Synthesis, Solid-State Structures, and EPR Spectroscopic Studies on Polycrystalline and Single-Crystal Samples of α-Diimine Cobalt(II) Complexes

Abstract

Cobalt compounds of the general formula [CoX2(a-diimine)], where X = Cl or I and the a-diimines are 1,4-diaryl-2,3-dimethyl- 1,4-diaza-1,3-butadiene (Ar-DAB) and bis(aryl)- acenaphthenequinonediimine (Ar-BIAN) were synthesized by the direct reaction of the anhydrous cobalt salts CoCl2 or CoI2 and the corresponding a-diimine ligand in dried CH2Cl2. The synthesized compounds are [Co(Ph-DAB)Cl2] (1a), [Co(o,o',p-Me3C6H2-DAB)Cl2] (1b), and [Co(o,o'- iPr2C6H3-DAB)Cl2] (1c) with the ligands Ar-DAB, and also [Co(o,o',p-Me3C6H2-BIAN)I2] (2'b) with the ligand Ar-BIAN. The crystal structures of all the compounds were solved by Introduction Cobalt is a 3d transition metal element that has been extensively studied over the last decades. Interest in cobalt compounds arises from their participation in many different processes, from industrial and technological applications as catalysts to the essential role in several biological systems of central importance in nature.[1–5] A large number of late transition metal complexes bearing a-diimine[6] ligands have been extensively studied in the commercial production of polyolefin from ethene and propene.[ 7,8] However, reports on cobalt complexes containing this type of ligands are still scarce.[9] Recently, some results from the insertion polymerization of ethylene have been reported using tetrahedral CoII complexes with related ligands.[ 10] a-Diimine ligands have also been the subject of different studies regarding the relative binding strengths,[11] as well as their reactivity with main group metals.[12] [a] REQUIMTE/CQFB, Departamento de Química, FCT, Universidade Nova de Lisboa, Caparica 2829-516, Portugal E-mail: tap@dq.fct.unl.pt [b] Centro de Química Estrutural, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal [c] Laboratoire DECOMET, ILB Université Louis Pasteur 4, rue Blaise Pascal, 67000 Strasbourg, France E-mail: welter@chimie.u-strasbg.fr [d] Departamento de Física, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, C.C. 242, 3000 Santa Fe, Argentina E-mail: brondino@fbcb.unl.edu.ar [e] INTEC, Universidad Nacional del Litoral, Güemes 3450, 3000 Santa Fe, Argentina Eur. J. Inorg. Chem. 2006, 4761–4769 © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4761 single-crystal X-ray diffraction. In all cases the cobalt atom is in a distorted tetrahedron, which is built up of two halide atoms and two nitrogen atoms of the a-diimine ligand. Xband EPR measurements of polycrystalline samples performed on compounds 1b, 1c, and 2'b indicate a high-spin CoII ion (S = 3/2) in an axially distorted environment. Singlecrystal EPR experiments on compounds 1b and 1c allowed us to evaluate the orientation of the g tensor in the molecular frame.