2 Homometallic Alkoxides

y Evans and co-workers: 160,161
Homometallic Alkoxides 25
THF
t
3YCl3 C 7NaOBu ! Y3⊲OBu t ⊳7Cl2⊲thf⊳2 C 7NaCl #
(Complex A, 80%)
THF
t
3YCl3 C 8NaOBu ! Y3⊲OBu t ⊳8Cl(thf) 2 C 8NaCl #
(Complex B, 80%)
⊲2.45⊳
⊲2.46⊳
X-ray structural determinations have shown complexes A and B to have structures
which can be represented as [Y3⊲ 3-OBu t ⊳⊲ 3-Cl⊳⊲ 2-OBu t ⊳3⊲OBu t ⊳3Cl(thf) 2] and
[Y3⊲ 3-OBu t ⊳⊲ 3-Cl⊳⊲ 2-OBu t ⊳3⊲OBu t ⊳4(thf) 2], respectively.
These workers further showed 161 that the complex A could be converted into B by
treating with the requisite amount of NaOBu t , but further reaction led to insoluble
products:
Complex A C NaOBu t !Complex B ⊲2.47⊳
Complex B C NaOBu t !Insoluble product ⊲2.48⊳
The above findings are rather unusual and intriguing in view of the general trends of
metal alkoxide chemistry and are somewhat at variance with the earlier findings (mainly
on isopropoxide derivatives) from the research groups of Mehrotra103,148–150,156–158 and Mazdiyasni. 54,55 Also, although most of the 1:3 reactions of lanthanide trichlorides
and alkali alkoxides (mainly methoxides, ethoxides, isopropoxides and even 2methoxyethoxides57
have been reported to be quantitative, yet a product (with incomplete
chloride substitution) had been reported159 as Nd6⊲OPr i ⊳17Cl with an interesting
structure, in the reaction of NdCl3 with three equivalents of NaOPr i .
By contrast, the reaction of LaCl3 with three equivalents of NaOBu t
in THF
was reported 160 to be straightforward, yielding the homoleptic alkoxide complex,
[La⊲OBu t ⊳3]3.2thf, as represented by Eq. (2.49):
THF
t
3LaCl3 C 9NaOBu ! La3⊲ 3-OBu t ⊳2⊲ 2-OBu t ⊳3⊲OBu t ⊳4⊲thf⊳2 C 9NaCl ⊲2.49⊳
Starting with the readily available (NH4)2Ce(NO3)6 (CAN), synthesis of Ce(IV)
alkoxides, Ce(OR)4, has been reported 162,163 by the reaction represented by Eq. (2.50):
⊲NH4⊳2Ce⊲NO3⊳6 C 4ROH C 6NaOMe !Ce⊲OR⊳4 C 6NaNO3 C 2NH3 C 6MeOH
⊲2.50⊳
where R D Me, Et, Pr i ,orn-octyl.
The above convenient method was extended by Evans and co-workers 164 in 1989
to the synthesis of a series of ceric tert-butoxide complexes with the general formula,
Ce(OBu t )n(NO3)4 n(solvent) by the reactions of CAN with NaOBu t in the appropriate
solvent (S D THF or Bu t OH):
⊲NH4⊳2Ce⊲NO3⊳6 C ⊲2 C n⊳NaOBu t
THF or ButOH ! Ce⊲OBu t ⊳n⊲NO3⊳4 n⊲S⊳2 C 2NH3 C ⊲n C 2⊳NaNO3 C 2Bu t OH ⊲2.51⊳