Orientational self-sorting in cuboctahedral Pd cages

Cuboctahedral coordination cages of the general formula [Pd12L24]24+ (L = low-symmetry ligand) were analyzed theoretically and experimentally. With 350 696 potential isomers, the structural space of these assemblies is vast. Orientational self-sorting refers to the preferential formation of particular isomers within the pool of potential structures. Geometric and computational analyses predict the preferred formation of cages with a cis arrangement at the metal centers. This prediction was corroborated experimentally by synthesizing a [Pd12L24]24+ cage with a bridging 3-(4-(pyridin-4-yl)phenyl)pyridine ligand. A crystallographic analysis of this assembly showed exclusive cis coordination of the 3- and the 4-pyridyl donor groups at the Pd2+ ions.

Amphiphilic Rhomboidal Organoplatinum(II) Metallacycles with Encapsulated Doxorubicin for Synergistic Cancer Therapy

Synergistic therapy with nanocarriers is a promising strategy for effective cancer treatment. Here, we synthesized an amphiphilic rhomboidal metallacycle M, in which a glucose-modified pyridine ligand was used to improve water-solubility and an organoplatinum(II) receptor acted as a platinum-based anticancer agent. Moreover, because of the amphiphilic properties, M self-assembled into micelles or nanobelts at different concentrations, and a drug delivery system (DDS) was developed by encapsulating the anticancer drug doxorubicin (DOX) into the micelles. The morphology, cell uptake, cytotoxicity, internalization, and antitumor effect of the DDS were investigated. Under low intracellular pH conditions, the DDS disassembled to release the loaded DOX in situ. The designed DDS exhibited good biocompatibility, synergistic antitumor efficacy, and negligible adverse effects in a U87 tumor-bearing mice model.

Redox-Induced Hydrogen Bond Reorientation Mimicking Electronic Coupling in Mixed-Valent Diruthenium and Macrocyclic Tetraruthenium Complexes

We present the coordination-driven self-assembly of three tetranuclear metallacycles containing intracyclic NH₂, OH, or OMe functionalities through the combination of various isophthalic acid building blocks with a divinylphenylene diruthenium complex. All new complexes of this study were characterized by means of nuclear magnetic resonance spectroscopy, ultrahigh-resolution ESI mass spectrometry, cyclic and square wave voltammetry and, in two cases, X-ray diffraction. The hydroxy functionalized macrocycle 4-BOH and the corresponding half-cycle 2-OH stand out, as their intracyclic OH···O hydrogen bonds stabilize their mixed-valent one- (2-OH, 4-BOH) and three-electron-oxidized states (4-BOH). Despite sizable redox splittings between all one-electron waves, the mixed-valent monocations and trications do not exhibit any intervalence charge-transfer band, assignable to through-bond electronic coupling, but nevertheless display distinct IR band shifts of their charge-sensitive Ru(CO) tags. We ascribe these seemingly contradicting observations to a redox-induced shuffling of the OH···O hydrogen bond(s) to the remaining, more electron-rich, reduced redox site.

How to Control the Rate of Heterogeneous Electron Transfer across the Rim of M6L12 and M12L24 Nanospheres

Catalysis in confined spaces, such as those provided by supramolecular cages, is quickly gaining momentum. It allows for second coordination sphere strategies to control the selectivity and activity of transition metal catalysts, beyond the classical methods like fine-tuning the steric and electronic properties of the coordinating ligands. Only a few electrocatalytic reactions within cages have been reported, and there is no information regarding the electron transfer kinetics and thermodynamics of redox-active species encapsulated into supramolecular assemblies. This contribution revolves around the preparation of M6L12 and larger M12L24 (M = Pd or Pt) nanospheres functionalized with different numbers of redox-active probes encapsulated within their cavity, either in a covalent fashion via different types of linkers (flexible, rigid and conjugated or rigid and nonconjugated) or by supramolecular hydrogen bonding interactions. The redox probes can be addressed by electrochemical electron transfer across the rim of nanospheres, and the thermodynamics and kinetics of this process are described. Our study identifies that the linker type and the number of redox probes within the cage are useful handles to fine-tune the electron transfer rates, paving the way for the encapsulation of electroactive catalysts and electrocatalytic applications of such supramolecular assemblies.

Confinement of a Au–N-heterocyclic carbene in a Pd6L12 metal–organic cage

A Au(i)–N-heterocyclic-carbene (NHC)-edged Pd₆L₁₂ molecular metal–organic cage is assembled from a Au(i)–NHC-based bipyridyl bent ligand and Pd²⁺. The octahedral cage structure is unambiguously established by NMR, electrospray ionization-mass spectrometry and single crystal X-ray crystallography. The electrochemical behaviour was analyzed by cyclic voltammetry. The octahedral cage has a central cavity for guest binding, and is capable of encapsulating PF₆⁻ and BF₄⁻ anions within the cavity.

A Au(i)–NHC-edged Pd₆L₁₂ molecular cage is assembled from a Au(i)–NHC-based bipyridyl bent ligand and Pd²⁺.

Self-assembled M12L24 nanospheres as a reaction vessel to facilitate a dinuclear Cu(i) catalyzed cyclization reaction

The application of large M12L24 nanospheres allows the pre-concentration of catalysts to reach high local concentrations, facilitating reactions that proceed through dinuclear mechanisms. The mechanism of the copper(i)-catalyzed cyclization of 4-pentynoic acid has been elucidated by means of a detailed mechanistic study. The kinetics of the reaction show a higher order in copper, indicating the formation of a bis-Cu intermediate as the key rate determining step of the reaction. This intermediate was further identified during catalysis by CIS-HRMS analysis of the reaction mixture. Based on the mechanistic findings, an M12L24 nanosphere was applied that can bind up to 12 copper catalysts by hydrogen bonding. This pre-organization of copper catalysts in the nanosphere results in a high local concentration of copper leading to higher reaction rates and turnover numbers as the dinuclear pathway is favored.

A facile approach to prepare a microporous polycarbazole P-tetra(4-(N-carbazolyl)phenyl)silane network with high CO2 storage and separation properties

A facile approach to prepare a microporous polycarbazole P-TCzPhSi network by FeCl₃ oxidative polymerization reaction.

Metal-driven self-assembly: the case of redox-active discrete architectures

The growing family of redox-active rings and cages prepared using the coordination-driven self-assembly strategy is reviewed.

‘Click’ to functionalise: synthesis, characterisation and enhancement of the physical properties of a series of exo- and endo-functionalised Pd2L4nanocages

Facile CuAAC ‘click’ chemistry has been utilised toexo-functionalise Pd₂L₄host nanocages with electrochemically active, emissive and solubilising groups.