Platinum s. a. Chloroplatinic

Pivalic acid as reagent 13, 700 Platinate s. Sodium platinate Platinum (s. a. Chloroplatinic acid)... 

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. 

Crude platinum from South America was also a source of rhodium. It is, however, not known whether it was the same sample in which Wollaston had discovered palladium. Having dissolved a certain amount of crude platinum in aqua regia and neutralized the excess of the acid with alkali, Wollaston first added an ammonium salt to precipitate platinum as ammonium chloroplatinate. Mercury cyanide was added to the remaining solution (here the experience in separating palladium proved useful) and palladium cyanide precipitated. Then Wollaston removed the excess of mercury cyanide from the solution and evaporated it to dryness a beautiful dark-red precipitate was formed which, in the scientist s opinion, was double chloride of sodium and of the new metal. 

A proposed mechanism [9] for the hydrosilylation of olefins catalyzed by platinum(II) complexes (chloroplatinic acid is thought to be reduced to a plati-num(II) species in the early stages of the catalytic reaction) is similar to that for the rhodium(I) complex-catalyzed hydrogenation of olefins, which was advanced mostly by Wilkinson and his co-workers [10]. Besides the Speier s catalyst, it has been shown that tertiary phosphine complexes of nickel [11], palladium [12], platinum [13], and rhodium [14] are also effective as catalysts, and homogeneous catalysis by these Group VIII transition metal complexes is our present concern. In addition, as we will see later, hydrosilanes with chlorine, alkyl or aryl substituents on silicon show their characteristic reactivities in the metal complex-catalyzed hydrosilylation. Therefore, it seems appropriate to summarize here briefly recent advances in elucidation of the catalysis by metal complexes, including activation of silicon-hydrogen bonds. 

Platinum on carbon did almost exactly the same thing but required a temperature of about 100°C to do so. With excess acetylene, only III formed. With tcrt-butylacetylene no II formed, probably because of steric hindrance, but I and III formed readily. 3-Hexyne reacted more slowly, required heat with chloroplatinic acid, and formed exclusively c/s-3-di-chlorosilyl-3-hexene. Trichlorosilane with platinum on carbon also added (57) to 1-alkynes or to phenylacetylene exclusively by cis addition to give only trans adducts. Later works (55) indicate that chloroplatinic acid and other soluble catalysts also give exclusively cis addition with a wide variety of Si—H compounds. 

The activity of the platinum-carbon catalyst is of prime concern in obtaining maximum yields of product in a minimum of time. It was found by Mehltretter and his associates14 that a modification of Trenner s procedure02 consistently produced an effective catalyst. In the modified method, platinum from an aqueous solution of chloroplatinic acid was deposited on acid-washed Darco G-60 brand of activated carbon by means of formaldehyde and sodium carbonate. To maintain high activ-... 

The TPD apparatus consisted of a stainless steel flow system connected to a thermal conductivity cell. Catalyst samples of 0.1 g were placed in one arm of an L-shaped, 6 mm Vycor tube. A dual adsorption bed containing alumina and Oxy-Trap (Alltech) was placed in the other arm to prevent contamination by water and respectively. Frequent regeneration in and He was required. This in-situ adsorption bed was found necessary despite purification traps on all gas lines coming into the flow system. Pulses of 0.25 cc of a 10% mixture of CO in He were injected into the He carrier gas and passed over the pretreated catalyst at room temperature. All runs were programmed heated at a rate of 20 K min . The Pt catalysts, either commercial or laboratory produced, were prepared by the impregnation of chloroplatinic acid on Cyanamid s Aero 1000 alumina, except for two catalysts which were prepared by platinum diamino dinitrite impregnation. 

Platinum bis-S-chlorovinylbis-jSjS jS"- trichlorotrivinylarsine, [(CHCl=CH)3As]jPt(CH=CHCl)si.—This product results from the interaction of a dilute alcoholic solution of chloroplatinic acid and an alcoholic solution of the tertiary arsine. It crystallises from alcohol in very pale yellow needles, and from benzene in pale yellow plates, M.pt. 198° C. with decomposition. 

Most research and industrial syntheses are carried out in the presence of platinum complexes, with H2PtCl6 commonly used as the initial precursor. A solution of this catalyst in isopropanol (1-10%) is referred to as Speier s catalyst [11]. In addition to isopropanol other solvents (alcohols, ketones, aldehydes, ethers, esters, THF, hydrocarbons) have also been used in the preparation of active catalysts from chloroplatinic acid. Since 1957 hundreds of catalysts based on chloroplatinic acid and other d -Pt and d °-Pt° complexes have been reported [1-5]. The Karstedt s type of catalyst obtained by treating hexachloroplatinic acid with divi-nyldisiloxane was discovered in 1973 [33] and has predominated in recent years. This catalyst has the empirical formula Pt2(CH2=CHMe2SiOSiMe2CH=CH2)3. Its structure was reported [34, 35]. 

Chloroplatinic acid, platinum on carbon or alumina, platinum(II) complexes with olefins, and platinum(O) complexes with phosphines have been used for hydrosilylation1,2. Chloroplatinic acid, H2PtCl6-6H20, is by far the most commonly used and efficient catalyst particularly for the hydrosilylation of a variety of olefinic substrates1 4. Chloroplatinic acid is frequently used as a solution in isopropanol and this system is referred to as Speier s catalyst , in recognition of the work of J. L. Speier in the discovery of its usefulness. 

The final choice (Balakrishnan et al., 1982) was a ZSM-S zeolite of silica-alumina ratio 100 1, particle size 0.5 microns, and platinum content 0.1%. This was formulated into extrudates of one-sixteenth inch. Pt impregnation of the calcined extrudate was done by soaking in chloroplatinic acid. The final step following platinum loading was steaming. 

Tetrammineplatinum(II) chloride may be prepared by heating any one of the following with excess aqueous ammonia until a colorless solution results platinum(II) chloride tetrammineplatinum(II) tetrachloroplatinate(II) (Magnus s green salt), [Pt(NH3)4][PtCl4] diamminedi-chloroplatinum, [Pt(NH3)2Cl2] or a solution of tetra-chloroplatinic(II) acid. The present method involves the preparation of pure tetrammineplatinum(II) tetrachloro-platinate(II) and its subsequent reaction with aqueous ammonia. 

Transition-metal-catalyzed hydrosilylation was first reported in the late 1950s with catalysts based on platinum, ruthenium, and iridium chlorides. For industrial applications, chloroplatinic acid (H PtCl nHjO) has been used extensively and is highly active for this process. This catalyst has become known as Speier s catalyst. This catalyst is spectacularly reactive, as indicated by the low catalyst loading for the reaction in Equation 16.17. A Pt(0) complex containing vinylsiloxane ligands (platinum divinyltetramethyl-disiloxane) shown in Figure 16.1 has also been used frequently in industrial settings as a catalyst for hydrosilylation. Tliis catalyst has become known as Karstedt s catalyst. ... 

Early concepts regarding the extremely efficient hydrosilylation catalysis by chloroplatinic acid involved the reduction of the complex to colloidal platinum, which was believed to be the real catalyst. However, the reports by Lewis and co-workers (e.g., (131,132)) have shown that the processes leading to colloid formation can account for the high activity of a hydrosilylation catalyst based on the complexes of Pt(0) with olefins and dienes such as divinyltetramethyldisiloxane (Karstedt s catalyst) and cyclooctadiene. The reactivity order of platinum group... 

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