KINETICS OF ELECTRON TRANSFER REACTIONS BETWEEN THALLIUM(III) AND A SERIES OF MONONUCLEAR AND BINUCLEAR RUTHENIUM COMPLEXES (FACTOR, ANALYSIS, PROGRAMS)

The two-electron redox couple Tl(III)/Tl(I) was used as a model system for multielectron redox processes which are usually slow. Slow reactions of such substrates with single electron reagents result primarily because the reaction must proceed through a highly unlikely termolecular step or through an unstable oxidation state. Molecules containing several single electron redox centers bound in a favorable geometry could circumvent the usual slowness of such reactions. Kinetic data for the reactions between Tl(III) and binuclear Ru(II) complexes, which serve as model catalysts, and related mononuclear complexes were obtained using either a stopped-flow or a diode array spectrophotometer. These data were compared to kinetic data obtained using Fe(III) as a one-electron oxidant. Various mathematical techniques including residuals analysis, simplex optimization curve fitting, and factor analysis of the multiwavelength kinetic data were useful in unraveling some of the interesting kinetic behavior for these reactions. The binuclear complexes (mu)-pyrazine-bis-pentaammineruthenium and (mu)-(4,4'-bipyridine)-bis-pentaammineruthenium are capable of transferring two electrons to Tl(III) in a nearly simultaneous fashion. Even though this capability could allow these binuclear complexes to reduce Tl(III) faster than the mononuclear analogs, the primary reason for the differences in observed rates was the changes in driving force associated with the various reactions.