Ir₄(CO)₁₂-Catalyzed Benzylic C(sp³)–H Silylation of 2-Alkylpyridines with Hydrosilanes Leading to 2-(1-Silylalkyl)pyridines

Abstract

The iridium-catalyzed C(sp)-H silylation of 2-alkylpyridines with hydrosilanes at the benzylic position to afford 2-(1-silylalkyl)pyridines is described. The low product yield was markedly improved by adding 3,5-dimethylpyridine. Norbornene is also an essential additive for the reaction to proceed as a hydrogen scavenger. Carbon monoxide plays an important role in the catalytic cycle as a ligand. Other transition-metal carbonyls such as Rh(CO) and Ru(CO) can also be used as catalysts for this C-H silylation.

Silylation of Pyridine, Picolines, and Quinoline with a Zinc Catalyst

“…In both instances, the silylation occurred on the methyl group, instead of on the pyridine ring. These results are similar to what Fukumoto and co-workers have reported in their silylation of 2- and 4-picolines with Ir 4 (CO) 12 . The silylation of 4-ethylpyridine occurs at the benzylic position as well, to afford 4-(1-triethylsilylethyl)­pyridine (14%, NMR-based yield) …”

“…Recently, there has been tremendous interest in transforming C–H bonds into C–Si bonds, since the resulting silylated compounds provide a versatile set of molecules that can be used in various cross-coupling reactions . An interesting subset of this transformation is the silylation of N -heteroarenes, such as pyridine, picolines, quinolines, and indoles, where a C–H bond has been replaced with a C–Si bond . These transformations have involved transition metals , and the rather unusual KO t Bu , as catalysts.…”

“…An interesting subset of this transformation is the silylation of N -heteroarenes, such as pyridine, picolines, quinolines, and indoles, where a C–H bond has been replaced with a C–Si bond . These transformations have involved transition metals , and the rather unusual KO t Bu , as catalysts. In addition, main group electrophilic Lewis acids, such as B­(C 6 F 5 ) 3 , can activate the silane to afford a silylated N -heteroarene. , Recently, Tsuchimoto and co-workers have reported the use of zinc salts as effective Lewis acid silylation catalysts for indoles .…”

Metal-catalyzed silylation of sp3C–H bonds

“…The silylation with pincer-Ru catalyst could also be performed at methyl primary sp 3 C-H bond of ortho alkyl group not attached to a hetero atom element in proximity with the Si-H bond (Scheme 60). 76 The intramolecular silylation of ortho alkyl of 2-alkyl arylsilanes was also observed previously using Rh(I) catalysts (see Schemes 45,46). 69 Scheme 60.…”

“…The silylation is performed with HSiEt3 and Ir4(CO)12 as catalyst in the presence of norbornene as hydrogen trap but in the presence of 3,5-dimethylpyridine ligand (Scheme 10). 46 Thus the 3,5-dimethylpyridine modifies strongly by coordination the Ir(0) catalyst which without this ligand favours silylation at 4-methyl pyridine. 45 Scheme 10.…”