Self-assembled nanospheres with multiple endohedral binding sites pre-organize catalysts and substrates for highly efficient reactions

Abstract

Tuning reagent and catalyst concentrations is crucial in the development of efficient catalytic transformations. In enzyme-catalysed reactions the substrate is bound-often by multiple non-covalent interactions-in a well-defined pocket close to the active site of the enzyme; this pre-organization facilitates highly efficient transformations. Here we report an artificial system that co-encapsulates multiple catalysts and substrates within the confined space defined by an M12L24 nanosphere that contains 24 endohedral guanidinium-binding sites. Cooperative binding means that sulfonate guests are bound much more strongly than carboxylates. This difference has been used to fix gold-based catalysts firmly, with the remaining binding sites left to pre-organize substrates. This strategy was applied to a Au(I)-catalysed cyclization of acetylenic acid to enol lactone in which the pre-organization resulted in much higher reaction rates. We also found that the encapsulated sulfonate-containing Au(I) catalysts did not convert neutral (acid) substrates, and so could have potential in the development of substrate-selective catalysis and base-triggered on/off switching of catalysis.

Control over Electrochemical Water Oxidation Catalysis by Preorganization of Molecular Ruthenium Catalysts in Self‐Assembled Nanospheres

“…The addition of more than 12 equiv of guest (ratio sulfonate/guanidinium=1) results in precipitation. Diffusion‐ordered spectroscopy (DOSY) of nanosphere demonstrates a clear single band at log  D =−9.6 m 2  s −1 , consistent with previously reported M 12 L 24 nanospheres of similar size 15, 16. Signals originating from bound Ru(bda)(PySO 3 TBA) 2 guests display the same log  D values as the nanosphere (Supporting Information, Figure S4d), in contrast to the free Ru(bda)(PySO 3 TBA) 2 complex (log D =−8.8 m 2  s −1 ), supporting quantitative encapsulation.…”

“…Endohedral binding of Ru(bda)(PySO 3 − ) 2 inside the nanosphere (up to 12 equiv) was confirmed by 1 H NMR (Supporting Information, Figure S3) 16. The addition of more than 12 equiv of guest (ratio sulfonate/guanidinium=1) results in precipitation.…”

“…We anticipate that these supramolecular nanospheres are ideal to preorganize Ru(bda)Het 2 type WOCs, as these should strongly benefit from high local concentration if they follow the preferred I2M mechanism. Herein, we report the application of the guanidinium functionalized M 12 L 24 nanospheres (Figure 1 a,b) as nanoconcentrators for the supramolecular encapsulation of a homogenous WOC Ru(bda)(PySO 3 TBA) 2 (Figure 1 c, PySO 3 − =pyridine‐3‐sulfonate, TBA=tetra( n ‐butyl)ammonium) by strong binding (>10 5   m −1 )16 between the guanidinium and sulfonate moieties. Encapsulation of 12 Ru(bda)(PySO 3 − ) 2 catalysts within the nanosphere enhanced the solution concentration of 2.5×10 −5   m to a local concentration of 0.54  m , resulting in a two orders of magnitude increase in the rate of electrochemical water oxidation (0.93–125 s −1 ).…”

Self-assembly of a supramolecular hexagram and a supramolecular pentagram

“…To date, the multiple bipyridine-based one-step, pentagonal and hexagonal molecular assemblies have been reported in reasonable yields and could be shape-exchanged by using different counterions, such as Cl − and SO 4 2+ (refs 20, 21, 22). The prospect of using octahedral <tpy–M 2+ –tpy> connectivity is considered to simplify the structural design and further, to introduce functionality for potential applications in sensing44, magnetics45, biomedicine4647, photonics4849 and catalysis15305051.…”

Ultra-large supramolecular coordination cages composed of endohedral Archimedean and Platonic bodies

“…In the last decades, the former class of compound received significant scientific attention5678910111213141516. Preparative efforts were primarily directed towards the synthesis of new cage topologies with controllable inner cavities whose chemical, geometrical and electronic attributes can give rise to space-restricted properties that are exploitable in catalytic processes561718, for separations1920, drug delivery21 and sensing2223. Most prominent synthetic approaches to functional capsules generally take advantage of kinetically stable building units with defined ligand-accessible coordination sites which direct the self-assembly into hollow structures, for example, in the presence of pyridine or imine ligands56724.…”