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Aromatic substitution of redox‐active aromatic compounds could be initiated by a preceding redox step. We report on the different reaction pathways of such redox‐induced substitution (RIAS) reactions between a redox‐active guanidino‐functionalized aromatic molecule (GFA) and an amine or guanidine. Oxidation of the GFA leads to an umpolung of the guanidine from a nucleophile to an electrophile and thereby enables addition of the amine or guanidine. Several examples are given, demonstrating the use of redox substitution in synthetic chemistry, e. g. for the convenient synthesis of novel N‐heteropolycyclic molecules and unsymmetrically‐substituted aromatics. [ABSTRACT FROM AUTHOR]

Dehydrogenative coupling (DC) reactions are of importance for the construction of new carbon‐element bonds in synthetic organic chemistry. In this work, we report on the synthesis and characterization of several redox‐active guanidino‐functionalized aromatic molecules (GFAs) for use in DC (C−C and C−O) reactions. In a systematic approach, we first characterize the new DC reagents in all relevant redox and protonation states, and compare their performance in competitive test proton‐coupled electron transfer (PCET) reactions. Then, their use in four different DC reactions with different mechanisms is evaluated. [ABSTRACT FROM AUTHOR]

In this work, we report the synthesis and characterization of new redox‐active tetraguanidine ligands with crown ether functions as secondary coordination spheres, namely a 2,3,12,13‐tetraguanidino‐dibenzo‐18‐crown‐6 and two 2,3,16,17‐tetraguanidino‐dibenzo‐24‐crown‐8 derivatives. Metal ion and organic cation coordination to the secondary crown ether coordination sphere is studied and its effect on the electronic structures and redox properties analysed. Then, the coordination and redox chemistry of di‐ and tetraguanidine ligands with crown‐ether functions is evaluated. Copper and cobalt complexes with the metals bound to the guanidino functions are prepared. Especially, the redox chemistry of CoII cobalt complexes with and without metal ion encapsulation to the crown ether function is compared. The results contribute to the development of a supramolecular chemistry with redox‐active guanidine ligands. [ABSTRACT FROM AUTHOR]

The electronic ground and excited states of the vanadium monoxide (VO) molecule were studied in detail. Electronic absorption spectra for the molecule isolated in Ne matrices complement the previous gas-phase spectra. A thorough quantum chemical (multi-reference configuration interaction) study essentially confirms the assignment and characterization of the electronic excitations observed for VO in the gas-phase and in Ne matrices and allows the clarification of open issues. It provides a complete overview over the electronically excited states up to about 3 eV of this archetypical compound. [ABSTRACT FROM AUTHOR]

By matrix isolation in solid Ne and Kr, VO, VO2, and the complexes VO2(O2) with one superoxo ligand and VO2(O2)2 with one superoxo and one neutral dioxygen ligand, as well as V2O2 and V2O4 have been generated. For VO2(O2), transitions of five vibrational modes have been observed, and for VO2(O2)2, transitions belonging to seven vibrational modes, confirming and extending former Ar matrix results. Attempts to stabilise the cyclic V(O2) peroxide by use of the heavier Kr matrix were not successful. By accompanying MRCI calculations on VO2 and V(O2), vibrational frequencies have been determined. Furthermore, the investigation is assisted by density functional calculations with the TPSS functional. Possibly, also one vibrational transition of the VO3 molecule has been observed. [ABSTRACT FROM AUTHOR]

By matrix isolation in solid Ne and Kr, VO, VO2, and the complexes VO2(O2) with one superoxo ligand and VO2(O2)2 with one superoxo and one neutral dioxygen ligand, as well as V2O2 and V2O4 have been generated. For VO2(O2), transitions of five vibrational modes have been observed, and for VO2(O2)2, transitions belonging to seven vibrational modes, confirming and extending former Ar matrix results. Attempts to stabilise the cyclic V(O2) peroxide by use of the heavier Kr matrix were not successful. By accompanying MRCI calculations on VO2 and V(O2), vibrational frequencies have been determined. Furthermore, the investigation is assisted by density functional calculations with the TPSS functional. Possibly, also one vibrational transition of the VO3 molecule has been observed. [ABSTRACT FROM AUTHOR]

N‐Heteropolycycles are among the most promising candidates for applications in organic devices. For this purpose, a profound understanding of the low‐energy electronic absorbance and emission characteristics is of crucial importance. Herein, we report high‐resolution absorbance and fluorescence spectra of pentacene (PEN) and 6,13‐diazapentacene (DAP) in solid neon obtained using the matrix‐isolation technique. Accompanying DFT calculations allow the assignment of specific vibrationally resolved signals to corresponding modes. Furthermore, we present for the first time evidence for the formation of van der Waals dimers of both substances. These dimers exhibit significantly different optical characteristics resulting from the change of electronic properties evoked by the incorporation of sp2 nitrogen into the molecular backbone. [ABSTRACT FROM AUTHOR]

Dinuclear compounds of early transition metals with a high metal–metal bond order are of fundamental interest due to their intriguing bonding situation and of practical interest because of their potential involvement in catalytic processes. In this work, two isomers of V2H2 have been generated in solid Ne by the reaction between V2 and H2 and detected by infrared spectroscopy: the linear HVVH molecule (3Σg− ground state), which is the product of the spin‐allowed reaction between V2 (3Σg− ground state) and H2, and a lower‐energy, folded V2(μ‐H)2 isomer (1A1 ground state) with two bridging hydrogen atoms. Both isomers are characterized by metal–metal bonding with a high bond order; the orbital occupations point to quadruple bonding. Irradiation with ultraviolet light induces the transformation of linear HVVH to folded V2(μ‐H)2, whereas irradiation with visible light initiates the reverse reaction. [ABSTRACT FROM AUTHOR]

