1 research outputs found
Imidazol(in)ium Hydrogen Carbonates as a Genuine Source of <i>N</i>-Heterocyclic Carbenes (NHCs): Applications to the Facile Preparation of NHC Metal Complexes and to NHC-Organocatalyzed Molecular and Macromolecular Syntheses
Anion metathesis of imidazol(in)ium chlorides with KHCO<sub>3</sub> afforded an easy one step access to air stable imidazol(in)ium
hydrogen
carbonates, denoted as [NHC(H)][HCO<sub>3</sub>]. In solution, these
compounds were found to be in equilibrium with their corresponding
imidazol(in)ium carboxylates, referred to as <i>N</i>-heterocyclic
carbene (NHC)-CO<sub>2</sub> adducts. The [NHC(H)][HCO<sub>3</sub>] salts were next shown to behave as masked NHCs, allowing for the
NHC moiety to be readily transferred to both organic and organometallic
substrates, without the need for dry and oxygen-free conditions. In
addition, such [NHC(H)][HCO<sub>3</sub>] precursors were successfully
investigated as precatalysts in two selected organocatalyzed reactions
of molecular chemistry and polymer synthesis, namely, the benzoin
condensation reaction and the ring-opening polymerization of d,l-lactide, respectively. The generation of NHCs from [NHC(H)][HCO<sub>3</sub>] precursors occurred <i>via</i> the formal loss
of H<sub>2</sub>CO<sub>3</sub> <i>via</i> a concerted low
energy pathway, as substantiated by Density Functional Theory (DFT)
calculations