Mixed-valence copper complexes with the organic donors as catalysts for dichlorobutene isomerization

Abstract

The formation of mixed-valence copper complexes with dialkyl sulfides or triphenylphosphine in the catalytic isomerization of dichlorobutenes was investigated kinetically and spectroscopically (UV–Vis, IR, EPR, NMR). These species were prepared both starting from Cu(I) and Cu(II) compounds. The complexes containing 3 or 4 copper ions in different oxidation states, substrate and donor molecules were found to play a key role in catalysis. Chlorolefins with allylic chlorine atom may stabilize mixed-valence complexes as bridging ligand between Cu(I) and Cu(II). The EPR spectra of these complexes provide the five-coordinated Cu(II) with a trigonal–bipiramydal geometry of coordination sphere. The simultaneous presence of Cu(I) and Cu(II) in polynuclear structure is proposed to favor the electron transfer step in the reaction mechanism.