Synthesis and isocyanate insertion reactions of tungsten(IV) imido complexes formed from W(CO)(acac)(N3)(PMe3)3 with azide as the oxidant

Article abstract of DOI:10.1016/j.ica.2010.10.032

Addition of excess trimethylphosphine and a halide source to a solution of W(CO)(acac)₂(η²-L) (L = NCPh and OCMe₂) leads to displacement of L and one acetylacetonate chelate to produce electron-rich, seven-coordinate complexes of the formula W(CO)(acac)(X)(PMe ₃)₃ (X = Cl, Br, and I). Use of NaN₃ instead of a halide source leads primarily to loss of carbon monoxide and dinitrogen, and protonation from adventitious water yields the cationic imido complex [W(NH)(acac)(PMe₃)₃]⁺. Heating [W(NH)(acac)(PMe₃)₃]⁺ in aromatic isocyanates at high temperature results in isocyanate insertion into the NH imido bond to form new C-N bonds. An alternate route to related imido complexes involves heating [W(O)(acac)(PMe₃)₃]⁺ with phenyl isocyanate at high temperatures to yield the substituted imido complex [W(NPh)(acac)(PMe₃)₃]⁺.

Full text of DOI:10.1016/j.ica.2010.10.032

Inorganica Chimica Acta 369 (2011) 19–31
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Synthesis and isocyanate insertion reactions of tungsten(IV) imido
complexes formed from W(CO)(acac)(N3)(PMe3)3 with azide as the oxidant
⇑
Chetna Khosla, Andrew B. Jackson, Peter S. White, Joseph L. Templeton
W.R. Kenan Laboratory, Department of Chemistry, University of North Carolina, Chapel Hill, NC 27599-3290, United States
a r t i c l e i n f o
a b s t r a c t
a halide source to a solution of W(CO)(acac)2(g
2-L)
Article history:
Available online 8 January 2011
Addition of excess trimethylphosphine and
(L = N„CPh and O@CMe2) leads to displacement of L and one acetylacetonate chelate to produce elec-
tron-rich, seven-coordinate complexes of the formula W(CO)(acac)(X)(PMe3)3 (X = Cl, Br, and I). Use of
NaN3 instead of a halide source leads primarily to loss of carbon monoxide and dinitrogen, and proton-
ation from adventitious water yields the cationic imido complex [W(NH)(acac)(PMe3)3]+. Heating
[W(NH)(acac)(PMe3)3]+ in aromatic isocyanates at high temperature results in isocyanate insertion into
the NH imido bond to form new C–N bonds. An alternate route to related imido complexes involves heat-
ing [W(O)(acac)(PMe3)3]+ with phenyl isocyanate at high temperatures to yield the substituted imido
complex [W(NPh)(acac)(PMe3)3]+.
This manuscript is submitted in recognition
of the outstanding ongoing contributions,
both professional and personal, of Robert
Bergman to the international
organometallic community.
Keywords:
Organometallic synthesis
Insertion chemistry
X-ray crystal structure
Tungsten imido chemistry
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
leads to substitution of the g
2-nitrile ligand and loss of one acac li-
gand, and in the presence of [X]ꢀ the putative [W(acac)(-
CO)(PMe3)3]+ fragment leads to neutral W(acac)(CO)(PMe3)3X
products. When azide is the added Xꢀ anion, three products can
be identified. One is the seven-coordinate analog of the halide
complexes, but the other two products reflect oxidation of W(II)
and loss of N2 from the [N3]ꢀ ligand. No simple terminal tungsten
nitride complex has been isolated, but the products derived from a
nucleophilic W„N: moiety include a protonated metal product
[W(„NH)(acac)(PMe3)3]+, and an unsymmetrical dinuclear com-
plex [(acac)(PMe3)2(OC)W„N–W(acac)(PMe3)2(CO)2]. An alterna-
tive route to monomeric tungsten(IV) imido products is available
Tungsten chemistry is rich with W(0) d6 complexes, many de-
rived from W(CO)6, and W(VI) d0 provides the other oxidation state
bookend for tungsten, with [WO4]2ꢀ as the progenitor complex [1–
5]. Thus W(0) and W(VI) complexes set boundary markers for
accessible intermediate oxidation state tungsten complexes. In
six-coordinate tungsten complexes there are opportunities for
bonding both to and from the metal when the d orbitals are par-
tially filled: for diamagnetic complexes the choices are either W(II)
d4 or W(IV) d2 [6]. Here we utilize bis(acetylacetonato)tungsten(II)
derivatives as reagents and explore both substitution and oxida-
tion reactions.
p-
p
in two steps from the reaction of W(„O)(g
2-N„CR)(acac)2 with
We have reported diverse reaction chemistry accessible to
tungsten(II)bis(acetylacetonate) complexes [7–10]. The W(CO)(a-
cac)2 (acac = acetylacetonato) fragment serves as a docking site
for ligands capable of providing four-electrons to the metal center.
PMe3 to form W(„O)(acac)(PMe3)3 followed by reaction with phe-
nyl isocyanate to generate the phenylimido derivative
[W(„NPh)(acac)(PMe3)3]+. The parent imido complex [W(„NH)
(acac)(PMe3)3]+, reacts with arylisocyanate reagents to form inser-
tion products reflecting H–N addition across the isocyanate N„C
bond to form amide linkages. Products of single and double inser-
tion of ArNCO have been isolated and characterized.
Like alkynes, nitriles also bind through both
through the nitrogen lone pair. Imines, ketones, and aldehydes
bind through both a C@X -bonding electron pair and a hetero-
p-bonds rather than
p
atom lone pair (X = O and NR) [7,8].
We now report that six-coordinate bis(acac)tungsten(II) re-
agents provide access to seven-coordinate, eighteen-electron com-
plexes upon substitution of the four-electron donor
2. Results and discussion
g
2-nitrile
2.1. Displacement of g
2-nitrile by isonitrile
ligand by isonitrile donors. In contrast, added trimethylphospine
Addition of two equivalents of tert-butyl isonitrile to
W(CO)(acac)2(
2-PhC„N) (1-PhC„N) results in displacement of
the
2-bound nitrile to form W(CO)(acac)2(tBuN„C)2 (2) (Eq.
⇑
g
Corresponding author. Fax: +1 919 843 8005.
E-mail address: joetemp@unc.edu (J.L. Templeton).
g
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.10.032

20
C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
(1)) [11]. A color change from amber to orange-red is noted
within minutes of isonitrile addition. In situ IR spectroscopy
at 142°. The two isonitrile ligands are cis to one another and
the bending may be due to steric interference since the isonitrile
ligands bend away from one another. The average tungsten-oxy-
gen bond length for 2 is 2.14 Å, slightly elongated relative to six-
coordinate bis(acac)tungsten structures (near 2.10 Å) in accord
with expectations for a crowded seven-coordinate molecule.
shows
a drop in frequency for the lone CO ligand (from
1895 cmꢀ1 to 1850 cmꢀ1), indicative of increased electron den-
sity at the metal center. For the metal-containing product, no
aromatic PhC„N protons are detected by NMR spectroscopy,
as the 1H NMR spectrum displays only three peaks at room tem-
perature: one for the two acac methine signals, one for the four
2.2. Displacement of nitrile by trimethylphosphine
t
acac methyl groups, and one for the two Bu groups. The decep-
tive simplicity of the spectrum at room temperature suggests
fluxionality, a common phenomenon for seven-coordinate com-
plexes. Low temperature NMR studies confirm the fluxionality
of 2. Each of the three proton signals decoalesces as the temper-
ature is lowered and at 210 K a total of eight separate reso-
nances are evident: two for the acac methines, four for the
Prompted by the results of g
2-nitrile displacement by two isoni-
trile ligands, trimethylphosphine was added to a methylene chlo-
ride solution of 1-PhC„N causing an immediate color change
from amber to orange. A solution IR spectrum after 10 min shows
loss of the starting material CO absorbance at 1895 cmꢀ1. After
stirring overnight an absorbance assigned to coordinated CO is
present at 1748 cmꢀ1; this low frequency is in the range for a CO
ligand bound to an electron rich metal center [12,13] and implies
that the product is not W(CO)(acac)2(PMe3)2. A 1H NMR spectrum
of the product indicates the presence of only one acac ligand with
equivalent acac methyl groups. Two trimethylphosphine 1H NMR
signals appear, one as a doublet and the other as a second order
pseudo-doublet integrating in a 9:18 ratio and compatible with a
W(acac)(PMe3)(PMe3)2 stoichiometry. The 31P NMR spectrum dis-
plays a doublet and a triplet with tungsten satellites of 269 Hz
and 315 Hz, respectively. These NMR data indicate a tris(trimethyl-
phosphine) product with two NMR equivalent PMe3 ligands [12–
14]. The 13C NMR spectrum exhibits a carbon monoxide signal at
290 ppm split into a doublet of triplets. The two trimethylphos-
phine methyl signals in the 13C NMR spectrum resonate as a dou-
blet and a doublet of triplets in a 1:2 ratio. Combining this spectral
information led us to formulate a monomeric tris(trimethylphos-
phine) product containing at least two equivalent trimethylphos-
phine groups, one acac ligand, and one carbonyl ligand [12,13].
t
acac methyl groups, and two for the isonitrile Bu groups.
ð1Þ
The solid-state structure of complex 2 shows two acac che-
lates and one carbonyl in the coordination sphere of the tung-
sten atom (Fig. 1). In addition, two tert-butyl isonitrile ligands
are
r-bound to the tungsten in place of the g
2-nitrile present
in the reagent. This seven-coordinate molecule possesses a sim-
ilar structure to geometries reported for W(CO)3(acac)2 and
W(CO)2(acac)2(PR3) [7]. The two isonitrile ligands and lone car-
bonyl ligand create a tripod with the tungsten atom as the ver-
tex, and this tripod has two sides with acute angles (72° and 76°
for the two C–W–C angles involving isonitrile carbon C9, and
one obtuse angle (the C1–W–C3 angle is 103°). Both isonitrile li-
gands are significantly distorted from linearity: the C3–N4–C5
angle is 164°, while the C9–N10–C11 angle is bent even more
A
solid-state structure revealed formation of W(CO)(a-
cac)(Cl)(PMe3)3 (3-Cl), with three trimethylphosphine groups and
a chloride ion in place of the original
2-nitrile ligand and an acac
g
chelate from 1-PhC„N. The methylene chloride solvent is presum-
ably the source of the Cl- ligand, but a more efficient synthesis of 3-
Cl was desirable, so a variety of reaction conditions were screened.
Addition of NaCl to the reaction solution to provide a Cl- source in
CH3CN produces 3-Cl in good yields (Eq. (2)). The product 3-Cl is
extracted with hexanes and filtered through a medium-porosity
glass frit to yield clean material. This synthetic method can be ex-
panded to use sodium bromide or sodium iodide salts as reagents
(Eq. (2)). Likewise addition of KSCN and PMe3 to 1-PhC„N pro-
duces
a seven-coordinate tungsten complex (3-SCN); a C–N
stretching frequency of 2093 cmꢀ1 indicates an S-bound thiocya-
nate ligand [15]. All of these complexes exhibit a characteristically
low frequency CO absorbance in the IR spectrum around
1760 cmꢀ1. These frequencies are consistent with M(CO)(PR3)3
fragments in the literature [12,13]. Electron-rich trialkylphosphine
ligands push electron density to the metal center and promote
stronger backbonding to CO resulting in a low CO frequency. For
all complexes of the form W(CO)(acac)(X)(PMe3)3, the NMR spectra
are similar to data described for 3-Cl.
ð2Þ
Fig. 1. ORTEP diagram of W(CO)(acac)2(tBuN„C)2 (2). Thermal ellipsoids
are displayed with 50% probability. Hydrogen atoms are omitted for clarity.
Selected interatomic distances (Å) and bond angles (°): W1–C1 = 2.943(2),
W1–C9 = 2.049(2), W1–C3 = 2.087(2), W1–O26 = 2.130(1), W1–O22 = 2.130(1),
W1–O15 = 2.137(1), W1–O19 = 2.163(1), O26–W1–O22 = 80.56(4), O15–W1–
O19 = 87.39(4), C3–N4–C5 = 163.7(2), C9–N10–C11 = 142.2(2).

