Activity For Ring-opening Polymerization Research Articles

Synthesis, characterisation and X-ray structure of Cu(II) and Zn(II) complexes bearing N,N-dimethylethylenamine-camphorylimine ligands: Application in the polymerisation of rac-lactide

We have synthesised the novel Cu(II) and Zn(II) complexes (CDM)CuCl2 and (CDM)ZnCl2, where CDM is (E)-N1,N1-dimethyl-N2-(1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)ethane-1,2-diamine. X-ray diffraction analysis revealed that the geometry around the Zn(II) centre can be best described as a distorted tetrahedron. In the Cu(II) complex, the bulk of camphor ligand suppresses the square planar geometry; the complex thus has a highly distorted square planar and distorted tetrahedral geometry. Alkoxy derivatives generated in situ proved to be highly efficient catalysts for the ring-opening polymerisation (ROP) of rac-lactide (rac-LA), yielding polylactide (PLA) with narrow polydispersity indexes (PDIs). (CDM)Cu(OCHMe2)2 exhibited a high activity for stereoselective ROP of rac-LA, with complete conversion within 2min, producing heterotactic-enriched PLA (Pr=0.85).

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).

An unprecedented Zn10O4 heteroadamantane cage containing anilido-pyridinate ligand and its activity for ring opening polymerization of l-lactide and ε-caprolactone.

(NPyC2OMe)8Zn10Et4(μ4-O)4 (1) has been synthesized in situ by hydrolysis of ZnEt2 in a one pot process and it was proved by applying X-ray structure analysis that the organozinc anilido-pyridinate moiety encapsulated the zinc oxide cluster, which demonstrated one self-assembled coordinate mode "Zn10O4". Moreover, the catalytic activity was investigated and good activity for l-lactide and ε-caprolactone ring opening polymerization was observed with both living and controllable properties.

Synthesis and crystal structures of antimony(III) and tin(IV) compounds with an amino-amido-silane ligand

Aminosilane bearing bulky substituents on nitrogen, LH2 (L=(NAr)2SiPh2, Ar=2,6-iPr2C6H3) was reacted with n-BuLi (ratio 1:1) in toluene with a small amount of tetrahydrofuran resulting in [η1-Ph2Si(NHAr)ArNLi·2C4H8O] (1). Compound 1 was used to synthesize unusual monodentate complexes [(η1-Ph2SiNHAr)ArNSbCl2] (2) and [(η1-Ph2SiNHAr)ArNSnMe3] (3) by reacting with SbCl3 and Me3 SnCl, respectively. The three new compounds were characterized by elemental analysis, 1H NMR, 13C NMR and single-crystal X-ray structural analysis. Compound 3 shows high catalytic activity in ring-opening polymerization (ROP) of ε-caprolactone (ε-CL).

Group 13 metal (Al, Ga, In) alkyls supported by N-heterocyclic carbenes for use in lactide ring-opening polymerization catalysis

The synthesis of several N-heterocyclic carbene (NHC) group 13 metal adducts of the type (NHC)MR3 [NHC=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IDipp); M=Al, Ga, In; R=Me, Et] is described. In the case of the In adduct (IMes)InMe3, characterization data include its X-ray crystallographic determined molecular structure. The prepared compounds act as efficient ring-opening polymerization (ROP) initiators of rac-lactide, allowing access to either linear poly(lactic acid) (PLA) or cyclic PLA depending on the nature of the initiator and the reaction conditions. For these NHC-MMe3 systems, the addition of benzyl alcohol (acting as a chain transfer agent) was found to be beneficial both to ROP activity and control. In particular, the Al and In systems (IMes)MMe3 (M=Al, In) in combination with BnOH are highly effective ROP initiators of rac-lactide at room temperature (TOF=600h−1).

Dual Catalysis for Selective Ring-Opening Polymerization of Lactones: Evolution toward Simplicity.

