Air‐stable copper derivatives as efficient catalysts for controlled lactide polymerization: Facile synthesis and characterization of well‐defined benzotriazole phenoxide copper complexes

Abstract

Air‐stable copper catalysts supported by bis‐BTP ligands (BTP = N,O‐bidentate benzotriazole phenoxide) were synthesized and structurally characterized. The reactions of Cu(OAc)2·H2O with 2.0 molar equivalents of sterically bulky 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐bis(1‐methyl‐1‐phenylethyl)phenol (CMe2PhBTP‐H) and 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐di‐tert‐butylphenol (t‐BuBTP‐H) in refluxing ethanol solution afforded monomeric copper complexes [(CMe2PhBTP)2Cu] (1) and [(t‐BuBTP)2Cu] (2), respectively. The four‐coordinated copper analogue [(TMClBTP)2Cu] (3) resulted from treatment of 2‐tert‐butyl‐6‐(5‐chloro‐2H‐benzotriazol‐2‐yl)‐4‐methylphenol (TMClBTP‐H) as the ligand under the same synthetic method with ligand to metal precursor ratio of 2:1, but treatment of complex 3 in acetone gave five‐coordinated monomeric complex [(TMClBTP)2Cu(Me2CO)] (4). X‐ray diffraction of single crystals indicates that Cu complex 4 assumes a distorted square pyramidal geometry, penta‐coordinated by two BTP ligands, and one Me2CO molecule. Catalysis for lactide (LA) polymerization of BTP‐containing Cu complexes in the presence of various alcohol initiators was investigated. Complex 3 initiated by 9‐anthracenemethanol catalyzes the ring‐opening polymerization effectively not only in a “living” fashion but also in an “immortal” manner, yielding polymers with the predictable molecular weights and narrow molecular weight distributions. Initiations from multifunctional alcohols were able to produce PLLAs with two‐arm linear and three‐arm star‐shaped molecular architectures. The controlled character of Cu complex 3 also enabled us to synthesize the PEG‐b‐PLLA copolymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3840–3849

Di‐nuclear zinc complexes containing tridentate imino‐benzotriazole phenolate derivatives as efficient catalysts for ring‐opening polymerization of cyclic esters and copolymerization of phthalic anhydride with cyclohexene oxide

“…1 H NMR spectrum of PLLA‐25 (Fig. S8, SI) indicates that the yielded polymer contains one 9‐anthracenemethyl ester and one hydroxyl moiety as the chain end, which is similar to that found in the earlier literatures . (b) We also investigated the stereoselective polymerization of rac ‐lactide catalyzed by 1 to understand the microstructure of the isolated PLA.…”

“…The latter Zn alkoxides were proven to be excellent initiators toward the controlled polymerization of lactide (LA), and their catalytic performances are dramatically affected by the electronic effect of these NNO‐tridentate Schiff‐base ligands. Most recently, our group and others have investigated the synthesis and catalysis of well‐characterized aluminum, copper, zinc, and group 4 metal complexes originated from benzotriazole phenolate ( BTP ) derivatives; Zn complexes were demonstrated to catalyze ROP of lactones with the good catalytic activity in a controlled manner.…”

Synthesis, structures, and catalytic efficiency in ring opening polymerization of rac-lactide with tridentate vs. bidentate cobalt(ii), zinc(ii), and cadmium(ii) complexes containing N-substituted N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amine ligands

“…5,6 Well-dened PLAs with controlled physical and mechanical properties have been employed in a vast range of applications, including packaging, medical implants, tissue engineering, and pharmacology. [7][8][9][10] In the recent past, numerous metal complexes, including complexes of Al, [11][12][13][14][15] Zn, 16,17 Ga, 18 In, 19 Cu, 20,21 Co, 22,23 and trivalent rare earths, 24 have been utilized as catalysts for the ring-opening polymerization (ROP) of lactide (LA); notably, such catalysts afforded excellent control over reaction initiation and propagation, as well as the stereochemical arrangement of the polymer chains. 25 The architecture of the ligand coordinating the metal center is one of the key factors determining the catalyst's ability to control the stereochemistry and properties of the resultant polymer, 26,27 alongside the identity of the metal center and the temperature at which the polymerization reaction is conducted.…”

Zn(II) and Cu(II) unsymmetrical formamidine complexes as effective initiators for ring‐opening polymerization of cyclic esters

“…Nevertheless, some tin compounds have appreciable cytotoxicity and are susceptible to atmospheric conditions which increase the production expenses . In this regard, research is now exploring the use of other organometallic compounds with lower toxicity such as alkali metals, magnesium, calcium, zinc, copper, iron, and aluminum all of which have shown promising results.…”