Oxidation of the zwitterionic tungsten amide (OC)5WNPhNPhC(OMe)Ph with Br2 and PCl5. Formation of [(PhN)W(CO)2X2]2 and (PhN)W(CO)2X2L (X = Br or Cl; L = MeCN, Me3

Article abstract of DOI:10.1039/a803989e

Oxidation of the zwitterionic tungsten amide (OC)₅WNPhNPhC(OMe)Ph 1 with Br₂ or PCl₃ produced [(PhN)W(CO)₂X₂]₂ (X = Cl or Br). These halide-bridged tungsten(IV) dimers reacted with MeCN to

Full text of DOI:10.1039/a803989e

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Oxidation of the zwitterionic tungsten amide
(OC)5WNPhNPhC(OMe)Ph with Br2 and PCl5. Formation of
[(PhN)W(CO)2X2]2 and (PhN)W(CO)2X2L (X ؍ Br or Cl;
L ؍ MeCN, Me3C6H2NH2 and i-BuNH2)
Yingxia He, Patrick C. McGowan, Khalil A. Abboud and Lisa McElwee-White*
Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA
Received 27th May 1998, Accepted 30th July 1998
Oxidation of the zwitterionic tungsten amide (OC)5WNPhNPhC(OMe)Ph 1 with Br2 or PCl5 produced
[(PhN)W(CO)2X2]2 (X = Cl or Br). These halide-bridged tungsten() dimers reacted with MeCN to give the
mononuclear complexes (PhN)W(CO)2X2(MeCN) (X = Cl or Br). The latter complexes can also be obtained directly
in high yield by oxidizing 1 in the presence of MeCN. The acetonitrile ligand can be substituted with Me3C6H2NH2
or i-BuNH2 to yield (PhN)W(CO)2X2L (X = Cl or Br, L = Me3C6H2NH2 or i-BuNH2) or with PMe3 to produce
(PhN)W(CO)Br2(PMe3)2. The oxidation of 1 with BrI resulted in the formation of [(PhN)W(CO)2Br(I)]2, which
reacts with MeCN to produce (PhN)W(CO)2Br(I)(MeCN). The structures of the dimers [(PhN)W(CO)2X2]2 were
determined by X-ray crystallography.
directly in more than 80% yield. The MeCN ligand can easily be
Introduction
substituted with amines to provide the series of complexes
Synthetic routes involving amido ligands have become import-
(PhN)W(CO)2X2L.
ant in the preparation of imido complexes.1 Although imido
moieties can be generated in a variety of ways,1,2 utilization of a
Results and discussion
Oxidation of (OC)5WNPhNPhC(OMe)Ph 1 with PCl5
Reaction of complex 1 with PCl5 in diethyl ether at 0 ЊC
resulted in precipitation of a red solid after about 25 min. Isol-
ation of the solid by filtration afforded the Cl-bridged dimer
3 in 63% yield (Scheme 1). When the reaction mixture was
preexisting metal–nitrogen bond is often very convenient. This
strategy has proven to be particularly successful in the prepar-
ation of low-valent imido complexes, which can be difficult
targets. As an example, abstraction of either a hydride or a
proton has been used to generate low-valent imido complexes
of the type TpЈ(OC) W᎐NRϩ [TpЈ = hydridotris(3,5-dimethyl-
᎐
2
pyrazolyl)borate] from the corresponding amido complexes.3
We have previously reported use of the zwitterionic amido
complex (OC)5WNPhNPhC(OMe)Ph 14 as a precursor to
tungsten imido complexes in a variety of oxidation states.
Cleavage of 1 under non-oxidative conditions generates the
tungsten(0) complex (OC) W᎐NPh as a reactive intermediate,5
Ph
Ph
X
OMe
N
W
X
(OC)5W
Ph
(i) or (ii)
X
X
CO
CO
OC
OC
N
N
W
N
Ph
᎐
5
1
while oxidation of 1 with I2 produces imido complexes of WIV
or WVI.6 Of particular interest is the dimeric complex [(PhN)-
W(CO)2I2]2 2 [eqn. (1)] which results from reaction of 1 with 1
Ph
(iii) or (iv)
3 X = Cl; 4 X = Br
MeCN
Ph
N
Ph
N
Ph
Ph
N
W
Ι
Ι
OMe
1 equivalent Ι2
Ph
X
L
OC
OC
(OC)5W
X
N
I
I
OC
OC
OC
OC
L
CO
CO
W
X
1
–
+
Ph
(1)
W
W
X
N
N
OMe
2
– 3 CO
NCMe
Ph
N
Ph
Ph
2
1
7
8
9
X = Cl; L = Me3C6H2NH2
X = Cl; L = i-C4H9NH2
X = Br; L = Me3C6H2NH2
5 X = Cl; 6 X = Br
equivalent of I2. Iodo-bridged dimer 2 is both a stoichiometric
reagent7a and a catalyst7b for the carbonylation of primary
amines to ureas. In addition, complexes of the type (PhN)-
W(CO)2I2L, which can be produced by reaction of 2 with two-
electron donor ligands L, show promise as precursors for the
chemical vapor deposition of tungsten nitride thin films.8 The
exploration of these applications led us to prepare derivatives
containing chloride and bromide ligands.
