Single – not double – 3D-aromaticity in oxidized closo icosahedral dodecaiodo-dodecaborate cluster

3D-aromatic compounds are scarce. The first known species with 3D-aromaticity were the closo boranes, such as [B10H10]2- or [B12H12]2- and derivatives. Not only closo boranes, but also carboranes, which result from single or double substitution of BH by isoelectronic CH+ units in closo boranes, are 3D-aromatic compounds. Apart from closo (car)boranes, fullerenes in certain spin and charge states and Zintl phases are other known 3D-aromatic compounds. On the other hand, doubly 3D-aromatic species are unknown.

In this work, we describe the experimental 11B{1H} NMR spectra of iodinate derivatives that result from the stepwise substitution of hydrogen atoms by iodine atoms in the neutral o-carborane (1,2-C2B10H12). These NMR spectra allows us to conclude the existence of I···I non-covalent interactions in substituted boron-iodinated o-carboranes (In-1,2-C2B10H12-n, n=1-10). The existence of such interactions in periodinated o-carboranes together with the well-known double 2D-aromaticity of C6I6+2 and related species, lead us to wonder whether it would be possible to generate doubly 3D-aromatic species by oxidation of [B12I12]2- to generate [B12H12] and [B12H12]2+. Magnetic properties of [B12H12]0/2+ species indicate that these two oxidized forms of closo icosahedral dodecaiodo-dodecaborate cluster behave as doubly 3D-aromatic compounds. Analysis of the electronic properties of [B12I12]0/2+ reveals an increase in delocalization within the iodine shell, yet it proves insufficient to fully support double 3D-aromaticity. Finally, an estimation of the energetic contribution of the potential double 3D-aromaticity through homodesmotic reactions shows that delocalization in the I12 shell, in contrast to the I6 ring in the hexaiodidebenzene dication, does not contribute to any stabilization of the system. Therefore, our conclusion is that the [B12I12]0/2+ species cannot be considered as doubly 3D-aromatic.

This work has been carried out by Prof. Jordi Poater from the University of Barcelona, Prof. Francesc Teixidor and Prof. Clara Viñas from the Institute of Material Science (CSIC, Bellaterra), Prof. Henrik Ottosson from Uppsala University, and Sílvia Escayola, Dr. Albert Poater, and Prof. Miquel Solà from the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona.

J. Poater, S. Escayola, A. Poater, F. Teixidor, H. Ottosson*, C. Viñas* and M. Solà*.Single – not double – 3D-aromaticity in oxidized closo icosahedral dodecaiodo-dodecaborate cluster.

J. Am. Chem. Soc., ASAP, DOI: 10.1021/jacs.3c07335. IF: 15.0, Q1. Open access.

Lewis Acid-Assisted C(sp3)–C(sp3) Reductive Elimination at Gold published in the J. Am. Chem. Soc.

The phosphine-borane iPr2P(o-C6H4)BFxyl2 (Fxyl = 3,5-(F3C)2C6H3) 1-Fxyl was found to promote the reductive elimination of ethane from [AuMe2(μ-Cl)]2. Nuclear magnetic resonance monitoring revealed the intermediate formation of the (1-Fxyl)AuMe2Cl complex. DFT calculations identified a zwitterionic path as the lowest energy profile, with an overall activation barrier more than 10 kcal/mol lower than without borane assistance. The Lewis acid moiety first abstracts the chloride to generate a zwitterionic Au(III) complex, which then readily undergoes C(sp3)–C(sp3) coupling. The chloride is finally transferred back from boron to gold. The electronic features of this Lewis-assisted reductive elimination at gold have been deciphered by intrinsic bond orbital analyses. Sufficient Lewis acidity of boron is required for the ambiphilic ligand to trigger the C(sp3)–C(sp3) coupling, as shown by complementary studies with two other phosphine-boranes, and the addition of chlorides slows down the reductive elimination of ethane.
This paper by Yago García-Rodeja and collaborators can be found in:

