Isolation of Ce(iv) centered polyoxoalkoxide sandwich-type complexes allows comparison of metal-oxygen bond covalency

The new Ceⁱⁱⁱ centered sandwich-type complex (TBA)₃[Ce{W₄O₁₃(OMe)₄MoNO}₂] is reported. The redox properties of this molecule, and its all-molybdenum analogue, (TBA)₃[Ce{Mo₅O₁₃(OMe)₄NO}₂], were investigated using cyclic voltammetry. The data reveals the presence of reversible Ce^iv/Ceⁱⁱⁱ redox couples at modest potentials. One electron oxidation of the complexes provides facile access to the corresponding Ce^iv derivatives, which were fully characterized. ¹⁷O NMR spectroscopy reveals that the chemical shifts of the oxygen nuclei directly bound to Ce^iv are much higher than the corresponding signals in isostructural, diamagnetic, Zr^iv, Hf^iv, or Th^iv centered complexes. Density functional theory (DFT) calculations indicate that the increase in chemical shift correlates with an increase in the covalency of the M^iv-O bonds, illustrating that ¹⁷O NMR spectroscopy is a powerful experimental tool for interrogating the nature of metal oxygen bonding in diamagnetic complexes.