Efficient Catalysts For Ring-opening Polymerization Research Articles

An unprecedented cobalt(ii)-containing Wells–Dawson-type tungstovanadate-based metal–organic framework as an efficient catalyst for ring-opening polymerization of ε-caprolactone

An unprecedented organic–inorganic hybrid material based on Wells–Dawson-type tungstovanadate building blocks and cobalt(ii)–organic framework with a bis(triazole) ligand was prepared and employed to catalyze solvent-free ROP of caprolactone.

Titanium, zirconium and hafnium complexes bearing amino-benzotriazole phenolate ligands as efficient catalysts for ring-opening polymerization of lactides

Group 4 catalysts incorporated in 2-(2H-benzotriazol-2-yl)-4-methyl-6-(morpholinomethyl)phenolate ligand (C1MOBTP) were synthesized and structurally characterized. The reaction of Ti(OiPr)4 or M(OiPr)4(iPrOH) (M = Zr, Hf) with C1MOBTP-H (2.0 M equiv.) in toluene produced the hexa-coordinated bis-adduct metal complex [(C1MOBTP)2M(OiPr)2] (M = Ti for 1, Zr for 2 and Hf for 3). Experimental results indicate that hafnium complex 3 displayed the higher catalytic activity than those of di-C1MOBTP-featuring complexes 1 and 2 for the controlled L-LA polymerization. Hafnium alkoxide 3 catalyzes the ring-opening polymerization effectively not only in a “controlled” fashion but also an “immortal” manner, giving the corresponding polymers with the expected molecular weights and narrow molecular weight distributions.

HNTs/GO composite as efficient catalyst for ring-opening polymerization of ε-Caprolactone

ABSTRACTPolycaprolactone (PCL) has been widely applied based on the biocompatibility and biodegradability. It is important to investigate the safe and efficient catalyst system for ring-opening polymerization of monomer ε-caprolactone (ε-CL). In our work, Halloysite/Graphene Oxide (HNTs/GO) composite is successfully prepared by electrostatic self-assembly and used as an effective catalyst for the ring-opening polymerization of ε-CL. The structures, morphologies and thermal properties of the products are subsequently characterized. The results show that the synthesized PCL are semi-crystalline and observed to be lamellar, which depend on the template effects of HNTs/GO composite. The HNTs/GO composite serves as an effective catalyst and a reinforcing filler simultaneously to improve the thermal stability of the prepared PCL.

Titanium complexes bearing benzotriazole iminophenolate ligands as efficient catalysts for ring-opening polymerization of cyclic esters

Titanium catalysts incorporated by imino-benzotriazole phenolate (IBTP) ligands (C1NNIBTP, C1FuIBTP and C1NOIBTP) were synthesized and structurally characterized. The reaction of Ti(OiPr)4 with C1NNIBTP-H (1.0 molar equiv.) in toluene produced hexa-coordinated mono-adduct titanium complex [(C1NNIBTP)Ti(OiPr)3] (1). However, six-coordinated bis-adduct Ti complex [(C1FuIBTP)2Ti(OiPr)2] (2) or [(C1NOIBTP)2Ti(OiPr)2] (3) resulted from treatment of Ti(OiPr)4 with C1FuIBTP-H or C1NOIBTP-H in CH2Cl2 using a Ti to ligand precursor ratio of 1:2. Catalytic studies for ring-opening polymerization of ε-caprolactone (ε-CL) or L-lactide utilizing complex 1 were detailedly investigated. Titanium complex 1 was shown to effectively catalyze the ε-CL polymerization not only in a “controlled” fashion but also an “immortal” manner, giving narrowly dispersed polymers having the expected molecular weights.

Developments in the use of rare earth metal complexes as efficient catalysts for ring-opening polymerization of cyclic esters used in biomedical applications

AbstractBiodegradable polymers represent a class of particularly useful materials for many biomedical and pharmaceutical applications. Among these types of polyesters, poly(ε-caprolactone) and polylactides are considered very promising for controlled drug delivery devices. These polymers are mainly produced by ring-opening polymerization of their respective cyclic esters, since this method allows a strict control of the molecular parameters (molecular weight and distribution) of the obtained polymers. The most widely used catalysts for ring-opening polymerization of cyclic esters are tin- and aluminium-based organometalliccomplexes; however since the contamination of the aliphatic polyesters by potentially toxic metallic residues is particularly of concern for biomedical applications, the possibility of replacing organometallic initiators by novel less toxic or more efficient organometallic complexes has been intensively studied. Thus, in the recent years, the use of highly reactive rare earth initiators/catalysts leading to lower polymer contamination has been developed. The use of rare earth complexes is considered a valuable strategy to decrease the polyester contamination by metallic residues and represents an attractive alternative to traditional organometallic complexes.

