Tetranuclear Copper(II) Complexes with Macrocyclic and Open-Chain Disiloxane Ligands as Catalyst Precursors for Hydrocarboxylation and Oxidation of Alkanes and 1-Phenylethanol.

Two new tetranuclear copper(II) complexes [Cu₄(μ₄-O)( L¹)Cl₄] ( 1) and [Cu₄(μ₄-O)( L²)₂Cl₄] ( 2), where H₂L¹ is a macrocyclic ligand resulting from [2+2] condensation of 2,6-diformyl-4-methylphenol (DFF) and 1,3-bis(aminopropyl)tetramethyldisiloxane, and HL² is a 1:2 condensation product of DFF with trimethylsilyl p-aminobenzoate, have been prepared. The structures of the products were established by X-ray diffraction. The complexes have been characterised by FTIR, UV/Vis spectroscopy, ESI mass-spectrometry and magnetic susceptibility measurements. The latter revealed that the tetranuclear complexes can be described as two ferromagnetically coupled dinuclear units, in which the two copper(II) ions interact antiferromagnetically. The compounds act as homogeneous catalyst precursors for a number of single-pot reactions, including (i) hydrocarboxylation, with CO, H₂O and K₂S₂O₈, of a variety of linear and cyclic( n = 5-8) alkanes into the corresponding C _n+1 carboxylic acids, (ii) peroxidative oxidation of cyclohexane, and (iii) solvent-free microwave-assisted oxidation of 1-phenylethanol. [ABSTRACT FROM AUTHOR]