Oxidation of the zwitterion (CO)5WNPhNPhC(OMe)Ph with I2. Formation of tungsten(IV) imido complexes and a tungsten(VI) metallacycle

Article abstract of DOI:10.1021/om950684x

Reaction of the zwitterion (CO)₅WNPhNPhC(OMe)Ph (1) with 1 equiv of I₂ produces the iodo-bridged imido dimer [(CO)₂W(NPh)I₂]₂ (2) and the imidate PhN=C(OMe)Ph. Oxidation of 1 with 2 equiv of I₂, however, leads to the formation of the unusual 16-electron tungsten(VI) metallacycle I₃(PhN)WNPhCPhO (8). The structure of 8 was determined by X-ray crystallography. Mechanistic studies on the formation of both 2 and 8 are consistent with initial iodination of the metal center of 1, followed by N-N bond cleavage to form (CO)₃W(NPh)I₂ as a common intermediate. Loss of a labile CO ligand and dimerization produces 2, while further oxidation with a second equivalent of I₂ and reaction with the side product PhN=C(OMe)Ph leads to 8 and MeI. Treatment of dimer 2 with two-electrondonor ligands results in the formation of compounds of the type (CO)₂I₂W(NPh)L, where L = THF, CH₃CN, pyridine, NEt₃, or 2,4,6-Me₃C₆H₂NH₂.

Full text of DOI:10.1021/om950684x

424
Organometallics 1996, 15, 424-428
Oxid a tion of th e Zw itter ion (CO)5WNP h NP h C(OMe)P h
w ith I2. F or m a tion of Tu n gsten (IV) Im id o Com p lexes
a n d a Tu n gsten (VI) Meta lla cycle
Nicholas D. R. Barnett, Scott T. Massey, Patrick C. McGowan, J ennifer J . Wild,
Khalil A. Abboud, and Lisa McElwee-White*
Department of Chemistry, University of Florida, Gainesville, Florida 32611
Received August 31, 1995X
Reaction of the zwitterion (CO)5WNPhNPhC(OMe)Ph (1) with 1 equiv of I2 produces the
iodo-bridged imido dimer [(CO)2W(NPh)I2]2 (2) and the imidate PhNdC(OMe)Ph. Oxida-
tion of 1 with 2 equiv of I2, however, leads to the formation of the unusual 16-electron
tungsten(VI) metallacycle I3(PhN)WNPhCPhO (8). The structure of 8 was determined by
X-ray crystallography. Mechanistic studies on the formation of both 2 and 8 are consistent
with initial iodination of the metal center of 1, followed by NsN bond cleavage to form
(CO)3W(NPh)I2 as a common intermediate. Loss of a labile CO ligand and dimerization
produces 2, while further oxidation with a second equivalent of I2 and reaction with the
side product PhNdC(OMe)Ph leads to 8 and MeI. Treatment of dimer 2 with two-electron-
donor ligands results in the formation of compounds of the type (CO)2I2W(NPh)L, where L
) THF, CH3CN, pyridine, NEt3, or 2,4,6-Me3C6H2NH2.
In tr od u ction
We recently reported the synthesis and characteriza-
tion of several tungsten(IV) imido complexes that con-
tain one and two carbonyl ligands.8 These compounds
were prepared by oxidation of the zwitterion (CO)5-
WNPhNPhC(OMe)Ph (1) with 1 equiv of I2. In this
reaction, 1 serves as a protected form of the low-valent
imido complex (CO)5WdNPh. Since the precursor
already contains five carbonyl ligands, the synthetic
difficulties of introducing multiple π-acid ligands into
a higher valent system are avoided. We now report the
extension of this strategy to the preparation of ad-
ditional compounds of the type (CO)2I2W(NPh)L. In
addition, we report further oxidation of 1 to the tung-
Interaction of the strong π-donor ligand [NR]2- with
π-acidic ligands such as CO, CNR, olefins, and acety-
lenes on a single metal center has been the focus of a
number of studies. To date, isolable metal imido
complexes of this type have been restricted to d2 species
with one1-6 and, in rare instances, two π-acidic ligands.7,8
Theoretical arguments based on the structural and
spectroscopic properties of stable complexes indicate
that both types of ligands are supported by a d2 electron
configuration where two empty d orbitals are available
for π-interactions with the [NR]2- moiety and one filled
d orbital participates in back-donation to the π-acceptor
ligand(s). When only a single π-acceptor is present,
back-donation from the filled d orbital is appreciable.
