Cyclic Carbonates from CO2 and Epoxides Catalyzed by Tetra- and Pentacoordinate Amidinate Aluminum Complexes

Synthesis and Characterization of Cardanol-Based Non-Isocyanate Polyurethane

This paper describes the synthesis of NIPU by using cardanol as starting material. A cardanol formaldehyde oligomer was first prepared through the reaction of cardanol and formaldehyde, catalyzed by citric acid. The resulting oligomer was then subjected to epoxidation with m-chloroperbenzoic acid to obtain an epoxide compound, which was subsequently used to fix carbon dioxide (CO2) and form a cyclic carbonate. Using this cyclic carbonate, along with an amine, cardanol-based isocyanate polyurethane (NIPU) was prepared. Different characterization methods, such as Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and thermogravimetric analysis (TGA), were used to confirm the synthesis of the four intermediate products and NIPU in the reaction process. This study highlights the promise of bio-based NIPU as a sustainable alternative in a number of applications while offering insightful information on the synthesis and characterization of the material.

Solvent- and Co-Catalyst-Free Cycloaddition of Carbon Dioxide and Epoxides Catalyzed by Recyclable Bifunctional Niobium Complexes

CO₂, as a cheap and abundant renewable C1 resource, can be used to synthesize high value-added chemicals. In this paper, a series of bifunctional metallic niobium complexes were synthesized and their structures were characterized by IR, NMR and elemental analysis. All of these complexes have been proved to be efficient catalysts for the coupling reaction of CO₂ and epoxides to obtain cyclic carbonates under solvent- and co-catalyst-free conditions. By using CO₂ and propylene oxide as a model reaction, the optimal reaction conditions were systematically screened as: 100 °C, 1 MPa, 2 h, ratio of catalyst to alkylene oxide 1:100. Under the optimal reaction conditions, the bifunctional niobium catalysts can efficiently catalyze the coupling reaction with high yield and excellent selectivity (maximum yield of >99% at high pressure and 96.8% at atmospheric pressure). Moreover, this series of catalysts can also catalyze the coupling reaction at atmospheric pressure and most of them showed high conversion of epoxide. The catalysts have good substrate suitability and are also applicable to a variety of epoxides including diepoxides and good catalytic performances were achieved for producing the corresponding cyclic carbonates in most cases. Furthermore, the catalysts can be easily recovered by simple filtration and reused for at least five times without obvious loss of catalytic activity and selectivity. Kinetic studies were carried out preliminarily for the bifunctional niobium complexes with different halogen ions (3a(Cl^-), 3b(Br^-), 3c(I^-)) and the formation activation energies (E_a) of cyclic carbonates were obtained. The order of apparent activation energy E_a is 3a (96.2 kJ/mol) > 3b (68.2 kJ/mol) > 3c (37.4 kJ/mol). Finally, a possible reaction mechanism is proposed.

Closing the loop in the synthesis of heteroscorpionate-based aluminium helicates: catalytic studies for cyclic carbonate synthesis

Novel polynuclear helical aluminium complexes supported by bulky heteroscorpionate ligands have been developed and characterised. The use of bulkier ligands has allowed the isolation of unprecedented intermediates for the preparation of helical aluminium complexes. The catalytic activity of these aluminium complexes for cyclic carbonates formation has also been investigated under mild reaction conditions. The combination of complex 16 and Bu₄NBr catalysed the synthesis of a broad range of monosubstituted cyclic carbonates from their corresponding epoxides and CO₂ at 25 °C and one bar of CO₂ pressure. This catalyst system also showed good catalytic activity for the preparation of disubstituted cyclic carbonates from internal epoxides and CO₂.

