Influence of Rotator Design on the Speed of Self-Assembled Four-Component Nanorotors: Coordinative Versus Dispersive Interactions

Interconversion between multicomponent slider-on-deck and palladium capsule: regulation of catalysis and encapsulation

When the slider-on-deck [Cu3(1)(2)]3+ and guest G were treated with palladium(II) ions, the biped 2 was released from [Cu3(1)(2)]3+ generating the nanocage [Pd2(2)4(G)]4+ with guest G being encapsulated (NetState-II). This transformation that was reversed by the addition of DMAP enabled modulation of both the overall fluorescence and the activity of copper(I) catalyzing an aza Hopf cyclization.

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

Supramolecular catalysis is reviewed with an eye on heteroleptic aggregates/complexation. Since most of the current metallosupramolecular catalytic systems are homoleptic in nature, the idea of breaking/reducing symmetry has ignited a vivid search for heteroleptic aggregates that are made up by different components. Their higher degree of functional diversity and structural heterogeneity allows, as demonstrated by Nature by the multicomponent ATP synthase motor, a more detailed and refined configuration of purposeful machinery. Furthermore, (metallo)supramolecular catalysis is shown to extend beyond the single "supramolecular unit" and to reach far into the field and concepts of systems chemistry and information science.

Dynamics of the alkyne → copper(i) interaction and its use in a heteroleptic four-component catalytic rotor

The dynamics of alkyne → copper(i) interactions has been determined and used to self-assemble a fast nanorotor, which underwent a self-catalyzed click transformation to a triazole rotor, an interesting process for the production of biohybrid devices.

Molecular rotor based on an oxidized resorcinarene

Rate of rotation of substituents in a molecular single stator-double rotor based on an oxidized resorcinarene with unsaturated hemiquinonoid groups at its meso positions (i.e., a fuchsonarene) has been controlled according to solvent polarity and acidity.

Off-Equilibrium Speed Control of a Multistage Molecular Rotor: 2-Fold Chemical Fueling by Acid or Silver(I)

Driving conformational motion in defined off-equilibrium oscillations can be achieved using chemical fuels. When the ultrafast turnstile 1 (k₂₉₈> 10¹² Hz) was fueled with 2-cyano-2-phenylpropanoic acid (Fuel 1), the diprotonated rotor [H₂(1)]²⁺ (k₂₉₈ = 84.0 kHz) formed as a transient regaining the dynamics of the initial turnstile after consumption of the fuel (135 min). Upon addition of silver(I) (Fuel 2) to turnstile 1, the metastable rotor [Ag₂(1)]²⁺ (k₂₉₈ = 1.57 Hz) was initially furnished, but due to a consequentially triggered S_N2 reaction, the Ag⁺ ions were consumed as insoluble AgBr along with regeneration of 1 (within 3 h). The off-equilibrium fast ⇆ slow rotor conversions fueled by acid and silver(I) were directly monitored by fluorescence and ¹H NMR. In addition, metal ion exchange was fueled enabling off-equilibrium oscillations between rotors [Li₂(1)]²⁺ ⇆ [Ag₂(1)]²⁺. In the end, both sustainability and efficiency of the process were increased in unison by using the interfering proton waste in the formation of a [2]pseudorotaxane.

Synthesis, characterization, and reactivity of oxoiron(IV) porphyrin π-cation radical complexes bearing cationic N-methyl-2-pyridinium group

Electronic charge near the active site is an important factor for controlling the reactivity of metalloenzymes. Here, to investigate the effect of the cationic charge near the heme in heme proteins, we synthesized new iron porphyrin complexes (1 and 2) having cationic 3-methyl-N-methyl-2-pyrdinium group and N-methyl-2-pyridinium group at one of the four meso-positions, respectively. The N-methyl-2-pyridinium groups could be introduced by Stille coupling used palladium catalysts. Oxoiron(IV) porphyrin π-cation radical complexes (Compound I) of 1 (1-CompI) and 2 (2-CompI) are soluble in most organic solvents, allowing direct comparison of their electronic structure and reactivity with Compound I of tetramesitylporphyrin (3-CompI) and tetrakis-(2,6-dichlorophenyl)porphyrin (4-CompI) under the same conditions. Spectroscopic data for 1-CompI are close to those for 3-CompI, but the redox potential for 1-CompI is close to that of 4-CompI. Kinetic analysis of the epoxidation reactions shows that 1-CompI and 2-CompI are (~250-fold) more reactive than 3-CompI, and comparable to 4-CompI. DFT calculations allow to propose that the positive shift of the redox potential and the enhanced reactivity of 1-CompI and 2-CompI is induced by the intramolecular electric field effect of N-methyl-2-pyridinium cation, not by the electron-withdrawing effect.

