Organocalcium Complex-Catalyzed Selective Redistribution of ArSiH3 or Ar(alkyl)SiH2 to Ar3SiH or Ar-2(alkyl)SiH

Calcium is an abundant, biocompatible, and environmentally friendly element. The use of organocalcium complexes as catalysts in organic synthesis has had some breakthroughs recently, but the reported reaction types remain limited. On the other hand, hydrosilanes are highly important reagents in organic and polymer syntheses, and redistribution of hydrosilanes through C-Si and SiH bond cleavage and reformation provides a straightforward strategy to diversify the scope of such compounds. Herein, we report the synthesis and structural characterization of two calcium alkyl complexes supported by beta-diketiminato-based tetradentate ligands. These two calcium alkyl complexes react with PhSiH3 to generate calcium hydrido complexes, and the stability of the hydrido complexes depends on the supporting ligands. One calcium alkyl complex efficiently catalyzes the selective redistribution of ArSiH3 or Ar(alkyl)SiH2 to Ar3SiH and SiH4 or Ar-2(alkyl)SiH and alkylSiH(3), respectively. More significantly, this calcium alkyl complex also catalyzes the cross-coupling between the electron-withdrawing substituted Ar(R)SiH2 and the electron-donating substituted Ar'(R)SiH2, producing ArAr'(alkyl)SiH in good yields. The synthesized ArAr'(alkyl)SiH can be readily transferred to other organosilicon compounds such as ArAr'(alkyl)SiX (where X = OH, OEt, NEt2, and CH2SiMe3). DFT investigations are carried out to shed light on the mechanistic aspects of the redistribution of Ph(Me)SiH2 to Ph-2(Me)SiH and reveal the low activation barriers (17-19 kcal/mol) in the catalytic reaction.