Disproportionation and coupling reactions of alkyl iodides on a Au(111) surface

An infrared spectroscopic and temperature-programmed desorption study of methyl iodide hydrogenation on Pd()

“…8) shows that this is close to the value on Pd(1 0 0) of 180 K [30]. Comparing with the ethylene desorption temperatures from ethyl species on Ni(1 0 0) (160 K [31]), Pt(1 1 1) (180 K [32]), Rh(1 1 1) (210 K [33]), Fe(1 0 0) (220 K [34]), Cu(1 0 0) (250 K [35]) and Au(1 1 1) (265 K [36]), shows that the trend in reactivity in this case is that this increases in going upwards and to the left in the periodic table. Finally, the rate of b-hydride elimination, which has an activation energy of $10.5 kcal/mol on Pd (1 1 1), is more rapid than the rate of a-hydride elimination which has an activation energy of $13.0 kcal/mol.…”

Thermal chemistry of diiodomethane on Ni(110) surfaces II. Effect of coadsorbed oxygen

“…In contrast, the direct coupling of methylene surface species does not involve any hydrogenation-dehydrogenation steps. Coupling such as this is actually more typical of late transition metals [62], and has been reported for methylene on Cu(1 1 0) [63], Pd(1 0 0) [24], and Rh(1 1 1) [27], and for other alkyls on Cu(1 1 1) [64], Ag(1 1 1) [65], and Au(1 1 1) [66], among others.…”

Surface chemistry of catalysis by gold

“…For C2-C4 iodoalkanes both disproportionation and coupling reactions were possible and occurred in the same temperature range, although their reaction channels were not competitive. Iodoethane was shown to produce C2H4, C2H6 and C4H10 between 260-270 K on both Au(111) (149) and Au(100) (150). However, the yield of ethene and ethane was observed to saturate at a rather low coverage of C2H5I whereas the yield of butane continued to increase until the monolayer was saturated.…”

“…They also observed that the methyl coupling reaction could be blocked by adsorption of trimethylphosphine (TMP). Heating the surface covered with CH3I and TMP, allowed for the observation of methyl radical desorption at 415 K. Bent's group found that higher iodoalkanes were even more reactive than iodomethane on gold single crystals (149,150). For C2-C4 iodoalkanes both disproportionation and coupling reactions were possible and occurred in the same temperature range, although their reaction channels were not competitive.…”