New Phosphoramidates: Spectroscopic Study and Ab Initio Computations

Abstract

New phosphoramidates with formula P(O)(X)[NH-N = C(C6H5)2]2, X = Cl (1), C6H5C(O)NH (2), CCl3C(O)NH (3), C6H5C(O)NHP(O)[NHCH(CH3)2]2 (4), and P(O)(Cl)[2-NH-C6H4-C(O)OC2H5]2 (5) were synthesized and characterized by 1H, 13C, 31P NMR, IR spectroscopy, and elemental analysis. The 1H and 13C NMR spectra of 4 display two sets of signals for the two unequivalent CH3 groups of the isopropyl substituents due to the presence of prochiral CH units. Interestingly, the 13C NMR spectrum of 5 indicates long-range 4 J(P,Cmeta) = 0.9 Hz. Such a coupling was not observed in previous studies for similar phosphoramidates. The geometries of phosphoramidates 1–5 were optimized by Gaussian 98 software at HF and B3LYP levels of theory with standard 6-31G* and 6-31+G** basis sets. The stabilization energies were calculated from the equation ΔE = E(molecule) – Σi E(i), i = atom. For all compounds, the B3LYP/6-31G* basis set provided the highest negative stabilization energies. The nuclear quadrupole coupling constants (χ) for 14N, 2H, and 35Cl nuclei were computed to be 4–6 MHz, 180–190 KHz, and 50, 80 MHz, respectively. The χ values for the 17O atoms of phosphoryl moieties (5.0 MHz) are almost half than those of C˭O bonds (10.0 MHz). Moreover, the χ values of amidic N atoms are smaller than those of amino N atoms. GRAPHICAL ABSTRACT