Oligomerization of phosphaalkynes mediated by bulky N-heterocyclic carbenes: avenues to novel phosphorus frameworks

Reactions of RC[triple bond, length as m-dash]P (R = tBu or Ad (admantyl)) with NHCs (SIMes, 1a; IMes, 1b and IDipp, 1d), leading to 1,2,3-triphosphetenes 2 and 3, a triphosphole 4, and a di-1,2-dihydro-1,2-diphosphete-substituted diphosphene 5, are reported. Compound 5 represents a novel P6 chain framework, as well as a newly discovered phosphaalkyne hexamer stabilized by two NHCs. Computational investigations suggest that the weak π-accepting ability of NHCs results in low stability of the initially formed 2H-phosphirenes, thus facilitating spontaneous oligomerization reactions. Such oligomerizations are highly susceptible to the electronic property and steric bulk of NHCs.