Metal vinylidene complexes exhibit rich reactivity and play pivotal roles in catalytic alkyne transformations; however, the reactivity of cyclic metal vinylidene complexes has been scarcely explored, largely due to the limited availability of such species caused by high ring strain. In this work, we report the diverse reactivity of a cyclic osmium vinylidene embedded in a CNC pincer framework. The cyclic osmium vinylidene complex reacts with aryl alkynes to unveil the first shuttle reaction of a metal vinylidene unit. In contrast, halogenation is observed upon treatment with N-halosuccinimides, occurring electrophilic substitution at an alternative site rather than electrophilic addition at the osmium vinylidene carbon, as further rationalized by Fukui function analysis for regioselectivity. Moreover, the reaction of the cyclic osmium vinylidene complexes with isocyanides affords the rarely crystallographically characterized metallacyclopropanimine. Collectively, these findings not only expand the distinctive reactivity of metal vinylidenes but also enrich the chemistry of CNC pincer complexes.

The discovery of ferrocene1 heralded the advent of modern organometallic chemistry. Characterized by the π-coordination of a metal by one or two planar annulene anions, ferrocenes and their analogues2-4 exemplify the archetype of out-of-plane annulene metal complexes. By contrast, the integration of metal within the annulene core to form in-plane annulene metal complexes featuring metal-carbon σ bonds has been obstructed not only by the synthetic difficulty and the non-planarity of annulenes with appropriate internal dimensions, but also by the difficulty of embedding the metal. These challenges have prevented the isolation of such in-plane annulene metal complexes. Here we report the preparation of three metal-centred planar [15]annulene frameworks. The most symmetrical fragment has D5h symmetry, with the metal centre shared by five identical five-membered rings. Density functional theory calculations demonstrate that metal d orbitals participate in conjugation with these five-membered rings, rendering all of them aromatic. The overall framework bears a loose structural and spectroscopic analogy to metallo-expanded porphyrins with multiple aza donors5, which thus provides a nexus between annulene chemistry and classic heteroatom-based coordination chemistry. The present systems display high stability and are easily functionalized. We thus suggest that metal-centred planar annulenes could emerge as promising building blocks for materials science.

Metallaaromatics represent a distinct class of aromatic systems wherein at least one metal atom is structurally integrated into the conjugated pi-framework of the aromatic ring structure. Carbolong complexes, one of the primary types, feature one metal center occupying the bridgehead position of at least two fused five-membered rings. This Backstory outlines the development process from carbolong complexes to in-plane metallo-annulenes, metallaaromatics in which the metal occupies the planar annulene cavity, and highlights the interplay between serendipitous discovery and rational design.

Transition metal-carbynes are efficient catalysts or key intermediates in a variety of chemical transformations. Significant research has focused on exploring their reactivity, aiming to understand the bonding characters and develop new applications. However, the radical addition reactions of metal-carbynes remain unknown, mainly due to the high polarity of metal-carbyne bonds, which is prone to electrophilic or nucleophilic additions. In this study, we report for the first time the radical addition reaction of metal-carbyne through the reactions of an osmium-carbyne located in aromatic ring with various radicals. The delocalized electronic structure and substantially steric hindrance of metallacycle provide sufficient stability for spectroscopic and/or structural characterizations of the radical addition intermediates, and endow high selectivity for the subsequent transformations. Notably, through this newly developed reaction, a spin-delocalized metalla-aromatic radical was achieved, which represents the first example of metal d-orbital participating in spin delocalization of open-shell π conjugated molecules, although considerable efforts have been dedicated to this field. This work not only opens up an avenue for the radical chemistry of metal-carbynes, but also provides a conceptually new strategy for preparing metal-contained open-shell π conjugated molecules in material science.

Four bidentate ruthenium(II) complexes 1-4 were tested as catalysts for the synthesis of quinolines via acceptorless dehydrogenative condensation (ADC) strategy, using o-aminobenzyl alcohol and ketones as the starting materials, and complex 4 exhibited the highest activity. With 0.3 mol% catalyst loading and 1.0 equivalent of KOH, 26 quinoline derivatives were isolated in high yields within 2 hours at 120 degrees C. Moreover, under similar conditions, this multifunctional catalyst is also applicable for the preparation of other N-heterocycles, and a series of naphthyridines, pyridines and pyrroles were generated.

