Reduction of an η2-iminoacyl ligand to η2- iminium enabled by adjacent carbon monoxide ligand replacement with a variable electron donor alkyne ligand in a cationic tungsten(II) bis(acetylacetonate) complex

Article abstract of DOI:10.1021/ic800738a

Cationic iminoacyl-carbonyl tungsten complexes of the type [W(CO) (η²-MeN=CR)(acac)₂]⁺ (acac = acetylacetonate; R = Ph (1a), Me (1b)) easily undergo thermal substitution of CO with two-electron donors to yield [W(L)(η²MeN=CR)(acac) ₂]⁺ (L = tert-butylisonitrile [R = Ph (2a), Me (2b)], 2,6-dimethylphenylisonitrile [R = Me (2c)], triphenylphosphine [R = Ph (3a), Me (3c)], and tricyclohexylphosphine [R = Ph (3b)]). Tricyclohexylphosphine complex 3b exhibits rapid, reversible phosphine ligand exchange at room temperature on the NMR time scale. Photolytic replacement of carbon monoxide with either phenylacetylene or 2-butyne occurs efficiently to form [W(η ²alkyne)(η²-MeN=CR)(acac)₂]⁺ complexes (5a-d) with a variable electron donor η²-alkyne paired with the η²-iminoacyl ligand in the W(II) coordination sphere. PMe₃ adds to 1a or 5b to form [W(L)(η²-MeN=C(PMe ₃)Ph)(acac)₂]⁺ [L = CO (4), MeC≡CMe (6)] via nucleophilic attack at the iminoacyl carbon. Addition of Na[HB(OMe) ₃] to 5b yields W(η²-MeC≡CMe)(η²- MeN=CHPh)(acac)₂, 8, which exhibits alkyne rotation on the NMR time scale. Addition of MeOTf to 8 places a second methyl group on the nitrogen atom to form an unusual cationic η²-iminium complex [W(η²-MeC≡CMe)(η²-Me₂N=CHPh) (acac)₂][OTf] (9[OTf], OTf = SO₃CF₃). X-ray structures of 2,6-dimethylphenylisonitrile complex 2c[BAr′₄] tricyclohexylphosphine complex 3b[BAr′₄], and phenylacetylene complex 5a[BAr′₄] confirm replacement of CO by these ligands in the [W(L)(η²-MeN=CR)(acac)₂]⁺ products. X-ray structures of alkyne-imine complexes 6[BAr′₄] and 8 show products resulting from nucleophilic addition at the iminoacyl carbon, and the X-ray structure of 9[BAr′₄] reflects methylation at the imine nitrogen to form a rare η²-iminium ligand.

Full text of DOI:10.1021/ic800738a

Inorg. Chem. 2008, 47, 8776-8787
Reduction of an η2-Iminoacyl Ligand to η2-Iminium Enabled by Adjacent
Carbon Monoxide Ligand Replacement with a Variable Electron Donor
Alkyne Ligand in a Cationic Tungsten(II) Bis(acetylacetonate) Complex
Andrew B. Jackson, Chetna Khosla, Peter S. White, and Joseph L. Templeton*
W.R. Kenan Laboratory, Department of Chemistry, UniVersity of North Carolina, Chapel Hill,
North Carolina 27599-3290
Received April 25, 2008
2
Cationic iminoacyl-carbonyl tungsten complexes of the type [W(CO) (η -MeNdCR)(acac)2]+ (acac ) acetylacetonate;
2
R ) Ph (1a), Me (1b)) easily undergo thermal substitution of CO with two-electron donors to yield [W(L)(η -
MeNdCR)(acac)2]+ (L ) tert-butylisonitrile [R ) Ph (2a), Me (2b)], 2,6-dimethylphenylisonitrile [R ) Me (2c)],
triphenylphosphine [R ) Ph (3a), Me (3c)], and tricyclohexylphosphine [R ) Ph (3b)]). Tricyclohexylphosphine
complex 3b exhibits rapid, reversible phosphine ligand exchange at room temperature on the NMR time scale.
2
Photolytic replacement of carbon monoxide with either phenylacetylene or 2-butyne occurs efficiently to form [W(η -
2
2
2
alkyne)(η -MeNdCR)(acac)2]+ complexes (5a-d) with a variable electron donor η -alkyne paired with the η -
iminoacyl ligand in the W(II) coordination sphere. PMe3 adds to 1a or 5b to form [W(L)(η -MeNdC(PMe3)Ph)(acac)2]+
2
[L ) CO (4), MeCt CMe (6)] via nucleophilic attack at the iminoacyl carbon. Addition of Na[HB(OMe)3] to 5b
2
2
yields W(η -MeCt CMe)(η -MeNdCHPh)(acac)2, 8, which exhibits alkyne rotation on the NMR time scale. Addition
2
of MeOTf to 8 places a second methyl group on the nitrogen atom to form an unusual cationic η -iminium complex
2
2
[W(η -MeCt CMe)(η -Me2NdCHPh)(acac)2][OTf] (9[OTf], OTf ) SO3CF3). X-ray structures of 2,6-dimethylphe-
nylisonitrile complex 2c[BAr′4], tricyclohexylphosphine complex 3b[BAr′4], and phenylacetylene complex 5a[BAr′4]
2
confirm replacement of CO by these ligands in the [W(L)(η -MeNdCR)(acac)2]+ products. X-ray structures of
alkyne-imine complexes 6[BAr′4] and 8 show products resulting from nucleophilic addition at the iminoacyl carbon,
2
and the X-ray structure of 9[BAr′4] reflects methylation at the imine nitrogen to form a rare η -iminium ligand.
Introduction
reduction when σ-bound to a metal center.9-14 However,
less is known about the reactivity of π-bound nitrile
ligands.5-8 We recently constructed a bis(acetylacetonate)
tungsten(II) d4 fragment that preferentially binds nitriles
through the Ct N π-system.15
Unsaturated organic molecules exhibit altered reactivity
patterns once they are in the coordination sphere of a
transition metal.1-11 Specifically, nitriles readily undergo
* To whom correspondence should be addressed. E-mail: joetemp@
unc.edu.
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8776 Inorganic Chemistry, Vol. 47, No. 19, 2008
10.1021/ic800738a CCC: $40.75  2008 American Chemical Society
Published on Web 08/28/2008

Reduction of an η2-Iminoacyl Ligand to η2-Iminium
Scheme 1. Facile Thermal Replacement of CO with Isonitrile
Reduction of π-bound nitrile complexes of the type
W(CO)(η2-nitrile)(acac)2to neutral imine-carbonyl complexes
of the general formula W(CO)(η2-imine)(acac)2 has been
accomplished via stepwise addition of electrophiles and
nucleophiles.8 The η2-imine ligand provides four electrons
to tungsten in W(CO)(acac)2(η2-imine) complexes.8,15 At-
tempts to convert the π-bound imine to an iminium ligand
have been unproductive with carbon monoxide as the
adjacent ligand in the coordination sphere. Presumably this
reflects the need for a four-electron donor ligand to stabilize
the six-coordinate d4 tungsten center.16 Addition of a second
electrophile to the nitrogen of the sidebound imine ligand
would remove two electrons from the metal, so electrophilic
addition at nitrogen is incompatible with the simple con-
straints imposed by electron counting in this system.
Figure 1. Oak Ridge Thermal Ellipsoid Plot (ORTEP) diagram of
2c[BAr′4]. Thermal ellipsoids are drawn with 50% probability. Hydrogen
atoms, the BAr′4 counterion, and 0.5 Et2O are omitted for clarity.
ancillary two-electron donor CO ligand in [W(CO)(η2-
RNdCR)(acac)2]+ with a variable electron donor alkyne.
Substitution of CO by an alkyne in the cationic iminoacyl-
CO tungsten(II) reagent relieves the ligand derived from η2-
RCt N of its responsibility to function as the sole four-
electron donor to tungsten. The nitrogen lone pair of the η2-
imine ligand, datively bound to tungsten when CO is the
ancillary ligand in the coordination sphere, becomes suf-
ficiently nucleophilic to react with potent electrophiles once
an alkyne replaces CO. Results presented here are comple-
mentary to reactions observed in low-valent Tp′ [Tp′ )
hydridotris(3,5-dimethylpyrazolyl)borate] tungsten(II) com-
plexes in which coordinated η1-acetonitrile undergoes se-
quential reduction to an amine.34,35
Iminium cations17 (R2NdCR2 ) are postulated as inter-
+
mediates in several fundamental organic reactions including
Knoevenagel condensations,18,19 decarboxylation of ꢀ-ke-
toacids,20,21 and Diels-Alder type cyclizations.22-24 Iminium
ligands in transition metal complexes have resulted from
direct reactions of iminium salts with metal reagents,25,26
from rearrangements involving group transfer to imine
ligands,27,28 from ꢀ-hydride elimination of amines,29,30 and
from nitriles using strong reductants or other harsh condi-
tions.31-33
Results and Discussion
Thermal Substitution of CO with RNC or PR3
Ligands. Addition of tert-butylisonitrile to a cold solution
of η2-iminoacyl complex [W(CO)(η2-MeNdCPh)(acac)2]+
1a leads to [W(CNtBu)(η2-MeNdCPh)(acac)2]+ (2a) (Scheme
1). No CO absorbance is observed via in situ IR spectroscopy
after 20 min of stirring at 0 °C; this is a surprisingly facile
substitution reaction. For complex 2a, the N-methyl reso-
nance in the 1H NMR spectrum shifts downfield to 5.67 ppm
from the 4.97 ppm value of the iminoacyl-carbonyl precursor.
