H2 addition to (Me4PCP)Ir(CO): studies of the isomerization mechanism

Abstract

Reduced steric demand of the ^Me4PCP pincer ligand (PCP = κ³-C₆H₄-1,3-[CH₂PR₂]₂, R = Me), allows for a more open metal center. This is evident through structure and reactivity comparisons between (^Me4PCP)Ir derivatives and other (^R4PCP)Ir complexes (R = ^tBu, ⁱPr, CF₃). In particular, isomerization from cis-(^R4PCP)Ir(H)₂(CO) to trans-(^R4PCP)Ir(H)₂(CO) is more facile when R = Me than when R = ⁱPr. Deuterium incorporation in the hydride ligands from solvent C₆D₆ was observed during this isomerization when R = Me. This deuterium exchange has not been observed for other analogous ^R4PCP iridium complexes. A kinetic study of the cis/trans isomerization combined with computational studies suggests that the cis/trans isomerization proceeds through a migratory-insertion pathway involving a formyl intermediate.