Kinetic Lability, Structural Diversity, and Oxidation Reactions of New Oligomeric, Anionic Carboxylate−Pyridine Complexes

The dimeric [M(2)(OAc)(5)(py)(2)&mgr;-(OH(2))]Et(4)N complexes, I (M = Mn, Fe, Co), have been isolated from pyridine solutions of M(II)(OAc)(2).xH(2)O and Et(4)N(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)(Et(4)N)(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 &mgr;(1), &mgr;(2) mode and two acetate ligands in the &mgr;(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)&mgr;(3)-(O)(OAc)(7)(OH(2))]Et(4)N(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 Mössbauer spectrum of III shows two quadrupole doublets in a 1:2 ratio with delta(Fe) = 1.29(1) and 0.48 mm/s; DeltaE(q) = 1.89 and 0.71 mm/s. The oxidation of I-Fe by H(2)O(2)/O(2) in pyridine solution in the presence of Cl(-) ligands affords Fe(4)&mgr;(3)-(O)(2)(OAc)(6)(py)(4)Cl(2) (IV). The X-ray structure of IV shows a rhombic {Fe(III)(4)(&mgr;(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)&mgr;(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.