Anilino Radical Complexes of Cobalt(III) and Manganese(IV) and Comparison with Their Phenoxyl Analogues

The pendent arm macrocyclic aniline ligands 1-(2-amino-3,5-di- tert -butylbenzyl)-4,7-dimethyl-1,4,7-triazacyclononane, H[L 1 ], and 1,4,7-tris(2-amino-3,5-di- tert -butylbenzyl)-1,4,7-triazacyclononane, H 3 [L 2 ], have been synthesized. The reaction of these ligands in methanol (1:1) and/or ethanol with Co II (ClO 4 ) 2 ·6H 2 O and potassium di- tert -butylacetylacetonate (1:1) or Mn II (acetate) 2 ·4H 2 O in the presence of air produced the anilido complexes [Co III (L 1 )(Bu 2 acac)](ClO 4 ) ( 1 ) and [Mn IV (L 2 )]X (X = ClO 4 ( 2 ), BPh 4 ( 2 ‘ )), respectively. The reaction of H 3 [L 2 ] and CuCl 2 ·2H 2 O in ethanol produced upon addition of NaClO 4 blue crystals of [Cu II (H 3 L 2 )Cl](ClO 4 ) ( 3 ) containing two coordinated and one uncoordinated aniline pendent arm. Complexes 1, 2, and 3 have been structurally characterized by X-ray crystallography. Electrochemically, 1 is reversibly oxidized with formation of the paramagnetic anilino radical species [Co III (L 1 • )(Bu 2 acac)] 2+ ( S = 1 / 2 ) whereas the cyclic voltammogram of 2 displays three ligand-centered one-electron-transfer oxidation waves where complexes [Mn IV (L 2 • )] 2+, [Mn IV (L 2 • • )] 3+, and [Mn IV (L 2 • • • )] 4+ containing one, two, and three coordinated anilino radicals are formed successively. These anilino radical species have been characterized by UV−vis, X-band EPR, and resonance Raman spectroscopy. The characteristic spectroscopic features of coordinated anilino radicals have been elucidated. In the Mn IV radical species strong intramolecular exchange coupling between the metal ion (t 2g 3 configuration, S = 3/2) and one, two, or three anilino radicals ( S rad = 1/2) produces the ground states S t = 1, S t = 1/2, and S t = 0 in the di-, tri-, and tetracation of the parent complex 2, respectively.