N,N'-dimethyl-N,N'-diarylurea anion radicals: an intramolecular reductive elimination.

The one-electron reduction of tertiary N,N'-dimethyl-N,N'-diarylureas (aryl = phenyl, beta-naphthyl, alpha-naphthyl), in HMPA, results in anion radicals that undergo novel intramolecular reductive elimination reactions leading to the formation of the anion radicals of the corresponding biaryls. These results are due to face to face pi-pi stacking interactions involving the two aromatic rings in the urea systems. The overlapping p(pi)() orbitals on the ipso carbons of opposing aryl groups evolve into a sigma bond leading to the formation of the biaryl anion radical. In the case of the N,N'-dimethyl-N,N'-di-2-pyrenylurea system, there is a node in the LUMO of the number 2 carbon, and the parent anion radical remains intact.