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

摘要

Cyclic voltammetric studies of 1-phenyl-3-(4-N,N-dimethylamino)phenyl urea (UH) in CH{sub}2Cl{sub}2 in the presence of several pyridine derivatives are described. By itself, UH undergoes a reversible one electron oxidation to the radical cation, UH{sup}+, 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{sup}+ wave. Possible explanations for the large shift are proton transfer between UH{sup}(2+) and the guest or very strong hydrogen bonding between the two. Computer simulation studies and comparison to known pK{sub}a 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.