DFT study of rhodium-catalyzed transformation of silacyclobutane with alkyne or H2O: Si–Cl bond reductive elimination vs. alkyne insertion

Abstract

Organosilicon compounds are essential structural units in organic synthesis, materials science, and drug molecule design. Despite significant strides in understanding the intramolecular C(sp²)–H/C(sp³)–H silylation mechanism, the intermolecular C(sp)–H/O–H silylation processes remain elusive. Here, density functional theory (DFT) calculations have been employed to uncover the mechanisms governing both the Rh/BINAP-catalyzed C(sp)–H silylation of silacyclobutane with alkyne and the O–H silylation of silacyclobutane with H₂O. Our investigation yielded several crucial insights, including the following: (1) C(sp)–H silylation and O–H silylation undergo a similar catalytic cycle rather than previously proposed different catalytic cycles; (2) the [Rh]–H species resulting from the precatalyst [Rh]–Cl with silacyclobutane is identified as the real active species; (3) a refined [Rh]–H-catalyzed mechanism involves C–Si bond activation, C–H bond formation, C(sp)–H bond activation of alkyne/σ-bond metathesis of H₂O, and C–Si bond reductive elimination. Simultaneously, the newly proposed reaction pathway sheds light on why silacyclobutane and alkyne yield distinct products in both the Rh/BINAP and Rh/PPh₃ systems. This discrepancy stems from steric hindrance induced by BINAP during the alkyne insertion step, thereby favoring the Si–Cl bond reductive elimination.