Protic metal-containing ionic liquids as catalysts: Cooperative effects between anion and cation

HCo(CO)4 is known to be the active species in the cobalt-catalyzed hydroformylation reaction. Although it is known that the anion [Co(CO)4]− is catalytically inactive, some cobalt carbonyl-containing ionic liquids are surprisingly able to catalyze hydroformylation reactions. However, only ionic liquids with protic cations demonstrate activity, whilst aprotic cations such as BMIM+ result in a completely inactive compound. The four applied cobalt-containing ionic liquids differ only by the cation component. Their different performance in catalytic activity allows the presumption of cooperative effects between the cation and the anion. These fundamental influences of the cation on the hydroformylation kinetics give hints for the reaction mechanism of biphasic hydroformylation reactions as well as on the reaction pathways of the conventional hydroformylation reaction under different reaction conditions.

Graphical abstractHCo(CO)4 is known to be the active species in the cobalt-catalyzed hydroformylation reaction. Although it is known that the anion [Co(CO)4]- is catalytically inactive, some cobalt carbonyl-containing ionic liquids are surprisingly able to catalyze hydroformylation reactions. However, only ionic liquids with protic cations demonstrate activity, whilst aprotic cations such as BMIM+ result in a completely inactive compound. The four applied cobalt-containing ionic liquids differ only by the cation component. Their different performance in catalytic activity allows the presumption of cooperative effects between the cation and the anion. These fundamental influences of the cation on the hydroformylation kinetics give hints for the reaction mechanism of biphasic hydroformylation reactions as well as on the reaction pathways of the conventional hydroformylation reaction under different reaction conditions.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Cobalt-containing protic ionic liquids are examined as catalysts for hydroformylation reaction. ► The activities of these metal-containing ionic liquids are determined by the proton of the anion. ► Ionic liquids can be recollected easily in a separate ionic-liquid phase.