N-Formylation of Amines by a Magnetically Separable Cobalt Nanocatalyst Using CO₂ as a C1 Source

Utilizing CO₂ for the synthesis of value-added chemicals offers an economically viable route while contributing to reducing greenhouse gas emissions. In this study, three ligands with N₂O₂ binding sites were designed and used to synthesize mononuclear three cobalt(III) complexes, 1-3, for catalytic activity in the N-formylation reaction. A comparative study was conducted using DMAB as a greener hydrogen donor compared to triethylsilane in the presence of CO₂ as a C1 source. All complexes were characterized by UV-Vis, FT-IR, and single-crystal X-ray analysis. Although complex 2 showed the highest activity, all three homogeneous complexes displayed comparable efficiency and were thus employed to develop magnetically separable nanocatalysts for improved recoverability and reusability. Immobilizing the Schiff base complexes onto graphene oxide, Fe₃O₄, and APTES yielded three magnetically separable GO@Fe₃O₄@APTES@CoL^1/2/3 nanocatalysts. The heterogeneous catalyst obtained from complex 2, i.e., GO@Fe₃O₄@APTES@CoL² (GOFeTESCoL²), was catalytically more efficient than the other two. This new heterogeneous magnetically separable nanocatalyst, GOFeTESCoL², was then characterized by FT-IR, scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, BET analysis, and X-ray photoelectron spectroscopy, which confirmed successful surface modification. GOFeTESCoL² is magnetically separable and can be reused for six cycles without any loss of catalytic activity or product yield. This reusability offers a cost-effective nonprecious metal-based catalytic approach that minimizes potential reaction losses.