P-Diketone complexes

Other examples of this synthetic strategy are known for example, a recent zirconium polymer by Illingsworth and Burke (8), who joined amine side groups of a zirconium bis(quadridentate Schiff-base) with an acid dianhydride to give amide linkages. Once again, caution is necesary, as Jones and Power (2) learned when they attempted to link metal bisO-diketonates) with sulfur halides that is, they obtained insoluble metal sulfides because the p-diketone complexes which they used were fairly labile and the insolubility drove the reactions to completion in the wrong direction. 

Tc(III), Tc(IV) and Tc(V) P-diketonate complexes are stable in acid solution. In fact, when a chloroform solution of TcCl2(acac)2 was shaken with 1 M hydrochloric acid solution, no detectable change in the distribution ratio of the complex - defined as the ratio of the concentration of technetium in the organic phase to that in the aqueous phase - was observed over a 24 h period [26]. However, when the technetium complexes were backextracted into aqueous alkaline solution, decomposition occurred [26-29]. In all the cases studied, spectrophotometric investigation revealed that pertechnetate was formed quantitatively as a final product. 

In closing, recovery of technetium from waste solution should be touched upon. Studies of the base hydrolysis of technetium P-diketone complexes revealed that all of the complexes studied decompose in an alkaline solution even at room temperature, until technetium is finally oxidized to pertechnetate. These phenomena are very important for the management of technetium in waste solutions. Since most metal ions precipitate in alkaline solution, only technetium and some amphoteric metal ions can be present in the filtrate [29]. A further favorable property of pertechnetate is its high distribution coefficient to anion exchangers. Consequently, it is possible to concentrate and separate technetium with anion exchangers from a large volume of waste solution this is especially effective using an alkaline solution [54],... 

The efficient and selective catalysis of some Diels-Alder reactions by lanthanide P-diketonate complexes has been known since 1975 [226, 227]. The fluorinated p-diketonate complexes Ln(fod)3 (cf. Scheme 12.5) selectively catalyze the Danishefsky transformation (Scheme 12.23) as a consequence of their mild Lewis acidity. Importantly, zeolites and Lewis acid modified silica or alumina also catalyze Diels-Alder reactions [228-232]. 

Figure43 Angle of twist 6 (degrees) and normalized bite b for tris(P-diketonate) complexes. Theoretical curve for most stable stereochemistry also shown...

In the above examples, the nucleophilic role of the metal complex only comes after the formation of a suitable complex as a consequence of the electron-withdrawing effect of the metal. Perhaps the most impressive series of examples of nucleophilic behaviour of complexes is demonstrated by the p-diketone metal complexes. Such complexes undergo many reactions typical of the electrophilic substitution reactions of aromatic compounds. As a result of the lability of these complexes towards acids, care is required when selecting reaction conditions. Despite this restriction, a wide variety of reactions has been shown to occur with numerous p-diketone complexes, especially of chromium(III), cobalt(III) and rhodium(III), but also in certain cases with complexes of beryllium(II), copper(II), iron(III), aluminum(III) and europium(III). Most work has been carried out by Collman and his coworkers and the results have been reviewed.4-29 A brief summary of results is relevant here and the essential reaction is shown in equation (13). It has been clearly demonstrated that reaction does not involve any dissociation, by bromination of the chromium(III) complex in the presence of radioactive acetylacetone. Furthermore, reactions of optically active... 

The electrophilic substitution of P-diketonate complexes appears to occur as for arenes, and a process involving initial coordination of the electrophile, followed by an intramolecular group transfer, has not been observed, although it has been postulated for the reaction of copper(II) acetylacetonate with thioacetals (equation 14).31... 

