Hydrogen Tunneling in Catalytic Hydrolysis and Alcoholysis of Silanes

An unprecedented quantum tunneling effect has been observed in catalytic Si-H bond activations at room temperature. The cationic hydrido-silyl-iridium(III) complex, {Ir[SiMe(o-C₆ H₄ SMe)₂ ](H)(PPh₃ )(THF)}[BAr^F ₄ ], has proven to be a highly efficient catalyst for the hydrolysis and the alcoholysis of organosilanes. When triethylsilane was used as a substrate, the system revealed the largest kinetic isotopic effect (KIE_Si-H/Si-D =346±4) ever reported for this type of reaction. This unexpectedly high KIE, measured at room temperature, together with the calculated Arrhenius preexponential factor ratio (A_H /A_D =0.0004) and difference in the observed activation energy [(E $$ -E $$ )=34.07 kJ mol^-1 ] are consistent with the participation of quantum tunneling in the catalytic process. DFT calculations have been used to unravel the reaction pathway and identify the rate-determining step. Aditionally, isotopic effects were considered by different methods, and tunneling effects have been calculated to be crucial in the process.