Postsynthetic Covalent and Coordination Functionalization of Rhodium(II)-Based Metal–Organic Polyhedra

Abstract

Metal-organic polyhedra (MOPs) are ultra-small (typically 1 nm to 4 nm) porous coordination cages made from the self-assembly of metal ions and organic linkers and amenable to the chemical functionalization of its periphery; however, it has been challenging to implement post-synthetic functionalization due to their chemical instability. Herein, we report the use of coordination chemistries and covalent chemistries to post-synthetically functionalize the external surface of 2.5 nm stable Rh(II)based cuboctahedra through their Rh-Rh paddlewheel units or organic linkers, respectively. We demonstrate that 12 N-donor ligands, including amino acids, can be coordinated on the periphery of Rh-MOPs. We used this reactivity to introduce new functionalities (e.g. chirality) to the MOPs and to tune their hydrophilicity/hydrophobic character, which allowed us to modulate their solubility in diverse solvents such as dichloromethane and water. We also demonstrate that all 24 organic linkers can be postsynthetically functionalized with esters via covalent chemistry. In addition, we anticipate that these two types of post-synthetic reactions can be combined to yield doubly-functionalized Rh-MOPs, in which a total of 36 new functional molecules can be incorporated on their surfaces. Likewise, these chemistries could be synergistically combined to enable covalent functionalization of MOPs through new linkages such as ethers. We believe that both reported post-synthetic pathways can potentially be used to engineer Rh-MOPs as scaffolds for applications in delivery, sorption and catalysis.

On/off porosity switching and post-assembly modifications of Cu4L4 metal–organic polyhedra

“…We note that covalent PAM of Cu 2 paddlewheel MOPs are rare 17,26 and the crystal packing of modied MOPs is rarely investigated. 27 Indeed, the deliberate instalment of the exterior aldehyde groups in 1 enabled us to carry out Lewis-acid catalysed imine condensation. Heating a DMF-d 7 solution of 1 at 45 C in the presence of 0.1 equivalents of Sc(OTf) 3 (ref.…”

Protection strategies for directionally-controlled synthesis of previously inaccessible metal–organic polyhedra (MOPs): the cases of carboxylate- and amino-functionalised Rh(ii)-MOPs

“…The synthesis of this class of MOPs entails assembly of 1,3-benzenedicarboxylic acid (H2bdc) derivatives and Rh(II)-Rh(II) paddlewheels, in which the 5-position of the bdc derivative dictates the outer functionality of the MOP. 19 Accordingly, the synthesis of COOH-RhMOP requires use of 1,3,5-benzenetricarboxylic acid (H3btc) as the linker. However, as expected, reaction of Rh(II) with H3btc tends to form extended coordination networks instead of the desired COOH-RhMOP.…”

Stabilizing Metal–Organic Polyhedra (MOP): Issues and Strategies

“…Because water, and particularly moisture, is ubiquitous in all kinds of applications, such as storage, separation, and transportation, it is imperative to treat this criterion with the utmost importance. In general, MOFs constructed from polyhedral SBBs, for example, prototypal nanoballs [Cu 2 (bdc) 2 L 2 ] 12 (bdc=isophthalate; L=pyridine, substituted pyridine, MeOH), are extremely susceptible to water/moisture and undergo irreversible structural disintegration . In general, MOPs constructed from metal clusters are extremely labile to humidity, largely because of the reversible nature of labile metal–ligand bonds.…”

“…In general, MOFs constructed from polyhedralS BBs, for example, prototypal nanoballs [Cu 2 (bdc) 2 L 2 ] 12 (bdc = isophthalate; L = pyridine, substituted pyridine, MeOH), [62] are extremelys usceptible to water/moisture and undergo irreversible structural disintegration. [63] In general,M OPs constructed from metal clusters are extremely labile to humidity,l argely because of the reversible nature of labile metal-ligand bonds. This instability under humidity has considerably limited the applications of MOPs.…”