Neodymium-based catalyst

A common feature of catalysts based on 4 and 5f block elements is that of being able to polymerize both butadiene and isoprene to highly cistactic polymers, independently of the ligands involved. Butadiene, in particular, can reach a cistacticity as high as 99% with uranium based catalysts (3) and cistacticity of > 98% with neodymium based catalysts (4). This high tacticity does not change with the ligand nature (Fig. 1) in contrast to conventional catalysts based on 3-d block elements. A second feature of f-block catalysts is that the cis content of polymer is scarcely... 

Si02-supported neodymium-based catalyst mixtures Nd(naph)3/Al2Et3Cl3/ A1( Bu)3 (54) and Al( Bu)2H (DIBAH), instead of Al( Bu)3, were also tested as initiators for the gas-phase polymerization of 1,3-butadiene by varying the polymerization temperature, nature and feed of co-catalyst and polymerization time (Table 12.8). High ds-1,4-contents (97.8-98.9%) and activities between 400 and 2300 kg-PBD molNd h bar were observed, but the polymers displayed broad molecular weight distributions of 2 < M /M < 8 [158-160]. 

Neodymium-based catalysts are favored over other Ln metals because they are highly active and the catalyst precursors are readily available for reasonable prices. In addition, Nd catalyst residues do not catalyze aging of the rubber. The use of didymium catalyst systems is also reported in the literature. Didymium consists of a mixture of the three lanthanides neodymium (72 wt. %), lanthanum (20 wt. %) and praseodymium (8 wt. %). 

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). 

The scope of this process has been extended in a more detailed investigation to the synthesis of quinolizines [175] and the influence of alkyl substituents in various positions of the aminodialkene substrate on product diastereoselectivity was probed. Neodymium-based catalysts are particularly efficient for six-membered ring formation (40). The methodology has found further application in the synthesis of tri- and tetracyclic alkaloidal skeletons (41) [176]. 

The earliest reported examples of group 3 or organolanthanide catalyzed hy-drosilylation reactions emphasized reactions with simple alkenes (e.g., 1-oc-tene) (Eq. 14) [33]. The lutetium- and neodymium-based catalysts utilized for these studies typically required 2 d at high temperatures (80-90 °C) to react and provided modest to good yields of the desired terminal (linear) organosilanes. Styrene provided mixtures of linear and branched organosilanes [Eq. (15)]. 

This gives rise to dual valency state (+3 and +4) (23). As to the activity of lanthanide based catalysts we confirm a singular behavior that has been already reported by Chinese scientists (22) and that is summarized in Fig. 9. The activity of lanthanides in promoting the polymerization of butadiene and isoprene shows a large maximum centered on neodymium, the only exception being represented by samarium and europium that are not active, reasonably because they are reduced to bivalent state by aluminum alkyls, as pointed out by Tse-chuan and associates (22). 

Neodymium Based Ziegler Catalysts -Fundamental Chemistry... 

Friebe, L., Nuyken, O. and Obrecht, W. Neodymium Based Ziegler/Natta Catalysts and their Application in Diene Polymerization. Vol. 204, pp. 1-154. 

Neodymium phosphate-based catalysts were used as early as in 1978 for the polymerization of IP by Monakov et al. [249,250]. At a later stage neodymium phosphate-based catalyst systems were claimed by Asahi in a patent issued in the mid 1980s [251,252]. A neodymium-phosphate which is predominantly mentioned in the context of diene polymerization is neodymium bis(2-ethylhexyl)phosphate (NdP). In Chinese scientific literature NdP (Scheme 5) is often abbreviated by its commercial name Nd(P204)3-... 

For the ternary neodymium phosphate-based catalyst systems (NdP/ DIBAH/EASC) a totally different dependence of polymerization rates on Ai/ Nd-rahos was reported [264-269,272]. According to these studies the catalyst system is highly active even at low Ai/MNd-ratios < 5 and polymerization rates decrease with increasing Ai/ Nd-ratios within the Ai/ Nd-range = 5-50 (Sect. 2.1.1.10) [272]. 

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