C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
21
The solid-state structure of 3-Cl shows a tungsten complex with
three phosphine groups oriented in a distorted meridional geome-
try around the seven-coordinate metal center (Fig. 2). A mirror
plane passing through one PMe3 ligand also contains CO and Cl,
and bisects the acac ligand. The two remaining phosphine ligands
are related by the mirror plane rendering them equivalent as ob-
served by NMR spectroscopy. The tungsten–phosphine bond
lengths are similar, averaging 2.44 Å. The W1–C1 bond length is
1.91 Å, typical for a tungsten carbonyl W–C linkage [13].
A number of seven-coordinate dicarbonyl acetylacetonate tung-
sten(II) complexes with the formula W(acac)(PR3)2(X)(CO)2 (X = Iꢀ,
Brꢀ, and Clꢀ) have been reported [16–18]. These complexes possess
IR absorbances in the range of 1800–1950 cmꢀ1 for the two car-
bonyl ligands, significantly higher than the lone CO frequency near
1760 cmꢀ1 observed for W(acac)(PR3)3(X)(CO) complexes, 3-X.
Although the preparative route utilized here differs dramatically
from earlier synthetic methods, the net result corresponds to sim-
ple CO replacement by PR3 relative to the complexes previously
reported.
2.3. Addition of sodium azide
Fig. 2. ORTEP diagram of W(CO)(acac)(Cl)(PMe3)3 (3-Cl). Thermal ellipsoids are
displayed with 50% probability. Hydrogen atoms are omitted for clarity. Selected
interatomic distances (Å) and bond angles (°): W1–C1 = 1.913(2), W1–
P1 = 2.437(5), W1–P2 = 2.456(5), W1–P3 = 2.439(5), W1–O7 = 2.144(1), W1–
O3 = 2.154(1), W1–Cl1 = 2.565(5), O7–W1–O3 = 82.81(5).
To explore the reactivity of the seven-coordinate tungsten com-
plexes, W(CO)(acac)(I)(PMe3)3 (3-I) was stirred in CH2Cl2 with
NaCl leading to exchange of iodide ligand for chloride to form 3-
Cl. However, addition of NaN3 to a CH3CN solution of 3-I does
not produce the expected simple exchange product W(CO)(a-
cac)(N3)(PMe3)3 (3-N3). Rather oxidation of tungsten and loss of
N2 is accompanied by proton addition to form a cationic imido-
tungsten(IV) product, [W(NH)(acac)(PMe3)3][I] (4-NH[I]) (Eq. (3)).
The proton on the added nitrogen presumably originates from
adventitious water. Sodium azide is known to produce imido prod-
ucts under aqueous conditions [19,20].
ð3Þ
The 1H NMR spectrum of 4-NH[I] displays one acac chelate with
inequivalent methyl groups, as opposed to the equivalent methyl
groups found in 3-I. The trimethylphosphine signals resonate as
a doublet corresponding to one PMe3 (2JP–H = 9 Hz) and a virtual
triplet (2JP–H = 4 Hz) corresponding to two PMe3 groups, consistent
with a meridional geometry for the three phosphine ligands
[14,21,22]. A broad singlet at 8.84 ppm is assigned as the imido
proton. The 31P NMR spectrum displays two singlets in a 2:1 ratio
with tungsten satellites of 310 and 410 Hz, respectively, as op-
posed to the doublet and triplet seen for the precursor complex.
In other words, 2JPP is too small for resolution in the cationic imido
complex, a phenomenon that has been noted in analogous carbyne
species [23–25]. The 13C NMR spectrum displays the trimethyl-
phosphine signals as a doublet and a triplet in a 1:2 intensity ratio.
The presence of hydrogen on the multiply-bound nitrogen atom is
confirmed by an intense and well-defined IR absorbance at
3161 cmꢀ1, indicative of an NH moiety.
The solid-state structure of 4-NH[I] as revealed by a single crys-
tal X-ray diffraction analysis confirms the meridional geometry of
the three phosphine ligands (Fig. 3). The imido hydrogen was not
located on the difference map. A mirror plane that contains the
acac chelate, one trimethylphosphine ligand, and the imido group
is easy to visualize. The two remaining phosphine ligands are re-
lated by the mirror plane. The W1–N1 bond length is 1.76 Å, a dis-
Fig. 3. ORTEP diagram of [W(NH)(acac)(PMe3)3][I], 4-NH[I]. Thermal ellipsoids are
drawn with 50% probability. Iodide counterion and hydrogen atoms omitted for
clarity. Selected interatomic distances (Å) and bond angles (°): W1–N1 = 1.757(5),
W1–P1 = 2.506(1), W1–P2 = 2.513(1), W1–P3 = 2.452(1), W1–O2 = 2.107(3), W1–
O6 = 2.076(4), O2–W1–O6 = 82.57(14).
tance indicative of a multiply-bound NH ligand [5,26–28]. The
tungsten-phosphine bond lengths differ somewhat in 4-NH[I].
The W1–P1 bond length is 2.51 Å, close to the W1–P2 bond length
of 2.51 Å. The phosphine ligand trans to the acac chelate, P3, has a
shorter W–P bond length of 2.45 Å. The W1–O2 bond length for the
oxygen trans to the imido ligand, is 2.11 Å, while the W1–O6 bond
length is 2.08 Å, with the longer W–O bond consistent with the
trans influence of the imido ligand.
To investigate the reactivity of the isolated imido complex, a
more efficient synthetic method was needed for preparation of 4-
NH. The use of photolysis to increase the rate of N2 loss from coor-

