Fluorinated beta-diketonates of the first row divalent transition metals: new approach to the synthesis of unsolvated species.

An original low-temperature solid-state route for the preparation of metal beta-diketonates in their unsolvated forms has been suggested. Four new first row divalent transition metal beta-diketonates, M(hfac)2 (M = Mn (1), Fe (2), Co (3), and Ni (4); hfac = hexaluoroacetylacetonate), have been isolated in quantitative yield. Compounds 1-3 have been obtained by comproportionation reaction between the corresponding M(hfac)3 and metal powder. Ni(hfac)2 (4) has been synthesized by oxidation of metallic nickel with Cu(hfac)2. All products have been characterized spectroscopically and by X-ray powder and single crystal diffraction techniques. The solid state structures of 1-4 feature polynuclear molecules, in which the coordinatively unsaturated metal centers fulfill an octahedral environment by Lewis acid-base interactions with the oxygen atoms of diketonate ligands acting in chelating-bridging fashion. Title transition metal diketonates have been shown to retain their polynuclear structures upon sublimation-deposition procedure as well as in solutions of non-coordinating solvents. In coordinating solvents the molecules of 1-4 quickly form the mononuclear M(hfac)2L2 (L = donor solvent) complexes.