Département de chimie moléculaire

Two di-tert-butylphenols incorporating an N-methylbenzimidazole moiety in the ortho or para position were synthesized (MeOH and pMeOH, resp.). Their x-ray structures evidence a hydrogen bond between the phenolic proton and the iminic nitrogen atom, whose nature is intra- and intermol., resp. MeOH is readily oxidized by an intramol. PET mechanism to form the hydrogen-bonded phenoxyl-N-methylbenzimidazolium system (MeOH).+, whereas oxidn. of pMeOH occurs by intermol. PET, affording the neutral phenoxyl benzimidazole (pMeO). system. The deprotonations of MeOH and pMeOH yield the corresponding phenolate species (MeO)- and (pMeO)-, resp., while that of the previously reported HOH (analogous to MeOH but lacking the N-Me group) produces an unprecedented hydrogen-bonded phenol benzimidazolate species, as evidenced by its x-ray structure. The latter is believed to be in equil. in soln. with its tautomeric phenolate form, as suggested by NMR, electrochem. and DFT studies. The 1-electron oxidns. of the anions occur by a simple ET process affording phenoxyl radical species, whose electronic structure was studied by HF-EPR spectroscopy and DFT calcns. In particular, anal. of the g1 tensor shows the order 2.0079{\textgreater}2.0072{\textgreater}2.0069{\textgreater}2.0067 for (MeO)., (HO)., (MeOH).+ and (HOH).+, resp. (MeO). exhibits the largest g1 tensor (2.0079), consistent with the absence of intramol. hydrogen bond. The g1 tensor of (HO). is intermediate between those of (MeOH).+ and (MeO). (g1 = 2.0072), indicating that the phenoxyl oxygen is hydrogen-bonded with a neutral benzimidazole partner. [on SciFinder(R)]