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  • 1
    ISSN: 1434-4475
    Keywords: Keywords. Alkali metal organophosphanylamide; Rubidium ; phosphorus bonding; Caesium ; carbon bonding; 18-crown-6 complexes; Caesium-phosphorane-iminato complex.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The metalation of bis(diphenylphosphanyl)amine, HN(PPh2)2 (5), with RbOtBu in the presence of N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDTA (3)) in toluene surprisingly affords the nearly PMDTA free RbN(PPh2)2 (6a). Recrystallization of 6a from tetrahydrofuran (THF) yields RbN(PPh2)2ċ0.5 THF (6b). Compounds 6a, b crystallize in thin needles; however, these are not suitable for X-ray structure analyses. The reactions of 5 with MOtBu (M=Rb, Cs) in the presence of 18-crown-6 in toluene yield the monomeric, pale yellow rubidium and caesium complexes [Rb(18-crown-6)(N(PPh2)2)] (7) and [Cs(18-crown-6)(N(PPh2)2)] (8), respectively. Allowing to stand a solution of 8 in THF for three months at 20°C results in a cleavage product of 8. This is identified as the dimeric yellow complex [(Cs(18-crown-6))2(μ-N*P(H)Ph2)2]ċTHF (9). The source of the hydrogen atom in the bridging phosphorane iminate anion [N*P(H)Ph2]− is uncertain. Compounds 7–9 are structurally characterized by X-ray analyses. These reveal that [N(PPh2)2]− acts as P-ligating chelate in 7, whereas it coordinates the Cs+ as N-donor as well as η2 C-donor with one phenyl group in 8. No phosphorus coordination is observed in 8. The two caesium cations in 9 are two-fold N-bridged by [N*P(H)Ph2]−. The coordination sphere of each caesium atom is completed by a 18-crown-6 ligand. The solid state 13C NMR spectrum of 8 reveals dynamic phenomena (rotation of the 18-crown-6 ligand). In the solid state 31P spectrum of 8, 31P, 31P–J-coupling is observed between the chemically non-equivalent phosphorus sites (J=390 Hz).
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  • 2
    ISSN: 1434-4475
    Keywords: Keywords. Paramagnetic; Five-fold coordinated trigonal bipyramidal cobalt(III) complex; Crystal structure; Octaphenyl-tetraphospha-diazene; Imido-tetraphenyl-diphosphinate; Octacarbonyldicobalt.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The reaction of Co2(CO)8 and Ph2P-N*PPh2-PPh2*N-PPh2 (1) in a molar ratio between 1:1 and 1:3 in toluene always leads to the formation of both the yellow by-product [fac-Co(CO)3(Ph2P-N*PPh2-PPh2*N-PPh2-P,P′)] [Co(CO)4] (4) and the red compound [(Co)2(μ-CO)(CO)4(μ-Ph2P-N-PPh2)2] (5) that has already been characterized by spectroscopic data and X-ray analysis. Whereas 4 is obtained as a precipitate, the red compound 5 stays in solution and reacts in presence of air with the remaining ligand 1 in a non-stoichiometrical reaction to the violet cobalt(III) complex [Co(η1-O-PPh2*N-PPh2*O)(η2-O-PPh2*N-PPh2*O)2] (6). The crystal structure of 6 proves a distorted trigonal bipyramidal coordination of the oxygen atoms at the Co(III) ion. Surprisingly, complex 6 shows an unusual paramagnetism according to four unpaired electrons (5.21±0.04 BM).
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. m117-m118 
    ISSN: 1600-5368
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The crystal structure of the title compound, [Rh(C8H12)2](CF3SO3), consists of [(C8H12)2Rh]+ cations and F3CSO3− anions. The cycloocta-1,5-diene ligands are chelated to the central metal atom to create a coordination geometry about rhodium which is essentially square planar.
