Microporous Polymers as Macroligands for Pentamethylcyclopentadienylrhodium Transfer‐Hydrogenation Catalysts

Abstract

Herein, we report the synthesis of two bipyridine‐based porous polymers and their use as platforms for the heterogenization of pentamethylcyclopentadienylrhodium catalytic species. These highly stable heterogeneous catalysts demonstrate their efficiency in the transfer hydrogenation of α‐aryl ketones. Moreover, we show that their catalytic activity is similar to that of homogeneous analogues, highlighting the absence of diffusion limitations in the solids. We rationalize the differences in the measured activities by using the Hammett parameter as a descriptor of the electronic environment of the catalytic site in both homogeneous and heterogeneous systems.

Molecular Porous Photosystems Tailored for Long‐Term Photocatalytic CO2 Reduction

“…Our synthetic strategy consists in integrating an active organometallic catalyst into a photosensitive porous organic matrix. We have chosen monomers based on photoactive perylene or pyrene cores to synthesize microporous macroligands that consist of alternating photosensitizers and metal binding sites called hereafter perylene‐ alt ‐bipyridine‐conjugated microporous polymers (PerBpyCMP) and pyrene‐ alt ‐bipyridine‐CMP (PyBpyCMP). Then the Cp*Rh catalytic synthon was coordinated to the different frameworks to obtain the heterogeneous photocatalysts Cp*Rh@PyBpyCMP and Cp*Rh@PerBpyCMP (Figure a), following a well‐established grafting procedure …”

Porous Macroligands: Materials for Heterogeneous Molecular Catalysis

“…(bpebpy: 5,5’‐bis(phenyl‐ethinylene)‐2,2’‐bipyridine, becbpy: bis‐ethyl(2,2’‐bipyridine)‐5,5’‐dicarboxylate). Adapted with permission from Copyright 2018 American Chemical Society and from Copyright 2018 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”

“…Furthermore, the Hammett concept, which was originally developed for molecular organic reactions, underlines the single‐site and molecular nature of the active sites within these heterogeneous catalysts. Introducing amino groups with strong electron donating properties on the POP backbone (BpyMP‐1‐NH 2 ) in a precise matter (second meta‐position with respect to the bipyridine binding sites), made it possible to obtain by‐design a better performing catalyst for the ketone transfer hydrogenation as anticipated by the calculated Hammett value (Figure ) …”

“…Macroligands thus allow for a modular approach by the use of co-monomers resulting in single-site active species via spatial dilution and in the possibility to introduce side functionalities for a tailored, and ultimately predictable, reactivity. [7][8][9][10] These important properties have so far rarely been considered, especially when comparing different host materials.…”

“…In two recent studies by our team, a series of heterogeneous catalysts based on Bpy macroligands was presented. [7,8] These catalysts where designed by constructing different types of environments around the Bpy-moieties resulting in MOF and POP-based porous macroligands. As of MOF-macroligands UiO-67(Zr) and MOF-253(Al) were prepared.…”