Organoaluminium Complexes Derived from Anilines or Schiff Bases for the Ring-Opening Polymerization of ε-Caprolactone, δ-Valerolactone andrac-Lactide

Reaction of Ph2C(X)(CO2H) (X = OH, NH2) with [VO(OR)3] (R = Et, nPr): structure, magnetic susceptibility and ROP capability

Reaction of [VO(OR)3] (R = Et, nPr) with 2,2'-diphenylglycine afforded the alkoxide-bridged dimers {[VO(OR)(μ-OR)][Ph2C(NH2)(CO2)]}2, whereas use of benzilic acid, in the presence of alkali metals, afforded 16-membered metallocycles {V8(O)4M(OR)8[Ph2C(OH)(CO2)]12} (M = <1 Na, K). For the ring systems, magnetic susceptibility data is consistent with mixed-valence vanadium with an average oxidation state of 3.5. The dimer and ring systems are capable of the ring opening polymerisation (ROP) of ε-caprolactone under N2, air, or as melts affording mostly low to medium molecular weight cyclic and linear products.

Ring Opening Polymerization of Lactides and Lactones by Multimetallic Titanium Complexes Derived from the Acids Ph2C(X)CO2H (X = OH, NH2)

The reactions of the titanium alkoxide [Ti(OR)4] (R = Me, nPr, iPr, tBu) with the acids 2,2’-Ph2C(X)(CO2H), where X = OH and NH2, i.e., benzilic acid (2,2’-diphenylglycolic acid, L1H2), and 2,2’-diphenylglycine (L2H3), have been investigated. The variation of the reaction stoichiometry allows for the isolation of mono-, bi-, tri or tetra-metallic products, the structures of which have been determined by X-ray crystallography. The ability of the resulting complexes to act as catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and r-lactide (r-LA) has been investigated. In the case of ε-CL, all catalysts except that derived from [Ti(OnPr)4] and L2H3, i.e., 7, exhibited an induction period of between 60 and 285 min, with 7 exhibiting the best performance (>99% conversion within 6 min). The PCL products are moderate- to high-molecular weight polymers. For r-LA, systems 1, 3, 4 and 7 afforded conversions of ca. 90% or more, with 4 exhibiting the fastest kinetics. The molecular weights for the PLA are somewhat higher than those of the PCL, with both cyclic and linear PLA products (end groups of OR/OH) identified. Comparative studies versus the [Ti(OR)4] starting materials were conducted, and although high conversions were achieved, the control was poor.

Collaboration between Trinuclear Aluminum Complexes Bearing Bipyrazoles in the Ring-Opening Polymerization of ε-Caprolactone

Trinuclear aluminum complexes bearing bipyrazoles were synthesized, and their catalytic activity for ε-caprolactone (CL) polymerization was investigated. D^Bu₂Al₃Me₅ exhibited higher catalytic activity than did the dinuclear aluminum complex L^Bu₂Al₂Me₄ (16 times as high for CL polymerization; [CL]:[D^Bu₂Al₃Me₅]:[BnOH] = 100:0.5:5, [D^Bu₂Al₃Me₅] = 10 mM, conversion 93% after 18 min at room temperature). Density functional theory calculations revealed a polymerization mechanism in which CL first approached the central Al atom and then moved to an external Al. The coordinated CL ring was opened because the repulsion of two tert-butyl groups on the ligands pushed an alkoxide initiator on an external Al to initiate CL. In these trinuclear Al catalysts, the central Al plays a role in monomer capture and then collaborates with the external Al to activate CL, accelerating polymerization.

Synthesis of Biodegradable Polymers: A Review on the Use of Schiff-Base Metal Complexes as Catalysts for the Ring Opening Polymerization (ROP) of Cyclic Esters

This review describes the recent advances (from 2008 onwards) in the use of Schiff-base metal complexes as catalysts for the ring opening polymerization (ROP) of cyclic esters. The synthesis and structure of the metal complexes, as well as all aspects concerning the polymerization process and the characteristics of the polymers formed, will be discussed.

