Synthesis and spectroscopic characterization of two pairs of phosphoric triamide enantiomers

Many chiral phosphorus compounds have been synthesized and used in different scientific domains such as medicine [1] and enantioselective catalysts [2], however few number of chiral phosphoric triamides were investigated [3]. In this study, two pairs of enantiomer phosphoric triamides, CCl3C(O)NHP(O)[(R)-(+)-NHCH(CH3)(C6H4-4-CH3)]2/CCl3C(O)NHP(O)[(S)-(–)-NHCH(CH3)(C6H4-4-CH3)]2, denoted (I)/(II), and CCl3C(O)NHP(O)[(R)-(+)-NHCH(C2H5)(C6H5)]2/CCl3C(O)NHP(O)[(S)-(–)NHCH(C2H5)(C6H5)]2, denoted (III)/(IV), have been synthesized and characterized by melting point, IR, NMR, mass. In the IR spectra of (I)/(II) and (III)/(IV), the bands centered at 3300 cm–1 for the first pair and at 3311/3307 cm–1 for the second pair are attributed to the NHamine stretching frequencies. The mass spectra, in 70 eV experiments, of (I)/(II) and (III)/(IV) reveal the presence of the molecular ion peaks at m/z = 477 (considering one 37Cl and two 35Cl). For (I)/(II) and (III)/(IV), the 31P signals appear at 4.30/4.24 ppm and 4.67/4.75 ppm, respectively. The signals of NCPH, in 1H NMR spectra, are observed at 9.29, 9.34, 9.55 and 9.42 ppm for (I) to (IV), respectively, all of them to be broad. The two chiral amine fragments in all of the compounds (I), (II), (III) and (IV) reveal two sets of signals in corresponding 1H and 13C NMR spectra. Typically,the two NH protons in each compound appear as two triplets. The triplet pattern is a result of vicinal H-H and geminal P-H couplings. In the 13C NMR spectra of (I)/(II) and (III)/(IV), the carbon atom of the C(O) group appears as a singlet.