A 10C-carbolong framework with three fused ruthenium-containing five-membered rings was constructed, which represents the longest carbolong skeleton based on a non-third-row transition metal.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Carbonylation reactions are a valuable synthetic method to construct carbonyl compounds and carbonylation reactions of aryl halides stand out as a highly significant tool for generating carbonyl substituted arenes.However,the important reactions have never been realized in aromatic metallacycles.Herein,we present the first carbonylation reactions of metallaaromatics,specifically alkoxycar-bonylation and aminocarbonylation reactions of an osmapentalyne.During the carbonylation process,the electronic and steric prop-erties of nucleophiles are regarded as critical factors.The alcohols with bulky substituents(isopropanol)require more reaction time and tert-butyl alcohol is inert in the reaction.Comparatively,amines,being stronger nucleophiles,exhibit divergent behaviors.Bulky amines undergo aminocarbonylation,whereas small amines prefer direct nucleophilic additions.Control experiments revealed that the intermediate derived from coupling of metal carbyne with CO plays a significant role in the carbonylation reaction.According to these observations,a divergent pathway for the reaction is proposed.Furthermore,the photophysical properties of these carbon-yl-functionalized osmapentalene complexes are studied,and the maximum absorption peak of compound with a carboxylic group ex-hibits a significant red-shift due to the smaller HOMO-LUMO gap.These findings contribute to expanding the reactivity of metallaaromatics and offer new opportunities for the synthesis of carbonyl-functionalized metallacycles.

Isomerization reactions of unsaturated molecules offer an efficient strategy in atom-economical synthesis. Although isomerization reactions of unsaturated organic and organometallic compounds, such as alkenes, alkynes, and metal carbynes, have been achieved, those of metal vinylidene units that contain cumulated double bonds have never been reported. Herein, we inaugurally discovered isomerization reactions of metal vinylidene units via protonation and deprotonation reactions of metal carbenes. Experimental and theoretical investigations indicate that the electrical characteristics of substituents on the rings play a crucial role in controlling the formation of metal vinylidene units. The isomerization reactions of metal vinylidene units were driven by thermodynamic forces. Moreover, one of the angles at metal vinylidenes was found as 126.9 degrees, representing the smallest angle in metal vinylidenes and the first cyclic 4d transition metal (Ru) vinylidene complex was successfully isolated. These investigations unveil novel structures and reactivity for metal vinylidenes, offering a fresh perspective on the isomerization reactions of unsaturated molecules containing cumulative unsaturated bonds. Isomerization reactions of unsaturated molecules offer an efficient strategy in atom-economical synthesis.

Carbolong complexes are one of the primary types of metallaaromatics, and they include metallapentalynes and metallapentalenes. A series of 7C-10C and 12C-carbolong complexes with planar ligand skeletons respectively containing 7-10 and 12 carbon atoms in their backbones, have been previously reported. Herein, two classes of strained substances, metallabenzyne-fused metallapentalenes and metallabenzene-fused metallapentalynes, were prepared, both representing 11C-carbolong complexes with a planar carbon-chain ligand. Furthermore, the former type is also the carbolong derivatives containing a metallabenzyne skeleton, another primary metallaaromatic framework. Metallabenzyne-fused metallapentalenes show versatile reactivities, and the most interesting one is the metal carbyne bond shift from a 6-membered to a more strained 5-membered ring, affording the above-mentioned metallabenzene-fused metallapentalyne. This work makes carbolong chemistry more complete, and provides a method to achieve metallabenzynes, which is anticipated to concurrently advance the development of these two types of metallaaromatics. 7C-10C and 12C-carbolong complexes with planar ligand skeletons containing 7-10 and 12 carbon atoms have been previously reported but 11C-carbolong complexes with a planar carbon-chain ligand are elusive. Here, the authors prepare metallabenzyne-fused metallapentalenes and metallabenzene-fused metallapentalynes, both representing 11C-carbolong complexes with a planar carbon-chain ligand

Comprehensive Summary Metallacyclopentadienes are important metallacycles and regarded as intermediates in many reactions, therefore, new methods to achieve them are anticipated. In this study, a formal [3+2] method, through the reactions of an osmapentalyne with benzyl carbanions, was developed. The reactions underwent a nucleophilic attack of carbanions to the Os≡C bond, followed by C—H activation to form the five‐membered osmacyclopentadiene ring. Most of the reactions were carried out at room temperature, the substituents on the aromatic rings of benzyl carbanions are diverse, and the resulting products contain an Os—H bond, representing a novel type of 10C‐carbolong complexes. This work provides a new convenient route to construct metallacyclopentadienes, which is expected to further promote the development of such a type of substances.

