4,4’-Bipyrazolate (bpz2-), a symmetric and linear molecule with four coordinating nitrogens, is of interest in the fields of coordination chemistry, coordination polymers and metal-organic frameworks, but the laborious synthetic routes necessary to access bpz2- have limited the investigation of bipyrazolate frameworks to date. Here we report the facile formation of 4,4’-bipyrazole (H2bpz) via the palladium-catalyzed oxidative homocoupling of a pyrazole boronic ester under aerobic conditions in the presence of water. The presented catalytic protocol enabled access to a bipyrazolate-based metal-organic framework, Co(bpz), with high surface area and previously unreported structural flexibility. Single-component N2, H2, and CO2 isotherms, along with in situ powder X-ray diffraction studies, demonstrate that Co(bpz) undergoes both adsorption-induced and temperature-induced phase changes. This structural flexibility, combined with the framework’s long-term stability to air and moisture, makes Co(bpz) a promising material for gas separation applications, and the facile route to H2bpz reported herein opens the door to future work on this and other bipyrazolate-based metal-organic frameworks that have been difficult to access previously.

Palladium-catalyzed oxidative homocoupling of pyrazole boronic esters to access bipyrazoles for metal-organic frameworks

2019 Fall National Meeting

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