The iminoacyl carbon resonates downfield at 239.7 ppm in
the 13C NMR spectrum. Low temperature 13C NMR spec-
troscopy (240 K) reveals the metal-bound isonitrile carbon
at 146.1 ppm, indicative of σ-bound isonitrile.
The solid state structure of 2c[BAr′4] (BAr′4 ) tet-
rakis[(3,5-trifluoromethyl)phenyl]borate) reflects simple sub-
stitution of the carbon monoxide ligand by 2,6-dimethylphe-
nylisonitrile (Figure 1). The nitrogen atom of the iminoacyl
ligand is distal with respect to the cis isonitrile ligand, thus
adopting the same orientation as the parent CO complex.
The W-C-N triangular geometry is barely perturbed by
replacement of CO with 2,6-dimethylphenylisonitrile.
Addition of triphenylphosphine to iminoacyl cation 1a also
leads to carbon monoxide replacement. The product is an
air and moisture sensitive deep purple complex, [W(PPh3)(η2-
We now report conversion of an η2-imine to an η2-iminium
ligand; this reaction is enabled by replacement of the
(16) Templeton, J. L. AdV. Organomet. Chem. 1989, 29, 1.
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Inorganic Chemistry, Vol. 47, No. 19, 2008 8777

Jackson et al.
Scheme 2. Thermal Replacement of CO with Bulky Phosphine
Reagents
MeNdCPh)(acac)2]+ (3a) (Scheme 2). Salient spectroscopic
data include a peak far downfield at 6.74 ppm in the 1H NMR
spectrum attributed to the nitrogen-bound methyl group; the
identity of this signal was confirmed via heteronuclear
multiple-bond correlation (HMBC) spectroscopy. The imi-
noacyl carbon resonates at 241.1 ppm in the 13C NMR
spectrum, and no phosphorus coupling is evident. The 31P
NMR spectrum displays a single resonance at -5.25 ppm
with tungsten satellites [1JP-W ) 349 Hz, 183W (14.28%), I
) 1/2]. These data are consistent with simple replacement of
CO by PPh3, although the intense purple color and 6.74 ppm
methyl chemical shift location are surprising.
Figure 2. ORTEP diagram of 3b[BAr′4]. Thermal ellipsoids are drawn
with 50% probability. Hydrogen atoms, the BAr′4 counterion, and a molecule
of Et2O are omitted for clarity.
Scheme 3. Behavior of the Iminoacyl Ligand Adjacent to Bulky
Phosphine Ligands
Tricyclohexylphosphine (PCy3) also replaces the CO
ligand in 1a, and [W(PCy3)(η2-MeNdCPh)(acac)2]+ (3b)
forms (Scheme 2). However, room temperature NMR
1
spectroscopy shows broad resonances in H, 13C, and 31P
spectra. A broad peak attributed to the nitrogen-bound methyl
1
group resonates at 8.44 ppm in the room temperature H
spectrum, a significant downfield shift from the analogous
resonance in 1a. Additionally, acetylacetonate methyl signals
at 4.14 and 3.58 ppm exhibit line broadening and unusual
downfield chemical shifts. The room temperature 13C NMR
spectrum shows broad peaks for the nitrogen-bound methyl
(43.9 ppm) and two of the acetylacetonate keto-carbons
(196.2 and 202.3 ppm). Room temperature 31P NMR
spectroscopy reveals a broad peak at -23.2 ppm devoid of
tungsten satellites. Variable temperature spectra indicate a
temperature dependence for the chemical shift of the
nitrogen-bound methyl group. Over a temperature range of
130 degrees with CD2Cl2 as solvent, the methyl resonance
varies from 6.94 ppm (185 K) to 8.94 ppm (315 K),
broadening as the temperature increases. At 200 K, the
iminoacyl carbon resonance appears at 247.1 ppm, and as
in the analogous complex 3a, shows no coupling to phos-
phorus. At 160 K using CDCl2F as a solvent the PCy3
phosphorus resonance appears as a sharp singlet at 18.0 ppm
(1JP-W ) 351 Hz).
iminoacyl carbon appears as a doublet at 235.2 ppm (2JP-C
) 36 Hz) in the 13C NMR spectrum. Note that PCy3 does
not replace CO in 1b.
The solid state structure of [W(PCy3)(η2-MeNd
CPh)(acac)2][BAr4′], 3b[BAr′4], confirms replacement of CO
with the bulky phosphine reagent (Figure 2). Most notable
is a change in the W-N-C triangle orientation as the
N2-C3 bond of the iminoacyl ligand is orthogonal to the
new W1-P1 bond (Scheme 3). Presumably, the increased
steric demand of PCy3 in the coordination sphere forces the
iminoacyl ligand to rotate 90° from the geometry observed
for CO complex 1a. The aromatic phenyl ring lies in the
plane defined by the W1-N2-C3 triangle, perhaps reflecting
π-delocalization. Bond distances from tungsten to the C and
N atoms in the iminoacyl ligand decrease relative to the same
bonds in 1a. Considerable shortening is observed for W1-C3
(1.990(4) Å), down from 2.069(8) Å in the CO-precursor.
The carbon nitrogen bond, N2-C3, lengthens 0.041 Å to
1.324(5) Å. This lengthening suggests the iminoacyl ligand
receives more backbonding from tungsten after replacing the
Addition of PPh3 to 1b produces [W(PPh3)(η2-
MeNdCMe)(acac)2]+, 3c, over the course of several hours.
This reaction with 1b proceeds more slowly than the
analogous reaction with reagent 1a. The N-methyl group in
3c resonates at 5.80 ppm in the 1H NMR spectrum, and the
8778 Inorganic Chemistry, Vol. 47, No. 19, 2008

Reduction of an η2-Iminoacyl Ligand to η2-Iminium
Scheme 4. Proposed Mechanism of Reversible Tricyclohexylphosphine
Dissociation
Scheme 5. Nucleophilic Attack at the Iminoacyl Carbon with PMe3
Scheme 6. Photolytic Replacement of CO with Alkyne Reagents
strong π-acid CO ligand with a poorer π-acid phosphine
ligand. A partially solved structure of PPh3 adduct 3c[BAr′4]
clearly shows that the NdC bond remains parallel to the
W-P bond suggesting that without a π-acid adjacent to the
iminoacyl ligand the rotational energy profile is relatively
shallow (Scheme 3). Disorder in one of the auxiliary
acetylacetonate chelates prevents refinement.
the imine-like nature of the sidebound ligand: a doublet
assigned to the “imine” carbon for the major diastereomer
resonates at 50.9 ppm (1JP-C ) 84 Hz). A doublet centered
at 241.1 ppm with phosphorus coupling (3JP-C ) 8 Hz) is
assigned to the CO carbon. Similar results were obtained
using PMe2Ph as a reagent, so the PMe3 and PMe2Ph
products reflect attack at the iminoacyl carbon, while the
larger PPh3 and PCy3 ligands replace CO in the coordination
sphere of tungsten.
Photolytic Replacement of CO with Alkyne. Because
of the propensity of tungsten(II) to bind a four-electron donor
ligand in a six-coordinate environment,8,15,40 we investigated
replacement of CO with alkyne ligands. Unlike linearly
ligating π-acid carbon monoxide ligands, alkynes are excel-
lent single-faced π-acids, and additionally alkynes can serve
as variable electrons donor ligands through their π⊥ elec-
trons.16 This π-donor feature has the ability to alter the
behavior of the adjacent η2-iminoacyl ligand.
Spectroscopic data indicate rapid, reversible phosphine
dissociation as one process responsible for the observed
fluxionality in [W(PCy3)(η2-MeNdCPh)(acac)2]+. Selective
line broadening is evident for this molecule with a pseudo-
octahedral framework. Phosphine dissociation could allow
the acetylacetonate chelate (AB) near the nitrogen-bound
methyl to swing up toward the vacant coordination site,
altering the geometry of the intermediate to a pseudotrigonal
bipyramid with a mirror plane relating the two ends of the
AB acetylacetonate that moved while leaving the other
acetylacetonate (CD) in the same NMR environment (Scheme
4). Recoordination of PCy3 could force the AB chelate either
back to its original position or swing acetylacetonate AB to
move end B into the position trans to PCy3 in the octahedron,
producing the enantiomer of the original complex. This
mechanism explains the broad NMR resonances observed
for only one acetylacetonate chelate and the phosphine, while
signals for the phenyl ring and the other acetylacetonate
chelate remain sharp.
