Swelling poly(ionic liquid)s supported silver N-heterocyclic carbene for efficient conversion of propargyl alcohols with CO2

Abstract

The conversion of propargyl alcohols and carbon dioxide (CO₂) represents a hot spot in the field of CO₂ utilization. In this study, a novel type of swelling poly(ionic liquid)s supported silver N-heterocyclic carbene (Ag-NHC@P(VBImOAc)-n) was designed and successfully synthesized through the free-radical copolymerization of silver N-heterocyclic carbene (Ag-NHC), 1-vinyl-3-butylimidazolium acetate ([VBIm]OAc) and the cross-linker N, N'-methylene bisacrylamide (MBA). The swelling behavior of Ag-NHC@P(VBImOAc)-n in various solvents was investigated and the corresponding molar swelling ratios were determined as 314.6 mmol/g in water, 73.0 mmol/g in acetonitrile (CH₃CN), and 56.8 mmol/g in 2-methyl-3-butyn-2-ol (1a). Notably, Ag-NHC@P(VBImOAc)-n exhibited a porous structure with a diameter of approximately ranging from 0.2 to 4 μm when swollen in CH₃CN, effectively dispersing Ag-NHC moieties within the channels of the poly(ionic liquid) matrix. Ag-NHC@P(VBImOAc)-n were applied as catalysts for the carboxylative cyclization and hydration of propargylic alcohols in the absence of any homogeneous base additives. The catalysts achieved high yields (99 %) of 4,4-dimethyl-5-methylene-1,3-dioxolan-2-one (2a) and 3‑hydroxy-3-methyl-2-butanone (3a) by synergistically utilizing active sites provided by both silver (Ag-NHC) and base ([VBIm]OAc) moieties under mild conditions. Moreover, the catalysts could be reused six times without obvious loss in catalytic activity and had good substrate generality.