In contrast to the many methods of selectively coupling olefins, few protocols catenate saturated hydrocarbons in a predictable manner. We report here the highly selective carbon-hydrogen (C-H) activation and subsequent dehydrogenative C-C coupling reaction of long-chain (>C(20)) linear alkanes on an anisotropic gold(110) surface, which undergoes an appropriate reconstruction by adsorption of the molecules and subsequent mild annealing, resulting in nanometer-sized channels (1.22 nanometers in width). Owing to the orientational constraint of the reactant molecules in these one-dimensional channels, the reaction takes place exclusively at specific sites (terminal CH(3) or penultimate CH(2) groups) in the chains at intermediate temperatures (420 to 470 kelvin) and selects for aliphatic over aromatic C-H activation.

No abstract

We report on a bottom-up approach of the selective and precise growth of subnanometer wide straight and chevron-type armchair nanoribbons (GNRs) on a stepped Au(788) surface using different specific molecular precursors. This process creates spatially well-aligned GNRs, as characterized by STM. High-resolution direct and inverse photoemission spectroscopy of occupied and unoccupied states allows the determination of the energetic position and momentum dispersion of electronic states revealing the existence of band gaps of several electron volts for straight 7-armchair, 13-armchair, and chevron-type GNRs in the electronic structure.

The homocoupling of alkynes at metal surfaces, which was disclosed recently, is a promising reaction for efficient construction of conjugated nanostructures at metal surfaces. However, the role of the metal substrate as well as the mechanistic course of this process have not been investigated. The metal surface could act cooperatively (a) for two-dimensional confinement to properly orient the organic reactant and (b) also as an active mediator in the C−C bond-forming reaction. Herein we report covalent coupling of the dimers of 1,4-diethynylbenzene at various metal surfaces. The model reaction was investigated experimentally by STM and also by theoretical DFT calculations. Detailed statistical analysis and the theoretical results strongly support the involvement of the metal surface in the C−C bond-forming process. On the basis of these investigations, a model with two possible reaction pathways is suggested to describe the process: C−C coupling via direct CH activation and C−C coupling via alkynyl activation by π-complex formation.