Tunable Cyclopentane-1,3-diyls Generated by Insertion of Isonitriles into Diphosphadiazanediyls

Diphosphadiazanediyl
([P­(μ-NTer)]2, 1) is known to readily
react with small molecules bearing multiple
bonds to give [2.1.1]­bicyclic species. On the contrary, in the reaction
of isonitriles with 1, planar five-membered heterocycles
(3) with biradical character are formed by insertion
of the carbon atom into one P–N bond. Under irradiation, heterocyclic
biradicaloids 3 are shown to generate housane-type [2.1.0]­bicyclopentanes
by transannular bond formation. However, these housane species thermally
equilibrate, reforming the open-shell singlet cyclopentanediyl. The
biradical character of 3 indicates high reactivity which
is further demonstrated in the activation of small molecules bearing
multiple bonds leading to [2.2.1]­bicyclic heterocycles. Depending
on the substituent of the isonitrile, the reaction with a second equivalent
of isonitrile is also observed for smaller substituents. By employing
suitable diisonitriles, even the catenation of two open-shell singlet
cyclopentane-1,3-diyls is achieved. CASSCF­(6,6) computations revealed
biradical character for 3 ranging between 26 and 27%.