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  • Cycloadditions  (2)
  • Nickel complexes  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 1715-1725 
    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.
    Additional Material: 4 Ill.
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  • 2
    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.
    Additional Material: 2 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    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.
    Additional Material: 5 Ill.
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  • 4
    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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