Unexpected lanthanide cation selectivity of bis-beta-ketovinylated diaza-18-crown-6 and open-chain diamines: cooperative effect of the second keto groupстатья
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Дата последнего поиска статьи во внешних источниках: 5 декабря 2014 г.
Аннотация:New diaza-18-crown-6 based ligands were prepared by the β-ketovinylation of diaza-18-crown-6 by TMS-protected ynones. The obtained N,N′-bis-(3-oxo-3-arylpropen-1-yl)-7,16-diaza-18-crown-6 ligands (aryl = p-MeOC6H4, p-Me2NC6H4) selectively bind the Ln3+ in preference to main group cations, showing high Ln3+/Zn2+ and Ln3+/Pb2+ selectivities (from 2 to 5.5 in log βML values determined by UV-spectrophotometric titration in CH3OH). The Me2N-derivative is also a holmium-selective fluoro-ionofore, as its intense emission is almost completely quenched by Ho3+ salts at concentrations as low as 10−5 mol l−1. The monoazacrown analogs with only one enaminone group complex less strongly with Ln3+ and are less selective, but bis-β-ketovinylated open-chain diamines (N,N′-dibenzyl-3,6-dioxaoctane-1,8-diamine and N,N′-dibenzyldecane-1,10-diamine) show almost the same binding constants with La3+ (log βML = 3.5–3.7) and Pb2+ (log βML = 1.6) as the corresponding diaza-18-crown-6 derivative. This and the changes observed in the 1H NMR spectra of the azacrown enaminone ligands in the presence of La3+ indicate the exocyclic coordination of Ln3+ with the carbonyl oxygens of the side arms. Rotation around the =C–N bond is restricted in enaminone ligands and especially in their complexes with Ln3+, which allows to explain the observation of two sub-sets of signals in the 1H NMR spectra of bis-β-ketovinylated diaza-18-crown-6 in the presence of La(NO3)3 by the existence of two rotamers of the ligands.