Molecular Addition Compounds of Boron. II. Thiophane-Borane and Related Adducts<sup>1,2</sup>

Coyle, T. D.; Kaesz, H. D.; Stone, F. G. A.

doi:10.1021/ja01521a018

Cited by 38 publications

(19 citation statements)

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“…These solutions are commercially available as convenient sources of BH 3 for organic synthesis. Stone and co-workers determined the enthalpy and entropy of dissociation of 1 in the gas phase to be 6.1 ± 0.5 kcal/mol and 18.0 eu, respectively, by variable-temperature saturation-pressure tensimetry . Therefore, at 298 K, 1 is 53% dissociated to dimethyl sulfide and diborane (eq 1).…”

Section: Resultsmentioning

confidence: 99%

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Gas-Phase Negative Ion Chemistry of Lewis Acid−Base Complexes

1998

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The gas-phase negative ion chemistry of a series of Lewis acid−base complexes [Me2SBH3 (1), Me3NBH3 (2), Me3PBH3 (3), Me2SBF3 (4), Me2OBF3, Et3NBH3, and Et2OBF3] was investigated with use of the flowing afterglow triple-quadrupole technique. Ab initio MO calculations using the G2(MP2) and CBS-4 models were carried out for 1 − 4 and related species. The gas-phase reaction between OH- and complex 1 produces a stable carbanion, MeS(BH3)CH2 - (1a), that does not isomerize under thermal conditions at room temperature to either of the lower energy borate isomers MeSCH2BH3 - (1b) and CH3CH2SBH3 - (1c). The structure of 1a was determined by tandem mass spectrometry and by ion/molecule reactions. The barriers for rearrangement of 1a to 1b and to 1c were calculated to be 29.3, and 27.6 kcal/mol, respectively, at the G2(MP2) level. The stable carbanions Me2N(BH3)CH2 - (2a), Me2P(BH3)CH2 - (3a), and MeS(BF3)CH2 - (4a) were also generated by proton abstraction from the corresponding neutral complexes. The gas-phase acidities (ΔH acid) of 1 − 3 were determined from bracketing experiments to be 372.5 ± 2.0, 393.0 ± 2.0, and 374.5 ± 2.0 kcal/mol, respectively. Compared to their uncomplexed bases, the acidities of 1 − 3 are enhanced by 18−20 kcal/mol. The acidity enhancements were shown to be mainly due to the increased electron binding energies of the carbanions in the deprotonated complexes that result from electrostatic interactions with the strongly dipolar Lewis acid−base bonds. Enhanced reactivity of the Lewis acid−base complexes was also characterized. The complexes 1, 2, and Me2OBF3 undergo nucleophilic substitution at carbon with F- or NH2 -, while no such reactions occur for the uncomplexed bases Me2S, Me3N, and Me2O. Similarly, facile β-elimination reactions occur between F- or OH- and the ethylated complexes Et3NBH3 and Et2OBF3, while the uncomplexed species are unreactive.

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Section: Resultsmentioning

confidence: 99%

“…b Enthalpy changes calculated at the CBS-4 level. c Experimental value, ref . d Experimental value from this work, derived from measured gas-phase acidity and the thermochemical cycle illustrated in Scheme .…”

Section: Resultsmentioning

confidence: 99%

Gas-Phase Negative Ion Chemistry of Lewis Acid−Base Complexes

1998

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“…[15] BF 3 forms more stable adducts with ethers than BH 3 , but for thioethers as bases, the opposite is true. [16] Experimental trendsh ave been explained by Pearson's principle of hard and soft acids andb ases (HSAB). [17] The leading contributions responsible for as trong interaction may likewise be deconvoluted by Drago's ECW scheme ( Figure 2b).…”

Section: Lewis Pair Formationmentioning

confidence: 99%

“…Taking BX 3 compounds as an example: for strong bases such as NH 3 , the affinity of BCl 3 is greater than that of BF 3 , but toward weak bases such as CO, BF 3 is the stronger acid . BF 3 forms more stable adducts with ethers than BH 3 , but for thioethers as bases, the opposite is true …”

Section: Lewis Pair Formationmentioning

confidence: 99%

Lewis Superacids: Classifications, Candidates, and Applications

Greb

2018

Chemistry A European J

244

242

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Lewis acids play a major role in all areas of chemistry. For a long time, toxic, corrosive and oxidizing SbF was considered as the strongest Lewis acid known. Lately, species significantly exceeding the Lewis acidity of SbF have been realized and were termed Lewis superacids (LSA). Prospective new candidates emerge steadily, which not only outperform SbF by their strength, but also in terms of their accessibility and ease of handling. In principle, Lewis superacids allow us to combine the outstanding activity of Brønsted superacids with the excellent selectivity of a common Lewis acid. However, the broad application of Lewis superacids in synthesis is all but popular. The present review deals with strong Lewis acids. First, it critically discusses Lewis acidity scaling methods and suggests an extended definition for Lewis superacidity. It then summarizes the properties and applications of the strongest currently known Lewis acids, indexed by the fluoride ion affinity (FIA). The supporting information contains a comprehensive list of experimentally and theoretically derived FIA data as a guide for the choice of Lewis acidic reagents/catalyst. This contribution shall encourage the search for new Lewis superacids and promote their application in non-specialized laboratories.

