An Efficient and Versatile Lanthanum Heteroscorpionate Catalyst for Carbon Dioxide Fixation into Cyclic Carbonates

A new lanthanum heteroscorpionate complex has shown exceptional catalytic activity for the synthesis of cyclic carbonates from epoxides and carbon dioxide. This catalyst system also promotes the reaction of bio-based epoxides to give an important class of bis(cyclic carbonates) that can be further used for the production of bio-derived non-isocyanate polyurethanes. The catalytic process requires low catalyst loading and mild reaction conditions for the synthesis of a wide range of cyclic carbonates.

Unique Base-Initiated Depolymerization of Limonene-Derived Polycarbonates

The depolymerization of poly(limonene carbonate) (PLC) initiated by 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was investigated. The strong organic base TBD was capable of deprotonating the OH-terminated PLC, leading to fast degradation via backbiting reactions at high temperature. An interesting feature of the base-initiated breakdown of PLC lies in the quantitative depolymerization into the corresponding initial limonene oxide monomer. This result implies the complete back-to-monomer recyclability of the fully biobased PLC, which accordingly can be considered as a really sustainable material. Additionally, the stability of PLC when exposed to TBD was enhanced by an end-capping reaction, which further supported the proposed degradation pathway.

One-Component Aluminum(heteroscorpionate) Catalysts for the Formation of Cyclic Carbonates from Epoxides and Carbon Dioxide

New neutral and zwitterionic chiral NNO-donor scorpionate ligands 1 and 2 were designed to obtain new mononuclear and dinuclear NNO-heteroscorpionate aluminum complexes. Reaction of 1 with [AlR₃ ] (R=Me, Et) in a 1:1 or 1:2 molar ratio afforded the neutral mononuclear alkyl complexes [AlR₂ (κ² -bpzappe)] {R=Me (3), Et (4); bpzappeH=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-(dimethylamino)phenyl]-1-phenylethanol} and bimetallic complexes [{AlR₂ (κ² -bpzappe)}(μ-O){AlR₃ }] [R=Me (5), Et (6)]. By reaction of complexes 3-6 with PhCH₂ Br, mononuclear and dinuclear cationic aluminum complexes [AlR₂ (κ² -bbpzappe)]Br {R=Me (7), Et (8); bbpzappeH=N-benzyl-4-[2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-hydroxy-1-phenylethyl]-N,N-dimethylbenzenaminium bromide} and [{AlR₂ (κ² -bbpzappe)}(μ-O){AlR₃ }]Br [R=Me (9), Et (10)] were synthesized. Both neutral aluminum complexes in the presence of Bu₄ NBr and cationic aluminum complexes were investigated as catalysts for cyclic carbonate formation from epoxides and carbon dioxide. Amongst them, complex 10 was found to be an efficient one-component catalyst for the synthesis of cyclic carbonates from both monosubstituted and internal epoxides and was shown to have broad substrate scope.

A Bimetallic Aluminium(Salphen) Complex for the Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide

A bimetallic aluminium(salphen) complex is reported as a sustainable, efficient and inexpensive catalyst for the synthesis of cyclic carbonates from epoxides and carbon dioxide. In the presence of this complex and tetrabutylammonium bromide, terminal and internal epoxides reacted at 50 °C and 10 bar carbon dioxide pressure to afford their corresponding cyclic carbonates in yields of 50-94 % and 30-71 % for terminal and internal cyclic carbonates, respectively. Mechanistic studies using deuterated epoxides and an analogous monometallic aluminium(salphen) chloride complex support a mechanism for catalysis by the bimetallic complex, which involves intramolecular cooperative catalysis between the two aluminium centres.

Computer-aided rational design of Fe(iii)-catalysts for the selective formation of cyclic carbonates from CO2 and internal epoxides

The mechanism of Fe-catalyzed cyclic carbonate formation of CO₂ and internal epoxides was studied to identify design strategies for more efficient catalysts.

