Steric effect for proton, hydrogen-atom, and hydride transfer reactions with geometric isomers of NADH-model ruthenium complexes

Brian W. Cohen, Dmitry Polyansky, Patrick Achord, Diane Cabelli, James Muckerman, Koji Tanaka, Randolph P. Thummel, Ruifa Zong, Etsuko Fujita

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Two isomers, [Ru(1)] 2+ (Ru = Ru(bpy) 2, bpy = 2,2′-bipyridine, 1 = 2-(pyrid-2′-yl)-1-azaacridine) and [Ru(2)] 2+ (2 = 3-(pyrid-2′-yl)-4-azaacridine), are bio-inspired model compounds containing the nicotinamide functionality and can serve as precursors for the photogeneration of C-H hydrides for studying reactions pertinent to the photochemical reduction of metal-C 1 complexes and/or carbon dioxide. While it has been shown that the structural differences between the azaacridine ligands of [Ru(1)] 2+ and [Ru(2)] 2+ have a significant effect on the mechanism of formation of the hydride donors, [Ru(1HH)] 2+ and [Ru(2HH)] 2+, in aqueous solution, we describe the steric implications for proton, net-hydrogen-atom and net-hydride transfer reactions in this work. Protonation of [Ru(2 •-)] + in aprotic and even protic media is slow compared to that of [Ru(1 •-)] +. The net hydrogen-atom transfer between *[Ru(1)] 2+ and hydroquinone (H 2Q) proceeds by one-step EPT, rather than stepwise electron-proton transfer. Such a reaction was not observed for *[Ru(2)] 2+ because the non-coordinated N atom is not easily available for an interaction with H 2Q. Finally, the rate of the net hydride ion transfer from [Ru(1HH)] 2+ to [Ph 3C] + is significantly slower than that of [Ru(2HH)] 2+ owing to steric congestion at the donor site.

Original languageEnglish
Pages (from-to)129-144
Number of pages16
JournalFaraday Discussions
Publication statusPublished - 2012


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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