Phosphorus−Nitrogen Compounds. 14. Synthesis, Stereogenism, and Structural Investigations of Novel N/O Spirocyclic Phosphazene Derivatives

The reactions of hexachlorocyclotriphosphazatriene, N₃P₃Cl₆, with N/O donor-type N-alkyl-o-hydroxybenzyl- and o-hydroxynaphthylamines result in novel mono- (3a, 4a and 4b), di- (5a and 5b), and tri- (3b, 6a, and 6b) spirocyclic phosphazene derivatives. The tetrakis-pyrrolidinophosphazene, 3b, has been obtained from the reaction of partly substituted compound 3a with the excess pyrrolidine in tetrahydrofuran. The relationship between the endocyclic NPN (α) and exocyclic NPO (α‘) bond angles of the analogous spirocyclic phosphazenes with the δP shifts of NPO phosphorus atoms have been presented. It was observed that there is a linearity between α angles and δP shifts, while no linear relationship has been observed for α‘ angles. In addition, we have found the correlation between Δ(P−N) and δ_NPO shifts, which implies a linear relationship. Δ(P−N) = (a − b), where a and b are the average lengths of two adjacent P−N bonds. The structural investigations of all of the compounds have been made by elemental analyses; mass spectrometry; Fourier transform infrared spectroscopy; one-dimensional ¹H, ¹³C, and ³¹P NMR; distortionless enhancement by polarization transfer; and two-dimensional correlation spectroscopy, heteronuclear shift correlation, and heteronuclear multiple-bond correlation homo- and heteronuclear correlation techniques. The solid-state structures of 3a, 4a, 4b, and 5a have been determined by X-ray crystallographic techniques. The asymmetric units of compounds 3a and 4a contain two independent molecules, and 3a has strong intermolecular N−H···N hydrogen bonds linking three phosphazene rings. The molecular structure of 6a looks like a propeller where the chemical environment of P1 is different from that of P2 and P3. On the other hand, compounds 5a and 5b are expected to exist as cis- or trans-geometric isomers and to be in cis (meso) or trans (racemic) configurations. The crystallographic and preliminary chiral solvating agents results show that both of them are trans (racemic). In addition, 6a and 6b are also expected to exist as cis−trans−trans- and cis−cis−cis-geometric isomers; both of them are found to be in cis−trans−trans geometries. According to the two-dimensional spectroscopic data, the possible conformations of 3a and 4a in CDCl₃ are the same with the solid-state structures.