Unusual Reaction of Isocyanides with Aromatic Aldehydes Catalyzed by a Supramolecular Capsule.

The supramolecular resorcinarene hexameric capsule efficiently promotes the unprecedented reaction between isocyanides and electron-deficient aromatic aldehydes leading to the formation of imines and carbon monoxide. The mechanism of the reaction was investigated via isotope labelling, kinetic analysis of the reaction, computational studies and the independent synthesis of a proposed intermediate. Control experiments indicate that the formation of the key aziridinone intermediate is limited to the cavity of the capsule.

Bufadienolides from Helleborus foetidus and their cytotoxic properties on MCF-7 breast cancer cells.

Twelve bufadienolides and six 19-norbufadienolides were isolated from the aerial parts of Helleborus foetidus. They consist of aglycons and glucosides and include nine previously undescribed compounds and a compound reported for the first time as a genuine natural product. Their structures were established by extensive spectroscopic analysis and the structure and absolute configuration of two previously unreported 3,4-epoxy derivatives were confirmed by single crystal X-ray diffraction analysis.

Atomically precise surface chemistry of zirconium and hafnium metal oxo clusters beyond carboxylate ligands.

The effectiveness of nanocrystals in many applications depends on their surface chemistry. Here, we leverage the atomically precise nature of zirconium and hafnium oxo clusters to gain fundamental insight into the thermodynamics of ligand binding. Through a combination of theoretical calculations and experimental spectroscopic techniques, we determine the interaction between the MO (M = Zr, Hf) cluster surface and various ligands: carboxylates, phosphonates, dialkylphosphinates, and monosubstituted phosphinates.

Toward Molecular Textiles: Synthesis and Characterization of Molecular Patches.

This works describes a new step into the assembly of molecular textiles by the use of covalent templating. To establish a well-founded base and to tackle pre-mature obstacles, expected during the fabrication of the desired 2D-material, we opted to investigate the in-solution synthesis of molecular patches e. g.

NSPs: chromogenic linkers for fast, selective, and irreversible cysteine modification.

The addition of a sulfhydryl group to water-soluble -alkyl(-nitrostyryl)pyridinium ions (NSPs) followed by fast and irreversible cyclization and aromatization results in a stable S-C sp-bond. The reaction sequence, termed Click & Lock, engages accessible cysteine residues under the formation of -hydroxy indole pyridinium ions. The accompanying red shift of >70 nm to around 385 nm enables convenient monitoring of the labeling yield by UV-vis spectroscopy at extinction coefficients of ≥2 × 10 M cm.

Window[1]resorcin[3]arenes: A Novel Macrocycle Able to Self-Assemble to a Catalytically Active Hexameric Cage.

The hexameric resorcin[4]arene capsule has been utilized as one of the most versatile supramolecular capsule catalysts. Enlarging its size would enable expansion of the substrate size scope. However, no larger catalytically active versions have been reported.

Complexation and disproportionation of group 4 metal (alkoxy) halides with phosphine oxides.

Group 4 Lewis acids are well-known catalysts and precursors for (non-aqueous) sol-gel chemistry. Titanium, zirconium and hafnium halides, and alkoxy halides are precursors for the controlled synthesis of nanocrystals, often in the presence of Lewis base. Here, we investigate the interaction of Lewis bases with the tetrahalides (MX, X = Cl, Br) and metal alkoxy halides (MX(OR), = 1-3, R = OPr, OBu).

Iron(III) Carbene Complexes with Tunable Excited State Energies for Photoredox and Upconversion.

Substituting precious elements in luminophores and photocatalysts by abundant first-row transition metals remains a significant challenge, and iron continues to be particularly attractive owing to its high natural abundance and low cost. Most iron complexes known to date face severe limitations due to undesirably efficient deactivation of luminescent and photoredox-active excited states. Two new iron(III) complexes with structurally simple chelate ligands enable straightforward tuning of ground and excited state properties, contrasting recent examples, in which chemical modification had a minor impact.

Reversible Photoinduced Ligand Substitution in a Luminescent Chromium(0) Complex.

Light-triggered dissociation of ligands forms the basis for many compounds of interest for photoactivated chemotherapy (PACT), in which medicinally active substances are released or "uncaged" from metal complexes upon illumination. Photoinduced ligand dissociation is usually irreversible, and many recent studies performed in the context of PACT focused on ruthenium(II) polypyridines and related heavy metal complexes. Herein, we report a first-row transition metal complex, in which photoinduced dissociation and spontaneous recoordination of a ligand unit occurs.

Ferromagnetically Coupled Chromium(III) Dimer Shows Luminescence and Sensitizes Photon Upconversion.

