Silavinylidene stabilized by an N-heterocyclic carbene: A theoretically predicted stable molecule

Quantum chemical calculations show that the N-heterocyclic carbene (NHC)-stabilized silavinylidene, NHC^tBu→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 NHC^tBu→E=ER₂ (E, E=C-Pb) which possesses a linear arrangement. The unusual bonding situation is explained in terms of donor-acceptor interactions between NHC^tBu as σ donor and C=SiR₂ in the doubly excited singlet state 3a ₁â‡'2b₂ which leads to a significantly shorter C-SiR₂ bond compared with free C=SiR₂. Quantum chemical calculations suggest that the N-heterocyclic carbene (NHC)-stabilized silavinylidene NHC^tBu→C=SiR₂ is a strongly bonded complex which, unlike all other Group 14 homologues NHC→E=ER₂ (E, E=C-Pb), has a linear arrangement of the donor and acceptor moieties.