Organohelium Compounds: Structures, Stabilities and Chemical Bonding Analyses. Issue 3 (2nd February 2014)

• Record Type: Journal Article
• Authors: Fourré, Isabelle; Alvarez, Elsa; Chaquin, Patrick
• Is Part Of: Chemphyschem. Volume 15:Issue 3(2014)
• Page Start: 467
• Page End: 477
• Publication Date: 2014-02-02
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201300932
• Languages: English
• ISSNs: 1439-4235

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>This paper deals with the possibility of forming short and relatively strong carbon–helium bonds in small typical organic molecules through substitution of one or several H atoms by He<sup>+</sup>. A structural and energetics study (based on high‐level calculations) of this unusual bonding, as well as a topological characterization of the resulting cations, is undertaken. Stable species generally requires substitution of about half of the hydrogen atoms for formation. Under these conditions, the number of such species appears to be potentially unlimited. "True" CHe bonds exhibit equilibrium distances ranging from 1.327 (C<sub>2</sub>H<sub>2</sub>He<sub>2</sub><sup>2+</sup>) to 1.129 Å (He<sub>2</sub>CO<sup>2+</sup>). The energies of neutral He releasing range from approximately 5 kcal mol<sup>−1</sup> [He<sub>2</sub>CO<sup>2+</sup>, (<italic>Z</italic>)‐C<sub>2</sub>H<sub>2</sub>He<sub>2</sub><sup>2+</sup>] to 25 kcal mol<sup>−1</sup> (C<sub>2</sub>HHe<sub>3</sub><sup>3+</sup>), but remain most frequently around 10 kcal mol<sup>−1</sup>. However, most of He<sup>+</sup>‐substituted hydrocarbons are metastable with respect to CC cleavage, except derivatives of ethene. Atoms in molecules (AIM) and electron localization function (ELF) topological descriptors classify the CHe bond as a weak charge‐shift interaction [S. Shaik, D. Danovich, B. Silvi, D. L. Lauvergnat, P. C. Hiberty, <ext-link ext-link-type="doi" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">Chem. Eur. J. 2005, 11, 6358–6371</ext-link>] in agreement with a recent publication by Rzepa [S. H. Rzepa, <ext-link ext-link-type="doi" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">Nat. Chem. 2010, 2, 390–393</ext-link>]. He<sub>2</sub>CO<sup>2+</sup> is the only investigated compound that presents a CHe bonding ELF basin, which indicates a non‐negligible covalent contribution to the bond. Other modifications in the electronic structure, such as the breaking of the triple bond in ethyne derivatives or the loss of aromaticity in C<sub>6</sub>H<sub>3</sub>He<sub>3</sub><sup>3+</sup>, are also nicely revealed by the ELF topology.</p> </abstract>