Visible-Light-Driven Alcohol Dehydrogenation with a Rhodium Catalyst

TLDR: In this paper, the photocatalytic dehydrogenation of alcohols with a Rh catalyst and I− in an acidic medium was reported, which increased linearly for 4 days with no significant decrease in activity.

Abstract: We report the photocatalytic dehydrogenation of alcohols with a Rh catalyst and I− in an acidic medium. The catalyst screening of a structurally diverse family of Rh complexes found [RhIII(dtbbpy)2(OSO2CF3)2](CF3SO3) (Rh7; dtbbpy=4,4′-di-tert-butyl-2,2′-bipyridine) to be the best catalyst. All components (Rh7, HI, alcohol, and light) were found to be essential for the dehydrogenation to occur. Under optimal conditions, generation of both H2 and acetone (for isopropyl alcohol) was observed, which increased linearly for 4 days with no significant decrease in activity. The proposed mechanism involves the formation of [RhIII(dtbbpy)2(I)2]+ [Rh7(a)] followed by the generation of photoinduced I3− via a ligand (I−) to metal (RhIII) charge transfer. The resulting RhI species reduces H+ and I3− oxidizes the alcohol, which completes the catalytic cycle. Supporting evidence for the catalytic mechanism was obtained by using UV/Vis spectroscopy, electrospray ionization mass spectrometry, cyclic voltammetry and time-dependent DFT calculations.