Forming Chemisorbed Single-Molecule Junctions through Loss of Stable Carbocations

High Resolution Image Download MS PowerPoint Slide Recent studies have found that “chemically inert” gold surfaces may drive S–C( sp 3 ) bond cleavage reactions in thioether (−SR) linker groups, providing access to single-molecule junctions with chemisorbed Au–S contacts following the elimination of R + . Here, we demonstrate that such transformations occur more readily at elevated temperatures, rough surfaces, and in nonpolar solvents. We further show that a greater proportion of chemisorbed bonds are formed when R = −CPh 3 or −C 7 H 7 than when R = − t Bu, consistent with the relative stability of [ t Bu] + < [CPh 3 ] + ∼ [C 7 H 7 ] + carbocations. Our contact chemistry assignments are supported by first-principles transmission calculations, and we apply potential energy calculations to expose the relatively small influence of applied external electric fields on this bond breaking process. Together, this work provides a deeper understanding of reactivity at metal surfaces, of broad relevance to heterogeneous catalysis and critical to the stability and function of molecular junctions and monolayers.