22
C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
dinated azides is well documented [5,27,28], and indeed if 3-I is
combined with NaN3 in CH3CN and photolyzed for 1 h, reasonably
clean 4-NH[I] forms. A method starting from 1-Me2C@O rather
than 3-I was desired. Stirring a mixture of 1-Me2C@O, NaN3,
PMe3, and NaBF4 in CH3CN overnight produces 4-NH[BF4] and a
small amount of 3-N3 on a 50 mg scale (Eq. (4)). The two products
are easily separated with hexanes extraction to remove 3-N3. Com-
pound 3-N3 possesses 1H, 31P, and 13C NMR spectral characteristics
similar to that of complex 3-I. The use of IR spectroscopy confirms
an absorbance at 2061 cmꢀ1, corresponding to an N3 ligand, thus
indicating production of W(CO)(acac)(N3)(PMe3)3 [29].
a W(II) d4 center. The two tungsten metal centers are linked by a
single bridging nitrido ligand. The W(IV) tungsten center
contains an acac chelate, one CO ligand, and two trimethylphos-
phine ligands in the coordination sphere such that an octahedral
geometry results when the N atom is included. The W(II) atom is
bound to one acac ligand, two CO ligands, and two trimethylphos-
phine groups to build a seven-coordinate environment. The W1–
N19 bond length, from W(II) to N3ꢀ, is 2.11 Å while the W2–N19
bond length, from W(IV) to N3ꢀ, is 1.75 Å, indicating a single bond
to W1 and a triple bond from the nitrogen to W2 [30,31]. The
W–N–W angle is nearly linear at 174°.
However, a large-scale synthesis (700 mg) produces a mixture
of 3-N3, 4-NH[BF4], and a third product as assessed by 1H and
31P NMR spectroscopy (Eq. (4)). After 3-N3 is collected as the solu-
ble metal product with a hexanes wash, the two hexanes-insoluble
products remaining in the residue can be chromatographed on alu-
mina with a solvent mixture of 5% CH3CN in CH2Cl2 to separate 4-
NH[BF4] from the unknown product which elutes first as an orange
fraction. Increasing the concentration of CH3CN then elutes 4-
NH[BF4] as a distinct red band.
An effective mirror plane exists containing the acac chelate
on W2, both tungsten centers, the central nitrogen atom, and
the two phosphine groups of the W1 d4 center. The acac ligand
on the W(II) center is perpendicular to the mirror plane, thus
rendering the two acac methyl groups equivalent. The two phos-
phines on W(II) differ dramatically since one is trans to the acac
ligand and the other is trans to the N3ꢀ bridge. This difference is
not observed on the NMR time scale, thus suggesting inter-
change of the phosphine ligands by an intramolecular fluxional
process. On the W(IV) center, the mirror plane contains the acac
ligand, placing these two acac methyl groups in different envi-
ronments. The trimethylphosphine groups on the W(IV) center
are also related to each other by the mirror plane. The strong
trans influence of the nitrido ligand is seen in the dissimilar
tungsten-oxygen bond lengths for the acac chelate, as in 4-
NH[I]. The W2–O22 bond length, with oxygen trans to nitride,
is 2.19 Å while W2–O26 is 2.09 Å.
The mechanism for conversion of 1-Me2C@O to 4-NH has not
been elucidated, but some of the reaction conditions that promote
formation of 4-NH deserve mention. First, trials with photolysis to
produce 4-NH do not yield either 3-N3 or dinuclear complex 5,
even in large scale reactions. Second, both 3-N3 and 5 convert to
4-NH when dissolved in moist organic solvents and exposed to
light, although the conversion is neither rapid nor complete. Third,
dry reaction conditions do not produce 3-N3 or 5, but instead yield
decomposition products. These limited results are consistent with
binding of trimethylphosphine and [N3]- to 1-Me2C@O with loss of
acetone and acac, followed by ꢀrelease of CO from the coordination
sphere and loss of N2 from N3 to form an unstable nitrido inter-
mediate. Carbon monoxide loss and dinitrogen release are acceler-
ated by photolysis. The nucleophilic nitrido species may react with
Identification of the complex in the orange fraction was first at-
tempted with spectroscopic methods. In situ IR spectroscopy, sur-
prisingly, shows three CO absorbances (1825, 1914, and
1951 cmꢀ1). In the 1H NMR spectrum, two distinct acac methine sig-
nals indicate two different acac environments, and the acac methyl
signals resonate in a 3:6:3 ratio, suggestive of a symmetry element.
Two trimethylphosphine 1H methyl signals are present, each inte-
grating for six protons or two PMe3 groups. One signal is a ‘‘filled-
in’’ triplet, indicating second-order coupling effects from two phos-
phine ligands. The second signal appears as a triplet. In the 13C NMR
spectrum, two signals appear far downfield, each assigned as a car-
bon monoxide resonance. One of these signals resonates as a triplet
at 246 ppm, clearly a carbon monoxide group coupled to two equiv-
alent phosphine ligands, while the other signal at 257 ppm resolves
as a weak, broad singlet. The downfield acac CO resonances are dis-
played in a 2:1:1 ratio, as are the upfield acac methyl groups. The 31
P
NMR spectrum shows two singlets with 1JW–P tungsten coupling of
325 Hz and 120 Hz. The coupling of 120 Hz is smaller than we previ-
ously observed in seven-coordinate trisphosphine complexes, but
similar to complexes with a phosphine group trans to a multiply
bound ligand such as carbyne [23–25]. IR and NMR data imply that
the orange fraction is a dinuclear complex.
ð4Þ
A solid-sꢀtate structure of 5 was obtained after anion metathesis
of the BF4 salt with Na[BAr04] (BAr04 = tetrakis[(3,5-trifluoro-
methyl)phenyl]borate) produced X-ray quality crystals of the
dinuclear species with an empirical formula of [W2N(acac)2
(CO)3(PMe3)4][BAr04], 5[BAr04] (Fig. 4). The dinuclear cation is a
mixed valence complex with W2 as a W(IV) d2 center and W1 as
other unsaturated tungsten compounds to generate transient dinu-
clear species, but reaction with adventitious water forms the final
W„NH product 4-NH. Bridging nitrido species are known to form
via N2 loss from azide complexes [30,31]. Dinuclear complex 5 is
likely formed when a dinuclear intermediate is trapped by free
CO in solution.

C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
23
Fig. 4. ORTEP diagram (50% probability) of [(acac)(CO)(PMe3)2W„N–W(acac)(CO)2(PMe3)2][BAr04], 5[BAr04]. BAr04 counterion, CH2Cl2 solvent, and hydrogen atoms omitted for
clarity. Selected interatomic distances (Å) and bond angles (°): W1–N19 = 2.114(3), W2–N19 = 1.748(3), W1–C1 = 1.951(4), W1–C3 = 1.951(4), W1–O10 = 2.137(3), W1–
O5 = 2.157(2), W1–P1 = 2.512(1), W1–P2 = 2.476(1), W2–C20 = 2.000(4), W2–O22 = 2.186(3), W2–O26 = 2.093(3), W2–P3 = 2.528(9), W2–P4 = 2.518(9), W1–N19–
W2 = 173.5(2), O5–W1–O10 = 81.1(1), O22–W2–O26 = 82.1(1).
2.4. Substitution at the imido ligand
sponding deuterium resonance is found in the 2H NMR spectrum.
No deuterium exchange is observed for the acac methine or methyl
protons.
Imido complexes are commonly produced from substituted
azides such as trimethylsilyl azide and phenyl azide rather than
from [N3]ꢀ [5,27,28], but decomposition of [N3]ꢀ to produce nitrido
complexes with N2 loss is also well documented [5,28,32–34].
These nitrido complexes can form imido complexes upon addition
of electrophiles such as methyl triflate. This precedent was the
rationale for our attempts to produce substituted imido complexes
of the formula [W(„NR)(acac)(PMe3)3]+ in this tungsten system.
Addition of a trapping reagent, MeI, to the reaction forming 4-NH
resulted in unidentifiable products. Addition of phenyl azide or tri-
methylsilyl azide in lieu of sodium azide under dry conditions
yielded only decomposition products.
Schrock and co-workers have reacted the isolable tungsten(VI)
imido complex Cp⁄WMe3(NH) with nBuLi to produce the oligomer
[Cp⁄WMe3(NLi)]x [35]. Addition of electrophiles such as MeOTf or
TMSCl to the oligomer leads to addition at nitrogen. Similarly,
deprotonation of [Tp0(CO)2W(NH)]+ with either NEt3 or KH pro-
duces the neutral nitride complex [34]. Addition of electrophiles
to the nitride complex produces substituted imido complexes. In
contrast to results with the electron-poor Tp0W(CO)2NH+ deriva-
tive, addition of base to 4-NH[BF4] followed by D2O leads to depro-
tonation and subsequent deuteration at the acac methyl groups
rather than at W„NH (Eq. (5)). Alkylation at the imido nitrogen
is not observed.
ð6Þ
2.5. Synthesis of a substituted imido complex
Reaction of isocyanates with metal oxo species to produce
substituted imido complexes and CO2 is well documented (Eq.
(7)) [5,26–28,36–38]. These reactions are proposed to proceed
through [2+2] cycloaddition of an isocyanate C@N bond to the me-
tal–oxo linkage to produce a cyclometallacarbamate [39,40]. This
method is a popular route for converting metal oxo complexes to
substituted imido complexes.
ð7Þ
We have synthesized a set of W(IV) bis(acac) oxo derivatives
[11]. Would it be possible to prepare the oxo analog of the ter-
minal imido complex utilizing a W(O)(acac)2 precursor? If so, we
could attempt conversion of the oxo to a substituted NR imido
complex. To probe the possibility of preparing analogous substi-
ð5Þ
tuted imido complexes, W(O)(acac)2(g
2-Me2C@O) was stirred for
three days in CH3CN with PMe3 and Na[BF4] to produce [W(O)(a-
cac)(PMe3)3][BF4] (4-O[BF4]) (Eq. (8)). Even after three days of
stirring, the reaction did not go to completion and a significant
amount of starting material was separated from the product
via chromatography on silica. Nonetheless, the 1H and 31P NMR
spectra of 4-O[BF4] are similar to spectra of 4-NH (without the
imido proton) and indicate successful preparation of the tung-
sten(IV) oxo analog of 4-NH.
Schrock and co-workers demonstrated exchange of the NH pro-
ton for deuterium upon addition of D2O [35]. The reaction is be-
lieved to be catalyzed by traces of acid, and [Cp⁄WMe3(NHD)]+ is
postulated as an intermediate. Addition of D2O to 4-NH[BF4] in-
deed results in deuterium exchange at the imido group (Eq. (6)).
The NH signal disappears in the 1H NMR spectrum and a corre-

