Silavinylidene Stabilized by an N-Heterocyclic Carbene: A Theoretically Predicted Stable Molecule

Quantum chemical calculations show that the N-heterocyclic carbene (NHC)-stabilized silavinylidene, NHCtBu -> C=SiR2 is a strongly bonded complex, which has a linear arrangement of the donor and acceptor moieties. The molecule is the energetically lowest lying isomer of the NHC-stabilized R2CSi isomers and it is stable towards dimerization when R is a bulky substituent. The silavinylidene complex is the only species of the silylidene homologues NHCtBu -> E=E'R-2 (E, E'=C-Pb) which possesses a linear arrangement. The unusual bonding situation is explained in terms of donor-acceptor interactions between NHCtBu as sigma donor and C=SiR2 in the doubly excited singlet state 3a(1)double right arrow 2b(2) which leads to a significantly shorter C-SiR2 bond compared with free C=SiR2.