Low-Symmetry β-Diketimine Aryloxide Rare-Earth Complexes: Flexible, Reactive, and Selective

Access to Polyhydroxyalkanoates with Diverse Syndiotacticity via Polymerization by Spiro-Salen Complexes and Insights into the Stereocontrol Mechanism

Polyhydroxyalkanoates (PHAs) have attracted broad interest as promising sustainable materials to address plastic pollution and resource scarcity. However, the chemical synthesis of stereoregular PHAs via ring-opening polymerization (ROP) has long been an elusive endeavor. In this contribution, we exploited a robust spiro-salen yttrium complex (Y3) as the catalyst to successfully prepare syndiotactic PHAs with diverse pendent groups. Simply altering the ratio of enantiomeric catalysts allowed to access of PHAs with diverse syndiotacticity (Pr=0.5-0.99, from sticky oil to tough materials), delivering tunable thermal properties (glass transition temperature, Tg from -52 to 70 °C and melting transition temperature, Tm from 38 to 223 °C). A combined experimental and computational study suggested a polymeric exchange mechanism could boost the polymerization activity and control the syndioselectivity.

Synthesis of Rare Earth Metal Complexes Stabilized by Amine Bridged Bis(phenolato) Ligands and Their Performance in the Polymerization of rac-β-Butyrolactone

A series of rare earth alkoxides bearing amine-bridged bis(phenolato) ligands were synthesized through sequential reactions of RE(C5H5)3(THF) (RE = Y, Lu) or Nd[N(SiMe3)2]3 with bis(phenols) LH2 and CF3CH2OH. Complexes REL(OCH2CF3)(THF)n (1-6) bearing different aryl-substituents were obtained in good yields of 59-70 %. They were applied in the ring-opening polymerization (ROP) of rac-β-butyrolactone (rac-BBL), which showed good activity (TOF up to 27,300 h-1), resulting in syndiotactically enriched poly(3-hydroxybutyrate) (PHB) (Pr up to 0.86) with narrow polydispersities (PDI ≤ 1.27). The yttrium complex 3 bearing bulky o-1,1-diphenylethyl substituents outperformed other complexes, suggesting that the smaller ionic radii of metal centers and bulky ortho substituents of ancillary ligands play crucial roles in controlling the activity and stereoselectivity in ROP of rac-BBL. Kinetics of the polymerization of rac-BBL initiated by complex 3 was investigated, which revealed first order dependences on the monomer and initiator concentrations, respectively.

Selective Transesterification to Control Copolymer Microstructure in the Ring-Opening Copolymerization of Lactide and ε-Caprolactone by Lanthanum Complexes

A series of novel lanthanum amido complexes, supported by ligands designed around the salan framework (salan = N,N'-bis(o-hydroxy, m-di-tert-butylbenzyl)-1,2-diaminoethane) were synthesized and fully characterized in the solid and solution states. The ligands incorporate benzyl or 2-pyridyl substituents at each tertiary amine center. The complexes were investigated as catalysts in the ring-opening homopolymerization of lactide (LA) and ε-caprolactone (ε-CL) and copolymerization of equimolar amounts of LA and ε-CL at ambient temperature. Solvent (THF or toluene) and the number of 2-pyridyl groups in the complex were found to influence the reactivity of the catalysts in copolymerization reactions. In all cases, complete conversion of LA to PLA was observed. The use of THF, a coordinating solvent, suppressed ε-CL polymerization, while the presence of one or more 2-pyridyl groups promoted ε-CL polymerization. Each copolymer gave a monomodal trace in gel permeation chromatography-size-exclusion chromatography (GPC-SEC) experiments, indicative of copolymer formation over homopolymerization. Copolymer microstructure was found to be dependent on catalyst structure and reaction solvent, ranging from blocky to close to alternating. Experiments revealed rapid conversion of LA in the initial stages of the reaction, followed by incorporation of ε-CL into the copolymer by either transesterification or propagation reactions. Significantly, the mode of transesterification (TI or TII) that occurs is determined by the structure of the metal complex and the reaction solvent, leading to the possibility of controlling copolymer microstructure through catalyst design.

MOFs-Modified Electrochemical Sensors and the Application in the Detection of Opioids

Opioids are widely used in clinical practice, but drug overdoses can lead to many adverse reactions, and even endanger life. Therefore, it is essential to implement real-time measurement of drug concentrations to adjust the dosage given during treatment, keeping drug levels within therapeutic levels. Metal-Organic frameworks (MOFs) and their composite materials modified bare electrode electrochemical sensors have the advantages of fast production, low cost, high sensitivity, and low detection limit in the detection of opioids. In this review, MOFs and MOFs composites, electrochemical sensors modified with MOFs for the detection of opioids, as well as the application of microfluidic chips in combination with electrochemical methods are all reviewed, and the potential for the development of microfluidic chips electrochemical methods with MOFs surface modifications for the detection of opioids is also prospected. We hope that this review will provide contributions to the study of electrochemical sensors modified with MOFs for the detection of opioids.