We now report the oxidation of zwitterion 1 with Br2 or PCl5
to yield the halide-bridged dimers [(PhN)W(CO)2X2]2 (X = Cl 3
or Br 4). In parallel with the chemistry of iodide complex 2,
derivatives of the type (PhN)W(CO)2X2L can be prepared from
dimers 3 and 4. In addition, when the oxidation of 1 is carried
out in the presence of MeCN, the acetonitrile complexes
(PhN)W(CO)2X2(MeCN) (X = Cl 5 or Br 6) can be obtained
10 X = Br; L = i-C4H9NH2
Scheme 1 (i) PCl5, ether, 0 ЊC; (ii) Br2, CH2Cl2, ether, Ϫ78 ЊC; (iii)
PCl5, MeCN, ether, 0 ЊC; (iv) Br2, MeCN, ether, 0 ЊC.
allowed to stir for more than 3 h dimer 3 began to decompose
into an insoluble blue-black solid which was not characterized.
Although chlorination with PCl5 was successful, reaction of 1
with Cl2 did not result in formation of 3. It is possible that the
limited solubility of both PCl5 and dimer 3 in ether at 0 ЊC
allowed 3 to form and precipitate before further chlorination
could occur.
Spectroscopic data for compound 3 can be found in Tables
1–3. The carbonyl bands (2084, 2016 cmϪ1) appear at higher
wavenumbers than those of its iodide analogue 2, consistent
J. Chem. Soc., Dalton Trans., 1998, 3373–3378
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with the poorer electron donation from the chloride ligands vs.
iodide. This effect is also evident in the 13C NMR signals for the
carbonyl carbons in dimers 2 and 3, where the chloride dimer 3
appears downfield of iodide 2.
stirring the reaction mixture for 4 h dimer 4 decomposed into
intractable material. Further attempts to optimize the reaction
conditions using PBr5 were also unsuccessful.
Oxidation of (OC)5WNPhNPhC(OMe)Ph 1 with BrI
Oxidation of (OC)5WNPhNPhC(OMe)Ph 1 with Br2 and PBr5
Upon addition of BrI–CH2Cl2 solution to an ether solution of
compound 1 at room temperature immediate reaction occurred.
The solution changed from black to greenish, then dark red,
and red solid began to precipitate within 10 min. After 2 h of
stirring a red solution containing an orange-red solid had
formed. Isolation of the solid yielded the dimer [(PhN)-
W(CO)2Br(I)]2 as the major product. As expected,9 formation
of this mixed bromide–iodide complex predominated. How-
ever, the reaction mixtures also contained trace amounts of
the iodide dimer 2 and the bromide dimer 4, which presumably
arise due to the equilibrium between BrI and Br2 ϩ I2.10 The
three dimers exhibited clear differences in their solubilities,
with 2 being the most soluble and 4 the least. The insolubility
of 4 allowed crystals to be grown from solutions in which
[(PhN)W(CO)2Br(I)]2 was the major component.
In contrast to the well behaved reactions of compound 1 with
PCl5 and I2, preparation of the analogous bromide dimer 4
proved problematic. When 1 was treated with 1 equivalent of
Br2–CH2Cl2 solution at Ϫ78 ЊC in ether containing a small
amount of CH2Cl2 no reaction occurred initially. However,
upon warming to Ϫ40 ЊC, the solution changed from black to
dark red and a dark red sticky solid formed over the course of
2 h. The sticky solid contained dimer 4 and unstable material,
which decomposed during the work-up. Purification of the
crude product afforded clean 4 in 13% yield (Scheme 1). The
spectroscopic data were similar to those for chloride dimer 3
and are summarized in Tables 1–3. Efforts to optimize the con-
ditions using other solvents (CH2Cl2 or hexane) and altered
reaction conditions were unsuccessful.
Given that the presence of an excess of I2 during oxidation
of compound 1 to 2 leads to overoxidation and formation of
the tungsten() metallacycle I3(PhN)W(NPhCPhO), it seemed
likely that the more strongly oxidizing Br2 could also be causing
overoxidation. In order to ensure low concentrations of Br2,
PBr5 was used as a Br2 equivalent. Reaction of 1 with PBr5 in
ether at 0 ЊC over 2 h afforded a red solution and a dark red
sticky solid. Dimer 4 was isolated from the sticky solid in 25%
yield. Once again the timing of the reaction was critical. Upon
Crystal structures of dimers 3 and 4
The chloride- and bromide-containing complexes [(PhN)W-
(CO)2X2]2 and (PhN)W(CO)2X2L are rare examples of d2 imido
complexes bearing two π-acid ligands3,6 and as such could
provide insight into the problem of accommodating both
strongly π-donating imido and π-acid carbonyl ligands on the
same metal center. Prior studies on d2 imido complexes bearing
a single π-acid ligand have been interpreted in terms of electron
donation from the imido ligand into two empty d orbitals in
conjunction with back donation of the two d electrons into the
empty orbitals of the π acid.11 For compounds with multiple π
acids, such as the [(PhN)W(CO)2X2]2 and (PhN)W(CO)2X2L
series, back donation will be affected by competition for the two
d electrons. In the chloride and bromide derivatives, which will
be less electron rich at the metal than iodide-containing dimer
2, the already weak back bonding should be even less potent.