Synthesis, characterisation, and X-ray structures of Zn(II) complexes containing bis-camphoryldiimine ligands: Application to polymerisation of rac-lactide

Novel Zn(II) complexes, (N1E,N2E)-N1,N2-bis(1,7,7-trimethylbicyclo [2.2.1]heptan-2-ylidene)butane-1,2-diamine (BCE) ZnCl2 and (N1E,N3E)-2,2-dimethyl-N1,N3-bis(1,7,7-trimethylbicyclo [2.2.1]heptan-2-ylidene)pentane-1,3-diamine (BCP) ZnCl2, were synthesised. X-ray diffraction analysis revealed that the geometry around the Zn(II) centre is distorted tetrahedral. The alkoxy derivatives, generated in situ, were highly efficient catalysts for ring-opening polymerisation (ROP) of rac-lactide (rac-LA), yielding polylactide (PLA) with good number-average molecular weights and narrow polydispersity indices. (BCP)Zn(OCHMe2)2 exhibited activity for stereoselective ROP of rac-LA, and complete conversion occurred within 8min to attain heterotactic PLA (Pr=0.78).

Aluminum alkyl complexes: synthesis, structure, and application in ROP of cyclic esters

Aluminum alkyl complexes have very useful applications as catalysts or reagents in small molecule transformations and as cocatalysts in olefin polymerization. This short review focuses on some recent developments in the design, synthesis and structure of aluminum(iii) alkyl complexes supported by various ligands bearing nitrogen, oxygen, sulfur or phosphorus atoms, and their catalytic applications in the ring-opening polymerization (ROP) of cyclic esters. The coordination chemistry of the Al metal centre and the catalytic activity changes of the complexes caused by ligand modifications are also discussed.

Palygorskite as Efficient Catalyst for Ring-Opening Polymerization of ϵ-Caprolactone

Fiber-like high-surface-area and natural nanostructure clay mineral palygorskite (or attapulgite, ATP) containing lots of hydroxyl groups is found to efficiently catalyze the ring-opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL). The products are subsequently characterized by FTIR, 1H NMR, GPC, DSC, SEM and XPS analysis. The results show that porous PCL with relatively high molecular weight is obtained. A mechanism is proposed to illustrate that ϵ-CL is initiated by the constituent water in ATP and catalyzed by three active centers relate to hydroxyl groups on the surface of ATP. The ATP acts as a proton shuttle via its acidic hydrogen atoms and basic oxygen atoms. Moreover, there exists synergetic catalytic effect between the metal centers and Si centers.

Synthesis and characterization of calcium complexes: Efficient catalyst for ring-opening polymerization of L-lactide

Four calcium complexes coordinated with N,N,O-tridentated pyrazolonate (1–2) or Schiff base (3–4) ligands have been prepared. These reactions can be monitored by 1H NMR spectroscopic studies with the chemical shift from 2.20 to 2.36 ppm for 1, and 2.22 to 2.28 ppm for 2 for the NMe2 group and the proton peak of the imino group shifted from 8.23 ppm to 7.95 ppm for 3, and 8.52 ppm to 8.14 ppm for 4. Single crystal X-ray studies reveal that complex 1 bears a mononuclear feature with a hexa-coordinated calcium metal center bonded to two NNO-tridentate ligands. Variable temperature dependent 1H NMR spectroscopic studies of 3 indicate that the nitrogen atom of NMe2 group dissociates slowly in solution ranging from − 20 to 80 °C. In the presence of alcohol, all of these complexes show good catalytic activity toward ring-opening polymerization of L-lactide in a well-controlled manner, yielding polymers with expected molecular weights and narrow polydispersity indexes. The activity of these complexes is affected by the basicity of donor atoms.

Anilido-imine zinc complexes: Efficient catalysts for ring-opening polymerization of L-lactide

A series of anilido-imine zinc complexes ortho-C6H4(CH=NAr)(NAr)ZnEt[Ar=2,6-Me2C6H3(2a); Ar=2,6-Et2C6H3(2b)] was synthesized, characterized and used as catalysts for the ring-opening polymerization of L-lactide in the presence of benzyl alcohol. The effects of the structures of catalysts and reaction conditions on the reactivity were investigated. The polymerization of L-lactide initiated by each of these complexes was found to take place with a controlled manner.

