Chiral metal complexes. Part 5. Cobalt(II) and some other transition-metal complexes of chiral vic-dioximate ligands derived from D-camphor and L-β-pinene

Abstract

Chiral bis(vic-dioximato)-complexes of Fe^II, Co^II, Ni^II, and Pd^II have been prepared from three geometrical isomers (α, β, and δ) of D-camphorquinone dioxime (Hcqd) and two (β and δ) of L-nopinoquinone dioxime (Hnqd). The co-ordination geometry has been investigated by ¹H and ¹³C n.m.r., i.r., and electronic spectroscopy to reveal a novel NO-chelation of the metal with the (E,Z)-dioximate isomers (α- and δ-cqd and δ-nqd). The (E,E)-dioximate isomers (β-cqd and β-nqd ) co-ordinate to a metal with the usual NN-chelation. The c.d. spectra of the free ligands and the corresponding metal complexes are utilized to investigate the chirality of the chromophores at the unco-ordinated and co-ordinated dioximate moiety. Opposite Cotton effects around 20 000 cm^–1 have been observed for [Co(α-cqd)₂]·H₂O and [Co(δ-nqd)₂]·H₂O indicating their ‘quasi-enantiomeric’ stereochemistries.