Ansa-bridged η5-cyclopentadienyl molybdenum and tungsten complexes: synthesis, structure and application in olefin epoxidation

Abstract

Ansa-bridged eta(5)-cyclopentadienyl molybdenum and tungsten tricarbonyl complexes of formula [M(eta(5)-C(5)H(4)(CH(2))(3)-eta(1)-CH(2))(CO)(3)] (M=Mo or W) were synthesized and the X-ray crystal structure of the tungsten complex is reported. In the epoxidation of cyclooctene the molybdenum compound shows a high catalytic activity, approaching the observed activities for the most reactive unbridged complexes of composition CpMo(CO)(3)X (X=Cl, CH(3)). The activity of the tungsten complex is also amongst the highest catalytic activities for the olefinic epoxidation of complexes with the composition CpW(CO)(3)X and WO(2)X(2)L(2), reported so far. The low ring strain of the ansa-bridged system improves the stability of the complexes under oxidative conditions considerably in comparison to derivatives with a shorter bridge and therefore paves the way to introduction of chirality in these systems.

Olefin Epoxidation with a New Class of Ansa‐Molybdenum Catalysts in Ionic Liquids

“…The biphasic epoxidation of selected olefins (namely cis-cyclooctene, 1-octene, and cis-stilbene), with the ansa-compounds Mo(h 6 ) were used. For all investigated reactions, both the yields and the TOFs for catalysis carried out in RTILs were much higher than in all conventional solvents.…”

“…[5] Among this class of compounds, we are currently exploring ansa complexes of the general type [Mo(h 5 -C 5 H 4 (CH(CH 2 ) n )-h 1 -CH)(CO) 3 ] as epoxidation catalysts. [6][7][8][9] We have previously reported the synthesis of new molybdenum and tungsten ansa complexes with cyclopentyl moieties and exceptionally stable bridging units, and performed first studies of these compounds as epoxidation catalysts.…”

Unequivocal assignments of C(2,5) and C(3,4) on the cyclopentadienyl ring of Cp2Fe, CpCr(CO)2(NO), and CpW(CO)3(CH3) bearing an electron-donating or electron-withdrawing substituent via resonance in 13C NMR spectra

“…In the cases of 10 and 13, the exocyclic carbon is bending toward (13, 4.90 ) or only slightly bent away (10, À0.58 ) from the metal atom with a positive, or a small negative, value of the angle q. Presumably, a higher negative q value would be anticipated if the steric strain between the Cp-substituent and the M-coordinated ligands was considered, as for complex [W(h 5 -C 5 H 4 (CH 2 ) 3 -h 1 -CH 2 ) (CO) 3 ] 22 (À4.69 ) [28]. The q angle is defined as the angle between the exocyclic CeC bond (C1eC6) and the corresponding Cp ring with a positive angle when bending toward the metal and a negative angle when bending away from the metal.…”

Aryl-substituted organomolybdenum(ii) complexes as olefin epoxidation catalysts

“…They also can be used as catalyst precursors for olefin epoxidation. [14][15][16][17][18][19] As in the Halcon-ARCO process, tert-butyl hydroperoxide (TBHP) proved to be the oxidant of choice, readily oxidizing the carbonyl compounds to active catalyst species and, usually more slowly, olefins to epoxides catalysed by the organometallic species created before.…”