The affinity for carbon monoxide, electrochemical and spectral properties of binuclear copper(I) complexes.

概要

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Binuclear copper(I) complexes [CuXL]2(X=Cl− and I−; L=2,2′-bipyridine, 1,10-phenanthroline, and their derivatives) have been synthesized in acetone, which react with CO reversibly to give crystalline carbonyl adducts [Cu2X2L2(CO)]. The cyclic voltammograms of [CuXL]2 and [Cu2X2L2(CO)] show two couples of coppercentered oxidation-reduction waves, indicative of binuclear structure. One couple of waves in [Cu2X2L2(CO)] alone shifts to the anodic region, exhibiting the formation of monocarbonylated complexes. All the half-wave potentials are primarily governed by the basicity of a ligand L, and the contribution of a coordinated CO to the stabilization of CuI state by π back-bonding is found. The equilibrium constants of the reaction, [CuXL]2+CO\oversetKco\rightleftharpoons[Cu2X2L2(CO)], are lowered with the decrease in the transition energy of the ligand←metal charge transfer of [CuXL]2. On this basis, it is concluded that CO competes with L concerning π back-bonding with copper(I). The νco values of the coordinated CO exhibit apparent L-dependence, which is accounted for by the competition between Cu–L and Cu–CO π-bonding, and hence, νco values are useful probe to inquire into the nature of Cu–CO bonding among these copper(I) complexes.
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