Highly Efficient NMR Enantiodiscrimination of Chiral Octanuclear Metalla-Boxes in Polar Solvent

Controlling Chiral Self-Sorting in Truxene-Based Self-Assembled Cages

Coordination driven self-assembly of achiral components, i.e., hexa-alkylated truxene ligands (L) with bis-metallic complexes (M2), afforded three chiral face-rotating stereoisomer polyhedra (M6L2). By tuning the length of the alkyl chains as well as the distance between both ligands facing each other in the self-assemblies (M6L2), one can control the diastereomeric distribution between the expected homo- and hetero-chiral structures.

Four- and two-armed hetero porphyrin dimers: their specific recognition and self-sorting behaviours

In this study we self-assembled the four-armed porphyrin hetero dimer capsule Cap4, stabilized through amidinium-carboxylate salt bridges, in CH₂Cl₂ and CHCl₃. The dimer capsule Cap4 was kinetically and thermodynamically more stable than the corresponding two-armed dimer Cap2. The number of arms strongly influenced their recognition behaviour; guests possessing small aromatic faces (e.g., 1,3,5-trinitrobenzene) preferred residing in the cavity of the two-armed capsule Cap2, rather than in Cap4, both thermodynamically and kinetically; in contrast, large aromatic guests (e.g., 9,10-dibromoanthracene) were encapsulated predominantly by Cap4 because of favourable entropic effects. The number of arms enabled self-sorting behaviour of the dimer formation; complexation studies using an equimolar mixture of the four porphyrin constituents of the two capsules revealed the quantitative formation of the corresponding dimers Cap2 and Cap4. Furthermore, we examined the specific molecular recognition of Cap2 and Cap4; NMR experiments of mixtures of Cap2 and Cap4 in the presence of favourable guests for Cap2 and Cap4 revealed that these guest molecules were encapsulated selectively by their preferred hosts.

Ruthenium-based assemblies incorporating tetrapyridylporphyrin panels: a photosensitizer delivery strategy for the treatment of rheumatoid arthritis by photodynamic therapy

Ruthenium-based assemblies containing tetrapyridylporphyrin derivatives in their structures have been evaluated as photosensitizers to treat rheumatoid arthritis by photodynamic therapy.

Encapsulation of Aromatic Guests in the Bisporphyrin Cavity of a Double-Stranded Spiroborate Helicate: Thermodynamic and Kinetic Studies and the Encapsulation Mechanism

A double-stranded spiroborate helicate bearing a bisporphyrin unit in the middle forms an inclusion complex with electron-deficient aromatic guests that are sandwiched between the porphyrins. In the present study, we systematically investigated the effects of size, electron density, and substituents of a series of aromatic guests on inclusion complex formations within the bisporphyrin. The thermodynamic and kinetic behaviors during the guest-encapsulation process were also investigated in detail. The guest-encapsulation abilities in the helicate increased with the increasing core sizes of the electron-deficient aromatic guests and decreased with the increasing bulkiness and number of substituents of the guests. Among the naphthalenediimide derivatives, those with bulky N-substituents at both ends hardly formed an inclusion complex. Instead, they formed a [2]rotaxane-like inclusion complex through the water-mediated dynamic B-O bond cleavage/reformation of the spiroborate groups of the helicate, which enhanced the conformational flexibility of the helicate to enlarge the bisporphyrin cavity and form an inclusion complex. Based on the X-ray crystal structure of a unique pacman-like 1:1 inclusion complex between the helicate and an ammonium cation as well as the molecular dynamics simulation results, a plausible mechanism for the inclusion of a planar aromatic guest within the helicate is also proposed.

