Maximizing Coordination Capsule–Guest Polar Interactions in Apolar Solvents Reveals Significant Binding

Abstract

Guest encapsulation underpins the functional properties of self-assembled capsules yet identifying systems capable of strongly binding small organic molecules in solution remains ac hallenge.M ost coordination capsules rely on the hydrophobic effect to ensure effective solution-phase association. In contrast, we showthat using non-interacting anions in apolar solvents can maximizef avorable interactions between ac ationic Pd 2 L 4 host and charge-neutral guests resulting in ad ramatic increase in binding strength. With quinone-type guests,association constants in excess of 10 8 m À1 were observed, comparable to the highest previously recorded constant for am etallosupramolecular capsule.M odulation of optoelectronic properties of the guests was also observed, with encapsulation either changing or switching-on luminescence not present in the bulk phase.Supportinginformation, includings ynthesis, characterization data, X-ray analysis, and details of titration experiments, and the ORCID identification number(s) for the author(s) of this article can be found under http://dx. ZuschriftenWe thank the University of Edinburgh for aP rincipals Career Devepment Scholarship (D.P.A.).

Effector Regulated Catalytic Cyclization of Alkynoic Acids Using Pt2L4 Cages

“…The cage C Pt was anticipated to bind, in agreement to previously reported Pd 2 L 4 cages, [4a–c, 5c] different guests inside its cavity (S1) through hydrogen bonding of the inner eight pyridine protons to hydrogen bond acceptors (Figure 3A). As suitable effectors to boost the proto‐demetallation, we choose maleic acid, levulinic acid and acrylic acid (Figure 3D).…”

“…Binding of the effectors to the inner cavity of C Pt was supported by downfield shift of the inner pyridine protons in 1 H NMR and binding constants of all compounds were determined (Figure 3B, 3C, see SI4, compare analogues Pd 2 L 4 [4a–c, 5c] ). For catalytic applications we ensured that the overall acid concentration is kept the same in the individual experiments (by adjustment of the substrate concentration).…”

Structural Flexibility in Metal-Organic Cages

“…In 2010 Hooley and co-workers reported the cage [Pd 2 ( 9 ) 4 ] 4+ ( Figure 2B ) and its SCXRD structure with an encapsulated OTf − anion ( Liao et al, 2010 ). More recently, Lusby and co-workers have examined this cage for its catalytic potential ( Spicer et al, 2020 ) and were able to obtain SCXRD data of the PF 6 − salt with pentacenedione bound in the cavity ( August et al, 2016 ). Although relatively minor, there was a difference of 0.36 Å in the Pd···Pd distance between the cage SCXRD structures (11.85 and 12.21 Å), and the torsion angle between the core phenyl and terminal pyridyl rings were greater for the longer cage (12.5° on average compared to 5.1°).…”

High‐Throughput Computational Evaluation of Low Symmetry Pd2L4Cages to Aid in System Design**

“…[8][9][10][11][12] Wide-ranging applications for these cages have been investigated, including in drug delivery, [13][14][15] biomedicine, [16][17][18][19][20][21] catalysis, [22][23][24][25] and guest encapsulation/recognition. [26][27][28][29][30][31][32] To simplify the self-assembly process, most previous reports have focussed on high-symmetry systems derived from single, symmetrical ligands. However, it is expected that through the controlled introduction of asymmetry, cages could be designed with more intricate, anisotropic binding sites with specific shapes and functionalities.…”