UC Santa Barbara

Photolysis of CpFe(CO)2(COCH3) (Cp = η5-C5H5) plus P(OCH3)3(L) in n-heptane solutions leads to the competitive decarbonylation to give CpFe(CO)2CH3 and ligand substitution to give CpFe(CO)L(COCH3). The application of hydrostatic pressure changes the relative quantum yields of the two processes, higher pressure strongly favoring the ligand photosubstitution pathway. These differences are interpreted in terms of the competitive reactions of the solvento intermediate CpFe(CO)(Sol)(COCH3) (S), shown previously (J. Am. Chem. Soc. 1991, 113, 9524–9528) to be formed by the initial photolysis step, i.e., the labilization of CO. The much more negative apparent activation volume for the ligand substitution pathway suggests that this proceeds via an associative mechanism of S, while the competing methyl migration to the metal may require simultaneous dissociation of the coordinated solvent molecule, Sol. © 1993, American Chemical Society. All rights reserved.