The outcome of phosphine addition to 1a reflects a
dependence on the size of the phosphine reagent.36-39 Unlike
PPh3 or PCy3, trimethylphosphine (PMe3) adds to 1a at the
iminoacyl carbon to form [W(CO)(η2-MeNdC(PMe3)Ph)
(acac)2]+ complex 4 (Scheme 5). This result mirrors reactivity
observed when Na[HB(OMe)3] or MeMgBr attacks the
cationic 1a and reduces the iminoacyl ligand to an imine.8
After PMe3 addition, IR spectroscopy shows a single CO
absorbance at 1904 cm-1, a decrease of ∼80 cm-1 from νCO
in the starting material. Addition of PMe3 to the iminoacyl
carbon indirectly pushes electron density to the metal center.
1H NMR spectroscopy shows two diastereomers in an
approximate ratio of 2:1. 13C NMR spectroscopy supports
Refluxing phenylacetylene and 1a in THF produces a small
amount of [W(η2-PhCt CH)(η2-MeNdCPh)(acac)2]+, 5a. On
the other hand, photolysis in methylene chloride produces
the alkyne-iminoacyl cation in good yields (65-75%)
(Scheme 6).
Note that for an unsymmetrical alkyne, four NMR
distinguishable isomers are possible (Figure 3). Each of the
four isomers shown has an enantiomer to total eight isomers.
All four alkyne-iminoacyl derivatives, including the two
phenylacetylene and the two 2-butyne complexes, yield two
isomers as observed by NMR spectroscopy. The isomer
distribution is independent of the symmetry of the alkyne
and is compatible with a single alkyne orientation relative
to the two acetylacetonate chelates combined with two
1
iminoacyl orientations. The room temperature H NMR
spectrum of the phenylacetylene adduct, 5a, shows two
isomers in a 3:1 ratio. The terminal alkyne proton on the
phenylacetylene ligand for the major isomer resonates
downfield at 13.45 ppm in the region typical of four-electron
(36) Pearson, J.; Cooke, J.; Takats, J.; Jordan, R. B. J. Am. Chem. Soc.
1998, 120, 1434.
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6205.
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Jackson et al.
Scheme 7. Displacement of Triphenylphosphine with Either Isonitrile
or Alkyne Reagents
Figure 3. Four possible isomers of asymmetric alkyne derivative 5a.
or alkyne reagents (Scheme 7). Following generation of 3a
in situ, addition of tert-butylisonitrile or phenylacetylene
quickly forms either 2a or 5a, respectively, as confirmed by
1H NMR spectroscopy. This stepwise substitution methodol-
ogy provides an attractive, two-step thermal route to com-
plexes 5a-d as an alternative to photolytic preparation.
Orbital Interactions and Electron Counting. Cationic
iminoacyl bis(acac) complexes 1a and 1b can be mapped to
the same MO model as analogous neutral bis(acac) η2-alkyne
or η2-nitrile complexes in terms of electron donation from
the iminoacyl ligand and the oxidation state of the tungsten
center (Figure 5). If the neutral W(L)(acac)2 (L ) CO, CNR)
fragment is counted as a low valent W(II) d4 fourteen-
electron moiety, four electrons must be supplied from the
cationic iminoacyl ligand (MeNdC+R), equivalent to a
nitrilium (MeN+t CR), to optimally utilize the available
electrons and orbitals. Carbon monoxide or isonitrile, situated
along the z-axis, will stabilize the dπ orbitals with z-character,
and thus dictate the location of the four W(II) metal-based
electrons. Binding the cationic iminoacyl fragment along the
x-axis further stabilizes dxz via backbonding, and also pushes
the empty dxy orbital up in energy as the antibonding
component reflecting donation from the filled π⊥ orbital on
the MeN+t CR ligand. This bonding description treats the
cationic four-electron donor ligand like an alkyne. The
Figure 4. ORTEP diagram of 5a[BAr′4]. Thermal ellipsoids are drawn
with 50% probability. Non-essential hydrogen atoms and the BAr′4
counterion are omitted for clarity.
donor alkynes. Both the alkyne and the iminoacyl ligands
appear to be static on the NMR time scale. At room
temperature the 13C NMR spectrum of 5a shows the
iminoacyl carbon resonance at 217.0 ppm. The alkyne
carbons of the major isomer resonate at 208.2 (PhCt CH)
and 204.6 ppm (PhCt CH).
The solid state structure of the cationic alkyne-iminoacyl
complex 5a[BAr′4] shows the iminoacyl ligand is rotated
90° relative to reagent 1a[OTf]. The C-N linkage in
5a[BAr′4] is roughly parallel to the trans O-W-O axis
(Figure 4). The alkyne and iminoacyl ligands are (i) π-bound
to the metal, (ii) cis to each other, and (iii) parallel to one
another. The N-methyl group is proximal to the terminal
alkyne proton on the phenylacetylene ligand, and the two
phenyl rings are proximal to each other. In spite of the
π-donor capability of the alkyne ligand, the two bonds from
tungsten to the iminoacyl differ only slightly from those in
the precursor carbonyl-iminoacyl cation. The W1-C3 bond
is 2.052(9) Å, and the W1-N2 bond is 1.990(8) Å.
Displacement of Triphenylphosphine. The triphenylphos-
phine ligand in 3a can be easily displaced by either isonitrile
Figure 5. Orbital diagram for 1 and 2.
8780 Inorganic Chemistry, Vol. 47, No. 19, 2008

Reduction of an η2-Iminoacyl Ligand to η2-Iminium
Figure 8. ORTEP diagram of 6[BAr′4]. Thermal ellipsoids are drawn with
50% probability. Hydrogen atoms and the BAr′4 counterion are omitted
for clarity.
Scheme 8. Nucleophilic Attack by PMe3 at Iminoacyl Carbon in 5b
Figure 6. Orbital diagram for 3a and 3b.
Mo, W) complexes,41,42 but the symmetry of two equivalent
alkyne donors is broken.43 Spectroscopic and structural data
imply that the alkyne ligand contributes more electron density
into dxz than the iminoacyl ligand in accord with electrone-
gativity expectations. In the end a total of six electrons will
be donated from the two η2-ligands, but combinations along
a continuum ranging from 2+4 through 3+3 to 4+2 from
the iminoacyl and alkyne ligands, respectively, are conceiv-
able in the absence of symmetry constraints.
Figure 7. Orbital diagram for 5.
Phosphine Addition to Cationic Iminoacyl-Alkyne
Complexes. Addition of PMe3 to 5b[BAr′4] produces the
cationic imine complex [W(η2-MeCt CMe)(η2-MeNd
C(PMe3)Ph)(acac)2][BAr′4], 6[BAr′4], (Scheme 8). Two
isomers are present in a ratio of ∼20:1. Room temperature
1H NMR data reveal hindered rotation of the alkyne as
evidenced by a broad singlet for each methyl group on
2-butyne (2.78 and 1.42 ppm). Additionally, the ortho and
meta phenyl protons are broad indicating hindered rotation
of the phenyl ring. Low temperature NMR studies show
sharpening and shifting of alkyne and phenyl resonances,
eventually slowing rotation of the phenyl ring to reveal five
distinct resonances at 203 K. 13C NMR data indicate
decreased electron donation from the alkyne in 6 with
resonances at 182.7 and 182.8 ppm compared to the alkyne
in 5b which has 13C signals at 208 ppm. The former
iminoacyl carbon shifts upfield to 52.8 ppm in 6 from 217.5
ppm in 5b. In spite of the direct P-C connection, no
phosphorus coupling can be distinguished in this broad C-13
resonance. The solid state structure shows retention of the
basic connectivity of 5a (Figure 8). The high diastereo-
selectivity (20:1) contrasts with the poor stereoselectivity
transparency of mapping RN+t CR onto RCt CR leads us
to favor this description for building a simple MO picture,
but it is worthwhile to note that the final result can be
constructed using RNdC--R and a d2 W(IV) formalism
with the anionic η2-iminoacyl providing a total of six
electrons to the metal.
A different orbital diagram emerges for phosphine complex
3a (Figure 6). No significant stabilization of the four dπ
electrons is expected from the phosphine. With no dominant
electronic preference for binding the η2-NC ligand either
parallel or orthogonal to the W-P bond, the steric interac-
tions between the bulky phosphine ligand and the phenyl
ring favor the observed orthogonal orientation of the imi-
noacyl ligand. The intense color and rapid decomposition
upon exposure to air are compatible with a high lying highest
occupied molecular orbital (HOMO) that lacks stabilization
by a π-acid ligand.
In contrast, complexes 5a-d feature a variable electron
donor alkyne that also serves as a single faced π-acid capable
of stabilizing the filled dyz orbital while the iminoacyl ligand
stabilizes the filled dxy orbital (Figure 7). Both of these
π-bound ligands compete to donate electrons from their
respective π⊥ orbitals into the empty dxz orbital, and the result
is a three-center four-electron interaction. This outcome
tracks orbital diagrams describing M(II)bis(alkyne) (M )
(41) Herrick, R. S.; Templeton, J. L. Organometallics 1982, 1, 842.
(42) Herrick, R. S.; Burgmayer, S. J. N.; Templeton, J. L. Inorg. Chem.
1983, 22, 3275.
(43) Etienne, M.; Carfagna, C.; Lorente, P.; Mathieu, R.; de Montauzon,
D. Organometallics 1999, 18, 3075.
Inorganic Chemistry, Vol. 47, No. 19, 2008 8781

Jackson et al.
