Cobalt‐Catalyzed Intramolecular C─H Silylation of Arenes

ABSTRACT Direct C−Si bond formation via C−H silylation offers an efficient atom‐economical route to organosilanes, yet existing strategies remain largely restricted to noble‐metal catalysis. Here, we disclose the first cobalt‐catalyzed intramolecular C−H silylation of arenes, enabled by the well‐defined hydride complex HCo(PMe 3 ) 4 . This catalyst sequentially activates Si−H and arene C─H bonds, enabling either an hydrosilylation/cyclization sequence or direct cyclization. The method features broad functional‐group tolerance and delivers diverse heterosilacycles and silafluorenes in high yields and is extended to germacycle. DFT studies support a two‐electron mechanism involving oxidative addition of the Si─H bond, H 2 elimination facilitated by a hydrogen acceptor, intramolecular C─H activation to form a cobaltacycle, and final reductive elimination to furnish the silacycle. Overall, this work establishes cobalt hydrides as a sustainable and effective alternative to noble metals for the synthesis of silacyclic architectures.