Cobalt-Catalyzed Hydrosilylation of 1,3-Enynes for the Synthesis of Conjugated Alkenylalkoxysilanes

Abstract

The hydrosilylation of unfunctionalized 1,3-enynes with tertiary alkoxysilanes poses significant challenges in regulating regioselectivity and stereoselectivity. In this study, we achieved highly efficient hydrosilylation of unfunctionalized 1,3-enynes with tertiary alkoxysilanes using a cobalt catalyst supported by a cyclopropane-fused bisphosphine ligand. Specifically, arylphosphine ligands enabled highly selective cis-α-hydrosilylation of aryl-substituted 1,3-enynes (yields up to 95%, regioselectivity > 95 : 5); in contrast, cyclohexylphosphine ligands promoted cis-β-hydrosilylation of alkyl-substituted 1,3-enynes (yields up to 99%, regioselectivity > 95:5). This protocol exhibits excellent functional group tolerance and can be readily scaled up to the gram scale, thus enabling the efficient synthesis of a series of structurally novel conjugated alkenylalkoxysilanes. The resulting products can be efficiently converted into organosilicon material precursors, laying a new material foundation for the development of advanced functional organosilicon materials. Mechanistic investigations reveal that the reaction is initiated by substrate activation via a Co(0) active species, proceeds through a two-electron redox cycle, and accomplishes hydrosilylation via ligand-to-ligand hydrogen transfer (LLHT). Specifically, arylphosphine ligands modulate regioselectivity through π-π stacking interactions with the aryl moiety of enyne substrates, whereas cyclohexylphosphine ligands dictate regioselectivity via abundant van der Waals interactions with alkyl-substituted 1,3-enynes, coupled with the higher polarizability of cobalt-hydrogen bonds.

Keywords

Cobalt catalysts / Hydrosilylation reactions / 1,3-Enynes / Conjugated alkenylsiloxanes / Tertiary alkoxysilanes

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