Coordination modes of 2-mercaptonicotinic acid: synthesis and crystal structures of palladium(II), platinum(II), rhenium(III) and molybdenum(VI) complexes

New Pd(II), Pt(II), Re(III), Mo (VI) and Mo(V) complexes with 2-mercaptonicotinic acid (HnicSH), [Pd(PPh3)(HnicS)2]·0.5CH3OH 1, [Pd(HnicS)2]·CH3OH 2, [Pt(PPh3)(HnicS)2]·NEt3·H2O 3, [Pt(HnicS)2] 4, [Pt(bipy)(HnicS)2]·CH3OH 5, [Re(PPh3)(OCH3)(HnicS)2] 6, [ReI2(PPh3)2(HnicS)] 7, [MoO2(CH3NicS)2] 8 and [Mo2O3(CH3nicS)4]·DMF 9 have been prepared. The crystal structures of compounds 1, 3, 8 and [ReI2(PPh3)2(HnicS)]·0.5H2O·DMF (7·0.5H2O·DMF) were determined by X-ray diffraction. Complexes 1 and 3 contain two HnicS− ligands bonded in two different coordination modes: monodentate (S) and chelating (N,S). Complexes 7 and 8 contain only one HnicS− ligand which is bidentate (N,S). Infrared, 1H and 13C-{1H} NMR spectroscopic data for the complexes are presented. The Mo(VI) complex 8 is active towards oxygen atom transfer reactions and can catalyse the oxidation of benzoin and PPh3 with dmso; the catalysis occurs via the Mo(V) complex 9 which has been isolated and characterized.