Lanthanoid chlorides

Gemal, A. L., Luche, J. L. Lanthanoids in organic synthesis. 6. Reduction of a-enones by sodium borohydride in the presence of lanthanoid chlorides synthetic and mechanistic aspects. J. Am. Chem. Soc. 1981, 103, 5454-5459. 

The lanthanoid basic carbonate is obtained by boiling a dilute lanthanoid chloride solution with urea.4 The dilute solution of freshly prepared hexafluorophosphoric acid is obtained by percolating a solution, containing 3.0 x 10-3 mole of ammonium hexafluorophosphate (Alfa products) in 20 mL of water, through an Amberlite IR — 120 H + column (1cm x 25 cm). The eluted solution is allowed to fall dropwise (—20 drops per minute) onto a suspension of 1 x 10 3 mole of the lanthanoid basic carbonate in 5 mL of water, under constant stirring. The addition of the acid is discontinued when a very small residue of the basic carbonate remained (pH > 5 < 6). The solution is then filtered, the residue washed with two portions of 3 mL of distilled water, and then allowed to evaporate at —30° to near dryness, using a flash evaporator and reduced pressure (—20 torr). It is necessary to evaporate carefully to a very small volume, because the solution decomposes, becoming acid and turbid. (This is a very critical point.)... 

The use of the bis(trimethylsilyl)cyclopentadienyl ligand, which has been introduced in the synthesis by Lappert et al, (50,59) also allows the preparation and isolation of the corresponding substituted dicyclopentadienyl lanthanoide chlorides of the early lanthanoides ... 

The interaction of anhydrous lanthanoid chlorides LnCl3 with other Si-alkyllithium reagent, (Me3Si)2CHLi, leads to the displacement of only two chlorine atoms by organic moieties. The ar -complex formed retains one Cl atom in the inner coordination sphere [44, 120] ... 

Two general types of lanthanoid compounds containing PR2 groups at the metal atom are known Ln(PR2)3 and Cp2LnPR2- The first of them are obtained from the reaction of LiPR2 with anhydrous lanthanoid chlorides in THF at room temperature [1] ... 

The anhydrous trihalides are readily hydrolysed to oxyhalides LnOX and attempted dehydration of hydrated lanthanoid chlorides also leads to LnOCl formation. 

Numerous compounds adopt the PbFCl structure. These include, apart from fluoride chlorides, oxide halides MOX (M = Bi, lanthanoids, actinoids X = Cl, Br, I), hydride halides like CaHCl and many compounds with metallic properties like ZrSiS or NbSiAs. 

Cerium is prepared by methods similar to those used for other lanthanoids. It is obtained by passing an electric current through cerium chloride ... 

Lutetium is the most difficult lanthanoid to obtain in pure form. The usual method used begins with either lutetium fluoride (LUF3) or lutetium chloride (LUCI3). An active metal, such as sodium (Na) or potassium (K) is then added to LUF3 or LUCI3 to obtain pure lutetium. For example ... 

The complexes having the general formula [Ln(dppa)6][PF6]3 are prepared in two ways (a) the concentrated lanthanoid hexafluorophosphate solution is diluted with 5 mL of absolute ethanol and treated with a solution of dppa (1 x 10 2 mole in 20 mL of absolute ethanol). The precipitate is collected in a sintered-glass filter funnel, washed with two 5-mL portions of absolute ethanol, and dried under vacuum over anhydrous calcium chloride (b) the concentrated aqueous solution of lanthanoid hexafluorophosphate is diluted with 5 mL of methanol and treated with a solution of dppa (1 X 10 2 mole in 10 mL of methanol), and the complex is then precipitated by addition of 30 mL of 2,2-dimethoxypropane (Aldrich). The precipitate is collected, washed with two portions of 5 mL of 2,2-dimethoxypropane, and dried as above.3... 

A common interpretation of this reaction invokes the use of the cerium(lll) chloride as a Lewis acid that bonds to the carbonyl system, to make 1,2-addition favored. However, lanthanoid ions are known to preferentially bind to alcohols rather than carbonyl groups.6 Additionally, if the cerium did bind with the carbonyl, one would expect that as dilution with methanol was increased, the observed regioselectivity, presumably due to this complexation, should be reduced. However, experimental results do not support this hypothesis. Since cerium complexation with methanol would result in increased acidity of the methanolic proton, the following scheme appears to be the more likely course of the reaction. 

With respect to the synthesis of organometallic compounds of the lanthanoides with n -bonded organyls, the cyclopentadienyllanthanoide halides take a key position. The first dicyclopentadienyllanthanoide chlorides were obtained by the reaction of LnCl3 with only two equivalents of NaC5H5, or by redistribution of LnCl3 and Ln(C5H5)3 (42) ... 

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