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| - Characterization of Steric and Electronic Properties of NiN2S2Complexes as S-Donor Metallodithiolate Ligands
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| - The physical properties and structures of a series of six complexes of the type (NiN2S2)W(CO)4have been used to establish electronic and steric parameters for square planar NiN2S2 complexes asbidentate, S-donor ligands. According to the ν(CO) stretching frequencies and associated computed Cotton−Kraihanzel force constants of the tungsten carbonyl adducts, there is little difference in donor abilities ofthe five neutral NiN2S2 metallodithiolate ligands in the series. The dianionic Ni(ema)2- (ema = N,N‘-ethylenebis(2-mercaptoacetamide)) complex transfers more electron density onto the W(CO)4 moiety. Aranking of donor abilities and a comparison with classical bidentate ligands is as follows: Ni(ema)=>{[NiN2S2]0} > bipy ≈ phen > Ph2PCH2CH2PPh2> Ph2PCH2PPh2. Electrochemical data from cyclicvoltammetry find that the reduction event in the (NiN2S2)W(CO)4 derivatives is shifted to more positivepotentials by ca. 0.5 V compared to the ca. −2 V NiII/I redox event in the free NiN2S2 ligand, consistent withthe electron drain from the nickel−dithiolate ligands by the W(CO)4 acceptor. Differences in NiII/I ΔE1/2values appear to have a ligand dependence which is related to a structural feature of the hinge angleimposed by the (μ-SR)2 bridges. Thus the angle formed by the intersection of NiN2S2/WS2C2 planes hasbeen established by X-ray diffraction analyses as a unique orientational feature of the nickel−dithiolateligands in contrast to classical diphosphine or diimine ligands and ranges in value from 136 to 107°. Variable-temperature 13C NMR studies show that the spatial orientations of the ligands remained fixed with respectto the W(CO)4 moiety to temperatures of 100 °C.
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