Catalytic system organoaluminum

Research by Ziegler and Natta showed that organoaluminum compounds in combination with titanium halogenides are active catalysts of the polymerisation of olefines at low pressure. This inspired the study of other organometal compounds (e.g., organotin compounds like tetraal-kyltin) in similar catalytic systems. It has been proved experimentally. 

Diene polymerization via lanthanide propanolate-based catalytic systems was first reported by U. Pedretti et al. [162], Several types of binary and ternary initiator systems have been developed since the late 1970s (see Table 7), including zz- and zsopropanolalc ligands [162], homo- and heteroleptic lanthanide species [163-165], and different types of organoaluminum cocatalysts [162,166-168]. Despite such extensive studies, structural evidence of the formation of alkylated rare-earth metal centers remained scarce. 

This catalytic system was successfully applied to the alkynylation of tosyl aziridine with adjacent ether functionality this should provide a promising method for the synthesis of amino alcohols. Treatment of tosyl aziridine 81 with PhC CLi in the presence of catalytic Mc3Al in toluene at 0 °C for 5 h gave rise to the corresponding alkynylation product 82 in 66 % yield (Sch. 53), whereas reaction in the absence of Me3Al proceeded sluggishly under similar reaction conditions (7 % yield). The control experiment with simple aziridine 83, in which addition of catalytic McaAl had almost no influence on the reaction rate, supports the proposed catalytic cycle its efficacy is based on the formation of the pentacoordinate organoaluminum complex. 

An excellent catalytic system is based on (R)- and (5)-2,2 -dihydroxybinaphthoPThe newly designed enantiomerically pure ( + )-(/ )-3,3 -bis(triarylsilyl)binaphthol reacts with trimethyl-aluminum to produce a chiral organoaluminum reagent 15 which is a very efficient catalyst for the hetero-Diels-Alder reaction. [4 + 2] Cycloaddition of aliphatic and aromatic aldehydes 2 to dienes 14 in the presence of 10 mol% of 15 yields m-dihydropyrones 3 together with a few percent of the trans-isomers with a diastereoselectivity as high as d.r. 98.5 1.5. 

The objective of this chapter is to examine the basic research on diene (butadiene, isoprene, and piperylene) polymerisation with the LnHalj-nL-AlRj (Ln = lanthanide, Hal = halogen, ligand (L) = tributyl phosphate (TBP), AlRj = triisobutylaluminum and diisobutylaluminum hydride) catalytic system. The chapter will analyse the role of such factors as the electronic and geometric structure of bimetallic active centres, anti-syn and 7t-o-transitions of the terminal units of the growing polymer chains and the nature of the lanthanide, diene, and organoaluminum component in the mechanism of stereoregulation. 

Sulfonated nickel ylide complex is a potent single-component catalyst for ethylene oligomerization in aromatic and polar solvents [226]. The modification of this complex with various organoaluminum compounds (AlEtjCl/AlEtCU or AlEt-O-Et) results in the formation of a new catalytic system with 10-20 times higher activity in ethylene oligomerization in aromatic solvents compared with that of the original ylide [201,227-229]. 

The polymerization of cyclooctene induced by catalytic systems derived from WClg and Et3Al, EtAlCl2, or other organoaluminum compounds produces mainly trans polyoctenamer [212]. By contrast, the use of WFg in conjunction with EtAlCl2 or the cis-specific carbene system Ph2C=W(CO)5 has yielded... 

The mode of action of external Lewis base—so called because it is added to the catalytic system together with the organoaluminum cocatalyst—is more difficult to account for. This base generally consists of a dialkoxysilane molecule, and its role would be to inhibit certain nonspecific sites in addition to the internal Lewis base or transform some of them into isospecific ones by the steric effect. It is admitted that it coordinates simultaneously to a titanium atom and an aluminum atom via its two oxygen atoms, thus corroborating the Rodriguez and Van Looy mechanism. 

In 1951, Robert Banks and J. Paul Hogan at Phillips Petroleum discovered a chromium trioxide-based catalyst, which was a landmark breakthrough in the commercial production of PE at mild temperature and pressure. In 1953, the German chemist Karl Ziegler, who shared the Nobel Prize for Chemistry in 1963 with Italian chemist Giulio Natta, developed a catalytic system based on titanium halides and organoaluminum compounds that worked at even milder conditions than the Phillips catalyst. The Phillips catalyst is less expensive and easier to work with, however, and both methods are widely used industrially. 

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