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Role of: Para -substitution in controlling phosphatase activity of dinuclear NiII complexes of Mannich-base ligands: Experimental and DFT studies
Published in Royal Society of Chemistry
Volume: 6
Issue: 77
Pages: 73534 - 73546
With an aim to study the electronic effect of the group lying in the para-position of phenol-based compartmental Mannich-base ligands, five dinuclear nickel(ii) complexes [Ni2L1-5(μ-NO3)(NO3)2] have been synthesized [R = Me (1), CHMe2 (2), CMe3 (3), Cl (4), and OMe (5)] having octahedral structures (fac-manner) in each case as confirmed by single-crystal X-ray diffraction (1-4). The Ni⋯Ni distance (3.42-3.49 Å) and Ni-O-Ni bridging bond angle (118.62-121.45°) of 1-4 is proportional to the electronic partial charge (I-effect) of the para-substituents as 3 < 2 ≈ 1 < 4. The phosphatase activity has been studied with the phosphomonoester 4-nitrophenylphosphate (4-NPP) in aqueous DMSO by spectrophotometry leading to the trend 3 > 2 > 5 > 1 > 4 in terms of kcat values (6-81 s-1), as per the Michaelis-Menten profile. DFT calculations establish that the electron-donating group decreases the reaction energy barrier via reducing the energy gap between the orbital of electron-sufficient para-substituted phenolate group and the electron-demanding leaving group. The exceptionally high activity of complex 3 also establishes the rationality of our catalyst design in our previous work (Inorg. Chem. 2015, 54, 2315-2324). © 2016 The Royal Society of Chemistry.
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JournalData powered by TypesetRSC Advances
PublisherData powered by TypesetRoyal Society of Chemistry