Four dimeric nickel(II) complexes [Ni2Cl2(BnC2S)2] [1], [Ni2Cl2(BnC3S)2] [2], [Ni2(PyC2S)2]Br2 [3]Br2, and [Ni2(PyC3S)2]Br2 [4]Br2 of four different thiolate-functionalized N-heterocyclic carbene (NHC) ligands were synthesized, and their structures have been determined by single-crystal X-ray crystallography. The four ligands differ by the alkyl chain length between the thiolate group and the benzimidazole nitrogen (two -C2- or three -C3- carbon atoms) and the second functionality at the NHC being a benzyl (Bn) or a pyridylmethyl (Py) group. The nickel(II) ions are coordinated to the NHC carbon atom and the pendent thiolate group, which bridges to the second nickel(II) ion creating the dinuclear structure. Additionally, in compounds [1] and [2], the fourth coordination position of the square-planar Ni(II) centers is occupied by the halide ions, whereas in [3]2+ and [4]2+, the additional pendant pyridylmethyl groups complete the coordination spheres of the nickel ions. The electrochemical properties of the four complexes were studied using cyclic voltammetry and controlled-potential coulometry methods. The thiolate-functionalized carbene complexes [1] and [2] appear to be poor electrocatalysts for the hydrogen evolution reaction; the complexes [3]Br2 and [4]Br2, bearing an extra pyridylmethyl group, show higher catalytic activity in proton reduction, indicating that the pyridine group plays an important role in the catalytic cycle.

中文翻译：

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硫酸酯官能化碳配体的双核镍配合物及其电化学性质。

四种二聚镍（II）配合物[Ni2Cl2（BnC2S）2] [1]，[Ni2Cl2（BnC3S）2] [2]，[Ni2（PyC2S）2] Br2 [3] Br2和[Ni2（PyC3S）2]合成了四种不同硫醇酸酯官能化的N-杂环卡宾（NHC）配体的Br2 [4] Br2，并通过单晶X射线晶体学确定了它们的结构。四个配体的不同之处在于硫醇盐基团与苯并咪唑氮原子（两个-C2-或三个-C3-碳原子）之间的烷基链长，而在NHC上的第二个官能团是苄基（Bn）或吡啶基甲基（Py）基团。镍（II）离子与NHC碳原子和侧基硫醇盐基团配位，后者与第二个镍（II）离子桥接形成双核结构。此外，在化合物[1]和[2]中，方平面Ni（II）中心的第四个配位位置被卤离子占据，而在[3] 2+和[4] 2+中，额外的吡啶甲基侧基完成了镍离子的配位球。使用循环伏安法和控制电位库仑法研究了四种配合物的电化学性质。硫醇盐官能化的卡宾配合物[1]和[2]似乎是析氢反应的不良电催化剂。带有额外吡啶甲基的配合物[3] Br2和[4] Br2在质子还原中显示出更高的催化活性，表明吡啶基在催化循环中起着重要的作用。硫醇盐官能化的卡宾配合物[1]和[2]似乎是析氢反应的不良电催化剂。带有额外吡啶甲基的配合物[3] Br2和[4] Br2在质子还原中显示出更高的催化活性，表明吡啶基在催化循环中起着重要的作用。硫醇盐官能化的卡宾配合物[1]和[2]似乎是析氢反应的不良电催化剂。带有额外吡啶甲基的配合物[3] Br2和[4] Br2在质子还原中显示出更高的催化活性，表明吡啶基在催化循环中起着重要的作用。