peri-Interactions in Naphthalenes, 6 [1]. On Hypercoordination of Phosphorus in 8-Dialkylamino-naphth-1-yl Phosphonium Salts

Under favourable conditions, the phosphorus centres in tetraorganophosphonium cations are sufficiently electrophilic to become hypercoordinate by reaction with strong nucleophiles. However, as a peri substituent at the naphthalene system, such a centre proved to be unable to induce the nitrogen of a peri-bound dialkylamino group to bond formation. The distortion of the naphthalene skeleton revealed by X-ray structure determination of four 8-dialkylaminonaphth- 1-yl phosphonium salts does not exhibit the criteria of N-P bond formation but rather those of intersubstituent repulsion.