Control of surface alkyl catalysis with thiolate monolayers†
Self-assembled monolayers of organic thiolates were used to control the selectivity of parallel reactions of a single alkyl reaction intermediate, resulting in a dramatic decrease in the rate of 1-hexene hydrogenation and a sharp increase in the selectivity of isomerization. Isotope tracing experiments verified the participation of surface H/D in the hydroisomerization reaction on both the coated and uncoated catalysts. These results strongly suggest that surface crowding affects not only the precursor state for olefin hydrogenation, as previously demonstrated, but also the reactivity of the intermediate alkyl species. Furthermore, the hydrogenation rate for internal olefins was reduced to an even greater extent by the monolayer, consistent with steric limitations playing a strong role in the regioselectivity of hydrogenation reactions.