Homogeneous and noncovalent immobilization of NHC-Cu catalyzed azide-alkyne cycloaddition reaction

Supramolecular Immobilization of Adamantyl and Carboxylate Modified N-Heterocyclic Carbene Ligand on Cucurbituril Substrates

Herein, the design, synthesis, supramolecular interactions and structural analysis of a novel bidentate carboxylate chelating N-heterocylic carbene (NHC) ligand is presented. The NHC structure was modified to strategically incorporate adamantyl moiety for the formation of a supramolecular complex with host molecules such as cucurbiturils. The adamantyl modified NHC ligand could potentially be used in recoverable homogeneous catalysts when Immobilized on a solid support via host–guest chemistry. As a versatile precursor, NHC ligand (8) was synthesized and characterized by ¹H-NMR, ¹³C-NMR, FTIR, single crystal x-ray crystallography and elemental analysis. A proof-of-principle non-covalent immobilization of the NHC ligand (8) with a Cucurbit[7]uril (CB7) host was demonstrated using ¹H-NMR titration.

Pyrene-based ammonium bromides combined with g-C3N4 for the synergistically enhanced fixation reaction of CO2 and epoxides

A new type of pyrene-based ammonium bromides (PABs) was synthesized via the reaction of bromomethyl pyrene and tertiary amines with different alkyl chains combined with graphitic carbon nitride (g-C₃N₄) through π–π stacking interactions. The new pyrene-based ammonium bromides were investigated both in homogenous phase and heterogeneous phase combining with g-C₃N₄ for the CO₂ fixation reaction of epoxides under mild conditions. Obviously, the combination was proved to be an efficient system for the conversion of epoxides. The interaction between g-C₃N₄ and PABs was confirmed by quantum chemical calculations. g-C₃N₄/Py-C₁₂ exhibited an excellent yield of cyclic carbonates (above 93%) at 80 °C, atmospheric pressure and solvent-free conditions. A preliminary kinetic study was performed using g-C₃N₄/Py-C₁₂ and the activation energy was calculated to be 61.5 kJ mol⁻¹.

The synergistic interaction of g-C₃N₄ and PABs plays an important role in the CO₂ fixation reaction with epoxides.