Precatalysts oligomerization

Figure 5.9 Selected iminoaryl units in oligomerization precatalysts 1 and 2.

Figure 5.10 Oligomerization precatalysts 8 and 9 with one or no N-aryl groups.

A brief overview on the very recent use of Cr complexes bearing [F/VJ bidentate ligands as ethylene oligomerization precatalysts should also be mentioned. As summarized in Scheme 40, Cr(II) amidophosphine complexes 110-114 were... 

The corresponding iron-catalyzed oligomerization of ethylene was developed by Gibson and coworkers [125]. A combination of an iron precatalyst with MAO (methyl aluminoxane) yields a catalyst that affords ethylene oligomers (>99% linear ot-olefin mixtures). The activity of ketimine iron complexes (R = Me) is higher than that of the aldimine analogs (R = H) and also the a-value of the oligomer is better (Scheme 41). 

A recent example where Co2(CO)8 serves as a precatalyst is in the preparation of linear and branched aldehydes via propylene hydroformylation in supercritical C02 (93-186 bar 66-108 °C). Cyclohexane carbaldehyde is produced from cyclohexene using Co2(CO)8 and an acid RCOOH, or else is successful with another established Co catalyst, Co(OOCR)2, assumed to form in situ in the former case. Oligomerization of aldehydes such as n-butanal is achieved with Co2(CO)6L2 as catalyst (L = CO, PR3).1364... 

In contrast, the related diamines 45 and 46 [cf. (3,5-/-Pr2C6H2-4-NH2)2CH2 above] give, on treatment with 2,6-diacetylpyridine, oligomeric polyimines that can be readily complexed with iron dichloride to afford 47 and 48, respectively (Fig. 14). Notably, on activation with MAO, 47 and 48 are active catalysts for ethylene polymerisation and indeed perform more efficiently at elevated temperatures than those of the original bis(imino)pyridine iron precatalyst 5 [166],... 

Thus, chiral precatalysts includ-RuCl2[(R)-binap](dmf) (oligomeric [NH2(C2H5)2][ RuCl[(R)-binap] 2-... 

As already mentioned, the mechanism of oligomerization is the same as discussed for polymerization, and a catalytic cycle similar to the one shown in Fig. 6.3 operates. Many nickel-phosphine complexes have been successfully used as the precatalysts 7.17 is one such example. As shown by 7.5, reaction of a phosphorous ylide with a suitable nickel-containing precursor makes this... 

An interesting study concerns the preparation of phosphoranediiminato complexes of NiCh (95 - 98) and their application as precatalysts for ethylene oligomerization. The selectivity in oligomerization can be tuned by the nature of the carbon backbone of the ligand. ... 

Changes to the metathesis step could not be assessed by quantifying the kinetic EM using the established method, as the precatalyst was changed to Gr2, which operates in the thermodynamic regime rather than the kinetic regime under such conditions, the product ratio does not necessarily reflect the relative rates of cyclization and oligomerization, as these products can... 

Oligomeric palladacyclopentadiene complexes 114 are useful in [2 + 2 + 2]alkyne cyclotrimerizations. An X-ray crystal structure of 114 was obtained.Palladacyclopentadienes have also been employed as precatalysts. 

Table 7 Ethylene oligomerization catalyzed by pyrazolyl-based chromiran precatalysts...

Although numbers of Ni-based catalysts for olefin polymerization have been reported over the past 50 years, examples of structurally characterized Ni/Al heterometaUic complexes resulting from the reaction of a Ni-based precatalyst and an organoaluminum cocatalyst were only recently reported [182, 183] (Fig. 13). Complex 115 oligomerizes ethylene with a moderate activity in the absence of any cocatalyst to selectively form 1-butene, while species 116 and 117 polymerizes ethylene in a controlled manner. 

As shown in Figure 6.8, under the reaction conditions of oligomerization, the precatalyst 6.46 generates a nickel-hydride intermediate 6.47. 

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