Studying reversible host-guest interactions is essential for developing flexible, efficient, and sustainable systems, as they enhance reusability, improve efficiency, and provide valuable insights for designing advanced materials and technologies. In this work, we describe the synthesis of a pyrene-naphthalenediimide-based heterocyclophane, which can be encapsulated in an iridium-cornered nanosized metallobox with a high binding affinity. Electrochemical studies of the resulting host-guest complex reveal that encapsulation significantly alters the cyclophane's redox behavior, with the processes being highly sensitive to guest uptake and release dynamics. Reduction of the cyclophane occurs at the naphthalenediimide (NDI) unit, generating a radical species that is stabilized upon encapsulation within the metallobox cavity. Host-guest dynamics were investigated using variable temperature 1H NMR spectroscopy, and the release and uptake of the guest can be precisely controlled by adding chloride or silver(I) ions. We believe that our studies can help the development of methodologies to controllably allow the release and uptake of guests from metallosupramolecular assemblies, which are central to many of the applications of these systems.

We report the preparation of two Pd(ii) complexes based on (CCC)-pincer-NHC (NHC = N-heterocyclic carbene) ligands. One of these complexes features an NDI unit (NDI = naphthalene-diimide) attached to the CCC-pincer ligand. Reacting these complexes with bromine results in the formation of the corresponding palladium(iv) complexes [PdBr3(NDI-CCC)] and [PdBr3(CCC)]. The NDI-containing pincer complex exhibits a strong sensitivity to fluoride ions, which can induce a one-electron reduction of the naphthalene-diimide moiety. We demonstrate that the addition of fluoride induces the reduction of the NDI moiety via the formation of hydroxide anions, which are the effective reducing agents of the process. The addition of fluoride significantly affects the reactivity of the NDI-containing palladium complexes. For example, the palladium(iv) complex [PdBr3(NDI-CCC)] can transfer bromide to styrene in a stoichiometric manner, but this reaction is inhibited in the presence of fluoride. Similarly, the palladium(ii) complex [PdI(NDI-CCC)] catalyzes the oxidative homocoupling of arylpyridines, but its catalytic activity is quenched when excess fluoride is added. Notably, we demonstrate that this process can be deactivated and reactivated by sequentially introducing an excess of fluoride and NOBF4, revealing a rare instance of a redox-switchable process within a Pd(ii)/Pd(iv) catalytic cycle. In contrast, the (CCC)-pincer palladium(ii) and (iv) complexes lacking the NDI unit show no sensitivity to fluoride. Our study demonstrates that a simple reagent, such as the fluoride anion, can effectively modulate the reactivity of the Pd(ii)/Pd(iv) pair. More broadly, it shows that fluoride serves as a simpler alternative to the metal-based reducing agents commonly used in redox-switchable catalysis.

Gaining insight into the dynamic behavior of supramolecular systems is essential for understanding selective guest encapsulation and for the rational design of nanodevices capable of precise, controllable motion at the molecular scale. In this work, we report the construction of a pseudo-rotaxane system through the encapsulation of a naphthalenediimide (NDI) derivative bearing long aliphatic chains within the cavity of a nanosized metallorectangle. Electrochemical studies reveal that encapsulation significantly alters the redox properties of the guest. In addition, upon reduction, the NDI-based radical is stably confined within the host cavity, forming a persistent host-guest complex. This encapsulated radical species can be released upon the addition of chloride ions, demonstrating a clear example of reversible, stimuli-responsive guest uptake and release. To elucidate the internal dynamics of the system, we employed variable-temperature 1H NMR spectroscopy in conjunction with computational modeling. These studies revealed two distinct modes of motion: a) a shuttling motion, in which the guest slides along the axis of the host cavity between central and peripheral positions; and b) a rocking motion, involving partial rotation of the guest enabled by the flexible movement of its aliphatic chains within the host interior.

We describe the synthesis of two rhodium and iridium complexes featuring a di-NHC macrocyclic ligand, which incorporates both a diphenylene moiety and a naphthalenediimide (NDI) unit. We observed that the addition of fluoride or chloride resulted in substantial alterations to the steric and electronic properties of both complexes. Specifically, fluoride addition led to the reduction of the NDI unit through the formation of an (OH-) NDI intermediate, while chloride produced a (Cl-)···NDI adduct. Both adducts were confirmed by mass spectrometry. The impact of fluoride and chloride addition on the steric and electronic properties of the rhodium and iridium NDI-containing complexes was examined using spectroscopic and computational methods. The presence of either halide significantly enhanced the catalytic activity of the complexes in the hydroboration of terminal alkenes. Finally, we demonstrated that this catalytic enhancement is reversible, with the catalytic process being activated and deactivated by the sequential introduction of excess halide and NOBF4. This observation reveals a rare example of a halide-induced redox-switchable catalytic (HIRSC) system.

