Sterically crowded peri-substituted naphthalene phosphines and their P^V derivatives

Three sterically crowded peri-substituted naphthalene phosphines, Nap[PPh₂][ER] (Nap=naphthalene-1,8-diyl; ER=SEt, SPh, SePh) 1–3, which contain phosphorus and chalcogen functional groups at the peri positions have been prepared. Each phosphine reacts to form a complete series of P^V chalcogenides Nap[P(E′)(Ph₂)(ER)] (E′=O, S, Se). The novel compounds were fully characterised by using X-ray crystallography and multinuclear NMR spectroscopy, IR spectroscopy and MS. X-ray data for 1, 2, n O, n S, n Se (n=1–3) are compared. Eleven molecular structures have been analysed by naphthalene ring torsions, peri-atom displacement, splay angle magnitude, X⋅⋅⋅E interactions, aromatic ring orientations and quasi-linear arrangements. An increase in the congestion of the peri region following the introduction of heavy chalcogen atoms is accompanied by a general increase in naphthalene distortion. P⋅⋅⋅E distances increase for molecules that contain bulkier atoms at the peri positions and also when larger chalcogen atoms are bound to phosphorus. The chalcogenides adopt similar conformations that contain a quasi-linear E⋅⋅⋅PC fragment, except for 3 O, which displays a twist-axial-twist conformation resulting in the formation of a linear O⋅⋅⋅SeC alignment. Ab initio MO calculations performed on 2 O, 3 O, 3 S and 3 Se reveal Wiberg bond index values of 0.02 to 0.04, which indicates only minor non-bonded interactions; however, calculations on radical cations of 3 O, 3 S and 3 Se reveal increased values (0.14–0.19).