Reduction of π-bound nitriles to π-bound imines in a tungsten(II) bis(acetylacetonate) coordination sphere

Article abstract of DOI:10.1021/om7009039

Addition of MeOTf (OTf = CF₃SO₃) to complexes of the type W(CO)(acac)₂(η²-N≡CR) (acac = acetylacetonate) [R = Ph (1a), Me (1b)] yields cationic iminoacyl triflate salts of the type [W(CO)-(acac)₂(η²-MeN=CR)][OTf]. Complexes 2a and 2b undergo nucleophilic attack at the iminoacyl carbon with Na[HB(OMe)₃] or MeMgBr to form neutral η²-imine complexes of the type W(CO)(acac)₂[η²-MeN=C(Nuc)R] [Nuc = H (3a, 3b), Me (4)]. Hydride addition to 2b results in W(CO)(acac) ₂(η²-MeN=CHMe), 3b, a complex that exhibits interconversion of diastereomers at ambient temperature on the NMR time scale. X-ray structures of cationic iminoacyl complex 2a and neutral imine complex 4 confirm η²-C=N bonding of both the iminoacyl and imine ligands.

Full text of DOI:10.1021/om7009039

1322
Organometallics 2008, 27, 1322–1327
Reduction of π-Bound Nitriles to π-Bound Imines in a Tungsten(II)
Bis(acetylacetonate) Coordination Sphere
Andrew B. Jackson, Chetna Khosla, Helen E. Gaskins, 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 September 10, 2007
Addition of MeOTf (OTf ) CF3SO3) to complexes of the type W(CO)(acac)2(η2-NtCR) (acac )
acetylacetonate) [R ) Ph (1a), Me (1b)] yields cationic iminoacyl triflate salts of the type [W(CO)-
(acac)2(η2-MeNdCR)][OTf]. Complexes 2a and 2b undergo nucleophilic attack at the iminoacyl carbon
with Na[HB(OMe)3] or MeMgBr to form neutral η2-imine complexes of the type W(CO)(acac)2[η2-
MeNdC(Nuc)R] [Nuc ) H (3a, 3b), Me (4)]. Hydride addition to 2b results in W(CO)(acac)2(η2-
MeNdCHMe), 3b, a complex that exhibits interconversion of diastereomers at ambient temperature on
the NMR time scale. X-ray structures of cationic iminoacyl complex 2a and neutral imine complex 4
confirm η2-CdN bonding of both the iminoacyl and imine ligands.
recently reported the reaction of W(CO)3(acac)224 with nitriles
Introduction
to form complexes of the type W(CO)(acac)2(η2-NtCR), where
The majority of organometallic nitrile complexes demonstrate
σ-bonding of the nitrile, in which the nitrile carbon is susceptible
to nucleophilic attack.1,2 Metal-mediated hydrolysis of nitriles
to amides and on to carboxylic acids involves initial hydroxide
attack at the nitrile carbon.1–6 Reduction from a nitrile to an
amine can be accomplished via alternating nucleophilic attack
at carbon and protonation at nitrogen beginning with initial
hydride attack at the nitrile carbon.7
the nitrile acts as a four-electron donor ligand to tungsten.25
Coordination of the RCtN triple bond leaves the nitrile
susceptible to alkylation at the nucleophilic nitrogen lone pair,
resulting in cationic η2-iminoacyl complexes.21–23 A number
of neutral π-bound iminoacyl complexes are known,26–39 but
cationic complexes that offer enhanced reactivity toward nu-
Less is known about the chemistry of π-bound nitriles.
Although rare compared to their σ-bound counterparts, π-bound
nitrile complexes have been known for two decades.8–23 We
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* To whom correspondence should be addressed. E-mail:
joetemp@unc.edu.
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10.1021/om7009039 CCC: $40.75
2008 American Chemical Society
Publication on Web 02/22/2008

