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Issue 31, 2015
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Triple decker sandwiches and related compounds of the first row transition metals with cyclopentadienyl and hexafluorobenzene rings: remarkable effects of fluorine substitution

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Abstract

The complete series of Cp2M2(μ-C6F6) (M = Ti, V, Cr, Mn, Fe, Co, Ni) structures have been examined theoretically for comparison with their unsubstituted Cp2M2(μ-C6H6) analogues. The singlet triple decker sandwich titanium complex Cp2Ti266-C6F6) with a closed shell electronic structure and a non-planar C6F6 ring is preferred energetically by a wide margin (>20 kcal mol−1) over other isomers and spin states. This is in contrast to the hydrogen analogue for which related triplet spin state structures are clearly preferred. A similar low-energy triple-decker sandwich Cp2V266-C6F6) structure is found for vanadium but with a quintet spin state. The later transition metals from Cr to Ni energetically prefer the so-called “rice-ball” cis-Cp2M2(μ-C6F6) structures with varying hapticities of metal-ring bonding, a range of formal orders of metal–metal bonding, and varying spin states depending on the metal atom. Thus the lowest energy Cp2Cr2(μ-C6F6) structures are triplet and quintet structures with pentahapto–trihapto η53-μ-C6F6 rings and formal Cr[double bond, length as m-dash]Cr double bonds. This contrasts with the structure of Cp2Cr2(μ-C6H6) having a bis(tetrahapto) η44-C6H6 ring and a formal Cr–Cr quadruple bond. The lowest energy Cp2Mn2(μ-C6F6) structures are trans and cis quintet spin state structures. This contrasts with Cp2Mn2(μ-C6H6) for which a closed-shell singlet triple decker sandwich structure is preferred. The lowest energy Cp2Fe2(μ-C6F6) structure is a triplet cis structure with a tetrahapto–dihapto η42-μ-C6F6 ring and a formal Fe–Fe single bond. The lowest energy Cp2Co2(μ-C6F6) structures are singlet spin state structures with formal M–M single bonds and either bridging bis(trihapto) η33-C6F6 or tetrahapto–dihapto η42-C6F6 rings. For Cp2Ni2(μ-C6F6) low energy singlet cis and trans structures are both found. The singlet cis-Cp2Ni2(μ-C6F6) structure has a Ni–Ni single bond of length ∼2.5 Å and a bridging bis(dihapto) η22-C6F6 ligand with an uncomplexed C[double bond, length as m-dash]C double bond. The singlet trans-Cp2Ni2(μ-C6F6) structure has a bis(trihapto) η33-C6F6 ligand.

Graphical abstract: Triple decker sandwiches and related compounds of the first row transition metals with cyclopentadienyl and hexafluorobenzene rings: remarkable effects of fluorine substitution

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Publication details

The article was received on 21 Mar 2015, accepted on 28 May 2015 and first published on 08 Jun 2015


Article type: Paper
DOI: 10.1039/C5CP01648G
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Citation: Phys. Chem. Chem. Phys., 2015,17, 20100-20113
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    Triple decker sandwiches and related compounds of the first row transition metals with cyclopentadienyl and hexafluorobenzene rings: remarkable effects of fluorine substitution

    S. Gong, Q. Luo, X. Feng, Q. Li, Y. Xie, R. B. King and H. F. Schaefer III, Phys. Chem. Chem. Phys., 2015, 17, 20100
    DOI: 10.1039/C5CP01648G

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