Neodymium alkoxides

The X-ray structure of a interesting homometallic five-coordinate neodymium alkoxide complex [(r-Bu3-CO)2Nd(/t-Cl)(thf)]2 (290) is shown in Fig. 40, and consists of a chloride-bridged dimer with an Nd2Cl2 planar ring. 

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]. 

Monomeric Ce(tritox)3 was claimed in 1989 [29]. However, the structure determination was hampered by disordering problems both in solvent-free Ce(tritox)3 and Nd(tritox)3(THF) [36]. Appropriate crystallization conditions were borrowed from cyclopentadienyl chemistry. The corresponding LnCp3 systems show remarkable crystallization behavior in the presence of neutral bases like acetonitrile and DMSO which impose polarities into the molecule [37], Indeed, this phenomenon could be transferred to Nd(tritox)3 in a 2-phase system n-pentane/acetonitrile at — 35°C [38], X-ray analysis revealed a monomeric alkoxide of formula Nd(tritox)3(NCCH3)2 with a trigonal bipyramidal geometry at the neodymium center (Fig. 2, Table 1). The alkoxide O-atoms and... 

Use of a flexible aminosubstituted cyclopentadienyl ligand afforded a mononuclear species with the bulky silox ligand as alkoxide component. Only one donor arm is required to achieve a sterically saturated 8-coordinated neodymium center (Fig. 30, Table 14) [207]. 

Herrmann, W.A., Anwander, R., Kleine, M., and Scherer, W. (1992) Lanthanides complexes. 1. Solvent free alkoxide complexes of neodymium and dysprosium. Crystal and molecular structure of trans-bis(acetonitrile)tris(tri-tert-butylmethoxy)neodymium. Chemische Berichte, 125, 1971-1979. 

An interesting as well as unusual structure (Fig. 29) was reported for the compex Nd6(0-/-Pr)17Cl (256) in 1978. This structure attested to the complexity possible in lanthanide alkoxide chemistry (28). The structure of the neodymium complex can be regarded as two triangular Nd3(jt3-OR)(ft2-OR)3(OR)6 (where R = O-i -Pr) units connected by sharing the /x3-Cl site (which becomes a /i6-Cl) and three terminal OR ligands (which become /t2-OR groups). 

In addition to the frequent incorporation of 0x0 and hydroxo groups into cluster core structures, halo ligands have also been found in many lanthanide alkoxide clusters. An early example is [Nd6(/i6"Cl)(/i3-OPr )2 (/i-OPr )9(OPr )6] (Andersen et al., 1978), a hexanuclear cluster obtained from the reaction of NdCla with NaOPr in HOPr. The six neodymium... 

Tetrakis(hexafluoroisopropoxides) of titanium, zirconium, and hafnium have been prepared by the reaction of sodium hexafluoroisopropoxide in an excess of hexafluoroisopropyl alcohol with the anhydrous metal chloride, and the spectroscopic properties are reported. The authors note that, in their experience, application to the Group IV transition metals of the previously published method for metal hexafluoroisopropoxide synthesis gives poor yields of material containing metal, fluorinated alkoxides, and co-ordinated ammonia. Dehydration of the hydrated metal chloride with methyl orthoformate and addition of hexafluoroisopropyl alcohol, followed by passage of dry ammonia through the solution, gives satisfactory yields for yttrium, lanthanum, neodymium, and erbium. 

The above route has also been utilized for the synthesis of neodymium and yttrium alkoxides as shown by Eqs (2.9) and (2.10) ... 

Similarly, preparation of anhydrous and/or unsolvated lanthanide tris-acetylacetonates remained a challenge till 1965, as the efforts to remove ligated water from Ln()S-dik>3.2H2O (obtained from aqueous media) led to hydrolyzed products. However, pure tris-j6-diketonates of lanthanum, praseodymium, and neodymium could be easily synthesized by the reactions of their alkoxides (methoxides/isopropoxides) with 3 equivalents of acetylacetone (acacH) ... 

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