MIOMeT - Artículos de revista

Design rules for Sb and bi porphyrin capsules: Para-substitution effects and pnictogen bond conformational control

2026-01-01T00:00:00Z

Herein, we investigate the interplay between the heavy pnictogen bridgehead atom (E) in the tris(3-pyridyl) linkers E(3-py)3 (E = Sb (1), Bi (2)), and meso-aryl substituents on the metalloporphyrin scaffolds MTPPX (M = Zn, Mg; TPPX = substituted tetraphenylporphyrin) with respect to capsule formation and conformational control. Coordination of 1 and 2 to para-substituted zinc porphyrins ZnTPPOMe and ZnTPPBr yielded partially encapsulated semicapsules {[E(3-py)3]·(ZnTPPX)2}, while MgTPPBr produced oligomeric structures, showing that relatively bulky para-substituents disfavor complete 1:3 capsule formation. In contrast, coordination of 1 and 2 to perfluorinated ZnTPPF5 promotes the formation of full 1:3 capsules {[E(3-py)3]·(ZnTPPF5)3}, stabilized by three intramolecular E···F pnictogen bonds (PnBs) that give rise to a unique “blocked” conformation. DFT calculations indicate that distal porphyrin coordination enhances Lewis acidity at E, deepening its σ-holes and strengthening E···F interactions, thus overcoming the negative cooperativity typically associated with multiple PnBs. This remote coordination effect offers a new supramolecular strategy to fine-tune σ-hole depth and Lewis acidity. The steric shielding of the bridgehead in this conformation markedly affects reactivity, as shown by the inhibition of Sb-catalyzed α-hydroxyketone oxidation. These studies illustrate the crucial role of PnBs in stabilizing capsules of this type and modulating their reactivity through conformational control.

Synthesis and reactivity of air stable Ni(II) complexes with isocyanides and dialkyldithiophosphate ligands: alkyl transfer and acyclic diaminocarbene formation

2023-01-01T00:00:00Z

A library of new neutral and cationic Ni(II) complexes containing isocyanide ligands and mono- or dialkyl-dithiophosphate have been prepared and fully characterized. They are subsequently shown to constitute excellent precursors to obtain new families of air stable Ni(II)-based acyclic diaminocarbene (Ni-ADCs) complexes by nucleophilic attack with various alkyl-substituted amines. Remarkably, the ADC is only produced at one of the isocyanide ligands. This was subsequently exploited to obtain an unpredecented dinuclear complex containing a bridging bis-carbene ligand using piperazine.

Ru(II)-based multitopic hosts for fullerene binding: impact of the anion in the recognition process

2025-01-01T00:00:00Z

The development of multitopic hosts for fullerene recognition based on nonplanar corannulene (C20H10) structures presents challenges, primarily due to the requirement for synergistic interactions with multiple units of this polycyclic aromatic hydrocarbon. Moreover, increasing the number of corannulene groups in a single chemical structure while avoiding the cost of increasing flexibility has been scarcely explored. Herein, we report the synthesis of a family of multitopic Ru(II)-polypyridyl complexes bearing up to six units of corannulene arranged by pairs, offering a total of three molecular tweezers. All of them are fixed by the central atom and organized in an octahedral structure. Their fullerene recognition capabilities have been thoroughly demonstrated toward C60 and C70 showing that they can reasonably accommodate up to three fullerenes per host in a noncooperative manner. There are, however, some features that diverge from comparable hosts in the literature, such as the low value of several association constants. This behavior, supported by theoretical studies, is attributed to the presence of two noninnocent BAr4F anions that interfere with the supramolecular binding through ion pair formation. These findings highlight the crucial role of selecting compatible ionic species in supramolecular host design as they can significantly influence the recognition process.

Multitopic corannulene–porphyrin hosts for fullerenes: a three-layer scaffold for precisely designed supramolecular ensembles

2024-01-01T00:00:00Z

A method to synthesize cofacial dimeric porphyrins bearing eight corannulene units has been developed. It relies on the stability of octahedral CO-capped Ru(II) complexes linked by N-donor ligands. This specific arrangement provides an optimal scaffold to accommodate fullerenes by imposing corannulene groups at a precise distance and relative orientation. Their capabilities for C60 recognition have been thoroughly assessed, revealing that each system can encapsulate up to four guests, giving rise to a compact supramolecular van der Waals complex echoing a discrete donor–acceptor–donor trilayer offering significant potential properties for further exploitation.

