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Vanadium(IV) magnetic centers are prime candidates as molecular quantum units. One longstanding question is how to obtain a scaffold that connects multiple centers and allows two communication modalities: magnetic and electronic. We have synthesized and studied a selection of vanadyl porphyrin dimers, as models of the most synthetically accessible linear porphyrin arrays. We show that a strongly π-conjugated backbone places the magnetic system in the strong coupling regime and protects the quantum coherence against electron pair flip-flop processes at low temperatures (

Vanadium(IV) magnetic centers are prime candidates as molecular quantum information units. One of the longstanding problems is to obtain an extendable scaffold that transmits the magnetic interaction to a degree usable for quantum processing, and allows upscaling to multiple centers, while preserving a sufficiently long coherence time. Here, we show that fused porphyrins allow tailored scaffolding of vanadyl quantum units, with an almost flat conjugated π-system that offers substantial advantages for communication between vanadyl ions, leading to the long spin-lattice (T1 = 30 ms) and coherence (Tm = 5.5 µs) times. The antiferromagnetic exchange coupling in these vanadyl dimers (J = 1 GHz) is stronger than the hyperfine interaction, resulting in complex EPR spectra in which both unpaired electrons couple equally to both I = 7/2 51V nuclei. Isolation of the syn- and anti-isomers, with vanadyls on the same or opposite sides of the con-jugated channel, showcases the sensitivity of quantum units to different configurational environments, and offers a way to tune the inter-action in poly-porphyrin systems by controlling the stereochemistry.

Spin-hosting graphene nanostructures are promising metal-free systems for elementary quantum spintronic devices. Conventionally, spins are protected from quenching by electronic band gaps, which also hinder electronic access to their quantum state. Here, we present a narrow graphene nanoribbon substitutionally doped with boron heteroatoms that combines a metallic character with the presence of localized spin 1/2 states in its interior. The ribbon was fabricated by on-surface synthesis on a Au(111) substrate. Transport measurements through ribbons suspended between the tip and the sample of a scanning tunneling microscope revealed their ballistic behavior, characteristic of metallic nanowires. Conductance spectra show fingerprints of localized spin states in the form of Kondo resonances and inelastic tunneling excitations. Density functional theory rationalizes the metallic character of the graphene nanoribbon due to the partial depopulation of the valence band induced by the boron atoms. The transferred charge builds localized magnetic moments around the boron atoms. The orthogonal symmetry of the spin-hosting state’s and the valence band’s wave functions protects them from mixing, maintaining the spin states localized. The combination of ballistic transport and spin localization into a single graphene nanoribbon offers the perspective of electronically addressing and controlling carbon spins in real device architectures., We gratefully acknowledge financial support from Grants PID2019-107338RB-C61, PID2019-107338RB-C62, PID2019-107338RB-C66, PID2019-110037GB-I00, and PCI2019-111933-2 and the Maria de Maeztu Units of Excellence Program CEX2020-001038-M funded by MCIN/AEI/10.13039/501100011033, the European Regional Development Fund, the European Union (EU) H2020 program through the FET Open project SPRING (Grant Agreement No. 863098), the Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03), the Dpto. Educación Gobierno Vasco (Grant Nos. PIBA-2020-1-0014, IT1246-19, and IT-1569-22) and the Programa Red Guipuzcoana de Ciencia, Tecnología e Innovación 2021 (Grant No. 2021-CIEN-000070-01. Gipuzkoa Next). The authors acknowledge the financial support received from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC on behalf of the Department of Education of the Basque Government.

The Cu‐catalyzed reaction of substituted α‐diazoesters with fluoride gives α‐fluoroesters with ee values of up to 95 %, provided that chiral indane‐derived bis(oxazoline) ligands are used that carry bulky benzyl substituents at the bridge and moderately bulky isopropyl groups on their core. The apparently homogeneous solution of CsF in C6F6/hexafluoroisopropanol (HFIP) is the best reaction medium, but CsF in the biphasic mixture CH2Cl2/HFIP also provides good results. DFT studies suggest that fluoride initially attacks the Cu‐ rather than the C‐atom of the transient donor/acceptor carbene intermediate. This unusual step is followed by 1,2‐fluoride shift; for this migratory insertion to occur, the carbene must rotate about the Cu−C bond to ensure orbital overlap. The directionality of this rotatory movement within the C 2‐symmetric binding site determines the sense of induction. This model is in excellent accord with the absolute configuration of the resulting product as determined by X‐ray diffraction using single crystals of this a priori wax‐like material grown by capillary crystallization., Let's work together: Even though bisoxazolines are privileged ligands in asymmetric catalysis, standard representatives give poor ee values in the copper catalyzed asymmetric fluorination of α‐diazoesters. The outcome was greatly improved, however, upon gem‐benzylation of the bridge, proper substitution of the core, and optimization of the medium. The reaction follows an unusual course in that the incoming fluoride first hits the metal rather than the C‐atom of the transient copper carbene complex.

