H-2 Addition To ((Pcp)-P-Me4)Ir(Co): Studies Of The Isomerization Mechanism

Reduced steric demand of the (PCP)-P-Me4 pincer ligand (PCP = kappa(3)-C6H4-1,3-[CH2PR2](2), R = Me), allows for a more open metal center. This is evident through structure and reactivity comparisons between ((PCP)-P-Me4)Ir derivatives and other ((PCP)-P-R4)Ir complexes (R = Bu-t, Pr-i, CF3). In particular, isomerization from cis-((PCP)-P-R4)Ir(H)(2)(CO) to trans-((PCP)-P-R4)Ir(H)(2)(CO) is more facile when R = Me than when R = Pr-i. 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 (PCP)-P-R4 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.