https://pubs.acs.org/doi/10.1021/jacs.3c01974

Facile Construction of New Hybrid Conjugation via Boron Cage Extension

Aromatic polycyclic systems have been extensively utilized as structural subunits for the preparation of various functional molecules. Currently, aromatics-based polycyclic systems are predominantly generated from the extension of two-dimensional (2D) aromatic rings. In contrast, polycyclic compounds based on the extension of three-dimensional (3D) aromatics such as boron clusters are less studied. Here, we report three types of boron cluster-cored tricyclic molecular systems, which are constructed from a 2D aromatic ring, a 3D aromatic nido-carborane, and an alkyne. These new tricyclic compounds can be facilely accessed by Pd-catalyzed B−H activation and the subsequent cascade heteroannulation of carborane and pyridine with an alkyne in an isolated yield of up to 85% under mild conditions without any additives. Computational results indicate that the newly generated ring from the fusion of the 3D carborane, the 2D pyridyl ring, and an alkyne is nonaromatic. However, such fusion not only leads to a 1H chemical shift considerably downfield shifted owing to the strong diatropic ring current of the embedded carborane but also devotes to new improved physicochemical properties including increased thermal stability, the emergence of a new absorption band, and a largely red-shifted emission band and enhanced emission efficiency. Besides, a number of bright, color-tunable solid emitters spanning over all visible light are obtained with absolute luminescence efficiency of up to 61%, in contrast to aggregation-caused emission quenching of, e.g., Rhodamine B containing a 2D-aromatics-fused structure. This work demonstrates that the new hybrid conjugated tricyclic systems might be promising structural scaffolds for the construction of functional molecules.

The paper has been highlighted by the Spanish Biophysical Society (https://sbe.es/paperhighlights-feb-2023-2/).

This work has been carried out by F. Sun, S. Tan, H.-J. Cao, C.-S. Lu, Dr. D. Tu and Prof. Hong Yan* from Nanjing University and Prof. Jordi Poater from the University of Barcelona and Prof. Miquel Solà from the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona.

Sun, S. Tan, H.-J. Cao, C.-S. Lu, D. Tu*, J. Poater*, M. Solà* and H. Yan*. Facile Construction of a New Hybrid Conjugate via Boron Cage Extension. Am. Chem. Soc., 145 (2023) 3577-3587, DOI: 10.1021/jacs.2c12526.

 

Aromaticity rules. A comment article in Nature Chemistry

Since the formulation of the Hückel’s rule, a variety of rules have been proposed to determine if a molecule is aromatic. These allow chemists to better understand molecules and their behavior, as well as identify the formation or elimination of (anti)aromatic species in a reaction, which helps understand and predict possible outcomes. In this comment article, Prof. Miquel Solà first briefly discusses the most widespread rules associated with different types of aromaticity, then draws attention to their limitations, and finally propose future directions for the development of this fascinating topic.

The paper can be read in Nature Chemistry journal through the following link:

https://www.nature.com/articles/s41557-022-00961-w

A new non-covalent interaction: the nido cage-···nido cage- interaction

Carboranes are boron–carbon clusters with important applications in fields of materials, catalysis, pharmaceuticals, etc. However, the non-covalent interactions that could determine the solid-state structures and properties of such boron clusters have been rarely investigated. Herein, inspired by the coordinate bond in metallacarborane or ferrocene, the boron cluster-based non-covalent interaction (denoted as cage···cage interaction) between two nido-carborane clusters was successfully realized by using a pyridinium-based molecular barrier. The X-ray diffraction studies uncover that the cage×××cage interaction has a contacting distance of 5.4-7.0 Å from centroid to centroid in the systems reported here. Theoretical calculations validate the formation of the non-covalent interaction and disclose its repulsive bonding nature that is overcome thanks to the positively charged pyridinium-based framework. Interestingly, such bulk crystalline materials containing the cage···cage interaction show relevant properties such as full-color absorption in the visible light range and important  photothermal effect, which are absent for the control compound without carboranes. This study may offer fundamental insights into the boron cluster-based non-covalent interactions and open a new research avenue to rationally design boron cluster-based materials. Finally, we have computationally shown that this π···π interaction is also possible in classical organic systems.

Synthesis of the clusters were done by the group of Prof. Hong Yan in Nanjing University and calculations were performed in the IQTCUB institute by Prof. Jordi Poater and in the DiMoCat group by Prof. Miquel Solà.

The paper has been highlighted by the Spanish Biophysical Society (https://sbe.es/paperhighlights-nov2021-2/).

The paper can be read in JACS Au journal through the following link:

https://pubs.acs.org/doi/10.1021/jacsau.1c00348

Photoinduced electron transfer in suit[3]ane species in the Front Cover of J. Mat. Chem. C!

Jesús Antonio Luque Urrutia wins the second prize for the best Spanish computational paper in 2020

On 19th May 2021, the evaluation committee of the prizes to the best articles produced by Spanish PhD students in the area of Chemistry and Computation in 2020 were announced by the Computation and Chemistry specialized group of the Spanish Royal Society of Chemistry. To our delight, Dr. Jesús Antonio Luque Urrutia, former member of our research group, won the second prize with the paper:

Jesús Antonio Luque-Urrutia, Albert Poater, Miquel Solà
Do carbon nano-onions behave as nanoscopic Faraday cages? A comparison of the reactivity of C60, C240, C60@C240, Li+@C60, Li+@C240, and Li+@C60@C240
Chem. Eur. J., 202026, 804-808
DOI: 10.1002/chem.201904650

Congratulations Xus!