Reduction of π-Bound Nitriles to π-Bound Imines
Organometallics, Vol. 27, No. 6, 2008 1323
Scheme 1. Addition of Alkyl Triflate to η2-Nitrile Complexes
cleophiles are rare.20–23,38–44 Common methods of formation
of π-bound iminoacyl complexes include (1) migratory insertion
of isocyanide into a metal-alkyl or a metal-hydride bond39
and (2) addition of alkyl halides to anionic isocyanide
complexes.26–28 Reactivity studies with the cationic π-bound
iminoacyl complexes have shown them to be agile reagents
susceptible to nucleophilic attack at the iminoacyl carbon to
form η2-imines.34,39,45–47
Figure 1. ORTEP diagram of [W(CO)(acac)2(η2-MeNdCPh)][OTf]
(2a). Thermal ellipsoids are drawn with 50% probability. Hydrogen
atoms and triflate counterion omitted for clarity.
We now report addition of strong alkylating reagents R′OTf
(R′ ) Me, Et) to π-bound nitrile ligands to form cationic
iminoacyl-carbonyl complexes, [W(CO)(acac)2(η2-R′NdCR)]-
[OTf]. Nucleophilic addition at the iminoacyl carbon of the
cationic complex forms η2-imines of the type W(CO)(acac)2(η2-
R′NdCRR′′) (R′′ ) H, Me). This is the first example of stepwise
addition of an electrophile and a nucleophile to an η2-nitrile.
Results and Discussion
Combining stoichiometric amounts of W(CO)(acac)2(η2-
NtCPh) (1a) and MeOTf in methylene chloride at room
temperature generates [W(CO)(acac)2(η2-MeNdCPh)][OTf]
(2a) (Scheme 1). In situ IR spectroscopy indicates the presence
of a single carbon monoxide absorbance at 1985 cm-1 in the
product, an increase of approximately 90 cm-1 from the starting
material. Alkylation of alkyl or aryl nitriles gives similar results.
Addition of either MeOTf or EtOTf to W(CO)(acac)2(η2-
NtCMe) (1b) generates W(CO)(acac)2(η2-R′NdCMe)][OTf]
[R′dMe (2b), Et (2c)].
Figure 2. Expanded IR spectrum of W(CO)(acac)2(η2-MeNd
CHPh) (3a) in hexanes showing the CO absorption frequency of
both diastereomers.
1
The H NMR spectrum of complex 2a shows a downfield
resonance at 4.97 ppm attributed to the newly added methyl
group on nitrogen. Complex 2b displays similar NMR results:
the methyl bound to nitrogen resonates at 4.79 ppm, while the
methyl group bound to carbon resonates at 4.11 ppm, shifted
downfield from 3.71 in the neutral η2-acetonitrile precursor 1b.
Each methyl peak associated with the iminoacyl ligand in 2b
appears as a sharp singlet at room temperature. As confirmed
by an HMQC experiment, the iminoacyl carbon in 2b appears
at 233.1 ppm in the 13C NMR spectrum, downfield from 208.7
ppm in the neutral η2-acetonitrile adduct. The carbonyl carbon
shifts upfield to 219.7 ppm from 237.6 ppm in the precursor
acetonitrile complex.25
monoxide ligand bound to tungsten defining five coordination
sites of an approximate octahedron. The sixth site is filled with
an iminoacyl ligand located cis to carbon monoxide with the
nitrogen atom positioned distal to the carbonyl ligand. The NdC
bond of the η2-iminoacyl ligand is parallel to the WsCtO axis,
reminiscent of the CtN orientation observed in the nitrile
complex.25 The tungsten-nitrogen bond distance, W1-N4,
decreases slightly from 2.018(5) Å in the nitrile complex to
1.977(7) Å, and the bond distance to the iminoacyl carbon,
W1-C5, increases slightly from 2.038(5) to 2.069(8) Å. The
carbon-nitrogen bond distance (1.283(10) Å) remains virtually
unchanged from the value observed for the analogous bond in
the nitrile complex (1.270(7) Å).25 In summary, formal addition
of a cationic methyl group to the lone pair of the η2-nitrile
nitrogen does little to distort the geometry of the robust
W-C-N triangle.
The solid state structure of cationic η2-iminoacyl complex
2a (Figure 1) shows two acetylacetonate chelates and one carbon
(41) Carrier, A. M.; Davidson, J. G.; Barefield, E. K.; Van Derveer,
D. G. Organometallics 1987, 6, 454.
(42) An˜tinolo, A.; Fajardo, M.; Gil-Sanz, R.; Lo´pez-Mardomingo, C.;
Mart´ın-Villa, P.; Otero, A.; Kubicki, M. M.; Mugnier, Y.; El Krami, S.;
Mourad, Y. Organometallics 1993, 12, 381.
Addition of Na[HB(OMe)3] to [W(CO)(acac)2(MeNd
CPh)][OTf] (2a) in THF at -78 °C reduces the iminoacyl ligand
to a coordinated imine in W(CO)(acac)2(η2-MeNdCHPh) (3a)
via nucleophilic attack of hydride at the iminoacyl carbon
(43) Temme, B.; Erker, G. J. Organomet. Chem. 1995, 488, 177.
(44) Cook, K. S.; Piers, W. E.; Patrick, B. O.; McDonald, R. Can.
J. Chem. 2003, 81, 1137.
1
(Scheme 2). The room temperature H NMR spectrum shows
(45) Galakhov, M. V.; Go´mez, M.; Jime´nez, G.; Royo, P.; Pellinghelli,
M. A.; Tiripicchio, A. Organometallics 1995, 14, 1901.
(46) Durfee, L. D.; Fanwick, P. E.; Rothwell, I. P.; Folting, K.; Huffman,
J. C. J. Am. Chem. Soc. 1987, 109, 4720.
two diastereomers in a 2:1 ratio, reflecting chirality at both
tungsten and carbon. The N-methyl on the imine ligand shifts
upfield to 3.71 ppm (major) from 4.97 ppm in the cationic
complex. Two resonances attributed to the imine C-H appear
(47) Chiu, K. W.; Jones, R. A.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1981, 2088.

