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A structural study of palladium complexes containing hemilabile ligands

- Thompson, Catharine

  • Authors: Thompson, Catharine
  • Date: 2012-09-06
  • Subjects: Palladium compounds , Chemical reactions , Ligands , Catalysis , Catalysts
  • Type: Thesis
  • Identifier: uj:9678 , http://hdl.handle.net/10210/7092
  • Description: D.Phil. , Palladium chemistry has advanced dramatically in the last few years, with a huge number of wide-ranging studies, particularly with respect to the application of palladium complexes as catalysts, having been performed. The discovery of the phenomenon of hemilability (the ability of a ligand to be bidentately coordinated but with one donor atom more weakly bound and thus able to decoordinate in the presence of a catalytic substrate) has further assisted the growth, since it has allowed a greater understanding of the mechanisms of catalytic-reactions. However, the focus of much of this work has been on ligands containing phosphorus and oxygen as potential donor atoms, with little attention being turned to ligands with other donor atoms. The current study concentrates on a series of palladium complexes containing potentially hemilabile thioether, selenoether and telluroether carboxylate ligands with the oxygen as the strongly coordinating atom. Each complex was completed by the palladium coordinating to a phenyl ligand trans to the oxygen of the hemilabile ligand and either one or two triphenylphosphine ligands, depending on whether or not the -hemilabile ligand was monodentately or bidentately coordinated. These complexes are of interest as possible catalysts for the oligomerisation of ethene, and had been previously synthesised and characterised by NMR spectroscopy, mass spectrometry and catalytic studies. In the current work the crystal and molecular structures of the various complexes were determined. Since a number of pairs of complexes containing the monodentate and bidentate forms of the ligands were identified the hemilability of the ligands was confirmed.
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Osoongenerering

- Denkema, Jacobus Francois

Synthesis, characterization and electrochemical properties of new ferrocenylimine and adamantylimine palladium(II) complexes and their application in Mizoroki-Heck and Suzuki-Miyaura carbon-carbon cross-coupling reactions

- Matsheku, Asanda Cleopatra

  • Authors: Matsheku, Asanda Cleopatra
  • Date: 2018
  • Subjects: Organic compounds - Synthesis , Organic reaction mechanisms , Palladium compounds - Synthesis , Chemical reactions
  • Language: English
  • Type: Masters (Thesis)
  • Identifier: http://hdl.handle.net/10210/290349 , uj:31519
  • Description: Abstract: Cross-coupling reactions are essential synthetic tools for the synthesis of polymers, natural products, agrochemicals, and pharmaceuticals. The most well-known and widely used cross-coupling reactions are the Mizoroki-Heck, Stille, Suzuki-Miyaura, Negishi, and Buchwald–Hartwig cross-coupling reactions, and palladium(II) complexes are generally used as catalyst precursors. Due to the significant role that these reactions play in organic synthesis, the search for metal complexes which can catalyse the reactions efficiently while maintaining high chemo- and regio-selectivities is ongoing. New ferrocenyl- and adamantyl-imine monodentate as well as N^N and N^P chelating ligands (L1 to L7) were successfully synthesized. Synthesis of the ligands was achieved via Schiff-base condensation reactions of acetyl ferrocene and adamantyl ketone with hydrazine monohydrate followed by a second Schiff base reaction, with appropriate aldehydes (2-pyridine carboxaldehyde and 2-diphenylphosphino benzaldehyde), or phosphination with chlorodiphenylphosphine (L2). The ligands were then used to prepare new palladium(II) complexes (C1 to C7) by reacting L1 to L7 with [PdCl2(MeCN)2]. All the ligands and complexes were fully characterized using common spectroscopic and analytical techniques such as 1H NMR and 13C NMR spectroscopy, FT-IR spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray diffraction (for C7). Cyclic voltammetry was used to study the electrochemical properties of the ferrocenyl imine ligands (L1, L2 and L4) and ferrocenylimine palladium(II) complexes (C1, C2 and C4). Both the ferrocenyl and adamantyl palladium(II) complexes (C1 to C7) were active catalyst precursors for Mizoroki-Heck and Suzuki-Miyaura carbon-carbon (C-C) cross-coupling reactions. In particular, ferrocenyl N^P chelating palladium(II) complexes (C2 and C3) showed the best activity in Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions. Catalyst precursors bearing an adamantyl moiety required slightly higher temperatures for optimal performance. At higher temperatures the adamantyl palladium(II) catalyst precursors showed enhanced catalytic activity, and this was observed for both N^N and N^P bidentate systems. The adamantyl palladium(II) (pre)catalysts (C6 and C7) showed remarkable activity in Mizoroki-Heck coupling reactions involving substrates with substituents on the olefin and aryl halide (including 4-Cl, 4-CH3, -CO2Me and -CO2Et), while the ferrocenyl palladium(II) catalyst precursors demonstrated moderate catalytic activity. Both ferrocenyl and adamantyl... , M.Sc. (Chemistry)
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Knoevenagel and Heck catalytic studies with Metal Organic Frameworks (MOFs)

- Burgoyne, Andrew R.

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