Syntheses, Characterization, and Application of Tridentate Phenoxyimino-Phenoxy Aluminum Complexes for the Coupling of Terminal Epoxide with CO2: From Binary System to Single Component Catalyst

A series of binuclear aluminum complexes 1–3 supported by tridentate phenoxyimino-phenoxy ligands was synthesized and used as catalysts for the coupling reaction of terminal epoxide with carbon dioxide. The aluminum complex 1, which is catalytically inactive toward the coupling of epoxide with CO2 by itself, shows moderate activity in the presence of excess nucleophiles or organic bases at high temperature. In sharp contrast to complex 1, bifunctional complexes 2 and 3, which incorporate tertiary amine groups as the built-in nucleophile, are able to efficiently transform terminal epoxide with CO2 to corresponding cyclic carbonates as a sole product by themselves at 100 °C. The number of amine groups on the ligand skeleton and the reaction temperature exert a great influence on the catalytic activity. The bifunctional complexes 2 and 3 are also active at low carbon dioxide pressure such as 2 atm or atmospheric CO2 pressure. Kinetic studies of the coupling reactions of chloropropylene oxide/CO2 and styrene oxide/CO2 using bifunctional catalysts under atmospheric pressure of CO2 demonstrate that the coupling reaction has a first-order dependence on the concentration of the epoxide.

Highly Active CO2 Fixation into Cyclic Carbonates Catalyzed by Tetranuclear Aluminum Benzodiimidazole-Diylidene Adducts

A set of tetranuclear alkyl aluminum adducts 1 and 2 supported by benzodiimidazole-diylidene ligands L1, N,N’-(1,5-diisopropylbenzodiimidazole-2,6-diylidene)bis(propan-2-amine), and L2, N,N’-(1,5-dicyclohexyl-benzodiimidazole-2,6-diylidene)dicyclohexanamine were synthetized in exceptional yields and characterized by spectroscopic methods. These compounds were studied as catalysts for cyclic carbonate formation (3a–o) from their corresponding terminal epoxides (2a–o) and carbon dioxide utilizing tetrabutylammonium iodide as a nucleophile in the absence of a solvent. The experiments were carried out at 70 °C and 1 bar CO2 pressure for 24 h and adduct 1 was the most efficient catalyst for the synthesis of a large variety of monosubstituted cyclic carbonates with excellent conversions and yields.

Amidinate based indium(III) monohalides and β-diketiminate stabilized In(II)-In(II) bond: synthesis, crystal structure, and computational study

Synthesis and bonding aspects of mononuclear bis-amidinate indium(iii) monohalides L2InX (1-3), where L = PhC(NtBu)2; X is F (1), Br (2) or I (3) and β-diketiminate (NacNac) stabilized In(ii) dimer (MesNacNac)2In2Br2 (4) with In-In bond are reported along with the single-crystal X-ray structures of 2-4.

Effect and Mechanism of Aluminum(III) for Guaiacol-Glyoxylic Acid Condensation Reaction in Vanillin Production

3-methoxy-4-hydroxymandelic acid (VMA) was the critical intermediate for the synthesis of vanillin by the glyoxylic acid method. Meanwhile, a valuable byproduct (2-hydroxy-3-methoxy-mandelic acid, o-VMA) was obtained during the reaction. Al3+ was found to be a helpful catalyst in increasing the selectivity for VMA and o-VMA. In the presence of Al3+, the selectivity for VMA and o-VMA increased from 83 to 88% and from 3 to 8%, respectively, while that of the helpless byproduct 2-hydroxy-3-methoxy-1,5-mandelic acid (di-VMA) decreased from 14% to less than 4%. The kinetics based on the kinetic equation of the condensation reaction was studied by the initial concentration method. The results indicated that the involvement of Al3+ could reduce the activation energy of the reaction on the basis of the Arrhenius equation. Combined with thermogravimetric analysis, in situ Fourier transform-infrared spectroscopy, and 1H NMR research, Al3+ was found to interact with guaiacol through Al-O and Al···H, which further improved the selectivity of the VMA and o-VMA and reduced the selectivity of di-VMA by adding the electronegativity of the ortho- and para-positions of hydroxyl groups of guaiacol.

An Aminopyridinium Ionic Liquid: A Simple and Effective Bifunctional Organocatalyst for Carbonate Synthesis from Carbon Dioxide and Epoxides

An aminopyridinium ionic liquid is presented as a green, tunable, and active metal-free one-component catalytic system for the atom-efficient transformation of oxiranes and CO₂ to cyclic carbonates. Inclusion of a positively charged moiety into aminopyridines, through a simple single-step synthesis, provides a one-component ionic liquid catalytic system with superior activity; effective in ring opening of epoxide, CO₂ inclusion, and stabilization of oxoanionic intermediates. An efficiency assessment of a variety of positively charged aminopyridines was pursued, and the impact of temperature, catalyst loading, and the kind of nucleophile on the catalytic performance was also investigated. Under solvent-free conditions, this bifunctional organocatalytic system was used for the preparation of 18 examples of cyclic carbonates from a broad range of alkyl- and aryl-substituted oxiranes and CO₂ , where up to 98 % yield and high selectivity were achieved. DFT calculations validated a mechanism in which nucleophilic ring-opening and CO₂ inclusion occur simultaneously towards cyclic carbonate formation.

