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Control over the adhesive properties are of great importance for both biological and chemical systems. Herein, we use amino‑yne click reaction to prepare metallacycle-crosslinked supramolecular polymer networks, which are further employed as reversible adhesive materials. The introduction of metallacyclic structures not only gives the formed polymer networks good emission and self-healing properties, but also affords improved adhesion strength and increased glass transition temperature, making them serve as reversible and emissive supramolecular adhesives. This study provides an efficient strategy for the preparation of functional supramolecular polymer networks towards adhesive applications.

International audience; Transition metal-based anticancer compounds, as an alternative to platinum derivatives, are raising scientific interest as they may present distinct although poorly understood mechanisms of action. We used a structure–activity relationship-based methodology to investigate the chemical and biological features of a series of ten (C^N)-chelated half-sandwich iridiumIII complexes of the general formula [IrCp*(phox)Cl], where (phox) is a 2-phenyloxazoline ligand forming a 5-membered metallacycle. This series of compounds undergoes a fast exchange of their chlorido ligand once solubilised in DMSO. They were cytotoxic to HeLa cells with IC50 values in the micromolar range and induced a rapid activation of caspase-3, an apoptosis marker. In vitro, the oxidative power of all the complexes towards NADH was highlighted but only the complexes bearing substituents on the oxazoline ring were able to produce H2O2 at the micromolar range. However, we demonstrated using a powerful HyPer protein redox sensor-based flow cytometry assay that most complexes rapidly raised intracellular levels of H2O2. Hence, this study shows that oxidative stress can partly explain the cytotoxicity of these complexes on the HeLa cell line and gives a first entry to their mechanism of action.

International audience; Coordination-driven Pt metallacycles have shown potential in controllable modular self-assembly, which has made a vital contribution to biomedicine, catalysis, and multiresponsive materials. Herein, pillar[5]arene units were integrated into one skeleton through coordination-driven self-assembly, resulting in the formation of a hexagonal Pt(II) metallacycle decorated with six pillar[5]arenes. The host–guest interactions of the as-prepared metallacycle (pillar[5]arenes as hosts) and 1-butyl-4-[4-(diphenylamino)styryl]pyridinium (guest) were investigated. The metallacycle was found to facilitate the coaggregation between the guests and pillar[5]arenes through a synergistic effect, thus engendering a sharp increase in fluorescence intensity. The resultant aggregate was investigated by DLS and TEM. Our studies imply that the pillar[5]arene-containing metallacycle can serve as a potential platform for realizing emission enhancement effects.

International audience; The assembly of binuclear Cu(i) metallaclips with 2,2'-bis-dipyrrin based metalloligands gives rise to a diversity of architectures featuring a recurring π-stacked compact tetranuclear metallacycle but differing in their nuclearity and dimensionality depending on the nature of the capping ligands and metal cations.

Transition-metal alkylidenes have exhibited wide applications in organometallic chemistry and synthetic organic chemistry, however, cyclic Schrock-carbene-like bis-alkylidenes of group 4 metals with a four-electron donor from an alkylidene have not been reported. Herein, the synthesis and characterization of five-membered cyclic bis-alkylidenes of titanium (4 a,b) and zirconium (5 a,b) are reported, as the first well-defined group 4 metallacyclopentatrienes, by two-electron reduction of their corresponding titana- and zirconacyclopentadienes. DFT analyses of 4 a show a four-electron donor (σ-donation and π-donation) from an alkylidene carbon to the metal center. The reaction of 4 a with N,N'-diisopropylcarbodiimide (DIC) leads to the [2+2]-cycloaddition product 6. Compound 4 a reacted with CO, affording the oxycyclopentadienyl titanium complex 7. These reactivities demonstrate the multiple metal-carbon bond character. The reactions of 4 a or 5 a with cyclooctatetraene (COT) or azobenzene afforded sandwich titanium complex 8 or diphenylhydrazine-coordinated zirconacyclopentadiene 9, respectively, which exhibit two-electron reductive ability.

Summary Mononuclear metal-peroxo species are invoked as the key intermediates in metalloenzymatic or synthetic catalysis. However, either transience or sluggishness reactivity of synthetic analogs of metal-peroxo species impedes our understanding of oxygen activation mechanism. Herein, we designed and characterized a dioxygen-derived mononuclear osmium-peroxo complex, in which the peroxo ligand is stabilized by internally aromatic metallacycle. We demonstrate that the osmium-peroxo species shows catalytic activity toward promoterless alcohol dehydrogenations. Furthermore, computational studies provide a new mechanism for the osmium-peroxo-mediated alcohol oxidation, starting with the concerted double-hydrogen transfer and followed by the generation of osmium-oxo species. Interestingly, the internally aromatic metallacycle also plays a vital role in catalysis, which mediates the hydrogen transfer from osmium center to the distal oxygen atom of Os–OOH moiety, thus facilitating the Os–OOH→Os=O conversion. We expect that these insights will advance the development of aromatic metallacycle toward aerobic oxidation catalysis., Graphical Abstract, Highlights • A dioxygen-derived mononuclear osmium-peroxo complex was characterized • The peroxo ligand is stabilized by internally aromatic metallacycle • O2 activation involves the reversible aromatization-dearomatization • A concerted double-hydrogen transfer mechanism for alcohol dehydrogenation, Chemistry; Inorganic Chemistry; Organometallic Chemistry; Catalysis

Platinum(II) binds to 21,23-ditelluraporphyrin forming a side-on complex, which can be easily transformed into an aromatic metallaporphyrin, that is, 21-platina-23-telluraporphyrin, with a platinacyclopentadiene unit built in the porphyrin skeleton in place of one pyrrole ring. The central platinum(II) ion with a CCNTe square-planar coordination sphere can be oxidized to platinum(IV) by chlorine, bromine, methyl iodide or allyl chloride to yield octahedral complexes. All platinatelluraporphyrins show dynamic behavior involving the platinum ion coordination sphere fluxionality and the porphyrin skeleton deformation, both in-plane and out-of-plane, as demonstrated by 1 H NMR spectroscopy.

