Hydrosilanes reactions

Catalytic C-H bond transformation is a very attractive research subject in organic and organometallic chemistry [1]. There are several procedures for C-H bond transformation. One is conversion of C-H bonds to C-Si bonds, i.e. the direct silylation of C-H bonds. Three procedures have been developed for silylation of C-H bonds - use of hydrosilanes (reaction 1 in Scheme 1), disilanes (reaction 2 in Scheme 1), and vinylsilanes (reaction 3 in Scheme 1) as silylating reagents. 

As mentioned above, three types of reaction are used for silylation of C-H bonds. In this section, we describe the reaction pathway of chelation-assisted silylation of C-H bonds with hydrosilanes (reaction 1). 

Reaction Mechanism. The proposed mechanism for the ozone-hydrosilane reaction (7) shown in Equation 2, as deduced by analyzing and correlating data on relative rates, substituent effects, deuterium isotope effects, low temperature NMR, and ultraviolet spectroscopy for a range of hydrosilanes, is a multistep one as follows ... 

The Pd-catalyzed hydrogenoiysis of acyl chlorides with hydrogen to give aldehydes is called the Rosenmund reduction. Rosenmund reduction catalyzed by supported Pd is explained by the formation of an acylpalladium complex and its hydrogenolysis[744]. Aldehydes can be obtained using other hydrides. For example, the Pd-catalyzed reaction of acyl halides with tin hydride gives aldehydes[745]. This is the tin Form of Rosenmund reduction. Aldehydes are i ormed by the reaction of the thio esters 873 with hydrosilanes[746,747]. 

The reaction of hydrosilanes with butadiene is different from other reactions. Different products are obtained depending on the structurelof the hydrosilanes and the reaction conditions. Trimethylsiiane and other trialkylsilanes react to give the I 2 adduct, namely the l-trialkylsilyl-2,6-octadiene 74, in high yields[67-69]. Unlike other telomers which have the 2,7-octadienyl chain, the 2,6-octadienyl chain is formed by hydrosilylation. On the other hand, the 1 I adduct 75 (l-trichlorosilyl-2-butene)is formed selectively with trichlorosilane, which is more reactive than trialkylsilanes[69]. The Reaction gives the Z form stereoselectively[70]. A mixture of the I 1 and I 2 adducts (83.5 and 5.2%) is... 

Silylation of alcohols, amines and carboxylic acids with hydrosilanes is catalyzed by Pd catalysts[l 19], Based on this reaction, silyl protection of alcohols, amines, and carboxylic acids can be carried out with /-butyldimethylsilane using Pd on carbon as a catalyst. This method is simpler and more convenient than the silylation with /-butyldimethylsilyl chloride, which is used commonly for the protection. Protection of P-hydroxymethyl-(3-lactam (125) is an example 120]. 

Poly(hydrosilane)s have been used as radical-based reducing agents for organic halides (RX, where X = Cl, Br, 1), rivaling the effectiveness of the (TMSlsSiH. A rate constant (fcn referring to each SiH moiety) in the range of (5-60) xlO M s is estimated for the reaction of primary alkyl radicals with 123. ... 

Organosilicon compounds are widely used in our daily life as oil, grease, rubbers, cosmetics, medicinal chemicals, etc. However, these compounds are not naturally occurring substances but artificially produced ones (for reviews of organosilicon chemistry, see [59-64]). Hydrosilylation reactions catalyzed by a transition-metal catalyst are one of the most powerful tools for the synthesis of organosilicon compounds. Reaction of an unsaturated C-C bond such as alkynes or alkenes with hydrosilane affords a vinyl- or alkylsilane, respectively (Scheme 16). 

The dehydration of primary amides with hydrosilane catalyzed by iron carbonyl clusters, such as [Et3NH][HFe3(CO)n] and Fe2(CO)9, was achieved by Seller and coworkers in 2009 (Scheme 43) [145]. This reaction shows good functional group tolerance (e.g., such as aromatic, heteroaromatic, and aliphatic substrates). 

A mechanistic proposal, which is based on the mthenium-catalyzed dehydration reaction reported by Nagashima and coworkers [146], is shown in Scheme 44. Reaction of a primary amine with hydrosilane in the presence of the iron catalyst affords the bis(silyl)amine a and 2 equiv. of H2. Subsequently, the isomerization of a gives the A,0-bis(silyl)imidate b and then elimination of the disiloxane from b produces the corresponding nitrile. Although the disiloxane and its monohydrolysis product were observed by and Si NMR spectroscopy and by GC-Mass-analysis, intermediates a and b were not detected. 

A catalytic mechanism, which is supported by deuterium-labeling experiments in the corresponding Ru-catalyzed procedure [146], is shown in Scheme 47. Accordingly, the reactive Fe-hydride species is formed in situ by the reaction of the iron precatalyst with hydrosilane. Hydrosilylation of the carboxyl group affords the 0-silyl-A,0-acetal a, which is converted into the iminium intermediate b. Reduction of b by a second Fe-hydride species finally generates the corresponding amine and disiloxane. 

Scheme 51 The Fe-catalyzed Si-O-Si bond formation reaction from hydrosilanes and DMF...

Hydride species were also formed in the dehydrogenative coupling of hydrosilanes with DMF [45]. The catalytic system is applicable to tertiary silanes, which are known to be difficult to be converted into disiloxanes (Fig. 17). The catalytic reaction pathway involves the intermediacy of a hydrido(disilyl)iron complex... 

As shown in Table 6 all the reactions proceed with complete chemoselectivity to the corresponding N,N-disilylamine. The reactions have been performed without solvent facilitating the collection of the products. With catalyst B, using HSiMc3, as hydrosilane reagent, quantitative yields of products have been obtained with ben-zonitrile, as well as with other nitriles, containing... 

Reaction conditions nitrile (9.8mmol), hydrosilane (49mmol), rhodium (0.1 mmol) T = GLC conversion of nitrile. 

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