Lanthanide metal alkoxides, homoleptic

The addition of a base, typically ammonia, to mixtures of transition metal halides and alcohols allows the synthesis of homoleptic alkoxides and phenoxides for a wide range of metals. Anhydrous ammonia was first used in the preparation of titanium alkoxides where the reaction is forced to completion by the precipitation of ammonium chloride.41 Although useful for the synthesis of simple alkoxides and phenoxides of Si, Ge, Ti, Zr, Hf, V, Nb, Ta and Fe, as well as a number of lanthanides,42-47 the method fails to produce pure /-butoxides of a number of metals.58 Presumably, secondary reactions between HC1 and Bu OH take place. However, mixing MC14(M = Ti, Zr) with the Bu OH in the presence of pyridine followed by addition of ammonia proves successful, giving excellent yields of the M(OBul)4 complexes.59... 

The influence of steric factors was thoroughly studied in the reaction of Ln(btsa)3 with the alcohol tritox-H. While the reaction takes place with larger lanthanides like neodymium to yield the homoleptic alkoxide complexes (Eq. 18) [264], the analogous reaction does not work with smaller metals like yttrium and thulium (Eq. 19). However, variation of the reaction conditions to a stoichiometric solid reaction yielded a fully exchanged product along with an unexpected and unusual silylamine degradation [265] (Eq. 20). This degradation reaction seems to be sterically forced and points out N-Si bond disruptions and C-Si bond formations under mild conditions [114]. 

Using a highly hindered phosphino-alkoxide ligand, lanthanoid metal complexes [Ln(OCBu2CH2PMe2)3l (Ln = Y or Nd) have been obtained [30], These are the first monomeric homoleptic examples of lanthanide alkoxide complexes. The bulky substituents... 

Lanthanide alkyl compounds are important alkyl transfer reagents and initiate a variety of catalytic reactions. The transformation of lanthanide alkoxide bonds to lanthanide alkyl bonds seems to be an attractive alternative to the alkylation of lanthanide halides with alkali metal alkyl compounds. For example, the ary-loxide route affords homoleptic lanthanide alkyls in good yield [Eq. (22)] [135]. 

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