Reactions of the excited state of polypyridyl chromium(III) ions

Abstract

<p>The quenching of the [superscript]2E state of CrL[subscript]3[superscript]3+ (where L = 2,2[superscript]'-bipyridine, 1,10-phenanthroline and their substituted analogues) by oxalate ions and by the organochromium complexes L[superscript]'CrR[superscript]2+ (where L[superscript]' = (15) aneN[subscript]4 and R = primary alkyl, secondary alkyl, arylalkyl) was studied. Also investigated was the reactions of the organochromiums with Ru(bpy)[subscript]3[superscript]3+. Both formation of CrL[subscript]3[superscript]2+ and the loss of [superscript]\*CrL[subscript]3[superscript]3+ can be monitored conveniently enabling the determination of the kinetics as well as the products of the reaction;The reaction of oxalate ions at neutral pH with the excited chromium polypyridyl complexes is an electron transfer process as shown by the trend in rate constants with the one electron reduction potentials of the various [superscript]\*CrL[subscript]3[superscript]3+ species. The quenching reaction apparently proceeds via an ion-pairing pathway. A reactive species is produced in the quench which either produces another equivalent of electron transfer products or a secondary transient depending on the identity of the chromium polypyridyl complex;Reaction of the [superscript]\*CrL[subscript]3[superscript]3+ with the organochromiums appears to be an electron transfer process based on the reactivity pattern in varying the chromium polypyridyl (and consequently the potential) as well as the trend in varying the organic moiety of the L[superscript]'CrR[superscript]2+. This last reactivity pattern is that observed in the reactions of the organochromiums and the good outer sphere electron transfer agent, Ru(bpy)[subscript]3[superscript]3+. One electron oxidation of L[superscript]'CrR[superscript]2+ produces an unstable species which may undergo a one electron reduction (back electron transfer) or homolyze producing organic radicals.</p>