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@Rn-1-MIL-101 (n = 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 n = 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 n = 7. Only the catalyst B(C6F5)3@R4-MIL-101 synthesized at n = 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.