1026465306

A bifunctional ammonium salt covalently bound to a polystyrene or silica support proved to be an efficient and recyclable catalyst for the solvent-free synthesis of cyclic carbonates from epoxides and CO₂. The catalyst can be easily recovered by simple filtration after the reaction and reused in up to 13 consecutive runs with retention of high activity and selectivity even at 90 °C. The scope and limitations of the reaction has been evaluated in terms of reaction conditions and substrate scope.

Do it again: Polystyrene and silica-supported bifunctional ammonium salts catalyze the addition of carbon dioxide to epoxide under mild and solvent-free reaction conditions. Those catalysts can be recycled up to 13 times without loss of activity. Moreover, a wide array of cyclic carbonates can be prepared in excellent yields utilizing those immobilized metal-free catalyst.

Branching at the alkyl side chain of the imidazolium cation in ionic liquids (ILs) was evaluated towards its effect on carbon dioxide (CO₂) solubilization at 10 and 80 bar (1 bar=1×10⁵ Pa). By combining high-pressure NMR spectroscopy measurements with molecular dynamics simulations, a full description of the molecular interactions that take place in the IL–CO₂ mixtures can be obtained. The introduction of a methyl group has a significant effect on CO₂ solubility in comparison with linear or fluorinated analogues. The differences in CO₂ solubility arise from differences in liquid organization caused by structural changes in the cation. ILs with branched cations have similar short-range cation–anion orientations as those in ILs with linear side chains, but present differences in the long-range order. The introduction of CO₂ does not cause perturbations in the former and benefits from the differences in the latter. Branching at the cation results in sponge-like ILs with enhanced capabilities for CO₂ capture.

Catch and retain: Introduction of a methyl group at the side chain of the imidazolium cation of an ionic liquid (IL) enhances CO₂ solubility. High-pressure NMR (HP NMR) spectroscopy and molecular dynamics data show that CO₂ uptake is a direct consequence of the liquid structure of the IL, which provides a matrix with a sponge-like nature to solubilize CO₂ without perturbing the supramolecular arrangement.

A new type of Lewis acid–base bifunctional M(salphen) complexes (M=Zn^II, Cu^II, and Ni^II) pending two N-methylhomo- piperazine groups as nucleophiles were prepared by a one-pot method. The Zn(salphen) complexes proved to be efficient and recyclable homogeneous catalysts towards the solvent-free synthesis of cyclic carbonates from epoxides and CO₂ in the absence of a co-catalyst. The catalysts can be easily recovered and five times reused without significant loss of activity and selectivity.

Bifunctional catalysts: A new type of Lewis acid–base bifunctional Zn(salphen) catalysts with an organic base, N-methylhomopiperazine, as a nucleophile were prepared by a one-pot method and successfully applied in the production of cyclic carbonates from CO₂ and epoxides. The catalysts used in this catalytic system are extremely stable and can be recycled at least five times and their activity is almost unchanged.