Azo-dimethylaminopyridine functionalized Ni(II)-Porphyrin as a Photoswitchable Nucleophilic Catalyst

Abstract

We present the synthesis and the photochemical and catalytic switching properties of an azopyridine as a photoswitchable ligand, covalently attached to a Ni(II)-porphyrin. Upon irradiation with 530 nm (green light), the azopyridine switches to the cis configuration and coordinates with the Ni2+ ion. Light of 435 nm (violet) isomerizes the ligand back to the trans configuration, which decoordinates for steric reasons. This so-called record player design has been used previously to switch the spin state of Ni2+ between singlet and triplet. We now use the coordination/decoordination process to switch the catalytic activity of the dimethylaminopyridine (DMAP) unit. DMAP is a known catalyst in the nitroaldol (Henry) reaction. Upon coordination to the Ni2+ ion, the basicity of the pyridine lone pair is attenuated and hence the catalytic activity is reduced. Decoordination restores the catalytic activity. The rate constants in the two switching states differ by a factor of 2.2, and the catalytic switching is reversible.

Solid-state photochromic arylazopyrazole-based transition metal complexes

“…On the other hand, specific designs are desired in metalbased molecular systems, which give additional advantages in modulating inherent physicochemical properties such as the electrocatalytic, magnetic, redox and biological behaviour of these complexes by light. Such complexes find applications in light-induced ligand-driven spin crossover complexes, [5][6][7] redox switches, 8,9 photoswitchable catalysts, [10][11][12] nonlinear optics, 13,14 logics and memories, 15 supramolecular chemistry, [16][17][18] etc. Indeed, phototunability can be introduced into transition metal complexes by incorporating different organic photochromes within the ligand frameworks.…”