A six-coordinate iron metallacyclopentane, (phen)2Fe(CH2)4, supported by two 1,10-phenanthroline (phen) ligands, has been synthesized and structurally and spectroscopically characterized. The complex is diamagnetic and an idealized octahedral geometry was observed in the solid state. The electronic structure of (phen)2Fe(CH2)4 was determined by a combination of X-ray diffraction, Mossbauer spectroscopy, and DFT analyses and is best described as a low-spin Fe(III) center antiferromagnetically coupled to a radical anion delocalized equally over both phen ligands. The reactivity of (phen)2Fe(CH2)4 under different conditions was explored. Thermolysis or photolysis promoted elimination reactions and mixtures of isomeric butenes and butane were observed. Reactions of (phen)2Fe(CH2)4 with ethylene and isoprene yielded 3% and 11% of reductive elimination product cyclobutane, respectively, along with butane and butene isomers. Addition of π-accepting ligands such as carbon monoxide, maleic anhydride, or 1,4-benzoquinone to (phen)2Fe(CH2)4 promoted C(sp3)-C(sp3) reductive elimination as judged by high selectivity for cyclobutane formation. Two electron oxidation of (phen)2Fe(CH2)4 with two equivalents of ferrocenium tetraphenylborate also exclusively yielded cyclobutane in 95% yield. The electronic structure and reactivity of related bis(bipyridine) iron dialkyl compounds previously isolated by Kochi and co-workers were also revisited and their electronic structures revised based on structural, spectroscopic and computational data.

Five soft metal complexes (1–5) of a 16-membered O2S3-macrocycle (L) with different topologies and coordination modes, including discrete to infinite forms, and endo-, exo-, and endo/exo-coordination, were prepared and structurally characterized. Both mercury(II) complexes, [Hg(L)(NO3)2] (1) and [Hg(L)(DMF)2](ClO4)2·DMF (2), with nitrate and perchlorate anions, respectively, show a typical endocyclic structure. Two nitrate ions in 1 occupy the coordination sites, while two DMF molecules participate to the coordination sphere in 2 remaining two perchlorate ions uncoordinated. It is found that the anion-exchange of 2 in the solid state induced the conversion to 1 which involves the rearrangement of the coordination sphere. In silver(I) complexations, nitrate afforded a cyclic dimer complex [Ag2(L)2(NO3)2] (3). While hexafluorophosphate gave a 1-D zigzag coordination polymer {[Ag(L)]PF6}n (4). Interestingly, triflate led to the isolation of a tetranuclear bis(macrocycle) complex, {[endoAg(L)(CF3SO3)]2[μ-exoAg2(CF3SO3)2]} (5), which are dominated by the coordination modes (endoAg and exoAg) of L toward two types of silver(I) centers. For instance, two endocyclic complex units, endoAg2(L)2(CF3SO3)2, are linked by exocyclic metallacycle, [μ-exoAg2(CF3SO3)2], to give a 4:2 (metal-to-ligand) stoichiometry. From the results, it is obviously clear that the role of anions mostly is responsible to such structural diversity based on the exo-coordination mode.

La atom reactions with 1,4-pentadiene and 1-pentyne are carried out in a laser-vaporization molecular beam source. Both reactions yield a predominant La(C5H6) radical from ligand dehydrogenation and a minor La(C3H4) species from C C bond cleavage. The metal-hydrocarbon radicals are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species formed by the two reactions are essentially identical and consist of a single vibronic band system for La(C5H6) and two band systems for La(C3H4). Each band system exhibits a strong origin band and several weak vibronic ones. Adiabatic ionization energies, metal-ligand vibrational frequencies, and low-frequency ligand-based modes are measured for the two species. La(C5H6) is identified as a six-membered lanthanacycle [La(CHCHCHCHCH2)] (Iso A, C1), whereas two isomers of La(C3H4) are a four-membered metallacycle La(CHCHCH2) (Iso 1, C1) and a three-membered ring La(CHCCH3) (Iso 2, Cs). The ground electronic state of each radical is a doublet and that of the singly charged cation is a singlet. The remaining two electrons that are associated with the isolated La atom or ion are spin paired in a molecular orbital that is bonding combination between a La 5d orbital and a π* antibonding orbital of the C5H6 or C3H4 fragment. For the 1,4-pentadiene reaction, the formation of the six-membered metallacycle La(C5H6) involves La addition to a C=C double bond, La insertion into two C(sp3) H bonds, and concerted H2 elimination, whereas the formation of the three- and four-membered La(C3H4) rings involves two hydrogen migrations followed by C C bond breakage to eliminate an ethylene molecule. For the 1-pentyne reaction, the formation of each species requires isomerization of a La(1-pentyne) adduct to a La insertion species and then proceeds with the same elemental steps as those for the diene reaction.

Pincer ligands have a remarkable ability to impart control over small molecule activation chemistry and catalytic activity; therefore, the design of new pincer ligands and the exploration of their reactivity profiles continues to be a frontier in synthetic inorganic chemistry. In this work, a novel, monoanionic NNN pincer ligand containing two phosphinimine donors was used to create a series of mononuclear Ni complexes. Ligand metallation in the presence of NaOPh yielded a nickel phenoxide complex that was used to form a mononuclear hydride complex on treatment with pinacolborane. Attempts at ligand metallation with NaN(SiMe(3))(2) resulted in the activation of both phosphinimine methyl groups to yield an anionic, cis-dialkyl product, in which dissociation of one phosphinimine nitrogen leads to retention of a square planar coordination environment about Ni. Protonolysis of this dialkyl species generated a monoalkyl product that retained the 4-membered metallacycle. The insertion of 2,6-dimethylphenyl isocyanide (xylNC) into this nickel metallacycle, followed by proton transfer, generated a new five-membered nickel metallacycle. Kinetic studies suggested rate-limiting proton transfer (KIE ≥ 3.9±0.5) from the α-methylene unit of the putative iminoacyl intermediate.

The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or (E)-piperylene with ethylene and α-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicates the diamagnetic η(4)-piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature (1)H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e(−) complexes occurs rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of ((Me)(Et)PDI)Fe(η(4)-piperylene) ((Me)(Et)PDI = 2,6-(2,6-Me(2)-C(6)H(3)N═CEt)(2)C(5)H(3)N), was determined by single-crystal X-ray diffraction and confirmed the s-trans coordination of the monosubstituted 1,3-diene. Possible relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and chemoselectivity of iron-mediated cycloaddition reactions are discussed.

