Tunable Arene Ruthenium Metallaprisms to Transport, Shield, and Release Porphin in Cancer Cells

Synthesis and metalation of polycatechol nanohoops derived from fluorocycloparaphenylenes

Due to their unique topology and distinct physical properties, cycloparaphenylenes (CPPs) are attractive building blocks for new materials synthesis. While both noncovalent interactions and irreversible covalent bonds have been used to link CPP monomers into extended materials, a coordination chemistry approach remains less explored. Here we show that nucleophilic aromatic substitution reactions can be leveraged to rapidly introduce donor groups (-OR, -SR) onto polyfluorinated CPP rings. Demethylation of methoxide-substituted CPPs produces polycatechol nanohoop ligands that are readily metalated to produce well-defined, multimetallic CPP complexes. As catechols are recurring motifs throughout coordination chemistry and dynamic covalent chemistry, the polycatechol nanohoops reported here open the door to new strategies for the bottom-up synthesis of atomically precise CPP-based materials.

Geometry-dependent valence tautomerism, magnetism, and electrical conductivity in 1D iron–tetraoxolene chains

Here we show how a simple change in the geometry of 1D iron–tetraoxolene chains dramatically alters the observed physical properties, including the presence of valence tautomerism, strong magnetic coupling, and electrical conductivity.

Disentangling contributions to guest binding inside a coordination cage host: analysis of a set of isomeric guests with differing polarities

Binding of a set of three isomeric guests (1,2-, 1,3- and 1,4-dicyanobenzene, abbreviated DCB) inside an octanuclear cubic coordination cage host H (bearing different external substitutents according to solvent used) has been studied in water/dmso (98 : 2) and CD₂Cl₂. These guests have essentially identical molecular surfaces, volumes and external functional groups to interact with the cage interior surface; but they differ in polarity with dipole moments of ca. 7, 4 and 0 Debye respectively. In CD₂Cl₂ guest binding is weak but we observe a clear correlation of binding free energy with guest polarity, with 1,4-DCB showing no detectable binding by NMR spectroscopy but 1,2-DCB having −ΔG = 9 kJ mol⁻¹. In water (containing 2% dmso to solubilise the guests) we see the same trend but all binding free energies are much higher due to an additional hydrophobic contribution to binding, with −ΔG varying from 16 kJ mol⁻¹ for 1,4-DCB to 22 kJ mol⁻¹ for 1,4-DCB: again we see an increase associated with guest polarity but the increase in −ΔG per Debye of dipole moment is around half what we observe in CD₂Cl₂ which we ascribe to the fact the more polar guests will be better solvated in the aqueous solvent. A van't Hoff analysis by variable-temperature NMR showed that the improvement in guest binding in water/dmso is entropy-driven, which suggests that the key factor is not direct electrostatic interactions between a polar guest and the cage surface, but the variation in guest desolvation across the series, with the more polar (and hence more highly solvated) guests having a greater favourable entropy change on desolvation.

The three dicyanobenzene isomers have obvious similarities but differ in their dipole moment: effects on binding in a coordination cage host in different solvents are discussed.

Porphyrin/Chlorin Derivatives as Promising Molecules for Therapy of Colorectal Cancer

Colorectal cancer (CRC) is a leading cause of cancer-related death. The demand for new therapeutic approaches has increased attention paid toward therapies with high targeting efficiency, improved selectivity and few side effects. Porphyrins are powerful molecules with exceptional properties and multifunctional uses, and their special affinity to cancer cells makes them the ligands par excellence for anticancer drugs. Porphyrin derivatives are used as the most important photosensitizers (PSs) for photodynamic therapy (PDT), which is a promising approach for anticancer treatment. Nevertheless, the lack of solubility and selectivity of the large majority of these macrocycles led to the development of different photosensitizer complexes. In addition, targeting agents or nanoparticles were used to increase the efficiency of these macrocycles for PDT applications. On the other hand, gold tetrapyrrolic macrocycles alone showed very interesting chemotherapeutic activity without PDT. In this review, we discuss the most important porphyrin derivatives, alone or associated with other drugs, which have been found effective against CRC, as we describe their modifications and developments through substitutions and delivery systems.

