Chemistry Reference
In-Depth Information
Lithium methoxide (Eq. 5.26) was used instead of sodium methoxide because uranyl
methoxide which was insoluble in methanol could thus be separated from lithium chlor-
ide which was soluble. The ethoxide [UO
2
OEt
2
EtOH
2
] was also prepared using
lithium ethoxide but the isopropoxide [UO
2
OPr
i
2
Pr
i
OH
], being appreciably soluble
in isopropanol, was prepared using sodium isopropoxide. The triphenyl phosphine
oxide adduct of uranyl
tert
-butoxide [UO
2
OBu
t
2
Ph
3
PO
2
] was prepared similarly
from [UO
2
Cl
2
Ph
3
PO
2
] and KOBu
t
.
44
The vanadium(
V
) oxo-trialkoxides [VO
OR
3
]
n
were readily prepared from VOCl
3
,
45-47
but the reaction of [Li
2
O
2
C
2
CF
3
4
] with
CrO
2
Cl
2
ledtoreductiontoCr(
V
) in the form of [LiCr
O
2
fO
2
C
2
CF
3
4
g].
48
Several
W(
VI
) oxo-tetra-alkoxides have been prepared from WOCl
4
by reactions with NaOR
or alcohol and ammonia.
49
2.4
Preparation of Metal Oxo-alkoxides from Metal Oxides
An alternative approach to the synthesis of metal oxo-alkoxides is the reaction of the
metal oxide with an alcohol (Eq. 5.26).
MO
x
C 2ROH ! MO
x
1
OR
2
C H
2
O
5
.
26
This is in effect a reversal of the hydrolysis of a metal alkoxide (Eqs 5.2 and 5.3),
although there is little evidence for the reversibility of the hydrolysis process. Never-
theless, the reaction of some organometallic oxo-compounds with alcohols to form
alkoxo derivatives is well documented (
e.g.
Eq. 5.27).
1
R
3
GeOGeR
3
C 2R
0
OH ! 2R
3
GeOR
0
C H
2
O
5
.
27
Several oxo-alkoxides of vanadium and molybdenum have been prepared from
reactions of the metal oxide or oxometallate anion with alcohols. Thus the
reaction of MoO
3
with ethyleneglycol gave [MoO
2
OC
2
H
4
OH
2
]
50
and with 2,2
0
-
oxodiethanol gave [MoO
2
OC
2
H
4
OC
2
H
4
O
].
51
Refluxing MoO
3
.
2H
2
O with methanol
in the presence of molecular sieve (4A) gave mainly [Mo
2
O
5
OMe
2
] with some
[Na
4
fMo
8
O
24
OMe
4
g]
.
8MeOH.
52
The vanadium(
V
) oxo-trialkoxides, [VO
OR
3
](RD Et, Pr
n
,Pr
i
,Bu
s
,Bu
t
,C
2
H
4
Cl,
C
2
H
4
F, CH
2
CCl
3
) were prepared by refluxing finely divided V
2
O
5
with alcohol and
benzene and removing the water produced (Eq. 5.28) by azeotropic distillation.
46
V
2
O
5
C 6ROH ! 2VO
OR
3
C 3H
2
O
5
.
28
Zubieta
et al
. have obtained the interesting polyoxovanadate anions
involving V(
IV
): [V
10
O
16
fEtC
CH
2
O
3
g
4
]
4
, [
10
O
13
fEtC
CH
2
O
3
g
5
]
,
53
[V
10
O
14
OH
2
f
OCH
2
3
CCH
2
OHg
4
]
2
,
54
[BafV
6
O
7
OH
3
gf
OCH
2
3
CMeg
3
]
.
3H
2
Oand
[Na
2
fV
6
O
7
gf
OCH
2
3
CEtg
4
]
55
by hydrothermal reactions of a mixture of vanadium oxides
[V(
III
)andV(
V
)]. Some mixed valency [V(
IV
), V(
V
)] species [V
10
O
16
f
OCH
2
3
CRg
4
]
2
(R D Et, Me)
54
and
Me
3
NH
[V
6
O
7
OH
3
f
OCH
2
3
CMeg
3
]
55
were similarly obtained.
Other syntheses have utilized the solubility of quaternary ammonium salts of polyvana-
dates to obtain the polyoxo-alkoxo vanadate ions [V
6
O
13
f
OCH
2
3
CRg
2
]
3
(R D Me,
