UBC Theses and Dissertations

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UBC Theses and Dissertations

Metal element multiply bonded group 6 complexes with 1,3-N,O-donor ligands Clarkson, Joseph Mitchell


This thesis discusses the synthesis and characterization of group 6 complexes that have metal element multiple bonds and 1,3-N,O-donor ligands. Furthermore, the evaluation of the metal-ligand interactions, including hemilability and metal-ligand cooperativity in E-H bond activation processes (where E=C or N), of the 1,3-N,O-donor ligands that resulted in reactivity of the metal element multiple bonds is reported. The 1,3-N,O-donor ligands in this thesis include amidates and pyridonates. The 1,3-N,O-donor ligands were installed on group 6 metals directly from the 1,3-N,O-proligands or as deprotonated sodium salts of the 1,3-N,O-proligands, by protonolysis or salt metathesis reactions respectively. Complexes such as di(1,3-N,O-chelate)bis(t-butylimido)tungsten and di(1,3-N,O-chelate)bis(dimethylamido)molybdenum, were synthesized by protonolysis reactions in chapters 2 and 4 respectively. In chapter 3 di(1,3-N,O-ligated)(neopentylidene)(oxo)tungsten complexes were synthesized by both protonolysis and salt metathesis reactions. These group 6 complexes with 1,3-N,O-donor ligands were characterized by single crystal X-ray diffraction, and in solution by multinuclear NMR spectroscopies, among other analytical methods. The solid-state molecular structures showed κ²-N,O, κ¹-O and µ²-N,O bonding modes, highlighting the flexibility of the 1,3-N,O-donor ligands. Solution NMR spectroscopy showed fluxional 1,3-N,O-donor ligands in all complexes at elevated temperatures, further highlighting the hemilability of these ligands. Throughout this thesis, pyridonate ligands showed more dynamic hemilability relative to amidate ligands. In chapter 2 pyridonate ligands were observed to have κ²-N,O, κ¹-O and µ²-N,O bonding modes in the solid state, whereas amidate ligands where exclusively bound in a κ²-N,O in the solid state. Variable temperature ¹H-NMR spectroscopy demonstrated that pyridonate ligands were fluxional at temperatures above -40 °C, whereas amidate ligands were fluxional at elevated temperatures (>60 °C). The steric parameters of 1,3-N,O-donor ligands influence how the ligands prefer to bond to the metal. Furthermore the steric demand also influences the hemilability of the 1,3-N,O-donor ligands. The differences in the electronic parameters between amidate and pyridonate ligands influences their hemilability, where pyridonates exhibit more dynamic hemilability in part due to the aryloxy imine motif. The metal-ligand cooperativity of the hemilabile 1,3-N,O-donor ligands towards E-H bond activations (where E=C or N) is reported in this thesis and applications of these processes are discussed.

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