and 4d bearing one or two branched alkyl groups (isopropyl, tert-butyl), whereas the diphenylphosphanyl derivatives were less active; 4d gave shorter oligomers than 2e or 2f.
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  • 154
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 447-454 
    ISSN: 1434-1948
    Keywords: Zinc ; Metalloporphyrins ; Porphyrins ; Cations ; Radicals ; ESR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zinc(II) complexes of substituted tetraphenylporphyrins, Zn[T(X-P)P], where X = H, p-F, p-Cl, m-Cl, p-CH3O, and m-CH3O, have been synthesized and characterized. Peripheral substitution shows marked changes in the chemical shifts of the phenyl proton resonances and E1/2 values of the redox couples in the anodic region while the UV/Vis spectra are unaffected. The monocation radicals of these complexes are generated by chemical oxidation with bromine. The ESR spectra reveal the formation of two types of radical species, Zn[T(X-P)P]+·Br- (species I) and Zn[T(X-P)(Brn-P)]+·Br- (species II): Species I at 298 K shows a spectrum, with well-resolved bromine hyperfine features, characteristic of a 2A2u electronic ground state while species II, except for the complex with X = m-CH3O, shows a featureless, isotropic resonance attributable to a 2A1u state. Zn[T(m-CH3O-P)(Brn-P)]+·Br-, on the other hand, exhibits nine resolved nitrogen hyperfine features corresponding to a 2A2u state. Variable temperature ESR spectra (77-298 K) indicate reduction in the bromine and nitrogen hyperfine coupling constants and an increase in the g value of species I from 2.0049 to 2.0060 with lowering temperature and suggest a labile electronic ground state for species I. The p-CH3O substituted complex exhibits an electronic transformation from 2A2u to 2A1u while the remaining complexes, including m-CH3O, show a transformation from 2A2u to an admixed 2A1u/2A2u state. The effect of substitution on the variable temperature ESR spectra are discussed.
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  • 155
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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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  • 156
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 477-483 
    ISSN: 1434-1948
    Keywords: Arsenic ; UV photoelectron spectroscopy ; Ab initio calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, we report the gas-phase characterization of two differently substituted amino(iminoarsanes), TmpAs=NSiMe3 and (SiMe2tBu)2NAs=N(SiMe2tBu), by coupling flash vacuum thermolysis (FVT) with UV photoelectron spectroscopy (PES). Quantum chemical calculations, using the DFT method (B3LYP) with the basis set 6-311G(d,p), have also been carried out on the R1As=NR2 unit with R1 = H, NH2, N(CH3)2, N(SiH3)2 and R2 = H, SiH3, in order to study the effect of substitution on the electronic properties and the thermodynamic stability of the As=N skeleton. Similarities with phosphorus analogues are also discussed.
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  • 157
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 987-991 
    ISSN: 1434-1948
    Keywords: Thermochemistry ; Alkaline-Earth Alkoxides ; Enthalpy of Formation ; Calcium ; Magnesium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enthalpies of formation of some alkaline-earth alkoxides were determined by reaction-solution calorimetry (ΔfHo[Mg(OMe)2] = -792.6±1.2 kJ/mol; ΔfHo[Mg(OEt)2] = -847.9±2.7 kJ/mol; ΔfHo[Ca(OMe)2] = -890.8±6.4 kJ/mol; ΔfHo[Ca(OEt)2] = -924.5±2.6 kJ/mol; ΔfHo[Ca(OBu)2] =-989.8±5.4 kJ/mol) and allowed us to extend a previously developed model for predicting the enthalpies of formation of Be, Sr and Ba alkoxides.
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  • 158
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1007-1013 
    ISSN: 1434-1948
    Keywords: Linkage isomerization ; NMR spectroscopy ; Nucleobases ; Platinum ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(9-methyladenine) complexes of cis-PtII(NH3)2 undergo slow linkage isomerization from the N7 to the N1 site in aqueous solution at elevated temperatures. The ratio of the isomeric complexes during the isomerization process indicates that whilst PtII prefers the N(7) site in the adenine moiety kinetically, it is the N(1) coordination mode which is thermodynamically more stable. The crystal structures of the isomers do not reveal any unusual features; the few apparently structurally significant differences in the bond angles in the N(1)-bound bis(complex) merely reflect the poor quality of the crystal and/or crystal packing effects rather than a direct result emanating from the coordination mode of the ligand.
