Electrochemistry Studies of (Ir(mu-pz)(COD))2 in Halocarbon and Acetonitrile Solutions. Solvent Control of Sequential Electro-Transfer Thermodynamics

摘要

Electrochemical studies of (Ir(mu-pz)(COD))2(mu-pz = bridging pyrazolyl, COD = 1,5-cyclooctadiene) in halocarbon and CH3CN solutions, the cyclic voltammogram (CV) of (Ir(mu-pz)(COD))2 exhibits two, thermodynamically distinct one-electron oxidations. The first oxidation is quasi-reversible. The second oxidation is chemically irreversible. The position of E sub p,a for the second oxidation is variable due to complexation of (Ir(mu-pz)(COD))2(2+) with the supporting anion. Bulk electrolysis at potentials positive of the quasi-reversible oxidation results in the removal of 2.0 electrons. A slow reaction on the CV time scale occurs between (Ir(mu-pz) COD))2 causes the second electrode process to shift to less positive potentials. The first wave does not shift. At (CH3CN) approx. 2.0 M, the second wave merges with the first to give a single feature that corresponds to a net two-electron process. The wave corresponding to this two-electron process also shifts toward negative potentials with increasing (CH3CN). In neat CH3CN/TBAH solutions, the two-electron oxidation process occurs at +0.262 V. Bulk electrolysis in neat CH3CN solutions at potential positive of the 2-electron process results in the removal of 2.0 electrons. The observed shifts in electron-transfer thermodynamics arise from the strong complexation of two CH3CN ligands with the two-electron oxidized (Ir(mu-pz)(COD))2(2+) complex.