Scheme 9. Nucleophilic Attack of 5a by PMe3 at the Terminal Carbon
of η2-PhCt CH
Scheme 10. Addition of Na[HB(OMe)3] to Produce the Alkyne-Imine
Complex 8
Figure 9. ORTEP diagram of 8. Thermal ellipsoids are drawn with 50%
probability. Non-essential hydrogen atoms are omitted for clarity.
Scheme 11. Alkylation with MeOTf to Form the Alkyne-Iminium
Complex 9[OTf]
observed in the analogous reaction to form complex 4 from
the CO complex 1a (d.r. ∼ 2:1) discussed above.
With a terminal alkyne adjacent to the iminoacyl ligand
in 5a[BAr′4], addition of PMe3 generates an η2-vinyl species,
[W(η2-MeNdCPh)(η2-PhC)C(H)PMe3)(acac)2][BAr′4], 7-
[BAr′4], via attack at the terminal alkyne carbon of the
coordinated phenylacetylene (Scheme 9). 1H NMR spectros-
copy confirms the presence of four isomers in a 10:4:3:2
ratio, and no acetylene proton is present at low field. The
former acetylenic proton resonates at 3.04 ppm (2JP-H ) 27
Hz) in the major isomer. The 13C NMR spectrum shows a
resonance at 31.6 ppm (1JP-C ) 85 Hz) corresponding to
the four-coordinate η2-vinyl carbon as confirmed with
HMQC spectroscopy. The other vinyl carbon resonates at
241 ppm, indicating alkylidene character. These resonances
are typical of η2-vinyl ligands, also known as metallocyclo-
propenes. Examples of η2-vinyls generated by nucleophilic
attack on a terminal η2-alkyne ligand have been known for
some time.45,46
Reduction of the Iminoacyl Ligand. Addition of Na[H-
B(OMe)3] to [W(η2-MeCt CMe)(η2-MeNdCPh)(acac)2]+,
5b, in tetrahydrofuran (THF) results in hydride addition to
form W(η2-MeCt CMe) (η2-MeNdCHPh)(acac)2, 8, (Scheme
10). The molecule is fluxional at room temperature in
solution, and NMR peak assignments were based on low
temperature spectra. At 200 K, rearrangement processes are
sufficiently slow to reveal the presence of four isomers (two
diastereomers for both imine orientations) resulting from
hydride addition at the iminoacyl carbon. The hydride added
to form the imine resonates at 2.40 ppm in the major isomer
of 8, well upfield from the analogous resonance of the
comparable carbonyl-imine complex at 5.56 ppm.8
K the imine carbon in the major isomer resonates at 73.6
ppm in the 13C NMR spectrum reflecting hybridization to a
pseudotetrahedral sp3 carbon resulting from hydride addition.
The two alkyne carbons in the major isomer resonate at 204.7
and 208.7 ppm.
X-ray data for 8 reveal the phenyl ring of the iminoacyl
ligand lying over the adjacent acetylacetonate chelate. This
contrasts with structures for 3b and 5a in which the N-methyl
group lies near the chelate ring in the two cis positions.
Significant lengthening of both the tungsten-carbon bond
[W1-C7 ) 2.220(3) Å, (+0.168 Å)] and the nitrogen-carbon
bond [N6-C7 ) 1.395(4) Å, (+0.134 Å)] results from
hydride addition to form the imine, consistent with reduction
to form an sp3 hybridized carbon. (Figure 9).
Formation of a Coordinated Iminium. Alkylation of
complex 8 with MeOTf yields four isomers of [W(η2-
MeCt CMe)(η2-Me2NdCHPh)(acac)2][OTf], 9[OTf] (Scheme
11). The proton attached to the iminium carbon resonates at
3.99 ppm (major), a downfield shift from the value observed
for 8 (2.40 ppm). The diastereotopic nitrogen-bound methyl
groups appear as singlets at 2.97 and 2.68 ppm, and the
terminal methyl groups on the 2-butyne ligand coincide at
2.82 ppm, probably because of rapid alkyne rotation. The
13C NMR spectrum clearly supports the role of the alky-
ne ligand as the lone four-electron donor in 7; the two alkyne
carbons resonate at 240 ppm. This chemical shift reflects
the role of the η2-iminium fragment as a simple two-electron
donor. The iminium carbon appears at 91 ppm. Overall, the
original benzonitrile ligand15 undergoes three additions
(electrophile, nucleophile, electrophile) and is formally
reduced to a coordinated iminium fragment.
One fluxional process in 8 that has no bearing on the
isomer distribution is rotation of the 2-butyne ligand.
Coalescence for 2-butyne rotation occurs at 247 K, corre-
sponding to a free energy value of 14.3 kcal/mol.44 At 200
(44) Gutowsky, H. S.; Holm, C. H. J. Chem. Phys. 1956, 25, 1228.
(45) Morrow, J. R.; Tonker, T. L.; Templeton, J. L. J. Am. Chem. Soc.
1985, 107, 6956.
(46) Frohnapfel, D. S.; Templeton, J. L. Coord. Chem. ReV. 2000, 206,
199.
8782 Inorganic Chemistry, Vol. 47, No. 19, 2008

Reduction of an η2-Iminoacyl Ligand to η2-Iminium
spectrometer. Elemental analysis was preformed by Atlantic Mir-
crolab, Norcross, GA, and Robertson Microlit, Madison, NJ. Mass
spectra (MS) and high resolution mass spectra (HRMS) were
acquired with a Bruker BioTOF II reflectron time-of-flight (reTOF)
mass spectrometer equipped with an Apollo electrospray ionization (ESI)
source. Mass spectral data are reported for the most abundant tungsten
isotope. Crystal and data collection parameters as well as salient crystal-
lographic and spectroscopic data are presented in Tables 1-3.
1
Representative [BAr′4]- NMR Data. H and 13C NMR data
for the [BAr′4]- counterion are reported separately for simplicity.
1H NMR (CD2Cl2, 193 K, δ): 7.77 (br, 8H, o-Ar′), 7.60 (br, 4H,
p-Ar′). 13C{1H} NMR (CD2Cl2, 193 K, δ): 162.2 (1:1:1:1 pattern,
2
1JB-C ) 50 Hz, Cipso), 135.3 (Cortho), 129.4 (qq, JC-F ) 30 Hz,
4JC-F ) 5 Hz, Cmeta), 125.1 (q, 1JC-F ) 270 Hz, CF3), 117.9 (Cpara).
[W(CO)(η2-MeNdCPh)(acac)2][BAr′4] (1a[BAr′4]). 1a[OTf]
(0.305 g, 0.450mmol) was dissolved in methylene chloride, and
NaBAr′4 (0.398 g, 0.449 mmol) was added under a backflow of
N2. The solution was stirred for 2 h and cannula filtered away from
the residual sodium salts. The red-brown solid was triturated with
methylene chloride and hexanes to yield a brown powder (0.450
g, 0.323 mmol, 72%).
[W(CO)(η2-MeNdCMe)(acac)2][BAr′4] (1b[BAr′4]). 1b[OTf]
(0.22 g, 0.36 mmol) was dissolved in methylene chloride, and
NaBAr′4 (0.35 g, 0.39 mmol) was added under a backflow of N2.
The solution was stirred for 1 h and cannula filtered away from
the residual sodium salts. The green-brown solid was triturated with
methylene chloride and hexanes to yield a green-brown powder
(0.350 g, 0.27 mmol, 76%).
Figure 10. ORTEP diagram of 9[BAr′4]. Thermal ellipsoids are drawn
with 50% probability. Non-essential hydrogen atoms and the BAr′4
counterion are omitted for clarity.
The solid state structure shows the added methyl group is
bound to the η2-iminium nitrogen and both N7 and C8 of
the iminium ligand assume a tetrahedral geometry (Figure
10). The W1-N7 linkage lengthens substantially to 2.190(4)
Å, reflecting a loss of double bond character present in the
neutral precursor molecule (1.952(3) Å).
Summary
The carbon monoxide ligand in the cationic iminoacyl-
carbonyl complexes (1a or 1b) is easily displaced thermally
with either isonitrile or bulky phosphine reagents, or pho-
tolytically with alkyne reagents to form [W(L)(η2-
MeNdCR)(acac)2]+ [L ) tBuNC, 2,6-Me2PhNC, PPh3, PCy3,
PhCt CH, MeCt CMe] complexes. Trimethylphosphine at-
tacks the iminoacyl carbon in these cationic complexes to
form [W(L)(η2-MeN-C(PMe3)Ph)(acac)2]+ (L ) CO, 2-bu-
tyne) complexes. Replacement of the π-acid CO ligand with
a four-electron donor alkyne allows further reduction of the
iminoacyl ligand to a sidebound iminium ligand via hydride
addition and subsequent methylation.
[W(CNtBu)(η2-MeNdCPh)(acac)2][OTf] (2a[OTf]). A 100 mL
Schlenk flask was charged with 1a[OTf] (85 mg, 0.13 mmol) which
was dissolved in methylene chloride (10 mL) at 0 °C resulting in
a burgundy solution. Addition of tert-butylisonitrile (20 µL, 0.17
mmol) caused a color change from burgundy to deep purple within
5 min. IR spectroscopy indicated no metal-carbonyl absorbances.