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  • 159
    ISSN: 1434-1948
    Keywords: Metal complexes ; Template synthesis ; Schiff bases ; Oxaazamacrocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New series of macrocyclic Schiff-base lanthanide(III), yttrium(III), and cadmium(II) complexes, [M(1)]Xn (X = NO3-, M = Y, Ln = La-Yb except Pm and Dy; X = ClO4-, M = Cd, La, Ce, Pr, Sm, Gd, or Er) and [M(3)]Xn (X = NO3-, M = Dy; X = ClO4-, M = Er and Cd), have been prepared by cyclocondensation of O1,O7-bis(2-formylphenyl)-1,4,7-trioxaheptane with O1,O7-bis(2-aninyl)-1,4,7-trioxaheptane (1) or tris(2-aminoethyl)amine (3) in the presence of the appropriate metal salt as a template agent. The Schiff-base macrocycles 1 and 3 are also formed in the absence of a metal ion. Treatment of 1 with NaBH4 in methanol gives the diamine macrocycle 2. The reactions of LnIII, CdII, and YIII ions with 2 have also been investigated. The crystal structures of the monoprotonated ligand 2 and of the complex [Cd(3)](ClO4)2 have been determined by X-ray diffraction analysis.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99352_s.pdf or from the author.
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  • 160
    ISSN: 1434-1948
    Keywords: Molybdenum ; Fluxionality ; Pyridylphosphanes ; Phosphane oxides ; Polydentate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pseudo-octahedral complexes [Mo(η3-allyl)Br(CO)2(PPynPh3-n-P,N)] (Py = 2-pyridyl; n = 2, 3) and [Mo(η3-allyl)Br(CO)2(OPPymPh3-m-O,N)] (m = 1, 2, 3) undergo three different dynamic processes in solution, depending on the chelating ligand. The complexes containing PPhPy2 and PPy3 as chelating P,N-donors undergo a novel “pivoted double switch” mechanism which scrambles two equatorial coordination sites with racemization, while maintaining the identity of the phosphorus atom trans to the allyl ligand. The complexes containing 2-pyridylphosphane oxides as chelating O,N-donors undergo a nondissociative intramolecular trigonal-twist (or turnstile) rearrangement which maintains the identity of the phosphane oxide oxygen atom coordinated in an equatorial position. All the complexes containing uncoordinated pyridyls undergo a slow dissociative exchange of pyridyls without coordination site scrambling. The structure of the complex [Mo(η3-allyl)Br(CO)2(OPPy3-O,N)] has been determined by X-ray diffraction.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99363_s.pdf or from the author.
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  • 161
    ISSN: 1434-1948
    Keywords: Silicon ; Silyl anions ; Lithium ; Silanes ; Polysilyl dianions ; α,ω-Dilithiooligosilanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (Me3Si)3Si(Me2Si)2(Me3Si)2SiLi (1) and LiSi(Me3Si)2(Me2Si)2Si(Me3Si)2Li (2) were synthesized by the reaction of (Me3Si)3Si(Me2Si)2Si(Me3Si)3 in THF with one or two mol-equivalents, respectively, of MeLi. Both 1 and 2 were characterized spectroscopically and by trapping reactions, and 1 also by X-ray crystallography.
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  • 162
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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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  • 163
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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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  • 164
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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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  • 165
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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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  • 166
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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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  • 167
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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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  • 168
    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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  • 169
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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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  • 170
    ISSN: 1434-1948
    Keywords: Photocatalysis ; Polyoxotungstates ; Catalytic oxidations ; Iron porphyrins ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photoexcitation of (nBu4N)4W10O32 is a suitable mean of oxidizing cyclohexene and cyclooctene with O2 at room temperature and pressure. This process can be carried out in homogeneous solution as well as using the decatungstate in a dispersed form after its heterogenisation on silica. Cyclohexene and cyclooctene are mainly oxidized to the corresponding hydroperoxides as a consequence of primary photoprocesses which lead to the formation of allylic radicals. The presence of the FeIII[meso-tetrakis(2,6-dichlorophenyl)porphyrin] chloride as cocatalyst strongly affects the photocatalytic properties of (nBu4N)4W10O32, playing a key role in the allylic-hydroperoxide dependent oxidation of the cycloalkenes. In the photooxidation of cyclohexene, the porphyrin increases the photocatalytic efficiency of the decatungstate in terms of total turnover number and catalyses the decomposition of cyclohexenyl hydroperoxide with the selective formation of cyclohex-2-en-1-ol. On the other hand, its presence during the photoinduced oxidation of cyclooctene favours the formation of cyclooctene epoxide by addition of ROO· and RO· radicals to the double bond. In the case of cyclooctene, the heterogenisation of the decatungstate on the solid support also affects the chemoselectivity of the photocatalytic process in the absence of the iron porphyrin complex.
