Transition Metal Carbonyl Complexes of an N-Heterocyclic Carbene Stabilized Silyliumylidene Ion

Silyliumylidene ions - Si(II) cations with a stereochemically active lone pair of electrons - can act as ligands in transition metal complexes comparable to silylenes. However, no investigations concerning their donor abilities have been carried out. Carbonyl complexes lend themselves exceptionally well to determine the donor/acceptor strength of various ligand systems. We now report the synthesis of novel group 6 and group 8 transition metal carbonyl complexes 2-5 of N-heterocyclic carbene (NHC) stabilized silyliumylidene ion 1b, including the first Cr, Mo, and Fe complexes of a Si(II) cation. The complexes were fully characterized by multinuclear NMR and IR spectroscopy and SC-XRD studies. A combination of experimentally determined IR bands together with theoretical calculations revealed weak σ-donor properties and a negligible π-acceptor ability of NHC-stabilized Si(II) cation 1b.