Rooney-Samman mechanism

Muller and Gault proposed (57) an adsorbed cyclopropane-like intermediate (Scheme VIIIB). The McKervey-Rooney-Samman mechanism involves a n complex like adsorption of two carbon atoms (88) (Scheme Vine). 

A monotonic decrease of benzene yield from methylpentanes is observed as a function of the hydrogen pressure over both metals (27a, 91a). The intermediates of bond shift type dehydroisomerization are likely to be unsaturated. This points to the McKervey-Rooney-Samman mechanism (55). This pathway obviously has a higher energy barrier over platinum than over palladium as compared with the aromatization of -hexane. This is reflected also by the similar aromatization selectivity (iS r) values of -hexane and methylpentanes over palladium (Table IV). 

The facile isomerization of strained bridged molecules was inconsistent with the involvement of triadsorbed species 15. Instead, a a-alkyl adsorbed species was proposed. Its further transformation leads to a it-complex-like species (17) with a three-center, two-electron bonding with its simultaneous attachment to the surface152,157 (McKervey-Rooney-Samman mechanism) ... 

Fig. 2. Mechanisms of bond-shift isomerization on metal catalysts, (a) Anderson-Avery mechanism (63). (b) Muller-Gault mechanism for isomerization of neopentane on Pt (64). (c) McKervey-Rooney-Samman mechanism (69). (d) Muller-Gault mechanism of isomerization of isobutane on Pd (64). (e) Clarke-Rooney mechanism (46). (f) Garin-Gault mechanism (65).

Although the Rooney-Samman mechanism nicely explains the peculiarities of the isomerization of caged molecules on platinum and palladium catalysts, its extension to simpler molecules is not completely obvious. As a matter of fact, none of the above mechanisms accounts in its original form for the different behaviors of platinum and palladium in skeletal rearrangements. 

Of the four basic mechanisms, two, the Anderson-Avery mechanism (Scheme 19) and the Garin-Gault mechanism (Scheme 25), should be associated with isomerization and hydrogenolysis two, the Muller-Gault mechanism (Scheme 20) and the Rooney-Samman or the Clarke-Rooney mechanism (Schemes 22 and 28) should promote only isomerization. 

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