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    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 1-11 
    ISSN: 1434-1948
    Keywords: Carbaalanes ; Cluster compounds ; Electron deficiency ; Aluminium ; Boron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cluster chemistry in the third main group has long been restricted to compounds of the lightest element boron. However, about 30 years ago the first compounds were synthesized and characterized in which single aluminium atoms adopted positions of high connectivity in polyhedral borane or carbaborane clusters. The next successful step in these efforts to establish a chemistry analogous to that of the polyboranes with the heavier elements of the third main-group was the synthesis of closo-dodecaaluminate [Al12iBu12]2- at the beginning of the nineties, which was the first homonuclear aluminium analogue of a polyborate anion and had a core exclusively formed by aluminium atoms. Another class of interesting new aluminium compounds was formed by the carbaalanes, which were synthesized and characterized for the first time only recently. They have clusters of aluminium and carbon atoms, and are similar to the carbaborane analogues in that their structures seem to be determined by the number of electron pairs in their molecular centers in accordance with the Wade rules.
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  • 172
    ISSN: 1434-1948
    Keywords: Pyrazolato complexes ; Dinuclear complexes ; Ketonic carbonyls ; Ruthenium ; Osmium ; Rhodium ; Iridium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The metal-metal bonded dicarbonyl compounds [(η6-p-cymene)M(μ-pz)2IrCl(CO)2](M-Ir) react stereospecifically with PPh3 to yield an enantiomeric pair of ketonic carbonyl compounds [(η6-p-cymene)M(μ-CO)(μ-pz)2IrCl(CO)(PPh3)] [M = Ru (1), Os (2)] in which the chloride ligand is trans to the bridging ketone group. However, the non metal-metal bonded isomers [(η6-p-cymene)MCl(μ-pz)2M′(CO)2], under similar conditions, eliminate CO forming the monosubstitution products [(η6-p-cymene)MCl(μ-pz)2M′(CO)(PPh3)] [M = Ru; M′ = Ir (3), Rh (4). M = Os; M′ = Rh (5)]. Removal of the chloride ligand in 1 affords [RuIr(η6-p-cymene)(CO)2(PPh3)(pz)2]BPh4 as two isomers, 6a,b. The related OsIr compound [(η6-p-cymene)Os(μ-CO)(μ-pz)2Ir(CO)(PPh3)]BPh4 (9) has been prepared from [(η6-p-cymene)Os(CO)(μ-pz)2Ir(CO)2]BPh4 (7) and PPh3. Again, the OsRh tricarbonyl related to 7 [(η6-p-cymene)Os(CO)(μ-pz)2Rh(CO)2]BPh4 (8) reacts differently with PPh3 affording [(η6-p-cymene)Os(CO)(μ-pz)2Rh(CO)(PPh3)]BPh4 (10).
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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) 
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    Keywords: Chemistry ; General Chemistry
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  • 175
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    Chemistry - A European Journal 1 (1995), S. i 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
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  • 176
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    Chemistry - A European Journal 1 (1995), S. 3-3 
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
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  • 177
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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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  • 178
    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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  • 179
    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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  • 180
    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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  • 181
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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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  • 182
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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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  • 183
    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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  • 184
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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
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  • 185
    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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  • 186
    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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  • 187
    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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  • 188
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    Chemistry - A European Journal 1 (1995), S. cpi 
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    Keywords: Chemistry ; General Chemistry
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  • 189
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    Chemistry - A European Journal 1 (1995) 
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    Keywords: Chemistry ; General Chemistry
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  • 190
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    Chemistry - A European Journal 1 (1995), S. i 
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    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 191
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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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  • 192
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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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  • 193
    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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  • 194
    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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  • 195
    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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  • 196
    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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  • 197
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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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  • 198
    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.
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  • 199
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    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
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  • 200
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    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.
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