Unsupported mu-Oxo- and mu-Hydroxo-Iron(III) Dimers and Mononuclear Iron(III) Complexes with Pyridylbis(aminophenol) Ligands

作者：Shakya Rajendra; Powell Douglas R; Houser Robert P^*

来源：European Journal of Inorganic Chemistry, 2009, 2009(35): 5319-5327.

DOI：10.1002/ejic.200900794

• Iron
• N,O ligands
• Bridging ligands
• Bioinorganic chemistry

Unsupported hydroxo- and oxo-bridged diiron(III) and mononuclear iron(III) complexes with pyridylbis(aminophenol) ligands (L(amine))(2-) and (L(tBu-amine))(2-) were synthesized and characterized [H(2)L(amine) = 2,2'-(2-methyl-2-(pyridin-2-yl)propane-1,3-diyl)bis(azanediyl)bis(methylene)diphenol; H(2)L(tbu-amine) = 6,6'-(2-methyl-2-(pyridin-2-yl)propane-1,3-diyl)bis(azanediyl)bis(methylene)bis(2,4-di-tert-butylphenol)]. Dimeric [(FeL(amine))(2)(mu-OH)]BPh(4) (1) and [(FeL(tBu-amino))(2)(mu-O)] (2), and monomeric [FeL(tBu-amine)(OCH(3))] (3) were synthesized from ferric perchlorate. Monomeric [FeL(amine)Cl] (4) and [FeL(tBu-amine)Cl] (5) were synthesized from ferric chloride. Complex 1 is comprised of two [FeL(amine)Cl](+) units, where (L(amine))(2-) is pentadentate, bridged by a single hydroxo ligand. Intramolecular H-bonding between the NH groups on one [Fe(Lamine)](+) unit and the phenolato O atoms of the other [FeL(amine)](+) unit stabilizes the structure. Complex 2 is an oxobridged dimer, but the steric constraints from the tert-butyl groups of (L(tBu-amine))(2-) prevent intramolecular H-bonding. Monomeric 4 and 5 are isostructural with pentadentate ligands (L(amine)])(2-) or (L(tBu-amine))(2-), respectively, and a chloro ligand in the sixth position of the six-coordinate iron(III) moieties. Conversion of 2 to its protonated hydroxa-bridged analog [(FeL(tBu-amine))(2)(mu-OH)](+) by treatment with mild acid was monitored spectroscopically and electrochemically, but the reaction was not reversible by treatment with base. Similarly, hydroxo-bridged 1 could not be deprotonated to generate its oxo-bridged analog, [(FeL(amine))(2)(mu-O)], suggesting that the pK(a) values of the hydroxo groups in 1 and [(FeL(tBu-amine))(2)(mu-OH)](+) are quite large. The CV of 2 revealed well-defined ligand-based redox couples, but no metal-based redox couples. When 2 was treated with mild acid, metal-based redox couples for [(FeL(tBu-amine))(2)(mu-OH)](+) grew in.

• 出版日期2009-12