New sterically-bulky nitrogen-donor ligands for organometallic chemistry

Chapter 1. An overview of the use of nitrogen-donor ligands in organometallic chemistry is presented. The design of two new sterically-bulky nitrogen-donor ligand systems is outlined, showing the rationale behind the ligand systems investigated in this dissertation.; Chapter 2. A series of new sterically-hindered amidinate ligands is synthesized. Lithium amidinate complexes are isolated by crystallization in the presence of TMEDA. Two independent routes to the formation of magnesium amidinates are demonstrated, producing both mono- and bis-amidinate magnesium complexes.; Chapter 3. A series of bis-amidinate complexes deriving from divalent transition metal halides is presented. Mono-amidinate nickel and copper complexes are synthesized and characterized. A mono-amidinate yttrium halide species is isolated, from which amido substitution proceeds to yield the corresponding mono- and bis-amido yttrium complexes.; Chapter 4. The sterically-bulky amidine ligands react with trimethylaluminum to form amidinate dimethylaluminum compounds. Activation by methyl abstraction reagents leads to formation of cationic aluminum species, all of which prove to be inactive as catalysts for olefin polymerization. Additionally, reaction of an amidine with ethyl dichloroaluminum produces an unexpected amidinium ethyltrichloroaluminate salt.; Chapter 5. A tacn-supported tantalum imido dichloride species exhibiting unique alkylation chemistry is synthesized. For example, when treated with Me3SiCH2Li, an unusual tantalum-lithium bridging alkyl complex is obtained. Thermolysis of this compound yields a tantalum-lithium bridging alkylidene complex by an alpha-hydrogen abstraction pathway.; Chapter 6. The reactivity of a wide array of electrophilic organic substrates with the heterobimetallic tantalum-lithium bridging alkylidene is presented. This bridging alkylidene reacts cleanly with proton sources of a wide range of acidity, resulting in protonation of the alkylidene ligand in all cases. A series of insertion reactions with unsaturated substrates, such as acetonitrile, carbon monoxide, and carbon disulfide, is observed. Additionally, double bond metathesis with benzophenone transforms the bridging alkylidene to a bridging oxo complex. Finally, reaction of the alkylidene with an acid chloride yields a tantalum enolate species.; Chapter 7. The tantalum-lithium bridging alkylidene complex is shown to form various early-late heterobimetallic alkylidene bridged complexes. These complexes include tantalum-iron, -rhodium, -copper, and -gold species.