Two dimetallic complexes of Au(I) and Ru(II), featuring a naphthalene‐diimide (NDI)‐linked bis‐N‐heterocyclic carbene (NHC) ligand, have been synthesized and fully characterized. Spectroscopic analyses, combined with structural data, reveal the presence of lone pair–π (lp–π) interactions between the chloride ligands coordinated to the metal centers and the central NDI unit. The nature of this interaction varies with the metal's coordination geometry: in the di‐Au(I) complex, the lp–π interaction is intermolecular, whereas in the di‐Ru(II) complex it is intramolecular, leading to the formation of two atropisomers that are distinguishable by conventional spectroscopic techniques. NMR studies of both complexes provided key insights into the lp–π interaction. For the di‐Ru(II) complex in particular, these studies enabled the determination of the kinetic and thermodynamic parameters governing the equilibrium between the atropisomers, revealing a barrier to interconversion (ΔH≠) of 10.4 kcal mol–1, indicative of a strong covalent character in the lp–π interaction.

Catalytic transfer hydrogenation (TH) is an alternative to the industrially relevant hydrogenation of carbonyl compounds, dismissing the use of pressurized reactors. Herein, we compare ruthenium and osmium pincer complexes as catalysts for the selective carbonyl reduction of the renewable methyl 10-undecenoate, myrtenal, and cinnamaldehyde. Their selective carbonyl reduction is challenging because they also have a C-C double bond susceptible to reduction or isomerization. The osmium complexes, used for the first time in TH, showed considerably better activity and selectivity than the ruthenium ones. The reactions were carried out at temperatures as low as 35 °C at short reaction times, and a solvent screening demonstrated that anisole, which has a high sustainability score, is also the most efficient solvent for these reactions. Finally, renewable ethanol was employed as a sacrificial hydrogen source, circumventing the use of the usually high-carbon-footprint dihydrogen.

The factors governing the acceleration of the oxidative addition of methyl iodide to pincer rhodium(I)-complexes induced by coronene have been computationally explored in detail using quantum chemical methods. Both the parent reaction and the coronene-mediated process proceed via a stepwise SN2-type mechanism. It is found that the acceleration of the process derives from the formation of an initial supramolecular complex, mainly stabilized by electrostatic and π-π interactions, which significantly increases the electron richness of the complex. The impact of this effect on the reaction barrier has been quantitatively analyzed by applying the activation strain model in combination with the energy decomposition analysis method. In addition, the influence of other polycyclic aromatic hydrocarbons on the oxidative reaction has been also considered.

A series of naphthalene-diimide (NDI) and perylene-diimide (PDI) connected bis-N-heterocyclic carbene complexes of iridium(III) have been prepared and fully characterized. The analysis of their NMR spectroscopic features, together with their molecular structures show that these species display lone-pair-π interactions between the chloride ligands of the Ir(III) complex and the heterocycles of the NDI/PDI moieties. The detection of this type of interaction in solution is due to the formation of two atropisomers, which are formed as a result of the restricted rotation about the Ir−C carbene bond imposed by the (Cl)lp⋅⋅⋅π interaction. Variable-temperature 1 H NMR analysis allowed the determination of the strength of this non-covalent interaction, which lies between ΔH=6.6 and 10 kcal/mol. The computational studies performed fully support the experimental findings.

First row transition metal complexes have attracted attention as abundant and affordable electrocatalysts for CO2 reduction. Manganese complexes bearing bis-N-heterocyclic carbene ligands defining 6-membered ring metallacycles have proven to reduce CO2 to CO selectively at very high rates. Herein, we report the synthesis of manganese carbonyl complexes supported by a rigid ortho-phenylene bridged bis-N-heterocyclic carbene ligand (ortho-phenylene-bis(N-methylimidazol-2-ylidene), Ph-bis-mim), which defines a 7-membered ring metallacycle. We performed a comparative study with the analogues complexes bearing an ethylene-bis(N-methylimidazol-2-ylidene) ligand (C2H4-bis-mim) and a methylene-bis(N-methylimidazol-2-ylidene) ligand (CH2-bis-mim), and found that catalysts comprising a seven-membered metallacycle retain similar selectivity and activity as those with six-membered metallacycles, while reducing the overpotential by 120-190 mV. Our findings reveal general design principles for manganese bis-N-heterocyclic carbene electrocatalysts, which can guide further designs of affordable, fast and low overpotential catalysts for CO2 electroreduction.

