Tuning formate surface coverage with cosolvents for liquid-phase catalytic transfer hydrogenation

Abstract

The synergistic effects of cosolvent and hydrogen-donor (formate) concentration on Pd-catalyzed transfer hydrogenation of vinylphenol are explored for water and water–alcohol mixtures, with a change in the optimum cosolvent mixture observed for different formate concentrations. The results are interpreted in terms of solvent-based tuning of the formate surface coverage, where an optimal formate coverage is required to facilitate hydrogen transfer without excessively blocking surface binding sites. This interpretation is supported by measurements of the formate surface coverage using adsorption-induced attenuation of self-diffusiophoretic Janus particle motion in water and a water–alcohol solvent. The adsorption isotherms demonstrated tuning of formate surface coverage by the cosolvent, with addition of the alcohol cosolvent increasing formate adsorption. The results contribute to rational solvent selection for transfer hydrogenation reactions and provide insight into the roles cosolvents can play in the design of liquid-phase catalytic reaction systems.