Instituto Universitario Centro de Innovación en Química y Materiales Avanzados (CINQUIMA)Instituto Universitario Centro de Innovación en Química y Materiales Avanzados (CINQUIMA)https://uvadoc.uva.es/handle/10324/285422024-03-28T22:21:59Z2024-03-28T22:21:59ZCounterintuitive torsional barriers controlled by hydrogen bondingBarbero San Juan, HéctorMeunier, AntoineKotturi, KondalaraoSmith, AshtonKyritsakas, NathalieKillmeyer, AdamRabbani, RaminNazimuddin, MdMasson, Erichttps://uvadoc.uva.es/handle/10324/663842024-02-22T20:00:53Z2020-01-01T00:00:00ZThe 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).
2020-01-01T00:00:00Z“Dual Layer” Self-Sorting with CucurbiturilsBarbero San Juan, HéctorThompson, Nathan A.Masson, Erichttps://uvadoc.uva.es/handle/10324/663552024-02-21T20:00:56Z2019-01-01T00:00:00ZPlatinum(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.
2019-01-01T00:00:00ZTemplating conformations with cucurbiturilsThompson, Nathan A.Barbero San Juan, HéctorMasson, Erichttps://uvadoc.uva.es/handle/10324/662912024-02-16T20:00:33Z2019-01-01T00:00:00ZThe 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.
2019-01-01T00:00:00ZEfficient access to polysubstituted tetrahydrofurans by electrophilic cyclization of vinylsilyl alcoholsBarbero Pérez, María AsunciónBarbero San Juan, HéctorGonzález Ortega, AlfonsoPulido Pelaz, Francisco JoséVal, PatriciaDiez de la Varga, AlbertoRodríguez Morán, Joaquínhttps://uvadoc.uva.es/handle/10324/662782024-02-15T20:01:28Z2015-01-01T00:00:00ZVinylsilyl 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.
2015-01-01T00:00:00ZCompetitive Silyl–Prins Cyclization versus Tandem Sakurai–Prins Cyclization: An Interesting Substitution EffectDiez de la Varga, AlbertoBarbero San Juan, HéctorPulido Pelaz, Francisco JoséGonzález Ortega, AlfonsoBarbero Pérez, María Asunciónhttps://uvadoc.uva.es/handle/10324/662562024-02-14T20:00:58Z2014-01-01T00:00:00ZTwo 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.
2014-01-01T00:00:00Zη6-Hexahelicene Complexes of Iridium and Ruthenium: Running along the HelixÁlvarez González, Celedonio ManuelBarbero San Juan, HéctorGarcía-Escudero, Luis A.Martín Álvarez, José MiguelMartínez-Pérez, CristinaMiguel San José, Danielhttps://uvadoc.uva.es/handle/10324/657972024-03-04T08:50:07Z2012-01-01T00:00:00ZThe 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.
2012-01-01T00:00:00ZSynthesis of a Tetracorannulene-perylenediimide That Acts as a Selective Receptor for C60 over C70García-Calvo, VíctorCuevas, José V.Barbero San Juan, HéctorFerrero, SergioÁlvarez González, Celedonio ManuelGonzález, Jesús A.Díaz de Greñu, BorjaGarcía-Calvo, JoséTorroba, Tomáshttps://uvadoc.uva.es/handle/10324/654592024-03-04T08:48:41Z2019-06-26T00:00:00ZWe 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.
2019-06-26T00:00:00ZOctapodal Corannulene Porphyrin-Based Assemblies: Allosteric Behavior in Fullerene HostingFerrero, SergioBarbero San Juan, HéctorMiguel, DanielGarcía-Rodríguez, RaúlÁlvarez González, Celedonio Manuelhttps://uvadoc.uva.es/handle/10324/654562024-03-04T08:48:09Z2020-03-10T00:00:00ZAn 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.
