Peroxomolybdenum complexes as epoxidation catalysts in biphasic hydrogen peroxide activation: Raman spectroscopic studies and density functional calculations

Density functional calculations and Raman spectroscopic data were correlate d with the unique catalytic epoxidation activity of peroxomolybdenum comple xes [MoO(O-2)(2)(OER3)] (E = N, P, As; R = n-dodecyl) in a biphasic chlorof orm-1-octene/aqueous hydrogen peroxide system. Crystal structure determinat ions on [MoO(O-2)(2)(OPtBu3)(OCMe2)] and two complexes containing chelating hemilabile ether-phosphane oxide and ether-arsane oxide ligands [MoO(O-2)( 2){iPr(2)E(O)CH2CH2OCH3}] (E-P, As) are reported. A mechanistic study with these model complexes reveals the importance of free coordination sites for peroxide activation. Calculations and Raman spectroscopic data indicate th e tendency of coordinatively unsaturated species [MoO(O-2)(2)(L)] to dimeri ze in noncoordinating solvents. The catalytic activity in the presence of w ater as competing ligand could be correlated with the calculated proton aff inity of the ligands OER3 (R = N, P, As). Elucidation of the vibrational be havior of the structurally characterized peroxo complexes was supported by normal-coordinate analyses.