Room temperature aerobic oxidation of alcohols using CuBr2 with TEMPO and a tetradentate polymer based pyridyl-imine ligand
A series of tetradentate pyridyl-imine terminated Schiff-base ligands has been investigated for their ability in the catalytic oxidation of alcohols when combined with copper bromide (CuBr2) and 2,2,6,6-tetramethylpiperidyl-1-oxy (TEMPO). Analogous bidentate ligands showed poorer catalytic activity and the ratio of Cu:ligand was of crucial importance in maintaining high yields. The polydimethylsiloxane (PDMS) derived pyridyl-imine terminated ligand combined with copper(II) ions affords an effective and selective catalyst for aerobic oxidations of primary and secondary alcohols under aqueous conditions. Preliminary mechanistic studies suggest that bimetallic complexes may be playing a role in the catalytic transformation.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (193 K)Download as PowerPoint slideHighlights► Polydimethylsiloxane-bis(pyridylimine) forms active catalyst for alcohol oxidation. ► PDMS-derived ligand is soluble in supercritical carbon dioxide. ► Good yields of aldehyde/ketone from challenging substrates (1-alkanols and 1-phenylethanol). ► Dicopper complexes were identified in catalytic reaction through mass spectrometry. ► Tetradentate ligands afford higher TOF and TON catalysts than bidentate versions.
Journal: Applied Catalysis A: General - Volumes 413–414, 31 January 2012, Pages 332–339