Cobalt complexes with α-amino acid ligands catalyze the incorporation of CO2 into cyclic carbonates

Arguably one of the largest research areas involving carbon dioxide (CO₂) fixation is the coupling of CO₂ to epoxides to form cyclic carbonates and polycarbonates. In this sense, there is an ever-increasing demand for the development of higher-performing catalytic systems that could counterbalance sustainability and energy efficiency in the production of cyclic carbonates. The use of abundant first-row transition metals combined with naturally occurring amino acids may be an ideal catalytic platform to fulfill this demand. Nevertheless, detailed information on the interactions between metal centers and natural products as catalysts in this transformation is lacking. Here a series of Co(III) amino acid catalysts operating in a binary system showed outstanding performance for the coupling reaction of epoxides and CO₂. Nine new complexes of the type trans(N)-[Co(aa)₂(bipy)]Cl (aa: ala, asp, lys, met, phe, pro, ser, tyr, and val) were used to explore the structure-activity relationship influenced by the complex outer coordination sphere, and its effect on the catalytic activity in the coupling reaction of CO₂ and epoxides.

Synthesis of Nonisocyanate Poly(hydroxy)urethanes from Bis(cyclic carbonates) and Polyamines

Nonisocyanate polyurethane materials with pending alcohol groups in the polymeric chain were synthesized by polyaddition reaction of bis(cyclic carbonates) onto diamines. For the platform molecule, 1,4-butanediol bis(glycidyl ether carbonate) (BGBC, 1) was used. The polyaddition reaction of 1 onto a wide range of diamines with different electronic and physical properties was explored. All PHUs were obtained quantitatively after 16 h at 80 °C temperature in MeCN as solvent. The low nucleophilicity of L-lysine has proven unable to ring-open the cyclic carbonate and, thus, no reaction occurred. The addition of DBU or TBD as the catalyst was tested and allows the obtention of the desired PHU. However, the presence of strong bases also led to the formation of polyurea fragments in the new PHU. The different poly(hydroxyurethane) materials were characterized using a wide range of spectroscopic techniques such as NMR, IR, MALDI-ToF, and using GPC studies. The thermal properties of the NIPUs were investigated by DSC and TGA analyses. Moreover, reactions employing different monomer ratios were performed, obtaining novel hydroxycarbamate compounds. Finally, sequential and one-pot experiments were also carried out to synthesize the PHUs polymers in one-step reaction.

Cycloaddition of di-substituted epoxides and CO2 under ambient conditions catalysed by rare-earth poly(phenolate) complexes

Lanthanum complex 1/TBAI is the first catalyst to achieve the cycloaddition of 1,2-disubstituted epoxides with 1 bar CO2 at room temperature. A DFT study discloses that the poly(phenolato) ligand plays a key role in the product dissociation step.

Acetylene hydrochlorination over tin nitrogen based catalysts: effect of nitrogen carbon-dots as nitrogen precursor

The catalysts comprising the main active compounds of Sn-Nx were synthesized using trichlorophenylstannane ((C6H5)Cl3Sn), nitrogen carbon-dots (NCDs), and activated carbon (AC) as starting materials, and the activity and stability of catalysts was evaluated in the acetylene hydrochlorination. According to the results on the physical and chemical properties of catalysts (TEM, XRD, BET, XPS and TG), it is concluded that NCDs@AC can increase (C6H5)Cl3Sn dispersity, retard the coke deposition of (C6H5)Cl3Sn/AC and lessen the loss of (C6H5)Cl3Sn, thereby further promoting the stability of (C6H5)Cl3Sn/AC. Based on the characterization results of C2H2-TPD and HCl adsorption experiments, we proposed that the existence of Sn-Nx can effectively strengthen the reactants adsorption of catalysts. By combing the FT-IR, C2H2-TPD and Rideal-Eley mechanism, the catalytic mechanism, in which C2H2 is firstly adsorbed on (C6H5)Cl3Sn to form (C6H5)Cl3Sn-C2H2 and then reacted with HCl to produce vinyl chloride, is proposed.

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.

Mn(iii)–porphyrin catalysts for the cycloaddition of CO2 with epoxides at atmospheric pressure: effects of Lewis acidity and ligand structure

Mn(iii)–porphyrin catalysts with electron-withdrawing substituents were designed to uncover electronic and structural aspects in the cycloaddition of CO₂ with epoxides.

Exploring a new dinuclear Fe(iii) complex for the fixation of atmospheric CO2 and optical recognition of nano-molar levels of Zn2+ ions

A dinuclear Fe(iii) complex (F1) of an imine derivative (L1) derived from 3-ethoxy-2-hydroxy-benzaldehyde and hydrazine, structurally characterised via single crystal X-ray studies, is employed for the catalytic conversion of epoxides to cyclic carbonates utilizing carbon dioxide. In addition, F1 is employed for the selective optical recognition of nano-molar levels of Zn²⁺ (42.23 nM) via a metal displacement approach. The Job plot reveals interactions between F1 and Zn²⁺ at a 1 : 3 molar ratio with an association constant of 7.71 × 10⁴ M⁻¹. Studies on the catecholase-like activity of F1 reveal a k_cat value of 4.42 × 10³ h⁻¹.

