Preparation and Structures of Group 12 and 14 Element Halide-Carbene Complexes

The synthesis of a series of N-heterocyclic carbene (NHC) complexes involving zinc, cadmium, and the heavy Group 14 elements germanium, tin, and lead is reported. The direct reaction between the bulky carbene IPr (IPr = (HCNDipp)(2)C:, Dipp = 2,6-(Pr2C6H3)-Pr-i) and the Group 14 halide reagents GeCl4 and SnCl4 afforded the 1 : 1 complexes IPr center dot ECl4 (E = Ge and Sn) in high yield; similarly, ZnI2 interacted with IPr in THF to give the THF-bound complex IPr center dot ZnI2 center dot THF. CdCl2 underwent divergent chemistry with IPr and the major product isolated was the imidazolium salt [IPrH][IPr center dot CdCl3], which could be converted into IPr center dot CdCl2 center dot THF upon treatment with Tl[OTf]. In addition, the stable Pb II amide adduct, IPr center dot PbBr (NHDipp), was prepared. Each of the new carbene-element halide adducts was treated with the hydride sources Li[BH4] and Li[HBEt3] in order to potentially access new element hydride adducts and/or clusters. In most instances scission of the element-carbene bonds transpired, except in the case of IPr center dot ZnI2 center dot THF, which reacted with two equivalents of Li[BH4] to yield the thermally stable bis(borohydride) zinc complex IPr center dot Zn(BH4)(2).