Chemistry Reference
In-Depth Information
Pentakis(2,2,2-trifluoroethoxy)arsorane has been prepared by passing chlorine gas
into the solution containing As
OCH
2
CF
3
3
and excess CF
3
CH
2
OH:
125
As(OCH
2
CF
3
3
C 2CF
3
CH
2
OH C Cl
2
! As(OCH
2
CF
3
5
C 2HCl "
2
.
125
2.10.2
From Metal-Carbon Bond Cleavage Reactions (J-2)
The polarity of metal - carbon and metal - hydrogen bonds allows protolysis to occur
with alcohols under moderate conditions. Consequently carbanionic metal alkyls react
with alcohols to give alkoxides, in excellent yields. The reaction assumes special impor-
tance as it forms the basis for the calorimetric measurements of a large number of
metal - alkyl bond dissociation energies.
384
This preparative route tends to be more
convenient owing to the volatility of the liberated alkane side-products. Organometal
alkoxides of beryllium,
385
,
385a
,
385b
magnesium,
386
,
386a
,
387
,
388a
,
389
and zinc,
390 - 392
were
prepared by the equimolar reactions of metal alkyls
MR
2
and an appropriate alcohol
R
0
OH
(
partial alcoholysis
):
MR
2
C R
0
OH ! 1
/
n
[RM
OR
0
]
n
C RH "
2
.
126
where M D Be, Mg, Zn; R D Me, Et, Bu
t
,Ph;R
0
D primary, secondary, and tertiary
alcohols;
n
D is generally 4 with sterically compact R and R
0
but may be 2 in cases
of sterically demanding R and R
0
.
Tributylgallium reacts readily with methanol and butanol at low temperatures to
yield dimeric dibutylgallium alkoxides in excellent yields.
393
Bu
3
Ga C ROH !
2
[Bu
2
Ga
-OR
]
2
C BuH
2
.
127
By contrast, reactions of GaMe
3
or GaBu
t
3
with ethanolamine or HOCPh
3
,respec-
tively, under refluxing conditions afford crystallographically characterized monomeric
products (Eq. 2.128):
GaR
3
C R
0
OH ! R
2
GaOR
0
C RH
(2.128)
(R D Me, R
0
D CH
2
CH
2
NH
2
;
394
R D Bu
t
,R
0
D CPh
3
395
)
lithium,
230
,
396
beryllium,
385
,
385b
magnesium,
397
Homoleptic
alkoxides
of
zirco-
nium,
398
,
398a
vanadium,
340
,
399
chromium,
400
rhodium,
401
copper,
402
cobalt,
403
nickel
404
aluminium
405
and
have
also
been
prepared
by
metal - carbon
bond
cleavage
reactions:
LiBu
n
!
2
[LiOCBu
t
3
]
2
C Bu
n
H "
396
(2.129)
n
-hexane
Bu
t
3
COH
LiBu
n
!
2
[LiOCBu
t
3
thf
]
2
C Bu
n
H
230
(2.130)
THF
MR
2
C 2R
0
OH ! M
OR
0
2
C 2ROH
2
.
131
(M D Be; R
/
R
0
D Me, Me,
385
Et/CH(CF
3
2
.
385b
M D Mg;
397
R D Bu
n
;R
0
D CBu
t
3
.)
