A polymer-bound oxidovanadium(IV) complex prepared from an L-cysteine-derived ligand for the oxidative amination of styrene

Abstract

The ligand H2sal-cys (I) derived from salicylaldehyde and Lcysteine has been covalently bonded to chloromethylated polystyrene cross-linked with 5% divinylbenzene. Upon treatment with [VO(acac)2] in dimethylformamide (DMF) the polystyrene-bound ligand PS-H2sal-cys (II) gave the oxidovanadium(IV) complex, PS-[VO(sal-cys)·DMF] (1). The corresponding neat complex, [VO(sal-eta)]2 (2), has also been prepared similarly in methanol. These complexes have been characterised by IR, electronic, EPR spectroscopic studies, magnetic susceptibility measurements and thermal as well as scanning electron micrographs studies. Complex [VO-(sal-eta)]2 exhibits a medium intensity band at 980 cm -1 in the IR spectrum due to ν(V=O) stretch. Broad features of the EPR spectrum for the neat complex along with magnetic susceptibility studies suggest the presence of antiferromagnetic exchange interaction between two vanadium centers in close proximity. Both complexes catalyze the oxidative amination of styrene, in mild basic conditions, with secondary amines (diethylamine, imidazole, and benzimidazole) and gave a mixture of two aminated products in good yields. Amongst the two aminated products, the anti-Markovnikov product is favored over the Markovnikov one due to the steric hindrance posed by the secondary amines. The polymeranchored heterogeneous catalyst is free from leaching during catalytic action and recyclable. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.