Investigation of Molybdenum Tetracarbonyl Complexes As Precursors to MoVI Catalysts for the Epoxidation of Olefins

The one-dimensional organic-inorganic hybrid material [MoO3(bipy)] (3) (bipy = 2,2'-bipyridine) is obtained rapidly and in quantitative yield by the reaction of the complex Cis-[Mo(CO)(4)(bipy)] (1) with excess tert-buty1hydroperoxide (TBHP) in n-decane/dichloromethane at room temperature. A similar oxidative decarbonylation of the complex (cis-[MO(CO)(4)(di-t-Bu-bipy)] (2) (di-t-Bu-bipy = 4,4'-di-tert-butyl-2,2'-bipyridine) leads to the isolation of the polynuclear complex [Mo8O24(di-t-Bu-bipy)(4)] (4). The structure of 4, its the CH2Cl2 solvate, was determined by X-ray crystallography. The unit cell contains two crystallographically independent octameric windmill-type complexes, formulated as [Mo8O24(di-t-Bu-bipy)(4)], both of which contain it central cubane-type Mo(mu 3-O)(4) core. Four peripheral [MoO2(di-t-Bu-bipy)](2+) units cap the long edges of the MO4 tetrahedron of the central cubane. The close packing of these complexes via weak offset pi-pi contacts involving the organic ligands leads to a structure having large channels (Occupied by solvent Molecules) running in various directions of the unit cell. Compounds 3 and 4 can be used as the basis For active catalytic systems for the liquid-phase epoxidation of cis-cyclooctene with TBHP its the oxidant, giving the corresponding epoxide as the only product. Notably higher activities, with no change in selectivity, are possible by using microwave-assisted heating instead of conventional oil bath heating and/or by increasing the reaction temperature from 55 degrees C to 75 degrees C. The excellent stability of these Mo-VI catalytic systems was confirmed by carrying out six consecutive reaction runs at 75 degrees C under microwave-assisted licating. The stable parent carbonyls (I and 2) can be used as catalyst precursors since they ARE transformed into 3 and 4 under the operating catalytic conditions.