Investigation of Molybdenum Tetracarbonyl Complexes As Precursors to Mo^VI Catalysts for the Epoxidation of Olefins

Abstract

The one-dimensional organic-inorganic hybrid material [MoO 3 (bipy)] (3) (bipy = 2,2 0 -bipyridine) is obtained rapidly and in quantitative yield by the reaction of the complex cis-[Mo(CO) 4 (bipy)] (1) with excess tert-butylhydroperoxide (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 0 -di-tert-butyl-2,2 0 -bipyridine) leads to the isolation of the polynuclear complex [Mo 8 O 24 (di-t-Bubipy) 4 ] (4). The structure of 4, as the CH 2 Cl 2 solvate, was determined by X-ray crystallography. The unit cell contains two crystallographically independent octameric windmill-type complexes, formulated as [Mo 8 O 24 (di-t-Bu-bipy) 4 ], both of which contain a central cubane-type Mo 4 (μ 3 -O) 4 core. Four peripheral [MoO 2 (di-t-Bu-bipy)] 2þ units cap the long edges of the Mo 4 tetrahedron of the central cubane. The close packing of these complexes via weak offset π-π 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 as 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 °C to 75 °C. The excellent stability of these Mo VI catalytic systems was confirmed by carrying out six consecutive reaction runs at 75 °C under microwave-assisted heating. The stable parent carbonyls (1 and 2) can be used as catalyst precursors since they are transformed into 3 and 4 under the operating catalytic conditions.

N-Heterocyclic Carbene-Based Molybdenum and Tungsten Complexes as Efficient Epoxidation Catalysts with H2O2 and tert-Butyl Hydroperoxide

“…For each complex, the reaction is faster in the second run compared with the first one indicating that the first step of the catalytic reaction involves the oxidative decarbonylation of complexes 1-4 with formation of oxo-peroxo species that are the active species in the epoxidation reaction. A similar effect has been observed in the epoxidation of cis-cyclooctene with TBHP using [Mo(CO) 4 L n ] complexes as catalysts [29]. The kinetic curves for the two runs are practically coincident for complexes 1-4, giving quantitative conversions at The catalytic reactions were also studied in ethanol since according with some literature reports, ethanol is a suitable solvent for H 2 O 2 affording in some cases better results compared to acetonitrile [27].…”

“…However, to the best of our knowledge, the catalytic performance of Mo(II) and W(II) carbonyl compounds in olefin epoxidation using H 2 O 2 has never been reported. Recently, tetracarbonyl complexes of the type [Mo(CO) 4 (L)] (L = bipyridyl) showed to exhibit good activity for epoxidation with TBHP, but they were inactive with H 2 O 2 (only a 6% conversion of cis-cyclooctene was obtained when aqueous H 2 O 2 was used as oxidant) [29]. In the present work, we demonstrate that molybdenum and tungsten g 3 -allyl dicarbonyl complexes of general formula [M(g 3 -allyl)Cl (CO) 2 [30,31].…”

Oxidation of [CpMo(CO)3R] olefin epoxidation precatalysts with tert-butylhydroperoxide

“…[38]). Formation of a precipitate during catalytic epoxidation of alkenes with similar Mo-based complexes has also been reported, but the nature of the precipitate has remained elusive [10,28,[44][45][46][47].…”

“…The technique of in situ precatalyst oxidation using TBHP and H 2 O 2 has also been used to obtain oxo complexes of several organo-molybdenum and -tungsten dicarbonyl and tetracarbonyl compounds for their application in olefin epoxidation [26][27][28][29]. Thus, it is necessary to evaluate the efficiency and selectivity of this oxidation process.…”

Cyclopentadienyl molybdenum dicarbonyl η3-allyl complexes as catalyst precursors for olefin epoxidation. Crystal structures of Cp′Mo(CO)2(η3-C3H5) (Cp′ = η5-C5H4Me, η5-C5Me5)

“…11.4169 (7) 13.4922(9) c ( A) 11.1609 (6) 11.4888 (7) b ( ) 103.381 (2) e Volume ( A 3 ) 1024.55 (10) 1477.16 (17) …”