The Structural Characterisation of new Pyridinyl Alcohol Cu(II) Complexes and their Application as Catalysts in the Oxidation of n–octane

Abstract In this study a series of pyridinyl alcohol ligands (2‐pyridinyl‐1‐cyclohexanol ( 1 ), 2‐pyridinyl‐1,1‐diphenyl methanol ( 2 ) and 2‐pyridinyl‐1‐phenyl‐1‐isopropylmethanol ( 3 ) have been coordinated to Cu ( Cu 1 – 3 ). These complexes have been characterised by single‐crystal X‐ray diffraction. The solid‐state structures of the Cu complexes obtained were dependent on the temperature and method used to grow crystals. In the selective oxidation of n ‐octane the copper catalysts gave yields of up to 25 % towards C8 oxygenates with predominant selectivity to C2‐C4 octanones. The exception was a chlorido‐bridged dimer, which showed high selectivity to 1‐octanol. Products from activation of the C‐1 position predominately form in higher yield in the catalytic reactions of copper(II) complexes that exhibit narrower N−Cu−O bite angles. The activity of the Cu catalysts can be attributed to metal‐ligand cooperative catalysis that involves the formation of Cu(II) peroxo intermediates. Characterisation of the recovered catalyst, in combination with the addition of a radical inhibitor during the partial oxidation reactions, indicated that the catalytic reaction progresses via a combination of an oxygen rebound mechanism and a radical chain reaction, with the latter mechanism usually dominating.