Metals acetylacetonate chelates

Kaeriyama and Shimura [34] have reported the photoinitiation of polymerization of MMA and styrene by 12 metal acetylacetonate complex. These are Mn(acac)3, Mo02(acac)2, Al(acac)3, Cu(bzac)2, Mg(acac)2, Co(a-cac)2, Co(acac)3, Cr(acac)3, Zn(acac)2, Fe(acac)3, Ni(a-cac)2, and (Ti(acac)2) - TiCU. It was found that Mn(a-cac)3 and Co(acac)3 are the most efficient initiators. The intraredox reaction with production of acac radicals is proposed as a general route for the photodecomposition of these chelates. 

Treatment of a series of metal acetylacetonates with the N-halogen suc-cinimides in boiling chloroform afforded the trihalogenated metal chelates in high yields. The use of bromine or iodine monochloride in buffered acetic acid also yielded the bromo- and iodochelates (7). 

Friedel-Crafts acylations of the metal acetylacetonate rings are much slower than the electrophilic substitutions described above, probably because of the considerable steric bulk at the reaction site. Furthermore, the strongly acidic conditions during the reaction and subsequent hydrolysis step give rise to considerable degradation, particularly in the case of the more sensitive chromium and cobalt chelates. This consideration places severe limitations on the reaction conditions that can be employed. 

Several of the unusual chemical properties of functional groups on metal acetylacetonate rings may be explained in terms of the considerable steric hindrance afforded the central carbon of the chelate ring by the flanking methyl groups. To examine this hypothesis the preparation of chelates of formyl acetone (XXXVIII) and malonaldehyde (XXXIX) was undertaken. 

The metal chelates are usually prepared from acetylacetone or trifluoroacetylacetone and are dissolved in a small quantity of stationary phase for the injection and separation. The UV absorbance of the derivatives is measured at 310 nm in a monitor equipped with a microflow cell. The separation of six metal acetylacetonates is shown in Fig.4.33 (column, SO cm X 2.7 mm I.D. particle diameter, 5-10 /am flow-rate, 1.8 mm/sec). 

To address a diverse but related concern, the effect of chelation of adsorbed copper and iron species on the catalytic degradation of paper was investigated. The stability of paper containing copper and iron species adsorbed from ionic solutions was compared with that of paper containing the acetylacetonate chelates of these metals. Nonpolar acetylacetonate complexes of metals have no affinity for adsorption on paper. These copper and iron chelates are neither adsorbed nor chemically bonded to the paper matrix. 

Rates of degradation observed in the presence of ionic iron and copper systems have been compared with those obtained for the respective acetylacetonate chelate systems in Tables X and XI. Lower relative lifetime and relative stability values are observed for the copper(II) acetylacetonate catalyzed system than those obtained in the presence of higher concentrations of the ionic copper species. A similar increase in the catalytic efficiency of copper upon coordination has been reported by Ericsson et al. (10). However, iron(III) acetylacetonate shows no catalytic effect at all. This observation of contrary effects on the stability of paper with the same chelates of two highly active transition metal catalysts is most interesting. Unlike the relatively stable octahedral iron(III) acetylacetonate molecule, the tetrahedral, tetracoordinate copper(II) chelate could accept two more ligands if it were to assume an... 

Aromatics such as benzene and toluene have also been used as a solvent for highly chelated metal complexes, such as in the preparation of supported metal acetylacetonates. Aromatics are a good choice for metal complexes formed with aromatic ligands such as bipyridil. Tetrahydrofuran (THF) has also been used as a solvent to prepare silica-supported Pd that was generated by the decoration of the surface with Pd(acac)2. °... 

Another example of geometrical hindrance acting on the cr,77-conjugation is the chelated metal acetylacetonates. We [together with Kursanov, Smolina, and Fames 125)] showed that, unlike acetylacetone, cobalt (III) or aluminum acetylacetonates did not exchange their protons for deuterium with DjO in dioxane. 

The Gp. IVA metals form chelates only with oxygen donors such as catechol and acetylacetone. 

VO(acac)(Tp )] and [VO(acac)(Tp )]-CH3CN were prepared and characterized by IR, UV-Vis, and NMR techniques.24 [VO(acac)(Tp )] and [VO(acac)2(Tp )] have been characterized by IR, NMR, and EPR methods. Thermoanalytical studies on [VO(acac)Tp ] and [VOlacachTp ] were performed by TG and DTG methods to study the influence of the chelating ligand L on the thermal stability of these metal acetylacetonate complexes.18... 

Chloro- and 1-bromobenzotriazoles halogenate metal acetylacetonates in the y-position with the preservation of the chelate structure or with the formation of complexes with the partial substitution of acetylacetone with benzotriazolyl moiety (96TMC457) (Scheme 61). 

The chemical reactivity of the thiocyano groups in these chelate rings has not been investigated, but the halogen atoms in the 3-halo metal acetylacetonates have been found to be quite inert and their behavior is different from that of aryl halides, since treatment of the tris(3-bromo-2,4-pentanediono)chromium(III) chelate with magnesium or lithium in benzene or tetrahydrofuran resulted in no reaction. Attempted nucleophilic displacement of the bromine atoms in this chelate by azide, acetate, nitrate, and iodide ions in hot dimethylformamide also failed. In most of these... 

