Exploring structural and electronic effects in three isomers of tris{bis(trifluoromethyl)phenyl}borane: towards the combined electrochemical-frustrated Lewis pair activation of H<sub>2</sub>

Blagg, Robin J.; Lawrence, Elliot J.; Resner, Katie; Oganesyan, Vasily S.; Herrington, Thomas J.; Ashley, Andrew E.; Wildgoose, Gregory G.

doi:10.1039/c5dt01918d

Cited by 33 publications

(40 citation statements)

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“…Alternative bulky groups with higher electron affinities should enhance acceptor strength while maintaining or even enhancing the desired chemical stability of the systems. [6,12,28,[36][37][38][57][58][59][60][61][62][63][64][65][66][67] Exploiting this favorable property, some of us recently reported a series of air-stable bis (fluoromesityl)boryl ((FMes) 2 B) derivatives, namely compounds 1-3 (Scheme 1) with different electron-donating groups for comparison, i. e., phenyl, 4-tert-butylphenyl and 4-N,N-diphenylaminophenyl, respectively, attached to the electron acceptor group (FMes) 2 B through BÀ C bonds. [12] Comparison of these (FMes) 2 B-containing donor-acceptor compounds with compound 4, which contains a (Mes) 2 B group (Scheme 1), confirms that (FMes) 2 B is a much stronger acceptor, leading to: (i) a larger quinoidal distortion in the ground state structure; (ii) significantly red-shifted emission in solution and in the solid state; (iii) stronger emission solvatochromism; and (iv) significantly lower reduction potentials.…”

Section: Introductionmentioning

confidence: 99%

Insights into the Optical Properties of Triarylboranes with Strongly Electron‐Accepting Bis(fluoromesityl)boryl Groups: when Theory Meets Experiment

et al. 2019

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The photophysical properties (absorption, fluorescence and phosphorescence) of a series of triarylboranes of the form 4‐D−C6H4−B(Ar)2 (D=tBu or NPh2; Ar=mesityl (Mes) or 2,4,6‐tris(trifluoromethylphenyl (Fmes)) were analyzed theoretically using state‐of‐the‐art DFT and TD‐DFT methods. Simulated emission spectra and computed decay rate constants are in very good agreement with the experimental data. Unrestricted electronic computations including vibronic contributions explain the unusual optical behavior of 4‐tBu−C6H4−B(Fmes)2 2, which shows both fluorescence and phosphorescence at nearly identical energies (at 77 K in a frozen glass). Analysis of the main normal modes responsible for the phosphorescence vibrational fine structure indicates that the bulky tert‐butyl group tethered to the phenyl ring is strongly involved. Interestingly, in THF solvent, the computed energies of the singlet and triplet excited states are very similar for compound 2 only, which may explain why 2 shows phosphorescence in contrast to the other members of the series.

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Section: Introductionmentioning

confidence: 99%

Insights into the Optical Properties of Triarylboranes with Strongly Electron‐Accepting Bis(fluoromesityl)boryl Groups: when Theory Meets Experiment

et al. 2019

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“…Two other interesting examples with similar structures are (2,4-Ar F ) 3 B (UMUHIT; Cornet et al, 2003) and (2,5-Ar F ) 3 B (AJAGID; Blagg et al, 2016), which feature boron centres with three aryl rings carrying one o-CF 3 group and one p-CF 3 (UMUHIT) or m-CF 3 group (AJAGID) each. The three B-C bonds are exactly equal in UMUHIT [1.582 (4) Å ] and are similar in AJAGID [1.568 (3), 1.582 (3) and 1.583 (3) Å ], but, astonishingly, the C-B-C bond angles show quite a variation [117.0 (2), 117.6 (2) and 124.7 (2) in UMUHIT, and 116.98 (17), 119.12 (17) and 123.60 (17) in AJAGID].…”

Section: Figurementioning

confidence: 99%

“…Recently, two homoleptic triarylboranes carrying 2,4-or 2,5-CF 3 -substituted phenyl rings have been introduced as FLP components (Blagg et al, 2016). In combination with Lewis bases, neither of these compounds exhibits any reactivity towards H 2 , which is due to both electronic and steric effects (Blagg et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Conformational studies on heteroleptic trifluoromethyl-substituted phenylboranes

et al. 2016

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Organoboranes carrying electron-withdrawing substituents are commonly used as Lewis acidic catalysts or cocatalysts in a variety of organic processes. These Lewis acids also became popular through their application in `frustrated Lewis pairs', i.e. combinations of Lewis acids and bases that are unable to fully neutralize each other due to steric or electronic effects. We have determined the crystal and molecular structures of four heteroleptic arylboranes carrying 2-(trifluoromethyl)phenyl, 2,6-bis(trifluoromethyl)phenyl, 3,5-bis(trifluoromethyl)phenyl or mesityl substituents. [3,5-Bis(trifluoromethyl)phenyl]bis[2-(trifluoromethyl)phenyl]borane, C22H11BF12, (I), crystallizes with two molecules in the asymmetric unit which show very similar geometric parameters. In one of the two molecules, both trifluoromethyl groups of the 3,5-bis(trifluoromethyl)phenyl substituent are disordered over two positions. In [3,5-bis(trifluoromethyl)phenyl]bis[2,6-bis(trifluoromethyl)phenyl]borane, C24H9BF18, (II), only one of the two meta-trifluoromethyl groups is disordered. In [2,6-bis(trifluoromethyl)phenyl]bis[3,5-bis(trifluoromethyl)phenyl]borane, C24H9BF18, (III), both meta-trifluoromethyl groups of only one 3,5-bis(trifluoromethyl)phenyl ring are disordered. [3,5-Bis(trifluoromethyl)phenyl]dimesitylborane, C26H25BF6, (IV), carries only one meta-trifluoromethyl-substituted phenyl ring, with one of the two trifluoromethyl groups disordered over two positions. In addition to compounds (I)-(IV), the structure of bis[2,6-bis(trifluoromethyl)phenyl]fluoroborane, C16H6BF13, (V), is presented. None of the ortho-trifluoromethyl groups is disordered in any of the five compounds. In all the structures, the boron centre is in a trigonal planar coordination. Nevertheless, the bond angles around this atom vary according to the bulkiness and mutual repulsion of the substituents of the phenyl rings. Also, the ortho-trifluoromethyl-substituted phenyl rings usually show longer B-C bonds and tend to be tilted out of the BC3 plane by a higher degree than the phenyl rings carrying ortho H atoms. A comparison with related structures corroborates the conclusions regarding the geometric parameters of the boron centre drawn from the five structures in this paper. On the other hand, CF3 groups in meta positions do not seem to have a marked effect on the geometry involving the boron centre. Furthermore, it has been observed for the structures reported here and those reported previously that for CF3 groups in ortho positions of the aromatic ring, disorder of the F atoms is less probable than for CF3 groups in meta or para positions of the ring.

