Molybdenum complexes alkene

Imido-nitrido complexes, with mono-Cp Ti(IV), 4, 425-426 Imido-supporting ligands, in molybdenum complexes alkenes, 5, 535 alkynes, 5, 548... 

We will focus on the development of ruthenium-based metathesis precatalysts with enhanced activity and applications to the metathesis of alkenes with nonstandard electronic properties. In the class of molybdenum complexes [7a,g,h] recent research was mainly directed to the development of homochi-ral precatalysts for enantioselective olefin metathesis. This aspect has recently been covered by Schrock and Hoveyda in a short review and will not be discussed here [8h]. In addition, several important special topics have recently been addressed by excellent reviews, e.g., the synthesis of medium-sized rings by RCM [8a], applications of olefin metathesis to carbohydrate chemistry [8b], cross metathesis [8c,d],enyne metathesis [8e,f], ring-rearrangement metathesis [8g], enantioselective metathesis [8h], and applications of metathesis in polymer chemistry (ADMET,ROMP) [8i,j]. Application of olefin metathesis to the total synthesis of complex natural products is covered in the contribution by Mulzer et al. in this volume. 

Secondary amines can be added to certain nonactivated alkenes if palladium(II) complexes are used as catalysts The complexation lowers the electron density of the double bond, facilitating nucleophilic attack. Markovnikov orientation is observed and the addition is anti An intramolecular addition to an alkyne unit in the presence of a palladium compound, generated a tetrahydropyridine, and a related addition to an allene is known.Amines add to allenes in the presence of a catalytic amount of CuBr " or palladium compounds.Molybdenum complexes have also been used in the addition of aniline to alkenes. Reduction of nitro compounds in the presence of rhodium catalysts, in the presence of alkenes, CO and H2, leads to an amine unit adding to the alkene moiety. An intramolecular addition of an amine unit to an alkene to form a pyrrolidine was reported using a lanthanide reagent. 

When alkenes are allowed to react with certain catalysts (mostly tungsten and molybdenum complexes), they are converted to other alkenes in a reaction in which the substituents on the alkenes formally interchange. This interconversion is called metathesis 126>. For some time its mechanism was believed to involve a cyclobutane intermediate (Eq. (16)). Although this has since been proven wrong and found that the catalytic metathesis rather proceeds via metal carbene complexes and metallo-cyclobutanes as discrete intermediates, reactions of olefins forming cyclobutanes,... 

Alkenes can be transformed into epoxides by hydroperoxides and a catalyst, which often is a high-valent titanium or molybdenum complex acting as a Lewis acid. The mechanism is not clear in great detail in Figure 2.34 a suggested mechanism is given. Coordination of the alkene to the metal prior to attack of the electrophilic oxygen is not considered as a necessary step. 

Molybdenum complexes A (Figure 3.46) react efficiently with terminal and internal alkenes in toluene (e.g. 500 eq. Z-2-pentene are metathesized in 2 min at 25 °C 20 eq. of styrene in 2 h at 25 °C). These catalysts also oligomerize 2,4-hexadiene [808] and 1,5-hexadiene [809] and promote RCM of enol ethers. Isomerization of alkenes by catalysts A is a potential catalytic side-reaction [810-812]. 

Transition metal complexes of unsaturated 1,2-dithiolates (metal dithiolenes) have attracted much attention because of their interesting structural and redox properties.169 Molybdenum dithiolene complexes have featured prominently170 in these studies and have special significance following the suggestion171,172 that the molybdenum-containing cofactor of the oxomolybdoen-zymes (Section 36.6.7) incorporates a molybdenum complex of an unsymmetrically substituted alkene-1,2-dithiolate. 

Molybdenum and tungsten compounds have long been known to catalyze the transformations of alkenes into epoxides and diols by hydrogen peroxide.171"173 This reaction was found to be suitable for the epoxidation of water-soluble alkenes such as allylic alcohols (equation 30)174,175 or unsaturated carboxylic acids (equation 31).171 Tungsten catalysts were found to be more active and selective in aqueous solution than molybdenum complexes. 

While some molybdenum complexes such as Mo03(dien) were found to be inactive,236 the rates of molybdenum-catalyzed epoxidation of alkenes were found to be independent of the structure of the complex used, after an induction period representing the time for exchange of anionic ligands by the alkyl hydroperoxide. cis-Dioxomolybdenum(VI) diolates such as (78) were isolated... 

The molybdenum complex 227 is an effective catalyst for epoxidation of alkenes and has allowed the development of the polystyrene-supported peptide-linked epoxidation catalyst 228351. 

A catalytic asymmetric oxidation of mono-, di-, and tri-substituted alkenes using a chiral bishydroxamic acid (BHA) complex of molybdenum catalyst in air at room temperature leads to good to excellent selectivity. It has been suggested that the Mo-BHA complex combines with the achiral oxidant to oxidize the alkene in a concerted fashion by transfer of oxygen from the metal peroxide to the alkene.78 The chiral BHA-molybdenum complex has been used for the catalytic asymmetric oxidation of sulfides and disulfides, utilizing 1 equiv. of alkyl peroxide, with yields up to 83% and ees up to 86%. An extension of the methodology combines the asymmetric oxidation with kinetic resolution providing excellent enantioselectivity (ee = 92-99%).79... 

The catalytic use of the mono-alkene molybdenum complex in converting H2C = CHSnR3 to H2C = CHCH2SnR3 has also been investigated.43 In this... 

The molybdenum complex [(CF3)2MeCO]2Mo(NAr)(=CHCMe2Ph) has been observed to be a more efficient catalyst for cyclization of vinyl silyl ether dienes than the ruthenium complex Cl2(PCy3)2Ru(=CHPh), probably because this type of alkene is sterically more demanding (than allyl derivatives) and therefore requires a catalyst less sensitive to steric bulkiness near the reaction center. However, some examples of the RCM of substituted vinylsilanes catalyzed by ruthenium complexes have been reported [127, 131] (Eq. 74). For more examples see Ref. [127]. 

The epoxidation of petrochemical alkenes is an intensely investigated oxidation reaction and in recent years numerous homogeneous catalysts have been developed for this reaction. However, so far the catalytic epoxidation of fatty compounds has been investigated only marginally. Sobczak and Ziolkowski reported on the epoxidation of oleic acid with organic hydroperoxides catalyzed by molybdenum complexes [37]. Typical homogeneous catalysts include Mo(CO)6 and Mo02(acac)2. 

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