Cooperative Catalytic Activation of Si-H Bonds by a Polar Ru-S Bond: Regioselective Low-Temperature C-H Silylation of Indoles under Neutral Conditions by a Friedel-Crafts Mechanism

Merging cooperative Si-H bond activation and electrophilic aromatic substitution paves the way for C-3-selective indole C-H functionalization under electronic and not conventional steric control. The Si-H bond is heterolytically split by the Ru-S bond of a coordinatively unsaturated cationic ruthenium(II) complex, forming a sulfur-stabilized silicon electrophile. The Wheland intermediate of the subsequent Friedel-Crafts-type process is assumed to be deprotonated by the sulfur atom, no added base required. The overall catalysis proceeds without solvent at low temperature, only liberating dihydrogen.