Recent applications of macrocycles in supramolecular catalysis

Numerous supramolecular macrocycles have been utilized for developing catalysts by exploiting their specific molecular recognition and ability to form inclusion complexes through noncovalent interactions. The cyclic structure and modified functional groups of these macrocycles can influence substrate and transition state stability, as well as reaction selectivity. The inner cavities of these macrocycles are particularly beneficial, as they enable substrates to adopt preorganized arrangements and serve as versatile platforms for highly efficient supramolecular catalytic systems. This minireview provides an overview of recent advancements in supramolecular catalysis using various macrocycles, such as crown ethers, cyclodextrins,calixarenes, pillararenes, cucurbiturils, and other novel macrocycles.

The emerging applications of pillararene architectures in supramolecular catalysis

Over the last decade,numerous research efforts have been devoted to pillar[n]arenes since their debut.The popularity of pillararenes is a reflection of current research trend in supramolecular and macrocyclic chemistry in general.Among the vast applications(such as chemosensors,drug delivery,transmembrance channels,and separation)of pillararenes,their utilization in catalysis is a relatively less explored area.However,soaring attention has been paid by researchers in recent years and this field has seen gradual increasing publications.Therefore,in this review we will discuss progress in the emerging applications of pillararene architectures in catalysis based on various reaction genre including reduction,oxidation,coupling,decomposition and others.Furthermore,this review not only focuses on the pillararenes based current progress in catalysis,but also provides the signs for future development in this research field.

Precise Assembly and Supramolecular Catalysis of Tetragonal-and Trigonal-Elongated Octahedral Coordination Containers

The construction of distorted or irregular coordination polyhedrons with specific shapes and functionalities is highly challenging.Here,we demonstrate a viable strategy for attaining a severely distorted octahedral coordination container through precise geometrical manipulation of its nanocavity along the C_(3) or C4 axis to turn on its supramolecular catalysis.We constructed a tetragonal-elongated octahedral coordination container utilizing sulfonylcalix[4]arene-capped Co4 units as six vertexes and tetragonalelongated from single-arm lengthened 5-[(4-carboxybenzyl)amino]isophthalate(L)as eight triangular faces.Through the concomitant introduction of C_(3)-symmetry cyclohexane-1,3,5-tricarboxylate as a secondary linker to construct two equilateral triangular base surfaces and L to build six isosceles triangular side planes,trigonal antiprismatic architecture(trigonal-elongated octahedron)was attained.The elongated octahedral containers exhibited distinctly higher binding capacity and stronger binding affinity toward reaction substrates than that of regular octahedral containers;thus,promoting geometry-dependent catalytic reactivity.Our geometrical manipulation strategy provides a viable approach for the convenient design of metal–organic materials with specific functionalities.

Supramolecular Template-Assisted Catalytic[2+2]Photocycloaddition in Homogeneous Solution

Supramolecular interactions can help recognize and organize substrates around an enzyme’s active sites and subsequently assemble a new molecule in a certain way.Inspired by nature’s control of reactions,in this work we designed a template catalyst equipped with ditopic Au(I)–N-heterocyclic carbene(NHC)functional sites that direct olefin substrates into reactive geometries via collaboration of coordination-driven interactions.Notably,this catalyst enables the realization of catalytic[2+2]photocycloadditions with as low as 2 mol%catalyst loading in homogeneous solution and the delivery of a series of cyclobutane derivatives with excellent conversions and stereoselectivities.The success of gram-scale reactions further demonstrates the feasibility of this strategy,which lays a solid foundation for the large-scale preparation of cyclobutane derivatives in the future.

Boosting Enantioselectivity of Chiral Molecular Catalysts with Supramolecular Metal-Organic Cages

The search for new methodologies to tune and control the enantioselectivities of molecular catalysts is of great importance in the field of asymmetric catalysis.Here,we have illustrated that chiral molecular catalysts can be boosted from very low enantioselectivity to high enantioselectivity when installed in supramolecular metal-organic cages.By deliberately designing two optically active 1,1′-spirobiindane-7,7′-diol(SPINOL)-based dipyridine linkers,we synthesized two chiral Pd_(3)L_(6) cages featuring chiral dihydroxyl or dimethoxymethyl auxiliaries in the nanosized cavities.After treatment with metal ions,the cage featuring dihydroxyl groups could serve as efficient catalysts for asymmetric conjugate addition of styrylboronic acids toα,β-enones to produce γ,δ-unsaturated ketone and the asymmetric addition of diethylzinc to aldehydes to afford secondary alcohols.While the molecular SPINOL display very low enantioselectivity,restriction of its freedom in the cages led to 91−99.6% and 80−99.9% enantiomeric excess(ee)of products,respectively,which were increased by up to 35% and 78% ee,compared with the molecular control.Thus,our present work paves a way of utilizing supramolecular porous assemblies to manipulate the enantioselectivities of molecular catalysts.

IBX Oxidation of Benzenedimethanols in the Presence of Cucurbit[8]uril

The cucurbit[8]uril (Q[8]) mediated oxidation of benzenedimethanols with o-iodoxybenzoic acid (IBX) inaqueous solution has been investigated, and the results reveal the supramolecular catalysis depends on the electronicand geometric structure of substrate. In the cases of o-benzenedimethanol (1a) and m-benzenedimethanol (1b), theIBX oxidation could be obviously enhanced by the addition of Q[8] at different extent. There is no observation ofthe catalytic activity of Q[8] when p-benzenedimethanol (1c) is subjected to the IBX oxidation. The additionamount of Q[8] is discussed herein, and the addition of more than 10% mol catalyst cannot improve the oxidationmuch more. The investigation of host-guest interactions by isothermal titration calorimetry implies the supramolecularcatalysis is related to the formation of complexes between benzenedimethanols and cucurbit[8]uril.

Anion-π interactions:From concept to application

Anion-π interactions as a new member of supramolecular weak interactions are still in the young stage,but they already attract considerable attentions. Now the concerns are shifting from recognition to construction of functional systems. In this review, the anion-π functional systems especially anion-πcatalysis and self-assembly were highlighted and summarized together with several solid and recent examples of host-guest recognition. These applications suggest that the great potential of these new interactions.