A pyridylhydrazone incorporating an anthracene moiety, designated as HLAnc, has been synthesized in order to examine its coordination behaviour towards rhodium(III). The complex [RhLAnc(PPh3)2Cl2], incorporating a four-membered metallacycle, has been isolated and authenticated by a single-crystal X-ray diffraction study. The complex shows interesting redox and optoelectronic properties, and to better understand these, theoretical investigations have been performed using density functional theory (DFT) and time-dependent DFT. The visible excitation for the complex arises from primarily mixed singlet-manifold 1ILCT and 1LLCT transitions.

Constructing polycyclic aromatics-based highly emissive fluorophores with good solubility, tunable aggregated structures and properties is of great importance for film fabrication, solution processing and relevant functionality studies. Herein, we describe a general strategy to endow conventional organic fluorophores with enhanced solubility and modulated fluorescent properties via the incorporation into coordination-driven self-assembled metallacycles. A widely used fluorophore, pyrene, was decorated with two pyridyl groups to yield functionalized pyrene (4). Mixing 4 with three aromatic dicarboxylates with different lengths and a 90° Pt(II) metal acceptor in a 2:2:4 stoichiometric ratio resulted in the formation of three metallacycles (1, 2, and 3). The metallacycles display good solubility in polar organic solvents, highly aggregation-dependent fluorescence, and size-dependent emissions at higher concentrations. Moreover, metallacycle 2- based, silica-gel supported film as fabricated is not only more emissive than the ligand, 4-based one, but also displays much improved sensing properties for amines in the vapor state as demonstrated by significantly increased response speed and decreased recovery time. The enhanced solubility, unique fluorescence behavior and multi-factor modulation character show that coordination-driven self-assembly can be utilized for the development of new fluorophores through simple modification of conventional fluorophores. The fluorophores synthesized this way possess not only complex topological structures but also good modularity and tunability in fluorescence behavior, which are important for grafting multi-stage energy transfer systems, both important for the development of high performance sensing materials.

We have determined the X-ray structure of Ir(pnbi)2(acac) (pnbi = 2-phenanthren-9-yl-1-phenyl-1H-benzimidazole; acac = acetylacetonate), which exhibits a six-membered metallocycle around the Ir center. This result stands in sharp contrast to previously postulated structures of Ir(pnbi)2(acac), which assumed a five-membered metallocycle. In this paper, we focus on the relative stability of five- and six-membered Ir(C^N) ring structures. DFT calculations of the total energies of Ir-(C^N) complexes indicated that six-membered structures are more stable when bulky substituents are present in the benzimidazole unit. When the phenanthrene group of pnbi was replaced with a naphthalene moiety, DFT calculations predicted that five-membered cycles are more stable than six-membered rings, which was confirmed experimentally by a single-crystal X-ray diffraction analysis. The steric bulk of the phenanthrene-containing polyaromatic ring ligand thus induces greater interligand repulsion between the two ligands, which plays an important role in determining the cyclometalation route. The Ir complexes examined in this study exhibit red emission (λem ≈ 660 nm) with relatively low quantum yields.

Self-assembly reactions of CoII ions in the presence of the 2,2-bipyrimidine (bpym) ligand produced both a dinuclear and an octanuclear cation with the nuclearity being governed by hydrogen-bonding versus anion-π interactions between the anions and the ligands.

Ammonia has a large volume energy density and consequently high potential for application as a fuel and energy reservoir in the future. In this study, the dinuclear FeIII metallacycle complex [Fe2(H2opba)2Cl2(dmso)2]·2CH2Cl2·2dmso (1) with excellent capacity to selectively adsorb ammonia (11.3 mmol g−1) was investigated, demonstrating a strong preference for nitrogenous compounds, especially short-chain amines. The adsorption results suggest that the cavity in the structure of 1 has an essential role in the adsorption mechanism i.e. it is the responsible for size selectivity of 1 during the adsorption process. To better understand the adsorption mechanism of ammonia, 1 was fully characterized before and after adsorption. Thermogravimetric-mass spectrometry (TG-MS) and ammonia isotherm experiments revealed that 8 ammonia molecules were physisorbed by the complex cavity (free ammonia) and 4 ammonia molecules were chemisorbed (coordinated ammonia) per dinuclear metallacycle unit. Further characterization also confirmed the proposed adsorption mechanism, corroborating the structural modification of the compound after its interaction with ammonia; in addition, reuse tests showed that despite a small loss of efficiency, the compound was capable of desorbing most of the ammonia and could be used consecutively for at least three cycles. Thus, 1 is a potential ammonia storage material and adsorbent for the removal of ammonia from effluents.

Here we report the coordination behaviour of an imidazole-based [S1]-donor ligand, 1,3-dimethyl-imidazole-2(3H)-thione (L1), and [S2]-donor ligand, 3,3'-methylenebis(1-methyl-imidazole-2(3H)-thione) (L2) or 4,4'-(3,3'-methylenebis-(2-thioxo-2,3-dihydro-imidazole-3,1-diyl))dibutanoic acid (L3), with HgX2 (X = Cl, Br or I) in solution and the solid state. NMR, UV-Vis spectroscopic, and single crystal X-ray studies demonstrated that L1 or L2 coordinated rapidly and reversibly to the mercury center of HgX2 through the thione moiety. Treatment of L2 with HgCl2 or HgBr2 afforded 16-membered metallacycle k1-(L2)2Hg2Cl4 or k1-(L2)2Hg2Br4 where two Cl or Br atoms are located inside the ring. In contrast, treatment of L2 with HgI2 afforded a chain-like structure of k1-[L2Hgl2]n, possibly due to the large size of the iodine atom. Interestingly, [S1] and [S2]-donor ligands (L1, L2, and L3) showed an excellent efficacy to protect liver cells against HgCl2 induced toxicity and the strength of their efficacy is in the order of L3 > L2 > L1. 30% decrease of ROS production was observed when liver cells were co-treated with HgCl2 and L1 in comparison to those cells treated with HgCl2 only. In contrast, 45% and 60% decrease of ROS production was observed in the case of cells co-treated with HgCl2 and thiones L2 and L3, respectively, indicating that [S2]-donor ligands L2 and L3 have better cytoprotective effects against oxidative stress induced by HgCl2 than [S1]-donor ligand L1. Water-soluble ligand L3 with N-(CH2)3CO2H substituents showed a better cytoprotective effect against HgCl2 toxicity than L2 in liver cells.

