Naphthalene-1,8-diyl Bis(Halogenophosphanes): Novel Syntheses and Structures of Useful Synthetic Building Blocks

• Published in: Chemistry : a European journal 2003-01, Vol.9 (1), p.215-222
• Main Authors: Kilian, Petr, Slawin, Alexandra M. Z., Woollins, J. Derek
• Format: Article
• Language: English
• Subjects: halogens; neighboring-group effects; phosphorus; strained molecules
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200390015

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 PP 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 σ3Pσ3P 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. The expected decrease in the coordination number of phosphorus with increasing bulkiness of the halogen atoms, accompanied by unexpected changes in bonding resulting from steric crowding are revealed by a series of halogeno‐1,8‐diphosphanaphthalenes Nap(PXn)2 (Nap=naphthalene‐1,8‐diyl). The maximum coordinated species known for each halogen are Nap(PCl2)(PCl4) (left), Nap(PBr2)2 and Nap(PI)2 (right).