Metal acetylacetonates

Metal acetylacetonates are coordination complexes derived from the acetylacetonate anion (CH3COCHCOCH−3) and metal ions, usually transition metals. The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(acac)3 and M(acac)2. Mixed-ligand complexes, e.g. VO(acac)2, are also numerous. Variations of acetylacetonate have also been developed with myriad substituents in place of methyl (RCOCHCOR′−). Many such complexes are soluble in organic solvents, in contrast to the related metal halides. Because of these properties, acac complexes are sometimes used as catalyst precursors and reagents. Applications include their use as NMR 'shift reagents' and as catalysts for organic synthesis, and precursors to industrial hydroformylation catalysts. C5H7O−2 in some cases also binds to metals through the central carbon atom; this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III).hexafluoroacetylacetonetrifluoroacetylacetoneTautomers and complexation of NacnacThe 'NMR shift reagent' Eufod Metal acetylacetonates are coordination complexes derived from the acetylacetonate anion (CH3COCHCOCH−3) and metal ions, usually transition metals. The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(acac)3 and M(acac)2. Mixed-ligand complexes, e.g. VO(acac)2, are also numerous. Variations of acetylacetonate have also been developed with myriad substituents in place of methyl (RCOCHCOR′−). Many such complexes are soluble in organic solvents, in contrast to the related metal halides. Because of these properties, acac complexes are sometimes used as catalyst precursors and reagents. Applications include their use as NMR 'shift reagents' and as catalysts for organic synthesis, and precursors to industrial hydroformylation catalysts. C5H7O−2 in some cases also binds to metals through the central carbon atom; this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III). A general method of synthesis is to treat a metal salt with acetylacetone, acacH: Addition of base assists the removal of a proton from acetylacetone and shifts the equilibrium in favour of the complex. Both oxygen centres bind to the metal to form a six-membered chelate ring. In some cases the chelate effect is so strong that no added base is needed to form the complex. Some complexes are prepared by metathesis using Tl(acac). Treatment of TiCl4 with acetylacetone gives cis-TiCl2(acac)2, a red-coloured, octahedral complex with C2 symmetry: This reaction requires no base. The complex TiCl2(acac)2 is fluxional in solution, the NMR spectrum exhibiting a single methyl resonance at room temperature. Unlike Ti(IV), Zr(IV) and Hf(IV) bind four bidentate acetylacetonates, reflecting the larger radius of these metals. Hafnium acetylacetonate and zirconium acetylacetonate adopt square antiprismatic structures. Vanadyl acetylacetonate is a blue complex with the formula V(O)(acac)2. This complex features the vanadyl(IV) group, and many related compounds are known. The molecule is square pyramidal, with idealized C2v symmetry. The complex catalyzes epoxidation of allylic alcohols by peroxides. Vanadium(III) acetylacetonate is a dark-brown solid. Vanadium β-diketonate complexes are used as precatalysts in the commercial production of ethylene-propylene-diene elastomers (EPDM). They are often evaluated for other applications related to redox flow batteries, diabetes and enhancing the activity of insulin, and as precursors to inorganic materials by CVD. Chromium(III) acetylacetonate, Cr(acac)3, is a typical octahedral complex containing three acac− ligands. Like most such compounds, it is highly soluble in nonpolar organic solvents. This particular complex, which has a three unpaired electrons, is used as a spin relaxation agent to improve the sensitivity in quantitative carbon-13 NMR spectroscopy. Chromium(II) acetylacetonate is a highly oxygen-sensitive, light brown compound. The complex adopts a square planar structure, weakly associated into stacks in the solid state. It is isomorphous with Pd(acac)2 and Cu(acac)2. It has been prepared by the comproportionation of the manganese(II) compound Mn(acac)2 with potassium permanganate in the presence of additional acetylacetone. Alternatively the direct reaction of acetylacetone with potassium permanganate. In terms of electronic structure, Mn(acac)3 is high spin. Its distorted octahedral structure reflects geometric distortions due to the Jahn–Teller effect. The two most common structures for this complex include one with tetragonal elongation and one with tetragonal compression. For the elongation, two Mn–O bonds are 2.12 Å while the other four are 1.93 Å. For the compression, two Mn–O bonds are 1.95 Å and the other four are 2.00 Å. The effects of the tetragonal elongation are noticeably more significant than the effects of the tetragonal compression.