Interaction of anions with the surface of a coordination cage in aqueous solution probed by their effect on a cage-catalysed Kemp elimination

An octanuclear M8L12 coordination cage catalyses the Kemp elimination reaction of 5-nitro-1,2-benzisoxazole (NBI) with hydroxide to give 2-cyano-4-nitrophenolate (CNP) as the product. In contrast to the previously-reported very efficient catalysis of the Kemp elimination reaction of unsubstituted benzisoxazole, which involves the substrate binding inside the cage cavity, the catalysed reaction of NBI with hydroxide is slower and occurs at the external surface of the cage, even though NBI can bind inside the cage cavity. The rate of the catalysed reaction is sensitive to the presence of added anions, which bind to the 16+ cage surface, displacing the hydroxide ions from around the cage which are essential reaction partners in the Kemp elimination. Thus we can observe different binding affinities of anions to the surface of the cationic cage in aqueous solution by the extent to which they displace hydroxide and thereby inhibit the catalysed Kemp elimination and slow down the appearance of CNP. For anions with a -1 charge the observed affinity order for binding to the cage surface is consistent with their ease of desolvation and their ordering in the Hofmeister series. With anions that are significantly basic (fluoride, hydrogen carbonate, carboxylates) the accumulation of the anion around the cage surface accelerates the Kemp elimination compared to the background reaction with hydroxide, which we ascribe to the ability of these anions to participate directly in the Kemp elimination. This work provides valuable mechanistic insights into the role of the cage in co-locating the substrate and the anionic reaction partners in a cage-catalysed reaction.

A Family of Externally-Functionalised Coordination Cages

New synthetic routes are presented to derivatives of a (known) M8L12 cubic coordination cage in which a range of different substituents are attached at the C4 position of the pyridyl rings at either end of the bis(pyrazolyl-pyridine) bridging ligands. The substituents are (i) –CN groups (new ligand LCN), (ii) –CH2OCH2–CCH (containing a terminal alkyne) groups (new ligand LCC); and (iii) –(CH2OCH2)3CH2OMe (tri-ethyleneglycol monomethyl ether) groups (new ligand LPEG). The resulting functionalised ligands combine with M2+ ions (particularly Co2+, Ni2+, Cd2+) to give isostructural [M8L12]16+ cage cores bearing 24 external functional groups; the cages based on LCN (with M2+ = Cd2+) and LCC (with M2+ = Ni2+) have been crystallographically characterised. The value of these is twofold: (i) exterior nitrile or alkene substituents can provide a basis for further synthetic opportunities via ‘Click’ reactions allowing in principle a diverse range of functionalisation of the cage exterior surface; (ii) the exterior –(CH2OCH2)3CH2OMe groups substantially increase cage solubility in both water and in organic solvents, allowing binding constants of cavity-binding guests to be measured under an increased range of conditions.

Orthogonal binding and displacement of different guest types using a coordination cage host with cavity-based and surface-based binding sites

