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 CO 2•- (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 (k7a = 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 (k8 = 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.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry