In Situ Generation of CoIII-Salen Complexes for Copolymerization of Propylene Oxide and CO2

Non-covalent interactions in molecular architectures and solvent-free catalytic activity towards CO2 fixation of mononuclear Co(III) complexes installed on modified Schiff base ligands

A set of mononuclear cobalt(III) octahedral complexes {[Co(LH)(acac)] (Co-1H), [Co(LBr)(acac)] (Co-1Br), and [Co(LNO2)(acac)] (Co-1NO2)} were synthesized using new-generation N/O donors, maleonitrile-tethered, tetradentate heteroscorpionate half-reduced Schiff base ligands, 2-((E)-2-hydroxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LH), 2-((E)-(5-bromo-2-hydroxybenzylidene)amino)-3-((pyridin-2-ylmethyl)amino)maleonitrile (H2LBr), and 2-((E)-2-hydroxy-5-nitrobenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LNO2). All the compounds were well characterized spectroscopically and structurally. The non-covalent interactions present in the lattice of Co-complexes were studied in detail to explain the molecular architecture using the Hirshfeld surface (HS) analysis. The catalytic activity of CO2 fixation towards epoxides under mild and solvent-free conditions was demonstrated. The synthesized complexes are catalysts that are well-active towards the CO2 activation under ambient conditions, whereas most of the reported catalysts require harsh conditions.

Dynamic kinetic resolution of transient hemiketals: a strategy for the desymmetrisation of prochiral oxetanols

Identification of an electron poor trifluoroacetophenone allows the formation of uniquely stable hemiketals from prochiral oxetanols. When exposed to a cobalt(ii) catalyst, efficient ring-opening to densely functionalized dioxolanes is observed. Mechanistic studies suggest an unprecedented redox process between the cobalt(ii) catalyst and the hemiketal that initiates the oxetane-opening. Based on this observation, a dynamic kinetic resolution of the transient hemiketals is explored that uses a Katsuki-type ligand for stereoinduction (up to 99 : 1 dr and 96 : 4 er) and allows a variety of 1,3-dioxolanes to be accessed (20 examples up to 98% yield).

Desymmetrization of prochiral oxetanols via an electron-deficient hemiketal intermediate is achieved. Key to this process is the catalyst's chiral recognition of one of the two hemiketal enantiomers enabling an efficient dynamic kinetic resolution.

No competitive inhibition of bicarbonate or carbonate for formate dehydrogenase from Candida boidinii -catalyzed CO2 reduction

Formate dehydrogenase from Candida boidinii (CbFDH) reversibly catalyzes the formate to CO2 with the redox coupling NAD+/NADH. While many studies on CbFDH-catalyzed formate oxidation in the presence of NAD+ are...

Synthesis, Characterization, and Catalytic Study of Amine-Bridged Bis(phenolato) Co(II) and Co(II/III)-M(I) Complexes (M = K or Na)

Co(II) complexes 1-3 bearing amine-bridged bis(phenolato) complexes have been synthesized through reactions of bis(phenols) with CoCl₂ or Co(OAc)₂. Oxidation of the Co(II) complex with air resulted in partial oxidation, generating mixed valence Co(II/III) complexes 4 and 5. In addition, due to the presence of alkali compounds (KOAc and NaOMe), 4 and 5 formed as Co-alkali metal heterometallic complexes, which are the first example of mixed valence Co(II/III)-M(I) (M = K or Na) complexes. Complexes 1-5 showed good activity in the cycloaddition of epoxides and CO₂ under atmospheric pressure, generating cyclic carbonates in 40-99% yields. Co(II/III)-Na(I) complex 5 performed better in reactions of bulkier substrates, underlining the enhanced activity of mixed valence Co-alkali metal heterometallic complexes. On the contrary, complex 5 showed limited activity in copolymerization of epoxide and CO₂.