Much work has been directed to the design of complex single-site catalysts for ring-opening polymerization (ROP) to enhance both activity and selectivity. More simply, however, cooperative effects between Lewis acids and organocatalytic nucleophiles/Lewis bases provide a powerful alternative. In this study we demonstrate that the combination of N-heterocyclic carbenes, 1,8-diazabicycloundec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP) with simple Lewis acids enables the ROP of the macrolactone pentadecalactone in a rapid and efficient manner. Remarkably, regardless of the nature of the nucleophile, the order of activity was observed to be MgX2 ≫ YCl3 ≫ AlCl3 and MgI2 > MgBr2 > MgCl2 in every case. The minimal influence of the organobase on polymerization activity allows for the use of simple and inexpensive precursors. Furthermore, extension of the study to other cyclic (di)ester monomers reveals the choice of Lewis acid to lead to monomer selective ROP activity and hence control over copolymer composition by choice of Lewis acid. This approach could lead to the realization of complex polymer structures with tunable physical properties from simple catalyst combinations.

Versatile metal complexes of 2,5-bis{N-(2,6-di isopropylphenyl)iminomethyl}pyrrole for epoxide–CO2 coupling and ring opening polymerization of ε-caprolactone

The catalytic activities of metal complexes of 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrole 1 for epoxide–CO2 coupling and ring opening polymerization (ROP) of e-caprolactone (CL) were explored. The Zn(II) 2, Cd(II) 3,4 and Cu(II) 5 complexes of 1, in the presence of tetrabutylammonium bromide (TBAB) as co-catalyst, effectively catalyzed the epoxide–CO2 coupling reaction at 1 atm of CO2 to produce cyclic carbonates. In addition, the catalytic activities of these complexes (2–5) were investigated for the ROP of CL in the presence and absence of benzyl alcohol (BnOH). All these complexes were active for ROP of CL at mild temperature. In particular, the complexes 2 and 5 exhibited remarkable catalytic activities for ROP of CL at 25 °C in toluene in the presence of BnOH. The ROP of CL catalyzed by 2 and 5 complexes, not only proceeded through living polymerization but also immortal.

Neutral and Cationic N‐Heterocyclic Carbene Zinc Adducts and the BnOH/Zn(C6F5)2 Binary Mixture – Characterization and Use in the Ring‐Opening Polymerization of β‐Butyrolactone, Lactide, and Trimethylene Carbonate

AbstractA variety of N‐heterocyclic carbene (NHC) zinc adducts of the type NHC–ZnMe2 [2a, NHC = 1,3‐dimesitylimidazol‐2‐ylidene; 2b, NHC = 1,3‐(2,6‐iPr2Ph)2‐imidazol‐2‐ylidene; 2c, NHC = 1,3‐di‐tert‐butylimidazol‐2‐ylidene] and NHC–Zn(C6F5)2 [4a, NHC = 1,3‐dimesitylimidazol‐2‐ylidene; 4b, NHC = 1,3‐(2,6‐iPr2Ph)2‐imidazol‐2‐ylidene; 4c, NHC = 1,3‐di‐tert‐butylimidazol‐2‐ylidene] were synthesized by reaction of the appropriate NHC ligand with ZnMe2 or (toluene)Zn(C6F5)2. The X‐ray molecular structures of derivatives 2b, 4b, and 4c confirmed their adduct nature, and their bonding and geometrical parameters are influenced by the nature of the Zn–X group. The ionization reaction of the dimethyl Zn species 2a and 2b with the methide abstracting reagent B(C6F5)3 in the presence of tetrahydrofuran (THF) afforded the NHC–Zn organocations (1,3‐dimesitylimidazol‐2‐ylidene)Zn(Me)(THF)2+ (3a+) and [1,3‐(2,6‐iPr2Ph)2‐imidazol‐2‐ylidene]Zn(Me)(THF)+ (3b+) as dissociated MeB(C6F5)3– salts, as deduced from NMR spectroscopic data. All of these NHC–Zn compounds and BnOH/Zn(C6F5)2 were tested as ring‐opening polymerization (ROP) initiators of β‐butyrolactone (β‐BL), rac‐lactide (rac‐LA), and trimethylene carbonate (TMC). Although cations 3a+ and 3b+ were both inactive ROP initiators, as they appear to decompose prior to any ROP activity, the NHC–Zn(C6F5)2 compounds readily mediate the ROP of β‐BL, rac‐LA, and TMC to afford the corresponding polymeric materials with a moderate level of control, as deduced from NMR, size‐exclusion chromatography (SEC), and mass spectrometric MALDI‐TOF data. In contrast, the use of the alcohol BnOH (instead of a NHC moiety) as a nucleophile for association with (toluene)Zn(C6F5)2 led to efficient, highly controlled, and immortal ROP of TMC and rac‐LA with the formation of controlled chain length and narrowly disperse materials.