24
C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
ð8Þ
A solid-state structure confirms the formation of 4-O[BF4]
(Fig. 5). The connectivity mirrors that of 4-NH[I] with the three
phosphine ligands positioned in a meridional geometry. Tung-
sten-phosphine bond lengths range from a relatively short W1–
P2 bond length of 2.47 Å trans to the acac ligand to W1–P1 with
a bond length of 2.52 Å and to W1–P3 with a bond length of
2.53 Å. The W1–O1 bond distance is 1.73 Å, typical for W@O bonds
[5,41]. The W1–O6 bond length, the acac oxygen trans to the oxo
ligand, is 2.12 Å while the W1–O2 bond length is significantly
shorter at 2.06 Å, reflecting the trans influence of the multiply
bound oxo ligand [5].
A J. Young NMR tube was loaded with 4-O[BF4], 10 equiv. of
phenyl isocyanate, and THF-d8 under an N2 atmosphere and heated
to 70 °C for 18 h. A 1H NMR spectrum shows no evidence of conver-
sion to an imido product. Literature examples require extended
heating in higher boiling solvents to promote related exchange
reactions [5,26–28,37,38]. Therefore, 4-O[BF4] was heated neat in
phenyl isocyanate to 100 °C for 4 h (Eq. (9)), at which point the iso-
cyanate solidified due to the formation of oligomers. Chromatogra-
phy led to separation of the product and a large amount of starting
material. The 1H and 31P NMR spectra of the product are similar to
that of 4-O[BF4] with additional signals in the aromatic region,
indicating formation of [W(NPh)(acac)(PMe3)3][BF4] (4-NPh[BF4]).
This reactivity does not appear to extend to other substituted iso-
cyanates; reaction of 4-O[BF4] with mesityl isocyanate results only
in decomposition products.
Fig. 5. ORTEP diagram of [WO(acac)(PMe3)3][BF4], 4-O[BF4]. Thermal ellipsoids are
drawn with 50% probability. BF4 counterion, CH2Cl2 solvent, and hydrogen atoms
are omitted for clarity. Selected interatomic distances (Å) and bond angles (°): W1–
O1 = 1.729(2), W1–P2 = 2.468(8), W1–P1 = 2.519(8), W1–P3 = 2.533(9), W1–
O6 = 2.115(2), W1–O2 = 2.058(2), O2–W1–O6 = 81.54(8).
ð9Þ
Salt metathesis of 4-NPh[BF4] with NaBAr04 produced 4-
NPh[BAr04]. Crystals of 4-NPh[BAr04] suitable for X-ray analysis
were obtained via evaporation from a solution of the metal imido
salt and methylene chloride and hexanes. The crystal structure
confirms the tungsten-nitrogen connectivity of 4-NPh[BAr04]
(Fig. 6). The phosphine atoms are again positioned in a meridional
geometry, similar to 4-NH[BF4]. The W1-N1 bond length is 1.76 Å,
mirroring the tungsten-nitrogen triple bond character of 4-
NH[BF4]. Other ligand-to-metal bond lengths are similar to those
in 4-NH[BF4] and 4-O[BF4].
Fig. 6. ORTEP diagram of [W(NPh)(acac)(PMe3)3][BAr04], 4-Ph[BAr04]. Two molecules
of 4-Ph[BAr04] are present in the asymmetric unit, but only one is shown. Thermal
ellipsoids are drawn with 50% probability. BAr04 counterion, CH2Cl2 solvent, and
hydrogen atoms are omitted for clarity. Selected interatomic distances (Å) and bond
angles (°): W1–N1 = 1.757(4), W1–P1 = 2.520(1), W1–P2 = 2.459(1), W1–
P3 = 2.500(1), W1–O12 = 2.073(3), W1–O8 = 2.092(3), W1–N1–C2 = 175.9(3), O8–
W1–O12 = 83.06(1).
2.6. Aryl isocyanate reactions with the tungsten–imido complex
Boncella and co-workers have recently demonstrated imido ex-
change in bis(imido) uranium(VI) complexes with aryl isocyanates
[42]. Exchange of one equivalent of aryl isocyanate occurs after
2 days at room temperature. Similar reactivity is also known for
molybdenum, chromium, titanium, and vanadium complexes
[43–46]. It is proposed that the imido ligand undergoes a Wittig-
like [2+2] cycloaddition with the isocyanate molecule to form the
new imido complex as in the case of isocyanate addition to oxo
complexes (Eq. (7)). However, the intermediate metallacycle pos-
tulated for imido exchange has never been isolated.
CD2Cl2. After 4 days at room temperature a new product represents
approximately 10% of the total metal reagent present. An addi-
tional 3 days at room temperature leads to a second product. Due
to the slow conversion, a large excess of phenyl isocyanate was
added and the mixture was heated to 35 °C. After 3 days of heating
no starting material remained; the first and second products were
present in a 3:4 ratio. The 1H and 31P NMR spectra of both com-
plexes show similarities to NMR spectra of 4-NH, but the signals
are shifted somewhat. The NMR data for both products indicate
retention of one acac ligand and three phosphine ligands in a
meridional geometry. Each new complex also displays an apparent
In an attempt to extend this reactivity to tungsten, an NMR tube
was loaded with 4-NH[BF4] and 10 equiv of phenyl isocyanate in

C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
25
N–H resonance in the 1H NMR spectrum; the first product has a
resonance at 9.0 ppm while the second product has a resonance
at 11.2 ppm. After heating the product mixture at 45 °C for an addi-
tional 4 days, complete conversion to the second product was
observed.
carbamoylimido complex at room temperature [47]. The reaction is
accelerated by addition of a catalytic amount of NEt3, presumably
resultinginformationof a nitridointermediate, followedbyaddition
of isocyanate and protonation at the incorporated nitrogen.
Due to the length of time required to produce the isocyanate
addition product, a more efficient synthesis was desired. Heating
4-NH[BF4] in neat phenyl isocyanate at 100 °C for 5 h produces
7-Ph[BF4] and isocyanate oligomers. Clean product is isolated via
fractional chromatography on silica or alumina with a CH3CN/
CH2Cl2 mixture.
To access other isocyanate insertion products that might be
more amenable to crystallization, a variety of substituted isocya-
nates were screened. Dissolving 4-NH[BAr04] in 3,5-bis(trifluoro-
methyl)phenyl isocyanate and heating to 90 °C for 1.5 h leads to
solidification of the mixture. The brown product is then dissolved
in CH3CN and filtered through a frit to remove organic byproducts.
Fractional chromatography on alumina leads to isolation of clean
product. NMR spectroscopy indicates a product consistent with
addition of a single isocyanate (Eq. (11)). In particular, the 1H
NMR spectrum shows an N–H resonance at 7.28 ppm, far upfield
from the resonance at 11.2 ppm seen in 7-Ph[BF4].
The compositions of the first and second product were not elu-
cidated by NMR spectroscopy. An intriguing possibility would be
the isolation of the final imido exchange product as well as the pos-
tulated metallacycle intermediate [42–46]. However, a high reso-
lution mass spectrum of the second product shows the presence
of two equivalents of phenyl isocyanate. Based on this data it is
proposed that both products reflect isocyanate C@N insertion into
the nitrogen-hydrogen bond of the imido ligand (Eq. (10)). The first
product reflects addition of a single equivalent of phenyl isocya-
nate to form [W(NC(O)NHPh)(acac)(PMe3)3][BF4], (6-Ph[BF4]).
Insertion of a second equivalent of isocyanate into the new N–H
bond would yield the final product, [W(NC(O)NPhC(O)NHPh)(a-
cac)(PMe3)3][BF4], (7-Ph[BF4]). 7-Ph[BF4] possesses an amide
hydrogen atom well-positioned for hydrogen bonding to the oxy-
gen atom of C@O through a six-membered ring, and such an inter-
action is compatible with the observed downfield shift for the NH
proton to 11.2 ppm. Attempts to grow crystals for a solid-state
structure of 7-Ph were unsuccessful even after counterion ex-
change with NaBAr04.
An X-ray structure was obtained of 3,5-bis(trifluoro-
methyl)phenyl isocyanate addition product, 6-Ar(CF3)2[BAr04]
(Fig. 7). Indeed, only one equivalent of isocyanate has inserted into
ð10Þ
ð11Þ
Mizobe and co-workers have observed similar addition of phe-
nyl isocyanate to a terminal imido molybdenum complex to form a
the nitrogen-hydrogen bond. The W1–N1 bond length is 1.78 Å,
only a slight increase from 1.76 Å in the 4-NH[I] precursor, indicat-

26
C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
Fig. 7. ORTEP diagram of [W(NC(O)NHAr(CF3)2)(acac)(PMe3)3][BAr04 (Ar = 3,5-bis(trifluoromethyl)phenyl). Thermal ellipsoids are drawn with 50% probability. BAr04
]
counterion and non-essential hydrogen atoms omitted for clarity. Selected interatomic distances (Å) and bond angles (°): W1–N1 = 1.783(5), W1–P1 = 2.525(2), W1–
P2 = 2.515(2), W1–P3 = 2.452(3), W1–O28 = 2.063(6), W1–O32 = 2.077(5), O28–W1–O32 = 82.3(2), C2–N1–W1 = 170.6(5).
ing little loss in W–N triple bond character. While there is no mir-
ror plane present in the solid state, the two trans phosphine li-
gands are coincidental in the NMR spectra, no doubt due to rapid
rotation about the W„N–C axis on the NMR time scale.
The reluctance of the 3,5-bis(trifluoromethyl)phenyl isocyanate
product to undergo a second isocyanate insertion was unexpected.
No other aryl isocyanates that we screened demonstrated this
selectivity for a single insertion. Perhaps the electron withdrawing
character of the trifluoromethyl substituents on the phenyl ring
prevents insertion of a second equivalent of aryl isocyanate.
In pursuit of a solid-state structure of a double insertion product
we turned to mesityl isocyanate, which proved to be more sensitive
to reaction conditions than other aryl isocyanates. Heating a neat
mixture of 4-NH[BF4] and mesityl isocyanate to 100 °C for 24 h pro-
duces a mixture of single and double insertion products in a 45:55
ratio. In anticipation of crystallizing a [BAr04] salt of the double inser-
tion product, 4-NH[BAr04] was heated in mesityl isocyanate at tem-
Fig. 8. ORTEP
diagram of [W(NC(O)NMesC(O)NHMes)(acac)(PMe3)3][BAr04
]
peratures above 70 °C, but this resulted only in decomposition.
Successful formation of a double insertion [BAr04] salt occurred upon
heating a mixture of 4-NH[BAr04] and mesityl isocyanate at 60 °C
for 8 days to produce [W(NC(O)NMesC(O)NHMes)(acac)(PMe3)3]
[BAr04] (7-Mes[BAr04] (Eq. (12)). Fractional chromatography on alu-
mina with CH3CN in CH2Cl2 elutes a clean brown product.
(Mes = mesityl). Thermal ellipsoids are drawn with 50% probability. BAr04 counter-
ion non-essential and hydrogen atoms omitted for clarity. W1–N17 = 1.769(3),
W1–P1 = 2.527(1), W1–P2 = 2.479(1), W1–P3 = 2.537(1), W1–O10 = 2.068(3), W1–
O14 = 2.056(3), W1–N17–C18 = 162.1(3), O10–W1–O14 = 82.51(11).
A solid-state structure was obtained of the double insertion
product with mesityl isocyanate (Fig. 8). One of the key features
ð12Þ

