Lanthanide silsesquioxanes

More recently, Aspinah et al. reported the synthesis of a series of lanthanide silsesquioxanes resulting from reactions of 3 with lanthanide tris(silylamides) Ln[N(SiMc3)2]3 (Ln = Y, La, Pr, Eu, Yb). However, single crystals of these materials suitable for X-ray diffraction could not be obtained. The somewhat complicated situation is illustrated in Scheme 25. The lanthanide tris(silylamides) reacted with two-third equivalents of the trisilanol 3 in THF to give the lanthanide silsesquioxanes 85, which are dimeric in solution at 233 K. Reaction of Ln[N(SiMe3)2]3 with one equivalent of 3 in THF resulted in complete conversion of 3 to the trisilylated compound 14, as did the reaction of Ln[N(SiMe3)2]3 with two-third equivalents of 3 in toluene. 

The chloro-functionalized lanthanide silsesquioxane complexes 86 (Ln = Y, La) are accessible by the reaction of 85 with one equivalent of Me3SiCl according to Scheme 27. ... 

Cy7Si70i2Ln(PMDTA) (87, Ln = Y, La, Yb) are depicted in Scheme 28. In all these cases severe disorder problems prevented a structural characterization of the lanthanide silsesquioxanes by X-ray diffraction. ... 

The first metallasilsesquioxanes incorporating lanthanides were described in 1994 by Herrmann et alJ More recently, several Ln silsesquioxanes resulting from reactions of 1 with lanthanide silylamides and aryloxides have been reportedJ Our own efforts in this field resulted in the isolation of a novel Ce(lV) silsesquioxane complex as well as the structural characterization of a bimetallic Yb/Li derivative.Treatment of [Ce N(SiMe3)2 3] or anhydrous CeCls with two equivalents of Cy8Si80n(0H)2 (42) in diethyl ether in the presence of an excess of pyridine exclusively afforded the diamagnetic complex (Cy8Si80]3)2Ce(py)3 (43, Scheme 29.11). Quite surprisingly, in both cases cerium was oxidized to the tetravalent oxidation state. 

All bridged dimers feature a central Ln202 core (type I), which in the presence of strong donor molecules such as THF, DME, OPPh3, or pyridine dissociate into mononuclear species with either octahedral (type II) or trigonal bipyramidal structures (type III). Similar structural motifs are found in cyclic silsesquioxane-based rare earth siloxides. In the presence of donors, distorted octahedral (V) or distorted trigonal bipyramidal complexes (IV) are formed, which in solution through loss of donor solvent may be in equilibrium with their respective dimers (see Lanthanides Coordination Chemistry) ... 

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