We report a manganese(I) complex of formula [Mn(NDI-CNC)(CO)(3)](BAr4F), in which NDI-CNC refers to a pincer pyridine-bis-imidazolylidene ligand functionalized with a naphthalene-diimide (NDI) moiety. Due to the presence of the NDI fragment, the electron-donating strength of the pincer ligand can be increased by producing an electrochemical reduction of the NDI moiety or by the addition of tetrabutylammonium chloride (TBACl). The extent of the changes produced in the electron-donating power of the pincer ligand can be quantified by studying the variation of the C-O stretching frequencies by infrared spectroscopy. It is observed that the catalytic activity of the manganese complex in the reductive methylation of a series of secondary amines with formic acid (or CO2) in the presence of PhSiH3 is almost negligible, but the catalyst can be turned very active in the presence of TBACl. This study constitutes a rare example of an anion-sensitive catalyst. Furthermore, the activity of the catalyst can be switched on and off for several cycles by subsequent addition of TBACl or NOBF4, respectively.

A tetra-rhodium( i )-based metallobox built from a corannulene-di-NHC ligand is described. This metallorectangle has exceptional geometrical features for the encapsulation of fullerenes.

An iridium-conjoined long and narrow metallorectangle was obtained by combining a quinoxalinophenanthrophenazine-connected Janus-di-imidazolylidene ligand and pyrazine. The size and shape of this assembly together with the fused polyaromatic nature of its panels provides it with properties that are uncommon for other metallosupramolecular assemblies. For example, this nanosized 'slit-like' metallobox is able show very large binding affinities with planar organic molecules in such a way, that the cavity is asymmetrically occupied by the guest molecule. This unsymmetrical conformation leads to the existence of a large amplitude motion of these guests, which slide between the two sides of the cavity of the host, thus constituting rare examples of molecular shuttles.

We herein describe the use of a gold complex with a naphthalene-di-imide-functionalized N-heterocyclic carbene (NDI-NHC) ligand, which was used as a photocatalyst for a variety of reactions. Due to the presence of the naphthalene moiety in the ligand, the complex can be used for the photogeneration of singlet oxygen, behaving as a photocatalyst in the endoperoxidation and peroxidation of cyclic and acyclic alkenes, and also in the selective oxidation of a simulant of sulfur mustard to its related nontoxic sulfoxide. The same complex was used as catalyst for two model oxidative C-C coupling reactions, namely, the coupling of aryldiazonium salts with alkynylsilanes and with mesitylene. These two catalytic reactions are a good indication that the (NDI-NHC)-Au(I) complex can behave as an effective dual metallophotoredox catalyst but with the particular feature that both the photosensitizer and the metal catalyst are contained in the same compound, thus constituting a very rare type of a "two-in-one" metallophotoredox catalyst. The participation of the Au(I)/Au(III) couple in the catalytic process was demonstrated by the isolation of a Au(III) complex, which was obtained via a self-photoactivated photoredox reaction.

An iridium-cornered nanosized metallorectangle was obtained by combining a quinoxalinophenanthrophenazine-connected Janus-di-imidazolylidene ligand and 4,4 '-bipyridine. This metallorectangle was used as host for a series of planar molecules, including pyrene, triphenylene, perylene, coronene, and N,N '-dimethyl-naphthalenetetracarboxy-diimide (NTCDI). The binding of coronene and NTCDI followed a strongly positive cooperative 1:2 stoichiometric binding model, as the inclusion of the first guest generates the geometrical requirements for the optimum encapsulation of the second planar molecule. The simultaneous encapsulation of coronene and NTCDI produces a heteroguest inclusion system, whose exchange dynamics was studied by means of variable temperature H-1 NMR spectroscopy.

