ACTIVATION OF CARBON-HYDROGEN BONDS IN ALKANES AND OTHER ORGANIC-MOLECULES BY IR(I), RH(I) AND IR(III) COMPLEXES

Pentamethylcyclopentadienyliridium(I) complexes are now known to undergo rapid and general oxidative addition reactions with a wide range of carbon-hydrogen bonds, including those in alkanes and isolated alkyl groups. The first part of this paper describes flash kinetic experiments carried out on pentamethylcyclopentadienylrhodium carbonyl complexes in liquid krypton and liquid xenon solvents at low temperature. These studies have established that noble gas complexes and alkane complexes (intermediates involving weak complexation of the noble gas or alkane C-H bonds to the metal center) are generated as precursors to the final oxidative addition products in these reactions. Information about the relative binding constants of alkanes of different sizes and isotopic substitution to the metal center has been obtained, and activation energies and entropies for the conversion of the alkane complexes to the final C-H oxidative addition products have been determined. In the second part of the study, a new alkane C-H activation process involving reactions of Ir(III) trifluoromethanesulfonates with alkanes and arenes is reported. Preliminary investigations indicate that cationic Ir(III) intermediates are involved in these reactions.