The high barriers to rotation of coordinated acetylene
and olefin ligands as well as the low carbonyl stretching
frequency in d2 imido complexes testify to the strength
of this interaction. However, in high-valent imido
complexes with multiple π-acids, back-donation from the
filled metal d orbital is significantly diminished due to
competition. This is evidenced by the high carbonyl
stretching frequencies found in tungsten(IV) complexes
containing the (RN)W(CO)2 fragment.7,8
sten(VI) metallacycle I3(PhN)WNPhCPhO.
Resu lts a n d Discu ssion
Treatment of a methylene chloride solution of the
zwitterion (CO)5WNPhNPhC(OMe)Ph (1) with 1 equiv
of I2 results in immediate effervescence as the solution
turns from black to green. Over the course of 30 min,
the green solution becomes red and the iodo-bridged
tungsten(IV) imido dimer [(CO)2W(NPh)I2]2 (2) can be
isolated (eq 1). This reaction is formally equivalent to
X Abstract published in Advance ACS Abstracts, December 1, 1995.
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162, C23-C26.
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Rickard, C. E. F. J . Chem. Soc., Chem. Commun. 1989, 1157-1159.
(d) Clark, G. R.; Nielson, A. J .; Rickard, C. E. F.; Ware, D. C. J . Chem.
Soc., Chem. Commun. 1989, 343-345.
oxidation of the transient zero-valent nitrene complex
(CO)5WdNPh, a species that is invoked in the thermal
0276-7333/96/2315-0424$12.00/0 © 1996 American Chemical Society

Formation of Tungsten(IV) Imido Complexes
Organometallics, Vol. 15, No. 1, 1996 425
Sch em e 1
the red dimer is dissolved in THF, a green solution
results. Removal of the solvent gives a green oil, which
was characterized as the THF adduct 3. Due to the
lability of the THF ligand, 3 could not be obtained in
pure form. Samples contained free THF and some
dimer 2 as an impurity. Under vacuum, complex 3 loses
THF and reverts to 2. Dimer 2 could also be quanti-
tatively converted to acetonitrile complex 4. Initially,
dimer 2 does not dissolve in acetonitrile. However, after
30 min of stirring, all of the dimer is consumed. The
acetonitrile ligand in complex 4 did not prove to be so
labile, and the complex could be cleanly isolated as a
solid. Syntheses of 5 and 6 in high yields are repre-
sentative of the reaction between dimer 2 and tertiary
amines. However, isolating the adducts of primary and
secondary amines has proven problematic. Large
amounts of the HI salt of the amine are often observed,
indicating that decomposition of the amine adduct
through loss of HI is occurring. In addition, many of
the adducts are oils that do not survive column chro-
matography, making purification difficult. Despite the
complications that arise from the reactions of primary
and secondary amines with 2, the highly hindered
amine 2,4,6-Me3C6H2NH2 produced an adduct (7) that
could be easily isolated as a solid in high yield.
The 13C NMR spectra of mononuclear complexes 3-7
each exhibit two inequivalent carbonyl signals,10 allow-
ing the assignment of the carbonyl ligands as cis. In
the case of 5, where L ) pyridine, a crystal structure
analysis has confirmed that both carbonyls are also cis
to the imido ligand.11 The 1H NMR spectra of the
adducts 3, 6, and 7, respectively, reflect the chirality of
the metal center as the â-hydrogens of the THF and
triethylamine ligands and the amine protons in the
2,4,6-Me3C6H2NH2 ligand are diastereotopic. The â-hy-
drogens of the THF ligand are a well-resolved, complex
multiplet at 4.73 ppm, and the triethylamine â-hydro-
gens are a doublet of quartets at 3.38 ppm. The
diastereotopic NH protons of the amine ligand in 7 are
seen as doublets at 6.44 and 5.51 ppm with a coupling
of 4 Hz.
decomposition of (CO)5WNPhNPhC(OMe)R (R ) Me, Ph
(1)).9 However, the first step of the oxidation reaction
cannot be the NsN bond cleavage of 1 to give PhNd
C(OMe)Ph and (CO)5WdNPh, since thermal decomposi-
tion of 1 occurs over several hours in the absence of
oxidizing agents, whereas the reaction between 1 and
I2 is complete in less than 5 s. Thus, oxidation of the
W(0) center of zwitterion 1 must be followed by rapid
NsN bond cleavage. The zwitterionic ligand of 1 may
be regarded as a protected imido functionality that is
unmasked in situ upon oxidation of the metal center.
Since oxidation of the metal center in 1 occurs before
NsN bond cleavage, the imido ligand is generated in a
higher valent complex that is more compatible with its
strongly donating nature.
