Issue 11, 2015

The multiple bonding in heavier group 14 element alkene analogues is stabilized mainly by dispersion force effects

Abstract

The structures and bonding in the heavier group 14 element olefin analogues [E{CH(SiMe3)2}2]2 and [E{N(SiMe3)2}2]2 (E = Ge, Sn, or Pb) and their dissociation into :E{CH(SiMe3)2}2 and :E{N(SiMe3)2}2 monomers were studied computationally using hybrid density functional theory (DFT) at the B3PW91 with basis set superposition error and zero point energy corrections. The structures were reoptimized with the dispersion-corrected B3PW91-D3 method to yield dispersion force effects. The calculations generally reproduced the experimental structural data for the tetraalkyls with a few angular exceptions. For the alkyls, without the dispersion corrections, dissociation energies of −2.3 (Ge), +2.1 (Sn), and −0.6 (Pb) kcal mol−1 were calculated, indicating that the dimeric E–E bonded structure is favored only for tin. However, when dispersion force effects are included, much higher dissociation energies of 28.7 (Ge), 26.3 (Sn), and 15.2 (Pb) kcal mol−1 were calculated, indicating that all three E–E bonded dimers are favored. Calculated thermodynamic data at 25 °C and 1 atm for the dissociation of the alkyls yield ΔG values of 9.4 (Ge), 7.1 (Sn), and −1.7 (Pb) kcal mol−1, indicating that the dimers of Ge and Sn, but not Pb, are favored. These results are in harmony with experimental data. The dissociation energies for the putative isoelectronic tetraamido-substituted dimers [E{N(SiMe3)2}2]2 without dispersion correction are −7.0 (Ge), −7.4 (Sn), and −4.8 (Pb) kcal mol−1, showing that the monomers are favored in all cases. Inclusion of the dispersion correction yields the values 3.6 (Ge), 11.7 (Sn), and 11.8 (Pb) kcal mol−1, showing that dimerization is favored but less strongly so than in the alkyls. The calculated thermodynamic data for the amido germanium, tin, and lead dissociation yield ΔG values of −12.2, −3.7, and −3.6 kcal mol−1 at 25 °C and 1 atm, consistent with the observation of monomeric structures. Overall, these data indicate that, in these sterically-encumbered molecules, dispersion force attraction between the ligands is of greater importance than group 14 element–element bonding, and is mainly responsible for the dimerization of the metallanediyls species to give the dimetallenes. In addition, calculations on the non-dissociating distannene [Sn{SiMetBu2}2]2 show that the attractive dispersion forces are key to its stability.

Graphical abstract: The multiple bonding in heavier group 14 element alkene analogues is stabilized mainly by dispersion force effects

Supplementary files

Article information

Article type
Edge Article
Submitted
24 jul 2015
Accepted
18 avg 2015
First published
19 avg 2015
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2015,6, 6235-6244

The multiple bonding in heavier group 14 element alkene analogues is stabilized mainly by dispersion force effects

J. Guo, D. J. Liptrot, S. Nagase and P. P. Power, Chem. Sci., 2015, 6, 6235 DOI: 10.1039/C5SC02707A

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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