During the last two decades aryne and bisaryne equivalents have been increasingly used as privileged building blocks for the synthesis of polycyclic aromatic hydrocarbons (PAHs). Here we report the synthesis and reactivity of an efficient precursor of the 2,6,10-triphenylenotriyne synthon, which constitutes the best example to date of a trisaryne equivalent on a benzofused polyaromatic core.

Four decades after the first (and only) reported synthesis of kekulene, this emblematic cycloarene has been obtained again through an improved route involving the construction of a key synthetic intermediate, 5,6,8,9-tetrahydrobenzo[m]tetraphene, by means of a double Diels–Alder reaction between styrene and a versatile benzodiyne synthon. Ultra-high-resolution AFM imaging of single molecules of kekulene and computational calculations provide additional support for a molecular structure with a significant degree of bond localization in accordance with the resonance structure predicted by the Clar model.

In recent years, synthetic transformations based on aryne chemistry have become particularly popular, mostly due to the spread of methods to generate these highly reactive intermediates in a controlled manner under mild reaction conditions. In fact, aryne cycloadditions such as the Diels-Alder reaction are nowadays widely used for the efficient preparation of polycyclic aromatic compounds. In 1998, our group discovered that arynes can undergo transition metal-catalyzed reactions, a finding that opened new perspectives in aryne chemistry. In particular, Pd-catalyzed [2 + 2 + 2] cycloaddition of arynes allowed the straightforward synthesis of triphenylene derivatives such as starphenes or cloverphenes. We found that this reaction is compatible with different substituents and sterically demanding arynes as starting materials. This transformation is especially useful to increase the molecular complexity in one single step, transforming molecules formed by n cycles in structures with 3n + 1 cycles. In fact, we took advantage of this protocol to prepare a large variety of sterically congested polycyclic aromatic hydrocarbons such as helicenes or twisted polyarenes. Soon after the discovery of the reaction, the co-cyclotrimerization of arynes with other reaction partners, such as electron deficient alkynes, significantly expanded the potential of this transformation. Also the use of catalysts based on alternative metals besides Pd (e.g., Ni, Cu, Au) or the use of other strained intermediates such as cycloalkynes or cycloallenes added value to this reaction. In addition, we realized that the Pd-catalyzed aryne cyclotrimerization reaction is particularly useful for the bottom-up preparation of well-defined nanographenes by chemical methods. Although the extreme insolubility of these planar nanographenes hampered their manipulation and characterization by conventional methods, recent advances in single molecule on-surface characterization by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) with functionalized tips under ultrahigh vacuum (UHV) conditions, permitted the impressive visualization of these nanographenes with submolecular resolution, together with the examination of the corresponding molecular orbital densities. Moreover, arynes have been shown to possess a rich on-surface chemistry. In particular, arynes have been generated and studied on-surface, showing that the reactivity is preserved even at cryogenic temperatures. On-surface aryne cyclotrimerization was also demonstrated to obtain large starphene derivatives. Therefore, it is expected that the combination of aryne cycloadditions and on-surface synthesis will provide notable findings in the near future, including the "a la carte" preparation of graphene materials or the synthesis of elusive molecules with unique properties.

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly successful in the synthesis of graphene nanoribbons, nanographenes and intrinsically reactive and instable, yet attractive species. It is based on the combination of solution chemistry aimed at preparation of appropriate molecular precursors for further ultra-high vacuum surface assisted transformations. This approach also owes its success to an incredible development of characterization techniques, such as scanning tunneling/atomic force microscopy and related methods, which allow detailed, local characterization at atomic scale. While the surface-assisted synthesis can provide molecular nanostructures with outstanding precision, down to single atoms, it suffers from basing on metallic surfaces and often limited yield. Therefore, the extension of the approach away from metals and the struggle to increase productivity seem to be significant challenges toward wider applications. Herein, we demonstrate the on-surface synthesis approach for generation of non-planar nanographenes, which are synthesized through a combination of solution chemistry and sequential surface-assisted processes, together with the detailed characterization by scanning probe microscopy methods.

