Benzene-sensitized photoreduction of bis(acetylacetonato)copper(II) under hydrogen

Abstract

New sets of conditions for sensitized photoreduction of Cu(acac)₂ to copper(I) complexes have been discovered. It was demonstrated that singlet excited-state benzene could sensitize the photoreduction just as well as triplet state benzophenone and hydrogen could act as a hydrogen-atom donor. E.s.r. spectroscopy was used to monitor the efficiency of these photoreductions. Better photoreduction efficiency at a higher pressure of hydrogen as well as deuterium incorporation is clear evidence that hydrogen-atom transfer is the rate-regulating step in the photoreduction. The quantum yield determination of Cu(acac)₂ photoreduction and benzene fluorescence quenching showed that singlet excited-state benzene was quenched by Cu(acac)₂ with a rate constant, K_q, of 3.6–5.5 × 10⁹ l mol^–1 s^–1. The quenching interaction is assumed to occur by energy-transfer mechanism.