This paper corresponds to the last chapter of the PhD thesis defended by Dr. Luque on 26th March 2021. If you are interested you can see his defense at:

https://www.twitch.tv/videos/1025916063?t=0h0m39s

The adaptive aromaticity of metallapentalenes in the Front Cover of Chem. Eur. J.!

The Chemistry: A European Journal features in its FRONT COVER of issue number 57 of volume 26 the recently published article “Proving the origin of adaptive aromaticity in 16-valence-electron metallapentalenes”. The work has been carried out by Prof. Jun Zhu at the University of Xiamen and Dandan Chen, Dr. Dariusz W. Szczepanik, and Prof. Miquel Solà members of the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona. The cover is the result of the artistic inspiration of Dandan Chen. The paper has been highlighted in Chem. Eur. J. 26 (2020) 12902

The aromaticity of boron clusters in the Front Cover of JACS!

The Journal of the American Chemical Society (JACS) features in its FRONT COVER the recently published article “Too Persistent to Give Up: Aromaticity in Boron Clusters Survives Radical Structural Changes”. The work has been carried out by Prof. Francesc Teixidor, Prof. Clara Viñas, and Dr. Ines Bennour of the Institute of Materials Science of Barcelona (ICMAB-CSIC), Prof. Jordi Poater at the University of Barcelona (previous DiMoCat member) and Sílvia Escayola and Prof. Miquel Solà members of the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona. The cover is the result of the artistic inspiration of Sílvia Escayola.

We paper is also highlighted by the editor in the Spotlights on Recent JACS Publications.

You can go to the JACS website to read the abstract and the full article “Too Persistent to Give Up: Aromaticity in Boron Clusters Survives Radical Structural Changes”.

Jordi Poater, Clara Viñas, Ines Bennour, Sílvia Escayola, Miquel Solà*, Francesc Teixidor*
J. Am. Chem. Soc. 2020, 1429396–9407.
DOI: https://doi.org/10.1021/jacs.0c02228

 

Aromaticity in Boron Clusters Survives Radical Structural Changes

Whereas the aromaticity of closo boranes is widely accepted, less is known about the aromaticity of nido boranes. This work carried out by Prof. Francesc Teixidor, Prof. Clara Viñas, and Dr. Ines Bennour of the Institute of Materials Science of Barcelona (ICMAB-CSIC), Prof. Jordi Poater at the University of Barcelona (previous DiMoCat member) and Sílvia Escayola and Prof. Miquel Solà members of the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona, experimentally shows that deboronation of m-C2B9H12 is a difficult task, whereas deboranation of o-C2B9H12 is quite easy. Moreover, it is widely known that o-C2B10H12 isomerizes to m-C2B10H12 upon heating at 400 ºC. These two facts indicate that m-C2B10H12 is more stable than o-C2B10H12. To find a reason for the different stability of these two isomers, authors have analyzed the thermodynamic stability and aromaticity of these closo carboranes and their nido counterparts. Results show that the higher thermodynamic stability of m-C2B10H12 is not related to aromaticity differences but to the location of the C atoms in the carborane structure. It is also demonstrated that the aromaticity observed in closo boranes and carboranes is also present in their nido counterparts and, consequently, authors conclude that aromaticity in boron clusters survives radical structural changes. Further, sandwich metallocenes (e.g. ferrocene) and sandwich metallacarboranes (e.g. [Co(C2B9H11)2]) have traditionally been considered similar. In this work, it is shown that they are not. Metallacarboranes display global aromaticity, whereas metallocenes present local aromaticity in the ligands. Remarkable and unique is the double probe given by 1H- and 11B-NMR tracing the reciprocally antipodal endocyclic open face Hec and B1. These magnetic studies have permitted to correlate both nuclei and relate them to a diatropic current in the plane at the middle of the nido-[C2B9H12]. This observation is the first and unique data that proves experimentally the existence of diatropic currents, thence aromaticity, in nido clusters and is comparable to the existence of diatropic currents in planar aromatic compounds.

 

 

Poater, J.; Viñas, C.; Bennour, I.; Escayola, S.; Solà*, M.; Teixidor*, F. Too Persistent to Give Up: Aromaticity in Boron Clusters Survives Radical Structural Changes. J. Am. Chem. Soc., 2020, DOI: 10.1021/jacs.0c02228

Financial support: This work has been supported by the Ministerio de Economía y Competitividad (MINECO) of Spain (Projects CTQ2017-85341-P, CTQ2016-77558-R, and MDM-2017-0767) and the Generalitat de Catalunya (projects 2017SGR39 and 2017SGR348). Excellent service by the Supercomputer center of the Consorci de Serveis Universitaris de Catalunya (CSUC) is gratefully acknowledged.