Abstract
The synergistic combination of a heterogeneous organic semiconductor mesoporous graphitic carbon nitride (mpg-CN) and a homogeneous nickel catalyst with visible-light irradiation at room temperatur...
Highlights
Metal-catalyzed cross-coupling reactions are standard synthetic methods in academia and industry.[1]
We recently reported that mesoporous graphitic carbon nitride, an organic semiconductor material, is a versatile photocatalyst capable of performing many organic transformations under diverse reaction conditions.[9] mpg-CN can be synthesized using inexpensive starting materials, and the polymeric material is stable toward reactive radicals or nucleophiles. mpg-CN possesses a suitable band gap between valence band maxima (VBM) and conduction band minima (CBM),[10] which allows the use of photoexcited mpg-CN for controlled oxidation and reduction of many substrates
We began our investigation with ethyl 4-bromobenzoate (1a) and potassium benzyl trifluoro borate (2a) as model substrates using Ni(cod)[2] as a catalyst, 4,4′-di-tert-butyl-2,2′-dipyridyl as a ligand, and mpg-CN as a heterogeneous photocatalyst
Summary
Metal-catalyzed cross-coupling reactions are standard synthetic methods in academia and industry.[1]. Reductive elimination from the Ni(III) species generates the desired cross-coupling product Molander demonstrated that such carbon-centered radicals are generated from the respective trifluoroborate salts, while MacMillan used αheteroatom-containing carboxylic acids for the generation of carbon-centered radicals by oxidative decarboxylation. O-Benzyl xanthates[6] or ammonium alkyl silicates[7] are alternative precursors yielding the respective nucleophilic alkyl radicals under visible-light photoredox conditions and the application of dual photo-nickel cross-coupling has been demonstrated in synthesis.[8] To improve the efficiency of this technology further, we have replaced the homogeneous iridium photocatalyst of the original reports by a heterogeneous organic semiconductor. Pieber and Seeberger reported the application of carbon nitrides in photoredox-nickel dual cross-coupling reactions using oxygencentered nucleophiles.[11] Recently, carbon nitride-based heterogeneous photocatalysts have been utilized for several other synthetic transformations.[12] We report here organoboron cross-coupling reactions using mpg-CN as a photocatalyst. C(sp2)−C(sp3) Cross-Coupling Using mpg-CN/ Ni Dual Photoredox Catalysis
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