Abstract
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-C(6) H(4) SMe)(2) ](H)(PPh(3) )(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 aD -E aH )=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.