The development of solvent‐free, metal‐free, recyclable organic catalysts is required for the current chemical fixation of carbon dioxide converted into cyclic carbonates. With the goal of reducing the cost, time, and energy consumption for the coupling reaction of CO2 and epoxides, a series of highly active heterogeneous catalysts, based on a thiourea and quaternary ammonium salt system, are synthesized by using a thiol‐ene click reaction under ultraviolet light. Benefitting from synergistic interactions of the electrophilic center (thiourea) and the nucleophilic site (ammonium bromide), the catalysts exhibit excellent catalytic selectivity (99 %) for the cycloaddition of carbon dioxide with a diverse range of epoxides under mild conditions (1.2 MPa, 100 °C). Moreover, the catalyst can be easily recycled by facile filtration and reused for 5 times without noticeable loss of activity and selectivity. This work provides a potential heterogeneous catalyst for the conversion of carbon dioxide into high value‐added chemicals with the combined advantages of low cost, easy recovery, and satisfactory catalytic properties.
The
bifunctional thiourea catalyst system with both electrophilic
and nucleophilic centers has been certified to be effective for fixing
CO2 under mild reaction conditions; however, many questions
remain, especially concerning the relationship between structure and
performance. Herein, we systematically studied a series of such bifunctional
catalysts with different chain lengths, nucleophilic anions, and substituents,
which impact obvious influence on the catalytic performance. The activation
energies of catalysts with different chain lengths are calculated
via in situ IR. On this basis, we disclosed for the first time that
the spacer length of tetramethylene −(CH2)6– is the optimal spatial effect for the coupling of epoxides
and CO2. Particularly, the single crystal X-ray diffraction
analysis of the molecular structures of the bifunctional catalyst C8 indicated the discovery of the existence of interaction
force between the sulfur atom on the thiourea group and one hydrogen
atom on the benzene ring, as well as the intermolecular hydrogen bonding
interaction of the bromide (Br–) and two NH groups
on the thiourea group. The catalyst structure performance, direct
observation of the crystal structure, the thermodynamic study, and
a wide range of substrates (12 examples) should be informative on
the optimization of the existing catalysts or the design of new catalysts
in the future.
A highly stereoregular polyphosphoester with a rigid cyclohexylene structure in the main chain was constructed via ring-opening polymerization (ROP) in the presence of an organic catalyst system.
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