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  • 4
    ISSN: 0948-5023
    Keywords: Keywords Macrocycle, Schiff base, NMR, chemical exchange, MD, proton template, ROESY, EXSY
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Schiff base condensation of the pentadentate tetrapodal amine 1 with 2,6-diformyl-4-methylphenol 2 leads in a [3 + 6] condensation to a previously not described macrocycle 3 which shows C 3-symmetry. X-ray analysis shows a truncated cone shape for 3. At T ≥ 100°C, the 1H-ROESY/EXSY spectrum reveals pairwise exchange of corresponding sites, indicative of inversion of the whole molecule in an umbrella-like fashion. Molecular dynamics simulations support this hypothesis.
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  • 5
    ISSN: 1573-4951
    Keywords: centrosymmetry ; CoMFA-Field fit ; GRID ; HIV-1 protease ; X-ray crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The functional groups of cage dimeric N-alkyl substituted 3,5-bis(hydroxymethyl)-4-(4-methoxyphenyl)-1,4-dihydropyridines are similar to those of cyclic and azacyclic ureas that are potent inhibitors of HIV-1 protease of the dihydroxyethylene- and hydroxyethylene type, respectively. In the following study the conformity of common functional groups is investigated concerning their orientation in space as well as in the enzyme HIV-1 protease. Starting from X-ray crystal data of the centrosymmetric cage dimeric N-benzyl derivative with ester groups, the derivative with hydroxymethylene groups was built and a systematic conformational search was performed for the conformationally important torsion angles considering electrostatic and van der Waals interactions. From the huge number of conformations those comprising centrosymmetrical and C2-symmetrical energy minima were selected and minimized. The three remaining conformers were fitted to the azacyclic urea A-98881 selected from the HIV-1 protease enzyme- inhibitor complex using the centroids of the corresponding aromatic residues and additionally by the field fit option of the Advanced CoMFA module of SYBYL. Interestingly, the energetically most favourable one, which, additionally, possesses C2-symmetry like the active site cavity of HIV-1 protease, showed the best fit. Comparing the electrostatic potential (EP) of the latter with the EP of A-98881 the aromatic residues show excellent accordance. Slight differences in the extent of the EP were found in the areas of the hydroxymethylene groups of the cage dimer and the single hydroxy group as well as the urea carbonyl group of A- 98881, respectively. In order to compare the binding possibilities to the enzyme HIV-1 protease for the cage dimer and A-98881, their interaction fields with certain probes (CH3 for alkyl, NHamide, and carbonyl, O− of COO−), representing the decisive functional groups of the active site, have been calculated using GRID and projected into the enzyme placing the structures according to the position of A-98881 in the enzyme- inhibitor complex. The strongest calculated fields of the O− probe were found near Asp 25 for both structures. Another respective conformity consists in the overlap of the fields for the NHamide probe near Ile 50 and 50′ for the investigated cage dimer and A-98881.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1213-1218 
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Diazatetraasteranes ; Crystal structure ; Solid-state chemistry ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Upon irradiation, crystalline 4-methoxyphenyl-1,4-dihy-dropyridines 1 undergo nearly quantitative [2+2]cyclo-addition to form, via the ring-open intermediates 2, the centrosymmetric, polyfunctionalized 3,9-diazatetraasteranes 3. The centrosymmetric character of 3 was confirmed by 1H NMR spectral data as well as by X-ray crystal structure analysis. The dimerization reactions prove to be topochemically controlled by the nearest distance between potentially reacting double bonds, as well as by the conformationally determined packing restraints. This latter factor is shown by the X-ray crystal structure analysis of one dimerizing and one photostable derivative of the monomers 1.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 245-249 
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Cage compounds ; Dimerizations ; Steric hindrance ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---On irradiation at λ ≥ 270 nm solutions of 4-aryl-1,4-dihydropyridines 1 yield cage dimers 2 as the main products beside small amounts of anti dimers 3. 1H-NMR data and X-ray crystal structure prove centrosymmetrical properties for both dimers with axially orientated 4-aryl substituents. Irradiation with filtered light (λ 〉 313 nm) leads to syn and anti dimers 4 and 3 in nearly equal yields. The poor yields of anti dimers 3 on irradiation with unfiltered light are demonstrated to result from a partial cleavage back to their monomeric starting materials 1.
