Abstract
Binuclear and multinuclear complexes have attracted much attention due to their unique catalytic performances for olefin polymerization compared with their mononuclear counterparts. In this work, a series of phenyl-bridged bis-β-carbonylenamine [O−NSR] (R = alkyl or phenyl) tridentate ligands and their binuclear titanium complexes (Ti2L1–Ti2L5) were synthesized and characterized by 1H NMR, 13C NMR, FTIR and elemental analysis. The molecular structure of ligand L2 (R = nPr) and its corresponding Ti complex Ti2L2 were further investigated by single-crystal X-ray diffraction, which showed that each titanium coordinated with six atoms to form a distorted octahedral configuration along with the conversion of the ligand from β-carbonylenamine to β-imino enol form. Under the activation of MMAO, these complexes catalyzed ethylene polymerization and ethylene/α-olefin copolymerization with extremely high activity (over 106 g mol (Ti)−1 h−1 atm−1) to produce high molecular weight polyethylene. At the same time, wider polydispersity as compared with the mononuclear counterpart TiL6 was observed, indicating that two active catalytic centers may be present, consistent with the asymmetrical crystal structure of the binuclear titanium complex. Furthermore, these complexes possessed better thermal stability than their mononuclear analogues. Compared with the complexes bearing alkylthio sidearms, the complex Ti2L5 bearing a phenylthio sidearm exhibited higher catalytic activity towards ethylene polymerization and produced polyethylene with much higher molecular weight, but with an appreciably lower 1-hexene incorporation ratio. Nevertheless, these bis-β-carbonylenamine-derived binuclear titanium complexes showed much higher ethylene/1-hexene copolymerization activity and 1-hexene incorporation ratios as compared with the methylene-bridged bis-salicylaldiminato binuclear titanium complexes, and the molecular weight and 1-hexene incorporation ratio could be flexibly tuned by the initial feed of α-olefin commoners and catalyst structures.
Highlights
Polyole ns are by far the most important and most produced synthetic polymers today, and the design and synthesis of effective catalysts for ole n polymerization and copolymerization is of great interest in both academic research and industrial applications
Claisen condensation of dimethyl isophthalate or methyl benzoate with pinacolone deprotonated by sodium amide, which reacted with alkylthio anilines to obtain bis- and mono-bcarbonylenamine [ONS] tridentate ligands L1–L6 in 68–83% yields
Crystallographic analysis showed that the acetyl group of 1phenylbutane-1,3-dione reacted with amine (L7, Fig. 3).9c in the case of our bis-b-carbonylenamine ligands L1–L5, the single-crystal XRD proved that the alkylthio anilines reacted with the carbonyl group adjacent to phenylene group (Path B), not the one next to the tbutyl group (Path A), which resulted in far-separated and relatively independent titanium centers in complexes Ti2L1–Ti2L5 and would profoundly in uence their catalytic performances for ethylenepolymerization
Summary
To further improve the catalytic performances of the bidentate anionic [N, O] chelated complexes towards ethylene (co) polymerization, Tang and coworkers have developed a series of mono-ligated tridentate [ONX]TiCl3 complexes (X 1⁄4 O, S, Se, and P) based on either salicylaldiminato or b-carbonylenamine backbone by introducing some sidearms with pendantcoordination heteroatom groups (C and D, Chart 1),[9] which exhibited better catalytic performances due to the tuning of the electronic and steric properties of the active species by the sidearm These complexes were especially effective for ethylene copolymerization with a-ole ns, cycloole ns or polar monomers, due partially to the less crowded coordination sphere. We describe the synthesis, structure and ethylene (co)polymerization behaviors of a series of novel phenyl-bridged bis-b-carbonylenamine [OÀNSR] (R 1⁄4 alkyl or phenyl) tridentate binuclear titanium complexes Ti2L1–Ti2L5 (Chart 2)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
