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In this study, guaiacolate derivatives‐containing tetranuclear sodium catalysts were synthesized, and their catalytic activity in l‐lactide (LA) polymerization was evaluated. Using LBF‐Na (sodium complex bearing 2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranolate) as a catalyst, the polymerization of LA was studied in various solvents. LBF‐Na polymerized LA in dichloromethane, tetrahydrofuran, and toluene, and the catalytic activity of LBF‐Na was similar in these solvents. Among the sodium complexes, LOH‐Na (sodium complex bearing guaiacolate) exhibited higher catalytic activity (5 min, conversion = 93%; MnGPC = 7200) than the other tetranuclear sodium complexes. Furthermore, LOH‐Na exhibited an "immortal" property after 20 equivalents of benzyl alcohol loading during LA polymerization and good controllability in polylactide production. Thus, guaiacolate ligands increase the catalytic activity of sodium catalysts in LA polymerization in both coordinating and halogen‐containing solvents and under the condition of extra alcohol loading. [ABSTRACT FROM AUTHOR]

Carbodicarbene (CDC), unique carbenic entities bearing two lone pairs of electrons are well‐known for their strong Lewis basicity. We demonstrate herein, upon introducing a weak Brønsted acid benzyl alcohol (BnOH) as a co‐modulator, CDC is remolded into a Frustrated Lewis Pair (FLP)‐like reactivity. DFT calculation and experimental evidence show BnOH loosely interacting with the binding pocket of CDC via H‐bonding and π‐π stacking. Four distinct reactions in nature were deployed to demonstrate the viability of proof‐of‐concept as synergistic FLP/Modulator (CDC/BnOH), demonstrating enhanced catalytic reactivity in cyclotrimerization of isocyanate, polymerization process for L‐lactide (LA), methyl methacrylate (MMA) and dehydrosilylation of alcohols. Importantly, the catalytic reactivity of carbodicarbene is uniquely distinct from conventional NHC which relies on only single chemical feature of nucleophilicity. This finding also provides a new spin in diversifying FLP reactivity with co‐modulator or co‐catalyst. [ABSTRACT FROM AUTHOR]

A series of zinc complexes, [LXZnEt] (1–5) and [LXZn2(OAc)3] (6–9), associated with NNO‐tridentate Schiff base ligands (2‐(((2‐((cyclohexyl[methyl]amino)methyl)phenyl)imino)methyl)phenolate (CAP) derivatives), were synthesized, and their activity toward ring‐opening polymerization (ROP) of L‐lactide (LA) and the reaction of CO2 with cyclohexene oxide were also investigated. All of [LXZnEt] revealed excellent catalytic activity to ring‐opening polymerization (ROP) of LA in the presence of benzyl alcohol. Among them, [LHZnEt] (1) showed the highest activity with 82% conversation within 45 s. In contrast, [LXZn2(OAc)3] (6–9) were inactive in ROP of L‐lactide. In addition, all of these Zn complexes demonstrated moderate activity in the reaction of CO2 with cyclohexene oxide in the presence of Bu4NCl. [ABSTRACT FROM AUTHOR]

A series of five-membered ring aluminum complexes bearing thiol-Schiff base ligands were synthesized, and their application in the ring-opening polymerization of ε-caprolactone (CL) was investigated. The complexes exhibited dramatically higher catalytic activity than the six-membered ring S2AlMe2 complex (approximately 4- to 10-fold higher) and the five-membered ring L5-PhAlMe2 complex (approximately 7- to 19-fold higher). Moreover, a shorter induction period was observed when the five-membered ring aluminum complexes bearing thiol-Schiff base ligands were used compared with the other types of aluminum complexes bearing Schiff base ligands. The electron-withdrawing groups enhanced the catalytic activity of the Al complexes compared with the electron donating groups. The thiol-Schiff base ligand and the five-membered ring aluminum catalysis had a synergistic effect that was stronger than the combination of their individual effects. [ABSTRACT FROM AUTHOR]

A series of bidentate ligands were examined to improve the catalytic activity of l-lactide ( LA) polymerization by using n-butyl lithium and BnOH. For LA polymerization, n-butyl lithium with tetraisopropyl methylenebis(phosphonate) ( L8 ) showed the greatest catalytic activity but with poor controllability of the polymer molecular weight. The polydispersity indices ( PDIs) could be improved without BnOH addition, but Mn GPC was much different from the Mn Cal . 1H NMR spectra confirmed that the cyclized PLA was obtained, thus implying that active chain-end mechanisms were operative in LA polymerization. [ABSTRACT FROM AUTHOR]

