EPR properties of two new cyclic phosphinylhydrazyl radicals and of their inclusion complexes with cyclodextrins

Two phosphorus-containing hydrazines, namely morpholin-4-ylphosphoramidic a cid diethyl ester (1a) and (2,2,6,6-tetramethylpiperidin-1-yl)phosphoramidi c acid diethyl ester (2a), have been synthesized. The corresponding hydrazy l radicals (1b and 2b) have been obtained, by in situ oxidation, and their properties have been investigated by EPR spectroscopy. The Ib radical shows spectra strongly dependent on temperature due to the inversion of the morp holin ring and to rotation about the N-N bond. Since, in the investigated t emperature range, both motions take place in the EPR time scale, a kinetic study of these process could be made by analyzing the spectral lineshape va riations. The 2b radical is highly persistent and shows a strong temperatur e and solvent dependence of the phosphorus splitting. The latter property w as usefully exploited to study the guest-host interaction of this radical w ith cyclodextrins. A method is also proposed for the determination of affin ity constants for cyclodextrins of nonparamagnetic compounds.