Hexanes were added to precipitate a dark purple powder (35 mg,
1
0.048 mmol, 38%). H NMR (CD2Cl2, 298 K, δ): 7.77-7.81 (m,
2H, m-C6H5), 7.62-7.65 (m, 2H, o-C6H5), 7.38-7.42 (m, 1H,
p-C6H5), 5.81, 5.90 (each a s, each 1H, acac CH), 5.67 (s, 3H,
N-CH3), 2.88, 2.59, 2.34, 2.15 (each a s, each 3H, acac CH3),
1.46 (s, 9H, -(CH3)3). 13C{1H} NMR (CD2Cl2, 298 K, δ): 25.0,
25.1, 26.4, 28.0 (acac CH3), 32.0 (-(CH3)3), 40.0 (N-CH3), 59.4
(CN-C-(CH3)3), 98.7, 102.9 (acac CH), 128.0 (p-C6H5), 128.6,
133.3 (o/m-C6H5), 135.7 (ipso-C6H5), 146.5 (CNtBu), 189.5, 190.0,
191.6, 200.0 (acac CO), 234.4 (NdC). MS (ESI) m/z Calc.: 583.2
Experimental Section
General Information. 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 use. Methylene chloride, diethyl ether, hexanes, and
pentane were purified by passage through an activated alumina
column under a dry argon atmosphere.47 THF was distilled from a
sodium ketal suspension. Methylene chloride-d2 was dried over
CaH2 and degassed. Complexes 1a[OTf] and 1b[OTf]8 and
NaBAr′448 were made in accordance with literature procedures. All
other reagents were purchased from commercial sources and used
without further purification. NMR data are given for one salt (OTf
or BAr′4); chemical shift differences between the two salts are
negligible.
t
(M+), 500.1 (M+ - BuNC). Found: 583.2, 500.1.
[W(CNtBu)(η2-MeNdCMe)(acac)2][BAr′4] (2b[BAr′4]). 1b-
[BAr′4] (51 mg, 0.038 mmol) was dissolved in methylene chloride
(10 mL) in a 100 mL Schlenk flask resulting in an olive green
solution. Addition of tert-butylisonitrile (10 µL, 0.084 mmol) at 0
°C caused a color change to red over 30 min of stirring. Hexanes
(25 mL) were added to precipitate a red solid (45 mg, 0.033 mmol,
85%). 1H NMR (CD2Cl2, 298 K, δ): 5.82, 5.73 (each a s, each 1H,
acac CH), 5.38 (s, 3H, N-CH3), 4.63 (s, 3H, NdC-CH3), 2.86,
2.55, 2.25, 2.10 (each a s, each 3H, acac CH3), 1.50 (s, 9H,
C-(CH3)3). 13C{1H} NMR (CD2Cl2, 298 K, δ): 18.6 (NdC-CH3),
24.7, 24.9, 26.3, 27.8 (acac CH 3), 32.8 (C-(CH3)3), 38.3 (N-CH3),
59.4 ( C-(CH3)3), 98.7, 102.3 (acac CH), 189.7, 190.2, 191.9, 200.3
(acac CO), 240.2 (NdC). 13C{1H} NMR (CD2Cl2, 240 K, δ): 146.2
NMR spectra were recorded on Bruker DRX400, AMX400, or
AMX300 spectrometers. Phosphorus chemical shifts were refer-
enced to H3PO4 as an external standard. Infrared spectra were
recorded on an ASI Applied Systems React IR 1000 FT-IR
(CNtBu). HRMS (ESI) m/z Calc.: 521.163 (M+), 438.089 (M+
tBuNC). Found: 521.148, 438.071.
-
[W(2,6-dimethylphenylisonitrile)(η2-MeNdCMe)(acac)2][BAr′4]
(2c[BAr′4]). A 100 mL Schlenk flask was charged with 1b[BAr′4]
(55 mg, 0.041 mmol) which was dissolved in methylene chloride
(47) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(48) Yakelis, N. A.; Bergman, R. G. Organometallics 2005, 24, 3579.
Inorganic Chemistry, Vol. 47, No. 19, 2008 8783

Jackson et al.
Table 1. Crystal and Data Collection Parameters for [W(CN-C6H3Me2)(η2-MeNdCMe)(acac)2][BAr′4] (2c[BAr′4]);
[W(PCy3)(η2-MeNdCPh)(acac)2][BAr′4] (3b[BAr′4]); and [W(η2-PhCt CH)(η2-MeNdCPh)(acac)2][BAr′4] (5a[BAr′4])
complex
2c[BAr′4]
3b[BAr′4]
5a[BAr′4]
1
empirical formula
fw
color
C54H41BF24N2O4W /2Et2O
1469.61
red/brown
C68H67BF24NO4PW·Et2O
1717.98
purple
C58H40BF24NO4W
1465.57
yellow
T (K)
100(2)
100(2)
100(2)
λ (Å)
0.71703
0.71703
triclinic
P1
0.71703
cryst syst
space group
a (Å)
triclinic
triclinic
j
j
j
P1
P1
13.0368(4)
13.0932(3)
20.0413(6)
76.898(2)
80.350(2)
78.311(2)
3236.10(16)
2
12.5105(2)
16.0383(3)
19.8966(4)
70.525(1)
86.315(1)
84.339(1)
3740.65(12)
2
12.9884(4)
14.3778(5)
17.9290(6)
111.900(2)
99.667(2)
99.845(2)
2960.84(17)
2
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
vol. (Å3)
Z
Fcalcd (mg/m3)
µ, mm-1
F(000)
1.508
1.90
1454
1.525
1.674
1732
1.644
2.073
1444
crystal size (mm3)
2θ range (deg)
index ranges
0.20 × 0.20 × 0.05
1.05 to 25.00
-15 e h e 15
-11 e k e 14
-23 e l e 19
24028
11344
11344/0/798
1.018
0.25 × 0.20 × 0.15
1.09 to 26.51
-15 e h e 15
-20 e k e 20
-22 e l e 24
51721
15443
15443/138/1007
1.024
0.15 × 0.15 × 0.10
1.64 to 25.00
-15 e h e 15
-17 e k e 17
-21 e l e 21
43710
10391
10391/0/808
1.074
reflections collected
independent reflections
data/restraints/parameters
goodness-of-fit on F2
R1, wR2[I > 2σ(I)]
R1, wR2 (all data)
0.0663, 0.1725
0.1088, 0.2064
0.0357, 0.0822
0.0458, 0.0878
0.0611, 0.1361
0.0789, 0.1450
Table 2. Crystal and Data Collection Parameters for [W(η2-MeCt CMe)(η2-MeNdC(PMe3)Ph) (acac)2][BAr′4] (6[BAr′4]);
W(η2-MeCt CMe)(η2-MeNdCHPh)(acac)2 (8); and [W(η2-MeCt CMe)(η2-Me2NdCHPh)(acac)2][BAr′4] (9[BAr′4])
complex
6[BAr′4]
8
9[BAr′4]
empirical formula
fw
C57H49BF24NO4PW
1493.60
C22H29NO4W
555.31
C55H44BF24NO4W
1433.57
color
yellow
orange
orange
T (K)
λ (Å)
cryst syst
space group
a (Å)
100(2) K
0.71073
monoclinic
P21/c
12.7556(3)
19.0951(5)
24.7718(6)
90
96.020(1)
90
6000.4(3)
4
1.653
2.072
2960
0.43 × 0.37 × 0.16
1.60 to 24.96
-15 e h e 15
-22 e k e 22
-29 e l e 29
110435
10560
10560/168/896
1.079
100(2) K
0.71703 Å
triclinic
100(2) K
1.54178
triclinic
j
j
P1
P1
8.4166(11)
10.2419(13)
13.3165(19)
99.903(6)
97.032(7)
92.263(6)
1120.1(3)
2
12.4372(3)
12.7720(3)
18.6366(5)
87.162(1)
80.333(1)
79.078(1)
2865.01(12)
2
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
vol. (Å3)
Z
Fcalcd (mg/m3)
µ, mm-1
F(000)
1.646
5.182
548
1.662
4.863
1416
crystal size (mm3)
2θ range (deg)
index ranges
0.25 × 0.20 × 0.10
1.57 to 30.00
-11 e h e 11
-14 e k e 14
-18 e l e 18
41685
6522
6522/0/260
1.110
0.30 × 0.15 × 0.10
2.41 to 67.00
-14 e h e 14
-15 e k e 15
-22 e l e 22
50256
9953
9953/18/811
1.108
reflections collected
independent reflections
data/restraints/parameters
goodness-of-fit on F2
R1, wR2[I > 2σ(I)]
R1, wR2 (all data)
0.318, 0.0750
0.0374, 0.0778
0.0274, 0.0765
0.0288, 0.073
0.0518, 0.1408
0.00521, 0.1411
(10 mL) resulting in an olive green solution. Addition of 2,6-
dimethylphenylisonitrile (6 mg, 0.046 mmol) at 0 °C caused a color
change to red over 30 min of stirring. Addition of hexanes (25
mL) led to precipitation of a red solid (47 mg, 0.033 mmol, 79%).
