Synthesis and reaction chemistry of various N,N,C- and O,N,C- palladium pincer complexes
thesisposted on 06.03.2017, 11:09 authored by Rena Simayi
In this thesis, the synthesis, characterisation and complexation chemistry of a series of related NNC and ONC pyridine based pincer ligands, together with some reaction chemistry of the metal complexes is described. The pro-ligands and the metal complexes have been characterised by a combination of multinuclear NMR spectroscopic techniques, IR spectroscopy, mass spectrometry and, for selected examples, by single crystal X-ray crystallography; remarkable spectroscopic and structural data are discussed. In Chapter 2, the synthesis and characterization of thirteen NNC and ONC pyridine based pincer ligands is described, including nine novel pincer ligands and four pyridine based pincers which have been previously reported. In Chapter 3, the palladium/platinum chemistry of NNCaryl and ONCaryl pyridine based pincer ligands is explored. Variation on the donor atoms has allowed an investigation of donor property influences on C-H activation, by giving peri-activated palladium pincer complexes for the ketimine-, aldimine-, amine- and biyridine-armed ligands and generating ortho-activated ONC palladium pincer complexes in the case of the alcohol-armed pro-ligand. Use of different palladium salts also led to different regioselective C-H activations. With the ketimine-armed naphthyl ligand (HL1ket-nap) as the example, the interconversion chemistry between the ortho- and peri-C-H activated products is also explored. In Chapter 4, sp3 C-H activation of the Et-armed ligand HL4Et with both palladium acetate and palladium chlorides has been unsuccessful, giving the N,N-coordinated bidentate species. The reaction of palladium acetate with the iPr-armed pro-ligand HL4iPr has resulted in minor amounts of C-H activated vinyl species with the major product being the non-activated palladium diacetate complex. Noticeably, upon reaction with Na2PdCl4, a mixture of the non-activated bis-chloride palladium complex and the sp3 C-H activated NNC-tridentate palladium species has been obtained, in a ratio of 1:1.5. Moreover, the sp3 C-H activation and the isolation of a rare sp3 C-H activated palladium complex have been achieved by reacting the tBu-armed pro-ligand HL4tBu with palladium acetate. The reaction of this ligand with Na2PdCl4 also resulted in the successful C-H activation of the tBu-arm to give a palladium pincer complex with a yield of 95%. Other than the NMR and FABMS analyses, the solid state X-ray structure of the latter complex confirmed the formation of the material as a rare sp3 C-H activated palladium complex. The stoichiometric reactivity of the (NNC/ONC)PdCl species towards AgBF4/AgPF6, and the subsequent ligand exchange reactions are disclosed in Chapter 5, together with the application of twelve palladium complexes as a series of promising catalysts in the allylic arylation of various allylic acetates with sodium tetraphenylborate.