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ortho-N-Substituted pyridinium cations with the weakly coordinating anion [B(C6F5)4]− have been studied and crucial structural features in the sp2 C–H borylation catalysis of 3-methylthiophene have been identified. The electron-deficiency of the aromatic core of the cation is essential for activity together with accessible protons. The spectroscopic yield of the borylation of 3-methylthiophene with catecholborane (CatBH) was optimized up to 86% and the method was further applied to other substrates such as N-alkylbenzenes. A mechanistic DFT study revealed the rate-limiting step in the catalysis to be the liberation of molecular H2 (ΔG‡ = 27.5 kcal mol−1), whereas the overall reaction was found to be exergonic by 5.1 kcal mol−1. [ABSTRACT FROM AUTHOR]

This article explores the potential of imidazo[1,2-a]pyridine-based donor-acceptor chromophores for the development of novel fluorophores and donor-acceptor chromophores. The authors conducted density functional theory calculations and proposed a modular synthesis approach to access the desired structures. The results show promising potential for the development of thermally activated delayed fluorescence emitters. The article also discusses the synthesis and characterization of a series of donor-acceptor chromophores with a 3-aminoimidazo[1,2-a]pyridine donor motif, highlighting the need for further adjustments and optimizations to improve their optoelectronic properties. The modular synthesis approach used in this study provides a versatile platform for the development of new fluorescent emitters. [Extracted from the article]

The synthesis of a new bis‐NHP complex (NHP=N‐heterocyclic phosphenium) of chromium via salt metathesis and studies of its reactivity are reported. Photochemical reactions with H2 and selected olefins give rise to non‐isolable H2‐ and π‐alkene complexes identified spectroscopically, while internal alkynes react via activation of the triple bond to yield isolable metalla‐phospha‐cyclobutenes characterized by spectroscopic and XRD data. DFT studies give a preliminary account of the bonding in H2‐ and alkene‐complexes and explain the different reactivity towards alkenes and alkynes as the consequence of kinetic effects. Photolysis of the bis‐NHP‐complex in the presence of H2 and olefins or alkenes enables the catalytic hydrogenation of the organic substrates, while the π‐ethene complex mediates the catalytic hydrogenation of ethene in a dark reaction. The similarities and differences between both catalytic processes are shortly discussed. [ABSTRACT FROM AUTHOR]

Herein, we present the formation of transient radical ion pairs (RIPs) by single‐electron transfer (SET) in phosphine−quinone systems and explore their potential for the activation of C−H bonds. PMes3 (Mes=2,4,6‐Me3C6H2) reacts with DDQ (2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone) with formation of the P−O bonded zwitterionic adduct Mes3P−DDQ (1), while the reaction with the sterically more crowded PTip3 (Tip=2,4,6‐iPr3C6H2) afforded C−H bond activation product Tip2P(H)(2‐[CMe2(DDQ)]‐4,6‐iPr2‐C6H2) (2). UV/Vis and EPR spectroscopic studies showed that the latter reaction proceeds via initial SET, forming RIP [PTip3]⋅+[DDQ]⋅−, and subsequent homolytic C−H bond activation, which was supported by DFT calculations. The isolation of analogous products, Tip2P(H)(2‐[CMe2{TCQ−B(C6F5)3}]‐4,6‐iPr2‐C6H2) (4, TCQ=tetrachloro‐1,4‐benzoquinone) and Tip2P(H)(2‐[CMe2{oQtBu−B(C6F5)3}]‐4,6‐iPr2‐C6H2) (8, oQtBu=3,5‐di‐tert‐butyl‐1,2‐benzoquinone), from reactions of PTip3 with Lewis‐acid activated quinones, TCQ−B(C6F5)3 and oQtBu−B(C6F5)3, respectively, further supports the proposed radical mechanism. As such, this study presents key mechanistic insights into the homolytic C−H bond activation by the synergistic action of radical ion pairs. [ABSTRACT FROM AUTHOR]

Two N-heterocyclic phosphines with exocyclic SCN substituents were synthesised via metathesis of chlorophosphine precursors with KSCN and fully characterised. The crystallographic studies reveal that the products exhibit pronounced structural differences. The thiocyanato unit binds in one case via the nitrogen atom to yield a molecular structure with a slightly elongated P-N single bond and, in the other case, via the sulfur atom to form a structure that is best described as an ion pair and forms a one-dimensional coordination polymer in the crystal. DFT calculations suggest that the P-N and P-S interactions can be described as covalent and dative bonds, respectively, and that the structural differences correlate with the different cation stabilities of the individual phosphenium cation fragments. Key words: N-heterocyclic phosphines, ambident Lewis bases, dative bonds, coordination isomerism. Nous avons synthétisé deux phosphines N-hétérocycliques portant des substituants SCN exocycliques par voie de métathèse de précurseurs chlorophosphine avec le KSCN, et nous les avons soumis à une caractérisation complète. Les analyses cristallographiques révèlent que les produits présentent des différences structurales importantes. L'unité thiocyanate se lie dans un cas par l'atome d'azote pour produire une structure moléculaire caractérisée par une liaison simple P-N légèrement allongée, et dans l'autre cas, par l'atome de soufre pour former une structure qui s'apparente davantage à une paire d'ions créant un polymère de coordination unidimensionnel dans le cristal. Les calculs DFT indiquent que les interactions P-N et P***S pourraient être décrites comme des liaisons covalentes et bipolaires, respectivement, et que les différences structurales sont corrélées avec la stabilité des différents fragments cationiques de phosphénium. [Traduit par la Rédaction] Mots-clés: phosphines N-hétérocycliques, bases de Lewis ambidentates, liaisons bipolaires, isomérisme de coordination., Introduction The reaction between a Lewis acid (electron pair acceptor) and a Lewis base (electron pair donor) to form a complex (or Lewis pair) is one of the most fundamental [...]