Visible-Light-Driven Alcohol Dehydrogenation with a Rhodium Catalyst.

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 [Rh^III(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 [Rh^III(dtbbpy)₂(I)₂]⁺ [ Rh7( a)] followed by the generation of photoinduced I₃⁻ via a ligand (I⁻) to metal (Rh^III) charge transfer. The resulting Rh^I 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. [ABSTRACT FROM AUTHOR]