Effect of Carboxylate Ligands on Alkane Dehydrogenation with (^<i>dm</i>Phebox)Ir Complexes

A series of carboxylate-ligated iridium complexes (dmPhebox)­Ir­(O2CR)2(H2O) (R = −CH3, −CH2CH3, −CMe3, −CH2C6H5, and −CHCMe2) were designed and synthesized to understand the carboxylate ligand effects on the reactivity of the complex for alkane dehydrogenation. Kinetic studies showed that the different R groups of the carboxylate iridium complexes can affect the reactivity with octane in the β-H elimination step. The rate constants for octene formation with different carboxylate ligands follow the order R = −CHCMe2 > −CMe3 > −CH2CH3 > −CH3 > −CH2C6H5. In contrast, there is no significant effect of carboxylate ligand on the rate of the C–H activation step at 160 °C. These experimental results support the findings in the previously reported density functional theory study of the (dmPhebox)Ir complex in alkane C–H activation.