Intrinsic Reactivity of Magnesium Surfaces toward Methyl Bromide

The chemisorption and subsequent decomposition of methyl bromide on a Mg(0001) single-crystal surface is found to lead cleanly to the formation of a surface bromide and gas-phase hydrocarbon products including ethane. Stable surface alkyls are not observed even at temperatures as low as -150°C. Co-adsorbed dimethyl ether does not perturb this reactivity pattern. The formation of either a thin surface bromide or a surface oxide passivates this material to further reaction under UHV conditions. The implications of these results with respect to the mechanisms of carbon-halogen bond cleavage on magnesium and the formation of Grignard reagents are discussed.