Olefins selectivity control

Carboxylation/Oxidation of Straight-Chain 1-Olefins. Selective carboxylation of a-olefins to predominately straight-chain aldehydes is realized through specific catalyst systems and by careful control of reaction conditions. The aldehyde produced is then air-oxidized to the acid using a Mn catalyst. Heptanoic acid [111-14-8] and pelargonic acid [112-05-0] are produced commercially in this manner. 

The complex Ni[(S2C2(CF3)2)]2 (392) is able to bind light olefins selectively and reversibly.1081 According to Scheme 4, the reaction of olefins with (392) can be controlled electrochemically, where the oxidation state-dependent binding and release of olefins is fast on the electrochemical timescale. Olefin binding is supposed to occur via the ligand S-donors. 

Selectivity Control in Nickel-Catalyzed Olefin Oligomerization... 

A convincing example of selectivity control in isomerization reactions is the formation of cis-2-butene from the isomerization of 1-butene using the catalyst [(C6H5)3P]2NiX2-P(CeH5)3-Zn-SnCl2 a ratio of c/i-2-bu-tene /ra .s-2-butene as high as 98 2 has been observed. Isomerization to the thermodynamically more stable /ra ns-olefin occurs only after conversion of all the 1-butene (98). Further examples of selective olefin isomerization will be discussed in Section IV,D. 

E)-olefin selectivity under kinetic control, J. Org. Chem. 52 (1987) 4637-4639. 

This rearrangement can be also performed with acyclic tetrasubstituted olefins, enabling control of two adjacent carbon centers. Thus, hydroboration of Z- and E-2,3-dimethylstilbene (43) with BH3.THF and subsequent heating at 70 °C for 12 h furnishes stereo selectively the syn and anti organoboranes 44, which after oxidative workup provide the corresponding alcohols syn-45 and anti-45 in 90 % yield and dr > 99.5 % (Scheme 7) [7-9]. 

For countries with higlier coal prices, the synthesis of valuable chemical products from coal seems economically more attractive than the production of liquid fuels. Thus, the Fischei-Tropsch reaction b reinvestigated for selectivity control towards chemical feedstocks such as olefins, alcohols, or poly methylene P-I4. ... 

Taylor reported kinetically controlled cross metathesis of homoallylic alcohols and allyl trimethyl silane with (4a) gave products with high E-olefin selectivity and good yields via a five-membered chelate intermediate (equation 20). ... 

Recent Developments in Theoretical Organometallic Chemistry, 15, 1 Redistribution Equilibria of Organometallic Compounds, 6, 171 Redistribution Reactions of Transition Metal Organometallic Complexes, 23, 9S Redistribution Reactions on Silicon Catalyzed by Transition Metal Complexes, 19, 213 Remarkable Features of (t) -Conjugated Diene) zirconocene and -hafnocene Complexes, 24, 1 Selectivity Control in Nickel-Catalyzed Olefin Oligomerization, 17, lOS Silyl, Germyl, and Stannyl Derivatives of Azenes, N H Part I. Derivatives of Diazene, N3H2, 23, 131... 

Selectivity control is again of primary importance in the production of petrochemicals, for example the propylene dimer 4-methyl-1-pentene is a monomer for the production of the speciality polymer poly(4-methyl-l-pentene) and linear a-olefins are required for the production of biodegradable detergents and synthetic lubricants. 

More than one of the three possible oop bond angle deformations are usually apparent in the distorted olefins. Nevertheless, it is possible to detect in most cases the dominant type of distortion. The kinetic stability of olefins with distorted double bonds is enhanced by steric shielding. Hence, distorted double bonds in bicyclic and polycyclic structures may not display the reactivity to be expected if the dominant type of the oop distortion is the selectivity-controlling factor. The strong preference of syn- over anti-addition in Bredt-olefins may be due to this steric shielding. 

Example 5. The non symmetrical coupling of an aiyl iodide bearing an o-electron-donating gronp, an aiyl bromide containing an electron-withdrawing substituent, and a terminal olefin illustrates the inportance of correctly tuning the electronic properties of the two aryl hahdes for selectivity control. ... 

A series of arylations of olefins by C-H bond cleavage without direction by an ortho functional group has also been reported, and these reactions can be divided into two sets. In one case, the C-H bond of an arene adds across an olefin to form an alkylarene product. This reaction has been called hydroarylation. In a second case, oxidative coupling of an arene with an olefin has been reported. This reaction forms an aryl-substituted olefin as product, and has been called an oxidative arylation of olefins. The first reaction forms the same t)q)es of products that are formed from Friedel-Crafts reactions, but with selectivity controlled by the irietal catalyst. For example, the metal-catalyzed process can form products enriched in the isomer resulting from anti-Markovnikov addition, or it could form the products from Markovnikov addition with control of absolute stereochemistry. Examples of hydroarylation and oxidative arylation of olefins are shown in Equations 18.63 - and 18.64. ... 

Cross Metathesis. Of the three major types of olefin metathesis, cross metathesis (CM) has been the most challenging to selectively control. CM is an intermolecular reaction between two olefins that releases ethylene gas, among a statistical mixture of combinatorial products it is a thermodynamically controlled reaction, where impurities arising from homodimerization are common. In addition, unlike ROMP, which relieves ring strain, and RCM, which forms stable 5- and 6-membered rings, CM has no enthalpic driving force (71). 

Both Lewis and Brdnsted acidity are involved in the dehydration reactions over acid catalysts, and selectivity control to limit the dehydration of DME to olefins and aromatics requires that the surface acidity not be too hi and the reaction temperature be below 300°C [65]. The olefins are generally thou t to be produced by a consecutive reaction in which methanol is first converted to DME, which in turn is converted to olefins and aromatics. Reaction mechanisms for DME formation have been proposed by various investi tors. According to Kubelkova et aL [78], the mechanism over Si-Al zeolites involves protonation of the hydroxyl group of methanol on a Bronsted acid site to form a skeletal methoxyL This methoxyl group reacts with a -phase methanol molecule to form DME at 180300°C and C2C5 aliphatics and aromatics above 300°C. According to these authors, Lewis acid sites (Al -OH), associated with nonskeletal alumina, can also form methoxyls according to the reaction... 

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