Harnessing the electronic differences between CAAC-stabilised 1,4-diborabenzene and 9,10-diboraanthracene for synthesis

Dietz, Maximilian; Arrowsmith, Merle; Gärtner, Annalena; Radacki, Krzysztof; Bertermann, Rüdiger; Braunschweig, Holger

doi:10.1039/d1cc05173c

Cited by 13 publications

(16 citation statements)

References 35 publications

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“…Similar edge-to-face CH/π interactions have recently been observed in CAAC-stabilized chalcogen-bridged 9,10-diboraanthracenes. 66 With phenyl azide, a twofold γ insertion into the B−B bond was observed, yielding the 1,3-bis(diazenyl)-1,3,2,4-diazadiboretidine 8 (Figure 7). 67 Compound 8 proved virtually insoluble in all common organic solvents.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The interaction of the Dip substituents with the naphthalene backbone in ( E , E )- 7 and ( E , Z )- 7 was confirmed by a NOESY experiment, which also revealed a chemical exchange between ( Z , Z )- 7 and ( E , Z )- 7 but not between ( E , E )- 7 and ( E , Z )- 7 . Similar edge-to-face CH/π interactions have recently been observed in CAAC-stabilized chalcogen-bridged 9,10-diboraanthracenes …”

Section: Resultsmentioning

confidence: 99%

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Highly Strained Arene-Fused 1,2-Diborete Biradicaloid

et al. 2022

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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.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Highly Strained Arene-Fused 1,2-Diborete Biradicaloid

et al. 2022

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“…70−74 Like its NHC analogue, 9,10-(CAAC) 2 -DBA activates O 2 via a [4 + 2] cycloaddition, as well as sulfur and selenium to form S-and Sebridged 9,10-DHDBA compounds, respectively. 75 Given that the optoelectronic properties of acenes can be tuned by the substitution pattern and the length of the acene, we wondered what influence acene elongation, boron atom positioning, and the acene substitution pattern would have on the structural and electronic features of CAAC-stabilized diboraacenes. In this combined experimental and theoretical study, we show that the structural conformation, H−L gap, and biradical character of CAAC-stabilized diboraacenes can be fine-tuned without the need for extensive acene elongation.…”

Section: ■ Introductionmentioning

confidence: 99%

“… DFT calculations show that 9,10-(CAAC) 2 -DBA exhibits an OSS biradical GS with a very small S–T gap of only 0.14 kcal mol –1 and a large closed-to-open shell singlet (C-OS) gap of −12.6 kcal mol –1 . The open-shell character of 9,10-(CAAC) 2 -DBA is favored by the two strongly π-accepting CAAC ligands, which help stabilize the unpaired electrons in radical main-group systems. − Like its NHC analogue, 9,10-(CAAC) 2 -DBA activates O 2 via a [4 + 2] cycloaddition, as well as sulfur and selenium to form S- and Se-bridged 9,10-DHDBA compounds, respectively …”

Section: Introductionmentioning

confidence: 99%

Structure and Electronics of a Series of CAAC-Stabilized Diboron-Doped Acenes from 1,4-Diboranaphthalene to 6,13-Diborapentacene

Dietz,

Arrowsmith,

Drepper

et al. 2023

J. Am. Chem. Soc.

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This combined experimental and theoretical study examines the influence of acene elongation, boron atom position, and acene substitution pattern on the structure and electronics of cyclic alkyl(amino)carbene (CAAC)-stabilized diboraacenes and presents the first syntheses of neutral diboranaphthalene (DBN) and diborapentacene (DBP). Whereas 2,3-diethyl-substituted 1,4-(CAAC)2-Et2DBN is isolated as a mixture of a planar (structurally characterized) NMR-active conformer and a presumably bent EPR-active conformer, 6,13-(CAAC)2-DBP resembles 9,10-(CAAC)2-DBA (DBA = diboraanthracene), with a highly puckered 6,13-DBP core and a typical biradical EPR signal. Both species are easily reduced to their puckered dianions. DFT calculations confirm that 6,13-(CAAC)2-DBP is only stable in its bent conformation, whereas 1,4-(CAAC)2-Et2DBN exists as both flat closed-shell and bent open-shell biradical conformers, which interchange by thermally activated ethyl and CAAC rotation/diboraacene bending processes. An in-depth computational study of the series of unsubstituted, CAAC-stabilized, symmetrically diboron-doped acenes from 1,4-(CAAC)2-DBN to 6,13-(CAAC)2-DBP was carried out. The results show interesting trends dependent on the position of the boron atoms within the acene framework as well as on the relative orientation of the CAAC ligands, which enable fine-tuning of the electronic and structural features.

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“…Anionic 9,10-diboraanthracenes reported by Wagner ( I , Figure a) show novel reactivity with a variety of small molecules (e.g., CO 2 , H 2 , alkenes) as a result of cooperative reactivity from both boron atoms . Similarly, neutral carbene-stabilized 9,10-diboraanthracenes synthesized by Harman ( II ) and Braunschweig ( III ) react with CO 2 , O 2 , CO, and other small molecules. Despite these promising results, diboraacenes (DBAs) beyond 9,10-diboraanthracenes are underexplored, and the overwhelming majority of structures contain both boron atoms in the same ring.…”

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confidence: 96%

Boron-Doped Pentacenes: Isolation of Crystalline 5,12- and 5,7-Diboratapentacene Dianions

et al. 2023

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The syntheses, molecular structures, reactivities, and computational assessment of dipotassium diboratapentacene isomers are described (1 and 2). These compounds represent the first examples of aromatized diboraacenes where the boron atoms are spatially separated in different rings of the acene framework. Both 1 and 2 react with carbon dioxide (CO2) via diastereoselective carboxylation of the pentacene backbone that likely proceeds by a frustrated Lewis pair-like mechanism. The placement of the boron atoms and the reactivity studies provide a platform for later stage functionalization of diboraacenes beyond the central ring of the polycyclic aromatic hydrocarbon core.

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Harnessing the electronic differences between CAAC-stabilised 1,4-diborabenzene and 9,10-diboraanthracene for synthesis

Abstract: The oxidation of doubly cyclic alkyl(amino)carbene-stabilised closed-shell 1,4-diborabenzene with sulphur or selenium yields S4/S5- or Se4-bridged hexa-1,4-dienes, respectively, whereas that of the related open-shell singlet biradical 9,10-diboraanthracene with O2, sulphur...

Cited by 13 publications

References 35 publications

Highly Strained Arene-Fused 1,2-Diborete Biradicaloid

Highly Strained Arene-Fused 1,2-Diborete Biradicaloid

Structure and Electronics of a Series of CAAC-Stabilized Diboron-Doped Acenes from 1,4-Diboranaphthalene to 6,13-Diborapentacene

Boron-Doped Pentacenes: Isolation of Crystalline 5,12- and 5,7-Diboratapentacene Dianions

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