Chemistry Reference
In-Depth Information
and other workers according to the general reaction shown in Eq. (2.243):
M
OR
x
C
y
C
z
HO—G—OH
benzene
! M
OR
x
2
y
z
O—G—O
y
O—G—OH
z
C
2
y
C
z
ROH
2
.
243
where
x
is the valency of the metal,
y
and
z
are integers and their values are dependent
on
n
:if
n
D 3then
y
D 1and
z
D 0or1.
Plausible structures, suggested mainly from molecular weight measurements, are
beginning to be elucidated
21
,
801
,
802
by X-ray crystallography.
In addition to the structures displayed in Fig. 2.13, other possibilities also exist
as depicted by Crans
et al
.
804
in the case of oxovanadium 1,2-diolates. It has also
been pointed out
804
that the structural differences of the glycol ligands result in very
different geometries and demonstrate subtle factors affecting the coordination chemistry
of such systems. These studies substantiate the very fine balance between coordination
geometries and the respective glycolate ligands in their metal complexes.
Reactions in 1:2 molar ratios of trihydric alcohols such as 1,1,1-tris(hydroxymethyl)-
ethane (THME-H
3
) and 1,1,1-tris(hydroxymethyl)propane (THMP-H
3
) with group 4
metal (Ti, Zr) triisopropoxides in toluene/THF solvent afford X-ray crystallographically
characterized tetranuclear products:
818
THME
2
M
4
OPr
i
10
and
THMP
2
M
4
OPr
i
10
;
these illustrate the propensity for forming a variety of bridging and chelating modes.
More recently,
819
an X-ray crystallographically characterized niobium(
V
) alkoxo
species derived from THME-H
3
namely [(
-THME)Nb(OEt)
2
]
2
has been reported to
be formed by the reaction of Nb(OEt)
5
with THME-H
3
.
4.8
Reactions of Oximes and N,N-Diethylhydroxylamine
The oxime group
>
C
D
N—OH
which may be considered to be derived from oxy-
imine is amphiprotic with slightly basic nitrogen and a mildly acidic hydroxyl group.
Diethylhydroxylamine
Et
2
N—OH
is a weaker base than NH
3
or NEt
3
, owing to the
electron-withdrawing effect of its hydroxyl group.
Both oximes
634
,
635
,
820
,
821
and
N,N
-diethylhdroxylamine
634
,
635
are ambidentate with
the possibility of coordination through oxygen alone or through both nitrogen and
oxygen, illustrated in Fig. 2.14.
The reactions of metal alkoxides with a wide range of oximes (Eq. 2.244) provide
a convenient and versatile route for the synthesis of a variety of interesting homo- and
heteroleptic oximate derivatives:
634
,
635
benzene
! M
OR
x
y
ONDCR
0
R
00
y
C
y
ROH
M
OR
x
C
y
R
0
R
00
CDNOH
2
.
244
where M D titanium
,
822 - 825
zirconium,
826
niobium,
827
,
828
tantalum,
827
,
829
boron,
822
aluminum,
830
silicon,
822
,
831
germanium,
822
tin,
708
arsenic,
832
and antimony.
833
R D Et
or Pr
i
;
x
is the valency of the metal;
y
D 1
,
2
,...
x
;R
0
D H, alkyl, or aryl; R
00
D alkyl
or aryl.
