Neodymium alcoholates

Polyisoprenes of 94—98% as-1,4 content were obtained with lanthanum, cerium, praseodymium, neodymium, and other rare-earth metal ions (eg, LnCl ) with trialkyl aluminum (R3AI) (34). Also, a NdCl 2THF(C2H3)3A1 catalyst has been used to prepare 95% <7j -l,4-polyisoprene (35). <7j -l,4-Polyisoprene of 98% as-1,4 and 2% 3,4 content was obtained with organoalurninum—lanthariide catalysts, NdCl where L is an electron-donor ligand such as ethyl alcohol or butyl alcohol, or a long-chain alcohol, and is 1 to 4 (36). 

In 1906, Matignon reported an enthalpy of solution of -21.54 kcal mol-1 (-90 kj mol ) for neodymium trichloride in ethanol (178). His ethanol may have been less than perfectly anhydrous, and the value for pure ethanol somewhat less negative than this, perhaps —80 or — 70 kJ mol 1. Certainly a value in this region is considerably less negative than his value for the enthalpy of solution of neodymium trichloride in water, —148 kj mol-1. The difference may reasonably be attributed to less favorable solvation qf the constituent ions in ethanol than in water. Ion solvation would be expected to be even less favorable in isopropanol, so it is not surprising to find an enthalpy of solution of about + 40 kJ mol-1 for neodymium trichloride in this alcohol. This estimate must be considered as only approximate, as it is derived from... 

The influence of steric factors was thoroughly studied in the reaction of Ln(btsa)3 with the alcohol tritox-H. While the reaction takes place with larger lanthanides like neodymium to yield the homoleptic alkoxide complexes (Eq. 18) [264], the analogous reaction does not work with smaller metals like yttrium and thulium (Eq. 19). However, variation of the reaction conditions to a stoichiometric solid reaction yielded a fully exchanged product along with an unexpected and unusual silylamine degradation [265] (Eq. 20). This degradation reaction seems to be sterically forced and points out N-Si bond disruptions and C-Si bond formations under mild conditions [114]. 

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... 

Scheme 3 Most commonly used neodymium alcoholates...

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. 

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

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... 

According to the reaction scheme put forward the reduction of NdV requires between 3 to 6 eq. of DIBAH. As a result of this reduction Nd alcoholate is obtained. The Nd-hydrido species is considered to be an important intermediate which can be formed from the alcoholate by two different reaction routes. If the Nd hydrido species is formed by hydride transfer from DIBAH to Nd alcoholate another equivalent of DIBAH is needed. If the Nd hydride species is formed by -hydride elimination no additional equivalent of DIBAH is required. As a consequence from these considerations in total 3-7 eq. of DIBAH are required for the generation of one Nd-hydrido derivative, which is considered to be the first active species. The total sequence of consecutive reactions which result in the neodymium-catalyzed polyinsertion of BD is summarized in Scheme 25. 

In 2004 Carpentier and co-workers were the first who isolated and characterized the active species from a Nd alcoholate/MgR2 mixture. The reaction of either a trinuclear or a monomeric Nd alcoholate precursor with Mg(CH2SiMe3)2 (Et20) yields an alkyl neodymium complex and a new het-erobimetallic Nd-Mg complex. The latter complex is considered to be the active species for the investigated catalyst system [621],... 

Rare earth nitrates can be prepared using nitric acid to react with a corresponding oxide, hydroxide, carbonate or metal. These nitrates dissolve easily in polar solvents such as water, alcohols, esters or nitriles. They are unstable to heat as the decomposition temperature for the nitrates of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, and samarium are 510,480, 780,450, 505, 830, and 750 °C, respectively. 

The sequential cyclization/silylation reactions of 1,5-dienes and 1,6-dienes are catalyzed by Cp 2YMe(THF). The reaction tolerates a number of functional groups and proceeds with good yields and diastereoselectivities to give phenylsilane products which can be converted easily to synthetically more versatile alcohols (Scheme 276). The hydrosilylation of dienes is also effectively catalyzed by the neodymium alkyl complex Cp 2NdCH(SiMe3)2. 

Normal azides are not known in group IIIB. Curtius and Darapsky [135] attempted to make them by dissolving, for example, lanthanum hydroxide in hydrazoic acid. The solution was assumed to contain the normal azide but only basic products were precipitated upon evaporation or by adding alcohol. The precipitate was insoluble in water, had the approximate composition La(OH)(N3)2 I.5H2O, and deflagrated upon heating. The same results were found with yttrium, cerium, dysprosium, thorium, and uranium azides. Based on the infrared spectra, Rosenwasser and Bryant [136] suggested two types of basic rare earth azides. The lanthanum type (a) was found for lanthanum, neodymium. 

The preparation of amalgams of lanthanum, neodymium, and cerium by electrolysis of the anhydrous chlorides in alcoholic solution has already been described. The electrolysis of a rare earth chloride in water solution proves unsatisfactory because of the production of a precipitate of hydrous oxide at the cathode and the liberation of chlorine at the anode. 

The permeability of ethanol and higher alcohols through Nafion has not been studied so extensively as methanol permeation. Verma and coworkers reported the permeability coefficients of ethanol through Nafion composites with NdaOa [90], neodymium triflate [91], and erbium triflate [92] and the corresponding Nafion recast membranes. Unexpectedly, the measured P for ethanol differ more than a factor 20 for recast membranes (P between 1.0 10 and 2.8.10 cm. s ). 

Barbora L, Singh R, Shroti N, Verma A (2010) Synthesis and characterization of neodymium oxide modified Nafion membrane for direct alcohol fuel cells. Mater Chem Phys 122 211-216... 

Shroti N, Barbora L, Verma A (2011) Neodymium triflate modified Nafion composite membrane for reduced alcohol permeability in direct alcohol fuel cell. Int J Hydrogen Energ 36 14907-14913... 

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