| Abstract
| - The effect of different cocatalysts on the activity and selectivity of ethylene trimerization and tetramerization with a Cr−PNP catalyst has been studied, and the nature of the anion has been found to exert a dramatic influence on the relative C6/C8 selectivity as well as the catalyst stability.
- The trimerization and tetramerization of ethylene to 1-hexene and 1-octene with a Cr/PNP/AlEt3 catalystsystem, in combination with a variety of cocatalysts, has been investigated. The cocatalysts B(C6F5)3 (1),Al(OC6F5)3 (2), [(Et2O)2H][Al(OC6F5)4] (3), [Ph3C][Ta(OC6F5)6] (4), (Et2O)Al{OCH(C6F5)2}3 (5), (Et2O)Al{OC(CF3)3}3 (6), [Ph3C][Al{OC(CF3)3}4] (7), [Ph3C][AlF{OC(CF3)3}3] (8), [Ph3C][{(F3C)3CO}3Al−F−Al{OC(CF3)3}3] (9), and [Ph3C][CB11H6Br6] (10) have been evaluated. The relative selectivity to1-hexene and 1-octene obtained shows a strong dependence on the nature of the cocatalyst, and a rangeof selectivities from <5% C8 (90% C6) to 72% C8 have been observed. The stability of several cocatalyststoward AlEt3 has been studied, and the poor performance of 1 and 2 is linked to degradation of thecocatalyst through ethyl group exchange with AlEt3. In contrast, the [Al{OC(CF3)3}4]- anion in 7 ismuch more stable and gives rise to a highly active and longer lived catalyst. The overall productivity andselectivity of the catalyst is dependent upon both cocatalyst stability and the nature of the anion present,and a reason for this effect has been suggested. Selectivity control by the cocatalyst has been ascribedto interaction of the anion with the active Cr center.
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