Oxidative addition of methyl iodide to [Rh(PhCOCHCOPh)(CO)(P(OCH2)(3)CCH3)]: an experimental and computational study

Abstract

The reaction rate of the oxidative addition and CO insertion steps of methyl iodide with [Rh(PhCOCHCOPh)(CO)(P(OCH₂ ) ₃ CCH₃ )] are presented. Large negative experimental values for the activation entropy and results from a density functional theory computational chemistry study indicated trans addition of the CH₃ I to [Rh(PhCOCHCOPh)(CO)(P(OCH₂ ) ₃ CCH₃ )]. A study of the molecular orbitals gives insight into the flow of electrons during the oxidative addition reaction. CO insertion leads to a square pyramidal [Rh(PhCOCHCOPh) (P(OCH₂ ) ₃ CCH₃ )(COCH₃ )(I)] acyl product with the COCH₃ moiety in the apical position. The strong electron donation of the P(OCH₂ ) ₃ CCH₃ ligand accelerates the oxidation addition step of methyl iodide to [Rh(PhCOCHCOPh)(CO)(P(OCH₂ ) ₃ CCH₃ )] by ca. 265 times faster (at 35°C) than that of the Monsanto catalyst, but inhibits the CO insertion step.