Observation and reactivity studies of an unusual RhI intermediate in H2 evolution catalysis

Abstract

Understanding mechanisms of hydrogen evolution is important for improving catalysts that generate clean fuels. Catalysts often operate via unknown mechanism(s) due to the difficulty of observing or isolating key intermediates in the 2e-/2H+ redn. process. For our study, we prepd. a family of RhI complexes bearing the pentamethylcyclopentadienyl (η5-Cp*) ligand in addn. to derivs. of 4,4'- bipyridyl or 1,10- phenanthroline (bound in the κ2 mode). Under carefully chosen conditions, these compds. formed intermediate species that suggest a previously unknown mechanism of H2 evolution involving protonhydride tautomerism driven by the Cp* ligand. This intermediate complex could be isolated in a MeCN soln., and even as a solid, making it amenable to further mechanistic investigations. The intermediate species were analyzed by mass spectrometry, 1H NMR, and 2H NMR (NMR is NMR spectroscopy). Results will be discussed concerning the properties and reactivity of these active intermediates.