The octanuclear Co(ii) cubic coordination cage system H (or HW if it bears external water-solubilising substituents) has two types of binding site for guests. These are (i) the partially-enclosed central cavity where neutral hydrophobic organic species can bind, and (ii) the six 'portals' in the centres of each of the faces of the cubic cage where anions bind via formation of a network of CH⋯X hydrogen bonds between the anion and CH units on the positively-charged cage surface, as demonstrated by a set of crystal structures. The near-orthogonality of these guest binding modes provides the basis for an unusual dual-probe fluorescence displacement assay in which either a cavity-bound fluorophore (4-methyl-7-amino-coumarin, MAC; λ_em = 440 nm), or a surface-bound anionic fluorophore (fluorescein, FLU; λ_em = 515 nm), is displaced and has its emission ‘switched on’ according to whether the analyte under investigation is cavity-binding, surface binding, or a combination of both. A completely orthogonal system is demonstrated based using a Hw/MAC/FLU combination: addition of the anionic analyte ascorbate displaced solely FLU from the cage surface, increasing the 515 nm (green) emission component, whereas addition of a neutral hydrophobic guest such as cyclooctanone displaced solely MAC from the cage central cavity, increasing the 440 nm (blue) emission component. Addition of chloride results in some release of both components, and an intermediate colour change, as chloride is a rare example of a guest that shows both surface-binding and cavity-binding behaviour. Thus we have a colourimetric response based on differing contributions from blue and green emission components in which the specific colour change signals the binding mode of the analyte. Addition of a fixed red emission component from the complex [Ru(bipy)₃]²⁺ (Ru) provides a baseline colour shift of the overall colour of the luminescence closer to neutral, meaning that different types of guest binding result in different colour changes which are easily distinguishable by eye.

Orthogonal binding of neutral or anionic fluorophores to the cavity or surface, respectively, of a coordination cage host allows a dual-probe displacement assay which gives a different fluorescence colorimetric response according to where analyte species bind.

Coordination-Driven Selective Formation of D2 Symmetric Octanuclear Organometallic Cages

The coordination-driven self-assembly of organometallic half-sandwich iridium(III)- and rhodium(III)-based building blocks with asymmetric ambidentate pyridyl-carboxylate ligands is described. Despite the potential for obtaining a statistical mixture of multiple products, D₂ symmetric octanuclear cages were formed selectively by taking advantage of the electronic effects emanating from the two types of chelating sites - (O,O') and (N,N') - on the tetranuclear building blocks. The metal sources and the lengths of bridging ligands influence the selectivity of the self-assembly. Experimental observations, supported by computational studies, suggest that the D₂ symmetric cages are the thermodynamically favored products. Overall, the results underline the importance of electronic effects on the selectivity of coordination-driven self-assembly, and demonstrate that asymmetric ambidentate ligands can be used to control the design of discrete supramolecular coordination complexes.

Synthesis, Structure, and Catalytic Hydrogenation Activity of [NO]-Chelate Half-Sandwich Iridium Complexes with Schiff Base Ligands

A series of N,O-coordinate iridium(III) complexes with a half-sandwich motif bearing Schiff base ligands for catalytic hydrogenation of nitro and carbonyl substrates have been synthesized. All iridium complexes showed efficient catalytic activity for the hydrogenation of ketones, aldehydes, and nitro-containing compounds using clean H₂ as reducing reagent. The iridium catalyst displayed the highest TON values of 960 and 950 in the hydrogenation of carbonyl and nitro substrates, respectively. Various types of substrates with different substituted groups afforded corresponding products in excellent yields. All N,O-coordinate iridium(III) complexes 1-4 were well characterized by IR, NMR, HRMS, and elemental analysis. The molecular structure of complex 1 was further characterized by single-crystal X-ray determination.

Outside the box: quantifying interactions of anions with the exterior surface of a cationic coordination cage

We describe a study of the binding of anions to the surface of an octanuclear coordination cage HW, which carries a 16+ charge, in aqueous solution. Anionic aromatic fluorophores such as fluorescein (and derivatives) and hydroxypyrene tris-sulfonate (HPTS) bind strongly to an extent depending on their charge and hydrophobicity. Job plots indicated binding of up to six such fluorescent anions to HW, implying that one anion can bind to each face of the cubic cage, as previously demonstrated crystallographically with small anions such as halides. The quenching of these fluorophores on association with the cage provides the basis of a fluorescence displacement assay to investigate binding of other anions: addition of analyte (organic or inorganic) anions in titration experiments to an HW/fluorescein combination results in displacement and restoration of the fluorescence from the bound fluorescein, allowing calculation of 1 : 1 binding constants for the HW/anion combinations. Relative binding affinities of simple anions for the cage surface can be approximately rationalised on the basis of ease of desolvation (e.g. F- < Cl- < Br-), electrostatic factors given the 16+ charge on the cage (monoanions < dianions), and extent of hydrophobic surface. The interaction of a di-anionic pH indicator (bromocresol purple) with HW results in a pKa shift, with the surface-bound di-anionic form stabilised by approximately 1 pKa unit compared to the non-bound neutral form due to the charge on the cage.