Supramolecular self-sorting predicted by a simple harmonic oscillator model

2024-01-01T00:00:00Z

Macrocycles that encapsulate two guests can self-sort those into homo- and heterodimers. We report here a family of self-sorting homobimetallic Pt(II) terpyridyl acetylide dimers secured together with a pair of Cucurbit[8]uril macrocycles (CB[8]). The rigid bridging unit between both Pt centers introduces varying “hinge” angles, resulting in disparities in Pt–Pt distances in the heterodimers, and leads to recognition motif mismatch. We found that the self-sorting process can be quantified using a simple model, in which each complex behaves as a simple harmonic oscillator, whose heteroassembly tends to minimize geometry distorsions through C(aryl)–C[triple bond, length as m-dash]C–Pt axis deformation.

1,2-Azolylamidino ruthenium(ii) complexes with DMSO ligands: electro- and photocatalysts for CO2 reduction

2023-01-01T00:00:00Z

New 1,2-azolylamidino complexes fac-[RuCl(DMSO)3(NHvC(R)az*-κ2 N,N)]OTf [R = Me (2), Ph (3); az* = pz (pyrazolyl, a), indz (indazolyl, b)] are synthesized via chloride abstraction from their corresponding pre- cursors cis,fac-[RuCl2 (DMSO) 3(az*H)] (1) after subsequent base-catalyzed coupling of the appropriate nitrile with the 1,2-azole previously coordinated. All the compounds are characterized by 1 H NMR, 13 C NMR and IR spectroscopy. Those derived from MeCN are also characterized by X-ray diffraction. Electrochemical studies showed several reduction waves in the range of −1.5 to −3 V. The electro- chemical behavior in CO2 media is consistent with CO2 electrocatalytic reduction. The catalytic activity expressed as [icat (CO 2)/ip (Ar)] ranged from 1.7 to 3.7 for the 1,2-azolylamidino complexes at voltages of ca. −2.7 to −3 V vs. ferrocene/ferrocenium. Controlled potential electrolysis showed rapid decomposition of the Ru catalysts. Photocatalytic CO 2 reduction experiments using compounds 1b, 2b and 3b carried out in a CO2 -saturated MeCN/TEOA (4 : 1 v/v) solution containing a mixture of the catalyst and [Ru (bipy)3 ]2+ as the photosensitizer under continuous irradiation (light intensity of 150 mW cm−2 at 25 °C, λ > 300 nm) show that compounds 1b, 2b and 3b allowed CO2 reduction catalysis, producing CO and trace amounts of formate. The combined turnover number for the production of formate and CO is ca. 100 after 8 h and follows the order 1b < 2b ≈ 3b.

Counterintuitive torsional barriers controlled by hydrogen bonding

2020-01-01T00:00:00Z

The torsional barriers along the Caryl–Caryl axis of a pair of isosteric disubstituted biphenyls were determined by variable temperature 1H NMR spectroscopy in three solvents with contrasted hydrogen bond accepting abilities (1,1,2,2-tetrachloroethane-d2, nitrobenzene-d5 and dimethyl sulfoxide-d6). One of the biphenyl scaffolds was substituted at its ortho and ortho′ positions with N′-acylcarbohydrazide groups that could engage in a pair of intramolecular N–H⋯O=C hydrogen bonding interactions at the ground state, but not at the transition state of the torsional isomerization pathway. The torsional barrier of this biphenyl was exceedingly low despite the presence of the hydrogen bonds (16.1, 15.6 and 13.4 kcal mol−1 in the three aforementioned solvents), compared to the barrier of the reference biphenyl (15.3 ± 0.1 kcal mol−1 on average). Density functional theory and the solvation model developed by Hunter were used to decipher the various forces at play. They highlighted the strong stabilization of hydrogen bond donating solutes not only by hydrogen bond accepting solvents, but also by weakly polar, yet polarizable solvents. As fast exchanges on the NMR time scale were observed above the melting point of dimethyl sulfoxide-d6, a simple but accurate model was also proposed to extrapolate low free activation energies in a pure solvent (dimethyl sulfoxide-d6) from higher ones determined in mixtures of solvents (dimethyl sulfoxide-d6 in nitrobenzene-d5).

