Aryl halosilanes and their hypervalent derivatives are versatile reagents for carbon-carbon [1][2] and carbon-heteroatom [3] bond formation in modern organic synthesis. Although they have been prepared by arylation of halosilanes with aryl magnesium or aryl lithium reagents, [4] and by Pd-catalyzed cross-coupling of halogenated disilanes with aryl electrophiles, [5] direct silylation of arenes through C À H bond activation would provide a more attractive route from the viewpoints of economy, efficiency, and environmental benignity. Indeed, aromatic CÀH silylation by disilanes [6] or hydrosilanes [6a, 7] catalyzed by a transition-metal complex has been developed by several research groups. However, the application of this protocol has been limited to the synthesis of aryl triorganosilanes. On the other hand, we recently found that Ir I complexes generated from 1/2[{IrCl(cod)} 2 ] (cod = 1,5-cyclooctadiene) or 1/2[{Ir(OMe)(cod)} 2 ] and 2,2'-bipyridine (bpy) or 4,4'-di-tert-butyl-2,2'-bipyridine (dtbpy) are excellent catalysts for aromatic C À H borylation by bis(pinacolato)diboron.[8] These results prompted us to extend the methodology to the aromatic C À H silylation of arenes (2) by 1,2-ditert-butyl-1,1,2,2-tetrafluorodisilane (tBuF 2 Si) 2 (1) in the presence of a 1/2[{Ir(OMe)(cod)} 2 ]-dtbpy catalyst. This process enables, for the first time, the direct synthesis of aryl halosilanes (3) through aromatic C À H bond activation (Scheme 1).Our initial investigation focused on the effects of substituents on the disilanes on the reaction. The reactions were carried out at 80 8C for 16 h in a resealable Schlenk tube by using disilanes (1.0 mmol), benzene (60 mmol), [{Ir(OMe)-(cod)} 2 ] (0.015 mmol), and dtbpy (0.03 mmol). Among the disilanes examined, 1 exhibited the highest reactivity to produce the corresponding phenylsilane in 28 % yield with 28 % conversion of 1. The use of tetrafluorodisilanes is critical as (Me 2 FSi) 2 gave the corresponding arylsilane in 9 % yield, and (tBuCl 2 Si) 2 or (Me 3 Si) 2 led to no reaction. The structures of alkyl substituents also had significant effects on silylation. For example, (sBuF 2 Si) 2 and (nBuF 2 Si) 2 formed no silylated product.The reaction of o-xylene with 1 was carried out at 120 8C to optimize catalyst precursors and ligands. Of the precursors and ligands examined, the combination of 1/2[{Ir(OMe)-(cod)} 2 ] and dtbpy was found to be the best catalyst to provide isomerically pure 4-silyl-1,2-dimethylbenzene in 99 % yield based on the molar amount of 1. Although the substrate has weaker benzylic CÀH bonds, [9] the reaction selectively occurred at the aromatic C À H bonds. ] as a catalyst precursor were markedly affected by steric and electronic properties of bipyridine ligands. Bpy, 4,4'-di-Me-bpy, 5,5'-di-Me-bpy, and even 6,6'-di-Me-bpy displayed moderate reactivity (49-55 % yields), while 3,3'-diMe-bpy showed little activity (8 % yield) owing to the importance of a parallel arrangement of two pyridine rings. Electronic effects of bpy derivatives were perplexing...
