Chemistry of pentacoordinated anti-apicophilic phosphorus compounds

Since the synthesis of the first pentacoordinated organophosphorus compound, Ph₅P, by Wittig, the chemistry of pentacoordinated phosphorus compounds has been extensively expanded. Pentacoordinated phosphorus compounds usually take a trigonal bipyramidal structure with two distinctive sites; apical and equatorial positions. In the trigonal bipyramidal structure, electronegative and small substituents prefer the apical positions. Such properties are widely recognized as the apicophilicity rule. However, several examples breaking the apicophilicity rule have been reported in the past few decades and novel properties and reactivities of these new classes of compounds have been found. In this review, the synthesis of novel pentacoordinated phosphoranes with anti-apicophilic arrangement will be introduced, as well as their structures, spectroscopic properties, and reactivities.