“Dual Layer” Self-Sorting with Cucurbiturils

2019-01-01T00:00:00Z

Platinum(II) complexes bearing terpyridyl (tpy) and thiolate ligands were used to test the design of a “dual layer” self-sorting system in the presence of Cucurbit[8]uril (CB[8]). Pt(II) thiolates and CB[8] form 2:1 assemblies, with both metallic centers sitting on top of one another at one of the macrocycle portals. We showed that any pair of these CB[8]-secured Pt(II) complex dimers bearing different tpy “heads” and thiolate “tails” scrambles to afford up to 10 ternary assemblies via two processes: (1) supramolecular exchanges (i.e., the egression and ingression of Pt complexes from and into CB[8]) and (2) ligand exchanges between the Pt thiolates. The mixtures of 10 assemblies were fully characterized by nuclear magnetic resonance spectroscopy. While the thiolate tails do not significantly affect the rate of the supramolecular exchanges, they were found to control (1) the kinetics of ligand exchange, with bulkier thiolates causing dramatic rate retardations, as well as (2) the thermodynamics of the self-sorting process, i.e., the distribution of assemblies at equilibrium, via intra-CB[8] assembly interactions between pairs of thiolates. Ligand exchanges are consistently slower than supramolecular exchanges. An associative pathway that involves the formation of dimers of CB[8]-secured Pt dimers (a total of 4 Pt complexes) during the ligand exchange process was invoked to rationalize the observed kinetics.

Templating conformations with cucurbiturils

2019-01-01T00:00:00Z

The trans- and cis conformations of 5,5′-substituted 2,2′-dithiophenes can be stabilized when those are secured with two Cucurbit[8]uril macrocycles (CB[8]) on top of rigid 2,6- and 2,7-substituted naphthalenes, which respectively mimic the trans and cis conformations of the dithiophene. The substituents are Pt(II) terpyridyl groups bearing CB[8]-binding sites at their 4′-position, as those form dimers in the presence of the macrocycle through Pt–Pt and dispersive interactions between the terpyridyl ligands.

Efficient access to polysubstituted tetrahydrofurans by electrophilic cyclization of vinylsilyl alcohols

2015-01-01T00:00:00Z

Vinylsilyl alcohols undergo intramolecular cyclization to provide di-, tri- or tetrasubstituted-tetrahydrofurans. The influence of the number and position of substituents in the stereoselectivity of the process has been studied. Moreover, DFT calculations have been performed to get better insight into the influence of the substitution pattern of the vinylsilyl alcohol in the stereoselectivity of the cyclization.

Competitive Silyl–Prins Cyclization versus Tandem Sakurai–Prins Cyclization: An Interesting Substitution Effect

2014-01-01T00:00:00Z

Two different mechanism pathways are observed for the reaction of allylsilyl alcohols 1 and aldehydes in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf). In the case of allylsilyl alcohols without allylic substituents, the reaction gives dioxaspirodecanes, which are the products of a tandem Sakurai–Prins cyclization. In contrast, allylsilyl alcohols with an allylic substituent (R2¼6 H) selectively provide oxepanes, thus corresponding to a direct silyl–Prins cyclization. Both types of product are obtained with excellent stereoselectivity. Theoretical studies have been performed to obtain some rationalization for the observed stereoselectivity.

