Issue 18, 1975

Transition metal-diene complexes. Part II. Isomerization of rhodium-complexed penta-1,4- and cis-penta-1,3-dienes

Abstract

Several 1,4-dienes and cis-methyl-substituted 1,3-dienes co-ordinated to RhI in the complexes [(diene)RhX][X =η-cyclopentadienyl (cp), pentane-2,4-dionate (pd), or bridging Cl] undergo virtually quantitative isomerization when heated in inert solvents. Co-ordinated cis-penta-1,3-diene and cis-3-methylpenta-1,3-diene yield complexes of the trans-isomers as sole products. Co-ordinated cyclohexa-1,4-diene gives co-ordinated cyclo-hexa-1.3-diene; a 1,3-hydrogen shift has been demonstrated for this reaction by means of deuterium labelling. Co-ordinated penta-1.4-diene and 3-methylpenta-1.4-diene isomerizeto the corresponding co-ordinated cis- and trans-1,3-isomers at equal rates, the cis product subsequently converting into the trans in a secondary process. First-order rate constants and activation parameters for some of the reactions in o-dichlorobenzene are derived. Reaction rates increase with increase in the electron-withdrawing nature of the counter ligand X. The results are examined in relation to current theories concerning the mechanism of metal-assisted alkene isomerization. A new mechanism is proposed in which the rate-determinjng step is formation of a symmetrical σ-allyl complex, this being a common transition state for the isomerization of the acyclic 1,4-dienes and the η-σ-η interconversipn of anti- and syn-η allys the key step in the isomerization of cis to trans-1,3-dienes. An important conclusion which probably has general significance is that the conversion of an η-alkene to a η-allyl complex involves prior formation of an σ-allyl complex.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1975, 1794-1802

Transition metal-diene complexes. Part II. Isomerization of rhodium-complexed penta-1,4- and cis-penta-1,3-dienes

M. Arthurs, M. Sloan, M. G. B. Drew and S. M. Nelson, J. Chem. Soc., Dalton Trans., 1975, 1794 DOI: 10.1039/DT9750001794

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements