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The employment of weak intermolecular interactions in supramolecular chemistry offers an alternative approach to project artificial chemical environments like the active sites of enzymes. Discrete molecular architectures with defined shapes and geometries have become a revolutionary field of research in recent years because of their intrinsic porosity and ease of synthesis using dynamic non-covalent/covalent interactions. Several porous molecular cages have been constructed from simple building blocks by self-assembly, which undergoes many self-correction processes to form the final architecture. These supramolecular systems have been developed to demonstrate numerous applications, such as guest stabilization, drug delivery, catalysis, smart materials, and many other related fields. In this respect, catalysis in confined nanospaces using such supramolecular cages has seen significant growth over the years. These porous discrete cages contain suitable apertures for easy intake of substrates and smooth release of products to exhibit exceptional catalytic efficacy. This review highlights recent advancements in catalytic activity influenced by the nanocavities of hydrogen-bonded cages, metal–ligand coordination cages, and dynamic or reversible covalently bonded organic cages in different solvent media. Synthetic strategies for these three types of supramolecular systems are discussed briefly and follow similar and simplistic approaches manifested by simple starting materials and benign conditions. These examples demonstrate the progress of various functionalized molecular cages for specific chemical transformations in aqueous and nonaqueous media. Finally, we discuss the enduring challenges related to porous cage compounds that need to be overcome for further developments in this field of work. [ABSTRACT FROM AUTHOR]

Numerous metalla‐supramolecular architectures have been designed using coordination‐driven self‐assembly, while the number of analogous organic architectures is still very limited. In this regard, mainly di‐, tri‐ and a few tetra‐aldehydes have been exploited as precursors in combination with appropriate di‐/tri‐amines to obtain the desired structures with limited complexities. We report here facile synthesis of two face‐directed tetrahedral organic cages (TC‐R and TC‐S) that were formed by [4+12] imine condensation of a new hexa‐aldehyde precursor with two enantiomers of 1,2‐diaminocyclohexane separately (CA‐R and CA‐S). The covalent imine cages are very large with an intrinsic porous cavity of ∼1250 Å3 and the faces of the cages consist of aromatic aldehyde units whereas each corner is occupied by three semi‐flexible diamine moieties. Palladium (PdNPs) nanoparticles (3.5±0.3 nm) were synthesized employing the cage TC‐R as a solid support via double‐solvent approach. Furthermore, the cage hosted PdNPs [Pd(0)@TC‐R‐A] exhibited efficient catalytic activity for selective homocoupling of aryl‐ and hetero‐aryl halides with high thermal stability and reusability. [ABSTRACT FROM AUTHOR]

Coordination‐driven self‐assembly of discrete molecular architectures of diverse shapes and sizes has been well studied in the last three decades. Use of dynamic imine bonds for designing analogous metal‐free architectures has become a growing challenge recently. This article reports an organic molecular barrel (OB4R) as a potential template for nucleation and stabilization of very tiny (<1.5 nm) Ag nanoparticles (AgNPs). Imine bond condensation of a rigid tetra‐aldehyde with a flexible diamine followed by imine‐bond reduction yielded the discrete tetragonal organic barrel (OB4R). The presence of a molecular pocket ornamented with eight diamine moieties gives the potential for encapsulation of silver(I). The organic barrel was finally used as a molecular vessel for the controlled nucleation of silver nanoparticles (AgNPs) with fine size tuning through binding of AgI ions in the confined space of the barrel followed by reduction. Transmission electron microscopy (TEM) analysis of the Ag0@OB4R composite revealed that the mean particle size is 1.44±0.16 nm. The composite material has approximately 52 wt % silver loading. The barrel‐supported ultrafine AgNPs [Ag0@OB4R] are found to be an efficient photocatalyst for facile Ullmann‐type aryl‐amination coupling of haloarenes at ambient temperature without using any additives. The catalyst was stable for several cycles of reuse without any agglomeration. The new composite Ag0@OB4R represents the first example of discrete organic barrel‐supported AgNPs employed as a photocatalyst in Ullmann‐type coupling reactions at room temperature. [ABSTRACT FROM AUTHOR]

