Intercalated Zirconium Phosphate Promotes Reductive Amination of Carbon Dioxide

The catalytic conversion of carbon dioxide into fine chemicals and intermediates is one of the most promising approaches to carbon recycling. In this work, we demonstrated that after the layered alpha-zirconium phosphate(alpha-ZrP) was exfoliated by using tetrabutylammonium hydroxide, a cationic Ru(II) complex ([RuH(CO)(dppp)(en)]Cl, dppp = 1,3-bis(diphenylphosphino)propane; en = ethylene-diamine) can be intercalated into ZrP layers. Notably, as the Ru(II) complex-intercalated ZrP was further modified by the ionic liquid (BMIMOAc, 1-butyl-3-methylimidazolium acetate), the resulting catalyst exhibited superior catalytic activity for the N-formylation of amines with CO2/H2 to produce formamide. The detailed characterization revealed that the ionic liquid was also encapsulated into the ZrP interlayer and played an additional role in exfoliating ZrP. In particular, further studies indicated that amine molecules can intercalate favorably into the interlayer under the reaction conditions and thus were easily accessible to the Ru(II) active sites, being beneficial for the N-formylation reaction. The reaction includes the following key steps: CO2 was synergistically activated by BMIMOAc and exfoliated ZrP layers; hydrogen was split by the Ru(II) active center to form Ru-H delta-; morpholine was intercalated into ZrP layers and then participated in the reaction. This implied that the reaction actually occurred within the ZrP interlayers, enhancing the reaction rate due to the enrichment of reactants. The formate species was detected as intermediates in this reaction, followed by dehydrating to afford formamide. This catalytic system exhibits the huge advantage of being easy accessibility, high efficiency, and recyclability.