Ethylene trimerization

The activity of CMe2-bridged Zr(II) and Hf(II) boratabenzene cationic complexes toward ethylene trimerization has been explored computationally using a gradient-corrected DFT approach the Zr species was calculated to be a highly efficient catalyst, exceeding the efficiency of the corresponding Cp system.108... 

Alvarez-Idaboy, Eriksson and LuneU have also studied the hole-catalyzed ethylene trimerization [52]. They find a stable complex between the 1-butene radical cation and ethylene that can rearrange with an activation energy of 9.2 kcal mol to the 1-hexene radical cation. In this case, there is apparently no 1-ethyl-tetramethylene radical cation intermediate. Once again, the results of the calculations are in accord with experimental findings. 

Aromatic primary amines are not only binucleophiles at the amino group, but they also exhibit the properties of C,N-binucleophiles. Their reactions with internal perfluoroolefins lead to quinoline derivatives (98JFC(88)169, 94JCS(CC)134, 98T4949). Thus the reaction of aniline with 2//-heptafluorobut-2-ene yields phenyl(2-trifluoromethylquinolin-4-yl) amine (00ZOR109) when the reaction is carried out with the tetrafluoro-ethylene trimer, it leads to 2-trifluoromethyl-3-(l-N-phenylimino-2,2,2-trifluoroethyl)-4-(N-phenylamino)quinoline (98JFC(88)169). 

Figure 16 Schematic representation of a possible path for ethylene trimerization involving 5- and 7-membered chromacycles.

The complexes (C5H4CMe2R)TiCl3 (R = Ph, 1,3-dimethylphenyl, Me), in the presence of MAO, are effective catalysts for the polymerization of ethylene and they are transformed in catalysts for the ethylene trimerization, producing 1-hexene, depending on the substituent R nature. The hemilabile behavior of the pendant Gp substituent seems to be the responsible for this catalytic performance.331 A mono-Gp trichloro complex containing a phenyl-ethyl-Cp ligand has also been prepared (Scheme 160 Section 4.05.3.1.1 (iii)).332... 

The activity of some mono-Cp and Cp-amido methyl Ti derivatives in a-olefin polymerization process has been studied and the effects of the co-catalyst based on perfluoroborate compounds evaluated.563 A detailed theoretical study of the ethylene trimerization at the cationic general features of previous proposals although they differ in other mechanistic details.561 A DFT study on ethylene trimerization catalyzed by (C5H4CMe2C6H5)TiCl3/MAO to selectively give 1-hexene has been performed.559,562... 

SCHEME 43 Selective ethylene trimerization on some Cr sites through a metallocycle intermediate. 

Linear alpha olefins (LAOs) are useful intermediates for a range of important commodity chemicals (including surfactants, lubricants, plasticizers, etc.). They are produced via ethylene oligomerisation, using transition metal catalysts. A major problem associated with these catalysts is the formation of a broad chain length distribution of ot-olefins. One approach to solving this problem, operating via a uniquely different mechanism, is ethylene trimerization and tetramerization to... 

Manyik RM, Walker WE, Wilson TP (1997) Soluble chromium based catalysts for ethylene trimerization and polymerization. J Catal 47 197-209... 

Skobelev lY, Panchenko VN, Lyakin OY et al (2010) In situ EPR monitoring of chromium species formed during Cr-pyrrolyl ethylene trimerization catalyst formation. Organometallics 29 2943-2950... 

The transformation from ethylene polymerization to ethylene nonselective oligomerization over the two model catalysts (3f and 9f) in the presence of Al-alkyl cocatalyst MAO with the increase in Al/Cr molar ratio is shown in Scheme 14. Such interesting transformation phenomenon could not be found using the same catalysts combined with TiBA. Similar polymerization/oligomerization transformation behavior has also been reported recently on Cr-based ethylene trimerization... 

McGuiness, D., Rucklidge, A., Tooze, R. and Slawin, A. (2007) Cocatalyst influence in selective oligomerization effect on activity, catalyst stability, and 1-hexene/1-octene selectivity in the ethylene trimerization and tetramerization reaction. Organometallics, 26, 2561-2569. 

Researchers at Sasol described chromium catalysts containing amido bisphosphine PNP or amido bis-thioether SNS pincer ligands for ethylene trimerization. ... 

Figure 6.16.6 Generally accepted metallacycle mechanism for the selective ethylene trimerization as first proposed by Briggs (Briggs, 1989).

Manyik, R.M., Walker, W.E., and Wilson, T.P. (1977) Soluble chromium-based catalyst for ethylene trimerization and polymerization. J. Catal, 47, 197-209. 

Figure 3.40 Preparation of ethylene trimerization catalysts. Reprinted from [45] with permission from the Royal Society of Chemistry.

Scheme 35 Synthesis and solid-state molecular structure of complex 91 and its proposed selfactivation pathway (A, B) for ethylene trimerization...

The proposal that catalyst activation is likely to go through a Cr(lll) to Cr(ll) reduction was also ruled out by studies on pyridine-centered SNpyS Cr systems (Scheme 34) [163]. For these systems, a loss of selectivity (in ethylene trimerization) was observed when going from Cr(III) to Cr(ll) analogues (Scheme 34, insert). Complex 88, resulting from the activation of the Cr species 87 by MAO, was stmcturaUy characterized, confirming the presence of a cationic Cr(II) center. 

Pyrrolyl-Based Chromium/Organoaluminum Catalysts New Insight into the Phillips Ethylene Trimerization Catalysf ... 

The Phillips catalyst, based on a Cr/2,5-dimethylpyrrole precursor and TEA as a cocatalyst, is the only commercial catalytic system for ethylene trimerization [164] and has thus been extensively studied [139, 140]. Based on DFT calculations, a redox mechanism involving a Cr(ll)/Cr(lV) couple has been proposed [154, 165]. Also, the pyrrole derivative ligand, able to interact with one or two metal centers through the nitrogen lone pair and/or the aromatic Jt-system, may play a key role for the stabilization of heterodinuclear Cr/Al species formed after activation. 

The first example of diphosphinoamine [PN(R)PR] ligands-hased Cr systems for the selective ethylene trimerization was reported in 2002 by researchers at BP. Such catalysts combine ligands of type 96, a Cr source and MAO as a cocatalyst (Fig. 11) [168]. These systems were found to be highly active (TOE > 1.8 x 10 h 20 bar) and selective toward 1-hexene formation (80-90%). Activities and selectivities of the [PN(R)P] Cr systems along with mechanistic studies have been comprehensively reviewed [152, 153, 169]. 

Scheme 3.10 Metallacydic mechanisms for selective ethylene trimerization to 1-hexene proposed by Manyik et al. (1977) (path (a)), Briggs (1989) (path (b)), and Hessen (Deckers et al., 2001, 2002) (path (c)).

Manyik et al. first patented Cr(2-EH)3/PIBAO system as ethylene polymerization catalyst with low ethylene trimerization reactivity (Manyik, 1967). Later on, the research from the same group showed that the activity and selectivity could be improved by adding DME to the Cr(2-EH)3/ PIBAO system (Manyik et al., 1977). In 1989, Briggs reported that the activity could be drastically increased to 2086 g/gCr per hour with much improved selectivity of 73% for ethylene trimerization catalyzed by... 

---