Reduction–oxidation properties of organotransition-metal complexes. Part 32. One-electron oxidation of [Co(η4-cot)-(η-C5Me5)](cot = cyclooctatetraene): redox-induced polycyclic ring transformations of the resulting dimer, and crystal structure of [Co2(η4:η′4-C16H16)(η-C5Me5)2]
- 1 January 1991
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 1,p. 1-9
- https://doi.org/10.1039/dt9910000001
Abstract
The complex [Co(η4-cot)(η-C5Me5)]4(cot = cyclooctatetraene) undergoes irreversible one-electron oxidation in CH2Cl2 at a platinum electrode; chemical oxidation with [Fe(η-C5H5)2]PF6 gives the dimeric dication [Co2(η5 : η′5-C16H16)(η-C5Me5)2][PF6]25 as a diastereomeric mixture. The reduction of 5 with two equivalents of [Co(η-C5H5)2] gives three asymmetric isomers [Co2(σ,η3 : η′4-C16H16)(η-C5Me5)2]8, [Co2(σ,η3 : η′4-C16H16)(η-C5Me5)2]9 and [Co2(η4 : η′4-C16H16)(η-C5Me5)2]10. Complex 8 is thermally isomerised to 10 which has been structurally characterised by a single crystal X-ray diffraction study. The two cobalt atoms, each carrying an η-C5Me5 ligand, are bonded to opposite sides of a tetracyclic C16H16 ligand which contains fused cyclooctatriene, cyclopentane, cyclopropane and cycloheptadiene rings; the cobalt atoms are bound viaη4-1,3- and η4-1,5-diene interactions involving the C7 and C8 rings respectively. Complex 10 is oxidised by [Fe(η-C5H5)2]PF6, to give [Co2(η2,η3 : η′5-C16H16)(η-C5Me5)2][PF6]213, and undergoes partial decomplexation with Me3NO·2H2O to yield the monometallic compound [Co(η4-C16H16)(η-C5Me5)]15. Stepwise rather than concerted mechanisms are proposed for the overall two-electron reduction of 5 and two-electron oxidation of 10.Keywords
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