Hiyama reaction silanes

Coupling of organosilane derivatives to RX species is known as the Hiyama reaction. This process is seen as more difficult to catalyze than the Stille reaction since a C-Si bond is less reactive than a C-Sn bond. However, addition of additives, such as B114NF or CsF, that form hypervalent silicon intermediates, or the use of more reactive silane precursors, such as Me3SiSiMc3, ArSiMc20H, or Cl2MeSi(vmyl), can overcome this limitation (equation 29). 

TBAF can promote hiaryl formation from triaflyl(aryl)silanes and a wide variety of aryl halide suhstrates. For example, chlorobenzenes undergo smooth cross-couphng with triallyl(aryl)silanes to give biaryls in good to excellent yields (eq 31). Surprisingly, an appreciable amount of added water is required to achieve high yields however, the role of added water is not yet clear.In a recent variant of the Hiyama reaction, TBAF and palladium-coated nickel nanoclusters were employed to prepare biaryl compounds from aryl bromides and phenyltrimethoxysilane. ... 

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]. 

Besides the reversible processes just mentioned, yS-SiRs ehmination from a silyl substituted metal alkyl or metallacycle is a well-documented process [185,186]. This reaction accounts for an easy loss of a silyl group that can be used to generate a M-S1R3 moiety in catalytic processes such as dehydrogenative silation reactions (see below). This reaction, and the analogous yS-SnRs elimination, may also be involved in the loss of regioselectivity found for some C-C coupling reactions of vinyl silanes or vinyl tin derivatives (cine substitution in Hiyama and Stille... 

The use of alkenylsilyl ethers in palladium-catalyzed cross-coupHng reactions has long been known. In fact, only a year after Hiyama s landmark report on the TBAF-promoted coupling reactions of vinyltrimethylsilane, Tamao and Ito capitahzed on the use of alkoxy-substituted silanes as viable components for such reactions (cf Scheme 7.4). The generahty of the silyl ether coupHng added a useful class of organosilicon substrates that are complementary to the fluorosilanes developed by Hiyama et al. These studies showed that other heteroatom-based... 

Scheme 2.104)." Without the activating reagent, the carbon-silicon bond of a vinyl silane 2324 proved to be inert, and a Heck reaction with aryl iodide 2326 occurred. A second aryl group could then be introduced by Hiyama coupling with iodide 2326 in the presence of an activator. 

Complex vinyl silanes may also be formed from simpler vinyl silanes by metathesis reactions. A ring closing metathesis (Section 8.3.3) to form a silicon heterocycle 2351, with a necessarily cis alkene was employed in a synthesis of brasilenyne 2.354 (Scheme 2.110). The RCM was followed by an intramolecular Hiyama... 

Chromium(II) chloride also mediates Wittig-type reactions of a-heteroatom-substituted gem-dihalides and aldehydes. In Scheme 5.27, representative examples of the preparation of alkenylboranes [38], -silanes [39], and -stannanes [40] are shown. In each case, high -selectivity was observed. As these compounds are very important substrates for Suzuki, Hiyama, and Stille couplings, their stereoselective formation enhances the value of the chromium(II) chloride mediated reactions. 

Palladium catalysed Hiyama-type cross-coupling reactions of benzylic phosphates (74) with the aryl-silane (75) afforded corresponding di-arylmethanes (76) (Scheme 21). The reaction tolerated either electron-donating or electron-withdrawing functional groups providing products (76) in high to excellent yields. ... 

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