Iron coordination chemistry of N -(bis(2-pyridyl)methyl)pyridine-2- carboxamide Shourong Zhu 1 , William W. Brennessel, Roger G. Harrison 2 , Lawrence Que, Jr. * Department of Chemistry, Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE., Minneapolis, MN 55455, USA Received 18 February 2002; accepted 26 March 2002 Dedicated to Professor Karl Wieghardt Abstract 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 à /L). A number of complexes have been isolated and structurally characterized, including [Fe II (L) 2 ](1), [Fe III (L Ã/OCH 3 )Br 2 (CH 3 OH)] (3), [Fe III 2 (m-OH) 2 (L à /OCH 3 ) 2 Br 2 ](4), and [Fe III 4 (m-OCH 3 ) 2 (L à /O) 2 Br 6 ](5). In these complexes L acts as a meridional tridentate ligand, as previously observed for the corresponding [Cu(L)Cl(CH 3 OH)] 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 In the cases of 3 and 4, the hydrogen of the tertiary carbon has been replaced by a methoxy group in the course of complex synthesis.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 FeBr 3 and H à /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 [Fe II Br 2 (pyridine-2-carboxamide)(di-2-pyridylketone)] (6). It is proposed that the coordination of the amide nitrogen of H à /L to an iron(III) center as an amidate activates the a-C à /H bond and results in the oxidation of the a-C à /N amide bond to an imine. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Crystal structure; Iron complexes; Carboxamide complexes; Amidate complexes 1. Introduction The synthesis of iron complexes with amidate ligands has drawn the interest of inorganic chemists as a means to model the metal coordination spheres of the anti- tumor drug bleomycin [1] and nitrile hydratase [2,3]. Prominent among these efforts are those of Mascharak, who has investigated in detail the structures and proper- ties of iron complexes of a number of amidate ligands based on the pyridine-2-carboxamide framework [4  /8]. We had earlier used bis(2-pyridyl)methylamine in the design of the neutral pentadentate ligand N4Py (N ,N - bis ( 2 - pyridylmethyl ) ( N - bis ( 2 - pyridyl ) methyl ) amine. N4Py provides a ligand environment that stabilizes a metastable [Fe III (N4Py)OOH] 2 intermediate [9] that models some properties of ‘activated bleomycin’ [1], the species believed to be responsible for the anti-tumor action of bleomycin. This effort led us to explore the iron coordination chemistry of the potentially tetraden- tate ligand N -(bis(2-pyridyl)methyl)pyridine-2-carboxa- mide (H Ã/L, Scheme 1) derived from the acylation of bis(2-pyridyl)methylamine by picolinic acid [10]. This investigation has resulted in the synthesis and structural characterization of several novel iron complexes with modified ligands resulting from the oxidation of the tertiary carbon à /nitrogen bond on the ligand. * Corresponding author. Tel.:  /1-612-625 0389; fax:  /1-612-624 7029 E-mail address: que@chem.umn.edu (L. Que, Jr.). 1 On leave from Nanki University, Tianjin, People’s Republic of China. 2 Present address: Department of Chemistry, Brigham Young University, Provo, UT 84602, USA. Inorganica Chimica Acta 337 (2002) 32  /38 www.elsevier.com/locate/ica 0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0020-1693(02)01032-0