2,4-Pentanedione, complexes with cobalt

Cobalt(III) l,5-diaIkyl-2,4-pentanedionate derivatives have been obtained by oxidation of C0L2 with hydrogen peroxide in water . Analogously, the vanadium(IV) derivative VO(acac)2 is oxidized by I2 to the polyiodide [VO(acac)2]l5 . Charge ti ansfer complexes of general formula [M(acac) I]l3 (M = Fe , Co , n = 3 M = Ni, n = 2 ) have been isolated and characterized from the reaction of M(acac) with diiodine. 

When a metal ion such as nickel (II) is absent, thiazoles and mercaptals are formed. Such reactions have been carried out in which the diketone was biacetyl, 2,3-pentanedione, 2,3-octanedione, l-phenyl-l,2-propane-dione, and 1,2-cyclohexanedione (51). In like manner, the tris complexes of W,W -dimethyl-2,3-butane diimine with iron(II), cobalt(II), and nickel(II) may be prepared from methylamine and biacetyl when the appropriate metal ion (27j 28j 41) is present. Replacing methylamine with hydroxylamine causes the formation of a-dioximes (13). 

With dipivaloylmethane, the zinc(II), cobalt(II) (12), and iron(II) complexes (19) are all isomorphous. A three-dimensional x-ray structural determination (12) of the Co(DPM)2 shows a tetrahedral configuration. The copper(II) complex of this ligand and the nickel(II) derivative are planar. The 3-phenyl-2,4-pentanedione derivative of copper(II) also is planar (7). 

Two convenient methods of synthesis of the nickel(II) and cobalt-(II) complexes are described here. Method A, based on reaction of the sodium enolate salt of l,l,l,5,5,5-hexafluoro-2,4-pentanedione with the transition-metal chlorides in dimethylformamide (dmf), gives almost quantitative yields of Ni(hfa)2(dmf)2 and Co(hfa)2(dmf)2. Method B gives lower yields (50-75%) of the same products but can be carried out rapidly in common laboratory equipment (Method A is best carried out by vacuum-line techniques7). 

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