Eu(fod)₃ binding on the ¹H‐NMR spectra of bis(2′‐ethylbenzoate)ethylene glycol podands

Abstract

The complexing and selective binding constants of Eu(fod)(3) with bis(2'-ethylbenzoate)ethylene glycol podands having one to four oxyethylene groups was observed on their (1)H-NMR spectra at 250 MHz and 295 K in CDCl(3). The Eu(fod)(3) interaction displayed the selective binding role of oxygen on H(2)C-O-CH(2) backbones with referring the (1)H chemical shifts. The estimated equilibrium constants, K(a), of 1:1 ratio of interactions were in accordance with the Eu(fod)(3) ionic radii to bind the oxygen sites depending on the size and conformation of the esters. Esters having one or two ethyleneoxy groups gave mainly 2:2 complexes using ester sites. The minimum lanthanide-podand ester distance displayed the maximum stability so that ester with four oxyethylene groups was found to bind the Eu(fod)(3) moderately, whereas ester with three oxyethylene groups showed a large induced chemical shift due to the stability of Eu(3+) complexes with larger ethyleneoxy groups.

Podand‐Based Dimeric Chromium(III)–Salen Complex for Asymmetric Henry Reaction: Cooperative Catalysis Promoted by Complexation of Alkali Metal Ions

“…In the titration experiments with CDCl 3 (Figure 1), the addition of KBAr F caused remarkable upfield shifts and broadening of the signals of oxyethylene protons due to the strong shielding effect of the BAr F − anion,13 indicating obvious association between K + and the podand chain. Meanwhile, signals of the aromatic protons on the phenyl groups that are linked to the polyether chain moved downfield, in a manner similar to that reported previously 5d. Furthermore, Nonlinear data fitting14 delivered the association constant K a =79±12 for binding a guest K + .…”