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

Student thesis: Doctoral Thesis

Abstract

Nickel catalysis is a rapidly developing field within synthetic chemistry with the potential to replace palladium in several cross-coupling reactions. However, mechanistic insight with regards to nickel lags far behind, this work has shed light onto the mechanisms involved during the oxidative addition step in nickel-catalysis. A kinetic study into the oxidative addition of alkyl halides to [Ni(COD)(dppf)] was carried out. The active species [Ni(dppf)2] (generate in-situ) undergoes halide abstraction with alkyl halides and radical recombination yields the oxidative addition products. Addition of 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 nickel intermediates, [Ni(dppf)L], followed a similar mechanism. The effect of the identity of added ligand on rates of oxidative addition with alkyl halides was investigated using kinetic experiments and DFT calculations. The halide abstraction step was found to not always be irreversible and this can have a significant effect on the rate of reaction. Addition of any ligand free ligand used in this study improved the performance of [Ni(COD)(dppf)] as a catalyst in Kumada-Tamao-Corriu cross-coupling of alkyl halides. The reaction of both vinyl and aryl triflates with [Ni(COD)(dppf)] was also investigated. Vinyl halides reacted faster than aryl triflates which is due to an initial displacement of COD to form the corresponding η2 complex prior to oxidative addition. Reactions can proceed through either a 3-centred or 5-centrered transition state for oxidative addition. Good conversion of both vinyl and aryl triflates was observed when employed as substrates in Kumada-Tamao-Corriu cross-couplings. Finally, a study into the effect of ancillary ligands on oxidative addition of aryl halides to a Ni0-dppf species was conducted. A variety of ligands were studied and most showed slower reactivity when compared to COD, which is the most common ligand employed for Ni0-dppf species.
Date of Award1 Oct 2021
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorDavid Nelson (Supervisor) & John Murphy (Supervisor)

Cite this

'