Chemistry Reference
In-Depth Information
Figure 4.19
Structure of [Bi
2
(
-
hfip)
2
(hfip)
4
(thf)
2
](hfip D OCH
CF
3
2
;
H and F atoms omitted).
hfip ligand an ammine was isolated [Sc
2
-hfip
2
(hfip)
4
NH
3
2
] containing octahedral
Sc in an edge-sharing dimer with
cis
terminal alkoxo groups
trans
to the bridging
alkoxo groups.
103
The ammonia ligands adopt the
trans
configuration (Fig. 4.20).
2.6.2
Yttrium
The first structurally characterized organoyttrium containing an alkoxo ligand was the
dimeric bis-cyclopentadienyl enolate [
C
5
H
4
CH
3
4
Y
2
-OCH
D
CH
2
2
]
.
104
The first
monomeric, homoleptic yttrium alkoxo compound involved a bulky functionalized
chelating ligand as in [Y(OCBu
t
2
CH
2
PMe
2
3
]
.
105
The first trinuclear alkoxo yttrium
compound reported was the mixed ligand species [Y
3
3
-OBu
t
3
-Cl
-
OBu
t
3
OBu
t
4
(thf)
2
] which has a triangular array of distorted octahedral yttrium
atoms capped by a
3
-OBu
t
on one side and a
3
-Cl on the other. The three
-OBu
t
ligands are in the triangular plane. Each metal has one terminal OBu
t
group, one has
a second
tert
-butoxide and the other two have terminal THF ligands.
106
This struc-
ture is related to that shown in Fig. 4.5. The same framework structure was found
in the related complex [Y
3
3
-OBu
t
3
-Cl
-OBu
t
3
Cl
OBu
t
(thf)
2
] in which one
of the terminal
tert
-butoxo groups is replaced by a chloride,
107
and also in [Y
3
3
-
OBu
t
2
-OBu
t
3
OBu
t
4
Bu
t
OH
2
]
.
6
A remarkable decameric compound was formed by the 2-methoxyethoxo ligand in
which each Y atom is seven-coordinated (pentagonal bipyramid) [Y
10
OC
2
H
4
OMe
30
]
(Fig. 4.21).
108
Each yttrium atom is linked to two neighbouring yttrium atoms by the
bridging alkoxo moiety of two ligands which also chelate through the OMe function.
One ligand acts as a monodentate group on each metal. The overall molecular structure
is a unique ten-membered ring. Replacing some MeOC
2
H
4
O groups by acac gave the
trinuclear species [Y
3
3
-OC
2
H
4
OMe
2
-OC
2
H
4
OMe
3
(acac)
4
] which has a triangle
of eight-coordinated yttrium capped above and below the Y
3
-plane by
3
-OC
2
H
4
OMe
groups which also chelate through the OMe function. Three
-OC
2
H
4
OMe groups
span the three yttriums, with two chelating and the third not. Each yttrium is also
chelated by an acac ligand (Fig. 4.22).
109
This molecule illustrates the versatility and
various bonding modes of the 2-methoxyethoxo ligand.
A novel trinuclear mono-cation has also been structurally characterized as [Y
3
3
-
OBu
t
3
-Cl
-OBu
t
3
OBu
t
3
(thf)
3
]
C
. It exhibits the familiar triangular Y
3
unit held
by
3
-OBu
t
and
3
-Cl capping ligands together with three in-plane
2
-OBu
t
ligands.