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  • 8
    ISSN: 1434-1948
    Keywords: S ligands ; P ligands ; Osmium ; Solvent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In search for osmium complexes with sulfur-dominated coordination spheres that potentially bind and activate or stabilize nitrogenase relevant small molecules, several osmium-sulfur complexes containing 1,2-bis(2-mercaptophenylthio)ethane(2-) (′S4′2-) and benzenedithiolate (′S2′2-) ligands were synthesized. [OsII(PR3)2(′S4′)] [R = Ph (1), Et (2)], [OsIV(PR3)2(′S2′)2] [R = Et (3), Pr(4), Me(5), Ph(6)], [OsIV(PCy3)(′S2′)2] (7), (PHCy3)[OsIII(′S2′)2] (8a), (NMe4)[OsIII(′S2′)2] (8b), and (NBu4)2[OsIV(′S2′)3] (9b) were obtained in reactions starting from commercially available osmium compounds and the sulfur and phosphane ligands. The presence or absence of reducing solvents strongly influenced these reactions. Octahedral (3), (4), and (PHCy3)2[OsIV(′S2′)3] (9a) were characterized by X-ray structure analysis, leading to the conclusion that despite the high oxidation state of the osmium centers, innocent dithiolate ligands are present. The stabilization of the OsIV centers is traced back to S→M π donation. Close inspection of 1 and 2 revealed a large influence of the phosphane ligands on the stability of OsII thioether complexes. While 1 is reasonable stable, 2 readily gives 3 and ethylene via intramolecular ′S4′2- ligand reduction and OsIII→ OsIV oxidation. UV-Vis spectra of 3-5 indicate phosphane dissociation in solution leading to pentacoordinate [Os(PR3)(′S2′)2] complexes. This was confirmed by the synthesis of pentacoordinate [Os(PCy3)(′S2′)2] (7).
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  • 9
    ISSN: 1434-1948
    Keywords: N ligands ; S ligands ; Iron ; Ruthenium ; Pentadentate ligands ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to obtain iron and ruthenium complexes which are analogous to [M(L)(′NHS4′)] and [M(L)(′N2H2S3′)] complexes [′NHS4′2- = 2,2′-bis(2-mercaptophenylthio)diethylamine(2-), ′N2H2S3′2- = 2,2′-bis(2-mercaptophenylamino)diethylsulfide(2-)] but have electron-richer metal centers, the new pentadentate amine thiolate ligand ′N3H3S2′-H2 [ = 2,2′-bis(2-mercaptophenylamino)diethylamine] (4) was synthesized. The dianion ′N3H3S2′2- reacted with FeII salts to give high-spin [Fe(′N3H3S2′)] (5) [μeff (293 K) = 3.94 μB], which yielded diamagnetic [Fe(CO)(′N3H3S2′)] (6) upon reaction with CO. Complex 6 exhibits a low-frequency ν(CO) band (1934 cm-1 in THF) indicating an electron-rich Fe center and a strong Fe-CO bond. In spite of this, 6 readily dissociated in solution to 5 and CO. The reaction of [RuCl2(PPh3)3] with ′N3H3S2′2- yielded [Ru(PPh3)(′N3H3S2′)] (7), which proved inert with respect to PPh3 substitution but could be methylated at the thiolate donors. The resulting [Ru(PPh3)(′N3H3S2′-Me2)]I2 (8) proved as inert towards substitution as 7. Complex 8 could reversibly be deprotonated to give [Ru(PPh3)(′N3H2S2′-Me2)]I (11), in the course of which the [RuPN3S2] cores rearrange from CS to C1 symmetry. Reversible protonation/deprotonation was also found with [Ru(NO)(′N3H2S2′)] (9) which formed from [RuCl3(NO)(PPh3)2] and ′N3H3S2′2- in the presence of one additional equivalent of LiOMe. Protonation of 9 with HBF4 gave [Ru(NO)(′N3H3S2′)]BF4 (10). The NMR spectra and the X-ray structure analysis of 8 proved that the [RuPN3S2] cores of 7 and 8 exhibit a CS-symmetrical meso structure. In all other complexes, however, the [MLN3S2] cores exhibit a C1-symmetrical structure. It results from the fac-mer coordination mode of the ′N3H3S2′2- ligand and favors the planarization of amide donors when NH functions are reversibly deprotonated.