Facile Synthesis of Well-Defined Titanium Alkoxides Based on Benzotriazole Phenoxide Ligands: Efficient Catalysts for Ring-Opening Polymerization of Cyclic Esters

New titanium alkoxide complexes incorporated by mono- or bis-BTP ligands (BTP = N,O-bidentate benzotriazole phenoxide) were synthesized and structurally characterized. The reaction of 2-(2H-benzotriazol-2-yl)-4-(2,4,4-trimethylpentan-2-yl)phenol (C8BTP-H) with Ti(OiPr)4 (1.0 mol equiv) in hexane produced the monoadduct complex [(μ-C8BTP)Ti(OiPr)3]2 (1), but treatment of Ti(OiPr)4 with 2.0 mol equiv of C8BTP-H at 50 °C gave the bis-adduct titanium complex [(C8BTP)2Ti(OiPr)2](2). The monomeric titanium analogue ([(t-BuBTP)2Ti(OiPr)2] (3), [(TMClBTP)2Ti(OiPr)2] (4)) was prepared by employing sterically bulky 2-(2H-benzotriazol-2-yl)-4,6-di-tert-butylphenol (t-BuBTP-H) or 2-tert-butyl-6-(5-chloro-2H-benzotriazol-2-yl)-4-methylphenol (TMClBTP-H) as the ligand according to the same synthetic route with a ligand to metal precursor ratio of 2:1. X-ray diffraction of single crystals indicates that 1 displays a dimeric Ti(IV) complex containing a Ti2O2 core bridging through one of the aryloxy oxygen atoms and the geometry around each Ti atom is distorted from an octahedral environment. Catalysis for lactone polymerizations of BTP-containing Ti complexes was investigated. Experimental results demonstrated that complex 1 is an active catalyst for the ring-opening polymerization of ε-caprolactone (ε-CL) and l-lactide (l-LA) with “living” and “immortal” characters. Kinetic studies of ε-CL polymerization initiated by 1 were investigated using in situ 1H NMR spectroscopy; the polymerization exhibited first-order dependence on both complex 1 and ε-CL concentrations.

Synthesis and structural characterization of aluminum complexes supported by NNO-tridentate ketiminate ligands: Efficient catalysts for ring-opening polymerization of l-lactide

Abstract Four NNO-tridentate ketiminate derivatives (HL-H, FL-H, OMeL-H and tBuL-H) were prepared through the condensation reaction of 1-(4-chlorophenyl)-4-(4-X-benzoyl)-3-methyl-1H-pyrazol-5(4H)-one (X = H, F, OMe, tBu) with N,N-dimethylenediamine (1.1 molar equiv) under reflux condition. Further reaction of AlMe3 (1.2 molar equiv) with HL-H, FL-H, OMeL-H and tBuL-H, respectively, affords penta-coordinated mono-adduct aluminum complexes [(HL)AlMe2] (1), [(FL)AlMe2] (2), [(OMeL)AlMe2] (3), and [(tBuL)AlMe2] (4) in high yield. Experimental results indicate complexes 1–4 are active catalysts for ring-opening polymerization of l -lactide ( l -LA) in the presence of benzyl alcohol (BnOH). Al complex 2 catalyzes efficiently not only in a “living” fashion but also an “immortal” manner, giving polymers with the expected molecular weights and narrow PDIs.

Efficient catalysts for ring-opening polymerization of ε-caprolactone and β-butyrolactone: Synthesis and characterization of zinc complexes based on benzotriazole phenoxide ligands

A series of efficient zinc catalysts supported by sterically bulky benzotriazole phenoxide (BTP) ligands are synthesized and structurally characterized. The reactions of diethyl zinc (ZnEt2) with CMe2PhBTP-H, t-BuBTP-H, and TMClBTP-H yield monoadduct [(μ-BTP)ZnEt]2 (1–3), respectively. Bisadduct complex [(t-BuBTP)2Zn] (4) results from treatment of ZnEt2 with t-BuBTP-H (2 equiv.) in toluene, but treatment of TMClBTP-H with ZnEt2 in the same stoichiometric proportion in Et2O produces five-coordinated monomeric complex [(TMClBTP)2Zn(Et2O)] (5). The molecular structures of compounds 1, 4, and 5 are characterized by X-ray crystal structure determinations. All complexes 1–5 are efficient catalysts for the ring-opening polymerization of ε-caprolactone (ε-CL) in the presence of 9-anthracenemethanol. Experimental results indicate that complex 3 exhibits the greatest activity with well-controlled character among these complexes. The polymerizations of ε-CL and β-butyrolactone catalyzed by 3 are demonstrated in a “living” character with narrow polydispersity indices (monomer-to-initiator ratio in the range of 25–200, PDIs ≤ 1.10). The “immortal” character of 3 provides a way to synthesize as much as 16-fold polymer chains of poly(ε-CL) (PCL) with narrow PDI in the presence of a catalyst in a small proportion. The controlled fashion of complex 3 also enabled preparation of the PCL-b-poly(3-hydroxybutyrate) copolymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis and structural characterization of zinc complexes supported by amino-benzotriazole phenoxide ligands: Efficient catalysts for ring-opening polymerization of ε-caprolactone and β-butyrolactone

