Wesley H. Bernskoetter

Effect of Sodium Cation on Metallacycle β-Hydride Elimination in CO2–Ethylene Coupling to Acrylates

The catalytic conversion of carbon dioxide and olefins into acrylates has been a long standing target, because society attempts to synthesize commodity chemicals in a more economical and sustainable fashion. Although nickel complexes have been known to successfully couple CO2 and ethylene for decades, a key β-hydride elimination step has proven a major obstacle to the development of a catalytic process. Recent studies have shown that Lewis acid additives can be used to create a lower-energy pathway for β-hydride elimination and facilitate a low number of catalytic turnovers. However, the exact manner, in which the Lewis acid promotes β-hydride elimination remains to be elucidated. Herein, we describe the kinetic and thermodynamic role that commercially relevant and weakly Lewis acidic sodium salts play in promoting β-hydride elimination from nickelalactones synthesized from CO2 and ethylene. This process is compared to a non-Lewis acid promoted pathway, and DFT calculations were used to identify differences between the two systems. The sodium-free isomerization reaction gave a rare CO2 -derived β-nickelalactone complex, which was structurally characterized.

Coordination Chemistry of Iridium Phosphine–Sulfonate Complexes

A family of new iridium phosphine–sulfonate complexes based on 2-dicyclohexylphosphino-4-benzenesulfonic acid was synthesized and characterized. An iridium(I) phosphine–sulfonate cyclooctadiene species was prepared from transmetalation of a silver salt of the phosphine–sulfonate ligand and iridium(I) cyclooctadiene chloride dimer. This diolefin iridium complex was found to be a functional precatalyst for cyclopentene hydrogenation. A corresponding iridium(I) phosphine–sulfonate dicarbonyl species was prepared by ligand substitution using carbon monoxide. Analysis by infrared spectroscopy established this metal–ligand platform as a relatively electron poor coordination environment. The iridium(I) phosphine–sulfonate cyclooctadiene species was further utilized as a precursor for the synthesis of two iridium(III) phosphine–sulfonate hydride compounds by treatment with strong acids.