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

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

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
Volume155
DOIs
Publication statusPublished - 2012

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Ruthenium
Hydrides
Isomers
NAD
ruthenium
hydrides
Protons
Hydrogen
hydrogen atoms
isomers
Atoms
protons
nicotinamide
congestion
Proton transfer
Niacinamide
Protonation
Carbon Dioxide
carbon dioxide
Metals

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Steric effect for proton, hydrogen-atom, and hydride transfer reactions with geometric isomers of NADH-model ruthenium complexes. / Cohen, Brian W.; Polyansky, Dmitry; Achord, Patrick; Cabelli, Diane; Muckerman, James; Tanaka, Koji; Thummel, Randolph P.; Zong, Ruifa; Fujita, Etsuko.

In: Faraday Discussions, Vol. 155, 2012, p. 129-144.

Research output: Contribution to journalArticle

Cohen, Brian W. ; Polyansky, Dmitry ; Achord, Patrick ; Cabelli, Diane ; Muckerman, James ; Tanaka, Koji ; Thummel, Randolph P. ; Zong, Ruifa ; Fujita, Etsuko. / Steric effect for proton, hydrogen-atom, and hydride transfer reactions with geometric isomers of NADH-model ruthenium complexes. In: Faraday Discussions. 2012 ; Vol. 155. pp. 129-144.
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AU - Cohen, Brian W.

AU - Polyansky, Dmitry

AU - Achord, Patrick

AU - Cabelli, Diane

AU - Muckerman, James

AU - Tanaka, Koji

AU - Thummel, Randolph P.

AU - Zong, Ruifa

AU - Fujita, Etsuko

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AB - 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.

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