The electronic structure for a representative late-transition-metal-methylene complex, Ru=CH2+, has been studied by ab initio methods (generalized Valence bond/configuration interaction). The electronic-state spectrum reveals five states close in energy (spread of 12.9 kcal/mol) that partition into two groups in terms of energy separation and mode of metal-carbon bonding. The ground state has 2A2symmetry and contains covalent M-C σ and π bonds (“metal-methylidene“); a 2 A1 state of the same bond character is only 1.2 kcal/mol higher. A cluster of three degenerate excited states (4A2,4B1,and 4B2) 12.9 kcal/mol above the ground state exhibits completely different bonding character, namely, σ-donor/π-acceptor M-C bonds are formed (“metal-carbene”). We conclude that for highly unsaturated, late-transition-metal systems, metal-carbene bonding may be competitive with metal-alkylidene bonding, leading to donor/acceptor bonds comparable in strength to that of covalent double bonds!.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry