Chemistry Reference
In-Depth Information
[
Bu
t
O
3
W
C-C
W
OBu
t
3
]theWC
2
W system is linear and the two W
OBu
t
3
moieties are staggered.
354
Another binuclear complex in which the W atoms are well separated by the
bridging ligand is [W
2
f
-CCCNH
C
6
H
3
Me
2
-2,6
OSiMe
2
Bu
t
5
gfCN
C
6
H
3
Me
2
g
4
]
obtained from the reaction of [W
2
-CCH
OSiMe
2
Bu
t
5
] with xylylisocyanide. The
bridging
-CCCNH
C
6
H
3
Me
2
ligand may be viewed as an
2
-aminoalkyne to one
tungsten (six-coordinated) and an alkylidyne to the other (five-coordinated).
355
Bridging
alkylidyne ligands are featured in [W
2
-CCHCHMe
-OSiMe
2
Bu
t
OSiMe
2
Bu
t
5
H]
(W-W,
2.658 A)
[W
2
f
-CC
CH
2
CHCH
2
g
-OSiMe
2
Bu
t
OSiMe
2
Bu
t
5
H]
and
(W-W, 2.561 A).
356
In [W
2
,
2
-CCH
2
CHCHS
-OBu
t
OBu
t
4
1
-CCHCHCHS
](W-W, 2.663 A)
the butadiene thiolate ligand is chelating one W atom and bridging to the other.
357
A similar situation is present in [W
2
-OBu
t
,
2
-CCH
2
CHCHO
OBu
t
4
1
-
CCHCHCHO
](W-W, 2.649 A).
357
In [W
2
-OBu
t
,
2
-C
4
H
4
OBu
t
5
CO
]
(W-W, 2.901 A) the Bu
t
O bridge is asymmetric with the long W-O bond (2.224 A,
cf.
2.000 A) being
trans
to the terminal carbonyl ligand in a confacial pseudo-octahedral
structure.
358
A few examples are known with phosphorus or phosphine bridges. In
[W
2
-OPr
i
-P
2
OPr
i
5
py
](W-W, 2.69 A) a pseudo-tetrahedral W
2
P
2
unit forms
the core of a confacial pseudo-octahedral structure in which the shorter W-O
bridging bond (1.989 A) is
trans
to the pyridine ligand.
359
In the diphenylphosphido
bridged complex [W
2
-NPh
2
2
OBu
t
4
]theW
2
P
2
unit is a puckered ring and each
W atom is in a distorted tetrahedral configuration, probably due to the presence
of a bent metal - metal bond (W-W, 2.59 A).
360
In the bis-cyclohexylphosphido
complex [W
2
f
-P
C
6
H
11
-
c
2
g
3
fPH
C
6
H
11
-
c
2
g
OCH
2
Bu
t
3
](W-W, 2.618 A) there
is a triple phosphido bridge with five-coordinated tungstens.
361
The diphosphine
ligand dmpm (dimethylphosphino methane) straddles the two W atoms in
[W
2
-dmpm
OPr
i
4
CH
2
Ph
2
](W-W, 2.347 A) and in [W
2
-dmpm
OPr
i
4
Bu
i
2
]
(W-W, 2.349 A).
362
The tertiary phosphine PMe
3
acts as a terminal ligand in [W
2
-H
-
CPh
OPr
i
4
PMe
3
3
](W-W, 2.54 A) and [W
2
-H
-CPr
i
OPr
i
4
PMe
3
3
](W-W,
2.50 A). Each molecule has one pseudo-octahedral W bonded to three PMe
3
ligands,
aterminalPr
i
O, the bridging hydride, and alkylidyne ligands whilst the other W is
five-coordinated by three terminal Pr
i
O ligands and the two bridging ligands.
362
By
contrast the dimethylphosphinoethane (dmpe) ligand acts as a chelate in [
dmpe
2
W
-
H
2
W
OPr
i
4
](W-W, 2.496 A) giving an edge-shared bi-octahedral structure in this
unsymmetrical molecule.
363
In contrast to the abundance of binuclear alkoxo tungsten compounds there are
relatively few trinuclear species. In [W
3
3
-CMe
-OPr
i
3
OPr
i
6
] the triangle
of W atoms is capped by the
3
-ethylidyne ligand and bridged by three Pr
i
O
ligands in the W
3
plane. Each metal has two terminal Pr
i
O ligands giving five-
coordination (square pyramidal) (Fig. 4.49).
364
The same general framework of
atoms is found in [W
3
3
-P
-OCH
2
Bu
t
3
OCH
2
Bu
t
6
].
365
In the imido complex
[W
3
3
-NH
3
-OPr
i
-OPr
i
3
OPr
i
6
] there are capping ligands above and below
the W
3
plane analogous to the oxo-complex [W
3
3
-O
OPr
i
10
].
366
A less symmetrical
structure obtains in [W
3
3
-CMe
-OPr
i
3
OPr
i
3
Cl
2
] in which W[1] - W[2] - W[3] D
81
Ž
(
cf.
60
Ž
for an equilateral triangle). One tungsten W[1] is in a pseudo-trigonal
