Synthesis and Structural Studies of Nickel(0) Tetracarbene Complexes with the Introduction of a New Four-Coordinate Geometric Index, τδ

The synthesis and characterization of two homoleptic chelating nickel(0) tetracarbene complexes are reported. These are the first group 10 M(0) (M = Ni, Pd, Pt) tetracarbene complexes. These species have geometries intermediate between C2v sawhorse and tetrahedral and show high UV–vis absorption in the 350–600 nm range, with extinction coefficients (ϵ) between 5600 and 9400 M–1 cm–1. Density functional theory analysis indicates that this high absorptivity is due to metal-to-ligand charge transfer. In order to better describe the unusual geometries encountered in these complexes, an adjustment to the popular τ4 index for four-coordinate geometries is introduced in order to better delineate between sawhorse and distorted tetrahedral geometries.本文报道了两种同配螯合型四卡宾镍(0)配合物的合成与表征。此类配合物为首例第10族M(0)（M=Ni、Pd、Pt）四卡宾配合物。该类配合物的几何构型介于C₂v对称锯马型与四面体型之间，在350~600 nm波段展现出强紫外-可见吸收，摩尔消光系数(ϵ)介于5600~9400 M⁻¹·cm⁻¹之间。密度泛函理论（Density Functional Theory, DFT）分析表明，该高吸收特性源于金属-配体电荷转移。为更精准地描述此类配合物中出现的非常规几何构型，本文对广为使用的四配位几何τ4指数（τ4 index）进行了修正，以更好地区分锯马型与畸变四面体型构型。