Abstract
AbstractThe reaction between epoxides and CO2 to yield cyclic carbonates is efficiently promoted under solvent‐free and relatively mild reaction conditions (0.5 mol % catalyst loading, 0.8 MPa, 125 °C) by zinc(II) complexes of pyridine containing macrocyclic ligands (Pc−L pyridinophanes). The zinc complexes have been fully characterized, including X‐ray structural determination. The [Zn(II)X(Pc−L)]X complexes showed good solubility in several polar solvents, including cyclic carbonates. The scope of the reaction under solvent‐free conditions has been studied and good to quantitative conversions with excellent selectivities have been obtained, starting from terminal epoxides. When solvent‐free conditions were not possible (solid epoxides or low solubility of the catalyst in the oxirane) the use of cyclic carbonates as solvents has been successfully investigated. The remarkable stability of the catalytic system has been demonstrated by a series of consecutive runs.
Highlights
Carbon dioxide is the principal greenhouse gas, largely recognized as responsible for global warming and related climate changes, but it represents an abundant C1 source
We have recently reported that iron(III) complexes of pyridine based 12 membered tetraaza macrocyclic ligands (PcÀ L) are efficient catalyst for the epoxidation of alkenes with H2O2 as the terminal oxidant and we have disclosed that under certain conditions they are suitable catalysts for the epoxide activation towards ring-opening with a nucleophile.[18]
As a continuation of our studies on the catalytic activity of pyridinophane type macrocyclic ligands,[18,19] we envisioned that Zn(II) complexes would be perfect candidates to promote a clean conversion of epoxides and CO2 in cyclic carbonates under mild reaction conditions and without the addition of any co-catalyst (Scheme 1)
Summary
Part of the “Franco Cozzi’s 70th Birthday” Special Collection. and thermodynamically stable and difficult to activate and use. The development of new catalysts for a so crucial reaction, able to work at mild process conditions with good performance, that are reusable and separable, is of high industrial interest. We have recently reported that iron(III) complexes of pyridine based 12 membered tetraaza macrocyclic ligands (PcÀ L) are efficient catalyst for the epoxidation of alkenes with H2O2 as the terminal oxidant and we have disclosed that under certain conditions they are suitable catalysts for the epoxide activation towards ring-opening with a nucleophile.[18]. As a continuation of our studies on the catalytic activity of pyridinophane type macrocyclic ligands,[18,19] we envisioned that Zn(II) complexes would be perfect candidates to promote a clean conversion of epoxides and CO2 in cyclic carbonates under mild reaction conditions and without the addition of any co-catalyst (Scheme 1).
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