Silicon hydrides reactions

The reaction of thiyl radicals with silicon hydrides (Reaction 8) is the key step of the so-called polariiy-reversal catalysis in the radical chain reduction. The reaction is strongly endothermic and reversible with alkyl-substituted silanes (Reaction 8). For example, the rate constants fcsH arid fcgiH for the couple triethylsilane/ 1-adamantanethiol are 3.2 x 10 and 5.2xlO M s respectively. 

PhSeSiRs reacts with BusSnH under free radical conditions and affords the corresponding silicon hydride (Reaction 1.8) [19,20]. This method of generating RsSi radicals has been successfully applied to hydrosilylation of carbonyl groups, which is generally a sluggish reaction (see Chapter 5). 

The reaction of thermally and photochemically generated tcrt-butoxyl radicals with silicon hydrides (Reactions 3.13 and 3.14) has been extensively used for the generation of silyl radicals in EPR studies, time-resolved optical techniques, and organic synthesis. 

Unfortunately, because self-condensation of silanols on the same silicone can occur almost spontaneously, the reaction of disdanol or trisilanol compounds with telechelic sdanol polymers to form a three-dimensional network is not feasible. Instead, the telechelic polymers react with cross-linkers containing reactive groups such as alkoxysdanes, acyloxysdanes, silicon hydrides, or methylethyloximesilanes, as in the reactions in equations 18—21 (155). 

Newer silicone adhesives having solids levels up to 97% are also commercially available [109]. Instead of using silanol condensation reactions, they rely on addition chemistry between vinyl functional silicone oligomers and silicon hydride terminated silicones. This addition reaction is typically facilitated with platinum derived catalysts. This hydrosilation process can be run at reduced oven temperatures, but the finished products typically do not yield the same balance of properties as seen for condensation cure materials. 

Although there are several possible methods for the synthesis of organofunctionally terminated disiloxanes, hydrosilation reactions have become the most popular and practical process. Hydrosilation is the term used for the addition of silicon hydrides... 

The hydrogen abstraction from the Si-H moiety of silanes is fundamentally important for these reactions. Kinetic studies have been performed with many types of silicon hydrides and with a large variety of radicals and been reviewed periodically. The data can be interpreted in terms of the electronic properties of the silanes imparted by substituents for each attacking radical. In brevity, we compared in Figure 1 the rate constants of hydrogen abstraction from a variety of reducing systems by primary alkyl radicals at ca. 80°C. ... 

The use of (TMSlsSiH with acyl selenides can also yield new C-C bond formation, as shown with the a,/l-unsaturated lactam ester (Reaction 67). The resulting ketone can be envisaged as potentially useful for the synthesis of 2-acylindole alkaloids. Both the effects of H-donating ability and steric hindrance by the silicon hydride are evident. 

Two closely related reactions, (a) and (b), illustrated by Eq. (12) (Rj = HPhj, Etj, Phj, CI3, CljPh) and (13), of silicon hydrides with transition metal complexes generate compounds with Si—M bonds with elimination of hydrogen (a) cleavage of metal-metal bonds and (b) reaction with transition metal hydrides. Reactions discussed in this section are relevant to... 

Reactions of silicon hydrides with m-(R3P)2PtCl2 (R = Bu, Ph) have been widely investigated. Alkyl- and aryl-silanes underwent metathetical H/Cl exchange [Eq, (18) (R = Et, Ph, PhCHj, C.H.j)] (55). 

The reactions of silicon hydrides with low-valent phosphine complexes of Fe, Co, and Ni have led to the isolation of a number of products in some of which the silicon moiety may be present as an [SiXj] anion (177). Examples are given in Eqs. (102)-(103). Definitive confirmation of these formulations... 

Ultrasound also promotes the reaction of potassium hydride with some silicon hydrides to give silyl anions in excellent yields and... 

In some cases, elements having electronegativities too low to give ionic bonding with hydrogen also tend to be unreactive, so that direct combination of the elements is not feasible. In such cases, the procedure just described can be used to prepare the hydride. For example, silicon hydride, SiH4 (known as silane), can be produced by the reactions... 

Reductions. Silicon hydrides such as 1, which can achieve intramolecular pentacoordination, show enhanced reducing properties. Thus they can reduce aldehydes or ketones to alcohols,1 and reduce carboxylic acids to aldehydes via thermal decomposition of a silyl carboxylate (equation I).2 Reaction of acid chlo-... 

The reactions of atoms or radicals with silicon hydrides, germanium hydrides, and tin hydrides are the key steps in formation of the metal-centered radicals [Eq. (1)]. Silyl radicals play a strategic role in diverse areas of science, from the production of silicon-containing ceramics to applications in polymers and organic synthesis.1 Tin hydrides have been widely applied in synthesis in radical chain reactions that were well established decades ago.2,3 Germanium hydrides have been less commonly employed but provide some attractive features for organic synthesis. 

The reaction of carbon-centered radicals with silicon hydrides is of great importance in chemical transformations under reducing conditions where an appropriate silane is either the reducing agent or the mediator for the formation of new bonds.23... 

Rate Constants for Reactions of Carbon-Centered Radicals with Silicon Hydrides... 

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