Ferrocene containing chelating ligands 3. Synthesis, spectroscopic characterization, electrochemical behaviour and interaction with metal ions of new ligands obtained by condensation of ferrocenecarboxaldehyde with 2-amino-benzoic acid derivatives. Crystal structures of 2-ferrocenylmethylamino-5-methyl-benzoic acid and 2-bis(ferrocenylmethyl)ammonium-5-methyl-benzoic acid perchlorate

Abstract

Ferrocenecarboxaldehyde reacts with 2-amino-benzoic acid, 2-amino-5-methyl-benzoic acid or 3-amino-2-naphthoic acid to give the corresponding Schiff-base derivatives 2-ferrocenylmethylidenimino-benzoic acid ( 1), 2-ferrocenylmethylidenimino-5-methyl-benzoic acid ( 2) and 3-ferrocenylmethylidenimino-2-naphthoic acid ( 3). 1, 2 and 3 are stable in the solid state but easily hydrolyze in solution. This hydrolysis has been studied kinetically in a methanol-water medium. In order to increase the stability in solution to use these compounds as ligands, the imino group from 1, 2 and 3 was reduced by NaBH 4 to give the amino derivatives 2-ferrocenylmethylamino-benzoic acid ( 4), 2-ferrocenylmethylamino-5-methyl-benzoic acid ( 5) and 3-ferrocenylmethylamino-2-naphthoic acid ( 6). 4, 5 and 6 are stable, both in the solid state and in solution, and potential chelating NO donor ligands containing ferrocenyl groups. The protonation of 4–6 and their complex formation with copper(II) have been investigated by potentiometry in dimethyl sulfoxide (dmso)-water (80:20 wt./wt.) mixtures at 25 °C and 0.1 mol dm −3 KClO 4. The molecular structure of 5 has been determined by single-crystal X-ray methods. It crystallizes in the triclinic system, space group P 1 ̄ , with a = 6.1747(7), b = 9.539(1), c = 13.511(4) A ̊ , α = 88.99(1), β = 87.00(1), γ = 82.34(1)°, V = 787.6(3) A ̊ 3 and Z = 2 . An unusual feature of the ferrocene-containing ligand 5 in its interaction with nickel(II) ions was found. Cleavage of the CN bond of the secondary amine 5 and molecular rearrangement yields the protonated tertiary amine 2-bis(ferrocenylmethyl)ammonium-5-methyl-benzoic acid perchlorate ( 7). Compound 7 crystallizes in the monoclinic system, space group P2 1/ c with a = 9.702(9), b = 27.153(17), c = 22.326(6) A ̊ , β = 97.39(6)°, V = 5833(12) A ̊ 3 and Z = 8 . Typical reversible oxidation waves were found for 4–7 whereas some degree of irreversibility was detected for their parent imines.