Multinuclear cobalt-salen complexes with phenylene linker for epoxide polymerizations

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.

Bimetallic Zinc Catalysts for Ring-Opening Copolymerization Processes

Novel bimetallic zinc acetate complexes supported by heteroscorpionate ligands have been developed for the ring-opening copolymerization of cyclohexene oxide and CO₂ and the terpolymerization of cyclohexene oxide, phthalic anhydride, and CO₂. Heteroscorpionate ligands precursors L₁-L₃ were reacted with two equivalents of zinc acetate to afford the dinuclear zinc complexes [{Zn(κ³-bpzappe)}(μ-O₂CCH₃)₃-{Zn(HO₂CCH₃)}] (1), [{Zn(κ³-bpzbdmape)}(μ-O₂CCH₃)₃-{Zn(HO₂CCH₃)}] (2), and [{Zn(κ³-bpzbdeape)}(μ-O₂CCH₃)₃{Zn(HO₂CCH₃)}] (3) in excellent yields. The molecular structure of these compounds was determined spectroscopically and confirmed by X-ray diffraction analysis. Zinc acetate complexes 1-3 were screened as catalysts for the copolymerization of cyclohexene oxide and CO₂ to produce poly(cyclohexene)carbonate, and complex 3 was found to be the most active catalyst for this process in the absence of a cocatalyst. Furthermore, the terpolymerization of cyclohexene oxide, phthalic anhydride, and CO₂ was studied using the combination of complex 3 and 4-dimethylaminopyridine as catalyst system yielding the corresponding polyester-polycarbonate materials.

Discrete and polymeric ensembles based on dinuclear molybdenum(vi) building blocks with adaptive carbohydrazide ligands: from the design to catalytic epoxidation

Discrete and polymeric ensembles based on dimolybdenum(vi) units with adaptive carbohydrazide ligands are described. The polymeric complexes are efficient catalysts for cyclooctene epoxidation under eco-friendly conditions.

Copolymerization of epoxides with cyclic anhydrides catalyzed by dinuclear cobalt complexes

The alternating copolymerization of epoxides with cyclic anhydrides (CAs) is a highly diverse synthetic method for polyesters as the polymers’ architectures and properties can be easily controlled depending on the combination of two monomers. Thus, a variety of catalyst designs has been reported to prepare the desired copolymers efficiently. We herein report dinuclear cobalt–salen complexes with a benzene ring as a linker and their activities in copolymerization reactions. The dinuclear cobalt complexes showed a higher catalytic activity for the copolymerization of propylene oxide with phthalic anhydride than the corresponding mononuclear cobalt–salen complex and achieved one of the highest turnover frequencies ever reported. A variety of epoxides and CAs were also found to be copolymerized successfully by the dinuclear cobalt complex with a high catalytic activity.

Bimetallic Chromium Catalysts with Chain Transfer Agents: A Route to Isotactic Poly(propylene oxide)s with Narrow Dispersities

Bimetallic chromium catalysts are investigated for the enantioselective polymerization of propylene oxide. The catalyst is composed of two salen chromium species linked by an alkyl chain, the length of which significantly impacts the rate of polymerization. While the use of a chloride initiator on the catalyst resulted in bimodal molecular weight distributions, switching to a trifluoroacetate initiating group and adding a diol chain transfer agent afforded polymers of controllable molecular weight with low, unimodal dispersities.

Dinuclear iron(iii) complexes bearing phenylene-bridged bis(amino triphenolate) ligands as catalysts for the copolymerization of cyclohexene oxide with carbon dioxide or phthalic anhydride

Dinuclear iron(iii) complexes bearing rigid ortho-, meta-, and para-phenylene bridges as effective catalysts for CHO/CO₂ and CHO/PA copolymerizations.