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.