Structural and Catalytic Aspects of Dioxomolybdenum(VI) Complexes with omega-Hydroxy Functionalized N-Salicylidene Hydrazides

The new cis-dioxomolybdenum(VI) complexes [MoO2(salhyhb)](2) (1). [MoO2(salhyhp)] (2), and [MoO2(salhyhh)(MeOH)] (3) with the hydrazone ligands H(2)salhyhb, Hsalhyhp, and H(2)salhyhh derived from salicyladehyde and omega-hydroxy carbonic acid hydrazides with different chain lengths, have been synthesized and spectroscopically characterized. The crystal structures of all three complexes reveal an octahedral environment for the molybdenum atoms with the same basic structural motif. In addition to the two oxo groups an [NO3] donor set is observed which is given by the tridentate Schiff-base ligand and an oxygen atom of a coordinating alcohol. Depending on the side chain length different modes of association are observed. For complex 1 a dimeric structure is obtained, which is linked by coordination of the side chain hydroxy group at the molybdenum atom of the other monomer. The extension of the side chain by one methylene group in complex 2 leads to a ploymeric structure , which is based on a similar intermolecular coordination of the side chain hydroxy group. The further increase of the side-chain length in complex 3 results in the coordination of a methanol molecule at the molybdenum atom. For compounds 2 and 3 the additional hydrogen-bonding network leads to the formation of layered structures in the solid state. The synthesized cis-dioxomolybdenum(VI) complexes were tested for their catalytic ability towards the oxidation of sulfides. Although no significant influence of the side chain lengths could be detected, these complexes are efficient catalysts for sulfoxidation.