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Title: Distinctive Stereochemically Linked Cooperative Effects in Bimetallic Titanium Olefin Polymerization Catalysts

Journal Article · · Organometallics
ORCiD logo [1];  [1];  [1];  [1];  [2];  [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry
  2. Univ. di Roma, Roma (Italy). Dipartimento di Scienze Chimiche
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The complex (μ-Me2C-3,3'){(η5-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'){(η5-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'){(η5-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'){(η5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)[(TiCH3)(Ti-η1-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'){(η5-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. In conclusion, these bimetallic polymerization catalysts exhibit distinctive cooperative effects influencing product Mn, tacticity, and comonomer selection, demonstrating that binuclear catalyst stereochemical factors are significant.

Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States); Northwestern Univ., Evanston, IL (United States)
Sponsoring Organization:
National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC02-06CH11357; FG02-03ER154757; CHE-1464488; FG02-03ER15457
OSTI ID:
1467593
Alternate ID(s):
OSTI ID: 1871003
Journal Information:
Organometallics, Vol. 36, Issue 22; ISSN 0276-7333
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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Chromium complexes supported by the bidentate PN ligands: synthesis, characterization and application for ethylene polymerization journal January 2018
Synthesis of poly(α-olefins) containing rare short-chain branches by dinuclear Ni-based catalysts journal January 2018

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Chart 1(p. 2)figure Chart 1
Chart 2(p. 2)figure Chart 2
Chart 3(p. 2)figure Chart 3
Figure 1(p. 3)figure Figure 1
Scheme 1(p. 3)figure Scheme 1
Scheme 2(p. 4)figure Scheme 2
Figure 2(p. 5)figure Figure 2
Figure 3(p. 5)figure Figure 3
Figure 4(p. 6)figure Figure 4
Scheme 3(p. 6)figure Scheme 3
Scheme 4(p. 6)figure Scheme 4
Chart 4(p. 7)figure Chart 4
Figure 5(p. 7)figure Figure 5
Figure 6(p. 8)figure Figure 6
Figure 7(p. 8)figure Figure 7
Scheme 5(p. 8)figure Scheme 5
Scheme 6(p. 8)figure Scheme 6
Scheme 7(p. 8)figure Scheme 7
Figure 8(p. 9)figure Figure 8
Table 1(p. 9)table Table 1
Table 2(p. 9)table Table 2
Figure 9(p. 10)figure Figure 9
Scheme 8(p. 10)figure Scheme 8
Table 3(p. 10)table Table 3
Scheme 9(p. 11)figure Scheme 9

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36 MATERIALS SCIENCE