REACTIVE INTERMEDIATES IN THE CARBONYLATION OF METAL ALKYL BONDS - TIME-RESOLVED INFRARED SPECTRAL TECHNIQUES

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on November 25, 2015 | http://pubs.acs.org Publication Date: May 5, 1993 | doi: 10.1021/ba-1993-0238.ch002 Reactive Intermediates in the Carbonylation of Metal-Alkyl Bonds Time-Resolved Infrared Spectral Techniques Peter C. Ford, David W. Ryba, and Simon T. Belt Department of Chemistry, University of California, Santa Barbara, CA In this chapter, we describe flash photolysis experiments using time-resolved infrared (TRIR) detection techniques to probe the reactivities of key intermediates proposed for the mechanisms of the thermal migratory insertion of CO into a metal-alkyl bond. The intermediates studied were generated by the photodissociation of CO from the metal complexes CpFe(CO)L(COCH ) (Cp is η -C H , L is CO or phosphine) and Mn(CO) (COCH ). Kinetic and spectroscopic evidence points to the formation of a solvated species in each case, which undergoes migration of the acyl methyl group to the metal center, competitive with trapping by addition of a ligand. In cyclohexane, the CpFe intermediate CpFe(CO)(sol)(COCH ) (sol is solvent) undergoes methyl migra­ tion at a rate (k = 5.6 x 1Ο M s ) several orders of magni­ tude faster than does the remarkably slow manganese analog (k = 6.0 M s ). Comparisons are also made to the reactivity of the unsaturated intermediate Mn(CO) (sol)(CH ) formed by CO photodissociation from Mn(CO) (CH ). -A T H O R O U G H U N D E R S T A N D I N G O F T H E MECHANISMS of the photoreactions of organometallic compounds requires far more than the measurements of quantum yields and the determinations of photoproduct © 1993 American Chemical Society In Photosensitive Metal—Organic Systems; Kutal, C., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1993.