Water binding stabilizes stacked conformations of ferrocene containing sheet-like aromatic oligoamides

While water clusters play an essential role in the stability of biological structures, their ability to stabilize synthetic oligomers is less understood. We have synthesized a heptameric sheet-like aromatic oligoamide foldamer with ferrocene as turn unit. It shows strong interactions with water in the solid state and in solution. The water binding limits the fluxional processes resulting from the flexible ferrocene unit, highlighting the importance of such interactions for conformational studies on this class of molecule.

Exchange Speed of Four-Component Nanorotors Correlates with Hammett Substituent Constants

Three distinct four-component supramolecular nanorotors were prepared, using, for the first time, bipyridine instead of phenanthroline stations in the stator. Following our established self-sorting protocol to multicomponent nanodevices, the nanorotors were self-assembled by mixing the stator, rotators with various pyridine head groups, copper(I) ions and 1,4-diazabicyclo[2.2.2]octane (DABCO). Whereas the exchange of a phenanthroline vs. a bipyridine station did not entail significant changes in the rotational exchange frequency, the para-substituents at the pyridine head group of the rotator had drastic consequences on the speed: 4-OMe (k298 = 35 kHz), 4-H (k298 = 77 kHz) and 4-NO2 (k298 = 843 kHz). The exchange frequency (log k) showed an excellent linear correlation with both the Hammett substituent constants and log K of the copper(I)–ligand interaction, proving that rotator–copper(I) bond cleavage is the key determining factor in the rate-determining step.

Double Rotors with Fluxional Axles: Domino Rotation and Azide-Alkyne Huisgen Cycloaddition Catalysis

The simple preparation of the multicomponent devices [Cu4 (A)2 ]4+ and [Cu2 (A)(B)]2+ , both rotors with fluxional axles undergoing domino rotation, highlights the potential of self-sorting. The concept of domino rotation requires the interconversion of axle and rotator, allowing the spatiotemporal decoupling of two degenerate exchange processes in [Cu4 (A)2 ]4+ occurring at 142 kHz. Addition of two equiv of B to rotor [Cu4 (A)2 ]4+ afforded the heteromeric two-axle rotor [Cu2 (A)(B)]2+ with two distinct exchange processes (64.0 kHz and 0.55 Hz). The motion requiring a pyridine→zinc porphyrin bond cleavage is 1.2×105 times faster than that operating via a terpyridine→[Cu(phenAr2 )]+ rupture. Finally, both rotors are catalysts due to their copper(I) content. The fast domino rotor (142 kHz) was shown to suppress product inhibition in the catalysis of the azide-alkyne Huisgen cycloaddition.

Synthesis of Double-Bridged Cofacial Nickel Porphyrin Dimers with 2,2'-Bipyridyl Pillars and Their Restricted Coordination Space

Double-bridged cofacial Ni porphyrin dimers 2 with 2,2'-bipyridyl pillars were effectively prepared by a one-step reductive homocoupling reaction of bis(chloropyridyl)-substituted Ni porphyrin derivatives followed by a specific separation of a cyanopropyl-modified silica gel column using pyridine eluent systems. The structural analyses of 2 and its Pd complex were carried out in their solid and solution states by means of X-ray single crystal analysis and NMR, respectively. The complexation of η³-allylpalladium chloride (Pd) with 2 on the spatially restricted 2,2-bipyridine moieties on 2 gave a 2:1 (Pd:2) complex, in which the 2,2'-bipyridine ligands only provided one of the N atoms on a 2,2'-bipyridine ligand to a Pd. Therefore, the 2,2-bipyridine moieties acted as a monodentate ligand.

Heterocomponent ternary supramolecular complexes of porphyrins: A review

Porphyrins are prominent host molecules which are widely used due to their structural characteristics and directional interaction sites. This review summarizes non-covalently bound ternary complexes of porphyrins, constructed from at least three non-identical species. Progress in supramolecular chemistry allows the creation of complex molecular machinery tools, such as rotors, motors and switches from relatively simple structures in a single self-assembly step. In the current review, we highlight the collection of sophisticated molecular ensembles including sandwich-type complexes, cages, capsules, tweezers, rotaxanes, and supramolecular architectures mediating oxygen-binding and oxidation reactions. These diverse structures have high potential to be applied in sensing, production of new smart materials as well as in medical science.

