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Magnesium-catalysed nitrile hydroboration

A β-diketiminato n-butylmagnesium complex is presented as a selective precatalyst for the reductive hydroboration of organic nitriles with pinacolborane (HBpin). Stoichiometric reactivity studies indicate that catalytic turnover ensues through the generation of magnesium aldimido, aldimidoborate and...

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Autores principales: Weetman, Catherine, Anker, Mathew D., Arrowsmith, Merle, Hill, Michael S., Kociok-Köhn, Gabriele, Liptrot, David J., Mahon, Mary F.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Royal Society of Chemistry 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5952893/
https://www.ncbi.nlm.nih.gov/pubmed/29896350
http://dx.doi.org/10.1039/c5sc03114a
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author Weetman, Catherine
Anker, Mathew D.
Arrowsmith, Merle
Hill, Michael S.
Kociok-Köhn, Gabriele
Liptrot, David J.
Mahon, Mary F.
author_facet Weetman, Catherine
Anker, Mathew D.
Arrowsmith, Merle
Hill, Michael S.
Kociok-Köhn, Gabriele
Liptrot, David J.
Mahon, Mary F.
author_sort Weetman, Catherine
collection PubMed
description A β-diketiminato n-butylmagnesium complex is presented as a selective precatalyst for the reductive hydroboration of organic nitriles with pinacolborane (HBpin). Stoichiometric reactivity studies indicate that catalytic turnover ensues through the generation of magnesium aldimido, aldimidoborate and borylamido intermediates, which are formed in a sequence of intramolecular nitrile insertion and inter- and intramolecular B–H metathesis events. Kinetic studies highlight variations in mechanism for the catalytic dihydroboration of alkyl nitriles, aryl nitriles bearing electron withdrawing (Ar(EWG)CN) and aryl nitriles bearing electron donating (Ar(EDG)CN) substitution patterns. Kinetic isotope effects (KIEs) for catalysis performed with DBpin indicate that B–H bond breaking and C–H bond forming reactions are involved in the rate determining processes during the dihydroboration of alkyl nitriles and Ar(EDG)CN substrates, which display divergent first and second order rate dependences on [HBpin] respectively. In contrast, the hydroboration of Ar(EWG)CN substrates provides no KIE and HBpin is not implicated in the rate determining process during catalysis. Irrespective of these differences, a common mechanism is proposed in which the rate determining steps are deduced to vary through the establishment of several pre-equilibria, the relative positions of which are determined by the respective stabilities of the dimeric and monomeric magnesium aldimide and magnesium aldimidoborate intermediates as a result of adjustments to the basicity of the nitrile substrate. More generally, these observations indicate that homogeneous processes performed under heavier alkaline earth catalysis are likely to demonstrate previously unappreciated mechanistic diversity.
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spelling pubmed-59528932018-06-12 Magnesium-catalysed nitrile hydroboration Weetman, Catherine Anker, Mathew D. Arrowsmith, Merle Hill, Michael S. Kociok-Köhn, Gabriele Liptrot, David J. Mahon, Mary F. Chem Sci Chemistry A β-diketiminato n-butylmagnesium complex is presented as a selective precatalyst for the reductive hydroboration of organic nitriles with pinacolborane (HBpin). Stoichiometric reactivity studies indicate that catalytic turnover ensues through the generation of magnesium aldimido, aldimidoborate and borylamido intermediates, which are formed in a sequence of intramolecular nitrile insertion and inter- and intramolecular B–H metathesis events. Kinetic studies highlight variations in mechanism for the catalytic dihydroboration of alkyl nitriles, aryl nitriles bearing electron withdrawing (Ar(EWG)CN) and aryl nitriles bearing electron donating (Ar(EDG)CN) substitution patterns. Kinetic isotope effects (KIEs) for catalysis performed with DBpin indicate that B–H bond breaking and C–H bond forming reactions are involved in the rate determining processes during the dihydroboration of alkyl nitriles and Ar(EDG)CN substrates, which display divergent first and second order rate dependences on [HBpin] respectively. In contrast, the hydroboration of Ar(EWG)CN substrates provides no KIE and HBpin is not implicated in the rate determining process during catalysis. Irrespective of these differences, a common mechanism is proposed in which the rate determining steps are deduced to vary through the establishment of several pre-equilibria, the relative positions of which are determined by the respective stabilities of the dimeric and monomeric magnesium aldimide and magnesium aldimidoborate intermediates as a result of adjustments to the basicity of the nitrile substrate. More generally, these observations indicate that homogeneous processes performed under heavier alkaline earth catalysis are likely to demonstrate previously unappreciated mechanistic diversity. Royal Society of Chemistry 2016-01-01 2015-10-20 /pmc/articles/PMC5952893/ /pubmed/29896350 http://dx.doi.org/10.1039/c5sc03114a Text en This journal is © The Royal Society of Chemistry 2016 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
Weetman, Catherine
Anker, Mathew D.
Arrowsmith, Merle
Hill, Michael S.
Kociok-Köhn, Gabriele
Liptrot, David J.
Mahon, Mary F.
Magnesium-catalysed nitrile hydroboration
title Magnesium-catalysed nitrile hydroboration
title_full Magnesium-catalysed nitrile hydroboration
title_fullStr Magnesium-catalysed nitrile hydroboration
title_full_unstemmed Magnesium-catalysed nitrile hydroboration
title_short Magnesium-catalysed nitrile hydroboration
title_sort magnesium-catalysed nitrile hydroboration
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5952893/
https://www.ncbi.nlm.nih.gov/pubmed/29896350
http://dx.doi.org/10.1039/c5sc03114a
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