Instability of the oxidation catalysts [(bpy)2(py)Ru(O)]2+ and [(trpy)(phen)Ru(O)]2+ in basic solution

The Ru(IV) complexes ((bpy)/sub 2/(py)Ru(O))/sup 2 +/ (1) and ((trpy)(phen)Ru(O))/sup 2 +/ (2) (bpy = 2,2'-bipyridine, py = pyridine, trpy = 2,2',2''-terpyridine, and phen = 1,10-phenanthroline) are unstable toward self-reduction in basic solution. Product analyses, performed by using UV-vis spectroscopy, cyclic voltammetry, HPLC, and GC, show that O/sub 2/ is not a product of the self-reductive chemistry and that ca. 80% of the reduced products that appear are the unmodified polypyridyl complexes of Ru(II), ((bpy)/sub 2/(py)Ru(OH))/sup +/ or ((trpy)(phen)Ru(OH))/sup +/. The remaining 20% of the products are accounted for by at least four different products, which are also Ru(II) but appear to have undergone varying degrees of ligand oxidation. Kinetic studies were performed with stopped-flow or conventional mixing techniques. For complex 2, plots of log absolute value A/sub infinity/ - A/sub t/ vs. time were linear from pH 12 to 14 and the experimental rate law can be described by -d(Ru(IV))/dt = k/sub a/ (OH/sup -/)/sup 2/, where k/sub a/ = 0.21 +/- 0.01 M/sup -1/ s/sup -1/ and k/sub b/ = 0.08 +/- 0.02 M/sup -2/ s/sup -1/ at 25/sup 0/C and ..mu.. = 1.0 M (Na/sub 2/SO/sub 4/). For the k/sub a/ path ..delta..H = 12 +/- 2more » kcal/mol and ..delta..S = -20 +/- 6 eu. For complex 1, plots of log absolute value A/sub infinity - A/sub t/ vs. time were not linear but could be resolved into two successive components to yield rate constants for the self-reduction of Ru(IV) and, following that, of Ru(III). 17 references, 11 figures, 3 tables.« less