Radical Dimerization of 5,5′-Diphenyl-3,3′,4,4′-tetramethoxy-2,2′-bipyrrole: π Dimer in the Crystal, σ Dimer in Solution.

The crystalline, spinless π dimer (1.+⋅PF6)2 was obtained by the oxidation of bipyrrole 1 with ferrocenium hexafluorophosphate. The diamagnetic species generated electrochemically in solution was identified as the σ dimer by NMR spectroscopy.