Ambiphilic behavior of hydrogen in trisubstituted silanes induced by substituent controlled polarity inversion.

Atomic partial charges are local, model-dependent descriptors that often fail to capture the global electrostatic environment governing chemical reactivity. This study demonstrates that the molecular electrostatic potential (ESP) at the Si-H hydrogen in trisubstituted silanes reliably predicts electrophilic versus nucleophilic behavior, whereas local charges alone can mislead. Electron-donating substituents generate hydridic hydrogens with negative ESP near hydrogen, favoring nucleophilicity. Electron-withdrawing substituents typically leave hydrogen with a negative local charge but generate a positive ESP region along the Si-H axis, promoting electrophilic character. Increasing solvent polarity amplifies these contrasts, driving minima more negative for electron-donating substituents and maxima more positive for electron-withdrawing substituents. The resulting positive region near hydrogen in electron-withdrawing silanes is directionally σ-hole-like, yet unlike classical σ-holes from lone-pair depletion, it reflects a collective molecular electrostatic effect. These findings highlight the importance of global electrostatics for understanding structure-reactivity relationships and predicting substituent-controlled behavior in silicon hydrides.