Electrochemically Controlled Hydrogen Bonding.Nitrobenzenes as Simple Redox-Dependent Receptors for Arylureas

摘要

Reduction of nitrobenzene derivatives in the presence of arylureas in aprotic solvents results in large positive shifts in potential of the nitrobenzene~(0/-) cyclic voltammetry wave with little change in wave shape.This behavior is indicative of reversible hydrogen bonding between nitrobenzene radical anions and arylureas.Computer fitting of the cyclic voltammetry of 4-nitroaniline,NA,plus 1,3-diphenylurea in DMF shows essentially no binding between urea and NA in the oxidized state (K_(ox) < 1 M~(-1)),but very strong binding in the reduced state (K_(red) = 8 x 10~4 M~(-1)),along with very rapid rates of hydrogen bond formation (k_f's approx= 10~8-10~(10) M~(-1) s~(-1)),making this system a fast on/off redox switch.