Selective imidazolidine ring opening during complex formation of iron(III), copper(II), and zinc(II) with a multidentate ligand obtained from 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine
M. Boca et al., Selective imidazolidine ring opening during complex formation of iron(III), copper(II), and zinc(II) with a multidentate ligand obtained from 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine, INORG CHEM, 39(15), 2000, pp. 3205-3212
The condensation of 2-pyridinecarboxaldehyde N-oxide and triethylenetetrami
ne yields a product with two imidazolidine rings, as proven by a solid-stat
e X-ray structure analysis as well as by NMR solution spectra. This ligand,
L-1, undergoes a ring-opening reaction on complex formation with Cu(II), y
ielding [CuL2](2+) where L-2 functions as a pentadentate ligand, containing
only one imidazolidine ring. On complexation with Zn(II) and Fe(III), both
rings are opened and the complexes [ZnL3](2+) and [FeL3](3+) with a hexade
ntate L-3 ligand are formed. The recrystallization of [ZnL3](2+) from DMSO
solution results in the complex [ZnL1(DMSO)(2)](2+) in which L-1 behaves as
a tetradentate ligand. Thus L-1, L-2, and L-3 are structural isomers with
two, one, or no imidazolidine rings, as confirmed by X-ray structure analys
es. The intramolecular ring formation is the result of the nucleophilic add
ition of the N(amino) group to the electrophilic sp(2)-hybridized -HCdelta=N site. Owing to the absence of the chelate effect on the sp(3)-hybridized
carbon atom belonging to the imidazolidine ring, the ring opening is facil
itated and readily observed upon complex formation with Cu(II), Zn(II), and
Fe(III).