191112-13-7Relevant academic research and scientific papers
Ethylene and propylene polymerization by a series of highly electrophilic, chiral monocyclopentadienyltitanium catalysts
Ewart, Sean W.,Sarsfield, Mark J.,Jeremic, Dusan,Tremblay, Tracey L.,Williams, Edan F.,Baird, Michael C.
, p. 1502 - 1510 (1998)
The compounds Cp*TiMe2C6F5, Cp*TiMe2OC6F5, and Cp*TiMe2Cl (Cp* = η5-C5Me5) react with the borane B(C6F5)3 to form the thermally unstable, chiral complexes Cp*TiMe(C6F5)-(μ-Me)B(C6F 5)3, Cp*TiMe(OC6F5)(μ-Me)B(C6F 5)3, and Cp*TiMeCl(μ-Me)B(C6F5)3, respectively, which are similar to the known Cp*TiMe2(μ-Me)B(C6F5)3. All four μ-Me compounds behave as sources of the highly electrophilic species [Cp*TiMeE]+ (E = Me, Cl, C6F5, OC6F5) when treated with the borane, the last three being chiral, and all four systems exhibit catalytic activities for the polymerization of ethylene to high-molecular-weight polyethylene. Despite the chirality at titanium of three of the compounds, polymerization of propylene by all of them results in the formation of atactic, elastomeric polypropylene. NMR analyses of the propylene polymers formed show that initiation involves 1,2-insertion into a Ti-Me bond, and while propagation involves primarily head-to-tail 1,2-insertions, an unusually high (by metallocene standards) proportion of the insertions also involves 2,1-misinsertions but essentially no 1,3-enchainment. The major olefinic end groups are vinylidene (CH2=CMe-), resulting from β-hydrogen transfer following a 1,2-insertion, and vinyl (CH2=CH-), resulting from β-hydrogen transfer from the methyl group following a 2,1-insertion or, more likely, β-methyl transfer following a 1,2-insertion. Small amounts of internal olefins are also formed via β-hydrogen transfer following a 2,1-insertion. An EPR study of the Cp*TiMe3/ B(C6F5)3 system in toluene indicates that a complex of titanium(III), suggesting that a contribution to catalysis by titanium(III) species is unlikely.
Solution structures and exchange phenomena of the new alkene polymerization initiators (η-C5Me5)TiMe(E)(μ-Me) B(C6F5)3 (E = C6F5, OC 6F5) and [(η-C5
Tremblay, Tracey L.,Ewart, Sean W.,Sarsfield, Mark J.,Baird, Michael C.
, p. 831 - 832 (2007/10/03)
The solution structures and dynamics of the new alkene polymerization initiators (η-C5Me5)TiMe(C6F 5)(μ-Me)B(C5F5)3 2, (η-C5Me5)TiMe(OC6F 5
Synthesis of a series of new, highly electrophilic, monocyclopentadienyltitanium olefin polymerization initiators
Sarsfield, Mark J.,Ewart, Sean W.,Tremblay, Tracey L.,Roszak, Aleksander W.,Baird, Michael C.
, p. 3097 - 3104 (2007/10/03)
The new compounds Ti(η-C5Me5)Me2E (E = C6F5 or OC6F5) and Ti(η-C5Me5)Me(OC6F5)2 have been synthesized and characterized by a variety of techniques, including 47/49Ti NMR spectroscopy. All three compounds react with the borane B(C6F5)3 to form the highly electrophilic but thermally unstable species Ti(η-C5Me5)Me(E)(η-Me)B-(C6F 5)3 and [η-C5Me5)Ti(OC6F5) 2][BMe(C6F5)3], the solution structures and dynamics of which are investigated and compared with those of the known compound Ti(η-C5Me5)Me2(η-Me)B(C 6F5)3,. Interestingly, Ti(η-C5Me5)-Me(C6F 5)(η-Me)B(C6F5)3 undergoes neither significant ion-pair dissociation to the solvent separated ions [(η-C5Me5)TiMe(C6F5)] + and [BMe(C6F5)3]- nor borane dissociation to its precursors (η-C5Me5)TiMe2(C6F5) and B(C6F5)3; indeed, both rotation about the Ti-C6F5 bond and inversion at the chiral metal are slow on the NMR time-scale. In contrast, Ti(η-C5Me5)Me(OC6F 5)(η-Me)B(C6F5)3 is more labile and, like Ti(η-C5Me5)Me2;(η-Me)-B(C 6F5)3, undergoes ion-pair dissociation, while [(η-C5Me5)Ti(OC6F5) 2][BMe(C6F5)3] exists in solution as the solvent separated ion species [(η-C5Me5)Ti(OC6F5) 2]- and [BMe(C6F5)3]- in equilibrium with its precursors, (η-C5Me5)TiMe(OC6F5)2 and B(C6F5)3.
