Preparation, structure and electrochemical behavior of dinuclear cyclooctadiene-chelated Ir(I) complexes with 2-aminopyridinato bridges

Dinuclear iridium(I) complexes with two bridging aminopyridinato ligands, [ Ir(mu-L)(COD)](2) (COD = 1,5-cyclooctadiene (1): L = 2-aminopyridinato (ap) (2): L = 2-anilinopyridinato (anp)), were prepared from [Ir(mu-Cl)(COD)](2 ) and Li+L- in a 24-36% yield. These compounds were characterized by X-ray structure analysis and H-1 NMR spectroscopy. Two iridium atoms were bridged by two aminopyridinato ligands and each iridium atom was coordinated by on e chelating GOD. The coordination sphere of each Ir(I) center, which was fo rmed by two N atoms and two olefinic pi bonds, was square planar. Ir ... Ir separations in 1 and 2 were 3.0998(6) and 3.0681(3) Angstrom, respectively . Cyclic voltammetry of 1 and 2 in n-Bu4NPF6/CH2Cl2 exhibited a chemically reversible oxidation wave at -0.41 and -0.36 V versus Fc(+)/Fc, respectivel y. These potentials were lower than those of [Ir(mu-form)(COD)](2) (form = anion of N,N'-di-p-tolylformamidine), [Ir(mu-hp)(COD)](2) (hp = anion of 2- hydroxypyridine), [Ir(mu-mhp)(COD)](2) (mhp = anion of 6-methyl-2-hydroxypy ridine) and [Ir(mu-pz)(COD)](2) (pz = anion of pyrazole). Electrolytic one- electron oxidation of 2 gave its stable cationic radical, [Ir(mu-anp)(COD)] (2)(+), of which frozen solution ESR spectrum was rhombic with g(1) = 2.43, g(2) = 2.30 and g(3) = 2.08 and no hyperfine splitting was resolved. (C) 1 999 Elsevier Science S.A. All rights reserved.