2020-03-10T00:00:00ZPreparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic UnitsFerrero, SergioBarbero San Juan, HéctorÁlvarez González, Celedonio Manuelhttps://uvadoc.uva.es/handle/10324/653772024-02-01T08:38:39Z2016-01-01T00:00:00ZThe 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.
2016-01-01T00:00:00ZPorphyrin-based systems containing polyaromatic fragments: decoupling the synergistic effects in aromatic-porphyrin-fullerene systemsFerrero, SergioBarbero San Juan, HéctorMiguel, DanielGarcía-Rodríguez, RaúlÁlvarez González, Celedonio Manuelhttps://uvadoc.uva.es/handle/10324/653752024-02-01T08:38:12Z2020-01-01T00:00:00Zn 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.
2020-01-01T00:00:00ZDesign and recognition of cucurbituril-secured platinum-bound oligopeptidesBarbero San Juan, HéctorMasson, Erichttps://uvadoc.uva.es/handle/10324/653742024-01-30T20:03:08Z2021-01-01T00:00:00ZPlatinum terpyridyl complexes, stacked on top of one another and secured as dimers with cucurbit[8]uril (CB[8]) in aqueous medium, were functionalized quantitatively and in situ with a pair of pentapeptides Phe-(Gly)3-Cys by grafting their cysteine residues to the Pt centers. The resulting CB[8]·(Pt·peptide)2 assemblies were used to target secondary hosts CB[7] and CB[8] via their pair of phenylalanine residues, again in situ. A series of well-defined architectures, including a supramolecular “pendant necklace” with hybrid head-to-head and head-to-tail arrangements inside CB[8], were obtained during the self-sorting process after combining only 3 or 4 simple building units.
2021-01-01T00:00:00ZEnhanced photoreduction of water catalyzed by a cucurbit[8]uril-secured platinum dimerRabbani, RaminSaeedi, SimaNazimuddin, MdBarbero San Juan, HéctorKyritsakas, NathalieWhite, Travis A.Masson, Erichttps://uvadoc.uva.es/handle/10324/653712024-01-30T20:03:07Z2021-01-01T00:00:00ZA cucurbit[8]uril (CB[8])-secured platinum terpyridyl chloride dimer was used as a photosensitizer and hydrogen-evolving catalyst for the photoreduction of water. Volumes of produced hydrogen were up to 25 and 6 times larger than those obtained with the corresponding free and cucurbit[7]uril-bound platinum monomer, respectively, at equal Pt concentration. The thermodynamics of the proton-coupled electron transfer from the Pt(II)–Pt(II) dimer to the corresponding Pt(II)–Pt(III)–H hydride key intermediate, as quantified by density functional theory, suggest that CB[8] secures the Pt(II)–Pt(II) dimer in a particularly reactive conformation that promotes hydrogen formation.
2021-01-01T00:00:00ZCucurbiturils mimicked by low polarizability solvents with pre-formed cavities: an empirical model to predict hydrocarbon selectivityNazimuddin, MdBarbero San Juan, HéctorRabbani, RaminMasson, Erichttps://uvadoc.uva.es/handle/10324/653702024-03-04T08:49:06Z2022-01-01T00:00:00ZRelative binding affinities of a series of nine rigid hydrocarbons towards the cavity formed by a portion of the inner wall of cucurbit[8]uril (CB[8]) and a positive auxiliary guest were determined by competitive 19F NMR titrations in deuterium oxide. The corresponding free binding energies were corrected by the hydrocarbon computed solvation energies to obtain their free energies of transfer from the gas phase to the CB[8]/auxiliary guest cavity. These energies correlate linearly with the hydrocarbon static polarizabilities, thereby suggesting that the selectivity is driven, perhaps exclusively, by dispersive interactions between the hydrocarbons and the tailor-made cavity, regardless of the degree of unsaturation of the guests. The free energies of transfer also correlate linearly with the energy released upon introduction of the hydrocarbon into a pre-formed cavity extruded from a solvent (benzene) selected to mimic the polarity and polarizability of the CB[8]/auxiliary probe cavity – and this, with a unity slope. Among other features, this empirical model also accurately predicts the relative binding affinities of various rigid hydrocarbons to CB[6] and CB[7], as well as noble gases to CB[5], when the macrocycles are mimicked with pre-formed cavities in perfluorohexane or perfluorohexane/benzene mixtures, both being notoriously non-polar and non-polarizable environments.