C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
27
is the H32–O19 contact within the six-membered ring conforma-
tion. The bond distance between the N32 and O19 atoms is only
1.97 Å, indicative of hydrogen bonding. This hydrogen bonding
can account for the orientation of the second isocyanate backbone
in this complex, and it could also explain why additional insertions
of mesityl isocyanate are not seen beyond the first two. Breaking
the hydrogen bond to insert a third equivalent of mesityl isocya-
nate may be energetically unfavorable. The W1–N17 bond length
is 1.77 Å, again indicative of a W–N multiple bond.
use. Methylene chloride, diethyl ether, and hexanes were purified
by passage through an activated alumina column under a dry ar-
gon atmosphere [48]. THF was distilled from a sodium ketal sus-
pension. Methylene chloride-d2 was dried over CaH2 and
degassed. Complexes W(CO)3(acac)2 [7] and W(CO)(acac)2(L)
[7,8] W(O)(acac)2(L) [11], and Na[BAr04] [49] were made in accor-
dance with literature procedures. All other reagents were pur-
chased from commercial sources and used without further
purification.
NMR spectra were recorded on Bruker DRX500, DRX400,
AMX400, or AMX300 spectrometers. 1H and 13C NMR chemical
shifts were referenced to the residual signals of the deuterated sol-
vents. 31P NMR chemical shifts were referenced to H3PO4 as an
external standard. NMR data are given for only one salt (either
BF4 or BAr04) for each complex; chemical shift differences between
the two salts are negligible. Typical NMR data for the BAr04 anion is
included at the end of the experimental section and is not pre-
sented repetitively. Infrared spectra were recorded on an ASI Ap-
plied Systems React IR 1000 FT-IR spectrometer. Elemental
analysis was performed by Robertson Microlit, Madison, NJ. Mass
spectra (MS) and high resolution mass spectra (HRMS) were ac-
quired with a Bruker BioTOF II reflectron time-of-flight (reTOF)
mass spectrometer equipped with an Apollo electrospray ioniza-
tion (ESI) source. Mass spectral data are reported for the most
abundant tungsten isotope. Crystal and data collection parameters
for all X-ray structures are found in Tables 1 and 2.
3. Summary
Replacement of the
g -
2-PhC„N ligand in W(CO)(acac)2(g2
PhC„N) by two isonitrile ligands leads to a fluxional 18-electron
W(CO)(acac)2(tBuN„C)2 complex. Displacement of both the nitrile
ligand and an acetylacetonate ligand from W(CO)(acac)2(g2
-
PhC„N) occurs when trimethylphosphine and a halide anion are
added to produce W(CO)(acac)(X)(PMe3)3. Use of NaN3 leads to
loss of carbon monoxide and dinitrogen, and protonation by trace
water then yields the cationic imido complex [W(NH)(a-
cac)(PMe3)3]+. Deuterium exchange occurs in the presence of D2O
to produce [W(ND)(acac)(PMe3)3]+. A substituted imido complex
is formed from the reaction of [W(O)(acac)(PMe3)3]+ with phenyl
isocyanate to produce [W(NPh)(acac)(PMe3)3]+. Reaction of
[W(NH)(acac)(PMe3)3]+ with isocyanates at high temperatures re-
sults in isocyanate insertion into the N–H bond to form new C–N
bonds.
4.2. Representative [BAr04]ꢀ NMR data
4. Experimental
13
1H and C NMR data for the [BAr04]ꢀ counterion are reported
4.1. General information
separately for simplicity. 1H NMR (CD2Cl2, 193 K, d): 7.77 (br, 8H,
o-Ar0), 7.60 (br, 4H, p-Ar0). 13C NMR (CD2Cl2, 193 K, d): 162.2
1
2
All air-and moisture-sensitive materials were handled using
Schlenk or glovebox techniques under a dry nitrogen or argon
atmosphere, respectively. All glassware was oven-dried before
(1:1:1:1 pattern, JB–C = 50 Hz, Cipso), 135.3 (Cortho), 129.4 (qq, JC–
4
1
F = 30 Hz, JC–F = 5 Hz, Cmeta), 125.1 (q, JC–F = 270 Hz, CF3), 117.9
(Cpara).
Table 1
Crystal data and refinement parameters for W(CO)(acac)2(CNtBu)2 (2), W(Cl)(CO)(acac)(PMe3)3 (3-Cl), [W(NH)(acac)(PMe3)3][I] (4-NH[I]), and [W2N(acac)2(CO)3(PMe3)4][BAr04
(5[BAr04]).
]
Complex
2
3-Cl
4-NH[I]
5[BAr04
]
Empirical formula
Formula weight
Color
C
21H32N2O5W
C15H34ClO3P3W
574.63
red
C14H35INO2P3W
653.08
red
C115H126B2Cl2F48N2O14P8W4
3747.82
red
576.34
red
T (K)
100(2)
0.71073
100(2)
0.71073
100(2)
1.54178
100(2)
0.71073
0
k (AÅ)
Crystal system
Space group
a (Å)
B (Å)
c (Å)
monoclinic
P21/n
8.8722(6)
15.7242(11)
17.5395(13)
90
103.252(3)
90
2340.51(6)
4
monoclinic
P21/n
12.5027(2)
11.2526(2)
16.3340(3)
90
100.860(1)
90
2256.84(7)
4
monoclinic
P21/c
9.2952(7)
14.0002(11)
18.9917(16)
90
96.099(3)
90
2457.5(3)
4
monoclinic
P21/c
14.3007(5)
19.3995(7)
25.9122(9)
90
97.376(2)
90
7129.2(4)
2
a
(°)
b (°)
(°)
c
Volume (Å3)
Z
qcalc (mg/m3)
1.607
4.881
1.691
5.459
1.762
20.581
1.746
3.462
l
(mmꢀ1
)
F(0 0 0)
1144
1136
1252
3668
Crystal size (mm3)
2h Range (°)
0.30 ꢁ 0.20 ꢁ 0.05
1.76–36.32
ꢀ14 ꢂ h ꢂ 14
ꢀ26 ꢂ k ꢂ 26
ꢀ29 ꢂ l ꢂ 29
123657
0.12 ꢁ 0.06 ꢁ 0.04
1.89–29.99
ꢀ17 ꢂ h ꢂ 17
ꢀ15 ꢂ k ꢂ 15
ꢀ21 ꢂ l ꢂ 22
60582
0.20 ꢁ 0.15 ꢁ 0.02
3.93–70.00
ꢀ11 ꢂ h ꢂ 11
ꢀ16 ꢂ k ꢂ 17
ꢀ23 ꢂ l ꢂ 22
21336
0.25 ꢁ 0.15 ꢁ 0.15
1.58–29.13
ꢀ19 ꢂ h ꢂ 19
ꢀ25 ꢂ k ꢂ 26
ꢀ35 ꢂ l ꢂ 35
78091
Index ranges
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
11534
11534/0/272
1.101
6579
6589/0/220
1.030
4447
4447/0/211
1.336
19175
19175/0/908
1.024
R1, wR2[I > 2
R1, wR2 (all data)
r
(I)]
0.0189, 0.0405
0.0277, 0.0439
0.0184, 0.0335
0.0240, 0.0349
0.0311, 0.1033
0.0316, 0.1051
0.0324, 0.0731
0.454, 0.0802

