- Olefin Polymerization by Dinuclear Zirconium Catalysts Based on Rigid Teraryl Frameworks: Effects on Tacticity and Copolymerization Behavior
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Toward gaining insight into the behavior of bimetallic catalysts for olefin polymerization, a series of structurally related binuclear zirconium catalysts with bisamine bisphenolate and pyridine bisphenolate ligands connected by rigid teraryl units were synthesized. Anthracene-9,10-diyl and 2,3,5,6-tetramethylbenzene-1,4-diyl were employed as linkers. Bulky SiiPr3 and SiPh3 substituents were used in the position ortho to the phenolate oxygen. Pseudo-Cs and C2 symmetric isomers are observed for the binuclear complexes of bisamine bisphenolate ligands. In general, binuclear catalysts show higher isotacticity compared to the monozirconium analogues, with some differences between isomers. Amine bisphenolate-supported dizirconium complexes were found to be moderately active (up to 1.5 kg mmolZr-1 h-1) for the polymerization of 1-hexene to isotactically enriched poly-1-hexene (up to 45% mmmm) in the presence of stoichiometric trityl or anilinium borate activators. Moderate activity was observed for the production of isotactically enriched polypropylene (up to 2.8 kg mmolZr-1 h-1 and up to 25.4% mmmm). The previously proposed model for tacticity control based on distal steric effects from the second metal site is consistent with the observed behavior. Both bisamine bisphenolate and pyridine bisphenolate supported complexes are active for the production of polyethylene in the presence of MAO with activities in the range of 1.1-1.6 kg mmolZr-1 h-1 and copolymerize ethylene with α-olefins. Little difference in the level of α-olefin incorporation is observed between mono- and dinuclear catalysts supported with the pyridine bisphenolate catalysts. In contrast, the size of the olefin affects the level of incorporation differently between monometallic and bimetallic catalysts for the bisamine bisphenolate system. The ratio of the incorporation levels with dinuclear vs mononuclear catalysts decreases with increasing comonomer size. This effect is attributed to steric pressure provided by the distal metal center on the larger olefin in dinuclear catalysts.
- Sampson, Jessica,Choi, Gyeongshin,Akhtar, Muhammed Naseem,Jaseer,Theravalappil, Rajesh,Al-Muallem, Hassan Ali,Agapie, Theodor
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supporting information
p. 1915 - 1928
(2017/06/13)
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- Bimetallic zirconium amine bis(phenolate) polymerization catalysts: Enhanced activity and tacticity control for polyolefin synthesis
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Binucleating multidentate amine bis(phenolate) ligands with rigid terphenyl backbones were designed to support two zirconium centers locked in close proximity. Polymerizations of propylene or 1-hexene with the synthesized bimetallic precatalysts resulted in polymers with significantly higher isotacticity (up to 79% mmmm) in comparison to the stereoirregular polymers produced with previously reported Cs-symmetric monometallic analogues. The bimetallic precatalysts also display higher activity (up to 124 kg of poly(1-hexene) (mmol of Zr)-1 h-1), in comparison to the monometallic analogues, and among the highest activities reported for nonmetallocene catalysts. The stereocontrol is consistent with a bimetallic mechanism involving remote steric interactions with the ligand sphere of the second metal center.
- Radlauer, Madalyn R.,Agapie, Theodor
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supporting information
p. 3247 - 3250
(2014/08/05)
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- Synthesis of benzyl-metal compounds
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Disclosed are methods of producing di-, tri- or tetrabenzyl-metal compounds comprising combining a metal salt with a (benzyl)nMgX2-n compound at from less than 30° C., wherein n is 1 or 2 and X is a monoanionic group; wherein the com
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Page/Page column 9; 11
(2008/06/13)
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- Carbon-oxygen and related R-X bond cleavages mediated by (silox)3Ti and other group 4 derivatives (silox = tBu3SiO)
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Halogen atom abstractions by (silox)3Ti (1) from CCl4, ClRh(PPh3)3, Br2 and I2 produced (silox)3TiCl (2), (silox)3TiBr (3) and (silox)3TiI (4), respectively. Treatment of 1 with MeI afforded a 1:1 mixture of 4 and (silox)3TiMe (5), regardless of [MeI], implicating a rough I abstraction rate constant of ka 5M-1 s-1. Exposure of 2 to NaI (THF) or MeMgBr (Et2O) provided independent syntheses of 4 and 5, respectively. Br abstraction by 1 from the radical clock H2C=CH(CH2)3CH2Br yielded 3 and (silox)3TiCH2(CH2)3CH=CH2 (6), according to 1H NMR spectroscopy, and trapping of 1 by hexenyl radical is roughly kt>2×107 M-1 s-1. A rationalization of the formation of (silox)3TiCH2CH2Ti(silox)3 (7) from 1 and C2H4 is presented. Na/Hg reduction of (silox)2TiCl2 (9) generated [(silox)2Ti]2(μ-Cl)2 (10) (μeff=0.75 μB/Ti at 300.6 K). Quenching of 10 with CCl4 and C6H4O2 produced 9 and [(silox)2TiCl]2-(μ:η1,η 1-p-OC6H4O) (11), respectively. Upon treatment of 10 with RC=CR (R=Et, Ph) or C2H4, disproportionation to 9 and (silox)2TiCR=CRCR=CR (R=Et (12); Ph (13)), also prepared via Na/Hg reduction of 9 in the presence of alkyne, or (silox)2TiCH2(CH2)2CH2 (14) occurred. According to 1H NMR spectroscopy, exposure of 12 to C2H4 gave 14, and 10 catalytically hydrogenated Me2C=CH2. Addition of THF to 1 yielded (silox)3TiOCH2(CH2)2CH 2Ti(silox)3 (17) via metallaradical ring-opening, while inclusion of ～ 10 equiv. of HSnPh3 provided a mixture of 17 and (silox)3Ti-OΠBu (19). Addition of PhCH2MgCl to (silox)3MCL (M=Ti (2); Zr (22)) and (silox)2TiCL2 (9) produced (silox)3MCH2Ph (M=Ti (21); Zr (23)) and (silox)2Ti(CH2Ph)2 (24), respectively, but (silox)2Zr(CH2Ph)2 (26) was synthesized from addition of (silox) H to Zr(CH2Ph)4. While 21 and 23 were photolytically inactive, photolysis of 24 in THF produced dibenzyl and [(silox)2TiOCH2(CH2)2CH 2]n (27, n=2 (tentative)), while related photolysis of 26 afforded [(silox)2ZrOCH2(CH2)2CH 2]2 (282,) and dibenzyl. Mass spectral analysis on dibenzyl derived from a 26:(silox)2Zr(CD2Ph)2 (26-d4) mixture showed that benzyl scrambling occurred. (Silox)2Zr(CH2-m-tolyl)2 (36) was prepared from Zr(CH2-m-tolyl)4 and H(silox). Crossover, i.e., detection of (silox)2Zr(CH2Ph)(CH2-m-tolyl) (38), occurred when a mixture of (silox)2Zr(CH2Ph)2 (26) and (silox)2Zr(CH2-m-tolyl)2 (36) was photolyzed, showing that benzyl scrambling, presumably via PhCH2, preceded THF scission. The mechanisms of THF ring-opening by 1 and, plausibly, (silox)2ZrCH2Ph (32), are discussed.
- Covert, Katharine J.,Mayol, Ana-Rita,Wolczanski, Peter T.
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p. 263 - 278
(2008/10/08)
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