Chemistry Reference
In-Depth Information
The heteroleptic chloride
tert
-butoxide of rhenium Re
3
(OBu
t
)
6
Cl
3
was prepared by
Wilkinson
et al
.
172
by the reaction in THF of Re
3
(
-Cl)
3
Cl
6
(thf)
3
with NaOBu
t
in 1:6
molar ratio:
THF
! Re
3
OBu
t
6
Cl
3
C 6NaCl #
Re
3
-Cl
3
Cl
6
thf
3
C 6NaOBu
t
2
.
56
In an attempt to prepare Re
3
(OPr
i
)
6
Cl
3
,Ho fman
et al
.
173
,
174
reacted Re
3
(
-
Cl)
3
Cl
6
(thf)
3
with NaOPr
i
in 1:6 molar ratio in THF and isolated the X-ray
crystallographically characterized
174
green complex Re
3
(
-OPr
i
)
3
(OPr
i
)
6
.
3
Pr
i
OH in a
very low (18%) yield. Naturally the unreacted Re
3
(
-Cl)
3
Cl
6
(thf)
3
had to be removed
from the reaction medium.
By contrast, an isopropyl alcohol-free product Re
3
(
-OPr
i
)
3
(OPr
i
)
6
has been prepared,
but again in a low (31%) yield according to Eq. (2.57):
THF
! Re
3
-OPr
i
3
OPr
i
6
C 9NaCl #
Re
3
-Cl
3
Cl
6
thf
3
C 9NaOPr
i
2
.
57
The yield of Re
3
(
-OPr
i
)
3
(OPr
i
)
6
(Eq. 2.57) could be improved (i.e. from 31%
to 53%) considerably by the addition of a few drops of acetone to the solvent of
crystallization.
174
The synthesis of simple generally insoluble alkoxides, M(OR)
2
(M D Mn,Fe,Co,Ni,
Cu, Zn; R D Me, Et, Pr
i
), was found not to be feasible owing to the difficulty of sepa-
rating them from the insoluble alkali metal (Na, K) chlorides (
cf.
preparation through
LiOR in Section 2.5.3). However, a soluble copper(
II
) fluoroalkoxide, Cu(OR
f
)
2
(py)
2
where R
f
D CH
CF
3
2
or C(CF
3
)
3
,
175
has been synthesized as shown in Eq. (2.58):
CuBr
2
C 2NaOR
f
C 2py ! Cu
OR
f
2
py
2
C 2NaBr #
2
.
58
where R
f
D CH
CF
3
2
or C(CF
3
)
3
.
In the absence of ancillary ligands such as C
5
H
5
,CO,PR
3
,andR
2
PCH
2
CH
2
PR
2
(R D alkyl or aryl) there are relatively few stable platinum group metal (Ru, Rh, Pd;
Os, Ir, Pt) alkoxides
9
,
10
,
21
because these metals prefer softer donor ligands (relative
to the hard (oxygen) donor alkoxo groups) and the alkoxide ligands when bonded to
platinum group metals are labile to thermal decomposition (Section 2.1), typically by
a
ˇ
-hydrogen elimination pathway. However, with the use of some special (fluorinated
and/or donor-functionalized) type of alkoxo ligands,
21
the synthesis of hydrocarbon-
soluble and monomeric alkoxides of later transition metals including palladium(
II
)and
platinum(
II
) can be achieved (Eqs 2.59 - 2.62):
cis
-
R
3
P
2
MCl
2
C 2NaOCH
CF
3
2
!
cis
-
R
3
P
2
MfOCH
CH
3
2
g
2
C 2NaCl #
2
.
59
M D Ni
,
R D Et;
176
M D Pt
,
R D Ph
176
C
6
H
6
/
MeOH
!
slight excess
(dppe)Pt
OCH
3
2
C 2NaCl #
177
(dppe)PtCl
2
C 2NaOCH
3
(2.60)
(2.61)
2KOH
M
2+
+
2H
+
2 HOC(CF
3
)
2
CH
2
PPh
2
M{OC(CF
3
)
2
CH
2
PPh
2
}
2
+
where M D Co,Ni,Pd,Pt.
10
,
24
