摘要：

Anefficient regioselective dearomatization of N -heteroarenesusing a ruthenium precatalyst [Ru-( p -cymene)-(PCy 3 )-Cl 2 ] 1 is achieved.Reactions were performed under mild and neat conditions. A wide varietyof N -heteroarenes undergo the addition of silanesin the presence of precatalyst 1 , leading to exclusive N -silyl-1,2-dihydroheteroarene products. This catalyticmethod displays a broad substrate scope; quinolines, isoquinolines,benzimidazoles, quinoxalines, pyrazines, pyrimidines, and pyridinesundergo highly selective 1,2-dearomatization. Both electron-donatingand electron-withdrawing substituents on N -heteroaromaticsare well tolerated in this protocol. Mechanistic studies indicatethe presence of [Ru-( p -cymene) (PCy 3 )-HCl] 4 in the reaction mixture, which may be the resting stateof the catalyst. The complete catalytic cycle as revealed from densityfunctional theory (DFT) studies show that the product formation isgoverned by N → Si tetrel bonding. Initially, PCy 3 dissociates from 1 , and further reaction of [( p -cymene)-RuCl 2 ] 20 with silane generatesthe catalytically active intermediate [( p -cymene)-RuHCl] 7 . Heteroarene coordinates with 7 , and subsequentdearomative 1,3-hydride transfer to the C2 position of the heteroarylligand generates an amide-ligated intermediate in which the reactionof silane occurs through a tetrel bonding and provides a selectivepathway for 1,2-addition. DFT studies also revealed that ruthenium-catalyzed1,4-hydroboration of pyridines is a facile process with a free energybarrier of 3.2 kcal/mol, whereas a pathway for the 1,2-hydroborationproduct is not observed due to the steric effects exerted by methylgroups on pinacolborane (HBpin) and p -cymene. Notably,enabled by the amine–amide inter-conversion of the coordinatedheteroarene ligand, the +2 oxidation state of ruthenium intermediatesremains unchanged throughout the catalytic cycle.

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