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Abstract Substitutional lability of the terminal methoxide ligand on a Zr(IV) substituted polyoxovanadate‐alkoxide (POV‐alkoxide) via protonolysis is presented. Addition of excess water or stoichiometric 2,2,2‐trifluoroethanol results in the exchange of the terminal methoxide ligand for a hydroxide or 2,2,2‐trifluoroethoxide ligand, respectively. The lability of the terminal methoxide ligand at zirconium is leveraged to access a relatively stable terminal peroxide bound to a POV‐alkoxide supported Zr(IV) center, via addition of hydrogen peroxide adducts compatible with organic solvent. Isolation of the terminal peroxide complex allows for investigation into the impact of the sterically protected, electron‐rich POV‐alkoxide support on the activation of hydrogen peroxide at Zr(IV). While the isolated peroxide complex is inactive towards the oxidation of thioethers, the methoxy terminated Zr(IV) functions as a precatalyst for the reaction. Mechanistic analysis reveals electrophilic oxidation conditions with hydrogen peroxide substrates, with a nucleophilic parameter ( ) of 0.09±0.02. In thioether oxidation reactions, selectivity for sulfoxide products (95–99 %) in acetonitrile is observed, suggesting the use of a reduced POV‐alkoxide prevents over‐oxidation of substrate. 

Abstract Without solvents present, the often far‐from‐equilibrium environment in a mechanochemically driven synthesis can generate high‐energy, non‐stoichiometric products not observed from the same ratio of reagents used in solution. Ball milling 2 equiv. K[A’] (A’=[1,3‐(SiMe₃)₂C₃H₃]⁻) with CaI₂yields a non‐stoichiometric calciate, K[CaA’₃], which initially forms a structure (1) likely containing a mixture of pi‐ and sigma‐bound allyl ligands. Dissolved in arenes, the compound rearranges over the course of several days to a structure (2) with only η³‐bound allyl ligands, and that can be crystallized as a coordination polymer. If dissolved in alkanes, however, the rearrangement of1to2occurs within minutes. The structures of1and2have been modeled with DFT calculations, and2initiates the anionic polymerization of methyl methacrylate and isoprene; for the latter, under the mildest conditions yet reported for a heavy Group 2 species (one‐atm pressure and room temperature).