Iron coordination chemistry of N-(bis(2-pyridyl)methyl)pyridine-2-carboxamide

The amidate function participates in the coordination chemistry of iron containing biomolecules such as the anti-tumor drug bleomycin and the enzyme nitrile hydratase. Our interest in amidate coordination prompted an investigation of the iron complexes of the potentially tetradentate ligand N-(bis(2-pyridyl)methyl)pyridine-2-carboxamide (H-L). A number of complexes have been isolated and structurally characterized, including [Fe-4(III)(L)(2)] (1), [Fe-III(L-OCH3)Br-2(CH3OH)] (3), [Fe-2(III) (mu-OH)(2)(L-OCH3)(2)Br-2](4), and [Fe-4(III) (mu-OCH3)(2)(L-O)(2)Br-6] (5). In these complexes L acts as a meridional tridentate ligand, as previously observed for the corresponding [Cu(L)Cl(CH3OH)] complex (Inorg. Chem. 39 (2000) 5326). In the cases of 3 and 4, the hydrogen of the tertiary carbon has been replaced by a methoxy group in the course of complex synthesis. In the case of 5, the tertiary hydrogen is replaced by hydroxide, and this oxygen and the dangling pyridine act as a bidentate ligand to a second iron ion. When the reaction of FeBr3 and H-L was carried out in acetonitrile in the presence of base but in the absence of air, the ligand was cleaved into two pieces, affording [(FeBr2)-Br-II(pyridine-2-carboxamide)(di-2-pyridylketone)] (6). It is proposed that the coordination of the amide nitrogen of H-L to an iron(III) center as an amidate activates the alpha-C-H bond and results in the oxidation of the alpha-C-N-amide bond to an imine. (C) 2002 Elsevier Science B.V. All rights reserved.