Calcium Pyrenide: A Room-Temperature Reagent for Stoichiometric Calciations and Reductive Ca²⁺ Intercalation Reactions

Chemical reductive insertion of metal ions using metal arenes has attracted significant attention due to its capability to readily modulate the electronic and structural properties of host materials. Despite extensive studies involving various metal arenes, systems capable of enabling reductive insertion with Ca²⁺ species have not been determined. Here, we report the synthesis of calcium pyrenide and demonstrate its effectiveness in facilitating reductive insertion into host frameworks. The nominal composition in solution was determined to be spectroscopically consistent with previously reported alkali metal pyrenides solutions and in DMF found to participate in the stoichiometric titrations of silver salts. Single crystals were grown from THF solutions and structurally characterized by X-ray diffraction. Signatures of the pyrenides radical anion were observed by EPR. The reduction potential was estimated by cyclic voltammetry of pyrene in a calcium perchlorate electrolyte solution where a reversible one electron reduction wave as observed at –2.52 V vs Fc/Fc+. To demonstrate the utility of this Ca(pyrene)₂ for screening materials capable of reversible calciation via reductive intercalation, the compounds, Cax(DMF)yMoS2 (0 < x < 0.34) were prepared from DMF solutions of calcium pyrenides and characterized by PXRD, SEM, ICP-OES, and TGA.