Efficient Production of Poly(Cyclohexene Carbonate) via ROCOP of Cyclohexene Oxide and CO2 Mediated by NNO-Scorpionate Zinc Complexes

New mono- and dinuclear chiral alkoxide/thioalkoxide NNO-scorpinate zinc complexes were easily synthesized in very high yields, and characterized by spectroscopic methods. X-ray diffraction analysis unambiguously confirmed the different nuclearity of the new complexes as well as the variety of coordination modes of the scorpionate ligands. Scorpionate zinc complexes 2, 4 and 6 were assessed as catalysts for polycarbonate production from epoxide and carbon dioxide with no need for a co-catalyst or activator under mild conditions. Interestingly, at 70 °C, 10 bar of CO₂ pressure and 1 mol % of loading, the dinuclear thioaryloxide [Zn(bpzaepe)₂{Zn(SAr)₂}] (4) behaves as an efficient and selective one-component initiator for the synthesis of poly(cyclohexene carbonate) via ring-opening copolymerization of cyclohexene oxide (CHO) and CO₂, affording polycarbonate materials with narrow dispersity values.

Discovery of a cobalt (III) salen complex that induces apoptosis in Burkitt like lymphoma and leukemia cells, overcoming multidrug resistance in vitro

A very small number of cobalt complexes is examined in oncology research. In this work, we investigate the cobalt (III) salen complex MBR-60 that turns out to be a promising anticancer drug. It induces apoptosis in Nalm6 leukemia and BJAB lymphoma cells and overcomes multidrug resistances by blocking the drug efflux pump P-glycoprotein. It further develops the apoptotic effects over the intrinsic pathway. An activation of caspase-3, caspase-8 and caspase-9 can be detected by western blot analysis. The independence of CD95 is shown by similar apoptotic inductions in BJAB and BJAB FADDdn cells. MBR-60 displays synergistic effects with daunorubicin and vincristine and has a selectivity to tumor cells. In comparison to the apoptotic effects of MBR-60 in BJAB lymphoma cells, the cobalt-free ligand 5 does not influence these cells. The research highlights that a cobalt complex has a therapeutic potential for cancer treating with a focus on drug-resistant tumors.

Aluminum porphyrins with quaternary ammonium halides as catalysts for copolymerization of cyclohexene oxide and CO2: metal-ligand cooperative catalysis

Bifunctional Al porphyrins worked as excellent catalysts for the copolymerization of cyclohexene oxide (CHO) and CO₂.

Bifunctional Al^III porphyrins with quaternary ammonium halides, 2-Cl and 2-Br, worked as excellent catalysts for the copolymerization of cyclohexene oxide (CHO) and CO₂ at 120 °C. Turnover frequency (TOF) and turnover number (TON) reached 10 000 h^–1 and 55 000, respectively, and poly(cyclohexene carbonate) (PCHC) with molecular weight of up to 281 000 was obtained with a catalyst loading of 0.001 mol%. In contrast, bifunctional Mg^II and Zn^II counterparts, 3-Cl and 4-Cl, as well as a binary catalyst system, 1-Cl with bis(triphenylphosphine)iminium chloride (PPNCl), showed poor catalytic performances. Kinetic studies revealed that the reaction rate was first-order in [CHO] and [2-Br] and zero-order in [CO₂], and the activation parameters were determined: ΔH^‡ = 12.4 kcal mol^–1, ΔS^‡ = –26.1 cal mol^–1 K^–1, and ΔG^‡ = 21.6 kcal mol^–1 at 80 °C. Comparative DFT calculations on two model catalysts, Al^III complex 2′ and Mg^II complex 3′, allowed us to extract key factors in the catalytic behavior of the bifunctional Al^III catalyst. The high polymerization activity and carbonate-linkage selectivity originate from the cooperative actions of the metal center and the quaternary ammonium cation, both of which facilitate the epoxide-ring opening by the carbonate anion to form the carbonate linkage in the key transition state such as TS3b (ΔH^‡ = 13.3 kcal mol^–1, ΔS^‡ = –3.1 cal mol^–1 K^–1, and ΔG^‡ = 14.4 kcal mol^–1 at 80 °C).

