Si-H Activation via Dynamic Permutational Isomerism: A Ligand-Directed Route to Dehydrogenative Coupling.

Abstract

Dehydrogenative coupling (DHC) of hydridosilanes with silanols under metal-free conditions provides a sustainable route to Si─O bond formation. Yet, the mechanistic origin of hydrogen release in such systems has remained unclear. Here, we show that dynamic permutational isomerism of pentacoordinate silicon intermediates is a key prerequisite for Si─H activation and H2 release. Using sterically tailored diaminohydridosilanes, we demonstrate that only ligands enabling access to axial hydride configurations facilitate Si─O coupling with productive H2 elimination. In contrast, N-tert-butyl substitution locks the hydride in the equatorial position and diverts reactivity toward Si─N bond cleavage. Multinuclear variable-temperature NMR spectroscopy, combined with quantum chemical calculations, reveals an equilibrium between equatorial and axial hydride configurations, enabling Berry pseudorotation and hydrogen evolution. These findings provide a mechanistic rationale for H2 release in hydridosilicates and establish ligand-directed isomerism as a general design principle for selective, metal-free Si─H activation.