Synthesis and Coordination Chemistry of 1-Cymantrenyl-2,3,4,5-tetraphenylborole

Braunschweig, Holger; Damme, Alexander; Gamon, Daniela; Kupfer, Thomas; Radacki, Krzysztof

doi:10.1021/ic200559d

Cited by 31 publications

(37 citation statements)

References 25 publications

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“…Thus, a new set of signals is detected for the Cp protons ( δ =3.55, 4.04, 4.10 ppm), whereas the aromatic protons of the BC 4 backbone ( δ =6.60 – 6.61, 6.94 – 7.11 ppm) and the Lewis base ( δ =7.42 – 7.43, 8.67 – 8.68 ppm) appear as two multiplets each. As expected, the UV/Vis spectrum of 5 features an absorption band at λ max =345 nm (Figure S2), which is found in the typical region for common borole Lewis acid/base adducts 9d. In stark contrast to the behavior encountered in the case of 5 , no color change was observed upon addition of 4‐CN‐NC 5 H 4 to a solution of 2 .…”

Section: Resultssupporting

confidence: 73%

“…These findings are rather surprising considering the characteristic color changes that are usually observed upon adduct formation 9b. d Instead, UV/Vis spectroscopy indicates a comparable electronic absorption behavior of 6 and its borole precursor 2 ( λ max =490 nm). The presence of Lewis acid/base adducts in the solid state was substantiated for both species by X‐ray diffraction (Figure 2).…”

Section: Resultsmentioning

confidence: 97%

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Synthesis, Structure, and Reactivity of Borole‐Functionalized Ferrocenes

Braunschweig

Chiu

Gamon

et al. 2012

Chemistry A European J

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Herein, we report on the synthesis of ferrocenylborole [Fc(BC(4)Ph(4))(2)] featuring two borole moieties in the 1,1'-positions. The results of NMR and UV/Vis spectroscopy and X-ray diffraction studies provided conclusive evidence for the enhanced Lewis acidity of the boron centers resulting from the conjugation of two borole fragments. This finding was further validated by the reaction of [Fc(BC(4)Ph(4))(2)] and the 4-Me-NC(5)H(4) adduct of monoborole [Fc(BC(4)Ph(4))], which led to quantitative transfer of the Lewis base. The coordination chemistry of ferrocenylboroles was further studied by examining their reactivity towards several pyridine bases. Accordingly, the strong Lewis acidity of boroles in general was nicely demonstrated by the reaction of [Fc(BC(4)Ph(4))] with 4,4'-bipyridine. Unlike common borane derivatives such as [FcBMe(2)], which only forms a 2:1 adduct, we also succeeded in the isolation of a 1:1 Lewis acid/base adduct, with one nitrogen donor of 4,4'-bipyridine remaining uncoordinated. In addition, the reduction chemistry of ferrocenylboroles [Fc(BC(4)Ph(4))] and [Fc(BC(4)Ph(4))(2)] has been studied in more detail. Thus, depending on the reducing agent and the reaction stoichiometry, chemical reduction of [Fc(BC(4)Ph(4))] might lead to the migration of the borolediide fragment towards the iron center, affording dianions with either η(5)-coordinated C(5)H(4) or η(5)-coordinated BC(4)Ph(4) moieties. In contrast, no evidence for borole migration was observed during reduction of bisborole [Fc(BC(4)Ph(4))(2)], which readily resulted in the formation of the corresponding tetraanion. Finally, our efforts to further enhance the borole ratio in ferrocenylboroles aiming at the synthesis of [Fc(BC(4)Ph(4))(4)] failed and, instead, generated an uncommon ansa-ferrocene containing two borole fragments in the 1,1'-positions and a B(2)C(4) ansa-bridge.

