Pyridine-directed palladium-catalyzed electrochemical phosphonation of C(sp2)–H bond

• One-step electrocatalytic method for aromatic ortho C–H phophonation was proposed.
• Redox properties of isolated [(PhPy)Pd(EtO)2P(O)]2 intermediate were compared with those of the acetate precursor.
• The electrosynthesis proceeds under mild conditions at [(PhPy)Pd(EtO)2P(O)]2 oxidation potentials.

A new electrocatalytic method for the phosphonation of 2-phenylpyridine was developed. The joint electrochemical oxidation of a mixture of palladium acetate, 2-phenylpyridine, and H-diethylphosphonate affords the ortho C–H phosphonation product. The electrocatalytic synthesis proceeds under mild conditions (room temperature) at potentials that clearly generate high oxidation state of palladium complexes without any specially added oxidizing agents. An intermediate dipalladium [(PhPy)Pd(EtO)2P(O)]2 complex was isolated, the structure was confirmed by X-ray analysis. Cyclic voltammetry studies reveal the [(PhPy)Pd(EtO)2P(O)]2 complex to be oxidized at more positive potentials compared with the acetate palladacycle [(PhPy)Pd(OAc)]2. Preparative oxidation of the diethylphosphonate palladium complex affords 2-phenylpyridine C–H bond phosphonation product.

The joint electrochemical oxidation of palladium acetate, 2-phenylpyridine, and H-diethylphosphonate mixture affords the ortho C–H phophonation product. The synthesis proceeds under mild conditions (room temperature) at potentials generating palladium complexes in high oxidation state without any specially added oxidizing agents. Preparative oxidation of [(PhPy)Pd(EtO)2P(O)]2 selectively affords arylphoshonate.Figure optionsDownload as PowerPoint slide