Olefins, epoxidation polymerization

Other examples involve the immobilization of ruthenium porphyrin catalysts [74]. While Severin et al. generated insoluble polymer-embedded catalysts 16 by co-polymerizing porphyrin derivatives with ethylene glycol dimethacrylate (EGD-MA) [74 a], Che et al. linked the ruthenium-porphyrin unit to soluble polyethylene glycol (PEG) 17 [74b]. Both immobilized catalysts were employed in a variety of olefin epoxidations with 2,6-dichloropyridine N-oxide (Gl2pyNO), providing similar conversions of up to 99% and high selectivities (Scheme 4.9). 

A major part of the work described in this section has been carried out with the aim of applying these silsesquioxane complexes of Ti, Zr and Hf in catalytic processes such as ethylene polymerization, olefin epoxidation and Oppenauer oxidation. These catalytic aspects have been highlighted in several recent review articles. 

Dinuclear Mn(IV) catalysts were successfully applied for the epoxidation of 4-benzoic acid and styrene in aqueous systems [18], for the epoxidation of styrene and dodecene in two-phase systems [19g] as weU as in methanol and acetone [17d, 19b,g,h], and for the epoxidation of olefins in acetonitrile [19i], aqueous acetonitrile [17f, 19c], acetone [17d, 19b,h], methanol [19i], and acetone-methanol-water mixtures [19j]. Enantioselective epoxidations of olefins have been reported for chiral triazacyclononane derivatives boimd to Mn(OAc2) 4 (H2O) in methanol [19k], Heterogenization of the Mn catalysts on silica for the epoxidation of styrene and cyclohexene, on zeolites for olefin epoxidation, and on a solid MnS04 H2O also for olefin epoxidation [20] has also been described. A polymeric structure bearing a dense arrangement of 1,4,7-triazacyclononane moieties can be synthesized by... 

In the same groundbreaking paper [21], CriveUo and coworkers also demonstrated that the anion plays no role in determining the photosensitivity of the iodonium salt and the photolysis rates of diaryliodonium salts having the same cations but different non-nucleophilic counterions (BF4, PFs, AsFs", or SbFe ) are identical. Likewise, the cation structure has little effect on the photodecomposition of diaryliodonium salts. The utility of iodonium salts as photoinitiators has been demonstrated in several cationic polymerizations using olefins, epoxides, cycUe ethers, lactones and cyclic sulfides as the monomers [21],... 

The polymerization of the higher olefin oxides proceeds by reactions essentially the same as those that will be discussed for propylene oxide and butylene oxide. Many of these have been described by Vandenberg (21). Health characteristics and animal and human responses can vary markedly from one olefin epoxide to another... 

Tetrafluoroethylene undergoes addition reactions typical of an olefin. It bums in air to form carbon tetrafluoride, carbonyl fluoride, and carbon dioxide (24). Under controlled conditions, oxygenation produces an epoxide (25) or an explosive polymeric peroxide (24). Trifluorovinyl ethers,... 

New interesting applications have been in the epoxidation of difficult olefin compounds (including hexafluoropropene) with NaOCl, side-chain chlorination of substituted toluenes, diazotization of pentafluoroaniline, polymerization with free radicals, etc. 

Spectacular achievements in catalytic asymmetric epoxidation of olefins using chiral Mnm-salen complexes have stimulated a great deal of interest in designing polymeric analogs of these complexes and in their use as recyclable chiral catalysts. Techniques of copolymerization of appropriate functional monomers have been utilized to prepare these polymers, and both organic and inorganic polymers have been used as the carriers to immobilize these metal complexes.103... 

Zinc compounds have recently been used as pre-catalysts for the polymerization of lactides and the co-polymerization of epoxides and carbon dioxide (see Sections 2.06.8-2.06.12). The active catalysts in these reactions are not organozinc compounds, but their protonolyzed products. A few well-defined organozinc compounds, however, have been used as co-catalysts and chain-transfer reagents in the transition metal-catalyzed polymerization of olefins. 

Peroxidases have been used very frequently during the last ten years as biocatalysts in asymmetric synthesis. The transformation of a broad spectrum of substrates by these enzymes leads to valuable compounds for the asymmetric synthesis of natural products and biologically active molecules. Peroxidases catalyze regioselective hydroxylation of phenols and halogenation of olefins. Furthermore, they catalyze the epoxidation of olefins and the sulfoxidation of alkyl aryl sulfides in high enantioselectivities, as well as the asymmetric reduction of racemic hydroperoxides. The less selective oxidative coupHng of various phenols and aromatic amines by peroxidases provides a convenient access to dimeric, oligomeric and polymeric products for industrial applications. 

Iodosylbenzene is sufficiendy reactive on its own to epoxidize electron-deficient olefins such as tetracyanoethylene (43). It is possible that coordinated monomeric iodosylbenzene is substantially more reactive than polymeric iodosylbenzene and that complexation of a monomeric form is sufficient to provide the requisite reactivity with normal olefins. 

The most relevant catalytic reactions approached by SOMC are olefin polymerization (and depolymerization), alkane activation (including a new reaction, discovered thanks to SOMC-alkane metathesis), alkene metathesis and epoxidation. All these reactions are discussed in this chapter. 

Since group 4 derived species are of particular interest as catalysts for olefin polymerization and epoxidation reactions, the thermal stability of surface metal-alkyl species, as weU as their reactivity towards water, alcohols and water, deserve some attention. On the other hand, mono(siloxy) metaUiydrocarbyl species can be converted into bis- or tris(siloxy)metal hydrides by reaction with hydrogen [16, 41, 46-48]. Such species are less susceptible to leaching and can be used as pre-catalysts for the hydrogenolysis of C-C bonds, alkane metathesis and, eventually, for epoxidation and other reactions. 

Epoxidation of olefins over Mo containing Y zeolites was studied by Lunsford et al. [86-90]. Molybdenum introduced in ultrastable Y zeolite through reaction with Mo(C0)g or M0CI5, shows a high initial activity for epoxidation of propylene with t-butyl hydroperoxide as oxidant and 1,2-dichloroethane as solvent [88]. The reaction is proposed to proceed via the formation of a Mo +-t-butyl hydroperoxide complex and subsequent oxygen transfer from the complex to propylene. The catalyst suffers however from fast deactivation caused by intrazeolitic polymerization of propylene oxide and resulting blocking of the active sites. 

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