Olefins oligomerization, polymerization

Sterically hindered Zr and Ti chelated phenoxide complexes represent a new class of homogeneous olefin oligomerization/polymerization catalysts when combined with cocatalysts such as MAO and FAB (eq 36).Spectroscopic investigations of the reaction between the Zr dibenzyl complex with FAB in toluene reveals the formation of the corresponding cationic complex associated with a benzylborate anion via Ph coordination (64 eq 36). Similar findings were obtained from bis(o-arylphenoxide)M(CH2Ph)2 complexes (M = Zr, Ti),2° while the corresponding dimethyl complexes yield unstable species after FAB activation. The products mediate the polymerization of ethylene and propylene. 

It was not fully realized until my breakthrough using superacids (vide infra) that, to suppress the deprotonation of alkyl cations to olefins and the subsequent formation of complex mixtures by reactions of olefins with alkyl cations, such as alkylation, oligomerization, polymerization, and cyclization, acids much stronger than those known and used in the past were needed. 

C3H5)Ni(EPh3)2](PF6) (E = P, As, Sb) are active catalysts for olefin oligomerization. The stibine species is the most active in the 1,4-polymerization of butadiene.707,708... 

The molecular design of stereospecific homogeneous catalysts for polymerization and oligomerization has now reached a practical stage, which is the result of the rapid developments in early transition metal organometallic chemistry in this decade. In fact, Exxon and Dow are already producing polyethylene commercially with the help of metallocene catalysts. Compared to the polymerization of a-olefins, the polymerization of polar vinyl, alkynyl and cyclic monomers seems to be less developed. 

Fig. 1 Early examples of late transition metal olefin oligomerization and polymerization catalysts...

Olefin metathesis technology, in polymer synthesis, 26 944-948 Olefin oligomerization, 16 111 Olefin oxides, alkanolamines from (with ammonia), 2 122-140 Olefin polymerization, organic titanium compounds in, 25 122 Olefin(ic) polymers, 17 699-709 ethylene-propylene elastomers, 17 705-707... 

At lower temperatures (or in solution) and at high monomer concentration, a second chain termination process that could occur is direct j -hydrogen transfer to a second molecule of monomer. This kind of chain transfer step is now generally accepted for many transition-metal-catalyzed polymerizations, where direct /1-elimination would be too much uphill to explain the observed molecular weights, for olefin oligomerization at aluminium, a similar situation applies. Since insertion and j -hydrogen transfer have an identical concentration dependence, their ratio does not depend much on the reaction conditions (except temperature) and hence limits the molecular weight attainable in the Aufbau reaction. 

Olefin oligomerization were found to occur on SAPO molecular sieves, though their activity was far less than the of zeolite ZSM-5[17]. While showing very different initial activity, the wide-pore SAPO-5 and the narrow pore SAPO-34 both deactivated severely (Figure 3). Both of these catalysts yielded a wide spectrum of products presumably following the pathway described by Tabak et. al. [5], in which numerous olefin polymerization and scission reactions take place. Strangely, medium pore SAPO-11 showed complete selectivity for olefin dimers... 

Catalvtic Olefin Oligomerization and Polymerization with Cationic Group IV Metal Complexes [CplMMe(THT)] + [BPh4]-, M = Ti, Zr, and Hf. 

Comparative data of the mechanism of polymerization on active centers containing non-transition metals. Olefin insertion into metal-carbon bond is also a key step not only for catalytic polymerization but also for olefin oligomerization with organoaluminium compounds. The latter process includes the same steps as the catalytic polymerization in the presence of transition metal compounds... 

Features of Catalytic Olefin Oligomerization and Polymerization Processes... 

While rare-earth metals are proven powerful olefin polymerization catalysts [21-24], there are only limited reports on controlled olefin oligomerizations or selective olefin dimerizations utilizing these elements [204,207,208], An ansa-scandocene [207] and the bis(indenyl)yttrium complex 41 (Fig. 25) [204] were reported to produce head-to-tail dimers from monosubstimted aliphatic alkenes (57). Complex 41 produces predominantly the tail-to tail adduct with styrene. The codimerization of an aliphatic alkene (including substrates containing various functionalities) with styrene affords tran -tail-to-tail dimers, apparently as a result of 1,2-insertion of the a-olefin followed by 2,1-insertion of styrene directed by the phenyl group (58). 

Alkene complexes of Ti, Zr and Hf have been intensively investigated with regard to the nature of bonding and the close relation to olefin oligomerization and polymerization. Alkene complexes of zirconocene and hafnocene are isolated as the trimethylphosphine adduct, Cp2M(T -alkene)(PMe3) (33) [92-94]. Cp 2Ti(CH2=CH2) (34) is a 16 electron ethylene complex with a rich reaction chemistry as summarized in Scheme 6.4 [95-99]. The reaction profile of 34 indicates that the metallacyclopropane canonical form makes an important contribution [100]. 

Oligomerizations, polymerizations and telomerizations are covered in other parts of this section, since C-C/C-C bond forming additions (dicarborations) are involved. Metal-mediated hydroalkylations of olefins with CH acidic compounds and hydroarylations with formal addition of aromatic C—H bonds to olefins are also known2, however, only a few examples of stereoselective applications have been reported (Section 1.5.8.2.6.). 

The advent of the energy crisis has caused us to examine traditional views of the relative costs of different monomers and to consider the potential of less costly monomers for polymerization. One can expect that catalysis of the coordinated anionic type will play a major role in any new developments in olefin and diene polymerizations. Finally, one should recall that Ziegler catalysts have found many uses in other areas of chemistry such as metathesis of olefins, oligomerization, isomerization, hydrogenation, and alkylation. The vast scope of these catalysts will almost certainly achieve a wider range as these types of studies continue in the future. 

The insertion of olefins is the most common, and insertions in M-H or metal alkyl bonds actually take place in the homogeneous hydrogenation, oligomerization, polymerization of olefins, etc. 

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