Detailed herein is the synthesis and characterization of [P,N]-ligated perfluoronickelacyclopentanes based on the bidentate ligand 2-(diphenylphosphino)phenyl-N-phenylaniline [P,NH]. A high-yielding substitution reaction between [P(O-o-tol)3]2Ni(C4F8) and [P,NH] gives the phosphine-amine-coordinated metallacycle [P,NH]Ni(C4F8). Alternatively, [P,NH]Ni(C4F8) is formed upon treatment of Ni[P(O-o-tol)3]4 with one equiv. of [P,NH] followed by tetrafluoroethylene. This product reacts quantitatively with base to give an anionic phosphine-amido-ligated nickelacycle. Reactivity studies of the new [P,NH]- and [P,N−]-ligated perfluoronickelacycles are presented and compared and contrasted with our previously reported [P,S] systems.

A series of new hydrazone mononuclear complexes of the type [(arene)MLCl]PF6 (M = Ru, Rh, Ir) have been synthesized in this study. All these complexes were fully characterized with the help of FT-IR, UV–Vis, mass and NMR spectroscopy. The molecular structures of representative complexes (1, 2, 7 and 8) were established by single crystal X-ray diffraction study. The molecular structures of the complexes revealed typical piano stool geometry around the metal center in which the ligand acts as NN′ donor chelating ligand. In the case of complexes (1–3), the ligand coordinates to the metal by using both the pyridine nitrogen atoms forming a six membered metallocycle whereas in complexes (4–9) one hydrazone nitrogen atom and one pyridine nitrogen atom coordinates to the metal ion forming a five membered metallocycle. These compounds were evaluated for their in vitro antibacterial activity by agar well diffusion method against two Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa, and two Gram-positive bacteria Staphylococcus aureus, Bacillus thuringiensis. Results show that all the complexes inhibit the growth of bacteria.

The faujasite-supported Rh(I) complex [Rh(C2H4)2]+ was suggested as the active species in experiments showing the catalytic dimerization of ethene to butene in a highly selective fashion (78%), with ethane as side product (19%). As previous theoretical work determined only ethane formation for the reported complex, the present computational work set out to identify a potential mechanism, a migratory insertion (Cossee–Arlman) or metallacycle type, employing a quantum mechanics/molecular mechanics (QM/MM) procedure. Our results exclude the bifunctional mechanism suggested by the experimentalists because we estimated pertinent C–C coupling activation barriers above 125 kJ mol−1. Next we turned to modelling more complex scenarios involving three ethene ligands at the metal center, [Rh(C2H4)3]+. For such an active complex, we determined the in situ generated diethyl intermediate [Rh(C2H4)(C2H5)2]+ as a branching point, yet found ethene hydrogenation favorable over dimerization via a Cossee–Arlman mechanism, with free activation energies of 55 kJ mol−1 and 103 kJ mol−1, respectively. Finally, we addressed a metallacycle mechanism for the dimerization of ethene that allows one to rationalize the experimental selectivity for butene. The crucial relative free energy barrier of the C–C coupling step is calculated at 68 kJ mol– 1. The latter barrier is lower by 6 kJ mol−1 in absolute terms than the hydrogen activation for the Cossee–Arlman mechanism, rendering the metallacycle mechanism the most preferred pathway. To arrive at a conclusive understanding of this chemistry, the present work serves to build a bridge to experimental research by addressing pertinent observations.

We report the syntheses and structural characterization of a Zn(II) metallacycle [Zn2{(L)2(DMF)2(NO3)2}]·(NO3)2 (1) along with a Cd(II) coordination polymer [{Cd1(L)2(DMF)2}·(NO3)2]n (2) (where L = N,N′-bis-(3-pyridyl)terephthalamide; DMF = dimethylformamide) and their utilization as fluorescent probes for highly selective recognition (turn-off) of Fe3+ and CrO42− ions. Compounds 1 and 2 were prepared by utilizing ligand L and the nitrate salt of zinc and cadmium, respectively. Single crystal X-ray analysis reveals that 1 adopts an overall Zn(II) metallacycle architecture, whereas 2 displays a one-dimensional (1D) polymeric structure. Both 1 and 2 showed high fluorescence stability in aqueous solution and selectively detected Fe3+ and CrO42− ions with high quenching constants and low detection limits of 2.34 × 106 M−1 and 0.153 μM for Fe3+, 6.72 × 105 and 0.205 μM for CrO42− (for 1); 3.25 × 106 and 0.193 μM for Fe3+, 6.94 × 105 and 0.155 μM for CrO42− (for 2). Notably, ligand L itself did not display any type of recognition for any ions in DMF as well as in aqueous media. Moreover, 1 and 2 were also employed as heterogeneous catalysts for the ring-opening reaction (ROR) of epoxides with various assorted amines and up to 95% yield (TON, 47.5 and TOF, 11.9 h−1) was observed with perfect regioselectivity in the case of styrene oxide.

