A Double Conformationally Restricted Dynamic Supramolecular System for the Substrate‐Selective Epoxidation of Olefins—A Comparative Study on the Influence of Preorganization

Abstract

A double conformationally restricted kinetically labile supramolecular catalytic system, the third generation, was designed and synthesized. We investigated the substrate selectivity of this system by performing competitive pairwise epoxidations of pyridyl‐ and phenyl‐appended olefins. We compared the obtained substrate selectivities to previous less preorganized generations of this system. Five different substrate pairs were investigated, and the present double conformationally restricted system showed higher normalized substrate selectivities (pyridyl versus phenyl) for two of the substrate pairs than the previous less conformationally restricted generations. As for the preorganization of the components of the system, the catalyst, and the receptor part, it was shown that for each substrate pair there was one generation that was better than the other to generate substrate‐selective catalysis.

Mimicking Enzymes: Taking Advantage of the Substrate-Recognition Properties of Metalloporphyrins in Supramolecular Catalysis

“…These self-assembly issues were in part circumvented by designing a supramolecular catalyst in which both the catalytically active site and the substrate-recognition site comprised a covalently-linked strap around them that sterically hamper external binding of the substrate, thus limiting unselective catalysis outside of the cavity. [84] A chromium-based version at the place of manganese has been reported although no catalytic activity is known at this stage. [85] Scheme 5.…”

“…These self-assembly issues were in part circumvented by designing a supramolecular catalyst in which both the catalytically active site and the substrate-recognition site comprised a covalentlylinked strap around them that sterically hampers external binding of the substrate, thus limiting unselective catalysis outside of the cavity. 84 A chromium-based version in place of manganese has been reported; however, no catalytic activity has been described at this stage. 85 In 2017, our group reported carbon-carbon bond-forming reactions in which halopyridine substrates were selectively bound to zinc(II)-containing scaffolds via Zn … N interactions, whilst a trivial palladium/triphenylphosphine catalytic system was operating (Figure 4).…”

Chemical Reactions Controlled By Remote Zn ⋯ N Interactions Between Substrates and Catalysts

“…[38,39] This difficulty prompted the design of more rigid supramolecular catalysts by introducing straps in the recognition as well as in the catalytically active site with the aim to suppress to some extent unselective catalysis occurring outside of the cavity. [40] In our laboratories, we have recently established a research line devoted to exploiting the substrate-recognition properties of porphyrins in transition metal catalysis with the aim to tackle issues difficult to address with traditional stereoelectronic ligand modification. In 2017, we showed that palladium-catalyzed cross-coupling reactions with halopyridine derivatives are controlled by the presence (or absence) of zinc(II)-containing scaffolds.…”