Reactions of Metallacyclopentadiene with Terminal Alkynes: Isolation and Characterization of Metallafulvenallene Complexes

Osmapentalenofurans Constructed by Reacting Os≡C1 of Osmapentalyne with Phenols

Over the past decade, significant research efforts have focused on osmapentalyne, characterized by the more reactive Os≡C7 (Carbon atoms numbered in a clockwise direction on the osmapentalyne skeleton), across areas encompassing electrophilic, nucleophilic, and addition reactions. Nevertheless, the reactivity of osmapentalyne featuring Os≡C1 remains ripe for further exploration. In this investigation, we effectively synthesized a lineage of osmapentalenofurans through the nucleophilic reaction of osmapentalyne incorporating Os≡C1 with phenols. These resulting complexes demonstrate near-infrared luminescence traits in both solid and liquid states. Particularly noteworthy is the osmapentalenofuran derived from tetraphenylethane (TPE) unit, which showcases remarkable aggregation-induced emission (AIE) property in the aggregated state. These osmapentalenofurans are also able to further extend their range of reactions, including reactions with base and isonitrile. This study not only broadens the scope of applications for metal aromatics but also furnishes valuable insights into the realm of specialized functional materials.

Synthesis, structure and aromaticity of metallapyridinium complexes

The first rhena-analogues of pyridinium (cyclopropametalla-2-isoquinolinium complexes) are obtained from o-ethynyl benzonitriles. Structural analysis and DFT calculations confirm their aromatic nature. Compared to rhenapyrylium, rhenapyridinium has a slightly stronger Hückel π-aromaticity, while a chlorine substituent on the rhenapyridinium ring decreases its aromaticity, which is revealed by NICS, EDDB, MCI and ΔBV(ELF_π) analysis.

Direct amidation of metallaaromatics: access to N-functionalized osmapentalynes via a 1,5-bromoamidated intermediate

The direct C–H amidation or imidation of metallaaromatics with N-bromoamides or imides has been achieved under mild conditions and leads to the formation of a family of N-functionalized metallapentalyne derivatives. A unique 1,5-bromoamidated species has been identified, and can be viewed as a σ^H-adduct intermediate in a nucleophilic aromatic substitution. The 1,5-addition of both electrophilic and nucleophilic moieties into the metallaaromatic framework demonstrates a novel pathway in contrast to the typical radical process of arene C–H amidation involving N-haloamide reagents.

The direct C–H amidation of metallapentalyne has been achieved under mild conditions in which key 1,5-bromoamidated intermediates was determined.

Vinylidene, allenylidene, cyclic oxycarbene, and η2-alkyne complexes from reactions of (η5-C5Me5)OsCl(PPh3)2 with alkynes and alkynols

Reactions of Cp*OsCl(PPh3)2 (Cp* = pentamethylcyclopentadienyl) with alkynes and alkynols are described. Treatment of Cp*OsCl(PPh3)2 with phenylacetylene and trimethylsilylacetylene gave the vinylidene complexes Cp*OsCl(=C=CHPh)(PPh3) and Cp*OsCl(=C=CH2)(PPh3), respectively. Treatment of Cp*OsCl(PPh3)2 with the internal alkyne dimethyl acetylenedicarboxylate produced the η2-alkyne complex Cp*OsCl(η2-MeO2C≡CCO2Me)(PPh3). Treatment of Cp*OsCl(PPh3)2 with the propargylic alcohol HC≡CC(OH)Ph2 gave the osmium allenylidene complex Cp*OsCl(=C = C=CPh2)(PPh3). The outcomes of the reactions of Cp*OsCl(PPh3)2 with ω-alkynols HC≡C(CH2)nOH are dependent on the length of the -(CH2)n- linker. The reaction with 3-butyn-1-ol produced the cyclic oxycarbene complex Cp*OsCl{=C(CH2)3O}(PPh3) exclusively. The reactions with 4-pentyn-1-ol produced a mixture of the hydroxyalkyl vinylidene complex Cp*OsCl{=C=CH(CH2)3OH}(PPh3) and the cyclic oxycarbene complex Cp*OsCl{=C(CH2)4O}(PPh3) in about 10:1 molar ratio. The reaction with 5-hexyn-1-ol gave exclusively the hydroxyalkyl vinylidene complex Cp*OsCl{=C=CH(CH2)4OH}(PPh3).