Switching the Lactide Polymerization Activity of a Cerium Complex by Redox Reactions

The old switcheroo! The ring-opening polymerization activity towards meso-lactide significantly differs when cerium complexes with two bis(phenolate) ligands (OSSO type) change their oxidation state from +4 to +3. This switch can be performed in situ by chemical reduction or oxidation of the catalyst. The redox switching is possible up to three times in a row. PLA=polylactide.

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity (Eur. J. Inorg. Chem. 35/2011)

AbstractThe cover picture shows a butterfly‐shaped dimetallic alkylzinc complex reported by researchers at Memorial University, which is shown in the background. The complex, reported in the article by F. M. Kerton et al. on p. 5347 ff, can be readily converted to an alkoxide species. This initiates ring‐opening polymerization of rac‐lactide and ϵ‐caprolactone under conventional heating or upon microwave irradiation. Financial support from the Publication Subvention Program of Memorial University of Newfoundland is acknowledged.magnified image

Lanthanide borohydrides supported by an ansa-bis(amidinate) ligand with a rigid naphthalene linker: Synthesis, structure and catalytic activity in ring-opening polymerization of lactide

The reactions of Ln(BH4)3(THF)2 with an equimolar amount of the dilithium derivative of a bridged bis(amidine) containing a conformationally rigid naphthalene linker afforded heterobimetallic ansa-bis(amidinate) lanthanide borohydrides [1,8-C10H6{NC(tBu)N-2,6-Me2-C6H3}2]Ln(BH4)(μ-BH4)Li(THF)2 (Ln=Nd, 2; Sm, 3). In the solid state, intermolecular contacts between the lithium atom and the terminal borohydrido groups of these compounds lead to the formation of one-dimensional zigzag coordination polymer chains. Compounds 2 and 3 are active in the ring-opening polymerization (ROP) of racemic lactide at 20°C, acting as single-site diinitiators with the two borohydride groups operative, and providing polymers with a slight heterotactic bias (Pr=0.54–0.62), controlled molecular weights and relatively narrow polydispersities (Mw/Mn=1.5–1.7).

Rare-Earth Complexes with Multidentate Tethered Phenoxy-Amidinate Ligands: Synthesis, Structure, and Activity in Ring-Opening Polymerization of Lactide

New multidentate tethered amidine-phenol pro-ligands {4,6-tBu2C6H2O-(2-C(N-R)═N-R}H2 ({LONR}H2, R = iPr, cyclohexyl (Cy), 2,6-iPr2C6H3 (Ar)) were synthesized from the corresponding carbodiimines an...

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

AbstractA series of zinc complexes was prepared from 4,6‐disubstituted (R,R′) o‐[(4‐methyl‐1‐piperazinyl)methyl]phenols ([ONNR′,R]H) and characterized by elemental analysis, 1H and 13C{1H} NMR spectroscopy, and X‐ray crystallography. Reaction of these products with diethylzinc gave Zn[ONNtBu,tBu]2 (1) as a monometallic complex and {[μ‐ONNR′,R]ZnEt}2 [R′ = Me, R = tBu, (2); R′ = R = tBu (3); R′ = R = tAm (4)] bimetallic species that have distorted tetrahedral environments about the Zn centres. Reaction of 3 and 4 with alcohols gave {[ONNtAm,tAm]Zn(μ‐OR″)}2 [R″ = Bn (5); R″ = Et (6)] bimetallic species in which the Zn centres are bridged by benzyl alkoxide and ethoxide groups, respectively. A morpholinyl derived ligand was also synthesized and characterized (L4H), and its 1:1 stoichiometric reaction with ZnEt2 resulted in complex 7, {[μ‐ONOtBu,tBu]ZnEt}2. The reactivity of complexes 2–7 in the ring‐opening polymerization of rac‐lactide (LA) and ϵ‐caprolactone (ϵ‐CL) was studied. Reactions of carbon dioxide with cyclohexene oxide in the presence of 6 or 7/ROH (R = Bn, Et) afforded cyclohexene carbonate.

