The research on chiral recognition and selection is not only fundamental in deciding the mystery of homochirality, but also informative in terms of substrate recognition in biological processes and asymmetric catalysis. We report an enantiomeric pair of phosphonium salts having chiral (R and S) amino substituents that are utilized towards the enantioselective recognition of a variety of chiral compounds having functional groups, such as carboxylic acid, amine, and alcohol. These simple phosphonium salts are found to exhibit a high enantiomeric discrimination for 1‐cyclohexylethylamine (CY). A remarkable guest selectivity (ξ) value of 5.3×108 is achieved for the enantiomer of R‐CY over S‐CY by using the R‐isomer of the phosphonium salt. Such high binding selectivities and discrimination capabilities is attributed to multiple non‐covalent interactions between the host and guest molecules as inferred from the DFT optimized structures of the host–guest pairs.

The design of porous materials for the recognition of multiple hydrocarbons is highly desirable for the energy‐efficient separation and recognition of chemical feedstock. Herein, three new iso‐structural porous discrete metal–organic cages of formula {[Pd3(NiPr)3PO]4(R‐AN)6} (R‐AN=anilate linkers) for the selective recognition of substituted aromatic hydrocarbons are reported. The tetrahedral cages 1, 2, and 3 containing anilate, chloranilate, and bromanilate linkers exhibited selective encapsulation of mesitylene, o‐xylene, and p‐xylene, respectively, over other analogous aromatic hydrocarbons. These selective encapsulations were driven by the variations in the portal diameters present at each of these cages and their interactions with the hydrocarbon guests. These observations are supported by mass spectrometry, NMR studies, and theoretical binding‐energy calculations.

The chemistry of the imido‐anions of the main group elements has been studied for more than three decades. The imido (NR)− group is isoelectronic to the oxo (=O) group and can coordinate with metal ions through its lone pairs of electrons. The polyimido‐P(V) anions are well explored as they resemble the phosphorus oxo moieties such as H3PO4, H2PO4−, HPO42− and PO43− species. These imido anions are typically generated using strong main group organometallic reagents such as nBuLi, Et2Zn, Me3Al and nBu2Mg, etc. As a result, their coordination chemistry has been restricted to reactions in anhydrous aprotic solvents for a few main group metal ions. This account presents our findings on using certain soft transition metal such Ag(I) and Pd (II) for isolating these imido‐P(V) anions as their corresponding self‐assembled clusters and cages. Using the various salts of Ag(I) ions in reaction with 2‐pyridyl (2Py) functionalized phosphonium salts and phosphoric triamides, we obtained the mono‐ and dianionic form of these imido ligands {[P(N2Py)2(NH2Py)2]−, [P(N2Py)2(NH2Py)]−, [PO(N2Py)(NH2Py)2]2−} and derived interesting examples of tri, penta, hepta and octanuclear Ag(I) clusters. Interestingly, by using the salts of Pd (II) ions, the elusive imido‐phosphate trianions of the type [(RN)3PO]3− (R=tBu, cHex, iPr) were generated in a facile one pot reaction as their corresponding tri‐ and hexanuclear clusters of the type {Pd3[(NR)3PO](OAc)3}n (n=1 or 2). These trianions acts as a cis‐coordinated hexadentate ligand for a trinuclear Pd (II) cluster and serve as the polyhedral building units for constructing hitherto unknown family of neutral cages in tetrahedral {Pd3[(NiPr)3PO]4(L)6} and cubic {Pd3[(NiPr)3PO]8(L)12} structures in the presence of suitable linker ligands (L2−). These cages show interesting host‐guest chemistry and post‐assembly reactions. Remarkably, by employing chiral tris(imido)phosphate trianions, enantiopure chiral cages of the type [(Pd3X*)4(L)6], ([X*]3−=RRR‐ or SSS‐[PO(N(*CH(CH3)Ph)3]3−), were synthesized and used for the chiral‐recognition and enantio‐separation of small racemic guest molecules. Some of these chiral cages were also shown to exhibit polyradical framework structures. In future, these and other similar types of cages are envisioned as potential molecular vessels for performing the reactions in their confined environment. The enantiomeric cages can be probed for asymmetric catalysis and the separation of a range of small chiral molecules.

The encapsulation of icosahedral closo-dicarbadodecaborane (o-, m-, and p-carboranes, Cb) as guest molecules at the intrinsic cavities of the three isostructural tetrahedral cages [{Pd3(NiPr)3PO}4(Cl-AN)6] (1), [{Pd3(NiPr)3PO}4(Br-AN)6] (2), and [{Pd3(NiPr)3PO}4(H-AN)6] (3) was studied. The formation of definite host–guest assemblies was probed with mass spectrometry, IR, and NMR spectral analysis. 2D DOSY 1H NMR of the Cb⊂Cage systems showed similar diffusion coefficient (D) values for the host and guest species, signifying the encapsulation of these guests inside the cage assemblies. The hydrodynamic radius (R H) derived from the D values of the host and guest species further confirmed the encapsulation of the Cb isomers at the cage pockets. The single-molecule energy optimization of the host–guest assemblies indicated the preferential binding of o-Cb as a guest inside the cages (1–3). The stabilization of these Cb guests inside these cages was further attributed to various possible nonclassical C–H···X-type interactions.

A primary criterion for the design of polyhedral metal− organic cages is the requirement of geometrically matched pairs of metal ions and ligand moieties. However, understanding the pathway it takes to reach the final polyhedral structure can provide more insights into the self-assembly process and improved design strategies. In this regard, we report two neutral tetrahedral cages with the formulas {[Pd 3 (N i Pr) 3 PO] 4 (L 1 ) 6 } (1-TD) and {[Pd 3 (N i Pr) 3 PO] 4 (L 2 ) 6 } (2-TD) s t a r t i n g f r o m t h e a c e t a t e -b r i d g e d c l u s t e r). When subtle variations in the reaction conditions w e r e m a d e , t w o n e w t e t r a m e r i c P d 1 2 a s s e m b l i e s , { [ P d 3 ( N i P r) 2 (OAc) 4 (OMe) 4 } (2-TM), were obtained from the same precursors. Detailed investigations using NMR, mass spectrometry, X-ray crystallography, and computational studies indicate that the macrocyclic complexes 1-TM and 2-TM are the reaction intermediates involved in the formation of the tetrahedral cages 1-TD and 2-TD, respectively. Moreover, the tetrahedral cages 1-TD and 2-TD exhibited intrinsic cavities of volume ∼85 Å 3 . Guest encapsulation studies revealed that the cage 1-TD can encapsulate a wide range of guest molecules such as CH 2 Cl 2 , CHCl 3 , CCl 4 , C 6 H 6 , and C 6 H 5 F. Interestingly, 1-TD was shown to exhibit a preferential binding of C 6 H 5 F and C 6 H 6 over other halogenated guest molecules, as determined from NMR titrations and computational studies.