Tetra-porphyrin molecular tweezers: two binding sites linked via a polycyclic scaffold and rotating phenyl diimide core

Abstract

The synthesis of a tetra-porphyrin molecular tweezer with two binding sites is described. The bis-porphyrin binding sites are aligned by a polycyclic scaffold and linked via a freely rotating phenyl diimide core. Synthesis was achieved using a divergent approach employing a novel coupling method for linking two polycyclic units to construct the core, with a copper(ii)-mediated phenyl boronic acid coupling found to extend to our polycyclic imide derivative. We expect this chemistry to be a powerful tool in accessing functional polycyclic supramolecular architectures in applications where north/south reactivity and/or directional interactions between modules are important. Porphyrin receptor functionalisation was undertaken last, by a four-fold ACE coupling reaction on the tetra-epoxide derivative of the core.

A Tetra‐Porphyrin Host Exhibiting Interannular Cooperativity

“…This would lead to a combination of optimised and non‐optimised binding sites within the tetra‐porphyrin tweezer, or a dynamic situation in which both binding sites compete for optimal complexation, which on average is never achieved by either binding site. Although no significant distortion was observed in the molecular model for tetra‐porphyrin⋅(DABCO) 2 , even a slight mismatch in geometry between the host with two included guests would likely result in negative cooperativity.…”

“…The freebase tetra-porphyrin tweezer 1 [8] was metallated with Zn II under standard conditions [9] (Supporting Information, sectionS1) to afford compound 2 (Figure 2) as confirmed by MS and NMR. MALDI-TOF MS of porphyrin compounds is reported to afford the radicalm olecular ion peak, [M]C + ,w ithoutt he uptake of H + or Na + .…”

“…This example significantly contributes to the small number of host systems reported in the literature to exhibit this type of cooperativity. The synthesis of the tetra‐porphyrin host 1 with two homotropic binding sites (Figure ) was recently reported by us, along with molecular modelling of the host–guest chemistry of Zn II ‐metallated 2 with the diamino ligand 1,4‐diazabicyclo[2.2.2]octane (DABCO). We reasoned that rigid polycyclic backbones separating four porphyrin receptors, connected by a centrally located phenyl diimide structural unit, would confer the host with interannular cooperativity between the two remote, but interdependent, bis‐porphyrin binding sites.…”

The Solid-State Structures of Cyclic NH Carboximides

“…One of these, compound 287 [240] (Figure 84) shows no hydrogen bonding probably due to the high degree of steric hindrance. The other, compound 288 [241], exhibits linear chains with the imide NH hydrogen equally bonded to both bridging oxygens, resulting in designation C 2 1 (6)[R 2 1 (6)].…”

Spectrophotometric Study of Bridging N-Donor Ligand-Induced Supramolecular Assembly of Conjugated Zn-Trisporphyrin with a Triphenylamine Core

“…Various strategies, such as ionic self-assembly [ 20 ], re-precipitation methods [ 21 ], ligand coordination [ 22 ], coordination polymerization [ 23 ], and surfactant assistance by either surfactants or amphipathic molecules [ 24 ], have been utilized to form porphyrin aggregates. However, covalent metalloporphyrins, such as dendrimers, double-stranded conjugated ladder porphyrins, porphyrin arrays, double-decker porphyrins, cyclic porphyrins, and tetra-porphyrins, readily self-assemble without any external stimuli and form a larger aggregation of porphyrin arrays in solution [ 25 , 26 , 27 , 28 , 29 , 30 ]. Among the various supramolecular architectures, tris-metalloporphyrins assembled with N -donor ligands, such as 1,4-diazabicyclo[2.2.2]octane (DABCO), form sandwich-type coordination cages that are attractive for supramolecular catalysis applications and artificial molecular receptor synthesis [ 31 , 32 , 33 ].…”