Oxidative functionalisation of alkanes: synthesis, molecular structure andcatalytic implications of anionic vanadium(v) oxo and peroxo complexes containing bidentate N,O ligands

A mixture of [NBu4][VO3] and pyrazine-2-carboxylic acid (Hpca) in acetonitr ile catalysed smoothly the reaction of alkanes RH (R = CH3 or C6H11) with m olecular oxygen (from air) and hydrogen peroxide to give the corresponding alkyl hydroperoxide ROOH as the primary product. The oxo and peroxo anions [VO2(pca)(2)](-) and [VO(O-2)(pca)(2)](-), isolated as the tetrabutylammoni um or ammonium salts from acetonitrile solution and fully characterised by single crystal structure analyses, are assumed to be involved in the cataly tic process. A screening of different N,O ligands showed Hpca to be the bes t co-catalyst, while anthranilic acid (Hana) proved to be almost inactive. The isolation and crystal structure analysis of the analogous oxo compound [NBu4][VO2(ana)(2)] showed a fundamental difference in the co-ordination of the bidentate N,O ligands which might explain the different catalytic acti vities: while in [VO2(pca)(2)](-) the two pca ligands are bonded through a nitrogen and an oxygen atom (N,O co-ordination), in [VO2(ana)(2)](-) the tw o ana ligands are co-ordinated via two oxygen atoms of the carboxylato grou p (O,O co-ordination).