Quinone-hydroquinone Based Late Transition Metal Complexes in Hypoxic Activation and Catalysis

Kumar, Alok (2014) Quinone-hydroquinone Based Late Transition Metal Complexes in Hypoxic Activation and Catalysis. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

We have presented here well characterized, easy to synthesize air stable quinone-hydroquinone (Q-H2Q) based ligands 2,3-bis(3,5-dimethyl-1H-pyrazol-1-yl)benzene-1,4-diol (H2L1) and 2,3-bis(3,5-dimethyl-1H-pyrazol-1-yl)cyclohexa-2,5-diene-1,4-dione (L2) and used them to synthesize four metal complexes using late transitions metal ions, PdII and PtII. All the complexes has been well characterized using various analytical techniques including single crystal X-ray crystallography for 1 and 2. The quinone ligand L2 shows good activity in hypoxia for MCF-7 cell line with an IC50 of 62(1) M as compared to a normoxic dose of 185(3) M for the same cell line. The metal complexes other than the PtII complex shows decrease in activity in presence of metal ions although the Q-HQ/H2Q redox potential shifts closer to zero (-0.25 V) from a more negative potential of -0.56 V with good reversibility. The quick hydrolysis of the complexes may be responsible for their poor activity due to unwanted reactions in solution leading to binding or deactivation by small molecules. However, more detailed studies are required to understand structure-activity co-relation better. The rich history of PdII in catalysis led us to probe the activity of the PdII-complex 1 in Suzuki-Miyaura cross coupling and nitroarene reduction. 1 shows promising activity towards Suzuki Miyaura cross coupling reactions of aryl halides with phenylboronic acids at room temperature and is also efficient in selective reduction of nitro arenes in presence of other functionalities like nitriles. The amount of catalyst required is low (0.25 mol%) and moreover the same catalyst performs both the C-C bond cross coupling followed by reduction of nitroarenes in one pot with a single loading of 0.25 mol% in a tandem fashion. The recyclability of the catalyst towards biaryl synthesis using Suzuki-Miyaura cross coupling and nitro reduction shows that it will be active upto five consecutive cycles with full conversion. Finally for halide substrates we found that the catalyst have potential for simultaneous dehalogenation and nitro reduction if the halides are Br- or I-.

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