Abstract: BF3 binds with the phosphoryl oxygen of the title phosphatrane 6 to form a neutral 10-P-5 adduct, Et3Si+ binds once or twice to the phosphoryl oxygen of 6 to yield a monovalent or a divalent 10-P-5 cation, respectively, which can be isolated, and H3P04 forms an isolable 1: l adduct with 6 in which the phosphoryl oxygen of 6 is protonated. Evidence is presented for the trigonal-bipyramidal stereochemistry of phosphorus in these ...