A Flexible Synthetic Strategy for the Preparation of Heteroleptic Metallacycles of Porphyrins

We present a stepwise synthetic strategy for the preparation of the unprecedented heteroleptic 2+2 neutral metallacycle [{t,c,c-RuCl₂(CO)₂}₂(4'cisDPyP)(3'cisDPyP)] (5), in which two different 5,10-meso-dipyridylporphyrins, 4'cisDPyP [i.e., 5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin] and 3'cisDPyP [i.e., 5,10-bis(3'-pyridyl)-15,20-diphenylporphyrin], are joined through equal 90°-angular Ru(II) connectors. The synthesis of 5 was accomplished through the preparation of a reactive ditopic intermediate in which one of the two pyridylporphyrins is linked to two neutral ruthenium fragments, each having one residual readily available coordination site (a dmso-O). Thus, compound 5 was obtained under mild conditions through two complementary routes: either by treatment of [{t,c,c-RuCl₂(CO)₂(dmso-O)}₂(4'cisDPyP)] (3) with 1 equiv of 3'cisDPyP or, alternatively, by treatment of [{t,c,c-RuCl₂(CO)₂(dmso-O)}₂(3'cisDPyP)] (4) with 1 equiv of 4'cisDPyP. Heteroleptic metallacycle 5 was isolated in pure form in acceptable yield and fully characterized. Spectroscopic data and a molecular model show that 5 has an L-shaped geometry, with the two porphyrins almost orthogonal to one another. The modular approach that we established is highly flexible and opens the way to several possible exciting developments.

Tuning the Reactivity of Cofacial Porphyrin Prisms for Oxygen Reduction Using Modular Building Blocks

We assembled eight cofacial porphyrin prisms using MTPyP (M = Co(II) or Zn(II), TPyP = 4-tetrapyridylporphyrin) and functionalized ruthenium-based "molecular clips" using coordination-driven self-assembly. Our approach allows for the rapid synthesis of these architectures in isolated yields as high as 98% for the assembly step. Structural and reactivity studies provided a deeper understanding of the role of the building blocks on the oxygen reduction reaction (ORR). Catalytic efficacy was probed by using cyclic and hydrodynamic voltammetry on heterogeneous catalyst inks in aqueous media. The reported prisms showed outstanding selectivity (>98%) for the kinetically hindered 4e^-/4H⁺ reduction of O₂ to H₂O over the kinetically more accessible 2e^-/2H⁺ reduction to H₂O₂. Furthermore, we have demonstrated significant cofacial enhancement in the observed catalytic rate constant k_s (∼5 orders of magnitude) over the mononuclear analogue. We conclude that the steric bulk of the clip plays an important role in the structural dynamics of these prisms, which in turn modulates the ORR reactivity with respect to selectivity and kinetics.

A Five-layer π-Aromatic Structure Formed through Self-assembly of a Porphyrin Trimer and Two Aromatic Guests

In this study we synthesized two- and four-armed porphyrins - bearing two carboxyl and four 2-aminoquinolino functionalities, respectively, at their meso positions - as a complementary hydrogen bonding pair for the self-assembly of a D₂ -symmetric porphyrin trimer host. Two units of the two-armed porphyrin and one unit of the four-armed porphyrin self-assembled quantitatively into the D₂ -symmetric porphyrin trimer, stabilized through ammidinium-carboxylate salt bridge formation, in CH₂ Cl₂ and CHCl₃ . The porphyrin trimer host gradually bound two units of 1,3,5-trinitrobenzene between the pair of porphyrin units, forming a five-layer aromatic structure. At temperatures below -40 °C, the rates of association and dissociation of the complexes were slow on the NMR spectroscopic time scale, allowing the 1 : 1 and 1 : 2 complexes of the trimer host and trinitrobenzene guest(s) to be detected independently when using less than 2 eq of trinitrobenzene. Vis titration experiments revealed the values of K₁ (2.1±0.4×10⁵  M^-1 ) and K₂ (2.2±0.06×10⁴  M^-1 ) in CHCl₃ at room temperature.

Cofacial porphyrin dimers assembled from N-heterocyclic carbene–metal bonds

Cofacial porphyrin dimers assembled from eight metal–carbene bonds were synthesized by using porphyrins with four imidazolium groups as precursors.

