Hydrosilylation chloroplatinic acid

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 proposed mechanism for the hydrosilylation of olefins catalyzed by chloroplatinic acid is outlined in Fig. 6. Catalysis by square-planar or trigonal bipyramidal rf complexes can be similarly described (54, 55, 105). 

Fig. 6. Hydrosilylation mechanism for chloroplatinic acid. L = unspecified ligand, presumably chlorine, hydrogen, or coordinated solvent.

It is probable that during hydrosilylations these Ni(II) complexes are reduced to 7r-olefin Ni(0) species which then undergo an oxidative addition in an identical manner to that already discussed for the chloroplatinic acid case. There is current interest in such oxidations (83), and the platinum analog (Ph3P)2Pt(olefin) has been shown in one case (olefin = C2H4) to be an excellent hydrosilylation catalyst (240). In this system, intermediate low oxidation state Pt species have been isolated their nature is dependent on the electronegativity of the other groups attached to silicon. 

Hydrosilylation, the addition of a silicon-hydrogen bond to multiple bonds, is a valuable laboratory and industrial process in the synthesis of organosilicon compounds. The addition to carbon-carbon multiple bonds can be accomplished as a radical process initiated by ultraviolet (UV) light, y irradiation, or peroxides. Since the discovery in the 1950s that chloroplatinic acid is a good catalyst to promote the addition, metal-catalyzed transformations have become the commonly used hydrosi-... 

Detailed studies concerning the active species in hydrosilylation catalyzed by chloroplatinic acid have pointed to the involvement of several oxidation states. It... 

The addition of Si—H bonds and the reactions of silyls with platinum complexes is of significance because of the early discovery of chloroplatinic acid as a hydrosilylation catalyst.53 This section focuses on the formation of hydrides from silanes. 

Like monodisperse carbosiloxane dendrimers, hyperbranched carbosiloxanes can be produced by hydrosilylation [100]. The first compounds of this kind were synthesised in 1991 by Mathias and Carothers [101] by polymerisation of an al-lyl-tris(dimethylsiloxy)silane monomer with addition of chloroplatinic acid hydrate (Fig. 4.52). The reaction proceeds relatively fast however, addition of more catalyst does not increase the molecular masses (19000 g/mol). The NMR spec-... 

Addition of hydrosilane to alkenes, dienes and alkynes is called hydrosilylation, or hydrosilation, and is a commercially important process for the production of many organosilicon compounds. As related reactions, silylformylation of alkynes is treated in Section 7.1.2, and the reduction of carbonyl compounds to alcohols by hydrosilylation is treated in Section 10.2. Compared with other hydrometallations discussed so far, hydrosilylation is sluggish and proceeds satisfactorily only in the presence of catalysts [214], Chloroplatinic acid is the most active catalyst and the hydrosilylation of alkenes catalysed by E PtCU is operated commercially [215]. Colloidal Pt is said to be an active catalytic species. Even the internal alkenes 558 can be hydrosilylated in the presence of a Pt catalyst with concomitant isomerization of the double bond from an internal to a terminal position to give terminal silylalkanes 559. The oxidative addition of hydrosilane to form R Si—Pt—H 560 is the first step of the hydrosilylation, and insertion of alkenes to the Pt—H bond gives 561, and the alkylsilane 562 is obtained by reductive elimination. 

As illustrated in Equations Si5.4 and Si5.5, hydrosilylation of alkynes produces vinylsilanes. Chloroplatinic acid is the reagent of choice and the reaction results in cis addition. Good regioselectivity may result when terminal alkynes are substrates with the silyl group adding to the least hindered end of the triple bond (Equation Si5.6). 

Siloxane Polymers. The synthesis of the ferrocene-modified siloxane polymers (A - E) has been described previously (25,27,32). Briefly, the methyl(2-ferrocenylethyl)-siloxane polymers were prepared by the hydrosilylation of vinylferrocene with the methylhydrosiloxane homopolymer or the methylhydrosiloxane-dimethylsiloxane copolymers (m n ratios of 1 1, 1 2, and 1 7.5 see Figure 1) in the presence of chloroplatinic acid as a catalyst. The methyl(9-ferrocenylnonyl)siloxane-dimethylsiloxane (1 2) copolymer was prepared via hydrosilylation of 9-ferrocenyl-l-nonene with the methylhydrosiloxane-dimethylsiloxane (1 2) copolymer. The molecular weight range of these ferrocene-modified siloxane polymers is approximately 5,000-10,000. Purification of the polymers was achieved by reprecipitation from chloroform solution, via dropwise... 

Instead of adding two hydrogen atoms to an alkynyl silane we could add H and SiMe3 to a simple alkyne by hydrosilylation (addition of hydrogen and silicon). This is a cis addition process catalysed by transition metals and leads to a tram (E-) vinyl silane. One of the best catalysts is chloroplatinic acid (H2PtCl6) as in this formation of the E-vinyl silane from phenylacetylene. In this case photochemical isomerization to the Z-isomer makes both available. Other than the need for catalysis, this reaction should remind you of the hydroboration reactions earlier in the chapter. The silicon atom is the electrophilic end of the Si-H bond and is transferred to the less substituted end of the alkyne. 

Methyl-( -ferrocenylethyl)- and methyl-[ -(r,3 -dimethylferrocenyl)ethyl]siloxane polymers 53 and 54, respectively were prepared by the hydrosilylation of vinyl-ferrocene and l,T-dimethylferrocene-3-vinylferrocene with methyl hydrosiloxane (molecular weight was originally reported to be 2270) or methylhydrosiloxane-dimethylsiloxane copolymer (molecular weight was originally reported to be 2000 — 2100) in the presence of chloroplatinic acid as a catalyst. The synthetic route is given in Seheme 10-25 [62], The reaction was monitored by IR spectroscopy until the complete disappearance of the Si-H absorption at 2161 cm". ... 

At 60°, chloroplatinic acid has been used to catalyze the hydrosilylation of butenes and the following activation energies were obtained butene-1 (1.40 kcal/mole), butene-2 (16.0 kcal/mole), and isobutene (32.0 kcal/ mole) 274). 

Among the many available procedures for preparing alkenylsilanes are hydrosilylation of alkynes and partial reduction of alkynylsilanes. Hydrosilylation of 1-alkynes with triethylsilane in the presence of catalytic chloroplatinic acid results in regioselective... 

This mechanism (Scheme 2), originally derived from studies of chloroplatinic acid as a precursor (Pt catalyst), presents an conventional oxidative addition-reductive elimination steps to explain the hydrosilylation. The oxidative addition of trisubstituted silanes, HSiR3 to a metal alkene complex configuration (usually... 

Early studies of the supported metal complexes utilized as hydrosilylation catalysts focused on the immobilization of H2PtCl6 on ion exchangers. Chloroplatinic acid and other Pt complexes have been used as efficient precursors of the catalysts anchored to silica or organic materials for the hydrosilylation of 1-alkenes, styrene, allyl derivatives, and acetylene [2, 84-87]. 

In the patent specification [147] there data on the chemical attachment to hydridesilica surface in the presence of the Reney nickel, chloroplatinic acid or metallic platinum deposited on activated carbon as a catalyst of the following unsaturated functional compounds divinylbenzene, ethylene glycol diacrylate, acetylene, allyl alcohol, allyl glycidyl ether, allyl isocyanate, acrylic acid. The chemical reactions result in the transformation of Si-H bonds of hydridesilica surface into Si-C bonds. Such transformations may be also classified as processes of solid-phase catalytic hydrosilylation of functional olefins. 

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