Chiral one-dimensional hydrogen-bonded architectures constructed from single-enantiomer phosphoric triamides

Abstract

The two single-enantiomer phosphoric triamides N-(2,6-difluorobenzoyl)-N′,N′′-bis[(S)-(−)-α-methylbenzyl]phosphoric triamide, [2,6-F2-C6H3C(O)NH][(S)-(−)-(C6H5)CH(CH3)NH]2P(O), denoted L-1, and N-(2,6-difluorobenzoyl)-N′,N′′-bis[(R)-(+)-α-methylbenzyl]phosphoric triamide, [2,6-F2-C6H3C(O)NH][(R)-(+)-(C6H5)CH(CH3)NH]2P(O), denoted D-1, both C23H24F2N3O2P, have been investigated. In their structures, chiral one-dimensional hydrogen-bonded architectures are formed along [100], mediated by relatively strong N—H...O(P) and N—H...O(C) hydrogen bonds. Both assemblies include the noncentrosymmetric graph-set motifs R 2 2(10), R 2 1(6) and C 2 2(8), and the compounds crystallize in the chiral space group P1. Due to the data collection of L-1 at 120 K and of D-1 at 95 K, the unit-cell dimensions and volume show a slight difference; the contraction in the volume of D-1 with respect to that in L-1 is about 0.3%. The asymmetric units of both structures consist of two independent phosphoric triamide molecules, with the main difference being seen in one of the torsion angles in the OPNHCH(CH3)(C6H5) part. The Hirshfeld surface maps of these levo and dextro isomers are very similar; however, they are near mirror images of each other. For both structures, the full fingerprint plot of each symmetry-independent molecule shows an almost asymmetric shape as a result of its different environment in the crystal packing. It is notable that NMR spectroscopy could distinguish between compounds L-1 and D-1 that have different relative stereocentres; however, the differences in chemical shifts between them were found to be about 0.02 to 0.001 ppm under calibrated temperature conditions. In each molecule, the two chiral parts are also different in NMR media, in which chemical shifts and P–H and P–C couplings have been studied.