The Structure and Reactivity of 1,2,3,3,-Tetrakis(4-(dimethylamino)pyridinium-1-yl)cyclopropene

The X-ray single crystal structure of 1,2,3,3-tetrakis(4-(dimethylamino)pyridinium-1-yl)cyclopropene, 1, is presented together with some reactions of 1. Both triphenylphosphine and 1-methylimidazole react with 1 to form the ring-opened products, (Z)-1-(triphenylphosphonio)-1,2,3,3-tetrakis(4-(dimethylamino)pyridinium-1-yl) allylide (6), and the isomeric (E)-and (Z)-1-(3-methylimidazolium-1-yl)-1,2,3,3-tetrakis(4-(dimethylamino)-pyridinium-1-yl)allylides (7), respectively. Cyclic voltammetry shows that 6 oxidizes to its corresponding allyl radical at 1.3 V vs SCE; the isomers of 7 oxidize at 0.48 and 0.61 V. The pK_a's of the conjugate acids of 6 and 7 are -1 and 3.0, respectively. Reaction of 1 with potassium nitrite gave an unexpected product, 1,1,2-tris(4-(dimethylamino)pyridinium-1-yl)ethylene. The reactivity of 1 was compared to some analogous systems, 2-phenyl-1,3,3-tris(4-(dimethylamino)pyridinium-1-yl)cyclopropene (12) and 2-phenyl-1,3,3-tris(3-methylimidazolium-1-yl) cy clopropene (13). The phenyl substituent significantly alters the reactivity of 12 and 13, such that both compounds do not form ring-opened products when treated with strong nucleophiles.