Multidentate PC_sp3P-type Ligands with Engineered Avenues for Metal-ligand Cooperation and Their Iridium Complexes

Phosphine-chelated iridium complexes have been long known to exhibit unique reactivity with respect to bond activation and molecular manipulation. Our attempt is to engineer phosphine-chelated iridium catalytic systems which allow for heightened reactivity and specific selectivity with a focus on bond activation allowing for the functionalization of small molecules. The activation of inert small molecules such as methane or carbon dioxide is inherently difficult; however, essential for continued improvements in the utilization of large chemical “feedstocks” such as natural gas. Transition-metal mediated processes provide a pathway for the conversion of these “feedstocks” as liquid fuels or fine chemical precursors. New avenues for activation are needed to increase the potency and selectivity of catalytic transformations.

With this intention, a novel synthetic approach to a series of PC_sp3P-type scaffold ligands has been developed in which ancillary positions have been modified in an attempt to promote metal-ligand cooperative ability. The full synthesis and characterization of the ligands PC^AnisP, PC^PhOHP, and PC^TolP as well as their C-H activated iridium complexes, and various substituted complexes will be discussed along with their subsequent reactivity. The robust complexes have shown their propensity for hemilability, aryl and alkyl intermolecular and intramolecular activation, alkane transfer dehydrogenation, unique coordination geometries, and heterolytic cleavage. The presented work represents a series of organometallic complexes that exhibit unique secondary ligand interactions which directly affect their resulting reactivity.