Organocalcium Complex-Catalyzed Selective Redistribution of ArSiH₃ or Ar(alkyl)SiH₂ to Ar₃SiH or Ar₂(alkyl)SiH

Abstract

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 Si–H 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 β-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 Ar2(alkyl)­SiH and alkylSiH3, 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 Ph2(Me)­SiH and reveal the low activation barriers (17–19 kcal/mol) in the catalytic reaction.

Cobalt‐Catalyzed Dehydrogenative C−H Silylation of Alkynylsilanes

“…Unfortunately, besides the desired product, we have also detected the redistribution of dihydrosilane in moderate quantity. Considering that at a lower temperature (RT–60 °C) the redistribution was not detected, we assumed that probably primary silanes (formed at elevated temperature) [17] are still true activators of the cobalt precatalysts.…”

Calcium Mediated C−H Silylation of Aromatic Heterocycles with Hydrosilanes

“…With these well‐established stoichiometric reactions in mind, we then firstly attempted the catalytic C−H silylation of 2‐methylthiophene with n ‐hexylsilane under the mild conditions (80 °C, 5 mol% cat). Due to the easy redistribution mediated by molecular group 2 metal hydrides, the other commercially available primary hydrosilane, phenylsilane, was excluded in this study [3r,6a,18] …”

Catalytic C(sp)–Si cross-coupling silylation of alkynyl bromides with hydrosilanes by palladium catalysis

“…3,4 In this context, hydrosilanes provide the most useful and essential reagents in the synthesis of structurally diverse organosilicon compounds through cross-coupling type silicon–hydrogen (Si–H) bond functionalization, 5 owing to their unique chemical and physical properties. 6 However, the transition metal-catalyzed C(sp)–Si bond-forming reaction with hydrosilanes to obtain alkynylsilane derivatives is less explored in homogeneous catalysis but it occurs smoothly in the presence of strong bases 7 or heterogeneous gold catalysts. 8 In addition, these reports are limited to strong bases or complicated organometallic complexes, and the chemistry typically requires elevated temperatures, which results in low chemoselectivity.…”