Sterically Congested LLX‐Type PNSi Tridentate Ligands for Iridium‐Catalyzed C(sp ³ )–H Borylation

Abstract Iridium catalysts bearing LLX‐type PNSi tridentate ligands (Ir/PNSi catalysts) were developed as new effective catalysts for the C(sp 3 )–H borylation of alkanes and alkyl groups that do not have directing groups. The Ir/PNSi catalysts were prepared in situ from [Ir(OMe)(cod)] 2 and 8‐diarylphosphino‐2‐[(di‐ tert ‐butylhydrosilyl)methyl]quinolines, which are readily synthesized from commercially available 8‐bromo‐2‐methylquinoline. The Ir/PNSi catalyst exhibited higher chemoselectivity than a standard Ir/Me 4 phen and our previously reported Ir/NNSi catalysts. Thus, the Ir/PNSi catalysts promoted selective borylation of the sterically less crowded C(sp 3 )–H bonds in 2‐methylheptane and dibutyldimethylsilane. The C(sp 3 )–H‐selective borylation in the presence of C(sp 2 )–H bonds was also achieved with the Ir/PNSi catalysts in the reaction of 4‐substituted alkylbenzenes. Such notable chemoselectivity may be due to the congested environment around the iridium center formed by the mer ‐tridentate coordination of the PNSi ligands.