Photo‐Assisted Transfer Hydrogenation of Ketones Catalyzed by PN Ruthenium Complexes
Douglas H. N. Santos, Maurizio Ballico, Beatriz E. Goi, Valdemiro P. Carvalho‐Jr, Walter BarattaABSTRACT
The PN acetate ruthenium(II) complex [Ru(κ 2 ‐OAc)(PPye) 2 ]OAc ( 1 ) was synthesized from [Ru(κ 2 ‐OAc) 2 (PPh 3 ) 2 ] and 1‐(diphenylphosphino)‐2‐(2‐pyridyl)ethane (PPye) in methanol and isolated in 70% yield. Treatment of [Ru(κ 2 ‐OAc) 2 (PPh 3 ) 2 ] with 2‐(diphenylphosphino)pyridine (PPy) afforded [Ru(κ 1 OAc)(PPh 3 )(PPy) 2 ]OAc ( 2 ) in high yield. The complexes 1 and 2 display photocatalytic activity in the TH of ketones using 2‐propanol. Complex 1 exhibits superior activity, affording quantitative conversion of aryl ketones under mild conditions (40°C), whereas no activity was observed in dark. On–off experiments confirmed a photoresponsive nature of the catalytic process. Mechanistic studies revealed the formation of different ruthenium monohydride species under thermal and irradiated conditions. Luminescence quenching studies in the presence of NaO i Pr support the involvement of excited‐state processes associated with alkoxide activation and hydride generation.