There has been much progress on mononuclear chromium(III) complexes featuring luminescence and photoredox activity, but dinuclear chromium(III) complexes have remained underexplored in these contexts until now. We identified a tridentate chelate ligand able to accommodate both meridional and facial coordination of chromium(III), to either access a mono- or a dinuclear chromium(III) complex depending on reaction conditions. This chelate ligand causes tetragonally distorted primary coordination spheres around chromium(III) in both complexes, entailing comparatively short excited-state lifetimes in the range of 400 to 800 ns in solution at room temperature and making photoluminescence essentially oxygen insensitive.

Leveraging Halogen Interactions for a Supramolecular Nanotube.

We demonstrate the formation of supramolecular nanotubes from molecular triangles in a single crystal by balancing the hydrogen bonds and halogen interactions between individual macrocycles. Thereby, we template the supramolecular nanotube growth by intermolecular interactions encoded directly in the macrocycles instead of those provided by the crystallization solvent. Ultimately, we show that replacing bromines for iodines in the macrocycle is necessary to achieve this supramolecular organization by enhancing the strength of the halogen interactions and concomitant reduction of the detrimental hydrogen bonds.

Introducing sterically demanding substituents and π-π-interactions into [Cu(P^P)(N^N)] complexes.

A series of ten N^N chelating ligands based on a 2,2'-bipyridine (bpy) metal-binding domain and featuring sterically hindering substituents in the 6- and 6,6'-positions has been synthesized and characterized. The ligands have been incorporated into a family of 15 heteroleptic complexes of type [Cu(P^P)(N^N)][PF] where P^P is the wide bite-angle bisphosphane ligand bis(2(diphenylphosphanyl)phenyl)ether (POP) or (9,9-dimethyl-9-xanthene-4,5-diyl)bis(diphenylphosphane) (xantphos). Substituents in several of the N^N ligands ligands possess phenyl rings remotely tethered to enable intra- and intermolecular π-π-interactions in the [Cu(P^P)(N^N)] cations.

Photoredox-active Cr(0) luminophores featuring photophysical properties competitive with Ru(II) and Os(II) complexes.

Coordination complexes of precious metals with the d valence electron configuration such as Ru(II), Os(II) and Ir(III) are used for lighting applications, solar energy conversion and photocatalysis. Until now, d complexes made from abundant first-row transition metals with competitive photophysical and photochemical properties have been elusive. While previous research efforts focused mostly on Fe(II), we disclose that isoelectronic Cr(0) gives access to higher photoluminescence quantum yields and excited-state lifetimes when compared with any other first-row d metal complex reported so far.

Enantioselective Allylation of Stereogenic Nitrogen Centers.

Most tertiary amines with a stereogenic nitrogen center undergo rapid racemization at room temperature. Consequently, the quaternization of amines under dynamic kinetic resolution seems feasible. -Methyl tetrahydroisoquinolines are converted into configurationally stable ammonium ions by Pd-catalyzed allylic alkylation.

Back to the future: asymmetrical DπA 2,2'-bipyridine ligands for homoleptic copper(i)-based dyes in dye-sensitised solar cells.

Metal complexes used as sensitisers in dye-sensitised solar cells (DSCs) are conventionally constructed using a push-pull strategy with electron-releasing and electron-withdrawing (anchoring) ligands. In a new paradigm we have designed new DπA ligands incorporating diarylaminophenyl donor substituents and phosphonic acid anchoring groups. These new ligands function as organic dyes.

Investigation of morpholine isosters for the development of a potent, selective and metabolically stable mTOR kinase inhibitor.

Upregulation of mechanistic target of rapamycin (mTOR) signaling drives various types of cancers and neurological diseases. Rapamycin and its analogues (rapalogs) are first generation mTOR inhibitors, and selectively block mTOR complex 1 (TORC1) by an allosteric mechanism. In contrast, second generation ATP-binding site inhibitors of mTOR kinase (TORKi) target both TORC1 and TORC2.

Expanded Ligands Based upon Iron(II) Coordination Compounds of Asymmetrical Bis(terpyridine) Domains.

The synthesis and characterization of two tritopic ligands containing a 2,2':6',2″-terpyridine (tpy) metal binding domain and either a 3,2':6',3″- or a 4,2':6',4″-tpy domain are detailed. The synthetic routes to these ligands involved the [Pd(dppf)Cl]-catalyzed coupling of a boronic ester-functionalized 2,2':6',2″-tpy with bromo-derivatives of 3,2':6',3″-tpy or 4,2':6',4″-tpy. The 2,2':6',2″-tpy domains of the tritopic ligands preferentially bind Fe in reactions with iron(II) salts leading to the formation of two homoleptic iron(II) complexes containing two peripheral 3,2':6',3″-tpy or 4,2':6',4″-tpy metal-binding sites, respectively.

Molecular Design Principles to Elongate the Metal-to-Ligand Charge Transfer Excited-State Lifetimes of Square-Planar Nickel(II) Complexes.

