Spectroscopic characterization and Ab initio calculations of new diazaphosphole and diazaphosphorinane

Abstract

Phosphoryl chloride is used as a starting material to synthesize new diazaphosphole, Open image in new window (1) and diazaphosphorinane, Open image in new window (2). The products are characterized by 1H, 13C, 31P NMR, and IR spectroscopy. A high value 2J(PNH) = 17.0 Hz, 17.2 Hz is measured for two non-equivalent NH protons of endocyclic nitrogen atoms in compound 1, while it greatly decreases to 4.5 Hz in 2. Also, great amounts are obtained for two 2J(P,C) as well as two 3J(P,C) in the 13C NMR spectrum of 1, but they are zero in 2. Here, the effect of ring strain and ring size on the structural and spectroscopic parameters is observed. The 31P NMR spectra reveal that δ(31P) of compound 1 is far much more downfield (12.63 ppm) relative to that of compound 2 (−10.39 ppm). Furthermore, ab initio quantum chemical calculations are performed to optimize the structures of these molecules by density functional theory (B3LYP) and Hartree-Fock (HF) methods, using the standard 6−31+G** basis set. The stabilization energies are calculated by the equation ΔEstabilization = Emolecule − ΣEi, where i = atom. To obtain the atomic hybridizations, NBO computations are made at the B3LYP/6−31+G** level. Also, by NMR calculations the 1H, 13C, 31P chemical shifts are obtained and compared with the experimental ones.