Haptotropic Rearrangement between Two Isomers of ((μ235-guaiazulene)Fe2(CO)5 Revisited: Both Thermal and Photochemical Processes Induce the Haptotropic Interconversion

Hideo Nagashima, Takahiko Fukahori, Mitsuharu Nobata, Akihiro Suzuki, Mitsuhiko Nakazawa, Kenji Itoh

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Abstract

Interconversion between two haptotropic isomers of (μ235-guaiazulene)Fe2(CO)5 (1a,b) occurred at 70-105 °C. The thermal equilibrium ratios between la and lb are around 55: 45 in this temperature range, indicating that la is more stable than lb by 0.1 kcal/mol. The activation energies estimated from kinetic studies are ΔG373 = 28 ± 1 kcal/mol, ΔH373 = 23 ± 2 kcal/mol, and ΔS373 = −15 ± 5 cal/(mol·deg) either from la to lb or from lb to la. UV or visible photolysis also induced the interconversion to give a mixture of la,b in a ratio of 35:65. The haptotropic rearrangement of the ruthenium analogues, ((μ235-guaiazulene)- Ru2(CO)5 (2a,b), also occurred either thermally or photochemically to give a mixture of isomers in a ratio of 55:45. Photochemical replacement of CO ligands in la,b by PEt3 gave a mixture of mono- and diphosphine compounds, ((μ235-guaiazulene)Fe2(PEt3)(CO)4 (4) and ((μ235-guaiazulene)Fe2(PEt3)2(CO)3 (5), the ratio of which was controlled by the amount of added PEts. Mechanistic aspects are discussed on the basis of the reaction profile of the haptotropic interconversion and the ligand substitution.

Original languageEnglish
Pages (from-to)3427-3433
Number of pages7
JournalOrganometallics
Volume13
Issue number9
DOIs
Publication statusPublished - Sep 1 1994
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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