Guest Induced Structural Transformations of Coordination Cages and their Role in Mediating Chemical Conversions

Abstract

Enzymes utilize several non-covalent interactions to perform catalytic reactions within small cavities. Coordination driven self-assembly has been found to be the simplest approach for constructing artificial enzyme analogues. The ability of the cages to efficiently catalyze reactions depends on the nature of cavities. Barrel-like metallacages with cylindrical architectures, and two open apertures have been found to act as ideal nanoreactors.1 The metal-ligand bond dynamicity often makes such cages stimuli-responsive, and the hosts may migrate to another architecture in the presence of different signals, for example, guest stimulus. Although guest-driven transformations are known in the literature, there is a dearth of applications in that field. My thesis presents guest-induced structural transformations of Pd(II) cages and explores their application. In the first part, I will discuss the synthesis of a molecular barrel that reversibly shuttles between a Pd6 and a multiple-fullerene encapsulated homologous Pd8 architecture in the presence and absence of fullerene (C60/C70) guests, respectively.2 Fullerenes are well-known photosensitizers; however they are ineffective in common organic solvents like acetonitrile due to insolubility. The encapsulation of multiple C70 molecules within acetonitrile-soluble barrels enables their photosensitizing properties to be utilized in such a solvent. In this regard, I will discuss oxidative transformations using a C70-complex under visible light.3 Next, I will demonstrate how such complexes can be utilized for carrying out ozonolysis-mimicking, ROS-mediated olefin oxidations under innocuous red light and ambient conditions.4 The last part of my presentation deals with guest-mediated transformations between isomeric forms of a water-soluble Pd6 host. I will demonstrate how the guest shape controls the geometry of the host. Furthermore, I will discuss how enzyme-like structural modulations of the cage assist the selective photo-dimerization of anthracene derivatives within its hydrophobic pocket in aqueous media.5

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