Mercury reaction with lanthanide metals

Transmetallation is a more convenient method to obtaining divalent organolanthanide complexes from lanthanide metals. Reaction of lanthanide metal powder with a mercury alkyl or aryl complex affords the corresponding divalent lanthanide complex (Equation 8.28) [94]. The preparation of divalent perfluorophenyl lanthanide complexes Ln(C6F5)2(THF) (Ln = Eu, n = 5 Ln = Yb, n=4) is a typical example. In most cases, the addition of a small amount of Lnl3 leads to acceleration of the reaction [95]. 

LANTHANIDE TRICHLORIDES BY REACTION OF LANTHANIDE METALS WITH MERCURY(II) CHLORIDE IN TETRAHYDROFURAN... 

Reaction of Lanthanide Metals with Mercury JI) Chloride in THF 287... 

In some instances the reaction is accelerated by either amalgamation or the addition of a catalyst (e.g. iodine or a mercury(n) halide, Eq. 6.11 °) while the stoichiometric reaction of mercury and thallium compounds with lanthanide metals has been shown to be a viable route to aryloxide derivatives (Eqs 6.12 and 6.13 ). 

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... 

Lanthanide triphenyl complexes have been known for about 40 years. These neutral triphenyl complexes [Ln(C6H5)3(THF) ] are synthesized by a transmetallation reaction of the lanthanide metal with diphenyl mercury or triphenyl bismuth in THF [34]. Recently, it has been reported that metathesis reaction of anhydrous lanthanide trichloride with aryllithium is a more convenient and reproducible method than the transmetallation reaction used previously for the synthesis of triaryl lanthanide complexes. Several lanthanide triphenyl and substituted triphenyl complexes have been synthesized (Equation 8.14) [35]. 

Anhydrous lanthanide trihalides, particularly the trichlorides, are important reactants for the formation of a variety of lanthanide complexes, including organometallics. Routes for the syntheses of anhydrous lanthanide trihalides generally involve high temperature procedures or dehydration of the hydrated halides.The former are inconvenient and complex for small scale laboratory syntheses, while dehydration methods may also be complex and have limitations, for example, use of thionyl chloride. - Moreover, the products from these routes may require purification by vacuum sublimation at elevated temperatures. Redox transmetalation between lanthanide metals and mercury(II) halides was initially carried out at high temperatures. However, this reaction can be carried out in tetrahydrofuran (THF, solvent) to give complexes of lanthanide trihalides with the solvent. These products are equally as suitable as reactants for synthetic purposes as the uncomplexed... 

Other small-scale laboratory procedures have been developed for the direct synthesis of the more reactive THF adducts, avoiding inconvenient high temperature treatment [59-62]. For example, the preparation of LnCl3(thf)x from metal powder and hexachloroethane is facilitated by sonication [Eq. (1)] [59]. Additional metal-based synthetic routes include the redox transmetallation with mercury(II) halides [Eq. (2)] [60] and the reaction with trimethylsilyl chloride and anhydrous methanol [Eq. (3)] [61]. Ammonia has been employed as an alternative donating solvent in the synthesis of lanthanide alkoxides starting from lanthanide chlorides [63]. 

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