Mechanical-Bond-Protected, Air-Stable Radicals

Radical templation centered around a heterotrisradical tricationic inclusion complex DB •+ ⊂ DAPQT 2(•+), assembled from an equimolar mixture of a disubstituted 4,4′-bipyridinium radical cation ( DB •+ ) and an asymmetric cyclophane bisradical dication ( DAPQT 2(•+) ), affords a symmetric [2]catenane ( SC ·7PF 6 ) and an asymmetric [2]catenane ( AC ·7PF 6 ) on reaction of the 1:1 complex with diazapyrene and bipyridine, respectively. Both these highly charged [2]catenanes have been isolated as air-stable monoradicals and characterized by EPR spectroscopy. X-ray crystallography suggests that the unpaired electrons are delocalized in each case across two inner 4,4′-bipyridinium (BIPY 2+ ) units forming a mixed-valence (BIPY 2 ) •3+ state inside both [2]catenanes, an observation which is in good agreement with spin-density calculations using density functional theory. Electrochemical studies indicate that by replacing the BIPY 2+ units in homo[2]catenane HC •7+ —composed of two mechanically interlocked cyclobis(paraquat- p -phenylene) rings—with “zero”, one, and two more highly conjugated diazapyrenium dication (DAP 2+ ) units, respectively, a consecutive series of five, six, and seven redox states can be accessed in the resulting SC ·7PF 6 (0, 4+, 6+, 7+, and 8+), HC ·7PF 6 (0, 2+, 4+, 6+, 7+, and 8+), and AC ·7PF 6 (0, 1+, 2+, 4+, 6+, 7+, and 8+), respectively. These unique [2]catenanes present a promising prototype for the fabrication of high-density data memories.