Cyclohexadienone diazeniumdiolates from nitric oxide addition to phenolates

Sterically hindered phenols react with nitric oxide under basic condititons to give either cyclohexadienone diazeniumdiolates or oximates. Phenols with 2,6-di-tert-butyl and 4-methyl (butylated hydroxy toluene, BHT), 4-ethyl, or 4-methoxy methylene substituents yield the corresponding 2,6-di-tert-butyl-2,5-cyclohexadienone-4-alkyl-4-diazeniumdiolate salts (4-methyl la, 4-ethyl 3a, 4-methoxymethylene 5a). Phenols with 2,6-di-tert-butyl and 4-methylene (2,6-di-tert-butylphenol) substituents yield 4-methoxymethylenediazeniumdiolate (5a) together with 2,6-di-tert-butyl benzoquinone oximate (6a), while phenols with 2,6-di-tert-butyl and 4-methylenedimethylamino or hydrogen substituents yield exclusively 2,6-di-tert-butyl benzoquinone oximate (6a). Alkylation of the silver salts of la, or treating the O-2-protonated diazeniumdiolate with diazomethane, both yield mixtures of O-1- and O-2-methylated isomers. All the compounds exhibit exothermic thermal decomposition except the quinuclidinium (le, 3e, 5e) and triethylenediammonium (If) salts which decompose endothermically. Three of the compounds namely "O-2-protonated" (Z)-1-[4-(2,6-di-tert-butyl-4-methyl-cyclohexadienonyl)]diazen-1-ium-1,2-diolinic acid(lb), O-2-methyl (Z)-1-[4-(2,6-di-tert-butyl-4-methyl-cyclohexadienonyl)]diazen-1-ium-1,2-diolate (Ic), and "O-2-protonated" (Z)-1-[4-(2,6-di-tert-butyl-4-methoxymethylenecyclohexadienonyl)]diazen-1-ium-1,2-diolinic acid (5b) were characterized by single-crystal X-ray diffraction studies. The diazeniumdiolate framework in all the structures is coplanar with considerable pi-bonding delocalized over the O-N-N-O framework.