Aluminum complexes with new non-symmetric ferrocenyl amidine ligands and their application in CO2 transformation into cyclic carbonates

A set of alkyl aluminum complexes supported by non-symmetric ferrocenyl amidine ligands were used as catalysts for the preparation of cyclic carbonates from epoxides and carbon dioxide using Bu₄NI as a co-catalyst.

Immobilized BiCl3@Bi@g-C3N4 on one-dimensional multi-channel carbon fibers as heterogeneous catalyst for efficient CO2 cycloaddition reaction

A novel heterogeneous catalyst (BBCNC), where the Bi, BiCl₃ and g-C₃N₄ were deposited on one-dimensional multi-channel carbon fibers (CNFs), was developed and characterized.

Efficient Aluminum Catalysts for the Chemical Conversion of CO2 into Cyclic Carbonates at Room Temperature and Atmospheric CO2 Pressure

A series of dimeric aluminum compounds [Al(OCMe₂ CH₂ N(R)CH₂ X)]₂ [X=pyridin-2-yl, R=H (Pyr^H ); X= pyridin-2-yl, R=Me (Pyr^Me ); X=furan-2-yl, R=H (Fur^H ); X= furan-2-yl, R=Me (Fur^Me ); X=thiophen-2-yl, R=H (Thio^H ); X= thiophen-2-yl, R=Me (Thio^Me )] containing heterocyclic pendant group attached to the nitrogen catalyze the coupling of CO₂ with epoxides under ambient conditions. In a comparison of their catalytic activities with those of aluminum complexes without pendant groups at N [X=H, R=H (H^H ); X=H, R=Me (H^Me )] or with non-heterocyclic pendant groups [X=CH₂ CH₂ OMe, R=H (OMe^H ); X=CH₂ CH₂ NMe₂ , R=H (NMe2^H ); X=CH₂ CH₂ NMe₂ , R=Me (NMe2^Me )], complexes containing heterocycles, in conjunction with (nBu)₄ NBr as a cocatalyst, show higher catalytic activities for the synthesis of cyclic carbonates under the same ambient conditions. The best catalyst system for this reaction is Pyr^H /(nBu)₄ NBr system, which gives a turnover number of 99 and a turnover frequency of 4.1 h^-1 , making it 14- and 20-times more effective than H^H /(nBu)₄ NBr and H^Me /(nBu)₄ NBr, respectively. Although there are no direct interactions between the aluminum and the heteroatoms in the heterocyclic pendants, electronic effects combined with the increased local concentration of CO₂ around the active centers influences the catalytic activity in the coupling of CO₂ with epoxides. In addition, Pyr^H /(nBu)₄ NBr shows broad epoxide substrate scope and seven terminal epoxides and two internal epoxides undergo the designed reaction.

Unexpected intramolecular N-arylcyano-β-diketiminate cyclization in new aminoquinoline derivative complexes of aluminium for CO2 fixation into cyclic carbonates

exo-Dig intramolecular cyclization of β-diketiminates allowed to obtain 4-amino-3-iminoquinolines ligands through a novel pathway. Al(III) complexes bearing these ligands where active towards the synthesis of cyclic carbonates from epoxides and CO₂.

Aromatic guanidines as highly active binary catalytic systems for the fixation of CO2 into cyclic carbonates under mild conditions

The formation of hydrogen bonding causes a considerable decrease in the reaction temperature and CO₂ pressure used in this process.

Ir-Catalyzed ring-opening of oxa(aza)benzonorbornadienes with water or alcohols

A highly efficient Ir-catalyzed ring-opening reaction of oxa(aza)benzonorbornadienes with water was firstly developed, which afforded a mild access to substituted dihydronaphthalene products with excellent yields (up to 99%) within 30 min.