New Insights into the Berg−Holm Oxomolybdoenzyme Model

Reaction of MoO2(L-NS2) [L-NS2 = 2,6-bis(2,2-diphenyl-2-thioethyl)pyridinate(2−)] with PPh3 in N,N-dimethylformamide (dmf), chloroform, or mixtures thereof results in the formation of purple, dinuclear, μ-oxo-Mo(V) compounds, Mo2O3(L-NS2)2·2sol (sol = dmf, CHCl3, or mixtures thereof), which can be dried at 80 °C under vacuum to give Mo2O3(L-NS2)2. 31P NMR experiments were consistent with the following reaction: 2MoVIO2(L-NS2) + PPh3 → MoV 2O3(L-NS2)2 + OPPh3. The compounds have been characterized by microanalysis, IR, and UV−visible spectroscopy, electrospray ionization mass spectrometry, and X-ray diffraction studies of Mo2O3(L-NS2)2·2dmf and Mo2O3(L-NS2)2·2CHCl3. Dinuclear Mo2O3(L-NS2)2 is comprised of five-coordinate, trigonal-bipyramidal Mo centers bridged by a strictly linear Mo−O−Mo unit with Mo−O = 1.8639(6) Å for the dmf disolvate [1.8703(4) Å for the CHCl3 disolvate]. Each Mo center is further coordinated by a tridentate L-NS2 ligand and a terminal oxo ligand (MoO = 1.681(5) Å [1.696(4) Å]). The [Mo2O3] core is planar, and the terminal oxo ligands adopt an anti disposition. These findings provide new insights into the oxomolybdoenzyme model first described by Berg and Holm (Berg, J. M.; Holm, R. H. J. Am. Chem. Soc. 1985, 107, 917 and 925; Craig, J. A.; Holm, R. H. J. Am. Chem. Soc. 1989, 111, 2111 and references therein), viz., (i) mononuclear MoIVO(L-NS2)(dmf) is not the product of the aforementioned reaction in dmf or mixed solvents, and (ii) comproportionation and dinucleation, rather than being absent, are defining reactions in the oxygen atom transfer chemistry of this system.