Dinickelaferrocene: A Ferrocene Analogue with Two Aromatic Nickeloles Realized by Electron Back-Donation from Iron

A Planar Nickelaspiropentane Complex with Magnesium-Based Metalloligands: Synthesis, Structure, and Synergistic Dihydrogen Activation

The nature of transition-metal-olefin bonding has been explained by the Dewar-Chatt-Duncanson model within a continuum of two extremes, namely, a π-complex and a metallacyclopropane. The textbook rule suggests that a low-spin late-transition-metal-ethylene complex more likely forms a π-complex rather than a metallacyclopropane. Herein, we report a low-spin late-transition-metal-bis-ethylene complex forming an unprecedented planar metalla-bis-cyclopropane structure with magnesium-based metalloligands. Treatment of LMgEt (L = [(DippNCMe)₂CH]^-, Dipp = 2,6-ⁱPr₂C₆H₃) with Ni(cod)₂ (cod = 1,5-cyclooctadiene) formed the heterotrimetallic complex (LMg)₂Ni(C₂H₄)₂, which features a linear Mg-Ni-Mg linkage and a planar coordination geometry at the nickel center. Both structural features and computational studies strongly supported the Ni(C₂H₄)₂ moiety as a nickelaspiropentane. The exposure of (LMg)₂Ni(C₂H₄)₂ to 1 bar H₂ at room temperature produced a four-hydride-bridged complex (LMg)₂Ni(μ-H)₄. The profile of H₂ activation was elucidated by density functional theory calculations, which indicated a novel Mg/Ni cooperative activation mechanism with no oxidation occurring at the metal center, differing from the prevailing mono-metal-based redox mechanism. Moreover, the heterotrimetallic complex (LMg)₂Ni(C₂H₄)₂ catalyzed the hydrogenation of a wide range of unsaturated substrates under mild conditions.

Electronic Structures and Properties of Bimetallic Plutonium Group 13 Carbonyl Compounds [XPuCO] (X = B, Al, and Ga)

Bonding features of heterobimetallic complexes containing f-block elements are fundamental content in actinide chemistry. In order to account for the structural periodicity of the X-Pu carbonyls and the formation of chemical bonds between bimetallic plutonium and group 13 carbonyl compounds, we report a comprehensively quantum-chemical study of the electronic structure and properties of XPuCO (X = B, Al, and Ga). With increasing atomic radii of the group 13 elements, the XPuCO structure alternates from cyclic [PuCBO] to linear [AlCPuO] and [GaCPuO]. The bonding analysis indicates that the donor-acceptor model is the best description for bonding interactions of metal and ligands with different donation patterns of CBO → Pu and XC → PuO (X = Al and Ga). The apparent XC ← PuO backdonation increases the C-Pu bond strength markedly and stabilizes the linear geometry of [AlCPuO] and [GaCPuO], while spin-orbit coupling is found to be significant in the stabilization of [PuCBO]. The ground electron configurations and natural orbital analysis indicate that cyclic [PuCBO] and linear [XCPuO] (X = Al and Ga) are considered as complexes of Pu(III) and Pu(V), respectively. The trend presents a valuable insight for the 5f/6d-np bonding interactions, especially for the fundamental understanding of transuranic elements.

Transmetalation Reactions of Aromatic Dilithionickelole: Synthesis of Heterobimetallic Complexes Featuring Metalloles as Diene Ligands

The aromatic metallole dianions are important metallaaromatic compounds because of their various reactivities and extensive synthetic applications. Herein we report the reactions of dilithionickelole with MgCl₂ , EtAlCl₂ , Cp*ScCl₂ , Cp*LuCl₂ and Pt(COD)Cl₂ (COD=1,5-cyclooctadiene) affording a series of Ni/M heterobimetallic complexes of the general formula (η⁴ -C₄ R₄ M)Ni(COD), in which the metalloles act as diene ligands, as suggested by single-crystal X-ray, NMR and theoretical analyses. In these reactions, two electrons of the nickelole dianion transferred to Ni, representing different reactivity compared with main-group metallole dianions.

Tin Metal Cluster Compounds as New Third-Order Nonlinear Optical Materials by Computational Study

It is quite appealing but challenging to predict and synthesize new nonlinear optical (NLO) materials with exceptional performance. Herein, the different Sn₄ cluster core structures and third-order NLO properties are studied through electronic structure, excited hole-electron, bonding character, and aromaticity analysis. As a result, Sn₄ clusters with ring core structure (Sn₄-R) not only have the smallest E_gap, the largest UV-vis response intensity, but also the strongest third-order NLO response in our work. As proved by natural bond orbitals' (NBO) analysis, electron localization function (ELF), and adaptive natural density partitioning (AdNDP), the Sn₄⁴⁺ has two in-plane four center-two electron (4c-2e) Sn-Sn σ-bonds, resulting in a good delocalization. For the first time, delocalization of metal cluster cores in tin clusters that is beneficial to the third-order NLO response is proposed, which provides a new guidance to design and prepare third-order NLO materials.

