Novel transition-metal (M=Cr, Mo, W, Fe) carbonyl complexes with bis(guanidinato)silicon(II) ligands.

The donor-stabilized silylene 2 (the first bis(guanidinato)silicon(II) complex) reacts with the transition-metal carbonyl complexes [M(CO)6 ] (M=Cr, Mo, W) to form the respective silylene complexes 7-10. In the reactions with [M(CO)6 ] (M=Cr, Mo, W), the bis(guanidinato)silicon(II) complex 2 behaves totally different compared with the analogous bis(amidinato)silicon(II) complex 1, which reacts with [M(CO)6 ] as a nucleophile to replace only one of the six carbonyl groups. In contrast, the reaction of 2 leads to the novel spirocyclic compounds 7-9 that contain a four-membered SiN2 C ring and a five-membered MSiN2 C ring with a MSi and MN bond (nucleophilic substitution of two carbonyl groups). Compounds 7-10 were characterized by elemental analyses (C, H, N), crystal structure analyses, and NMR spectroscopic studies in the solid state and in solution.