New 1,3,2-diazaphosphorinanes;synthesis,spectroscopic characterization,X-ray crystallography and ab initio calculations

Abstract

Using phosphoryl chloride as a starting material, new 1,3,2-diazaphosphorinanes with formula 4-X-C₆H₄NHP(O)[NHCH₂C(Y)₂CH₂NH] (1–6) where [X = F (1), Cl (2), Br (3), I (4), OCH₃ (5); Y = CH₃] and [X = OCH₃, Y = H (6)] were synthesized and characterized by ¹H, ¹³C, ³¹P NMR, IR spectroscopy and elemental analysis. The structures of compounds 1, 2, 5 and 6 have been determined by X-ray crystallography. Compound 1 exists as two symmetrically independent molecules in the crystalline lattice. The endocyclic nitrogen atoms in compounds 1, 1′ and 6 are very close to planar, but in 2 and 5 are distorted from planarity. These structures form two-dimensional polymeric chains through –P=O···H–N– hydrogen bonds. ¹H NMR spectra of compounds 1–5 indicate high value ³J(PNCH) coupling constants about 25.0 Hz which is related to H_equatorial with P–N–C–H torsion angle near to 180° obtained from X-ray crystallography. Ab initio quantum chemical calculations were performed with Gaussian 98 program at HF level of theory to optimize the structures of compounds 1, 2, 5 and 6. The stabilization energy of a molecule highly increases when the level of the basis set increases. Also, the two conformers 1 and 1′ have exactly the same stabilization energies, bond lengths and angles in the gas-phase calculations and they only show differences in the sign of their related torsion angles.