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Palladium-Mediated Formation of Alkyl–Nitrogen Bonds

  • Author(s): Peacock, David Matthew
  • Advisor(s): Hartwig, John F
  • et al.
Abstract

The following dissertation discusses reactions of palladium complexes to form sp3 carbon–nitrogen bonds. Both stoichiometric reductive elimination reactions to form alkylamines from characterized alkylpalladium(II) complexes and new palladium-catalyzed methods for the synthesis of N-alkylbenzophenone imines are reported.

Chapter 1 provides an overview of methods for the N-alkylation of nitrogen nucleophiles. Metal-catalyzed substitution reactions of nitrogen nucleophiles with alkyl electrophiles are discussed with a focus on the fundamental organometallic reactions that may form carbon–nitrogen bonds in these reactions. Examples of reductive elimination reactions from characterized alkylmetal complexes are covered in more detail because of their relevance to later chapters.

Chapter 2 discusses continued work in the Hartwig group studying the reductive elimination of norbornylamines from syn-2-methylnorbornylpalladium(II) amido complexes. This work focuses on the effects of phosphine ancillary ligands on the rate of reductive elimination and yield of alkylamine. These studies led to the design of bidentate P,O ligands that stabilize Pd(II) amido complexes while still enabling the reductive elimination of alkylamines to occur in good yield.

Chapter 3 presents the reductive elimination of N-neopentyl anilines and N-neopentyl imines from palladium(II) complexes. The P,O ligand structures developed as part of the work described in Chapter 2 proved particularly valuable to the study of neopentylpalladium(II) complexes and enabled the synthesis of stable, four-coordinate Pd(II) anilido and methyleneamido complexes that undergo reductive elimination to form N-neopentyl anilines and N-neopentyl imines in good yields.

Chapter 4 discusses the development of palladium catalysts for the cross-coupling of imines and primary alkyl bromides. The addition of fluorinated iminoquinolines as ancillary ligands was found to greatly increase the rate of the reaction. Mechanistic studies suggest that this reaction occurs through a two-electron pathway that may involve oxidative addition to a cyclometallated palladium(II) complex.

Chapter 5 expands the palladium-catalyzed cross-coupling of imines to include reactions with synthetically valuable secondary and tertiary alkyl halides. This method was applied to form a variety of imines bearing secondary and tertiary alkyl groups on nitrogen. Mechanistic studies suggest that this reaction occurs through single-electron transfer from a palladium(0) complex to form an alkyl radical intermediate. The intermediacy of this alkyl radical enabled this method to be expanded to include the intramolecular carboamination of unsaturated alkyl bromides.

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