Skeletal reshaping between aromatic frameworks remains challenging. The rearrangements between azulene and naphthalene structures are some of the only examples to date. Metallaaromatics, an important class of aromatic compounds, attract broad attention for their fascinating structures and diverse reactivities. Herein, we report the reshaping of cyclopropametallaindole to metallaquinolinium, demonstrating both aromaticity and structure switching. The proposed electrophilic addition and elimination mechanism has been investigated by radical trapping experiment and theoretical study. This transformation achieves both the aromaticity and structure switching of a metallacycle, and demonstrates a new synthetic route for metallaaromatics.

Only half-sandwich ruthenacyclopentatrienes have been reported to date, and their (anti)aromaticity remains unverified. Herein, we synthesize and characterize novel ruthenacyclopentatrienes adopting an octahedral geometry, which are antiaromatic. The reactivity of the ruthenacyclopentatrienes towards 1-hexyne and reductants has been investigated. One-electron reduction with NaBH4 produces a dihydridoborate-ruthenacyclopentatrienyl radical exhibiting NIR-I/NIR-II absorption.

The metal center of metallacycles can adopt different oxidation states, which would result in the change of structure and property. In this work, metallabenzofuran complexes with a Re(V) center are obtained from the reaction of ReOCl 3 (PPh 3 ) 2 with o -ethynyl phenols. Further oxidation of these Re(V)-metallacycles produces Re(VII)-metallabenzofurans as rare examples of high valent conjugated d 0 -metallacycles of late transition metals. Although they have a delocalized five-membered rhenafuran structure, density functional theory studies show that these Re(V)- and Re(VII)-metallacycles are nonaromatic.

1-Haloalkynes or alkynyl halides (X-C - C-R) are valuable substrates for organic and organometallic syntheses. The formation of sigma-acetylene-metal complexes from C(sp)-X bond activations have been demonstrated on Ni, Pt, Ir, Rh, Pd, and Au metals, which are the key intermediates of many catalytic reactions. In this work, we report the first examples of C(sp)-X bond activation on Re center, generating novel Re(VI) carbyne complexes.

Click reactions with a “catch‐and‐release” functionality featuring both cross‐linking and bond cleavage may have unique biomedical applications. However, despite the high demand, such reactions are rarely known in the toolbox of biochemists. Herein we introduce a robust click reaction of selenoalkynes that not only facilitates mild cross‐linking with azides but also permits exceptionally facile cleavage of the C─Se bond in the adducts. This highly efficient ruthenium‐catalyzed protocol features high chemoselectivity and regioselectivity, mild conditions, broad substrate scope, and good tolerance of functional groups and solvents. The compatibility with air and water as well as biomolecules has been demonstrated in parallel with the “catch‐and‐release” functionality.

The metal center can form multiple sigma-bonds with a polydentate ligand. In this work, novel rhenapolycycles with up to six sigma-bonds (four Re-C and two Re-N sigma-bonds) are obtained from the reaction of ReCl3(PPh3)2(NCCH3) or ReOCl2(OEt)(PPh3)2 with 2-ethynylaniline. The key step is proposed to be the coupling of two Re-C bonds in Re(V)bisvinyl or bis(alkenyl ylide) structures.

Osmacyclopentadiene complexes were obtained from the reactions between OsCl2(PPh3)3 and 1,8-dialkynyl naphthalene compounds. These complexes exhibited paramagnetism as they adopted triplet ground states. Reactions of osmacyclopentadienes with alkynes were investigated, which produced novel η6-fluoranthene complexes, showing their potential in organometallic synthesis.

Several antiaromatic metallacycles have been reported in the past 5 years, opening an emerging area of (anti)aromaticity and organometallic chemistry. In this work, we briefly review the synthesis and characterization of these complexes. Generally, experimental criteria, including planarity, bond length alternation, NMR chemical shift, chemical transformation, and theoretical criteria, mainly involving NICS, AICD, ASE or ISE, are applied for the antiaromaticity judgement.

