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Early metal complexes of an iminophosphorane containing ligand framework

University of British Columbia

A new tridentate, dianionic ligand containing two amido donors and a central iminophosphorane, [NNN]H₂, was synthesized as an adaptation from the [tolylNPN*]H₂ ligand framework. The [NNN] system was designed as an extension to the ortho-phenylene bridged [NPN*] frameworks, which have been studied extensively with zirconium and tantalum. Zirconium amido and chloride complexes stabilized by [NNN] were synthesized via protonolysis routes, and the zirconium dibenzyl complex was synthesized from the halide precursor. Reduction of the zirconium dichloride species with alkali metal reagents led to cleavage of the iminophosphorane P=N bond. The LUMO of [NNN]ZrCl₂(THF) showed antibonding character of the iminophosphorane P=N, by DFT analysis. Steric calculations of [NNN]ZrX₂ complexes (G Value, %Vbur) showed increased steric hindrance of [NNN] relative to [NPN*] ligands. A neutral donor substitution competition experiment corroborated the steric calculations. Tantalum alkyl and alkyne complexes [NNN]TaMe₃ and [NNN]Ta(BTA)Cl were synthesized via salt metathesis reactions with the dipotassium salt of [NNN]. Treatment of [NNN]TaMe₃ with dihydrogen at elevated temperature led to cleavage of the iminophosphorane P=N bond, likely through reduced tantalum intermediate species. Treatment of [NNN]Ta(BTA)(benzyl) with dihydrogen did not generate tantalum-hydride species or hydrogenate the alkyne ligand. Addition of 4-isopropylphenylazide to [NNN]Ta(BTA)Cl led to the tantalum-imido compound [NNN]Ta=N(4-iPrPh)Cl via displacement of the alkyne ligand, BTA. Alternative ligand systems were also examined. A tetradentate ligand [PNNP]H₂ with ortho-phenylene linkers and an ethylene tether was synthesized, and installed on zirconium amido and chloride precursors. Reduction of [PNNP]ZrCl₂ with potassium graphite was unsuccessful in attempt to activate dinitrogen. A redesigned ligand with a propylene tether could not be synthesized, through several routes. A tridentate, monoanionic ligand with ortho-phenylene linkers and silylamide functionality was designed based on the [NPN*] and silylamide [PNP] ligands. The tridentate framework could not be synthesized through several routes, however, a new bidentate ligand with a secondary silylamide ortho to a phosphine group, a first of its class, was synthesized.

Text

2016-09-02

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/59045

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/