Unique Properties and Emerging Applications of Carbolong Metallaaromatics

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Aromatic compounds are important in synthetic chemistry, biomedicines, and materials science. As a special type of aromatic complex, transition-metal-based metallaaromatics contain at least one transition metal in an aromatic framework. The chemistry of metallaaromatics has seen much progress in computational studies and synthetic methods, but their properties and applications are still emerging. In recent years, we have disclosed a series of metal-centered conjugated polycyclic metallacycles in which a carbon chain is chelated to a metal center through at least three metal−carbon bonds. These are termed carbolong complexes and exhibit good stability to water, oxygen, light, and heat on account of their polydentate chelation and aromaticity, making them easy to handle. Carbolong complexes are not only special π-conjugated aromatics but also organometallics; therefore, they have the properties of both species. In this Account, we showcase the recent advances in their applications based on their different properties.First, carbolong complexes are a special kind of π-conjugated aromatic, with the ability to transmit electrons, allowing them to function as single-molecule conductors and candidates for electron transporting layer materials (ETLs) in solar cells. A series of carbolong complexes have been proved to be useful as achievable ETLs which enhance device performance in both organic solar cells and perovskite solar cells. Second, due to the involvement of d orbitals in the conjugation, carbolong complexes normally exhibit strong and broad absorption, even in some cases extending to the near-infrared region (NIR). The absorbed optical energy can be converted into light, heat, and ultrasound; consequently, carbolong compounds can be used as core moieties in smart materials. For example, 7C carbolong complexes were found to exhibit aggregation-enhanced near-infrared emission (AIEE). Some 12C carbolong complexes have been designed into the core moieties of NIR-responsive polymers, such as cylindrical NIR-responsive materials, self-healing materials, and shape memory materials. In contrast to the stereotypically toxic osmium compounds such as the highly toxic OsO 4 , some osmium carbolong complexes exhibit low cell cytotoxicity and good biocompatibility; consequently, they also have potential applications in the biomedical area. For example, benefiting from broad absorption in the NIR, 9C and 12C carbolong complexes have been used in photoacoustic imaging and photothermal therapy, respectively. In addition, photodynamic therapeutic applications which take advantage of a carbolong peroxo complex are discussed. Third, as special transition-metal complexes chelated by carbon-based ligands, a carbolong peroxo complex has displayed catalytic activity in the dehydrogenation of alcohols and a bimetallic carbolong complex has been used to catalyze difunctionalization reactions of unactivated alkenes. Overall, aromatic carbolong complexes have been applied to photovoltaics, s...

Construction of a Metallacyclopentadiene Ring through the Attack of Carbanions to M≡C Bond Followed by C—H Activation†

“…[18j] Furthermore, carbolong complexes have shown potential applications in several areas. [ 19‐20 ] Metallapentalynes contain an ambiphilic M≡C bond, which can be nucleophilically attacked. [18l‐n] Herein, we used carbanions as the nucleophiles, and interestingly, when they reacted with an osmapentalyne, C—H activation would occur to construct an osmacyclopentadiene ring via a formal [3+2] cycloaddition, affording a new type of 10C‐carbolong complexes (Figure 1D).…”

Metallaaromaticity involving a d0 early transition metal centre: synthesis, structure, and aromaticity of tantallapyridinazirine complexes

“…4 Represented by metallabenzene and metallabenzynes, a vast array of metallaaromatic compounds have been synthesised and characterised, varying in sizes of metallacycles, topologies of polycyclic structures (fused and spiro), types of aromaticity-contributing orbitals (π, σ), and the presence of heteroatoms or not. 5 However, very narrow scope of metals is known to form isolable metallaaromatic compounds so far, 5 dominated by late transition metals (Chart 1). 6,7 In 2021, Xi and co-workers reported two examples of aromatic, anionic tris-spiro metalloles of V and Cr with d 5 electron configuration, representing scarce examples of early transition metallaaromatic compounds.…”

Reactions of Ruthenabenzene with Propynols Involving Hydrogen-Bonding-Induced [2 + 2] Cycloaddition

“…Up to date, a number of metal carbene complexes with aromaticity, known as metalla-aromatics, − have been demonstrated to undergo stoichiometric − or catalytic metathesis reactions. , We have been studying metalla-aromatics with group VIII transition metals, which display characteristic reactivities of aromatics and transition metal carbenes. ,− We now examine their ability to stabilize the intermediates in chemical bond activation processes, which can be potentially useful for our understanding of the effects of supporting ligands in transition-metal reactivity and catalysis. Herein, we report the [2 + 2] reactivity of ruthenabenzene with propynols (Scheme b), in which the hydrogen-bond-acceptor properties of the [Ru–Cl] unit and the polycyclic structural rigidity account for the conversions of metallacyclobutenes, thereby facilitating the following nucleophilic addition reactions of the resulting metallacyclobutenes to give η 3 -allyl structures.…”