Benzene surface coordination chemistry

Toluene surface coordination chemistry was quite different from that of benzene. Toluene chemisorption on all the clean surfaces was thermally irreversible. In addition, toluene was not displaced from these surfaces by trimethylphosphine nor by any other potentially strong field ligand examined to date, e.g., carbon monoxide or methyl isocyanide. In the thermal decomposition of toluene on these surfaces (attempted thermal desorption experiments), there were two thermal desorption maxima for H2 (or D2 from perdeuterotoluene) with the exception of the Ni(110) surface. This is illustrated in Figure 6 for Ni(lll)-C7Dg. 

The stepped nickel 9(lll)x(lll) and stepped-kinked Ni 7(lll)x(310) surfaces displayed a benzene coordination chemistry that was quantitatively and qualitatively identical with that of the Ni(lll) surface except that not all the benzene was displaced by trimethylphosphine indicating that either a small percentage ( 10%) of the benzene on these surfaces either was present in different environments or was dissociatively (9) chemisorbed see later discussion of stereochemistry. Benzene chemisorption behavior on Ni(110) was similar to that on Ni(lll) except that the thermal desorption maximum was lower, vl00°C, and that trimethylphosphine did not quantitatively displace benzene from the Ni(110)-C H surface. In these experiments, no H-D exchange was observed with CgHs + C D mixtures. 

Stereochemical Features of Benzene and Toluene Coordination Chemistry. Benzene forms an ordered chemisorption state on the flat Ni(lll) and Ni(100) surfaces at 20°C with unit cells of (2/3x2/3)R 30° and c(4x4), respectively (13). The symmetry data do not fix the registry of the benzene with respect to the metal atoms nor the orientation of the ring plane to the surface plane. However, basic coordination principles would suggest that the benzene ring plane should be parallel to the surface plane. In Figures 8 and 9, possible registries of the benzene with respect... 

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