Monoanionic N,N,O-Scorpionate Ligands and their Iron(II) and Zinc(II) Complexes: Models for Mononuclear Active Sites of Non-Heme Iron Oxidases and Zinc Enzymes

Abstract

The chemical behavior of two bis(3,5-dialkylpyrazol-1-yl)acetic acids and their coordination properties towards ZnCl 2 and FeCl 2 was studied. Reaction of bis(3,5-dimethylpyrazol-1-yl)acetic acid (bdmpza) (1) with ZnCl 2 and FeCl 2 gave the 2:1 complexes [(bdmpza) 2 Zn] (4) and [(bdmpza) 2 Fe] (5). Crystal structures of both complexes were obtained. In contrast, the sterically more hindered ligand bis(3,5-di-tert-butylpyrazol-1-yl)acetic acid (bdtbpza) (3) coordinates only once to zinc(II) resulting in the complex [(bdtbpza)ZnCl] (6). This provides a structural model complex for the active sites of zinc enzymes such as thermolysin or carboxypeptidase.[a]

Biomimetic Applications of Metal Systems Supported by Scorpionates

“…Alkyl zinc complexes bearing various bis(pyrazol-1-yl)acetato ligands (HC(pz R,R' ) 2 (COO) -) offer an easy access to better structural model complexes for zinc peptidases with a 2-His-1-carboxylate motif. Starting from methyl complexes [(HC(pz R,R' ) 2 (COO)ZnCH 3 ] so far several complexes with carboxylato-, thiolato-and also hydroxamato-ligands have been obtained by methane releasing reactions with carboxylic acids, thiols and hydroxamic acids (Beck et al, 2001;Hegelmann et al, 2003;Smith et al, 2003;Smith et al, 2005). According to the NMR spectra these complexes often exhibit a κ 1 /κ 2 equilibrium (Fig.…”

“…Thiolates, carboxylates and hydroxamates are the most common zinc binding groups used in zinc peptidase inhibitors such as ACE inhibitors. Most of these models for carboxypeptidases have been characterised by X-ray structure determinations (Beck et al, 2001;Hegelmann et al, 2003;Smith et al, 2003;Smith et al, 2005), the model complexes helping to develop new zinc binding groups for potential peptidase inhibitors.…”

Synthesis and structural characterization of mono- and dinuclear Mo(V)-oxo-complexes containing bis(3,5-dimethylpyrazol-1-yl)acetate anion as ligand

“…Due to the increasing interest in the chemistry of the non-heme iron enzymes, which are required in oxygen activation, several tripodal heteroscorpionate N,N, O-, and N,N,Sand N,N,N-ligands based on bis(pyrazol-1-yl)acetate, -thioacetate and -ethoxide with pyrazolyl rings substituted at 3 and 5 positions, have been prepared [2]. So far, the complexes with almost one third of d-elements in different oxidation states have been synthesized, and structurally characterized with bis (3,5-dimethylpyrazol-1-yl) acetate as a ligand: first [NbCl 2 (bdmpza)(PhCCMe)] [3], later the compounds with Ti(IV), Zr(IV) and Hf(IV) [4], Nb(III) [3,5], Cr(III), Mo(V) and Mo(VI) [6], Mn(I), Re(I), Re(V) and Re(VII) [7], Fe(II), Fe(III), Ru(II), Ru(III) and Ru(IV) [8], Cu(II) [9], and Pd(II) [10]. Compounds are mostly mononuclear, several of them are dinuclear, and one complex of Zr(IV) is hexanuclear [4c].…”

“…In an ideal case, the molecules 1 and 2 could have a C s symmetry but due to the crystallographic packing interactions both Mo-X as well as Mo-N bond lengths slightly differ from each other (Mo-Cl distances in 1 are 2.3319(9)/2.3142 (8) and ( (1)°and can be considered the primary cause of the more distorted octahedral geometry round the Mo atom in comparison with those in 1 and 2. The octahedral angles range from 78.52 (9) to 101.05(8)°in 1, from 78.38 (8) to 100.66(6)°in 2, but from 76.47(5) to 106.50 (7) Although there is only one electron in valence shell of Mo V (4d 1 ), an unambiguous interpretation of UV-visible spectra of related complexes are not always possible [17]. The oxygen atom, bound by the double bond to the central Mo atom, represents a stronger chromophore in comparison with other ligand atoms in complexes 1 and 2.…”

“…A reaction scheme for the synthesis of 1/2 and 3. (7), Cl1-Mo-N1b 91.68 (7), Cl2-Mo-O1 90.50 (7), Cl2-Mo-O3 101.05 (8), Cl2-Mo-N1a 92.64 (7), Cl2-Mo-N1b 168.75 (7), O1- , O1- , O1- , O(3) -Mo-N1a 89.45 (11), O3- , N1a-Mo-N1b 83.00 (9). 2: Mo-Br1 2.5012(3), , Mo-O1 2.1314(19), , , (2) can be ascribed to the LMCT (ligand to metal charge transfer) absorption.…”