Transition-Metal Complexes of Heavier Cyclopropenes: Non-Dewar-Chatt-Duncanson Coordination and Facile Si═Ge Functionalization

Abstract

Transition-metal complexes of cyclopropenes occur as fleeting intermediates of numerous metal-catalyzed organic transformations. A heavier analogue has now been obtained from the reaction of an NHC-stabilized silagermenylidene, bis(1,5- cyclooctadiene)nickel(0), and 1 equiv of N-heterocyclic carbene (NHC). The residual chloro functionality at the germanium end of the coordinated GeSi moiety of the thus formed 1H-disilagermirene is easily exchanged by treatment with anionic nucleophiles, which provides access to a series of differently substituted Si2Ge-cyclopropenes as nickel complexes in excellent yields. NMR spectroscopic data, X-ray crystallographic analysis, and DFT calculations indicate a coordination mode different from the metallacyclopropane and π-complex extremes of the Dewar−Chatt−Duncanson model: the σ-component of the GeSi double bond acts as donor and acceptor, leaving behind a nearly unsupported Si−Ge π-bond.