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

The complex (μ-Me 2C-3,3'){(η 5-cyclopentadienyl)[1-Me 2Si-( tBuN)](TiMe 2)} 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-Me 2C-3,3'){(η 5-cyclopentadienyl)[1-Me 2Si( tBuN)][(μ-CH 2)Ti]}2 (rac-4). Activation of rac-3 and meso-3 with 1 equiv of Ph 3C +B(C 6F 5) 4– yields [(μ-CMe 2-3,3'){(η 5-cyclopentadienyl)[1-Me 2Si( tBuN)]} 2(μ-CH 2)(μ-CH 3)Ti 2] +B(C 6F 5) 4– (5; rac-5 and meso-5, respectively). Interestingly, meso-5 is stable in the presence of an additional 1 equiv of Ph 3C +B(C 6F 5) 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(C 6F 5) 3 to yield meso-[(μ-CMe 2-3,3'){(η 5-cyclopentadienyl)[1-Me 2Si( tBuN)]} 2(μ-CH 2)(μ-CH 3)Ti 2]+MeB(C 6F 5) 3– (meso-7) containing the same meso-5 cation but with a MeB(C 6F 5) 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-octenemore » 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-C 5H 3)SiMe 2N tBu]TiMe 2 (Ti 1). In ethylene/styrene copolymerizations, rac-3 produces polymers with 3.1× higher M n and 2.1× greater styrene incorporation versus Ti 1, while meso-3 catalyzes only ethylene-free styrene homopolymerization. In 1-octene homopolymerizations, meso-3 + B(C 6F 5) 3 (i.e., meso-7) produces highly isotactic poly-1-octene (mmmm 91.7%), while rac-3 + Ph 3C +B(C 6F 5) 4– (i.e., rac-5), rac-3 + B(C 6F 5) 3 (i.e., rac-7), and meso-3 + Ph 3C +B(C 6F 5) 4– (i.e., meso-5) produce only atactic poly-1-octene. In conclusion, these bimetallic polymerization catalysts exhibit distinctive cooperative effects influencing product M n, tacticity, and comonomer selection, demonstrating that binuclear catalyst stereochemical factors are significant.« less
Authors:
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
Publication Date:
Grant/Contract Number:
AC02-06CH11357; FG02-03ER154757
Type:
Accepted Manuscript
Journal Name:
Organometallics
Additional Journal Information:
Journal Volume: 36; Journal Issue: 22; Journal ID: ISSN 0276-7333
Publisher:
American Chemical Society
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE
OSTI Identifier:
1467593

Liu, Shaofeng, Invergo, Anna M., McInnis, Jennifer P., Mouat, Aidan R., Motta, Alessandro, Lohr, Tracy L., Delferro, Massimiliano, and Marks, Tobin J.. Distinctive Stereochemically Linked Cooperative Effects in Bimetallic Titanium Olefin Polymerization Catalysts. United States: N. p., Web. doi:10.1021/acs.organomet.7b00641.
Liu, Shaofeng, Invergo, Anna M., McInnis, Jennifer P., Mouat, Aidan R., Motta, Alessandro, Lohr, Tracy L., Delferro, Massimiliano, & Marks, Tobin J.. Distinctive Stereochemically Linked Cooperative Effects in Bimetallic Titanium Olefin Polymerization Catalysts. United States. doi:10.1021/acs.organomet.7b00641.
Liu, Shaofeng, Invergo, Anna M., McInnis, Jennifer P., Mouat, Aidan R., Motta, Alessandro, Lohr, Tracy L., Delferro, Massimiliano, and Marks, Tobin J.. 2017. "Distinctive Stereochemically Linked Cooperative Effects in Bimetallic Titanium Olefin Polymerization Catalysts". United States. doi:10.1021/acs.organomet.7b00641. https://www.osti.gov/servlets/purl/1467593.
@article{osti_1467593,
title = {Distinctive Stereochemically Linked Cooperative Effects in Bimetallic Titanium Olefin Polymerization Catalysts},
author = {Liu, Shaofeng and Invergo, Anna M. and McInnis, Jennifer P. and Mouat, Aidan R. and Motta, Alessandro and Lohr, Tracy L. and Delferro, Massimiliano and Marks, Tobin J.},
abstractNote = {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.},
doi = {10.1021/acs.organomet.7b00641},
journal = {Organometallics},
number = 22,
volume = 36,
place = {United States},
year = {2017},
month = {11}
}