The synthesis and reactivity of tantalum diamidophosphine complexes featuring an activated alkyne unit

• Main Author: Parker, Kyle Daniel James
• Language: English
• Published: University of British Columbia 2014
• Online Access: http://hdl.handle.net/2429/47058

A series of tantalum complexes supported by the diamidophosphine ligand [PhNPN*] were synthesized using Ta(alkyne)Cl₃(DME), Ta(V) reagents that feature a reduced alkyne unit: [PhNPN*]Ta(3-hexyne)X, and [PhNPN*]Ta(BTA)X (X = Cl, H, alkyl, N₃; BTA = bis(trimethylsilyl)acetylene). For these complexes, the bonding and reactivity at tantalum is best understood as a combination of both the high-valent ‘Ta(V)-alkenediyl’ and low-valent ‘Ta(III)-alkyne’ structural formalisms. The synthesis and reactivity of a series of Ta imide complexes, generated via the displacement of the alkyne ligand with an aryl azide from corresponding [PhNPN*]Ta alkyne complex is reported. In addition, the synthesis and attempted synthesis of Ta alkyne azide and nitride complexes are discussed. The further reactivity of the Ta imide complexes with aryl azides, and the synthesis of a triazenide moiety is presented. The reactivity of [PhNPN*]Ta alkyne monohydrides with a variety of small molecules was explored. These monohydride complexes combine with 2,6-dimethylphenyl isocyanide and phenylacetylene to form five-membered tantallacyclic products by coupling with the Ta-bound alkyne ligand. A kinetic study of the thermal rearrangement of a Ta alkyne phenylvinyl complex to the corresponding tantallacycle is included. The synthesis of formate and methylene diolate moieties via the reaction of carbon dioxide with multiple equivalents of Ta monohydride was also explored. The hydrogenolysis of [PhNPN*]TaMe₃, and several [PhNPN*]Ta alkyne alkyl and hydride complexes were investigated. The motivation for this work came from the remarkable reactivity observed by a previously reported Ta tetrahydride, ([NPNSi]Ta)₂(μ-H)₄ (1.71) with various small molecules, including N₂. An analogous tetrahydride complex, ([PhNPN*]Ta)₂(μ-H)₄, (5.4) was synthesized via the high-pressure hydrogenolysis of the [PhNPN*]Ta complexes. Unfortunately, the inertness of 5.4 with respect to N2 means that comparisons to the reactivity observed with 1.71 could not be made. The synthesis and structure of the Ta alkene hydride intermediates formed via low-pressure hydrogenolysis of the Ta alkyne complexes is presented. Possible mechanisms for the formation of these intermediates are discussed. The synthesis and proposed structure of a cationic [PhNPN*]Ta imide complex is presented, and potential catalytic applications of this complex are discussed. Newly synthesized compounds were structurally characterized by a combination of NMR spectroscopy and X-ray crystallographic studies. === Science, Faculty of === Chemistry, Department of === Graduate