Abstract
Direct C–H functionalization catalyzed by a robust and recyclable heterogeneous catalyst is highly desirable for sustainable fine chemical synthesis. Bipyridine units covalently incorporated into the backbone of a porous organic polymer were used as a porous macroligand for the heterogenization of a molecular nickel catalyst. A controlled nickel loading within the porous macroligand is achieved, and the nickel coordination to the bipyridine (bpy) sites is assessed at the molecular level using IR and solid-state NMR spectroscopy. The heterogenized Ni-bpy catalyst was successfully applied to the direct and fully selective C2 arylation of benzothiophenes, thiophene, and selenophene, as well as for the arylation of free NH-indole. Recyclability of the catalyst was achieved by employing hydride activators to reach a cumulative turnover number of more than 300 after seven cycles of catalysis, which corresponds to a total productivity of 12 g of 2-phenylbenzothiophene, chosen as model target biaryl, per gram of catalyst.
Highlights
The BpyMP-1 is a bpy-containing porous polymer synthesized from a protocol first developed by the group of Thomas for nonfunctionalized POPs39 and adapted by our group for a mixed monomers approach (Scheme 2).[29,38]
We demonstrate here the heterogeneously catalyzed direct and fully regioselective C2-H arylation of various heteroarenes, including benzothiophene as an important building block for active pharmaceutical ingredients (API)
The catalyst was designed by covalently integrating an earth-abundant nickel catalyst into the matrix of a porous organic polymer used as a porous macroligand
Summary
The use of earth-abundant metals (EAM) for the direct C-H activation through a heterogeneous protocol would allow reaching appealing sustainability for the synthesis and derivatization of fine chemicals[1,2] since this approach would enable at the same time (i) the use of accessible resources, (ii) a beneficial atomand step-economy of non-activated substrates, and (iii) the ability to reuse the catalyst and to separate it from products.3–. Among organo-based porous materials offering functional derivatizable building blocks, porous organic polymers (POPs) are appealing platforms for the design of porous macroligands due to their chemical robustness arising from their covalent C-C bonds network Such stable network appear to be well suited to the strong basic conditions used in the homogeneous Ni-catalyzed benzothiophene C-H arylation reaction.[27] POP-type materials were already reported for the immobilization of nickel catalyst for the ethylene oligomerization,[34] or for Suzuki-Miyaura coupling.[35] While proof-of-concept heterogeneous C-H activation catalysts were recently published by the group of Yamada for palladiumcatalyzed thiophene arylation[36] and by the group of Sawamura for nickel-catalyzed benzoxazole arylation,[37] a general protocol is still missing.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
