Heterocycle formation using [PhP(Se)(m-Se)]₂. The crystal structures of [PhP(Se)(m-Se)]₂, PhP(Se)Se₂(C₇H₁₀) and PhP(Se)(m-Se)(m-NPh)P(Se)Ph

An X-ray crystallographic study of [PhP(Se)(mu -Se)](2) 1, the oxidation product of the homocycle (PhP)(5) with ten equivalents of selenium, revealed that the molecule is centrosymmetric with a planar central P-2(mu -Se)(2) core and trans disposition of exocyclic P=Se bonds. In the reaction of 1 with norbornene (bicyclo[2.2.1]hept-2-ene), crystallographic analysis of the product 2 revealed exo addition of a PhP(Se)Se-2 unit across the C=C bond, giving a 1,2-diselena-3-phospholane (C2PSe2) ring. Norbornadiene (bicyclo[2.2.1]hepta-2,5-diene) reacts more slowly with 1, allowing the isolation of a 1,2-selenaphosphetane (C2PSe ring) in addition to a diselenaphospholane. The reaction of 1 with azobenzene proceeds with cleavage of the N=N bond and substitution of a bridging selenium atom in 1 by an NPh unit, giving the first crystallographically characterised selenaazadiphosphetane (P2SeN) ring.