Titanium complexes polymerization studies

Density functional calculations on the chain initiation reaction shown in Scheme 136 for the ethylene polymerization catalyzed by bis-alkoxo titanium complexes have been studied. Activation barriers of 6.4kcal mol-1 are found for the titanium sulfur-bridged catalysts with higher insertion barriers of 10-15 kcalmol-1 for the GH2-bridged catalysts. 

The synthesis of the Ind-amido titanium complexes [(C9H5R)SiMe2NBut]TiX2 (Scheme 304) with alkoxo and amido substituents at 2- and 3-indenyl position has been reported and the molecular structures of the derivatives for R = NMe2 and N(CH2)4 have been determined by X-ray diffraction. The methyl derivatives are activated with B(C6F5)3 and studied as catalytic systems for the ethylene/l-octene co-polymerization. A dramatic effect of the indenyl substituent nature on catalyst efficiency and polymer properties is observed.740... 

Studies on ct-olefin polymerization with Cp-amido titanium complexes have been performed. 

DFT calculations combined with molecular mechanics methods have been used to study the first (R = Me) and the second (R = propyl) insertion of the ethylene monomer into the Ti-R bond of (CpSiMe2NBut)(R)Ti(/t-Me)B(C6F5)3. The influence of the counterion and the solvent effects on the energetic profile of the polymerization have been evaluated. Theoretical investigations have also been directed at mechanistic aspects of olefin polymerizations catalyzed by mono-Cp titanium complexes. The chain propagation mechanism, the chain termination and... 

Atactic polypropene has been synthesized with homogeneous catalytic systems based on mono-Cp trialkoxo titanium complexes activated by MAO.951 Syndiotactic polystyrene has been synthesized with different mono-Gp trialkoxo titanium derivatives activated by MAO and AlMe3, and the catalytic efficiency has been compared with bis-Cp titanium catalysts.952 The titanium ligands affect both catalytic activity and stereoregularity of the polypropylene obtained. For the CpTi(OPrn)3/MAO system, factors influencing the propylene polymerization, such as temperature, Al/Ti molar ratio, and monomer pressure, have been studied. 

The most relevant E/O co-polymerization reports with rzmzz-Cp-amido titanium complexes include ethylene/1-butene,537,538 ethylene/l-hexene,539,540 and ethylene/l-octene.91,442,454,456,457,464,506,541 Ethylene/4-methyl-l-pen-tene co-polymerizations have been reported as well.457,542 The thermal and physical properties of the octene co-polymers produced with ansa-G -amido titanium complexes have been studied.543-546 The importance of the activator has been pointed out in many instances.91,108... 

A more recent and in-depth polymerization study of a tight bite angle A,0-chelated early transition metal being utilized for alkene polymerization was presented by Sun s group [10b] in 2010. A set of bis(chloro)mono(cyclopentadienyl)mono(amidate) titanium complexes, in a half-sandwich configuration, were synthesized. Electronic... 

Figure 14 Tethered bis(amidate) titanium complex for preliminary studies as initiators for ethylene polymerization. Ar=4-tert-butylphenyl, X=NMe or Cl [10a]...

It should be mentioned that simple metal complexes immobilized on polymer supports were initially used for polymerization (1965/1966) in the Solvay catalysts based on titanium complexes bound to macromolecular ligands with C=0, C=N and C=N groups. Until now the data are mainly available in patent literature, and there are few kinetic studies of polymerization processes involving the action of macromolecular complexes. At the same time the use of metal complexes bound to inorganic supports has been extensively developed in polymerization catalysis. This indicates that there has been inadequate study of the application of metal complexes immobilized on polymer supports to the catalysis of polymerization and copolymerization of different monomers, mainly olefins. 

In addition to their work on DA reaction, Seebach et al. also studied polymeric titanium catalyst 82,83 (see Figure 7.7) in the [3 + 2] cycloaddition of 3-crotonoyloxazolidinone and diphenyl nitrone (Table 7.5). The use of soluble catalysts 81a,b,d (entries 1-3) and supported-titanium catalysts 83a,b,d (entries 4-6) afforded similar performances in terms of yield, dia-stereoselectivity and enantioselectivity in favour of adduct 89a. Interestingly, the enantioselectivity was better in heterogeneous conditions with polymeric TADDOL-titanium complex 83d (entry 6, 56% enantiomeric excess) than using soluble catalysts (entries 1-3). 

Chmura et al. also prepared air and moisture resistant chiral imino phenoxide complexes of zirconium and titanium, 14 [16]. They envisioned to study the effect of supporting ligand chirality on the stereoselectivity of LA ROP reaction. But at the end, they did not gain acceptable evidence enable to support any relationship. They showed that all isolated polymers had similar and moderate heterotactic microstructure which implied simple chain end control mechanism and resulted to the selective racemic enchainment during the propagation process. First, they investigate polymerization in toluene at 80°C and ambient temperature in which titanium complexes were absolutely inactive and zirconium coxmterparts showed moderate activity after 2 and 24 hours, respectively. Then they checked out solvent free conditions at 130°C and received almost complete conversion after 30 minutes for both titanium and zirconium alkoxide complexes (Table 7.2, entry 33-36). In this condition, titanium coxmterpart, in contrast to zirconium, resulted to full atactic polymer. Their investigation also showed that zirconium complex retained its activity in moisture or with lactic acid impurity in crude monomer which is deleterious for most metal alkoxide catalysts. 

The use of the binaphthyl-based chiral polymers in catalysis has been explored. We have demonstrated that incorporation of aluminum metal centers into the rigid binaphthyl polymer backbones leads to greatly enhanced catalytic activity over the monomeric aluminum complex. The catalytic activity of the polymeric aluminum and titanium complexes in the Mukaiyam aldol reaction has been studied. These polymeric metal complexes represent a new generation of polymer-based catalysts... 

Titanium complexes with acetylacetonate (acac) ligands were first tested for the polymerization of styrene by Ishihara et al." and Zambelli et al When activated with MAO, Ti(acac)2Cl2 and Ti(acac)3 can produce syndiotactic polystyrene with low activities, whereas their zirconium analogues only afford atactic polystyrene. Hu and coworkers studied a series of MAO activated 1,3-diketonato titanium complexes (Figure 14.11, 53-57) and found that their activities increased in the following... 

In studies of the reaction of TiMe2(dmpe)2 with PhSiHs Girolami and coworkers could isolate two interesting oligosilane titanium complexes (Scheme 34) which can be considered as intermediates in a dehydrocoupling polymerization... 

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