Homocoupling of terminal alkynes on calcite (10.4)

Abstract

On-surface synthesis has been identified as highly versatile strategy to prepare molecular structures on surfaces with single-atom precision. Inspired by the classical Glaser coupling, homocoupling of terminal alkynes has attracted great attention for on-surface synthesis. This coupling is known for providing a rigid and linear linkage, which is highly interesting for the synthesis of molecular wires. For molecular wire formation, non-conductive substrates are needed for electronic decoupling. So far, however, coupling of terminal alkynes has not been performed on a bulk insulator surface. Here, we present an atomic force microscopy study, indicating that 4,4″-diethynyl-[1,1′:4′,1″-terphenyl]-2′,5′-dicarboxylic acid undergoes dimerization by homocoupling of the terminal alkyne moiety on the (10.4) surface of the bulk insulator calcite. Our results suggest that upon low-temperature deposition monomers are found on the surface, which can be dimerized by annealing the sample. When following a high-temperature deposition protocol, the dimerization appears to happen already in the crucible and dimers are deposited directly. Our work, thus, indicates that homocoupling of terminal alkynes can also be performed on a non-metallic surface, in line with a recent theoretical study that suggest the role of the surface being the constrain of the chemical motion rather than contributing in terms of electron transfer.