Supramolecular Catalysis And Structure Transformation Of Coordination Pd₄L₂ Cage

Supramolecular chemistry has developed at full speed due to the interdisciplinaryintrinsic characteristic in recent years.A vast number of samples revealed the potential applications of supramolecular hosts in the recognition,catalysis,diagnosis,and treatment of diseases.Among them,coordination self-assembly metal-organic cages have attracted tremendous attention due to esthetic structural diversity and potential applications.In this thesis,we use pyridinium salt functionalized semi-rigid coordination supramolecular cage Pd₄L₂ which has a large hydrophobic cavity and expanded windows to explore the potential application in the field of stimuli-responsive behavior and catalysis.The specific contents are as follows:1.A condition-controlled supramolecular catalysis has been described in this chapter.We report a Pd₄L₂-type molecular cage(1)catalyzed reactions of spiroepoxy naphthalenone(5)in water,where the selective formation of2-(hydroxymethyl)naphthalene-1,4-dione(6)via aerobic oxidation,or1-hydroxy-2-naphthaldehyde(7)via photo-induced rearrangement under N₂ have been accomplished.Encapsulation of four molecules of guest 5 within cage 1 has been confirmed by NMR and a final host-guest complex of 6?1 has also been determined by single-crystal X-Ray diffraction study.The catalytic cycle can be realized in the oxidation reaction,and the accelerating effect of the cavity is determined by the substrate inhibition experiment.While the photo-induced ring-opening isomerization from 5 to 7 is known,the appearance of charge-transfer absorption on(5)₄?1 allows low-power blue LEDs irradiation to promote this process.This approach promised a potential application for cage catalyzed oxidation and photo-isomerization reactions.2.An unexpected structure transformation from a known Pd₄L₂ cage(1)to Pd₆L₃(2)conjoined twin cage featuring two separate cavities caused by the guest reaction was revealed in the process of stabilization a highly reactive organic intermediate o-QMs(ortho-Quinone Methide)precursor G1(1-hydroxymethyl-2-naphthol).Confined G1molecules within the nanocavity undergo self-coupling dimerization reaction to form2,2'-dihydroxy-1,1'-dinaphthylmethane(G2)which then triggers the cage to twin-cage mitosis.The same conversion also proceeds,at a much faster rate,via the direct templation of G2,confirming the induced-fit transformation mechanism.Taken together all the above results and previous reports,we propose a plausible mechanism for this unique guest reaction-driven host transformation process.To the best of our knowledge,this host structure transformation stimulated by the guest reaction from a bigger cavity cage into two separate smaller cavities twin-cage,like the mitosis of cells,has never been observed before and shed light on some natural phenomena such as enzyme deactivation and allosteric protein regulation.3.Based on the conjoined molecular cage structure in the previous chapter,we propose a strategy to complete the similar stimuli-responsive structural transformation of semi-rigid molecular cage 1 through the synergism of multiple non-covalent interactions and guest geometry size effect.A series of bis(sulfonate)guests(2a-2d)with good hydrophilic groups were selected as the guest.The crystal structures of all the host-guest complexes were obtained,and the structural transformation of cage 1 was successfully induced.Moreover,the different binding modes in the solid phase were verified.Also,multiple non-covalent interactions between host-guest and guest-guest molecules were studied by theoretical calculation and IGM(Independent Gradient Model)analysis,and the feasibility of the collaborative strategy was further verified.In particular,the work of transforming a Pd₄L₂ cage into two Pd₆L₃ cages(3 and 4)with different topologies has not been reported,which enriches the content of structural transformation with stimulus-response.This strategy is expected to be applied in the design of stimulus responsive materials and the construction of new topologies.