Sterically Crowded peri-Substituted Naphthalene Phosphines and their PV Derivatives

Three sterically crowded pen-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-Y chalcogenides Nap[P(E')-(Ph-2)(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, nO, nS, nSe (n = 1-3) are compared. Eleven molecular structures have been analysed by naphthalene ring torsions, pen-atom displacement, splay angle magnitude, X center dot center dot center dot 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. PE 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 center dot center dot center dot P-C fragment, except for 30, which displays a twist-axial-twist conformation resulting in the formation of a linear O center dot center dot center dot Se-C alignment. Ab initio MO calculations performed on 20, 30, 3S and 3Se reveal Wiberg bond index values of 0.02 to 0.04, which indicates only minor non-bonded interactions; however, calculations on radical cations of 30, 3S and 3Se reveal increased values (0.14-0.19).