Salts lanthanide complexes

Shortly after the key mechanistic papers on rhodium-catalyzed hydroboration, Marks reported a hydroboration reaction catalyzed by lanthanide complexes that proceeds by a completely different mechanism.63 Simple lanthanide salts such as Sml3 were also shown to catalyze the hydroboration of a range of olefins.64 The mechanism for this reaction was found to be complex and unknown. As in other reactions catalyzed by lanthanides, it is proposed that the entire catalytic cycle takes place without any changes in oxidation state on the central metal. 

Castellani Bisi (98) has synthesized complexes of lanthanide perchlorates with DMP which have a L M of 8 1 for the lighter lanthanide and 7 1 for the heavier lanthanide complexes. These complexes were prepared by reacting the respective metal salts with an excess of the ligand. When the complexes were prepared under conditions of lower concentrations of the ligand, complexes of DMP with a L M of 6 1 were obtained. The perchlorate groups in all three groups of complexes are ionic. 

The complexes Mnr(dtc)3 (Mni = Np, Pu) are obtained by treating the metal tribromide with Na(dtc) in anhydrous ethanol. Pu(dtc)3 is fairly stable to oxidation, but Np(dtc)3 and the even less stable U(dtc)3 are rapidly oxidized to M(dtc)4, so that neither can be isolated. However, the anionic complexes, (NEt4)[Mm(dtc)4] (M11 = Np, Pu), have been prepared and the geometry about the metal atom is a distorted dodecahedron, best regarded as a planar pentagon of five S atoms with one S atom above and two S atoms below the pentagon.23 These salts of the [M(dtc)4] ion are isostructural with the analogous lanthanide complexes, whereas Pu(dtc)3 is not isostructural with any of the lanthanide Ln(dtc)3. 

Figure 5.3 Synthetic conditions for the mixed-ligand Pc complexes, containing one Pc ligand. Route 1 interaction of o-dicyanobenzene(s) and their analogues with lanthanide salts. Route 2 metallation reaction of the macrocyclic ligand or its dianione by lanthanide compounds. Route 3 reactions of axial substitution in the environment of the central atom in lanthanide complexes ([96] and references cited therein). (From Ref. 96, with permission.)...

This section describes systems which are at the border of what has been defined as being the scope of this review and therefore does not pretend to be comprehensive. Indeed, if there is a wealth of strictly inorganic materials and glasses into which NIR-crnitting lanthanide ions have been incorporated and which are clearly excluded from the review, there also exist a continuum between these materials and molecular entities, for instance coordination polymers and clusters which have been described in the two preceding sections. In continuity with these concepts are micro- and mesoporous materials into which lanthanide salts or complexes can be incorporated or attached. These are essentially zeolites and sol-gel materials, either conventional or the so-called inorganic-organic hybrids, as well as polymers. 

An interesting class of homoleptic lanthanide complexes has become available through the use of heteroallylic diphosphinomethanide ligands. The first member of the series was the lanthanum derivative, [CH(PPh2)2]3La (59c), which was characterized by X-ray crystallography (Fig. 19) [74]. The preparation of 59c involved treatment of anhydrous lanthanum trichloride with the potassium salt of the ligand ... 

Synthesis of several lanthanide complexes requires anhydrous conditions. Hydrated lanthanide salts undergo decomposition in the process of dehydration under vacuum at elevated temperatures. Thus special procedures are required for the preparation of anhydrous salts. 

The initial starting materials for the preparation of lanthanide complexes must be such that the counterions do not compete with the ligand in the formation of complexes. Among the lanthanide salts the complex formation tendency is in the order SO - > NO3 > CIOJ and hence lanthanide perchlorates are the preferred starting materials for the synthesis of complexes. 

The lanthanide triflates may also be obtained by the addition of triflic acid to lanthanide carbonates in ethanol or acetonitrile [18]. Filtration and concentration of the filtrate yield a solid salt which is washed with solvent. Lanthanide salts of poorly coordinating anions such as PFg, BF4 or BiCftHs) have been also used in the synthesis of lanthanide complexes as starting materials. Adducts of acetonitrile with europium tetrafluoroborate (BF4) and hexafluorophosphate (PF ) have been prepared [19]... 

