Lanthanide halides alcohols

Lanthanide halide complexes free of coordinated Lewis bases, such as alcohols, phosphates, amines, dimethylsulfoxide, or THF, suffer from low solubilities in non-coordinating solvents. Therefore, catalytic systems based on LnCl3 generally require preformation or aging in order to reach maximum activities. In contrast, lanthanide tetrahalogenoaluminate complexes are soluble in aromatic solvents. Such simple Ln/Al heterobimetallic halide... 

This method makes use of the production of a less soluble metal salt (MX) to drive the reaction to completion. One commonly encountered problem with this route is the low solubility of the starting lanthanide halides. Exposure to anhydrous NH3 gas helps dissolve lanthanide halides [22]. Eollowing the addition of alkali metal and the appropriate alcohols, the desired alkoxide complexes can be obtained. This reaction is thought to proceed with the formation of a triamide... 

Indium-mediated allylation of an unreactive halide with an aldehyde132 was used to synthesize an advanced intermediate in the synthesis of antillatoxin,133 a marine cyanobacteria (Lyngbya majus-cula) that is one of the most ichthyotoxic compounds isolated from a marine plant to date. In the presence of a lanthanide triflate, the indium-mediated allylation of Z-2-bromocrotyl chloride and aldehyde in saturated NH4C1 under sonication yielded the desired advanced intermediate as a 1 1 mixture of diastereomers in 70% yield. Loh et al.134 then changed the halide compound to methyl (Z)-2-(bromomethyl)-2-butenoate and coupled it with aldehyde under the same conditions to yield the desired homoallylic alcohol in 80% yield with a high 93 7 syn anti selectivity (Eq. 8.55). 

For the less electropositive metals, direct reaction between the bulk metal and alcohols does not readily occur. However, for the Group II, III and lanthanide metals, reaction will occur in the presence of a catalyst.12,15 Typical catalysts are iodine or a mercury(II) halide and their action is believed to be either in cleaning the metal surface or in forming intermediate halide derivatives which then undergo facile reaction with the alcohol (equation 2).12... 

With the more electropositive metals such as the lanthanides,31 the dissolution of their chlorides into alcohols results only in the formation of solvates such as LaCl3 SPr OH.31 For most of the early J-block elements, only partial replacement of halide ligands occurs on alcoholysis (equations 5 and... 

The addition of a base, typically ammonia, to mixtures of transition metal halides and alcohols allows the synthesis of homoleptic alkoxides and phenoxides for a wide range of metals. Anhydrous ammonia was first used in the preparation of titanium alkoxides where the reaction is forced to completion by the precipitation of ammonium chloride.41 Although useful for the synthesis of simple alkoxides and phenoxides of Si, Ge, Ti, Zr, Hf, V, Nb, Ta and Fe, as well as a number of lanthanides,42-47 the method fails to produce pure /-butoxides of a number of metals.58 Presumably, secondary reactions between HC1 and Bu OH take place. However, mixing MC14(M = Ti, Zr) with the Bu OH in the presence of pyridine followed by addition of ammonia proves successful, giving excellent yields of the M(OBul)4 complexes.59... 

In a difference from the above, the majority of metal halides of secondary subgroups of Group I, II, and VII and lanthanides are low-soluble in the examined solvents, so synthesis of their complexes is carried out in comparatively high-polar solvents (water, alcohols, and aqueous-alcohol mixtures). To carry out syntheses in water, the corresponding conditions, necessary to obtaining soluble derivatives of organic compounds (for example, halide hydrates of amines or N-containing hetero-... 

Many studies on the absorption spectra of lanthanides in alcoholic media have been made and the observations and anomalies have been explained in terms of entry of a chloride ion into the coordination sphere of the lanthanide ion. The composition and stability of halide complexes of lanthanides in alcohol and aqueous alcoholic solutions have been studied by spectral techniques. The halide ions have been found to cause marked changes in the spectra of lanthanides in alcoholic and aqueous media. The observed spectral changes may be attributed to changes in the immediate coordination environment of the lanthanide ion [223]. 

Rare earth oxides are useful for partial oxidation of natural gas to ethane and ethylene. Samarium oxide doped with alkali metal halides is the most effective catalyst for producing predominantly ethylene. In syngas chemistry, addition of rare earths has proven to be useful to catalyst activity and selectivity. Formerly thorium oxide was used in the Fisher-Tropsch process. Recently ruthenium supported on rare earth oxides was found selective for lower olefin production. Also praseodymium-iron/alumina catalysts produce hydrocarbons in the middle distillate range. Further unusual catalytic properties have been found for lanthanide intermetallics like CeCo2, CeNi2, ThNis- Rare earth compounds (Ce, La) are effective promoters in alcohol synthesis, steam reforming of hydrocarbons, alcohol carbonylation and selective oxidation of olefins. 

Lanthanide alkoxide complexes can be prepared using a number of methods. The key difference lies in the nature of lanthanide starting materials. These include elemental metals, halides, alkoxides, amides, carboxylates, hydrides, and organometallic species [1, 11], The organic ligands come from aliphatic alcohols, phenols, or their metal salts. 

I. The initial compound of the lanthanide can be obtained by reacting its halide with the corresponding organic base [5]. The research is usually carried out with complexes containing various electron donor ligands, L, such as alcohols [6, 7], cyclic ethers [8], aliphatic esters of orthophosphoric acid [9-15], aliphatic, and cyclic sulfoxides... 

For the synthesis of metalloid (B, Si) alkoxides, the method generally employed consists of the reaction of their covalent halides (usually chlorides) with an appropriate alcohol. However, the replacement of chloride by the alkoxo group(s) does not appear to proceed to completion, when the central element is comparatively more electropositive. In such cases (e.g. titanium, niobium, iron, lanthanides, thorium) excluding the strongly electropositive s-block metals, the replacement of halide could in general be pushed... 

Studies on OCH(CF3)2, OCMe(CF3)2, OCMc2(CF3), and 0C(CF3)3 derivatives of the alkali metds, alkaline earth metals, transition metals, and the lanthanide elements are reviewed, with emphasis on work reported since 1988. Alkali and alkaline earth fluoroalkoxides are generally made from reaction between the alcohol and the metal, its hydride, or organometallics. Most syntheses of transition metal derivatives involve reaction between metal halides and alkali or alkaline earth salts, or the alcoholysis of metal alkyls, alkoxides and amides. Coordination between organic fluorine and electropositive metals (ie. Na, Ba, Tl, Pr) is often observed in the crystal structures of these fluoroalkoxides and may be related to their use as chemical vapor dqx)sition precursors for metal fluorides. 

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