Chemistry Reference
In-Depth Information
2.5.2
The Sodium (or Potassium) Alkoxide Method (E-2)
This procedure, sometimes referred to as transmetallation or (metathesis or salt-
elimination) reaction, is by far the most versatile synthetic method for a wide range of d-
and p-block metal alkoxide complexes. The alkali metal (usually sodium or potassium)
alkoxide is treated in the presence of excess alcohol with the corresponding metal(loid)
halide either in a hydrocarbon (generally benzene) or an ether solvent (Eq. 2.41):
MCl
x
C
x
M
0
OR ! M(OR)
x
C
x
M
0
Cl #
2
.
41
where M D a metal or metalloid and M
0
D Na or K.
Although this procedure normally results in complete substitution, except for the
sterically more demanding alkoxo groups, 100% synthetic predictability is not likely
to be achieved. The generality and limitations of Eq. 2.41 for a wide variety of elements
may be reflected by the group-wise discussion that follows.
2.5.2.1 s-Block metals
The reaction between CaI
2
and KOC(Ph)
2
CH
2
C
6
H
4
Cl-4 in (THF) affords a soluble
and monomeric alkoxide complex
147
(Eq. 2.42):
CaI
2
C 2KOC(Ph)
2
CH
2
C
6
H
4
Cl-4
THF
![CafOC(Ph)
2
CH
2
C
6
H
4
Cl-4g
2
(thf)
n
] C 2KI #
(2.42)
Interaction of BaI
2
and the potassium salt of a donor-functionalized alcohol gives a
dimeric product
53
according to Eq. (2.43):
THF
!
2KI
BaI
2
C 2KOC
Bu
t
CH
2
OPr
i
2
1
2
[BafOC
Bu
t
CH
2
OPr
i
2
g
2
]
2
2
.
43
2.5.2.2 Group 3 and f-block metals
The addition of a sodium (or potassium) isopropoxide to an appropriate LnCl
3
.
3Pr
i
OH
in a medium of isopropyl alcohol and benzene results in the precipitation of NaCl
(or KCl), which is removed by filtration. From the filtrate, quantitative yields of
[Ln
OPr
i
3
]
x
can be isolated (Eq. 2.44):
103
,
148 - 158
LnCl
3
.
3Pr
i
OH C 3MOPr
i
!
1
n
[Ln
OPr
i
3
]
n
C 3Pr
i
OH C 3MCl #
2
.
44
where Ln D Y,
103
,
148
,
149
La,
150
,
156
Pr,
150 - 153
Nd,
150 - 153
Sm,
154
,
155
Gd,
149
,
154
,
156
,
157
Ho,
158
Er,
149
,
152
,
156
,
157
Yb.
103
,
148
,
149
The above reactions (Eq. 2.44) are frequently not straightforward; a plethora of
different (generally unusual) products are generated
18
,
21
in such reactions even by
slight variations in the experimental conditions/manipulations, the order of reactant(s)
addition, the stoichiometry of reactants,
159
and the nature of the alkoxide groups.
159 - 161
Although there appears to be little synthetic control over the nature or structures of
the products, an impressive series of structurally novel species have been obtained
via
reactions of alkali metal alkoxides with the appropriate lanthanide chloride or ceric
ammonium nitrate, as illustrated below.
Interesting partial substitution reactions between yttrium trichloride and sodium
tert
-
butoxide in different (1:2 and 1:3) molar ratios have been reported (Eqs 2.45 and 2.46)