The moderate yield of 2 originally reported8 (42%
based on 1) reflects difficulty in purifying the product,
rather than low conversion of 1 to 2. In a modification
of the previously described experimental procedure, a
significant improvement in the yield of 2 is achieved if
the reaction is carried out in diethyl ether. Over a
period of 1 h, dimer 2 precipitates as a bright red powder
while the PhNdC(OMe)Ph byproduct remains in solu-
tion. Filtering the reaction mixture followed by washing
with Et2O results in pure 2 in 76.5% yield.
The imido dimer 2 and complexes 3-7 belong to an
unusual class of transition-metal complexes that possess
both strong π-donor and π-acceptor ligands. Since the
imido ligand is a hard base, it prefers the empty, low-
lying d orbitals found in high-valent metal systems for
donation of electron density. However, soft π-acids such
as carbonyl ligands prefer the filled, diffuse metal d
orbitals found in low-valent metals for effective dπ-pπ
back-donation. Competition between the two carbonyl
ligands for available electrons on the d2 metal center is
reflected in the IR spectrum, where high carbonyl
stretching frequencies are found in complexes of the
type Tp′W(CO)2(NR)+,7 imido dimer 2, and monomers
3-7 (Scheme 1). To date, these are the only complexes
of this type that have been fully characterized.
The enhanced yield of dimer 2 from the simplified
synthetic procedure has enabled the preparation of 2
on a multigram scale. Dimer 2 is thus a synthetically
viable precursor to a series of mononuclear W(IV) imido
complexes. Addition of Lewis bases to 2 results in the
replacement of the weak iodide bridges to give com-
plexes of the type (CO)2I2LWNPh (Scheme 1). When
(7) (a) Pe´rez, P. J .; White, P. S.; Brookhart, M.; Templeton, J . L.
Inorg. Chem. 1994, 33, 6050-6056. (b) Powell, K. R.; Pe´rez, P. J .; Luan,
L.; Feng, S. G.; White, P. S.; Brookhart, M.; Templeton, J . L.
Organometallics 1994, 13, 1851-1864. (c) Feng, S. G.; White, P. S.;
Templeton, J . L. J . Am. Chem. Soc. 1994, 116, 8613-8620. (d) Luan,
L.; Brookhart, M.; Templeton, J . L. Organometallics 1992, 11, 1433-
1435. (e) Pe´rez, P. J .; Luan, L.; White, P. S.; Brookhart, M.; Templeton,
J . L. J . Am. Chem. Soc. 1992, 114, 7928-7929. (f) Luan, L.; White, P.
S.; Brookhart, M.; Templeton, J . L. J . Am. Chem. Soc. 1990, 112, 8190-
8192.
Oxid a tion of Zw itter ion 1 w ith 2 Equ iv of I2. In
contrast to the reaction between zwitterion 1 and 1
equiv of I2, oxidation of 1 with 2 equiv of I2 eventually
results in a blue solution from which dark metallic blue
(8) McGowan, P. C.; Massey, S. T.; Abboud, K. A.; McElwee-White,
L. J . Am. Chem. Soc. 1994, 116, 7419-7420.
(9) (a) Maxey, C. T.; Sleiman, H. F.; Massey, S. T.; McElwee-White,
L. J . Am. Chem. Soc. 1992, 114, 5153-5160. (b) Arndtsen, B. A.;
Sleiman, H. F.; Chang, A. K.; McElwee-White, L. J . Am. Chem. Soc.
1991, 113, 4871-4876. (c) Sleiman, H. F.; Mercer, S.; McElwee-White,
L. J . Am. Chem. Soc. 1989, 111, 8007-8009. (d) Sleiman, H. F.;
McElwee-White, L. J . Am. Chem. Soc. 1988, 110, 8700-8701.
(10) Only a single resonance for the carbonyls of 6 could be found
in its 13C NMR spectrum. However, on the basis of the similarity of
the IR and 1H NMR spectra of 6 to the rest of the compounds in the
series, the most reasonable conclusion is that its structure is analogous
and the 13C NMR resonances are coincidental.
(11) Massey, S. T. Ph.D. Dissertation, Stanford University, 1995.

426 Organometallics, Vol. 15, No. 1, 1996
Barnett et al.
Sch em e 2
F igu r e 1. Thermal ellipsoid drawing of compound 8.
