Electron self-exchange, oxidation, and reduction reactions of bis(2,9-dimethyl-4,7-diphenyl- 1,10-phenanthroline)copper(II/I) and bis(6,6'-dimethyl-2,2'-bipyridine)copper(II/I) couples in acetonitrile: gated ET for the reduction, oxidation, and self-exchange processes

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The electron self-exchange rate constant for the Cu(dmbp)22+/+ couple (dmbp = 6,6'-dimethyl-2,2'-bipyridine) was measured in acetonitrile by the NMR method (kex = 5.5 × 103 kg mol-1 s-1, ΔH* = 35.0 ± 0.3 kJ mol-1 and ΔS* = -56 ± 1 J mol-1 K-1). Reduction reactions of Cu(bcp)22+ (bcp = 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) and Cu(dmbp)22+ with Co(bipy)32+ (bipy = 2,2'-bipyridine) and ferrocene (Fe(Cp)2 = bis(cyclopentadienyl)iron(II)), and oxidation reactions of Cu(bcp)2+ and Cu(dmbp)2+ by Ni(tacn)23+ (tacn = 1,4,7-triazacyclononane) and Mn(bipyO2)33+ (bipyO2 = N,N'-dioxo-2,2'-bipyridine) were also studied in acetonitrile. The electron self-exchange rate constants, kex, estimated for the Cu(bcp)22+/+ and Cu(dmbp)22+/+ couples from the oxidation reactions of Cu(bcp)2+ and Cu(dmbp)2+ by Ni(tacn)23+ and Mn(bipyO2)33+ were consistent with the directly measured values by NMR, while kex estimated from the reduction reactions of Cu(bcp)22+ and Cu(dmbp)22+ by Co(bipy)32+ ([Cu(bcp)22+]0, [Cu(dmbp)22+]0 >> [Co(bipy)32+]0) were 103 times smaller than those directly measured by the NMR method. The pseudo-first-order rate constant for the reduction reaction of Cu(bcp)22+ and Cu(dmbp)22+ by Fe(Cp)2 was not linear against the concentration of excess amounts of Fe(Cp)2. Analyses of the reactions revealed that the reductions of Cu(bcp)22+ and Cu(dmbp)22+ involve slow paths related to the deformation of Cu(II)N4 center from tetragonal to tetrahedral coordination. The energetic preference for the deformation of Cu(II) species rather than that of Cu(I) was discussed on the basis of the ligand field activation energy (LFAE).Key words: electron transfer, copper(II) and copper(I) complexes, gated behavior.