Distinctive Stereochemically Linked Cooperative Effects in Bimetallic Titanium Olefin Polymerization Catalysts

Shaofeng Liu, Anna M. Invergo, Jennifer P. McInnis, Aidan R. Mouat, Alessandro Motta, Tracy L. Lohr, Massimiliano Delferro, Tobin J. Marks

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


The complex (μ-Me2C-3,3′){(n5-cyclopentadienyl)[1-Me2Si-(tBuN)](TiMe2)}2 (3) was prepared as a new binuclear catalyst motif for homogeneous olefin polymerization. Complex 3 exists as rac-3 and meso-3 diastereomers, which can be separated and characterized by solution NMR spectroscopy and single-crystal X-ray diffraction. While meso-3 has high thermal stability, rac-3 undergoes thermolysis in solution to quantitatively form the dimeric methylidene complex (μ-Me2C-3,3′){(n5-cyclopentadienyl)[1-Me2Si(tBuN)][(μ-CH2)Ti]}2 (rac-4). Activation of rac-3 and meso-3 with 1 equiv of Ph3C+B(C6F5)4- yields [(μ-CMe2-3,3′){( n 5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)(μ-CH3)Ti2]+B(C6F5)4- (5; rac-5 and meso-5, respectively). Interestingly, meso-5 is stable in the presence of an additional 1 equiv of Ph3C+B(C6F5)4-, while rac-5 reacts to yield rac-[(μ-CMe2-3,3′){( n 5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)[(TiCH3)(Ti- n 1-Ph3C)]2+[B(C6F5)4-]2 (rac-6) as indicated by multinuclear NMR spectroscopy and DFT computation. meso-3 reacts with 2 equiv of B(C6F5)3 to yield meso-[(μ-CMe2-3,3′){( n n 5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)(μ-CH3)Ti2]+MeB(C6F5)3- (meso-7) containing the same meso-5 cation but with a MeB(C6F5)3-counteranion. These findings, along with catalytic results, indicate that rac-3 and meso-3 remain structurally intact during polymerization, consistent with the observed diastereoselectivity effects. Under identical ethylene/1-octene copolymerization conditions, only activated bimetallic rac-3 produces appreciable polymer, with meso-3 exhibiting low activity, but both yield polymer with a branch density >2× that of the monometallic control [(3-tBu-C5H3)SiMe2NtBu]TiMe2 (Ti1). In ethylene/styrene copolymerizations, rac-3 produces polymers with 3.1× higher Mn and 2.1× greater styrene incorporation versus Ti1, while meso-3 catalyzes only ethylene-free styrene homopolymerization. In 1-octene homopolymerizations, meso-3 + B(C6F5)3 (i.e., meso-7) produces highly isotactic poly-1-octene (mmmm 91.7%), while rac-3 + Ph3C+B(C6F5)4- (i.e., rac-5), rac-3 + B(C6F5)3 (i.e., rac-7), and meso-3 + Ph3C+B(C6F5)4- (i.e., meso-5) produce only atactic poly-1-octene. These bimetallic polymerization catalysts exhibit distinctive cooperative effects influencing product Mn, tacticity, and comonomer selection, demonstrating that binuclear catalyst stereochemical factors are significant.

Original languageEnglish
Pages (from-to)4403-4421
Number of pages19
Issue number22
Publication statusPublished - Nov 27 2017

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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