The first naphthodiazaphosphorinane in the solid phase; syntheses, spectroscopic studies and X-ray crystallography of some new 1,3,2-diheterophosphorus compounds

Abstract

New heterocyclic compounds of diazaphosphorinanes, diazaphospholes, and oxazaphospholes were synthesized and characterized by 1H, 13C, 31P, NMR, IR spectroscopy, and CHN elemental analysis. The 3D structure of compound Open image in new window (5) was determined by X-ray crystallography. Since benzo- or naphthodiazaphospholes/diazaphosphorinanes containing aromatic rings are usually unstable in the solution state, their single crystal structures are rarely reported and, to the best of our knowledge, this structure is the first occasion of naphthodiazaphosphorinanes obtained here. It is noticeable that the P=O and C=O bonds are closer to syn than anti configuration and the P=O bond is placed in a pseudo-equatorial position. This structure produced a 3D polymeric chain via strong hydrogen bonds and electrostatic short contacts. Due to the ring strain of five-membered rings, for all diazaphospholes great 2J(PNHendocyclic) coupling constants (about 18.0 Hz), as well as high 2,3J(P,C) coupling constants for the aromatic carbon atoms connected to the five-membered ring (about 14.5, 13.5 Hz, respectively) were measured. Replacement of one NH group in a diazaphosphole ring by an oxygen atom caused exceedingly decreased ring strain and hence highly diminished 2J(PNHendocyclic) coupling constant. Furthermore, 31P NMR spectra of oxazaphospholes, like the spectra of diazaphosphorinanes, indicated highly shielded phosphorus atoms relative to those of their diazaphospholes analogs.