Description
This thesis presents a mechanistic study of two phenylenediamine derivatives. The first is a disubstituted phenylenediamine with a phenyl-urea substituted para to a dimethylamino group. The phenyl-urea moiety offers two N-H sites for hydrogen bonding and proton transfer. This is UHH. The second, is a disubstituted phenylenediamine with an isocytosine-urea moiety substituted para to a dimethylamino group. The combined isocytosine-urea-phenylenediamine forms a redox active 4-hydrogen bond array where the urea moiety offers two N-H sites for proton donation and the isocytosine offers two sites for hydrogen bond acceptance. This is UpyH. Initial cyclic voltammetry (CV) experiments for UHH show reversible CV behavior in CH₂Cl₂ and irreversible CV behavior in CH₃CN. With the inclusion of two UHH analogs, one with both N-H sites "blocked" with methyl substituents, UMeMe, and a second analog with a single urea N-H site, UMeMe, CV analysis continued. From these studies, in addition to a UV-vis/ CV study, it was determined that the dimethylamino on a fully reduced UHH or UMeH could abstract a proton from a second radical cation urea N-H. This was immediately followed by a thermodynamically favorable second electron transfer. Thus the products at the end of the first oxidation wave from a 2 e-, 1H+ transfer are a quinoidal cation and a fully reduced/protonated UHH or UMeH. On the return scan, UHH in CH₃CN and UMeH in both solvents undergo a thermodynamically non-favored back proton transfer at a more energetic reduction potential. UHH in CH₂Cl₂ accesses a lower energy pathway through the formation of a hydrogen bond complex as part of a wedge scheme. Both pathways are supported by results from concentration and scan rate dependent CV studies that show two return waves correlating to two pathways. UV-vis results show a protonated/reduced species, but no radical cation. In the UpyH project, by using the same CV and UV-vis analysis in addition to an ¹HNMR study in CH₂Cl₂/NBu₄PF₆, we show UpyH favors a dimerized form but as the dimer undergoes oxidation it breaks apart then reforms on the return scan. To our knowledge this the first account for electrochemically breaking apart a Upy derivative.
