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

Abstract

Unprotected dibenzo-7λ³-phosphanorbornadiene derivatives RP<b>A</b> (<b>A</b> = C₁₄H₁₀ or anthracene; R = ^<i>t</i>Bu, dbabh = N<b>A</b>, HMDS = (Me₃Si)₂N, ^<i>i</i>Pr₂N) are synthesized by treatment of the corresponding phosphorus dichloride RPCl₂ with Mg<b>A</b>·3THF, in cold THF (∼20% to 30% isolated yields). Anthracene and the corresponding cyclic phosphane (RP)_<i>n</i> form as coproducts. Characteristic NMR features of the RP<b>A</b> 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 (²<i>J</i>_PH ∼14 Hz). The X-ray structures of the <b>A</b>N–P<b>A</b> and (HMDS)­P<b>A</b> derivatives are discussed. Thermolysis of RP<b>A</b> benzene-<i>d</i>₆ solutions leads to anthracene extrusion. This process has a unimolecular kinetic profile for the ^<i>i</i>Pr₂NP<b>A</b> derivative. The 7-phosphanorbornene <i>anti</i>-^<i>i</i>Pr₂NP­(C₆H₈) could be synthesized (70% isolated yield) by thermolysis of ^<i>i</i>Pr₂NP<b>A</b> in 1,3-cyclohexadiene