The reaction of 2-(trimethylsilyl)thiophen-3-yl triflate with CsF in the presence of 2,3,4,5-tetraphenylcyclopentadienone affords 4,5,6,7-tetraphenylbenzo[b]thiophene, as it would be expected from the hypothesized generation and trapping of 2-thiophyne. However, a detailed experimental and computational study discards the intermediacy of this elusive 5-membered hetaryne. Instead, a complex mechanism involving the generation of an intermediate ketocarbene, which adds to the cyclopentadienone to give an isolable tricyclic intermediate, followed by thermal rearrangements, is proposed Financial support from the Spanish Agencia Estatal de Investigación (Nos. PID2019-110037GB-I00 and PCI2019-111933-2), the European Union’s Horizon 2020 (FET-Open project, Grant No. 863098), the Xunta de Galicia (No. ED431C 2020/22 and Centro Singular de Investigación de Galicia accreditation 2019-2022, ED431G 2019/03) and the European Union (European Regional Development Fund-ERDF, is gratefully acknowledged. The authors thank the Centro de Supercomputación de Galicia (CESGA) for generous allocation of computer time. I.P. thanks Xunta de Galicia and the European Union (European Social Fund, ESF) for the award of a predoctoral fellowship SI

Graphene nanoribbons (GNRs), low-dimensional platforms for carbon-based electronics, show the promising perspective to also incorporate spin polarization in their conjugated electron system. However, magnetism in GNRs is generally associated with localized states around zigzag edges, difficult to fabricate and with high reactivity. Here we demonstrate that magnetism can also be induced away from physical GNR zigzag edges through atomically precise engineering topological defects in its interior. A pair of substitutional boron atoms inserted in the carbon backbone breaks the conjugation of their topological bands and builds two spin-polarized boundary states around them. The spin state was detected in electrical transport measurements through boron-substituted GNRs suspended between the tip and the sample of a scanning tunneling microscope. First-principle simulations find that boron pairs induce a spin 1, which is modified by tuning the spacing between pairs. Our results demonstrate a route to embed spin chains in GNRs, turning them into basic elements of spintronic devices., We gratefully acknowledge financial support from Spanish Agencia Estatal de Investigación (AEI) (MAT2016-78293, PID2019-107338RB, FIS2017-83780-P, and the Maria de Maeztu Units of Excellence Programme MDM-2016-0618), from the European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant. No. 863098), the Basque Departamento de Educación through the PhD fellowship No. PRE_2019_2_0218 (S.S.), the Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03), the University of the Basque Country (Grant IT1246-19), and the European Regional Development Fund (ERDF). I. P. also thanks Xunta de Galicia and European Union (European Social Fund, ESF) for the award of a predoctoral fellowship

Synthesis of a triporous nanographene with 102 sp2 carbon atoms by combining solution and surface chemistry., The synthesis of porous nanographenes is a challenging task for solution chemistry, and thus, on-surface synthesis provides an alternative approach. Here, we report the synthesis of a triporous nanographene with 102 sp2 carbon atoms by combining solution and surface chemistry. The carbon skeleton was obtained by Pd-catalyzed cyclotrimerization of arynes in solution, while planarization of the molecule was achieved through two hierarchically organized on-surface cyclodehydrogenation reactions, intra- and inter-blade. Remarkably, the three non-planar [14]annulene pores of this nanographene further evolved at higher temperatures showing interesting intra-porous on-surface reactivity.

The synthesis of an efficient precursor of the novel 1,7-naphthodiyne synthon is reported. Preliminary experiments demonstrate the usefulness of this platform for the synthesis of sterically congested polyarenes, such as helicenes and angularly fused acene derivatives. Furthermore, a novel intramolecular aryne trapping reaction is described Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO, CTQ2013-44142-P and MAT2013-46593-C6-6-P), the European Union (Project PAMS, contract no. 610446), Xunta de Galicia (GPC2014/25) and FEDER is gratefully acknowledged SI

International audience; Using high-resolution atomic force microscopy (AFM) with CO-functionalized tips, we atomically resolved individual molecules from Murchison meteorite samples. We analyzed powdered Murchison meteorite material directly, as well as processed extracts that we prepared to facilitate characterization by AFM. From the untreated Murchison sample, we resolved very few molecules, as the sample contained mostly small molecules that could not be identified by AFM. By contrast, using a procedure based on several trituration and extraction steps with organic solvents, we isolated a fraction enriched in larger organic compounds. The treatment increased the fraction of molecules that could be resolved by AFM, allowing us to identify organic constituents and molecular moieties, such as polycyclic aromatic hydrocarbons and aliphatic chains. The AFM measurements are complemented by high-resolution mass spectrometry analysis of Murchison fractions. We provide a proof of principle that AFM can be used to image and identify individual organic molecules from meteorites and propose a method for extracting and preparing meteorite samples for their investigation by AFM. We discuss the challenges and prospects of this approach to study extraterrestrial samples based on single-molecule identification.

Controlling selectivity of reactions is an ongoing quest in chemistry. In this work, we demonstrate reversible and selective bond formation and dissociation promoted by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied voltage pulses from the tip of a combined scanning tunneling and atomic force microscope. Characterization of voltage dependence of the reactions and determination of reaction rates demonstrate selectivity in constitutional isomerization reactions and provide insight into the underlying mechanisms. With support of density functional theory calculations, we find that the energy landscape of the isomers in different charge states is important to rationalize the selectivity. Tip-induced selective single-molecule reactions increase our understanding of redox chemistry and could lead to novel molecular machines.