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Complexes of adamantane‐based group 13 Lewis acids and superacids: Bonding analysis and thermodynamics of hydrogen splitting
Author(s) -
ElHamdi Majid,
Solà Miquel,
Poater Jordi,
Timoshkin Alexey Y.
Publication year - 2016
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.24328
Subject(s) - chemistry , adamantane , crystallography , homo/lumo , heterolysis , bond dissociation energy , density functional theory , lewis acids and bases , natural bond orbital , hydrogen bond , carbon group , computational chemistry , acceptor , standard enthalpy of formation , stereochemistry , dissociation (chemistry) , molecule , group (periodic table) , organic chemistry , physics , condensed matter physics , catalysis
The electronic structure and chemical bonding in donor–acceptor complexes formed by group 13 element adamantane and perfluorinated adamantane derivatives EC 9 R′ 15 (E = B, Al; R′ = H, F) with Lewis bases XR 3 and XC 9 H 15 (X = N, P; R= H, CH 3 ) have been studied using energy decomposition analysis at the BP86/TZ2P level of theory. Larger stability of complexes with perfluorinated adamantane derivatives is mainly due to better electrostatic and orbital interactions. Deformation energies of the fragments and Pauli repulsion are of less importance, with exception for the boron‐phosphorus complexes. The MO analysis reveals that LUMO energies of EC 9 R′ 15 significantly decrease upon fluorination (by 4.7 and 3.6 eV for E = B and Al, respectively) which results in an increase of orbital interaction energies by 27–38 (B) and 15–26 (Al) kcal mol −1 . HOMO energies of XR 3 increase in order PH 3 < NH 3 < PMe 3 < PC 9 H 15 < NMe 3 < NC 9 H 15 . For the studied complexes, there is a linear correlation between the dissociation energy of the complex and the energy difference between HOMO of the donor and LUMO of the acceptor. The fluorination of the Lewis acid significantly reduces standard enthalpies of the heterolytic hydrogen splitting H 2 + D + A = [HD] + + [HA] − . Analysis of several types of the [HD] + ···[HA] − ion pair formation in the gas phase reveals that structures with additional H···F interactions are energetically favorable. Taking into account the ion pair formation, hydrogen splitting is predicted to be highly exothermic in case of the perfluorinated derivatives both in the gas phase and in solution. Thus, fluorinated adamantane‐based Lewis superacids are attractive synthetic targets for the construction of the donor–acceptor cryptands. © 2016 Wiley Periodicals, Inc.