An NMR Study of Metal Complexes Containing Acetylacetone and Related Compounds. I. The Preparation, Halogenation and NMR Spectra of Cobalt(III) Complexes Containing Acetylacetone and Bis(acetylacetone)ethylenediimine

Abstract

A mixed cobalt(III) complex containing both bis(acetylacetone) ethylenediimine and acetylacetone anions, [Co(bean)(acac)] (bean=dianion of bis (acetylacetone) ethylenediimine, acac=anion of acetylacetone), was newly prepared and its electrophilic substitution reaction at the chelate ring protone was studied by means of NCS, NBS, and NIS (NCS, NBS and NIS are the abbreviated forms of N-chloro-, N-bromo- and N-iodosuccinimide). The structures of this complex, [Co(baen)-(acac)], and of the halogenated complex were both determined to be of the β-form (cis with respect to the coordinated two oxygen atoms of baen) on the basis of their NMR spectra. The ring protons of the imine chelates were found to be more reactive than that of the acetylacetone chelate in the chlorination reaction. Then, a bi-substituted complex, [Co(baen-Cl₂)(acac)], in which two chlorine atonies were attached to the two imine chelate rings, was prepared. Tri-substituted complexes, [Co(baen-X₂)(acac-X)] (X=Cl, Br and I), were also prepared. The quasiaromaticity of both the acetylacetone and imine rings was considered on the basis of their NMR spectra. A new complex, [Co(baen)(OH)(H₂O)], was also prepared in order to assign the NMR spectrum of the complex, [Co(baen)(acac)]. The IR, UV, and visible absorption spectra were also considered.