Aromaticity generally describes a cyclic structure composed of sp2-hybridized carbon or hetero atoms with remarkable stability and unique reactivity. The doping of even one sp3-hybridized atom often damages the aromaticity due to the interrupted electron conjugation. Here we demonstrate the occurrence of an extended hyperconjugative aromaticity (EHA) in a metalated indole ring which contains two gem-diaurated tetrahedral carbon atoms. The EHA-involved penta-aurated indolium shows extended electron conjugation because of dual hyperconjugation.
Besides its mathematical importance, the Möbius topology (twisted, single-sided strip) is intriguing at the molecular level, as it features structural elegance and distinct properties; however, it carries synthetic challenges. Although some Möbius-type molecules have been isolated by synthetic chemists accompanied by extensive computational studies, the design, preparation, and characterization of stable Möbius-conjugated molecules remain a nontrivial task to date, let alone that of molecular Möbius strips assembling into more complex topologies.
Although the formation of metal–carbon σ bonds is a fundamental principle in organometallic chemistry, the direct bonding of one organic molecule with one metal center to generate more than two metal–carbon σ bonds remains a challenge. Herein, we report an aromaticity-driven method whereby multiyne chains are used to construct three metal–carbon σ bonds in a one-pot reaction under mild conditions. In this method, multiyne chains act as ligand precursors capable of chelating an osmium center to yield planar metallapolycycles, which exhibit aromaticity and good stability.
Polymetalated aromatic compounds are particularly challenging synthetic goals because of the limited thermodynamic stability of polyanionic species arising from strong electrostatic repulsion between adjacent carbanionic sites. Here we describe a facile synthesis of two polyaurated complexes including a tetra-aurated indole and an octa-aurated benzodipyrrole. The imido trinuclear gold(I) moiety exhibits nucleophilicity and undergoes an intramolecular attack on a gold(I)-activated ethynyl to generate polyanionic heteroaryl species.
Aromaticity, a highly stabilizing feature of molecules with delocalized electrons in closed circuits, is generally restricted to ‘Hückel’ systems with 4n+2 mobile electrons. Although the Möbius concept extends the principle of aromaticity to 4n mobile electron species, the rare known examples have complex, twisted topologies whose extension is unlikely. Here we report the realization of osmapentalenes, the first planar Möbius aromatic complexes with 16 and 18 valence electron transition metals.