Chemistry Reference
In-Depth Information
with the earlier conclusion(s) on the effect of steric factors on the molecular association
of analogous derivatives, [Al
OSiPh
3
2
acac
] becomes monomeric with a tetrahedral
structure.
729
Dhammani
et al
.
730 - 732
have carried out the reactions shown in Eqs (2.224) - (2.226),
characterizing similar products by colligative, IR and NMR (
1
H,
13
Cand
27
Al) measure-
ments:
fAl
CH
3
COCHCOR
OPr
i
2
g
2
C Ph
3
SiOH
Pr
i
OH
! [
CH
3
COCHCOR
2
Al
-OPr
i
2
Al
OSiPh
3
OPr
i
]
2
.
224
fAl
CH
3
COCHCOR
OPr
i
2
g
2
C 2Ph
3
SiOH
2Pr
i
OH
! [
CH
3
COCHCOR
2
Al
-OPr
i
2
Al
OSiPh
3
2
]
2
.
225
fAl
CH
3
COCHCOR
OPr
i
2
g
2
C HOSiPh
2
OH
2Pr
i
OH
! [
CH
3
COCHCOR
2
Al
-OPr
i
2
Al
OSiPh
2
O
]
2
.
226
where R D CH
3
,OC
2
H
5
,C
6
H
5
.
Stepwise reactions of isopropoxides of other tervalent metals (lanthanides,
733 - 735
gallium,
736
and antimony
737
) have also been carried out by similar procedures and a
number of isopropoxide-
ˇ
-diketonates as well as tris-
ˇ
-diketonates have been charac-
terized by physico-chemical techniques.
By contrast, homoleptic tetrakis-
ˇ
-diketonates of titanium and tin(
IV
) could not be
prepared by this route; reactions of Ti(OR)
4
and Sn(OR)
4
(with R D Et, Pr
i
) with
excess of
ˇ
-diketones/
ˇ
-ketoesters yield bisalkoxide bis-
ˇ
-diketonate derivatives only.
The reactions of titanium alkoxides with
ˇ
-diketones and
ˇ
-ketoesters in 1:1 and 1:2
molar ratios have been investigated by several workers;
738 - 740
the 1:2 products were
characterized as monomeric derivatives, but there has been a difference of opinion about
the dimeric or monomeric nature of 1:1 products which awaits further investigation.
In another investigation,
741
Ti(OEt)
2
(acac)
2
and Ti
OPr
i
2
acac
2
wereshowntobe
monomeric volatile products, in which the alkoxide component(s) have been shown to
be highly reactive. In addition to facile replacement by hydroxylic reagents,
Ti(OEt)
2
(acac)
2
was found to react with 2 mol HCl, to yield a monomeric volatile
product TiCl
2
(acac)
2
which could be converted into Ti(OEt)
2
(acac)
2
by reaction with
EtOH in the presence of anhydrous NH
3
; this led to a correction
742 - 745
of the well-
quoted trimeric nature of the covalent TiCl
2
(acac)
2
as fTi
acac
3
g
2
TiCl
6
746
on the basis
of its reaction with FeCl
3
to yield a product of the formula fTi
acac
3
gfFeCl
4
g, a species
the actual nature of which awaits further elucidation by more refined physico-chemical
investigations (crystal structure or more refined NMR investigations).
In reactions of titanium alkoxides with benzoylacetone,
747
methylacetoacetate
748
and ethylacetoacetate, bis-
ˇ
-diketonate or ketoester derivatives were the final prod-
ucts even when excess of these ligands was used. The nonreplaceability of the third
or fourth alkoxy groups with
ˇ
-diketones or ketoesters may most probably be due
to the preferred coordination number of 6 for titanium in the bis-derivatives. The
trialkoxide monomethylacetoacetate disproportionated to the bis-derivative and tetra-
alkoxide, when heated under reduced pressure, whereas bis-derivatives distilled out
