Synthesis and Characterization of an Osmapentalene Derivative Containing a β-Agostic Os···H–C(sp3) Interaction

Synthesis and Characterization of Rhena[10]annulynes

Most of the reported metallacycles were limited to small cyclic complexes that contain six-membered or smaller rings. Larger-membered metallacycles are still rare and mainly focus on the dimetallacycles. Herein, we...

Metallaaromatic Chemistry: History and Development

Since the prediction of the existence of metallabenzenes in 1979, metallaaromatic chemistry has developed rapidly, due to its importance in both experimental and theoretical fields. Now six major types of metallaromatic compounds, metallabenzenes, metallabenzynes, heterometallaaromatics, dianion metalloles, metallapentalenes and metallapentalynes (also termed carbolongs), and spiro metalloles, have been reported and extensively studied. Their parent organic analogues may be aromatic, non-aromatic, or even anti-aromatic. These unique systems not only enrich the large family of aromatics, but they also broaden our understanding and extend the concept of aromaticity. This review provides a comprehensive overview of metallaaromatic chemistry. We have focused on not only the six major classes of metallaaromatics, including the main-group-metal-based metallaaromatics, but also other types, such as metallacyclobutadienes and metallacyclopropenes. The structures, synthetic methods, and reactivities are described, their applications are covered, and the challenges and future prospects of the area are discussed. The criteria commonly used to judge the aromaticity of metallaaromatics are presented.

Synthesis and Characterization of Cyclopropaosmanaphthalenes Containing a Fused σ-Aromatic Metallacyclopropene Unit

Metalla-aromatics are important complexes that show unique properties owing to their highly conjugated systems, which show Hückel or Möbius aromaticity. Recently, several metalla-aromatics showing spiro-aromaticity or σ-aromaticity have been reported. Herein, we report the isolation of the first cyclopropametallanaphthalenes, in which the metallacyclopropene ring shows σ-aromaticity and weak hyperconjugative aromaticity. The reaction of OsCl₂ (PPh₃ )₃ with o-ethynylphenyl alkynes in the presence of PPh₃ followed by protonation with HCl yielded the first cyclopropametallanaphthalenes. The reaction mechanism and the aromaticity were also investigated by density functional theory studies.

Synthesis and characterization of metallapentalenoxazetes by the [2+2] cycloaddition of metallapentalynes with nitrosoarenes

The cycloaddition of metallapentalynes with nitrosoarenes produces metallapentalenoxazetes, in which two unstable frameworks are stabilized with a metal fragment.

Carbolong Chemistry: A Story of Carbon Chain Ligands and Transition Metals

The construction of metal-carbon bonds is one of the most important issues of organometallic chemistry. However, the chelation of polydentate ligands to a metal via several metal-carbon bonds is rare. Metallapentalyne, which can be viewed as a 7-carbon (7C) chain coordinated to a metal via three metal-carbon bonds, was first reported in 2013. Although metallapentalyne contains a metal-carbon triple bond in a five-membered ring (5MR) and the bond angle around the carbyne carbon is only 129.5°, metallapentalyne exhibits excellent stability to air, moisture, and heat. Metallapentalyne possesses the rare planar Möbius aromaticity, which is in sharp contrast to the Hückel antiaromaticity in pentalyne. The metal fragment not only relieves the large ring strain present in pentalyne but also results in the transformation of the antiaromaticity in pentalyne to aromaticity in metallapentalyne. With the extension of the carbon chain from 7 to 12 carbon atoms, a series of novel polycyclic frameworks were constructed via the formation of several metal-carbon bonds. Some interesting phenomena were observed for these complexes. For instance, (1) the carbyne carbon of the 7C framework could react with both nucleophilic and electrophilic reagents, leading to the formation of 16- and 18-electron metallapentalenes; (2) σ aromaticity was first observed in an unsaturated system in the 8C framework; (3) two classical antiaromatic frameworks, cyclobutadiene and pentalene, were simultaneously stabilized in the 9C framework for the first time; (4) three fused 5MRs bridged by a metal are coplanar in the 10C framework; (5) the first [2 + 2 + 2] cycloaddition of a late transition metal carbyne complex with alkynes was realized during the construction of an 11C framework; (6) the largest number of carbon atoms coordinated to a metal atom in the equatorial plane was observed in the 12C framework; and (7) sharing of the transition metal by multiple aromatic units has seldom been observed in the metalla-aromatics. Therefore, the term carbolong chemistry has been used to describe the chemistry of these novel frameworks. More interestingly, carbolong complexes exhibit diverse properties, which could lead to potential future applications. As the discovery and creation of molecular fragments lead to advancements in chemistry, medical science, and materials chemistry, these novel polydentate carbon chain chelates might have important influences in these fields due to their facile synthesis, high stability, and unique properties.