Nitroxide derivatives of acetylacetone as spin-labelled ligands

Abstract

Electron spin resonance spectra are reported from a number of radicals derived from 2,4-pentadione substituted at the 3 position with nitroxide-containing groups. If the substituent is t-butyl nitroxide no metal complexes are formed. This is attributed to steric factors which prevent the formation of the en01 form of the P-diketone. If the substituent is trifluoromethyl nitroxide two types of metal complex have been observed. The esr spectra of the first type are very similar to that of the uncomplexed radical. Such complexes are formed with Co(II1) and Al(II1). The esr spectra of the second type show considerably increased I4N and I9F hyperfine coupling constants and in some cases large couplings to the metal nucleus. Complexes for the second type have been observed with Pd(II), Pt(II), and Rh(II1). The possible structures of these radicals are discussed. 156(1981). On rapporte les spectres de rpe d'un certain nombre de radicaux provenant de la pentadione-2,4 portant en position 3 un substituant contenant le groupe nitroxyde. I1 ne se forme pas de complexes mCtalliques si le substituant est le tert-butylnitroxyde. On attribue ce fait a des facteurs steriques qui empgchent la formation de l'enol de la P-dicetone. Si le substituant est le trifluoromethylnitroxyde, on observe deux types de complexes metalliques. L e spectre de rpe du premier type est trks semblable celui du radical non complex^. De tels complexes se forment avec le Co(1II) et le AI(II1). Dans les spectres rpe du deuxieme type, on note une augmentation considerable des constantes de couplage hyperfin du I4N et du I9F et dans certains cas de grands couplages avec le metal. On a observe des complexes du deuxieme type avec le Pd(II), le Pt(I1) et le Rh(II1). On discute des structures possibles de ces radicaux.[Traduit par le journal]