Chromium-catalyzed ethylene

Bhaduri S, Mukhopadhyay S, Kulkarni SA Density functional studies on chromium catalyzed ethylene trimerization, / Organomet Chem 694(9—10) 1297—1307, 2009. 

W. Janse van Rensbnrg, C. Grove, J. P. Steynberg, K. B. Stark, J. J. Huyser and P. J. Steynberg. A DFT study toward the mechanism of chromium-catalyzed ethylene trimerization. Organomet allies 23, 2004, 1207—1222. 

It is incorrect to regard only one particular valence state of chromium as the only one capable of catalyzing ethylene polymerization. Active catalysts have been made from organochromium compounds with every valence from Cr(I) to Cr(IV). On the commercial Cr(VI)/silica catalyst the predominant active valence after reduction by ethylene is probably Cr(II), but other states, particularly Cr(III), may also polymerize ethylene under certain conditions. 

Organic sources of Cr(VI) have also been investigated as the chromium source. Baker and Carrick [148] first investigated bis(triphenylsilyl) chromate as a homogeneous model for the surface chromate structures postulated to exist on the Phillips catalyst. This chromate ester is quite stable, but like Cr(VI) /silica, it can also be reduced by olefins under polymerization conditions to give the corresponding aldehyde and Cr(II) or Cr(III). Thus, it mimics the behavior of Cr(VI)/silica in many respects [149]. Bis(triphenylsilyl) chromate does catalyze ethylene polymerization,... 

Emrich R, Heinemann O, Jolly PW et al (1997) The role of metallacycles in the chromium-catalyzed trimerization of ethylene. Organometallics 16 1511-1513... 

The selective, chromium catalyzed trimerization of ethylene to 1-hexene was disclosed in a patent by SASOL [247]. In this work a biphasic reaction system was explored using alkylchloroaluminate ionic liquids as the catalyst phase. 

Kuhhnann, S., Paetz, C., Haegeli, C. et al. (2009) Chromium catalyzed tetramerization of ethylene in a continuous tube reactor - proof of concept and kinetic aspects. Journal of Catalysis, 262, 83-91. 

Garcia RA, Carrero A, Aroca M, Prieto O, Dominguez C Slow crack growth resistance in resin blends of chromium and metallocene catalyzed ethylene-hexene copolymers for pipe appHcations, Polym Eng Sci 48(5) 925—933, 2008. 

Klemps C, Payet E, Magna L, et al PCNCP ligands in the chromium-catalyzed oligomerization of ethylene tri- versus tetrametization, Chem EurJ 15(33) 8259-8268, 2009. 

Katz and Sivavec, who used a Fischer tungsten carbene complex as a catalyst. After the report of a chromium-catalyzed reaction by Mori et al., they disclosed the utility of ruthenium-carbene complexes for the enyne metathesis (Scheme 24.44). The Ru-carbene-catalyzed reaction under the ethylene atmosphere brought about good results in the case of terminal alkyne substrates such as 164b. ... 

There are many ways to produce acetaldehyde. Historically, it was produced either hy the silver-catalyzed oxidation or hy the chromium activated copper-catalyzed dehydrogenation of ethanol. Currently, acetaldehyde is obtained from ethylene hy using a homogeneous catalyst (Wacker catalyst). The catalyst allows the reaction to occur at much lower temperatures (typically 130°) than those used for the oxidation or the dehydrogenation of ethanol (approximately 500°C for the oxidation and 250°C for the dehydrogenation). 

We have previously described a class of cationic chromium(III) alkyls of the type [Cp Cr(L)2R] X% which catalyze the polymerization of ethylene at ambient temperature and pressure.[3] The most efficient of these catalysts was the complex shown below. 

A further dramatic comparison of the comparative reactivities of chromium alkyls in diverse oxidation states was furnished by another set of benzyl complexes. [7] Shown below, these three compound are isomers, yet they range in oxidation state from Cr to Cr °. Of the three, only the mixed-valent complex Cp G0i-ti n3-Bz)Cr(Bz)Cp, containing a Bivalent chromium bound to an T)3-benzyl and a ni-benzyl ligand, catalyzed the polymerization of ethylene. 

Constrained geometry chromium alkyls catalyzed the polymerization of ethylene however, the reaction was relatively slow, and elevated pressures (PC2H4 = 500 psi) were required to generate significant amounts of polymer. Not surprisingly then, no homopolymoization or copolymerization of a-olefins was observed. Instead, catalytic isomerization and dimerization of the alkyl-substituted olefins was found. 

Although polymerization plays an important role in today s organometallic catalysis, almost no reports exist about the application of NHCs in this reaction. Ethylene polymerization catalyzed by a chromium-NHC complex was reported but the efficiency of this catalyst is only moderate. After activation with MAO the... 

Cr/silica does not catalyze the polymerization of ethylene until it has been calcined between about 300 and 1000°C. While heat is necessary to cause the esterification of Cr03 to the silica surface, this is probably not the only purpose of the high temperature calcining step. Figure 8 shows how the activity develops as the calcining temperature increases. A respectable activity does not appear until about 500°C, whereas the esterification of Cr(VI) is complete at 300°C (76). Furthermore, other sources of chromium behave similarly in activity even though the particular mechanism and... 

The reaction is catalyzed by all but the weakest acids. In the dehydration of ethanol over heterogeneous catalysts, such as alumina (342—346), ether is the main product below 260°C at higher temperatures both ether and ethylene are produced. Other catalysts used include silica—alumina (347,348), copper sulfate, tin chloride, manganous chloride, aluminum chloride, chrome alum, and chromium sulfate (349,350). 

Chromocene (CrCp2) supported on silica is used to generate certain chromium-based catalysts for the polymerization of ethylene (e.g., Phillips and Union Carbide catalysts). The nature of the organometallic species responsible for the catalysis is not known with certainty, though it is noteworthy that some Crm alkyls such as [Cp Cr(CH2Ph)(THF)2]+BPh catalyze the polymerization of ethylene.19... 

Trimerization of Ethylene into 1-Hexene Catalyzed by Chromium Complexes... 

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