Lanthanum compounds/complexes

Mono(guanidinate) complexes of lanthanum and yttrium have been synthesized as illustrated in Scheme 58.The lanthanum compounds were made starting from La[N(SiMe3)2]3 and dicyclohexylcarbodiimide. Both mono (guanidinate) derivatives are monomeric in the solid state with a four-coordinate La center. ... 

The only complexes of lanthanum or cerium to be described are [La(terpy)3][C104]3 175) and Ce(terpy)Cl3 H20 411). The lanthanum compound is a 1 3 electrolyte in MeCN or MeN02, and is almost certainly a nine-coordinate mononuclear species the structure of the cerium compound is not known with any certainty. A number of workers have reported hydrated 1 1 complexes of terpy with praseodymium chloride 376,411,438), and the complex PrCl3(terpy)-8H20 has been structurally characterized 376). The metal is in nine-coordinate monocapped square-antiprismatic [Pr(terpy)Cl(H20)5] cations (Fig. 24). Complexes with a 1 1 stoichiometry have also been described for neodymium 33, 409, 411, 413, 417), samarium 33, 411, 412), europium 33, 316, 411, 414, 417), gadolinium 33, 411), terbium 316, 410, 414), dysprosium 33, 410, 412), holmium 33, 410), erbium 33, 410, 417), thulium 410, 412), and ytterbium 410). The 1 2 stoichiometry has only been observed with the later lanthanides, europium 33, 411, 414), gadolinium, dysprosium, and erbium 33). 

Finally, a fascinating development in the field of lanthanum-BINOL complexes remains to be mentioned [25]. These compounds so far have proved to catalyze enantioselectively hydrophos-phonylations of imines [26], nitroaldol reactions [27], Michael additions [28] and cpoxidations of... 

The first structure of a [Ln(phen)2(N03)3] complex was reported in 1992 for the lanthanum compound.It closely resembled the established bipy analogue in that the three nitrate groups were bidentate and the lanthanum was 10-coordinate. The structural information was complemented by a multinuclear solution ( H-, C-, O-, and La) NMR study. The structure of the other extreme member of the series, the lutetium complex, was reported in 1996. Unlike the La complex, but like [Lu(bipy)2(N03)3], the study was not complicated by disorder. The complexes appear to form an isomorpohous and isostructural series. On moving from the lanthanum to the lutetium compound, the Ln—N distances decrease from 2.646(3)-2.701(3) A (La) to 2.462(8)-2.479(8) A (Lu), and the range of Ln—O distances decreases from 2.580(3)-2.611(3) A for the lanthanum compound to 2.364(8)-2.525(6) A for the lutetium complex. Several structures have subsequently been reported of other [Ln(phen)2(N03)3] systems. [Ln(phen)2(N03)3] (Ln = Pr, Lu, Dy, are isostructural the individual complex... 

Better results were obtained in the methyl methacrylate polymerization reactions (Scheme 12). 153-156 showed high catalytic activity with a strong dependence on the ionic radius of the center metal. The lanthanum complex 154 was the most active catalyst and initiated the polymerization without any cocatalyst. Addition of small amounts of AlEts as cocatalyst increased the yield significantly. Polymerization initiated by 154 depended on the temperature and a low temperature (—78°C) was required to afford almost quantitative yields. The resulting polymers were basically syndiotactic and exhibited high molar masses and narrow polydispersities. The catalytic reaction with the lanthanum compound 157 showed no increase of catalytic activity but led to a larger fraction of atactic poly(methyl methacrylate). Moreover, the catalytic activity of all utilized initiators was solvent dependent. 153, 155, and 156 only showed catalytic activity by the addition of a cocatalyst. 153 afforded lower yield after changing the solvent from toluene into THF. 

The catalytic activity of the chiral complexes [Ln(L)Z2] shown in Scheme 70 was investigated in NMR-scale intramolecular hydroamination/cyclization reactions [135]. The rate dependence on the ionic radii of the center metal was studied by using 5 mol% bisoxazoline L32 and [Ln N(SiMe3)2 3] as precatalysts and 2,2-dimethyl-4-penten-l-amine as substrate (Scheme 71). The reaction rate as well as the enantioselectivities increased with increasing radius of the center metal. Therefore, the lanthanum compound 184 was the most active catalyst among the investigated complexes. 

A binuclear compound with bridging butadiene ligand has been obtained in the reaction of halide-free "magnesiumbutadiene" with a lanthanum atc-complex [13]... 

Some of the first works on the use of soluble rare earth salts in relation to tribocorrosion were published in 1996 (Lian et al, 1996a, 1996b). The authors studied the addition of RE complexes into lubricants. In these two works the authors prepared two types of additives, lanthanum and zinc dodecyl-polyethylene epoxyphosphates, and evaluated their anti-wear properties in water and paraffin. Although both compounds were effective for increasing resistance to wear in water, the optimal properties in this medium were supplied by the zinc compound. Conversely, the lanthanum compound exhibited better anti-wear properties in paraffin. 

With the exception of the lanthanum compound, the rare earth vanadites are isomorphic. The orthorhombic structure can be described as distorted perovskite and thus they are not in fact complex compounds but mixed oxides (Wold and Ward, 1954 Geller, 1957). According to Kestigian et al. (1957) and Brusset et al. (1972), lanthanum vanadite is tetragonal in structure, although there is also one report of a cubic structure. 

The compounds R[A1(0C3H7)4]3 have been synthesized in a variety of ways (Mehrotra et al., 1973a). These complexes are volatile and can be distilled under reduced pressure. As expected, the scandium compound is the most volatile boiling at 145°C at 0.5 mm Hg, whereas the lanthanum compound is least volatile... 

There are a number of interferences that can occur in atomic absorption and other flame spectroscopic methods. Anything that decreases the number of neutral atoms in the flame will decrease the absorption signal. Chemical interference is the most commonly encountered example of depression of the absorption signal. Here, the element of interest reacts with an anion in solution or with a gas in the flame to produce a stable compound in the flame. For example, calcium, in the presence of phosphate, will form the stable pyrophosphate molecule. Refractory elements will combine with 0 or OH radicals in the flame to produce stable monoxides and hydroxides. Fortunately, most of these chemical interferences can be avoided by adding an appropriate reagent or by using a hotter flame. The phosphate interferences, for example, can be eliminated by adding 1 % strontium chloride or lanthanum chloride to the solution. The strontium or lanthanum preferentially combines with the phosphate to prevent its reaction with the calcium. Or, EDTA can be added to complex the calcium and prevent its combination with the phosphate. 

---