New Insights into the Berg−Holm Oxomolybdoenzyme Model

Reaction of MoO 2 (L-NS 2 ) [L-NS 2 = 2,6-bis(2,2-diphenyl-2-thioethyl)pyridinate(2−)] with PPh 3 in N,N -dimethylformamide (dmf), chloroform, or mixtures thereof results in the formation of purple, dinuclear, μ-oxo-Mo(V) compounds, Mo 2 O 3 (L-NS 2 ) 2 ·2sol (sol = dmf, CHCl 3, or mixtures thereof), which can be dried at 80 °C under vacuum to give Mo 2 O 3 (L-NS 2 ) 2 . 31 P NMR experiments were consistent with the following reaction: 2Mo VI O 2 (L-NS 2 ) + PPh 3 → Mo V 2 O 3 (L-NS 2 ) 2 + OPPh 3 . The compounds have been characterized by microanalysis, IR, and UV−visible spectroscopy, electrospray ionization mass spectrometry, and X-ray diffraction studies of Mo 2 O 3 (L-NS 2 ) 2 ·2dmf and Mo 2 O 3 (L-NS 2 ) 2 ·2CHCl 3 . Dinuclear Mo 2 O 3 (L-NS 2 ) 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 CHCl 3 disolvate]. Each Mo center is further coordinated by a tridentate L-NS 2 ligand and a terminal oxo ligand (Mo O = 1.681(5) Å [1.696(4) Å]). The [Mo 2 O 3 ] 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 Mo IV O(L-NS 2 )(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.