Cu Photoredox Catalysts Supported by a 4,6-Disubstituted 2,2 '-Bipyridine Ligand: Application in Chlorotrifluoromethylation of Alkenes

Interest in base metal catalysis motivates the development of Cu-based photoredox catalysts for organic synthesis. However, only a few Cu catalysts have been applied in photoredox reactions, the majority of which contain one or two 1,10-phenanthroline ligands. Here we design a 4,6-disubstituted 2,2'-bipyridine ligand for Cu. Two heteroleptic [Cu(NN)(PP)][PF6] complexes, where NN stands for the 2,2'-bipyridine ligand and PP stands for a bisphosphine ligand, have been synthesized and characterized. They exhibit longer excited state lifetimes and higher Cu(I) / Cu(II) potentials compared to the most widely used Cu catalyst, [Cu-(dap)(2)]Cl. The complex with Xantphos as the PP ligand is an efficient catalyst for chlorotrifluoromethylation of terminal alkenes, especially styrenes, which had been challenging substrates for previously reported photoredox reactions. This chlorotrifluoromethylation method enables the convenient introduction of a trifluoromethyl group into organic molecules under mild conditions, which is important for medicinal chemistry.