Another possible mechanism involves the bromination of the free ligand which is in equilibrium with the metal acetylacetonate and the metal ion, the reaction proceeding until the metal acetylacetonate is completely converted into the 3-halo compound. The results of the experiments carried out with C14-labeled acetylacetone have shown conclusively that for the inert metal chelates, at least, bromination does not occur via this mechanism (112). 

The only authenticated cases of reactions involving intact metal chelate rings are those of the metal acetylacetonates. In all the other systems that will be described in this review, it is presumed that the chelate ring retains its integrity throughout the course of the reaction or at least during some critical phase of the reaction. 

The metal acetylacetonates have been successfully nitrated with several nitrating agents that have been used to nitrate reactive aromatic systems. Nitrating agents commonly used to nitrate aromatic and aliphatic compounds will destroy the metal chelate. 

Further reaction of the sulfenyl chlorides to the sulfides does not take place. It can also be deduced that the substitution reaction occurred with the chelate ring unruptured, since no sulfides (usually obtained with sulfur dichloride and the enol form of 2,4-pentanedione) were obtained. The structures of the sulfenyl chlorides of the metal acetylacetonates were confirmed by their infrared spectra, and by conversion of the sulfenyl chloride to a thiocyano group by reaction with cyanide ions. The tris(3-thiocyano-... 

The acylation of the metal chelates of /3-diketones has been studied quite extensively. In early work on the benzoylation of acetylacetone chelates, C-acylation as well as O-acylation was reported to occur (47,156), and a recent study on the benzoylation of dibenzoylmethane chelates confirmed this (153). In an investigation of the reaction of m- or p-nitro-benzoyl chloride with the copper(II) chelate of acetylacetone, it was found that on shaking the reactants together in CHC13 for 12-24 hours at room temperature a triketone was obtained together with a precipitate of cupric chloride. The triketone could be converted to a /3-diketone by treatment with aqueous ammonia followed by acidification with HC1 (20) ... 

Kinetic studies were carried out in order to determine the mechanism of the autoxidation reactions. The results indicate that the reactions do not proceed via the usual type of radical-chain mechanism involving hydroperoxides, and that not all metal acetylacetonates follow the same mechanism. A relatively simple mechanism has been proposed for the destructive autoxidation of iron(III) acetylacetone that postulates an intramolecular oxidation-reduction of the chelate with the formation of stable radicals, which are intercepted by highly reactive radicals produced by the decomposition of initiators. A triketone, 2,3,4-pentanetrione, is postulated as the intermediate from which most of the reaction products are derived (4, 5). 

Despite the recent interest in the preparation and properties of thermally stable metal chelates, only a few attempts have been made to study in a systematic manner the chemical reactions that take place when metal chelates are thermally decomposed. The thermal stabilities of the acetyl-acetonates of a number of metal ions were compared by measuring the increase in pressure caused by the formation of volatile decomposition products in a closed system containing the metal acetylacetonate and nitrogen gas. A comparison of the data obtained at 191°C indicated that the rate and extent of decomposition were dependent on the nature of the metal ion. The acetylacetonates of Zr(IV), Co(III), Fe(III), and Mn(III) had the lowest thermal stability whereas the Li(I), Mg(II), Be(II), Cu(II), Ni(II), Ga(III), and Cr(III) chelates were among the most stable (44)- In contrast, acetylacetone itself does not decompose under the same conditions (4 ). 

The infrared spectra 174) show no absorptions above 1600 cm , except for the C-H-stretching frequencies, thus supporting the conclusion that the products are free of hydrolytic impurities. The infrared spectra of M(acac)2X2, M(acac)gX, and M(acac)4 are generally similar to the spectra of other metal acetylacetonates in the chelating carbonyl stretching region. The observed carbonyl frequency shifts are in accord with the expectation that a coordination number increase results in a... 

The direct substitution of bromine into the chelate rings of metal acetylacetonates is an example of the reaction of a coordinated ligand. Tris(3-bromoacetylacetonato)chro-mium(III) has been prepared by the action of elementary bromine on chromium(III) acetylacetonate [2,4-pentane-dionatochromium(III)]. The procedure given here is... 

Chem. Descrip. Acetylacetonate chelate Uses Catalyst for esterification and olefin polymerization crosslinking agent for automotive prods., coatings, elastomers, films/paints, graphic arts, plastics surf, modifier for coatings, cosmetics, electronics, films, glass, graphic arts, metals, petrol, prods., plastics Propetties Red liq. m.w. 364 sol. in IPA, IPA-water, ethyl acetate, IPA sp.gr. 0.99 vise. 15 cP flash pt. (PMCC) 12 C 75% in IPA Tyzor DC [DuPont]... 

The chelated complexes CpFe Ti3-C5H3[L,M]CH2NMe2 [LnM = Mo02(acac), WOCI3, Th(acac)a, U02(acac)] are formed in the reactions of CpFe Tj5-C5H3Li(CH2NMc2)) and the corresponding metal acetylacetonate or oxychloride.2 ... 

In a systematic analysis of C-H- -tt interactions occurring between metal acetylacetonate complexes and phenyl rings, it was demonstrated that the acetylacetonate chelate... 

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