Acidity enhancement of unsaturated bases of group 15 by association with borane and beryllium dihydride. Unexpected boron and beryllium Brønsted acids

Abstract

The intrinsic acidity of CH 2 vCHXH 2 , HCuCXH 2 (X = N, P, As, Sb) derivatives and of their complexes with BeH 2 and BH 3 has been investigated by means of high-level density functional theory and molecular orbital ab initio calculations, using as a reference the ethyl saturated analogues. The acidity of the free systems steadily increases down the group for the three series of derivatives, ethyl, vinyl and ethynyl. The association with both beryllium dihydride and borane leads to a very significant acidity enhancement, being larger for BeH 2 than for BH 3 complexes. This acidity enhancement, for the unsaturated compounds, is accompanied by a change in the acidity trends down the group, which do not steadily decrease but present a minimum value for both the vinyl-and the ethynyl-phosphine. When the molecule acting as the Lewis acid is beryllium dihydride, the π-type complexes in which the BeH 2 molecules interact with the double or triple bond are found, in some cases, to be more stable, in terms of free energies, than the conventional complexes in which the attachment takes place at the heteroatom, X. The most important finding, however, is that P, As, and Sb ethynyl complexes with BeH2 do not behave as P, As, or Sb Brønsted acids, but unexpectedly as Be acids.

Revisiting the beryllium bonding interactions from energetic and wavefunction perspectives

“…Recently, Manuel Yáñez et al [17][18][19][20][21][22][23] has substantiated the existence of another kind of noncovalent weak interactions, namely, beryllium bonds, which may have some significant implications in different fields. It is well established that the association of beryllium fluoride to ADP inhibits protein action.…”

Design of new organic superacids with fused and isolated pyrrole and cyclopentadiene rings and assessment of effect of –BX2(X = H, F, Cl, CN) substituents on the acidity enhancement: A DFT analysis

“…[26][27][28] By combination of one or more Lewis acids such as BeX 2 , BX 3 (X = H, F, Cl, Br), AlF 3 , AuF 5 , and SbF 5 with a Brønsted inorganic acid, strong acids are obtained. [29][30][31][32][33][34][35][36] The magic acid, (SbF 5 + HSO 3 F), [11] and SbF 5 + HF, with ΔG acid of 260.5 kcal mol −1 , [37] are well known examples of this category. Also, acidity assessment of superhalogens has shown that these compounds can act as inorganic superacids.…”

“…[38,39] Other than inorganic superacids, acidity enhancement in the organic compounds due to interaction with Lewis acids such BX 3 , BeX 2 , AlX 3 , and MgX 2 has been studied both theoretically and experimentally. [34,[40][41][42][43][44][45][46] Interaction with Lewis acids may change organic bases into organic strong acids. For instance, interaction of BH 3 with amines leads to acidity enhancement from 40 to 47 kcal mol −1 [41] and its interaction with methyl phosphine enhances its acidity by about 29 kcal mol −1 .…”

Beryllepin, C6H6Be, and “Beryllium‐Inserted Benzenes,” C6H6Ben, n = 2–6: A Density Functional Computational Investigation

“…C 2015 Wiley Periodicals, Inc. Heteroatom Chem. Beryllepin is best described as a planar singlet heterocyclic conjugated triene with marginal aromatic character containing a C-Be-C moiety forced to be nonlinear (ࢬC-Be-C = 146.25°) by the cyclic constraints of the sevenmembered ring.…”

“…Of the remaining nine beryllium-inserted benzenes, with the exception of the 11-membered ring containing five beryllium atoms and the 12-membered ring containing six beryllium atoms, which were calculated to exist as a ground state pentet and septet, respectively, all were calculated to be ground state triplet systems. C 2015 Wiley Periodicals, Inc. Heteroatom Chem. 27:37-43, 2016; View this article online at wileyonlinelibrary.com.…”