Cyclic voltammetric study of acid hydrolysis of tris(bipyridine) chromium(II): a critical appraisal of CV determination of kinetic parameters

Abstract

Cyclic voltammetry has been exploited to reinvestigate discrepancies in the reported rate constant for the reaction: k f cr(bipy):+ + 2H20 + ~r ( b i~~)~(~~~) : + + bipy which follows electrode reduction of the substitution inert cr(bipy):'. It is shown that the problems arise from oversimplified treatment of residual currents when estimating the anodic peak current, i,. A "two scan" procedure for estimating the background currents is introduced which appears to resolve discrepancies. The kinetic studies were extended to a methylsubstituted bipyridine. Since ring methylation has very little effect on kf, it appears that the aquation reaction is initiated by a rate-determining step which requires a minimum of bipyridine rearrangement. SHACHAR D. NADLER, JAMES G. DICK et COOPER H. LANGFORD. Can. J. Chem. 63, 2732Chem. 63, (1985.Utilisant la voltamttrie cyclique, on a reexamine les divergences rapporttes au sujet de la vitesse de la rkaction:Cette mtthode permet de suivre 1'Cvolution de la rduction 2i 17Clectrode du cr(bipy):' qui est inerte 2i la substitution. On dCmontre que les probBmes proviennent d'une trop grande simplification des courants rksiduels lorsqu'on tvalue le courant anodique maximal, i,. On introduit une mCthode 2i double balayage pour Cvaluer les courants rCsiduels et cette mCthode semble Climiner les irrCgularitCs. On a Ctendu les ttudes cinCtiques h une bipyridine substituCe par un mtthyle. Puisque la mCthylation du cycle n'a qu'un minime effet sur kf, il semble que la rkaction reprtsentte par 1'Cquation est initik par une Ctape determinant la vitesse qui nkcessite un minimum de transposition de la part de la bipyridine.[Traduit par le journal] IntroductionThe behaviour of the tris-(2,2-bipyridine) chromium(111) has been the subject of several electrochemical studies which have challenged the capacity of various electrochemical techniques to extract chemical kinetic information. The system has been reinvestigated in order to resolve discrepancies and refine the procedures for accurate extraction of kinetic parameters. Sato and Tanaka (1) have demonstrated that in aprotic solvents, [Cr(bipy),13+ is reduced in four, one electron steps to the [Cr(bipy),ll-anion. The aqueous behaviour of this chromium complex has been shown to be somewhat more complicated, notably because of solvolytic ligand exchange. Using conventional polarographic techniques, Tucker et al. (2) and Baker and Metha (3) obtained four polarographic waves for the reduction of aqueous [Cr(bipy),13+. They observed that the nature of these waves (size and shape) was a function of pH and temperature. From the behaviour of the first two polarographic waves Baker suggested the following reactions:

Recent Advances in Chromium(II)- and Chromium(III)-Mediated Organic Synthesis

“…Most easily these chromium(III)-complexes are recycled directly, without prior release of the product. This can be considered a likely course of events in one compartment setups and is supported by voltammetric studies, 266,300 and, most striking, by the formation of different products after the first cycle. 226 Nevertheless, a number of chromium(II) reactions with electrochemical recycling of the ion have been reported.…”

“…153 An alternative pathway not discussed by FŸrstner could be the reduction of the chromium(III) alcoholate directly by manganese (or via Cr(II) ↔ Cr(III) shuffling, see above) to the exchange labile chromium(II) alcoholate prior to reaction with TMS-Cl. 300 The feasability of such a course of events is supported by electrochemically driven catalytic versions of the same reaction without added TMSCl (vide infra 301 ). However, the formation of the TMS-ether bond appears to be a crucial driving force in the chemical catalytic reaction and it provides the chloride ions consumed in the catalytic cycle.…”

Oxygen radical-mediated DNA damage by redox-active chromium(III) complexes

“…Figure 5 shows a typical cyclic voltammogram for one of the mutagenic complexes and its aquated analog at varying sweep rates. The electrochemical behavior of both this complex, [Cr(bpy)2Cl2]1+, and its tris-bidentate analog, [Cr-(bpy)3]3+, has been the subject of several studies (Nadler et al, 1985;Soignet & Hargis, 1972,1973Baker & Dev Mehta, 1965). The other mutagenic complex, [Cr(phen)2Cl2]1+, because of the ligand similarity, demonstrates redox behavior much like that of the [Cr(bpy)2Cl2]1+ complex.…”

Electrochemistry and surface-enhanced Raman spectroscopy (SERS) of adsorbed chromium–bipyridyl complexes†

“…Reduction of [Cr(bpy) 3 ] 3+ by one electron results in substitution of one or more of the bipyridine ligands by coordinated water takes place initially via an EC mechanism (where E = electrochemical [reduction] step, C = chemical [ligand substitution] step) as in the C1 step of Scheme 1. [6][7][8] In fact, the inclusion of the homogeneous electron transfer step C2 in Scheme 1 satisfies the criteria for an ? ECE / reaction of the type first described by Feldberg and Jeftic.…”