Rational Design of Core–Shell Structured Pd@MIL-100(Fe) for Efficient Visible Light-Initiated Syntheses of Secondary Amines from Nitro Aromatics and Benzyl Alcohols

A rational design of MNPs@MOFs (MNPs = metal nanoparticles, MOFs = metal–organic frameworks) nanocomposites is important for their application as multifunctional catalysts for light-initiated one-pot tandem/cascade reactions. Herein, the Pd@MIL-100(Fe) nanocomposite with a core–shell structure, in which Pd colloids of ca. 3 nm are encapsulated inside the matrix of MIL-100(Fe), was constructed successfully via self-assembly of MIL-100(Fe) in preformed PVP-capped Pd colloids (PVP = polyvinylpyrrolidone) at room temperature. Via a successful combination of MOF-based photocatalysis with Pd-based hydrogenation, Pd rpvp @MIL-100(Fe), with PVP partially removed, exhibited superior performance for the reaction between nitro aromatics and benzyl alcohols to produce secondary amines. Comparison of activity over Pd rpvp @MIL-100(Fe) with that of the other two types of MNPs/MIL-100(Fe) nanocomposites suggests that its superior activity can be attributed to the presence of well-stabilized stable Pd nanoparticles (NPs) for hydrogenation and the unoccupied cavities in MOFs to promote the mass diffusion, especially in the case of larger substrates, as well as an efficient charge transfer from the MOF to Pd NPs for their cooperation. This study indicates that a rational strategy in the construction of metal NPs/MOFs nanocomposites is important for their application as multifunctional catalysts for light-initiated one-pot tandem/cascade reactions.