Synthesis of Polycarbonates and Poly(ether carbonate)s Directly from Carbon Dioxide and Diols Promoted by a Cs2CO3/CH2Cl2 System

Recently, polycarbonates have attracted considerable research interest because of their potential biodegradability and sustainability. Here, we present a direct route for the synthesis of polycarbonates and poly(ether carbonate)s from carbon dioxide (CO₂) and diols, promoted by Cs₂CO₃ and CH₂Cl₂ under 1 atm of CO₂. Quantitative conversion of diols and polymers with up to 11 kg/mol molecular weight could be obtained. While benzylic diols lead to predominantly carbonate linkage, aliphatic diols result in the incorporation of the methylene unit of CH₂Cl₂ that produces poly(ether carbonate)s. Both primary and secondary diols have been successfully incorporated into the polymer chain.

Chemoselective Polymerizations from Mixtures of Epoxide, Lactone, Anhydride, and Carbon Dioxide

Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymerization (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides, and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers-ε-caprolactone, cyclohexene oxide, phthalic anhydride, and carbon dioxide-are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity, resulting in block sequence control and predictable compositions (esters and carbonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically controlled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.

Catalysts for CO2/epoxide ring-opening copolymerization

This article summarizes and reviews recent progress in the development of catalysts for the ring-opening copolymerization of carbon dioxide and epoxides. The copolymerization is an interesting method to add value to carbon dioxide, including from waste sources, and to reduce pollution associated with commodity polymer manufacture. The selection of the catalyst is of critical importance to control the composition, properties and applications of the resultant polymers. This review highlights and exemplifies some key recent findings and hypotheses, in particular using examples drawn from our own research.

Ring-opening copolymerisation of cyclohexene oxide and carbon dioxide catalysed by scorpionate zinc complexes

New bimetallic heteroscorpionate zinc complexes have been developed and used as efficient catalysts for the synthesis of poly(cyclohexene carbonate).

State-of-the-art catechol porphyrin COF catalyst for chemical fixation of carbon dioxide via cyclic carbonates and oxazolidinones

A highly porous, crystalline catechol porphyrin COF was synthesized and applied as an organocatalyst for the fixation of carbon dioxide to synthesize value-added chemicals such as cyclic carbonates and oxazolidinones under solvent and transition-metal-free conditions.

Macrocyclic Dizinc(II) Alkyl and Alkoxide Complexes: Reversible CO2 Uptake and Polymerization Catalysis Testing

The synthesis of three new dizinc(II) complexes bearing a macrocyclic [2 + 2] Schiff base ligand is reported. The bis(anilido)tetraimine macrocycle reacts with diethylzinc to form a bis(ethyl)dizinc(II) complex, [L(Et)Zn2Et2] (1). The reaction of complex 1 with isopropyl alcohol is reported, forming a bis(isopropyl alkoxide)dizinc complex, [L(Et)Zn2((i)PrO)2] (2). Furthermore, complex 1, with 2 equiv of alcohol, is applied as an initiator for racemic lactide ring-opening polymerization. It shows moderately high activity, resulting in a pseudo-first-order rate coefficient of 9.8 × 10(-3) min(-1), with [LA] = 1 M and [initiator] = 5 mM at 25 °C and in a tetrahydrofuran solvent. Polymerization occurs with good control, as evidenced by the linear fit to a plot of molecular weight versus conversion, the narrow dispersities, and the limited transesterification. The same initiating system is inactive for the ring-opening copolymerization of carbon dioxide (CO2) and cyclohexene oxide at 80 °C and 1 bar of CO2 pressure. However, stoichiometric reactions between complex 2 and CO2, at 1 bar pressure, result in the reversible formation of new dizinc carbonate species, [L(Et)Zn2((i)PrO)((i)PrOCO2)] (3a) and [L(Et)Zn2((i)PrOCO2)2] (3b), and the reaction was studied using density functional theory calculations. All of the new complexes, 1-3b, are fully characterized, including NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.

Carbon dioxide capture and utilization: using dinuclear catalysts to prepare polycarbonates

The copolymerization of epoxides, including cyclohexene oxide and vinyl-cyclohexene oxide with carbon dioxide are presented. These processes are catalyzed using a homogeneous di-zinc complex that shows good activity and very high selectivities for polycarbonate polyol formation. The polymerizations are investigated in the presence of different amounts of exogenous reagents, including water, diols and diamines, as models for common contaminants in any carbon dioxide capture and utilization scenario.

Zr(iv) complexes containing salan-type ligands: synthesis, structural characterization and role as catalysts towards the polymerization of ε-caprolactone, rac-lactide, ethylene, homopolymerization and copolymerization of epoxides with CO2

Three new Zr(iv) complexes bearing salan-type diamine bis(phenolato) ligands were synthesized and their activities towards the ROP of ε-CL, rac-LA and homopolymerization, copolymerization and coupling of epoxides with CO₂ were investigated.

