Bis- and tris-pyridyl amino and imino thioether Cu and Fe complexes. Thermal and microwave-assisted peroxidative oxidations of 1-phenylethanol and cyclohexane in the presence of various N-based additives

Abstract

The new [Cu(OTf)(L)](OTf) 1, [Cu(L)(H 2O)](OTf) 2 1′, [Cu(OTf)(L Me)](OTf) 2 and [Cu(L py)](OTf) 2 4, and [Fe(OTf) 2(L Me)] 3 and [Fe(OTf)(L py)](OTf) 5 complexes, bearing bis- and tris-pyridyl amino and imino thioether ligands, have been synthesized and fully characterized by IR, ESI +-MS and elemental analyses, and also by X-ray diffraction structural analyses (for 1, 1′, 2 and 4). In the presence of various N-based additives, they show a very good catalytic activity for the solvent- and halogen-free microwave-assisted oxidation of 1-phenylethanol by t-BuOOH (model reaction). The combination of pyridazine with the Cu complex 2 provided the most efficient catalytic system, resulting in a maximum yield of acetophenone of 99% after 30 min at 80 °C. The maximum turnover frequency (TOF) of 5220 h −1 (corresponding to 87% yield) was achieved just after 5 min of reaction time under the very low microwave power of 10 W. The catalytic properties of those complexes were also evaluated for the mild oxidation of cyclohexane, to cyclohexanol and cyclohexanone, in acetonitrile with H 2O 2, leading to yields up to 29% (based on the alkane substrate) that are comparable to the best reported Fe and Cu catalytic systems. The effects of various factors, such as nature and amount of the additives and metal centres (Cu or Fe), temperature, time and type of peroxide used, were also investigated.