Optical resolution and racemisation of [Fe(acac)3]

Optical resolution of [M(acac)3] complexes, where acac− is the acetylacetonato ligand, was achieved decades ago for metal ions such as Co3+ and Cr3+, i.e. for metal ions forming configurationally inert complexes. Complete optical resolution of [Fe(acac)3] have so-far been unsuccessful due to the high rate of racemisation. By means of spontaneous resolution of its carbon tetrachloride solvate, we have been able to prepare optically pure samples of [Fe(acac)3]. These samples displayed circular dichroism in the solid state, as well as in diethyl ether solution, and the CD-spectra could be correlated to the correct absolute configuration. Using CD-spectroscopy, the optical half-life was estimated to be 3.3 min in diethyl ether solution at ambient temperature. In the same solvent, no sign of racemisation was observed after 23 h at −80 °C. Racemic [Fe(acac)3] is a useful catalyst in organic synthesis.