Kinetic lability, structural diversity, and oxidation reactions of new oligomeric, anionic carboxylate-pyridine complexes

The dimeric [M-2(OAc)(5)(py)(2) mu-(OH2)]Et4N complexes, I (M = Mn, Fe, Co), have been isolated from pyridine solutions of M-II(OAc)(2) . xH(2)O and Et4N(OAc). 4H(2)O. The X-ray structures of I (M = Mn, Fe, Co) have been determined and show the metal ions asymmetrically bridged by two acetate ligands and a water molecule. One of the metal ions is bound by a pyridine ligand and two monodentate acetate ligands that are hydrogen bonded to the bridging water molecule. The second metal ion is bound to a bidentate acetate ligand and a pyridine ligand. Recrystallization of I from acetonitrile leads to the reorganization of I and isolation of the M-3(OAc)(8)(Et4N)(2) complexes, II (M = Mn, Fe, Co). The X-ray structure of II (M = Mn, Co) has been determined and shows the three metal ions connected by four bridging acetate ligands in a mu(1), mu(2) mode and two acetate ligands in the mu(1),eta(1) mode, with a bidentate acetate ligand on each of the external metal ions completing the distorted octahedral geometry. Air oxidation of I-Fe in propionitrile leads to the formation of the mixed-valence [Fe-3 mu(3)(O)(OAc)(7)(OH2)]Et4N (III). The X-ray structure of III has been determined and resembles the core of the basic acetate complexes; however, it has five bridging acetate ligands. The Mossbauer spectrum of III shows two quadrupole doublets in a 1:2 ratio with delta(Fe) = 1.29(1) and 0.48 mm/s; Delta E-q = 1.89 and 0.71 mm/s. The oxidation of I-Pe by H2O2/O-2 in pyridine solution in the presence of Cl- ligands affords Fe-4 mu(3)-(O)(2)(OAc)(6)(py)(4)Cl-2 (IV). The X-ray structure of TV shows a rhombic {Fe-4(III)(mu(3)-O)(2)} core previously found in iron and manganese chemistry. The reaction of ferrocenium ion with I-Fe under basic conditions in dichloromethane solution led to the formation of the familiar mixed-valence Fe-3 mu(3)-(O)(OAc)(6)(py)(3) complex (V) with the basic acetate structure. Complexes I-Fe, II-Fe, III, and IV catalyze the reaction of O-2 With adamantane under GiF conditions to give adamantanols and adamantanone. The similarity of the results in comparison to similar studies previously reported for iron/carboxylate complexes are noted and discussed.