Triethoxysilane-Enabled Weak Lewis Acidic Boron Catalysis in Nitrile Hydroboration with Pinacolborane
Year: 2026
Type: preprint
Abstract: Triethoxysilane was an efficient precatalyst for the hydroboration of nitriles with pinacolborane (HBPin). The system accommodated a broad range of aromatic and aliphatic substrates, affording the corresponding diborylamines in excellent yields and tolerating both electron-donating and electron-withdrawing substituents. Notably, this transformation exhibited markedly different reactivity from the analogous reaction with alkynes. Competition experiments indicated that catalytic efficiency was governed primarily by steric effects, with minimal sensitivity to electronic variation. The use of the fluorinated analogue HSi(OCH 2 CF 3 ) 3 as a precatalyst, however, had only a minimal impact on the reaction rate. The presence of the N atom in nitriles was found to profoundly alter the nature of the catalytically active species, accounting for the significant differences in reactivity observed relative to alkynes and resulting in the identification of the in situ generated silylboronic ester PinB–Si(OEt) 3 as the predominant species involved in product formation. Changes in the chemical shifts upon addition of HSi(OEt) 3 or HBPin to 4-fluorobenzonitrile revealed a stronger preference of the nitrile for interaction with boron over silicon, consistent with a Lewis acid–base interaction between the B center of PinB–Si(OEt)₃ and the nitrile N atom that facilitates substrate activation during catalysis. The presence of the Si(OEt) 3 group in PinB–Si(OEt) 3 was found critical for efficient catalysis, suggesting that the silyl group may modulate the Lewis acidity and steric environment of the B center or participate directly in interactions with the substrates facilitating their activation.
Source: ChemRxiv
Authors: Harleen Kaur, Diksha Sharma, Rebeca Arevalo
Institution: University of California, Merced
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
Funder: National Science Foundation
OpenAlex ID: W7211899473