Molybdenum complexes olefin

The kinetics of the [Mo02(acac)2]-catalyzed epoxidation of cyclohexene by tert-hutyl hydroperoxide in cyclohexane have also been examined [385]. Reactions are nearly first order in catalyst but of nonintegral order in olefin with rates more nearly proportional to [olefin] at low concentrations than at high. A similar behavior was noted for hydroperoxide. This kinetic behavior was ascribed to the formation of molybdenum hydroperoxide and molybdenum olefin complexes. Kinetic evidence for the formation of a wide variety of metal-olefin and metal-hydroperoxide complexes has been reported during the molybdenum versatate-catalyzed epoxidation of cyclohexene with ethyl benzene hydroperoxide, and equilibrium constants for their formation were calculated [386]. 

Molybdenum allyl complexes react with surface OH groups to produce catalysts active for olefin metathesis.34 35 Using silica as a support for the heterog-enization of Ti and Zr complexes for the polymerization of ethylene did not give clear results.36 In these cases, HY zeolite appeared to be a more suitable support. The comparable productivity of the zeolite-supported catalyst with... 

The metal-catalysed olefin metathesis (equation 122) when applied to dienes results in ring-closure and expulsion of an olefin (equation 123). Thus the molybdenum carbene complex 241 promotes the decomposition of the 1,6-heptadiene derivative 242 to a mixture of the cyclopentene 243 and ethylene (equation 124)122. An analogous reaction of the alcohol 244 gives 245 (equation 125), and 4-benzyloxy-l,7-decadiene (246) affords the cyclohexene 247 and 1-butene (equation 126). These transformations, which occur in benzene at room temperature, proceed in excellent yields122. 

The ruthenium compounds described above show a distinctly lower metathetic activity than the molybdenum alkenylidene complex 24 developed by Schrock et al. (Fig. 4, see also the chapter by R.R. Schrock, this volume) [18], which is another standard catalyst for any type of olefin metathesis reaction. However, they... 

The reaction conditions applied for transfer dehydrogenation using complex 5a are compatible with the conditions required for olefin metathesis with Schrock s molybdenum alkyhdene complex 10 [21]. 

The molybdenum-hydroperoxide complex (Step 3) reacts with the olefin in the rate-determining step to give the epoxide, alcohol, and molybdenum catalyst. This mechanism explains the first-order kinetic dependence on olefin, hydroperoxide, and catalyst, the enhanced reaction rate with increasing substitution of electron-donating groups around the double bond, and the stereochemistry of the reaction. 

Since the discovery of ruthenium and molybdenum carbene complexes that efficiently catalyze olefin metathesis under mild reaction conditions and that are compatible with a broad range of functional groups, olefin metathesis has increasingly been used for the preparation of alkenes on insoluble supports. In particular, the ruthenium complexes Cl2(PCy3)2Ru=CHR, developed by Grubbs, show sufficient catalytic activity even in the presence of air and water [781] and are well suited for solid-phase synthesis. 

Diperoxo(oxo)molybdenum(IV) complex bearing (S)-lactic acid piperidineamide as a chiral ligand has been used for the epoxidation of E-2-butene (Scheme 6B.8) and moderate enantiose-lectivity (49%) is achieved wherein the reaction is stoichiometric [16]. Two possible mechanisms have been proposed for this reaction. One mechanism includes coordination of an olefin prior to epoxidation, which makes the olefin electrophilic and facilitates the nucleophilic attack of the proximal oxygen atom of the peroxide on the olefin. The other one is that an olefin nucleophilically attacks the peroxo group of the molybdenum complex. 

Hoveyda and Schrock attached (97a) to polymer via attached styrene groups yielding the first reported supported chiral molybdenum olefin metathesis catalyst, (290) (Scheme 27). Supported complex (290) is less active than (97a), but it gives similar ranges of ees for enantioselective transformations like desymmetrization. The catalyst is recyclable and, even though the conversions have eroded, the enantioselectivity is still relatively high. Table 14. 

Efficient catalysts for direct episulfidation of alkenes by sulfur-atom donors are also diethyldithiocarbamate and dithiophosphonate molybdenum oxo complexes 302 and 303, respectively (Equation 43 Scheme 88 Table 13) <2003JA3871>. The most efficient sulfur-atom donor in this reaction is 2-phenylthiirane. The best results were obtained, in most cases, when 1 equiv of 2-phenylthiirane was used as sulfur-atom donor in deuterated benzene at 80 °C for 30 min. Reaction of /ra r-cyclooctene catalyzed by either of the oxomolybdenum complexes gave trans-epithiocyclooctane. When this reaction was carried out in the presence of 302, the yield of the corresponding thiirane was only 20%, whereas catalyst 303 converted the olefin in almost quantitative yield (Table 14). 

Molybdenum -peroxo complexes give oxiranes in high yields. " For anhydrous hydrogen peroxide, a three-step mechanism is assumed, with an a-hydroxyhydroperoxide intermediate. Detailed studies have been made on the mechanism of the reaction of the MoO(02)2-HMPT complex with olefins (Eq. 27). 2 ... 

Heterobimetallic complexes of zirconium and molybdenum have also been prepared from zirconocene olefin complexes. Displacement of 1-butene from the phosphine-substituted zirconocene 1-butene complex, (775-C5H4PPh2)2Zr( 72-CH2=CHCH2CH3) 107, by addition of /< //-butyl isonitrile in the presence of Mo(CO)4(norbornadiene) furnishes the formal zirconium(n)-molybdenum(0) compound, 108 (Equation (4)).47... 

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