Unique example of flexible phenol coordination in mononuclear manganese compounds
Abstract
The synthesis and characterization of six novel mononuclear MnII and MnIII complexes are presented. The tripodal ligands 2-((bis(pyridin-2-ylmethyl)amino)methyl)-4-nitrophenol (HL1), 2-[[((6-methylpyridin-2-yl)methyl)(pyridin-2-ylmethyl)amino]methyl]-4-nitrophenol (HL2), (2-pyridylmethyl)(6-methyl-2-pyridylmethyl)(2-hydroxybenzyl)amine (HL3) and 2-((bis(pyridin-2-ylmethyl)amino)methyl)-4-bromophenol were used. All ligands provide an N3O donor set. The compounds [MnII(HL1)Cl2]·CH3OH (1), [MnIII(L1)Cl2] (2), [MnII(HL2)(EtOH)Cl2] (3), [MnII(HL3)Cl2]·CH3OH (4), [MnIII(HL4)Br2] (5) and [MnIII(L1)(tcc)] (6), with tcc = tetrachlorocatecholate dianion, were synthesized and characterized by various techniques such as X-ray crystallography, mass spectrometry, IR and UV-vis spectroscopy, cyclic voltammetry, and elemental analysis. Compound 1 crystallizes in the triclinic space group P, compounds 2, 3 and 4 were solved in the monoclinic space group P21/c, whereas the structure determination of 5 and 6 succeeded in the orthorhombic space groups Pbca and P212121, respectively. Notably, the crystal structures of 1 and 3 are the first MnII complexes featuring a non-coordinating phenol moiety. Compound 2 oxidizes 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone exhibiting saturation kinetics at high substrate concentrations with a turnover number of kcat = 173 h−1. The electronic influence of different substituents in para position of the phenol group is lined out.