Porphyrin and phthalocyanine photosensitizers designed for targeted photodynamic therapy of colorectal cancer

Colorectal cancer is of particular concern due to its high mortality rate count. Recent investigations on targeted phototherapy involving novel photosensitizers and drug-delivery systems have provided promising results and realistic prospects for a successful medical treatment. New research trends have been focused particularly on development of advanced molecular systems offering effective photoactive species which could be selectively delivered directly into the affected cells. Porphyrins and phthalocyanines have been considered extremely attractive for this purpose due to their molecular versatility, excellent photochemical properties and multifunctional nature. In this review it has been demonstrated that such macrocyclic compounds may effectively contribute to the inhibition of the growth of colon cancer cells and eventually to their photonecrosis. Purposely designed and tailored porphyrin and phthalocyanine derivatives in combination with smart drug-carriers have proved suitable for photodynamic therapy (PDT) and related antitumor treatments. This survey comprises a choice of potentially applicable ideas developed since 2010 involving 9 different tumor cell lines and featuring 32 photosensitizers.

Supramolecular coordination complexes as diagnostic and therapeutic agents

The metal-based drugs represented by cisplatin, carboplatin, and oxaliplatin, prevail in cancer treatment, whereas new therapeutics are extremely slow to step into the clinic. Poor pharmacokinetics, multidrug resistance, and severe side effects greatly limit the development of metal-based anticancer drugs. The robustness and modular composition of supramolecular coordination complexes allow for the incorporation of novel diagnostic and therapeutic modalities, showing promising potentials for precise cancer theranostics. In this mini review, we highlight the recent advances in the development of supramolecular coordination complexes as diagnostic and therapeutic agents. The key focuses of these reports lie in searching sophisticated coordination ligands and nanoformulations that can potentially solve the issues faced by current metal-based drugs including imaging, resistance, toxicity, and pharmacological deficiencies.

Interactions of Small-Molecule Guests with Interior and Exterior Surfaces of a Coordination Cage Host

Coordination cages are well-known to act as molecular containers that can bind small-molecule guests in their cavity. Such cavity binding is associated with interactions of the guests with the surrounding set of surfaces that define the cavity; a guest that is a good fit for the cavity will have many favourable interactions with the interior surfaces of the host. As cages have exterior as well as interior surfaces, possibilities also exist for ‘guests’ that are not well-bound in the cavity to interact with the exterior surface of the cage where spatial constraints are fewer. In this paper, we report a combined solid-state and solution study using an octanuclear cubic M8L12 coordination cage which illustrates the occurrence of both types of interaction. Firstly, crystallographic studies show that a range of guests bind inside the cavity (either singly or in stacked pairs) and/or interact with the cage exterior surface, depending on their size. Secondly, fluorescence titrations in aqueous solution show how some flexible aromatic disulfides show two separate types of interaction with the cage, having different spectroscopic consequences; we ascribe this to separate interactions with the exterior surface and the interior surface of the host cage with the former having a higher binding constant. Overall, it is clear that the idea of host/guest interactions in molecular containers needs to take more account of external surface interactions as well as the obvious cavity-based binding.

