Lanthanide alkoxides characterization

Boyle, T.J. and Ottley, L.A.M. (2008) Advances in structurally characterized lanthanide alkoxide aryloxide and silyloxide compounds. Chemical Reviews, 108, 1896-1917. 

The absence of structurdly characterized dimeric lanthanide alkoxides [9] prompted us to determine the crystal-structure of 3 by single-crystal X-ray diffraction [10]. As Figure 1 indicates, 3 is a dimer with a pseudotetrahedral geometry about each Ce atom. A crystallographic inversion center constrains the Ce and the bridging O atoms to a single plane and a dihedral angle of 84.1° relates this plane to the 0(terminal)-Ce-0(terminal) plane. 

For alkoxides of the Group I and II elements and the lanthanides, typical adducts involve coordinating O-donors such as Et20 or THF. For example, the sparingly soluble, anhydrous aryloxide LiOAr (OAr = 2,6-di-r-butylphenoxide) will dissolve in ethers to give dimeric adducts of the type [(OAr )Li(L)]2 (L = Et20, THF, py), which have been structurally characterized.22 ... 

Simple CH-alkoxides continue to reveal surprising new structure chemistry and the composition of Ln(OMe)3 and Ln(OEt)3 is not yet determined. Mononuclear lanthanide aryloxide complexes are well-examined and are the only fully characterized 3-coordinate, homoleptic Ln(OR)3 species. The variation of the steric environment in pure CH- and CHF-alkoxides with respect to volatility (molecular mass optimization) seems to be rather exhausted. It was shown that functionalization can ensure volatility and although the entire MOCVD-busi-ness gets somewhat stuck, CHF- and CHdo-alkoxides are promising alternatives to the /J-diketonates. Sol gel technology can fall back on highly soluble CH- and CHdo-alkoxides. 

We have noted the affinity of lanthanides for water and this affinity is extended to alcohols to form alcoholates [180]. Alcoholates are generally unstable. Lanthanide triisopropoxide has been synthesized and characterized [204], The lanthanide triisopropoxide may be used as a starting material in the preparation of other alkoxides by alcoholysis. Triisopropoxides of lanthanides are reported to be in dimeric and tetrameric forms as evidenced by mass spectrometry. 

As described above, with the combination of appropriate lanthanide reducing agents, solvents, and substrates, almost all types of the key intermediates involved in the reduction of ketones have been isolated and structurally characterized (Scheme 21), such as the one-electron reduction product (ketyl radical 21), its reversible coupling product (pinacolate 24), hydrogen abstraction product (alkoxide 23) and further one-electron reduction product (ketone dianion 22), and the selective protonation products of the ketone anion (alkoxide 23 and eno-... 

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