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“…A hydride-halide exchange reaction between a Lewis base complex of a boron trihalide and 2 might equilibrate a haloalane product due to the comparably high stability of many hydridoborane adducts. 59,60 One would expect the degree of hydrogenation at the boron atom to reflect the of the aluminium centre which would allow monitoring of the reaction progress by proton-coupled 11 B NMR spectroscopy. We chose the boron tribromide dimethylsulphide complex 61,62 as a suitable bromide-transfer reagent because it can be conveniently stored and handled as a solid under an inert atmosphere, yet, it readily undergoes bromide-hydride exchange reactions in solution.…”

Section: Dft Calculations Of Related Aluminium Dihydridesmentioning

confidence: 99%

Synthesis, characterization and reactivity of an imidazolin-2-iminato aluminium dihydride

2014

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The reaction of bis(2,6-diisopropylphenyl)imidazolin-2-imine (LH, 1) with Me 3 N·AlH 3 furnishes {μ-LAlH 2 } 2 (2). The marked tendency of 2 to release its hydride substituents is ascribed to the strong electron-donor character of the imidazolin-2-iminato ligand. This is supported by its reactivity study and DFT calculations.In fact, compound 2 was further converted with Me 3 SiOTf, Me 2 S·BH 3 , Me 2 S·BBr 3 , and BX 3 (with X = Cl, Br, and I) into {μ-LAl(H)OTf} 2 (3), {μ-LAl(BH 4 ) 2 } 2 (4), and {μ-LAlX 2 } 2 (5, X = Br; 6, X = Cl; 7, X = I), respectively.For all new aluminium complexes the formulation as dimers was evidenced by high resolution mass spectrometry, as well as single-crystal X-ray diffraction analysis. A prominent structural motif of these compounds is the square-planar four-membered Al 2 N 2 ring with two bridging bulky imidazolin-2-imino moieties. IntroductionAluminium hydrides -versatile reagents with rich chemistry For many years, chemical synthesis has been gaining immense benefit from the distinct reactivity of the aluminium-hydrogen bond. The strong need for highly selective transformations, increased focus on safety considerations, and efficiency in handling and storage are only some reasons why we find the chemically rogue parent aluminium hydride tamed into more suitable forms today. A variety of hydridoalanes has been tailored and very often reactivity adjustment is realized by steric congestion at the aluminium centre and by attaching strongly electron-donating substituents to the aluminium atom. Furthermore, hydridoalanes are used in a diverse range of applications. For instance, the hydroalumination of carbonyl 1,2 and alkyne 3-7 functionalities is a common application for this class of compounds in organic synthesis. Though the intermediate aluminium species in these reactions are often elusive, the use of aluminium hydrides such as I 8 ( Fig. 1) that bear highly sophisticated ligands grants access to all types of isolatable and well-defined model complexes. Compound I can be categorized as an aluminium dihydride and is related to the parent aluminium trihydride by replacement of one hydride for an anionic ligand. Thus, an ancillary ligand may be introduced, and yet, two reactive functional groups at the metal centre are preserved for the purpose of follow-up chemistry. The β-diketimino group, in particular, has been a key ligand to a rich chemistry of respective aluminium dihydrides. 9-12 A prominent example is II (Fig. 1), which can View Article OnlineView Journal | View Issue be used for the activation of non-polar element-element bonds as demonstrated by its conversion with elemental sulphur or selenium. 9,10 In a different field of applied science one finds chemical vapour deposition technology exploiting the thermodynamic properties of molecular aluminium hydrides for the purpose of creating composite materials. 1,13-15Aluminium hydrides are considered as fuel storagematerials with reasonable prospects in a hydrogen-based alternate energy-supply concept. 16,17 Moreover, the...

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Molecular Addition Compounds of Boron. II. Thiophane-Borane and Related Adducts^1,2

Cited by 38 publications

References 0 publications

Gas-Phase Negative Ion Chemistry of Lewis Acid−Base Complexes

Gas-Phase Negative Ion Chemistry of Lewis Acid−Base Complexes

Lewis Superacids: Classifications, Candidates, and Applications

Synthesis, characterization and reactivity of an imidazolin-2-iminato aluminium dihydride

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Molecular Addition Compounds of Boron. II. Thiophane-Borane and Related Adducts1,2

Cited by 38 publications

References 0 publications

Gas-Phase Negative Ion Chemistry of Lewis Acid−Base Complexes

Gas-Phase Negative Ion Chemistry of Lewis Acid−Base Complexes

Lewis Superacids: Classifications, Candidates, and Applications

Synthesis, characterization and reactivity of an imidazolin-2-iminato aluminium dihydride

Contact Info

Product

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Molecular Addition Compounds of Boron. II. Thiophane-Borane and Related Adducts^1,2