Chemistry Reference
In-Depth Information
3.1
Alkali Metal Dimetallic Alkoxides
3.1.1
Lithium
Complexes of general formula [Li
4
K
4
OSiMe
3
8
x
OBu
t
x
] have been prepared and
the structure of [Li
4
K
4
OSiMe
3
6
.
8
OBu
t
1
.
2
] has been determined. The array of metals
comprises two orthogonal trigonal prisms fused at their base which consists of a
near square plane of potassium ions with two lithiums above and two below the
plane. The trimethylsiloxo or
tert
-butoxo ligands cap each of the four triangular
and four trapezoidal faces.
446
The lithiums are three-coordinated and the potas-
siums four-coordinated. The lithium-bridged spirocyclic magnesiasiloxane complex
[f
py
2
Lig
2
-fOSi
Ph
2
OSi
Ph
2
OSi
Ph
2
Og
-fOSi
Ph
2
OSi
Ph
2
OgMg]
has
four-
magnesium
447
coordinated
lithium
and
four-coordinated
(distorted
tetrahedral)
(Table 4.17, pp. 339 - 345).
Four-coordinated Li and pseudo-four-coordinated yttrium are found in [Li
thf
2
-
OBu
t
2
YfC
5
H
4
SiMe
3
g
2
].
448
In the trinuclear complex [
thf
2
Li
-OBu
t
,
2
-
CH
2
SiMe
2
Y
CH
2
SiMe
3
-OBu
t
Li
thf
2
] the four-coordinated lithiums are bridged
by Bu
t
OandMe
2
Si
CH
2
2
ligands, giving the Y a distorted square pyramidal
configuration.
449
In the remarkable salt [f
thf
Lig
4
4
-OBu
t
4
4
-
Cl
Y
CH
2
SiMe
3
x
OBu
t
1
x
]
C
[Y
CH
2
SiMe
3
4
]
salt the pentanuclear cation has a
five-coordinated Y and four-coordinated Li.
450
Interestingly, the chloride ion is incor-
porated into the same structure as the lithiums. The dinuclear complex
[
thf
Li
-OBu
t
2
YfCH
SiMe
3
2
g
2
] has three-coordinated (trigonal planar) Li and
four-coordinated (pseudo-tetrahedral) Y.
451
The [
thf
3
Li
-Cl
Y
OCBu
t
3
3
] complex
also has four-coordinated metals.
452
With titanium(
IV
) the tetranuclear compound [Li
2
3
-OPr
i
2
-OPr
i
4
Ti
2
OPr
i
4
]
has distorted tetrahedral Li and distorted TBP titanium.
453
In the tetranuclear mixed
[f
thf
Lig
2
3
-OMe
2
-OPr
i
4
fTi
OPr
i
2
g
2
]
ligand
complex
the
lithium
is
four-
coordinated and the Ti(
IV
) is octahedrally coordinated.
176
The bulky ligand Bu
t
3
CO gave rise to the dinuclear complex [
Et
2
O
2
Li
-
Cl
ZrCl
OCBu
t
3
2
] with four-coordinated Li and the pseudo-trigonal bipyramidal
zirconium(
IV
).
454
In the heterometallasiloxane [
Me
5
C
5
2
Zr
,
2
-OSiPh
2
O
-
OH
Li
-OH
Li
,
2
-OSiPh
2
O
Zr
C
5
Me
5
2
] another tetranuclear structure involves
three-coordinated Li and pseudo-four-coordinated zirconium.
455
In the hafnium complex [Li
2
3
-OPr
i
2
-OPr
i
4
Hf
2
OPr
i
4
] the hafniums are in
an edge-bridged bi-octahedral structure Hf
2
OPr
i
10
which is bridged by two lithiums
in pyramidal three-coordinated configurations.
200
The corresponding Nb(
V
) complex
[
EtOLi
2
3
-OEt
2
-OEt
4
Nb
2
OEt
2
OH
2
] has octahedral niobium and four-
coordinated lithium.
456
However, in [Li
-OEt
4
Nb
OEt
2
]
n
an infinite helical polymer
occurs owing to the
cis
configuration of the terminal Nb-OEt groups.
457
In the structure
of the tetranuclear [
Me
3
SiCH
2
O
3
Nb
3
-OCH
2
SiMe
3
-OCH
2
SiMe
3
2
Li
2
3
-
OCH
2
SiMe
3
-OCH
2
SiMe
3
2
Nb
OCH
2
SiMe
3
3
],
the
two
niobium
octahedra
are
bridged by the two lithium atoms which are each bonded to four alkoxo groups.
In the lithiatantalasiloxane complex [
py
2
Lif
,
2
-O
SiPh
2
O
2
g
2
f
2
-O
SiPh
2
O
2
Tag]
the three tetraphenyl siloxanediolate ligands chelate the octahedral Ta(
V
) and two of them
bridge the lithium.
459
