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.

Frustrated Lewis Pair-Mediated Cycloisomerization of Propargylaniline and Aryl Propargyl Ether Derivatives via a 6-endo-dig Cyclization/Dehydrogenation Sequence

An efficient FLP-mediated cycloisomerization is described, providing easy access to quinolinium and chromenylium derivatives by treatment of readily available propargylanilines and aryl propargyl ethers with Lewis acidic boranes, respectively. The reaction proceeds via a 6-endo-dig cyclization/dehydrogenation sequence. The heteroatom functions serve as Lewis bases in combination with Lewis acidic boranes to effect synergistic activation of an alkynyl triple bond and a C-H bond.

Synthesis and Photochemical Uncaging of Alkene-Protected, Polymer-Bound Vicinal Frustrated Lewis Pairs

Polymeric materials bearing Frustrated Lewis Pair (FLP) functionality are promising candidates for use as heterogeneous catalysts and adaptive materials, but synthetic access to FLP-functional polymers remains limited due to the incompatibility of FLPs with standard polymerization chemistries. Herein, we describe a synthetic approach that "cages" highly reactive vicinal phosphine-borane FLPs as covalent alkene adducts, which are stable to Ni-mediated vinyl addition polymerization. We discovered that the caged FLP adducts can be photochemically activated to liberate vicinal FLPs, enabling spatiotemporally controlled release of FLPs from polymeric precursors.

Insights into Single-Electron-Transfer Processes in Frustrated Lewis Pair Chemistry and Related Donor-Acceptor Systems in Main Group Chemistry

The activation and utilization of substrates mediated by Frustrated Lewis Pairs (FLPs) was initially believed to occur solely via a two-electron, cooperative mechanism. More recently, the occurrence of a single-electron transfer (SET) from the Lewis base to the Lewis acid was observed, indicating that mechanisms that proceed via one-electron-transfer processes are also feasible. As such, SET in FLP systems leads to the formation of radical ion pairs, which have recently been more frequently observed. In this review, we aim to discuss the seminal findings regarding the recently established insights into the SET processes in FLP chemistry as well as highlight examples of this radical formation process. In addition, applications of reported main group radicals will also be reviewed and discussed in the context of the understanding of SET processes in FLP systems.

Oxidative cross-coupling of quinoxalinones with indoles enabled by acidochromism

An oxidative cross-coupling of quinoxalinones with indole derivatives via B(C₆F₅)₃·H₂O induced acidochromism of quinoxalinone derivatives was developed under mild and external photocatalyst-free conditions. The reaction shows excellent substrate scope, accommodating a wide range of functional groups. The usefulness of this strategy was demonstrated by the synthesis of the natural products Azacephalandole A and Cephalandole A in high yields. Moreover, the products are fluorophores showing prevalent fluorescence properties with a wide emission range and good relative quantum yields.