Chemistry Reference
In-Depth Information
The product (B) is also obtained in an exothermic equimolar reaction between
Zr
OBu
t
4
and MeOH.
For alcohols with highly electron-withdrawing groups such as R
0
D CH
CF
3
2
, only
partial substitution
272
is observed when reactions for example, of Ti
OR
4
(R D Et or
Pr
i
) with
CF
3
2
CHOH were carried out
toluene
! TifOCH
CF
3
2
g
2
OR
2
HOR
C ROH
Ti
OR
4
C 2HOCH(CF
3
)
2
(excess)
2
.
195
In a comparative study of the alcoholysis reactions of titanium alkoxides,
270
the
facility of replacement reactions appears to follow the trend: OBu
t
>
OPr
i
>
OEt
>
OMe. This type of comparative trend appears to be particularly marked in the alkoxides
of some later 3d transition metals.
7
,
225
For example, primary alkoxides of d
8
nickel(
II
)
do not appear to undergo alcoholysis reactions with secondary or tertiary and other
primary alcohols, whereas the reactions of nickel(
II
)
tert
-butoxide with primary alcohols
are highly facile.
The compound Mo
2
OPr
i
6
shows no tendency to associate but upon partial alco-
holysis with MeOH the tetranuclear crystalline compound Mo
4
OPr
i
10
OMe
2
was
isolated.
648
The reactions of M
2
OBu
t
6
(M D Mo, W) with less sterically demanding alcohols
RCH
2
OH (R D
c
-C
4
H
7
,
c
-C
5
H
9
c
-C
6
H
11
,Pr
i
) afford a series of structurally related
homoleptic alkoxides M
4
OCH
2
R
12
according to Eq. (2.196):
649
hexane
! M
4
OCH
2
R
12
C 12Bu
t
OH
2M
2
OBu
t
6
C 12RCH
2
OH
2
.
196
Investigations on alcohol-interchange reactions of copper alkoxides with various
fluorinated alcohols have produced exciting and diverse results. For example, it has
been observed that approximately 50% substitution of
tert
-butoxo groups occurred
in reactions between copper(
I
)
tert
-butoxide and a wide variety of fluoroalcohols.
650
Similarly copper(
II
) methoxide reacts with excess
CF
3
2
CHOH in refluxing benzene to
produce an insoluble solid of approximate stoichiometry [CufOCH
CF
3
2
g
OMe
]
n
.
175
However, reactions of copper(
II
) methoxide with fluoroalcohols in diethyl ether in the
presence of a variety of amines (pyridine (py),
N,N,N
0
,
N
0
-tetraethylethylenediamine
(teeda),
N,N,N
0
,
N
-tetramethylethylenediamine (tmeda), 2,2
0
-bipyridine (bipy)) yield the
corresponding solvated copper(
II
) fluoroalkoxides (Eq. 2.197):
175
1
n
[Cu
OMe
2
]
n
C 2R
f
OH C L ! Cu
OR
f
2
L
C 2MeOH
2
.
197
R
f
D CH
CF
3
2
;LD
py
2
,
bipy
,
teeda
,
tmeda
.
R
f
D CMe
CF
3
2
;LD
py
2
,
bipy
,
tmeda
Interestingly, reaction of Cu
OBu
t
2
with a moderate excess of
CF
3
3
COH in
hydrocarbon solvents affords two primary products: [Cu
4
-OBu
t
6
fOC
CF
3
3
g
2
]and
[Cu
3
(
-OBu
t
)
4
fOC
CF
3
3
g
2
], with their relative amounts determined by the stoichiom-
etry of the reactants.
651
