Pierpoint, Colin (1981) 1, 4-dienes : complexations to, and rearrangements promoted by metals. PhD thesis, University of Warwick.

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Abstract

The co-ordination chemistry of monoenes and conjugated dienes to Rh(I) is well documented, but little is known about the co-ordination of "skipped" dienes (1,4-dienes). Hence, the model compounds, (E,E)~, (E,Z)~, (Z,Z)-hepta-2,5-diene, the corresponding dien-4-ols and dienol-acetates were prepared and their complexations to E2Rh(I) pd and EjRMllhfp<f were studied. (E,E)~ and (E,Z)-hepta-2,5- diene reacted with both complexes to give bidentate complexes whereas the (Z,Z)-isomer gave only an unstable bis(monodentate) complex. Interestingly, with E2Rh(I)hfpd, (E,E)-hepta-2,5-dien-4-ol gave a bidentate complex whereas the corresponding (E,Z)~ and (Z,Z)~ isomers gave only crystalline complexes which were characterised (by 'h n.m.r., i.r., m.s., and combustion analysis) as bis(monodentate) complexes. It is believed that these complexes are stabilised by an intramolecular hydrogen bond interaction, and this is supported by i.r. spectral studies and the observations that other allylic alcohols (e.g. prop-2-en-l-ol and but-3-en-2-ol) also form crystalline complexes when reacted with E2Rh(I)hfpd. With the dienol acetates only (E,E)~ 4-acetoxyhepta-2,5-diene formed a stable complex and it was later deduced that all of the isomeric dienol acetates were catalytically transformed from 3-acetoxy-l,4-dienes to l-acetoxy-2,4-dienes. The regio- and stereospecificity of these rearrangements was not thought to be of great use for selective modification.

The results of the above complexations were used as a guide for the study of the complexations of fatty acid substrates to E2Rh(I)pd and E2Rh(I)hfpd. Hence, (E)~ and (Z)-9-octadecene, (Z,Z)~ octadeca-6,9-diene, and (Z,Z,Z)-octadeca-3,6,9-diene were prepared and reacted with E2Rh(I)pd and E2Rh(I)hfpd. Two equivalents of both (E)- and (Z)-9-octadecene displaced ethylene from the complexes to give bis(monoene) complexes whereas the (Z,Z)~ and (Z,Z,Z)-isomers gave unstable bis(monodentate) complexes. Similar reactions were observed for the corresponding methyl esters, but methyl (E,E)-octadec- 9,I2-dienoate was observed to give a bidentate complex. Similarly, the triglycerides, 1,2-dioleyl-3-palmitoylglycerol and 1,3-dielaideyl- 3- palmitoylglycerol gave bidentate complexes.

Although the Rh(I) promoted rearrangements of the isomeric 4- acetoxyhepta-2,5-dienes were of little use for selective modification, cis- bis(benzonitrile/acetonitrile)palladium(II)chloride, [Pd(II)a/b] and tetrakis(triphenylphosphine)palladium(0), {[P(Ph>3]^Pd(0)} were observed to facilitate the catalytic transformation of "skipped" dienol acetates, within minutes at RT, in a highly regio- and stereospecific manner. Thus, the Pd(II)-catalysed isomerisation of (E,E)-4-acetoxyhepta-2,5-diene gave (E,E)-2-acetoxyhepta-3,5-diene while (Z,Z)-4-acetoxyhepta-2,5- diene gave (E,Z)-2-acetoxyhepta-3,5-diene. Most interestingly (E,Z)- 4-acetoxyhepta-2,5-diene was transformed to (E,Z)-2-acetoxyhepta-3,5-diene indicating a highly regio- and stereospecific reaction at the (E)-double bond. The Pd(0)-catalysed isomerisation of (E,E)~, (E,Z)~ and (Z,Z)~ 4-acetoxyhepta-2,5-dienes gave only (E,E)-2-acetoxyhepta-3,5-diene. The belief that different mechanisms are operating for the Pd(0) and Pd(Il)-catalysed isomerisations was further supported by the observations that (E)- and (Z)-3-acetoxyhexa-1,4-diene were catalytically transformed by Pd(0) to give only (E,E)-1-acetoxyhexa-2,4-diene whereas Pd(II)-catalysed isomerisation of the (E)-isomer gave only (E)-2- acetoxyhexa-3,5-diene while the (Z)-isomer gave 'v 60% (E)-2-acetoxy- hexa-3,5-diene plus ~ 30% (E,E)-1-acetoxyhexa-2,4-diene. All of the above results were further supported by the results of the isomerisations of some C10 dienol acetates.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Diolefins, Acetates, Fatty acids, Esters
Official Date:	1981
Dates:	Date Event 1981 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Golding, Bernard T.
Extent:	xiii, 219 leaves : illustrations
Language:	eng

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