Chemistry Reference
In-Depth Information
With CH
2
Bu
t
and SiMe
3
groups
361
,
362
the initial complexes were molecular adducts of
Me
2
NH, e.g. Mo
2
(OR)
6
(HNMe
2
)
2
, from which dimethylamine-free product could be
obtained above 60
Ž
C under reduced pressure. However, the addition of excess EtOH
to Mo
2
NMe
2
6
affords Mo
4
(OEt)
12
.
By contast, the reactions of W
2
(NMe
2
)
6
with MeOH and EtOH
366
,
367
give tetra-
nuclear products W
4
(OR)
16
containing W—W bonds of order 1 or lower (Eq. 2.114).
2W
2
NMe
2
6
C 16ROH ! W
4
OR
16
C 12Me
2
NH "C2H
2
"
2
.
114
Analogous reactions involving cyclohexanol
368
and Pr
i
OH
369
,
370
give W
2
(O-
c
-C
6
H
11
)
6
and [W
2
-H
OPr
i
7
]
2
, respectively.
When W
2
(NMe
2
)
6
and Pr
i
OH reacts in pyridine (py), the black crystalline product
W
2
(OPr
i
)
6
(py)
2
is obtained.
369
,
370
A series of molybdenum(
IV
) alkoxides of empirical formula Mo
OR
4
have been
prepared according to Eq. (2.115).
371
Mo(NMe
2
4
C 4ROH !
1
2
.
115
n
[Mo(OR)
4
]
n
C 4Me
2
NH "
where R D Me, Et, Pr
i
,Bu
t
and CH
2
Bu
t
.
The properties of the above products [Mo(OR)
4
]
n
depend upon the nature of the
group R. For example, of the above only [Mo
OPr
i
4
]
2
is diamagnetic. It is a fluxional
molecule and the low temperature NMR spectra indicate the structure (Pr
i
O)
3
Mo
-
OPr
i
2
Mo
OPr
i
3
, which appears to be corroborated by X-ray crystallography.
372
The
bulky
tert
-butoxide appears to be monomeric (
n
D 1) in benzene, but its structure is
not known in the solid state.
Reactions of Mo
NMe
2
4
with two equivalents of alcohol (ROH) (where R D
4-methylcyclohexyl and diisopropyl) afford compounds of formula Mo
NMe
2
2
OR
2
373
which are dimeric
via
apairof
-NMe
2
ligands both in solution and in the solid state.
Interaction between 1,2-Mo
Bu
i
2
NMe
2
4
and an excess of isopropyl alcohol in
hexane affords
374
Mo
2
OPr
i
4
HOPr
i
4
(Eq. 2.116):
1
,
2-Mo
2
Bu
i
2
NMe
2
4
C
>
10Pr
i
OH
hexane
!
0
°
C
Mo
2
OPr
i
4
HOPr
i
4
C Me
2
C
D
CH
2
C Me
3
CH C 4Me
2
NH
2
.
116
In related reactions involving 1,2-Mo
2
Bu
i
2
NMe
2
4
and both cyclopentanol and
cyclohexanol (ROH), thermally unstable compounds of formula Mo
2
OR
4
HOR
4
have been prepared and characterized by X-ray crystallography when R D Pr
i
or
c
-
pentyl.
374
Interestingly, alcoholysis reactions of Mo
2
NMe
2
6
with fluorinated alcohols such
as Me
2
CF
3
COH, Me
CF
3
2
COH, and (CF
3
)
3
COH give incomplete or complex reac-
tions.
376
,
377
This probably arises from the low nucleophilicity of fluoroalcohols and the
poor
-bonding characteristics of fluoroalkoxide ligands.
24
,
378
However, triply bonded
hexakis
(fluoroalkoxo) dimolybdenum derivatives Mo
2
[OCMe
3
x
CF
3
x
]
6
(
x
D 1or
2) have been conveniently prepared
170
in high yield by metathetical reactions involving
Mo
2
Cl
6
(dme)
2
(where dme D 1,2-methoxyethane) and an alkali (Li or Na) metal
fluoroalkoxide.
