Catechol Oxidation with Dinuclear Copper Complexes of Aliphatic Tripodal Amino Alcohols

Abstract

AbstractA set of unsymmetrical tripodal (aminoalkyl)bis(hydoxyalkyl)amine ligands H4‐2 to H4‐6 with either ethyl or propyl ligand arms has been prepared and characterized. These ligands react with copper hydroxide and ammonium hexafluorophosphate, copper(II) bromide or tris(triphenylphosphane)copper(I) bromide to give di‐ and polynuclear complexes. The dinuclear copper complexes 9a–f catalyze the oxidation of 3,5‐di‐tert‐butylcatechol (DTBC). The coordination geometry at the copper center is influenced by the length of the side arms resulting in a different reactivity of complexes 9a–f in the DTBC oxidation. Alternative preparation procedures lead in selected cases to the formation of coordination polymers 10a and 10b. The reversible formation of the poly(dinuclear) cations in 10a illustrates that the apical alcohol groups are labile. The solid‐state structures are neither necessarily identical with solution structure nor do they represent the catalytically active species. Electronic spectra, however, agree with a dinuclear structures in solution as indicated by the characteristics of the oxygen–copper‐CT. The observation of comparable catalytic activities for complexes 9a–9d renders the bridging coordination of the catechol by both copper ions of a dinuclear complex moiety unlikely. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)