Interplay between β-Diimino and β-Diketiminato Ligands in Nickel Complexes Active in the Proton Reduction Reaction

Two Ni complexes are reported with κ⁴-P₂N₂ β-diimino (BDI) ligands with the general formula [Ni(XBDI)](BF₄)₂, where BDI is N-(2-(diphenylphosphaneyl)ethyl)-4-((2-(diphenylphosphaneyl)ethyl)imino)pent-2-en-2-amine and X indicates the substituent in the α-carbon intradiimine position, X = H for 1(BF₄)₂ and X = Ph for 2(BF₄)₂. Electrochemical analysis together with UV-vis and NMR spectroscopy in acetonitrile and dimethylformamide (DMF) indicates the conversion of the β-diimino complexes 1²⁺ and 2²⁺ to the negatively charged β-diketiminato (BDK) analogues (1-H)⁺ and (2-H)⁺ via deprotonation in DMF. Moreover, further electrochemical and spectroscopy evidence indicates that the one-electron-reduced derivatives 1⁺ and 2⁺ can also rapidly evolve to the BDK (1-H)⁺ and (2-H)⁺, respectively, via hydrogen gas evolution through a bimolecular homolytic pathway. Finally, both complexes are demonstrated to be active for the proton reduction reaction in DMF at E_app = -1.8 V vs Fc^+/0, being the active species the one-electron-reduced derivative 1-H and 2-H.

Synthesis of N-Methyl-o-phenylenediamine-Bridged Bis(phenolato) Lanthanide Alkoxides and Their Catalytic Performance for the (Co)Polymerization of rac-Butyrolactone and l-Lactide

A series of lanthanide alkoxo complexes supported by ONNO salalen ligands were synthesized and characterized. A one-pot reaction of LH₂ (L = (2-O-C₆H₂-^tBu₂-3,5)CH═N-C₆H₄-N(CH₃)CH₂(2-O-C₆H₂-^tBu₂-3,5)) with LnCp₃(THF) in a 1:1 molar ratio followed by the addition of 1 equiv of ROH (R = Bn, ⁱPr, and CF₃CH₂), afforded the dimeric lanthanide alkoxo complexes [LLn(μ-OCH₂Ph)]₂ [Ln = Lu (1), Yb (2), Sm (3), Nd (4)], [L²Yb(μ-OⁱPr)]₂ (5), and [L²Yb(μ-OCH₂CF₃)]₂ (6) in good isolated yields. All these lanthanide complexes were characterized by elemental analysis and FT-IR spectroscopy. In addition, complex 1 has been characterized by NMR spectroscopy. Single-crystal X-ray diffraction analysis of complexes 1, 2, 5, and 6 showed that these lanthanide alkoxo complexes are dimeric in the solid state. Complexes 1-6 showed good activity toward the homopolymerization of rac-butyrolactone (rac-BBL) to give atactic PHB, and ionic radii of central metals have profound influence on the polymerization. The polymerization behavior of l-lactide (l-LA) initiated by complex 2 was also explored. The kinetic study revealed that the polymerizations of rac-BBL and l-LA initiated by salalen lanthanide akoxide are first order for both the monomer and the initiator concentrations. Furthermore, it was found that complexes 1 and 2 showed good activity in the copolymerization of l-LA and rac-BBL, affording gradient copolymers.

N-Oxides amplify catalyst reactivity and isoselectivity in the ring-opening polymerization of rac-β-butyrolactone

N-Oxides can amplify the performance of a lanthanum aminobisphenolate catalyst in the ring-opening polymerization (ROP) of rac-β-butyrolactone (rac-BBL) to unprecedented levels (TOF/P_m; At RT: 1900 h^-1/0.73, At -30 °C: 200 h^-1/0.82). Experiments and computations establish donor electronics control catalyst activity, while donor sterics control catalyst deactivation.

The versatile roles of neutral donor ligands in tuning catalyst performance for the ring-opening polymerization of cyclic esters

The use of neutral donor ligands is an effective strategy to modify catalyst structure and performance in the synthesis of sustainable polymers through the ring-opening polymerization (ROP) of cyclic esters.

Yttrium and lanthanum bis(phosphine-oxide)methanides: structurally diverse, dynamic, and reactive

Homoleptic yttrium and lanthanum complexes of bis(phosphineoxide) methanides, RE(HPhL)3 and RE2(HMeL)6, promote the first rare-earth mediated Horner-Wittig and acid-base chemistry consistent with multifunctional reactivity (Lewis-acid/Brønstedbase).