Thesis

Understanding reactions between Nickel(0) and substrates relevant to cross-coupling reactions

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Awarding institution
  • University of Strathclyde
Date of award
  • 2021
Thesis identifier
  • T16031
Person Identifier (Local)
  • 201785381
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Abstract
  • Nickel catalysis is a rapidly developing field within synthetic chemistry with the potential toreplace palladium in several cross-coupling reactions. However, mechanistic insight withregards to nickel lags far behind, this work has shed light onto the mechanisms involvedduring the oxidative addition step in nickel-catalysis.A kinetic study into the oxidative addition of alkyl halides to [Ni(COD)(dppf)] wascarried out. The active species [Ni(dppf)2] (generate in-situ) undergoes halide abstractionwith alkyl halides and radical recombination yields the oxidative addition products. Additionof excess dppf alongside [Ni(COD)(dppf)], thus generating high concentrations of [Ni(dppf)2],dramatically increased product formation in Kumada-Tamao-Corriu cross-couplings.This reaction was not specific to [Ni(dppf)2] and other three-coordinate nickelintermediates, [Ni(dppf)L], followed a similar mechanism. The effect of the identity of addedligand on rates of oxidative addition with alkyl halides was investigated using kineticexperiments and DFT calculations. The halide abstraction step was found to not always beirreversible and this can have a significant effect on the rate of reaction. Addition of anyligand free ligand used in this study improved the performance of [Ni(COD)(dppf)] as acatalyst in Kumada-Tamao-Corriu cross-coupling of alkyl halides.The reaction of both vinyl and aryl triflates with [Ni(COD)(dppf)] was alsoinvestigated. Vinyl halides reacted faster than aryl triflates which is due to an initialdisplacement of COD to form the corresponding ?²complex prior to oxidative addition.Reactions can proceed through either a 3-centred or 5-centrered transition state foroxidative addition. Good conversion of both vinyl and aryl triflates was observed whenemployed as substrates in Kumada-Tamao-Corriu cross-couplings.Finally, a study into the effect of ancillary ligands on oxidative addition of aryl halidesto a Niº-dppf species was conducted. A variety of ligands were studied and most showedslower reactivity when compared to COD, which is the most common ligand employed forNiº-dppf species.
Advisor / supervisor
  • Nelson, David
Resource Type
Note
  • Previously held under moratorium from 3rd October 2022 until 5th October 2026.
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