An Interpretation of Gated Behavior:  Kinetic Studies of the Oxidation and Reduction Reactions of Bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in Acetonitrile

Abstract

Reduction reactions of Cu(dmp)(2)(2+) (dmp = 2,9-dimethyl-1,10-phenanthroline) by ferrocene (Fe(Cp)(2) = bis(cyclopentadienyl)iron(II)), decamethylferrocene (Fe(PMCp)(2) = bis(pentamethylcyclopentadienyl)iron(II)), and Co(bpy)(3)(2+) (bpy = 2,2'-bipyridine) and oxidation reactions of Cu(dmp)(2)(+) by Ni(tacn)(2)(3+) (tacn = 1,4,7-triazacyclononane) and Mn(bpyO(2))(3)(3+) (bpyO(2) = N,N'-dioxo-2,2'-bipyridine) were studied in acetonitrile for the purpose of interpreting the gated behavior involving copper(II) and -(I) species. It was shown that the electron self-exchange rate constants estimated for the Cu(dmp)(2)(2+/+) couple from the oxidation reaction of Cu(dmp)(2)(+) by Ni(tacn)(2)(3+) (5.9 x 10(2) kg mol(-)(1) s(-)(1)) and Mn(bpyO(2))(3)(3+) (2.9 x 10(4) kg mol(-)(1) s(-)(1)) were consistent with the directly measured value by NMR (5 x 10(3) kg mol(-)(1) s(-)(1)). In contrast, we obtained the electron self-exchange rate constant of Cu(dmp)(2)(2+/+) as 1.6 kg mol(-)(1) s(-)(1) from the reduction of Cu(dmp)(2)(2+) by Co(bpy)(3)(2+). The pseudo-first-order rate constant for the reduction reaction of Cu(dmp)(2)(2+) by Fe(Cp)(2) was not linear against the concentration of excess amounts of Fe(Cp)(2). A detailed analysis of the reaction revealed that the reduction of Cu(dmp)(2)(2+) involved the slow path related to the deformation of Cu(dmp)(2)(2+) (path B in Scheme 1). By using Fe(PMCp)(2) (the E degrees value is 500 mV more negative than that of Fe(Cp)(2)(+/0)) as the reductant, the mixing with another pathway involving deformation of Cu(dmp)(2)(+) (path A in Scheme 1) became more evident. The origin of the "Gated Behavior" is discussed by means of the energy differences between the "normal" and deformed Cu(II) and Cu(I) species: the difference in the crystal field activation energies corresponding to the formation of pseudo-tetrahedral Cu(II) from tetragonally distorted Cu(II) and the difference in the stabilization energies of the tetrahedral and tetragonal Cu(I) for the activation of Cu(I) species. The reduction reaction of Cu(dmp)(2)(2+) by Fe(PMCp)(2) confirmed that the mixing of the two pathways takes place by lowering the energy level corresponding to the less favorable conformational change of Cu(I) species.

New low-spin Co(II) complexes with novel tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane ligand: electron transfer kinetics and spectroscopic characterization of Co(II)P6 and Co(II)P3S3 ions in aqueous solution

“…Therefore, the kinetic studies with excess reductants and the kinetic studies of the oxidation reactions of such Co(III/II) couples are scarce, although such a study is essential to examine the mechanisms postulated to date, including the gating phenomenon. Recently several nonconcerted ET reactions have been reported in which the innersphere reorganization process takes place before the very fast outersphere ET with minimal outersphere reorganizations (33)(34)(35)(36).…”

Flipping of the coordinated triazine moiety in Cu(i)–L2and the small electronic factor, κel, for direct outer-sphere cross reactions: syntheses, crystal structures and redox behaviour of copper(ii)/(i)–L2complexes (L = 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine)

“…[10][11][12][13][14] The kinetic results were analyzed by using the following equation derived for the Square Scheme by Rorabacher and co-workers. [10][11][12][13][14] The kinetic results were analyzed by using the following equation derived for the Square Scheme by Rorabacher and co-workers.…”

“…[5][6][7][8][9][10][11][12][13][14] On the other hand, we found that the electron transfer (cross) reactions between different copper complexes and the electron self-exchange reactions are not gated. Single crystal analyses revealed that [Cu(pdt) 2 (H 2 O) 2 ](BF 4 ) 2 was in the D 2h symmetry with two axial water molecules and two symmetrically coordinated equatorial pdt ligands, while the coordination structure of [Cu(pdt) 2 ]BF 4 was a squashed tetrahedron (dihedral angle = 54.87 o ) with an asymmetric coordination by two pdt ligands: one pdt ligand coordinated to Cu(I) through pyridine-N and triazine-N2 while another pdt through pyridine-N and triazine-N4, and a stacking interaction between the phenyl ring on one pdt and the triazine ring on another pdt caused the squashed structure and nonequivalent Cu-N bond lengths.…”

“…[5][6][7][8][9][10][11][12][13][14] On the other hand, we found that the electron transfer (cross) reactions between different copper complexes and the electron self-exchange reactions are not gated. the structural change (inner-sphere reorganization) is the essential factor that induces gated phenomena.…”

H2S Sensing by Hybrids Based on Nanocrystalline SnO2 Functionalized with Cu(II) Organometallic Complexes: The Role of the Ligand Platform

“…Also widely studied are Cu(II/I) systems containing different polypyridyl ligands: 2,2-bipyridine, 1,10-phenanthroline, and their substituted derivatives [ 24 , 25 , 26 ]. One example is the reduction, which was convincingly shown for the reactions of Cu(II)(diphenyldimethylbipyridine) 2 and Cu(II)(dimethylbipyridine) 2 with ferrocene and decamethylferrocene [ 27 , 28 ].…”