1,8-bis[(dimethoxy)phospino]naphthalene: A new bis-phosphonite ligand witha rigid C-3-backbone and unexpected reaction chemistry

1,8-Bis[(diethylamino)phosphino]naphthalene (1) reacted with dry methanol i n dichloromethane to form the new bis-phosphonite ligand 1,8-bis[(dimethoxy )phosphino]-naphthalene (dmeopn, 2). By oxidation of 2 with H2O2. (H2N)(2)C (:O) the corresponding bis-phosphonate, 1,8-bis[(dimethoxy)phosphoryl]napht halene (3), was obtained quantitatively. Reaction of 3 with phosphorus tric hloride unexpectedly furnished at 2.4:1 mixture of the bis-phosphonate anhy drides rac- and meso-1,3-dimethoxy-1,3-dioxo-2,3-dihydro-1,3-diphospha-2-ox aphenalen (rac-4 and meso-4) from which rac-4 could be fractionally crystal lised. The bis-phosphonite 2 behaved as a normal bidentate chelate ligand t owards Mo-0 and Pd-II, and furnished the complexes [(dmeopn)Mo(CO)(4)] (5) and [(dmeopn)PdCl2] (6) when treated with [(nor)Mo(CO)(4)] or [(cod)PdCl2] (nor=nor-bornadiene, cod = cycloocta-1,8-diene). Attempts to prepare 1,8-di phosphinonaphthalene (7) by reducing 2 or 3 with LiAlH4 or LiAlH4/TMSCl (1: 1) (TMSCI = trimethyl chlorosilane) in THF led to inseparable mixtures of p hosphorus-containing products. Compounds 2-6 were characterized by H-1-, C- 13-, and P-31-NMR spectroscopy, IR spectroscopy, mass spectrometry and elem ental analysis. X-ray crystal structure analyses were carried out for the b is-phosphonate anhydride rac-4 and palladium (II) complex 6. The geometry o f compound rac-4, in which the phosphorus atoms are connected by an oxygen atom, reveals a relief of strain from the bis-phosphine 1, whereas the 1,8- P,P'-naphthalenediyl group in 6 is surprisingly distorted; the P atoms are displaced from the naphthalene best plane by -46.7 and 54.5 pm.