This effect can be detected in the variation of carbonyl stretch-
ing frequencies as the halide is changed (Table 1). In order to
see if it would also be detectable in the structures of the com-
plexes, a crystallographic study of dimers 3 and 4 was carried
out for comparison to iodide dimer 2, whose structure was pub-
lished previously.6a
The structures of complexes 3 and 4 appear in Figs. 1 and 2,
respectively. Selected bond lengths and angles can be found in
Table 4. As is also observed for iodide dimer 2, the tungsten
centers are octahedral and bear triply bonded imido ligands
[W–N1 1.757(4) Å for 3; 1.757(10) for 4]. Within experimental
error, the W–C bond lengths are the same for dimers 2
[2.051(14), 2.022(13) Å], 3 [2.043(5), 2.040(5) Å] and 4
[2.051(13), 2.029(13) Å]. The C–O bond lengths within the carb-
onyls are also indistinguishable in the three dimers. There is
Table 1 Infrared and 13C NMR data for carbonyl ligands.
ν (CO)
(CH2Cl2)/cmϪ1 δ(CDCl3, 20 ЊC)
13C NMR,
Complex
a
2 [(PhN)W(CO)2I2]2
2068, 2007
2080, 2012
2084, 2016
2080, 2017
202.7
208.3b
210.4b
207.7
4 [(PhN)W(CO)2Br2]2
3 [(PhN)W(CO)2Cl2]2
[(PhN)W(CO)2Br(I)]2
(PhN)W(CO)2I2(MeCN)a
6 (PhN)W(CO)2Br2(MeCN)
5 (PhN)W(CO)2Cl2(MeCN)
(PhN)W(CO)2Br(I)(MeCN)
2072, 2003
2078, 2005
2081, 2013
2087, 2011
206.4, 203.0
208.9, 207.1
212.3, 210.4b
207.0, 204.2
(PhN)W(CO)2I2(Me3C6H2NH2)a
9 (PhN)W(CO)2Br2(Me3C6H2NH2) 2076, 1995
7 (PhN)W(CO)2Cl2(Me3C6H2NH2) 2087, 2011
2064, 1984
209.1, 207.2
211.9, 211.6
213.7, 212.4
10 (PhN)W(CO)2Br2(i-C4H9NH2)
8 (PhN)W(CO)2Cl2(i-C4H9NH2)
2076, 1988
2078, 1993
213.8, 211.3b
216.0, 211.6
(PhN)W(CO)Br2(PMe3)2
1953
241.9b
a Data taken from ref. 6(b). b Spectrum obtained in CD2Cl2.
Table 2 Proton and 13C NMR data (δ, J/Hz) for phenyl groups.
Complex
1H NMR, δ(CDCl3), C6H5
7.48 (t, 4 H), 7.42 (m, 2 H), 7.08 (t, 4 H)
13C NMR, δ(CDCl3, 20 ЊC)
3*
154.2, 129.4, 128.5, 125.9
153.9, 139.0, 129.4, 126.9
152.7, 138.0, 129.7, 126.6
153.4, 129.2, 128.8, 126.3
154.6, 130.2, 129.5, 127.8
153.5, 132.2, 129.2, 126.0
153.1, 138.9, 129.5, 126.3
153.9, 129.7, 129.4, 126.2
154.9, 129.3, 127.3, 124.9
153.8, 129.9, 129.3, 127.1
153.4, 129.1, 126.0, 125.6
5*
7.59 (m, 1 H), 7.37 (d, J = 8, 2 H), 7.30 (t, 2 H)
7.27 (m, 1 H), 7.16 (t, 2 H), 6.64 (d, J = 8, 2 H)
7.34 (t, 2 H), 7.29 (m, 1 H), 7.22 (d, J = 8, 2 H)
7.58 (d, J = 8, 4 H), 7.39 (t, 4 H), 7.23 (m, 2 H)
7.42 (m, 1 H), 7.31 (d, J = 7, 2 H), 7.22 (t, 2 H)
7.35 (t, 1 H), 7.18 (t, 2 H), 6.72 (d, J = 8, 2 H)
7.44 (m, 1 H), 7.33 (t, 2 H), 7.28 (t, 2 H)
7.51 (m, 2 H), 7.29 (m, 1 H), 7.14 (t, 2 H)
7.61 (m, 4 H), 7.50 (m, 2 H), 7.37 (m, 4 H)
7.67–7.32 (m, 5 H)
7
8
4
6
9*
10*
(PhN)W(CO)Br2(PMe3)2*
[(PhN)W(CO)2Br(I)]2
(PhN)W(CO)2Br(I)(MeCN)
* Spectrum obtained in CD2Cl2.
