An unprecedented π-electronic circuit involving an odd number of carbon atoms in a grossly warped non-planar nanographene

/0 Comments/in /by

Aromaticity in macrocycles has been less studied than aromaticity in small polycyclic aromatic hydrocarbons (PAHs). In the work carried out by Dr. Álvaro Muñoz Castro from the Grupo de Química Inorgánica y Materiales Moleculares of the Universidad Autónoma de Chile and by 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, the authors analyze the most efficient circuits for π-delocalization in a grossly warped nanographene (C80H30), containing five- and seven-membered rings inserted into a six-membered mesh. DFT calculations of different aromaticity indices (FLU, HOMA, EDDB, and ring currents) indicate that one of the two most favorable circuits for π-electron delocalization formally has 50 π-electrons abiding by Hückel’s rule, whereas the second one formally has 75 π-electrons and, remarkably, it does not follow any of the known rules of aromaticity. The nanographene studied display both local aromaticity in the external six-membered rings and macrocyclic aromaticity in the 50 amd 75 π-electrons circuit. This is the first time that a π-electronic circuit has an odd number of electrons, and also that the circuit involves cross-conjugated pathways (ie they do not have alternating single and double bonds).

This finding has been highlighted by Chemistry World, as can be seen in the following link.

S. Escayola, A. Poater, A. Muñoz-Castro* and M. Solà*. An unprecedented π-electronic circuit involving an odd number of carbon atoms in a grossly warped non-planar nanographene. Chem. Commun., 2021, DOI: 10.1039/D1CC00593F

Hückel-Baird Hybrid Aromatic Character of Pro-Aromatic Quinoidal Compounds

/0 Comments/in /by

A recent paper (Kim et al. Nature Commun. 2019, 10, 4983) claims that there is a double charge transfer in the first singlet excited singlet state in TMTQ (an oligomer composed of a central 1,6-methano[10]annulenes, M10A, and 5-diacyanomethyl-thiophene exocyclic groups, see Figure 1) that is stabilized by the Baird aromaticity acquired by the central M10A ring. In a previous work (Jorner et al. Chem. Eur. J. 2016, 22, 2793), some of us found that the charge transfer in the first excited singlet and triplet states in TMTQ is minor and that the central ring in these low-lying excited states is a Hückel-Baird hybrid with a ca. 85% of Hückel and 15% of Baird character. In the light of the new existing experimental data, Claire Tonnelé and Prof. Henrik Ottosson of the Uppsala University, Dr. David Casanova and Dr. Eduard Matito of the Donostia International Physics Center (previous DiMoCat member), and Sílvia Escayola, Dr. Albert Poater, and Prof. Miquel Solà members of the DiMoCat group of the Institute of Computational Chemistry and Catalysis of the University of Girona decided to reinvestigate the problem using (time-dependent) density functional theory methods. We considered not only TMTQ but also a series of symmetrically substituted conjugated rings that can generate Baird aromaticity in the lowest-lying excited states. This work shows that the interpretation by Kim et al. needs to be revised because low-lying excitations of symmetrically substituted conjugated rings including TMTQ hold very weak charge transfer character. Our computational results also allow us to establish general guidelines for the rational design of molecules with excited state Hückel/Baird aromaticity in pro-aromatic quinoidal compounds We found that high Baird character of the central ring is achieved only with anionic and small conjugated central rings with electron donating groups as substituents and small exocyclic groups with electron withdrawing substituents. Our study aims to warn about the need to make correct interpretations of the experiments in this growing area of research, as only then can the excited state aromaticity concept develop in a useful tool for the design of high-performance organic electronic devices.

Figure 1. Quinoidal, diradical, and ionic resonance structures of importance for TMTQ (10R-T) involved in the description of S0, S1, and T1 states.

 

Escayola, C. Tonnelé, E. Matito, A. Poater, H. Ottosson*, M. Solà* and D. Casanova*. Guidelines for Tuning the Excited State Hückel-Baird Hybrid Aromatic Character of Pro-Aromatic Quinoidal Compounds. Angew. Chem. Int. Ed., 2021, DOI: 10.1002/anie.202100261.

Gibu George joints the DiMoCat group as a PhD researcher in training

/0 Comments/in /by

At the beginning of November 2021, Gibu George joined the DiMoCat group as a PhD researcher in training with a FI-SDUR fellowship financed by the Generalitat de Catalunya. During his PhD, he will be working on charge transfer processes with a focus to fullerene donor/acceptor dyads and fullerene:perovskite hybrid solar cells. His work will be supervised by Prof. Miquel Solà and Dr. Antony Stasyuk.

Gibu George (1996) obtained his B.Sc. in Chemistry in 2017 and his M.Sc. in Pharmaceutical Chemistry in 2019, both at Mahatma Gandhi University (India). During his master’s, he worked under the supervision of Dr. Jayasree E.G at the University of Kerala (India). After that, he moved to Cochin University of Science and Technology (India) for about 3 months to work with Dr. Susmita De.

Because of the COVID-19 pandemic, it has not been easy for Gibu to get the visa (Spanish embassy was closed) and the flight to come to Girona. Fortunately, finally was able to get the visa and he joined our group on 2nd November 2020. We wish him good luck with his PhD!

All-metal Baird aromaticity in the Front Cover of Chem. Commun.!

/0 Comments/in /by

The FRONT COVER of issue number 83 of volume 56 refers to the recently published article “All-metal Baird aromaticity”. 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 by ChemistryWorld. Inthe same issue, others members of DiMoCat have published another paper entitled “Photoinduced electron transfer in nanotube⊃C70 inclusion complexes: phenine vs. nanographene nanotubes“.

Aromaticity in Boron Clusters Survives Radical Structural Changes

/0 Comments/in , , , /by

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.

