Ring size effects in sesquibicyclic hydrazines and hydrazine cation radicals, and their electron transfer properties

The Diels-Alder addition of dienes to protonated diazenes was shown to be general for a large number of dienes and protonated diazenes in the preparation of bis-N,N{dollar}spprime{dollar}-bicycloalkyl Bredt's-rule-protected tetraalkyl-hydrazines. The yields isolated after deprotonation range from 8% for the addition product of cycloheptadiene to protonated 2,3-diazabicyclo(3.2.2.) non-2-ene (1), 2,8-diazatetracyclo(7.3.2.2.{dollar}sp{lcub}3,7{rcub}{dollar}.0{dollar}sp{lcub}2,8{rcub}{dollar}) hexadec-12-ene (6), to 90% for the addition product of cyclohexadiene to protonated 2,3-diazabicyclo(2.2.1) -hept-2-ene (3), 2,7-diazatetracyclo(6.2.2.1{dollar}sp{lcub}3,6{rcub}{dollar}.0{dollar}sp{lcub}2,7{rcub}{dollar}) tridec-9-ene (10). Addition of dienes to 3H{dollar}sp+{dollar} shows that the products are those expected from Alder-Endo addition. Hydrogenation of the adducts is done using Pd on BaCO{dollar}sb3{dollar} catalyst, except for the adduct from 3H{dollar}sp+{dollar} and cyclopentadiene, 11H{dollar}sp+{dollar}, which requires acidic diimide reduction to avoid neutral 11 decomposition. The large difference in basicity between azo compound and hydrazine (measured in water) provides a driving force for the Proton-Driven Diels-Alder reaction of 12.6-14.1 kcal/mol for the formation of 10H{dollar}sp+{dollar}, 11H{dollar}sp+{dollar}, and 2,7-diazatetracyclo(6.2.2.2{dollar}sp{lcub}3,6{rcub}{dollar}.0{dollar}sp{lcub}2,7{rcub}{dollar}) tetradec-4-ene, 8H{dollar}sp+{dollar} to make an otherwise unfavorable reaction of dialkyldiazine and diene exothermic.; The barrier to double nitrogen inversion in 2,7-diazatetracyclo(6.2.1.1.0) dodecane (21), measured by observing the rate of equilibration of 21-d{dollar}sb6{dollar} isomers by {dollar}sp1{dollar}H NMR {dollar}(Delta{dollar}G{dollar}sp{lcub}ddagger{rcub}{dollar} (90{dollar}spcirc{dollar}C) = 27.0 kcal/mol), is exceptionally large, suggesting simultaneous double nitrogen inversion.; Six new sesquibicyclic hydrazine cation radicals are isolated in this work, the nitrate salts of {dollar}{lcub}bf 7sp{lcub}+.{rcub}{rcub}{dollar}, {dollar}{lcub}bf 10sp{lcub}+.{rcub}{rcub}{dollar}, {dollar}{lcub}bf 17sp{lcub}+.{rcub}{rcub}{dollar}, {dollar}{lcub}bf 18sp{lcub}+.{rcub}{rcub}{dollar}, {dollar}{lcub}bf 20sp{lcub}+.{rcub}{rcub}{dollar}, and {dollar}{lcub}bf 21sp{lcub}+.{rcub}{rcub}{dollar}. The kinetic stability of these cation radicals allows convenient study of the effects of changing bicyclic ring size on pyramidality at nitrogen by ESR and UV spectroscopy. The thermodynamics of electron removal is studied by measuring first and second oxidation potentials by cyclic voltammetry. The thermodynamics of first electron loss is dominated by the decrease in nonbonded steric interaction when the nitrogens flatten upon electron removal, although the nitrogens remain pyramidal in the cation radicals. The barrier to double nitrogen inversion in {dollar}{lcub}bf 21sp{lcub}+.{rcub}{rcub}{dollar} is measured by dynamic ESR experiments on 21-d{dollar}sb{lcub}12{rcub}{lcub}bfsp{lcub}+.{rcub}{rcub}{dollar}, giving {dollar}Delta{dollar}H{dollar}sp{lcub}ddagger{rcub}{dollar} = 4.6 kcal/mol, 17% of the double nitrogen inversion barrier of neutral {dollar}{lcub}bf 21sp{lcub}+.{rcub}{rcub}{dollar}. A correlation of {dollar}pi,pisp*{dollar} optical absorption of hydrazine cation radicals with second oxidation potentials is observed. Rate constants for "self" electron exchange between neutral hydrazine and its own cation radical are measured by {dollar}sp1{dollar}H NMR line broadening. Experimental factors make the numbers determined most accurate for 21, k{dollar}sb{lcub}rm et{rcub}{dollar} {dollar}(spcirc{dollar}C) = 1.6{dollar}sb6{dollar} {dollar}times{dollar} 10{dollar}sp4{dollar} M{dollar}sp{lcub}-1{rcub}{dollar}s{dollar}sp{lcub}-1{rcub}{dollar}, and 2,8-diazatetracyclo-(7.2.2.2{dollar}sp{lcub}3,7{rcub}.0sp{lcub}2.8{rcub}rbrack{dollar}pentadec-11-ene,...