Chemistry Reference
In-Depth Information
adopting the gauche configuration whereas in [W
2
OSiPh
3
2
NMe
2
4
](W W,
2.295 A) the
anti
configuration occurs.
300
The structure of optically active
C
[W
2
OC
10
H
19
6
](W W, 2.338 A) containing mentholato ligands has also been
determined.
301
In the mixed ligand symmetrical dimer [W
2
OBu
t
4
O
3
SCF
3
2
PMe
3
2
]
(W
W, 2.421 A) the eclipsed conformation is found with the
tert
-butoxo
ligands
trans
to one another.
302
The symmetrical dimer [W
2
hftb
4
NMe
2
2
]has
the staggered
anti
conformation.
321
The benzyltungsten isopropoxide diketonate
[
PhCH
2
tmhd
Pr
i
O
WW
OPr
i
tmhd
CH
2
Ph
](W W, 2.328 A) also has a
nonbridged metal - metal triple bond with the ligands in a staggered conformation.
303
In
the symmetrical carbonyl complex [W
2
tftb
6
CO
2
](WW, 2.450 A) the two halves
of the molecule are eclipsed and the carbonyls are in the
syn
configuration.
304
Studies
on the chemical reactivity of the ditungsten species [
RO
3
WW
OR
3
] have produced
a multitude of interesting new dinuclear species containing a variety of different
bridging ligands.
In [W
2
-OMe
2
OMe
8
] the edge-shared bi-octahedral structure (Fig. 4.2) was
found.
306
The diamagnetism and W-W distance (2.790 A) indicated the presence
of a single W-W bond. A similar structure occurs in the W(
V
) chloride ethoxide
[W
2
-OEt
2
OEt
4
Cl
4
](W-W, 2.715 A) in which the chlorines are
cis
and the
terminal ethoxo ligands
trans
to one another.
307
Interestingly the W(
IV
) complexes
[W
2
-OR
2
OR
2
ROH
2
Cl
4
](RD Me, Et; W
D
W, 2.481, 2.483 A) have nearly the
same structure with an ROH ligand replacing a terminal alkoxo group on each
tungsten. Hydrogen bonding ROH
....
OR occurs between
syn
-alcohol and alkoxo
ligands across the metal - metal bond.
308
Exchange reactions with other alcohols R
0
OH
produced a series of mixed ligand complexes [W
2
-OR
2
OR
0
2
R
0
OH
2
Cl
4
](RD Et,
R
0
D Pr
i
;RD Et, R
0
D Et
2
CH) and [W
2
-OPr
i
2
OPr
i
2
Pr
i
OH
2
Cl
4
] all having the
same overall edge-shared bi-octahedral structure.
309
Reaction of [W
2
OEt
4
Cl
4
EtOH
2
] with ketones R
2
CO gave rise to novel W(
V
)
dinuclear complexes [W
2
-OEt
2
OCR
2
CR
2
O
2
Cl
4
] containing the bridging diolate
ligands in place of the terminal ethoxo and ethanol ligands (Fig. 4.46).
310
On the other
hand
˛
-diketones R
0
CO.COR
0
reacted with
RO
3
WW
OR
3
to give centrosymmetrical
dinuclear molecules [W
2
-OR
2
OR
4
OCR
0
DCR
0
O
2
](RD Pr
i
;R
0
D Me,
p
-tolyl;
W-W, 2.745, 2.750 A) in which the alkylene diolate ligands are chelated to tungsten(
V
)
(Fig. 4.47).
311
In the W(
VI
) complex [W
2
-OBu
t
2
OBu
t
4
CNMe
2
2
]themetalis
five-coordinated (TBP) with a carbyne CNMe
2
and a bridging Bu
t
O occupying axial
positions. The bridging Bu
t
O in the equatorial position is shorter (W-O, 1.95 A) than
Figure 4.46
Structure of [W
2
-
OEt
2
OC
2
Me
4
O
2
Cl
4
](Hatoms
omitted).