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Section: Resultssupporting

confidence: 73%

Section: Resultsmentioning

confidence: 97%

Synthesis, Structure, and Reactivity of Borole‐Functionalized Ferrocenes

Braunschweig

Chiu

Gamon

et al. 2012

Chemistry A European J

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“…[1,6,15] The substituent at the boron atom is variable over a broad range from halogen, [4,6,12] amino, [4] and aryl groups [2,5,6,14,15] to transition metals [10,23] and cyclopentadienyl moieties in transition-metal complexes. [3,11,16,17] Variation of the substituent at the boron center significantly affects the HOMO-LUMO transition, thereby resulting in different photophysical properties. [1] The vacant p z orbital of the tricoordinate boron center in combination with an-ylborole and 4-picoline as well as 1-chloro-2,3,4,5-tetraphenylborole with various donors.…”

Section: Introductionmentioning

confidence: 99%

“…tiaromatic π conjugation induces a pronounced Lewis acidity so that even weak Lewis bases such as CO, [19] ethers, [1,12] nitriles, [1] as well as stronger donors like pyridine derivatives, [4,11,12,16] N-heterocyclic carbenes (NHC), [7,12] or phosphanes [12] readily coordinate to the boron center. As a result, π conjugation within the five-membered ring is interrupted, thus leading to enhanced stability of the Lewis acid-base adducts.…”

Section: Introductionmentioning

confidence: 99%

Lewis Acid–Base Adducts of 1‐Mesityl‐ and 1‐Chloro‐2,3,4,5‐tetraphenylborole

et al. 2013

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Electron‐deficient borole compounds exhibit a pronounced Lewis acidity that is enhanced due to their antiaromatic character so that even weak donors datively coordinate to form Lewis acid–base adducts. This contribution presents the synthesis and structural characterization of Lewis acid–base adducts formed by the reaction of 1‐mesityl‐2,3,4,5‐tetraphenylborole and 4‐picoline as well as 1‐chloro‐2,3,4,5‐tetraphenylborole with various donors. The new compounds are characterized by means of multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction techniques and compared to related systems.

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“…The incorporation of electronegative halogen substituents (2, 3) at boron, despite their electron-withdrawing inductive effect, has hardly any effect on the observed antiaromaticity (see Table 1). The change in antiaromaticity relative to 1 is also small for boroles with ferrocenyl (4) [5] or cymantrenyl (σ-η 5 -C5H4Mn(CO)3) substituents at the boron atom (5), [45] although Raman spectroscopic data indicates a significant decrease in the antiaromatic character due to electron donation of a filled metal d orbital to the vacant 2p orbital on boron. This is further reflected in the bending of the borolyl unit toward the metal center in the molecular structures.…”

Section: Monoborolesmentioning

confidence: 99%

A theoretical study of the aromaticity in neutral and anionic borole compounds

et al. 2015

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Abstract:In this contribution, we have evaluated the (anti)aromatic character of thirty-four different borole compounds in their neutral and reduced states based on two aromaticity indices, namely nucleus-independent chemical shift (NICS) and multicenter indices (MCI), calculated at the PBE0/6-31+G(d,p) level of theory. Both indices corroborate the notion that neutral borole compounds are antiaromatic and become increasingly aromatic upon addition of electrons. Effects of the ring substituents on the degree of (anti)aromaticity are discussed together with differences in the two theoretical methods, which are on the one hand based on magnetic (NICS) and on the other hand based on electronic criteria (MCI).

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Synthesis and Coordination Chemistry of 1-Cymantrenyl-2,3,4,5-tetraphenylborole

Abstract: In this contribution, we report the synthesis of base-free 1-cymantrenyl-2,3,4,5-tetraphenylborole and two of its Lewis base adducts. In addition, the structural characterization and investigation of the photophysical properties are provided.

Cited by 31 publications

References 25 publications

Synthesis, Structure, and Reactivity of Borole‐Functionalized Ferrocenes

Synthesis, Structure, and Reactivity of Borole‐Functionalized Ferrocenes

Lewis Acid–Base Adducts of 1‐Mesityl‐ and 1‐Chloro‐2,3,4,5‐tetraphenylborole

A theoretical study of the aromaticity in neutral and anionic borole compounds

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