3374
J. Chem. Soc., Dalton Trans., 1998, 3373–3378

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Table 3 Proton and 13C NMR data (δ, J/Hz) for ancillary ligands.
δ(CDCl3, 20 ЊC)
Complex
Ligand
1H NMR
13C NMR
5a
7
MeCN
NH2C6H2Me3
2.68 (s, 3 H, CH3CN)
6.81 (s, 2 H, C6H2)
6.30 (d, J = 12, 1 H, NH2)
5.57 (d, J = 12, 1 H, NH2)
2.42 (s, 6 H, CH3)
129.2, (CH3CN), 4.7 (CH3CN)
135.1, 128.8, 128.6, 127.1 (C6H2), 20.5, 18.0 (CH3C6H2)
2.28 (s, 3 H, CH3)
8
MeCHCH2Me
|
4.23 (dd, 1 H, NH2)
3.77 (dd, 1 H, NH2)
3.33 (m, 1 H, CH)
1.64 (m, 2 H, CH2)
1.33 (t, 3 H, CH3)
56.5 (H2NCH)
31.7 (H2NCHCH3)
21.5 (H2NCHCH2)
10.0 (CHCH2CH3)
NH2
0.99 (t, 3 H, CH3)
2.75 (s, 3 H, CH3CN)
6.85 (s, 2 H, C6H2)
6
9
MeCN
NH2C6H2Me3
125.3 (CH3CN), 5.1 (CH3CN)
135.7, 130.1, 129.9, 129.2 (C6H2), 20.6, 18.5 (CH3C6H2)
6.32 (d, J = 11, 1 H, NH2)
5.55 (d, J = 12, 1 H, NH2)
2.42 (s, 6 H, CH3C6H2)
2.26 (s, 3 H, CH3C6H2)a
4.27 (dd, 1 H, NH2)
3.88 (dd, 1 H, NH2)
3.38 (m, 1 H, CH)
10a
MeCHCH2Me
|
57.8 (H2NCH)
32.1 (H2NCHCH3)
21.7 (H2NCHCH2)
10.2 (CHCH2CH3)
NH2
1.64 (m, 2 H, CH2)
1.32 (t, 3 H, CH3)
1.00 (t, 3 H, CH3)
1.74 (t, 18 H, PMe3)
2.78 (s, 3 H, CH3CN)
a,b
c
PMe3
MeCN
16.4 [t, P(CH3)3]
124.9 (CH3CN), 4.9 (CH3CN)
a Spectrum obtained in CD2Cl2. b Complex (PhN)W(CO)Br2(PMe3)2: 31P NMR (CD2Cl2) δ Ϫ26.0 (t, JWP = 285.0 Hz, PMe3). c (PhN)W(CO)2-
Br(I)(MeCN).
Fig. 1 Thermal ellipsoid diagram of [(PhN)W(CO)2Cl2]2 3 showing
the crystallographic numbering scheme.
Fig. 2 Thermal ellipsoid diagram [(PhN)W(CO)2Br2]2 4 showing the
crystallographic numbering scheme.
(MeCN) 6, respectively. Similar behavior has been reported for
iodide dimer 2.6 Reaction of the mixed bromide–iodide dimer
[(PhN)W(CO)2Br(I)]2 with MeCN overnight yielded only the
mixed halide complex (PhN)W(CO)2Br(I)(Me3CN). Neither
(PhN)W(CO)2I2(MeCN) nor (PhN)W(CO)2Br2(MeCN) 6 were
produced from [(PhN)W(CO)2Br(I)]2. This result suggests that
the bridging halides in the latter are either both iodide or both
bromide. We have no experimental evidence to distinguish
between the possibilities, as X-ray quality crystals could not be
obtained. However, the precedent from molecules such as
thus no structural evidence for variation in the back bonding to
the carbonyl ligands as the halide ligands are changed. The W–
X bond distances in 3 [terminal 2.4349(12); bridging 2.4991(12)
Å] and 4 [terminal 2.6729(13); bridging 2.7204(11) Å] fall with-
in the normal ranges.12 The structural differences in the W2X2
cores of the dimers can be attributed to the variation in W–X
bond lengths as X is varied.
Reactions of dimers 3, 4 and [(PhN)W(CO)2Br(I)]2 with donor
ligands
9
[Mo(µ-I)Br(CO)3(PPh3)]2 suggests that iodide bridging would
When dimers 3 and 4 are dissolved in MeCN dissociation and
solvent co-ordination result in formation of the acetonitrile
complexes (PhN)W(CO)2Cl2(MeCN) 5 and (PhN)W(CO)2Br2-
be preferred.
