On the stability of copper(II) organic compounds with the σ bond Cu-C: A quantum-chemical study

Abstract

143 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: g 1 = 2.082 ± 0.003, g 2 = 2.033 ± 0.001, and g 3 = 2.024 ± 0.001; A 1 ( 63 Cu) = 4.1 ± 0.2 mT, A 2 ( 63 Cu) = 3.8 ± 0.1 mT, and A 3 ( 63 Cu) = 11.02 ± 0.2 mT. The half widths for these signals are as follows: ∆ H 1 = 10.0, ∆ H 2 = 3.7, and ∆ H 3 = 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. It was of interest to perform quantum-chemical calculations of some model copper(II) organic compounds with the Cu(II)–C σ bond, as well as of the energies of possible reactions involving these compounds in order to confirm the possibility of their formation and predict On the Stability of Copper(II) Organic Compounds with the s Bond Cu–C: A Quantum-Chemical Study