28
C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
Table 2
Crystal data and refinement parameters for [W(O)(acac)(PMe3)3][BF4] (4-O[BF4]), [W(NPh)(acac)(PMe3)3][BAr04
Ar(CF3)2[BAr04]), and [W(NC(O)NMesC(O)NHMes)(acac)(PMe3)3][BAr04] (7-Mes[BAr04]).
]
(4-NPh[BAr04]), [W(NC(O)NArH)(acac)(PMe3)3][BAr04
] (6-
Complex
4-O[BF4]
14H34BF4O3P3W
613.98
red
100(2)
1.54178
4-NPh[BAr04
]
6-Ar(CF3)2[BAr04 7-Mes[BAr04
]
]
Empirical formula
Formula weight
Color
C
C52H51BF24NO2P3W
1465.51
green-brown
200(2)
C55H50BF30N2O3P3W
1644.54
C66H69BF24N3O4P3W
1711.81
brown
brown
T (K)
100(2)
100(2)
0
1.54178
1.54178
0.71073
k (AÅ)
Crystal system
Space group
a (Å)
B (Å)
c (Å)
orthorhombic
P212121
12.2589(2)
13.7021(2)
13.9339(2)
90
monoclinic
P2/c
35.2205(5)
18.0478(2)
19.2251(2)
90
monoclinic
P21/n
12.9606(4)
27.3257(8)
18.7119(6)
90
monoclinic
P21/c
21.0034(3)
19.4110(2)
20.2569(2)
90
a
(°)
b (°)
90
90
94.3940(10)
90
12184.6(3)
8
1.598
5.280
101.211(2)
90
6500.5(3)
4
1.680
5.178
114.458(1)
90
7517.58(15)
4
1.512
1.706
c
(°)
Vol. (Å3)
2340.51(6)
4
1.742
Z
qcalc (mg/m3)
l
(mmꢀ1
)
11.479
F(0 0 0)
1208
5808
3248
3432
Crystal size (mm3)
2h Range (°)
0.25 ꢁ 0.20 ꢁ 0.10
4.53–69.98
ꢀ14 ꢂ h ꢂ 13
ꢀ16 ꢂ k ꢂ 13
ꢀ16 ꢂ l ꢂ 16
19452
0.08 ꢁ 0.18 ꢁ 0.20
2.45–66.59
ꢀ41 ꢂ h ꢂ 41
ꢀ21 ꢂ k ꢂ 20
ꢀ22 ꢂ l ꢂ 19
60841
0.15 ꢁ 0.15 ꢁ 0.02
2.90–66.59
ꢀ12 ꢂ h ꢂ 14
ꢀ31 ꢂ k ꢂ 32
ꢀ22 ꢂ l ꢂ 16
41566
0.25 ꢁ 0.10 ꢁ 0.05
2.02–25.03
ꢀ24 ꢂ h ꢂ 25
ꢀ21 ꢂ k ꢂ 22
ꢀ23 ꢂ l ꢂ 24
49496
Index ranges
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
4290
4290/0/247
1.167
20933
20933/0/1535
1.038
11259
10959/150/924
1.051
13171
13171/144/993
1.006
R1, wR2[I > 2
R1, wR2 (all data)
r
(I)]
0.0181, 0.0458
0.0181, 0.0458
0.0425, 0.1090
0.0585, 0.1195
0.0567, 0.1273
0.0834, 0.1389
0.0340, 0.0680
0.0576, 0.0772
4.3. W(CO)(acac)2(tBuN„C)2 (2)
4.4.2. Method B
W(CO)(acac)2(
solved in CH3CN. Excess NaCl (0.065 g, 1.1 mmol) was added to
the solution under backflow of N2 and PMe3 (0.10 mL,
g
2-O@CMe2) (0.080 g, 0.171 mmol) was dis-
In a 200-mL Schlenk flask W(CO)(PhC„N)(acac)2 (0.352 g,
0.686 mmol) was dissolved in CH2Cl2 and stirred under an atmo-
sphere of N2. To this solution was added tert-butyl isonitrile
(0.165 mL, 1.39 mmol). A color change from amber to orange/red
quickly occurred. In situ IR spectroscopy revealed a new CO stretch
around 1850 cmꢀ1. The reaction was allowed to stir 30 min before
the solvent volume was reduced in vacuo. Hexanes were added
(ꢃ80 mL) and the solvent volume was reduced further. The dark
red hexanes solution was placed in the freezer at ꢀ30 °C overnight
to induce crystallization of a dark red solid (0.300 g, 0.521 mmol,
a
0.97 mmol) was syringed into the solution. The solution was al-
lowed to stir overnight to produce a red-orange solution with a
precipitate. Solvent was removed and the product was extracted
with hexanes. The solution was filtered through a frit and sol-
vent was removed via rotary evaporation. Yield: 0.058 g,
0.101 mmol, 59%. IR (hexanes):
m .
CO = 1760 cmꢀ1 1H NMR
(CD2Cl2, 298 K, d): 5.59 (s, 1H, acac CH), 2.02 (s, 6H, acac CH3),
2
1.37 (pseudo d, 18H, eq P(CH3)3), 1.14 (d, 9H, ax P(CH3)3, JP–H
2
76%). IR (hexanes):
m
CO = 1847 cmꢀ1
.
1H NMR (CD2Cl2, 298 K, d):
= 8 Hz). 31P NMR (CD2Cl2, 298 K, d): 11.0 (t, 1P, ax PMe3, JP–P
1
2
1
5.50 (s, 2H, acac CH), 2.01 (s, 12H, acac CH3), 1.48 (s, 18H, –
= 20 Hz, JP–W = 315 Hz), 6.7 (d, 2P, eq PMe3, JP–P = 20 Hz, JP–W
C(CH3)3). 1H NMR (CD2Cl2, 210 K, d): 5.63, 5.37 (s, 1H, acac CH),
= 269 Hz). 13C NMR (CD2Cl2, 298 K, d): 289.5 (dt, CO, JC–P = 27,
39 Hz), 185.1 (t, acac CO, JC–P = 3 Hz), 101.5 (acac CH), 27.7 (acac
CH3), 17.2 (d, eq P(CH3)3, JC–P = 26 Hz), 15.3 (dt, ax P(CH3)3, JC–
P = 32 Hz, JC–P = 14 Hz). Anal. Calc. for WC15H34ClO3P3: C, 31.35;
2
2.09, 1.97, 1.95, 1.88 (s, 3H, acac CH3), 1.48, 1.33 (s, 9H, Bu). 13C
t
3
1
1
1
NMR (CD2Cl2, 210 K, d): 245.4 (CO, JC–W = 198 Hz), 188.3, 188.2,
3
185.0, 184.9 (acac CO), 100.9, 100.0 (acac CH), 59.5, 57.5 (–
C(CH3)3) 30.5, 29.9 (–C(CH3)3), 27.8, 27.5, 27.2, 26.2 (acac CH3).
Anal. Calc. for WC21H32N2O5: C, 43.76; H, 5.60; N, 4.86. Found: C,
42.14; H, 5.56; N, 4.85%.
H, 5.96. Found: C, 30.99; H, 5.65%.
4.5. W(Br)(CO)(acac)(PMe3)3 (3-Br)
4.4. W(Cl)(CO)(acac)(PMe3)3 (3-Cl)
Synthesized using Method B but with NaBr added in place of
NaCl. Yield: 0.061 g, 0.989 mmol, 46%. IR (hexanes):
4.4.1. Method A
m .
CO = 1762 cmꢀ1 1H NMR (CD2Cl2, 298 K, d): 5.62 (s, 1H, acac
A Schlenk flask was charged with W(CO)(acac)2(
g
2-PhC„N)
CH), 2.02 (s, 6H, acac CH3), 1.45 (pseudo d, 18H, eq P(CH3)3),
2
(0.100 g, 0.195 mmol) under an nitrogen atmosphere. CH2Cl2
(20 mL) was syringed in followed by PMe3 (0.2 mL, 1.9 mmol).
The red-brown solution was stirred for 3 days. Solvent was re-
moved and the product was extracted with hexanes. The solution
was filtered through a frit and solvent was removed via rotary
evaporation. Yield: 0.050 g, 0.087 mmol, 47%. A concentrated hex-
anes solution was stored at ꢀ30 °C to yield crystals suitable for X-
ray analysis.
1.14 (d, 9H, ax P(CH3)3, JP–H = 11 Hz). 31P NMR (CD2Cl2, 298 K,
2
1
d): 11.4 (t, 1P, ax PMe3, JP–P = 20 Hz, JP–W = 324 Hz), 3.6 (d,
2P, eq PMe3, JP–P = 20 Hz, JP–W = 265 Hz). 13C NMR (CD2Cl2,
2
1
2
298 K, d): 287.1 (dt, CO, JC–P = 26, 40 Hz), 185.2 (t, acac CO,
3JC–P = 4 Hz), 101.8 (acac CH), 27.7 (acac CH3), 16.8 (d, eq
1
1
3
P(CH3)3, JC–P = 27 Hz), 16.2 (dt, ax P(CH3)3, JC–P = 33 Hz JC–P
= 16 Hz). Anal. Calc. for WC15H34IO3P3: C, 29.10; H, 5.54. Found:
C, 29.24; H, 5.53%.

