Spectroscopic and dynamic NMR study, X-ray crystallography and DFT calculations of two phosphoramidates: (C4H3O2)P(O)(Cl)C6H14N and (C4H3O2)P(O)(C6H11NH)2

In recent years, research in organophosphorus compounds, particularly phosphoramidates, has attracted attention because of their many applications. In this work, we report a combined experimental and theoretical study on the molecular structure and NMR spectra of two phosphoramidates (furan-2-yl N,N-diisopropylamidochlorophosphate (1) and furan-2-yl N,N,N′,N′-dicyclohexylamidophosphate (2)). In the NMR time scale a free rotation of the CN/PN single bonds was observed at room temperature (298 K) while the rotation freezes below 195 K for compound 1. From dynamic NMR analysis, the activation free energy (ΔG#) for rotation of the CN/PN bonds was calculated as 9.9 ± 0.3 kcal mol−1. The experimental data were reinforced by theoretical calculation using the density functional theory method B3LYP and the 6-31G(d) basis set which provided activation energy (ΔE‡) of 9.2 kcal mol−1. The structures of compounds 1 and 2 were determined by single crystal X-ray diffraction method. Compound 1 is formed by a racemic mixture, whose presence was evidenced only in the structure determination by X-ray.