Reactivity of Mo−Ot Terminal Bonds toward Substrates Having Simultaneous Proton- and Electron-Donor Properties:  A Rudimentary Functional Model for Oxotransferase Molybdenum Enzymes

In order to study the reactivity pattern of Mo−O t bonds associated with anionic sulfur ligands, precursor complexes MoO 2 L·D (H 2 L = S -methyl 3-(2-hydroxyphenyl)methylenedithiocarbazate; D = CH 3 OH ( 1 ), H 2 O ( 2 )) were synthesized. Complex 2 crystallizes in the orthorhombic space group P 2 1 2 1 2 1, with a = 6.079(1) Å, b = 11.638(2) Å, c = 17.325(2) Å, V = 1225.7(4) Å 3, and Z = 4. In its reaction with PhNHOH, 1 forms a seven-coordinate oxaziridine compound [MoO(η 2 -ONPh)L·CH 3 OH] ( 3 ) by oxo-rearrangement (elimination−substitution) without a change in the molybdenum oxidation state. The crystal data for 3 are a = 9.573(3) Å, b = 9.859(2) Å, c = 10.604(3) Å, α = 95.90(2)°, β = 95.81(2)°, γ = 112.12(2)°, V = 911.5(4) Å 3, Z = 2, and triclinic space group P 1̄. In contrast to that of the precursor compound 1 (Mo−O t = 1.700(4) Å), the terminal Mo−O t distance in 3 (1.668(2) Å) is typical of Mo−O bonds of order 3, which drives the formation of an apparently unstable three-membered metallacycle via spectator oxo stabilization (Rappé, A. K.; Goddard, W. A., III. J. Am. Chem. Soc . 1982, 104, 448). With thioglycolic acid, 1 undergoes an oxo-transfer reaction through a coupled electron−proton transfer mechanism involving two steps, each having first-order dependence on H 2 tga concentration. The system offers an interesting reactivity model for the oxo-transfer pathway of oxidoreductase Mo enzymes.