Covalent Au-C Contact Formation and C-C Homocoupling Reaction from Organotin Compounds in Single-Molecule Junctions

Formation of new chemical species has been achieved under an electric field by the use of the scanning tunneling microscope break junction technique, yet simultaneous implementation of catalytic reactions both at the organic/metal interface and in the bulk solution remains a challenging task. Herein, we show that n-butyl-substituted organotin-terminated benzene undergoes both an efficient cleavage of the terminal tributyltin group to form a covalent Au-C bond and a homocoupling reaction to yield biphenyl product when subjected to an electric field in the vicinity to Au electrodes. By using ex situ characterization of high-performance liquid chromatography with an UV-vis detector, we demonstrate that the homocoupling reaction can occur with high efficiency under an extremely low tip bias voltage of ∼5 mV. Additionally, we show that the efficiency of the homocoupling reaction varies significantly in different solvents; the choice of the solvent proves to be one of the methods for modulating this reaction. By synthesizing and testing varied molecular backbone structures, we show that an extended biphenyl backbone undergoes homocoupling to form a quarterphenylene backbone, and the C-C coupling reactions are prohibited when additional aurophilic or bulky chemical groups that exhibit a steric blockage are introduced.