Reactions of Halogermylenes with NHCs: Selective Formation of Low Valent Ge(II) Species

Abstract

The reactions of the Rind‐based 1,2‐dihalodigermenes, (Eind)BrGe=GeBr(Eind) (1a) and (EMind)ClGe=GeCl(EMind) (1b), with two types of N‐heterocyclic carbenes (NHCs) (Im‐iPr2Me2 and Im‐Me4) resulted in the formation of the halogermylene mono‐NHC adducts, (Im‐iPr2Me2)(Eind)GeBr (2a') and (Im‐iPr2Me2)(EMind)GeCl (2b'), and the germyliumylidene cation bis‐NHC adducts, [(Im‐Me4)2(Eind)Ge]+[Br–] (3a) and [(Im‐Me4)2(EMind)Ge]+[Cl–] (3b). The resulting Ge(II) species are stabilized by the bulky Rind groups and the strongly σ‐donating NHC ligands, whose structures were confirmed by a single‐crystal X‐ray diffraction (SC‐XRD) analysis. Based on DFT and QTAIM calculations of 2a' and the cationic part of 3a, it was concluded that while the Ge–C(Eind) and Ge–C(NHC) bonds exhibit distinct differences in their degrees of polarization, all the Ge–C bonds display a partially polarized covalent character. Both reaction energy calculations and experimental studies suggested the potential liberation of an NHC ligand from the germyliumylidene cation bis‐NHC adducts, leading to the exchange of the NHC ligands. The formation mechanism of 3a from 1a and two NHC molecules via (Im‐Me4)(Eind)GeBr (2a) is discussed based on DFT calculations.