Covalent Cages with Inwardly Directed Reactive Centers as Confined Metal and Organocatalysts

Abstract

Covalent cages with a well‐defined cavity located close to a reactive center are of increasing interest because of their outstanding ability to mimic the catalytic properties of enzymatic systems. The size and shape of such synthetic nanosized reactors strongly affect the behavior of the trapped reaction partners, which can adopt specific conformations and orientations. In particular, the use of molecular cages with confined reactive functions strongly modifies the outcome of catalytic transformations that are carried out therein. This review article describes covalent molecular cages presenting an endohedral functionalization of their inner space and reports on their catalytic activities compared with those of model systems that lack cavity.

Halide-Controlled Extending–Shrinking Motion of a Covalent Cage

“…Besides shedding light on the halide-induced conformational rearrangements of an interesting class of anion receptors, the obtained insights can be of great interest for the important applications in which covalent organic cages are involved (as, e.g., molecular hosts, nanoreaction vessels, and catalysts). ,− ,− ,− …”

“…In recent years, organic cages have been gaining attention for potential applications as nanoreaction vessels, , in catalysis, , sensing, stabilization of reactive compounds, and as materials for separation processes . When applied as molecular hosts, − guest selectivity is mainly driven by the complementarity of shape, size, and interaction sites between the cavity of the organic cage and the guest.…”

“…Molecular cages with a rigid cavity, hardly adapting to different guests, generally lead to a higher degree of selectivity. This is also important in the solid state, where shape-persistent cages (i.e., whose rigid structure prevents collapse) have emerged as materials for gas storage, separation, and heterogeneous catalysis. ,, In recent years, organic cages have also been utilized as building blocks for molecular machines and stimuli-responsive systems. − Within this frame, molecules with a flexible framework are generally privileged. In particular, cages of special interest are those with a cavity of controllable shape and size under an external chemical stimulus, for example, pH variation or addition of guests. , The input may induce large conformational changes and even modify the binding tendencies of the cage-like host.…”

Phosphines and other P(III)‐derivatives with Cavity‐shaped Subunits: Valuable Ligands for Supramolecular Metal Catalysis, Metal Confinement and Subtle Steric Control

“…A more application‐oriented approach for accessing complexes with their active centre placed in a confined space consists in using covalently‐constructed ligands which prefigure a capsular structure. These may, in principle, lead to more stable complexes, and therefore facilitate their recovery after catalysis [45] …”

“…These may, in principle, lead to more stable complexes, and therefore facilitate their recovery after catalysis. [45] An example of diphosphine suitable for capsule formation is the double resorcinarene-phosphine 62 (Figure 12). [46] Its reaction under high-dilution conditions with [PtCl 2 (PhCN) 2 ] gave trans-[PtCl 2 (62)] (63) in 39 % yield (along with the cis-isomer in 3 % yield), the metallo-capsular structure of which was proven by an X-ray structure determination.…”