Daniel Pursche

Catalytic oxidation of 3,5-Di-tert-butylcatechol by a series of mononuclear manganese complexes: synthesis, structure, and kinetic investigation.

The manganese compounds [Mn(bpia)(OAc)(OCH 3 )](PF 6 ) (1), [Mn(bipa)(OAc)(OCH 3 )](PF 6 ) (2), [Mn(bpia)(Cl) 2 ](ClO 4 ) (3), [Mn(bipa)(Cl) 2 ](ClO 4 ) (4), [Mn(Hmimppa)(Cl) 2 ].CH 3 OH (5), and [Mn(mimppa)(TCC)].2CHCl 3 (6) (bpia= bis-(picolyl)(N-methylimidazole-2-yl)amine; bipa = bis(N-methylimidazole-2-yl)(picolyl)amine; Hmimppa = ((1-meth-ylimidazole-2-yl)methyl)((2-pyridyl)methyl)(2-hydroxyphenyl)amine; TCC = tetrachlorocatechol) were synthesized and characterized by various techniques such as X-ray crystallography, mass spectrometry, IR, EPR, and UV/vis spectroscopy, cyclic voltammetry, and elemental analysis. 1 and 2 crystallize in the triclinic space group P1 (No. 2), 4 and 6 crystallize in the monoclinic space group P2 1 /n (No. 14), and 5 crystallizes in the orthorhombic space group Pna2 1 . Complexes 1-4 are structurally related to the proposed active site of the manganese-dependent extradiol-cleaving catechol dioxygenase exhibiting an N 4 O 2 donor set (1 and 2) or N 4 Cl 2 donor set (3 and 4). Cyclic voltammetric data show that the substitution of oxygen donor atoms with chloride causes a shift of redox potentials to more positive values. These compounds show high catalytic activity regarding the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone exhibiting saturation kinetics at high substrate concentrations. The turnover numbers k c a t = (86 ′ 7) h - 1 (1), k c a t = (101 ′ 4) h - 1 (2), k c a t = (230 ′ 4) h - 1 (3), and k c a t = (130 ′ 4) h - 1 (4) were determined from the double reciprocal Lineweaver-Burk plot. Compounds 5 and 6 can be regarded as structural and electronic Mn analogues for substituted forms of Fe-containing intradiol-cleaving catechol dioxygenases. To our knowledge 5 is the first mononuclear Mn(II) compound featuring an N 3 OCl 2 donor set.

New dinuclear Co(II) and Mn(II) complexes of the phenol-based compartmental ligand containing formyl and amine functions: structural, spectroscopic and magnetic properties

The phenol-based compartmental ligand Hpy2ald contains a tridentate amino arm and a weak donor aldehyde group at the 2 0 and at the 6 0 positions of the phenol ring, respectively. This ligand reacts with cobalt(II) perchlorate, cobalt(II) tetrafluoroborate and manganese(II) perchlorate, yielding dinuclear complexes, where two metal ions are doubly bridged by two deprotonated cresolate moieties. The coordination environment around the metal ions is then completed to a very distorted octahedron by three nitrogen donor atoms from the pendant amino arm and the oxygen atom of the aldehyde group. The crystal structures of the complexes, their spectroscopic and magnetic properties are reported. 2003 Elsevier B.V. All rights reserved.

A Tetranuclear Manganese Cluster with a Star‐Shaped Mn4O6 Core Motif: Directed Synthesis using a Mononuclear Precursor Complex

The tetranuclear manganese(II) complex [Mn4(ppi)6](BPh4)2 (2) (Hppi = 2-pyridylmethyl-2-hydroxy phenylimine) is prepared by using the precursor complex [Mn(ppi)2]·H2O (1). Based on UV/Vis- and IR-spectroscopy data in combination with mass spectrometry it has been concluded that 1 is a mononuclear neutral MnII complex, in which two ppi ligands chelate the manganese atom. Compound 2 crystallizes in the triclinic space group P1¯ (no. 2), with a = 17.500(3), b = 17.955(4), c = 19.101(4) A, α = 113.79(3)°, β = 111.33(3)°, γ = 93.91(3)°, V = 4950(2) A3 and Z = 2. In the tetranuclear [Mn4(ppi)6]2+ complex cation Mn(1), Mn(2), and Mn(3) are equivalently coordinated by two deprotonated Hppi ligands leading to a N4O2 donor set. The environment of the central Mn(4) is formed by coordination of three [Mn(ppi)2] fragments resulting in a phenoxo bridged star-shaped Mn4O6 core motif. The average distance of directly adjacent manganese ions is 3.310 A, whereas the average distance of Mn(1), Mn(2), and Mn(3) among each other is 5.732 A.

Unique example of flexible phenol coordination in mononuclear manganese compounds

The synthesis and characterization of six novel mononuclear Mn(II) and Mn(III) 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 [Mn(II)(HL1)Cl2].CH3OH (1), [Mn(III)(L1)Cl2] (2), [Mn(II)(HL2)(EtOH)Cl2] (3), [Mn(II)(HL3)Cl2].CH3OH (4), [Mn(III)(HL4)Br2] (5) and [Mn(III)(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 P1, compounds 2, 3 and 4 were solved in the monoclinic space group P2(1)/c, whereas the structure determination of and succeeded in the orthorhombic space groups Pbca and P2(1)2(1)2(1), respectively. Notably, the crystal structures of 1 and 3 are the first Mn(II) 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.