Steric Hindrance in Metal Coordination Drives the Separation of Pyridine Regioisomers Using Rhodium(II)‐Based Metal–Organic Polyhedra

Abstract

The physicochemical similarity of isomers makes their chemical separation through conventional techniques energy intensive.H erein, we report that, instead of using traditional encapsulation-driven processes,s teric hindrance in metal coordination on the outer surface of Rh II -based metalorganic polyhedra (Rh-MOPs) can be used to separate pyridine-based regioisomers via liquid-liquid extraction. Through molecular dynamics simulations and wet experiments,w ed iscovered that the capacity of pyridines to coordinatively bind to Rh-MOPs is determined by the positions of the pyridine substituents relative to the pyridine nitrogen and is influenced by steric hindrance.T hus,w e exploited the differential solubility of bound and non-bound pyridine regioisomers to engineer liquid-liquid self-sorting systems.A saproof of concept, we separated four different equimolecular mixtures of regioisomers,including amixture of the industrially relevant compounds 2-chloropyridine and 3chloropyridine,i solating highly pure compounds in all cases.

Surface chemistry of metal–organic polyhedra

“…Therefore, molecules can be separated according to their capacity to coordinate to Rh( ii )-based MOPs, which is influenced by the basicity and steric hindrance of their constituent coordinating heteroatoms. 61 This approach could prove highly valuable for diverse applications, including currently low-yielding catalytic reactions that are limited by solubility restraints of the reagents and/or catalysts. Thus, we believe that further refinement of this coordinative solubilising methodology will enable researchers to surpass the solubility constraints in homogeneous organic chemistry.…”

Influence of the Surface Chemistry of Metal–Organic Polyhedra in Their Assembly into Ultrathin Films for Gas Separation

“…Previous studies have shown that cuboctahedral rhodium-based MOPs (Rh-MOPs), which are assembled from 1,3-benzenedicarboxylate and dirhodium paddlewheels, offer very interesting possibilities for separation processes. The cavity of Rh-MOPs can be used for selective entrapment of gases/molecules, whereas their reactive surface can be used to coordinatively attach selected molecules . The chemical robustness of Rh-MOPs enables them to sustain their performance even when exposed to harsh conditions, such as exposure to water, acids, or competing coordinating ligands .…”

“…The cavity of Rh-MOPs can be used for selective entrapment of gases/molecules, 12 whereas their reactive surface can be used to coordinatively attach selected molecules. 13 The chemical robustness of Rh-MOPs enables them to sustain their performance even when exposed to harsh conditions, such as exposure to water, acids, or competing coordinating ligands. 14 In addition, the surface of Rh-MOPs can be functionalized to modulate their solubility from water to polar/non-polar organic solvents, which increases their processability and enables using them under homogeneous conditions or shaping them into functional macroscopic objects.…”