Light-initiated reversible conversion of macrocyclic endoperoxides derived from half-sandwich rhodium-based metallarectangles

A series of metallarectangles were synthesized by an anthracene-based ligand and three different half-sandwich rhodium precursors. The photochemical reactions show that these metallarectangles can be reversibly converted to the macrocyclic endoperoxides.

Chiral two bladed ML2 metallamacrocycles: design, structures and solution behavior

Chiral two bladed complexes of [Co(L)₂][BF₄]₂ (1) and [Zn(L)₂][BF₄]₂ (2) containing an atropoisomeric semi-rigid bidentate ligand L were synthesized and characterized. They are obtained as homochiral species but in a racemic mixture via a ligand self-sorting mechanism. These enantiomers can be differentiated in solution using optically active anions.

Controlled Orthogonal Self-Assembly of Heterometal-Decorated Coordination Cages

Multiple orthogonal coordinative interactions were utilized to construct heterometal-decorated tetrahedral cages from in situ formed trinuclear Zr^IV clusters through the combination with other metal ions such as Cu^II or Pd^II . Through effective use of the hard/soft acid/base principle, the orthogonal self-assembly process of Zr-bpydc-CuCl₂ (H₂ bpydc=2,2-bipyridine-5,5-dicarboxylic acid) can be finely controlled using three strategies: post-synthetic metallization, a stepwise metalloligand approach, or a one-pot reaction.

The Biological Side of Water-Soluble Arene Ruthenium Assemblies

This review article covers the synthetic strategies, structural aspects, and host-guest properties of ruthenium metalla-assemblies, with a special focus on their use as drug delivery vectors. The two-dimensional metalla-rectangles show interesting host-guest possibilities but seem less appropriate for being used as drug carriers. On the other hand, metalla-prisms allow encapsulation and possible targeted release of bioactive molecules and consequently show some potential as drug delivery vectors. The reactivity of these metalla-prisms can be fine-tuned to allow a fine control of the guest’s release. The larger metalla-cubes can be used to stabilize the formation of G-quadruplex DNA and can be used to encapsulate and release photoactive molecules such as porphins. These metalla-assemblies demonstrate great prospective in photodynamic therapy.

Selective detection of multicarboxylate anions based on "turn on" electron transfer by self-assembled molecular rectangles

Two new large molecular rectangles (4 and 5) were obtained by the reaction of two different dinuclear arene ruthenium complexes [Ru(2)(arene)(2)(OOOO)(2)Cl(2)] (arene = p-cymene; OOOO = 2,5-dihydroxy-1,4-benzoquinonato (2), 6,11-dihydroxy-5,12-naphthacene dionato (3)) with the unsymmetrical amide NN (N-[4-(pyridin-4-ylethynyl)phenyl]isonicotinamide) donor ligand 1 in methanol in the presence of AgO(3)SCF(3), forming tetranuclear cations of the general formula [Ru(4)(arene)(4)(NN)(2)(OOO O)(2)](4+). Both rectangles were isolated in good yields as triflate salts and were characterized by multinuclear NMR, ESI-MS, UV/Vis, and photoluminescence spectroscopy. The crystal structure of 5 was determined by X-ray diffraction. Luminescent rectangle 5 was used for anion sensing with an amide ligand as a hydrogen-bond donor and an arene-ruthenium acceptor as a signaling unit. Rectangle 5 strongly bound multicarboxylate anions, such as oxalate, tartrate, and citrate, in UV/Vis titration experiments in 1:1 ratios, in contrast to monoanions, such as F(-), Cl(-), NO(3)(-), PF(6)(-), CH(3)COO(-), and C(6)H(5)COO(-). The fluorescence titration experiment showed a large fluorescence enhancement of 5 upon binding to multicarboxylate anions, which could be attributed to blocking of the photoinduced electron transfer process from the arene-ruthenium moiety to the amidic donor in 5; this was likely to be a result of hydrogen bonding between the ligand and the anion. On the other hand, rectangle 5 was not selective towards any other anions. To the naked eye, multicarboxylate anions in a solution of 5 in methanol appear greenish upon irradiation with UV light.

