Issue 4, 2004

Lanthanide(iii)/actinide(iii) differentiation in coordination of azine molecules to tris(cyclopentadienyl) complexes of cerium and uranium

Abstract

Reaction of azine molecules L with the trivalent metallocenes [M(C5H4R)3] (M = Ce, U; R = But, SiMe3) in toluene gave the Lewis base adducts [M(C5H4R)3(L)] (L = pyridine, 3-picoline, 3,5-lutidine, 3-chloropyridine, pyridazine, pyrimidine, pyrazine, 3,5-dimethylpyrazine and s-triazine), except in the cases of M = U and L = 3-chloropyridine, pyridazine, pyrazine and s-triazine where oxidation of U(III) was found to occur. In the pairs of analogous compounds of Ce(III) and U(III), i.e. [M(C5H4But)3(L)] (L = pyridine, picoline) and [M(C5H4SiMe3)3(L)] (L = pyridine, lutidine, pyrimidine and dimethylpyrazine), the M–N and average M–C distances are longer for M = Ce than for M = U; however, within a series of azine adducts of the same metallocene, no significant variation is noted in the M–N and average M–C distances. The equilibria between [M(C5H4R)3], L and [M(C5H4R)3(L)] were studied by 1H NMR spectroscopy. The stability constants of the uranium complexes, KUL, are greater than those of the cerium counterparts, KCeL. The values of KML are much greater for R = SiMe3 than for R = But and a linear correlation is found between the logarithms of KML and the hydrogen-bond basicity pKHB scale of the azines. Thermodynamic parameters indicate that the enthalpy–entropy compensation effect holds for these complexation reactions. Competition reactions of [Ce(C5H4R)3] and [U(C5H4R)3] with L show that the selectivity of L in favour of U(III) increases with the π donor character of the metallocene and is proportional to the π accepting ability of the azine molecule, measured by its reduction potential.

Graphical abstract: Lanthanide(iii)/actinide(iii) differentiation in coordination of azine molecules to tris(cyclopentadienyl) complexes of cerium and uranium

Supplementary files

Article information

Article type
Paper
Submitted
11 Nov 2003
Accepted
23 Dec 2003
First published
16 Jan 2004

Dalton Trans., 2004, 579-590

Lanthanide(III)/actinide(III) differentiation in coordination of azine molecules to tris(cyclopentadienyl) complexes of cerium and uranium

T. Mehdoui, J. Berthet, P. Thuéry and M. Ephritikhine, Dalton Trans., 2004, 579 DOI: 10.1039/B313992A

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