Hydrogen atoms are omitted for clarity. Thermal ellipsoids
are drawn at the 50% probability level.
crystals are obtained. An IR spectrum of the blue
material revealed that all of the metal carbonyls had
been lost from the starting material. 1H and 13C NMR
spectra indicated three inequivalent phenyl groups, and
the 13C NMR resonance of the old imidate carbon could
1
be found at 181.7 ppm. In addition, H NMR spectra
of reaction mixtures demonstrated clean conversion of
zwitterion 1 to the blue product, and methyl iodide was
detected as the only side product. Since the lack of
carbonyl groups and additional protons other than
phenyl made spectroscopic characterization difficult, the
structure of 8 was determined by X-ray crystallography
(eq 2).
structural similarities with the recently reported Mo bis-
(carbamate) complex Mo(N-2,6-iPr2C6H3)2[NPhC(O)Ot-
Bu]2,15 which contains two Mo-N-C-O rings. The
O-Mo-N angles of 59.59(7) and 58.63(7)° are very
similar to the O1-W-N2 value of 60.1(5)° observed for
8. The Mo-N and Mo-O bond lengths of 2.103(2) and
2.381(2) Å, respectively, are again close to the analogous
values for 8.
Mech a n ism for th e F or m a tion of Dim er 2 a n d
Meta lla cycle 8. The proposed mechanism for the
formation of dimer 2 and metallacycle 8 is shown in
Scheme 2. Addition of 1 or 2 equiv of I2 to a methylene
chloride solution of zwitterion 1 results in immediate
effervescence, and the solution turns green. An IR
spectrum taken after 1 min in each reaction reveals that
all of the zwitterion 1 (νCO 2060, 1911, 1869 cm-1) has
been consumed and the imidate PhNdC(OMe)Ph (νCdN
) 1662 cm-1) has been produced. The same two
carbonyl stretches at 2082 and 2038 cm-1 are observed
in the IR spectrum of each reaction mixture at this time,
implying the same initial pathway and a common
intermediate. The green intermediate (9) was assigned
as I2(CO)3WtNPh, since the presence of two carbonyl
signals with high stretching frequencies in the IR
spectrum is consistent with a (CO)3W moiety16 with very
limited back-bonding to the carbonyl ligands. This
green intermediate slowly disappears over time with
effervescence. When only 1 equiv of I2 is reacted with
1, the carbonyl signals of dimer 2 grow in at the expense
A thermal ellipsoid diagram of 8 is shown in Figure
1. The W center has a pseudooctahedral conformation,
but it is heavily distorted due to the four-membered
W-O1-C7-N2 ring with its O1-W-N2 bond angle of
60.1(5)°. The three terminal iodide ligands have an
average bond length of 2.706 Å. As also seen in 2, the
short W-N1 bond length of 1.743(12) Å and nearly
linear W-N1-C1 angle of 174.2(9)° are indicative of a
W-N triple bond.12 Other features of interest are the
long W-N2 and W-O1 bond lengths of 2.063(14) and
2.238(11) Å, respectively.13 The O1-C7 bond length of
1.26(2) Å is intermediate between the values for a single
2-
and double Csp O bond, indicating some double-bond
(13) The average bond lengths for W-NR2 and W-OR are 1.952
and 1.900 Å, respectively: Orpen, A. G.; Brammer, L.; Allen, F. H.;
Kennard, O.; Watson, D. G.; Taylor, R. J . Chem. Soc., Dalton Trans.
1989, S1-S83.
(14) March, J . Advanced Organic Chemistry, 4th ed.; Wiley-Inter-
science: New York, 1992; p 21.
character, while the C7-N2 bond of 1.36(2) Å is in the
14
2-
range of a Csp N single bond. Complex 8 shares many
(12) (a) Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple Bonds;
Wiley-Interscience: New York, 1988; pp 145-219. (b) Wigley, D. E.
Prog. Inorg. Chem. 1994, 42, 239-482.
(15) Gibson, V. C.; Redshaw, C.; Clegg, W.; Elsegood, M. R. J . J .
Chem. Soc., Chem. Commun. 1994, 2653.

Formation of Tungsten(IV) Imido Complexes
Organometallics, Vol. 15, No. 1, 1996 427
of the green intermediate. This is consistent with loss
of a labile carbonyl ligand from I2(CO)3WtNPh to give
10, which quickly dimerizes. Note that effervescence
observed during the conversion of the green intermedi-
ate 9 to dimer 2 implies that 9 has more than two CO
ligands. This allows assignment of 9 as a (CO)3W
species instead of a cis-(CO)2W species, which would also
exhibit two strong CO stretches in the IR.
ing by providing the required electron density. This
type of interaction has been proposed for d0 zirconocene
carbonyl species, where the carbonyl stretching fre-
quency is lowered through the interaction of the π* CO
orbital with orbitals primarily associated with M-L
bonding to the ancillary ligands.19 Moreover, structural
and kinetic studies have provided convincing evidence
for three-centered bonding between the imido ligand,
the metal center, and the carbonyl π* orbital in d2 imido
complexes.3 In the case of I2(CO)3WtNPh and [I3-
(CO)2WtNPh]+, the CO π* orbitals could receive ad-
If excess I2 remains in solution after formation of the
green intermediate 9, no dimer 2 is observed during the
course of the reaction. Instead, further oxidation occurs
and PhNdC(OMe)Ph is consumed to give metallacycle
8. Additional information is provided by a control
experiment where dimer 2, which is presumably in
equilibrium with a small amount of the unsaturated
mononuclear complex 10, is reacted with 1 equiv of I2.
