A kinetic study of the reactions of methyl- and acetyl-pentacarbonylmanganese with acetylenes

Abstract

The reaction between [MnMe(CO)₅] and dimethyl acetylenedicarboxylate to give [[graphic omitted]Me)(CO)₂Me}(CO)₄ has been studied under pseudo-first-order conditions in various solvents and has been found to obey the rate law, rate =k₁+k₂[MeO₂CC₂CO₂Me]. The k₁ term arises from a ‘solvent-assisted’ two-step methyl to acetyl migratory-insertion reaction, while the k₂ term arises from a direct second-order reaction in which the electron-deficient acetylene appears to stabilize the transition state for methyl to acetyl migration. The reaction between [Mn(COMe)(CO)₅] and MeO₂CC₂CO₂Me is first-order in the manganese complex, but independent of acetylene concentration consistent with a rate-determining step involving CO ligand dissociation.