Chemistry Reference
In-Depth Information
First homoleptic dimers of tungsten(
V
) (Eq. 2.166) and rhenium(
V
) (Eq. 2.167) have
been prepared
429
according to the following reactions:
i
Li
!
THF
ii
NaOMe
!
THF
WF
6
C Me
3
SiOMe ! WF
2
OMe
4
W
2
F
x
OMe
10
x
x
D 1 - 3
W
2
OMe
10
2
.
166
i
Si
OMe
4
!
CH
3
CN
,
40
°
C
ii
Mg
OMe
2
HOMe
2
!
THF
ReF
6
Re
2
OMe
10
(2.167)
An unusual exchange reaction takes place when the organoactinide hydrides
[AnH
2
5
-C
5
Me
5
2
]
2
are treated with trimethyl phosphite.
430
A methoxo group is
transferred to the metal atom while phosphorus is hydrogenated to give a PH bridge:
5[AnH
2
5
-C
5
Me
5
2
]
2
C 4P
OMe
3
toluene
!
25
°
C
fAn
OMe
5
-C
5
Me
5
2
g
2
PH C 3An
OMe
2
5
-C
5
Me
5
2
C 3H
2
2
.
168
In contrast to the expected elimination of an ester in the reaction of Sn
OBu
t
4
with
Sn
OAc
4
as well as with Me
3
SnOAc in a refluxing hydrocarbon solvent, only ligand
exchanges of the types shown below have been demonstrated to occur in coordinating
solvents such as pyridine:
431
3Sn
OBu
t
4
C 3Sn
OAc
4
pyridine
! 2Sn
OBu
t
OAc
3
C 2Sn
OBu
t
2
OAc
2
C 2Sn
OBu
t
3
OAc
2
.
169
pyridine
! Sn
OBu
t
3
OAc
py
C Me
3
Sn
OBu
t
2
.
170
Sn
OBu
t
4
C Me
3
SnOAc
The X-ray crystallographically characterized
431a
derivative of zinc, Zn
2
OAc
3
(OMe),
has been prepared by the reaction shown in Eq. (2.170a):
2Zn
OAc
2
C Bu
2
Sn
OMe
2
! Zn
2
OAc
3
OMe
C Bu
2
Sn
OAc
OMe
2
.
170a
3
PHYSICAL PROPERTIES
3.1
Introduction and Structural Characteristics
The physical properties of the metal alkoxides [M(OR)
x
]
n
are largely influenced by
the size and shape of the alkyl (R) group as well as by the valency (
x
), atomic
radius, stereochemistry, and coordination number of the metal. Owing to the high
electronegativity of oxygen (3.5 on Pauling scale), the M-OR bonds (in alkoxides
of metallic elements) would be expected to possess significant ionic character. Thus
metal - oxygen bonds (M
υ
C
—O
υ
—C) in metal alkoxides could be expected to possess
around 65% ionic character for metals with electronegativity values of the order of
1.5 - 1.3 (aluminium, titanium, and zirconium) to about 80% ionic character for more