Reaction of bromide dimer 4 with an excess of PMe3 in
CH2Cl2 results in formation of the bis(PMe3) complex (PhN)-
J. Chem. Soc., Dalton Trans., 1998, 3373–3378
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Table 4 Selected bond lengths (Å) and angles (Њ) for complexes 3 and 4.
formation of the Me3C6H2NH2 complexes 7 and 9 (Scheme 1)
within 2 h. The IR spectrum of 9 exhibited two CO bands at
2076 and 1995 cmϪ1, while the two CO bands for 7 appeared
at 2087 and 2011 cmϪ1. These values are higher than the corre-
sponding 2064 and 1984 cmϪ1 for the iodide derivative, con-
sistent with the weakening of electron donation to the metal
upon proceeding from iodide to bromide to chloride.
Similarly, reaction of compounds 5 and 6 with 1 equivalent
of i-BuNH2 in CH2Cl2 solution yielded the i-BuNH2 complexes
8 and 10. Owing to the chirality of the metal center and the
amine a mixture of diastereomers was obtained. This was
reflected in the 1H NMR spectra, which exhibited broad multi-
plets at δ 1.64 for the CH2 group next to the chiral carbon. In
addition the 13C NMR spectra contained two sets of carbon
signals for the isobutyl groups of the diastereomers. The
reported data (Tables 1–3) correspond to the major isomers.
Complex 3
Complex 4
W–N1
W–C7
W–C8
W–Cl2
W–Cl1
W–Cl1A
N1–Cl
C7–O8
C8–O8
1.757(4)
2.043(5)
2.040(5)
2.4349(12)
2.4991(12)
2.5085(12)
1.387(6)
1.131(7)
1.125(7)
W–N1
W–C7
W–C8
W–Br2
W–Br1
W–Br1A
N1–Cl
O7–C7
O8–C8
1.757(10)
2.051(13)
2.029(13)
2.6729(13)
2.7204(11)
2.7318(11)
1.37(2)
1.12(2)
1.14(2)
N1–W–C8
N1–W–C7
C7–W–C8
89.3(2)
90.0(2)
89.0(2)
170.99(13)
83.8(2)
84.2(2)
96.77(13)
94.4(2)
172.5(2)
89.54(4)
98.65(13)
170.92(14)
95.3(2)
88.72(4)
80.35(4)
99.65(4)
174.9(3)
118.5(4)
120.3(4)
178.4(5)
178.0(5)
N1–W–C8
N1–W–C7
C8–W–C7
91.4(5)
91.3(5)
89.3(5)
170.2(3)
81.4(4)
82.1(4)
96.8(3)
93.2(4)
171.5(4)
90.25(4)
98.3(3)
169.9(4)
93.2(4)
89.26(4)
82.92(3)
97.08(3)
177.1(9)
120.0(12)
119.2(11)
177.0(13)
177.3(13)
N1–W–Cl2
C8–W–Cl2
C7–W–Cl2
N1–W–Cl1
C8–W–Cl1
C7–W–Cl1
Cl2–W–Cl1
N1–W–Cl1A
C8–W–Cl1A
C7–W–Cl1A
Cl2–W–Cl1A
Cl1–W–Cl1A
W–Cl1–W0A
C1–N1–W
N1–C1–C2
N1–C1–C6
O8–C8–W
N1–W–Br2
C8–W–Br2
C7–W–Br2
N1–W–Br1
C8–W–Br1
C7–W–Br1
Br2–W–Br1
N1–W–Br1A
C8–W–Br1A
C7–W–Br1A
Br2–W–Br1A
Br1–W–Br1A
W–Br1–W0A
C1–N1–W
N1–C1–C2
N1–C1–C6
O7–C7–W
Conclusion
Oxidation of the zwitterionic amide complex (OC)5WNPhN-
PhC(OMe)Ph 1 with Br2 and PCl5 at low temperature in ether
solution results in formation of the dimeric complexes [(PhN)-
W(CO)2X2]2 (X = Cl; 3 or Br 4). These dimers are congeners of
the previously reported iodo-bridged dimer 2, but are more
reactive than it due to the poorer bridging ability of Br and Cl.
Reaction of them with two-electron donor ligands L produces
complexes of the type (PhN)W(CO)2X2L. When oxidation of
1 with Br2 and PCl5 is conducted in the presence of the
co-ordinating solvent MeCN, the mononuclear complexes
(PhN)W(CO)2X2(MeCN) (X = Cl 5 or Br 6) are obtained
directly in more than 80% yield. The MeCN ligand in com-
plexes 5 and 6 can easily be replaced with amines such as
Me3C6H2NH2 and i-BuNH2.
O7–C7–W
O8–C8–W
W(CO)Br2(PMe3)2. As is also observed for the chemistry of
iodide dimer 2,6 one of the CO ligands is replaced by the more
strongly nucleophilic PMe3. The 31P NMR spectrum exhibits a
signal at δ Ϫ26.0 for PMe3. The signal is shifted downfield with
respect to its iodide analogue (PhN)W(CO)I2(PMe3)2 (δ Ϫ38.8)
as expected for the more electron poor bromide complex.
