Structural differences/similarities of diastereotopic groups in three new chiral phosphoramides

The crystal structures of two single-enantiomer amidophosphoesters with an (O)₂P(O)(N) skeleton and one single-enantiomer phosphoric triamide with an (N)₂P(O)(N) skeleton were studied. The compounds are diphenyl [(R)-(+)-α-4-dimethylbenzylamido]phosphate, (I), and diphenyl [(S)-(-)-α-4-dimethylbenzylamido]phosphate, (II), both C₂₁H₂₂NO₃P, and N-(2,6-difluorobenzoyl)-N',N''-bis[(R)-(+)-α-ethylbenzyl]phosphoric triamide, C₂₅H₂₈F₂N₃O₂P, (III). The asymmetric units contain two amidophosphoester molecules for (I) and (II), and one phosphoric triamide molecule for (III). In the crystal structures of (I) and (II), molecules are assembled in a similar one-dimensional chiral ribbon architecture, but with almost a mirror-image relationship with respect to each other through N-H...O(P) and C-H...O(P) hydrogen bonds along [010]. In the crystal structure of (III), the chiral tape architecture along [100] is mediated by N-H...O(P) and N-H...O(C) hydrogen bonds, and the tapes are connected into slabs by C-H...O interactions (along the ab plane). The differences/similarities of the two diastereotopic phenoxy groups in (I)/(II) and the two chiral amine fragments in (III) were studied on the grounds of geometry, conformation and contribution to the crystal packing, as well as ¹H and ¹³C signals in a solution NMR study.