Probing the Redox Chemistry of Bimetallic Rare Earth-Catecholate Complexes

A catecholate proligand, 2,3–dihydroxy–4,6–di–tert–butyl–benzaldehyde ([trenHC=N(H2tBu2cat)3]), capable of binding two metal cations, and its complexes RE2[trenHC=N(tBu2cat)3], RE = La, Nd, Dy were synthesized. X-ray structures of the complex-es showed that C–O bond lengths, ranging from 1.317(4)–1.334(3) Å, and C–C bond lengths, ranging from 1.426(3)–1.443(3) Å, of the complexes were consistent with the cate-cholate form of the ligand in all cases. Cyclic voltammetry (CV) measurements revealed the oxidation of the catecholate ligand arms to the semiquinonate form in all three metal complexes. The oxidation potentials for the metal complexes are modulated to shift towards more positive potentials with increasing Lewis acidity. The results support the hy-pothesis that differences in ligand oxidation potentials can be exploited for realizing systems for separations of rare earth metals.