Experimental
General
Standard inert atmosphere techniques were used throughout.
Hexane, acetonitrile and methylene chloride were distilled from
CaH2, diethyl ether and THF from Na/Ph2CO. The NMR
solvents were degassed by three freeze–pump–thaw cycles and
stored over 3 Å molecular sieves in a dry-box. Iodine mono-
bromide was purchased from Aldrich as a 1.0 M solution in
CH2Cl2 and used as received. All other reagents were purchased
in reagent grade and used without further purification. The
1H, 13C and 31P NMR spectra were recorded on Gemini-300
or VXR-300 spectrometers, IR spectra on a Perkin-Elmer
1600 spectrometer. High resolution mass spectrometry was
performed by the University of Florida analytical service.
Elemental analyses were performed by Robertson Microlit
Laboratories, Madison, NJ.
Oxidation of (OC)5WNPhNPhC(OMe)Ph 1 with Br2 and PCl5
in the presence of MeCN
Although acetonitrile complexes 5 and 6 are accessible via reac-
tion of dimers 3 and 4 with MeCN, poor yields during the
dimer syntheses result in low overall yields for 5 and 6. There-
fore, more direct routes to them were developed. Oxidation of
zwitterion 1 with Br2 in the presence of MeCN at Ϫ78 ЊC
resulted in formation of a red solution containing a red precipi-
tate of MeCN complex 6. Simple filtration and washing of the
solid afforded 81% yield. A similar protocol involving oxidation
of 1 with PCl5 in the presence of MeCN at 0 ЊC produced com-
plex 5 in 88% yield. Clearly, the yields of MeCN complexes
obtained upon oxidation in the presence of a co-ordinating
solvent are much higher than the yields of dimer obtained in
non-co-ordinating solvents. This effect can be attributed to
trapping of the unsaturated intermediate [X2(OC)2W(NPh)]
before side reactions can compete with dimerization.
Syntheses
[(PhN)W(CO)2Cl2]2 3. Zwitterion 1 (1.3 g, 2.1 mmol) and
PCl5 (432.5 mg, 2.08 mmol) were placed in a Schlenk vessel and
cooled to 0 ЊC. Diethyl ether (25 mL) and 4 mL of CH2Cl2 were
added via syringe. After 25 min a red solid began to form. The
solution was stirred at 0 ЊC for 1.5 h. The solvent was removed
by cannulation and the solid washed with ether (5 mL × 3) to
yield complex 3 as an orange-red solid. Yield 524 mg, 62.7%
(Found: C, 23.62; H, 1.29; N, 3.75. Calc. for C8H5Cl2NO2W:
C, 23.91; H, 1.25; N, 3.48%).
Substitution of the MeCN ligand in (PhN)W(CO)2X2(MeCN)
with Me3C6H2NH2 and i-BuNH2
Since MeCN complexes 5 and 6 were readily available we
explored substitution of the acetonitrile ligand as a means of
generating derivatives. The hindered arylamine 2,4,6-Me3C6-
H2NH2 had been demonstrated to serve as a ligand in the iodide
system, where the amine was treated with dimer 2 to generate
(PhN)W(CO)2I2(Me3C6H2NH2).6b Treatment of 5 and 6 with 1
equivalent of Me3C6H2NH2 in CH2Cl2 solution results in the
(PhN)W(CO)2Cl2(MeCN) 5. Zwitterion 1 (1.37 g, 2.19
mmol) and PCl5 (456 mg, 2.19 mmol) were placed in a Schlenk
vessel and cooled to 0 ЊC. Ether (15 mL) was added, then 3 mL
of MeCN were added within 5 min. A vigorous reaction
occurred upon addition of MeCN, as evidenced by a change
3376
J. Chem. Soc., Dalton Trans., 1998, 3373–3378

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Table 5 Crystallographic data for complexes 3 and 4*
from black to dark red. The reaction mixture was stirred for
1.5 h at 0 ЊC followed by 0.5 h at room temperature, during
which a purple-red solid formed. The solvent was removed by
cannulation and the solid washed with ether (5 mL × 3) to yield
complex 5 as a purple-red solid. Yield 852 mg, 87.8% (Found:
C, 27.28; H, 1.67; N, 6.19. Calc. for C10H8Cl2N2W: C, 27.12;
H, 1.82; N, 6.33%).
