A Guanidine-Supported π-Complex of Germanium Amenable to Intramolecular C-C Cleavage in Arene and Ge Atom Transfer.

Abstract

The germylone dimNHCGe (dimNHC = diimino N-heterocyclic carbene) reacts with azides N3R (R = SiMe3 or p-tolyl) to furnish the first examples of germanium π-complexes, i.e. guanidine-ligated compounds (dimNHI-SiMe3)Ge (NHI= N-heterocyclic imine, R= SiMe3) and (dimNHI-Tol)Ge (R= p-tolyl). DFT calculations suggest that these species are formed by a Staudinger type replacement of dinitrogen in the azide by a nucleophilic germylone, leading to a transient carbene adduct of iminogermylidene. Heating a solution of compound (dimNHI-SiMe3)Ge to 70 °C results in extrusion of the iminogermylidene that further aggregates to produce the known [Me3SiNGe]4 tetramer, whereas the imidazolylidene fragment transforms into an unusual heptatriene species that can be considered as a product of carbene insertion into the C-C bond of a pendant Ar substituent at the imidazolylidene nitrogen of the dimNHC. Reaction of (dimNHI-SiMe3)Ge with tetrachloro-o-benzoquinone results in the net transfer of a germanium atom and formation of the free diimino-guanidine ligand. This ligand also forms when (dimNHI-SiMe3)Ge is treated with azide N3(p-Tol), with the germanium product being [(p-Tol)NGe]n.