Characterization of Steric and Electronic Properties of NiN2S2 Complexes as S-Donor Metallodithiolate Ligands
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- 作者：Marilyn V. Rampersad ; Stephen P. Jeffery ; Melissa L. Golden ; Jonghyuk Lee ; Joseph H. Reibenspies ; Donald J. Darensbourg ; and Marcetta Y. Darensbourg
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：December 14, 2005
- 年：2005
- 卷：127
- 期：49
- 页码：17323 - 17334
- 全文大小：349K
- 年卷期：v.127,no.49(December 14, 2005)
- ISSN：1520-5126
文摘
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 
(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 
E1/2values appear to have a ligand dependence which is related to a structural feature of the hinge angleimposed by the (
-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.
(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 E1/2values appear to have a ligand dependence which is related to a structural feature of the hinge angleimposed by the (-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.