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Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes
In the presence of bidentate 1,n-bis-diphenylphosphinoalkane-CoCl(2) complexes {Cl(2)Co[P ∼ P]} and Me(3)Al or methylaluminoxane, acyclic (E)-1,3-dienes react with ethylene (1 atmosphere) to give excellent yields of hydrovinylation products. The regioselectivity (1,4- or 1,2-addition) and the alkene...
Autores principales: | , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
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Royal Society of Chemistry
2015
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4587399/ https://www.ncbi.nlm.nih.gov/pubmed/26430505 http://dx.doi.org/10.1039/c5sc00929d |
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author | Timsina, Yam N. Sharma, Rakesh K. RajanBabu, T. V. |
author_facet | Timsina, Yam N. Sharma, Rakesh K. RajanBabu, T. V. |
author_sort | Timsina, Yam N. |
collection | PubMed |
description | In the presence of bidentate 1,n-bis-diphenylphosphinoalkane-CoCl(2) complexes {Cl(2)Co[P ∼ P]} and Me(3)Al or methylaluminoxane, acyclic (E)-1,3-dienes react with ethylene (1 atmosphere) to give excellent yields of hydrovinylation products. The regioselectivity (1,4- or 1,2-addition) and the alkene configuration (E- or Z-) of the resulting product depend on the nature of the ligand and temperature at which the reaction is carried out. Cobalt(ii)-complexes of 1,1-diphenylphosphinomethane and similar ligands with narrow bite angles give mostly 1,2-addition, retaining the E-geometry of the original diene. Complexes of most other ligands at low temperature (–40 °C) give almost exclusively a single branched product, (Z)-3-alkylhexa-1,4-diene, which arises from a 1,4-hydrovinylation reaction. A minor product is the linear adduct, a 6-alkyl-hexa-1,4-diene, also arising from a 1,4-addition of ethylene. As the temperature is increased, a higher proportion of the major branched-1,4-adduct appears as the (E)-isomer. The unexpectedly high selectivity seen in the Co-catalysed reaction as compared to the corresponding Ni-catalysed reaction can be rationalized by invoking the intermediacy of an η(4)-[(diene)[P ∼ P]CoH](+)-complex and its subsequent reactions. The enhanced reactivity of terminal E-1,3-dienes over the corresponding Z-dienes can also be explained on the basis of the ease of formation of this η(4)-complex in the former case. The lack of reactivity of the X(2)Co(dppb) (X = Cl, Br) complexes in the presence of Zn/ZnI(2) makes the Me(3)Al-mediated reaction different from the previously reported hydroalkenylation of dienes. Electron-rich phospholanes, bis-oxazolines and N-heterocyclic carbenes appear to be poor ligands for the Co(ii)-catalysed hydrovinylation of 1,3-dienes. An extensive survey of chiral ligands reveals that complexes of DIOP, BDPP and Josiphos ligands are quite effective for these reactions even at –45 °C and enantioselectivities in the range of 90–99% ee can be realized for a variety of 1,3-dienes. Cobalt(ii)-complex of an electron-deficient Josiphos ligand is especially active, requiring only <1 mol% catalyst to effect the reactions. |
format | Online Article Text |
id | pubmed-4587399 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2015 |
publisher | Royal Society of Chemistry |
record_format | MEDLINE/PubMed |
spelling | pubmed-45873992015-09-29 Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes Timsina, Yam N. Sharma, Rakesh K. RajanBabu, T. V. Chem Sci Chemistry In the presence of bidentate 1,n-bis-diphenylphosphinoalkane-CoCl(2) complexes {Cl(2)Co[P ∼ P]} and Me(3)Al or methylaluminoxane, acyclic (E)-1,3-dienes react with ethylene (1 atmosphere) to give excellent yields of hydrovinylation products. The regioselectivity (1,4- or 1,2-addition) and the alkene configuration (E- or Z-) of the resulting product depend on the nature of the ligand and temperature at which the reaction is carried out. Cobalt(ii)-complexes of 1,1-diphenylphosphinomethane and similar ligands with narrow bite angles give mostly 1,2-addition, retaining the E-geometry of the original diene. Complexes of most other ligands at low temperature (–40 °C) give almost exclusively a single branched product, (Z)-3-alkylhexa-1,4-diene, which arises from a 1,4-hydrovinylation reaction. A minor product is the linear adduct, a 6-alkyl-hexa-1,4-diene, also arising from a 1,4-addition of ethylene. As the temperature is increased, a higher proportion of the major branched-1,4-adduct appears as the (E)-isomer. The unexpectedly high selectivity seen in the Co-catalysed reaction as compared to the corresponding Ni-catalysed reaction can be rationalized by invoking the intermediacy of an η(4)-[(diene)[P ∼ P]CoH](+)-complex and its subsequent reactions. The enhanced reactivity of terminal E-1,3-dienes over the corresponding Z-dienes can also be explained on the basis of the ease of formation of this η(4)-complex in the former case. The lack of reactivity of the X(2)Co(dppb) (X = Cl, Br) complexes in the presence of Zn/ZnI(2) makes the Me(3)Al-mediated reaction different from the previously reported hydroalkenylation of dienes. Electron-rich phospholanes, bis-oxazolines and N-heterocyclic carbenes appear to be poor ligands for the Co(ii)-catalysed hydrovinylation of 1,3-dienes. An extensive survey of chiral ligands reveals that complexes of DIOP, BDPP and Josiphos ligands are quite effective for these reactions even at –45 °C and enantioselectivities in the range of 90–99% ee can be realized for a variety of 1,3-dienes. Cobalt(ii)-complex of an electron-deficient Josiphos ligand is especially active, requiring only <1 mol% catalyst to effect the reactions. Royal Society of Chemistry 2015-07-01 2015-04-23 /pmc/articles/PMC4587399/ /pubmed/26430505 http://dx.doi.org/10.1039/c5sc00929d Text en This journal is © The Royal Society of Chemistry 2015 https://creativecommons.org/licenses/by/3.0/This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0) |
spellingShingle | Chemistry Timsina, Yam N. Sharma, Rakesh K. RajanBabu, T. V. Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes |
title | Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes
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title_full | Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes
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title_fullStr | Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes
|
title_full_unstemmed | Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes
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title_short | Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes
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title_sort | cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes |
topic | Chemistry |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4587399/ https://www.ncbi.nlm.nih.gov/pubmed/26430505 http://dx.doi.org/10.1039/c5sc00929d |
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