Water-Soluble Rhenium Phosphine Complexes Incorporating the Ph2C(X) Motif (X = O-, NH-): Structural and Cytotoxicity Studies

Reaction of [ReOCl₃(PPh₃)₂] or [ReO₂I(PPh₃)₂] with 2,2'-diphenylglycine (dpgH₂) in refluxing ethanol afforded the air-stable complex [ReO(dpgH)(dpg)(PPh₃)] (1). Treatment of [ReO(OEt)I₂(PPh₃)₂] with 1,2,3-triaza-7-phosphaadamantane (PTA) afforded the complex [ReO(OEt)I₂(PTA)₂] (2). Reaction of [ReOI₂(PTA)₃] with dpgH₂ led to the isolation of the complex [Re(NCPh₂)I₂(PTA)₃]·0.5EtOH (3·0.5EtOH). A similar reaction but using [ReOX₂(PTA)₃] (X = Cl, Br) resulted in the analogous halide complexes [Re(NCPh₂)Cl₂(PTA)₃]·2EtOH (4·2EtOH) and [Re(NCPh₂)(PTA)₃Br₂]·1.6EtOH (5·1.6EtOH). Using benzilic acid (2,2'-diphenylglycolic acid, benzH) with 2 afforded the complex [ReO(benz)₂(PTA)][PTAH]·EtOH (6·EtOH). The potential for the formation of complexes using radioisotopes with relatively short half-lives suitable for nuclear medicine applications by developing conditions for [Re(NCPh₂)(dpg)I(PTA)₃] (7)[ReO₄]^- in a 4 h time scale was investigated. A procedure for the technetium analog of complex [Re(NCPh₂)I₂(PTA)₃] (3) from ^99mTc[TcO₄]^- was then investigated. The molecular structures of 1-7 are reported; complexes 3-7 have been studied using in vitro cell assays (HeLa, HCT116, HT-29, and HEK 293) and were found to have IC₅₀ values in the range of 29-1858 μM.

Living/controlled ring-opening (co)polymerization of lactones by Al-based catalysts with different sidearms

It remains a challenging task to synthesize well-defined multi-block copolymers through the controlled/living ring-opening polymerization (ROP) of lactones without transesterification, the most common side reaction occurring during copolymerization. A series of Al-based complexes with different sidearms were prepared for living ROP of lactones such as ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) in the presence of BnOH at room temperature (RT), affording medium to high molecular weight (MW) linear polyesters with Mw up to 303 kg mol-1 and narrow molecular weight distributions (MWD, Đ as low as 1.12). The coordination-insertion polymerization mechanism was proposed based on the combination of the detailed experimental data and polymerization kinetics. It should be noted that the sidearm plays a significant important role in the reactivity of these Al-based catalyst systems. More specifically, the Al2 system with a butyl substituent on the sidearm exhibited the highest polymerization activity and the Al5 system with the bulkiest sidearm showed the lowest one among the investigated catalysts. Moreover, the Al4 system with a pyridine group on the sidearm could effectively inhibit transesterification and maintain a well-defined block copolymer structure even after heating at 50 °C for 10 h, which could also be confirmed by chain-end analyses of the produced polymers with the MALDI-TOF MS measurement.

