Boron reluctantly forms B=X (X=O, S, Se, Te) moieties, which has stimulated the quest for such species in the past few years. Based on the N,N′‐chelating β‐diketiminato ligand (HNacNac), a new amido imidazoline‐2‐imine ligand system (HAmIm) is presented, giving rise to the isolation of an exhaustive series of Lewis acid free, monomeric chalcogen B=X boranes with documented π‐bond character between boron and the chalcogen. The chalcogenoboranes are isoelectronic and isolobal to the respective ketones. The chemical behavior of the oxoborane (B=O) strongly resembles the classical carbonyl reactivity in C=O bonds. The improved stability provided by HAmIm arises from the formation of more‐stable five‐membered boron chelates versus the six‐membered NacNac analogues and from the imidazoline‐2‐imine moiety providing enhanced σ‐ and π‐donation. The HAmIm ligand class may supersede the widely employed NacNac system in certain applications.

No abstract

Boron reluctantly forms B=X (X=O, S, Se, Te) moieties, which has stimulated the quest for such species in the past few years. Based on the N,N′‐chelating β‐diketiminato ligand (HNacNac), a new amido imidazoline‐2‐imine ligand system (HAmIm) is presented, giving rise to the isolation of an exhaustive series of Lewis acid free, monomeric chalcogen B=X boranes with documented π‐bond character between boron and the chalcogen. The chalcogenoboranes are isoelectronic and isolobal to the respective ketones. The chemical behavior of the oxoborane (B=O) strongly resembles the classical carbonyl reactivity in C=O bonds. The improved stability provided by HAmIm arises from the formation of more‐stable five‐membered boron chelates versus the six‐membered NacNac analogues and from the imidazoline‐2‐imine moiety providing enhanced σ‐ and π‐donation. The HAmIm ligand class may supersede the widely employed NacNac system in certain applications.

aza-)BODIPY dyes (boron dipyrromethene dyes) are well-established fluorophores due to their large quantum yields, stability, and diversity,which led to promising applications including imagingt echniques, sensors, organic (opto)electronic materials, or biomedical applications. Although the control of the optical properties in (aza-)BODIPY dyes by peripheral functional groups is well studied, we herein present an ovel approach to modify the 12 p-electron core of the dipyrromethene scaffold.T he replacemento ft wo carbon atoms in the b-positiono faBODIPYd ye by two nitrogen atoms affordeda14 p-electron system, which was termed BODIIM( boron diimidazolylmethene)i ns ystematic analogyt ot he BODIPYd yes. Remarkably,t he BODIIM dye was obtained with aB H 2 -rigidifying entity,w hich is currently elusive and highly sought after for the BODIPY dye class. DFT-Calculations confirmt he [12+ +2] p-electron relationship between BODIPY and BODIIM and reveal as trong shapec orrelationbetween LUMO in the BODIPY and the HOMO of the BODIIM.The modification of the p-system leads to ad ramatic shifto ft he optical properties, of whicht he fluorescent emissioni smost noteworthy and occurs at much larger Stokess hift, that is, % 500 cm À1 in BODIPY versus > 4170 cm À1 in BODIIM system in all solvents investigated. Nucleophilic reactivity was found at the meso-carbona tom in the formation of stable borane adducts with as ignificant shift of the fluorescent emission, and this behavior contrasts the reactivity of conventional BODIPY systems. In addition, the reversedecomplexation of the borane adducts was demonstrated in reactions with ar epresentative N-heterocyclic carbene to retain the strongly fluorescent BODIIM compound, which suggestsa pplications as fully reversible fluorescent switch.

No abstract