d2 Complexes of tungsten containing p-toluonitrile as a four- or two-electron donor and oxidative addition giving the two-electron donor acylimido ligand NCOC6H4Me-4
Abstract
Reaction of benzonitrile with WCl
6
in the presence of
CCl
2
CCl
2
gave the complex
[{WCl
4
(NCPh)}
x
] of undetermined
structure which does not show equivalent chemistry to the d
0
complexes [{WCl
4
(PhC
2
Ph)}
2
]
and [{WCl
4
(NPh)}
2
]. The complex
[WCl
2
(η
2
-NCC
6
H
4
Me-4)
(PMe
3
)
3
] 1 can be prepared by reduction of
[WCl
4
(PMe
3
)
3
] with 2 equivalents of
Na/Hg amalgam in the presence of p-toluonitrile. The nitrile
carbon in the
13
C-{
1
H} NMR spectrum
appears at δ 232.2 consistent with a four-electron donor nitrile
ligand. Reaction of
[WCl
2
(NC
6
H
3
Pr
i
2
-
2,6)(PMe
3
)
3
] with purified p-toluonitrile
in refluxing toluene or reduction of
[WCl
3
(NC
6
H
3
Pr
i
2
-
2,6)(PMe
3
)
2
] in benzene with 1 equivalent of Na/Hg
amalgam in the presence of p-toluonitrile led to
[WCl
2
(NC
6
H
3
Pr
i
2
-
2,6)(η
2
-NCC
6
H
4
Me-4)(PMe
3
)
2
] 2 as shown by
1
H,
13
C-{
1
H} and
31
P-{
1
H} NMR spectroscopy. The position
of the nitrile carbon in the
13
C-{
1
H}
NMR spectrum (δ 178.9) is consistent with a two-electron donor
nitrile ligand. Reaction of
[WCl
2
(NC
6
H
3
Pr
i
2
-
2,6)(PMe
3
)
3
] with unpurified
p-toluonitrile gave
[WCl
2
(NC
6
H
3
Pr
i
2
-
2,6)(NCOC
6
H
4
Me-4)(OPMe
3
)(PMe
3
)] 3 in addition to 2. A crystal structure determination showed
cis orientated imido and acylimido ligands [W–N 1.769(5)
and 1.823(6) Å, W–N–C 174.5(5) and 158.9(5)°],
cis-chloro ligands and a cis orientation of the
PMe
3
and OPMe
3
ligands. The bond lengths and
angles about the NCOPh function are not significantly different to those
of a variety of uncomplexed organic amide groups. Hartree–Fock and
density-functional calculations performed on the model complex
[WCl
2
(NMe)(NCOH)(OPH
3
)(PH
3
)] 4 showed
structural parameters in good agreement with those of 3 when the phenyl
groups were removed. An NBO (natural bond orbital) analysis of the
W–NMe bond generated one σ and two π bonds between
nitrogen s and p atomic orbitals (AOs) and tungsten d AOs. The nitrogen
of the NCOH ligand binds to tungsten via one σ and one
π bond. In contrast to the NMe ligand, the NBO analysis located a
nitrogen ‘lone pair’ orbital on the NCOH ligand which
overlaps somewhat with the C–O π orbitals (11% for carbon, 5%
for oxygen) and with tungsten (8%). The structural and theoretical
studies indicate the NMe ligand nitrogen atom dominates the π
donation.
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