Chloride ion-driven activation of Ru-CeO2 for efficient methoxycarbonylation of long-chain alkenes

Despite great progress on the heterogeneous catalytic methoxycarbonylation of alkenes, the research on long-chain substrates is yet undeveloped. In this study, an efficient protocol was built by introducing 1-butyl-3-methylimidazole chloride (BmimCl) additive to the catalytic system of ceria-supported Ru clusters (Ru-CeO 2 ), providing the aliphatic esters with yields over 80 %. Experimental results combined mechanism studies demonstrated that the adsorption of chloride ion at oxygen vacancy (Vö) of CeO 2 during the catalysis delivered surfaces with reduced local concentration of Vö and electron-richer Ru sites. The synergistic effect between Vö and chloride ion boosted methanol (CH 3 OH) dissociation, providing higher coverage of dissociated CH 3 O species with lower adsorption energy and thereby accelerating the rate-limiting step of methoxycarbonylation. Importantly, the β-H elimination for competitive isomerization process was greatly inhibited on the electron-richer Ru sites. Meanwhile, the side hydrogenation was further suppressed by the restrained freedom of adsorbed H at such surfaces. These positive effects jointly offer a heterogeneous catalytic system of both efficient and selective on the challenging long-chain alkene substrates, taking methyl-4-pentenoate and chain alkenes with 6, 8, 10 and 12 carbon atoms as examples.