Chemistry Reference
In-Depth Information
ligand.
277
A similar structure was exhibited by [W
2
-OEt
2
OEt
4
Cl
2
NPh
2
] with
the phenylimido ligand
trans
to one bridging ethoxo (W-O, 2.213 A) and a
terminal ethoxo
trans
to the other (W-O, 2.003 A).
318
Other similar structures with
unsymmetrical alkoxo bridges were found in [W
2
-OMe
2
OMe
6
NC
6
H
4
Me
2
]and
[W
2
-OPr
i
2
OPr
i
6
NC
6
H
4
Me
2
] but in
NBu
4
C
[W
2
-OMe
-Cl
2
Cl
4
NPh
2
]
the anion has a distorted confacial bi-octahedral structure in which one of the bridging
chlorides is
trans
to both terminal phenylimido groups.
319
The typical edge-shared
bi-octahedral structure was found for [W
2
-OPr
i
2
OPr
i
6
NPh
2
].
279
An unusual dinuclear complex was formed by pinacolate (2,3-dimethyl
butane-2,3-diolate) ligands with the phenylamido-tungsten (W-N-C, 134
Ž
) moiety,
[
pinacolato
2
PhNH
W
-OCMe
2
CMe
2
O
W
pinacolato
2
NHPh
]. Each tungsten is
in a distorted octahedral coordination with two chelating pinacolates, a phenylamido
group, and the bridging pinacolate.
320
In the binuclear complex [W
2
-NHMeC
2
H
4
NHMe
OEt
6
](W
W, 2.296 A) the
dimethylethylenediamine ligand straddles the metal- metal bond giving an eclipsed
conformation to the ethoxo groups.
324
The linking of alkyne and nitrile functions at ditungsten centres has led to the formation
of several interesting dinuclear compounds. An example is the unsymmetrical diene -
diimido complex [W
2
-OCH
2
Bu
t
2
-NCMe
D
CMeCMe
D
CMeN
OCH
2
Bu
t
4
py
]
(W-W, 2.617 A) in which the diimido ligand chelates one tungsten and bridges the
other in a confacial bi-octahedral structure.
325
A similar configuration is found in the
related molecule [W
2
-OPr
i
2
-NCMeC
2
H
2
CMeN
OPr
i
5
](W-W, 2.576 A).
325
In
[W
2
-OBu
t
-NCPhCHCH
OBu
t
5
](W-W, 2.674 A) the alkylidene imido ligand
chelates one tungsten through C and N donors but bridges the other through N.
325
The
confacial bi-octahedral configuration is found in [W
2
-OPr
i
2
-NCPhCHCH
2
OPr
i
5
]
(W-W, 2.584 A).
325
Addition of bis-
p
-tolyldiazomethane
MeC
6
H
4
2
CN
2
to W
2
OBu
t
6
gave the binuclear [W
2
f
-NNC
C
6
H
4
Me
2
g
2
OBu
t
6
](W-W, 2.675 A) in which each
W atom is in a distorted (TBP) configuration with the NNC
C
6
H
4
Me
2
ligands bridging
a common axial - equatorial edge.
305
The compound [W
2
f
-NPhCO
OBu
t
g
2
OBu
t
4
](W W, 2.290 A) formed by
insertion of PhNCO into the W-OBu
t
bonds of W
2
OBu
t
6
, is a centrosymmetric
molecule with two
trans
bridging bidentate ligands.
243
The precursor molecule
[W
2
-OCNPh
OBu
t
6
](W-W, 2.488 A) was converted by addition of PMe
3
into
the insertion product [W
2
f
-NPhCO
OBu
t
g
OBu
t
5
PMe
3
](W-W, 2.361 A).
326
The
bis-
p
-tolylcarbodiimide adduct [W
2
f
-N
C
6
H
4
Me
CN
C
6
H
4
Me
g
OBu
t
6
](W-W,
2.482 A) has a similar structure to the isocyanate adduct.
327
The bis-isopropyl and bis-
cyclohexyl carbodiimides gave analogous structures (data in Table 4.11).
328
In the CO
2
insertion product [W
2
-O
2
COBu
t
2
OBu
t
4
](W
W, 2.315 A) the bidentate bridging
ligands adopt the cisoid conformation.
329
The pivalato ligand Bu
t
CO
2
also spans the
WW in the symmetrical molecule [W
2
-O
2
CBu
t
2
OBu
t
4
](WW, 2.312 A) in
which the two carboxylates adopt a cisoid configuration which is also found in the
related molecule [W
2
-O
2
CBu
t
2
OBu
t
2
NPr
i
2
](WW, 2.336 A).
330
Addition of
˛
,
ˇ
-unsaturated ketones and aldehydes to [W
2
OCH
2
Bu
t
6
py
2
]gaverise
to some novel complexes. With acrolein a bis-adduct was formed [W
2
-
OCH
2
Bu
t
2
-OCH
2
CH
2
CH
2
2
-OCHCH
ž
CH
2
OCH
2
Bu
t
4
] in which one ligand is
chelating (O,C) and bridging whilst the other is a terminally bonded
2
-OC.
331
With
methylvinylketone a symmetrical molecule [W
2
-OCHMeCH
2
CH
2
2
OCH
2
Bu
t
6
]is
