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

Article abstract of DOI:10.1021/ic960670z

In order to study the reactivity pattern of M_o-O_t bonds associated with anionic sulfur ligands, precursor complexes MoO₂L-D (H₂L = S-methyl 3-(2-hydroxyphenyl)methylenedithiocarbazate; D = CH₃OH (1), H₂O (2)) were synthesized. Complex 2 crystallizes in the orthorhombic space group P2₁2₁2₁, with a = 6.079(1) ?, b = 11.638(2) ?, c = 17.325(2) ?, V = 1225.7(4) ?³, and Z = 4. In its reaction with PhNHOH, 1 forms a seven-coordinate oxaziridine compound [MoO(η²-ONPh)L-CH₃OH] (3) by oxo-rearrangement (elimination-substitution) without a change in the molybdenum oxidation state. The crystal data for 3 are a = 9.573(3) ?, b = 9.859(2) ?, c = 10.604(3) ?, α = 95.90(2)°, β== 95.81(2)°, γ = 112.12(2)°, V = 911.5(4) ?³, Z = 2, and triclinic space group P1. In contrast to that of the precursor compound 1 (M_o-O_t = 1.700(4) ?), the terminal M_o-O_t distance in 3 (1.668(2) ?) 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 H₂tga concentration. The system offers an interesting reactivity model for the oxo-transfer pathway of oxidoreductase Mo enzymes.