Lanthanide iodides preparation

Complexes of lanthanide chlorides 156,173), bromides (256), and iodides 174) with 2,6-DMePyO have also been prepared and characterized. The presence of bridging 2,6- DMePyO molecules has been suggested in the complexes of lanthanide iodides. Vicentini and De Oliveira (2 73) have reported tetrakis-2,6-DMePyO complexes with lanthanide nitrates. However, by changing the method of synthesis, tris-2,6-DMePyO complexes with the lanthanide nitrates could be prepared in this laboratory (252). All the nitrate groups in the tris-2,6-DMePyO complexes are bidentate. In the 2,4,6-TMePyO complexes (252) also the nitrate groups are coordinated to the lanthanide ion in a bidentate fashion. 

Ln-Halides. The complexation/solvation criteria is just one reason why lanthanide halides are the most common precursors in organolanthanide chemistry. In this evaluation, lanthanide iodides are often preferred to bromides and chlorides, however the former are more difficult to synthesize and are much more expensive [96f. Waterfree, solid Ln-halides are ionic substances with high melting points which immediately absorb water when exposed to air, forming hydrates (I > Br > Cl ). Therefore, they have to be handled under an inert gas atmosphere. The main use of the halides is for the production of pure metals [96]. Some methods of preparing Ln(III)-chlorides are summarized in Scheme IV [96],... 

The first non-classical divalent lanthanide iodide Tml2(DME)3 (DME = dimethoxyethane), which is prepared by the reaction of thulium metal with iodine under argon (Equation 8.33), was reported in 1997 [101]. Subsequently, Dyl2(DME)3 andNdl2(THF)5 have been synthesized by an analogous manner. The success of the synthesis of non-classical divalent lanthanide iodides opens up a new area in divalent lanthanide chemistry [102, 103]. 

Namy, J. L., Girard, P., Kagan, H. B. A new preparation of some divalent lanthanide iodides and their usefulness in organic synthesis. 

The dimeric mono(cyclooctatetraenyl)lanthanide chlorides [(COT)Ln(/r-Cl)(THF)2]2 are long known and still represent the most useful precursors in (COT)Ln chemistry. A recently reported alternative preparation of the Sm derivative involves the reaction of samarium metal with COT in THF in the presence of a small amount of I IgCL. The molecular structure of [(COT)Sm(/i-CI)(TT 11 )2]2 has been determined.805,806 Iodo-(cyclooctatetraenyl)lanthanide iodides of the type (COT)Lnl(TIIF) (Ln = La, Ce, Pr, n = 3 Ln = Nd, n = 2 Ln = Sm, n l) are readily accessible in a one-pot reaction of metallic lanthanides with COT in the presence of an equimolar amount of iodine. Bromo- and chloro-bridged binuclear complexes of samarium, [(COT)Sm(/.t-X)(THF )2]2 (X = Br, Cl), were also prepared by the reaction of samarium metal with COT in the presence of 1,2-dibromoethane or Ph3PCl2, respectively.807 Alternatively, the iodo complexes (COT)LnI(THF)3 (Ln = Nd, Sm) can be synthesized directly from the lanthanide triiodides and K2COT. The molecular structure of (COT)Ndl(THF)3 has been determined by X-ray diffraction.808 A clean preparation of the monomeric half-sandwich complex (GOT)TmI(THF)2 involves treatment of Tml2 with equimolar amounts of COT in THF at room temperature (Scheme 227). The product was isolated as red crystals in 75% yield.628... 

Lanthanide(III) isopropoxides show higher activities in MPV reductions than Al(OiPr)3, enabling their use in truly catalytic quantities (see Table 20.7 compare entry 2 with entries 3 to 6). Aluminum-catalyzed MPVO reactions can be enhanced by the use of TFA as additive (Table 20.7, entry 11) [87, 88], by utilizing bidentate ligands (Table 20.7, entry 14) [89] or by using binuclear catalysts (Table 20.7, entries 15 and 16) [8, 9]. With bidentate ligands, the aluminum catalyst does not form large clusters as it does in aluminum(III) isopropoxide. This increase in availability per aluminum ion increases the catalytic activity. Lanthanide-catalyzed reactions have been improved by the in-situ preparation of the catalyst the metal is treated with iodide in 2-propanol as the solvent (Table 20.7, entries 17-20) [90]. Lanthanide triflates have also been reported to possess excellent catalytic properties [91]. 

Undoubtedly, the best method for the production of pure anhydrous lanthanide trihalides involves direct reaction of the elements. However, suitable reaction vessels, of molybdenum, tungsten, or tantalum, have to be employed silica containers result in oxohalides (27). Trichlorides have been produced by reacting metal with chlorine (28), methyl chloride (28), or hydrogen chloride (28-31). Of the tribromides, only that of scandium has been prepared by direct reaction with bromine (32). The triiodides have been prepared by reacting the metal with iodine (27, 29, 31, 33-41) or with ammonium iodide (42). 

Probably, the first series of lanthanide complexes with neutral oxygen donor ligands is that of AP with the lanthanide nitrates. In 1913, Kolb (79) reported tris-AP complexes with lighter lanthanide nitrates and tetrakis-AP complexes with heavier lanthanide nitrates. Subsequently, complexes of lanthanide nitrates with AP which have a L M of 6 1 and 3 1 have also been prepared (80-82). Bhandary et al. (83) have recently shown through an X-ray crystal and molecular structure study of Nd(AP)3(N03)3 that all the nitrates are bidentate and hence the coordination number for Nd(III) is nine in this complex. Complexes of AP with lanthanide perchlorates (81, 84), iodides (81, 85), and isothiocyanates (66, 86, 87) are known. While the perchlorates and iodides in the respective complexes remain ionic, two of the isothiocyanates are coordinated in the corresponding complexes of AP with lanthanide isothiocyanates. 

