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  • 1.
    Brea, Oriana
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mó, Otilia
    Yáñez, Manuel
    Merced Montero-Campillo, M.
    Alkorta, Ibon
    Elguero, José
    Are beryllium-containing biphenyl derivatives efficient anion sponges?2018In: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 24, no 1, article id 16Article in journal (Refereed)
    Abstract [en]

    The structures and stabilities of 2,2'-diBeX-1,1'-biphenyl (X = H, F, Cl, CN) derivatives and their affinities for F-, Cl-, and CN- were theoretically investigated using a B3LYP/6-311 + G(3df, 2p)//B3LYP/6-31 + G(d,p) model. The results obtained show that the 2,2'-diBeX-1,1'-biphenyl derivatives (X = H, F, Cl, CN) exhibit very high F-, Cl-, and CN- affinities, albeit lower than those reported before for their 1,8-diBeX-naphthalene analogs, in spite of the fact that the biphenyl derivatives are more flexible than their naphthalene counterparts. Nevertheless, some of the biphenyl derivatives investigated are predicted to have anion affinities larger than those measured for SbF5, which is considered one of the strongest anion capturers. Therefore, although weaker than their naphthalene analogs, the 2,2'-diBeX-1,1'-biphenyl derivatives can still be considered powerful anion sponges. This study supports the idea that compounds containing -BeX groups in chelating positions behave as anion sponges due to the electron-deficient nature and consequently high intrinsic Lewis acidity of these groups.

  • 2. Merced Montero-Campillo, M.
    et al.
    Brea, Oriana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mó, Otilia
    Alkorta, Ibon
    Elguero, José
    Yáñez, Manuel
    Gas-phase reactivity tuned through the interaction with alkaline-earth derivatives2019In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 138, no 5, article id 62Article in journal (Refereed)
    Abstract [en]

    The cooperativity between MX2:XH alkaline-earth bonds and XH:NH3 hydrogen bonds (M=Mg, Ca; X=F, Cl) was investigated at the G4 level of theory. The cooperativity between these two non-covalent linkages is extremely large, to the point that the increase in their bond dissociation enthalpies may be as large as 240%. More importantly, the weaker the interaction, the larger the increase, so in some cases the linkage that stabilizes the most is the alkaline-earth bond, whereas in others is the hydrogen bond. In all cases, the formation of the MX2:XH:NH3 ternary complex is followed by a spontaneous proton transfer, very much as previously found for the Be-containing analogues. Similarly, MX2:FCl:NH3 complexes evolve from a chlorine-shared ternary complex (MX2FClNH3) or from an ion pair (MX2F-NH3Cl+) if M=Ca. Although F is the only halogen without sigma-hole, MgCl2 derivatives induce the appearance of a sigma-hole on it, though less deep than those induced by BeCl2. We have also studied whether Mg and Ca bond-containing complexes MR2:FY (R=H, F, Cl; Y=NH2, OH, F, Cl) may react to form radicals, as it has been found for the Be-containing analogues. These interactions provoke a drastic decrease in the F-Y bond dissociation enthalpy, very much as the one reported for the corresponding Be-analogues, to the point that in some cases the formation of the corresponding MR2F center dot+Y radicals becomes exothermic. Hence, the general conclusion of this study is that Mg or Ca derivatives give place to similar or even larger perturbations on the electron density than those induced by Be, a result not easily predictable.

  • 3. Merced Montero-Campillo, M.
    et al.
    Brea, Oriana
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mó, Otilia
    Alkorta, Ibon
    Elguero, José
    Yáñez, Manuel
    Modulating the intrinsic reactivity of molecules through non-covalent interactions2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 5, p. 2222-2233Article in journal (Refereed)
    Abstract [en]

    Non-covalent interactions unavoidably involve a certain disturbance of the electronic density of the interacting systems. Such perturbations are particularly strong when dealing with electron deficient systems such as boron, beryllium, magnesium (pre-p elements) or calcium (a pre-d element) derivatives. Indeed, these compounds have been shown to modify the intrinsic reactivity of the systems interacting with them. In the first part of this paper, we present an overview on (i) how electron deficient systems, acting as Lewis acids, modulate the intrinsic acidity of Lewis bases, explaining for instance why a typical base, such as aniline, can be converted by association with borane into an acid as strong as phosphoric acid; (ii) how other weak non-covalent interactions, such as halogen bonds, permit one to modulate the intrinsic basicity of typical oxyacids changing them into strong BrOnsted bases; (iii) how cooperativity between different non-covalent interactions may lead to the spontaneous formation of ion-pairs in the gas phase; (iv) how non-covalent interactions generate sigma-holes in systems where this feature is not present; and (v) how these interactions can induce exergonic and spontaneous formation of neutral radicals. In the second part of the paper, we show, by using G4 high-level ab initio calculations, that the acidity enhancement phenomenon is a general mechanism whenever a given base interacts with non-protic and protic acids. In the non-protic acid case, the underlying mechanism behind the enhancement is similar to the one reported for electron-deficient compounds, whereas the protic acid case appears in complexes stabilized through conventional hydrogen bonds. We also show that the former could be classified as an a priori mechanism, whereas the latter would be an a posteriori mechanism. This same a posteriori mechanism is behind the significant basicity enhancement of water and ammonia when interacting with conventional N-bases. Finally, we present a detailed analysis of the role that deformation can play in the intensity and nature of these enhancements.

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