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  • 10
    ISSN: 1434-1948
    Keywords: Nickel complexes ; Platinum complexes ; S ligands ; C-S cleavage ; Hydride complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nickel and platinum complexes with tridentate ligands, having [S3] or [NS2] donor sets were investigated in order to model active sites of enzymes such as hydrogenases or CO dehydrogenases. Starting from diphenyl sulfide, a preparative synthesis was developed for ‘S3’-H2 [‘S3’-H2 = bis(2-mercaptophenyl) sulfide]. Reactions of ‘S3’-H2 or anionic ‘S3’2- with nickel and platinum precursors resulted in the formation of binuclear [Ni(‘S3’)]2 (1) and trinuclear [Pt(‘S3’)]3 (5). Complex 1 was cleaved by PMe3 or CN- to give the mononuclear complexes [Ni(‘S3’)(PMe3)] (2) and NMe4[Ni(‘S3’)(CN)] (3). Attempts to coordinate hydride to the [Ni(‘S3’)] fragment led to C-S bond cleavage of the ligand and formation of (NMe4)2[{Ni(μ-SC6H5)(S2C6H4)}2] (4). Oxidative addition of Li[‘S3’-H] to [Pt(PPh3)4] afforded the platinum hydride complexes Li[Pt(H)(‘S3’)] and Li[Pt(H)(PPh3)(‘S3’)] which, however, could not be separated from each other and yielded [Pt(‘S3’)(PPh3)] (6) when treated with MeOH. In order to investigate electronic effects of the donor set, the ‘S3’ ligand was modified by alkylation of one thiol group to give ‘RS3’-H derivatives (R = Me, Et, Cy) and by replacing a mercaptophenyl unit by an amine in ‘Et2NS2’-H [‘Et2NS2’-H = N,N-diethyl-2-(2-mercaptothiophenyl)ethylamine]. Reactions of NiII or Ni0 compounds with these ligands in a 1:1 ratio yielded the 1:2 complexes [Ni(‘MeS3’)2] (7), [Ni(‘EtS3’)2] (9) and [Ni(‘CyS3’)2] (10), with ‘RS3’- acting as bidentate ligands only. Complex 7 reversibly reacted with PMe3 to form cis-[Ni(PMe3)2(‘MeS3’)2] (8), exhibiting monodentate ‘MeS3’ ligands. [Ni(‘Et2HNS2’)2]Br2 (11) reacted reversibly with bases to presumably give octahedral [Ni(‘Et2NS2’)2]. Complexes 7, 9 and 10 also did not yield any [Ni(‘RS3’)(H)] hydride complex when treated with hydride sources. Oxidative addition of ‘CyS3’-H to [Pt(PPh3)4] yielded the hydride complexes [Pt(H)(‘CyS3’)] and [Pt(H)(PPh3)(‘CyS3’)] which, however, formed an inseparable mixture and underwent C-S bond cleavage when heated, affording [Pt(o-S2C6H4)(PPh3)2]. The molecular structures of 1, 2, 3, 5, 6, 7, and 11 were determined by X-ray crystallography, revealing butterfly-like shapes for the [MS3L] cores of the complexes.
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