The carbon monoxide adduct of an unhindered and highly reactive CAAC-bound arylborylene, [(CAAC)B(CO)Ar] (CAAC = cyclic (alkyl) (amino)carbene), has been prepared using a transfer reaction from the linear iron borylene complex [(PMe) (CO)Fe=BAr]. [(CAAC)B(CO)Ar] is a source of the dicoordinate [(CAAC)ArB:] borylene that can be liberated by selective photolytic CO extrusion and that, although highly reactive, is sufficiently long-lived to react intermolecularly. Through trapping of the borylene generated in this manner, we present, among others, the first metal-free borylene(I) species containing a nitrogen-based donor, as well as a new boron-containing radical.

The one-electron reduction of a cyclic (alkyl)(amino)carbene (CAAC)-stabilized arylborylene carbonyl complex yields a dimeric borylketyl radical anion, resulting from an intramolecular aryl migration to the CO carbon atom. Computational analyses support the existence of a [(CAAC)B(CO)Ar] •radical anion intermediate. Further reduction leads to a highly nucleophilic dianionic (boraneylidene)methanolate.

We report a detailed computational and experimental study of the fixation and reductive coupling of dinitrogen with low-valent boron compounds. Consistent with our mechanistic findings, the selectivity toward nitrogen fixation or coupling can be controlled through either steric bulk or the reaction conditions, allowing for the on-demand synthesis of nitrogen chains. The electronic structure and intriguing magnetic properties of intermediates and products of the reaction of dinitrogen with borylenes are also elucidated using high-level computational approaches.

The reactions of carbodiimides with the iron arylborylene complex [Fe=BDur(CO) 3 (PMe 3 )] (Dur = 2,3,5,6-Me 4 C 6 H) and the iron bis(borylene) complex [Fe{=BDur}{=BN(SiMe 3 ) 2 }(CO) 3 ] yield a wide variety of temperature-dependent products, including known FeBNC and novel FeBNB metallacycles, complexes of Nheterocyclic boracarbene and spiro-boracarbene ligands and a unique 1,3,2,4-diazadiborolyl pianostool complex, characterized by NMR spectroscopy and X-ray crystallography. The product distributions can be rationalized by considering sequences of cycloaddition, metathesis, insertion, and CÀ H activation pathways mainly governed by sterics.

Bei der Einelektronenreduktion eines durch eine cyclisches (Alkyl)(amino)carben (CAAC) stabilisierten Arylborylen‐Carbonylkomplexes erfolgt die Bildung eines dimeren Borylketyl‐Radikalanions, bedingt durch eine intramolekulare Arylmigration zum CO Kohlenstoffatom. Computergestützte Analyse liefert Hinweise auf eine radikalanionische [(CAAC)B(CO)Ar].− Zwischenstufe. Weiterführende Reduktion des entstandenen Komplexes liefert ein hoch nukleophiles (Boranyliden)methanolat.