Brønsted‐Lewis Dual Acid H 3 PMo 12 O 40 @MIL‐100(Fe) Catalyzes DMC‐Mediated N‐Methylation of Amines: Synergistic Catalysis and Deactivation Mechanism

ABSTRACT Polyoxometalate‐based host‐guest composite (POMs@MOFs) H 3 PMo 12 O 40 @MIL‐100(Fe) was employed for the first time to catalyze the N‐methylation reactions using dimethyl carbonate (DMC) as the methylation agent. H 3 PMo 12 O 40 @MIL‐100(Fe) with five different Mo/Fe molar ratios were prepared via an in situ hydrothermal method. The results of X‐ray diffraction (XRD), Fourier transform infrared spectra (FT‐IR), and X‐ray photoelectron spectroscopy (XPS) indicated that H 3 PMo 12 O 40 molecules were effectively encapsulated within the pores of MIL‐100(Fe). More importantly, H 3 PMo 12 O 40 and MIL‐100(Fe) formed host‐guest interactions while maintaining their structural integrity. In the recycling experiments, the transformation of the coordination mode of carboxylate groups (COO − ) in the ligand from syn‐syn to syn‐anti resulted in significant changes in crystallinity, surface morphology, and pore structure. These changes subsequently led to a decline in the selectivity towards the N‐methylation. A synergistic catalytic mechanism was proposed and then verified by poisoning experiments. This work reveals the crucial role of synergistic catalysis between Brønsted and Lewis acid sites and provides new insights for the development of green catalysts for N‐methylation reactions of amines with DMC.