Figure 4.42. Molecular structures of commonly used CVD precursor classes. Shown are (a) metal p-diketonate (acetylacetonate, acac) complex to grow a metal oxide film (H2 as the coreactant gas yields a metal film) (b) a heteroleptic (more than one type of ligand bound to the metal) p-diketonate complex to yield a Cu film the ancillary ligand helps prevent oligomerization, enhancing volatility (c) various types of complexes to deposit metallic, oxide, nitride, or oxynitride films (depending on coreactant gas(es) used - respective ligands are p-ketoiminato, p-diketiminato, amidinato, and guanidinato (d) a metal azolato complex commonly used to deposit lanthanide metal thin films.

The parent ligands exhibit a rich, smectic pol5unorphism, but when modified with a fused cyclopentene ring, nematic phases dominate. Reaction of the ligands with tetrachloroplatinate(II) leads to poorly soluble, dimeric complexes that can be cleaved using dimethylsulfoxide the resulting monomeric complexes are then readily converted to the P-diketonate complexes. All of the complexes are mesomoiphic, and the P-diketonate complexes... 

Binnemans, K. (2005) Rare earth p-diketonate complexes functionalities and applications, in Handbook on the Physics and Chemistry of Rare Earths, Vol. 35 (eds K.A. Gschneidner, J.C.G BiinzU, and V.K. Pecharsky), Elsevier Science, North Holland, pp. 107—272. 

Baker, M.H., Dorweiler, J.D., Ley, A.N., etal (2009) Structure and emission spectra of dinuclear landianide(lll) P-diketonate complexes widi abridging 2,2 -bipyrimidine ligand. Polyhedron, 28, 188—194. 

Terbium complexes reported for electroluminescence can be separated mainly into two classes terbium carboxylates and P-diketone complexes. Terbium carboxylates have good luminescence but they are difficult to use as efficient emission materials in OLEDs due to their multi-coordination mode and consequent formation of inorganic polymers with poor solubility or volatility. For these reasons, in this section we will focus on use of the newly developed f)-diketonate terbium complexes in OLEDs. 

Wang, Y.Y., Wang, L.H., Zhu, X.H., etal. (2007) Efficient electroluminescent tertiary europium(III) P-diketonate complex with functional 2,2 -bipyridine ligand. Synthetic Metals, 157, 165-169. 

Sun, M., Xin, H., Wang, K.Z., et al. (2003) Bright and monochromic red light-emitting electroluminescence devices based on a new multifunctional europium ternary complex. Chemical Communications, 702-703. Liang, L.S., Zhou, Q.G, Cheng, Y.X., and Wang, L.X. (2003) Oxadiazole-functionalized europium(III) P-diketonate complex for efficient red electroluminescence. Chemistry of Materials, 15, 1935-1937. 

Kang, T.S., Harrison, B.S., Bouguettaya, M., et al. (2003) Near-infrared light-emitting diodes (LEDs) based on poly(phenylene)/Yb-tris(P-diketonate) complexes. At/vanceti Functional Materials, 13, 205-210. 

Acetylacetonates. — The p-diketonate complexes of the trivalent rare earths are among the more stable of the complex species. The general... 

The first asymmetric catalyst to be evaluated was the commercially available chiral lanthanide P-diketonate complex Eu(hfc)3 [10]. The initial result was obtained from the reaction of benzaldehyde with diene 5, which showed 18% enantiomeric excess [11]. Attempts to improve the asymmetric induction by varying the substituents on the diene were undertaken (Scheme 4). Substitution at either C2 or C4 of the diene seemed to increase the asymmetric induction. By using the... 

The first catalyst to be evaluated was the commercially available chiral lanthanide p-diketonate complex Eu(hfc)3. The reaction of benzaldehyde with diene (8) was chosen as the system to screen various catalysts for their enantiofacial selectivity. A simple method to assess the extent and sense of the optical induction was also developed. This was accomplished by optical and NMR measurements on compound (68), obtained from (64) and (65) by a previously described protocol (Scheme 22).- - - The en-antioselectivity with diene (8) and benzaldehyde is 18%. ... 

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