Two amino-benzotriazole phenol ligands, 2-(2H-benzotriazol-2-yl)-6-((diethylamino)methyl)-4-alkyl-phenol (alkyl = CH3, C1DEABTP-H, and alkyl = C8H17, C8DEABTP-H) were prepared through the Mannich condensation of 4-alkyl-2-(2H-benzotriazol-2-yl)phenol with the mixtures of excess paraformaldehyde and diethylamine under reflux conditions. Zinc complexes supported by amino-benzotriazole phenoxide ligands (C1DEABTP− and C8DEABTP−) were synthesized and fully characterized. The reaction of ZnEt2 with DEABTP-H (1 equiv.) produces the tetra-coordinated dimeric zinc complexes [(μ-C1DEABTP)ZnEt]2 (1) and [(μ-C8DEABTP)ZnEt]2 (2). Experimental results indicate that complex 1 catalyzes the ring-opening polymerization of ε-caprolactone and β-butyrolactone with good catalytic activities in a controlled character.

Synthesis, structural characterization and reactivity of aluminium complexes supported by benzotriazole phenoxide ligands: air-stable alumoxane as an efficient catalyst for ring-opening polymerization of l-lactide

Aluminium complexes bearing sterically bulky benzotriazole-phenoxide ligands are synthesized and characterized structurally. The reaction of 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol ((CMe2Ph)BTP-H) or 2-(2H-benzotriazol-2-yl)-4,6-di-tert-butylphenol ((t-Bu)BTP-H) with AlMe(3) (1.2 molar equiv.) in toluene yields [((CMe2Ph)BTP)AlMe(2)] (1) or [((t-Bu)BTP)AlMe(2)] (2) as a four-coordinated monomeric aluminium complex. Compound 1 reacts further with (CMe2Ph)BTP-H in a stoichiometric proportion, affording penta-coordinated monomeric aluminium methyl complex [((CMe2Ph)BTP)(2)AlMe] (3). Complex 3 is also obtained directly upon treatment of AlMe(3) with (CMe2Ph)BTP-H (two molar equiv.) in refluxing toluene in high yield. In the presence of H(2)O (half a molar equiv.), hydrolysis of 3 in a mixed solvent of THF and toluene at ambient temperature affords [{((CMe2Ph)BTP)(2)Al}(2)(μ-O)] (4), in which the oxo ligand acts as a chelating group linearly bridging two aluminium centers. Air-stable alumoxane 4 is an efficient catalyst for the ring-opening polymerization of L-lactide (L-LA) in the presence of 9-anthracenemethanol (9-AnOH). Complex 4 catalyzes the polymerization of L-LA in a controlled manner, yielding PLLAs with the expected molecular weights and narrow polydispersity indices (PDIs).

Ｎ‐ヘテロ環状カルベン化学の新展開：高分子合成への応用

N-Heterocyclic carbene (NHC) has been widely used as a ligand for transition metal complexes and as an organocatalyst. Herein, the recent progress of synthetic polymer chemistry made by NHC is briefly reviewed. NHC serves as an efficient catalyst for ring-opening polymerization of cyclic esters and group transfer polymerization of (meth)acrylates. Living polymerization of ethylene oxide proceeds by NHC initiator. New polymeric materials such as dynamic covalent polymers and main chain organometallic polymers can be prepared from difunctional NHC.

Synthesis and Structural Studies of Heterobimetallic Alkoxide Complexes Supported by Bis(phenolate) Ligands: Efficient Catalysts for Ring-Opening Polymerization of l-Lactide

