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Tuning the reactivity of low valent nickel complexes towards epoxide ring-opening and exploring the reactivity of nickel η²-carbonyl complexes

University of British Columbia

This thesis explores the effects of tuning the ancillary phosphine ligands of low-valent nickel complexes on the ring-opening of epoxide, and also the reactivity of nickel η²-carbonyl complexes that are derived from epoxide isomerization. Chapter 1 describes the history of 2-metallaoxetanes, as well as the history of η²-carbonyl nickel complexes. Chapter 2 discusses the reactivity of low valent nickel complex 2.1 towards a variety of epoxides. While styrenyl and stilbene oxides were found to isomerize to η²-carbonyl complexes, tetrasubstituted epoxide 2.13 was found to form a 5-membered metallacycle, due to rapid β-hydride elimination and rapid reinsertion. Efforts in synthesizing a well-defined 2-nickelaoxetane by tuning the phosphine ligands on a nickel(0) centre are illustrated. Results show that monodentate phosphines such as triphenylphosphine and triisopropylphosphine lead to side reactions instead of facilitating the formation of 2-nickelaoxetanes. When triisopropylphosphine is used in combination with Ni(COD)₂ and epoxide 1.62, cyclotrimerization of the alkyne was observed instead of epoxide ring-opening . Chapter 3 explores the reactivity of epoxide-derived η²-carbonyl complexes towards a series of nucleophiles and electrophiles. These carbonyl complexes show no reactivity towards organozinc reagents. However, reaction with electrophiles such as benzyl bromide leads to the formation of dibromide complex 3.20, while reaction with Ph₃CBF₄ gives an unknown nickel (II) complex.  

Text

2018-08-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/67022

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/