A new strategy for the synthesis of a “cationic-cage” (CC-Ag) has been developed via metal–carbene (M–CNHC) bond formation followed by imine bond condensation. Reaction of a trigonal trisimidazolium salt H3L(PF6)3 functionalized with three flexible N-phenyl-aldehyde pendants with silver oxide yielded a trinuclear tricationic organometallic cage (OC-Ag). Subsequent treatment of the organometallic cage (OC-Ag) with 1,4-diaminobutane links the two tris–NHC ligands via imine bond condensation, which thus generates a 3D ‘cationic-cage’ (CC-Ag). Furthermore, post-synthetic replacement of the Ag(i) with Au(i) leading to the formation of CC-Au was achieved via trans-metalation, with the retention of the molecular architecture. [ABSTRACT FROM AUTHOR]

A spiropyran-decorated covalent organic cage (PC2) has been designed, employing dynamic imine chemistry followed by imine bond reduction. The molecule is capable of altering its color upon exposure to external stimuli such as heat and light. Construction of a 3D organic cage introduces a new piece to the system by swapping the closed form with the open form in the solid state with diverse color change. Moreover, this material has high chemical stability and is capable of reversible stimuli-responsive color change without any degradation for an extended period. [ABSTRACT FROM AUTHOR]

Two shape-persistent covalent cages (CC1r and CC2r) have been devised from triphenyl amine-based trialdehydes and cyclohexane diamine building blocks utilizing the dynamic imine chemistry followed by imine bond reduction. The cage compounds have been characterized by several spectroscopic techniques which suggest that CC1r and CC2r are [2+3] and [8+12] self-assembled architectures, respectively. These state-of-the-art molecules have a porous interior and stable aromatic backbone with multiple palladium binding sites to engineer the controlled synthesis and stabilization of ultrafine palladium nanoparticles (PdNPs). As-synthesized cage-embedded PdNPs have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and powder X-ray diffraction (PXRD). Inductively coupled plasma optical emission spectrometry reveals that Pd@CC1r and Pd@CC2r have 40 and 25 wt% palladium loading, respectively. On the basis of TEM analysis, it has been estimated that as small as ~1.8 nm PdNPs could be stabilized inside the CC1r, while larger CC2r could stabilize ~3.7 nm NPs. In contrast, reduction of palladium salts in the absence of the cages form structure less agglomerates. The well-dispersed cage-embedded NPs exhibit efficient catalytic performance in the cyanation of aryl halides under heterogeneous, additive-free condition. Moreover, these materials have excellent stability and recyclability without any agglomeration of PdNPs after several cycles. [ABSTRACT FROM AUTHOR]

An unprecedented, 22-valence-electron triple-decker sandwich complex [(Cp*Mo)2{μ-η6:η6-B4H4Ru2(CO)6}], 2, has been prepared. In an effort to generate analogous triple-deckers with group 6 metal carbonyl fragments in the middle deck, we have isolated [(Cp*MoCO)2(μ-H)2B4H4], 3, that provides the first direct evidence for the missing link between [(Cp*MoCl)2B3H7] and [(Cp*Mo)2B5H9] clusters. [ABSTRACT FROM AUTHOR]

Cage compounds, Enantiomeric cages, Heterogeneous catalysis, Palladium, Self-assembly Keywords: Cage compounds; Enantiomeric cages; Heterogeneous catalysis; Palladium; Self-assembly EN Cage compounds Enantiomeric cages Heterogeneous catalysis Palladium Self-assembly 1 1 1 03/11/22 20220309 NES 220309 B The Cover Feature b shows the formation of two face-directed truncated tetrahedral enantiopure organic cages by employing dynamic imine condensation reactions of a hexa-aldehyde precursor with I trans i -oriented enantiopure diamines separately. Cover Feature: Face-Directed Tetrahedral Organic Cage Anchored Palladium Nanoparticles for Selective Homocoupling Reactions (Eur. J. Inorg. [Extracted from the article]

Morphology of nanomaterials has a strong impact on their chemical/physical properties, and controlled synthesis of such materials with desirable morphology is a major challenge. This article presents the role of a building block in the morphology of organic cage particles. In this context, three organic cages ( A3X2, B3X2, and C3X2) were devised from triphenylamine-based dialdehydes ( A- C) and a flexible triamine ( X) by utilizing dynamic imine chemistry. All of the synthesized cages were characterized by various spectroscopic techniques, which suggested the formation of [3+2] assembled architectures. Though the cages are isostructural, structural variation in the aldehyde building blocks imparted by the incorporation of phenyl moieties into the triphenylamine core produces morphologically diverse cage particles, as indicated by SEM. The synthesized cages were found to be fluorescent; the reduced analogue of cage A3X2 ( A3X2 r) was tested to explore its use as a chemosensor for the detection of nitroaromatic explosives. The experimental findings suggest high selectivity and sensitivity of A3X2 r towards picric acid (PA) among the various nitroaromatics tested. A theoretical investigation of fluorescence quenching suggested that formation of a ground-state charge-transfer complex with a resonance energy-transfer (RET) process could be the main reason behind such selectivity of the cage towards PA. [ABSTRACT FROM AUTHOR]

