Studies on Deprotonation from OH Groups of Alditols by Heavy Rare Earth Ions

This study investigates single-crystal structures of Lu3+/erythritol and nine rare earth–glycerol complexes, revealing deprotonation of normally inert OH groups via μ2-bridging (so-called DIOμ2 phenomenon). The pH drops upon alditol addition correlate with the deprotonation extent, showing increased deprotonation with decreasing lanthanide ionic radius (lanthanide contraction) and exceptionally high deprotonation for Sc3+. In all the rare earth/alditol complexes with the DIOμ2 phenomenon, two μ2-bridges merge into an M2O2 cluster (M is a rare earth ion) that is not very stable due to the Coulombic repulsion between two M3+ and between two O–. To stabilize the M2O2 cluster, the formation of more auxiliary five- and six-membered chelating rings between rare earth ions and alditol ligands is needed. Increment of the number of auxiliary five- and six-membered chelating rings favors the DIOμ2 reaction. This is the reason why the DIOμ2 reaction shows a progressively enhanced tendency when the alditol ligands change from myo-inositol to glycerol to erythritol and galactitol. The reaction is endothermic, as an increased temperature enhances deprotonation. The above results may be useful in the rational design of catalysts that efficiently activate inert OH bonds and facilitate related chemical processes.

Ҳали таржима қилинмаган