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.

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 {(Me(3)Si)(2)N}(2)El, El = Ge and Sn, react with CuCl with transfer of one (Me(3)Si)(2)N ligand to yield the known copper tetramer {(Me(3)Si)(2)NCu}(4). The cyclic Me(2)Si(μ-N(t)Bu)(2)Ge, 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 {Me(2)Si(μ-N(t)Bu)(2)SnCl}(-) ions then coordinate one copper ion via their tin atoms while sandwiching the remaining three copper ions in an unprecedented κ(2)-N,N' fashion. Chemically-harder Cr(II)--created in a redox reaction of Me(2)Si(μ-N(t)Bu)(2)Sn with CrCl(3)(THF)(3)--is not coordinated by tin, but chelated by both nitrogen atoms of one {Me(2)Si(μ-N(t)Bu)(2)SnCl}(-) ion and more weakly through the tin-bound chloride.