A Ferrocene-Functionalized Covalent Organic Framework for Enhancing Chemodynamic Therapy via Redox Dyshomeostasis

Chemodynamic therapy (CDT), which induces cell death by decomposing high levels of H₂ O₂ in tumor cells into highly toxic ·OH, is recognized as a promising antineoplastic approach. However, current CDT approaches are often restricted by the highly controlled and upregulated cellular antioxidant defense. To enhance ·OH-induced cellular damage by CDT, a covalent organic framework (COF)-based, ferrocene (Fc)- and glutathione peroxidase 4 (GPX4) inhibitor-loaded nanodrug, RSL3@COF-Fc (2b), is fabricated. The obtained 2b not only promotes in situ Fenton-like reactions to trigger ·OH production in cells, but also attenuates the repair mechanisms under oxidative stress via irreversible covalent GPX4 inhibition. As a result, these two approaches synergistically result in massive lipid peroxide accumulation, subsequent cell damage, and ultimately ferroptosis, while not being limited by intracellular glutathione. It is believed that this research provides a paradigm for enhancing reactive oxygen species-mediated oncotherapy through redox dyshomeostasis and may provide new insights for developing COF-based nanomedicine.

Metalla-aromatics: Planar, Nonplanar, and Spiro

ConspectusThe concept of aromaticity is one of the most fundamental principles in chemistry. It is generally accepted that planarity is a prerequisite for aromaticity, and typically the more planar the geometry of an aromatic compound is, the stronger aromatic it is. However, it is not always the case, particularly when transition metals are involved in conjugation and electron delocalization of aromatic systems, i.e., metalla-aromatics. Because of the intrinsic nature of transition-metal orbitals, besides planar geometries, the most stable molecular structures of metalla-aromatic compounds could take nonplanar and even spiro geometries. In this Account, we outline several unprecedented types of metalla-aromatics developed recently in our research group.Around seven years ago, we found that 1,4-dilithio-1,3-butadienes, dilithio reagents with π-conjugation, could function as non-innocent ligands and react with low-valent transition-metal complexes, generating monocyclic metalla-aromatic compounds. Later on, by taking advantage of the unique behavior of dilithio reagents and the intrinsic nature of different transition metals, we have synthesized a series of metalla-aromatic compounds, of which four types are discussed here, and each of them represents the first of its kind. First, nearly planar aromatic dicupra[10]annulenes, a 10 π-electron aromatic system with two bridging Cu atoms participating in the orbital conjugation and electron delocalization, are synthesized by annulating two dilithio reagents with two Cu(I) complexes.Second, four kinds of spiro metalla-aromatics, featuring planar (with Pd, Pt, or Rh as the spiro atom) geometry with a whole 10π aromatic system, octahedral (tris-spiro metalla-aromatics with V as the spiro atom) geometry with an entire 40π Craig-Möbius aromatic system, tetrahedral (with Mn as the spiro atom) geometry having two independent and perpendicular 6π planar aromatic rings, and tetrahedral (with Mn as the spiro atom) geometry with one planar and one nonplanar 6π aromatic rings, respectively, are generated. In sharp contrast to spiroaromaticity with carbon acting as the spiro atom described in Organic Chemistry, the metal spiro atom herein takes part in orbital conjugation and electron delocalization.Third, nonplanar aromatic butadienyl diiron complexes are realized. Different from planar aromatic systems featuring delocalized π-type overlap, this nonplanar metalla-aromaticity is achieved by the novel σ-type overlap between the two Fe 3d_xz orbitals and the butadienyl π orbital, forming a 6π aromatic system. Fourth, dinickelaferrocene, a ferrocene analogue with two aromatic nickeloles, is synthesized from our monocyclic aromatic dilithionickelole and FeBr₂. The aromaticity of dinickelaferrocene and its nickelole ligands is realized by electron back-donation from the Fe 3d orbital to the π* orbital of nickeloles, which also deepens our understanding of the origin of aromaticity.The search for unprecedented and exciting aromatic systems, particularly with transition metals being involved, will continue to drive this intriguing research field forward. Given the synthetic strategies and various types of metalla-aromatics developed and described, diversified metalla-aromatics of interesting structures and reaction chemistry, novel chemical bonding modes, and useful functions can be expected.

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.