67825-24-5Relevant articles and documents
Mono-BHT heteroleptic magnesium complexes: Synthesis, molecular structure and catalytic behavior in the ring-opening polymerization of cyclic esters
Nifant'Ev,Shlyakhtin,Bagrov,Minyaev,Churakov,Karchevsky,Birin,Ivchenko
, p. 12132 - 12146 (2017)
Numerous heteroleptic 2,6-di-tert-butyl-4-methylphenolate (BHT) magnesium complexes have been synthesized by treatment of (BHT)MgBu(THF)2 with various alcohols. Molecular structures of the complexes have been determined by X-ray diffraction. The magnesium coordination number in [(BHT)Mg(μ-OBn)(THF)]2 (3) and [(BHT)Mg(μ-O-tert-BuC6H4)(THF)]2 (4) is equal to 4. Complexes formed from esters of glycolic and lactic acids, [(BHT)Mg(μ-OCH2COOEt)(THF)]2 (5) and [(BHT)Mg(μ-OCH(CH3)COOCH2COOtBu)(THF)]2 (6) contain chelate fragments with pentacoordinated magnesium. Compounds 3-6 contain THF molecules coordinated to magnesium atoms. Complex {(BHT)Mg[μ-O(CH2)3CON(CH3)2]}2 (7) does not demonstrate any tendency to form an adduct with THF. It has been experimentally determined that complexes 3 and 5 are highly active catalysts of lactide polymerization. The activity of 4 is rather low, and complex 7 demonstrates moderate productivity. According to DOSY NMR experiments, compounds 3 and 5 retain their dimeric structures even in THF. The free energies of model dimeric [(DBP)Mg(μ-OMe)(Sub)]2 and monomeric (DBP)Mg(OMe)(Sub)2 products on treatment of [(DBP)Mg(μ-OMe)(THF)]2 with a series of σ-electron donors (Sub) have been estimated by DFT calculations. These results demonstrate that the substitution of THF by Sub in a dimeric molecule is an energetically allowed process, whereas the dissociation of dimers is energetically unfavorable. DFT modeling of ?-CL and (dl)-lactide ROP catalyzed by dimeric and monomeric complexes showed that a cooperative effect of two magnesium atoms occurs within the ROP for binuclear catalytic species. A comparison of the reaction profiles for ROP catalyzed by binuclear and mononuclear species allowed us to conclude that the binuclear mechanism is favorable in early stages of ROP initiated by dimers 3 and 5.
Comparative Study of lactide polymerization with lithium, sodium, magnesium, and calcium complexes of BHT
Chen, Hsuan-Ying,Mialon, Laurent,Abboud, Khalil A.,Miller, Stephen A.
, p. 5252 - 5261,10 (2020/08/31)
A series of Li, Na, Mg, and Ca complexes with 2,6-di-tert-butyl-4- methylphenol (BHT) as the ligand has been synthesized, and their reactivity for the ring-opening polymerization of lactide has been studied. The Ca complex with 2,2′-ethylidenebis(4,6-di-tert-butylphenol) (EDBP) as the ligand also has been synthesized to compare with the BHT systems. All complexes, in the presence of benzyl alcohol as initiator, exhibit high activity for the ring-opening polymerization of lactide. Polymerization activities follow the order of Na ? Li > Ca ? Mg. Additionally, metal-BHT systems are more efficient than metal-EDBP systems, and this superiority was pronounced in THF solution. Four model metal-BHT complexes with coordinated dimethoxyethane (DME) have been characterized by single-crystal X-ray diffraction. These complexes exhibited a wide variation in the Cipso-O-metal angle (159.3° to 180.0°), and DFT calculations suggested that this flexibility allows the metal to vary its electron density and thereby expedite the catalytic cycle that requires both monomer activation and substrate lability.
