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 1a, 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 1a, 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 (1e, 3e, 5e) and triethylenediammonium (1f) 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 (1b), O(2)-methyl (Z)-1-4-(2, 6-di-tert-butyl-4-methyl-cyclohexadienonyl)]diazen-1-ium+ ++-1,2-diolate (1c), 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.