DETAILS OF POTENTIAL-ENERGY SURFACES INVOLVING C-C BOND ACTIVATION - REACTIONS OF FE+, CO+, AND NI+ WITH ACETONE

Product kinetic energy release distributions (KERDs) for reactions of Fe+, Co+, and Ni+ with acetone to eliminate C2H6 and CO have been meas ured. These distributions are statistical and are very sensitive to th e energy of the rate-limiting transition state, We argue this transiti on state is most likely due to initial C-C bond insertion. The rate-li miting transition state acts to restrict high angular momentum reactan t collision complexes from going on to products, thereby reducing the average kinetic energy released. By modeling the experimental KERDs, t he rate-limiting transition state was determined to lie in the range o f 9 +/- 3 kcal/mol below the energy of the M(+) + acetone reactants fo r all three metal ions. Bond energies for M(+)-CO and M(+)-C2H6 have a lso been determined:D-0(o)(Co+-CO) 39.1 +/- 3 kcal/mol, D-0(o)(Fe+-C2H 6) = 17.9 +/- 3 kcal/mol, and D-0(o)(Ni+-C2H6) = 28.7 +/- 3 kcal/mol. In addition, modeling the experimental KERDs indicates that the MC(2)H (6)(+) product formed in the reaction of M(+) with acetone is nearly e xclusively an ethane adduct, with a maximum 10-15% of the dimethyl com plex being formed. Finally, arguments relating the initial rate-limiti ng transition state to the C-H bond activation transition state in pro pane are made and suggest that the C-C bond activation transition stat e in small alkanes is 6 +/- 5 kcal/mol higher in energy than C-H bond activation.