DIOXOMOLYBDENUM(VI) COMPLEXES STABILIZED BY POLYDENTATE LIGANDS WITH NO3, N2O2, AND NS2 DONOR-ATOM SETS

Dioxomolybdenum(VI) complexes of the general formula LMoO2 (L = (OCH2C H2)2N(CH2CH2OH) (1), O(CH2)2-NMe(CH2)2NMe(CH2)2O (2), HN(CH2CH2S)2 (3) ) have been synthesized and characterized. The structures of all comp ounds have unambiguously been determined in solution with the use of N MR spectroscopy. Complexes 1 and 2 have a distorted octahedral coordin ation about Mo with cis oxo groups and two alkoxo oxygen atoms in the apical positions. The coordination sphere is completed by amino and al koxo oxygen atoms in 1 and by two N atoms in 2. Dissolution of 1 in H2 O promotes hydrolysis of the remaining hydroxy arm of the ligand to gi ve the anionic species H[MoO2(OCH2CH2)3N] in which all the alkoxo arms are equivalent. In 3, the cis-MoO2(2+) core is coordinated in a disto rted trigonal-bipyramidal arrangement by two sulfur atoms in axial pos itions, by a nitrogen atom, and by two cis oxygen atoms. As shown by a single-crystal X-ray diffraction analysis, 3 retains the trigonal-bip yramidal structure in the solid state: orthorhombic Pnma, a = 9.814(1) angstrom, b = 11.960(2) angstrom, c = 7.119(1) angstrom, Z = 4, R = 0 .031. The reactions of 1-3 with some inorganic (PPh3) and organic subs trates (p-thiocresol, thioanisole, benzyl alcohol, benzaldehyde) have been investigated. Only complex 3 undergoes selective reduction of the metal center by triphenylphosphine and p-thiocresol converting to the dimer Mo2O3[HN(CH2CH2S)2]2. Our results confirm that a bulky ligand w ith sulfur donors is required to make LMoO2 complexes capable of catal yzing oxygen-transfer reactions.