The photolysis of [M2(CO)10] (M=Re or Mn) with BH3⋅thf at room temperature yields arachno -1 and 2, [(CO)8M2B2H6] ( 1: M =Re, 2: M =Mn). Both the compounds show a butterfly structure with seven skeletal electron pairs and 42 valence electrons. This result presents a new method for general access to low-boron-content metal-boron compounds without the cyclopentadienyl ligand at the metal centers. This new synthetic route is superior to the existing procedures because it avoids the use of [LiBH4] and metal polychlorides, for which the synthesis is very tedious. Compound 1 catalyzes the cyclotrimerization of a series of internal and terminal alkynes to yield mixtures of 1,3,5- and 1,2,4-substituted benzenes. The reactivity of 1 with alkynes demonstrates for the first time that the introduction of the [B2H6] moiety into the [Re2(CO)10] framework significantly enhances the catalytic activity. Note that [Re2(CO)10] catalyzes the same set of alkynes under harsh conditions over a prolonged period of time. Quantum-chemical calculations using DFT methods are applied to afford further insight into the electronic structure, stability, and bonding of 1 and 2. All the compounds are characterized by IR and 1H, 11B, and 13C NMR spectroscopy, and the geometry of 1 is established unambiguously through crystallographic analysis. [ABSTRACT FROM AUTHOR]

Thermolysis of an in situ generated intermediate [(Cp*Ta)2(BH3)2Cl2], 1 generated from the reaction of [Cp*TaCl4], (Cp* = η5-C5Me5) and [LiBH4·thf], in presence of [Ru3(CO)12] yielded pileo-[Cp*TaCl(μ-Cl)-B2H4Ru3(CO)8], 2 having two electrons fewer than seven pairs required for the observed square pyramidal geometry. Cluster 2 is the first example of an unsaturated cluster comprising early and late transition metals in a square pyramid core. This reaction also yielded [(Cp*Ta)2(B2H6)(B2H4Cl2)], 3 as a by-product. In addition, the reaction of [Cp*MoCl4] (Cp* = η5-C5Me5) with [LiBH4.thf] in presence of excess [MeI] at mild condition led to the isolation of periodinated dimolybdatetraborane [(Cp*Mo)2B4H3I5], 4 that hints a possible existence of [(Cp*Mo)2B4H8]. After the isolation of periodinated 4, we extended this chemistry towards the late transition metallaborane [(Cp*Rh)3B4H4], 5 using [PtBr2] as brominating source. Although all the attempts to isolate perbrominated rhodaborane failed, we have isolated partially brominated rhodaborane clusters [(Cp*Rh)3(BH)-(BBr)3], 6 and [(Cp*Rh)3(BH)3(BBr)], 7. All the compounds were characterized by IR and 1H, 11B and 13C NMR spectroscopy in solution, and the solid-state structures of 2, 4 and 6 were established by crystallographic analysis. [ABSTRACT FROM AUTHOR]

The reaction of metal carbonyl compounds with group 6 and 8 metallaboranes led us to report the synthesis and structural characterization of several novel mixed-metal chalcogenide tetrahedral clusters. Thermolysis of arachno-[(Cp*RuCO)2B2H6], 1, and [Os3(CO)12] in the presence of 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Os3(CO)9}S], 3, and [Cp*Ru(μ-H){Os3(CO)11}], 4. In a similar fashion, the reaction of [(Cp*Mo)2B5H9], 2, with [Ru3(CO)12] and 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Ru3(CO)9}S], 5, and conjuncto-[(Cp*Mo)2B5H8(μ-H){Ru3(CO)9}S], 6. Both compounds 3 and 5 can be described as 50-cve (cluster valence electron) mixed-metal chalcogenide clusters, in which a sulfur atom replaces one of the vertices of the tetrahedral core. Compounds 3 and 5 possess a [M3S] tetrahedral core, in which the sulfur is attached to an exo-metal fragment, unique in the [M3S] metal chalcogenide tetrahedral arrangements. All the compounds have been characterized by mass spectrometry, IR, and 1H, 11B and 13C NMR spectroscopy in solution, and the solid state structures were unequivocally established by crystallographic analysis of compounds 3, 5 and 6. [ABSTRACT FROM AUTHOR]