2,4-Pentanedione, complexes with 1,1,1,5,5,5-hexafluoro-, complex

The major breakthrough that transformed metal chelate GC into a useful analytical technique was the introduction of fluorinated beta-diketone ligands, which formed complexes of greater volatility and thermal stability. Trifluoroacetylacetone (l,l,l-trifluoro-2,4-pentanedione—HTFA) and hexafluoro-acetylacetone (l,l,l,5,5,5-hexafluoro-2,4,-pentanedione—HHFA) are the fluorinated ligands most frequently employed. HTFA extended the range of metals that may be gas chromatographed with little or no evidence of decomposition to include Ga3+, In3+, Sc3+, Rh3+ and V4+. An example of a recent application is the analysis for beryllium in ambient air particulates. After filter sampling and extraction/chelation, packed column GC with electron capture detection allowed ppm level beryllium quantitation in collected particulates which corresponded to levels of 2-20 x 10 5 pg/m3 in the sampled air. 

Recently Bonati and Wilkinson4 reported that tetracarbonyl-di-jti-chloro-dirhodium(I) reacts with various 1,3-diketones in the presence of barium carbonate to give compounds such as Rh(C0)2(CgH702). Similarly, chloro(pentacarbonyl)manga-nese(I) and l,l,l,5,5,5-hexafluoro-2,4-pentanedione afford the complex Mn(C0)4(CsHF602) in low yields (14%).5... 

Experimental information on the energetics of silver-olefin bonds comes from a 1973 study by Partenheimer and Johnson26. Using titration calorimetry with the inert dichloromethane as solvent, these authors measured the enthalpies of reaction 14 for several olefin complexes (hfacac = 1, 1, 1, 5, 5, 5-hexafluoro-2,4-pentanedionate) whose structure (1) is illustrated below for olefin = cyclohexene. 

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). 

We have also expanded our studies to include chromium(III) systems. However, for the chromium centers we have chosen the more volatile tri-fluoro (tfa") and hexafluoro (hfa ) derivatives of 2,4-pentanedione. Since the fluorinated derivatives are deactivated relative to the electrophilic attack used in these polymerizations, the Cr(acac)2(tfa) mixed ligand complex has been used initially to obtain polymeric products with sulfur halides. Whereas the intrinsic viscosity of one of the polymers so obtained was 0.17 dL/g, the GPC results suggest only oligomeric products. 

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