RADICAL IONS AND GERMYLOXYAMINOXYLS FROM NITROSPIRO[INDOLINE-NAPHTHOPYRANS] - A COMBINED ELECTROCHEMICAL AND EPR STUDY

The radical ions from 5-nitrospiro[indoline-2,3'-naphthopyran] 1, 8'-nitrospiro[indoline-2,3'-naphthopyran] 2, and 5,8'-dinitrospiro[indoline-2,3'-naphthopyran] 3 have been investigated electrochemically and by means of electron paramagnetic resonance spectroscopy. The first reduction potentials of these compounds reflect the position of the nitro groups and vary between -1.53(3) V for 1 and -1.27(2) V for 2 vs. SCE, while 3 exhibits two reduction waves at potentials similar to those of 1 and 2, suggesting no or very little interaction between the two moieties of the molecules. The oxidation potentials are dominated by the indolinic moiety increasing in the order 2 < 1 < 3. The reduction with butoxide in DMF leads to the EPR observation of the expected radical anions of 1 and 2, while the spectrum observed with 3 shows, against expectations, reduction of the indolinic moiety. Photoreduction with Bu4NBH4 in THF affords the radical anions of 2 and 3 but not of 1, the measured hfs constants being similar to those measured in DMF without light. Addition of in situ generated triphenylgermyl radicals to 1-3 affords rather persistent germyloxyaminoxyls which give identical spectra both under UV irradiation and in the dark.