Dioxo-Molybdenum(VI) Complexes Stabilized by Polydentate Ligands with NO3, N2O2 and NS2 Donor-Atom Sets

Dioxomolybdenum(V1) complexes of the general formula LMo02 (L = (OCH2CH2)2N(CH2CH20H) (l), O(CH2)2- NMe(CH2)2NMe(CH2)20 (2), HN(CH2CH2S)2 (3) ) have been synthesized and characterized. The structures of all compounds have unambiguously been determined in solution with the use of NMR spectroscopy. Complexes 1 and 2 have a distorted octahedral coordination about Mo with cis oxo groups and two alkoxo oxygen atoms in the apical positions. The coordination sphere is completed by amino and alkoxo oxygen atoms in 1 and by two N atoms in 2. Dissolution of 1 in H2O promotes hydrolysis of the remaining hydroxy arm of the ligand to give the anionic species H[MoO~(OCH~CH~)in~ Nwh]i ch all the alkoxo arms are equivalent. In 3, the cis-M0022+ core is coordinated in a distorted trigonal-bipyramidal arrangement by two sulfur atoms in axial positions, by a nitrogen atom, and by two cis oxygen atoms. As shown by a single-crystal X-ray diffraction analysis, 3 retains the trigonalbipyramidal structure in thewdid state: orthorhombic Pnma, a = 9.814(1) A, b = 11.960(2) A, c = 7.119(1) A, Z = 4, R = 0.03 1. The reactions of 1-3 with some inorganic (PPh3) and organic substrates @-thiocresol, thioanisole, benzyl alcohol, benzaldehyde) have been investigated. Only complex 3 undergoes selective reduction of the metal center by triphenylphosphine and pthiocresol converting to the dimer Mo zO~[HN(CH~CH~S)O~u]r~ r.e sults confirm that a bulky ligand with sulfur donors is required to make LMoO2 complexes capable of catalyzing oxygentransfer reactions.