84927-91-3Relevant articles and documents
Molybdenum complexes. 3. Bis(hydroxamates) of dioxomolybdenum(VI) and their reactions: Control of redox activity by substituent effects, protic equilibria, and oxaziridine formation
Ghosh, Phalguni,Chakravorty, Animesh
, p. 1322 - 1327 (2008/10/08)
The synthesis, characterization, and spectra (1H NMR, IR, and UV) of a group of molybdenum hydroxamates of type MoO2(RX)2 (2) are reported (RX = RN(O-)C(=O)C6H4X R = H, Me, Ph; X = OMe, Me, H, Cl, NO2). These exist in only one isomeric form in which the MoO2 group is cis and the carbonyl oxygen is trans to a terminal oxo function. The CO stretching frequency of 2 is low due to the presence of hydroxamate-hydroximate resonance in metal-bound RX. The Mo(VI)-Mo(V) redox activity of 2 is systematically examined by using cyclic voltammetry at the mercury electrode. In acetonitrile the reduction peak (Epc) is readily seen but the corresponding oxidation peak (Epa) is absent except in MoO2(HX)2- (rapid decomposition of MoO2(PhX)2- and MoO2(MeX)2-). For a given X, Epc decreases as R changes in the order H > Ph > Me. For a given R, Epc values, which decrease with X as NO2 > Cl > H > Me > OMe, correlate linearly with Hammett constants. The reaction of MoO2(PhX)2 with p-YC6H4NHOH (Y = H, Cl, Me) yields a red-orange solution thought to contain MoO(YC6H4NO)(PhX)2, whose Epc is ～ 300 mV lower than that of MoO2(PhX)2. A span of more than 1 V is covered by the Epc values (-0.60 to -1.64 V vs. SCE) of the various complexes. The complex MoO2(HH)2 undergoes proton dissociation in aqueous media (pK1 = 3.45 ± 0.05 and pK2 = 5.85 ± 0.05), and the current corresponding to Epc progressively diminishes with increasing pH. This effect, which is reversible, is shown to arise from MoO2(HH)2 alone being electroactive while [MoO2(H)(HH)]- and [MoO2(H)2]2- are inactive.
