A Family of Externally-Functionalised Coordination Cages

Abstract

New synthetic routes are presented to derivatives of a (known) M8L12 cubic coordination cage in which a range of different substituents are attached at the C4 position of the pyridyl rings at either end of the bis(pyrazolyl-pyridine) bridging ligands. The substituents are (i) –CN groups (new ligand LCN), (ii) –CH2OCH2–CCH (containing a terminal alkyne) groups (new ligand LCC); and (iii) –(CH2OCH2)3CH2OMe (tri-ethyleneglycol monomethyl ether) groups (new ligand LPEG). The resulting functionalised ligands combine with M2+ ions (particularly Co2+, Ni2+, Cd2+) to give isostructural [M8L12]16+ cage cores bearing 24 external functional groups; the cages based on LCN (with M2+ = Cd2+) and LCC (with M2+ = Ni2+) have been crystallographically characterised. The value of these is twofold: (i) exterior nitrile or alkene substituents can provide a basis for further synthetic opportunities via ‘Click’ reactions allowing in principle a diverse range of functionalisation of the cage exterior surface; (ii) the exterior –(CH2OCH2)3CH2OMe groups substantially increase cage solubility in both water and in organic solvents, allowing binding constants of cavity-binding guests to be measured under an increased range of conditions.

Disentangling contributions to guest binding inside a coordination cage host: analysis of a set of isomeric guests with differing polarities

“…This necessitates use of the cage H PEG with the same octanuclear core structure and cavity as H and H w but bearing more solubilising substituents. 20 It was immediately apparent that a far larger excess of the DCB guests was required to be able to observe new signals for the cage/guest complex ( Fig. 6 ).…”

“… 12 The cage H PEG similarly has a set of 24 tri-ethyleneglycol monomethyl ether substituents, which confer much improved solubility compared to H in both water and organic solvents such as CH 2 Cl 2 because of the flexibility of the PEG chains which allows them to adopt both polar or non-polar conformations as required. 20 The structures of these are summarised in Fig. 1 .…”

Inside or outside the box? Effect of substrate location on coordination-cage based catalysis

“…Control experiments with no H w present, but using instead 0.1 mM CoCl 2 or 0.1 mM L peg (the PEG-ylated version of the ligand used in the cage, which is water soluble), 11 showed no difference in the rate of DAF hydrolysis compared to the background reaction (the ‘no H w ’ line in Fig. 2a ), confirming that the assembled cage – with its combination of hydrophobic surface and high positive charge – is required to achieve the catalytic effect.…”

“…2b) to obtain a second-order reaction rate constant of 1.0 × 10 −2 M −1 s −1 , which is comparable to what we observed for external-surface catalysed hydrolysis of some phospho-triester based insecticides under similar conditions. 8 Control experiments with no H w present, but using instead 0.1 mM CoCl 2 or 0.1 mM L peg (the PEG-ylated version of the ligand used in the cage, which is water soluble), 11 showed no difference in the rate of DAF hydrolysis compared to the background reaction (the 'no H w ' line in Fig. 2a), confirming that the assembled cagewith its combination of hydrophobic surface and high positive chargeis required to achieve the catalytic effect.…”

Spin Crossover Induced By Changing the Identity Of the Secondary Metal Species In A Face-Centred FeII8NiII6 Cubic Cage

“…The design and assembly of discrete polynuclear materials that incorporate an internal cavity remains an active goal in metallo-supramolecular chemistry. 1,2 Such molecules have shown potential in a range of future applications which take advantage of host-guest interactions, including sensing, 3-6 catalysis, [7][8][9][10] drug encapulation 11,12 and the selective uptake of guest molecules [13][14][15][16] . In addition, there has been continuing interest in the construction of new cage systems as photoactive [17][18][19] and magnetic materials, 20 with the latter including spin crossover (SCO) systems.…”