Kinetic and mechanistic understanding of oxidative addition and reductive elimination of Pt(II) and Pt(IV) complexes

The catalytic functionalization of unreactive small molecules such as methane via C-H activation and C-E (E = C, N, O, or other heteroatom) is a long-standing goal in organometallic chemistry. To achieve this goal, we must develop better understanding of the fundamental steps of the catalytic cycle. Towards this end, we have been studying oxidative addition and reductive elimination of Pt complexes, which have demonstrated ability to functionalize small molecules, including methane. We have established, for the first time, intermolecular oxidative addition of simple aryl iodides. We have also established that reductive elimination is facilitated by the generation of unsaturated metal species from which oxidative addition and reductive elimination reactions may occur. We report the preparation of 4-membered P,N metallacycles of Pt(II) and Pt(IV) exhibiting hemilabile character, resulting in facile oxidative addition of C-X bonds and reductive elimination of alkanes. It was found that large, electron rich phosphines were required to allow for chelate formation, and the intimate mechanism of reductive elimination and ligand effects on the barrier to reductive coupling of C-C bonds from Pt(IV) were investigated. The challenges and ligand design strategies associated with the preparation of these strained metallacycles will be discussed along with the comparative reactivity toward oxidative addition and reductive elimination of these species with less-strained P,N metallacycles.