Biomimetic iron(iii) complexes of N3O and N3O2 donor ligands: protonation of coordinated ethanolate donor enhances dioxygenase activity

Abstract

A series of iron(III) complexes 1-4 of the tripodal tetradentate ligands N,N-bis(pyrid-2-ylmethyl)-N-(2-hydroxyethyl)amine H(L1), N,N-bis(pyrid-2-ylmethyl)-N-(2-hydroxy- propyl)amine H(L2), N,N-bis(pyrid-2-ylmethyl)-N-ethoxyethanolamine H(L3), and N-((pyrid-2-ylmethyl)(1-methylimidazol-2-ylmethyl))-N-(2-hydroxyethyl)amine H(L4), have been isolated, characterized and studied as functional models for intradiol-cleaving catechol dioxygenases. In the X-ray crystal structure of [Fe(L1)Cl(2)] 1, the tertiary amine nitrogen and two pyridine nitrogen atoms of H(L1) are coordinated meridionally to iron(III) and the deprotonated ethanolate oxygen is coordinated axially. In contrast, [Fe(HL3)Cl(3)] 3 contains the tertiary amine nitrogen and two pyridine nitrogen atoms coordinated facially to iron(III) with the ligand ethoxyethanol moiety remaining uncoordinated. The X-ray structure of the bis(μ-alkoxo) dimer [{Fe(L5)Cl}(2)](ClO(4))(2)5, where HL is the tetradentate N(3)O donor ligand N,N-bis(1-methylimidazol-2-ylmethyl)-N-(2-hydroxyethyl)amine H(L5), contains the ethanolate oxygen donors coordinated to iron(III). Interestingly, the [Fe(HL)(DBC)](+) and [Fe(HL3)(HDBC)X] adducts, generated by adding ∼1 equivalent of piperidine to solutions containing equimolar quantities of iron(III) complexes 1-5 and H(2)DBC (3,5-di-tert-butylcatechol), display two DBC(2-)→ iron(III) LMCT bands (λ(max): 1, 577, 905; 2, 575,915; 3, 586, 920; 4, 563, 870; 5, 557, 856 nm; Δλ(max), 299-340 nm); however, the bands are blue-shifted (λ(max): 1, 443, 700; 2, 425, 702; 3, 424, 684; 4, 431, 687; 5, 434, 685 nm; Δλ(max), 251-277 nm) on adding 1 more equivalent of piperidine to form the adducts [Fe(L)(DBC)] and [Fe(HL3)(HDBC)X]. Electronic spectral and pH-metric titration studies in methanol disclose that the ligand in [Fe(HL)(DBC)](+) is protonated. The [Fe(L)(DBC)] adducts of iron(III) complexes of bis(pyridyl)-based ligands (1,2) afford higher amounts of intradiol-cleavage products, whereas those of mono/bis(imidazole)-based ligands (4,5) yield mainly the auto-oxidation product benzoquinone. It is remarkable that the adducts [Fe(HL)(DBC)](+)/[Fe(HL3)(DBC)X] exhibit higher rates of oxygenation affording larger amounts of intradiol-cleavage products and lower amounts of benzoquinone.

(Acetato-κO)(aqua-κO)(2-{bis[(3,5-dimethyl-1H-pyrazol-1-yl-κN2)methyl]amino-κN}ethanol-κO)nickel(II) perchlorate monohydrate

“…In this work, N, N-bis(3,5-dimethyl-pyrazol-1-ylmethylene)aminoethanol (Malachowski et al, 1992) was reacted with nickel acetate in the presence of sodium perchlorate to yield the title complex as blue crystals in 68% yield. Related structures have been reported previously (Shin et al, 2011;Sundaravel et al, 2011;Xia et al, 2001).…”

“…For background to hydrolytic enzymes, see: Koike et al (1995); Lipscomb & Strä ter (1996). For related structures, see: Shin et al (2011); Sundaravel et al (2011); Xia et al (2001).…”

Mechanism of magnetisation relaxation in {MIII2DyIII2} (M = Cr, Mn, Fe, Al) “Butterfly” complexes: how important are the transition metal ions here?

“…All reactions were carried out under aerobic conditions. N -(2-Pyridylmethyl)iminodiethanol was prepared according to the literature procedure 43. The elemental analyses (C, H, and N) were carried out using an Elementar Vario EL analyser.…”

Butterfly M2IIIEr2 (MIII = Fe and Al) SMMs: Synthesis, Characterization, and Magnetic Properties

“…N -(2-Pyridylmethyl)iminodiethanol was prepared according to the literature procedure. 11 The elemental analyses (C, H, and N) were carried out using an Elementar Vario EL analyzer. Fourier transform IR spectra (4000–400 cm –1 ) were measured on a PerkinElmer Spectrum GX spectrometer with samples prepared as KBr disks.…”