Oxidation-Based, Redox-Dependent Hydrogen Bonding Utilizing Dimethylamino- Substituted Diarylureas

Cyclic voltammetric studies of 1-phenyl-3-(4-N,N-dimethylamino)phenyl urea (UH) in CH2Cl2 in the presence of several pyridine derivatives are described. By itself, UH undergoes a reversible one electron oxidation to the radical cation, UH+, and a second less reversible oxidation at more positive potentials. Addition of ten equivalents of 1,8-naphthyridine or pyridine causes the second oxidation to shift 700 mV negative, resulting in a quasi-reversible two electron oxidation at the potential of the UH/UH+ wave. Possible explanations for the large shift are proton transfer between UH2+ and the guest or very strong hydrogen bonding between the two. Computer simulation studies and comparison to known pKa values suggest that neither by themselves are adequate to explain the observed voltammetry. A mechanism involving both hydrogen bonding and proton transfer is more likely