STRUCTURAL CHARACTERIZATION OF POSSIBLE INTERMEDIATES IN VANADIUM-CATALYZED SULFIDE OXIDATION

Reaction between 3-methoxysalicylaldehyde and (R,R)-1,2-diaminocyclohe xane with VO2+ as a template yielded the racemic Schiff-base complex [ VO(L(1))][H(2)L(1) = N,N'-bis(3-methoxysalicylidene)cyclohexane- 1,2-d iamine] which is converted into trans-[VCl2(L(1))] with SOCl2. The cry stal structures of both have been determined. The former is a tetragon al-pyramidal complex, whereas the structure of the latter is best desc ribed as an octahedron distorted towards a trigonal prism. The complex [VO(acac)(2)] (acac = acetylacetonate) reacted with HN(CH2CH2OH)(2) i n the presence of oxygen to yield [VO(acac){PhN(CH2CH2O)(2)}], the cry stal structure of which reveals a co-ordination geometry in-between te tragonal-pyramidal and octahedral (provided by a weak vanadium-to-nitr ogen bonding interaction). Aeration of a reaction mixture consisting o f [VO(acac)(2)] and the Schiff base (H(2)L(2)) formed between H2NCH2CH 2OH and o-hydroxynaphthaldehyde afforded [{VO(L(2))}O-2] having a bent and slightly asymmetric axe-bridge, and an additional weak bridging i nteraction between one of the V-O (ethanolate) centres and the second vanadium centre (crystal structure). In solution, the inequivalency of the two vanadium centres is offset. The reactivity of the complexes t owards Me,SO and/or PhSMe has been studied by EPR and V-51 NMR spectro scopy.