Co-catalyst and Metal-free CO2 Fixation into Cyclic Carbonates: COPs to the Rescue

Rational Design of Porous Organic Framework (POF) for Efficient Conversion of CO2 to Cyclic Carbonates and 2-Oxazolidinones at Atmospheric Pressure Conditions

Carbon dioxide (CO2) capture and its subsequent catalytic fixation into usable compounds represent a potential approach for addressing the energy problem and the implications of global warming. Hence, it is necessary to develop effective catalytic systems required for the transformation of CO2 into valuable chemicals/fuels. Herein, we rationally designed a hydroxyl-functionalized porous organic framework (OH-POF) consisting of both acidic (OH) as well as basic N sites for the transformation of CO2 using epoxides for the production of cyclic carbonates (CCs), a useful commodity chemical under environmental-friendly, metal/solvent/co-catalyst-free conditions. Moreover, OH-POF was post-synthetically modified to anchor non-noble metal, Zn(II) to generate Zn-POF and further explored it for the efficient functionalization of CO2 with propargylic amines to generate valuable bioactive 2-oxazolidinones. Significantly, both OH-POF and Zn-POF demonstrated exceptional reusability with catalytic efficacy retained across numerous cycles of use. Notably, this study showcases a green and sustainable process for utilization of CO2 under environmentally favorable ambient conditions into two highly valuable compounds, viz cyclic carbonates and 2-oxazolidinones.

Amine-rich Nickel(II)-Xerogel as a Highly Active Bifunctional Metallo-organo Catalyst for Aqueous Knoevenagel Condensation and Solvent-free CO2 Cycloaddition

Metallogels formed from supramolecular interactions of low-molecular-weight gelators (LMWGs) combine the qualities of heterogeneous catalysts and offer the advantages of multifunctionality owing to the facile installation of desired task-specific moieties on the surface and along the channels of the gels. We discuss the applications of a triazole-based Ni(II) gel-derived xerogel (NiXero) having a high density of Ni(II)-nodes and appended primary amines as a recyclable heterogeneous catalyst for Knoevenagel condensation of aldehyde and malononitrile in water and the solvent-free cycloaddition of CO2 to form a series of cyclic carbonates with near-quantitative conversion of the respective epoxides, with low catalyst loading (0.59 mol %), high catalyst stability, and recyclability. The structural advantages of NiXero, due to the concurrent presence of bifunctional Lewis acid-base sites on the channels, open Ni(II) nodes, Ntriazole, pendant -NH2 and its chemical stability, are conducive to the cooperative heterogeneous catalytic activity under mild conditions. This work emphasizes the effective amalgamation of metals with purpose-built ligand systems for the construction of metallogels and their utility as heterogeneous catalysts for desired organic transformations.