Vanadium(V) Catalysts with High Activity for the Coupling of Epoxides and CO2: Characterization of a Putative Catalytic Intermediate

Vanadium(V) complexes derived from aminotriphenolate ligands are demonstrated to be highly active catalysts for the coupling of various terminal and internal epoxides with carbon dioxide to afford a series of substituted organic carbonates in good yields. Intriguingly, a V(V) complex bearing peripheral chloride groups on the ligand framework allowed for the formation and isolation of a rare complex that incorporates a ring-opened epoxide with one of the phenolate-O atoms acting as a nucleophile and the metal center as a Lewis acidic site. This unusual structure was characterized by X-ray diffraction and 51V NMR and was shown to exhibit catalytic activity for the coupling of propylene oxide and CO2 when it was combined postsynthetically with these substrates. The results obtained herein clearly show that vanadium complexes in a high oxidation state are effective catalysts for the activation of challenging internal epoxides and their conversion into cyclic organic carbonates.