Abstract

The use of N-H N heterocyclic carbene ligands (NHC's) in organometallic chemistry has become a field of interest due to their unique properties that lead to new and interesting reactivity. The hydrogen on the nitrogen of the NHC can be deprotonated, creating an anionic species, or it can participate in hydrogen-bonding with different substrates. In this work we will explore the unique reactivity of N-H NHC palladium complexes in different cross coupling reactions, including the Suzuki-Miyaura and Heck reactions. Our work demonstrates that N-H NHC complexes of palladium can be accessed from 2-phosphinoimidazole ligands via non-oxidative insertion of the palladium into the P-C bond in the presence of a proton source (alcohol solvent). The resulting mixed NHC/phosphinite complexes of palladium are highly active in various cross coupling reactions, likely due to formation of anionic imidazolyl-type ligands from the N-H NHC under the reaction conditions. Specifically, my efforts have led to the discovery that varying the alcohol used in formation of the N-H NHC from the 2-phosphinoimidazole leads to a variety of new phosphinite-ligated N-H NHC palladium complexes that differ in the identity of the OR group on the phosphinite (which comes from the alcohol solvent). Changing the OR group in this matter is shown to have a dramatic effect on reactivity, and Suzuki cross couplings with less reactive aryl chloride substrates is achieved in good yield. We also demonstrate selective, sequential couplings of bromochloroarenes that are achieved by transforming the phosphinite during the reaction by addition of a second alcohol solvent. In a second project, my work also demonstrates that the N-H on the imidazole of our new NHC/phosphinite complexes can be used to hydrogen bond with substrates to engage them during catalysis. This leads to dramatic improvements in rates and regioselectivities in the Heck reaction with H-bonding substrates. Substrates that do not contain hydrogen bonding groups are much less reactive and selective with our N-H NHC catalyst. Future studies will investigate the substrate scope and potential of this H-bonding catalysis strategy in the Heck and other reactions.

Degree

MS

College and Department

Computational, Mathematical, and Physical Sciences; Chemistry and Biochemistry

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2024-03-13

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd13542

Keywords

Suzuki-Miyaura, Heck, 2-phosphinoimidazole

Language

english

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