Unexpected lanthanide cation selectivity of bis-β-ketovinylated diaza-18-crown-6 and open-chain diamines: cooperative effect of the second keto group
作者:Petr K. Sazonov、Vasily Yu. Stolyarenko、Mikhail M. Shtern、Irina P. Beletskaya
DOI:10.1007/s10847-013-0345-7
日期:2014.6
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. Diaza-18-crown-6 and open-chain diamines with two β-ketovinyl side arms selectively bind rare earth group cations in preference to main group cations (Pb2+, Zn2+ and Ba2+) through the exocyclic coordination of Ln3+ with the carbonyl oxygens of the side arms. The presence of the second β-ketovinyl group is essential, as ligands with only one β-ketovinyl group do not show such selectivity.
通过 TMS 保护的炔酮对重氮-18-冠醚-6 进行β-酮乙炔化反应,制备了基于重氮-18-冠醚-6 的新配体。得到的 N,N′-双(3-氧代-3-芳基丙烯-1-基)-7,16-重氮-18-冠醚-6 配体(芳基 = p-MeOC6H4, p-Me2NC6H4)优先于主族阳离子选择性地结合 Ln3+,显示出较高的 Ln3+/Zn2+ 和 Ln3+/Pb2+ 选择性(从 2 到 5。5)。Me2N 衍生物也是一种钬选择性荧光离子,因为在浓度低至 10-5 mol l-1 时,其强烈的发射几乎完全被 Ho3+ 盐淬灭。只有一个烯酮基团的单氮冠类似物与 Ln3+ 的络合强度较低,选择性也较差,但双-β-酮乙烯基开链二胺(N,N′-二苄基-3,6-二氧杂辛烷-1,8-二胺和 N,N′-二苄基-1,10-癸烷-1,10-二胺)与 La3+ 的结合常数几乎相同(log ;βML = 3。5-3.7)和 Pb2+(log βML = 1.6)的结合常数与相应的重氮-18-冠醚-6 衍生物几乎相同。这一点以及在 La3+ 存在时氮冠烯酮配体的 1H NMR 光谱中观察到的变化表明,Ln3+ 与侧臂的羰基氧根发生了环外配位。环绕 =C-N 键的旋转在烯酰胺酮配体中,特别是在它们与 Ln3+ 的配合物中受到限制,这就可以解释在 La(NO3)3 存在下,双-β-酮乙烯基化二氮杂-18-冠醚-6 的 1H NMR 光谱中观察到的两组子信号,即配体存在两个旋转体。重氮-18-冠醚-6 和具有两个 β-酮乙烯基侧臂的开链二胺通过 Ln3+ 与侧臂羰基氧根的环外配位,选择性地结合稀土类阳离子,而不是主族阳离子(Pb2+、Zn2+ 和 Ba2+)。第二个 β-酮乙烯基的存在至关重要,因为只有一个 β-酮乙烯基的配体不会显示出这种选择性。