Active O,Npy,N-Titanium(IV) Fluoride Pre-Catalysts for Ethylene Polymerization; Exploring “Fluoride Effects” on Polymer Properties and Catalytic Performance
posted on 2016-04-08, 10:30authored byGregory Adam Solan, Luka A. Wright, Eric G. Hope, Warren B. Cross, Kuldip Singh
Three examples of discrete six-coordinate O,Npy,N-bearing titanium(IV) trifluoride complexes, [{2-(C5H4N)-6-(CMe2O)C5H3N}TiF3] (1), [{2-(C6H4-2′-O),6-(CMe═N(2,6-i-Pr2C6H3))C5H3N}TiF3] (2a), and [{2-(3-C12H8-2-O)-6-(CMe═N(2,6-i-Pr2C6H3))C5H3N}TiF3] (3a), were prepared using a one-step HF elimination protocol from cis-[(THF)2TiF4] and the corresponding pincer ligand precursor (HL1, HL2H, and HL2Ph). A mer configuration of the three fluoride ligands is adopted in their solid-state structures, which is mirrored in solution, as shown by mutual two-bond F–F coupling in their 19F{1H} NMR spectra. For purposes of comparison, the chloride counterparts of 2a and 3a, [{2-(C6H4-2′-O),6-(CMe═N(2,6-i-Pr2C6H3)C5H3N}TiCl3] (2b) and [{2-(3-C12H8-2-O)-6-(CMe═N(2,6-i-Pr2C6H3))C5H3N}TiCl3] (3b), are also reported. On treatment with excess MAO, 1 is scarcely active in ethylene polymerization, 2a is more active, and the most sterically protected system, 3a, represents the most active nonmetallocene metal-fluoride precatalyst reported to date (340 g mmol–1 h–1 bar–1) and produces ultra-high-molecular-weight polyethylene (UHMWPE). Similar structure–activity correlations are displayed for chloride-containing 2b and 3b, but, in general, they are significantly more active than their fluoride counterparts, with 3b being the most productive of the series (990 g mmol–1 h–1 bar–1). Using fluoride rather than chloride in the precatalyst has a marked effect on not only the molecular weight but also the molecular weight distribution, with broad dispersities (Đ) being a feature of the polymers obtained from 2a and 3a, whereas those for chloride-containing 2b and 3b are appreciably narrower. Single-crystal X-ray structures are reported for 1, 2a, 2b, and 3a.
History
Citation
Organometallics, 2016 (Articles ASAP (As Soon As Publishable))
Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Chemistry
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