Mono- and dinuclear copper complexes coordinated on NNO-tridentate Schiff-base derivatives for copolymerization of cyclohexene oxide and cyclic anhydrides

A series of bimetallic penta-coordinated copper complexes [Lⁿ₂Cu₂(OAc)₂] (1, 3-7), a mononuclear tetra-coordinated copper complex [LⁿCu(OAc)] (8 and 9), and a penta-coordinated copper complex [L²Cu(OAc)(H₂O)] (10) were prepared by the reaction of Cu(OAc)₂·H₂O with a variety of NNO-tridentate Schiff-base ligands (L¹-H-L⁹-H) in refluxing 95% ethanol, respectively. However, a dinuclear copper complex [(L²)₂Cu₂(OAc)₂] (2) can be obtained from the treatment of L²-H with a stoichiometric amount of anhydrous Cu(OAc)₂ in refluxing absolute EtOH under a dry nitrogen atmosphere. All of these copper complexes are active for the alternating copolymerization of cyclohexene oxide and cyclic anhydride, affording polyesters with moderate polydispersity. In particular, dinuclear copper complexes 1 and 2 performed satisfactorily to produce polyesters with controllable molecular weights and high ester linkages. This is the first example of well-defined copper acetate catalysts active for the copolymerization of cyclohexene oxide-phthalic anhydride or cyclohexene oxide-succinic anhydride which may be advantageous in terms of obviating the use of co-catalysts and low cost as well as an effective copolymerization for the formation of biodegradable polyesters in a controlled fashion.

Tetracoordinate aluminum complexes bearing phenoxy-based ligands as catalysts for epoxide/anhydride copolymerization: some mechanistic insights

Phenoxy-imine aluminum complexes, in combination with DMAP, produce efficient catalysts for the alternating copolymerization of epoxides and anhydrides. A zwitterionic species is formed in the initiation step.

Facile Preparation of Stereoblock PLA From Ring-Opening Polymerization of rac-Lactide by a Synergetic Binary Catalytic System Containing Ureas and Alkoxides

Ring-opening polymerization (ROP) of cyclic esters/lactones by efficient catalysts is a powerful method for synthesis of biodegradable and biocompatible polyesters with well-defined structures. To develop catalytic systems that are fast, selective and controlled is a persistent effort of chemists. In this contribution, we report a binary urea/alkoxide catalytic system that could catalyze ROP of rac-LA in a fast (over 90% conversion within 1-2 min), stereoselective (P i up to 0.93) and controlled manner, indicated by narrow MW distributions, linear relationship between the monomer conversions and M ns, end-group fidelity, and chain extension experiments. Remarkably, the catalytic system described here is simple, easily prepared, and structurally tunable and thus has versatile catalytic performances.

Dinuclear iminophenoxide copper complexes in rac-lactide polymerisation

Dinuclear bis(R'-(R''-iminomethyl)phenoxide) copper complexes L2Cu2(μ-OR)2 were prepared from the reaction of copper methoxide with ROH and LH (ROH = dimethylaminoethanol or pyridylmethanol, R' = H, 4,6-tBu, 1,3-Cl, R'' = benzyl, cyclohexyl, diphenylmethyl and 2,6-dimethylphenyl). Preparation was complicated by formation of homoleptic L2Cu and only 9 of the 24 possible combinations could be prepared. All complexes were characterized by single crystal X-ray diffraction studies and crystallized as dinuclear penta-coordinated complexes. Homoleptic complexes L2Cu were inactive in lactide polymerization at room temperature. Most heteroleptic complexes showed modest to good activities with full conversion in less than 6 h at room temperature. Complexes with R' = H showed poor molecular weight control, complexes with R' = Cl were inactive in polymerization. In pyridylmethoxide-containing complexes, only one alkoxide initiated chain growth. All complexes produced atactic polymer.

Copolymerization of cyclic esters, epoxides and anhydrides: evidence of the dual role of the monomers in the reaction mixture

A block copolyester derived from ROCOP of CHO/SA followed by ROP of ε-CL was obtained from the mixture of monomers. The lactone comonomer acts as an endogen cocatalyst during the SA/CHO ROCOP step and as a monomer during ROP.

Aluminium complexes containing salicylbenzothiazole ligands and their application in the ring-opening polymerisation of rac-lactide and ε-caprolactone

This paper is the first report on the use of aluminium salicylbenzothiazole complexes for the ROP of rac-LA and ε-CL.