Reactivity of Alkylaluminums

Aryloxide (phenolate) ligands provide rigid and versatile ancillary ligand sets in order to study the multifunctional reactivity of alkylaluminum and alkylmagnesium reagents toward Ln-OR moieties. Several types of symmetrically substituted phenolate ligands — summarized in Chart 4 — were employed for the synthesis of a variety of heterobimetallic lanthanide(III) and lanthanide(II) metal complexes. Alkylation reactions revealed the preferred... 

The chlorinated solvents, CH3CI, C2H5CI and CH2CI2 do not affect the trends of reactivity of alkylaluminums. 

In view of the chemical nature of alkylaluminums and methyl halides, complexation is most likely to be rapid and complete, i. e. K is large. Indeed Me3 Al and a variety of Lewis bases were found to complex rapidly2. Initiation, i.e., f-butyl cation attack on monomer, is also rapid since it is an ion molecule reaction which requires very little activation energy. Thus, it appears that Rj t. and hence initiator reactivity are determined by the rate of displacement Ri and ionization R2. 

As described above, an organocopper reagent derived from alkyl lithium, such as Me2CuLi, readily reacts with y,y-difluoro-a,P-enoate 42 to form a reductive defluorinated metal species 43, exclusively (see Scheme 10.12). To facilitate the reactivity of fluorine as a leaving group, we also investigated the effects of alkylaluminum on this reaction as... 

Choosing a selective solvent for the catalyst is one of the most significant steps in the development of such a process. Due to moisture sensitivity and reactivity of the Dimersol alkylaluminum co-catalyst, protic media like butanediol or water are not suitable at all. At an early stage, Chauvin et al. anticipated that ionic liquids (ILs) could meet biphasic liquid-liquid solvent requirements [8]. 

The use of ketones as enophiles in Lewis acid catalyzed ene reactions is much less well developed. This is not surprising since ketones are less reactive than aldehydes due to both steric and electronic effects. Furthermore the tertiary alcohols which would be produced are unstable to acid. Proper choice of alkylaluminum halide catalyst allows some of these ene reactions to be carried out. 25 Reaction of 49 with 1 equivalent of Me2AlQ at 25 gives a 58% yield of a 4.5 1 mixture of ene adducts 50a and 50b. Reactionof 51 with 2 equivalent of MeAlQ2 at 0 C gives a 60% yield of 52 by cyclization to the zwitterion followed by a 1,2-hydride and 1,2-methyl shift analogously to the conversion of 38 to 41. 

In previous papers1,2 we described reactivity studies of cationic isobutylene polymerization using r-butyl halide initiators, alkylaluminum coinitiators and methyl halide solvents. The effects of these reagents as well as temperature on the overall rate of polymerization and polyisobutylene (PIB) yield were studied and reactivity orders were established. These results were explained by a modified initiation mechanism based on an earlier model proposed by Kennedy and co-workers3,4. This paper concerns the effects of f-butyl halide, alkylaluminums and methyl halide, as well as temperature and isobutylene concentration on PIB molecular weights. 

From the analysis of 13C NMR spectra of polypropylenes, Doi96) found that the sequence distribution of inverted propylene units follows first-order Markov statistics. Table 4 lists the two reactivity ratios rQ and rt, for the polymerization of propylene with the soluble catalysts composed of VC14 and alkylaluminums at — 78 °C ... 

Almost all group 4 metal complexes require a cocatalyst to generate an active metal-alkyl cationic species. Ordinary alkylaluminums - used in conventional Ziegler Natta catalysts - are insufiicient to activate these compounds on their own. The principal activator nsed is methylalumoxane (MAO), a structurally enigmatic material with a mixture of nuclearities. Its purpose is to alkylate the metal dichloride and to abstract one of the reactive hgands to form the ion pair active catalyst. The interaction is dynamic and a large excess of MAO is needed for effective catalyst performance, thus inhibiting a comprehensive characterization of these catalysts. 

Cycloolefins and nonterminal olefins, although less reactive than terminal olefins, also enter into displacement . Starting from i-BujAl and keeping T = 135°C with continual removal of isobutene di-s-alkylaluminum hydrides are obtained in good yield ... 

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