Dinuclear compounds of early transition metals with a high metal–metal bond order are of fundamental interest due to their intriguing bonding situation and of practical interest because of their potential involvement in catalytic processes. In this work, two isomers of V2H2 have been generated in solid Ne by the reaction between V2 and H2 and detected by infrared spectroscopy: the linear HVVH molecule (3Σg− ground state), which is the product of the spin‐allowed reaction between V2 (3Σg− ground state) and H2, and a lower‐energy, folded V2(μ‐H)2 isomer (1A1 ground state) with two bridging hydrogen atoms. Both isomers are characterized by metal–metal bonding with a high bond order; the orbital occupations point to quadruple bonding. Irradiation with ultraviolet light induces the transformation of linear HVVH to folded V2(μ‐H)2, whereas irradiation with visible light initiates the reverse reaction. [ABSTRACT FROM AUTHOR]

Dinuclear compounds of early transition metals with a high metal–metal bond order are of fundamental interest due to their intriguing bonding situation and of practical interest because of their potential involvement in catalytic processes. In this work, two isomers of V2H2 have been generated in solid Ne by the reaction between V2 and H2 and detected by infrared spectroscopy: the linear HVVH molecule (3Σg− ground state), which is the product of the spin‐allowed reaction between V2 (3Σg− ground state) and H2, and a lower‐energy, folded V2(μ‐H)2 isomer (1A1 ground state) with two bridging hydrogen atoms. Both isomers are characterized by metal–metal bonding with a high bond order; the orbital occupations point to quadruple bonding. Irradiation with ultraviolet light induces the transformation of linear HVVH to folded V2(μ‐H)2, whereas irradiation with visible light initiates the reverse reaction. [ABSTRACT FROM AUTHOR]

Dinuclear compounds of early transition metals with a high metal–metal bond order are of fundamental interest due to their intriguing bonding situation and of practical interest because of their potential involvement in catalytic processes. In this work, two isomers of V2H2 have been generated in solid Ne by the reaction between V2 and H2 and detected by infrared spectroscopy: the linear HVVH molecule (3Σg− ground state), which is the product of the spin‐allowed reaction between V2 (3Σg− ground state) and H2, and a lower‐energy, folded V2(μ‐H)2 isomer (1A1 ground state) with two bridging hydrogen atoms. Both isomers are characterized by metal–metal bonding with a high bond order; the orbital occupations point to quadruple bonding. Irradiation with ultraviolet light induces the transformation of linear HVVH to folded V2(μ‐H)2, whereas irradiation with visible light initiates the reverse reaction. [ABSTRACT FROM AUTHOR]

V2O4 was generated in solid Ne and characterized by infrared spectroscopy and additionally by multireference configuration interaction and density functional calculations. Four vibrational transitions at 1003, 731.7, 640.9, and 309.1 cm-1 (16O2) were observed and, based on the calculations, assigned to bu, au, bu, and bu modes, respectively, of the C2h symmetric structure. The calculated bond distances are in good agreement with the results of previous calculations. [ABSTRACT FROM AUTHOR]

Detailed knowledge of the electronic structure of vanadium oxide clusters provides the basis for understanding and tuning their significant catalytic properties. However, already for the simple four-atom V2O2 molecule, there are contradictory reports in the literature regarding the electronic ground state and a possible vanadium-vanadium bond. We herein show through a combination of experimental (matrix isolation) studies and theoretical results that there is a multiple vanadium-vanadium bond in this benchmark vanadium oxide molecule. [ABSTRACT FROM AUTHOR]

Die detaillierte Kenntnis der elektronischen Struktur von Vanadiumoxidclustern bildet die Basis für das Verständnis und die Abstimmung ihrer wichtigen katalytischen Eigenschaften. Allerdings existieren in der Literatur schon für das einfache vieratomige V2O2‐Molekül widersprüchliche Berichte bezüglich des elektronischen Grundzustandes und einer möglichen Vanadium‐Vanadium‐Bindung. Mit einer Kombination aus experimentellen (Matrixisolation) und theoretischen Ergebnissen zeigen wir hier, dass eine Vanadium‐Vanadium‐Bindung in diesem prototypischen Vanadiumoxidmolekül gebildet wird. Wohin mit den Elektronen? Die Aufklärung der elektronischen Struktur des scheinbar einfachen V2O2‐Moleküls, einer prototypischen Verbindung für katalytisch aktive Vanadiumoxide, erfordert eine gründliche kombinierte experimentelle und theoretische Studie. [ABSTRACT FROM AUTHOR]

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Detailed knowledge of the electronic structure of vanadium oxide clusters provides the basis for understanding and tuning their significant catalytic properties. However, already for the simple four-atom V2O2 molecule, there are contradictory reports in the literature regarding the electronic ground state and a possible vanadium-vanadium bond. We herein show through a combination of experimental (matrix isolation) studies and theoretical results that there is a multiple vanadium-vanadium bond in this benchmark vanadium oxide molecule. [ABSTRACT FROM AUTHOR]