The product was dissolved in a small amount of diethyl ether and
layered with hexanes in an inert atmosphere at -30 °C. After 3
days red-brown needles formed, and these were suitable for X-ray
analysis. 1H NMR (CD2Cl2, 298 K, δ): 7.26 (d, 2H, m-C6H3Me2),
7.05 (t, 1H, p-C6H3Me2), 5.82, 5.78 (each a s, each 1H, acac CH),
5.26 (s, 3H, N-CH3), 4.61 (s, 3H, NdC-CH3), 2.83, 2.51, 2.28,
2.13 (each a s, each 3H, acac CH3), 2.51 (s, 6H, C6H3(CH3)2).
13C{1H} NMR (CD2Cl2, 298 K, δ): 18.7 (C6H3(CH3)2), 19.4
8784 Inorganic Chemistry, Vol. 47, No. 19, 2008

Reduction of an η2-Iminoacyl Ligand to η2-Iminium
Table 3. Salient Crystallographic and Spectroscopic Data
13C, Nt
(δ)
C
13C, Ct
(δ)
C
IR, νCO
(cm-1
complex
W-N (Å)
W-C (Å)
C-N (Å)
)
CO-Nitrile15
1a[OTf]8
CO-Imine8
2c[BAr′4]
3b[BAr′4]
4[OTf]
5a[BAr′4]
6
7[BAr′4]
8[BAr′4]
2.018(5)
1.977(7)
1.905(5)
1.963(9)
1.957(3)
n/a
1.990(8)
1.952(3)
2.190(4)
1.925(3)
2.038(5)
2.069(8)
2.274(2)
2.027(11)
1.990(4)
n/a
2.052(9)
2.220(3)
2.168(5)
2.211(4)
1.270(7)
1.283(10)
1.383(2)
1.323(14)
1.324(5)
n/a
1.264(12)
1.395(4)
1.444(7)
1.395(5)
211.2
226.2
59.3, 60.6
239.8
247.1
50.9, 48.4
217.0
76.2
91.4
52.7
n/a
1895
1976
1881, 1885
n/a
n/a
1904
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
204.6, 208.2
204.7, 208.7
240.1
182.7, 182.8
(NdC-CH3), 24.9, 25.1, 26.4, 27.9 (acac CH3), 38.7 (N-CH3),
98.7, 103.0 (acac CH), 128.1, 130.3, 137.2 (C6H3Me2), 189.4, 190.0,
191.4, 200.0 (acac CO), 239.8 (NdC). HRMS (ESI) m/z Calc.:
569.164(M+), 438.090 (M+ - ArNC). Found: 569.166, 438.093.
[W(PPh3)(η2-MeNdCPh)(acac)2][OTf] (3a[OTf]). 1a[OTf] (61
mg, 0.090 mmol) was dissolved in methylene chloride (10 mL) in
a 100 mL Schlenk flask resulting in a burgundy solution. Addition
of triphenylphosphine (24 mg, 0.092 mmol) caused a color change
to deep red-purple within 20 min. IR spectroscopy indicated no
metal-carbonyl absorbances. Hexanes were added to precipitate a
2.22, 2.11, (each a s, each 3H, acac CH3). 13C{1H} NMR (CD2Cl2,
298 K, δ): 17.6 (NdC-CH3), 23.9, 24.6, 26.5, 27.6 (acac CH3),
36.8 (N-CH3), 96.9, 102.4 (acac CH), 189.6, 191.1, 193.0, 200.8
(acac CO), 235.2 (d, NdC, 2JP-C ) 36 Hz). 31P{1H} NMR (CD2Cl2,
1
298 K, δ): 7.46 (s, PPh3, JP-W ) 305 Hz).
[W(CO)(η2-MeN-C(PMe3)Ph)(acac)2][OTf] (4[OTf]). 1a[OTf]
(66 mg, 0.097 mmol) was dissolved in methylene chloride (15 mL)
in a 100 mL Schlenk flask resulting in burgundy solution.
Trimethylphosphine (20 µL, 0.19 mmol) was added causing a color
change to red-brown. Reaction progress was monitored via in situ
IR spectroscopy and was complete once a single CO absorbance
appeared at 1904 cm-1. Solvent volume was reduced in vacuo, and
hexanes were added to precipitate a brown solid (62 mg, 0.081
1
dark purple solid (79 mg, 0.087 mmol, 96%). H NMR (CD2Cl2,
298 K, δ): 6.74 (s, 3H, N-CH3), 6.02, 5.85 (each a s, each 1H,
acac CH), 3.43, 2.84, 2.80, 2.07 (each a s, each 3H, acac CH3).
13C{1H} NMR (CD2Cl2, 298 K, δ): 25.4, 26.2, 27.8, 34.9 (acac
CH3), 36.4 (N-CH3), 98.9, 104.2 (acac CH), 189.0, 192.3, 196.5,
199.3 (acac CO), 241.1 (NdC). 31P{1H} NMR (CD2Cl2, 298 K,
1
mmol, 84%). IR (CH2Cl2): νCO ) 1904 cm-1; H NMR (CD2Cl2,
298 K, δ, major diastereomer): 7.38-7.43 (m, 3H, m and p-C6H5),
7.08-7.10 (d, 2H, o-C6H5), 5.70, 5.64 (each a s, each 1H, acac
CH), 4.07 (s, 3H, N-CH3), 2.39, 2.22, 2.16, 2.12 (each a s, each
1
δ): -5.25 (s, PPh3, JP-W ) 349 Hz).
[W(PCy3)(η2-MeNdCPh)(acac)2][OTf] (3b[OTf]). A 100 mL
Schlenk flask was charged with 1a[OTf] (56 mg, 0.083 mmol) and
methylene chloride (15 mL) resulting in a burgundy solution.
Addition of tricyclohexylphosphine (27 mg, 0.096 mmol) caused
a color change to deep purple within 20 min. IR spectroscopy
indicated no metal-carbonyl absorbances. Hexanes were added to
precipitate at dark purple solid (75 mg, 0.081 mmol, 98%). 1H NMR
(CD2Cl2, 298 K, δ): 8.44 (br, s, 3H, N-CH3), 7.98 (d, 2H, o-C6H5),
7.84 (t, 2H, m-C6H5), 7.23 (t, 1H, p-C6H5), 6.40, 5.97 (each a s,
each 1H, acac CH), 4.11, 3.54, 2.83, 2.11 (each a s, each 3H, acac
CH3).13C{1H} NMR (CD2Cl2, 298 K, δ): 43.9 (br, N-CH3), 98.2,
105.0 (acac CH), 127.6 (m-C6H5), 134.1 (o-C6H5), 136.8 (p-C6H5)
192.6, 199.3 (acac CO), 196.2, 202.3 (br, acac CO).13C{1H} NMR
(CD2Cl2, 200 K, δ): 247.1 (NdC). 31P{1H} NMR (CD2Cl2, 298 K,
δ): -23.2 (br, PCy3). 31P{1H} NMR (CDCl2F, 160 K, δ): 18.0 (s,
2
3H, acac CH3), 1.97 (d, 9H, P-(CH3)3, JP-H ) 13 Hz); 13C{1H}
NMR (CD2Cl2, 298 K, δ, major diastereomer): 10.9 (d, P-(CH3)3,
1JP-C ) 52 Hz), 25.3, 25.6, 27.8, 28.1 (acac CH3), 43.7 (N-CH3),
1
50.9 (d, N-C-P, JP-C ) 84 Hz), 99.9, 102.7 (acac CH), 122.8
(p-C6H5), 127.1 (d, o-C6H5, 3JP-C ) 3 Hz), 129.0 (m-C6H5), 142.0
2
(d, ipso-C6H5, JP-C ) 30 Hz), 186.9, 187.2, 194.7, 196.2 (acac
3
CO), 241.1 (d, Ct O, JP-C ) 8 Hz); 31P{1H}NMR (CD2Cl2, 298
K, δ, major diastereomer): 49.1 (s, PMe3).
W(η2-PhCt CH)(η2-MeNdCPh)(acac)2][BAr4′] (5a[BAr′4]).
In the drybox, 125 mg of 1a[BAr′4] (0.090 mmol) was placed in
a Schlenk tube. Methylene chloride was added (50 mL) followed
by phenylacetylene (50 µL, 0.45 mmol). The vessel was placed in
a photolysis chamber for 3 h, resulting in a color change from
burgundy to light yellow. The solvent was removed in vacuo
yielding a yellow/brown solid. Column chromatography on silica
using methylene chloride eluted a dark yellow band (92 mg, 0.063
mmol, 70%). Yellow crystals suitable for X-ray diffraction formed
1
PCy3, JP-W ) 351 Hz). MS (ESI) m/z Calc.: 780.3 (M+), 500.1
(M+ - PCy3). Found: 780.4, 500.1.
[W(PCy3)(η2-MeNdCPh)(acac)2][BAr′4] (3b[BAr′4]). 3b[BAr′4]
was produced from 1a[BAr′4] in an analogous manner to 3b[OTf].
