Anions mediated electron-rich metalloporphyrin ionic framework as recyclable catalyst for conversion of urea into cyclic carbonates

Abstract

As CO2 typical derivative, urea has the potential to be uniquely economical and green raw materials in generating cyclic carbonates via alcoholysis. Nonetheless, the existing processes for obtaining cyclic carbonates from urea alcoholysis reaction pose considerable challenges in achieving efficient catalyst recycling. Functional organic heterogeneous compounds are emerging materials for catalysis and enhanced reusability due to their large number of coordination sites, but they still fall short of effectively modulating the charge distribution of metal ions. Herein, drawing inspiration from the capacity of ionic liquids (ILs) to effectively control the distribution and transfer of spatial charges within materials, metalloporphyrin ionic framework catalysts were developed by combining metal ions and ILs for the transformation of urea into cyclic carbonates. This heterogeneous catalyst, featuring an adjustable structure and stable metal coordination sites on its surface, exhibits remarkable stability, resulting in a 2.7-fold reduction in catalyst dosage compared to other reported supported catalysts. Based on detailed experiments and DFT calculations, this tunable performance can be mainly explained by the effect of porphyrin zinc (II) and IL anions via molecular engineering. These atom-economical transformations provide a direct and selective access to valuable compounds from cheap and available urea using an efficient organic heterogeneous catalyst.