Neodymium borohydride complexes supported by diamino-bis(phenoxide) ligands: diversity of synthetic and structural chemistry, and catalytic activity in ring-opening polymerization of cyclic esters

New heterobimetallic borohydrido neodymium complexes {[OONN]1Nd(BH4)(μ-BH4)Li(THF)}2 (1) and [OONN]3Nd(BH4)(μ-BH4)Li(THF)2 (3) supported by diamino-bis(phenoxide) ligands ([OONN]1 = {CH2N(Me)CH2-3,5-Me,t-Bu-C6H2O}2; [OONN]3 = C5H4NCH2N{CH2-3,5-Me,t-Bu-C6H2O}2) were synthesized by the reactions of Nd(BH4)3(THF)2 with equimolar amounts of dilithium derivatives of diamino-bis(phenol)s Li2[OONN]n and isolated in high yields. In the case of Li2[OONN]2 ([OONN]2 = Me2NCH2CH2N{CH2-3,5-t-Bu-C6H2O}2), the same synthetic procedure afforded the heterobimetallic bis(phenoxide) complex Li{Nd[OONN2]2} (2). The structures of complexes 1–3 were established by X-ray diffraction studies. Compounds 1–3 act as single-site initiators for the ring-opening polymerization (ROP) of racemic lactide and racemic β-butyrolactone under mild conditions (20 °C), providing atactic polymers with controlled molecular weights and relatively narrow polydispersities (Mw/Mn = 1.07–1.82). While 1 and 3 initiate polymerizationvia their borohydride groups, ROP with 2 proceeds viainsertion into the Nd–O(ligand) bond.

Scandium alkyl and amide complexes containing a cyclen-derived (NNNN) macrocyclic ligand: synthesis, structure and ring-opening polymerization activity toward lactide monomers

Cyclic polyamine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me(3)TACD)H (= Me(3)[12]aneN(4)), reacted with [K{N(SiHMe(2))(2)}] in benzene-d(6) to give [K{(Me(3)TACD)SiMe(2)N(SiHMe(2))}] (1) under hydrogen evolution. Single-crystal X-ray diffraction of 1 shows a dinuclear structure in the solid state, featuring a bridging μ-amido and a weak β-agostic Si-H bond. 1,7-Dimethyl-1,4,7,10-tetraazacyclododecane (Me(2)TACD)H(2) (= Me(2)[12]aneN(4)) and (Me(3)TACD)H were reacted with [Sc{N(SiHMe(2))(2)}(3)(thf)] in benzene-d(6) to give [{(Me(2)TACD)SiMe(2)N(SiHMe(2))}Sc{N(SiHMe(2))(2)}] (2) and [(Me(3)TACD)Sc{N(SiHMe(2))(2)}(2)SiMe(2)] (3), respectively. Both compounds are monomeric in solution and X-ray diffraction studies showed the scandium metal centers to be six-coordinate. The scandium alkyl complex [Sc(Me(3)TACD)(CH(2)SiMe(3))(2)] (4) was obtained by reacting (Me(3)TACD)H with [Sc(CH(2)SiMe(3))(3)(thf)] in benzene-d(6). The scandium amide complexes 2 and 3 catalyzed the ring-opening polymerization (ROP) of meso-lactide to give syndiotactic polylactides.

Alkaline earth metal amide complexes containing a cyclen-derived (NNNN) macrocyclic ligand: synthesis, structure, and ring-opening polymerization activity towards lactide monomers

Cyclic tetra-amine 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane, (Me3TACD)H (= Me3[12]aneN4) was reacted with [M{N(SiMe3)2}2(thf)x] (M = Mg, x = 0; M = Ca, x = 2) in n-pentane to give thf-free complexes [{Me3TACD}M{N(SiMe3)2}] (M = Mg (1); M = Ca (2)). Both compounds are monomeric in solution and X-ray diffraction studies showed the metal centers to be five-coordinated. The proligand (Me3TACD)H reacted with [Ca{N(SiHMe2)2}2(thf)2] in benzene-d6 to give [{(Me3TACD)SiMe2N(SiHMe2)}Ca{N(SiHMe2)2}] (3) with hydrogen evolution. Single-crystal X-ray diffraction showed 3 to be monomeric with a six-coordinated calcium center in the solid state. The alkaline earth metal amide complexes 1 to 3 catalyzed the ring-opening polymerization of lactide monomers to give syndiotactic-rich polylactides from meso-lactide and isotactic-rich polylactides from rac- and L-lactide.

