Chemistry Reference
In-Depth Information
Figure 4.22
Structure of [Y
3
(
3
-
OC
2
H
4
OMe)
2
(OC
2
H
4
OMe)
3
(acac)]
(acac D acetylacetonate;
H
atoms
omitted).
the seven-coordinated yttrium has a OBu
t
group and a chloride in the axial posi-
tions with the five THF ligands occupying the equatorial positions.
110
Some struc-
tures have also been determined on mono- and bis-cyclopentadienyl yttrium alkoxo
compounds. The dimeric species [
C
5
H
4
SiMe
3
4
Y
2
-OMe
2
]
,
111
[(C
5
Me
5
2
Y
2
-
OBu
t
2
(OBu
t
2
], [(C
5
H
5
2
Y
2
-OBu
t
2
], [(C
5
H
4
SiMe
3
2
Y
2
-OBu
t
2
(OBu
t
2
]and
[(C
9
H
7
2
Y
2
-OBu
t
2
(OBu
t
2
] all contained Y(
-OR
2
Y bridges (data in Table 4.6,
pp. 256 - 257).
112
The bridging propensity of the alkoxo ligand can be reduced both sterically by using
bulky alkyl groups and electronically by using electronegative alkyl groups, which
reduce the electron density on the alkoxo oxygen donor atom. Both factors are oper-
atinginthefluorinated tertiary alkoxo groups, and the mononuclear yttrium compounds
[YfOCMe
CF
3
2
g
3
(thf)
3
]and[YfOCMe
CF
3
2
g
3
diglyme
] (Fig. 4.23) were obtained
using the hexafluoro-
tert
-butoxo (hftb) ligand.
113
Both complexes are octahedral with
the facial configuration. The tris-THF complex exhibits the same structure as the previ-
ously reported tris-triphenylsiloxo complex [Y(OSiPh
3
3
(thf)
3
] (Fig. 4.24).
114
The homoleptic tris-triphenylsiloxide forms an unsymmetrical dimer [Y
2
-
OSiPh
3
2
OSiPh
3
4
] with distorted tetrahedral yttrium atoms.
115
Interestingly a mono-
nuclear five-coordinated adduct [Y(OSiPh
3
3
OPBu
3
2
] was formed with tri-
n
-butyl-
phosphine oxide ligands occupying the axial positions in a TBP configuration.
116
In the
salt [K(dme)
4
]
C
[Y(OSiPh
3
4
dme
]
the yttrium mono-anion adopts a distorted octa-
hedral configuration.
116
The dimethyl
tert
-butylsiloxo ligand gave rise to the mononu-
clear adduct [Y(OSiMe
2
Bu
t
3
(thf)
3
] in the presence of THF but in the presence of
excess silanol the novel unsymmetrical dinuclear species [
Me
2
Bu
t
SiOH
Me
2
Bu
t
SiO
2
Y
-OSiMe
2
Bu
t
2
Y
OSiMe
2
Bu
t
2
] was formed.
116
One yttrium is in a distorted tetra-
hedral configuration while the other one is approximately trigonal bipyramidal, and
this is reflected in the bond lengths (Table 4.6).