Aromatic metalla-annulenes are important aromatic compounds, research into which has been mainly concentrated on metal-benzenes and their lower homologues. Reports on their superior homologs are rare, and this has greatly limited the systematic study of their properties. In this work, a series of osma-dehydro[11]annulenes with good air and thermal stability were prepared in high yields through a simple [10+1] strategy, by incorporating a metal fragment into conjugated ten-carbon chains in a one-pot reaction. They are the first monometallic aromatic metalla-[n]annulenes with the ring size larger than 6, and their Craig-Hückel hybrid aromaticity is supported by various physical and computational parameters. Besides, these complexes show versatile reactivities, not only giving further evidence for their aromaticity, but also demonstrating their physical and chemical properties can easily be regulated. This work enriches the metalla-aromatic chemistry, and provides a new avenue for the synthesis of large metalla-annulenes with different ring sizes.

Metallacyclobutadienes (MCBDs) are key intermediates of alkyne metathesis reactions. There are in principle two isomerization pathway from kinetic to thermodynamic MCBDs, intermolecular and intramolecular. However, systems that simultaneously isolate two kinds of MCBD isomers have not been achieved, thus restricting the mechanistic studies of the isomerization. Here the reactivity of a metallapentalyne that contains an M≡C bond within the aromatic ring, with alkynes to afford a series of MCBD-fused metallapentalenes is studied. In some cases, both kinetic and thermodynamic products are isolated in the same system, which has never been observed in previous MCBD reactions. Furthermore, the isomerization of MCBD-fused metallapentalenes is investigated both experimentally and theoretically, indicating that it is an intramolecular process involving a metallatetrahedrane (MTd) intermediate. This research provides experimental evidence demonstrating that one MCBD can undergo intramolecular rearrangement to transform into another.

Metallacyclopentadienes play a vital role in transition-metal mediated and catalyzed cycloaddition reactions of alkynes. Though versatile reactions of metallacyclopentadienes with alkynes have been disclosed, [2+1] cycloadditions of metallacyclopentadienes and alkynes have never been discovered. In present work, we report the formal [2+1] cycloadditions of a metallacyclopentadiene unit with a broad scope of commercial alkynes, providing a facile strategy to construct tetracyclic conjugated compounds. The deuterated experiment indicates a metal vinylidene intermediate has been involved in [2+1] cycloaddition. Moreover, the electrophilic substitution reaction of the tetracyclic conjugated compound with the aid of density functional theory (DFT) calculated Fukui functions is investigated. These tetracyclic conjugated compounds exhibit broad absorption spectra in the whole visible region which could be employed as potential photovoltaic materials.

Four diaza-osmapentalenes were prepared by two-step reactions, through the treatment of an alkyne-coordinated osmium complex with azo compounds, followed by the addition of AgSbF6/CO. Their aromaticity was confirmed by crystal parameters, NMR spectra and theoretical calculations. These complexes are the first diaza-metallapentalenes representing a new class of metallaaromatics.

The σ bond is an important concept in chemistry, and the metal-carbon (M-C) σ bond in particular is a central feature in organometallic chemistry. Synthesis of stable complexes with five coplanar M-C σ bonds is challenging. Here, we describe the synthesis of two different types of stable complexes with five coplanar M-C σ bonds, and examine the stability of such complexes which use rigid conjugated carbon chains to chelate with the metal center. Density functional theory (DFT) calculations show that the M-C σ bonds in these complexes have primarily a covalent character. Besides the σ nature, there are also a π conjugation component among the metal center and carbons, which causes delocalization. This work expanded the coplanar M-C σ bonds to five.

Strong intermolecular interactions usually facilitate charge transport, but impede photoluminescence, therefore, the development of organic π‐conjugated materials that exhibit both semiconducting and light‐emissive properties remains challenging. Herein, a series of perylene diimide (PDI)‐based carbolong complexes with d π ‐ p π conjugation is synthesized. The resulting alcohol‐soluble products exhibit broad and strong absorption combined with outstanding electronic and optical properties, and are applied as electron transport layer materials in organic solar cells, achieving power conversion efficiencies up to 17.36%. In addition, these complexes exhibit an uncommon aggregation‐induced emission phenomenon. These results will aid in future design of π‐conjugated materials with increased functionality.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.