Strong Dissimilarities Between the Gas‐Phase Acidities of Saturated and α,β‐Unsaturated Boranes and the Corresponding Alanes and Gallanes

Gámez, José A.; Guillemin, Jean‐Claude; Mó, Otília; Yáñez, Manuel

doi:10.1002/chem.200701254

Cited by 13 publications

(16 citation statements)

References 41 publications

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“…Keywords: ab initio calculations · acidity · gas-phase reactions · ion cyclotron resonance · phosphanes slightly stronger acid than methane, reflecting the fact that the electron affinity of the BH 2 radical is greater than that of the methyl radical. [9] Quite unexpectedly, for boron a dramatic increase in acidity occurs on methyl substitution, and methylborane is predicted to have an intrinsic acidity almost 200 kJ mol À1 larger than that of BH 3 , but also much larger than that of methane, in spite of being a carbon acid. This acidity enhancement reflects the large reinforcement of the C À B bond, which on deprotonation becomes a double bond through donation of the lone pair created on the carbon atom into the empty p orbital on boron.…”

Section: Is Amentioning

confidence: 95%

“…For the same reason, saturated and a,b-unsaturated boranes are much stronger acids than the corresponding hydrocarbons, in spite of also being carbon acids. [9] The formation of a complex between a primary phosphine and borane will completely change the acidity of the hydrogen atoms on the phosphorus and boron atoms. Moreover the role of the substituent could be completely changed by the presence of the boron compound in the molecule.…”

Section: Is Amentioning

confidence: 99%

“…The gas-phase acidity of boranes has also attracted some attention. [8,9] In recent studies [9] it was concluded that, although carbon is more electronegative than boron, BH 3 …”

Section: Introductionmentioning

confidence: 99%

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The Ever‐Surprising Chemistry of Boron: Enhanced Acidity of Phosphine⋅Boranes

Hurtado

Yáñez

Herrero

et al. 2009

Chemistry A European J

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The acidity-enhancing effect of BH(3) in gas-phase phosphineboranes compared to the corresponding free phosphines is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. Thus, the enhancement of the acidity of protic acids by Lewis acids usually observed in solution is also observed in the gas phase. For example, the gas-phase acidities (GA) of MePH(2) and MePH(2)BH(3) differ by about 118 kJ mol(-1) (see picture).The gas-phase acidity of a series of phosphines and their corresponding phosphineborane derivatives was measured by FT-ICR techniques. BH(3) attachment leads to a substantial increase of the intrinsic acidity of the system (from 80 to 110 kJ mol(-1)). This acidity-enhancing effect of BH(3) is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. This indicates that the enhancement of the acidity of protic acids by Lewis acids usually observed in solution also occurs in the gas phase. High-level DFT calculations reveal that this acidity enhancement is essentially due to stronger stabilization of the anion with respect to the neutral species on BH(3) association, due to a stronger electron donor ability of P in the anion and better dispersion of the negative charge in the system when the BH(3) group is present. Our study also shows that deprotonation of ClCH(2)PH(2) and ClCH(2)PH(2)BH(3) is followed by chloride departure. For the latter compound deprotonation at the BH(3) group is found to be more favorable than PH(2) deprotonation, and the subsequent loss of Cl(-) is kinetically favored with respect to loss of Cl(-) in a typical S(N)2 process. Hence, ClCH(2)PH(2)BH(3) is the only phosphineborane adduct included in this study which behaves as a boron acid rather than as a phosphorus acid.

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Section: Is Amentioning

confidence: 95%

Section: Is Amentioning

confidence: 99%

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The Ever‐Surprising Chemistry of Boron: Enhanced Acidity of Phosphine⋅Boranes

Hurtado

Yáñez

Herrero

et al. 2009

Chemistry A European J

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“…The ethylberyllium hydride exhibits an unexpected high acidity compared with the methyl derivative because deproto-culiar behavior as acids in the gas phase. [34] The first unexpected result is that methyl substitution increases the acidity of BH 3 by about 200 kJ mol…”

Section: Introductionmentioning

confidence: 94%

α,β‐Unsaturated and Saturated Derivatives of Be, Mg, and Ca: Are They Carbon or Metal Acids in the Gas Phase?

Eizaguirre¹,

Mó²,

Yáñez³

et al. 2008

Chemistry A European J

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The gas-phase acidity of R--XH (R=H, CH(3), CH(2)CH(3), CH==CH(2), C[triple chemical bond]CH; X=Be, Mg, Ca) alkaline-earth-metal derivatives has been investigated through the use of high-level CCSD(T) calculations by using a 6-311+G(3df,2p) basis set. BeH(2) is a stronger acid than BH(3) and CH(4) for two concomitant reasons: 1) the dissociation energy of the Be--H bond is smaller than the dissociation energies of the B--H and C--H bonds, and 2) the electron affinity of BeH(.) is larger in absolute value than those of BH(2) (.) and CH(3) (.). The acidity also increases on going from BeH(2) to MgH(2) due to these two same factors. Quite importantly, despite the fact that the X--H bonds in the R--XH (X=Mg, Ca) derivatives exhibit the expected X(delta+)--H(delta-) polarity, they behave as metal acids in the gas phase and only Be derivatives behave as carbon acids in the gas phase. The ethylberyllium hydride exhibits an unexpected high acidity compared with the methyl derivative because deprotonation of the system is accompanied by a cyclization that stabilizes the anion. Similarly to that found for derivatives that contain heteroatoms from groups 14, 15, and 16, the unsaturated compounds are stronger acids than the saturated counterparts, with the only exception of the Ca-vinyl derivative. Most importantly, among ethyl, vinyl, and ethynyl derivatives containing a heteroatom of the main group of the Periodic Table, those containing Be, Mg, and Ca are among the strongest gas-phase acids.

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“…Aluminium and boron belong to group III in the periodic table but there is large difference in their chemistry [1][2][3] . Only a few hydrides of aluminium are known along with monomer AlH 3 and dimer Al 2 H 6 while boron has a richer chemistry 4,5 in the inorganic as well as organic chemistry.…”

Section: Introductionmentioning

confidence: 99%

Hydroalumination of Cyclopropane: A Transition State Study

2013

Chem Sci Trans

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Abstract:The hydroalumination of cyclopropane has been investigated using the B3LYP density functional method employing several split-valence basis sets. It is shown that the reaction proceeds via a four-centered transition state. Calculations at higher levels of theory were also performed at the geometries optimized at the B3LYP level, but only slight changes in the barriers were observed. Structural parameters for the transition state are also reported.

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Strong Dissimilarities Between the Gas‐Phase Acidities of Saturated and α,β‐Unsaturated Boranes and the Corresponding Alanes and Gallanes

Cited by 13 publications

References 41 publications

The Ever‐Surprising Chemistry of Boron: Enhanced Acidity of Phosphine⋅Boranes

The Ever‐Surprising Chemistry of Boron: Enhanced Acidity of Phosphine⋅Boranes

α,β‐Unsaturated and Saturated Derivatives of Be, Mg, and Ca: Are They Carbon or Metal Acids in the Gas Phase?

Hydroalumination of Cyclopropane: A Transition State Study

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