Multinuclear Clusters of Manganese and Lithium with Silsesquioxane-Derived Ligands: Synthesis and Ligand Rearrangement by Dioxygen- and Base-Mediated Si-O Bond Cleavage

The synthesis of manganese cluster complexes templated by polyhedral oligomeric silsesquioxane-derived ligands is described. Mn(PhSiO)Pyr () and Mn(PhSiO)(Bpy)(Py) () are prepared by replacement of the amide ligands of Mn(NR) (R = SiMe) via ligand protolysis by the acidic proton of the respective silsesquioxane-derived silanols. Complex is shown to undergo ligand rearrangement by reaction with O, which results in oxidation of the cluster to a mixed Mn cluster, concomitant with cleavage of the Si-O bonds of the ligand, releasing a [PhSi-O] unit, opening a new ligating siloxide group, and resulting in the formation of Mn(PhSiO)Pyr (). The ligand framework of can also be perturbed by a base. The addition of LiOH/BuLi delivers a soluble equivalent of LiO to , resulting in cleavage of the Si-O bonds and linkage of the resulting exposed silicon atoms by the new oxide, giving a linked ligand variant that templates a LiMn cluster, MnLi(PhSiOOPhSiO)DMFPyr (). These systems are characterized by single-crystal X-ray diffraction, absorption spectroscopy, Fourier transform infrared, cyclic voltammetry, and CHN combustion analysis. Mechanistic implications for the Si-O bond cleavage events are discussed.