Hydrogenolysis, cyclopropane

In contrast to propane hydrogenolysis, the Arrhenius plots for cyclopropane hydrogenolysis on both surfaces exhibit no deviations from linearity over the entire temperature range studied, and the reaction orders in both hydrogen and cyclopropane are essentially zero". These results have... 

Comparison of Initial Specific Rate Data for the Cyclopropane Hydrogenolysis on Platinum Catalysts... 

In addition, the same studies that were carried out on the Pt(lll) crystal face result in reaction rates identical to those found on stepped crystal surfaces of platinum. These observations support the contention that well-defined crystal surfaces can be excellent models for polycrystalline supported metal catalysts. It also tends to verify Boudart s hypothesis that cyclopropane hydrogenolysis is an example of a structure-insensitive reaction. The initial specific reaction rates, which were reproducible.within 10%, are within a factor of two identical to published values for this reaction on highly dispersed platinum catalysts. The activation energies that were observed for this reaction, in addition to the turnover number, are similar enough on the various platinum surfaces so that we may call the agreement excellent. 

Fig. 20.4 A cyclopropane hydrogenolysis mechanism based on the Horiuti-Polanyi alkene hydrogenation mechanism.

It is clear, then, that the prediction of the product stereochemistry from a cyclopropane hydrogenolysis is not straightforward. In some cases such as the cleavage of the phenyl bicycloheptane, 16 (Eqn. 20.8), the product stereochemistry was that expected if the simple mechanism depicted in Fig. 20.4 were operational. In other cases it appeared that an olefmic intermediate may be formed and that the product resulted from the hydrogenation of that intermediate. There are also some instances in which neither explanation seems to apply. 

CYCLOPROPANE HYDROGENOLYSiS ON SUPPORTED Pd CATALYSTS. THE ROLE OF THE HYDRIDE AiND VARIABLES THAT AFFECT ITS FORMATION... 

TABLE 7.4. Kinetic Parameters for Cyclopropane Hydrogenolysis Over Metal Catalysts... 

A geminal dimethyl group is found in a wide variety of natural products, particularly in terpenoids. Hydrogenolysis of 1,1-disubstituted cyclopropanes provides an efficient way to construct such a unit [41]. For example, the geminal dimethyl group of ( )-hirsutene was furnished through a cyclopropanation-hydrogenolysis sequence from the exo-methylene compound 63 (Scheme 8.11) [42,43]. 

Shibasaki et al. employed the cyclopropanation-hydrogenolysis sequence in the enantioselective total synthesis of (-)--capnellene (Scheme 8.12) [44,45]. 

Figure 6, (a) Qualitative discrimination among poisoning models (26) (b) results of interpretation of deactivation data for cyclopropane hydrogenolysis on supported Ft... 

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