Anthracene crude oil is a common source of phenanthrene for its industrial use. The isolation of phenanthrene from this source is a challenging task due to very similar physical properties to its isomer anthracene. We report here a water-soluble Pd(II) molecular boat (MB1) with unusual structural topology that was obtained by assembling a flexible tetrapyridyl donor (L) with a cis-Pd(II) acceptor. The flexible backbone of the boat enabled it to breathe in the presence of a guest optimizing the fit within the cavity. The boat binds phenanthrene more strongly than anthracene, which enabled separation of phenanthrene with an >98% purity from an equimolar mixture of the two isomers using MB1 as an extracting agent. MB1 represents a unique example of a coordination receptor suitable for selective aqueous extraction of phenanthrene from anthracene with reusability of several cycles.
Two tetragonal molecular barrels TB1 and TB2 were successfully synthesized by coordination-driven self-assembly of a tetrapyridyl donor ( L ) of the thiazolo[5,4- d ]thiazole backbone with cis -blocked 90° Pd(II) and Pt(II) acceptors, respectively. The single-crystal structure analysis of TB1 revealed the formation of a two-face opened tetragonal Pd 8 molecular barrel architecture. In contrast, the isostructural Pt(II) barrel ( TB2 ) is water-soluble. The large confined hydrophobic molecular cavity including wide open windows and good water solubility of the barrel TB2 made it a potential molecular container for the encapsulation of guests with different sizes and properties. This has been exploited to encapsulate and stabilize the open form of a photochromic molecule ( G2 ) in water, while the same photochromic molecule exists exclusively in a cyclic zwitterionic form in aqueous medium in the absence of the barrel TB2 . This cyclic form is very stable in water and does not go back to its parent open form under common external stimuli. Surprisingly, reverse switching of the cyclic form to a colored hydrophobic open form was also possible instantly in water upon addition of the solid barrel TB2 into an aqueous solution of G2 . Such a fast reverse isomerization of an irreversible process in aqueous medium by utilizing host–guest interaction of the barrel TB2 and the guest G2 is interesting. The barrel TB2 was also capable of encapsulating the water-insoluble radical initiator G1 in aqueous medium.
Coordination-driven self-assembly of discrete molecular architectures of diverses hapesa nd sizes has been well studied in the last three decades. Use of dynamic imine bonds ford esigning analogous metal-free architectures has become ag rowing challenge recently.T his article reports an organic molecular barrel (OB4 R)a sapotential templatef or nucleation and stabilization of very tiny (< 1.5 nm) Ag nanoparticles (AgNPs). Imine bond condensation of ar igid tetraaldehyde with af lexible diamine followed by imine-bond reduction yielded the discrete tetragonal organic barrel (OB4 R). The presence of am olecular pocket ornamented with eight diamine moieties gives the potential for encapsulation of silver(I). The organic barrelw as finally used as amolecular vesself or the controlled nucleation of silver nanopar-ticles (AgNPs) with fine size tuning through bindingo fA g I ions in the confined space of the barrel followed by reduction. Transmission electronm icroscopy (TEM) analysiso ft he Ag 0 @OB4 R composite revealed that the mean particles ize is 1.44 AE 0.16 nm. The composite materialh as approximately 52 wt %s ilver loading.T he barrel-supported ultrafine AgNPs [Ag 0 @OB4 R ]a re found to be an efficient photocatalystf or facile Ullmann-type aryl-amination coupling of haloarenes at ambient temperature without using anya dditives. The catalyst was stable fors everal cycles of reuse without any agglomeration. The new composite Ag 0 @OB4 R represents the first example of discrete organic barrel-supported AgNPs employed as ap hotocatalyst in Ullmann-typec oupling reactions at room temperature.
Supramolecular architectures have flowered over the past few decades as an inventive class of functional materials for various applications. Discrete porous molecular cages are anticipated to be potential supramolecular catalysts that mimic enzyme-like catalytic activities. In this context, dynamic covalent chemistry (DCC)-driven organic cages received an enormous research interest due to the easy engineering of these porous cages with desired shapes, sizes, and functionalities. Herein, we have highlighted the role of DCC-driven stable porous cages as catalysts where catalysis occurs via the activation of the encapsulated substrates. As a result, in many cases these hosts result in better yields and stereoselectivity compared to conventional reactions without cages. This perspective presents the use of dynamic covalent bond-driven organic cages as efficient supramolecular catalysts under both homogeneous and heterogeneous reaction conditions. Specifically, the implementation of imine/amine organic cages as solid supports for ultrafine metal nanocatalysts is briefly focused on. Furthermore, various aspects of postsynthetically modified stable organic cages as efficient supramolecular hosts in different organic transformations are emphasized. Overall, we have critically analyzed the potential of porous organic cages as suitable platforms for organic transformations and for generating catalytically active metal nanoparticles.
A two-dimensional molecular square (MC) was obtained by the self-assembly of a bis(tetrazole) linker, 4,4′-bis(1H-tetrazol-5-yl)-1,1′-biphenyl (H2 L 1 ), with a square-planar metal acceptor M [M = (tmeda)Pd(NO3)2, where tmeda = N,N,N′,N′-tetramethylethane-1,2-diamine] in dimethyl sulfoxide (DMSO) followed by crystallization. The uncommon 2,3-binding mode through N atoms of the tetrazole rings in this assembly leads to the formation of an octanuclear molecular square. The molecular square MC [Pd8(L 1 )4(NO3)8] is unstable in DMSO and slowly converts to a dynamic mixture of a 3D tetrahedral cage T1 [Pd12(L 1 )6(NO3)12] and the macrocycle MC. A tetrahedral cage (T1) is formed by the usual 1,3-binding mode of the tetrazole rings. However, self-assembly of the T1 [Pd12(L 1 )6(PF6)12] was possible to access in the pure form in a less polar solvent like acetonitrile. The pure T1 [Pd12(L 1 )6(PF6)12] also converts to a mixture of T1 and MC in DMSO. Interestingly, when a tris(tetrazole) linker, tris(4-(1H-tetrazol-5-yl)phenyl)amine (H3 L 2 ), was treated with the acceptor M, it produced a tetrahedral nanocage T2 [Pd12(L 2 )4(NO3)12] through 1,3-binding mode of the tetrazole rings without any trace of an octahedral cage through 2,3-binding mode of the tetrazole moieties.
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