Graphitic carbon nitride as a photocatalyst for decarboxylative C(sp2)-C(sp3) couplings via nickel catalysis

The development of robust and reliable methods for the construction of C(sp2)–C(sp3) bonds is vital for accessing an increased array of structurally diverse scaffolds in drug discovery and development campaigns. While significant advances towards this goal have been achieved using metallaphotoredox chemistry, many of these methods utilise photocatalysts based on precious-metals due to their efficient redox processes and tuneable properties. However, due to the cost, scarcity, and toxicity of these metals, the search for suitable replacements should be a priority. Here, we show the use of commercially available heterogeneous semiconductor graphitic carbon nitride (g-C3N4) as a photocatalyst, combined with nickel catalysis, for the cross-coupling between aryl halide and carboxylic acid coupling partners. g-C3N4 has been shown to engage in single-electron-transfer (SET) and energy-transfer (ET) processes for the formation of C–X bonds, and in this manuscript we overcome previous limitations to furnish C–C over C–O bonds using carboxylic acids. A broad scope of both aryl halides and carboxylic acids is presented, and recycling of the photocatalyst demonstrated. The mechanism of the reaction is also investigated.