Synthesis and X-ray crystal structure of dichloro[S-1-phenyl-N-(S-pyrrolidin-2-ylmethyl)ethanamine]zinc(II) and its catalytic application to rac-lactide polymerization

New dichloro zinc(II) complex ligated by the homochiral bidentate ligand S-1-phenyl-N-(S-pyrrolidin-2-ylmethyl)ethanamine (PPMA) was synthesized and characterized by X-ray crystallography. The geometry of the (PPMA)ZnCl2 is a distorted tetrahedron comprising of zinc metal as a center linked with two N atoms of the PPMA in a bidentate coordination mode along with two chloro ligands. The catalytic capacity of the complex was evaluated in ring opening polymerization (ROP) of rac-lactide. The active catalyst species was generated in situ by treating MeLi to complex (PPMA)ZnCl2. The dimethyl derivative of the (PPMA)ZnCl2 showed highly activity in ROP of rac-lactide and gave preference to heterotactic polylactide.

Synthesis, structures and ε-caprolactone polymerization activity of aluminum N,N′-dimethyloxalamidates

Alkyl aluminum N,N′-dimethyloxalamidates R 4Al 2(dmoa) ( 1, R = Me; 2, R = Et; 3, R = i Bu; 4, R = t Bu) (dmoa-H 2 = N,N′-dimethyloxalamide) have been prepared and characterized. Molecular structures of the compounds 1 and 4 have been determined by X-ray crystallography. The centrosymmetric molecules of the compounds consist of one N,N′-dimethyloxalamidate unit bonded to two four-coordinated aluminum atoms. Each of the aluminum atoms is bonded to two alkyl groups, and oxygen and nitrogen atoms originating from two different amidate groups. A skeleton framework of the molecules of 1 and 4 consists of two fused AlNOC 2 heterocyclic rings, which are flat and positioned in one plane. It was shown that compounds 1– 3 were initiators in a process of ring opening polymerization (ROP) of ε-caprolactone. The compound 4 exhibited low activity in ROP.

Titanium complexes containing new dianionic tetradentate [ONNO]-type ligands with benzyl substituents on bridging nitrogen atoms: Syntheses, X-ray structures, and catalytic activities in ring opening polymerization of lactide

Several titanium isopropoxides 1– 8 have been prepared by the reaction of Ti(O- i-Pr) 4 with a series of corresponding tetradentate Salan-type [ONNO] ligands with benzyl or methyl substituents on bridging nitrogen atoms. They have been characterized by 1H NMR, 13C{ 1H} NMR, and elemental analysis. Solid state structures of compounds 2, 4, 6, and 7 have been determined by X-ray crystallography. X-ray diffraction analysis and 1H NMR confirmed that these titanium complexes were all monomeric species with a six-coordinated central titanium in their solid and solution structures. Complexes 2, 4, 6, and 8 with benzyl substituents on bridging nitrogens gave PLA with higher molecular weight than compounds 1, 3, 5, and 7 with methyl substituents did.

Ring-opening polymerization of ε-caprolactone and cyclohexene oxide initiated by aluminum β-ketoamino complexes: steric and electronic effect of 3-position substituents of the ligands

A series of aluminum complexes supported by β-ketoamino, ligand-bearing, 3-position substituentsLAlEt2 (L=CH3C(O)C(Cl)=C(CH3)NAr (L 1), L=CH3C(O)C(H)=C(CH3)NAr (L 2), L=CH3C(O)C(Ph)=C(CH3)NAr (L 3), and L=CH3C(O)C(Me)=C(CH3)NAr (L 4), Ar=2,6-Pr2C6H3) were synthesized in situ and employed in the ringopening polymerization (ROP) of e-caprolactone (e-CL) and cyclohexene oxide (CHO). The 3-position substituents on the β-ketoamino ligand backbone of the aluminum complexes influenced the catalyst activity remarkably for both ROP of e-CL and CHO. Aluminum β-ketoamino complexes displayed different catalytic behavior in ROP of e-CL and CHO. The order of the catalytic activity ofLAlEt2 wasL 1AlEt2>L 2AlEt2>L 3AlEt2>L 4AlEt2 for ROP of e-CL, being opposite to the electron-donating ability of the 3-position substituents on the β-ketoamino ligand, while the order of the catalytic activity for ROP of CHO wasL 1AlEt2>L 3AlEt2>L 4AlEt2>L 2AlEt2. The effects of reaction temperature and time on the ROP were also investigated for both e-CL and CHO.