Addition of I2 to dimer 2 results in a cherry red solution
after 20 min. An IR spectrum demonstrates that dimer
2 has been replaced by a new organometallic species
(11) with carbonyl stretching frequencies at 2076 and
2016 cm-1. Over the course of 2 h, this species decom-
poses to give an intractable material. However, intro-
duction of PhNdC(OMe)Ph to the solutions of the red
intermediate 11 resulted in a blue solution after 20 min.
An IR spectrum confirmed that most of the imidate and
all of the intermediate had been consumed, and 1H NMR
spectroscopy showed the presence of metallacycle 8 and
MeI. Therefore, we propose that attack of I2 on 10
produces [I3(CO)2WtNPh]+ or a similar electron-poor
species as the transient red intermediate 11.17 Any
such d0 species would have extremely labile carbonyl
ligands and should also be prone to nucleophilic attack
by the imidate (which is a poor nucleophile). Note that
during formation of the metallacycle the original imi-
date methyl group is lost. The observation of MeI in
the reaction mixtures is consistent with its removal via
nucleophilic attack by I-.
The postulated intermediates I2(CO)3WtNPh and [I3-
(CO)2WtNPh]+ are highly unusual species and bear
some comment. I2(CO)3WtNPh is a d2 complex with
three competing π-acids, and [I3(CO)2WtNPh]+ is a d0
species with two π-acids. Thus, back-donation to the
metal carbonyls is expected to be extremely weak or, in
the case of [I3(CO)2WtNPh]+, nonexistent. The limited
π-back-donation in the green intermediate 9 and the red
intermediate 11 is evidenced by the high carbonyl
stretching frequencies in the IR spectrum of each, yet
clearly some donation is occurring since the frequencies
are much lower than that of free CO (νCO 2143 cm-1).
In carbonyl adducts where back-donation is not possible,
the carbonyl stretching frequencies are found to be
higher than that of free CO.18 However, the formal
oxidation state of the metal center is not an adequate
indicator of its back-bonding capability. Other ligands
on the metal may be involved in metal-carbonyl bond-
ditional electron density from the iodide ligands.
A
strong precedent exists for direct donation of electron
density from a halide pσ orbital into the π* orbitals of
cis-carbonyl ligands, an effect which is particularly
significant in iodides.20 These types of interactions may
become more pronounced in metal complexes with very
few d electrons and multiple carbonyl ligands. With
respect to the low carbonyl stretching frequencies
observed in the IR spectra for intermediates 9 and 11
(compared to free CO), a combination of electron dona-
tion from the imido ligand and iodides could weaken
the CsO π-bond to an extent that is unanticipated,
given the formal oxidation state of the metal.
Exp er im en ta l Section
Gen er a l Con sid er a t ion s. Standard inert-atmosphere
Schlenk, cannula, and glovebox techniques and freshly distilled
solvents were used in all experiments unless stated otherwise.
Diethyl ether and tetrahydrofuran were distilled from sodium/
benzophenone. Toluene was distilled over sodium. Chloro-
form, methylene chloride, and hexane were distilled over
calcium hydride. All NMR solvents were degassed by three
freeze-pump-thaw cycles and then stored in an inert-
atmosphere glovebox over 3 Å molecular sieves. All other
chemicals were purchased in reagent grade and used with no
further purification unless stated otherwise.
(CO)5WdC(OMe)Ph was prepared according to the method
of Fischer.21 cis-Azobenzene was prepared according to the
method of Cook.22 The imidate PhNdC(OMe)Ph was synthe-
sized according to the method reported by Lander.23
1H and 13C NMR spectra were recorded on a Varian Gemini
300 or a General Electric QE 300 spectrometer. IR spectra
were recorded on a Perkin-Elmer 1600 FTIR. Elemental
analysis and high-resolution mass spectrometry were per-
formed by the University of Florida analytical service.
