Platinum catalysts redistribution

Another example of the data provided by our approach is shown in Fig. 4, which tracks the platinum-catalyzed redistribution of two silanes [16], one charge-tagged with a phosphonium group. This demonstrates the ability of the technique to monitor air-sensitive reactions in non-routine solvents in this case, fluorobenzene. The temperature of the reaction was increased from room temperature to reflux at 20 min the catalyst used was Karstedt s catalyst, Pt[(H2C = CHMe2Si)20]2(Fig.5). 

We have obtained oligomeric silanes from Eg.l but we have decided not to focus our initial studies on this route because of the inherent complexities. There are several possible platinum catalyst precursors present in Eg.l the platinum-silicon 4HR, the starting material (Et3P)2PtCl2, and finely divided platinum (colloids). Preliminary studies of these latter two catalyst precursors with PhSiH3 indicate that both are considerably slower than any platinum-silicon 4MR (see below) and both give primarily redistribution products. ... 

The redistribution reaction in lead compounds is straightforward and there are no appreciable side reactions. It is normally carried out commercially in the liquid phase at substantially room temperature. However, a catalyst is required to effect the reaction with lead compounds. A number of catalysts have been patented, but the exact procedure as practiced commercially has never been revealed. Among the effective catalysts are activated alumina and other activated metal oxides, triethyllead chloride, triethyllead iodide, phosphorus trichloride, arsenic trichloride, bismuth trichloride, iron(III)chloride, zirconium(IV)-chloride, tin(IV)chloride, zinc chloride, zinc fluoride, mercury(II)chloride, boron trifluoride, aluminum chloride, aluminum bromide, dimethyl-aluminum chloride, and platinum(IV)chloride 43,70-72,79,80,97,117, 131,31s) A separate catalyst compound is not required for the exchange between R.jPb and R3PbX compounds however, this type of uncatalyzed exchange is rather slow. Again, the products are practically a random mixture. 

Difficulties (41, 42) associated with the use of pentamethyldisilane in hydrosilations catalyzed by usual metal complex catalysts led Yamamoto et al. to study the interaction of penta- and tetramethyldisilanes with transition metal complexes (43). Bis(phosphine)platinum chlorides effectively catalyzed the redistribution in Eq. (66) (R = Me, H). Yamamoto et al. 

Recently, a new class of platinum silyl complexes was reported (89-91). The complexes of type 49, formed from LPtfQH (L = bulky phosphine) and trialkylsilanes, are extremely efficient hydrosilation catalysts. Upon heating, 49 is converted into 50 via an ill-defined a-elimination process. In all examples of redistributions, the presence of at least one hydro-... 

The parameters that affect the degradation of supported platinum and palladium automotive exhaust catalysts are investigated. The study includes the effects of temperature, poison concentration, and hed volume on the lifetime of the catalyst. Thermal damage primarily affects noble metal surface area. Measurements of specific metal area and catalytic activity reveal that supported palladium is more thermally stable than platinum. On the other hand, platinum is more resistant to poisoning than palladium. Electron microprobe examinations of poisoned catalyst pellets reveal that the contaminants accumulate almost exclusively near the skin of the pellet as lead sulfate and lead phosphate. It is possible to regenerate these poisoned catalysts by redistributing the contaminants throughout the pellet. 

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