Tungsten hexachloride catalyst

Ethylaluminum dichloride Ethylaluminum sesquichloride Tetrabutyl titanate Tetraisopropyl titanate Triethylborane Trimethylaluminum catalyst, olefin polymers Tungsten hexachloride catalyst, olefin/diene polymerizationscatalyst olefin polymerizations Tri-n-hexylaluminum catalyst, olefinic addition Methanesulfonic acid catalyst, one-component RTV s Dibutyltin diisooctylmaleate catalyst, organic compounds chlorination Manganese chloride (ous), tetrahydrate catalyst, organic reactions Beryllium oxide Chromium oxide (ic) Copper bromide (ous) Copper phosphate (ic) Ferric chloride... 

ADMET polymerization is based on step condensation chemistry where high molecular weight polymers are generated via the formation and removal, in vacuo, of a small molecule (Figure 2). The key to successful ADMET chemistry is dependent on the removal of acids from the catalyst system. This can be illustrated in Figure 3, where the adverse effect of acids is manifested in the attempted polymerization of 1,9-decadiene. In this example, the well known tungsten hexachloride catalyst system... 

In die last 10 years or so an exciting new strategy has emerged for the formation of carbon-carbon double bonds, namely olefin metathesis. This work grew out of the development of Ziegler-Natta catalysts for die polymerizarion of cyclic olefins. It was found that when 2-pentene was treated with a catalyst prepared from tungsten hexachloride and ethylaluminum dichloride, a mixture of 2-pentene, 2-butene, and 3-hexene was produced in minutes at room temperature (rt) ... 

In 1967, Calderon, Chen, and Scott4) reported a homogeneous catalyst system comprised of tungsten hexachloride, ethanol, and ethylaluminum dichloride would disproportionate internal olefins. These authors used the term olefin metathesis to describe the reaction. At room temperature 2-pentene was transformed in one to three minutes into a mixture containing, at equilibrium, 25, 50, and 25 mole per cent of 2-butene, 2-pentene, and 3-hexene, respectively. Double-bond isomerization was not detected and a quantitative reaction selectivity was obtained. Additional reports by Calderon and cowor-... 

Dall Asta, of Moiitccaiini Edison, investigated the metathesis of cycloalkenes in the presence of a catalyst consisting of tungsten hexachloride, aluminium trichloride and carbon dioxide as the catalyst promoter. The products, the polyalkenamcrs, were vulcanized to give an elastic rubber useful for lires (304,... 

We found in 1974 that phenylacetylene polymerizes with tungsten hexachloride (WC16) and molybdenum pentachloride (MoC15) 6). Since then, we have exploited new effective catalysts, and polymerized various substituted acetylenes. An account of the polymerization by Mo and W catalysts has been reported7). 

Metal Chloride Complexes. Optimum conditions for employing lithium aluminium halide as co-catalyst with tungsten hexachloride have been esta-... 

Tungsten hexachloride reacts with dry silica gel to form a surface complex with average composition ( i02)WCl4. Van Roosmalen and associates reported that with tetramethyltin the complex yields a solid catalyst for the metathesis of alkenes with the same activity as the WOQ4-SnMe4 system, but is less active for the metathesis of methyl oleate. The supported complex can be used several times without additional SnMe4. ... 

SYNTHESIS Ring-opening polymerization of cyclopentene. Trflns-jxrlypentenamer is produced by Ziegler-Natta polymerization employing a catalyst based on aluminum triethyl/tungsten hexachloride compound. Aluminum diethylchloride/ molybdenum pentachloride compounds may be employed to produce the as isomer. Both macrocycles and linear chains are produced during polymerization. 

Tungsten hexachloride can apparently also act as a catalyst without the aluminum alkyl. In that case it is believed to be activated by oxygen. The propagation reaction based on the tungsten caibene mechanism can be shown as follows ... 

Some cycloolefins can undergo either a regular cationic polymerization or a metathesis one, depending upon the catalyst. One of them is norbomene and its derivatives. For instance, 5-methylene-2-norbomene polymerizes by a cationic mechanism with a 1 1 combination of tungsten hexachloride with tetraalkyltin. A 1 4 combination of a tungsten halide with either C2H5AICI2, or... 