Theoretical study on CO2 reduction catalyzed by formate dehydrogenase using the cation radical of a bipyridinium salt with an ionic substituent as a co-enzyme

Mechanism for formate dehydrogenase from Candida boidinii catalyzed CO₂ reduction to formate with the cation radical of a 4,4′-bipyridinium salt with an ionic substituent as a co-enzyme was clarified by theoretical studies.

Artificial co-enzyme based on carbamoyl-modified viologen derivative cation radical for formate dehydrogenase in the catalytic CO2 reduction to formate

The interaction between the single-electron reduced carbamoyl-modified-4,4-bipyridinium salt and CbFDH in the CO₂ reduction to formate is elucidated by enzymatic kinetic analysis, the docking simulation and density functional theory calculation.

Trivalent metal ions promote the malic enzyme-catalyzed building of carbon–carbon bonds from CO2and pyruvate

ME is an attractive biocatalyst for building carbon–carbon bonds through carboxylation of pyruvate with CO₂. The carboxylation of pyruvate with CO₂was promoted by adding a trivalent metal ion. In particular, Al³⁺accelerates ME-catalyzed carboxylation of pyruvate with CO₂.

En route to CO2-containing renewable materials: catalytic synthesis of polycarbonates and non-isocyanate polyhydroxyurethanes derived from cyclic carbonates

The strategies and challenges in the preparation of fully renewable materials prepared from CO₂ and biomass enabled by catalysis are presented.

Cobalt amino-bis(phenolate) complexes for coupling and copolymerization of epoxides with carbon dioxide

Electron-withdrawing groups on phenolate donors enhance polycarbonate production from CO₂ and cyclohexene oxide by Co(ii) amino-bis(phenolate) complexes.

Indium Catalysts for Low-Pressure CO2/Epoxide Ring-Opening Copolymerization: Evidence for a Mononuclear Mechanism?

The alternating copolymerization of CO₂/epoxides is a useful means to incorporate high levels of carbon dioxide into polymers. The reaction is generally proposed to occur by bimetallic or bicomponent pathways. Here, the first indium catalysts are presented, which are proposed to operate by a distinct mononuclear pathway. The most active and selective catalysts are phosphasalen complexes, which feature ligands comprising two iminophosphoranes linked to sterically hindered ortho-phenolates. The catalysts are active at 1 bar pressure of carbon dioxide and are most effective without any cocatalyst. They show low-pressure activity (1 bar pressure) and yield polymer with high carbonate linkage selectivity (>99%) and isoselectivity ( P_m > 70%). Using these complexes, it is also possible to isolate and characterize key catalytic intermediates, including the propagating indium alkoxide and carbonate complexes that are rarely studied. The catalysts are mononuclear under polymerization conditions, and the key intermediates show different coordination geometries: the alkoxide complex is pentacoordinate, while the carbonate is hexacoordinate. Kinetic analyses reveal a first-order dependence on catalyst concentration and are zero-order in carbon dioxide pressure; these findings together with in situ spectroscopic studies underpin the mononuclear pathway. More generally, this research highlights the future opportunity for other homogeneous catalysts, featuring larger ionic radius metals and new ligands, to operate by mononuclear mechanisms.

Mechanistic Insights into the Carbon Dioxide/Cyclohexene Oxide Copolymerization Reaction: Is One Metal Center Enough?

A detailed study on the mechanism for the alternating copolymerization of cyclohexene oxide (CHO) and CO₂ mediated by an [Al{amino-tri(phenolate)}]/NBu₄ I binary catalyst system was performed by using DFT-based methods. Four potential mechanisms (one monometallic and three bimetallic) were considered for the first propagation cycle of the CHO/CO₂ copolymerization. The obtained Gibbs free energies provided a rationale for the relative high activity of a non-covalent dimeric structure formed in situ and thus for the feasibility of a bimetallic mechanism to obtain polycarbonates quantitatively. Gibbs free energies also indicated that the alternating copolymerization was favored over the cyclic carbonate formation.