Synthesis and characterization of annelated nitronyl nitroxides
Bowles, Steven E. (Steven Edward), 1978-
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The heteroaromatic 2'-phenylbenzimidazole 1-nitronyl nitroxide (PBNN), 2'-pyridylbenzimidazole nitronyl nitroxide (2PBNN), 4'-pyridylbenzimidazole nitronyl nitroxide (4PBNN), 2'-thienylbenzimidazole nitronyl nitroxide (2TBNN), and 3'-thienylbenzimidazole nitronyl nitroxide (3TBNN) radicals were synthesized, and the 2-position heterocyclic group was found to have little effect on electronic structure. The structural change from tetramethyl to benzimidazole shifted the reductive potential to -0.300 V and raised the oxidation potential to 1.1 V. The band gap for BNN radical was found to be 1.5 eV, consistent with both electrochemical and UV-Vis spectroscopy techniques. Analysis of the EPR and calculations showed that the radical had a delocalized SOMO on the benzimidazole, with predictable high spin density on the annelated benzene ring. The X-ray structures for 2TBNN and 3TBNN were determined and showed the formation of slipped stacks. The magnetic susceptibility for 2TBNN was found to be antiferromagnetic and weak, and 3TBNN was found to be have long range antiferromagnetic exchange of J = -42.2 cm-1 and theta = 3.23 K using an infinite chain model.Three new radicals, 2-phenyl-5-azabenzimidazole nitronyl nitroxide ( P3PNN), 2-phenyl-4-azabenzimidazole nitronyl nitroxide (P2PNN ), and 2-phenylimidazo[4,5-b]quinoxaline nitronyl nitroxide ( PQNN), were synthesized and characterized using EPR and DFT calculations. The substitution of nitrogen in the benzimidazole ring decreased the chemical stability of these radicals in solution. PQNN was determined to be the first example of an extended stable annelated nitronyl nitroxide.A series of new brominated 2-phenylbenzimidazole 1-oxyl-3-oxides, 2-4 '-hexylphenyl-5-bromobenzimidazole 1-oxyl-3-oxide, 2-phenyl-5-bromobenzimidazole 1-oxyl-3-oxide, 2-ethyl-5-bromobenzimidazole 1-oxyl-3-oxide, and 2-4 '-t-butylphenyl-5-bromobenzimidazole 1-oxyl-3-oxide, were synthesized using methods developed and optimized in the synthesis of 2-phenylbenzimidazole 1-oxyl-3-oxides. Solubility was found to be a major problem with the 5-bromo-2-phenylbenzimidazole 1-oxyl-3-oxide class of molecules. The reactivity of benzofuroxan with functional groups on the 3- and 6-positions was investigated and it was found that their reactivity is drastically different, with the functional groups interfering with standard reaction conditions for the parent class.
- Chemistry