Anticancer Activity of Electron-Deficient Metal Complexes against Colorectal Cancer in vitro Models

An evaluation of the in vitro cytotoxicity of nine electron-deficient half-sandwich metal complexes towards two colorectal cancer cell lines (HCT116 p53+/+, HCT116 p53-/-) and one normal prostate cell line (PNT2) is presented herein. Three complexes were found to be equally cytotoxic towards both colorectal cancer cell lines, suggesting a p53-independent mechanism of action. These complexes are 12 to 34× more potent than cisplatin against HCT116 p53+/+ and HCT116 p53-/- cells. Furthermore, they were found to exhibit little or no cytotoxicity towards PNT2 normal cells, with selectivity ratios greater than 50. To gain an insight into the potential mechanisms of action of the most active compounds, their effects on the expression levels of a panel of genes were measured using qRT-PCR against treated HCT116 p53+/+ and HCT116 p53-/- cells, and cell-cycle analysis was carried out.

Novel tetranuclear ruthenium(II) arene complexes showing potent cytotoxic and antimetastatic activity as well as low toxicity in vivo

Ruthenium complexes have attracted a surge of interest as anticancer drug candidates because of their low toxicity, diversity in mode-of-actions and non-cross drug resistance with conventional platinum-based agents. Despite remarkable advances, only a limited number of ruthenium complexes have been demonstrated to kill cancer cells and suppress metastasis simultaneously. Here, two organometallic tetranuclear Ru(II) arene complexes (Ru-1 and Ru-2) have been synthesized and evaluated for their in vitro activity against a panel of human cancer cell lines, including a cisplatin-resistant human lung cancer A549 cell line. A superior cytotoxic activity of the ruthenium complexes compared to cisplatin across distinct cell lines was observed. Further examination of the mechanism indicated that anticancer activity was accomplished by inducing apoptosis in cancer cells. In addition, we found that such compounds exhibited promising antimetastatic activity and reduced the invasiveness of cancer cells. Importantly, choosing Ru-1 as a target compound, a significantly enhanced safety profile relative to cisplatin in animals was validated, suggesting that these complexes can be used as promising candidates for cancer therapy and deserve further investigation.

Catalytic hydrogenation of carbonyl and nitro compounds using an [N,O]-chelate half-sandwich ruthenium catalyst

A series of N,O-chelate half-sandwich ruthenium complexes have been synthesized, which exhibited high activity for the catalytic hydrogenation of carbonyl and nitro compounds in aqueous solution.

Self-Assembled BODIPY-Based Iridium Metallarectangles: Cytotoxicity and Propensity to Bind Biomolecules

A new 4-ethynylpyridine 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based ligand L, which was synthesized by means of the Sonogashira coupling method, was used to obtain two new [2+2] iridium-based metallarectangles, 3 and 4. Ligand L and metallarectangles 3 and 4 were fully characterized through various analytical techniques. The structure of rectangle 4 was further confirmed by single-crystal X-ray diffraction analysis, which showed the formation of an expected [2+2] supramolecule, in which the iridium metal centers were bridged with ligand L to form the desired metallarectangle 4. In the context of the growing biological interest in metallarectangles, rectangle 4 was found to be highly active against two types of cancer cells, with IC₅₀ values almost threefold superior to those of cisplatin. Both 3 and 4 showed dose-dependent abilities to bind bovine serum albumin and salmon sperm DNA; this indicated their tendency to interact with such biomolecules as a potential mode of action.

Catalysis in a Cationic Coordination Cage Using a Cavity-Bound Guest and Surface-Bound Anions: Inhibition, Activation, and Autocatalysis

The Kemp elimination (reaction of benzisoxazole with base to give 2-cyanophenolate) is catalyzed in the cavity of a cubic M₈L₁₂ coordination cage because of a combination of (i) benzisoxazole binding in the cage cavity driven by the hydrophobic effect, and (ii) accumulation of hydroxide ions around the 16+ cage surface driven by ion-pairing. Here we show how reaction of the cavity-bound guest is modified by the presence of other anions which can also accumulate around the cage surface and displace hydroxide, inhibiting catalysis of the cage-based reaction. Addition of chloride or fluoride inhibits the reaction with hydroxide to the extent that a new autocatalytic pathway becomes apparent, resulting in a sigmoidal reaction profile. In this pathway the product 2-cyanophenolate itself accumulates around the cationic cage surface, acting as the base for the next reaction cycle. The affinity of different anions for the cage surface is therefore 2-cyanophenolate (generating autocatalysis) > chloride > fluoride (which both inhibit the reaction with hydroxide but cannot deprotonate the benzisoxazole guest) > hydroxide (default reaction pathway). The presence of this autocatalytic pathway demonstrates that a reaction of a cavity-bound guest can be induced with different anions around the cage surface in a controllable way; this was confirmed by adding different phenolates to the reaction, which accelerate the Kemp elimination to different extents depending on their basicity. This represents a significant step toward the goal of using the cage as a catalyst for bimolecular reactions between a cavity-bound guest and anions accumulated around the surface.