C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
29
4.6. W(I)(CO)(acac)(PMe3)3 (3-I)
4.10. [W(NH)(acac)(PMe3)3][BF4] (4-NH[BF4])
2-O@CMe2)(acac)2 (0.050 g, 0.107 mmol) was dis-
Synthesized using Method B but with NaI added in place of
NaCl. Yield: 0.605 g, 0.908 mmol, 85%. IR (hexanes):
W(CO)(g
solved in CH3CN (not anhydrous). NaN3 (0.022 g, 0.339 mmol)
and NaBF4 (0.013 g, 0.118 mmol) were added under a backflow of
N2. PMe3 (0.06 mL, 0.58 mmol) was syringed into the red solution
resulting in a color change to orange. After 24 h of stirring, the sol-
vent was removed under vacuum and the red product was washed
with hexanes and filtered through a sintered glass frit with CH2Cl2
to yield a blood-red solution. Solvent was removed and the solid
was triturated with hexanes to produce a red powder. Yield:
0.035 g, 0.057 mmol, 53%. 1H NMR (CD2Cl2, 298 K, d): 8.44 (br s,
1H, NH), 5.87 (s, 1H, acac CH), 2.71, 2.28 (s, 3H, acac CH3), 1.77
m
CO = 1767 cmꢀ1 1H NMR (CD2Cl2, 298 K, d): 5.68 (s, 1H, acac
.
CH), 2.01 (s, 6H, acac CH3), 1.58 (pseudo d, 18H, eq P(CH3)3),
2
1.12 (d, 9H, ax P(CH3)3, JP–H = 9 Hz). 31P NMR (CD2Cl2, 298 K,
2
1
d): 11.6 (t, 1P, ax PMe3, JP–P = 18 Hz, JP–W = 328 Hz), ꢀ0.6 (d,
2
1
2P, eq PMe3, JP–P = 18 Hz, JP–W = 258 Hz). 13C NMR (CD2Cl2,
2
298 K, d): 284.1 (dt, CO, JC–P = 25, 41 Hz), 185.4 (t, acac CO,
3JC–P = 3 Hz), 102.5 (acac CH), 27.6 (acac CH3), 17.9 (dt, ax
1
3
1
P(CH3)3, JC–P = 34 Hz, JC–P = 18 Hz), 16.2 (d, eq P(CH3)3, JC–P
= 27 Hz). Anal. Calc. for WC15H34IO3P3: C, 27.05; H, 5.14. Found:
C, 27.26; H, 5.17%.
2
(d, 9H, P(CH3)3, JP–H = 9 Hz), 1.25 (pseudo t, 18H, P(CH3)3,
2JP–H apparent = 4 Hz). 31P NMR (CD2Cl2, 298 K, d): ꢀ12.0 (s, 1P,
1
1
PMe3, JP–W = 409 Hz), ꢀ14.1 (s, 2P, PMe3, JP–W = 308 Hz). 13C
4.7. W(SCN)(CO)(acac)(PMe3)3 (3-SCN)
NMR (CD2Cl2, 298 K, d): 187.1, 186.4 (acac CO), 100.4 (acac CH),
26.7, 26.0 (acac CH3), 23.3 (d, P(CH3)3, JC–P = 31 Hz), 16.2 (t,
P(CH3)3, JC–P = 13 Hz). Anal. Calc. for WC14H35NO2P3BF4: C, 27.43;
1
Synthesized using Method B but with KSCN added in place of
1
NaCl. Yield: 0.020 g, 0.033 mmol, 75%. IR (KBr):
m ;
CO = 1753 cmꢀ1
H, 5.75; N, 2.28. Found: C, 27.70; H, 5.48; N, 2.20%.
m
CN = 2093 cmꢀ1 1H NMR (CD2Cl2, 298 K, d): 5.63 (s, 1H, acac
.
CH), 2.05 (s, 6H, acac CH3), 1.37 (pseudo d, 18H, eq P(CH3)3), 1.11
4.11. [(PMe3)2(acac)(CO)W„N–W(CO)2(acac)(PMe3)2][BF4] (5[BF4])
2
(d, 9H, ax P(CH3)3, JP–H = 9 Hz). 31P NMR (CD2Cl2, 298 K, d): 8.6
2
1
(t, 1P, ax PMe3, JP–P = 17 Hz, JP–W = 290 Hz), 7.5 (d, 2P, eq PMe3,
The procedure for the synthesis of [(PMe3)2(acac)(CO)W„N–
W(CO)2(acac)(PMe3)2][BF4] (5[BF4]) was the same as for
W(N3)(CO)(acac)(PMe3)3. After washing with hexanes the remain-
ing red solid consisted of two products by 31P NMR spectroscopy.
These two products were chromatographed on alumina to separate
them. First an orange fraction was eluted with 5% CH3CN in CH2Cl2.
Solvent was removed to yield pure product. The remaining red
fraction was eluted with 25:75 CH3CN:CH2Cl2 and was shown to
be [W(NH)(acac)(PMe3)3][BF4] by NMR spectroscopy. Yield of
(5[BF4]): 0.113 g, 0.107 mmol, 7%. IR (KBr): 1810, 1903, 1916,
1947 cmꢀ1 (CO). 1H NMR (CD2Cl2, 298 K, d): 5.89, 5.55 (s, 1H, acac
CH), 2.29, 2.05, 1.92 (s, 3:6:3H, acac CH3), 1.72 (pseudo t, 18H,
2JP–P = 17 Hz, JP–W = 261 Hz). 13C NMR (CD2Cl2, 298 K, d): 288.0
(dt, CO, JC–P = 26, 28 Hz), 185.6 (t, acac CO, JC–P = 3 Hz), 101.0
(acac CH), 27.2 (acac CH3), 15.9 (d, eq P(CH3)3, JC–P = 27 Hz), 15.1
(dt, ax P(CH3)3, JC–P = 31 Hz, JC–P = 13 Hz). Anal. Calc. for
WC16H34NO3P3S: C, 32.17; H, 5.74; N, 2.35. Found: C, 31.92; H,
5.47; N, 2.56%.
1
2
3
1
1
3
4.8. W(N3)(CO)(acac)(PMe3)3 (3-N3)
W(CO)(g
2-O@CMe2)(acac)2 (0.700 g, 1.50 mmol) was dissolved
in CH3CN that had been dried over sieves. NaN3 (0.30 g, 4.6 mmol)
and NaBF4 (0.17 g, 1.5 mmol) were added under a backflow of N2.
PMe3 (0.6 mL, 5.8 mmol) was syringed into the red solution. After
3 days of stirring the solvent was removed and the red product
was washed with hexanes to yield an orange solution. Solvent
was removed to yield an orange powder. Yield: 0.123 g,
2
P(CH3)3, JP–H apparent = 5 Hz), 1.36 (pseudo t, 18H, P(CH3)3,
2JP–H apparent = 4 Hz). 31P NMR (CD2Cl2, 298 K, d): 1.1 (s, 2P, PMe3,
1
1JP–W = 120 Hz), ꢀ9.7 (s, 2P, PMe3, JP–W = 325 Hz). 13C NMR
(CD2Cl2, 298 K, d): 257.0 (br s, W(IV) CO), 246.2 (t, W(II) CO,
2JC–P = 30 Hz), 192.5, 188.9, 187.4 (1:1:2, acac CO), 103.0, 102.1
(acac CH), 27.9, 27.8, 27.7 (1:2:1, acac CH3), 16.6 (m, P(CH3)3),
0.211 mmol, 14%. IR (KBr): m , m .
CO = 1737 cmꢀ1 N3 = 2061 cmꢀ1 1H
NMR (CD2Cl2, 298 K, d): 5.64 (s, 1H, acac CH), 2.08 (s, 6H, acac
1
15.6 (t, P(CH3)3, JC–P = 14 Hz). [(PMe3)2(acac)(CO)W„N–W(CO)2
(acac)(PMe3)2][BAr04] (5[BAr04]). [W2N(acac)2(CO)3(PMe3)4][BF4]
(0.030 g, 0.028 mmol) was dissolved in CH2Cl2. NaBAr04 (0.027 g,
0.030 mmol) was added and the solution was stirred for 3 h to en-
sure complete counterion exchange. The resulting product was
chromatographed on alumina with 10% CH3CN in CH2Cl2. The or-
ange product was dissolved in CH2Cl2, layered with hexanes, and
stored at ꢀ30 °C for 3 days to form crystals suitable for X-ray anal-
ysis and elemental analysis. Anal. Calc. for W2C57H62NO7P4BF24: C,
37.38; H, 3.41; N, 0.76. Found: C, 37.21; H, 3.09; N, 0.64%.
CH3), 1.37 (pseudo d, 18H, eq P(CH3)3), 1.12 (d, 9H, ax P(CH3)3,
2
2JP–H = 8 Hz). 31P NMR (CD2Cl2, 298 K, d): 10.6 (t, 1P, ax PMe3, JP–P
1
2
1
= 18 Hz, JP–W = 294 Hz), 9.27 (d, 2P, eq PMe3, JP–P = 18 Hz, JP–W
= 274 Hz). 13C NMR (CD2Cl2, 298 K, d): 290.8 (dt, CO, JC–P = 28,
38 Hz), 185.8 (t, acac CO, JC–P = 3 Hz), 101.5 (acac CH), 27.7 (acac
2
3
1
CH3), 16.8 (d, eq P(CH3)3, JC–P = 26 Hz), 15.8 (dt, ax P(CH3)3,
1JC–P = 30 Hz, JC–P = 13 Hz).
3
4.9. [W(NH)(acac)(PMe3)3][I] (4-NH[I])
4.12. Attempted deprotonation of [W(NH)(acac)(PMe3)3][BF4]
A
Schlenk flask was charged with W(CO)(acac)(I)(PMe)3
(0.104 g, 0.156 mmol) and CH3CN (20 mL). NaN3 (0.110 g,
1.69 mmol) was added under a backflow of N2. After stirring for
24 h, a color change red-orange to blood-red occurred. The product
was washed with hexanes and filtered though a sintered glass frit
with CH2Cl2. Yield: 0.060 g, 0.092 mmol, 59%. Crystals suitable for
X-ray analysis were formed by slow evaporation of a solution of
A
Schlenk flask was loaded with 4-NH[BF4] (0.020 g,
0.033 mmol) and NaH (0.001 g, 0.04 mmol). The flask was cooled
to ꢀ78 °C and THF was slowly syringed in. The solution was al-
lowed to warm to room temperature after 5 min and then stirred
for 45 min at room temperature. D2O was added and the solution
was stirred for 1 h. NMR spectroscopy indicated deuteration of
the acetylacetonate methyl protons. 1H NMR (CD2Cl2, 298 K, d):
8.36 (br s, 1H, NH), 5.87 (s, 1H, acac CH), 2.72, 2.28 (br s, less than
the product in CH2Cl2/hexanes. IR (KBr):
m .
NH = 3161 cmꢀ1 1H
NMR (CD2Cl2, 298 K, d): 8.84 (br s, 1H, NH), 5.86 (s, 1H, acac CH),
2
2
2.71, 2.27 (s, 3H, acac CH3), 1.80 (d, 9H, P(CH3)3, JP–H = 9 Hz),
1H, acac CH3), 1.77 (d, 9H, P(CH3)3, JP–H = 9 Hz), 1.25 (pseudo t,
1.26 (pseudo t, 18H, P(CH3)3, 2JP–H apparent = 4 Hz). 31P NMR (CD2Cl2,
18H, P(CH3)3, JP–H apparent = 4 Hz). 31P NMR (CD2Cl2, 298 K, d):
2
1
1
1
298 K, d): ꢀ12.6 (s, 1P, PMe3, JP–W = 410 Hz), ꢀ14.9 (s, 2P, PMe3,
ꢀ12.0 (s, 1P, PMe3, JP–W = 409 Hz), ꢀ14.1 (s, 2P, PMe3, JP–W
1JP–W = 311 Hz).
= 306 Hz).

