Silylations aromatic, triethylsilane

The silylation of benzylic G-H bonds is achieved by using Ru3(GO)12 catalyst in the presence of norbornene as a hydrogen acceptor.145 The reaction of 2-(2,6-dimethylphenyl)pyridine with triethylsilane in the presence of Ru3(CO)i2 catalyst and norbornene affords mono- and disilylation products in 30% and 55% yields, respectively (Equation (106)). The reaction of 2-(2-tolyl)pyridine shows that the silylation of the aromatic C-H bond is more facile than that of the benzylic C-H bond. 

Fig. 17.72. Ionic hydrogena-tion/hydrogenolysis of an aromatic ketone (meto-nitroace-tophenone). CF3C00H causes a reversible protonation of the ketone to the ion A. The reducing agent triethylsilane then transfers a hydride ion onto A to form a benzylic alcohol. This alcohol presumably is silylated, protonated, and converted into the benzyl cation B. A second hydride transfer yields the final product.

Again, no reaction was observed in the absence of mercaptoethanol. The mechanistic steps for the transformation were elucidated by the Chatgilialoglu et ah and are represented in Scheme 4.13, in analogy with the pathway reported for the radical reduction of aromatic azides with triethylsilane in toluene, with the addition of silyl radicals to the azide function, liberation of nitrogen and formation of silyl-substituted aminyl radical. The thiol is the hydrogen atom donor to this intermediate and it can be regenerated by its interaction with the silane, thus propagating the chain. The hydrolysis of the silylamine occurred... 

The cationic Ru complex 4 also promotes silylative dimerisation of aromatic aldehydes with hydrosilanes. For example, the reaction of benzaldehyde and triethylsilane in the presence of a catalytic amount of 4 affords the dimerisation product 19 along with a small amount of the hydrosilylation product PhCH20SiEt3 (Equation 7). This type of silylative dimerisation of aldehydes is relatively scarce in the literature common ruthenium complexes such as [RuCl2(PPh3)3] and [Ru3(CO)j2] give only the hydrosilylation products. 

Catalytic Silylation of Aromatic C-H Bonds. Direct, catalytic functionalizations of ortho C-H bonds in aromatic ox-azolines have been extended to silylation. Treatment of pheny-loxazolines with triethylsilane using Ru3(CO)i2 as a catalyst and tert-butylethylene as a hydrogen scavenger gives 2-(2-triethyl-silyl)phenyloxazolines in good yields (eq Vajjous func-... 

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