2022-01-01T00:00:00ZNon‐Chelate‐Assisted Palladium‐Catalyzed Aerobic Oxidative Heck Reaction of Fluorobenzenes and Other Arenes: When Does the C−H Activation Need Help?Villalba, FranciscoAlbéniz, Ana C.https://uvadoc.uva.es/handle/10324/650522024-01-25T20:02:16Z2021-01-01T00:00:00ZThe pyridone fragment in the ligand [2, 2’-bipyridin]-6(1H)-one (bipy-6-OH) enables the oxidative Heck reaction of simple arenes with oxygen as the sole oxidant and no redox mediator. Arenes with either electron-donating or electron-withdrawing groups can be functionalized in this way. Experimental data on the reaction with toluene as the model arene shows that the C-H activation step is turnover limiting and that the ligand structure is crucial to facilitate the reaction, which supports the involvement of the pyridone fragment in the C-H activation step. In the case of fluoroarenes, the alkenylation of mono and 1,2-difluoro benzenes requires the presence of bipy-6-OH. In contrast, this ligand is detrimental for the alkenylation of 1,3-difluoro, tri, tetra and pentafluoro benzenes which can be carried out using just [Pd(OAc)2]. This correlates with the acidity of the fluoroarenes, the most acidic undergoing easier C H activation so other steps of the reaction such as the coordination-insertion of the olefin become kinetically important for polyfluorinated arenes. The use of just a catalytic amount of sodium molybdate as a base proved to be optimal in all these reactions.
2021-01-01T00:00:00ZA different polynorbornene backbone by combination of two polymer growth pathways: vinylic addition and ring opening via β-C eliminationPérez-Ortega, IgnacioAlbéniz, Ana C.https://uvadoc.uva.es/handle/10324/650512024-01-25T20:02:14Z2022-01-01T00:00:00ZA new polynorbornene skeleton has been found that contains bicyclic norbornane units and cyclohexenyl methyl linkages. The polymers have been synthesized using a nickel catalyst in the presence of a controlled amount of ligands with low or moderate coordination ability. The backbone structure is the result of a vinylic addition polymerization, via sequential insertions of norbornene into a Ni–C bond (bicyclic units) combined with an unusual ring opening of the norbornene structure by a b-C elimination (cyclohexenyl methyl units) to give a new Ni–C(alkyl) bond that continues the polymerization. The ring opening events are favored when the rate of propagation of the vinylic addition polymerization decreases, and this can be modulated by making the coordination of norbornene to the metal center less favorable using additional ligands.
2022-01-01T00:00:00ZPalladium-Catalyzed Ortho C–H Arylation of Unprotected Anilines: Chemo- and Regioselectivity Enabled by the Cooperating Ligand [2,2′-Bipyridin]-6(1H)-onePinilla, CintyaSalamanca, VanesaLledós, AgustíAlbéniz, Ana C.https://uvadoc.uva.es/handle/10324/650492024-01-25T20:02:13Z2022-01-01T00:00:00ZMetal-catalyzed C−H functionalizations on the aryl ring of anilines usually need cumbersome N-protection−deprotection strategies to ensure chemoselectivity. We describe here the Pd-catalyzed direct C−H arylation of unprotected anilines with no competition of the N-arylation product. The ligand [2,2′-bipyridin]-6(1H)-one drives the chemoselectivity by kinetic differentiation in the product-forming step, while playing a cooperating role in the C−H cleavage step. The latter is favored in an anionic intermediate where the NH moiety is deprotonated, driving the regioselectivity of the reaction toward ortho substitution.
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