As a fundamental chemical property, aromaticity guides the synthesis of novel structures and materials. Replacing the carbon moieties of aromatic hydrocarbons with transition metal fragments is a promising strategy to synthesize intriguing organometallic counterparts with a similar aromaticity to their organic parents. However, since antiaromaticity will endow compound instability, it is a great challenge to obtain an antiaromatic organometallic counterpart based on such transition metal replacement in aromatic hydrocarbons.
Osmapentalyne and osmapentalene complexes, now termed as carbolong species, have attracted considerable attention due to their novel structures, reactivities, chelating properties as well as Möbius and adaptive aromaticity. On the other hand, boron monofluoride (BF), a 10-electron diatomic molecule isoelectronic to carbon monoxide (CO), is unstable below 1800°C in the gas phase, and preparation of its metal complex is particularly challenging.
Benzene, the prototype of aromatics, has six equivalent C‐C bonds (1.397 Å), which are intermediate between a C‐C double bond and a C‐C single bond. For over 80 years, chemists have spent much effort on freezing a localized structure to obtain a distorted bond‐length alternating benzene ring in the ground state, leading to various localized trisannelated benzene rings. However, most of the central benzene rings are still aromatic or nonaromatic. Here we report an antiaromatic benzene ring caused by hyperconjugation.
Olefin metathesis is a fundamental organic reaction of great importance that led to the 2005 Nobel Prize in Chemistry. As a variation of olefin–olefin metathesis, carbonyl–olefin metathesis (COM) is less developed, but still significant progress has been made recently. However, how the aromaticity affects the reaction mechanisms remains unclear. Here we perform density functional theory calculations on iron(III) catalyzed COM in 2,5- and 3,5-hexadienals.
Fluorine is the most electronegative element in the periodic table. Thus, activation of the carbon–fluorine (C−F) bond, the strongest single bond to carbon, has attracted considerable interest from both experimentalists and theoreticians. In comparison with numerous approaches to activate C−F bonds, the aromaticity‐promoted method is less developed. Herein, we demonstrate that the C−F bond activation could be achieved by a facile tautomerization, benefitting from aromaticity, which can stabilize both the transition states and products.
Transition-metal-containing metallaaromatics have attracted considerable interest from both experimental and computational chemists because they can display properties of both organometallic compounds and aromatic organic compounds. In general, the transition metal in a metallabicycle prefers a nonbridged position to the bridgehead one because of the larger ring strain caused by the rigidity in the bridgehead position, as exemplified by metallanaphthalene and metallanaphthalyne.
Polycyclic complexes containing a bridgehead transition metal are interesting species because the transition metal is shared by all the rings simultaneously. In this study, we present a novel osmium–bridgehead system with three fused five-membered rings. This novel framework can be viewed as a 10-atom carbon chain coordinating to the osmium center. In sharp contrast to the nonplanar organic analogue, this unique metallacycle exhibits good planarity, which was unambiguously verified by means of X-ray diffraction.
As one of the most important chemical reactions, SN2 reactions play a central role in both synthetic chemistry and the development of mechanistic paradigms. Most of the previous attention has centered on substitution at carbon, whereas displacement at nitrogen is clearly less studied and less understood. The SN2@N reactions have enormous synthetic potential, especially in heterocyclic chemistry, which is a cornerstone of medicinal chemistry, and has been receiving increasing attention, both experimentally and computationally.
Density functional theory (DFT) calculations were carried out to investigate the stability and aromaticity of metallapentalocyclobutadienes. The results reveal unexpected higher stabilisation achieved with a 3d ruthenium fragment compared to the 4d osmium counterpart. Moreover, direct 1–3 metal–carbon bonding in the metallabutadiene unit of these two complexes is negligible.