Promoting Frustrated Lewis Pairs for Heterogeneous Chemoselective Hydrogenation via the Tailored Pore Environment within Metal–Organic Frameworks

Abstract

Frustrated Lewis pairs (FLPs) have recently been advanced as efficient metal-free catalysts for catalytic hydrogenation, but their performance in chemoselective hydrogenation, particularly in heterogeneous systems,h as not yet been achieved. Herein, we demonstrate that, via tailoring the pore environment within metal-organic frameworks (MOFs), FLPs not only can be stabilized but also can develop interesting performance in the chemoselective hydrogenation of a,bunsaturated organic compounds,w hichc annot be achieved with FLPs in ah omogeneous system. Using hydrogen gas under moderate pressure,the FLP anchored within aMOF that features open metal sites and hydroxy groups on the pore walls can serve as ah ighly efficient heterogeneous catalyst to selectively reduce the imine bond in a,b-unsaturated imine substrates to affordunsaturated amine compounds.

Catalysis, FLPs, and Beyond

“…26 Strong Lewis bases such as alkali-metal amides and phosphides have also proved effective, thus demonstrating the generality of the concept. Although the notion of FLP has also been adapted for heterogeneous reductions, [27][28][29] perhaps the most elegant advancement has been the modification of FLP catalysts for highly enantioselective hydrogenations of a variety of substrates. 30 Cat.…”

“…These systems provide substrate-selective catalysts that are also stable and recyclable, features that are certainly cost saving. 27,59 Perhaps a richer, more exciting avenue for FLP catalysis lies in the unknown. The ability to activate a wide variety of small molecules suggests possibilities for unrivaled reactivity of substrates traditionally viewed as challenging targets, such as N 2 , CO, and CH 4 .…”

Highly Diastereoselective Functionalization of Piperidines by Photoredox Catalyzed C–H Arylation and Epimerization

“…Optimization and Scope of C-H Arylation. To optimize the yield and diastereoselectivity of the C-H arylation reaction, we explored a variety of conditions for arylating trisubstituted piperidine 1a (R 1 = H, R 2 = Me, R 3 = R 4 = Et) with 1,4-dicyanobenzene (DCB) to give 2a (Tables S2 and S3 in the Supporting Information). Ir(ppy)3 (ppy = 2-phenylpyridine) was determined to be the optimal photocatalyst for the α-arylation in agreement with MacMillan's earlier report.…”

“…Photoredox catalysis utilizing transition metalpolypyridyl complexes has provided a powerful strategy to access novel reactivity manifolds. 2 Although the utility of αamino radicals has long been appreciated, 3 the MacMillan group provided a seminal study using a transition metal photoredox catalyst for the synthesis of α-branched amines via α-amino radical coupling with electron deficient cyano(hetero)arene derivatives (Scheme 1A). 4 Following this report, many groups have developed transformations using α-amino radicals as the reactive intermediate for additions to alkenes and other unsaturated π-bonds, 5 (hetero)arenes, 6 and other coupling partners.…”

Construction of C-C bonds via photoreductive coupling of ketones and aldehydes in the metal-organic-framework MFM-300(Cr)

“…Upon light irradiation, the organic ligands of MOFs can serve as antennas to harvest light, generate photo-induced electrons and activate the metal centre, thus facilitating the “ligand-to-metal charge-transfer” (LMCT) 17 . More importantly, the micropore environment offers a unique platform to activate the substrates via confined adsorption arising from the specific host–guest interactions 18 – 20 . The impact of host–guest interactions on the activation of adsorbed substrates and catalytic activity in supramolecular cages 21 – 23 and zeolites 24 , 25 have been widely studied.…”