Further exploration of the physicochemical nature of μ2-bridge-relevant deprotonations via the elucidation of four kinds of alditol complexes

Abstract

Single-crystal structures of four alditol complexes are presented. In LuCl₃/galactitol and ScCl₃/myo-inositol complexes, μ₂-bridge-relevant deprotonations were observed. The polarization from two rare earth ions in the μ₂-bridge activates the chemically inert OH and promotes deprotonation. Additionally, mass spectrometry, pH experiments, and quantum chemistry calculations were conducted to enhance our understanding of the μ₂-bridge-relevant deprotonations. A common structural feature of the complexes where μ₂-bridge-relevant deprotonation takes place is that two metal ions and two oxygen atoms in two μ₂-bridges form an M₂O₂ cluster. The four atoms in the M₂O₂ cluster make up a parallelogram. Such a structure is useful to balance the strong coulombic repulsions between two M³⁺ and between two O⁻. In the ScCl₃/myo-inositol complex, the deprotonation exhibits a characteristic of regional/chiral selectivity. Galactitol is a third alditol ligand where μ₂-bridge-relevant deprotonation is observed. The flexible backbone of the galactitol allows the formation of more five-membered chelating rings and six-membered chelating rings, which are used to stabilize the rare earth ions of the μ₂-bridge. The coordination makes the backbone of galactitol deviate from the zigzag conformation. The above results are helpful in the rational design of high-performance catalysts.