3
4
Empirical formula
M
C16H10Cl4N2O4W C16H10Br4N2O4W2
803.76
981.60
a/Å
b/Å
c/Å
7.1433(3)
10.1298(4)
14.9460(7)
95.139(1)
1077.15(8)
7669
2475
11.191
1.13
7.1118(1)
10.4920(1)
15.7374(1)
95.079(1)
1169.66(2)
8334
2685
16.682
1.12
β/Њ
(PhN)W(CO)2Cl2(Me3C6H2NH2) 7. Complex 5 (317 mg, 0.59
mmol) was dissolved in 8 mL of CH2Cl2 and Me3C6H2NH2
(105.5 µL, 0.59 mmol) was added via syringe. The solution was
stirred at room temperature for 2 h, during which the solution
changed from purple-red to bright red. The solvent was
removed under vacuum and the residue extracted with 10 mL
of ether. Removal of the ether via vacuum yielded pure 7 as a
red powder. Yield 282 mg, 89% (Found: C, 38.31; H, 3.49; N,
5.16. Calc. for C17H18Cl2N2O2W: C, 38.02; H, 3.38; N, 5.22%).
V/Å3
Total reflections measured
Unique reflections
µ(Mo-Kα)/mmϪ1
Goodness of fit S
R1/Reflections [I > 2σ(I)]
wR2/Reflections
Minimum, maximum peaks
in Fourier-difference map/
e ÅϪ3
3.10/2334
6.75/2475
Ϫ1.48, 0.98
4.90/2423
12.53/2685
Ϫ1.90, 2.67
* Details in common: monoclinic, space group P21/n; Z = 2; R1 =
(PhN)W(CO)2Cl2(i-C4H9NH2) 8. Complex 5 (237.5 mg, 0.54
mmol) was dissolved in 8 mL of CH2Cl2 and i-C4H9NH2 (56
µL, 0.54 mmol) was added via syringe. The solution was stirred
for 2 h, then the solvent was removed under vacuum. The
residue was extracted with ether–hexane (5:1) to yield a red
solution from which complex 8 was obtained as a red powder
upon evaporation of the solvent. Yield 184 mg, 71.7% (Found:
C, 30.57; H, 3.64; N, 6.13. Calc. for C12H16Cl2N2O2W: C, 30.34;
H, 3.40; N, 5.90%).
¹
2
Σ( Fo| Ϫ |Fc )/Σ|Fo|; wR2 = [Σw(Fo2 Ϫ Fc2)2/Σw(Fo )2]²; S = [Σw(Fo2 Ϫ
¹
Fc2)2/(n Ϫ p)]², n = number of reflections, p = number of parameters
2
2
refined; w = 1/[σ2(Fo ) ϩ (0.0370p)2 ϩ 0.31p], p = [max(Fo ,0) ϩ 2Fc2]/3.
the residue extracted with 15 mL of ether. Removal of the ether
yielded complex 10 as a sticky red solid. Yield 44 mg, 60.0%.
HRMS (FAB): (M Ϫ 2CO)ϩ, found 507.9343, calc. 507.9174.
(PhN)W(CO)Br2(PMe3)2. Dimer 4 (320 mg, 0.33 mmol) was
dissolved in 10 mL of CH2Cl2 and PMe3 (5 equivalents) was
added via syringe. The solution was stirred at room temperature
for 2 h, then the solvent was removed and the residue extracted
with ether–hexane (2:1). Removal of the solvent yielded the
complex as a purple-red solid. Yield 280 mg, 64.0%. HRMS
(FAB): (M Ϫ CO)ϩ, found 586.9229, calc. 586.9167.
[(PhN)W(CO)2Br2]2 4. Zwitterion 1 (1.95 g, 3.12 mmol) was
dissolved in 100 mL of ether and cooled to Ϫ78 ЊC, after which
a solution of Br2 in CH2Cl2 (499 mg, 3.12 mmol in 6 mL of
CH2Cl2) was added via syringe. The solution was stirred for 2 h
while the temperature was allowed to rise from Ϫ78 to Ϫ20 ЊC.
During this period some dark red sticky solid formed and the
solution changed from black to red. The reaction was allowed
to continue for 0.5 h at room temperature and the ether was
then removed by cannulation. The sticky solid was recrystal-
lized with CH2Cl2–ether (1:3 by volume). The mother liquor
was separated and the solvent removed from it by evaporation.
The residue was then washed with ether to yield dimer 4 as a red
solid. Yield 205 mg, 13.4% (Found: C, 19.47; H, 1.03; N, 2.81.
Calc. for C8H5Br2NO2W: C, 19.58; H, 1.03; N, 2.85%).
[(PhN)W(CO)2Br(I)]2. Zwitterion 1 (2.0 g, 3.20 mmol) was
dissolved in 15 mL of ether at 0 ЊC and BrI–CH2Cl2 solution
(3.20 mL, 1.0 M in CH2Cl2) was added via syringe. Reaction
occurred immediately as evidenced by a change from black to
red and the dimer began to precipitate as an orange red solid.
The solution was stirred for 2 h and the solvent then removed
by cannulation. The resulting solid was washed with ether (2
mL × 3) to yield an orange-red solid. Yield 980 mg, 57%
(Found: C, 17.83; H, 1.08; N, 2.43. Calc. for C8H5BrINO2W:
C, 17.87; H, 0.94; N, 2.61%).