Efficient and Rapid Mechanochemical Assembly of Platinum(II) Squares for Guanine Quadruplex Targeting

We present a rapid and efficient method to generate a family of platinum supramolecular square complexes, including previously inaccessible targets, through the use of ball milling mechanochemistry. This one-pot, two-step process occurs in minutes and enables the synthesis of the squares [Pt₄(en)₄(N∩N)₄][CF₃SO₃]₈ (en= ethylenediamine, N∩N = 4,4'-bipyridine derivatives) from commercially available precursor K₂PtCl₄ in good to excellent yields. In contrast, solution-based assembly requires heating the reagents for weeks and gives lower yields. Mechanistic investigations into this remarkable rate acceleration revealed that solution-based assembly (refluxing for days) results in the formation of large oligomeric side-products that are difficult to break down into the desired squares. On the other hand, ball milling in the solid state is rapid and appears to involve smaller intermediates. We examined the binding of the new supramolecular squares to guanine quadruplexes, including oncogene and telomere-associated DNA and RNA sequences. Sub-micromolar binding affinities were obtained by fluorescence displacement assays (FID) and isothermal titration calorimetry (ITC), with binding preference to telomere RNA (TERRA) sequences. ITC showed a 1:1 binding stoichiometry of the metallosquare to TERRA, while the stoichiometry was more complex for telomeric quadruplex DNA and a double-stranded DNA control.

Coordination-Driven Self-Assembly Using Ditopic Pyridyl-Pyrazolyl Donor and p-Cymene Ru(II) Acceptors: [2]Catenane Synthesis and Anticancer Activities

Coordination-driven self-assembly of m-bis[3-(4-pyridyl)pyrazolyl]xylene (L) and [(p-cymene)₂Ru₂(OO∩OO)₂(OTf)₂] (A₁) (OO∩OO = 6,11-dioxido-5,12-naphthacenedione) in methanol resulted in a mixture of [2]catenane 1 and macrocycle 2, and self-assembly in nitromethane resulted in pure macrocycle 2, whereas the coordination-driven self-assembly of L and similar acceptors [(p-cymene)₂Ru₂(OO∩OO)₂(OTf)₂] [OO∩OO = 5,8-dioxido-1,4-naphthoquinonnato (A₂); 2,5-dioxido-1,4-benzoquinonato (A₃); oxalato (A₄)] resulted in the formations of monomeric macrocycles 3-5, respectively. All self-assembled macrocycles were obtained in excellent yields (>90%) as triflate salts and were fully characterized by multinuclear NMR, elemental analysis, and electrospray ionization mass spectrometry (ESI-MS). The structures of [2]catenane 1 and macrocycles 5 were confirmed by single-crystal X-ray diffraction analysis. The X-ray structure of 1 confirmed an edge-to-face interaction between the tetracene moiety in parallel-displaced π-π stacks (3.5 Å), and CH···π (2.5 Å) stabilizes the [2]catenane topology. Macrocycles 2-5 were assessed for anticancer activities using human cancer cell lines of different origins, and the macrocycle 3 was found to exhibit the best inhibitory effect and to do so in a dose-dependent manner. Further examination with the Tali apoptosis assay suggested the growth inhibitory effect of 3 involved the induction of the programmed cell death, and this suggestion was supported by observations of PARP and caspase 3 cleavage after treating cells with 3. In addition, exposure to 3 increased the expression of Bax and repressed the expression of Bcl-2, thus indicating the involvement of macrocycle 3 upstream of Bax and Bcl-2 in the apoptotic signaling pathway. Macrocycle 3 also tended to repress metastasis as evidenced by changes in the transcriptional expressions E- and N-cadherin (markers of metastasis). Furthermore, a stability assay demonstrated macrocycle 3 remained stable at high concentration.

