Cyclopropane over nickel

Dechlorination of 7,7-dichloronorcarane (7,7-dichlorobicyclo[4.1.0]heptane) (78) with Raney Ni is accompanied by the rupture of the cyclopropane ring to give methyl-cyclohexane.209 Isogai et al. studied in details the dehalogenation products of 78 over nickel catalysts in methanol in the absence or presence of potassium hydroxide under ordinary conditions (eq. 13.115).210... 

In Fig. 10, curves 1 and 3 represent the hydrogenation of cyclopropane over Pt. The shapes are similar, but curve 2, for nickel, shows a maximum TOF at a d of about 1.2 nm, the lowest value used for the platinum data. 

Tn recent years ultrahigh vacuum methods have been applied to cata-lytic studies on initially clean metal surfaces having low surface area. In several instances (the hydrogenolysis of cyclopropane over platinum (I) and the catalytic methanation reaction over rhodium (2) and nickel (3)) a link between ultrahigh vacuum methods and conventional catalytic measurements was established. That is, specific reaction rates over low area cm ) catalyst samples agreed with specific reaction... 

The above described experiments over atomically clean single crystal catalysts have been extended to studies of the kinetics of various catalytic reactions over chemically modified catalysts. Examples are recent studies Into the nature of poisoning by sulfur of the catalytic activity of nickel, ruthenium, and rhodium toward methana-tlon of CO (11,12) and CO2 (15). ethane (12) and cyclopropane (20) hydrogenolysls, and ethylene hydrogenation (21). 

Phenyl, vinyl or carbonyl substituted cyclopropanes are more easily hydrogenolyzed than are the alkyl substituted species. Such compounds are commonly cleaved over palladium catalysts at room temperature and atmospheric pressure. Hydrogenolyses run over platinum, rhodium or nickel catalysts frequently result in the saturation of the double bond, the benzene ring or the carbonyl group with the cyclopropane ring remaining intact or cleaved to only a slight extent. 20 As illustrated in Fig. 20.22 the bond broken in the... 

It appears that this facile bond cleavage is the result of an assisted adsorption of the cyclopropane ring promoted by the adsorption of the unsaturated species on the catalyst surface adjacent to the hydrogenolysis active site as depicted in Fig. 20.3. Unsaturated substituents are not the only species that can assist in the adsorption of the cyclopropane ring. Cyclopropyl amines are hydrogenolyzed over palladium or Raney nickel at 80°C and 50 atmospheres by breaking one of the bonds adjacent to the amine group.26,27... 

Halogens on a cyclopropane ring can be removed without hydrogenolysis of the ring itself. The selective removal of one bromine from 1,1-dibromo-cyclopropanes occurred over palladium on charcoal or platinum oxide in methanolic potassium hydroxide at room temperature and atmospheric pressure. Complete debromination resulted from the use of Raney nickel under the same conditions (Eqn. 20.56). 31... 

In the presence of CuCl, exo-3-tricyclo[3.2.1.02 4]octene-6-yl-3-hexene-2-oic acid methyl ester (72) is isolated after TLC in 60% yield (Z E = 1.5 1) 67c). This is comparable to the course of the cyclopropanation of norbornadiene with both the Simmons-Smith reagent and diazomethane-CuCl. In both cases the exo-anti route is favored over the exo-syn 63). It is important to notice, that in the above mentioned nickel(O) catalyzed reactions (Eq. 11) hexatriene derivatives have never been observed. 

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