RESUMO
carbo-Benzene is an aromatic molecule devised by inserting C2 units within each C-C bond of the benzene molecule. By integrating the corresponding carbo-quinoid core as bridging unit in a π-extended tetrathiafulvalene (exTTF), it is shown that a carbo-benzene ring can be reversibly formed by electrochemical reduction or oxidation. The so-called carbo-exTTF molecule was thus experimentally prepared and studied by UV-visible absorption spectroscopy and cyclic voltammetry, as well as by X-ray crystallography and by scanning tunneling microscopy (STM) on a surface of highly oriented pyrolytic graphite (HOPG). The molecule and its oxidized and reduced forms were subjected to a computational study at the density functional theory (DFT) level, supporting carbo-aromaticity as a driving force for the formation of the dication, radical cation, and radical anion. By allowing co-planarity of the dithiolylidene rings and carbo-quinoidal core, carbo-exTTFs present a promising new class of redox-active systems.
RESUMO
The interest in and use of dual gold catalysts is forever increasing, but little is known of the mechanism for the catalyst transfer and its effect on the continued high turnover frequency. Herein, we present a computational investigation of the mechanism for the final intermolecular catalyst transfer in the synthesis of dibenzopentalene from 1-ethynyl-2-(phenylethynyl)benzene. Three different scenarios have been explored: a single catalyst transfer from the monoaurated product complex, the analogous water mediated single transfer, and a dual catalyst transfer from the diaurated product complex. Transition structures have been found for each step of the three possible pathways, and a stepwise dual catalyst transfer has proven to be the lowest energy pathway. We here describe a three-step transfer of two gold moieties from one dibenzopentalene to one diyne. This process directly gives the σ,π-gold coordinated diyne for the further intramolecular cyclization reaction.
