Chemistry Reference
In-Depth Information
In addition to hetero-bimetallic and -trimetallic alkoxides, some heterotetrametallic
alkoxides have also been reported
9
as illustrated already by Eqs (3.76) and (3.77).
In spite of considerable initial scepticism, the synthesis of an increasing
number of well-characterized heterometallic alkoxides is now well established and
attempts are being directed towards the synthesis of “single-source” precursors for
preparation of mixed metal- oxide ceramic materials by the sol - gel or MOCVD
processes.
12
,
20
,
22
,
24 - 27
,
43
Before proceeding to a brief account of some novel types of
heterometal glycolate and aminoalkoxide derivatives, it is appropriate to mention four
review articles
47
,
163 - 165
summarizing the state of knowledge about the conventional
heterometallic alkoxide systems at the end of the twentieth century.
2.4
Synthesis of Heterometallic Glycolate Alkoxide Derivatives
The facile dissolution of alkaline earth metals in alcohols in the presence of alkox-
ides of metals like aluminium (Section 2.1.2) has been ascribed to the formation of
R
alcohol adducts of the metal alkoxides
rendering the proton of
O
Al(OR)
3
H
the adduct alcohol more labile. A similar type of lability of protons of glycol molecules
coordinated in derivatives like titanium trisglycolate
166
has been utilized
43
,
167
,
168
for
synthesis of bi- and triheterometallic glycolate alkoxides by reactions of the types
shown in Eqs (3.87) - (3.89):
O
O
OH
benzene
M(OPr
i
)
4
4Pr
i
OH
+
3G
G
M
G
+
↑
OH
(3.87)
O
O
2
H
(1)
Soluble
OH
OH
=
where
M = Ti, Zr, Hf, Sn(
IV
); G
2-methylpentane-2,4-diol.
O
2Al(OPr
i
)
3
[{Al(OPr
i
)
2
}
2
2Pr
i
OH
(1)
+
M
G
]
+
↑
(3.88)
O
3
(2)
Soluble
O
2Nb(OPr
i
)
5
[{Nb(OPr
i
)
4
}
2
2Pr
i
OH
(1)
+
M
G
]
+
↑
(3.89)
O
3
These two reactions can also be carried out in two consecutive stages of 1:1
molar reactions with Al
OPr
i
3
and Nb
OPr
i
5
, yielding a heterotrimetallic derivative
O
[{Al(OPr
i
)
2
}{Nb(OPr
i
)
4
}
{M
G
}]
.
O
3
