Approximate molecular orbital calculations on carbene ligands and complexes: the ability of the carbene ligands to act as σ donors and π acceptors

Abstract

Non-parameterized molecular orbital calculations have been performed on a series of carbene ligands, C̈(X)Y, and carbene complexes, (CO) 5CrC(X)Y. In accord with previously obtained experimental data, methoxycarbenes were found to be better π acceptors than aminocarbenes. All of the carbene ligands were found to accept less charge from the chromium than the carbonyl ligand. While the eigenvalues of the highest occupied and lowest unoccupied molecular orbitals were found to be important factors in determining the σ donating and π accepting abilities of the ligands, other factors (such as the spatial localizations and degeneracies of the orbitals) were also found to affect these abilities. An explanation is given for the absence of a significant trans influence in most carbene complexes.