A Kekulé Diradicaloid with a Naphthalene Spacer

The availability of a diverse array of carbenes led to the generation of a catalog of carbene based Kekulé diradicaloids, but the linker in such molecules is mostly limited to phenylene or biphenylene. Here we have prepared a closed-shell Kekulé diradicaloid (2) separated by a naphthalene moiety and stabilized by two capping 5-SIDipp [5-SIDipp = 1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene] from the reduction of the corresponding dication (1). The combined experimental and computational studies confirm that 2 is in a closed-shell singlet state exhibiting a singlet–triplet energy difference (ΔES–T) of 18.7 kcal/mol, which is considerably lower than Thiele’s version (29.1 kcal/mol).