Control of the Regioselectivity of Alkyne Hydrostannylation by Tuning the Metal Pair of Heterobimetallic Catalysts: A Theoretical Study

In
this work, the detailed reaction mechanisms of two distinct
Sn–H bond activation modes of the [Cu–Fe] and [Cu–Mn]
heterobimetallic catalysts were computationally investigated using
density functional theory calculations. Our calculation results show
that the alkyne hydrostannylation catalyzed by the [Cu–Fe]
and [Cu–Mn] catalysts involves three steps: Sn–H bond
activation, alkyne insertion, and vinylstannane formation. The Sn–H
bond activation step is an essential process during two distinct catalytic
cycles, where two divergent Sn–H bond activation modes are
produced by the [Cu–Fe] and [Cu–Mn] heterobimetallic
catalysts. In the [Cu–Mn] catalytic process, the Sn–H
bond is divided into (CH3)3Sn–Mn­(CO)5 and MeCuH, whereas in the [Cu–Fe] catalytic process,
HFe­(CO)2 and MeCu–Sn­(CH3)3 are obtained. The alkyne insertion process is the rate-determining
step. Both our calculation and experimental results have shown that
using a [Cu–Mn] heterobimetallic catalyst, only the (E)-β-product ((E)-β-Pro) can
be easily obtained at about 60 °C. Using a [Cu–Fe] heterobimetallic
catalyst, both α-Pro and (E)-β-Pro can
be easily obtained at room temperature. The different regioselectivity
of alkyne hydrostannylation catalyzed by different heterobimetallic
catalysts is controlled by the Cu/M pair. Our calculation results
are consistent with and provide an explanation for the experimental
observations, which would be particularly helpful for the further
development of alkyne hydrostannylation and the design of other heterobimetallic
catalysts.