Copolymerization of carbon dioxide with cyclohexene oxide catalyzed by bimetallic dysprosium complexes containing hydrazine-functionalized Schiff-base derivatives

Novel salenCo(iii) photoinitiators and their application for cycloaddition of carbon dioxide

Carbon dioxide (CO₂) is a renewable carbon resource that can be effectively used in the production of polycarbonate (PPC) and cyclic carbonate (CPC) through open-loop copolymerization with epoxides and CO₂. SalenCo(iii) can successfully break the carbon-oxygen link between propylene oxide (PO) and CO₂. On this basis, we prepared four different types of photosensitive salenCo(iii) complexes and investigated their catalytic copolymerization of CO₂ and PO. The results show that the catalytic performance of 1,2-cyclohexamediamine complexes is better than that of 1,2-o-phenylenediamine complexes. The catalytic efficiency of salenCo(iii) catalyst increases with the expansion of the photosensitive conjugate system. In addition, the introduction of light can improve the catalytic efficiency. When we increased the power of the external light source from 100 W to 200 W, the TON of the catalyst [C4] increased by nearly 50%.

Novel Mn4-Co2 nanocluster@photosensitizers/SalenCo(iii) catalyze the copolymerization of carbon dioxide and propylene oxide

In general, transition metals (TMs) often facilitate highly efficient catalysis. Herein, we synthesized a series of nanocluster composite catalysts by combining with photosensitizers and SalenCo(iii) for the first time and studied the catalytic copolymerization of CO2 and propylene oxide (PO). Systematic experiments have shown that the selectivity of copolymerization products can be improved by the nanocluster composite catalysts, and their synergistic effects significantly improved the photocatalytic performance of carbon dioxide copolymerization. At specific wavelengths, I@S1 can achieve a TON of 536.4, which is 2.26 times that of I@S2. Interestingly, in the photocatalytic products of I@R2, CPC reached 37.1%. These findings provide a new idea for the study of TM nanocluster@photosensitizers for carbon dioxide photocatalysis, and may provide guidance for exploring low cost and highly efficient carbon dioxide emission reduction photocatalysts.

Heterocyclic-Additive-Activated Dinuclear Dysprosium Electrocatalysts for Heterogeneous Water Oxidation

Heterogeneous catalysis based on air-stable lanthanide complexes is relatively rare, especially for electrochemical water oxidation and reduction. Therefore, it is highly desired to investigate the synergy caused by cocatalysts on the lanthanide complex family for heterogeneous catalysis because of their structural diversity, air/moisture insensitivity, and easy preparation under an air atmosphere. Two mononuclear and three dinuclear dysprosium complexes containing a series of Schiff-base ligands have been demonstrated as robust electrocatalysts for triggering heterogeneous water oxidation in alkaline solution, in which the complex [Dy₂(hmb)₂(OAc)₄]·MeCN(3) was revealed to have the best activity toward heterogeneous water oxidation among all five complexes in the present study. The molecular activation of dysprosium complexes has also been investigated with a series of N-containing heterocyclic additives [i.e., 4-(dimethylamino)pyridine (DMAP), bis(triphenylphosphine)iminium chloride ([PPN]Cl), indole, and quinoline]. In particular, the corresponding overpotential was effectively enhanced by 211 mV (at a current density of 10 mA cm^-2) with the assistance of DMAP. On the basis of electrochemical and ex situ/in situ spectroscopic investigations, the best catalyst, DMAP-complex 3 on a carbon paper electrode, was confirmed with well-maintained molecular identity during heterogeneous water oxidation free of forming any dysprosium oxide and/or undesired products.

Rare-Earth Metal Complexes Supported by Polydentate Phenoxy-Type Ligand Platforms: C-H Activation Reactivity and CO2/Epoxide Copolymerization Catalysis

Mono- and dinuclear group 3 metal complexes incorporating polydentate bis(imino)phenoxy {N²O}^- and bis(amido)phenoxy {N²O}^3- ligands were synthesized by alkane elimination reactions from the tris(alkyl) M(CH₂SiMe₃)₃(THF)₂ and M(CH₂C₆H₄-o-NMe₂)₃ (M = Sc, Y) precursors. Complex 1a-Y was used for the selective C-H activation of 2-phenylpyridine at the 2'-phenyl position affording the corresponding bis(aryl) product 3a-Y, which was found to be reacted reluctantly with weak electrophiles (styrene, imines, hydrosilanes). The mechanism of formation of 3a-Y was established by DFT calculations, which also corroborated high stability of the complex toward insertion of styrene, apparently stemming from the inability to form the corresponding adduct. Copolymerization of cyclohexene oxide and CO₂ promoted by 1a-Y (0.1-0.5 mol %) was demonstrated to proceed under mild conditions (toluene, 70 °C, P_CO2 = 12 bar) giving polycarbonates with high efficiency (maximal TON of 460) and selectivity (97-99% of carbonate units).

