Neodymium-based complexes

Neodymium-based complexes, analogous to those previously discussed for high cis-1,4-polybutadiene, also polymerize isoprene with high cis selectivity (>95%). ... 

Scheme 51 Stereospecific butadiene polymerization based on a MMAO-activated neodymium methyl complex supported by a dianionic modification of neutral 2,6-diimino-pyridine [190]...

Neodymium-based Ziegler-Natta systems play a major role in the industrial polymerization of 1,3-butadiene to poly-cw-1,4-butadiene [182-184]. Therefore, the catalytic activity of the neodymium complex 229 was investigated for the polymerization of 1,3-butadiene [181]. The observed catalytic... 

In contrast to the large number of publications on group 4-based catalysts for syndiospecific styrene polymerization, reports on analogous rare-earth metal catalysts are stiU hmited [5], Early investigations on neodymium-based sandwich complexes (1-3) activated by methylaluminoxane (MAO) (Fig. 7.1) have shown that these systems are promising candidates for styrene polymerization catalysis with the resulting polymers syndiotactically enriched. The selectivity as well as the activity of these systems are moderate [6]. 

Lanthanide label kits are commercially available and will become more and more widely used as the nature of the visibly luminescent europium (red) and terbium (green) complexes utilized is optimized. Significant growth can also be expected in the development of lanthanide labels based on neodymium and ytterbium as their luminescence in the NIR, whilst of shorter lifetimes and requiring specialist detection equipment, is at a wavelength where tissue is optimally transparent, making in vivo uses a distinct possibility. 

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... 

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... 

Many factors affect coordination numbers and coordination polyhedra. It was recognized during 1962-1975 that the chemistry of yttrium and lanthanides is dominated by large coordination numbers. Although the structure of Nd(Br0.3>3 9H2O had been determined as early as 1939 by Helmholtz [6] and shown that the central neodymium ion was bound to nine water molecules in a face-centred trigonal prismatic structure, the commonly held opinion was that the rare earth ions formed six-coordinate, octahedral complexes [7]. This notion was based on the known octahedral, six-coordination known at that time for the most... 

Lanthanide elements (referred to as Ln) have atomic numbers that range from 57 to 71. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). With the inclusion of scandium (Sc) and yttrium (Y), which are in the same subgroup, this total of 17 elements are referred to as the rare earth elements (RE). They are similar in some aspects but very different in many others. Based on the electronic configuration of the rare earth elements, in this chapter we will discuss the lanthanide contraction phenomenon and the consequential effects on the chemical and physical properties of these elements. The coordination chemistry of lanthanide complexes containing small inorganic ligands is also briefly introduced here [1-5]. 

The presence of water has been postulated to cause the thermal instability of many of the hydrates (3, 4, 20), and attempts to chromatograph neodymium (III) trifluoroacetylacetonate dihydrate have failed (23). There is some evidence that hydrolysis occurs at elevated temperatures (3, 4, 20). Furthermore, there are indications that certain complexes undergo hydrolysis when allowed to stand in vacuo, even at room temperature (20). For these reasons the chelates are difficult to dehydrate by conventional means. Many of the claims in the older literature that anhydrous tris chelates were obtained must be considered questionable because the assignments of composition were either arbitrary or were based on analytical methods relatively insensitive to the amount of water present. Some investigators, however, have reported reasonably well-characterized anhydrous tris complexes 4,11,15), but most of these are not sufficiently volatile and stable to be chromatographed. 

Coordination Chemistry. The coordinative unsaturation of the three-coordinate derivatives suggests that these molecules should have a rich coordination chemistry. This has not been found, doubtless due to the steric congestion about the metal atom. Neodymium tris[bis(trimethylsilyl)amide] forms pale blue 1 1 coordination complexes with the sterically small Lewis bases B NC and Bu CN. Triphenylphosphine oxide yields a 1 1 complex with the silylamides of La, Eu, and Lu (16). 

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