Metallaromatics such as metallabenzene and its heteroatom-containing analogues have aroused interests both in experimental and theoretical studies. While various six-membered metallaaromatics have been explored, a general synthetic methodology is still undeveloped. Herein, we report the skeletal editing of five-membered metallacyclopentadiene involving the insertion of the sixth atoms (S, Se, N, C) into the Os–C bond, as a general approach for osmafluoranthene derivatives containing osmathiabenzene, osmaselenabenzene, osmapyridine, and osmabenzene units. These complexes show broad UV-Vis absorptions, and their aromaticity has been authenticated spectroscopically, structurally and computationally. Six-membered metallaromatics have attracted interest, but a general synthetic methodology that enables access to such molecules remains undeveloped. Here, the authors present a skeletal editing approach towards six-membered metallacycles, enabling the creation of osmafluoranthene derivatives with diverse main-group elements.

d 2 Re( v ) carbyne complexes Re(CR)Cl 2 (PMePh 2 ) 3 , can undergo stoichiometric metathesis with a range of terminal aryl and aliphatic alkynes (HCCR′), yielding substituted carbyne complexes Re(CR′)Cl 2 (PMePh 2 ) 3 and HCCR.

The reactions of ReCl3(PMePh2)3 with o-halophenylacetylenes (halo = Cl, Br, I) were investigated, producing two kinds of rhenacyclopropene complexes. Complex 1 with a fused five-membered rhenacycle containing a Re-I dative bond, and spiro bi(rhenacyclopropene) complexes 2-4 were isolated and characterized. The reaction selectivity and the aromatic property of metallacyles were studied by DFT calculations. In the model complex M, the iodo-rhenacycle 5MR was non-aromatic, while the rhenacyclopropene 3MR was aromatic.

Metallaaromatics are attractive due to their special structures and properties. In this work, the first metalla-phenalenyl complexes containing CReC units were obtained from ReCl3(PMePh2)3 and 1,8-diethynylnaphthalene compounds. The delocalized rhenaphenalenyl structure exhibits good planarity. DFT studies show that the 3MR rhenacyclopropene units are σ-aromatic, while the 6MR rhenacycle is nonaromatic. Though the rhenapolycycle is stable, it can be oxidized with one 3MR broken, resulting in another rhenaphenalenyl structure.

Substituted cyclopentadienyl (Cp) radicals, as well as other Cp and fluorenyl-based radicals, exhibit deviations from ideal fivefold D5h symmetric structures due to Jahn-Teller distortion. The unpaired electron is unequally distributed on the five carbons. Herein, we report the metalla-analogs of Cp radicals from one-electron reduction of antiaromatic osmacyclopentatriene complexes. The novel osmacyclopentatrienyl radicals are nonaromatic, with the single unpaired electron delocalized over the entire five-membered osmacycle. Furthermore, these osmacyclopentatrienyl radicals can be oxidized to regenerate osmacyclopentatrienes and reduced to form osmacyclopentadienes. This discovery provides new insights into radical chemistry and organometallic chemistry.

Additions of nucleophiles like phosphines to coordinated alkynes are important processes in organometallic synthesis. In this work, exocyclic alkenyl ylide phenolate ( 1 -2 ) and benzoate ( 5 ) Re(V) complexes are obtained from the reactions of internal 2-alkynylphenols, and 2-ethynylbenzoic acid with ReOCl 2 (OEt)(PPh 3 ) 2 , respectively. The Re(V) complexes 1 -2 can be reduced to eta 2 -alkyne Re(III) complexes 3 -4 with P -C bond cleavage.

Metallacycloprop-1-ene and metallacycloprop-2-ene complexes are the smallest unsaturated metallacycles, and have attracted continuing attention for their importance in organometallic synthesis and catalysis. This feature article summarizes the syntheses of monocyclic and fused metallacycloprop-2-enes, and monocyclic, spiro, and fused metallacycloprop-1-enes, all with crystallographically characterized structures. The aromatic properties of mononuclear metallacyclopropene complexes are also described.

There is no report on the (anti)aromaticity of metallacyclopentatrienes, one kind of common and important five-membered metallacycles. This work presents the novel synthesis of osmium cis-biscarbene complexes and their oxidation to osmacyclopentatrienes. The osmacyclopentatriene unit is antiaromatic, as revealed by experimental and theoretical studies. This finding provides new insight into the discovery of antiaromatic species.

