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 t Bu →CSiR 2 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 R 2 CSi 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 t Bu →EE′R 2 (E, E′=C–Pb) which possesses a linear arrangement. The unusual bonding situation is explained in terms of donor–acceptor interactions between NHC t Bu as σ donor and CSiR 2 in the doubly excited singlet state 3a 1 ⇒2b 2 which leads to a significantly shorter CSiR 2 bond compared with free CSiR 2 .