Expanding the useful range of ionic liquids: melting point depression of organic salts with carbon dioxide for biphasic catalytic reactions

Abstract

Large and previously unreported melting point depressions (even exceeding DeltaTm of 100 degrees C) were observed for simple ammonium and phosphonium salts in the presence of compressed CO2, bringing them well within the range of typical ionic liquids; possible applications include biphasic catalysis in IL/scCO2 systems as demonstrated for rhodium complex catalyzed hydrogenation, hydroformylation, and hydroboration of 2-vinyl-naphthalene using a CO2-induced molten sample of [NBu4][BF4] as a catalyst phase at temperatures in the range of 55-75 degrees C, i.e. 100 degrees C below the normal melting point of the organic salt.