Mono-Cp titanium complexes

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... 

Scheme 350 shows the structures of a number of mono-Cp titanium complexes with more elaborately substituted aryloxo ligands. The compounds are formed by the reaction of Cp TiCl3 with 1 equiv. of the substituted phenol in the presence of an excess of pyridine or by treatment of the lithium phenoxide with Cp TiCl3 some of them have been... 

Reduction of the group 4 M(IV) center by MAO or trialkylaluminum to lower-valent species is a common phenomenon, especially for titanium complexes and sometimes for zirconium complexes as These reductive processes are not considered to be deactivation but rather part of generating the true catalytically active species in the case of mono-Cp titanium complexes for syndiospe-cific styrene polymerization (vide supra). Addition of a monomer to an active catalytic system often surprisingly increases the quantity of Ti(III) ° or Zr-... 

Recently, Baird and co-workers have reported (75) examples of polymerizations by a simple mono-Cp titanium complex, (C5(CH3)5)Ti(CH3)3 activated with a Lewis acid (B(C6F5)3) that not only copolymerizes ethylene and a-olefins but also induces polymerization of monomers normally associated with cationic polymerization such as isobutylene and vinyl ethers. Shaffer and Ashbaugh foimd (76) that for isobutylene and a-methylstyrene, the metal complex is an initiator rather than a catalyst (if it even participates at all), but that a transition from cationic to coordination polymerization occurs in styrene polymerization as temperature is raised. Even if it merely functions as an initiator, however, these investigations have revealed new polymerization systems based on anions such as [RB(C6F5)3l (R = alkyl, CeFs) that are less prone to side reactions tending to limit the MW and degree of polymerization of monomers like isobutylene at moderate temperatures (T > -80°C). 

FIGURE 14.4 Structures of mono-Cp titanium complexes 7-10 with different Cp ring substituents. 

Amidocarbonylation aldehydes, 11, 512 enamides, 11, 514 overview, 11, 511-555 Amido complexes with bis-Cp titanium, 4, 579 Group 4, surface chemistry on oxides, 12, 515 Group 5, surface chemistry on oxides, 12, 524 with molybdenum mono-Cp, 5, 556 with mono-Cp titanium(IV) alkane elimination, 4, 446 amine elimination, 4, 442 characteristics, 4, 413 via dehalosilylation reactions, 4, 448 HCL elimination, 4, 446 metathesis reactions, 4, 438 miscellaneous reactions, 4, 448 properties, 4, 437... 

Mono-Cp titanium derivatives show reactivity as catalyst precursors for olefin polymerizations, particularly for the polymerization of styrene and functionalized monomers. A review highlighting the developments in the design and applications of non-metallocene complexes, including mono-Cp derivatives, as catalyst systems for a-olefin polymerization has appeared.440 Titanium complexes bearing Cp in addition to chloro ligands and activated by aluminum... 

Mono-Cp titanium binuclear complexes with trisiloxane bridges have been synthesized. In the presence of MMAO, these complexes initiate the polymerizations of ethylene and styrene.938... 

Macrocyclic mono-Cp titanium(iv) complexes with peptide-derived ligands coordinated to the titanium atom have been described by the reaction of the pseudo-nonapeptide with 3 equiv. of NaOMe in CH2C12 and subsequent reaction with Cp TiCl3 (Cp = Cp, Cp ) (Scheme 395). The molecular structure of the Cp derivative has been determined by X-ray diffraction and shows a distorted pseudo-octahedral titanium environment.939... 

Ethane- and propane-1,2-dithiolato Cp titanium derivatives have been reported. They are reduced by boron and tin hydrides.1013,1014 Mono-Cp titanium(iv) sulfido complexes have been made by treatment of CpTiCl3 with dithiols in the presence of donor ligands such as imidazole or PMe3 under different reaction conditions (Scheme 418).1015 The structures of the compounds have been reported. Electrochemical studies suggest that these compounds are formed through a radical mechanism.1016... 

MAO activated mono-cyclopentadienyl titanium complexes containing one alkoxide a-ligand appear to have a superior catalyst performance as compared to the analogous trichlorides, Cp TiCl3 CpTiCl2(OR)/MAO systems have polymerization activities that are double or... 

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