INVESTIGATIONS INTO RARE COORDINATION ENVIRONMENTS OF AL, P AND PD SPECIES: SYNTHESIS AND APPLICATIONS
Date
2015-10-23
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Degree Level
Doctoral
Abstract
This research work includes three parts, with the first section describing the synthesis and applications of neutral 3-coordinate aluminum complexes. As demonstrated in this part, aluminum complexes in a 3-coordinate geometry can be formed only with a ring size greater than or equal to a 6-member ring when supported by diamido ligands. It is found that 1,2-diamido ligands designed for 5-member ring formations can accommodate the formation of only 4-coordinate dinuclear species, which show no activity when used as a single component catalyst in the ring-opening polymerization (ROP) of cyclic esters under specified reaction conditions. Three-coordinate neutral (1,4-diamido)AlMe complexes are successfully synthesized, revealing a higher activity in the ROP of cyclic esters than the existing 6-member analogues under the same reaction conditions. A detailed discussion of the structure-reactivity relationship of Al catalysts in the ROP of cyclic esters is presented.
The second part of this thesis project consists of investigations into the applications of 1,4-diamido ligands for the formation of 3-coordinate NHP (N-heterocyclic phosphine) and 2-coordinate NHP+ cations (phosphenium cations). These novel NHP species are the first to be shown in a 7-member ring supported by 1,4-diamido ligands. Various N-substituents in the 1,4-diamido ligands are examined for the formation of a cyclic structure based on their steric hindrance. It is found that a Dipp (2,6-diisopropylphenyl) group is unable to allow for the formation of a 7-member NHP due to its excessive steric bulk. The less bulky mesityl (2,4,6-trimethylphenyl) group at the N-positions in the ligands leads to successful formation of these novel NHPs and NHP+ species. Furthermore, an investigation is carried out to explore their π-accepting property by means of 31P NMR studies. The NHP and NHP+ species synthesized in this project show chemical shifts downfield relative to the existing 5- and 6-member analogues in 31P NMR experiments, suggesting a high potential of 7-member NHPs to be used as π-acceptor ligands. The second section also examined the resulting NHPs and NHP+ species for coordinating to various metals.
The last part of this research work is dedicated to presenting the first example of chelating 3–triNHC (tri-N-heterocyclic carbene) ligands that allow for the formation of (triNHC)Pd(II) complexes in a meridional fashion, wherein the triNHC ligand coordinates to the metal center in a pseudo-meridional fashion. Novel [(triNHC)MePdX]X (X = Cl or acetate) complexes are successfully synthesized, and they display extraordinary stability against air and heat. Low activities of the resulting complexes are found in promoting C-C coupling reactions, possibly due to the low solubility of the resulting complexes in organic solvents. Various attempts to change the N-substituents to groups other than methyls are conducted to improve the solubility of the complexes in organic solvents for higher activities in C-C coupling reactions. The results from these attempted modifications to these complexes are discussed in detail.
All complexes are characterized by standard spectral methods such as mass spectrometry, X-ray crystallography, elemental analysis, 1H NMR, 13C NMR and 31P NMR spectroscopy.
Description
Keywords
aluminum, NHC, phosphine, NHP, N-heterocyclic phosphine, triNHC, trisNHC, palladium, 3-coordinate, 2-coordinate, 1,2-diamine, 1,4-diamine
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Chemistry
Program
Chemistry