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“…All energiesa re in kcal mol À1 .R egarding the LA in entry 3a nd entries 4-7-see Refs [19]. All energiesa re in kcal mol À1 .R egarding the LA in entry 3a nd entries 4-7-see Refs [19].…”

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confidence: 99%

“…The barrier heights, DE # (DG # ), for the heterolytic H 2 -cleavage by as eries of [LA-OH 2 acetone]c omplexes plus dioxane as Lewis basic solvent molecule;a nd,t he total change of the potentiala nd the Gibbsf ree energies, DE (DG), for the resultanth ydrogenationo fa cetone.T he bulk solvent (dioxane)i sd escribed by the continuums olvent model COSMO. All energiesa re in kcal mol À1 .R egarding the LA in entry 3a nd entries 4-7-see Refs [19]. and[20] for details,respectively.…”

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confidence: 99%

Computational Elucidation of a Role That Brønsted Acidification of the Lewis Acid‐Bound Water Might Play in the Hydrogenation of Carbonyl Compounds with H₂ in Lewis Basic Solvents

Heshmat

Privalov

2017

Chemistry A European J

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Brønsted acidification of water by Lewis acid (LA) complexation is one of the fundamental principles in chemistry. Using transition-state calculations (TS), herein we investigate the role that Brønsted acidification of the LA-bound water might play in the mechanism of the hydrogenation of carbonyl compounds in Lewis basic solvents under non-anhydrous conditions. The potential energy scans and TS calculations were carried out with a series of eight borane LAs as well as the commonly known strong LA AlCl in 1,4-dioxane or THF as Lewis basic solvents. Our molecular model consists of the dative LA-water adduct with hydrogen bonds to acetone and a solvent molecule plus one additional solvent molecule that participates is the TS structure describing the cleavage of H at acetone's carbonyl carbon atom. In all the molecular models applied here, acetone (O=CMe ) is the archetypical carbonyl substrate. We demonstrate that Brønsted acidification of the LA-bound water can indeed lower the barrier height of the solvent-involving H -cleavage at the acetone's carbonyl carbon atom. This is significant because at present it is believed that the mechanism of the herein considered reaction is described by the same mechanism regardless of whether the reaction conditions are strictly anhydrous or non-anhydrous. Our results offer an alternative to this belief that warrants consideration and further study.

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Exploring structural and electronic effects in three isomers of tris{bis(trifluoromethyl)phenyl}borane: towards the combined electrochemical-frustrated Lewis pair activation of H₂

Cited by 33 publications

References 49 publications

Insights into the Optical Properties of Triarylboranes with Strongly Electron‐Accepting Bis(fluoromesityl)boryl Groups: when Theory Meets Experiment

Insights into the Optical Properties of Triarylboranes with Strongly Electron‐Accepting Bis(fluoromesityl)boryl Groups: when Theory Meets Experiment

Conformational studies on heteroleptic trifluoromethyl-substituted phenylboranes

Computational Elucidation of a Role That Brønsted Acidification of the Lewis Acid‐Bound Water Might Play in the Hydrogenation of Carbonyl Compounds with H₂ in Lewis Basic Solvents

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Exploring structural and electronic effects in three isomers of tris{bis(trifluoromethyl)phenyl}borane: towards the combined electrochemical-frustrated Lewis pair activation of H2

Cited by 33 publications

References 49 publications

Insights into the Optical Properties of Triarylboranes with Strongly Electron‐Accepting Bis(fluoromesityl)boryl Groups: when Theory Meets Experiment

Insights into the Optical Properties of Triarylboranes with Strongly Electron‐Accepting Bis(fluoromesityl)boryl Groups: when Theory Meets Experiment

Conformational studies on heteroleptic trifluoromethyl-substituted phenylboranes

Computational Elucidation of a Role That Brønsted Acidification of the Lewis Acid‐Bound Water Might Play in the Hydrogenation of Carbonyl Compounds with H2 in Lewis Basic Solvents

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Exploring structural and electronic effects in three isomers of tris{bis(trifluoromethyl)phenyl}borane: towards the combined electrochemical-frustrated Lewis pair activation of H₂

Computational Elucidation of a Role That Brønsted Acidification of the Lewis Acid‐Bound Water Might Play in the Hydrogenation of Carbonyl Compounds with H₂ in Lewis Basic Solvents