Single-Molecule Resolution of an Organometallic Intermediate in a Surface-Supported Ullmann Coupling Reaction

We have studied the organometallic intermediate of a surface-supported Ullmann coupling reaction from 4, 4 ''-dibromo-p-terphenyl to poly(para-phenylene) by scanning tunneling microscopy/spectroscopy and density functional theory calculations. Our study reveals at a single-molecular level that the intermediate consists of biradical terphenyl (ph)(3) units that are connected by single Cu atoms through C-Cu-C bridges. Upon further increasing the temperature, the neighboring biradical (ph)(3) units are coupled by C-C bonds forming poly(para-phenylene) oligomers while the Cu atoms are released.