The complexes may also be prepared by the addition of a solution of carboxylic ligand to an equivalent amount of (i) a lanthanide carbonate [28], (ii) hydroxide [29] or (iii) oxide [30] with a slight excess of the latter. The insoluble part is filtered and the filtrate evaporated to obtain crystalline complex. Anhydrous lanthanide complexes of small chain carboxylic acids may be prepared by (i) the dissolution of lanthanide carbonate in excess of the carboxylic acid, followed by heating to obtain complete dissolution of the suspension and partial evaporation of the solution to obtain the crystals [31], (ii) anhydrous lanthanide is converted into the corresponding monochloroacetate by the addition of an excess of monochloroacetic acid, followed by heating under reflux at reduced pressure for 2 h. Then ether is added to precipitate the salt [32], (iii) the addition of dimethyl formamide and benzene to lanthanide acetates and distillation of the water azeotropes to obtain anhydrous complexes. The last procedure yielded lighter lanthanide complexes solvated with dimethyl formamide [33], The DMF may be removed by heating in a vacuum at 120°C. 

Lanthanide complexes of poorly coordinating ligands such as aldehydes and ketones [24], esters [25], and ligands containing sulphur and phosphorus [26] have been prepared. The procedure consists of mixing a solution of hydrated lanthanide salt with a solution of the... 

Lanthanide complexes with macrocyclic polyethers [64] have been obtained by mixing solutions of the ligand and solution of a hydrated lanthanide salt [65]. 

In the process of lanthanide complex formation with the porphyrins, the ligand loses two protons and yields lanthanide hydroxy porphyrin or lanthanide porphyrin X, where X = C1, Br, NOJ, etc. Many lanthanide complexes with substituted porphyrins have been prepared by heating a mixture of porphyrin and the lanthanide salt in imidazole melt in the range 210-240°C. When the complex formation is complete the solvent (i.e.) imidazole is eliminated by either sublimation [81] or by dissolution of the mixture in benzene, followed by washing with water [82]. Further purification requires column chromatography. The starting material can be anhydrous lanthanide chloride or hydrated lanthanide acetylacetonate. After purification the final product tends to be a monohydroxy lanthanide porphyrin complex. 

Phthalocyanines are tetraaza tetrabenzo analogues of porphyrins. Lanthanide complexes with phthalocyanines are prepared by the condensation of phthalonitrile (4 moles) with a lanthanide salt. The monocomplexes were prepared by heating a 1 4 mixture of lanthanide saltiphthalonitrile at 275°C. The molten solution solidified after an hour and purification of the complex is done by removal of excess phthalonitrile and impurities with organic solvents. Final purification is done by chromatography [85]. The bis complexes are prepared in a similar fashion but with a large excess of phthalonitrile [86]. Mixed ligand... 

Trifluoromethane sulfonate salts of lanthanides are used as starting materials for the preparation of other lanthanide complexes instead of perchlorates for safety reasons. 

Polyhedra in these high coordination numbers are often necessarily irregular, but when all the ligands are identical, near-icosahedral geometries occur for the 12-coordinate [Pr(l,8-naphthyridine)6] + and [La(N03)6] ions in crystalline salts. It should also be remembered that the geometries discussed here are found in the solid state, but on dissolution in a solvent, where the influence of counter-ions is lessened, matters may be different (see the aqua ions. Sections 4.3.1 and 4.3.2). In principle, isomers are often possible, but because of the lability of lanthanide complexes they are very rarely observed. 

Alternatively, and this procedure is preferred for the lanthanoid complexes [135], the imidazolium salt can be deprotonated in situ and reacted with a suitable trialkyl lanthanide or reacted without deprotonation with an anionic tetraalkyl lanthanide complex (see Figure 4.63). 

Tris(cyclopentadienyl)lanthanide complexes with steri-cally more crowded Cp ligands such as C5Me4R (R = Me, Et, Tr, and SiMe3) are not assessable by simple metathesis between lanthanide trihalides and the respective alkali metal salt of the bulky Cp ligand. For instance, Cp 3Sm, obtainable from Cp 2Sm and cyclooctatetraene, reacts with THF with ring-opening forming Cp 2Sm[0(CH2)4Cp ](THF) (equation 14). 

Tris(indenyl)lanthanide complexes of all rare earth metals can be prepared analogously from the lanthanide trichlorides with alkali or magnesium indenyl salts. All five-membered rings are -bonded to the metal. They form base adducts with... 

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