Hydroosmiation of Allenes and Reductive Elimination of Olefin in Unsaturated Osmium(IV) Polyhydrides: Hydride versus Chloride

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.

Syntheses, structural characterisation and electronic structures of ferrocenyl-osmafuran heterobinuclear organometallic complexes

The electron transfer through the backbone of metallafurans was studied by spectroelectrochemistry and theoretical calculation.

Aromatic Osmacyclopropenefuran Bicycles and Their Relevance for the Metal-Mediated Hydration of Functionalized Allenes

The aromatic osmacyclopropenefuran bicycles [OsTp{κ³ -C¹ ,C² ,O-(C¹ H₂ C² CHC(OEt)O)}(Pⁱ Pr₃ )]BF₄ (Tp=hydridotris(1-pyrazolyl)borate) and [OsH{κ³ -C¹ ,C² ,O-(C¹ H₂ C² CHC(OEt)O)}(CO)(Pⁱ Pr₃ )₂ ]BF₄ , with the metal fragment in a common vertex between the fused three- and five-membered rings, have been prepared via the π-allene intermediates [OsTp(η² -CH₂ =CCHCO₂ Et)(OCMe₂ )(Pⁱ Pr₃ )]BF₄ and [OsH(η² -CH₂ =CCHCO₂ Et)(CO)(OH₂ )(Pⁱ Pr₃ )₂ ]BF₄ , and their aromaticity analyzed by DFT calculations. The bicycle containing the [OsH(CO)(Pⁱ Pr₃ )₂ ]⁺ metal fragment is a key intermediate in the [OsH(CO)(OH₂ )₂ (Pⁱ Pr₃ )₂ ]BF₄ -catalyzed regioselective anti-Markovnikov hydration of ethyl buta-2,3-dienoate to ethyl 4-hydroxycrotonate.