Heavier carbene analogues and their derivatives as κ-El, κ2-El,N, and κ2-N,N′ ligands: different reactivity patterns for acyclic and cyclic diamidogermylenes and -stannylenes

Abstract

Because of the increasing importance of N-heterocyclic carbenes in organometallic chemistry we investigated the ligand properties of structurally-related acyclic and cyclic heavier carbene analogues with transition metal chlorides. Acyclic {(Me₃Si)₂N}₂El, El = Ge and Sn, react with CuCl with transfer of one (Me₃Si)₂N ligand to yield the known copper tetramer {(Me₃Si)₂NCu}₄. The cyclic Me₂Si(μ-N^tBu)₂Ge, by contrast, binds copper through germanium only, furnishing a tetranuclear ladder structure with both terminal and bridging germylenes. The tin homologue, however, inserts into the CuCl bond, and the ensuing {Me₂Si(μ-N^tBu)₂SnCl}⁻ ions then coordinate one copper ion via their tin atoms while sandwiching the remaining three copper ions in an unprecedented κ²-N,N′ fashion. Chemically-harder Cr(II)—created in a redox reaction of Me₂Si(μ-N^tBu)₂Sn with CrCl₃(THF)₃—is not coordinated by tin, but chelated by both nitrogen atoms of one {Me₂Si(μ-N^tBu)₂SnCl}⁻ ion and more weakly through the tin-bound chloride.