Electronic structure of transition metal carbene complexes

The analysis of the electronic structure of transition metal (V, Nb, Ta) carbene complexes is given. The properties and peculaiarities of the electronic structure of Fischer and Schrock type complexes are compared. The results of the most accurate nonempirical calculations of the simplest systems simulating the transition metal-carbene ligand and some less strict semiempirical and nonempirical calculations which permit to find out the regularities of the electronic structure of carbene complexes, depending on position of the metal in the Periodic system and the nature of ligand surrounding, are discussed. Main factors causing the stabilization of covalently bound or donor-acceptor systems are singled out