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Homoleptic and heteroleptic ketodiiminate zinc complexes for the ROP of cyclic l-lactide.

ABSTRACT: Homo- and heteroleptic ketodiiminate zinc complexes L¹₂Zn₂ (1, L¹ = [Me₂NC₂H₄NC(Me)CH]₂CO), L²(ZnCp)₂ (2, L² = [Me₂NC₃H₆NC(Me)CH]₂CO, Cp = C₅H₅) and L²HZnCp* (3, Cp* = C₅Me₅) were synthesized and characterized by ¹H and ¹³C NMR and IR spectroscopy as well as by elemental analysis and single crystal X-ray diffraction (sc-XRD, 2, 3). The catalytical activity of heteroleptic complexes 2 and 3 were tested in the ring-opening polymerization (ROP) of l-lactide. Homobimetallic complex 2 showed the highest activity and selectivity for the synthesis of cyclic polylactide (cPLLA; TOF = 17 460 h^-1) at 100 °C in toluene solution, while linear polymers are formed with mononuclear complex 3.

SUBMITTER: Glockler E

PROVIDER: S-EPMC10568404 | biostudies-literature | 2023 Oct

REPOSITORIES: biostudies-literature

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Homoleptic and heteroleptic ketodiiminate zinc complexes for the ROP of cyclic l-lactide.

Glöckler Eduard E Kapp Leon L Wölper Christoph C Schumacher Marcel M Gröschel André H AH Schulz Stephan S

RSC advances 20231012 43

Homo- and heteroleptic ketodiiminate zinc complexes L12Zn2 (1, L1 = [Me2NC2H4NC(Me)CH]2CO), L2(ZnCp)2 (2, L2 = [Me2NC3H6NC(Me)CH]2CO, Cp = C5H5) and L2HZnCp* (3, Cp* = C5Me5) were synthesized and characterized by 1H and 13C NMR and IR spectroscopy as well as ...[more]

PMID: 37842672

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Project description:Six homo- or heteroleptic tricationic Ir(R1-tpy)(R2-tpy)3+ complexes (Ir1-Ir6, R1/R2 = Ph, 4'-N(CH3)2Ph, pyren-1-yl, or 4'-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}Ph, tpy = 2,2';6',2"-terpyridine) were synthesized and tested for photodynamic therapy (PDT) effects. The ground- and excited-state characteristics of these complexes were studied systematically via spectroscopic methods and quantum chemistry calculations. All complexes possessed intraligand charge transfer (1ILCT) / metal-to-ligand charge transfer (1MLCT) dominated transition(s) in their low-energy absorption bands, which red-shifted with the increased electron-releasing strength of the R1/R2 substituent. Five of the complexes exhibited ligand-centered 3 π,π*/3ILCT/3MLCT emission. With a stronger electron-releasing R1/R2 substituent, the degree of charge transfer contribution increased, leading to a decrease of the emission quantum yield. When the 4'-N(CH3)2Ph substituent was introduced on both tpy ligands, the emission of Ir3 was completely quenched. Our study on the transient absorption of these complexes demonstrated that they all possessed broadband triplet excited-state absorption in the 400-800 nm region. Pyrenyl substitution of one or more tpy ligands, as in Ir4 and Ir5, increased the lifetimes of the lowest triplet excited state and the singlet oxygen (1O2) production efficiencies. Ir1-Ir5 were nontoxic toward SK-MEL-28 cells, with photocytotoxicities that varied from 0.18 to 153 µM. Among them, Ir4 had the highest 1O2 quantum yield (0.81) in cell-free conditions, showing the largest photocytotoxicity against SK-MEL-28 cells for Ir(III) PSs to date, and was the most efficient generator of reactive oxygen species (ROS) in vitro. Ir4 possessed a very large phototherapeutic index (PI = dark EC50 / light EC50) of >1657, the largest reported for an Ir(III) complex photosensitizer upon broadband visible light (400-700 nm) activation. Ir4 also exhibited a very strong PDT effect toward MCF-7 breast cancer cells and its xenograft tumor model. Upon 450-nm light activation, Ir4 dramatically inhibited the xenograft tumor growth and exhibited negligible side effects upon PDT treatment.

Project description:A seemingly simple combination of [Zn(quin)2(H2O)] (quin- = quinaldinate) and a selected secondary cyclic amine, piperidine (pipe), pyrrolidine (pyro) or morpholine (morph), afforded in acetonitrile a number of products: anionic homoleptic quinaldinate, neutral heteroleptic quinaldinate/amine and quinaldinate/amidine complexes. The piperidine and pyrrolidine systems underwent reaction with acetonitrile to give amidines. The in situ formed piperidinoacetamidine (pipeam) or pyrrolidinoacetamidine (pyroam) coordinated to zinc(ii). Reactions with piperidine led to trans-[Zn(quin)2(pipe)2]·2CH3CN (1), [Zn(quin)2(pipe)]·cis-[Zn(quin)2(pipe)2] (2), pipeH[Zn(quin)3]·CH3CN (3), [Zn(quin)2(pipeam)]·CH3CN (4a), [Zn(quin)2(pipeam)]·2CHCl3 (4b), pipeamH[Zn(quin)3] (5) and pipeamH[Zn(quin)2(CH3COO)]·acetamide (6) (pipeH+ and pipeamH+ denote protonated amine or amidine). By analogy, [Zn(quin)2(pyro)2] (7), pyroH[Zn(quin)3]·CH3CN (8), pyroH[Zn(quin)2Cl] (9), [Zn(quin)2(pyroam)]·CH3CN·0.5pyroam·0.5H2O (10a), [Zn(quin)2(pyroam)]·2CHCl3 (10b), [Zn(quin)2(pyroam)]·CH2Cl2 (10c) and pyroamH[Zn(quin)3] (11) were obtained in the pyrrolidine reactions. The morpholine system allowed isolation of only two novel products, trans-[Zn(quin)2(morph)2] (12) and morphH[Zn(quin)3]·CH3CN (13). Importantly, no amidine could be isolated. Instead, in autoclaves at 105 °C morpholine degraded to ammonia, as confirmed by mass spectrometry of the gas phase. pyroamH[Zn(quin)3] exists in two polymorphs which differ in the binding modes of quinaldinate ligands. In 11triclinic, the metal ion of [Zn(quin)3]- features a five-coordinate environment, whereas that in 11monoclinic is surrounded by six donors. Stabilities of the [Zn(quin)3]- isomers were assessed with DFT calculations. The one with a six-coordinate zinc(ii) ion was found to be more stable than its five-coordinate counterpart. Favorable intermolecular interactions in the solid state stabilize both and reduce the energy difference between them. The calculations show the conversion of the five-coordinate [Zn(quin)3]- into its coordinatively saturated isomer to be an almost barrierless process.

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Homoleptic and heteroleptic ketodiiminate zinc complexes for the ROP of cyclic l-lactide.

Publications

Homoleptic and heteroleptic ketodiiminate zinc complexes for the ROP of cyclic l-lactide.

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