Forming chemisorbed single-molecule junctions through loss of stable carbocations

Recent studies have found that “chemically inert” gold surfaces may drive S-C(sp3) 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, and perhaps surprisingly, in non-polar solvents. We further show that a greater proportion of chemisorbed bonds are formed when R = -CPh3 or -C7H7 than when R = -tBu, consistent with the relative stability of [tBu]+ < [CPh3]+ ~ [C7H7]+ 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 heterogenous catalysis and critical to the stability and function of molecular junctions and monolayers.