η6-Hexahelicene Complexes of Iridium and Ruthenium: Running along the Helix

2012-01-01T00:00:00Z

The first η6-complexes of iridium and ruthenium coordinated to helicenes have been obtained. Hexahelicene (1), 2,15-dimethylhexahelicene (2), and 2,15-dibromohexahelicene (3) react with [Cp*IrCl2]2 and AgBF4 in CD3NO2 to afford quantitatively the complexes [Cp*Ir(η6-1)][BF4]2 (4A), [Cp*Ir(η6-2)][BF4]2 (5A), and [Cp*Ir(η6-3)][BF4]2 (6A), respectively. In all cases, the final thermodynamic products are similar, and they exhibit coordination between the 12 e– metal fragment [IrCp*]2+ and the terminal ring of the helicene. Monitoring the reaction by NMR shows formation of intermediates, some of which have been fully characterized in solution. These intermediates exhibit the metal fragment coordinated to the internal rings. We have also synthesized the bimetallic complex [(Cp*Ir)2(μ2-η6:η6-2)][BF4]4 (7), achieving coordination between two units [IrCp*]2+ and the helicene 2. Following an analogous methodology, we have prepared the complex [(η6-cymene)Ru(η6-2)][BF4]2 (8), which has been studied by X-ray diffraction, confirming the preferential binding to the terminal aromatic ring.

Synthesis of a Tetracorannulene-perylenediimide That Acts as a Selective Receptor for C60 over C70

2019-01-01T00:00:00Z

We report the use of a tetraborylated perylenediimide as starting material for the preparation of a tetracorannulene-perylenediimide that is able to bind up to two fullerene-C60 molecules by host–guest molecular recognition with preference over C70. Titration with fullerene-C60 is followed by a dramatic shift of the aromatic signals in 1H NMR and an initial increase in the fluorescence of the system. By this simple mechanism, fluorogenic sensing of fullerene-C60 is easily accomplished by an unprecedented fluorescent turn-on mechanism.

Octapodal Corannulene Porphyrin-Based Assemblies: Allosteric Behavior in Fullerene Hosting

2020-01-01T00:00:00Z

An octapodal corannulene-based supramolecular system has been prepared by introducing eight corannulene moieties in a porphyrin scaffold. Despite the potential of this double picket fence porphyrin for double-tweezer behavior, NMR titrations show exclusive formation of 1:1 adducts. The system exhibits very strong affinity for C60 and C70 (K1 = (2.71 ± 0.08) × 104 and (2.13 ± 0.1) × 105 M–1, respectively), presenting selectivity for the latter. Density functional theory (DFT) calculations indicate that, in addition to the four corannulene units, the relatively flexible porphyrin tether actively participates in the recognition process, resulting in a strong synergistic effect. This leads to a very strong interaction with C60, which in turn also induces a large structural change on the other face (second potential binding site), leading to a negative allosteric effect. We also introduced Zn2+ in the porphyrin core in an attempt to modulate its flexibility. The resulting metalloporphyrin also displayed single-tweezer behavior, albeit with slightly smaller binding constants for C60 and C70, suggesting that the effect of the coordination of fullerene to one face of our supramolecular platform was still transmitted to the other face, leading to the deactivation of the second potential binding site.

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

2016-01-01T00:00:00Z

The main purpose of this video is to show 6 reaction steps of a convergent synthesis and prepare a complex molecule containing up to three nonplanar polyaromatic units, which are two corannulene moieties and a racemic hexahelicene linking them. The compound described in this work is a good host for fullerenes. Several common organic reactions, such as free-radical reactions, C-C coupling or click chemistry, are employed demonstrating the versatility of functionalization that this compound can accept. All of these reactions work for planar aromatic molecules. With subtle modifications, it is possible to achieve similar results for nonplanar polyaromatic compounds.

Porphyrin-based systems containing polyaromatic fragments: decoupling the synergistic effects in aromatic-porphyrin-fullerene systems

2020-01-01T00:00:00Z

In this work, we report a two-step synthesis that allows the introduction of four pyrene or corannulene fragments at the para position of meso-tetraarylporphyrins using a microwave-assisted quadruple Suzuki–Miyaura reaction. Placing the PAHs at this position, further from the porphyrin core, avoids the participation of the porphyrin core in binding with fullerenes. The fullerene hosting ability of the four new molecular receptors was investigated by NMR titrations and DFT studies. Despite having two potential binding sites, the pyrene derivatives did not associate with C60 or C70. In contrast, the tetracorannulene derivatives bound C60 and C70, although with modest binding constants. In these novel para-substituted systems, the porphyrin core acts as a simple linker that does not participate in the binding process, which allows the system to be considered as two independent molecular tweezers; i.e., the first binding event is not transmitted to the second binding site. This behavior can be considered a direct consequence of the decoupling of the porphyrin core from the binding event.