C–H Borylation of Arylsilane Catalyzed by an Iron Amido Complex

The selective functionalization of C–H bonds over
reactive
Si–H bonds in hydrosilanes is a challenge in synthetic chemistry.
We report the synthesis and characterization of a four-coordinate,
high-spin (S = 2) iron amido complex bearing a PNN
pincer ligand. The complex adopts a structure wherein one amido group
coordinates to the iron center while the other binds to the ligand’s
quinoline moiety. As a catalyst, this complex promotes the meta- and para-C–H borylation of
dimethylphenylsilane. While both C–H and Si–H borylated
products were observed at the early stage of the reaction, the Si–H
borylated species was subsequently consumed, leading to an increase
in the amount of C–H borylated products after 20 h. Mechanistic
investigations, including control experiments and DFT calculations,
suggest a pathway involving an in situ-generated
silylborane intermediate. This transient species is consumed in the
thermodynamically favorable C–H borylation step, accounting
for the observed selectivity. This work describes a catalytic system
that achieves the chemoselective functionalization of arylsilanes
by channeling the reactive intermediate silylborane into C–H
borylated products.