On the Role of Aromaticity in Bonding Hydrocarbons to Metal Surfaces
The stable bonding configurations adopted by cyclic C5 and C6 hydrocarbons on Os(0001), Ir(111) and Pt(111) surfaces is discussed in terms of the energetics of competing metal-carbon σ-bonding and 6-electron aromatic π-bonding. Previous work which Pt(111) has shown that these are the adsorbed cyclopentadienyl and benzene respectively which are both π-bondcd in a manner which retains a significant level of 6-clectron aromatic stabilisation. New work on Ir(111) is presented to show that while benzene adsorbs in a stable π-configuration, the stable species arising from the thermal evolution of both c-C5H6 and c-C5H8 adsorption is an adsorbed c-C5H3; the bonding of which is dominated by carbon-iridium σ-coordination. Less stable adsorbed cyclopenladienyl and c-C5H6 species have been identified as intermediates in the thermal evolution of c-C5H6 and c-C5H8 respectively, on Ir(111). The stable adsorbed c-C5H3 species appears to be the analogue of a recently reported stable c-C6H4 species derived benzene adsorption on Os(000l). The sequence of stability of these adsorbed species is qualitatively correlated with the DRE of the aromatics and the strength of carbon-metal σ-bonding.
KeywordsChromium Benzene Hydrocarbon Alkane Acetylene
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