Syn th esis of (CO)5WNP h NP h C(OMe)P h (1). The fol-
lowing procedure is a modification of the previously published
method.9a A solution of cis-azobenzene (2.00 g, 11.0 mmol) in
50 mL of hexane was added to a solution of (CO)5WdC(OMe)-
Ph (4.86 g, 11.0 mmol) in 50 mL of hexane. The solution
immediately turned dark greenish black. After 5 min of
stirring at room temperature an additional 100 mL of hexane
was introduced and the reaction mixture cooled to -30 °C for
12 h. Zwitterion 1 precipitated out of solution as a fine black
powder (4.73 g, 79% yield) which was collected by filtration
and washed with 3 × 20 mL aliquots of cold hexane. 1H NMR
(19) (a) Antonelli, D. M.; Tjaden, E. B.; Stryker, J . M. Organome-
tallics 1994, 13, 763-765. (b) Guo, Z.; Swenson, D. C.; Guram, A. S.;
J ordan, R. F. Organometallics 1994, 13, 766-773. (c) Marsella, J . A.;
Curtis, C. J .; Bercaw, J . E.; Caulton, K. G. J . Am. Chem. Soc. 1980,
102, 7244-7246.
(20) (a) Kostic´, N. M.; Fenske, R. F. Organometallics 1982, 1, 489-
496. (b) Hall, M. B.; Fenske, R. F. Inorg. Chem. 1972, 11, 1619-1624.
(c) J ernigan, R. T.; Brown, R. A.; Dobson, G. R. J . Coord. Chem. 1972,
2, 47-52. (d) Keeling, G.; Kettle, S. F. A.; Paul, I. J . Chem. Soc. A
1971, 3143-3147. (e) Fenske, R. F.; DeKock, R. L. Inorg. Chem. 1970,
9, 1053-1060.
(21) Fischer, E. O.; Maasbo¨l, A. Chem. Ber. 1967, 100, 2445-2456.
(22) Cook, A. H. J . Chem. Soc. 1938, 876-881.
(23) Lander, G. D. J . Chem. Soc. 1902, 591-598.
(16) (a) Orgel, L. E. Inorg. Chem. 1962, 1, 25-29. (b) Cotton, F. A.;
Kraihanzel, C. S. J . Am. Chem. Soc. 1962, 84, 4432-4438.
(17) Note that other species such as an I2 complex of the unsaturated
species 10 or an I3 complex would also be consistent with the IR
spectral data.
(18) (a) Hurlburt, P. K.; Rack, J . J .; Dec, S. F.; Anderson, O. P.;
Strauss, S. H. Inorg. Chem., 1993, 32, 373-374. (b) Willner, H.;
Schaebs, J .; Hwang, G.; Mistry, F.; J ones, R.; Trotter, J .; Aubke, F. J .
Am. Chem. Soc., 1992, 114, 8972-8980. (c) Hurlburt, P. K.; Anderson,
O. P.; Strauss, S. H. J . Am. Chem. Soc., 1991, 113, 6277-6278. (d)
Willner, H.; Aubke, F. Inorg. Chem., 1990, 29, 2195-2200. (e) Calder-
azzo, F. J . Organomet. Chem., 1990, 400, 303-320. (f) Tevault, D.;
Nakamoto, K. Inorg. Chem. 1976, 15, 1282-1287.
-

428 Organometallics, Vol. 15, No. 1, 1996
Barnett et al.
(CDCl3): δ 7.62 (m, 2H), 7.55 (m, 3H), 7.46 (m, 3H), 7.38 (m,
2H), 6.99 (t, 2H), 6.61 (d, 2H), 6.46 (t, 1H), 3.81 (s, OMe, 3H).
13C NMR (CDCl3, -20 °C): δ 203.16 (trans CO), 198.46 (cis
CO), 171.97 (CdN), 160.34, 139.47, 132.73, 130.64, 129.71,
128.71, 128.65, 126.32, 125.50, 125.44, 115.48, 114.73 (Ph),
61.78 (OMe). IR (CH2Cl2): νWCO 2060, 1911, 1869 cm-1. Anal.
Calcd for C25H18N2O6W: C, 47.95; H, 2.90; N, 4.47. Found:
C, 48.19; H, 2.81; N, 4.38.
Syn th esis of [(CO)2W(NP h )I2]2 (2). A solution of I2 (1.65
g, 6.05 mmol) in 15 mL of dry ether was quickly added via
cannula to a freshly prepared solution of 4.00 g (6.39 mmol)
of zwitterion 1 in 40 mL of ether. The reaction mixture
immediately began to effervesce and turned green. After 10-
15 min of stirring, the red dimer 2 began to precipitate. The
reaction mixture was stirred for 2 h, and then dimer 2 was
collected as a fine red powder by filtration and washed with 2
× 10 mL of ether (2.86 g, 76.5% yield). Spectral data for 2
prepared in this manner are identical with those obtained on
samples prepared as originally reported.8
ν
CO 2064, 1984 cm-1
.
