LANTHANIDE(III)-CATALYZED SYNTHESIS OF 2-(CARBOXYMETHYL)-2,4-(R),5-(R)-TRICARBOXY-1,3-DIOXOLANE AND ITS COORDINATION TO LANTHANIDE(III) AND CALCIUM(II)

The Michael-type addition of l-tartrate and acetylenedicarboxylate is performed using a lanthanide (Ln(III)) alkoxide catalyst. The thermodynamics of the complexation of the adduct 2-(carboxymethyl)-2,4-(R),5-(R)-tricarboxy-1,3-dioxolane (L) with Ln(III) and Ca(II) is investigated using potentiometry and calorimetry. The curves of Delta H-101 and Delta S-101 for the 1:1 complexation vs the atomic number of Ln(III) are parallel with a change of slope between Eu(III) and Dy(III). Ln(III)-induced O-17 NMR shifts show that both LnL and LnL(2) constitute series with constant hydration numbers. Ln(III)-induced H-1 shifts suggest that no abrupt geometrical change occurs in the middle of the Ln(III) series. Comparison of the entropy data with literature values for other neutral oxygen donor ligands indicates that the change in the Delta S-101 values at Eu-Dy is not due to a structural change of the coordination of L within LnL across the Ln(III) series, but may be attributed to a difference in the hydration of the aquo ions between the light and the heavy Ln(III). A complete assignment of the C-13 NMR resonances of L is offered from the CH-coupling data and the Nd(III)- and Gd(III)-induced C-13 longitudinal relaxation rate enhancements. The coordination of L in LnL is tetradentate via three carboxylate groups and one ether oxygen. The two carboxylate groups of highest pK(a)s are involved in coordination, as shown by C-13 NMR shifts. As one carboxylate group remains uncoordinated in LnL and LnL(2), the complex TmL(2) was tested as a Na-23 NMR shift reagent. However, its performance is moderate, due to a large Tm(III)-Na(I) distance, a low stability of LnL(2) with Na(I), and a small uptake of Na(I).