One-pot syntheses of rhena-2-benzopyrylium complexes with a fused metallacyclopropene unit

Facile syntheses of the first cyclopropametalla-2-benzopyrylium complexes containing fused metallapyrylium and metallacyclopropene units.

Acetylenic Carbon-Containing Stable Five-Membered Metallacycles

Due to the linear property around an acetylenic carbon, the introduction of such an atom to a small cycle would result in high ring strain. Currently, the smallest isolated rings are five-membered, including metallacycloalkynes and metallapentalynes. Both types contain at least one unusual small bond angle around the acetylenic carbon, thus exhibiting abnormal reactivities. This feature article gives a comprehensive overview on these two kind complexes. The synthesis and reactivities are extensively described, the source of stability is presented, and the future prospect is discussed. The article aims to provide a better development for the chemical diversity of five-membered metallacycloalkynes and metallapentalynes.

Recent Advances in the Reactions of Cyclic Carbynes

The acyclic organic alkynes and carbyne bonds exhibit linear shapes. Metallabenzynes and metallapentalynes are six- or five-membered metallacycles containing carbynes, whose carbine-carbon bond angles are less than 180°. Such distortion results in considerable ring strain, resulting in the unprecedented reactivity compared with acyclic carbynes. Meanwhile, the aromaticity of these metallacycles would stabilize the ring system. The fascinating combination of ring strain and aromaticity would lead to interesting reactivities. This mini review summarized recent findings on the reactivity of the metal-carbon triple bonds and the aromatic ring system. In the case of metallabenzynes, aromaticity would prevail over ring strain. The reactions are similar to those of organic aromatics, especially in electrophilic reactions. Meanwhile, fragmentation of metallacarbynes might be observed via migratory insertion if the aromaticity of metallacarbynes is strongly affected. In the case of metallapentalynes, the extremely small bond angle would result in high reactivity of the carbyne moiety, which would undergo typical reactions for organic alkynes, including interaction with coinage metal complexes, electrophilic reactions, nucleophilic reactions and cycloaddition reactions, whereas the strong aromaticity ensured the integrity of the bicyclic framework of metallapentalynes throughout all reported reaction conditions.

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.

Gas-Phase Formation of Fulvenallene (C7H6) via the Jahn-Teller Distorted Tropyl (C7H7) Radical Intermediate under Single-Collision Conditions

The fulvenallene molecule (C₇H₆) has been synthesized via the elementary gas-phase reaction of the methylidyne radical (CH) with the benzene molecule (C₆H₆) on the doublet C₇H₇ surface under single collision conditions. The barrier-less route to the cyclic fulvenallene molecule involves the addition of the methylidyne radical to the π-electron density of benzene leading eventually to a Jahn-Teller distorted tropyl (C₇H₇) radical intermediate and exotic ring opening-ring contraction sequences terminated by atomic hydrogen elimination. The methylidyne-benzene system represents a benchmark to probe the outcome of the elementary reaction of the simplest hydrocarbon radical-methylidyne-with the prototype of a closed-shell aromatic molecule-benzene-yielding nonbenzenoid fulvenallene. Combined with electronic structure and statistical calculations, this bimolecular reaction sheds light on the unusual reaction dynamics of Hückel aromatic systems and remarkable (polycyclic) reaction intermediates, which cannot be studied via classical organic, synthetic methods, thus opening up a versatile path to access this previously largely obscure class of fulvenallenes.