Speier s catalyst

The most common catalyst used to date is chloroplatinic acid (also known, after its discoverer, as Speier s catalyst) it is now clear that, contrary to earlier views (23), hydrosilylation is a homogeneous process (25, 208). A major problem is that of reproducibility, and efforts are being made to utilize soluble transition metal complexes. Information about such systems has been used in the interpretation of some related catalytic heterogeneous reactions (232). 

The ubiquitous hydrosilation reaction, popular especially in silicone manufacturing,132 has been utilized by Houser and Keller for the synthesis of the networked polymers (104) (Fig. 64) from the reaction of the l,7-bis(vinyltetramethyldisiloxyl)-w-carborane monomer with the polymeric crosslinker, poly(methylhydrosiloxane).133 The reactions were catalyzed by the Speier s catalyst, H2PtCl6. Three samples were... 

We have studied polyhydrosilylation reactions of a/o-oligodiorganodihydnde siloxanes and l,4-bis(dihydridedimetylsilyl)benzene with dialylsilazanes (DAS) in the presence of Speier s catalyst (0.1 mole solution of H2PtCl6 6H20 in isopropanol) [3-7] in dry toluene and in mass. 

The conventional hydrosilylation of alkenes catalyzed by late transition metal catalysts such as Speier s catalyst are generally assumed to proceed by... 

Hydrosilylation. In addition to the two most prominent catalysts, Speier s catalyst (H2PtCl6 in 2-propanol) and the catalyst developed by Karstedt ([Pt(CH2=CHSi Me2)3], and Group VE metals, new families of catalysts have been developed and... 

Detailed mechanistic studies with respect to the application of Speier s catalyst on the hydrosilylation of ethylene showed that the process proceeds according to the Chalk-Harrod mechanism and the rate-determining step is the isomerization of Pt(silyl)(alkyl) complex formed by the ethylene insertion into the Pt—H bond.613 In contrast to the platinum-catalyzed hydrosilylation, the complexes of the iron and cobalt triads (iron, ruthenium, osmium and cobalt, rhodium, iridium, respectively) catalyze dehydrogenative silylation competitively with hydrosilylation. Dehydrogenative silylation occurs via the formation of a complex with cr-alkyl and a-silylalkyl ligands ... 

It is likely that more silicon-carbon bonds are produced by the hydrosilylation of olefins than by any other method except the direct process. This deceptively simple addition of an Si-H bond to a C-C multiple bond can be promoted by a variety of means, but transition metal catalysis is by far the most significant. Two relatively old catalysts, H2PtCl6 ( Speier s catalyst ) and Pt2(Me2ViSiOSiMe2Vi)3 ( Karstedt s catalyst ), remain the most effective, and the remarkable rates and turnover numbers observed in these systems are among the most impressive in all of organometallic chemistry. The bulk of the literature on hydrosilylation falls outside the scope of this review, and readers are directed to the comprehensive work on hydrosilylation edited by Marciniec.93... 

Hydrosilylation of divinyl ether has been applied for the synthesis of silacyclopentane 12 using Speier s catalyst (Scheme l)13. One of the two carbon-carbon double bonds was hydrosilylated first with a dialkyl(ethoxy)silane, giving silylethyl vinyl ether 10 in 53-59% yield, which was reduced with LiAlELr to hydrosilane 11. The intramolecular hydrosilylation of 11 affords silacyclopentane 12 in moderate yields (Scheme 1). The reaction with HSiEt2(OEt) gives 12a exclusively in 45% yield, while silacyclohexane 13b is formed as the minor product when HSiMe2(OEt) is used as the hydrosilane (12b/13b = 2.3/1 50% total yield)13. Other intramolecular hydrosilylation reactions useful in organic syntheses will be discussed in the section n.C. (vide infra). 

Hydrosilylation-polymerization provides a new approach to the syntheses of macromonomers such as poly(arylene-silylethylene) and poly(aralkylene-silylethylene) (274) that possess reactive ethenyl and SiH termini for further manipulations through self-polyaddition of 273 promoted by Speier s catalyst (equation 103)272. 

Hydrosilylation is by far the most important route for obtaining monomers and other precursors to fluorinated polysiloxanes. Hydrosylilation80 is the addition of silicon hydride moiety across an unsaturated linkage using transition metal complexes of platinum or rhodium such as Speier s catalyst, hexachloroplatinic acid in isopro-... 

We have also used free radical initiators and other transition metal complexes besides Speier s catalyst to attach some olefins to the silica hydride intermediate [26,28]. 

This reaction is catalyzed by a platinum catalyst such as Speier s catalyst, chloroplatinic acid. Because the catalyst also isomerizes the terminal double bond, the reaction maybe run with an excess of vinyl to make sure all the reactive sites on the silicone are reacted. SiH also reacts with ROH and, for this reason, alkoxy end-capped polyethers maybe preferred. Alkoxy end-capped polyethers are also useful when the surfactant will be used in a chemically reactive system such as polyurethane foam manufacture. 

Historically, hexachloroplatinic acid in alcohol, so-called Speier s catalyst, was the first homogeneous catalyst and remained the most used for a long time. This platinum (IV) complex has been replaced by other (II) or (0) species, some of which are presented in Scheme 1. Their advantages are a reactivity that can be tuned by the choice of solvent or inhibitor and the absence of hydrochloride formation. Moreover, they are now commercially available as homogeneous solutions, which ensures a perfect dissolution of the complex, and some of them are colorless. 

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