(PhN)W(CO)2Br2(MeCN) 6. Zwitterion 1 (1.20 g, 1.92
mmol) was dissolved in 15 mL of ether and cooled to Ϫ78 ЊC. A
solution of Br2 in CH2Cl2 (307 mg, 1.92 mmol in 4 mL of
CH2Cl2) was added via syringe, then 2 mL of MeCN were
introduced. Within 10 min the solution changed from black to
red and red solid began to form. The solution was stirred for 2 h
while the temperature rose from Ϫ78 ЊC to room temperature
and then was stirred for 0.5 h at room temperature. The solvent
was removed by cannulation and the solid washed with ether
(2 × 5 mL) to yield complex 6 as a dark red solid. Yield 830 mg,
81.3%. HRMS (FAB): (M Ϫ CO)ϩ, found 503.8535, calc.
503.8479.
(PhN)W(CO)2Br(I)(MeCN). The above dimer (432 mg, 0.40
mmol) was dissolved in 10 mL of MeCN and the solution was
stirred at room temperature overnight, during which it became
dark red. The solvent was removed under vacuum and the resi-
due recrystallized with CH2Cl2–hexane to yield the complex as
a red solid. Yield 252 mg, 54.4%. HRMS (FAB): (M Ϫ CO)ϩ,
found, 549.8339, calc. 549.8355.
X-Ray crystallography
Crystals of complex 4 were obtained by slow recrystallization
in CH2Cl2–toluene (60:1) at Ϫ20 ЊC. Crystals of complex 3
were obtained from CH2Cl2–toluene (20:1) under similar con-
ditions. Data for both compounds were collected at 173 K on a
Siemens CCD SMART PLATFORM equipped with a CCD
area detector and a graphite monochromator utilizing Mo-Kα
radiation (λ = 0.71073 Å). Cell parameters were refined using
6121 and 5919 reflections from the bromo dimer 4 and chloro
dimer 3 data sets, respectively. A hemisphere of data (1381
frames) was collected using the ω-scan method (0.3Њ frame
width). The first 50 frames were remeasured at the end of data
collection to monitor instrument and crystal stability (max-
imum correction on I was <1%). Absorption corrections were
applied based on the ψ scan using the entire data sets.
(PhN)W(CO)2Br2(Me3C6H2NH2) 9. Complex 6 (81 mg, 0.15
mmol) was dissolved in 8 mL of CH2Cl2 and Me3C6H2NH2
(22.5 µL, 0.15 mmol) added via syringe. The solution was
stirred for 1 h, during which it changed from dark red to bright
red. The solvent was removed under vacuum and the residue
extracted with ether. Removal of the ether yielded complex 9 as
a red powder. Yield 54 mg, 57.5% (Found: C, 32.57; H, 2.65; N,
4.53. Calc. for C17H18Br2N2O2W: C, 32.62; H, 2.90; N, 4.48%).
(PhN)W(CO)2Br2(i-C4H9NH2) 10. Complex 6 (71 mg, 0.13
mmol) was dissolved in 10 mL of CH2Cl2 and i-C4H9NH2
(13.70 µL, 0.13 mmol) added via syringe. The solution was
stirred at room temperature for 2 h, during which a bright red
color developed. The solvent was removed under vacuum and
J. Chem. Soc., Dalton Trans., 1998, 3373–3378
3377

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and J. L Templeton, Organometallics, 1994, 13, 1851; L. Luan,
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7 (a) J. E. McCusker, K. A. Abboud and L. McElwee-White,
Organometallics, 1997, 16, 3863; (b) J. E. McCusker, J. Logan and
L. McElwee-White, Organometallics, in press.
8 S. W. Johnston, Y.-X. He, T. J. Anderson and L. McElwee-White,
unpublished work.
9 P. K. Baker, K. R. Flower, H. M. Naylor and K. Voigt, Polyhedron,
1993, 12, 357.
10 F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 5th
edn., Wiley-Interscience, New York, 1988, pp. 570–572.
11 F.-M. Su, J. C. Bryan, S. Jang and J. M. Mayer, Polyhedron, 1989, 8,
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13 G. M. Sheldrick, SHELXL 97, Program for the refinement of crystal
structures. University of Göttingen, 1997.
Both structures were solved by direct methods in SHELXL
97,13 and refined using full-matrix least squares on F2. The non-
H atoms were refined with anisotropic thermal parameters. All
of the H atoms were included in the final cycle of refinement
riding on the atoms to which they are bonded. A total of 128
parameters were refined in the final cycle of refinement of each
compound using 2423 and 2334 reflections for 4 and 3, respect-
ively, with I > 2σ(I) to yield R1 and wR2 of 0.049 and 0.1253
for 4 and 0.031 and 0.067 for 3. Crystallographic data are
given in Table 5.
CCDC number 186/1110.
See http://www.rsc.org/suppdata/dt/1998/3373/ for crystallo-
graphic files in .cif format.
Acknowledgements
Funding for this research was provided by the Office of Naval
Research. K. A. A. wishes to acknowledge the National Science
Foundation and the University of Florida for funding the pur-
chase of the X-ray equipment. Y. H. thanks Ms. Karen Torraca
and Ms. Jennifer McCusker for helpful discussion.
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3378
J. Chem. Soc., Dalton Trans., 1998, 3373–3378