EFFECT OF ALIPHATIC AMINE BASES ON THE AGGREGATION OF ALKALI-METAL SALTS OF 3,5-DI-TERT-BUTYLSEMIQUINONE (3,5-DBSQ)

The alkali metal salts (Li+, Na+, K+) of 3,5-di-tert-butylsemiquinone anion (3,5-DBSQ) have been prepared in the presence of three amine bas es, triethylamine (TEA), tetramethylethylenedismine (TMEDA), and penta methyldiethyltriamine (PMDTA), as well as in the absence of amine in t wo solvents, toluene and THF. EPR spectral evidence shows that for M(3 ,5-DBSQ), aggregation of the lithium and sodium salts is effectively p rohibited by Lewis basic amines PMDTA and TMEDA, with the former being mole effective than the latter. The EPR spectra of the least Lewis ac idic metal ion, K+, are unaffected by addition of amines. In the absen ce of amines, the coordinating solvent, THF, is effective at preventin g aggregation, while substantial aggregation occurs in the noncoordina ting solvent, toluene. The effectiveness of PMDTA is so great that M(3 ,5-DBSQ) (M = Li+ and Na+) aggregation is prevented even in toluene. T he combination of solution and frozen solution spectra is best for det ermining the presence of aggregates due to aggregation-induced line br oadening in solution spectra and fine structure in spectra of S > 1/2 species. The results of the frozen solution spectral studies indicates that, for the amines studied, PMDTA is singular in its ability to pre vent aggregation and Li+ and Na+ salts are best chelated by PMDTA. Fin ally, we show the success of this method by preparing a solution of Na 2I that is stable for several hours and is amenable to EPR spectral ch aracterization.