- Synthesis and characterization of rare-earth metal complexes supported by a new pentadentate Schiff base and their application in heteroselective polymerization of rac-lactide
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A series of neutral rare-earth metal aryloxides and amides supported by a new pentadentate (N2O3) salen ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of rac-lactide (rac-LA) were explored. The protolysis reactions of N,N′-bis(3,5-di-tert-butylsalicylidene)-2,2′-diaminodiphenyl ether (LH2) with (ArO)3Ln(THF) (ArO = 2,6-But2-4-MeC6H2O) and Ln[N(SiMe3)2]3 in a 1:1 molar ratio in THF gave the neutral rare-earth metal aryloxides LLn(OAr)(THF)n [n = 0, Ln = Sc (1), Yb (2); n = 1, Ln = Y (3), Sm (4) and Nd (5)] and rare-earth metal amides LLnN(SiMe3)2 [Ln = Yb (6), Y (7)], respectively. X-ray structural determination showed that complexes 1, 2, 6 and 7 have monomeric structures, in which the coordination geometry around the rare-earth metal atom can be best described as a distorted trigonal prism. Complexes 3 and 5 are THF-solvated monomers and each of the rare-earth metal atoms is seven-coordinated to form a distorted capped trigonal prism. It was found that all of these complexes can efficiently initiate the ring-opening polymerization (ROP) of rac-LA to give heterotactic-rich polylactides (PLAs). The highly heterotactic PLA (Pr up to 0.93) was obtained using complex 2 as the initiator at a polymerization temperature of 0 °C. The observed increasing order of activity of 1 2 3 4 ≈ 5 is in agreement with the order of their ionic radii, whereas the order of stereoselectivity is in the reverse order. The rare-earth metal salen amides can initiate rac-LA polymerization in a controlled manner, while polymerization using the rare-earth metal salen aryloxides is less controlled at room temperature.
- Cui, Yu,Gu, Weikai,Wang, Yaorong,Zhao, Bei,Yao, Yingming,Shen, Qi
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- Vanadium(III) phenoxyimine complexes for ethylene or ε-caprolactone polymerization: Mononuclear versus binuclear pre-catalysts
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The mononuclear {[C6H4NCH(ArO)]2VCl(THF)} (Ar = 2,4-t-Bu2C6H2 (1), Ar = C 6H4 (2)), {O[C6H4NCH(ArO)] 2}VCl(THF) (Ar = 2,4-t-Bu2C6H2 (3), Ar = C6H4 (4)) and the binuclear vanadium(iii) complexes {[C6H4NCH(ArO)]VCl2(THF)2} 2(μ-CH2CH2) (Ar = 2,4-t-Bu2C 6H2 (5), Ar = C6H4 (6)), have been synthesized and fully characterized. The compounds [C6H 5NCH(ArO)]VCl2(THF)2 (Ar = 2,4-t-Bu 2C6H2 (7), Ar = C6H4 (8)), [2,4,6-Me3-C6H2NCH(ArO)]VCl2 (Ar = 2,4-t-Bu2C6H2 (9), Ar = C 6H4 (10)) and [2,6-i-Pr2-C6H 3NCH(ArO)]VCl2(THF)2 (Ar = 2,4-t-Bu 2C6H2 (11), Ar = C6H4 (12)), {μ-CH2CH2[NCH(C6H4O)] 2VCl(THF)} (14) and {C6H4[NCH(C 6H4O)]2VCl(THF)} (15) were synthesized for comparative polymerization studies. The dizwitterionic compound [2,6-i-Pr 2-C6H3N+(H)CH(C6H 4O)]2VCl2O (13) was also isolated, and presumably formed via a fortuitous hydrolysis reaction. The complexes 2, 5 and 13 have been structurally characterized; the molecular structure of the parent ligand (L5) in 5 is also reported. All complexes have been screened for ethylene as well as ε-caprolactone polymerization, and results are compared against those for known related mono- and bi-nuclear counterparts to evaluate for possible cooperative effects. The compounds 10 and 12 have been supported on modified SiO2, analysed by XPS and subjected to homo-polymerization (ethylene) and co-polymerization (1-hexene and ethylene) studies. The Royal Society of Chemistry 2013.
- Clowes, Lucy,Walton, Mark,Redshaw, Carl,Chao, Yimin,Walton, Alex,Elo, Pertti,Sumerin, Victor,Hughes, David L.
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p. 152 - 160
(2013/04/10)
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