A kinetic study of the oxidative addition of methyl iodide to [Rh((C 4H 3S)COCHCOCF 3)(CO)(PPh 3)] utilizing UV/vis and IR spectrophotometry and 1H, 19F and 31P NMR spectroscopy. Synthesis of [Rh((C 4H 3S)COCHCOCF 3)(CO)(PPh 3)(CH 3)(I)

Abstract

IR and UV/vis spectrophotometric and 1H, 19F and 31P NMR spectroscopic techniques have been utilized to study the kinetics of oxidative addition of CH 3I to [Rh(tta)(CO)(PPh 3)] with Htta = (C 4H 3S)COCH 2COCF 3 = 2-thenoyltrifluoroacetone. Two definite reactions steps involving isomers of at least two distinctly different classes of Rh III-alkyl and a Rh III-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)(PPh 3)] isomers was the same, but the rate of formation of the two isomers of the final Rh III-alkyl2 reaction product, [Rh(tta)(CO)(CH 3)(PPh 3)(I)], differs. Results provided the following reaction mechanism. [Display omitted] The equilibrium K 2 was fast enough to be maintained during the [Rh(tta)(CO)(PPh 3)] depletion in the first reaction step and during the Rh III-alkyl2 formation in the second reaction step. The molecular formulae of all the Rh III-alkyl and Rh III-acyl species are [Rh(tta)(CH 3)(CO)(PPh 3)(I)] and [Rh(tta)(COCH 3)(PPh 3)(I)], respectively, but the geometries are different due to different co-ordination positions of the ligands. The final Rh III-alkyl2 reaction product is isolated and characterized.