The 3,3-Dimethyl-2-azabicyclo[2.2.2]octyl System as a Bredt's Rule Kinetically Stabilized Dialkylamino Group in Electron-Transfer Studies

PE and CV data are reported for electron removal from 2-substituted 3,3-dimethyl-2-azabicyclo[2.2.2]octyl (2-ADO) derivatives in which the substituent is chloro, dimethylamino, 2-ADO, and —N=N-2-ADO and compared with that for their 9-azabicyclo[3.3.1]nonyl (9-ABN) analogues. The differences observed in both IP1and E°′ in the two series of compounds are dominated by their steric differences; 2-ADO has tert,sec-alkyl substitution at N while 9-ABN has sec,sec-alkyl substitution. The E°′ values for chloramines and 2-tetrazenes are dominated by the ease of flattening at nitrogen, but RN-N′R interactions dominate the E°′ observed for the hydrazines. The 2-ADO dimer (3) has ΔG⧧ of 18.8 kcal/mol (+63 °C) for methyl interconversion, which is >8.8 kcal/mol greater than twice that of its 2-dimethylamino analogue (5). 3 is argued to have significant flattening at both nitrogens at the transition state, in contrast to all previously studied tetraalkylhydrazines. 3+·PF6−proved isolable.