Implementation of CO2 as a renewable C1 building block for chemical syntheses has attracted great attention. N-formylation of amine is one of the reactions which requires a carbonyl source to generate formamides, which are key intermediates for organic syntheses and pharmaceutical applications. Recently, the utilization of CO2 as a carbonyl source has been researched to replace toxic CO. In order to activate thermodynamically inert CO2, a base catalyst is required. Lindqvist-type metal oxide clusters ([M6O19]8−, M = Nb, Ta) exhibit high basicity, which have been applied for CO2 fixation and conversion reactions. In this study, platinum-incorporated heteropolyoxoniobate, Cs2K10Pt(Nb6O19)2●18H2O (Pt(Nb6)2), was synthesized by a hydrothermal reaction between K8Nb6O19●15H2O and Pt(OH)4(H2O)2. The resultant sandwich-type structure contains a combination of one PtO6 unit connecting the two [Nb6O19]8− units that could function as redox catalyst and base catalyst, respectively. The fabrication of Cs2K10Pt(Nb6O19)2●18H2O was confirmed by ESI-MS, and the structural features were characterized by FT-IR, XRD, and XAS. Pt(Nb6)2 was employed as a catalyst for N-formylation of piperidine as a model reaction using CO2 as a carbonyl source to produce 1-formylpiperidine. A linear increment of product yield over the course of 36 h could be observed, suggesting a good dependence on the reaction time. In an absence of CO2, H2, or Pt species, only a trace amount of product could be observed. In addition to piperidine, this catalyst could be applied for other secondary amines with high yields. Characterization of the catalysts after reactions revealed a formation of Pt nanoparticles decorated by Nb polyoxometalates on NbOx support (NbPOM-PtNPs/NbOx) depicted in Scheme 1, which exhibited bifunctional catalysis and was responsible for N-formylation of amines using CO2 as a carbonyl source.

Bifunctional catalytic N-formylation of amine of metal-oxide-cluster-derived catalyst using CO2

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