Thioether-triphenolate bimetallic iron(iii) complexes as robust and highly efficient catalysts for cycloaddition of carbon dioxide to epoxides

The selective and effective synthesis of organic carbonates under mild conditions, starting from carbon dioxide and oxiranes, catalyzed by metal complexes is currently a focus of interest for both industrial and academic researchers. We recently developed a novel thioether-triphenolate iron(iii) catalyst (Ct-Bu) that has proven to be highly active for the coupling of CO₂ with epoxides, resulting in cyclic organic carbonates under solvent-free conditions. In the current work, the properties of this novel class of catalysts were extensively investigated. In particular, the steric properties of the ligand were modulated by changing the substituents of the aromatic rings in order to obtain a deeper knowledge of the relationship between the complex structure and catalytic performance/selectivity for these iron complexes. Notably, the less steric demanding iron(iii) CH complex synthesized shows, when activated by n-tetrabutylammonium bromide, an impressive turnover frequency (TOF) of 3800 h⁻¹ for the formation of propylene carbonate and glycerol carbonate which are, by far, the highest reported for an iron based catalyst and compares well with the most active catalyst based on other metals.

Ring-opening copolymerization (ROCOP): synthesis and properties of polyesters and polycarbonates

This feature article highlights the opportunities presented by ring-opening copolymerization (ROCOP) as a controlled route to prepare polyesters and polycarbonates.

Kinetics of the (salen)Cr(iii)- and (salen)Co(iii)-catalyzed copolymerization of epoxides with CO2, and of the accompanying degradation reactions

The catalytic cycle of the (salen)M(iii)-catalyzed copolymerization for a variety of epoxides with CO₂ is elucidated using computational chemistry, and factors that control the kinetics and product distribution of these reactions are described.

A MALDI-TOF MS analysis study of the binding of 4-(N,N-dimethylamino)pyridine to amine-bis(phenolate) chromium(iii) chloride complexes: mechanistic insight into differences in catalytic activity for CO2/epoxide copolymerization

Amine-bis(phenolato)chromium(iii) chloride complexes, [LCrCl], are capable of catalyzing the copolymerization of cyclohexene oxide with carbon dioxide to give poly(cyclohexane) carbonate. When combined with 4-(N,N-dimethylamino)pyridine (DMAP) these catalyst systems yield low molecular weight polymers with moderately narrow polydispersities. The coordination chemistry of DMAP with five amine-bis(phenolato)chromium(iii) chloride complexes was studied by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The amine-bis(phenolato) ligands were varied in the nature of their neutral pendant donor-group and include oxygen-containing tetrahydrofurfuryl and methoxyethyl moieties, or nitrogen-containing N,N-dimethylaminoethyl or 2-pyridyl moieties. The relative abundance of mono and bis(DMAP) adducts, as well as DMAP-free ions is compared under various DMAP : Cr complex ratios. The [LCr]⁺ cations show the ability to bind two DMAP molecules to form six-coordinate complex ions in all cases, except when the pendant group is N,N-dimethylaminoethyl (compound 3). Even in the presence of a 4 : 1 ratio of DMAP to Cr, no ions corresponding to [L3Cr(DMAP)₂]⁺ were observed for the complex containing the tertiary sp³-hybridized amino donor in the pendant arm. The difference in DMAP-binding ability of these compounds results in differences in catalytic activity for alternating copolymerization of CO₂ and cyclohexene oxide. Kinetic investigations by infrared spectroscopy of compounds 2 and 3 show that polycarbonate formation by 3 is twice as fast as that of compound 2 and that no initiation time is observed.

Carboxylic acid derivatives via catalytic carboxylation of unsaturated hydrocarbons: whether the nature of a reductant may determine the mechanism of CO2incorporation?

Advances and recent breakthroughs in catalytic synthesis of carboxylic acids and their derivatives starting from unsaturated hydrocarbons are discussed.

Insights into hydrogen bond donor promoted fixation of carbon dioxide with epoxides catalyzed by ionic liquids

Experimental and DFT studies demonstrated that additional EG could cooperate with ILs to facilitate the cycloaddition reactionviahydrogen bond activation.