Synthesis and characterization of a spirocyclic phosphaverdazyl radical - cyclophosphazene hybrid: Evidence for spin transfer from a verdazyl radical to a phosphazene ring

Abstract

The synthesis and characterization of a new 6-phosphaverdazyl radical incorporated into a spirocyclic framework containing a cyclotriphosphazene ring is described. Reaction of 1,1,3,3-bis[spiro-2',2''-dioxy-1',1''-biphenyl]-5,5-bis(1-methylhydrazido)-1,3,5,2,4,6-cyclotriphosphazene (7) with trimethylorthobenzoate yielded 6-[2,2,4,4-bis(2,2'-dioxy-1,1'-biphenyl)-2,4,6,1,3,5-cyclotriphosphazen-6-yl]-1,2,5,6-tetrahydro-1,5-dimethyl-3-phenyl-1,2,4,5,6-tetrazaphosphorine (8), which was characterized spectroscopically and by X-ray diffraction. Oxidation of 8 yielded 6-[2,2,4,4-bis(2,2'-dioxy-1,1'-biphenyl)-2,4,6,1,3,5-cyclotriphosphazen-6-yl]-1,5-dimethyl-3-phenyl-6-phosphaverdazyl (5), which was characterized by EPR and ENDOR spectroscopy. Analysis of both spectra indicate that spin density from the phosphaverdazyl ring induces spin polarization into the phosphazene ring, as evidenced by hyperfine coupling to all three phosphorus nuclei.Key words: heterocycle, phosphorus–nitrogen compounds, phosphazenes, stable radicals, verdazyls.