On the Stability of Copper(II) Organic Compounds with the σ Bond Cu-C: A Quantum-Chemical Study

摘要

Until recently, it was assumed that stable organic compounds of copper(II) with the Cu(II)-C σ bond were nonexistent [1]. However, in a later obtained crystalline complex with nitrogen-containing ligands, the existence of such a bond was suggested [2]. At the same time, there is reliable experimental evidence of the formation of analogous labile complexes on photolysis and radiolysis of Cu(II) compounds as well as by the reaction of Cu~(2+) ions with organic radicals in water and organic solvents [3-6]. In particular, the electronic absorption spectra of the products of photochemical and thermal reactions of copper chloride complexes in organic solvents show new bands at 430-450 nm, which can be assigned to n → d transitions [5,6]. The corresponding EPR spectrum also shows a new signal. In particular, for the product of photolysis of quaternary ammonium tetrachlorocuprate, the g values and HFC tensors A(Cu) are as follows: g1 = 2.082 ± 0.003, g2 = 2.033± 0.001, and g3 = 2.024 ± 0.001; A1(~(63)Cu) = 4.1 ± 0.2 mT, A2(~(63)Cu) = 3.8 ± 0.1 mT, and A3(~(63)Cu) = 11.02 ± 0.2 mT. The half widths for these signals are as follows: ΔH1 = 10.0, ΔH2 = 3.7, and ΔH3 = 6.6 mT. These values are typical of copper(II) complexes [6]. However, these compounds are stable in frozen solvent matrices only below 100 K and their lifetime under common conditions is 10~(-6)-10~(-8) s. Therefore, it is accepted that copper(II) organic compounds are unstable and readily decompose with cleavage of the Cu-C bond. However, in our opinion, the rapid disappearance of such complexes in solutions can be due to their high reactivity in various bimolecular processes, the rate of which in solids is diffusion-controlled.