1H NMR (CDCl3): δ 7.38 (t, 1H), 7.15 (t,
2H), 6.81 (m, 4H), 6.45 (d, 1H, NH), 5.62 (d, 1H, NH), 2.43 (s,
6H, o-Me), 2.27 (s, 3H, p-Me). 13C NMR (CDCl3): δ 209.1,
207.2 (CO), 139.3, 135.4, 129.2, 129.1, 129.0, 127.0, 124.8, 20.6,
19.0. Anal. Calcd for C17H18I2N2O2W: C, 28.50; H, 2.50; N,
3.91. Found: C, 28.30; H, 2.44; N, 3.73.
Syn th esis of I3(P h N)WNP h CP h O (8). To a stirred solu-
tion of zwitterion 1 (1.00 g, 1.60 mmol) in 20 mL of CH2Cl2
was added 2 equiv of I2 (0.81 g, 3.20 mmol) in 10 mL of CH2-
Cl2. Immediate effervescence was observed, and the solution
became green. After approximately 20-30 min the solution
had undergone a color change from dark green to dark blue.
The solvent and methyl iodide were removed under vacuum,
and a dark blue microcrystalline powder was obtained (1.29
g, 95% yield). X-ray-quality crystals were obtained by redis-
solving the blue powder in a minimum amount of CH2Cl2,
cooling the solution to -40 °C for a period of 1 week, and
isolating the crystals by filtration. 1H NMR (CDCl3): δ 7.65
(m, 5H), 7.30 (m, 5H), 7.12 (m, 2H), 6.98 (m, 3H). 13C NMR
(CDCl3): δ 181.7, 149.8, 145.5, 134.4, 133.4, 130.5, 129.9, 129.4,
128.8, 128.0, 127.3, 121.9. Anal. Calcd for C19H15I3N2OW: C,
26.76; H, 1.76; N, 3.28. Found: C, 26.37; H, 1.55; N, 2.60.
Rea ction of Zw itter ion 1 w ith 1.25 Equ iv of I2. I2 (25
mg, 0.10 mmol) was dissolved in 15 mL of CHCl3 and added
to 50 mg (0.080 mmol) of zwitterion 1. Immediate efferves-
cence was observed, and the reaction mixture turned green.
An IR spectrum taken after 1 min showed that zwitterion 1
(νCO 2060, 1911, 1869 cm-1) had been completely consumed
and large amounts of imidate (νCdN ) 1662 cm-1) had been
produced. Carbonyl signals at 2082 and 2038 cm-1 were
observed at that time. IR spectra taken periodically over 3 h
showed that the carbonyl stretching frequencies for dimer 2
grow in at the expense of the green intermediate (νCO 2082,
2038 cm-1).
Rea ction of Zw itter ion 1 w ith 2.5 Equ iv of I2. I2 (50
mg, 0.20 mmol) was dissolved in 20 mL of CHCl3 and added
to 50 mg (0.080 mmol) of zwitterion. Immediate effervescence
was observed, and the reaction mixture turned green. An IR
spectrum taken after 1 min showed that zwitterion 1 (νCO 2060,
1911, 1869 cm-1) had been completely consumed and large
amounts of imidate (νCdN ) 1662 cm-1) had been produced.
Carbonyl signals at 2082 and 2038 cm-1 were observed at that
time. After 10 min, the carbonyl and imidate signals had
disappeared.
Rea ction of Dim er 2 w ith I2, F ollow ed by Ad d ition of
P h NdC(OMe)P h . Dimer 2 (100 mg, 0.086 mmol) was dis-
solved in 5 mL of CH2Cl2. I2 (45 mg, 0.18 mmol) was added
with stirring. Over 20 min, the solution became cherry red.
An IR spectrum of the solution taken at that time revealed
that dimer 2 had been completely consumed, and two new car-
bonyl signals at 2076 and 2016 cm-1 were present. Addition
of 37 mg (0.18 mmol) of PhNdC(OMe)Ph resulted in a deep
blue solution after 20 min. An IR spectrum taken at that time
demonstrated that much of the imidate had been consumed.
The solvent was removed, and 1H NMR spectroscopy of the
residue showed the presence of metallacycle 8 and methyl
iodide.
