Synthesis, characterization and reactivity of a Mn(III)–hydroxido complex as a biomimetic model for lipoxygenase.

Manganese hydroxido (Mn–OH) complexes supported by a tripodal N,N′,N″ -[nitrilotris(ethane-2,1-diyl)]tris(P,P -diphenylphosphinic amido) ([poat]3−) ligand have been synthesized and characterized by spectroscopic techniques including UV–vis and electron paramagnetic resonance (EPR) spectroscopies. X-ray diffraction (XRD) methods were used to confirm the solid-state molecular structures of {Na 2 [MnIIpoat(OH)]} 2 and {Na[MnIIIpoat(OH)]} 2 as clusters that are linked by the electrostatic interactions between the sodium counterions and the oxygen atom of the ligated hydroxido unit and the phosphinic (P=O) amide groups of [poat]3−. Both clusters feature two independent monoanionic fragments in which each contains a trigonal bipyramidal Mn center that is comprised of three equatorial deprotonated amide nitrogen atoms, an apical tertiary amine, and an axial hydroxido ligand. XRD analyses of {Na[MnIIIpoat(OH)]} 2 also showed an intramolecular hydrogen bonding interaction between the MnIII–OH unit and P=O group of [poat]3−. Crystalline {Na[MnIIIpoat(OH)]} 2 remains as clusters with Na+---O interactions in solution and is unreactive toward external substrates. However, conductivity studies indicated that [MnIIIpoat(OH)]− generated in situ is monomeric and reactivity studies found that it is capable of cleaving C-H bonds, illustrating the importance of solution-phase speciation and its direct effect on chemical reactivity. Synopsis : Manganese–hydroxido complexes were synthesized to study the influence of H-bonds in the secondary coordination sphere and their effects on the oxidative cleavage of substrates containing C-H bonds. [Display omitted] • A synthetic MnIII–OH complex capable of C-H bond cleavage is reported • Reactivity of MnIII–OH complexes with H-bond acceptors • Modulating the secondary coordination sphere of metal-hydroxide complexes [ABSTRACT FROM AUTHOR]