Barium 2,4-pentanedionate

Another possibility is anionic polymerization with alkyllithium in combination with barium compounds such as barium 2,4-pentanedionate [192-194, 203-205]. Also, cobalt(II) chloride in combination with diethylaluminum chloride and triethylamine is used, yielding a polymer with 91% trans-l A and 9% 1,2 structures. 

In dim red light, the weighed hydrazide contained in one of the 500 ml flasks (ca. 67 g 95% of theory) is washed into a 1000 ml beaker with 263 ml IN hydrochloric acid. 239 ml distilled water, 239 ml ethanol (95%), and 37 ml 2,4-pentanedione are added, and the well-mixed solution left to stand in the dark at room temperature until the reaction is complete, i.e., about 30 minutes. The reaction mixture is neutralized with the addition of 263 ml 1 N sodium hydroxide, and the beaker covered with parafilm and refrigerated to ensure complete precipitation. The pyrazole is filtered at the pump, the mother liquor being returned to the beaker and used to wash out the last few crystals, washed with cold water, and sucked dry under a stream of dry nitrogen. The product is dried in vacuo over barium oxide or phosphorus pentoxide for at least twelve hours before proceeding to the next step, wherein anhydrous conditions will increase yield. Hofmann calls for drying the pyrazole in vacuo at 60°, which indicated the product to be fairly stable. So all the hydrazide is converted prior to aminization. 

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... 

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