Lanthanides reactivity

The lanthanides are very electropositive and reactive metals. With the exception of Yb... 

Because ketones are generally less reactive than aldehydes, cycloaddition reaction of ketones should be expected to be more difficult to achieve. This is well reflected in the few reported catalytic enantioselective cycloaddition reactions of ketones compared with the many successful examples on the enantioselective reaction of aldehydes. Before our investigations of catalytic enantioselective cycloaddition reactions of activated ketones [43] there was probably only one example reported of such a reaction by Jankowski et al. using the menthoxyaluminum catalyst 34 and the chiral lanthanide catalyst 16, where the highest enantiomeric excess of the cycloaddition product 33 was 15% for the reaction of ketomalonate 32 with 1-methoxy-l,3-butadiene 5e catalyzed by 34, as outlined in Scheme 4.26 [16]. 

Thenoyltrifluoroacetone(TTA), C4H3S,CO,CH2,COCF3. This is a crystalline solid, m.p. 43 °C it is, of course, a /1-diketone, and the trifluoromethyl group increases the acidity of the enol form so that extractions at low pH values are feasible. The reactivity of TTA is similar to that of acetylacetone it is generally used as a 0.1-0.5 M solution in benzene or toluene. The difference in extraction behaviour of hafnium and zirconium, and also among lanthanides and actinides, is especially noteworthy. 

Ladder polymer, synthesis of, 503 Lanthanide catalysts, 288 Lanthanide compounds, 73 Latent-reactive polymers, 455 Laurolactam, 136... 

A technologically important effect of the lanthanide contraction is the high density of the Period 6 elements (Fig. 16.5). The atomic radii of these elements are comparable to those of the Period 5 elements, but their atomic masses are about twice as large so more mass is packed into the same volume. A block of iridium, for example, contains about as many atoms as a block of rhodium of the same volume. However, each iridium atom is nearly twice as heavy as a rhodium atom, and so the density of the sample is nearly twice as great. In fact, iridium is one of the two densest elements its neighbor osmium is the other. Another effect of the contraction is the low reactivity—the nobility —of gold and platinum. Because their valence electrons are relatively close to the nucleus, they are tightly bound and not readily available for chemical reactions. 

A review article entitled "Bulky amido ligands in rare-earth chemistry Syntheses, structures, and catalysis" has been published by Roesky. Benzamidinate ligands are briefly mentioned in this contexD The use of bulky benzamidinate ligands in organolanthanide chemistry was also briefly mentioned in a review article by Okuda et al. devoted to "Cationic alkyl complexes of the rare-earth metals S mthesis, structure, and reactivity." Particularly mentioned in this article are reactions of neutral bis(alkyl) lanthanide benzamidinates with [NMe2HPh][BPh4] which result in the formation of thermally robust ion pairs (Scheme 55). ... 

Metathetical routes using bulky lithium guanidinates as starting materials have also been employed to synthesize bis(guanidinato) lanthanide halides as well as reactive alkyls and hydrides. Scheme 63 shows as a typical example the formation of the lutetium chloro precursor, which was isolated in 76% yield. ... 

Here we try to gain insight into the trends in reactivity of the metals without getting lost in too much detail. We therefore invoke rather crude approximations. The electronic structure of many metals shows numerous similarities with respect to the sp band, with the metals behaving essentially as free-electron metals. Variations in properties are due to the extent of filling of the d band. We completely neglect the lanthanides and actinides where a localized f orbital is filled, as these metals hardly play a role in catalysis. 

Kornienko AY, Emge TJ, Brennan JG (2001) Chalcogen-rich lanthanide clusters Cluster reactivity and the influence of andllary ligands on structure. J Am Chem Soc 123 11933-... 

The indium-mediated allylation of trifluoroacetaldehyde hydrate (R = H) or trifluoroacetaldehyde ethyl hemiacetal (R = Et) with an allyl bromide in water yielded a-trifluoromethylated alcohols (Eq. 8.56).135 Lanthanide triflate-promoted indium-mediated allylation of aminoaldehyde in aqueous media generated (i-airiinoalcohols stereoselectively.136 Indium-mediated intramolecular carbocyclization in aqueous media generated fused a-methylene-y-butyrolactones (Eq. 8.57).137 Forsythe and co-workers applied the indium-mediated allylation in the synthesis of an advanced intermediate for azaspiracids (Eq. 8.58).138 Other potentially reactive functionalities such as azide, enone, and ketone did not compete with aldehyde for the reaction with the in situ-generated organo-indium intermediate. 

Europium is the most reactive lanthanide metal, and may ignite on exposure to air if finely divided. 

Metal vapor chemistry showed that the lanthanides had quite an extensive chemistry with unsaturated hydrocarbons. Some of the early surveys of metal vapor reactions with unsaturated hydrocarbons included some lanthanide metals and showed that reactivity was present for these metals (14-18). Subsequent synthetic studies in which the products were isolated and characterized led to some of the most unusual organolanthanide complexes currently known (19-28). 

The simple hydrocarbon substrates included ethene, 1,2-propa-diene, propene and cyclopropane (22). Their reactivity with Sm, Yb and Er was surveyed. In contrast to the reactions discussed above, lanthanide metal vapor reactions with these smaller hydrocarbons did not provide soluble products (with the exception of the erbium propene product, Er(C H ) ). Information on reaction pathways had to be obtained primarily by analyzing the products of hydrolysis of the metal vapor reaction product. 

---