THEORETICAL COMPARISON OF THE BONDING OF CHALCOCARBONYL LIGANDS

Fenske-Hall molecular orbital calculations on the complexes CpFe(CO)(2 )(CX)(+) (X = O, S, Se, and Te) have been used to quantify the nature of bonding between the CX ligands and the metal atom. In addition, con clusions have been reached about the reactivity of the complexes under both nucleophilic and electrophilic attack. The previously establishe d trend of increasing metal-ligand bond strength as X changes from O t o S to Se is demonstrated by our molecular orbital calculations, and f ound to extend to Te. The mechanism for nucleophilic attack, Variously explained in the past by either charge control or orbital control, is quantitatively ascribed to orbital control only. The nature of electr ophilic attack on these complexes is also found to begin with orbital control.