Reaction of dioxygen with poly[(3,5-dimethylpyrazolato)copper]. Crystal structure, reactivity, and catalytic properties of [Cu8(dmpz)8(OH)8]

Abstract

The species [Cu8(dmpz)8(OH)8] (2) (Hdmpz = 3,5-dimethylpyrazole) has been obtained by reacting [Cu(dmpz)]n (1) with O2 at atmospheric pressure and room temperature in wet solvents. Crystal data for [Cu8(dmpz)8(OH)8].2C6H5NO2 (22-degrees-C): a = 10.229 (3) angstrom, b = 27.217 (2) angstrom, c = 14.532 (1) angstrom, beta = 98.51 (1)-degrees with Z = 2 in the space group P2(1)/m. [Cu8(dmpz)8(OH)8] consists of a discrete octameric molecule with a cyclic planar system of copper(II) atoms, bridged by OH and dmpz ligands, forming a molecule of toroidal shape; in the crystal, its cavity (viable diameter of ca. 6 angstrom) contains crystallographically disordered, possibly water, molecules; in addition, fully orderd clathrated nitrobenzene molecules have been found between the octameric units. Complex 2 is catalytically active in the oxidation reactions of organic substrates such as triphenylphosphine, aromatic primary amines, dibenzylamine, and carbon monoxide, triphenylphosphine oxide, azobenzenes, N-benzylidenebenzylamine and carbon dioxide being respectively formed. Its reaction with PPh3 under an inert atmosphere gave 4 mol of O=PPh3 per mole of 2, suggesting that 2 gives rise, in solution, to tautomeric species of the general formula [Cu8(dmpz)8(O)x(OH)8-2x(H2O)x] (x = 1-4), which might behave as the active species. Complex 2 allowed also the stoichiometric oxidation of cyclohexyl isocyanide into the corresponding isocyanate in the absence or in the presence of O2. The reaction of 2 with primary alcohols R'OH(R' = Me, Et, Pr(n), allyl) affords the octaalkoxo derivatives [Cu8(dmpz)8(OR')8] (3) whose formulation is suggested on the basis of analytical and spectroscopic data, as well as on chemical properties.