Naphthalene-1,8-diyl bis(halogenophosphanes): Novel syntheses and structures of useful synthetic building blocks

A series of new bay region disphospha-functionalised naphthalenes is reported. The reduction of ylidic phosphonium phosphoride NapP(2)Cl(6) (1) (Nap = naphthalene-1,8-diyl) with MeOPCl2 gives the important synthon Nap(PCl2)(2) (2) in nearly quantitative yield. Reaction of I with magnesium metal affords (NapP(2))(n) (3), which reacts with Br-2 and I-2 yielding Nap(PBr2)(2) (4) and Nap(PI)(2) (5), respectively. X-ray structure determinations reveal a twisted geometry of the naphthalene ring in sterically strained 2 and 4, whilst the presence of a P-P bond in 5 results in the release of the steric strain and generation of the planar NapP(2) moiety. Although the tetrahedral P environments are severely distorted the sigma(3)P-sigma(3)P bonding in 5 represents a new type of P-P bonding environment in 1,8-diphosphanaphthalenes. Compounds 1, 4 and 5 each represent the highest coordination, achievable by direct halogenation. The new compounds 2-5 were fully characterised by NMR, IR, and Raman spectroscopy, mass spectrometry, and elemental analysis.