Metal-free and dicopper(II) complexes of schiff base [2 + 2] macrocycles derived from 2,20-iminobisbenzaldehyde: Syntheses, structures, and electrochemistry

摘要

Three new bis-terdentate Schiff base [2 + 2] macrocycles (H_2LEt, H_2L~(Pr), and H_2L~(Bu)) have been prepared in high yields by 1:1 condensation of 2,20- iminobisbenzaldehyde with 1,2-diaminoethane, 1,3-diaminopropane, and 1,4-diaminobutane, respectively. Metalation of these macrocycles yields the corresponding dicopper(II) acetate (1, 2, and 3) and tetrafluoroborate (4, 5, and 6) complexes. The structures of H_2Et~(Pr), H_2L~(Pr), H_2L ~(Bu), [CuII _2Li(OAc)_2] _3 solvents (where i is Et, Pr or Bu) and [Cu~(II)_2LPr(DMF)_4] (BF_2)_2 3 0.5H2Oare reported. Intramolecular hydrogen bonding is a feature of the metal-free macrocycles. The copper(II) centers in [Cu~(II)_2Li(OAc)_2] 3 solvents are four coordinate, and the macrocycles have U-shaped (Et, Bu) or stepped (Pr) conformations. Complex 5 crystallizes with two dimethylformamide (DMF) molecules bound per five coordinate copper(II) center. Electrochemical studies revealed ligand based oxidations for all of the macrocycles and complexes. Complexes 1 and 2 undergo two quasi-reversible oxidations in DCM which are associated with the deposition of a visible film on the electrode after multiple scans in this oxidative region, suggestive of electropolymerization. Complexes 4-6, studied in MeCN, have CuII f CuI redox potentials at more positive potentials than for 1-3.