Pseudo electron-deficient organometallics: limited reactivity towards electron-donating ligands

This work presents the unusual reactivity of a family of electron-deficient half-sandwich metal complexes.

A Quantitative Study of the Effects of Guest Flexibility on Binding Inside a Coordination Cage Host

We have performed a systematic investigation of the effects of guest flexibility on their ability to bind in the cavity of a coordination cage host in water, using two sets of isomeric aliphatic ketones that differ only in the branching patterns of their alkyl chains. Apart from the expected increase in binding strength for C9 over C7 ketones associated with their greater hydrophobic surface area, within each isomeric set there is a clear inverse correlation between binding free energy and guest flexibility, associated with loss of conformational entropy. This can be parameterized by the number of rotatable C-C bonds in the guest, with each additional rotatable bond resulting in a penalty of around 2 kJ mol-1 in the binding free energy, in good agreement with values obtained from protein/ligand binding studies. We used the binding data for the new flexible guests to improve the scoring function that we had previously developed that allowed us to predict binding constants of relatively rigid guests in the cage cavity using the molecular docking programme GOLD (Genetic Optimisation of Ligand Docking). This improved scoring function resulted in a significant improvement in the ability of GOLD to predict binding constants for flexible guests, without any detriment to its ability to predict binding for more rigid guests.

Spheroid Metallacycles and Metallocavitands with Calixarene- and/or Cleft-Shaped Receptors on the Surface

Flexible hexatopic ligands, 1,2,3,4,5,6-hexakis(1H-naphtho[2,3-d]imidazol-1-ylmethyl)benzene (L(2)) and 1,2,3,4,5,6-hexakis(4,5-diphenylimidazol-1-ylmethyl)benzene (L(3)), containing six neutral naphthanoimidazolyl and 4,5-diphenylimidazolyl N donors were synthesized and used to assemble M6L6L'-type [M = Re(CO)3, L = anionic angular rigid NN donors, and L' = flexible hexatopic N donors] spheroid metallacycles. These molecules with a diameter of ∼17 Å were obtained from Re2(CO)10, H-L (imidazole, benzimidazole, and naphthanoimidazole), and L' [1,2,3,4,5,6-hexakis(benzimidazol-1-ylmethyl)benzene (L(1)), L(2), and L(3)] in a one-step process. Ligands L(2) and L(3) were characterized by elemental analysis, electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), and (1)H NMR spectroscopy. Metallacycles 1-5 were characterized by elemental analysis, ESI-TOF-MS, Fourier transform infrared spectroscopy, and single-crystal X-ray diffraction analysis. Molecules 1, 2, and 4 can be considered as metallocavitands and contain multiple solvent-accessible receptors, i.e., two metallocalix[3]arene units and six/four calix[4]arene-/cleft-shaped receptors, on the surface. Guests such as acetone molecules could be accommodated in the calix[4]arene/cleft-shaped receptor of the metallocavitands.

[NO]- and [NN]-coordination mode rhodium complexes based on a flexible ligand: synthesis, reactivity and catalytic activity

Two rhodium(i) complexes were synthesized by the reaction of an [NON]-flexible ligand with Rh(COD)₂BF₄ under different reaction conditions.

Antitumor and biological investigation of doubly cyclometalated ruthenium(ii) organometallics derived from benzimidazolyl derivatives

In this study, we report the synthesis, anticancer and biological properties of three doubly cyclometalated phenylbenzimidazole derived ruthenium(ii) organometallics (1–3) and their corresponding three organic ligands.