The catalyst may be homogeneous or heterogeneous. The former usually consists of a transition metal compound such as tungsten hexachloride with a Lewis acid or organometallic compound such as ethylaluminium chloride, tetramethyl or tetrabutyltin, or triethylboron. Heterogeneous catalysts are usually oxides or carbonyls of molybdenum or tungsten on alumina or silica. 

The term of alkene (olefin) metathesis was introduced by Calderon and coworkers in 1967 [13] to describe a reaction in which 2-pentene is converted to 2-butene and 3-hexene in the presence of tungsten hexachloride, ethanol, and ethyl aluminum dichloride (Scheme 6.1). Nowadays, this term covers all reactions associated with the exchange of carbene (alkylidene) groups between alkenes, and the reaction has become a key process in polymer chemistry, as well as in fine and basic chemical synthesis, including petrochemistry [14, 15]. Alkene metathesis only takes place in the presence of an appropriate catalyst, and considerable research efforts have been devoted to design more active, selective, and stable catalysts [16-24]. In this field, computational chemistry has contributed considerably by bringing information that could not be derived from experimental studies. 

Kamphaus, J.M. (2007) Evaula-tion of tungsten hexachloride as a ROMP active catalyst precursor for self-healing polymers. Doctoral dissertation. Department of Aerospace Engineering, University of Illinois Urbana-Champaign. 

Wideman [137] has reported a catalyst based on tungsten. The active catalyst is prepared by heating tungsten hexachloride and 2,6-dimethylaniline in a minimum amount of chlorobenzene and subsequently treating with diethylaluminum chloride. A conversion of 176,000 mol of ethylene/mol of tungsten is achieved in 1 h at 40°C and 27 atm of ethylene pressure. The yield of 1-butene is 92% in the process. An increase in pressure from 27 to 34 atm resulted in the conversion of 184,000 mol of ethylene/mol of tungsten, thereby achieving a better yield of 1-butene (98%) at a faster rate. 

Tropilidene, MA Diels-Alder adduct, 117 Tropolones, MA Diels-Alder adduct, 117 Tropone, MA Diels-Alder adduct, 118 Trypsin, MA copolymer coupled, 448, 451 Tungsten hexachloride, 289 Tungsten oxide, promoter for MA catalyst, 36 Tungstic acid, epoxidation catalyst, 69... 

It must also be noticed that generally tungsten hexachloride derived catalysts are reactive towards / -olefins, whereas molybdenum salts are most widely used with a-olefins. In each case however, the main observation to be made (as with heterogeneous catalysts) is that it is necessary to have a cocatalyst besides the transition metal salt. This fact must be taken in account where mechanistic studies are undertaken on the generation of the active species for these reactions. 

By the mid-1980s considerable advancements had been made in the field of olefin metathesis chemistry (Grubbs, 2004). This mild carbon-bond-forming reaction was discovered by accident in the late 1960s when researchers at Goodyear exposed a mixture of a-olefins to a combination of tungsten hexachloride and a Lewis acid with the intent to find a new catalyst for the polymerization of vinyl olefins (Calderon et a/., 1968 Calderon et al, 1967). Instead of high polymer the research team observed a complex mixture of scrambled olefin products. The mechanism of this reaction, first proposed by Yves Chauvin (Herrison and Chauvin, 1971) in... 

Since the middle seventies soluble polyacetylenes with not too small molecular weight were obtained. Using for the first time tungsten hexachloride (WClg) and molybdenum pentachloride (Mods) catalysts, Masuda et al (5) were able to polymerize phenylacetylene, hereafter noted PPA, with a molecular weight larger than 1()4. 

Winterfeldt and co-workers discovered that ergosterol acetate 35 can be used to prepare macrocycle 37 by Diels-Alder/retro-Diels-Alder reactions. Cycloaddition of ergosterol acetate 35 to propargylic aldehyde in the presence of tungsten hexachloride as a Lewis acid catalyst produced a.jS-unsaturated aldehyde 36. When it was heated in toluene, the macrocyclic benzaldehyde 37 was obtained in 85% yield (Scheme 16.5). This skeletal... 

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