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

Louis J. Farrugia, Cameron Evans, Dieter Lentz, Max Roemer

Research output: Contribution to journalArticlepeer-review

125 Citations (Scopus)

Abstract

Experimental charge densities for (C5H5)Mn(CO) 3 (2), (η6-C6H6)Cr(CO) 3 (3), and (E)-{(η5-C5H4)- CF=CF(η5-C5H4)}(η5-C5H5)2Fe2 (4) 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-Cring 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 n-hapto (ηn- CnH n)M unit, there is generally a very similar level of chemical bonding for all M-Cring; interactions, as expected on the basis of chemical experience.

Original languageEnglish
Pages (from-to)1251-1268
Number of pages18
JournalJournal of the American Chemical Society
Volume131
Issue number3
DOIs
Publication statusPublished - 2009
Externally publishedYes

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