Dioxomolybdenum species

Oxo complexes dominate the chemistry of molybdenum in its higher oxidation states,5 80,92 93 and play a major role in the catalytic activity of molybdenum in biological systems (see Section 36.6.7). MoIV complexes have been characterized containing the monooxo (MoO 2+ and the trans-dioxomolybdenum(IV) Mo02 cores, but no compound has been isolated analogous to the ds-dioxomolybdenum(VI) species described in Section 36.5. Crystal structure determinations have been accomplished for a number of MoIV complexes, and some typical examples are listed in Table 3.80... 

The distorted octahedral oxomolybdenum(V) complexes [MoO(S-S-X-S-S)] were prepared by reaction of [M0CI4 (NCMe)2] with the free pentadentate ligand (HS S X S SH, (28)) or its Ni + complex in wet thf, or by oxidation in air of [Mo(CO)2(S-S-X-S S)]. Related dioxomolybdenum(VI) species [Mo02(S-S-X-S-S)J were also reported. 

Many of these complexes also participated in oxygen-atom transfer reactions, giving dioxomolybdenum(VI) species and reduced substrates, and associated kinetic studies have been... 

The oxidation is a six-electron process, and it is regarded as eertain that the a-H abstraction with formation of the 71-allyl complex is the rate-determining step. Both the dioxomolybdenum cations and the diimino species are believed to be involved in the formation of acrylonitrile. On the basis of selectivity measurements, the stoichiometry shown in Equation 8-9 was assumed [L32]. 

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