Complexes with FeIII2(μ-O)(μ-OH) Core Surrounded by Hydrogen-Bonding Interaction

Abstract

Three new complexes with FeIII2(μ-O)(μ-OH) core surrounded with one, two, and three amino groups, that is, (6-amino-2-pyridylmethyl)bis(pyridylmethyl)amine (MAPA), bis(6-amino-2-pyridylmethyl)(pyridylmethyl)amine (BAPA), and tris(6-amino-2-pyridylmethyl)amine (TAPA), which act as hydrogen-bonding sites, were synthesized and characterized by electronic absorption spectroscopy and X-ray diffraction analysis. Their structural bond parameters, Fe–N(pyridine), Fe–N(amine), and Fe–μ-O(H) bonds, Fe···Fe distance, and Fe–O–Fe angle, could be explained in terms of a combination of two conflicting interactions between NH2 and μ-O(H) groups, that is, a steric repulsion and a hydrogen-bonding interactions. The LMCT bands of μ-O to iron(III) may be affected by hydrogen-bonding interactions between NH and μ-O(H) groups, which are discussed in connection with the formation processes of compound Q and compound X in sMMO and RNR-R2, respectively.

Sc3+-Promoted O–O Bond Cleavage of a (μ-1,2-Peroxo)diiron(III) Species Formed from an Iron(II) Precursor and O2 to Generate a Complex with an FeIV2(μ-O)2 Core

“…For diiron­(IV) species 3 -DU isomer, DFT calculations predict Fe–N distances of 1.96–1.97 Å for the benzimidazole donors and 2.13 Å for the amines, an Fe···Fe distance of 2.70 Å, and Fe–O–Fe angles of 98°, in very good agreement with the EXAFS analysis. The 3 -DD form is less stable than 3 -DU by 16.1 kcal/mol, which is consistent with the structures of related crystallographically characterized Fe 2 O 2 diamond-core complexes reported so far. ,,, As it is difficult to visualize how 2 -DD could easily transform into 3 -DU, we have assumed that both 2 and 3 are in fact in the DU form.…”

Quasi-Three-Coordinate Iron and Cobalt Terphenoxide Complexes {AriPr8OM(μ-O)}2 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2; M = Fe or Co) with M(III)2(μ-O)2 Core Structures and the Peroxide Dimer of 2-Oxepinoxy Relevant to Benzene Oxidation

“…Short Fe···Fe distances have also been seen in the iron-imide clusters Fe 2 (μ-N t Bu) 2 Cl 2 (NH 2 t Bu) 2 , Fe 2 (μ-N t Bu) 2 Cl 2 (DMAP) 2 , and Fe 2 (μ-N t Bu) 2 Cl 2 (PEt 3 ) 2 , which have Fe 2 (μ-N t Bu) 2 cores . The Fe···Fe distance in 1 is more than 0.2 Å shorter than those in other reported Fe 2 (μ-O) 2 species, such as {Fe 2 (μ-O) 2 (6-Me 3 -TPA) 2 }­{(ClO 4 ) 2 } (2.716(2) Å), {Fe 2 (μ-O) 2 (5-Et 3 -TPA) 2 }­{(ClO 4 ) 3 } (2.683(1) Å), and {Fe 2 (μ-O) 2 (TAPA) 2 }­{(ClO 4 ) 2 } (2.706(3) Å) . Within the Fe 2 (μ-O) 2 core the Fe–O distances (Fe(1)–O(3) 1.818(3) Å, Fe(1)–O(4) 1.824(2) Å, Fe(2)–O(3) 1.829(2) Å, Fe(2)–O(4) 1.816(2) Å) are relatively uniform and shorter than the terminal Fe–O bond lengths (1.864(2) and 1.874(2) Å) to the aryloxide ligands.…”

“…Within the Fe 2 (μ-O) 2 core the Fe–O distances (Fe(1)–O(3) 1.818(3) Å, Fe(1)–O(4) 1.824(2) Å, Fe(2)–O(3) 1.829(2) Å, Fe(2)–O(4) 1.816(2) Å) are relatively uniform and shorter than the terminal Fe–O bond lengths (1.864(2) and 1.874(2) Å) to the aryloxide ligands. In contrast, the tris­(2-pyridylmethyl)­amine (TPA) model compounds all display more asymmetric bridging bonding modes, with variation in the Fe–O bond lengths of 0.05–0.07 Å, − probably because the ligands in those models are not as symmetric as the terphenyl ligand and are also multidentate in character. The reason that 1 has such a short iron–iron distance is probably similar to the Fe 2 (μ-N t Bu) 2 cases: the combination of the short Fe–O bonds, the very symmetric diamond core structure, the interatomic repulsions between oxygen atoms in the diamond core, and the pseudotetrahedral coordination for iron which favors a wide O–Fe–O angle.…”

“…This value is shorter than the 2.52 Å interatomic distance in iron metal 49 and approaches the value of 2.46 Å observed 15 50 The Fe•••Fe distance in 1 is more than 0.2 Å shorter than those in other reported Fe 2 (μ-O) 2 species, such as {Fe 2 (μ-O) 2 (6-Me 3 -TPA) 2 }{(ClO 4 ) 2 } (2.716(2) Å), 19 {Fe 2 (μ-O) 2 (5-Et 3 -TPA) 2 }{(ClO 4 ) 3 } (2.683(1) Å), 20 and {Fe 2 (μ-O) 2 (TAPA) 2 }{(ClO 4 ) 2 } (2.706(3) Å). 21 2) and 1.874(2) Å) to the aryloxide ligands. In contrast, the tris(2-pyridylmethyl)amine (TPA) model compounds all display more asymmetric bridging bonding modes, with variation in the Fe−O bond lengths of 0.05−0.07 Å, 19−21 probably because the ligands in those models are not as symmetric as the terphenyl ligand and are also multidentate in character.…”

“…Metal-mediated oxidation of C–H bonds is of fundamental importance in organic synthesis, industrial catalytic processes, and enzymatic reactions. − For the latter, methane monooxygenase (MMO), which catalyzes the oxidation of methane to methanol, has been proposed featuring a high-valent Fe 2 (μ-O) 2 diamond core structure as the key oxidizing species in the proposed mechanism of the catalytic cycle. − A number of synthetic complexes featuring Fe 2 (μ-O) 2 diamond cores with six-coordinate iron and Fe···Fe distances in the range 2.6–2.8 Å have been structurally characterized. − A recently reported complex [{( N , N ′-Pipiso)­Fe­(μ-O)} 2 ] (Pipiso – = [(DippN) 2 C­( cis -2,6-Me 2 NC 5 H 8 )] − , Dipp = C 6 H 3 Pr i 2 -2,6) containing a bis­(μ-oxo)­diiron­(III) core structure has a relatively short Fe···Fe distance (2.475(1) Å) with four-coordinate iron ions …”