A series of ligands were tested to meliorate the catalytic activity of ε-caprolactone (CL) and l-lactide (LA) polymerization by Sn(Oct) and BnOH. There are seven ligands (methyl 2-(dibenzylamino)acetate (MDBAA), di(1 H-pyrazol-1-yl)methane, benzanide, 8-aminoquinoline, 2-bromo-1-phenylethanone, 2,6-di- tert-butyl-4-methylphenol, and dipyridine) were found to be useful in increasing the polymerization rate for CL polymerization. For LA polymerization, there are only two ligands (8-aminoquinoline and p-thiocresol) effectively raised the polymerization rate. Moreover, the kinetic study reveals a first-order dependency on [CL] and second-order dependency on [LA], indicating different polymerization mechanisms in Sn(Oct) catalytic system. The mechanistic study also explains that MDBAA could potentially modify the framework of the catalytic intermediate and produce the hydrogen, thereby increasing the rate of CL polymerization. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

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 lactidehas been studied. The Ca complex with 2,2′-ethylidenebis(4,6-di-tert-butylphenol) (EDBP) as the ligand also has been synthesizedto compare with the BHT systems. All complexes, in the presence ofbenzyl alcohol as initiator, exhibit high activity for the ring-openingpolymerization of lactide. Polymerization activities follow the orderof Na ≫ Li > Ca ≫ Mg. Additionally, metal–BHTsystems are more efficient than metal–EDBP systems, and thissuperiority was pronounced in THF solution. Four model metal–BHTcomplexes with coordinated dimethoxyethane (DME) have been characterizedby single-crystal X-ray diffraction. These complexes exhibited a widevariation in the Cipso–O–metal angle (159.3°to 180.0°), and DFT calculations suggested that this flexibilityallows the metal to vary its electron density and thereby expeditethe catalytic cycle that requires both monomer activation and substratelability. [ABSTRACT FROM AUTHOR]

• Comparison study of CL polymerization by six-membered ring Al complexes. • Al complexes bearing aminophenolate ligands revealed the greatest catalytic activity. A series of 6-membered ring aluminum (Al) complexes bearing Schiff base, benzotriazole phenolate, aminophenolate, carboxamide phenolate, and carboxylate phenolate were synthesized, and their applications in ε-caprolactone (CL) polymerizations were studied. The decreasing catalytic rates for CL polymerization were ranked as follows: Al complexes bearing aminophenolate > benzotriazole phenolate > carboxylate phenolate > Schiff base > carboxamide phenolate. The Al complex bearing aminophenolate (LBu-prop) revealed an appreciably higher (10–100 fold) polymerization rate and a shorter induction period than the other 6-membered ring Al complexes in the CL polymerization. Further investigation of the steric effect in the phenolate ring of aminophenolate ligands demonstrated that Al complexes with the tert -butyl groups on 2,4 positions of the phenolate ring had the highest catalytic activity, followed by that of the cumyl groups, and it was also discovered that the hydrogen substituents were responsible for the largest decrease in the catalytic activity of Al complexes. The bulky substituents on the amino group increased the catalytic activity of associated Al complexes as well as the aminophenolate ligands with the third chelating atoms on the amino group. However, the aminophenolate ligands with the fourth chelating atoms on the amino group slightly decreased the catalytic activity. [ABSTRACT FROM AUTHOR]

A series of aluminum complexes bearing heterocyclic amine ligands were synthesized, and their application in ε -caprolactone (CL) and L -Lactide (LA) polymerization and copolymerization were studied. The CL polymerization results revealed that ligands containing the higher electronegativity atom increased the polymerization rate of CL polymerization. Among these Al complexes, NON-AlMe 3 bearing benzofurazan ligand was the best catalyst in CL polymerization ([ NON-AlMe 3 ] = 10 mM, conversion = 94% after 4 min at room temperature). In LA polymerization, the catalytic trend of Al complexes was random, and NCN-AlMe 3 bearing 1-benzylbenzimidazole ligand was the best catalyst ([ NCN-AlMe 3 ] = 10 mM, conversion = 90% after 45 min at 80 °C). The selectivity of the production of a PLA- gradual -PCL copolymer could be controlled by different Al complexes. Our study revealed that the four-coordinated trimethyl Al complexes bearing heterocyclic amine ligands were easily synthesized and constitute an ideal catalyst design in CL polymerization. Image 1 • NON-AlMe 3 was the best catalyst in CL polymerization. • NCN-AlMe 3 was the best catalyst in LA polymerization. • PLA- gradual -PCL copolymer could be controlled by different Al complexes. [ABSTRACT FROM AUTHOR]

