A series of new bay region disphospha-functionalised naphthalenes is reported. The reduction of ylidic phosphonium phosphoride NapP2Cl6 (1) (Nap=naphthalene-1,8-diyl) with MeOPCl2 gives the important synthon Nap(PCl2)2 (2) in nearly quantitative yield. Reaction of 1 with magnesium metal affords (NapP2)n (3), which reacts with Br2 and I2, 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 PP bond in 5 results in the release of the steric strain and generation of the planar NapP2 moiety. Although the tetrahedral P environments are severely distorted the σ3Pσ3P bonding in 5 represents a new type of PP 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.