Characterization of Steric and Electronic Properties of NiN2S2 Complexes as S-Donor Metallodithiolate Ligands

The physical properties and structures of a series of six complexes of the type (NiN2S2)W(CO)4
have been used to establish electronic and steric parameters for square planar NiN2S2 complexes as
bidentate, 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 of
the 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. A
ranking of donor abilities and a comparison with classical bidentate ligands is as follows:  Ni(ema)= >
{[NiN2S2]0} > bipy ≈ phen > Ph2PCH2CH2PPh2 > Ph2PCH2PPh2. Electrochemical data from cyclic
voltammetry find that the reduction event in the (NiN2S2)W(CO)4 derivatives is shifted to more positive
potentials by ca. 0.5 V compared to the ca. −2 V NiII/I redox event in the free NiN2S2 ligand, consistent with
the electron drain from the nickel−dithiolate ligands by the W(CO)4 acceptor. Differences in NiII/I ΔE1/2
values appear to have a ligand dependence which is related to a structural feature of the hinge angle
imposed by the (μ-SR)2 bridges. Thus the angle formed by the intersection of NiN2S2/WS2C2 planes has
been established by X-ray diffraction analyses as a unique orientational feature of the nickel−dithiolate
ligands 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 respect
to the W(CO)4 moiety to temperatures of 100 °C.

一系列六种(NiN2S2)W(CO)4型配合物的物理性质及结构已被用于确立方形平面NiN2S2配合物作为双齿配体、S供体配体的电子和立体参数。根据钨羰基加合物的ν(CO)伸缩振动频率及其相关的计算Cotton−Kraihanzel力常数，该系列中五种中性NiN2S2金属二硫代酸根配体的供体能力差异不大。二阴离子Ni(ema)2-（ema = N,N‘-乙烯双(2-巯基乙酰胺)）配合物将更多的电子密度转移至W(CO)4基团。供体能力的排序及与经典双齿配体的比较如下：Ni(ema)= {[NiN2S2]0} > bipy ≈ phen > Ph2PCH2CH2PPh2 > Ph2PCH2PPh2。循环伏安法测得的电化学数据显示，(NiN2S2)W(CO)4衍生物的还原事件相对于自由NiN2S2配体的约-2 V NiII/I氧化还原事件，正向偏移了约0.5 V，这与W(CO)4受体从镍-二硫代酸根配体中抽取电子一致。NiII/I ΔE1/2值的变化似乎与配体有关，这与其由(μ-SR)2桥所施加的铰链角的结构特征相关。因此，由NiN2S2/WS2C2平面交点形成的角度已被X射线衍射分析确立为镍-二硫代酸根配体独特的取向特征，与经典的二膦或二亚胺配体形成对比，其值介于136°至107°之间。变温13C核磁共振研究表明，配体的空间取向相对于W(CO)4基团在100 °C的温度下保持固定。