Silanes cross-coupling with halides

Radical-mediated silyldesulfonylation of various vinyl and (a-fluoro)vinyl sulfones 21 with (TMSlsSiH (Reaction 25) provide access to vinyl and (a-fluoro)vinyl silanes 22. These reactions presumably occur via a radical addition of (TMSlsSi radical followed by /)-scission with the ejection of PhS02 radical. Hydrogen abstraction from (TMSlsSiH by PhS02 radical completes the cycle of these chain reactions. Such silyldesulfonylation provides a flexible alternative to the hydrosilylation of alkynes with (TMSlsSiH (see below). On oxidative treatment with hydrogen peroxide in basic aqueous solution, compound 22 undergoes Pd-catalyzed cross-couplings with aryl halides. 

Alkynyl(trimethyl)silanes smoothly couple with alkenyl halides at room temperature in the presence of a palladium catalyst and TASF (Eq. 5) [4]. The difference in reactivity between alkynylstannanes and -silanes were utilized in a palladium-catalyzed three component cross-coupling reaction. Thus, the palladium-catalyzed sequential reaction of tributylstannyl(trimethylsilyl)ethyne... 

The cross-coupling reaction of alkenyl(fluoro)silanes with aryl halides sometimes produces, in addition to the desired ipso-cowpled products, small amounts of cmc-coupled products [14]. The czne-coupling is often striking in the reaction with organotin compounds. The isomer ratio of products produced by the reaction of l-fluoro(dimethyl)silyl-l-phenylethene with aryl iodides is found to depend on the electronic nature of a substituent on aryl iodides (Eq. 11) an electron-withdrawing group like trifluoromethyl and acetyl favors the formation of the ipso-coupled product. To explain the substituent effect, the mechanism depicted in Scheme 3 is proposed for the transmetalation of alkenylsilanes with palladium(ll) complexes. It is considered that an electron-donating substituent on Ar enhances... 

Alkyl(trifluoro)silanes are also applicable to the cross-coupling reaction with aryl halides (Eq. 34) [41,42]. TBAF in excess is required for giving products in acceptable yields, as the coproduced Sip4 is readily converted into (SiFs) or (SiFa)2-. 

The Pd-catalyzed cross-coupling reaction of vinyl(2-pyridyl)silanes 5.48 with organic halides gave substituted vinyl(2-pyridyl)silanes 5.49 in high yields. The mechanism of this reaction involves the carbometallation pathways (Scheme 5.18). 

Palladium-catalyzed cross couplings of organofluorosilanes with vinyl [37] and aryl [38] halides and triflates are known, where the activation of the Si—C bond by fluoride ion plays an essential role in the coupling. The pentacoordinated fluoroorganic silanes promote the transmetallation to the aryl halide-palladium complexes strongly. At least one fluorine... 

Coupling Reactions. The palladium-catalysed cross-coupling of E—(1-alkyl-l-alkenyl)boronates with alkyl halides has been shown to permit stereo- and regio-specific access to trisubstituted alkenes in which the introduced alkyl group occupies the position formerly occupied by the boron substituent.201 A1lyl-silanes may be obtained... 

We sought to examine the enzymatic dioxygenation of aryl silanes using a number of different aromatic dioxygenases in order to determine if such transformations were possible and to define the substrate-specificity profile. We were also motivated by the rich chemistry of silicon-based materials, which includes the hydrosilylation of alkenes and ketones, the addition of electrophiles to vinyl and allyl silanes, and palladium catalyzed cross-coupling of vinyl silanes with aryl halides (13). As a result, silyl functional cw-diols have potential as chiral intermediates for drug development, as polymer precursors/modifiers and as elements in non-linear optical materials. 

The aim of this work is to present the synthesis of several bis(trimethylsilyl)diaminosilanes by cross-coupling reactions with lithium and the cleavage of the amino groups by different hydrogen halides to afford the 2,2-dihalogenohexamethyltrisilanes, which constitute suitable cyclization reagents for cyclic diaminobis(trimethyl)silanes. 

The palladium-catalyzed Hiyama reaction is a cross-coupling between aryl halides and silanes (Scheme 19.47) [65]. Silane derivatives are easily available. They are stable with a low toxicity. However, they exhibit a low reactivity, and the reactions must be performed at high temperatures. Reactions are promoted by fluoride ions [65]. 

Some alkenes with heteroatoms can be used in cross-coupling reactions. Vinyl boranes are an important group, as the carbon-boron bond can subsequently be converted into so many other functional groups, such as halides (Scheme 8.97). ° An example of cross-metathesis of a vinyl borane, followed by Suzuki coupling, can be found in Scheme 11.40. An example of a vinyl silane metathesis can be found in Scheme 2.110. 

Cross-coupling Reactions. Trimethylsilylmethylmagnesium chloride reacts with organic halides (or pseudohalides), especially aryl and alkenyl halides, in the presence of transition metal catalysts. The reactions directly provide allylic or benzylic trimethyl-silanes of significant synthetic use. 

The most commonly accepted mechanism for this coupling was initially proposed by Hiyama and Hatanaka, which involves three steps.The first step is the oxidative addition of the aryl halide to the palladium(O) catalyst to give arylpalladium complex 1. The second step involves the transmetallation of the arylpalladium complex 1 with the anionic arylsilicate 2 to give bis(aryl)palladium complex 3. Finally, the cross-coupled product 4 is produced and the palladium(O) catalyst is regenerated through reductive elimination of the bis(aryl)palladium(II) complex 3. The key intermediate to this process is the requirement for the pentacoordinate arylsilicate anion 2, typically formed by treatment of the tetracoordinate silane with the activating anion, such as tetrabutylammonium fluoride (TBAF). 

Cross-Coupling Reaction of Alkyl(triorgano)silanes with Aryl Halides A General Procedure ... 

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