The product was dissolved in a 50:50 mixture of diethyl ether and
hexanes and placed in an inert atmosphere at -30 °C. Purple
crystals suitable for X-ray diffraction formed in 2 weeks.
[W(PPh3)(η2-MeNdCMe)(acac)2][BAr′4] (3c[BAr′4]). A 100
mL Schlenk flask was charged with 1b[BAr′4] (50 mg, 0.038 mmol)
and in methylene chloride (15 mL) resulting in an olive green
solution. Addition of triphenylphosphine (20 mg, 0.076 mmol)
caused a color change to red-purple within 2 h. The reaction was
allowed to stir several hours under nitrogen to ensure completion.
IR spectroscopy indicated no metal-carbonyl absorbances. Hexanes
were added to precipitate a dark red-purple solid. The supernatant
was removed via cannula, and the solid placed under vacuum (32
in after few days via evaporation of a 50:50 mixture of methylene
1
chloride and hexanes. IR (KBr): νCt ) 1735 cm-1. H NMR
C
(CD2Cl2, 298 K, δ, major isomer): 13.45 (s, 1H, PhCt CH), 5.90,
5.88 (each a s, each 1H, acac CH), 3.80 (s, 3H, N-CH3), 2.62,
2.60, 1.92, 1.86 (each a s, each 3H, acac CH3). 1H NMR (CD2Cl2,
298 K, minor isomer): 13.47 (s, 1H, PhCt CH), 5.88, 5.63 (each a
s, each 1H, acac CH), 4.21 (s, 3H, N-CH3), 2.67, 2.48, 1.90, 1.80
(each a s, each 3H, acac CH3). 13C{1H} NMR (CD2Cl2, 298 K, δ,
major isomer): 25.2, 26.7, 28.3, 28.4 (acac CH3), 38.7 (N-CH3),
104.6, 105.1 (acac CH), 184.6, 189.0, 191.7, 195.1 (acac CO), 204.6
(PhCt CH), 208.2 (PhCt CH), 217.0 (NdC). 13C{1H} NMR
(CD2Cl2, 298 K, δ, minor isomer): 25.8, 26.4, 28.5, 28.9 (acac CH3),
37.2 (N-CH3), 104.3, 104.8 (acac CH), 186.5, 188.1, 192.2, 196.2
1
mg, 0.020 mmol, 54%). H NMR (CD2Cl2, 298 K, δ): 7.34-7.50
(m, PPh3), 5.80 (s, 3H, N-CH3), 5.73, 5.40 (each a s, each 1H,
4
acac CH), 4.06 (d, 3H, NdC-CH3, JP-H ) 1 Hz), 3.06, 2.23,
Inorganic Chemistry, Vol. 47, No. 19, 2008 8785

Jackson et al.
(acac CO), 206.4 (PhCt CH), 214.1 (PhCt CH), 221.5 (NdC).
Anal. Calcd for WC58H40O4F24NB: C, 47.54; H, 2.75; N, 0.96.
Found: C, 47.52; H, 2.44; N, 1.06%.
191.5, 195.2 (acac CO), 210.9 (MeCt CMe), 230.1 (NdC). Anal.
Calcd for WC49H38O4F24NB: C, 43.42; H, 2.83; N, 1.03. Found:
C, 43.40; H, 2.73; N, 1.06%.
[W(η2-MeCt CMe)(η2-MeNC(PMe3)Ph)(acac)2][BAr4′] (6-
[BAr′4]). A Schlenk flask was charged with 5b[BAr′4] (52 mg,
0.037 mmol) and CH2Cl2 (15 mL) resulting in a yellow solution.
Addition of PMe3 (10 µL, 0.097 mmol) produced no visible color
change over the course of stirring for 20 min. Hexanes (20 mL)
were added to precipitate a pale yellow powder (32 mg, 0.021
mmol, 59%). Yellow crystals suitable for X-ray analysis were
obtained by layering pentane over a methylene chloride solution
of the product in an inert atmosphere and storing at -30 °C for
[W(η2-MeCt CMe)(η2-MeNdCPh)(acac)2][BAr4′] (5b[BAr′4]). In
the drybox, 270 mg of 1a[OTf] (0.399 mmol) was placed in a
Schlenk tube. Methylene chloride was added (60 mL) followed by
2-butyne (100 µL, 1.27 mmol). The tube was placed in a photolysis
chamber for 3 h, resulting in a color change from burgundy to light
yellow. Counterion exchange occurred by adding Na[BAr4′] (350
mg, 0.0395 mmol) and stirring for 2 h. Column chromatography
on silica using methylene chloride eluted a yellow band (367 mg,
1
0.259 mmol, 65%). H NMR (CD2Cl2, 298 K, δ, major isomer):
1
several days. H NMR (CD2Cl2, 298 K, δ, major diastereomer):
5.83, 5.82 (each a s, each 1H, acac CH), 3.72 (s, 3H, N-CH3),
3.19 (s, 6H, H3C-Ct C-CH3), 2.64, 2.55, 1.89, 1.81 (each a s,
7.36 (br s, 3H, o/m-C6H5), 7.08 (t, 1H, p-C6H5), 6.30 (br s, 1H,
o-C6H5), 5.75, 5.48 (each a s, each 1H, acac CH), 3.66 (s, 3H,
N-CH3), 2.78, 1.42 (each a s, each 6H, CH3-Ct C-CH3), 2.43,
2.34, 1.86, 1.76 (each a s, each 3H, acac CH3), 1.71 (d, 9H,
1
each 3H, acac CH3). H NMR (CD2Cl2, 298 K, δ, minor isomer):
5.86, 5.55 (each a s, each 1H, acac CH), 4.05 (s, 3H, N-CH3),
3.17 (s, 6H, H3C-Ct C-CH3), 2.69, 2.46, 1.88, 1.75 (each a s,
each 3H, acac CH3). 13C{1H} NMR (CD2Cl2, 298 K, δ, major
isomer): 18.4 (H3C-Ct C-CH3), 25.3, 26.8, 28.2, 28.5 (acac CH3),
37.8 (N-CH3), 104.1, 104.5 (acac CH), 185.2, 189.6, 191.6, 194.6
(acac CO), 211.0 (MeCt CMe), 217.5 (NdC). Anal. Calcd for
WC54H40O4NBF24: C, 45.75; H, 2.85; N, 0.99. Found: C, 45.96;
H, 2.91; N, 0.89%.
2
1
P-(CH3)3, JP-H ) 13 Hz); H NMR (CD2Cl2, 203 K, δ, major
2
diastereomer): 7.27, 6.17 (each a d, each 1 H, o-C6H5, JH-H ) 6
Hz), 7.38, 7.13 (each a t, each 1H, m-C6H5, JH-H ) 6 Hz), 6.98
2
2
(t, 1H, p-C6H5, JH-H ) 6 Hz), 2.69, 1.16 (each a s, each 6H,
CH3-Ct C-CH3). 13C{1H} NMR (CD2Cl2, 203 K, δ, major
1
diastereomer): 11.6 (d, P-(CH3)3, JP-C ) 51 Hz), 13.0, 15.8
(CH3-Ct C-CH3), 25.9, 26.4, 27.4, 28.2 (acac CH3), 42.9
(N-CH3), 52.8 (N-C-PMe3), 101.6, 102.7 (acac CH), 123.1,
125.4, 128.0, 141.7 (C6H5), 182.7, 182.8 (MeCt CMe), 184.2,
185.5, 188.0, 191.6 (acac CO). 31P NMR (CD2Cl2, 203 K, δ, major
diastereomer): 35.1 (PMe3). Anal. Calcd for WC57H49BF24NO4P:
C, 45.84; H, 3.31; N, 0.94. Found: C, 45.82; H, 3.28; N, 0.83%.
[W(η2-PhC)C(H)PMe3)(η2-MeNdCPh)(acac)2][BAr4′] (7-
[BAr′4]). A Schlenk flask was charged with 5a[BAr′4] (48 mg,
0.033 mmol) and CH2Cl2 (15 mL) resulting in a yellow solution.
Addition of PMe3 (10 µL, 0.097 mmol) produced no visible color
change over the course of stirring for 20 min. Hexanes (20 mL)
were added, and the solvent was removed to produce a yellow
[W(η2-PhCt CH)(η2-MeNdCMe)(acac)2][BAr4′] (5c[BAr′4]). In the
drybox 50 mg of 1b[BAr′4] (0.038 mmol) was placed in a Schlenk
tube. Methylene chloride was added (40 mL) followed by pheny-
lacetylene (15 µL, 0.14 mmol). The vessel was placed in a
photolysis chamber for 3 h, resulting in a color change from olive
green to light yellow. The solvent was removed in vacuo yielding
a yellow/brown solid. Column chromatography on silica using
methylene chloride eluted a dark yellow band (38 mg, 0.027 mmol,
1
72%). H NMR (CD2Cl2, 298 K, δ, major isomer): 13.25 (s, 1H,
PhCt CH), 5.84 (s, 2H, acac CH), 3.45 (s, 3H, N-CH3), 3.15 (s,
3H, NdC-CH3), 2.58, 2.55, 1.87, 1.86 (each a s, each 3H, acac
CH3). 1H NMR (CD2Cl2, 298 K, minor isomer): 13.36 (s, 1H,
PhCt CH), 5.90, 5.73 (each a s, each 1H, acac CH), 3.76 (s, 3H,
N-CH3), 2.94 (s, 3H, NdC-CH3), 2.61, 2.51, 1.87, 1.86 (each a
s, each 3H, acac CH3). 13C{1H} NMR (CD2Cl2, 298 K, δ, major
isomer): 16.7 (NdC-CH3), 25.0, 26.6, 28.3, 28.9 (acac CH3), 37.6
(N-CH3), 104.3, 105.1 (acac CH), 183.8, 188.8, 192.0, 195.6 (acac
CO), 204.5 (PhCt CH), 209.9 (PhCt CH), 229.0 (NdC). Anal.
