Ureas are widely used in supramolecular complexes due to their strong H-bonding capabilities. Electroactive ureas are of interest because they open up the possibility of redox control over supramolecular assembly if the electron transfer strongly perturbs the H-donating ability of an urea NH. While several different N-ferrocene-ureas have been studied, oxidation of ferrocene does not appear to have a strong effect on the acidity. In contrast, we have been studying a dimethylaminophenyl urea, U(H)H, in which oxidation does have a strong effect on acidity. As we have recently reported (Clare et al., J. Am. Chem. Soc. 2013, 135, 18930-41), the oxidized urea is acidic enough to transfer a proton to the dimethylamino group on another urea leading to immediate removal of a second electron to give the quinoidal cation, eq 1.  In the presence of good H-bonding basic guests such pyridine (1 H-bond) or 1,8-naphthyridine (2 H-bonds) the proton is transferred to the guest instead. In a non-competitive solvent such as CH2Cl2 the electron transfer is reversible due to the stability of the product H-bond complex. In this presentation the results of current work will be reported in which we are extending the urea/guest systems to 3 H-bond heterogeneous dimers and 4 H-bond homogeneous dimers. Oxidation of the latter should greatly destabilize the dimer due to the change in H-bonding pattern and unfavorable electrostatics. 

Use of an electroactive urea to control binding strength in linear hydrogen bond arrays

248th National Meeting (2014)

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