29 Feb 15:19
by Wun‐Chang Pan,
Carina Mützel,
Soumyajyoti Haldar,
Hendrik Hohmann,
Stefan Heinze,
Jeffrey M. Farrell,
Ronny Thomale,
Matthias Bode,
Frank Würthner,
Jing Qi
A planar diboraperylene diborinic acid B2−Per self-assembles into a chiral kagome supramolecular network on an Ag(111) substrate and is stabilized by hydrogen bonding between BOH subunits of adjacent molecules. The kagome supramolecular network exhibits a dispersionless flat band at ca. 0.33 eV above the Fermi level, which is observed by scanning tunneling microscopy/spectroscopy and further proved by tight-binding model calculations.
Abstract
Replacement of sp2-hybridized carbon in polycyclic aromatic hydrocarbons (PAHs) by boron affords electron-deficient π-scaffolds due to the vacant pz-orbital of three-coordinate boron with the potential for pronounced electronic interactions with electron-rich metal surfaces. Using a diboraperylene diborinic acid derivative as precursor and a controlled on-surface non-covalent synthesis approach, we report on a self-assembled chiral supramolecular kagome network on an Ag(111) surface stabilized by intermolecular hydrogen-bonding interactions at low temperature. Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal a flat band at ca. 0.33 eV above the Fermi level which is localized at the molecule center, in good agreement with tight-binding model calculations of flat bands characteristic for kagome lattices.
06 Jun 16:09
by Jesús Sanjosé-Orduna, Daniel Gallego, Alèria Garcia-Roca, Eddy Martin, Jordi Benet-Buchholz, Monica Helvia Perez-Temprano
Abstract
Despite Cp*CoIII catalysts having emerged as a very attractive alternative to noble transition metals for the construction of heterocyclic scaffolds through C−H activation, the structure of the reactive species remains uncertain. Herein, we report the identification and unambiguous characterization of two long-sought cyclometalated Cp*CoIII complexes that have been proposed as key intermediates in C−H functionalization reactions. The addition of MeCN as a stabilizing ligand plays a crucial role, allowing the access to otherwise highly reactive species. Mechanistic investigations demonstrate the intermediacy of these species in oxidative annulations with alkynes, including the direct observation, under catalytic conditions, of a previously elusive post-migratory insertion seven-membered cobaltacycle.
Cyclic Co complex caught: The first direct observation and full characterization of elusive cobaltacycle species in Cp*CoIII-catalyzed C−H oxidative alkyne annulation is reported. The exceptional ability of MeCN to stabilize otherwise highly reactive intermediates has paved the way to uncover previously inaccessible mechanistic features of these transformations.