Calcd for WC53H38O4F24NB: C, 45.36; H, 2.73; N, 1.00. Found:
C, 45.43; H, 2.67; N, 1.01%.
1
powder (35 mg, 0.023 mmol, 69%). H NMR (CD2Cl2, 298 K, δ,
major isomer): 5.81, 5.57 (each a s, each 1H, acac CH), 3.83 (s,
2
3H, N-CH3), 3.04 (d, 1H, CdC-H, JP-H ) 27 Hz), 2.25, 2.24,
1.94, 1.82 (each a s, each 3H, acac CH3), 1.70 (d, 9H, P-(CH3)3,
2JP-H ) 13 Hz); 13C{1H} NMR (CD2Cl2, 298 K, δ, major isomer):
1
13.0 (d, P-(CH3)3, JP-C ) 55 Hz), 26.3, 27.5, 27.7, 28.1 (acac
1
CH3), 31.6, (d, C)C(H)PMe3, JP-C ) 85 Hz), 35.3 (N-CH3),
102.2, 102.4 (acac CH), 185.4, 187.0, 190.5, 190.9 (acac CO), 218.2
(NdC), 240.9 (CdC(H)PMe3); 31P NMR (CD2Cl2, 298 K, δ, major
2
isomer): 34.8 (PMe3, JP-W ) 34 Hz).
[W(η2-MeCt CMe)(η2-MeNdCMe)(acac)2][BAr4′] (5d[BAr′4]). In
the drybox 50 mg of 1b[BAr′4] (0.038 mmol) was placed in a
Schlenk tube. Methylene chloride was added (40 mL) followed by
2-butyne (0.10 mL, 1.28 mmol). The vessel was placed in a
photolysis chamber for 3 h, resulting in a color change from olive
green to light yellow. The solvent was removed in vacuo yielding
a yellow/brown solid. Column chromatography on silica using
methylene chloride eluted a dark yellow band (38 mg, 0.028 mmol,
75%). IR (KBr): νCt C ) 1764 cm-1. 1H NMR (CD2Cl2, 298 K, δ,
major isomer): 5.79, 5.75 (each a s, each 1H, acac CH), 3.34 (s,
3H, N-CH3), 3.12 (s, 6H, H3C-Ct C-CH3), 3.01 (s, 3H,
NdC-CH3), 2.56, 2.49, 1.84, 1.81 (each a s, each 3H, acac CH3).
1H NMR (CD2Cl2, 298 K, minor isomer): 5.82, 5.63 (each a s,
each 1H, acac CH), 3.64 (s, 3H, N-CH3), 3.08 (s, 6H,
H3C-Ct C-CH3), 2.78 (s, 3H, NdC-CH3), 2.63, 2.45, 1.84, 1.79
(each a s, each 3H, acac CH3). 13C{1H} NMR (CD2Cl2, 298 K, δ):
15.7 (NdC-CH3), 18.0 (H3C-Ct C-CH3), 25.1, 26.8, 28.4, 28.7
(acac CH3), 36.7 (N-CH3), 103.7, 104.3 (acac CH), 183.9, 189.2,
W(η2-MeCt CMe)(η2-MeNdCHPh)(acac)2 (8). 5b[OTf] was
generated in situ from 1a[OTf] (210 mg, 0.310 mmol) according
to the above procedure. The solvent was removed, and the solid
was washed with hexanes (40 mL). The brown powder was
dissolved in THF (10 mL) resulting in a brown solution. In a
separate flask, Na[HB(OMe)3] (50 mg, 0.39 mmol) was dissolved
in THF (7 mL). This solution was cannula transferred to the flask
containing 5b[OTf] resulting in a color change from brown to dark
orange. The solvent volume was reduced in vacuo after 15 min of
stirring, and hexanes (40 mL) were added to precipitate residual
salts. The supernatant was cannula filtered to a separate flask, and
the remaining solvent was removed in vacuo yielding an orange
solid. Purification occurred via column chromatography on silica
using a mixture of CH2Cl2 and diethyl ether (90:10) to elute an
orange band (119 mg, 0.214 mmol, 69%). Orange crystals suitable
for X-ray analysis formed after a few days in a concentrated pentane
1
solution at -30 °C. H NMR (CD2Cl2, 200 K, δ, major isomer):
5.50, 4.69 (each a s, each 1H, acac CH), 3.43 (s, 3H, N-CH3),
8786 Inorganic Chemistry, Vol. 47, No. 19, 2008

Reduction of an η2-Iminoacyl Ligand to η2-Iminium
3.08, 2.62 (each a s, each 3s, H3C-Ct C-CH3), 2.45, 1.90, 1.68,
1.59 (each a s, each 3H, acac CH3), 2.40 (s, 1H, NdC-H). 13C{1H}
NMR (CD2Cl2, 200 K, δ, major isomer): 15.3, 17.9
(H3C-Ct C-CH3), 26.2, 26.3, 27.9, 28.4 (acac CH3), 45.8
(N-CH3), 73.6 (NdC), 98.8, 101.3 (acac CH), 147.0 (ipso-C6H5),
184.7, 186.5, 188.1, 191.0 (acac CO), 204.7, 208.7 (MeCt CMe).
Anal. Calcd for WC22H29O4N: C, 47.58; H, 5.27; N, 2.52. Found:
C, 47.74; H, 5.10; N, 2.50%.
[W(η2-MeCt CMe)(η2-Me2NdCHPh)(acac)2][BAr4′] (9[BAr′4]).
In a Schlenk flask 8 (338 mg, 0.609 mmol) was combined with
methylene chloride (15 mL) resulting in an orange solution. Methyl
trifluoromethylsulfonate (MeOTf) was added (50 µL, 0.44 mmol),
and the reaction mixture was allowed to stir for 2 h. The solvent
volume was reduced in vacuo, and hexanes (40 mL) were added
to aid in precipitating an orange solid. The supernatant was removed
via cannula filtration. For counterion exchange, the product was
dissolved in methylene chloride (15 mL) and combined with
Na[BAr′4] (540 mg, 0.609 mmol). The reaction mixture was allowed
to stir for 4 h, at which point the orange liquid was cannula filtered
away from residual salt to a separate flask and the solvent was
removed in vacuo. Purification of the orange solid was achieved
via column chromatography on silica using methylene chloride to
elute an orange band (542 mg, 0.378 mmol, 62%). Orange needles
suitable for X-ray analysis were obtained via evaporation of a
solution of 50:50 methylene chloride and hexanes. 1H NMR
(CD2Cl2, 298 K, δ, major isomer): 7.45 (t, 2H, m-C6H5), 7.32 (d,
2H, o-C6H5), 7.17 (s, 1H, p-C6H5), 5.98, 5.73 (each a s, each 1H,
acac CH), 3.99 (s, 1H, NdC-H), 2.97, 2.64 (each a s, each 3H,
N-CH3), 2.82 (s, 6H, CH3-Ct C-CH3), 2.50, 2.49, 2.01, 1.83
(each a s, each 3H, acac CH3). 13C{1H} NMR (CD2Cl2, 298 K, δ,
major isomer): 19.8 (CH3-Ct C-CH3), 25.1, 26.8, 28.4, 28.6 (acac
CH3), 51.4, 53.1 (N-CH3), 91.4 (NdC), 103.7, 105.5 (acac CH),
184.2, 188.8, 194.5, 194.9 (acac CO), 240.1 (MeCt CMe). Anal.
Calcd for WC55H44O4NBF24: C, 46.08; H, 3.10; N, 0.98. Found:
C, 46.32; H, 3.39; N, 0.83%.
Acknowledgment. We thank the National Science Foun-
dation (CHE-0717086) for financial support, and Dr. Mat-
thew C. Crowe and Dr. Sohrab Habibi for mass spectral
measurements.
Supporting Information Available: Full details of the crystal
structure analyses for 2c[BAr′4], 3b[BAr′4], 4[BAr′4], 5a[BAr′4],
6[BAr′4], 8, and 9[BAr′4] in CIF format and NMR spectra of
3a[OTf], 3b[OTf], 4[OTf], 6[BAr′4], and 7[BAr′4]. This material
is available free of charge via the Internet at http://pubs.acs.org.
IC800738A
Inorganic Chemistry, Vol. 47, No. 19, 2008 8787