30
C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
4.13. [W(ND)(acac)(PMe3)3][BF4] (4-ND[BF4])
1H NMR (CD2Cl2, 298 K, d): 11.2 (s, 1H, NH), 7.14–7.63 (C6H5),
6.04 (s, 1H, acac CH), 2.94, 2.51 (s, 3H, acac CH3), 1.92 (d, 9H,
4-NH[BF4] was dissolved in D2O in an NMR tube. A 1H NMR
P(CH3)3, JP–H = 9 Hz), 1.17 (pseudo t, 18H, P(CH3)3, JP–H apparent
2
2
1
spectrum after 5 min showed loss of the imido proton signal at
= 4 Hz). 31P NMR (CD2Cl2, 298 K, d): ꢀ18.7 (s, 1P, PMe3, JP–W
9.0 ppm. IR (KBr):
m
ND = 2321 cmꢀ1
.
1H NMR (CD2Cl2, 298 K, d):
= 390 Hz), ꢀ19.9 (s, 2P, PMe3, 1JP–W = 298 Hz). HRMS (ESI) m/z Anal.
Calc.: 764.214 (M+), 688.169 (M+–PMe3), 645.176 (M+–PhNCO),
612.125 (M+–2PMe3). Found: 764.211, 688.167, 645.174,
612.123%. [W(NC(O)NHPh)(acac)(PMe3)3][BF4] (6-Ph[BF4]). Ob-
served as intermediate in the synthesis of 7-Ph[BF4]. 1H NMR
(CD2Cl2, 298 K, d): 9.00 (s, 1H, NH), 6.9–7.8 (C6H5) 6.05 (s, 1H, acac
CH), 3.02, 2.45 (s, 3H, acac CH3), 1.89 (d, 9H, P(CH3)3, 2JP–H = 10 Hz),
1.29 (br s, 18H, P(CH3)3). 31P NMR (CD2Cl2, 298 K, d): ꢀ15.1 (s, 1P,
PMe3), ꢀ17.2 (s, 2P, PMe3).
5.81 (s, 1H, acac CH), 2.52, 2.13 (s, 3H, acac CH3), 1.60 (d, 9H,
2
P(CH3)3, JP–H = 9 Hz), 1.11 (pseudo t, 18H, P(CH3)3). 2H NMR
(CD2Cl2, 298 K, d): 8.44 (br s, ND). 31P NMR (CD2Cl2, 298 K, d):
1
1
ꢀ13.2 (s, 1P, PMe3, JP–W = 409 Hz), ꢀ14.9 (s, 2P, PMe3, JP–W
= 306 Hz).
4.14. [W(O)(acac)(PMe3)3][BF4] (4-O[BF4])
W(O)(acac)2(g
2-O@CMe2) (0.123 g, 0.270 mmol) was dissolved
in dry CH3CN. NaBF4 (0.071 g, 0.647 mmol) was added under a
backflow of N2 followed by PMe3 (0.2 mL, 1.9 mmol). The solution
was stirred overnight. Solvent was removed and the product was
washed with hexanes to remove yellow starting material. The
remaining brown product was chromatographed on silica first with
4.17. [W(NC(O)NHAr(CF3)2)(acac)(PMe3)3][BAr04] (6-Ar(CF3)2[BAr04])
A Schlenk tube was charged with [W(NH)(acac)(PMe3)3][BAr04]
(0.105 g, 0.076 mmol) which was produced from counterion ex-
change of [W(NH)(acac)(PMe3)3][BF4] with NaBAr04 3,5-bis(trifluo-
romethyl)phenyl isocyanate was added and the mixture was
heated to 90 °C for 1.5 h. At that time, the brown mixture solidified.
The product was dissolved in CH3CN, filtered through Celite, and
fractionally chromatographed on alumina with 10% CH3CN in
CH2Cl2. 31P NMR analysis of the fractions allowed identification
of the brown product. Yield: 0.052 g, 0.032 mmol, 42%. Slow evap-
CH2Cl2 to elute W(O)(acac)2(g
2-O@CMe2), and then with a mixture
of 20% CH3CN in CH2Cl2 to elute the product. Yield: 0.033 g,
0.054 mmol, 20%. 1H NMR (CD2Cl2, 298 K, d): 6.01 (s, 1H, acac
2
CH), 2.93, 2.38 (s, 3H, acac CH3), 1.88 (d, 9H, P(CH3)3, JP–H
2
= 9 Hz), 1.31 (pseudo t, 18H, P(CH3)3, JP–H apparent = 4 Hz). 31P
1
NMR (CD2Cl2, 298 K, d): ꢀ16.3 (s, 1P, PMe3, JP–W = 465 Hz),
ꢀ17.4 (s, 2P, PMe3, 1JP–W = 343 Hz). Anal. Calc. for WC14H34BF4O3P3:
oration of a
solution of 6-Ar(CF3)2[BAr04] in CH2Cl2/hexanes
C, 27.39; H, 5.58. Found: C, 27.23; H, 5.35%.
yielded green-brown crystals suitable for X-ray analysis. 1H NMR
(CD2Cl2, 298 K, d): 8.00 (s, 2H, o-Ar), 7.66 (s, 1H, p-Ar), 7.28 (s,
1H, NH), 6.08 (s, 1H, acac CH), 3.01, 2.46 (s, 3H, acac CH3), 1.89
4.15. [W(NPh)(acac)(PMe3)3][BF4] (4-NPh[BF4])
2
(d, 9H, P(CH3)3, JP–H = 9 Hz), 1.26 (pseudo t, 18H, P(CH3)3,
[W(O)(acac)(PMe3)3][BF4] (0.100 g, 0.163 mmol) was dissolved
in phenyl isocyanate (3.8 mL, 35 mmol) under a N2 atmosphere.
The solution was heated to 100 °C for 5 h before the solution solid-
ified. The brown reaction mixture was dissolved in CH3CN and the
solution was filtered through a frit. The product mixture was chro-
matographed on silica with CH2Cl2 to elute a significant amount of
organic material, followed by elution with a solution of 25% CH3CN
in CH2Cl2 to elute the product as a green-brown fraction, and final-
ly a solution of 50:50 CH3CN:CH2Cl2 was used to elute the starting
material in a brown fraction. Yield: 0.015 g, 0.022 mmol, 13%. 1H
NMR (CD2Cl2, 298 K, d): 7.30 (t, 2H, m-C6H5), 7.23 (t, 1H, p-C6H5),
7.04 (d, 2H, o-C6H5), 5.93 (s, 1H, acac CH), 2.80, 2.32 (s, 3H, acac
2JP–H apparent = 3 Hz). 31P NMR (CD2Cl2, 298 K, d): ꢀ17.7 (s, 1P,
1
1
PMe3, JP–W = 359 Hz), -19.6 (s, 2P, PMe3, JP–W = 269 Hz). 13C
NMR (CD2Cl2, 298 K, d): 189.1 (br s, acac CO), 188.6 (m, acac CO),
2
159.4 (s, C@O), 139.1 (s, Ar), 132.7 (q, m-Ar, JC–F = 34 Hz), 123.5
1
(q, ArCF3, JC–F = 273 Hz), 119.4 (br s, Ar), 118.0 (t, p-Ar), 100.0 (br
1
s, acac CH), 26.4, 25.6 (acac CH3), 22.1 (d, P(CH3)3, JC–P = 32 Hz),
1
15.7 (t, P(CH3)3, JC–P = 14 Hz). Anal. Calc. for WC55H50BF30N2O3P3:
C, 40.17; H, 3.06; N, 1.70. Found: C, 40.25; H, 2.87; N, 1.59%.
4.18. [W(NC(O)NMesC(O)NHMes)(acac)(PMe3)3][BAr04] (7-
Mes[BAr04])
2
CH3), 1.82 (d, 9H, P(CH3)3, JP–H = 9 Hz), 1.25 (pseudo t, 18H,
A Schlenk tube was loaded with [W(NH)(acac)(PMe3)3][BAr04]
and 2,4,6-trimethylphenyl isocyanate. The mixture was heated to
60 °C to form a melt and the solution was stirred for 8 days. The
product was dissolved in CH3CN, filtered through Celite, and frac-
tionally chromatographed on alumina with 10% CH3CN in CH2Cl2.
After 31P NMR analysis of the fractions, a brown product was iso-
lated. Yield: 0.020 g, 0.012 mmol, 33%. Slow evaporation of a solu-
tion of the product in CH2Cl2/hexanes produced X-ray quality
brown crystals. 1H NMR (CD2Cl2, 298 K, d): 10.2 (s, 1H, NH), 7.01,
6.92 (s, 1H, Mes CH), 6.00 (s, 1H, acac CH), 3.02, 2.42 (s, 3H, acac
CH3), 2.33, 2.27, 2.22, 2.21 (s, 3:3:6:6, Mes CH3), 1.85 (d, 9H,
2
P(CH3)3, JP–H apparent = 4 Hz). 31P NMR (CD2Cl2, 298 K, d): ꢀ13.8 (s,
1
1
1P, PMe3, JP–W = 398 Hz), ꢀ15.9 (s, 2P, PMe3, JP–W = 303 Hz). 13C
NMR (CD2Cl2, 298 K, d): 188.0, 187.1 (acac CO), 153.2 (ipso-C6H5),
129.4, 126.2, 125.9 (C6H5), 100.6 (acac CH), 27.0, 25.9 (acac CH3),
1
1
23.0 (d, P(CH3)3, JC–P = 31 Hz), 15.7 (t, P(CH3)3, JC–P = 13 Hz).
[W(NPh)(acac)(PMe3)3][BAr04] (4-NPh[BAr04]). [W(NPh)(acac)(P-
Me3)3][BF4] (0.012 g, 0.017 mmol) was dissolved in CH2Cl2. NaBAr04
(0.030 g, 0.039 mmol) was added and the solution was stirred for
3 h to ensure complete counterion exchange. The green-brown
product was dissolved in a mixture of CH2Cl2/hexanes and the
solution was allowed to evaporate to produce crystals suitable
for X-ray analysis.
2
2
P(CH3)3, JP–H = 9 Hz), 1.06 (pseudo t, 18H, P(CH3)3, JP–H apparent
= 3 Hz). 31P NMR (CD2Cl2, 298 K, d): ꢀ20.1 (s, 1P, PMe3, JP–W
1
= 382 Hz), ꢀ20.8 (s, 2P, PMe3, JP–W = 298 Hz). 13C NMR (CD2Cl2,
1
4.16. [W(NC(O)NPhC(O)NHPh)(acac)(PMe3)3][BF4] (7-Ph[BF4])
298 K, d): 189.3, 188.0 (acac CO), 151.4 (C@O), 139–128 (Ar), 99.4
(br s, acac CH), 26.2, 25.4 (acac CH3), 21.1, 21.0, 18.6, 18.4 (Mes
1
1
A
Schlenk tube was charged with 4-NH[BF4] (0.110 g,
CH3), 22.3 (d, P(CH3)3, JC–P = 32 Hz), 15.2 (t, P(CH3)3, JC–P
= 14 Hz). Anal. Calc. for WC66H69BF24N3O4P3: C, 46.31; H, 4.06; N,
2.45. Found: C, 46.57; H, 4.14; N, 2.46%.
0.179 mmol) and evacuated. Under a N2 atmosphere phenyl isocy-
anate (10 mL, 92 mmol) was added. The solution was stirred at
100 °C for 5 h. Isocyanate oligomers formed and solidified upon
cooling. The product was dissolved in CH3CN, filtered through Cel-
ite, and chromatographed on silica. The remaining oligomers were
eluted with CH2Cl2 and the product was then eluted as a brown
band with 25% CH3CN in CH2Cl2. Yield: 0.054 g, 0.063 mmol, 35%.
Acknowledgment
We thank the National Science Foundation (CHE-0717086) for
financial support.

C. Khosla et al. / Inorganica Chimica Acta 369 (2011) 19–31
31
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