Two‐Dimensional Metal‐Organic Layers for Electrochemical Acceptorless Dehydrogenation of N‐Heterocycles

Abstract

The catalytic acceptorless dehydrogenation (CAD) is an attractive synthetic route to unsaturated compounds because of its high atomice fficiency.H erew e report electrochemical acceptorless dehydrogenation of N-heterocycles to obtain quinoline or indole derivatives using metal-organic layer (MOL) catalyst. MOL is the twodimensional version of metal-organic frameworks (MOF), and it can be constructed on conductive multi-walled carbon nanotubes via facile solvothermal synthesis to overcome the conductivity constraint for MOFs in electrocatalysis. TEMPO-OPO 3 2À was incorporated into the system through al igand exchange with capping formate on the MOL surface to serve as the active catalytic centers. The hybrid catalyst is efficient in the organic conversion and can be readily recycled and reused.The catalytic acceptorless dehydrogenation (CAD) of N-heterocycles is an atomically efficient way to synthesize quinoline and indole rings, [1] whicha re widely found in pharmaceuticals and bioactive molecules. [2] Moreover,t hese N-heterocycles are also proposed asH 2 carriers for liquid organic H 2 storage. [3] Conventional dehydrogenations require oxidants or sacrificial hydrogen acceptors, which usually produce byproducts such as toxic metal salts. [4] Recent development of acceptorless dehydrogenation produces H 2 to avoid the use of an oxidant. A number of catalysts based on noble metalss uch as iridium, [5] palladium, [6] platinum [6b, 7] and ruthenium, [8] and nom-noble metals such as iron, [9] cobalt [10] and nickel, [11] and organic borane compounds [12] are active for this transformation. However,m ost of the above catalysts are homogeneous complexes that requires catalyst removal after the reaction, increasing the overall cost of synthesis. Therefore, it is still of interest to perform dehydrogenation in the absence of these homogeneous catalysts, especiallym etal complexes, to avoid the tedious separation step or the contamination of the product. Electrosyn-[a] L.

Synthesis of Acridinium Photocatalysts via Site-Selective C–H Alkylation

“…2). As a start, the addition of organotrifluoroborate to 1 was induced by 0.5 h of blue LED irradiation, followed by the addition of TEMPO 26,[39][40][41][42] as redox catalyst and KPF 6 as supporting electrolyte. Electrolysis of the resultant reaction mixture at a constant current of 10 mA afforded the desired 3-alkylated acridinium product in good to excellent yields (73-97%) without the detection of any other regioisomers.…”

“…This method demonstrated excellent compatibility with primary (3-10), secondary (11)(12)(13)(14)(15)(16)(17)(18), and tertiary (19)(20)(21)(22) alkylorganotrifluoroborates, providing easy access to acridinium dyes with different steric properties. A highly useful feature of our method is that the monoalkylated product can be alkylated again following the above experimental procedures to furnish novel, 3,6-dialkylated acridinium dyes, using the same (28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45) The alkylation reaction could be scaled up to decagram without difficulty by employing a continuous-flow photochemical reactor 45,46 and a electrochemical batch reactor, as demonstrated in the synthesis of 10.88 g of 36 in 80% yield (Fig. 4A).…”

Metal–Organic Frameworks for Photo/Electrocatalysis

“…Compared with vast reports of MOFs for electrocatalytic water splitting, ORR, and CO 2 RR applications, there are only several reports of MOFs in electro‐organic synthesis applications. [ 227,228 ] Much more studies are needed in this promising field.…”

“…Yang et al fabricated a nanocomposite by decorating 2D ultrathin MOF nanosheets of Hf 6 (μ 3 ‐O) 4 (μ 3 ‐OH) 4 (μ 1 ‐OH) 2 (μ 1 ‐OH 2 ) 2 (HCO 2 ) 4 (NTB) 2 , also called metal–organic layers (MOL), onto conductive multiwalled CNTs (CNT/MOL) to improve the conductivity of MOFs in electrocatalysis ( Figure A). [ 227 ] Then CNT/MOL was modified with TEMPO‐OPO 3 H 2 (CNT/MOL‐TEMPO‐OPO 3 2− ) and loaded on a macroporous reticulated vitreous carbon (RVC, 100 PPI) electrode to act as an efficient electrocatalyst for electrochemical acceptorless dehydrogenation of N ‐heterocycles to obtain quinoline or indole derivatives. The monolayer structure of MOL can accelerate the diffusivity of organic substrates and afford high densities of active sites, and CNTs can efficiently improve the conductivity of catalyst.…”

“…Reproduced with permission. [ 227 ] Copyright 2019, Wiley‐VCH GmbH. B) Schematic representation of the synthetic procedures for MIL‐101(Cr)‐HIMBr for electrocatalytic oxidative self‐coupling of benzylamine.…”