| Popis: |
Diels-Alder addition of bicyclic azo compounds to cyclic dienes would produce bis-N,N'-bicyclic hydrazines, but this reaction proves to be endothermic. The greater basicity of the adduct than of the azo compound makes the addition reaction 13.6–14.1 kcal mol -1 less endothermic: (in water) if the protonated azo compound is employed instead of the neutral compound, and the addition reactions proceed well in acetonitrile if HBF 4 Ėt 2 O is used to protonate the azo compound before adding the diene. Preparations of the neutral hydrazines derived from 2,3-diazabicyclo[2.2.2]oct-2-ene( 5 ) with 1,3-cyclohexadiene( 6 ) and from 2,3-diazabicyclo [2.2.1] hept-2-ene ( 10 ) with 6 and 1,3-cycloheptadiene ( 7 , 11 , and 13 , respectively) as well as the saturated hydrazines derived by catalytic hydrogenation ( 9 , 12 , and 14 , ropectively) are reported. The neutral adduct of 10H + and cyclopentadiene, 15 , proves to be too thermally unstable for isolation, and the saturated form, 16 , is prepared by diimide reduction of 15H + . The neutral hydrazines all give radical cations and dications with appreciable solution lifetimes, and 9 2+ (BF 4 - ) 2 is the first isolable hydrazine dication. The thermodynamics of electron loss for these hydrazines are studied by cyclic voltammetry, and prove to be dominated by non-bonded steric interactions between the alkyl groups. Compound 9 is the most easily oxidized hydrazine known, at E °' = -0.54V vs SCE. |
