Aerobic Oxidation Of Hydrocarbons With Ir(iii) Pincer Complexes

Sophie Rubashkin, University of Pennsylvania

Abstract

The development of transition-metal catalyzed alkane valorization methods under mild conditions is an important component of ongoing efforts to reduce the energy costs and environmental impact of the petrochemical industry. Incorporation of “green” reagents such as molecular oxygen in these types of reactions is a crucial part of developing truly scalable technology because oxygen is abundant, environmentally benign, inexpensive, and non-toxic. In this dissertation, two different aerobic alkane functionalization routes are investigated: dehydrogenation of linear alkanes to olefins and oxygenation of cyclohexane to make cyclohexanone, cyclohexanol, and adipic acid. Olefins, cyclohexanone, cyclohexanol, and adipic acid are all widely used platform chemicals in industry. In chapters 2 – 4 novel n-heterocyclic carbene ligated (CCCMesityl) IrIII pincer complexes are demonstrated to undergo C-H activation of n-octane under mild conditions, and each step of an aerobic octane dehydrogenation cycle is demonstrated and optimized. Kinetic studies on the C-H activation step and O2-mediated catalyst regeneration step were carried out, and the results informed design of a new, less sterically bulky CCCMethyl ligand that shows a lowered barrier to C-H activation of benzene. In chapter 5, the aerobic oxidation of cyclohexane to a mixture of cyclohexanone, cyclohexanol, and adipic acid is shown to be promoted by Phebox-ligated Ir complexes. This aerobic autoxidation reaction was optimized for the oxidation of neat cyclohexane, as well as the concomitant oxidation of a mixture of cyclohexanone, cyclohexanol, and cyclohexane.