Projects per year
Abstract
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.
Original language | English |
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Pages (from-to) | 628-641 |
Number of pages | 14 |
Journal | Chemical Science |
Volume | 7 |
Issue number | 1 |
Early online date | 20 Oct 2015 |
DOIs | |
Publication status | Published - 1 Jan 2016 |
Fingerprint
Dive into the research topics of 'Magnesium-catalysed nitrile hydroboration'. Together they form a unique fingerprint.Projects
- 1 Finished
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Group 2: Elements of 21st Century Catalysis
Hill, M. (PI)
Engineering and Physical Sciences Research Council
23/05/11 → 31/03/15
Project: Research council
Profiles
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Michael Hill
- Department of Chemistry - Professor
- Centre for Sustainable Chemical Technologies (CSCT)
- Centre for Doctoral Training in Aerosol Science
Person: Research & Teaching
Equipment
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MC2- Nuclear Magnetic Resonance (NMR)
Material and Chemical Characterisation (MC2)Facility/equipment: Technology type
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MC2- X-ray diffraction (XRD)
Material and Chemical Characterisation (MC2)Facility/equipment: Technology type