The reduction of a cyclic alkyl(amino)carbene (CAAC)‐stabilized organoberyllium chloride yields the first neutral beryllium radical, which was characterized by EPR, IR, and UV/Vis spectroscopy, X‐ray crystallography, and DFT calculations.
The
stepwise reduction of a doubly cyclic alkyl(amino)carbene (CAAC)-stabilized
2,3-bis(dibromoboryl)naphthalene enables the isolation of the corresponding
mono- and bis(boryl) radicals (one- and two-electron reduction), a
2π-aromatic 1,2-diborete (four-electron reduction), which shows
biradical character in the solid-state EPR spectrum, and its cyclic
bis(alkylidene)diboron dianion (six-electron reduction). The X-ray
crystallographic analysis of the diborete shows a highly strained
and twisted four-membered ring with a formal cis-diborene
motif featuring a very elongated B–B double bond. Calculations
based on DFT and multireference approaches reveal that the diborete
possesses an open-shell singlet biradicaloid ground state, which is
slightly energetically preferred to its EPR-active triplet-state congener.
The addition of CO to the diborete resulted in B–B bond splitting
and the formation of the corresponding closed-shell singlet, doubly
Lewis base-stabilized bis(borylene), whereas a twofold γ insertion
of phenyl azide generates a 1,3-bis(diazenyl)-1,3,2,4-diazadiboretidine.
The first examples of Lewis base adducts of the parent boraphosphaketene (H 2 B-PCO) and their cyclodimers are prepared. One of these adducts is shown to undergo mild decarbonylation and phosphinidene insertion into a BÀC bond of a borole, forming very rare examples of 1,2-phosphaborinines, B/P isosteres of benzene. The strong donor properties of these 1,2-phosphaborinines are confirmed by the synthesis of their p complexes with the Group 6 metals. Figure 1. Top: phosphaketenes and their decarbonylation chemistry. Bottom: boron-functionalized phosphaketenes and their phosphaethynolate constitutional isomers.
Dihalodiboranes(4) react with a N-heterocyclic silylene (NHSi) to generate NHSi adducts of 1-aryl-2-silyl-1,2-diboraindanes, as was confirmed by X-ray crystallography, featuring the functionalization of both B-X (X=halogen) bonds and a sp - or sp -C-H bond under mild conditions. Coordination of a third NHSi to the proposed 1,1-diaryl-2,2-disilyldiborane(4) intermediates, generated by a twofold B-X insertion, may be crucial for the C-H borylation that leads to the final products. Notably, our results demonstrate the first C-H borylation with a strong B-F bond activated by silylene insertion.
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.
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