A kinetic study of the oxidative addition of methyl iodide to [Rh((C4H3S)COCHCOCF3)(CO)(PPh3)] utilizing UV/vis and IR spectrophotometry and 1H, 19F and 31P NMR spectroscopy. Synthesis of [Rh((C4H3S)COCHCOCF3)(CO)(PPh3)(CH3)(I)]

IR and UV/vis spectrophotometric and 1H, 19F and 31P NMR spectroscopic techniques have been utilized to study the kinetics of oxidative addition of CH3I to [Rh(tta)(CO)(PPh3)] with Htta = (C4H3S)COCH2COCF3 = 2-thenoyltrifluoroacetone. Two definite reactions steps involving isomers of at least two distinctly different classes of RhIII-alkyl and a RhIII-acyl species were observed. NMR spectroscopy revealed that each reaction product exists in solution of two observable isomers in equilibrium with each other. The observed rate of oxidative addition of iodomethane to the different [Rh(tta)(CO)(PPh3)] isomers was the same, but the rate of formation of the two isomers of the final RhIII-alkyl2 reaction product, [Rh(tta)(CO)(CH3)(PPh3)(I)], differs. Results provided the following reaction mechanism. uilibrium K2 was fast enough to be maintained during the [Rh(tta)(CO)(PPh3)] depletion in the first reaction step and during the RhIII-alkyl2 formation in the second reaction step. The molecular formulae of all the RhIII-alkyl and RhIII-acyl species are [Rh(tta)(CH3)(CO)(PPh3)(I)] and [Rh(tta)(COCH3)(PPh3)(I)], respectively, but the geometries are different due to different co-ordination positions of the ligands. The final RhIII-alkyl2 reaction product is isolated and characterized.