Siloxides lanthanide

Scheme 40 Formation of heterobimetallic Ln/Al complexes from lanthanide siloxide/TMA mixtures [142,200]...

Two principle strategies have been employed for the synthesis of siloxide-containing molecular precursors. The first involves a silanolysis, or condensation, reaction of the Si - OH groups with a metal amido, alkyl, hahde, or alkoxide complex. The second method involves salt metathesis reactions of an alkali metal siloxide with a metal hahde. Much of our work has been focused on formation of tris(tert-butoxy)siloxide derivatives of the early transition metals and main group elements. The largely imexplored regions of the periodic table include the lanthanides and later transition metals. 

Routes to monomeric , mononuclear , monolanthanide alkoxides, enolates, siloxides and aryloxides - an expanded title which will put the scope of the article in a more concrete form. The synthesis of mononuclear alkoxides, in particularly homoleptic derivatives [1], was decisively stimulated by the discovery of high temperature superconducting ceramics based on YBa2Cu307<, where yttrium represents the lanthanide elements [2]. The support of volatile and highly soluble molecular precursors is a prerequisite for synthesizing thin films of these materials by means of MOCVD [3] and sol gel processes [4], respectively. More recently, lanthanide alkoxide reagents became established in... 

Scheme 5. Siloxide ligands employed in lanthanide chemistry...

In contrast, Nd2(OCHiPr2)6 cannot be deoligomerized by these solvents, including pyridine. This is in accord with the lower nucleophilicity of the siloxide O-atom which is reflected in the less distinct tendency to bridge the oxophilic lanthanide centers [20]. 

Heterogeneous diene polymerization catalysts based on modified and unmodified silica-supported lanthanide complexes are known as efficient gas-phase polymerization catalysts for a variety of support materials and activation procedures (see Sect. 9). Metal siloxide complexes M(()SiR3 )x are routinely employed as molecular model systems of such silica-immobilized/ grafted metal centers [196-199]. Structurally authenticated alkylated rare-earth metal siloxide derivatives are scarce, which is surprising given that structural data on a considerable number of alkylated lanthanide alkoxide and aryloxide complexes with a variety of substitution patterns is meanwhile available. 

Lanthanides Coordination Chemistry Luminescence Lanthanide Oxide/Hydroxide Complexes Rare Earth Siloxides Organic Syntiiesis. 

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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