Hydrophobic B(C₆F₅)₃@R₄-MIL-101: A Water-Resistant Heterogeneous Catalyst for Frustrated Lewis Pairs-Mediated Reductive Amination

B(C₆F₅)₃-based frustrated Lewis pairs (FLPs) have made remarkable progress in metal-free catalytic reduction. However, the high affinity of B(C₆F₅)₃ for oxygen makes it susceptible to irreversible poisoning when exposed to H₂O, limiting its widespread application in reductive amination. To overcome the influence of H₂O, a hydrophobic catalyst, B(C₆F₅)₃@R_<i>n-</i>1-MIL-101 (<i>n</i> = 3, 5, 7), was developed by confining B(C₆F₅)₃ within the nanocages of metal-organic frameworks (MOFs) modified with alkyl chains. The hydrophobic strength of the catalyst could be adjusted by varying the length of the alkyl chain. At <i>n</i> = 3, the alkyl chain was too short to be hydrophobic, while the excessively long alkyl chain blocked the pore channels and adversely affected the loading of B(C₆F₅)₃ at <i>n</i> = 7. Only the catalyst B(C₆F₅)₃@R₄-MIL-101 synthesized at <i>n</i> = 5 could effectively facilitate the reductive amination of aldehydes or ketones with amines in a "wet solvent." The strategy of combining hydrophobic MOFs with B(C₆F₅)₃ to prepare heterogeneous catalysts for FLP catalysis not only provides a fresh avenue for investigating catalytic systems for reductive amination but also represents an innovative approach to advancing FLP chemistry.