Mechanism of electron transfer to pentaammine(pyridine)cobalt(III) complexes by aliphatic radicals, hexaaquovanadium(II), and hexaammineruthenium(II) ions

Electron Transfer from Aliphatic Radicals to Ring-Substituted PyridineN-Oxides and Their Cobalt−Ammine Complexes in Aqueous Solution

“…In our earlier work on the reduction of pyridines and their metal complexes by • CMe 2 OH, we have relied heavily on the Hammett ρ values as a mechanistic indicator. , For the reduction of the chromium complexes (H 2 O) 5 Cr(X-py) 3+ , the value of ρ (7.2) is similar to that for free X-pyH + ions (6.6), suggesting a chemical mechanism for the reduction of (H 2 O) 5 Cr(X-py) 3+ . The reaction is initiated by the reduction of the pyridine ligand, followed by intramolecular electron transfer to the metal.…”

“…Of the donor radicals that one might choose for this task, one advantage of • CMe 2 OH is that it has been used in earlier work for related studies of pyridine , and imidazole , derivatives; its continued use for this series as well will enable comparisons between the new results and those already obtained without the need to compensate for another variation. Another reason for the selection of • CMe 2 OH has to do with a particular kinetic technique that allows the quantitative determination of rate constants over a range much wider than those accessible by techniques of flash photolysis and pulse radiolysis.…”

“…Another reason for the selection of • CMe 2 OH has to do with a particular kinetic technique that allows the quantitative determination of rate constants over a range much wider than those accessible by techniques of flash photolysis and pulse radiolysis. The technique we have employed is the method of “stored free radicals”, ,− which employs the organometallic cation (H 2 O) 5 Cr−CMe 2 OH 2+ , a species that reversibly releases the free radical. A steady state is set up, and the kinetics of the competitive reaction with the substrate of interest, here the pyridine N -oxide or its derivative, can be determined from the overall kinetics.…”