Neodymium carboxylate

Neodymium carboxylate Cocatalyst Halide donor cis-1,4-Content/% Refs. 

The solubility of neodymium carboxylates in organic solvents is also improved by the addition of electron donors such as acetylacetone, tetrahy-drofuran, N,N -dimethylformamide, thiophene, diphenylether, triethylamine, pyridine, organic phosphorus compounds etc. Also the storage stability of neodymium carboxylates in organic solutions (reduction of sediment formation) is increased by these additives. Mixtures of the Nd-precursor and the respective additives are reacted in the temperature range 0-80 °C. The sequential addition of Al-compound and halide donor yield the active polymerization catalysts [409,410]. 

Fischbach et al. isolated and characterized products which are obtained from the reaction of various highly substituted neodymium carboxylates with trimethyl aluminum. Several reaction schemes are presented which account for the whole variety of reactions and isolated Nd species [185,186]. 

We found that completely soluble compounds can be obtained in two ways. The first method, which is widely applicable, is to react a rare earth carboxylate with a small amount of an aluminum alkyl (11). Neodymium octoate can be converted into a product which is completely soluble in cyclohexane by reacting one mole of it with 1 to 5 moles of triethylaluminum. We also found that the rare earth salts of certain tertiary carboxylic acids are very readily soluble in non-polar solvents (12). In conjunction with a Lewis acid and aluminum alkyls, these compounds form highly active catalysts for the polymerization of butadiene. The neodymium Lewis acid aluminum alkyl molar ratio is within the range 1 (0.4-2.0) (10-40). 

Figure 2. Effect of polymerization temperature (0) and AlR, Nd(vers), molar ratio (O) on molecular weight. Et,Al/ Ndivers), molar ratio was kept at 40 1 when the temperature was varied, and the temperature was maintained at 60°C when Et,Al/Nd(vers), molar ratio was varied. Nd(vers), is the neodymium salt of Versatic 10, which is a mixture of isomeric tertiary carboxylic acids.

According to the number of citations in patents and in scientific literature neodymium(III) carboxylates have found widespread application. These systems were first reported by Monakov et al. in 1977 [152,153]. In 1980 the use of the highly soluble neodymium(III) versatate (NdV) was patented by Bayer [154,155]. At sufficiently low concentrations the most commonly used Nd-carboxylates (Scheme 2) are completely soluble in hydrocarbon solvents. Because of this, Nd-carboxylates are the focus of many studies and are often referred to in the literature. 

Scheme 2 Most commonly used neodymium(III) carboxylates Nd versatate (NdV), Nd octanoate (NdO), Nd isooctanoate (NdzO), Nd naphthenate (NdN)...

Neodymium-alcoholates were mentioned in the patent literature prior to Nd-carboxylates [37,38,224-228]. The Nd-alcoholates most frequently mentioned in literature comprise Nd(OBu)3 [224,225,229,230], Nd(0 Pr)3 [231-233], and Nd aryl oxides [185,234,235] (Scheme 3). Also adduct compounds... 

The usual cocatalysts for the activation of Nd-alcoholates comprise common aluminum alkyls, alumoxanes and magnesium alkyls which have already been described for the activation of the Nd halides (Sect. 2.1.1.1) and Nd carboxylates (Sect. 2.1.1.2) AlMe3 (TMA) [185,234], TIBA [224,225, 229,230], DIBAH [226,227,232], MAO [232,246], modified methyl alumox-ane (MMAO) [231] and MgR2 [235]. The ratios of cocatalyst/Nd-alcoholate are comparable with those described for the activation of Nd carboxylates. Table 4 gives a selection of catalyst systems based on neodymium alcoholates. 

Though a vast number of studies on the characteristics of neodymium-mediated polymerizations were performed to the present day, only a few studies focus on the influence of the anion of the Nd precursor. As already mentioned in Sect. 2.1.1.2 Wilson systematically varied the structure of carboxylates and studied the influence on hydrocarbon solubility and on polymerization activity [183]. The dependence of polymerization activity on various halogenated Nd-carboxylates Nd(OCOR)3 (R = CF3, CCI3, CHCI2, CH2C1, CH3) was the target of a study by Kobayashi et al. [ 177]. 

In addition to these two studies the polymerization kinetics of three different Nd-compounds which were activated by DIBAH and EASC were comparatively studied. In this investigation a Nd alcoholate [NdA = neodymium(III) neopentanolate], a Nd phosphate [NdP = neodymium(III) 2-ethyl-hexyl-phosphate] and a Nd carboxylate (NdV) were compared with a special focus on the variation of the molar ratios of zzdibah/hncI and ci/ Nd [272]. For each of these ternary catalyst systems the polymerization activities depend... 