The impact of ion pair association upon the 1H NMR spectra of cationic complexes akin to Grubbs catalysts

A reconsideration of the (1)H NMR spectra of cationic transition metal complexes exhibiting the features of cyclophanes on the basis of Mislow's classification of topic groups arrives at the conclusion that the spectral changes triggered by chiral counterions reflect an intracationic diastereotopication of enantiotopic protons rather than the existence of pairs of long-lived diastereomeric ion pairs.

Synthesis, Characterization and Anticancer Activity of Porphyrin-Containing Organometallic Cubes

Self‐assembly of 5,10,15,20‐tetra(4‐pyridyl)porphyrin (tpp‐H2) and 5,10,15,20‐tetra(4‐pyridyl)porphyrin‐M(ii) (M = Ni (tpp‐Ni); Zn (tpp‐Zn)) tetradentate panels with the dinuclear p‐cymene ruthenium clips [Ru2(p-cymene)2(C2O4)Cl2] and [Ru2(p-cymene)2(C6H2O4)Cl2] (C2O4 = oxalato; C6H2O4 = 2,5‐dioxydo‐1,4‐benzoquinonato) affords the cationic organometallic cubes: [Ru8(p-cymene)8(tpp‐H2)2(C2O4)4]8+ (1); [Ru8(p-cymene)8(tpp‐Ni)2(C2O4)4]8+ (2); [Ru8(p-cymene)8(tpp‐Zn)2(C2O4)4]8+ (3); [Ru8(p-cymene)8(tpp‐H2)2(C6H2O4)4]8+ (4); [Ru8(p-cymene)8(tpp‐Ni)2(C6H2O4)4]8+ (5); and [Ru8(p-cymene)8(tpp‐Zn)2(C6H2O4)4]8+ (6). In addition, the new dinuclear arene ruthenium 2,5‐dioxydo‐1,4‐benzoquinonato clips [Ru2(indane)2(C6H2O4)Cl2] (7) and [Ru2(nonylbenzene)2(C6H2O4)Cl2] (8) react in methanol with tpp‐H2 in the presence of silver triflate to afford the corresponding cationic cubes [Ru8(indane)8(tpp‐H2)2(C6H2O4)4]8+ (9) and [Ru8(nonylbenzene)8(tpp‐H2)2(C6H2O4)4]8+ (10) respectively. All cationic metalla‐cubes were isolated as triflate salts and characterized by NMR, infrared, electro‐spray mass spectrometry and UV‐visible spectroscopy. Moreover, the formation of unsymmetrical metalla‐cubes built using a mixture of the different porphyrin panels during the self‐assembly of the 2,5‐dioxydo‐1,4‐benzoquinonato metalla‐cubes, [Ru8(p-cymene)8(tpp‐H2)(tpp‐Ni)(C6H2O4)4]8+ (11), [Ru8(p-cymene)8(tpp‐H2)(tpp‐Zn)(C6H2O4)4]8+ (12), and [Ru8(p-cymene)8(tpp‐Ni)(tpp‐Zn)(C6H2O4)4]8+ (13), was studied by electro‐spray mass spectrometry. The cytotoxicities of all metalla‐cubes as well as the mixtures containing the unsymmetrical metalla‐cubes were established on human ovarian A2780 and A2780cisR cancer cell lines. All symmetrical compounds are equally cytotoxic (IC50 = 7–15 μM) (IC50 being the drug concentration necessary for 50% inhibition of cell viability) against both A2780 and cisplatin‐resistant A2780cisR cancer cells, with stronger cytotoxicities (IC50 = 2–5 μM) observed for the mixtures containing the unsymmetrical 2,5‐dioxydo‐1,4‐benzoquinonato metalla‐cubes.

Interactions of ruthenium coordination cubes with DNA

The interactions of four octacationic ruthenium coordination cubes with duplex and quadruplex (telomeric and c-myc) DNA have been studied by FID and SPR, showing these cubes to bind strongly to tetrastranded DNA structures.