Reactions of o-alkyl naphthol compounds with ReCl3(PMePh2)(3) produced naphtho-rhenafuran complexes, which adapted different ground states (singlet S(0 )and triplet T-0). These polycyclic structures have been characterized experimentally and theoretically. Their electronic behaviors have been studied by UV-Vis absorption and DFT calculations.

The oxidation state of the metal center is important for a conjugated metallacycle. Although high valent d0-metallacycles of main groups and early transition metals have been reported, such examples of late transition metals are limited. The reactions of ReOCl3(PPh3)2 with 2-ethynyl anilines produced alkenyl amino Re(v) complexes, which can be further oxidized to Re(vii) aza-metallacycles. The conjugated rhenacycle is nonaromatic, however, with close to zero NICS values and localized currents observed by AICD and GIMIC studies.

While alkyne metathesis reactions involving d(0) carbynes (alkylidynes) are well documented, those involving well-defined non-d(0) carbynes are still rare. This work reports the synthesis and alkyne metathesis activity of d(2) Re(V) carbyne complexes supported by a [LXL]-type monoanionic [PNP]-pincer ligand, a [LLX]-type monoanionic [PNO]-pincer ligand, and a [ONOH]-bidentate ligand derived from the Schiff base 2-[(2-hydroxyphenyl)iminomethyl]phenol. Treatment of Re(equivalent to CCH2Ph)Cl-2(PMePh2)(3) (1) with bis(2-diphenylphosphino-4-tolyl)amine (PNHP) and 2-{(2-diphenylphosphino-phenyl)iminomethyl}phenol (PNOH) in the presence of NEt3 produced the pincer complexes Re(equivalent to CCH2Ph)Cl(PMePh2)(PNP) (2) and Re(equivalent to CCH2Ph)Cl(PMePh2)(PNO) (3), respectively. The Schiff base 2-[(2-hydroxyphenyl)iminomethyl]phenol (HONOH) reacted with Re(equivalent to CCH2Ph)Cl-2(PMePh2)(3) (1) to give Schiff base complex Re(equivalent to CCH2Ph)Cl(PMePh2)(ONOH) (4) (ONOH = o-O-C6H4-CH & boxH;N-(o-C6H4OH)) bearing a [ONOH]-bidentate ligand. The [PNP]- and [PNO]-pincer complexes are catalytically active for homometathesis of neat 1-methoxy-4-(1-propyn-1-yl)benzene at 150 degrees C, while the complex bearing the [ONOH]-bidentate Schiff base ligand is catalytically inactive under similar conditions. The energy profiles for metathesis reactions of model pincer rhenium alkyne-carbyne complexes have been calculated with DFT methods.

Selective hydrogenation of CC double bond in α, β-unsaturated carbonyl compounds is of great significance in the production of fine chemicals, and the design and preparation of hydrogenation catalysts with high selectivity is the key to realize the industrialization of this reaction. Controlling and adjusting the steric hindrance between substrate molecules and active center of catalysts is an effective strategy to achieve high selectivity. In this work, the spatially hindered “Frustrated Lewis pairs” (FLPs) was used as the active component and metal-organic frameworks (MOFs) materials with a certain window size were used as the catalyst support. We designed and synthesized a heterogeneous hydrogenation catalyst B(C6F5)3/DO-MIL-101 by immobilizing FLP onto metal-organic frameworks (MIL-101). Characterizations and catalytic performance tests revealed that the catalytically active species B(C6F5)3/DO was confined in MIL-101 nanocavities via Cr–O coordination bond. The resulting B(C6F5)3/DO-MIL-101 catalyst not only realized the recycling of FLP, but also showed excellent catalytic activity and high selectivity in the selective hydrogenation of CC double bond in α, β-unsaturated carbonyl ketones. It should be noted that the steric hindrance between FLP and substrate molecules, as well as the shape selectivity of MOFs nanocages, are the principal factors for the high selectivity of the catalyst.