Synthesis and structural characterization of a tetracopper(I) complex of 2,6-(bis(3- dimethylamino)-propyliminomethyl)-4- methylthiophenolate

The compound 2,6-diformyl-4-methylphenyl (1) has been made by hydrolysis of S-(2,6- diformyl-4-methylphenyl)dimethylthiocarbamate followed by oxidation with I₂. Condensation of 1 with 4 equiv. of 3-dimethylaminopropylamine and subsequent reduction with Na/benzophenone results in the sodium salt of the Schiff base binucleating ligand 2,6-(bis(3-dimethylamino)-propyliminomethyl)-4-methyl-thiophenolate (2, NaL). The ligand (L) binds 2 eq of Cu(I) and crystallizes from MeCN solution to give an air sensitive tetracopper(I) complex with the formula [Cu₄L₂(MeCN)](PF₆)₂ (3)·0.5 MeCN·0.25 MeOH as determined by X-ray crystallography. The complex contains three distorted trigonal planar and one distorted tetrahedral Cu¹ centers with Cu---S bond lengths short for their respective coordination geometries. In DMSO solution, ¹H NMR spectra of 3 reflect free ligand symmetry suggesting dissociation into dimers. Cyclic voltammetry of 3 in MeCN reveals one irreversible oxidation at 110 mV (vs SCE).