Reversible Interconversion of a Static Metallosupramolecular Cage Assembly into a High-Speed Rotor: Stepless Adjustment of Rotational Exchange by Nucleophile Addition

The self-assembled cage ROT-1 was prepared from the pyridine-terminated rotator 1, the phenanthroline-appended stator 2, DABCO, and copper(I) ions in a ratio of 1:1:1:4. This four-component assembly is held together by two pyridine→[Cu(phenAr₂)]⁺ as well as two DABCO→zinc porphyrin interactions (phenAr₂ = 2,9-diarylphenanthroline) and does not show any motion on the NMR time scale ( k < 0.1 s^-1, 298 K). However, it is converted to the fast nanorotor ROT-1 _x^CD₃CN by addition of CD₃CN [ x = (v/v)% of acetonitrile in dichloromethane] due to acceleration of both pyridine→copper(I) dissociation steps. Now the rotator is able to visit all four copper(I)-loaded phenanthroline stations of the stator. Depending on the amount of CD₃CN, the exchange frequency of the nanorotor varies from 0.7 s^-1 (CD₃CN:CD₂Cl₂ = 1:29) to 8000 s^-1 (CD₃CN:CD₂Cl₂ = 1:5) at 25 °C. When iodide (I^-) is added to the static assembly ROT-1, the rotational speed increases even more drastically ( k = 20 000 s^-1), again due to accelerating the rate-determining pyridine→copper(I) dissociation step. In both cases, a sigmoidal relationship is established between exchange frequency and the concentration of added nucleophile (CD₃CN or iodide) that suggests the presence of a cooperative effect. Reversible switching between the static assembly and fast rotor was performed several times without any decomposition of the system. In contrast, addition of the common nucleophile PPh₃ to ROT-1 does not increase the rotational speed, a finding that is explained on thermodynamic grounds.

Cation exchange reversibly switches rotor speed and is monitored by a networked fluorescent reporter

The three-step transformation of a turnstile into a zinc rotor (8 kHz) and then into a copper rotor (30 kHz) was achieved with the last transformation being monitored by a fluorescence reporter.

Machine Metathesis: Thermal and Catalyzed Exchange of Piston Rods in Multicomponent Nanorotor/Nanoslider Ensemble

Three-component nanorotor R1 ( k₂₉₈ = 80 kHz) and two-component slider-on-deck DS2 ( k₂₉₈ = 440 kHz) were prepared from rotator S1 and stator [Cu₃(1)]³⁺ and from S2 and deck D, respectively. Mixing of R1 with DS2 leads to clean metathesis, furnishing the slower nanodevices R2 ( k₂₉₈ = 29.6 kHz) and DS1 ( k₂₉₈ = 32.2 kHz). Exchange of the piston rods S1 and S2 is completed within 22 min (uncatalyzed) or 3 min (catalyzed) at 298 K.

Heteroleptic copper phenanthroline complexes in motion: From stand-alone devices to multi-component machinery

Two and a half decades of copper phenanthroline-based switches, devices and machines have illustrated the rich dynamic nature of these metal complexes. With an emphasis on the metal-ligand dissociation as the rate-determining step the present review summarizes not only spectacular examples of machinery, but also highlights rate data collected during a variety of investigations. Copper-ligand exchange reactions are mostly triggered by redox processes, addition of metal ions or addition of ligands. While the rate data spread over >8 orders of magnitude, individual effects of solvent, steric bulk, flexibility, σ-basicity and the trajectory (intra- vs. intermolecular dissociation) have large impact. Unfortunately, in many cases the exact mechanism in the rate-determining step (nucleophile-induced vs. monomolecular metal-ligand dissociation) has not been determined, suggesting to invest further efforts in the physical (in)organic chemistry of such coordination-driven systems.

Oscillating Emission of [2]Rotaxane Driven by Chemical Fuel

A molecular shuttle consisting of a dibenzo-24-crown-8 macrocycle and an axle with two degenerate peripheral triazolium stations, a central dibenzyl ammonium station, and two anthracenes stoppers was exposed to 2-cyano-2-phenylpropanoic acid as a chemical fuel. Protonation/deprotonation of the amine reversibly switches the rotaxane from a static and little emissive to a dynamic fluorescent shuttling device, the latter exhibiting rapid motion (15 kHz at 25 °C). Four fuel cycles were run.

Catalytically active nanorotor reversibly self-assembled by chemical signaling within an eight-component network

As an example of advanced molecular cybernetics eight components work together through chemical signaling reversibly setting up multifunctional nanomachinery.

Supramolecular five-component nano-oscillator

A five-component self-sorted metallo-supramolecular nano-oscillator was designed based on the full orthogonality of three different dynamic complexation motifs.