Alkoxide and aryloxide ligands

Chart 3 Alkoxide and aryloxide ligands used in lanthanide diene polymerization catalysts and model compounds... 

Alkoxide and aryloxide ligands are excellent ligands for the actinides. As a result, these ligands have been studied extensively in the coordination chemistry and reactivity of tri-, tetra-, penta-, and hexavalent actinides. The alkoxides and aryloxides can be synthesized by a variety of routes the two most popular routes include direct reaction of actinide halides with alkali metal salts of the alkoxide or aryloxide of interest and protonolysis of actinide amides by alcohols. 

Figure 1 Coordination modes of alkoxide and aryloxide ligands...

The Activation of CH Bonds in Alkoxide and Aryloxide Ligands 15.4 REFERENCES... 

A common structural feature of transition metal hydroxide, alkoxide, and aryloxide ligands is their tendency to bridge two or more metals. The extent of such aggregation is reduced when the complexes contain more sterically hindered alkoxides, such as OBu, OCBu y bulky trialkylsiloxides, and 2,6-di-lerl-butylphenoxide. ... 

The alkoxides and aryloxides, particularly of yttrium have excited recent interest. This is because of their potential use in the production of electronic and ceramic materials,in particular high temperature superconductors, by the deposition of pure oxides (metallo-organic chemical vapour deposition, MOCVD). They are moisture sensitive but mostly polymeric and involatile and so attempts have been made to inhibit polymerization and produce the required volatility by using bulky alkoxide ligands. M(OR)3, R = 2,6-di-terr-butyl-4-methylphenoxide, are indeed 3-coordinate (pyramidal) monomers but still not sufficiently volatile. More success has been achieved with fluorinated alkoxides, prepared by reacting the parent alcohols with the metal tris-(bis-trimethylsilylamides) ... 

REACTIONS OF METAL ALKOXIDES AND ARYLOXIDES 15.3.5.1 Ligand Coordination... 

The reaction of metal halides with an alkoxide or aryloxide (most commonly an alkali metal alkoxide), can resnlt in metathetic exchange to give the required complex (equation 6). Such reactions can also result in the formation of heterometallic species (such as NaZr2(OR)4) this can be a problem when homometallic aUcoxides are desired, but it is an important route to heterometallic alkoxides and aryloxides. The nature of the product can be influenced by the alkali metal, the alkoxide ligand, and the relative amounts of the reactantsd ... 

It is important to note that efforts to synthesize metal alkoxides and aryloxides (particularly lanthanide and actinide complexes) have sometimes produced unexpected products, incorporating halide or oxide ligands, for example. As a result, some early literature may contain incorrect formulations. ... 

---