Exploration of bis(pentafluorophenyl)borinic acid as an electronically saturated, bench-top stable Lewis acid catalyst

Abstract

In efforts to develop air- and moisture-stable Lewis acid “frustrated Lewis pair” catalysts, we explored the catalytic reactivity of 9-(bis(perfluorophenyl)boraneyl)-9H-carbazole (1) towards the hydrosilylation of carbonyls. The stability of 1 was followed using nuclear magnetic resonance (NMR) spectroscopy. It was found that 1 cleanly decomposed via hydrolysis to bis(pentafluorophenyl)borinic acid (2). The borinic acid 2 was shown to be stable under ambient atmospheric conditions for upwards of 3 months in the solid-state and 2 weeks dissolved in solution. The Lewis acidity of 2 was evaluated and similarly reactivity towards hydrosilylation was observed. The use of an air-stable, inexpensive, and more sustainable silane, poly(methylhydrosiloxane) (PMHS), affords the reduction of aldehydes to alcohols under atmospheric conditions using 2, emphasizing 2 as a more sustainable, bench-top stable Lewis acid catalyst.