ChemInform Abstract: Preparation, Structure, and Redox Activity of Nickel(II), Palladium(II), and Copper(II) Cofacial Binuclear Bis(β‐keto enamine) Complexes.

Abstract

ChemInform Abstract The bis(β-keto enamine) ligand (IV) is prepared starting with 5-tert.-butyl-m-xylene (I) as shown in the scheme. This ligand reacts with Ni(II) nitrate or PdCl2(NCMe)2 in the presence of NEt3 to give the cis-anti isomer (V) of the corresponding cofacial binuclear complexes (V) (space group P21/c, Z=2). An analogous product is obtained from Cu(II) salts, however the high crystallographic symmetry of the Cu complex (C2/m, Z=2) prevents identification of the specific isomer present. The Ni complex (Va) and its Cu analogue exhibit quasireversible two-electron-oxidation waves in cyclic voltammetry, whereas the analogous mononuclear complexes of 2-amino-2-penten-4-one show irreversible one-electron oxidation. Initial electrochemical oxidation of the Pd complex (Vb), while involving only one electron, is easier than that of bis(2-amino-2-penten-4-onato)-Pd. Thus, the binuclear species exhibit new types of redox processes, and their relatively rigid structure appears to lead to unusual kinetic stability.