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

Abstract

Herein we report that strategic use of protecting groups in coordination reactions enables directional inhibition that leads to synthesis of metal–organic polyhedra (MOPs) highly functionalized with carboxylic acid and amine groups.

Synthesis of Polycarboxylate Rhodium(II) Metal–Organic Polyhedra (MOPs) and their use as Building Blocks for Highly Connected Metal–Organic Frameworks (MOFs)

“…Next, we prepared a cuboctahedral MOP functionalized with 24 carboxylic acid groups, using a covalent route based on selective carboxylic group protection [23] . In it, the 24 edges of the cuboctahedron are functionalized with carboxylic acid groups using a protective synthetic strategy (Figure 1, bottom) [24] . We anticipated that the different number and location of carboxylic acid groups on the periphery of both Rh II ‐MOPs, which define a 12‐c cuboctahedral SBB and a 24‐c rhombicuboctahedral SBB, could be used to anticipate their structural outcome upon assembly with metallic secondary building units (SBUs).…”

Synthesis of Polycarboxylate Rhodium(II) Metal–Organic Polyhedra (MOPs) and their use as Building Blocks for Highly Connected Metal–Organic Frameworks (MOFs)

“…Next, we synthesized the 24‐c rhombicuboctahedral SBB via the covalent route. We began by preparing the Rh II ‐MOP with formula [Rh 2 (COOH‐bdc) 2 (H 2 O)(DMF)] 12 (hereafter named COOH‐RhMOP), following our own previously reported protocol entailing the use of stoichiometric protecting groups [24] . Crystals of COOH‐RhMOP suitable for SCXRD were obtained by slow diffusion of diethyl ether vapors into a DMF solution of this MOP.…”

“…[23] In it, the 24 edges of the cuboctahedron are functionalized with carboxylic acid groups using a protective synthetic strategy (Figure 1, bottom). [24] We anticipated that the different number and location of carboxylic acid groups on the periphery of both Rh II -MOPs, which define a 12-c cuboctahedral SBB and a 24-c rhombicuboctahedral SBB, could be used to anticipate their structural outcome upon assembly with metallic secondary building units (SBUs). To demonstrate the utility of these SBBs for constructing MOFs, we combined both a 12-c SBB with a paddle-wheel 4-c SBU, and a 24-c SBB with a triangular 3-c Cu II SBU to construct atomically-precise bimetallic MOFs having (4,12)-c ftw and (3,24)-c rht topologies, respectively.…”

“…We began by preparing the Rh II -MOP with formula [Rh 2 (COOH-bdc) 2 (H 2 O)(DMF)] 12 (hereafter named COOH-RhMOP), following our own previously reported protocol entailing the use of stoichiometric protecting groups. [24] Crystals of COOH-RhMOP suitable for SCXRD were obtained by slow diffusion of diethyl ether vapors into a DMF solution of this MOP. Formation of the cuboctahedral Rh II -MOP functionalized with 24 free carboxylic acid groups on its edges was confirmed by SCXRD.…”

Assembly and Covalent Cross-Linking of an Amine-Functionalised Metal-Organic Cage

“…Advances in this area have been made possible by fundamental studies into the compatibility of M 2 paddlewheel-based MOCs with various surface functionalities. These include coordinatively competitive groups such as hydroxyl ( Niu et al, 2015 ), carboxylate ( Albalad et al, 2019 ), carbonyl ( Bloch et al, 2020 ), and amine substituents ( Albalad et al, 2019 ; Schneider et al, 2020 ; Taggart et al, 2020 ) which can be installed onto the MOC exterior through ligand design or post-assembly modifications ( Zeng et al, 2020 ). Of these functionalities, amine moieties offer considerable synthetic versatility for post-assembly reactions, owing to their tunable basicity and nucleophilicity.…”