A series of heterobimetallic titanium(IV) complexes [LTi(O(i)Pr)(mu-O(i)Pr)(2)Li(THF)(2)], [LTi(O(i)Pr)(mu-O(i)Pr)(2)Na(THF)(2)], [LTi(mu-O(i)Pr)(2)Zn(O(i)Pr)(2)], and [LTi(mu-O(i)Pr)(2)Mg(O(i)Pr)(2)] (where L = bidentate bisphenol ligands) have been synthesized and characterized including a structural determination of [L(1)Ti(mu(2)-O(i)Pr)(2)(O(i)Pr)Li(THF)(2)] (1a). These complexes were investigated for their utility in the ring-opening polymerization (ROP) of l-lactide (LA). Polymerization activities have been shown to correlate with the electronic properties of the substituent within the bisphenol ligand. In contrast to monometallic titanium initiator 1e, all the heterobimetallic titanium initiators (Ti-Li, Ti-Na, Ti-Zn, and Ti-Mg) show enhanced catalytic activity toward ring-opening polymerization (ROP) of l-LA. In addition, the use of electron-donating methoxy or methylphenylsulfonyl functional ligands reveals the highest activity. The bisphenol bimetallic complexes give rise to controlled ring-opening polymerization, as shown by the linear relationship between the percentage conversion and the number-average molecular weight. The polymerization kinetics using 2c as an initiator were also studied, and the experimental results indicate that the reaction rate is first-order with respect to both monomer and catalyst concentration with a polymerization rate constant, k = 81.64 M(-1) min(-1).

Heterobimetallic aluminium and zinc complex with N-arylanilido-imine ligand: Synthesis, structure and catalytic property for ring-opening polymerization of ε-caprolactone

Treatment of a N-arylanilido-imine ligand [ ortho-C 6H 4(NHAr)CH N] 2CH 2CH 2 (Ar = 2,6-Me 2C 6H 3) ( LH 2) with one equiv. of AlMe 3 affords a monometallic complex [C 6H 4(NHAr)–CH N)]CH 2CH 2(C 6H 4(NAr)CH NAlMe 2) ( 1). The monometallic complex 1 reacts with one equiv. of ZnEt 2 to give a heterobimetallic complex [C 6H 4(NAr)–CH NZnEt]CH 2CH 2[C 6H 4(NAr)–CH NAlMe 2] ( 2). Both complexes were characterized by 1H and 13C NMR spectroscopy and elemental analyses, and the molecular structures of 1 and 2 were determined by X-ray diffraction analysis. The complexes 1 and 2 both are efficient catalysts for ring-opening polymerization of ε-caprolactone in the presence of benzyl alcohol yielding polymers with narrow polydispersity values and complex 2 initiates the polymerization in a controllable manner.

Undecyltin Trichloride Grafted onto Cross-Linked Polystyrene: An Efficient Catalyst for Ring-Opening Polymerization of ϵ-Caprolactone

The activity, recyclability, and chemical stability as a catalyst of undecyltin trichloride grafted to cross-linked polystyrene, [P-H](1−t)[P-(CH2)11-SnCl3]t, with [P-H] the monomeric unit of the nonfunctionalized polymer and t the organotin-functionalized monomer fraction, are assessed in the ring-opening polymerization (ROP) of ϵ-caprolactone. Quantitative conversion is obtained within 2 h under conditions in which conversion is by far incomplete for two other organotin grafts, [P-H](1−t)[P-(CH2)11-SnBuCl2]t and [P-H](1−t){[P-(CH2)11-SnBuCl]2O}t/2. Even after 15 min of reaction, conversions of at least 70% are achieved for the grafted tin trichloride. The catalytic reactions of the grafted undecyltin trichloride, more particularly its chemical integrity and recycling ability, are monitored, in situ, at the solid–liquid interface, using high-resolution magic angle spinning (HR-MAS) 1H and 119Sn NMR. Residual tin contents in the reaction products were assessed by inductively coupled plasma/atomic emission...

Bimetallic anilido-aldimine Al or Zn complexes for efficient ring-opening polymerization of ε-caprolactone

Four bimetallic Al or Zn complexes supported by anilido-aldimine ligands (o-C6H4(NHAr)-CH=N)2CH2CH2 (Ar = 2,6-Me2C6H3,L1H2; Ar = 2,6-iPr2C6H3, L2H2) have been synthesized and characterized. Treatment of L1H2 or L2H2 with two equiv. of AlMe3 gives bimetallic complex L1(AlMe2)2 1 or L2 (AlMe2)2 2, respectively. Reaction of L1H2 or L2H2 with two equiv. of ZnEt2 leads to bimetallic complex L1(ZnEt)2 3 or L2(ZnEt)2 4, respectively. All of the complexes 1-4 are efficient catalysts for ring-opening polymerization of epsilon-caprolactone (CL) in the presence of benzyl alcohol and catalyze the polymerization of CL in living fashion yielding polymers with a narrow polydispersity index. The activity of bimetallic Zn complexes 3 and 4 is higher than bimetallic Al complexes 1 and 2.