Chemistry Reference
In-Depth Information
The general reaction of metal alkoxides with monofunctional bidentate (Figs 2.15a - c,
designated as SBH) and bifunctional tri- and tetradentate (Figs 2.15d - f, designated as
SBH
2
) ligands can be represented by Eqs (2.246) and (2.247).
benzene
! M
OR
x
y
SB
y
C
y
ROH
M
OR
x
C
y
SBH
2
.
246
benzene
! M
OR
x
2
y
SB
y
C 2
y
ROH
M
OR
x
C
y
SBH
2
2
.
247
where R is generally Et or Pr
i
,and
x
is the valency of the metal or metalloid.
This synthetic procedure has been employed to prepare a wide variety of Schiff
base and
ˇ
-ketoamine derivatives of lanthanides: La,
847 - 851
Pr,
847 - 851
Nd,
847
,
849 - 851
Sm,
852
Er,
847
Yb;
850
transition metals: Ti,
853 - 863
Zr
853
,
858
,
862 - 867
Hf,
868
Nb,
863
,
869 - 874
Ta;
870
,
872
,
873
,
875
,
876
B,
877 - 879
Al,
859
,
863
,
878 - 886
and
main
group
metal(loid)s:
Ga,
847
,
862
,
887
,
888
As,
879
and Sb.
879
,
889
It is pertinent to mention the salient features of the reactions represented by Eqs
(2.246) and (2.247) and their products. These reactions offer attractive possibilities
for preparing derivatives with the metal in interesting coordination environments. For
example, reactions of titanium alkoxides with bifunctional tridentate Schiff base ligands
SBH
2
855 - 858
like
o
-HOC
6
H
4
CH
D
NCH
2
CH
2
n
OH (
n
D 1 or 2) afford dialkoxide
derivatives of the type Ti
OR
2
SB
, which exhibit a dimeric octahedral structure
involving bridging when R is stercally compact, but monomeric with sterically bulky
RsuchasBu
t
:
858
R
O
R
O
O
O
N
Ti
Ti
N
O
O
O
R
O
R
Equimolar reaction of Ti
OPr
i
4
with a bifunctional tetradentate Schiff base ligand like
salenH
2
(
N
,
N
0
-ethylenebis(salicylideneimine)) affords
858
a six-coordinate monomeric
derivative:
OPr
i
O
O
Ti
C
NN
C
H
H
OPr
i
Similar reactions of Al
OPr
i
3
with bifunctional tri- and tetradentate
ˇ
-ketoamines
847
afford dimeric and monomeric species, respectively in which aluminium atoms are in
a five-coordinated environment.
In general, Schiff base and
ˇ
-ketoamine derivatives of metals and metalloids exhibit
variations in the degree of molecular association depending upon their empirical for-
mulae, the valency and covalent radius of the metal, as well as the ligand type.
