Size‐Selective Hydroformylation by a Rhodium Catalyst Confined in a Supramolecular Cage

Abstract

Size‐selective hydroformylation of terminal alkenes was attained upon embedding a rhodium bisphosphine complex in a supramolecular metal–organic cage that was formed by subcomponent self‐assembly. The catalyst was bound in the cage by a ligand‐template approach, in which pyridyl–zinc(II) porphyrin interactions led to high association constants (>10 5 m −1 ) for the binding of the ligands and the corresponding rhodium complex. DFT calculations confirm that the second coordination sphere forces the encapsulated active species to adopt the ee coordination geometry (i.e., both phosphine ligands in equatorial positions), in line with in situ high‐pressure IR studies of the host–guest complex. The window aperture of the cage decreases slightly upon binding the catalyst. As a result, the diffusion of larger substrates into the cage is slower compared to that of smaller substrates. Consequently, the encapsulated rhodium catalyst displays substrate selectivity, converting smaller substrates faster to the corresponding aldehydes. This selectivity bears a resemblance to an effect observed in nature, where enzymes are able to discriminate between substrates based on shape and size by embedding the active site deep inside the hydrophobic pocket of a bulky protein structure.

Increasing structural and functional complexity in self-assembled coordination cages

“…136 In a similar fashion, Reek utilized Fe II -based cages built from Zn II -porphyrines for encapsulation of a variety of catalysts. [138][139][140] In these cages, the Zn II -porphyrine-based ligands play a dual function: with their four terminal diimine donors, they coordinate the Fe II vertices, and the central Zn II -cation contributes to catalyst encapsulation by coordinating the pyridine-donors included in the ligands of the catalyst. Especially for reactions in which the redox state and thus, the charge and coordination ability of the catalyst are changing, such additional anchors are quite important.…”

Metal–Organic Capsules with NADH Mimics as Switchable Selectivity Regulators for Photocatalytic Transfer Hydrogenation

“…29 These results indicate that the formation of the host−guest complex was preorganized for efficient substrate activation. 30,31 Highly Selective Photocatalytic Transfer Hydrogenation. The activity of macrocycle catalyst Zn−FPB was first studied by chemical reduction of the different types of double bonds (carbonyl, imine, olefin, and nitro).…”

Cell mimicry as a bottom‐up strategy for hierarchical engineering ofnature‐inspiredentities

“…In addition to the above‐mentioned ArMs, compounds with macrocyclic cavities, either natural or synthetic, which could form inclusion complex with substrates via noncovalent interactions, such as cyclodextrin (Wang, Qu, et al, 2017; Wang & Bols 2017), cucurbituril (Kubota et al, 2018), crown ether (Ning, Ao, Wang, & Wang, 2018), and so on were widely considered to provide this microenvironment to confine substrates and allow for more effective and selective catalysis. Except for these macromolecular models, self‐assembled nanocompartments, such as molecular cages (Marti‐Centelles, Lawrence, & Lusby, 2018; Nurttila et al, 2019; Roy et al, 2017), micelles (Arifuzzaman & Zhao, 2018; Dou et al, 2017), vesicles (Blackman et al, 2018; Fuhrmann et al, 2018), dendrimers (Li et al, 2018; Morshed et al, 2019), and core–shell particles (Keller, Beloqui, Martinez‐Martinez, Ferrer, & Delaittre, 2017), which could immobilize either natural enzymes or AEs and generate a protective and substrate‐dependent environment for the active molecules and improve the catalytic efficiency and selectivity, were also extensively evaluated. We recently demonstrated the preparation of micelles loaded with a salen‐manganese complex (EUK), which exhibited catalase‐like activity (Figure 1bi,bii; Ade et al, 2019).…”