Mechanism of Hydride Donor Generation Using a Ru(II) Complex Containing an NAD+ Model Ligand: Pulse and Steady-State Radiolysis Studies

The mechanistic pathways of formation of the NADH-like [Ru(bpy)2(pbnHH)]2+ species from [Ru(bpy)2(pbn)]2+ were studied in an aqueous medium. Formation of the one-electron-reduced species as a result of reduction by a solvated electron (k = 3.0 × 1010 M−1 s−1) or CO2 •− (k = 4.6 × 109 M−1 s−1) or red...

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Published in:Inorganic chemistry 2008-05, Vol.47 (10), p.3958-3968
Main Authors: Polyansky, Dmitry E, Cabelli, Diane, Muckerman, James T, Fukushima, Takashi, Tanaka, Koji, Fujita, Etsuko
Format: Article
Language:English
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Summary:The mechanistic pathways of formation of the NADH-like [Ru(bpy)2(pbnHH)]2+ species from [Ru(bpy)2(pbn)]2+ were studied in an aqueous medium. Formation of the one-electron-reduced species as a result of reduction by a solvated electron (k = 3.0 × 1010 M−1 s−1) or CO2 •− (k = 4.6 × 109 M−1 s−1) or reductive quenching of an MLCT excited state by 1,4-diazabicyclo[2.2.2]octane (k = 1.1 × 109 M−1 s−1) is followed by protonation of the reduced species (pK a = 11). Dimerization (k 7a = 2.2 × 108 M−1 s−1) of the singly reduced protonated species, [Ru(bpy)2(pbnH•)]2+, followed by disproportionation of the dimer as well as the cross reaction between the singly reduced protonated and nonprotonated species (k 8 = 1.2 × 108 M−1 s−1) results in the formation of the final [Ru(bpy)2(pbnHH)]2+ product together with an equal amount of the starting complex, [Ru(bpy)2(pbn)]2+. At 0.2 °C, a dimeric intermediate, most likely a π-stacking dimer, was observed that decomposes thermally to form an equimolar mixture of [Ru(bpy)2(pbnHH)]2+ and [Ru(bpy)2(pbn)]2+ (pH < 9). The absence of a significant kinetic isotope effect in the disproportionation reaction of [Ru(bpy)2(pbnH•)]2+ and its conjugate base (pH > 9) indicates that disproportionation occurs by a stepwise pathway of electron transfer followed by proton transfer.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic702139n