By incorporating a semi-rigid ether-based unsymmetrical tetracarboxylic acid [H4detc = 2,3,3′,4′-diphenyl ether tetracarboxylic acid] with various ancillary dipyridyl ligands [phen = 1,10-phenanthroline, bipy = 4,4′-bipyridine, bpea = 1,2-bis(4-pyridyl)ethane, and bpee = 1,2-bis(4-pyridyl)ethylene], eight new coordination compounds were hydrothermally synthesized. [Mn(H2detc)(phen)2]·H2O (1) and [Cd(H3detc)2(bipy)2·H2O]·6H2O (2) are two supramolecular networks built from binuclear and mononuclear structures, respectively. [Cd2(detc)(phen)2]·0.5H2O (3) and [Zn(H2detc)(bipy)] (4) are two luminescent 1D loop chain structures with [M2(detc)2] metallacycle units. [Ni2(detc)(bpee)2·5H2O]·1.5H2O (5) exhibits a 2D fishbone-like double-layered network. [Co2(detc)(bpea)2·H2O] (6) features a 3D framework containing a 1D [Co2(μ2-COO)(μ2-Ocarboxylate)] chain. [Cu2(detc)(bpee)·2H2O]·4H2O (7) possesses a two-fold interpenetration 3D framework with a pcu net topology. [Ni2(detc)(bpea)2·3H2O]·3H2O (8) displays a three-fold interpenetration 3D framework with a (3,3,4)-connected new topological net. Magnetic susceptibility measurements indicate antiferromagnetic exchange interactions between the Co(II) ions in 6. The photoluminescence spectra of compounds 2, 3 and 4 show the corresponding emission bands of their ancillary dipyridyl ligands.

The synthesis and characterisation of a 1-titanacyclobuta-2,3-diene complex, an organometallic analog of elusive 1,2-cyclobutadiene, is presented., The synthesis of an unusual 1-metalla-2,3-cyclobutadiene complex [rac-(ebthi)Ti(Me3SiC3SiMe3)] (rac-ebthi = rac-1,2-ethylene-1,1′-bis(η5-tetrahydroindenyl)), a formal metallacyclic analogue of a non-existent four-membered 1,2-cyclobutadiene, is described. By variation of the cyclopentadienyl ligand of the titanocene precursor it was possible to stabilise this highly exotic compound which selectively reacts with ketones and aldehydes to yield enynes by oxygen transfer to titanium. Analysis of the bonding and electronic structure of the metallacycle shows that the complex is best described as an unusual antiferromagnetically coupled biradicaloid system, possessing a formal Ti(iii) centre coordinated with a monoanionic radical ligand.

The chemical structures and topologies of the crosslinks in supramolecular networks play a crucial role in their properties and functions. Herein, the preparation of a type of poly(N-isopropylacrylamide) (PNIPAAM)-based supramolecular networks crosslinked by emissive hexagonal metallacycles is presented. The topological connections in these networks greatly affect their properties, as evidenced by their differences in absorption, emission, lower critical solution temperature, and modulus along with the variation of crosslinking densities. The integration of PNIPAAM and metallacycles in the networks benefits them improved bioavailability, making them serve as reagents for bacterial imaging and killing. This study provides a strategy to prepare cavity-crosslinked polymer networks for antibacterial applications.

New polyfunctional sterically hindered 3,5-di-tert-butylcatechols with an additional phenolic group in the sixth position connected by a bridging sulfur atom&mdash, (6-(CH2-S-tBu2Phenol)-3,5-DBCat)H2 (L1), (6-(S-tBu2Phenol)-3,5-DBCat)H2 (L2), and (6-(S-Phenol)-3,5-DBCat)H2 (L3) (3,5-DBCat is dianion 3,5-di-tert-butylcatecolate)&mdash, were synthesized and characterized in detail. The exchange reaction between catechols L1 and L3 with triphenylantimony(V) dibromide in the presence of triethylamine leads to the corresponding triphenylantimony(V) catecholates (6-(CH2-S-tBu2Phenol)-3,5-DBCat)SbPh3 (1) and (6-(S-Phenol)-3,5-DBCat)SbPh3 (2). The electrochemical properties of catechols L1-L3 and catecholates 1 and 2 were investigated using cyclic voltammetry. The electrochemical oxidation of L1-L3 at the first stage proceeds with the formation of the corresponding o-benzoquinones. The second process is the oxidation of the phenolic moiety. Complexes 1 and 2 significantly expand their redox capabilities, owing to the fact that they can act as the electron donors due to the catecholate metallocycle capable of sequential oxidations, and as donors of the hydrogen atoms, thus forming a stable phenoxyl radical. The molecular structures of the free ligand L1 and complex 1 in the crystal state were determined by single-crystal X-ray analysis.

A series of Cu complexes bearing N-heterocyclic carbene were synthesized, and their application for the copper-catalyzed azide–alkyne cycloaddition reaction was studied. The catalytic results demonstrated that [L2Cu]Br exhibited the most activity, and the trend of the other complexes was I > Br > Cl ∼ BF4 > PF6. The 1H NMR spectrum of the reaction of LCuCl and phenylacetylene demonstrated that the NHC ligand dissociated from the Cu atom and deprotonated phenylacetylene to produce phenylacetylide. The conductivity study also proved this phenomenon. According to the density functional theory calculations, a mechanism was proposed in which acetylide copper halide was formed after NHC ligand dissociation and phenylacetylene deprotonation. Then, the six-membered metallacycle from the cycloadditions of methyl azide with mononuclear copper acetylide reacted with the second copper catalyst, (NHC)CuX, to form the dinuclear intermediate, which in turn underwent a rapid ring contraction to form another more stable d...

As a common phenomenon in biological systems, supramolecular transformations of biomacromolecules lead to specific biological functions as outputs, which thus inspire people to construct biomimetic dynamic systems through supramolecular transformation strategy. It should be noted that well-modulating the artificial macromolecules to fine-tune their properties is of great significance yet still remains a big challenge in polymer chemistry. In this study, through the combination of coordination-driven self-assembly and postassembly ring-opening polymerization, a six-armed star polymer linked by well-defined hexagonal metallacycle as core was successfully prepared. At the same time, the trans-platinum acetylide moieties as transformation sites were anchored onto the discrete metallacycle scaffold. Subsequently, the simple phosphine ligand-exchange reaction induced the conversions of platinum acetylide building blocks with the varied binding angles, which thus resulted in the successive hexagon-rhomboid-hexagon transformations of metallacyclic scaffold, therefore allowing for the corresponding supramolecular transformation of metallacycle-linked star polymers. More importantly, accompanied by such transformation process, property modulation of the resultant polymers has been successfully realized. In a word, by taking advantage of dynamic nature of metal-ligand coordination bonds and simple phosphine ligand-exchange reactions, facile architecture transformation of a star polymer to a linear polymer and back to a star polymer was successfully realized, which may provide a promising approach toward the construction of new dynamic polymeric materials.

