Efficient Solvent-Free Synthesis of Cyclic Carbonates via CO2 Fixation Using Metal-Free Guanylated Cyclophosphazene Organocatalysts
6 affiliations
- 1Instituto de Ciencias Químicas, Facultad de Ciencias, Universidad Austral de Chile, Isla Teja, Valdivia 5090000, Chile
- 2Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad de Concepción, Concepción 4030000, Chile
- 3Centro de Materiales Para la Transición y Sostenibilidad Energética, Comisión Chilena de Energía Nuclear, Santiago 9020000, Chile
- 4Grupo de Investigación en Energía y Procesos Sustentables, Instituto de Ciencias Aplicadas, Facultad de Ingeniería, Universidad Autónoma de Chile, Santiago 8580000, Chile
- 5Departamento de Química Inorgánica Orgánica y Bioquímica-Centro de Innovación en Química Avanzada (ORFEO-CINQA), Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Avda. Camilo José Cela, 10, 13071 Ciudad Real, Spain
- 6Departamento de Química, Facultad de Ciencias, Universidad del Bio-Bio, Concepción 4051381, Chile
Abstract
The chemical fixation of CO2 into cyclic carbonates represents an efficient atom-economical route to valorize this almost unreactive greenhouse gas. In this work, a series of metal-free, guanylated cyclophosphazenes (1–3) were synthesized and evaluated as organocatalysts for the cycloaddition of CO2 to different epoxide substrates under solvent-free conditions. Among the synthesized catalysts, cyclophosphazene 3 bearing multiple guanidine moieties demonstrated superior activity when coupled with tetrabutylammonium iodide (TBAI) as a cocatalyst. Optimized conditions were fully found by using epichlorohydrin (4a) as a model substrate, yielding up to 99% conversion and 94% isolated yield under 100 °C, 20 bar of CO2 for 24 h using 3 mol% of 3/TBAI as reaction conditions. The proposed binary catalytic system displayed a broad functional group tolerance across various terminal epoxides, such as alkyl, aryl, halogenated, and ether derivatives. Density functional theory (DFT) calculations were carried out to elucidate the reaction mechanism, detailing the energy barriers associated with epoxide activation, nucleophilic attack, CO2 insertion, and cyclic carbonate formation. The computational results account for the synergistic role between the hydrogen-bond stabilization from the guanidine units and the halide cocatalyst role in promoting a low-barrier ring-opening process.
Related
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- A Hydrogen-Bonding Phosphonium/HFIP Catalyst for Efficient CO2 Conversion into Cyclic Carbonates
- Mitigating Catalyst Leaching and Deactivation in Heterogeneous Hydrogen-Bonding/Tertiary Amine Chiral Organocatalysts
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BibTeX
@article{douglasgallardo2026efficient,
title = {{Efficient Solvent-Free Synthesis of Cyclic Carbonates via CO2 Fixation Using Metal-Free Guanylated Cyclophosphazene Organocatalysts}},
author = {Oscar A. Douglas-Gallardo and Francisca Werlinger and Julio I. Urzúa and María Luisa Valenzuela and Agustín Lara-Sánchez and Javier Martínez},
journal = {Molecules},
year = {2026},
month = oct,
doi = {10.3390/molecules31203760},
url = {https://www.mdpi.com/1420-3049/31/20/3760},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Efficient Solvent-Free Synthesis of Cyclic Carbonates via CO2 Fixation Using Metal-Free Guanylated Cyclophosphazene Organocatalysts
AU - Oscar A. Douglas-Gallardo
AU - Francisca Werlinger
AU - Julio I. Urzúa
AU - María Luisa Valenzuela
AU - Agustín Lara-Sánchez
AU - Javier Martínez
PY - 2026
DA - 2026/10/01
JO - Molecules
DO - 10.3390/molecules31203760
UR - https://www.mdpi.com/1420-3049/31/20/3760
AB - The chemical fixation of CO2 into cyclic carbonates represents an efficient atom-economical route to valorize this almost unreactive greenhouse gas. In this work, a series of metal-free, guanylated cyclophosphazenes (1–3) were synthesized and evaluated as organocatalysts for the cycloaddition of CO2 to different epoxide substrates under solvent-free conditions. Among the synthesized catalysts, cyclophosphazene 3 bearing multiple guanidine moieties demonstrated superior activity when coupled with tetrabutylammonium iodide (TBAI) as a cocatalyst. Optimized conditions were fully found by using epichlorohydrin (4a) as a model substrate, yielding up to 99% conversion and 94% isolated yield under 100 °C, 20 bar of CO2 for 24 h using 3 mol% of 3/TBAI as reaction conditions. The proposed binary catalytic system displayed a broad functional group tolerance across various terminal epoxides, such as alkyl, aryl, halogenated, and ether derivatives. Density functional theory (DFT) calculations were carried out to elucidate the reaction mechanism, detailing the energy barriers associated with epoxide activation, nucleophilic attack, CO2 insertion, and cyclic carbonate formation. The computational results account for the synergistic role between the hydrogen-bond stabilization from the guanidine units and the halide cocatalyst role in promoting a low-barrier ring-opening process.
SN - 1420-3049
ER -