Formation of organometallic hydroxo and oxo complexes by oxidation of transition metal hydrides in the presence of water.: X-ray structures of [CpMo(OH)(PMe3)3][BF4] and [CpMo(O)(PMe3)2][BF4]

The decomposition of complex [CpMoH(PMe3)(3)](+), 1(+), in wet, weakly coordinating solvents (THF and acetone) leads to the formation of the Mo(III) hydroxo compound [CpMo(OH)(PMe3)(3)][BF4], 2, and the Mo(IV) oxo compound [CpMo(O)(PMe3)(2)][BF4], 3. Both of these have been characterized by X-ray crystallography. The formation of these products is rationalized by a mechanism which involves water coordination followed by multiple steps of tandem oxidation and deprotonation reactions. The proposed [CpMoH(PMe3)(3)(H2O)](2+) intermediate is observed by NMR spectroscopy. EPR monitoring of the oxidation of 1 with ferrocenium shows also the formation of a species characterized by a binomial triplet resonance and interpreted as the neutral Mo(III)-oxo complex CpMo(O)(PMe3)(2), 4. The proposed mechanism is in harmony with the previously investigated mechanism of decomposition of 1(+) in dry solvents and with the coupled proton and electron transfer processes that relate aqua, hydroxo, and oxo species in the chemistry of Mo enzymes. Computational studies at the DFT level were carried out on a model system where the PMe3 ligand was replaced by PH3. Their results are consistent with the proposed mechanism.