Elsevier

Chemical Physics Letters

Volume 763, 16 January 2021, 138195
Chemical Physics Letters

Research paper
Nonconventional C(sp3)⋯Cl halogen bond in complexes of alkyl carbanions

https://doi.org/10.1016/j.cplett.2020.138195Get rights and content

Highlights

  • The properties of the C(sp3)⋯Cl halogen bond in carbanion complexes were studied.

  • The high energy of the carbanion lone pair makes the C(sp3)⋯Cl interaction partially covalent.

  • The orbital-orbital interaction energy correlates with the p-character of the Cl-hybrid orbital.

  • The charge transfer contribution to the binding energy is twice larger than the electrostatic component.

Abstract

Based on NBO analysis, Bader's theory, and decomposition of the interaction energy, the unique properties of the C(sp3)⋯Cl halogen bond in carbanionic complexes were revealed. In contrast to “electrostatic” complexes of hydroxyl and halide anions, in complexes of alkyl carbanions, charge transfer makes the main contribution to the binding energy. The C(sp3)⋯Cl interaction is partially covalent, and the interaction energy grows very slowly with an increase in the electron density at BCP of the intermolecular contact. The nature of the halogen bonds involving the C(sp3) atom of alkyl carbanions is determined by the high energy of the carbon lone pair.

Graphical abstract

Influence of donor lone pair on Cl-hybrid orbital and ENBO energy.

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Introduction

Weak intermolecular interactions play an important role in physicochemical processes and biochemical systems. The most important intermolecular interaction is hydrogen (H-) bonding. Like hydrogen atom, halogen can also participate in noncovalent interaction with electron donor with the formation so-called “halogen bonds”, intensively studied in recent years. The halogen bonds have some analogies in their properties with H-bonds, where electrostatic interaction makes the main contribution to the binding energy. It is now generally accepted that the stabilization of molecular complexes with hydrogen D⋯H–A and halogen D⋯Hal–A bonds is determined by the presence of a σ-hole [1], [2], [3], [4], [5], [6], an electron-deficient region located near the bridging atom. This region of positive charge interacts electrostatically with the electron-pair donor D (the Lewis base), providing binding of monomers.

In Hal-A molecules, the positive charge and electrostatic potential (ESP) ​​of the σ-hole strongly depend on the electronegativity of the A atom covalently bonded to the halogen atom. This effect is well studied in the literature and can be illustrated by Fig. 1, which shows maps of the electrostatic potential of diatomic Cl-A molecules. As seen in the figure, the ESP maximum value on the van der Waals surface of the molecule near the Cl atom consistently decreases with a decrease in the electronegativity of the neighboring atom, from 41 kcal/mol in the Cl-F molecule to 17 kcal/mol in the Cl-H molecule. For this reason, the D⋯Cl–A halogen bond is weakened in the series D⋯Cl–F > D⋯Cl–Cl > D⋯Cl–Br > D⋯Cl–H.

On the other hand, the role of the electron-pair donor in halogen bonding remains relatively little studied in the literature. In particular, investigations of anionic complexes were carried out mainly for halide ions [7], [8], [9], [10], [11], [12], and the effect of the nature of the anion on the characteristics of halogen bonds was not discussed. It seemed interesting to the author of the present paper to carry out a comparative analysis of the properties of halogen-bonded anionic complexes, where donors of the lone pair are electronegative atoms and “non-electronegative” carbon. As an electron-pair donor, the C(sp3) atom of alkyl carbanions is of great interest for both theoretical and experimental chemistry. Alkyl carbanions are known to be very strong Lewis bases and are involved in a number of important reactions of organic synthesis [13]. Recently, it was shown that the carbanion C(sp3) atom can be involved in hydrogen bonding [14]. This suggests that alkyl carbanions are also capable of forming halogen bonds.

The aims of the work discussed below were the following: (1) to analize the properties of halogen bonds formed by the C(sp3) atom of alkyl carbanions, (2) to study the role of the lone pair of anions in halogen bonding for a wide range of electron donors in order to look insight the interplay between the lone pair energy and the origin of the bonding, (3) to compare the properties of halogen and hydrogen bonds in binary complexes formed by the same anions. In the performed computations, the HCl molecule serves as the Lewis acid, since it can participate in the formation of both the D⋯Cl–H halogen bond and the D⋯H–Cl hydrogen bond.

Section snippets

Computational methods

Quantum chemical calculations of isolated monomers and binary complexes formed by the anion and the HCl molecule were carried out by the MP2 method [15] of the second-order Møller-Plesset perturbation theory. As shown in previous studies of noncovalent interactions, the MP2 method demonstrates high reliability in calculations of small anionic complexes with halogen and hydrogen bonds [16], [17], [18], [19]. The structures of the halogen-bonded complexes with D⋯Cl–H halogen bonds were found in

Geometry and binding energy

Some selected characteristics of anionic halogen-bonded complexes with D⋯Cl–H halogen bonds (A-complexes) calculated by the MP2/aug-cc-pVTZ method are given in Table 1. The table also lists the parameters found in the calculations of H-bonded complexes (B-complexes) formed by the same anions with the HCl molecule. As seen from the table, the binding energies Ebind in the halogen-bonded complexes agree well with the values ​​of the intermolecular distance; the latter is often considered as a

Summary

Quantum chemical MP2/aug-cc-pVTZ calculations of anionic complexes with D⋯Cl halogen bonds for a wide range of anions showed that the nature of halogen bonding depends on the energy of the lone pair orbital of the donor D, which can be considered as an indicator of the orbital-orbital interaction between monomers. The stabilization of complexes formed by H3C, H3CH2C, and H3CH2CH2C alkyl carbanions possessing the carbon lone pair of high energy is mainly determined by the charge transfer from

CRediT authorship contribution statement

Alexander N. Isaev: Conceptualization, Investigation, Project administration, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This investigation was supported by the Russian Foundation for Basic Research (Grant N15-07-00361).

References (46)

  • P. Politzer et al.

    Theor. Chem.

    (2012)
  • T. Clark et al.

    J. Mol. Model.

    (2007)
  • Y. Zhang et al.

    Chem. Phys. Lett.

    (2012)
  • B.B. Cao et al.

    J. Mol. Graph. Model.

    (2016)
  • A.N. Isaev

    Comput. Theor. Chem.

    (2017)
  • M.S. Gordon et al.
  • J.E. Del Bene et al.

    Chem. Phys. Lett.

    (2017)
  • C. Wang et al.

    J. Comput. Chem.

    (2016)
  • O. et al.

    J. Mol. Struct. (Theochem)

    (1994)
  • E. Espinosa et al.

    Chem. Phys. Lett.

    (1998)
  • S. Scheiner

    Int. J. Quantum Chem.

    (2013)
  • T. Clark

    WIREs Comput. Mol. Sci.

    (2013)
  • P. Politzer et al.

    J. Mol. Model.

    (2007)
  • P. Politzer et al.

    PCCP

    (2010)
  • Y. Lu et al.

    J. Phys. Chem. A

    (2011)
  • S. Ruiz-Botella et al.

    RSC Adv.

    (2017)
  • A. Bauza et al.

    J. Phys. Chem. A

    (2013)
  • M. Domagała et al.

    J. Phys. Chem. A

    (2018)
  • D.J. Cram

    Fundamentals of Carbanion Chemistry

    (1965)
  • C. Moller et al.

    Phys. Rev.

    (1934)
  • J.E. Del Bene

    Struct. Chem.

    (1989)
  • T.J. Lee

    J. Am. Chem. Soc.

    (1989)
  • Y.S. Chen

    J. Phys. Chem. A

    (2013)
  • View full text