A Neutral Three-Membered 2π Aromatic Disilaborirane and the Unique Conversion into a Four-Membered BSi2 N-Ring

We report the design, synthesis, structure, bonding, and reaction of a neutral 2π aromatic three‐membered disilaborirane. The disilaborirane is synthesized by a facile one‐pot reductive dehalogenation of amidinato‐silylene chloride and dibromoarylborane with potassium graphite. Despite the tetravalent arrangement of atoms around silicon, the three‐membered silicon‐boron‐silicon ring is aromatic, as evidenced by NMR spectroscopy, nucleus independent chemical shift calculations, first‐principles electronic structure studies using density functional theory (DFT) and natural bond orbital (NBO) based bonding analysis. Trimethylsilylnitrene, generated in situ, inserts in the Si−Si bond of disilaborirane to obtain a four‐membered heterocycle 1‐aza‐2,3‐disila‐4‐boretidine derivative. Both the heterocycles are fully characterized by X‐ray crystallography.

Bond-Strengthening Backdonation in Aminoborylene-Stabilized Aminoborylenes: At the Intersection of Borylenes and Diborenes

Singly NHC-coordinated (aminoboryl)aminoborenium salts react with Na₂ [Fe(CO)₄ ] to yield stable coordination complexes of aminoborylene-stabilized aminoborylenes, which exhibit exceptional σ-donor properties. Upon photolytic CO extrusion from the metal center, the diboron ligand adopts a novel η³ -BBN coordination mode, where bond-strengthening backdonation from the metal center into the vacant B-B π-orbital is observed. This bonding situation can be alternatively described as a Fe-diaminodiborene complex. In a related reduction of CAAC-stabilized (aminoboryl)aminoborenium with KC₈ , the reduced species can be captured with nucleophiles to form three-coordinate (diaminoboryl)borylenes, where both amino groups have migrated to the distal boron atom. Collectively, these reactions illustrate the isomeric flexibility imparted by amino groups on this reduced diboron system, thus opening multiple avenues of novel reactivity.

Reactivity of a Tetra(o-tolyl)diborane(4) Dianion as a Diarylboryl Anion Equivalent

Lithium and magnesium salts of tetra(o-tolyl)diborane(4) dianion, having B=B double bond character, were synthesized. It was clarified that the lithium salt of the dianion has a high-lying HOMO and a narrow HOMO-LUMO gap, which were perturbed by dissociation of Li⁺ cation, as judged by UV/Vis spectroscopy and DFT calculations. The lithium salt of the dianion reacted as two equivalents of a diarylboryl anion with CH₂ Cl₂ or S₈ to give boryl-substituted products.

Release of Isonitrile- and NHC-Stabilized Borylenes from Group VI Terminal Borylene Complexes

A family of doubly isonitrile-stabilized terphenyl borylenes could be obtained by addition of three equivalents of isonitrile to the corresponding Cr and W terminal terphenyl-borylene complexes. The mechanism of isonitrile- and carbon-monoxide-induced borylene liberation was investigated computationally and found to be significantly exergonic in both cases. Furthermore, addition of a small N-heterocyclic carbene (NHC) to a terminal Cr borylene complex results in release of an NHC-stabilized borylene carbonyl species, whereas the analogous reaction with bulkier phosphines results in metal-centered substitution.