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UBC Theses and Dissertations

New ligands for early metal activation of molecular nitrogen Ménard, Gabriel

Abstract

The synthesis of two new proligands for early metal activation of dinitrogen is reported. The new diamidophosphine [NPN]SH ₂([NPN]SH₂ = {N-(2,4,6-Me₃C₆H₂)(3- NH-SC₄H₂)}₂PPh)proligand features a bridging thiophene ring between the phosphine and amide donors and was synthesized as a variation to other recent aryl bridged NPN ligands. The potentially dianionic linear-linked aryloxide proligand [000]H ₂([000]H₂ = 2,6-bis(3 -adamantyl-5 -t-butyl-2-hydroxybenzyl)-4-t-butylanisole) was also synthesized as a variation to other similar known compounds. The precursor to the proligand [NPN] SH₂was successfully synthesized by a high yielding N-aryl amination reaction. The second step in the synthesis produces the [NPN] SH₂ compound; however, the product has an unexpected regiochemistry. Detailed mechanistic investigations suggest a possible mechanism involving competitive lithiumhalogen and deprotonation reactions. Zr and Ti complexes of the [000] ligand could not be synthesized; however, a new “half-on” [000(H)JTaC1₄ complex was synthesized and features a pendant phenol with the ligand locked in an S-conformation. Attempts to “close” this ligand to the U conformation and form the desired [000]TaCl₃ complex have thus far failed. In contrast, Zr complexes of the [NPN]S ligand could be readily synthesized and were fully characterized. These include: [NPN]SZr(NMe₂)₂ [NPN]SZrC1₂ and [NPN] SZrI₂. Attempts to reduce [NPN] SZrC1₂ to form a dinitrogen complex have thus far failed; however, reduction of [NPN] SZrI₂ in Et₂O using KC₈ as reducing agent shows promising signs of a dinitrogen complex similar to a previously reported case in our laboratory.

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