Silylated Ge Clusters as New Ligands for Cyclic (Alkyl)amino and Mesoionic Carbene Copper Complexes.

The coordination of Ge Zintl clusters at (carbene)Cu moieties is explored, and the complexes [(CAAC)Cu][η-Ge{Si(TMS)}] (1), (CAAC)Cu[η-Ge{Si(TMS)}] (2), and (MIC)Cu[η-Ge{Si(TMS)}] (3) are compared with their known N-heterocyclic carbene (NHC) derivatives (A and B), where CAAC = cyclic (alkyl)amino carbene, MIC = mesoionic carbene, and TMS = trimethylsilane. In analogy to the NHC derivatives, the synthesis of 1-3 proceeds by single-step reactions of (CAAC)CuCl or (MIC)CuCl with the [GeR] and [GeR] [R = Si(TMS)] cluster ligands, respectively, and yields complexes of (carbene)Cu (carbene = CAAC, MIC) moieties exhibiting η-coordination modes of the Ge deltahedron to the Cu atom. In 1, [GeR] acts as a η-bridging unit for two (CAAC)Cu moieties, and 2 and 3 feature single (carbene)Cu (CAAC and MIC) fragments η-connected to [GeR] units. Analysis of the bond lengths in comparison with known examples shows a bond expansion within the coordinated Ge triangular faces for all (carbene)CuGe complexes (carbene = NHC, MIC, CAAC). All compounds are characterized by single-crystal X-ray diffractometry, NMR spectroscopy [H, C{H}, and Si{H}], electrospray ionization mass spectometry, elemental analysis (C, H, and N), and for the first time also by IR and Raman investigations (for 2 and 3). The new complexes add to the known NHC derivatives and extend the exploration of Ge clusters with carbene ligands at Cu atoms.