Square-planar Ni complexes and their electronically excited states play key roles in cross-coupling catalysis and could offer new opportunities to complement well-known isoelectronic Pt luminophores. Metal-to-ligand charge transfer (MLCT) excited states and their deactivation pathways are particularly relevant in these contexts. We sought to extend the lifetimes of MLCT states in square-planar Ni complexes by creating coordination environments that seemed particularly well adapted to the 3d valence electron configuration.

Multitopic 3,2':6',3''-terpyridine ligands as 4-connecting nodes in two-dimensional 4,4-networks.

The tetratopic 1,4-bis(2-phenylethoxy)-2,5-bis(3,2':6',3''-terpyridin-4'-yl)benzene (1) and 1,4-bis(3-phenylpropoxy)-2,5-bis(3,2':6',3''-terpyridin-4'-yl)benzene (2) ligands have been prepared and fully characterised. Combination of ligand 1 or 2 and [M(hfacac)]·HO (M = Cu, = 1; M = Zn, = 2) under conditions of crystal growth by layering led to the formation of [Cu(hfacac)(1)] ·3.6(1,2-ClCH)·2CHCl, [Zn(hfacac)(1)] ·MeCH·1.

Borylation in the Second Coordination Sphere of Fe Cyanido Complexes and Its Impact on Their Electronic Structures and Excited-State Dynamics.

Second coordination sphere interactions of cyanido complexes with hydrogen-bonding solvents and Lewis acids are known to influence their electronic structures, whereby the non-labile attachment of B(CF) resulted in several particularly interesting new compounds lately. Here, we investigate the effects of borylation on the properties of two Fe cyanido complexes in a systematic manner by comparing five different compounds and using a range of experimental techniques. Electrochemical measurements indicate that borylation entails a stabilization of the Fe-based t-like orbitals by up to 1.

The effects of introducing terminal alkenyl substituents into the 2,2'-bipyridine domain in [Cu(N^N)(P^P)] coordination compounds.

The N^N chelating ligands 6,6'-bis(but-3-en-1-yl)-2,2'-bipyridine (1), 6-(but-3-en-1-yl)-6'-methyl-2,2'-bipyridine (2), 6,6'-bis(pent-4-en-1-yl)-2,2'-bipyridine (3) and 6-(pent-4-en-1-yl)-6'-methyl-2,2'-bipyridine (4) have been prepared, characterized, and incorporated into the heteroleptic [Cu(N^N)(P^P)][PF] complexes in which P^P is either POP (bis(2-(diphenylphosphanyl)phenyl)ether) or xantphos (9,9-dimethyl-9-xanthene-4,5-diyl)bis(diphenylphosphane). The eight coordination compounds have been fully characterized, including the single crystal structures of [Cu(1)(xantphos)][PF], [Cu(1)(POP)][PF]·CHCl, [Cu(2)(xantphos)][PF], [Cu(2)(POP)][PF] and [Cu(3)(POP)][PF]·0.5EtO.

A Tail Does Not Always Make a Difference: Assembly of Nets from Co(NCS) and 1,4-bis(-Alkyloxy)-2,5-bis(3,2':6',3″-terpyridin-4'-yl)benzene Ligands.

The consistent assembly of a (6.8) net is observed in reactions of cobalt(II) thiocyanate with 1,4-bis(-alkyloxy)-2,5-bis(3,2':6',3″-terpyridin-4'-yl)benzene ligands in which the alkyloxy substituents are -propyl (ligand ), -butyl (), -pentyl (), -hexyl (), -heptyl (), and -octyl (). Crystals were grown by layering a methanol solution of Co(NCS) over a 1,2-dichlorobenzene solution of each ligand.

Correction: A 3-dimensional {4·8} lvt net built from a ditopic bis(3,2':6',3''-terpyridine) tecton bearing long alkyl tails.

[This corrects the article DOI: 10.1039/C4CE02347A.].

Megalo-Cavitands: Synthesis of Acridane[4]arenes and Formation of Large, Deep Cavitands for Selective C70 Uptake.

Deep cavitands, concave molecular containers, represent an important supramolecular host class that has been explored for a variety of applications ranging from sensing, switching, purification and adsorption to catalysis. A major limitation in the field has been the cavitand volume that is restricted by the size of the structural platform utilized (diameter approx. 7 Å).

Circularly Polarized Luminescence in a Möbius Helicene Carbon Nanohoop.

We present the first helicene carbon nanoohop that integrates a [6]helicene into [7]cycloparaphenylene. The [6]helicene endows the helicene carbon nanohoop with chiroptical properties and configurational stability typical for higher helicenes, while the radially conjugated seven para-phenylenes largely determine the optoelectronic properties. The structure of the helicene carbon nanoohop was unambiguously characterized by NMR, MS and X-ray analysis that revealed that it possesses a topology of a Möbius strip in the solid state and in solution.