Bis-[cyclic(alkyl)(amino)carbene]-derived diradicals

Crystalline polymeric structures of trans-1,4-cyclohexylene bridged N-tethered bis-CAACs in the form of their LiOTf adducts were synthesized and isolated. These were further used as building blocks for the synthesis of crystalline (amino)(carboxy)-based diradicals. The triplet diradical character of these compounds was unambiguously confirmed by the presence of a half-field signal in their EPR spectra. Theoretical calculations show that the singlet state is marginally more stable than the triplet state. Crystalline (amino)(carboxy)-based diradicals were synthesized from newly designed N,N '-trans-1,4-cyclohexylene bridged bis-CAACs. A half-field EPR signal unambiguously confirms their triplet diradical character.