Complexations of 1,4-Dienes to Rhodium(I) Pentane-2,4-dionates; Thermal Rearrangements of the Complexes

Article abstract of DOI:10.1039/DT9840000219

As models for natural products containing a 'skipped' diene fragment (-CH=CHCH2CH=CH-), a series of hepta-2,5-dienes, hepta-2,5-dien-4-ols, and hepta-2,5-dien-4-ol acetates have been prepared.Some of these dienes react with either bis(ethylene)(pentane-2,4-dionato)rhodium(I) or bis(ethylene)(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)rhodium(I) to afford 1:1 complexes, e.g. <(E,E)-hepta-2,5-diene>(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)rhodium(I).Other dienes, e.g. (Z,Z)-hepta-2,5-diene, form 2:1 complexes in which for each molecule of diene, one double bond is co-ordinated to rhodium, whereas the other is not.The (Z,Z)-dienes do not form 1:1 complexes because there would be a severe steric interaction between the terminal substituents of each double bond in such complexes.For the complexes of the dienols and certain allylic alcohols (e.g. prop-2-en-1-ol), evidence was obtained for the presence of a stabilizing intramolecular hydrogen bond between each OH and its nearest CO of the pentane-2,4-dionate.When heated in benzene with 5 mol percent of bis(ethylene)-(pentane-2,4-dionato)rhodium(I) each dienol rearranged to give an enone as the main product .Their acetates rearranged to isomeric conjugated dienes .The hepta-2,5-dienes were recovered unchanged.The mechanism of the rearrangements observed are explained in terms of intermediate (?-allyl)rhodium complexes.

Full text of DOI:10.1039/DT9840000219

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