Cargando…

From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP′ precatalysts for the asymmetric transfer hydrogenation of acetophenone

A novel PNN ligand bearing an orthophenylene group and a primary amine was synthesized with the aid of a palladium-catalyzed amination and reacted with phosphonium dimers [–PR(2)CH(2)CH(OH)–](2)[Br](2) R = Et, iPr, Cy, Ph, xylyl, and o-Tol, and [Fe(OH(2))(6)](2+) to produce a new series of cis-β iro...

Descripción completa

Detalles Bibliográficos
Autores principales: Demmans, Karl Z., Seo, Chris S. G., Lough, Alan J., Morris, Robert H.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Royal Society of Chemistry 2017
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5627452/
https://www.ncbi.nlm.nih.gov/pubmed/28989679
http://dx.doi.org/10.1039/c7sc02558k
_version_ 1783268719788556288
author Demmans, Karl Z.
Seo, Chris S. G.
Lough, Alan J.
Morris, Robert H.
author_facet Demmans, Karl Z.
Seo, Chris S. G.
Lough, Alan J.
Morris, Robert H.
author_sort Demmans, Karl Z.
collection PubMed
description A novel PNN ligand bearing an orthophenylene group and a primary amine was synthesized with the aid of a palladium-catalyzed amination and reacted with phosphonium dimers [–PR(2)CH(2)CH(OH)–](2)[Br](2) R = Et, iPr, Cy, Ph, xylyl, and o-Tol, and [Fe(OH(2))(6)](2+) to produce a new series of cis-β iron(ii) PNNP′ precatalysts cis-β-[Fe(Br)(CO)(PNNP′)]BPh(4) as a pair of diastereomers. The more stable orthophenylene amido group was chosen to imitate and replace the enamido moiety of a highly active iron precatalyst for the asymmetric transfer hydrogenation (ATH) of ketones in an attempt to prevent its deactivation caused by reduction of the enamido group. This objective was partially achieved using the complex with a PEt(2) group which catalyzed the transfer hydrogenation in isopropanol of 150 000 equivalents of acetophenone to racemic 1-phenylethanol. With a low acetophenone to catalyst ratio of 500 to 1, the catalytic activity was moderate and the enantiomeric excess (ee) of the product 1-phenylethanol ranged surprisingly from 94% (R) to 95% (S) depending on the nature of PR(2) and whether the precatalyst contained an imine or amine donor. The amine precatalyst with a PEt(2)-group produced a more stable hydride species when activated, allowing the reaction mixture to be heated to 75 °C to obtain a TON of 8821 for acetophenone while retaining the high ee of 95% (S). The activation pathway in basic isopropanol (iPrOH) was studied for three precatalysts to elucidate that the cis-β precatalysts rearrange to form trans hydride complexes. The study suggests that the enantioselectivity of these complexes is determined by from which side of the PNNP′ plane the hydride transfer occurs.
format Online
Article
Text
id pubmed-5627452
institution National Center for Biotechnology Information
language English
publishDate 2017
publisher Royal Society of Chemistry
record_format MEDLINE/PubMed
spelling pubmed-56274522017-10-06 From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP′ precatalysts for the asymmetric transfer hydrogenation of acetophenone Demmans, Karl Z. Seo, Chris S. G. Lough, Alan J. Morris, Robert H. Chem Sci Chemistry A novel PNN ligand bearing an orthophenylene group and a primary amine was synthesized with the aid of a palladium-catalyzed amination and reacted with phosphonium dimers [–PR(2)CH(2)CH(OH)–](2)[Br](2) R = Et, iPr, Cy, Ph, xylyl, and o-Tol, and [Fe(OH(2))(6)](2+) to produce a new series of cis-β iron(ii) PNNP′ precatalysts cis-β-[Fe(Br)(CO)(PNNP′)]BPh(4) as a pair of diastereomers. The more stable orthophenylene amido group was chosen to imitate and replace the enamido moiety of a highly active iron precatalyst for the asymmetric transfer hydrogenation (ATH) of ketones in an attempt to prevent its deactivation caused by reduction of the enamido group. This objective was partially achieved using the complex with a PEt(2) group which catalyzed the transfer hydrogenation in isopropanol of 150 000 equivalents of acetophenone to racemic 1-phenylethanol. With a low acetophenone to catalyst ratio of 500 to 1, the catalytic activity was moderate and the enantiomeric excess (ee) of the product 1-phenylethanol ranged surprisingly from 94% (R) to 95% (S) depending on the nature of PR(2) and whether the precatalyst contained an imine or amine donor. The amine precatalyst with a PEt(2)-group produced a more stable hydride species when activated, allowing the reaction mixture to be heated to 75 °C to obtain a TON of 8821 for acetophenone while retaining the high ee of 95% (S). The activation pathway in basic isopropanol (iPrOH) was studied for three precatalysts to elucidate that the cis-β precatalysts rearrange to form trans hydride complexes. The study suggests that the enantioselectivity of these complexes is determined by from which side of the PNNP′ plane the hydride transfer occurs. Royal Society of Chemistry 2017-09-01 2017-07-14 /pmc/articles/PMC5627452/ /pubmed/28989679 http://dx.doi.org/10.1039/c7sc02558k Text en This journal is © The Royal Society of Chemistry 2017 https://creativecommons.org/licenses/by-nc/3.0/This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 3.0 Unported License (http://creativecommons.org/licenses/by-nc/3.0/ (https://creativecommons.org/licenses/by-nc/3.0/) ) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
spellingShingle Chemistry
Demmans, Karl Z.
Seo, Chris S. G.
Lough, Alan J.
Morris, Robert H.
From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP′ precatalysts for the asymmetric transfer hydrogenation of acetophenone
title From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP′ precatalysts for the asymmetric transfer hydrogenation of acetophenone
title_full From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP′ precatalysts for the asymmetric transfer hydrogenation of acetophenone
title_fullStr From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP′ precatalysts for the asymmetric transfer hydrogenation of acetophenone
title_full_unstemmed From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP′ precatalysts for the asymmetric transfer hydrogenation of acetophenone
title_short From imine to amine: an unexpected left turn. Cis-β iron(ii) PNNP′ precatalysts for the asymmetric transfer hydrogenation of acetophenone
title_sort from imine to amine: an unexpected left turn. cis-β iron(ii) pnnp′ precatalysts for the asymmetric transfer hydrogenation of acetophenone
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5627452/
https://www.ncbi.nlm.nih.gov/pubmed/28989679
http://dx.doi.org/10.1039/c7sc02558k
work_keys_str_mv AT demmanskarlz fromiminetoamineanunexpectedleftturncisbironiipnnpprecatalystsfortheasymmetrictransferhydrogenationofacetophenone
AT seochrissg fromiminetoamineanunexpectedleftturncisbironiipnnpprecatalystsfortheasymmetrictransferhydrogenationofacetophenone
AT loughalanj fromiminetoamineanunexpectedleftturncisbironiipnnpprecatalystsfortheasymmetrictransferhydrogenationofacetophenone
AT morrisroberth fromiminetoamineanunexpectedleftturncisbironiipnnpprecatalystsfortheasymmetrictransferhydrogenationofacetophenone