By changing the method of preparation, complexes of the formula Ln(Py0)3(N03)3, in which all the nitrates are coordinated to the lanthanide ion in a bidentate fashion, could be prepared (152). PyO yields complexes with lanthanide chlorides (156), bromides (156), iodides (157) and hexathiocyanatochromate (159) all of which have a L M of 8 1. However, by changing the synthetic procedure, Sivapullaiah and Soundararajan (158) could prepare complexes of the formula [Ln(PyO)6 Br2(H20)2]Br... 

Substitution at the 2-position of the pyridine ring in PyO introduces steric hindrance to coordination as is evident from the formation of Heptakis-2-MePyO complexes with lanthanide perchlorates (167) and pentakis-2-MePyO complexes with the corresponding bromides (168), iodides (162) and chlorides (169). The lanthanide nitrate complexes prepared by Ramakrishnan and Soundararajan (170) have the formula Ln(2-MePy0)3(N03)3 -xH20in which all the nitrate groups are bidentate. 

Preparation of lanthanide bromides and iodides is performed under similar but aggravating conditions, according to Scheme IV [96fj. Small-scale syntheses of solvated iodides are given in Scheme V [110-112], Strongly donating solvents such as iV-methylimidazole (iV-Melm) can accomplish complete anion-cation separation, as has been shown for [Sm(lV-MeIm)8]l3 under anaerobic conditions [113],... 

P. Girard, J. L. Namy, and H. B. Kagan, Divalent lanthanide derivatives in organic synthesis. 1. Mild preparation of samarium iodide and ytterbium iodide and their use as reducing or coupling agents,. /. Am. Chem. Soc., 102 (1980) 2693-2698. 

The complexes of lanthanide ions with the heavy halides, particularly iodide, are often extremely weak. In many cases preparation of these complexes in or from solution is very difficult if not impossible. The donor properties of any otherwise satisfactory solvent or the donor properties of difficult to remove solvent impurities are such that they effectively compete with the halide ion and prevent its entering the metal coordination sphere. The preparative method discussed here, which is applicable to the preparation of salts of bromo... 

Imamura et al. (1984, 1986a) described a new way of preparing Raney catalysts using intermetallic compounds as starting materials. They found that, when treated with 1,2-diiodoethane (or dibromoethane) the lanthanide could be etched from the alloy to form the iodide (bromide), leaving a spongy, high-surface-area skeleton of the other element (Ni or Co) ... 

The synthesis of lanthanide and actinide compounds was the subject of a book (Meyer and Morss 1991). Detailed information is given on the synthesis of lanthanide fluorides (Muller 1991), binary lanthanide halides, RX3 (X=Cl,Br,l) (Meyer 1991a), complex lanthanide(in) chlorides, bromides and iodides (Meyer 1991b), and on two alternative routes to reduced halides, the conproportionation route (Corbett 1991) and the action of alkaU metals on lanthanide(lll) halides (Meyer and Schleid 1991). Therefore, a brief outline of the main preparative routes and synthetic strat es might be sufficent. 

The lanthanide and actinide halides remain an exceedingly active area of research since 1980 they have been cited in well over 2500 Chemical Abstracts references, with the majority relating to the lanthanides. Lanthanide and actinide halide chemistry has also been reviewed numerous times. The binary lanthanide chlorides, bromides, and iodides were reviewed in this series (Haschke 1979). In that review, which included trihalides (RX3), tetrahalides (RX4), and reduced halides (RX , n < 3), preparative procedures, structural interrelationships, and thermodynamic properties were discussed. Hydrated halides and mixed metal halides were discussed to a lesser extent. The synthesis of scandium, yttrium and the lanthanide trihalides, RX3, where X = F, Cl, Br, and I, with emphasis on the halide hydrates, solution chemistry, and aspects related to enthalpies of solution, were reviewed by Burgess and Kijowski (1981). The binary lanthanide fluorides and mixed fluoride systems, AF — RF3 and AFj — RF3, where A represents the group 1 and group 2 cations, were reviewed in a subsequent Handbook (Greis and Haschke 1982). That review emphasized the close relationship of the structures of these compounds to that of fluorite. 

All of the actinide elements are metals with physical and chemical properties changing along the series from those typical of transition elements to those of the lanthanides. Several separation, purification, and preparation techniques have been developed considering the different properties of the actinide elements, their availability, and application. Powerful reducing agents are necessary to produce the metals from the actinide compounds. Actinide metals are produced by metallothermic reduction of halides, oxides, or carbides, followed by the evaporation in vacuum or the thermal dissociation of iodides to refine the metals. 

The actinide ions in aqueous solution resemble the tripositive lanthanide ions in their precipitation reactions, allowing for differences in the redox properties of early members of the actinide series. The chloride, bromide, nitrate, bromate, and perchlorate anions form water-soluble salts, which can be isolated as hydrated solids by evaporation. The acetates, iodates, and iodides are somewhat less soluble in water. The sulfates are sparingly soluble in hot solutions, somewhat more soluble in the cold. Insoluble precipitates are formed with hydroxide, fluoride, carbonate, oxalate, and phosphate anions. Precipitates formed from aqueous solution are usually hydrated, and the preparation of anhydrous salts from the hydrates without formation of hydrolyzed species can only be accomplished with difficulty. The actinide(iv) ions resemble Ce(iv) in forming fluorides and oxalates insoluble even in acid solution. The nitrates, sulfates, perchlorates, and sulfides are all water-soluble. The iv state actinide ions form insoluble iodates and arsenates even in rather strong acid solution. The... 

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