Update and Challenges in Carbon Dioxide-Based Polycarbonate Synthesis

The utilization of carbon dioxide as a comonomer to produce polycarbonates has attracted a great deal of attention from both industrial and academic communities because it promises to replace petroleum-derived plastics and supports a sustainable environment. Significant progress in the copolymerization of cyclic ethers (e.g., epoxide, oxetane) and carbon dioxide has been made in recent decades, owing to the rapid development of catalysts. In this Review, the focus is to summarize and discuss recent advances in the development of homogeneous catalysts, including metal- and organo-based complexes, as well as the preparation of carbon dioxide-based block copolymer and functional polycarbonates.

Carbonyl group and carbon dioxide activation by rare-earth-metal complexes

The rare-earth elements (Ln = Sc, Y, La-Lu) are widely used in stoichiometric and catalytic carbonyl group transformations. Sufficient availability, non-toxicity, high oxophilicity, tunable ion size/Lewis acidity and enhanced ligand exchangeability have been major driving factors for their successful implementation. Routinely employed reagents for stoichiometric carbonyl group transformations are divalent ytterbium and samarium compounds (e.g., ketone reduction), bimetallic CeCl3/LiR (C-C coupling), or ceric ammonium nitrate CAN (cyclic ketone oxidation). Rare-earth-metal triflates, and in particular Sc(OTf)3, are prominent examples of Lewis acid catalysts for versatile use in organic synthesis (e.g., Aldol and Michael reactions). Moreover, Ln(ii) and Ln(iii) complexes efficiently catalyze the (co)polymerization of carbonyl group-containing monomers including lactones, lactides, acrylates, and carbon dioxide. Featuring the most notorious greenhouse gas, CO2 is currently assessed as a cheap, abundant, and non-toxic C1 building block. Ln(iii) complexes are not only capable of efficient CO2 capture via reversible insertion but also of CO2 activation for catalytic conversions (copolymerization/cycloaddition with epoxides). This perspective focuses on structurally elucidated Ln complexes resulting from ketone or carbonyl derivative activation/insertion as well as carbon dioxide insertion products. The respective compounds will be sorted by structural motifs and, if applicable, details on reactivity and feasibility of catalytic reactions are presented. The article is subdivided in three parts: (i) donor and insertion products of ketones and aldehydes, (ii) redox-enhanced activation of carbonyl derivatives, and (iii) CO2 insertion/redox products and homogeneous catalytic conversion.

Monometallic lanthanide salicylhydrazone complexes exhibiting strong near-infrared luminescence

We report the synthesis of monometallic lanthanide complexes supported by one salicylhydrazone ligand. Complexes of neodymium, erbium, and ytterbium have been synthesized, and exhibit near infrared luminescence with modest to high quantum yields. The luminescence of ytterbium is increased by a factor of five when comparing our complex to other salicylhydrazone-supported complexes.

Phenylacetylene and Carbon Dioxide Activation by an Organometallic Samarium Complex

Small molecule activation is a topic of growing importance and the use of low-valent f-elements to perform these reactions is nowadays well established. The complex Cptt2Sm(thf) (1, Cptt = 1,3-(tBu)2Cp) is shown to activate the alkyne C–H bond of phenylacetylene to form the Cptt2Sm(C≡C–Ph)(thf) complex. The subsequent reaction of this Sm(III) complex with CO2 leads to the CO2 insertion, yielding a dimeric [Cptt2Sm(O2C–C≡C–Ph)]2 complex (2), in which the carbon dioxide has been inserted in the Sm–C bond. Along with the experimental chemical structure analysis, theoretical calculations have been performed in order to rationalize the formation of 1 and 2.