We report the rhodium(I) complex [Rh(CNC−NDI)(CO)] + , in which CNC−NDI refers to a pincer-CNC ligand decorated with a naphthalenediimide moiety. Due to the presence of the planar CNC ligand and the naphthalenediimide moiety, the electronic nature of the complex can be modulated by means of supramolecular and redox stimuli, respectively. The metal complex shows a strong π–π-stacking interaction with coronene. This interaction has an impact on the electron-richness of the metal, as demonstrated by the shifting of the ν(CO) stretching band to a lower frequency. The addition of tetrabutylammonium fluoride facilitates the sequential one- and two-electron reduction of the NDI moiety of the ligand, thus resulting in a situation in which the ligand can increase its electron-donor strength in two levels. The nature of the interaction with the fluoride anion was studied computationally. The catalytic activity of the [Rh(CNC−NDI)(CO)] + complex was tested in the cycloisomerization of alkynoic acids, where it is observed that the activity of the catalyst can be modulated between four levels of activity, which correspond to i) the use of the unmodified catalyst, ii) catalyst+coronene, iii) catalyst+2 equivalents of fluoride, and iv) catalyst+5 equivalents of fluoride.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Two different metallotweezers, each with two pyrene-imidazolylidene-gold(I) arms, were used as hosts for a series of planar aromatic guests. The metallotweezer with a dibenzoacridinebis(alkynyl) spacer (1) orients the two pyrene-imidazolylidene-gold(I) arms in a parallel disposition, with an interpanel distance of about 7 Å. The second metallotweezer (2) contains a carbazolylbis(alkynyl) spacer that directs the two pyrene panels in a diverging orientation. Determination of the association constants via 1H NMR titrations demonstrates that the binding strength shown by 1 is significantly larger than that found by 2, with binding affinities as large as 104 M-1 (in CDCl3), for the encapsulation of N,N'-dimethylnaphthalenetetracarboxydiimide with 1. The differences in the binding affinities are due to binding models associated with formation of the related host-guest complexes. While 1 operates via a "lock and key" model, in which the host does not suffer distortions upon formation of the inclusion complex, 2 operates via a guest-induced fit model. The large association constants shown by 1 with two planar guests were used for promotion of the template-directed synthesis of 1, which in the absence of an external template is produced in an equimolecular mixture with its self-aggregated congener, clippane [12]. This observation strongly suggests that the mechanically interlocked clippane is formed through a self-template-directed mechanism, while bonds are broken/formed during the synthetic protocol.

Mechanically interlocked molecules (MIMs) have gained increasing interest during the last decades, not only because of their aesthetic appeal, but also because their unique properties have allowed them to find applications in nanotechnology, catalysis, chemosensing and biomedicine. Herein we describe how a pyrene molecule with four octynyl substituents can be easily encapsulated within the cavity of a tetragold(I) rectangle-like metallobox, by template formation of the metallo-assembly in the presence of the guest. The resulting assembly behaves as a mechanically interlocked molecule (MIM), in which the four long limbs of the guest protrude from the entrances of the metallobox, thus locking the guest inside the cavity of the metallobox. The new assembly resembles a metallo-suit[4]ane, given the number of protruding long limbs and the presence of the metal atoms in the host molecule. However, unlike normal MIMs, this molecule can release the tetra-substituted pyrene guest by the addition of coronene, which can smoothly replace the guest in the cavity of the metallobox. Combined experimental and computational studies allowed the role of the coronene molecule in facilitating the release of the tetrasubstituted pyrene guest to be explained, through a process that we named "shoehorning", as the coronene compresses the flexible limbs of the guest so that it can reduce its size to slide in and out the metallobox.

A series of dimetallic and monometallic Cp*Ir(III) complexes bearing naphthalene-diimide-decorated N-heterocyclic carbene/pyridine [NDI-(NHC-pyridine)] ligands were prepared and characterized. The complexes show a C,C-chelating coordination of the NHC-pyridine ligand, with the pyridine ring of the ligand bound to the metal via cyclometallation rather than by its nitrogen atom, although the coordination by the nitrogen atom could be achieved by subjecting one of the complexes to reaction with a strong acid. The spectroelectrochemical studies of the new compounds reveal that the complexes are able to undergo two successive reduction events, associated with the sequential reduction of the NDI moiety of the ligand. The new complexes were tested in the dehydrative etherification by cross-coupling of primary alcohols, where they showed good activity and selectivity toward the cross-coupled products. The mechanistic studies allowed us to propose a reaction mechanism which likely involves a redox-neutral acid-catalyzed pathway.

1 H NMR studies using a cationic complex with a pyridine-di-imidazolylidene pincer ligand of formula [Rh(CNC)(CO)]+ revealed that this compound showed high binding affinity with coronene in CH2 Cl2 . The interaction between coronene and the planar RhI complex is established by means of π-stacking interactions. This interaction has a strong impact on the electron-donating strength of the pincer CNC ligand, which is increased significantly, as demonstrated by the shifting of the ν(CO) stretching bands to lower frequencies. The addition of coronene increases the reaction rate of the nucleophilic attack of methyl iodide on the rhodium (I) pincer complex, and also has a positive effect on the performance of the complex as a catalyst in the cycloisomerization of 4-pentynoic acid. These findings highlight the importance of supramolecular interactions for tuning the reactivity and catalytic activity of square-planar metal complexes.