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The reaction of a cyclic alkyl(amino)carbene (CAAC)-stabilized thiazaborolo[5,4-d]thiazaborole (TzbTzb) with strong Brønsted acids, such as HCl, HOTf (Tf=O

A one-pot synthesis of a CAAC-stabilized, unsymmetrical, cyclic diborene was achieved via consecutive two-electron reduction steps from an adduct of CAAC and B\(_2\)Br\(_4\)(SMe\(_2\))\(_2\). Theoretical studies revealed that this diborene has a considerably smaller HOMO–LUMO gap than those of reported NHC- and phosphine-supported diborenes. Complexation of the diborene with [AuCl(PCy\(_3\))] afforded two diborene–Au\(^I\) π complexes, while reaction with DurBH\(_2\), P\(_4\) and a terminal acetylene led to the cleavage of B−H, P−P, and C−C π bonds, respectively. Thermal rearrangement of the diborene gave an electron-rich cyclic alkylideneborane, which readily coordinated to Ag\(^I\) via its B=C double bond.

A doubly cyclic (alkyl)(amino)carbene-stabilised dihydroboronium cation undergoes fully reversible 2e– reduction to a stable hydroboryl anion via B-to-C hydrogen migration. Subsequent 1e– oxidation yields a bench-stable neutral hydroboryl radical., The addition of Lewis bases to a cyclic (alkyl)(amino)carbene (CAAC)-supported dihydroboron triflate yields the mixed doubly base-stabilised dihydroboryl cations [(CAAC)BH2L]+. Of these, [(CAAC)2BH2]OTf (OTf = triflate) underwent facile two-electron reduction with KC8 owing to a 1,2-hydride migration from boron to the carbene carbon to yield a stable hydroboryl anion. One-electron oxidation of the latter yielded the first neutral hydroboryl radical, which is bench-stable in the solid state.

Doubly base-stabilised cyano- and isothiocyanatoborylenes of the form LL′BY (L = CAAC = cyclic alkyl(amino)carbene; L′ = NHC = N-heterocyclic carbene; Y = CN, NCS) coordinate to group 6 carbonyl complexes via the terminal donor of the pseudohalide substituent and undergo facile and fully reversible one-electron oxidation to the corresponding boryl radical cations [LL′BY]˙+. Furthermore, calculations show that the borylenes have very similar proton affinities, both to each other and to NHC superbases. However, while the protonation of LL′B(CN) with PhSH yielding [LL′BH(CN)+][PhS−] is fully reversible, that of LL′B(NCS) is rendered irreversible by a subsequent B-to-CCAAC hydrogen shift and nucleophilic attack of PhS− at boron., Borylenes of the form (CAAC)(NHC)BY (Y = CN, NCS; CAAC = cyclic alkyl(amino)carbene; NHC = N-heterocyclic carbene) coordinate to group 6 carbonyl complexes via Y, and show reversible boron-centered Brønsted basicity and one-electron oxidation.

The first examples of Lewis base adducts of the parent boraphosphaketene (H2B‐PCO) and their cyclodimers are prepared. One of these adducts is shown to undergo mild decarbonylation and phosphinidene insertion into a B−C 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 π complexes with the Group 6 metals., The first examples of Lewis base adducts of the parent boraphosphaketene (H2B−PCO) are prepared, and their dimerization, decarbonylation and use as synthons for phosphinidenes is explored, leading to a number of different B/P‐containing heterocycles and transition‐metal complexes thereof.

Die ersten Beispiele für Lewis-Basen-Addukte des Stammboraphosphaketens H\(_{2}\)B-PCO und ihre cyclischen Dimere wurden hergestellt. Eines dieser Addukte zeigt unter milden Bedingungen eine Decarbonylierung und anschließende Insertion des Phosphinidens in die B-C-Bindung eines Borols, was in der Bildung sehr seltener Beispiele für 1,2-Phosphaborinine, B,P-Isostere von Benzol, resultiert. Die starken Donoreigenschaften dieser 1,2-Phosphaborinine wurden durch die Synthese ihrer π-Komplexe mit Metallen der Gruppe 6 bestätigt.

Reduction of (CAAC)BBr2(NCS) (CAAC=cyclic alkyl(amino)carbene) in the presence of a Lewis base L yields tricoordinate (CAAC)LB(NCS) borylenes which undergo reversible E/Z‐isomerization. The same reduction in the absence of L yields deep blue, bis(CAAC)‐stabilized, boron‐doped, aromatic thiazolothiazoles resulting from the dimerization of dicoordinate (CAAC)B(NCS) borylene intermediates., While the reduction of cyclic alkyl(amino)carbene‐stabilized isothiocyanatoboranes in the presence of a Lewis base yields tricoordinate isothiocyanatoborylenes, the reduction in the absence of a Lewis base yields the first examples of deep blue, boron‐doped, aromatic thiazolothiazoles.

We report the selective insertion of a range of borylene fragments into the E-E bonds (E = S, Se, Te) of cyclic boron dichalcogenides. This method provides facile synthetic access to a variety of symmetrical and unsymmetrical four- and five-membered rings.

While the one-electron reduction of (CAACMe )BH2 Br (CAACMe =1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) yields a hydride-shift isomer of the corresponding tetrahydrodiborane, a further reversible reduction leads to the first stable parent boryl anion, [(CAACMe )BH2 ]- , which acts as a powerful boron nucleophile.

While the one-electron reduction of (CAAC

Diaryldihalodiboranes(4) were reacted with bis(amidinato)- and bis(guanidinato)silylenes to generate the first neutral diborane-centered radicals. These formally non-aromatic 5π electron systems are stable in the solid state as well as in solution and were characterized by solid-state structure determination, high-resolution mass spectrometry, and EPR spectroscopy. The reactivity of one of these radicals with the oxidant 1,4-benzoquinone led to ring-opening and B-O bond formation.