Elimination of R-H from iridium acyl hydrides without loss of CO: evidence for the intervention of metal cation/carbanion pairs.

Abstract

Instead of reductive elimination of aldehyde, or decarbonylation to give a trifluoroalkyl hydride, heating Cp*(PMe3)Ir(H)[C(O)CF3] leads to the quantitative formation of Cp*(PMe3)Ir(CO) and CF3H. Kinetic experiments, isotope-labeling studies, solvent effect studies, and DFT calculations support a mechanism which involves dissociation of trifluoromethyl anion to give the transient ion-pair intermediate [Cp*(PMe3)Ir(H)(CO)]+[CF3]-. Further evidence for the ability of CF3 to act as a leaving group came from investigation of the analogous methyl and chloride derivatives Cp*(PMe3)Ir(Me)[C(O)CF3] and Cp*(PMe3)Ir(Cl)[C(O)CF3]. Both of these compounds undergo a similar loss of trifluoromethyl anion, generating an iridium carbonyl cation and CF3D in CD3OD.