Farrugia, L.J., Evans, C., Lentz, D. and Roemer, M. (2009) The QTAIM approach to chemical bonding between transition metals and carbocyclic rings: a combined experimental and theoretical study of (η5-C5H5)Mn(CO)3, (η6-C6H6)Cr(CO)3, and (E)-{(η5-C5H4)CF=CF(η5-C5H4)}(η5-C5H5)2Fe2. Journal of the American Chemical Society, 131(3), pp. 1251-1268. (doi: 10.1021/ja808303j)
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Abstract
Experimental charge densities for (C<sub>5</sub>H<sub>5</sub>)Mn(CO)<sub>3</sub> (<b>2</b>), (η<sup>6</sup>-C<sub>6</sub>H<sub>6</sub>)Cr(CO)<sub>3</sub> (<b>3</b>), and (<i>E</i>)-{(η<sup>5</sup>-C<sub>5</sub>H<sub>4</sub>)-CF=CF(η<sup>5</sup>-C<sub>5</sub> H<sub>4</sub>)}(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>Fe<sub>2</sub>(<b>4</b>)have been obtained by multipole refinement of high-resolution X-ray diffraction data at 100 K. The resultant densities were analyzed using the quantum theory of atoms in molecules (QTAIM). The electronic structures of these and related π-hydrocarbyl complexes have also been studied by ab initio, density functional theory calculations, and a generally good agreement between theory and experiment with respect to the topological parameters was observed. The topological parameters indicate significant metal-ring covalency. A consistent area of disagreement concerns the topology of the metal-ring interactions. It is shown that because of the shared-shell bonding between the metal and the ring carbons, an annulus of very flat density ρ and very small ∇ρ is formed, which leads to topologically unstable structures close to catastrophe points. This in turn leads to unpredictable numbers of metal-C bond paths for ring sizes greater than four and fewer M-C bond paths than expected on the basis of the formal hapticity. This topological instability is a general feature of metal-π-hydrocarbyl interactions and means that a localized approach based on individual M-C-<sub><i>ring</i></sub> bond paths does not provide a definitive picture of the chemical bonding in these systems. However, other QTAIM indicators, such as the virial paths, the delocalization indices, and the source function, clearly demonstrate that for the <i>n</i>-hapto (η<sup><i>n</i></sup>-C<sub><i>n</i></sub>H<sub><i>n</i></sub>)M unit, there is generally a very similar level of chemical bonding for all M-C<sub><i>ring</i></sub> interactions, as expected on the basis of chemical experience.
| Item Type: | Articles |
|---|---|
| Status: | Published |
| Refereed: | Yes |
| Glasgow Author(s) Enlighten ID: | Farrugia, Dr Louis |
| Authors: | Farrugia, L.J., Evans, C., Lentz, D., and Roemer, M. |
| Subjects: | Q Science > QD Chemistry |
| College/School: | College of Science and Engineering > School of Chemistry |
| Journal Name: | Journal of the American Chemical Society |
| ISSN: | 0002-7863 |
| ISSN (Online): | 1520-5126 |
| Published Online: | 22 December 2008 |
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