Facile Synthesis of Dibenzo-7λ3‑phosphanorbornadiene Derivatives Using Magnesium Anthracene

Unprotected dibenzo-7λ3-phosphanorbornadiene derivatives RPA (A = C14H10 or anthracene; R = tBu, dbabh = NA, HMDS = (Me3Si)2N, iPr2N) are synthesized by treatment of the corresponding phosphorus dichloride RPCl2 with MgA·3THF, in cold THF (∼20% to 30% isolated yields). Anthracene and the corresponding cyclic phosphane (RP)n form as coproducts. Characteristic NMR features of the RPA derivatives include a doublet near 4 ppm in their 1H NMR spectra and a triplet peak in the 175–212 ppm region of the 31P NMR spectrum (2JPH ∼14 Hz). The X-ray structures of the AN–PA and (HMDS)­PA derivatives are discussed. Thermolysis of RPA benzene-d6 solutions leads to anthracene extrusion. This process has a unimolecular kinetic profile for the iPr2NPA derivative. The 7-phosphanorbornene anti-iPr2NP­(C6H8) could be synthesized (70% isolated yield) by thermolysis of iPr2NPA in 1,3-cyclohexadiene.