Herein, we present a method for the preparation of supramolecular polymers with tunable fluorescence via the combination of metal-ligand coordination and phenanthrene-21-crown-7(P21C7)- based host-guest interaction. A suite of rhomboidal metallacycles with different substituents were prepared via the coordination-driven self-assembly of a P21C7- based 60° diplatinum (II) acceptor and 120° dipyridyl donors. By the variation of the substituents on the dipyridyl donors, the metallacycles exhibit emission wavelengths spanning the visible region (λ(max) = 427–593 nm). Metallacycle-cored supramolecular polymers were obtained via host-guest interactions between bisammonium salts and P21C7. The supramolecular polymers exhibit similar emission wavelengths of the individual metallacycles and higher fluorescent efficiency in solution and thin films. Utilizing a yellow-emitting supramolecular polymer thin film with high quantum yield (0.22), a white-light-emitting LED was fabricated by painting the thin film onto an ultra violet-LED. This study presents an efficient approach for tuning the properties of fluorescent supramolecular polymers and potential of metallacycle-cored supramolecular polymers as a platform for the fabrication of light-emitting materials with good processability and tunability.

Diarylamine-substituted osmanaphthalyne complexes that feature two redox centers linked by the rigid skeleton of the metallacycle (C^C+), specifically, [OsCl2(PPh3)2{(C^C+)NAr2}][BF4 ] (Ar=Ph (1 a), p-MeOPh (1 b)) and their open-ring precursors [OsHCl2(PPh3)2{(CC(PPh3 +)= CHPh)NR2}][BF4 ] (Ar=Ph (2 a), p-MeOPh (2 b)), were successfully synthesized and characterized by 1 H, 13C, and 31P NMR spectroscopy, ESI-MS, and elemental analysis. The solid-state molecular structures of complexes 1 a and 2 a were ascertained by single-crystal X-ray diffraction. The OsC bond length in both complexes 1 a and 2 a fell within the range reported for similar osmanaphthalynes and osmium carbyne complexes, respectively. The structural parameters determined for complex 1 a, which were successfully reproduced by theoretical calculations, point to a p-delocalized metallacycle structure. The purple color of compounds 1 a and b was explained by the diarylamine!Os(metallacycle) chargetransfer absorption in the visible region. The neutral, oneelectron-oxidized and one-electron-reduced states of compounds 1 a, b, and a reference complex that lacked the diarylamine substituent, [OsCl2(PPh3)2{(C^C+)}][BF4] (1’), were investigated by cyclic and square-wave voltammetry, UV/Vis/NIR spectroelectrochemistry, and DFT calculations. The spin density in singly oxidized complexes [1 a]+ and [1 b]+ predominantly resided on the aminyl segment, with osmium involvement controlled by the diphenylamine substitution. Spin density in stable, singly-reduced [1’] was distributed mainly over the osmanaphthalyne metallacycle.

Density functional theory (DFT) calculations were performed to probe the mechanism of tantalum-catalyzed hydroaminoalkylation, a reaction that affords Csp3–Csp3 bond formation via α-alkylation of a secondary amine with an alkene. Electronic effects in catalyst design were probed to reveal key features in the energy profile of the proposed mechanism, corroborating experimental trends in which electrophilic metal centers demonstrate enhanced reactivity. Modeling of the energy profile with an N,O-chelating amidate Ta catalyst (I) revealed profound differences in relative energetics, rationalizing improvements that have been observed using sterically and electronically varied ligands. N,O-Chelating ligands electronically promote preferential reactivity in the equatorial plane. The turnover-limiting step can be completely changed depending upon the ligand; for sterically bulky monoamidate complexes, the protonolysis of an intermediate metallacycle is the turnover-limiting step rather than C–H activation, as ha...

Combining the star-shaped alkynyl ligands with low-nuclearity gold-copper triphosphane clusters produces 3D metallocage aggregates, which demonstrate room temperature phosphorescence in solution (max Φem =0.6). Their luminescence mainly originates from cluster-localized metal-to-ligand charge transfer excited state. These supramolecular assemblies can be easily converted into the isostructural gold-silver congeners by the direct exchange of the metal ions. Such modification of the terminal metal cores switches the emission to the intraligand (alkyne) electronic transitions of the triplet manifold, that represents an unusual optical functionality among the metallocycle/metallocage complexes.

Computational studies were carried out to provide mechanistic insights into the Rh(I)-catalyzed activation of cyclopropenes and the detailed mechanistic pathways of [3+2+1] carbonylative carbocyclization of tethered ene- and yne-cyclopropenes. Computational results suggest that it is more favorable for the cyclopropene moiety of tethered ene-cyclopropenes to initially undergo heterolytic cleavage of a C-C σ-bond to form a vinyl Rh(I) carbenoid intermediate than to proceed through homolytic C-C σ-bond cleavage to generate a rhodacyclobutene intermediate. The yielded vinyl Rh(I) carbenoid intermediate could undergo cyclization to generate a Rh(III) metallacyclobutene intermediate, which could further lead to a thermodynamically more stable six-coordinated Rh(III) metallacycle intermediate in the presence of additional CO. Afterward, it is more feasible for the yielded six-coordinated Rh(III) metallacycle to sequentially undergo CO migratory insertion, cyclization, and reductive elimination to furnish the final cyclohexenone product. The origin of stereoselectivity of the product was also discussed. The proposed mechanistic pathway can also be applied to the Rh(I)-catalyzed carbonylative carbocyclization of tethered yne-cyclopropenes and vinyl cyclopropenes to produce phenol derivatives. The main mechanistic difference for the vinyl cyclopropene substrate is that the conversion of Rh(I) carbenoid intermediate to the Rh(III) metallacycle proceeds via intramolecular 6π electrocyclization.

Cyclic structures are highly represented in organic molecules, motivating a wealth of catalytic methods targeting their synthesis. Among the various ring-forming processes, cyclooligomerization reactions possess several attractive features but require addressing a unique challenge associated with controlling ring-size selectivity. Here we describe the catalytic reductive cocyclooligomerization of an enone and three carbene equivalents to generate a cyclopentane, a process that constitutes a formal [2 + 1 + 1 + 1]-cycloaddition. The reaction is promoted by a (quinox)Ni catalyst and uses CH2Cl2/Zn as the C1 component. Mechanistic studies are consistent with a metallacycle-based pathway, featuring sequential migratory insertions of multiple carbene equivalents to yield cycloalkanes larger than cyclopropanes.

