A laser flash photolysis study of photochemical carbonyl substitution in M(CO)6 (M = Cr, Mo, W) with 1,10-phenanthroline

Abstract

Photoreactions of M(CO)/sub 6/ (M = Cr, Mo, W) with 1,10-phenanthroline (phen) have been investigated by laser flash photolysis. A transient spectrum due to Cr(CO)/sub 5/(phen), where phen ligates in a monodentate fashion, was observed. In the cases of Mo and W, the growth curve of the final product, Mo(CO)/sub 4/(phen), was found to accord with the kinetics of consecutive first-order reactions. These facts indicate that, even with a ligand as well-suited to bidentate bonding as phen, the coordination of M(CO)/sub 5/ to phen does not concert with the extrusion of the second carbonyl. Both these reactions, however, were found to be significantly accelerated compared with those for pyridine derivatives, suggesting a profound electronic interaction between the metal atom and the noncoordinated nitrogen in M(CO)/sub 5/(phen). The wavelength shift of the d-d band in Cr(CO)/sub 5/(phen) is also attributable to this interaction. However, at this stage, it cannot be concluded whether the interaction is coordination, that is, whether M(CO)/sub 5/(phen) can be considered as the 7-coordinate 20-electron complex of an associative substitution mechanism.