Modeling the Syn Disposition of Nitrogen Donors at the Active Sites of Carboxylate-Bridged Diiron Enzymes. Enforcing Dinuclearity and Kinetic Stability with a 1,2-Diethynylbenzene-Based Ligand

Abstract

The syn coordination of histidine residues at the active sites of several carboxylate-rich non-heme diiron enzymes has been difficult to reproduce with small molecule model compounds. In this study, ligands derived from 1,8-naphthyridine, phthalazine, and 1,2-diethynylbenzene were employed to mimic this geometric feature. The preassembled diiron(II) complex [Fe(2)(micro-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(THF)(2)] (1), where Ar(Tol)CO(2)(-) is the sterically hindered carboxylate 2,6-di(p-tolyl)benzoate, served as a convenient starting material for the preparation of iron(II) complexes, all of which were crystallographically characterized. Use of the ligand 2,7-dimethyl-1,8-naphthyridine (Me(2)-napy) afforded the mononuclear complex [Fe(O(2)CAr(Tol))(2)(Me(2)-napy)] (2), whereas dinuclear [Fe(2)(micro-DMP)(micro-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(THF)] (3) resulted when 1,4-dimethylphthalazine (DMP) was employed. The dinuclear core of compound 3 is kinetically labile, as evidenced by the formation of [Fe(O(2)CAr(Tol))(2)(vpy)(2)] (4) upon addition of 2-vinylpyridine (vpy). The diiron analogue of 4, [Fe(2)(micro-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(vpy)(2)] (5), was prepared directly from 1. When the sterically more demanding ligand 2,6-di(4-tert-butylphenyl)benzoate (Ar(4-tBuPh)CO(2)(-)) was used, mononuclear [Fe(O(2)CAr(4)(-)(tBuPh))(2)(THF)(2)] (6) and [Fe(O(2)CAr(4)(-)(tBuPh))(2)(DMP)(2)] (7) formed. The difficulty in stabilizing a dinuclear core with these simple (N)(2)-donor ligands was circumvented by preparing a family of 1,2-diethynylbenzene-based ligands, from which were readily assembled the complexes [Fe(2)(Et(2)BCQEB(Et))(micro-O(2)CAr(Tol))(3)](OTf) (15) and [Cu(2)(Et(2)BCQEB(Et))(micro-I)(2)] (16), where Et(2)BCQEB(Et) is 1,2-bis(3-ethynyl-8-carboxylatequinoline)benzene ethyl ester. The Et(2)BCQEB(Et) framework provides both structural flexibility and the desired syn nitrogen donor geometry, thus serving as a good first-generation ligand in this class.

3,5-Diamino-4H-1,2,4-triazol-1-ium (6-carboxypyridine-2-carboxylato)(pyridine-2,6-dicarboxylato)cuprate(II) trihydrate

“…The study of the construction of metal organic frameworks indicates that under suitable conditions, the transfer of the acidic protons to appropriate bases will result in increased intermolecular interactions and as a result enhanced stabilization of the resulting system (Aghajani et al, 2009). The study of metal carboxylates has always been fascinating for the researchers because they play important roles not only in synthetic chemistry, considering the vast array of coordination modes of the carboxylate group, but also in biological activities (Tshuva et al, 2004;Kuzelka et al, 2003) and physiological effects (Aghabozorg et al, 2007). In our ongoing research to study the packing features of molecules containing metal chelate and triazole rings, the title Cu complex (I) was prepared from 3,5-diamino-1,2,4-triazole and dipicolinic acid.…”

“…For general background to and applications of supramolecular arrangements, see: Lehn (1995); Aghajani et al (2009) ;Tshuva & Lippard (2004); Kuzelka et al (2003). For crystal structures of related complexes, see: Aghabozorg et al (2007); Ramos Silva et al (2008); Wang et al (2004); MacDonald et al (2004).…”

Synthesis, characterization, crystal structures, and solution studies of Ni(II), Cu(II) and Zn(II) complexes obtained from pyridine-2,6-dicarboxylic acid and 2,9-Dimethyl-1,10-Phenanthroline

“…The research on the metal carboxylates has always been intriguing in that they play important roles not only in synthetic chemistry with the essence of labile coordination modes of carboxylate group, such as architecture of open and porous framework [1,2], but also in biologic activities [3,4] and physiological effects [5].…”

Unique Metal‐Diyne, ‐Enyne, and ‐Enediyne Complexes: Part of the Remarkably Diverse World of Metal‐Alkyne Chemistry

“…The ability of this general suite of ligands to potentially build bridging structures, especially the rigid 3-pyridyl and quinoline R-groups constructs, coupled with the rigid 2-pyridyl trans-binding ligand reported by Thummel and co-workers (556), has contributed to the development of dimeric (557)(558)(559) and higher order (560-567) metal-containing architectures (Fig. 31).…”