Chemistry Reference
In-Depth Information
bridged dimer [Me
4
Ti
2
-OMe
2
tritox
2
] has titanium in the square pyramidal
configuration.
187
The bulky tritox ligands occupy the apical positions with the Ti
atoms located 0
.
71 A above the basal planes comprising two
cis
methyl groups and
two bridging methoxides with the two tritox groups being
trans
across the dimer. The
1,3-bis-(trimethylsilyl)cyclopentadienyl titanium
cis
-1,3,5-cyclohexan-triolate forms a
monomer [fMe
3
Si
2
C
5
H
3
gTi
O
3
C
6
H
9
].
188
The bis-cyclopentadienyl titanium(
III
) alkoxides are dimeric [
C
5
H
5
4
Ti
2
-
OR
2
](RD Me, Et) and paramagnetic, exhibiting antiferromagnetic behaviour.
189
A novel mononuclear Ti(
III
) alkoxide was obtained using the functionalized alcohol
Me
2
PCH
2
CBu
t
2
OH
.Thecomplex[TiCl
OCBu
t
2
CH
2
PMe
2
2
] involves titanium in a
TBP configuration with the P atoms of the chelating alkoxo ligands occupying the
axial positions and the oxygens and the chlorine in the equatorial positions.
190
2.9.2
Zirconium
Relatively few structures of alkoxo zirconium compounds have been reported.
Although a dimeric structure [Zr
2
-OPr
i
2
OPr
i
6
Pr
i
OH
2
] had been proposed for
the crystalline zirconium isopropoxide isopropanolate many years ago
191
the edge-
shared bi-octahedral structure was not properly determined by X-ray crystallography
until 1990.
192
An interesting feature of this structure is the location of the coordinated
isopropanol molecules which are each linked by a hydrogen bond to the terminal
isopropoxo ligand on the adjacent zirconium atom Pr
i
O-H
....
OPr
i
. This causes a
marked distortion due to bending of the Zr-OPr
i
bonds which are drawn together by
the hydrogen bond. A similar situation occurs in the Hf,
170
,
200
Ce(
IV
)
122
,
192
and Sn(
IV
)
analogues.
88
,
89
The bulky tris(trimethylsilyl)silyl ligand formed the monomeric four-
coordinated zirconium
tert
-butoxo compound [
Me
3
Si
3
SiZr
OBu
t
3
] which contains
aZr-Si bond.
193
The bidentate ligand
trans
-1,2-cyclohexanediolate bridges two
ZrCl
3
moieties in the binuclear compound [
thf
2
Cl
3
Zr
O
2
C
6
H
10
ZrCl
3
thf
2
].
194
The
octahedral Zr atoms are each bonded to three chlorines in a meridional configuration
cis
to the Zr-O bonds. The remarkable pentanuclear amido imidonitride cluster
Zr
5
5
-N
3
-NH
4
-NH
2
4
OCBu
t
3
5
] is stabilized by the terminal tritox ligands.
195
The zirconiums are all octahedral and the structure bears a striking resemblance to
the pentanuclear oxo isopropoxo clusters [M
5
5
-O
3
-OPr
i
4
-OPr
i
5
](MD Sc,
Y, Ln). The structure of monomeric Zr
hftb
4
hftb D OCMe
CF
3
2
) revealed an
essentially tetrahedral configuration about the Zr atom.
196
Another mononuclear mixed
ligand complex is [
oep
Zr
OBu
t
2
](oepD octaethylporphyrin) where the
tert
-butoxo
groups occupy
cis
positions above the plane of the porphyrin ring.
197
The Zr-O-C
bonds are practically linear.
The tridentate ligand tris(hydroxymethyl)ethane forms a tetranuclear complex
[Zr
4
f
-OCH
2
3
CMeg
2
-OPr
i
2
OPr
i
8
], which exhibits a different structure from the
titanium analogue.
169
2.9.3
Hafnium
Only a few structures of hafnium alkoxo compounds have been reported. As expected,
hafnium isopropoxide [Hf
2
-OPr
i
2
OPr
i
6
Pr
i
OH
2
] has the edge-shared bi-
octahedral structure like that of the analogous zirconium compound.
200
The coordinated
