Catalysts Karstedt

Under the same reaction conditions traditional catalysts, such as H2PtCl6 in PrOH (Speier catalyst) and Pt2(divinyltetramethyldisiloxane)3 (Karstedt Catalyst) are completely inactive. 

Recently, Kolel-Veetil and Keller have modified this system to produce elastomeric networked polymers. The ambient-condition hydrosilation reactions between monomeric vinyl- or ethynyl-terminated carboranylenesiloxane and three different monomeric branched siloxane cross-linkers in hexane yielding these systems were catalyzed by the Karstedt catalyst.134 The reactions involving the vinyl-carboranylenesiloxane were reported to produce a set of completely hydrosilated networked polymers (105) (Fig. 65). In the case of the ethynyl monomer, the reactions were carried out at two different ratios, yielding a partially (106) and a com-... 

Figure 65 The hydrosilated networked polymers 105, 106, and 107 obtained from Karstedt catalyst-catalyzed hydrosilations involving monomeric vinyl- or ethynyl-terminated carboranylenesiloxane and a branched siloxane cross-linker in hexane. The Si-bound methyl groups have been omitted for clarity. (Adapted from ref. 134.)...

Kinetic experiments Either PMHS or HMS-301 reacted in toluene at 60 °C with peracetylated monoaUyl P-cyclodextrin in stoichiometric amounts with respect to Si-H. The concentration of P-cyclodextrin and Si-H was 0.032mol/L. The concentration of Karstedt catalyst was 20ppm of platinum content. Ahquots of the reaction medium were coUected at different times and the solutions were directly analyzed by IR spectroscopy in a hquid cell. The absorbance of the Si-H band at 2160cm was normalized to the absorbance of the C=0 stretching band of the ester at 1740cm . The decrease of the Si-H band was plotted as a function of time. The conversion is the complement to 100%. 

It has been shown that the kinetics of hydrosilylation of a-olefins (1-decene) by PMHS was first order with respect to the concentrations of Si-H and Karstedt catalyst [33], The first order kinetics was observed for the HMS-301 copolymer in the present instance since the plot of... 

Although the platinum-catalyzed reactions are not as practical as palladium used for the same purpose, several types of unique discoveries still are noteworthy. Besides electrophihc C-H activation, the platinum complexes are efficient catalysts for hydrosilation see Hydrosilation Catalysis) that is important to silicon polymer industry. Platinum carbene catalysts are prepared from Karstedt catalyst (9) and imidazolium salts. The trials of model hydrosilylation reactions show very high yields of regioselective products (<1% impurity) with remarkable TON (see Turnover) (<30ppm catalyst load) (Scheme 81). ... 

With the purpose of evaluating the correctness of the chosen method, we compared Zeise salt calculation results with literature data of X-ray diffraction analysis. A simplified Karstedt catalyst... 

The state-of-the-art silicone systems used in label stock application are normally solventless and thermal curing. Base polymers for these systems are vinyl-functionalized polydimethylsiloxanes having viscosities of around 200 - 600 mPa.s. Cross-linkers normally are hydride-functionalized polydimethylsiloxanes with a viscosity of around 25 mPa.s. These two components are cross-linked by a platinum catalyst, which can be the Karstedt catalyst. Additionally an inhibitor is added to the silicone mixture to prevent curing before it is applied on the substrate. These inhibitors ate... 

The number of examples of highly selective dehydrogenative silylation is still limited. The most convincing examples are Ru3(CO)i2- and Fe3(CO)i2-cata-lyzed reactions of styrene [106, 114] and vinylsilane [115] with HSiEts, RuH2(H2)2PCy3)2-catalyzed reaction of ethylene with HSiEt3 [116], and cationic rhodium complex-catalyzed dehydrogenative silylation, e.g., [117], as well as the nickel equivalent of the Karstedt catalyst [105]. 

Further investigations showed that other platinum catalysts can also be used with high yields, for instance, platinumdichloride and the Karstedt catalyst, a plati-num(0)-divinyltetramethyldisiloxane complex [86], Oleochemicals with internal double bonds were also found to be reactive in platinum-catalyzed hydrosilylations [87] methyl linolenate (with two internal double bonds) reacted with chlorohydrosi-lanes giving yields up to 83%. The hydrosilylation of methyl linolenate (with three internal double bonds) gave a mixture of regioisomeric 1 1- and 2 1-hydrosilylation adducts, however, only in total yields of 40%. 

---