A unique variant of catalyst preformation in the absence of dienes was described by Enichem in an early patent on Nd-BR. The active Nd catalyst was prepared by the reaction of neodymium oxide with carboxylic acid and (BuCl in vaseline at 80 °C. Subsequently, aqueous HC1 was added at 80 °C. Finally, the addition of the aluminum alkyl co catalyst yielded the active Nd catalyst [389,390]. 

Evans et al. sequentially reacted the Nd carboxylate precursor Nd[C>2CC (CH3)2CH2CH3]3 % first with DEAC and then with TIBA. By this reaction catalytically active systems are obtained which polymerize IP. In the first reaction step in which Nd carboxylate is reacted with DEAC mixed ligand complexes are formed which contain neodymium and aluminum as well as halide and ethyl groups. Upon crystallization NdC -based compounds are obtained in which solvent is coordinated. These compounds exhibit a more complex... 

Numerous binary and ternary diene polymerization initiator systems with neodymium as the rare-earth metal component have been designed empirically and investigated since the early discoveries in the 1960s. Commercially used neodymium-based catalysts mostly comprise Nd(III) carboxylates, aluminum alkyl halides, and aluminum alkyls or aluminum alkyl hydrides [43, 48,50-52]. Typically, the carboxylic acids, which are provided as mixtures of isomers from petrochemical plants carry solubilizing aliphatic substituents R. They are treated with the alkylaluminum reagents to generate the active catalysts in situ (Scheme 11). 

First structural evidence for the formation of heterobimetallic Ln/Al complexes in carboxylate-based catalytic systems was obtained from the reaction of homoleptic rare-earth metal trifluoroacetates with equimolar amounts of z -Bu2A1H and EtsAl, respectively [132], Alkylated yttrium, neodymium, and... 

Crucially, discrete Ln/Al organometallics were unambiguously identified as intermediates of the commercially applied neodymium-based diene polymerization and subsequently employed in binary initiator mixtures. Particularly for the industrially relevant O-only bonded carboxylate- and alk(aryl)oxide rare-earth metal components, the use of pre-alkylated Ln derivatives developed into valuable structure-reactivity relationships partially uncovering the blackbox, which is provided by ternary Ziegler Misch-katalysatoren. Accordingly, rare-earth metal centers provide a unique stereo-... 

A second form of Nd2(malonate)3 6H2O complex has been reported [169]. In this complex neodymium is nine-coordinate surrounded by six carboxylate, and three water oxygen atoms and the geometry is intermediate between the distorted capped square antiprism and the distorted tricapped trigonal prism. 

A series of investigations (32-35, 101) on the extraction of these elements with carboxylic acids has been carried out by workers in the Soviet Union. Miller and associates (86) extracted lanthanides with 2,5-dimethyl-2-hydroxyhexanoic acid in chloroform. The heavy lanthanides after samarium were not extracted. In the extraction of neodymium the extracted species such as NdA3(HA)5 and Nd2A6(HA) were found together with small amounts of Nd2A6 and still smaller amounts of further aggregates (NdA3) - (86). 

Figure 1.24 The structure of the complex [Nd2(C204)3-6H20]-4H20 [22]. (Reprinted from E. Hansson, Structural studies on the rare earth carboxylates 5. The crystal and molecnlar structure of neodymium (Ill)oxalate 10.5-hydrate, Acta Chemica Scandinavica, 24, 2969-2982, 1970, with permission from Forlagsforeningen Acta Chemica Scandinavica.)... 

Birnbaum, E.R. and Darnall, D.W. (1973) A study of carboxylic and amino acid complexes of neodymium(III) by difference absorption spectroscopy. Bioinorganic Chemistry, 3 (1), 15-26. 

Fundamental studies have been reported using the cationic liquid ion exchanger di(2-ethylhexyl) phosphoric acid in the extraction of uranium from wet-process phosphoric acid (H34), yttrium from nitric acid solution (Hll), nickel and zinc from a waste phsophate solution (P9), samarium, neodymium, and cerium from their chloride solutions (12), aluminum, cobalt, chromium, copper, iron, nickel, molybdenum, selenium, thorium, titanium, yttrium, and zinc (Lll), and in the formation of iron and rare earth di(2-ethylhexyl) phosphoric acid polymers (H12). Other cationic liquid ion exchangers that have been used include naphthenic acid, an inexpensive carboxylic acid to separate copper from nickel (F4), di-alkyl phosphate to recover vanadium from carnotite type uranium ores (M42), and tributyl phosphate to separate rare earths (B24). 

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