Soluble Monometallic Salen Complexes Derived from O‐functionalized Salicylaldehydes as Metalloligands for the Synthesis of Heterobimetallic Complexes

The reaction of 2,3‐diamino‐2,3‐dimethylbutane (tmen) with 3‐hydroxysalicylaldehyde (3hsal), 4‐hydroxysalicylaldehyde (4hsal), and 5‐hydroxysalicylaldehyde (5hsal) or 3‐carboxysalicylaldehyde (3csal) gave the hydroxy‐functionalized salen ligands H 4 3hsaltmen, H 4 4hsaltmen and H 4 5hsaltmen, or the 3‐carboxy‐functionalized ligand H 4 3csaltmen, which were characterized by 1 H, 13 C{ 1 H} NMR and IR spectroscopy. The nickel(II) and copper(II) complexes [Ni(H 2 3hsaltmen)], [Ni(H 2 4hsaltmen)], [Ni(H 2 5hsaltmen)], [Cu(H 2 3hsaltmen)] and [Cu(H 2 4hsaltmen)] were synthesized in high yield (78–99 %) starting from H 4 3hsaltmen, H 4 4hsaltmen and H 4 5hsaltmen and the corresponding metal(II) acetates. The complexes are soluble in acetone, ethanol, methanol, thf and dmso. The reaction of H 4 3csaltmen and nickel(II) acetate gave [Ni(H 2 3csaltmen)] in 40 % yield. The disodium salt of the corresponding copper(II) complex [Cu(Na 2 3csaltmen)] was obtained in 66 % yield in a template reaction from 3‐carboxysalicylaldehyde, tmen, copper(II) acetate and sodium hydroxide, and was characterized by EPR spectroscopy and mass spectrometry. All complexes were identified by IR spectroscopy and elemental analysis, the nickel complexes also by NMR spectroscopy, and [Ni(H 2 3hsaltmen)], [Ni(H 2 4hsaltmen)] and [Ni(H 2 3csaltmen)] by X‐ray crystallography. The homobinuclear copper complex [Cu 2 (3hsaltmen)] was prepared in 91 % yield from H 4 3hsaltmen, two equivalents of Cu(CH 3 COO) 2 ·H 2 O and four equivalents of LiOH·H 2 O and was characterized by IR spectroscopy, elemental analysis and mass spectrometry. The trinuclear complex [Zr{Ni(3hsaltmen)} 2 ] was obtained from [Zr(NEt 2 ) 4 ] and [Ni(H 2 3hsaltmen)] (ratio 1:2) and characterized by FAB and APPI mass spectrometry and X‐ray crystallography. The redox potential of the trinuclear complex [Zr{Ni(3hsaltmen)} 2 ] is shifted by 0.04 V to positive potential compared to [Ni(H 2 3hsaltmen)], while the redox potential of the binuclear copper complex [Cu 2 (3hsaltmen)] is shifted by 0.22 V to negative potential compared to [Cu(H 2 3hsaltmen)].