C-H functionalization is a powerful transformation in the construction of complex molecules from simple feedstock chemicals. Diazo compounds, with far-reaching applications in C-H functionalization including cyclopropanations, C-H and C-X bond activation, and ylide formation, have received rigorous attention. However, their unstable nature and safety concerns limit their long-term storage and use in large-scale syntheses. One way to overcome the safety issue is through flow chemistry where the diazo compounds can be synthesized in situ and consumed immediately in downstream reactions with other transition metal catalysts. The synthesis of diazo compounds through the catalytic aerobic oxidation of hydrazones is more favorable than synthetic methods that rely on stoichiometric oxidants. The aerobic oxidation of hydrazones can be carried out under mild conditions with water as the only byproduct. We recently reported a Co(II) complex supported by a bis(amidophenyl)amine redox-active ligand that can be used as an efficient homogeneous catalyst for the aerobic oxidation of hydrazone to diazo compounds. This discovery has inspired us to seek modified redox-active ligands that can be easily incorporated into heterogeneous catalytic systems and/or attached to solid supports so that we can apply this technology to syntheses in flow reactors. In efforts to anchor an efficient homogeneous catalyst onto a solid support, we have designed and synthesized two asymmetric alkyne-functionalized bis(amidophenyl)amine redox-active ligands. In this poster, we will discuss the synthesis of two redox-active ligands N-(2-((2-isopropylamidophenyl)amino)phenyl)hex-5-ynamide (H3LiprLhexyne), N-(2-((2-(hex-5-ynamido)phenyl)amino)phenyl)-2,4,6-triisopropylbenzamide (H3LTRIPLhexyne) and their metalation with Co(II). Characterization of the ligands and their corresponding Co(II) complexes by various spectroscopic techniques and X-ray crystallography, as well as their oxidative reactivity will also be discussed.

Synthesis and metalation of alkyne modified redox-active ligands for applications in flow chemistry

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ACS Fall 2022

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