• 5-membered ring Mg complexes had higher activity in lactide polymerization. • Mg complexes with thiophene groups revealed the highest catalytic activity. • BnOH approaches LA through the hydrogen bond with phenolate, and then initiates LA. A series of magnesium complexes bearing 2-(arylideneamino)phenolate (forming 5-membered ring Mg complexes) and 2-((arylimino)methyl)phenolate (forming 6-membered ring Mg complexes) ligands were synthesized, and their application in the ring-opening polymerization of L -lactide (LA) was investigated. The Mg complexes with 5-membered rings exhibit a higher polymerization rate and controllability for polylactide production than those with 6-membered rings do (one-fold to three-fold for LA polymerization). The density function theory calculation results revealed that benzyl alcohol approaches LA through the hydrogen bond with phenolate oxygen, and then initiates LA, with the proton transferring to phenolate oxygen to form the LA-OBn adduct. The LA-OBn adduct was activated using the proton present on phenolate oxygen to open the ring of the LA-OBn adduct. Moreover, the LA polymerization using L5ThioMg as a catalyst needs to overcome a 17.7 kcal/mol activation free energy that is lower than that of L6ThioMg (21.0 kcal/mol) [ABSTRACT FROM AUTHOR]

A series of pyridine and polypyridine-zinc complexes were synthesized, and their application in ε-caprolactone and l -lactide polymerization was studied. In ε-caprolactone polymerization, zinc complexes bearing 1,10-phenanthroline derivatives exhibited a higher polymerization rate than did diethyl zinc (2–10 times). In l -lactide polymerization, zinc complexes bearing 1,10-phenanthroline derivatives exhibited a considerably higher polymerization rate than did diethyl zinc (2–220 times). According to density functional theory results, the ortho -hydrogens of polypyridine ligand can co-activate the carbonyl group of monomers with zinc metal center to increase the catalytic activity of zinc catalysts. Image 1 • The polypyridne-zinc complexes were synthesized. • 1,10-Phenanthroline derivatives enhanced the catalytic activity of Zn complexes. • Hydrogens of polypyridine co-activate the carbonyl group of monomers. [ABSTRACT FROM AUTHOR]

The ring-opening polymerizations of ε-caprolactone (CL) using 5- and 6-membered ring Zn complexes bearing Schiff base as catalysts were comparatively studied. The 5-membered ring Zn complexes exhibited a considerably higher polymerization rate than the 6-membered ring Zn complexes (2–12 fold for CL polymerization) did. X-ray data revealed that 5-membered ring L 5-Ph 2 Zn creates larger empty space around the Zn center than 6-membered ring L 6-Bn 2 Zn. This allows higher interaction between the initiator and Zn complex and easy CL coordination. Image 1 • The 5-membered ring Zn complexes exhibited a considerably higher polymerization rate. • X5-membered ring L5-Ph 2 Zn creates larger empty space around the Zn center than 6-membered ring L6-Bn 2 Zn [ABSTRACT FROM AUTHOR]

Main-group metal-based catalysts have attracted considerable attentions due to their complementary reactivities to transition metals. In searching for the catalytic application of heavy divalent Group 14 derivatives, we came to discover that the benzannulated N -heterocyclic plumbylene (1) could serve as an effective catalyst for ring-opening polymerization of l -lactide (L- LA) at room temperature. In the presence of benzyl alcohol (BnOH), 97% conversion of L- LA was accomplished in 10 min under a catalyst loading of merely 0.3 mol% ([LA]:[1]:[BnOH] = 400:1.2:1.2, [1] = 1.2 mM). Compared to the polymeric plumbylene ([Pb(μ -O i Pr) 2 ∞), the excellent catalytic activity of 1 at ambient temperature may be ascribed to the steric and electronic stabilizations of the Pb2+ center by the organic backbone. Thus, thermal activation is no longer required to expose the Lewis acidic metal center for polymerization. Image 1 • N -Heterocyclic plumbylene is an efficient catalyst in ring-opening polymerization of l -lactide. • 97% conversion of L- LA was accomplished in 10 min under a catalyst loading of merely 0.3 mol%. • N -Heterocyclic plumbylene reveals outstanding controllability in l -lactide polymerization. [ABSTRACT FROM AUTHOR]