Metal-Free Organocatalytic Formylation by CO₂-Masked Carbene Functionalized Graphene Oxide Nanosheets

Despite considerable scientific advancements, there is an urgent need for sustainable, cost-effective, and efficient methods for chemically transforming CO₂ into valuable chemicals. A stable heterogeneous platform is presented that incorporates four key innovations: 1) the first Tröger's base (TB) chemistry in solids via selective four-electron reductive functionalization of CO₂, 2) an effective heterogeneous organocatalyst for the chemoselective formylation of both NH and SH functionalities with CO₂, 3) a methodology for metal-free heterogeneous S-formylation of bioactive thiols, and 4) a direct covalent immobilization of CO₂-protected N-heterocyclic carbenes (NHCs) on graphene oxide nanosheets (GONs). The CO₂-protected catalyst is developed by covalently attaching imidazole (Im) to GONs and functionalizing them with dimethyl carbonate. The resulting CO₂-protected NHC-functionalized GONs serves as an effective catalyst for the metal-free, selective formylation of NH and SH bonds under mild conditions. To address gaps in the understanding of TB chemistry in GONs, a metal-free formylation method is discovered that utilizes an in situ-generated TB linker produced by converting CO₂ with excess silane. The ability of this catalyst to revert to its CO₂-protected state enables excellent recyclability. This accessible and efficient platform offers an unprecedented pathway for sustainable CO₂ conversion, supported by both theoretical and experimental evidence.