Coupling of different heterocyclic nitriles at group 4 metallocenes was investigated. The product of 2,6-dicyanopyridine coupling at [Cp*2Ti] (1Ti) reacts with [Cp*2Zr(η2-Me3SiC2SiMe3)] to yield the novel trinuclear TiZr2 complex 2, which further reacts with smaller heteroaromatic nitriles 2-cyanofuran and 2-cyanothiophene to form the homocoupling products 3Zr and 4Zr. Similar products were formed in the direct coupling of these nitriles at [Cp*2M] (M = Ti, Zr). Mixed 1-metalla-2,5-diazacyclopenta-2,4-dienes 5Ti and 5Zr can be accessed by using mixtures of both nitriles, or in the case of 5Zr by stepwise addition of different nitriles to [Cp*2Zr(η2-Me3SiC2SiMe3)]. Metallacycle transfer using titanocene complexes 3Ti and 4Ti and SOCl2 yields the corresponding thiadiazole oxides 3SO and 4SO, as well as the mixed thiadiazole oxide 5SO, which were isolated and fully characterized. DFT calculations were done to further look into the process of nitrile exchange at metallocene.

Reactions of methylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol) (1) with one or two equivalents of bulk Li, Na or K metals in THF or DMSO render mono or dialkali metal complexes depending on the stoichiometric ratio of the reactants. The metal-methylamino-N-(2-methylene-4,6-tert-butylphenol) N-(2-methylene-4,6-tert-butylphenolate) complexes, 2Li, 2Na and 2K, are generated upon the substitution of a single phenol hydrogen of 1. In the solid state, complex 2Na is a dimer due to the establishment of two symmetric hydrogen bonds between two adjacent molecules. The Na center also engages into the formation of a ten-membered metallacycle ring with a butterfly-like structure. Due to dimerization, an intermolecular six-membered core is formed involving two sodium and four oxygen atoms. The weakly coordinated nitrogen atom from the ligand is nearly perpendicular to the hexagonal core. The dimetal-methylamino-N,N′-bis(2-methylene-4,6-di-tert-butylphenolate) complexes, 3Li, 3Na and 3K result from metal substitution of the two phenol hydrogens from ligand 1. The SC-XRD structures of 3Li and 3Na are discreet, each incorporating two metal atoms in different coordination environments. Ten-membered rings with boat-boat conformations are also observed as are rhombic central M2O2 cores. The molecular structure of 3K in DMSO shows a higher degree of aggregation. It effectively comprises four K atoms, two ligand backbones and seven solvent molecules forming a central four-membered K2O2 ring perpendicular to an eight-membered structure formed also by K and O atoms spanning over the two ligand moieties.

The processes of 1-ethyl-3-R-alumolane (R= n-Alk, iBu, Ph, Bn, SiMe3, p-methoxybenzyl) self-association in toluene, benzene, cyclohexane and dichloromethane were studied for the first time by multinuclear NMR spectroscopy and quantum chemical modeling. Using 1H, 13C, and 27Al NMR spectroscopy in non-polar solvents, the examined alumolanes were identified as an equilibrium mixture of isomeric dimers formed via coordination of Al-C ring bonds of the metallacycle. The structures of twenty energetically more favorable dimers were found on the basis of thermodynamic parameter calculations of self-association reactions. A multicenter character of binding in аlumolane dimers was proposed.

Treating a scandium mixed alkyl/diaryloxide complex with phosphino-substituted alcohols resulted in the formation of scandium mixed alkoxyl/diaryloxide complexes Sc[OC(CH3)2CH2PR2][O-2,6- tBu2-C6H3]2[THF] (6, R = Ph; 8, R = tBu). The reactivity of Sc-based Lewis pair complexes 6 and 8 toward a wide range of substrates was investigated. A ligand substitution reaction occurred when complex 6 was treated with benzophenone. The reaction of complex 6 with sulfur afforded a phosphane oxidative product. Complexes 6 and 8 also exhibited typical Sc/P frustrated Lewis pair (FLP) reactivity. They added to the carbonyl group of phenyl isocyanate to form seven-membered metallacycles. Complex 6 underwent selective Sc/P 1,4-addition reactions with α,β-unsaturated carbonyl compounds to give the corresponding nine-membered metallacyclic products. The reaction of 6 with 0.5 mol of dimethyl acetylenedicarboxylate led to the formation of bicyclo[7.7.0]cetane-derived metallacycle 16 in a distinctive double 1,4-addition pattern. With benzil complex 6 underwent a 1,4-addition reaction to afford a cis-enediolate which was coordinated to the Sc/P FLP through Sc-O and P-O bonds. Treatment of complex 6 with cyclopropyl phenyl ketone afforded the 10-membered metallaheterocycle 18, in which a scandium Lewis acid added to the oxygen atom and the phosphine Lewis base attacked the cyclopropyl group with ring opening. A ring-opening reaction also took place when epoxycyclohexane was employed as a substrate. Complex 6 successfully cleaved the C-Br bond of benzyl bromide to give zwitterionic complex 20 with newly formed Sc-Br and P-C bonds. Scandium phosphazine complex 21 was generated by a Sc/P 1,1-addition to the terminal nitrogen atom of (trimethylsilyl)diazomethane. Aided by the phosphorus Lewis base, scandium Lewis acid was able to abstract chloride from (Ph3P)AuCl to produce heterobimetallic Sc/Au complexes 22 and 23. Many complexes in this study were characterized by single-crystal X-ray diffraction.

Metal-containing dithienylethenes offer new opportunities for variations in photochromic behavior. This work reports a series of copper(I) complexes containing dithienylethene-based bidentate phosphine ligands displaying varying photochromic properties. A copper dimer is used as a common precursor, allowing diverse photochromic functionality to be achieved. Calculations show that ring closing of the peripheral dithienyl moiety leads to a slight expansion of the five-membered metallacycle. The photochromic properties and photoreaction quantum yields of these complexes are tunable by variation of the ancillary ligands. Photoswitchable catalysis of a hydroboration reaction with one of the copper complexes is demonstrated.

