REACTIVITY OF MO-O-T TERMINAL BONDS TOWARD SUBSTRATES HAVING SIMULTANEOUS PROTON-DONOR 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 wi th anionic sulfur ligands, precursor complexes MoO2L . D (H2L = S-meth yl 3-(2-hydroxyphenyl)methylenedithiocarbazate; DCH3OH (1), H2O (2)) w ere synthesized. Complex 2 crystallizes in the orthorhombic space grou p P2(1)2(1)2(1), With a = 6.079(1) Angstrom, b = 11.638-(2) Angstrom, c = 17.325(2) Angstrom, V = 1225.7(4) Angstrom(3) and Z = 4. In its re action with PhNHOH, 1 forms a seven-coordinate oxaziridine compound [M oO(eta(2)-ONPh)L . CH3OH] (3) by ore-rearrangement (elimination-substi tution) without a change in the molybdenum oxidation state. The crysta l data for 3 are a = 9.573(3) Angstrom, b = 9.859(2) Angstrom, c = 10. 604(3) Angstrom, alpha = 95.90(2)degrees, beta = 95.81(2)degrees, gamm a = 112.12(2)degrees, V = 911.5(4) Angstrom(3), Z = 2, and triclinic s pace group <P(1)over bar>. In contrast to that of the precursor compou nd 1 (Mo-O-t 1.700(4) Angstrom), the terminal Mo-O-t distance in 3 (1. 668(2) Angstrom) is typical of Mo-O bonds of order 3, which drives the formation of an apparently unstable three-membered metallacycle via s pectator oxo stabilization (Rappe, A. K.; Goddard, W. A., III. J. Am. Chem, Sec. 1982, 104, 448). With thioglycolic acid, 1 undergoes an oxo -transfer reaction through a coupled electron-proton transfer mechanis m involving two steps, each having first-order dependence on H(2)tga c oncentration. The system offers an interesting reactivity model for th e ore-transfer pathway of oxidoreductase Mo enzymes.