Effect of Carboxylate Ligands on Alkane Dehydrogenation with (dmPhebox)Ir Complexes

Hongmei Yuan, William W. Brennessel , and William D. Jones* 

Department of Chemistry, University of Rochester, Rochester, New York 14627, United States

ACS Catal., 2018, 8, pp 2326–2329

DOI: 10.1021/acscatal.7b04057

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.

Keywords: 

concerted-metalation−deprotonation; C−H activation; dehydrogenation; iridium; kinetics