Reduction of Ru(bpy)₂(AB)²⁺ (bpy = 2,2‘-bipyridine, AB = 2,2‘:3‘,2‘‘:6‘‘,2‘‘‘-quaterpyridine) in Aqueous Solution. A Pulse Radiolysis Study

Abstract

The one-electron reduction of Ru(bpy)2(AB)2+, hereafter RuAB2+, where bpy = 2,2‘-bipyridine and AB = 2,2‘:3‘,2‘‘:6‘‘,2‘‘‘-quaterpyridine, in aqueous solution has been studied using pulse radiolysis. RuAB2+ is reduced by eaq - (k = 6.2 × 1010 M-1 s-1 at ambient ionic strength (I) and k = 4.6 × 1010 M-1 s-1 at I = 0.1 M) and by CO2 •- radical (k = 1 × 108 M-1 s-1 at I = 0.1 M), generating RuAB•+. The spectra of RuAB•+ and its conjugated acid (RuABH•2+) were obtained; the pK a of RuABH•2+ (8.0) has been determined. The rate constants for the protonation of RuAB•+ (k H = 7.9 × 109 M-1 s-1) and the deprotonation of RuABH•2+ (k - H = 79 s-1) have been evaluated as have the rate constants for proton exchange (k f = 3.4 × 107 M-1 s-1 and k r = 5.5 × 106 M-1 s-1) between the RuAB•+/RuABH•2+ and H2PO4 -/HPO4 2- couples. The results from this work are compared with those obtained previously for 13 Ru(II) complexes that contain bpy, bpm (2,2‘-bipyrimidine), bpz (2,2‘-bipyrazine), and pypm (2-(2‘-pyridyl)pyrimidine) ligands. In addition, since RuAB2+ can be viewed as a substituted Ru(bpy)3 2+ complex that contains a bpy residue, a comparison is also made of the reductions of RuAB2+ and bpy.

Photochemical Stereospecific Hydrogenation of a Ru Complex with an NAD+/NADH-Type Ligand

“…The minimum energies for these dimers indicate that the Δ−Λ dimer (Figure ) is roughly 5.0 kcal mol −1 more stable than the Δ−Δ dimer, presumably because of the larger Ru−Ru distance (10.88 vs 9.23 Å; see Figure S4 in the Supporting Information) separating the positively charged metal centers. Because the calculational model did not include counterions to screen Coulombic repulsion, both Δ−Λ and Δ−Δ dimer structures correspond to local minima, with the Δ−Λ minimum 17.7 kcal mol −1 higher than the energy of two isolated, solvated [ 1 ·H] 2+ monomers. , This result is consistent with the fact that neither dimer structure exhibits a local minimum in the gas phase. Owing to these uncertainties, the calculated geometries and energetics are not quantitative but offer semiquantitative support for the existence and stereosepecificity of π-stacking dimer intermediates.…”

7 Radiation chemistry

“…The pK and spectra of the radical have been obtained by pulse radiolysis. 183 The radiation-chemical processes in aqueous solutions of dichromate, isopolymolybdate, and isopolytungstate induced their reduction. The yield of reduction decreases from 20 to 6 on increasing the pH of the solution.…”