Trinuclear first row transition metal complexes of a hexapyridyl, trialkoxy 1,3,5-triarylbenzene ligand

Abstract

Trinuclear complexes of Mn II , Fe II , Co II , Ni II , Cu II , and Zn II were synthesized using a ligand architecture based upon a 1,3,5-triarylbenzene core decorated with six pyridines and three alkoxide moieties. Characterization via X-ray diffraction, NMR, and magnetism studies is discussed.The active sites of several enzymes involved in dioxygen chemistry (laccase, ascorbate oxidase, the oxygen evolving center of photosystem II) display three or more first row transition metal centers. 1 Synthetic catalysts for water oxidation are also proposed to be multinuclear. 2 In continued efforts to rationally design multinucleating scaffolds, a 1,3,5-triarylbenzene framework was utilized to hold three multidentate binding sites near each other. 1,3,5-tris(2-(di(2-pyridyl)hydroxymethyl)phenyl)benzene (H 3 L, Scheme 1) is accessible in two steps from commercially available starting materials. 3 Trinuclear copper complexes supported by framework L have been synthesized containing a conserved Cu 3 (m-OR) 3 central moiety; varying the capping anions from halides, phosphate, tetrafluoroborate, and triflate causes subtle structural changes that affect the magnetism of these complexes. 3 Protonated and deprotonated dipyridylhydroxymethyl moieties are known to exhibit an array of coordination modes, from tridentate N,O,N coordination of a single metal center to more complicated bridging patterns of up to three metals. 4 Although the M II 3 (m-OR) 3 structural motif is commonly found in higher nuclearity clusters in complexes of 2,2 0 -dipyridylketone 4 and as part of self-assembled tetranuclear clusters such as cubanes 5 and defective dicubanes, 6 the motif is less common in trinuclear complexes. 7 To further investigate the metal coordination potential of H 3 L and its control over cluster nuclearity, trinuclear complexes of L containing other first row transition metals were targeted.Metallation studies were initiated with the acetate salts of the first-row metals Mn II , Fe II , Co II , Ni II , Cu II , and Zn II in the presence of base. Addition of three equivalents of solid M II (OAc) 2 ÁxH 2 O to a suspension of H 3 L in acetonitrile or a mixture of acetonitrile-water followed by three equivalents of a base such as sodium hydroxide or triethylamine resulted in complete dissolution of insoluble materials within 12 h. Analytically pure crystals were obtained by vapor diffusion of diethyl ether into dichloromethane or chloroform solutions of the reaction products.Single crystal X-ray diffraction (XRD) studies demonstrate the trinucleating nature of the deprotonated H 3 L framework to give complexes generally formulated as LM 3 (OAc) 3 (Fig. 1a). The three metal centers are bridged by three alkoxides forming a six membered ring, and the pendant pyridines coordinate with the two pyridines of each dipyridyl moiety bound to adjacent metal centers. The coordination environment is completed by acetate counterions.The LM 3 core displays pseudo-C 3 symmetry induced by a twist of each dipyridylmethoxide arm. This binding mode re...

Reduction potentials of heterometallic manganese–oxido cubane complexes modulated by redox-inactive metals

“…The strontium compound [LSrMn 3 O 4 (OAc) 3 Fig. 2, DMF, N,N-dimethylformamide) was prepared analogously to 1-Ca from a lowoxidation-state trimanganese precursor supported by a triarylbenzene architecture appended with pyridine and alkoxide donors (31,32 (25).…”

Oxygen Atom Transfer and Oxidative Water Incorporation in Cuboidal Mn3MOn Complexes Based on Synthetic, Isotopic Labeling, and Computational Studies

“…Improving upon the published procedures, [13,14] in the glovebox, a 1L Erlenmeyer flask was equipped with a stir bar and charged with 1,3,5-tris(2-bromophenyl)benzene (8.83 g, 16.26 mmol) and Et 2 O (325 mL). The off-white suspension was frozen in the cold well.…”

“…Spectral features match those found in previous work. [13,14] 4.2 Synthesis of LMn II 3 (OAc) 3 (1).…”

“…Improving upon the published procedure, [14] Recrystallization of this material from vapor diffusion of Et 2 O into a CH 2 Cl 2 solution gave crystals amenable to X-ray diffraction studies.…”

Trinuclear Manganese Complexes of Unsymmetrical Polypodal Diamino N3O3 Ligands with an Unusual [Mn3(μ-OR)4]5+ Triangular Core: Synthesis, Characterization, and Catalase Activity

“…37,38 In line with this, the trimetallic [Mn 3 (μ-OR) 4 ] 5+ structure of 1 + can be envisaged as a precursor for synthesis of the heterometallic tetranuclear core through incorporation of Ca to the Mn 3 core via the acetate bridge, thus highlighting the interest in this unique and peculiar structural unit.…”