Syn th esis of W(NP h )I2(CO)2(THF ) (3). Dimer 2 (300 mg,
0.258 mmol) was dissolved in 5 mL of THF to give a green
solution, which was stirred for 2 h. Removal of the solvent
gave a green oil which was contaminated with some THF and
2. Attempts to remove the free THF under vacuum led to
increased amounts of 2. IR (CH2Cl2): νCO 2066, 1988 cm-1
.
1H NMR (CDCl3): δ 7.70-7.20 (m, Ph), 4.73 (m, THF), 2.14
(dt, THF). 13C NMR (CDCl3): δ 212.7 (CO, J WC ) 173.6 Hz),
207.0 (CO, J WC ) 168.6 Hz), 153.2, 129.5, 129.2, 124.8 (Ph),
81.1, 26.6 (THF).
Syn th esis of W(NP h )I2(CO)2(CH3CN) (4). Dimer 2 (2.33
g, 2.00 mmol) was added to 105 mL of CH3CN. The dimer is
initially insoluble but eventually disappears after 30 min of
stirring to give a dark green solution. The solution was stirred
for an additional 8 h; then the solvent was removed under
vacuum to give 4 as a pure solid in 93% yield (2.17 g). IR
(CH2Cl2): νCO 2072, 2003 cm-1
.
1H NMR (CDCl3): δ 7.60-
7.20 (m, 5H, Ph), 2.78 (s, 3H, Me). 13C NMR (CDCl3): δ 206.4,
203.0 (CO), 135.0, 129.9, 129.2, 125.0, 103.4, 4.6 (Me). HRMS
(FAB): found 597.8228 (M+ - CO), calcd 597.8234.
Syn th esis of W(NP h )I2(CO)2(p y) (5). To a stirred solu-
tion of 2 (0.939 g, 0.803 mmol) in CH2Cl2 (25 mL) was added
2 equiv of pyridine (0.13 mL, 1.6 mmol). After 20 min, the
solution had changed from red to a red/green dichroic solution.
After 2 h, the solution was reduced to about 10 mL and toluene
(20 mL) was added. Upon addition of hexane to the solution,
5 precipitated as a green solid (0.746 g, 70% yield). IR (CH2-
Cl2): νCO 2068, 1992 cm-1 1H NMR (CDCl3): δ 9.40 (dd, 2H),
.
7.94 (tt, 2H), 7.51 (m, 3H), 7.27 (m, 3H). 13C NMR (CDCl3):
208.3, 207.6, 154.9, 153.1, 139.5, 129.5, 129.2, 125.7, 124.8.
Anal. Calcd for C13H10I2N2O2W: C, 23.52; H, 1.52; N, 4.22.
Found: C, 23.80; H, 1.53; N, 4.21.
Syn th esis of W(NP h )I2(CO)2(NEt3) (6). Dimer 2 (2.52 g,
2.16 mmol) was dissolved in 30 mL of THF, and then 1.20 mL
(8.61 mmol) of triethylamine was added and the mixture
stirred overnight. Removal of the solvent and excess trieth-
ylamine gave a green oil, which became a solid under high
vacuum (crude yield: 95%). The residue was taken up in 20
mL of CH2Cl2, and hexane (25 mL) was added to precipitate 6
as a red/black solid which was isolated by filtration in 70%
Ack n ow led gm en t. Funding for this work was pro-
vided by the Office of Naval Research. We thank
Desmond Man Lung Kwan for preliminary experiments
on complex 5.
yield (2.03 g). IR (CH2Cl2): νCO 2058, 1984 cm-1
.
1H NMR
(CDCl3): δ 7.5-7.1 (5H, Ph), 3.38 (dq, 6H, CH2), 1.39 (t, 9H,
CH3). 13C NMR (CDCl3): δ 208.3 (2 CO, coincident), 155.1,
129.2, 128.1, 124.1 (Ph), 65.8, 15.3 (Et). HRMS (FAB): found
657.9167 (M+ - CO), calcd 657.9158.
Syn th esis of W(NP h )I2(CO)2(2,3,5-Me3C6H2NH2) (7). To
a stirred solution of dimer 2 (2.00 g, 1.72 mmol) was added 2
equiv of 2,4,6-trimethylaniline (0.51 mL, 3.4 mmol). After
about 5 min, a color change from red to dark purple had
occurred. The CH2Cl2 was then removed under vacuum, and
the resulting dark red powder (1.42 g, 91% yield) was washed
with 50 mL of hexane, followed by 25 mL of 1:1 ether/hexane.
The resulting powder was isolated by filtration. IR (CH2Cl2):
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data, bond distances, bond angles, positional pa-
rameters, and anisotropic displacement parameters for 8 (7
pages). This material is contained in many libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, can be ordered from the ACS, and can
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OM950684X