Scope and Mechanism of Carbonyl Carbon and α-Carbon Bond Cleavage of Ketones by Iridium(III) Porphyrin Complexes

Chemoselective carbonyl carbon and a-carbon bond activation (CCA) of ketones (RCOR') was successfully achieved with various iridium(III) tetrakis-4-tolylporphyrinato complexes Ir(ttp)X (X = (BF4)(CO), Cl(CO), and Me) to give the corresponding Ir(ttp)COR (R = Ar, Me, or Et) and Ir(ttp)R' (R' = Me or Et) complexes. Ir(ttp)(BF4)(CO) exhibited the highest reactivity toward CCA, as it possesses a higher Lewis acidity in catalyzing the aldol condensation of ketones to give water, which hydrolyzes the kinetic products, C H bond activation (CHA) complexes, into the proposed Ir(ttp)OH for a subsequent CCA process. The CCA step is nonregioselective in giving both Ir(ttp)R' and Ir(ttp)COR. However, Ir(ttp)R' was kinetically less stable toward hydrolysis to give Ir(ttp)OH. Thus, only Ir(ttp)COR was observed as the sole CCA product.