Quaternary Ammonium Salts: Catalysts for Hydrosilylation of Alkynes with Hydrosilanes

Abstract Mixing i ‐PrI and DABCO in solvent EtCN gave two quaternary ammonium salts (QASs) quantitatively, one of which is monocationic ( QAS‐1 ) and the other is dicationic ( QAS‐2 ). These QASs were found to catalyze hydrosilylation of alkynes with hydrosilanes (HAH) without the aid of metal and metalloid catalysts. This organocatalysis can be applied to a variety of alkynes: terminal/internal aryl and alkyl alkynes with/without a functional group. With dihydrosilanes (H 2 Si ), the HAH occurred with high E ‐selectivity through syn addition, which was exclusively observed when using terminal alkyl alkynes, irrespective of a hydrosilane used. A scalable HAH is also feasible. The H−Si unit remaining in alkenylsilanes derived from H 2 Si is available for dehydrogenative alkynylation and N‐heteroarylation under zinc–pyridine catalysis. This synthetic application delivers unique silicon compounds that have, for instance, alkyl, aryl, alkenyl, and alkynyl groups in a single molecule. Mechanistic studies suggested that alkynes activated by QASs irreversibly react with hydrosilanes that become more nucleophilic by the coordination of EtCN. A radical pathway is unlikely. The QAS catalysts can be recovered and reused at least 5 times.