A new Fe(iii) complex (F1), structurally characterised using single crystal X-ray studies, was explored for CO₂ fixation, Zn²⁺ recognition and catecholase activity.

MIL-101(Cr) for CO2 Conversion into Cyclic Carbonates, Under Solvent and Co-Catalyst Free Mild Reaction Conditions

Mild reaction conditions (nearly room temperature and atmospheric CO2 pressure) for the cycloaddition of CO2 with epoxides to produce cyclic carbonates were investigated applying MIL-101(Cr) as a catalyst. The MIL-101 catalyst contains strong acid sites, which promote the ring-opening of the epoxide substrate. Moreover, the high surface area, enabling the adsorption of more CO2 (substrate), combined with a large pore size of the catalyst is essential for the catalytic performance. Additionally, epoxide substrates bearing electron-withdrawing substituents or having a low boiling point demonstrated an excellent conversion towards the cyclic carbonates. MIL-101(Cr) for the cycloaddition of carbon dioxide with epoxides is demonstrated to be a robust and stable catalyst able to be re-used at least five times without loss in activity.

Cobalt-Salen-Based Porous Ionic Polymer: The Role of Valence on Cooperative Conversion of CO2 to Cyclic Carbonate

Cobalt-salen-based porous ionic polymers, which are composed of cobalt and halogen anions decorated on the framework, effectively catalyze the CO₂ cycloaddition reaction of epoxides to cyclic carbonates under ambient conditions. The cooperative effect of bifunctional active sites of cobalt as the Lewis acidic site and the halogen anion as the nucleophile responds to the high catalytic performance. Moreover, density functional theory results indicate that the cobalt valence state and the corresponding coordination group influence the rate-determining step of the CO₂ cycloaddition reaction and the nucleophilicity of halogen anions.

Novel Cobalt Complex as an Efficient Catalyst for Converting CO2 into Cyclic Carbonates under Mild Conditions

Based on the ligand H2dpPzda (1), a novel cobalt complex [Co(H2dpPzda)(NCS)2]·CH3OH(2) has been synthesized and characterized. The Complex 2 exhibited excellent catalytic performance for converting CO2 into cyclic carbonates under mild conditions. For propylene oxide (PO) and CO2 synthesis of propylene carbonate (PC), the catalytic system showed a remarkable TOF as high as 29,200 h−1. The catalytic system also showed broad substrate scope of epoxide. Additionally, the catalyst could be recycled to maintain the integrity of the structure and remained equal to the level of its catalytic activity even after seven catalytic rounds. Additionally, a possible catalytic mechanism was proposed due to the high catalytic activity which might be owing to the synergism of Lewis acidic metal centers and N group.

Metal β-diketonate complexes as highly efficient catalysts for chemical fixation of CO2 into cyclic carbonates under mild conditions

The potential of metal β-diketonate complexes for the catalysis of the chemical fixation of CO₂ into cyclic carbonates at 1 atm CO₂ and near room temperature was demonstrated. Their potential for the capture and simultaneous conversion of CO₂ in a dilute CO₂ stream was also determined. The catalysts were easily synthesized and commercially available. Therefore, this CO₂ transformation was less energy- and material-consuming, which made this reaction closer to true "green" chemistry.

Green Synthesis of Novel Polyesterurethane Materials from Epoxides and Carbon Dioxide by New Set of One-Dimensional Coordination Polymer Catalyst

Two novel polyesterurethane materials, PEU1 and PEU2, were synthesized via nontoxic and isocyanate-free route by simple conversion of two epoxides 1,2-epoxy-3-phenoxy propane (2) and styrene epoxide (3) utilizing CO₂. Epoxides 2 and 3 were converted to the respective cyclic carbonates 4 and 5 by a new set of cobalt-based catalyst 1a in the presence of 10 bar of CO₂ and 80 °C temperature without using cocatalyst tetrabutylammonium bromide (TBAB). The mechanistic pathway of the catalysis reaction for the cycloaddition of epoxides with CO₂ to generate the cyclic carbonates was investigated by several spectroscopic techniques and utilizing analogous zinc-based 1D coordination polymer 1b, which does not act as an efficient catalyst in the absence of TBAB. Cyclic carbonates 4 and 5 were converted to the respective polyesterurethanes PEU1 and PEU2 sequentially by first synthesizing the ring-opened diols 6 and 7 reacting with ethylenediamine and subsequently annealing the respective diols 6 and 7 at 120 °C in the presence of terepthalyl chloride and triethylamine. The polyesterurethanes PEU1 and PEU2 were characterized by multinuclear NMR and FTIR. PEU1 was also characterized by MALDI-TOF mass spectrometry. The thermal studies of PEU1 and PEU2 showed the stability up to 200-270 °C. The number-average and weight-average molecular weights were determined for PEU1 and PEU2 by GPC analysis. The weight-average molecular weight for PEU1 was found to be 5948 with a polydispersity of 1.1, and PEU2 showed the weight-average molecular weight as 4224 with a polydispersity of 1.06.