A benzimidazolydine-based novel ligand L2 was prepared from 1,2-bis(benzimidazol-1-yl)ethane (L1) and synthesis of metallocycle complexes such as Ag(I)–N-Heterocyclic Carbene abbreviated as Ag–NHC and Cu(I)–N-Heterocyclic Carbene complex as Cu–NHC were synthesized and then estimated for antimicrobial and antioxidant properties. Synthesis of Ag–NHC and Cu–NHC metallocycle complexes was described. The benzimidazolydine ligand precursor and its Ag–NHC and Cu–NHC were successfully characterized by FT-IR, FT-Raman, 1D and 2D NMR, HR-ESI mass spectra, and cyclic voltammetric studies. In the present work, antimicrobial study discloses that ligand (L1 and L2) do not show inhibitory activity against various pathogens; however, it was gradually increased, when they were coordinated to metals like Ag and Cu. Among the four compounds, the Ag–NHC strongly hampers the growth of fungal strains. The minimal inhibitory concentration (MIC) ranged between 46 and 750 μg mL−1. A distinctive cell growth reduction was observed in C. albicans when treated with minimum concentration of Ag–NHC complex. Ag–NHC exhibited the ability to prevent the growth of C. albicans by causing severe membrane damage and accumulation of intracellular reactive oxygen species (ROS), which were revealed by fluorescence spectroscopic studies. The tested (L1, L2, Ag–NHC and Cu–NHC) compounds demonstrated significant activity with IC50 values range (0.20–30 μM) for DPPH, OH and NO antioxidant activity. Ascorbic acid was used as standard drug. The radical scavenging potencies of the compounds were explored by employing DPPH, OH and NO assays, in which Ag–NHC exhibited highest inhibitory effect on the radicals [IC50 = 57.3 μM (DPPH), 57.7 μM (OH), 52.3 μM (NO)].

Magnetic aromaticity and antiaromaticity of closed shell metalloaromatics with 4d transition metals (Nb, Tc, Rh) is strictly correlated with the orbital topology (Möbius or Hückel) of their π-HOMO, investigated computationally with DFT methods. A surprisingly simple rule emerged: the metallacycle is aromatic (antiaromatic) when the number of π MOs is even and the π-HOMO is of Möbius (Hückel) topology-and vice versa when the number of π MOs is odd.

A new bidentate directing group, 3-amino-1-methyl-1H-pyridin-2-one, is introduced to achieve a powerful PdII metallacycle for selective γ-C(sp3)–H activation and arylation of aromatic and aliphatic carboxylic acid derivatives. The versatility of the directing group is validated for remote arylation of β-C(sp3)–H, β-C(sp2)–H, and γ-C(sp2)–H to achieve therapeutically important 2-pyridone analogues and arylated acid synthons. The traceless removal of the directing group to retrieve the directing element and carboxylic acids makes this method more interesting.

The iridium(III)/copper(II)-catalyzed dehydrogenative coupling of salicylaldehydes with internal alkynes proceeds efficiently under atmospheric oxygen through aldehyde C-H bond cleavage and decarbonylation. A variety of benzofuran derivatives can be synthesized by the environmentally benign procedure. DFT calculations suggest that this unique transformation involves the facile deinsertion of CO in the key metallacycle intermediate, which is in marked contrast to the corresponding rhodium(III) catalysis that leads to CO-retentive chromone derivatives.

As an effective and noninvasive treatment of various diseases, photodynamic therapy (PTD) relies on the combination of light, a photosensitizer, and oxygen to generate cytotoxic reactive oxygen species that can damage malignant tissue. Much attention has been paid to covalent modifications of the photosensitizers to improve their photophysical properties and to optimize the pathway of the photosensitizers interacting with cells within the target tissue. Herein we report the design and synthesis of a supramolecular heterometallic Ru-Pt metallacycle via coordination-driven self-assembly. While inheriting the excellent photostability and two-photon absorption characteristics of the Ru(II) polypyridyl precursor, the metallacycle also exhibits red-shifted luminescence to the near-infrared region, a larger two-photon absorption cross-section, and higher singlet oxygen generation efficiency, making it an excellent candidate as a photosensitizer for PTD. Cellular studies reveal that the metallacycle selectively accumulates in mitochondria and nuclei upon internalization. As a result, singlet oxygen generated by photoexcitation of the metallacycle can efficiently trigger cell death via the simultaneous damage to mitochondrial function and intranuclear DNA. In vivo studies on tumor-bearing mice show that the metallacycle can efficiently inhibit tumor growth under a low light dose with minimal side effects. The supramolecular approach presented in this work provides a paradigm for the development of PDT agents with high efficacy.

The [2 + 2 + 2] cyclotrimerization of diynes and nitrile provides an efficient method for the synthesis of pyridine and its derivatives which can be extended in the total synthesis of natural products. Use of Grubbs type ruthenium catalysts in the cyclotrimerization reaction expands the applicability of Ru(II) catalysts. Two plausible pathways, viz. metathesis and non-metathesis for the cyclotrimerization reaction between a diyne and a nitrile are elucidated with Grubbs second generation and Hoveyda-Grubbs catalysts using DFT techniques. A ruthenacyclobutene like complex is obtained as a stable intermediate in the metathesis pathway while the formation of a five membered metallacycle is invoked to explain the non-metathesis pathway using a decomposed catalyst. The study reveals the influence of N-substituents on N-heterocyclic ligands (NHC) as well as substituent on carbene ligand in controlling the energetic of both metathesis and non-metathesis pathways. Incorporating NHC ligand with reduced steric influence in catalyst design is desirable for improving the efficiency of cyclotrimerization reaction of alkynes with nitriles. If the catalyst is not decomposed, metathesis is the reaction route and the preferred product will be a benzene derivative. The heterocycle formation observed by Perez-Castells et al. (Org. Lett.,14, 2012, 4982–4985) in presence of excess activated nitriles can only be described using the decomposed catalyst through a non-metathesis pathway.