Two ICREA Acadèmia awards at IQCC: Anna Company and Albert Poater

/1 Comment/in /by

ICREA announced the list of winners of the ICREA Acadèmia awards 2019, among which are three (!!!) names from the University of Girona: Sebastià Puig (Engineering), Anna Company and Albert Poater (both IQCC and Chemistry). Albert Poater belongs to DIMOCAT group.

 

                                             

Unprecedented Selectivity of Ruthenium Iodide Benzylidenes in Olefin Metathesis Reactions

/0 Comments/in /by

Olefin metathesis seems to be a complex chemical reaction, but if we say that leads to the formation of polymers, i.e. plastics, it is really simple and it is valid in any item that currently we have in our hands. This field of olefin metathesis is mature, after the Nobel Prize in 2005 of Chauvin, Schrock and Grubbs, but still here with two simple modifications we have been able to get novel catalysts that lead to amazing selectivity. In collaboration with the Ben-Gurion University of the Negev, the IQCC team from DIMOCAT led by Albert Poater shows that cis-diiodo sulfur chelated ruthenium benzylidenes do not react with strained cycloalkenes and internal olefins, but can effectively catalyze metathesis reactions of terminal dienes. Surprisingly, internal olefins may partake in olefin metathesis reactions once the ruthenium methylidene intermediate is generated. This unexpected behavior allows the facile formation of strained cis-cyclooctene by the RCM reaction of 1,9-undecadiene. Once in silico calculations confirmed the promising different behavior of those novel catalysts, the impressively latent catalyst was activated experimentally by addition of an external chloride source, unveiling a novel method for controlled polymerization of DCPD.

B. Nechmad, R. Phatake, E. Ivry, A. Poater, N. G. Lemcoff; “Unprecedented Selectivity of Sulfur Chelated Ruthenium Iodide Benzylidenes in Olefin Metathesis Reactions”; Angew. Chem. Int. Ed. 2020, accepted. DOI: 10.1002/anie.201914667

 

Amazing combination of factors transforms chemistry into green chemistry

/0 Comments/in /by

In search of green or sustainable chemistry there are different objectives to achieve, and already achieve successfully one already represents a step forward to improve the world that surrounds us. Here, in this collaborative work between the experimental team of the University of Normandy (France) led by Prof. Jean Luc Renaud, and from Girona, Dr. Albert Poater the computational complementary part, has been able to achieve not only find a catalyst capable of fixing CO2, but to find out one that is not based on noble metals, expensive, and of high toxicity, and furthermore, dealing with water as a solvent. An iron, most abundant metal catalyst of the Earth’s layer has been employed.  Overall, a highly efficient, stable, phosphine-free, and easy-to-synthesize iron catalyst system for the reduction of CO2, hydrogenocarbonate, and carbonate in pure water is reported.

Coufourier, Q. Gaignard-Gaillard, J.-F. Lohier, A. Poater, S. Gaillard, J.-L. Renaud; “Hydrogenation of CO2, Hydrogenocarbonate, and Carbonate to Formate in Water using Phosphine Free Bifunctional Iron Complexes”; ACS Catal. 2020, 10, 2108-2116. DOI: 10.1021/acscatal.9b04340

Two new PhD students in the DiMoCat group

/0 Comments/in , , , /by

We have recently incorporated two new PhD students in our group with two cotutelle agreements.

First, Daniel Eduardo Trujillo that will perform a theoretical study of the electronic structure and reaction mechanisms of reactions of multiple-bound boron compounds that can activate C-C and C-H bonds. Daniel will be supervised by J. Oscar C. Jimenez-Halla and Gerardo Gonzalez in the University of Guanajauto (Mexico) and Miquel Solà in the University of Girona.

A photo of Daniel E. Trujillo

Second, Dandan Chen that will be working in the study of aromatic species with special emphasis in metalloaromatic species in excited states. Dandan will be supervised by Jun Zhu in Xiamen University (China) and Miquel Solà in the University of Girona.


A photo of Dandan Chen

We wish Daniel and Dandan a great success with their PhD research!

Two recent DiMoCat works highlighted by ChemistryWorld

/0 Comments/in , , , , /by

ChemistryWorld has recently highlighted two works of our group:

The jellium model assumes a uniform distribution of positive charge corresponding to the cluster atomic nuclei and their innermost electrons in which the interacting valence electrons move. The energy levels of valence electrons for such a model are 1S21P61D102S21F142P61G182D103S2…, where S, P, D, F, and G letters denote the angular momentum and numbers 1, 2, 3 indicate the radial nodes. The abundance found in experimental mass spectra of alkali, alkaline earth metals, and gold clusters of 2, 8, 18, 20, 34, 40… atoms are justified taken into account that these numbers correspond to closed-shell electronic structures in the jellium model. We have proven that if the last energy level of valence electrons for the jellium model is half-filled with same-spin electrons, the system has also an aromatic character that provides extra stability. This situation is reached for the magic numbers of valence electrons of 1 (S =1/2), 5 (S = 3/2), 13 (S = 5/2), 19 (S = 1/2), 27 (S = 7/2), 37 (S = 3/2), 49 (S = 9/2)… This new set of magic numbers may become a powerful tool for researchers who work in the quest for stable single high-spin molecules for their use as single-molecule based magnets. The paper has been published in Chem. Commun. and can be found in the following link Chem. Commun., 55 (2019) 5559-5562.

In this recent Chem. Commun. paper, we have proved that C18 (a cycle of 18 carbon atoms connected with alternating single and triple bonds) it is an electron acceptor of similar characteristics as C60. C18  when coupled with a range of donor molecules can readily accept electrons. Electron acceptors are important components in molecular electronic devices and solar cells, and, therefore, C18 is added to the list of organic electron acceptors that can be potentially useful in photovoltaics.