1324 Organometallics, Vol. 27, No. 6, 2008
Jackson et al.
Scheme 2. Addition of Sodium Trimethoxyborohydride to
Cationic Iminoacyl Complexes
Scheme 3. Addition of Methylmagnesium Bromide to 2a
ligand is π-bound to the metal center, cis to carbon monoxide,
with the nitrogen atom distal to the metal–carbonyl ligand. Both
substituents on the imine carbon skew from the plane defined
by the W-C-N triangle in accord with an aziridine geometry.
The methyl group bound to nitrogen deviates only slightly from
the same plane. Bond distances from the metal to the imine
ligand reflect a large change in the geometry of the W-C-N
triangle upon addition of a nucleophile at carbon. The
tungsten-carbon bond, W1-C3, lengthens considerably from
2.069(8) to 2.274(2) Å, and the W1-N2 bond decreases from
1.977(7) to 1.905(5) Å, suggestive of lone pair dona-
tion from the nitrogen to tungsten, effectively resulting in a
double bond from nitrogen to the metal. The carbon-nitrogen
bond distance in the imine ligand, N2-C3, elongates from
1.283(10) to 1.383(2) Å, indicating a loss of C-N multiple bond
character upon nucleophilic attack. These values mirror those
of W(CO)(acac)2(η2-PhNdCHPh), an imine complex derived
from direct addition of an N-benzylideneaniline to
W(CO)3(acac)2.25 Note that no rearrangement in W-C-N
connectiVity occurs in the transformation from nitrile to
iminoacyl and on to imine. Each η2-CdN ligand remains
π-bound to tungsten in the same orientation of the ligating
carbon and nitrogen atoms relative to the rest of the unaltered
coordination sphere.
between 5 and 6 ppm, the same region as the acac methines. A
COSY experiment shows the imine C-H peaks at 5.56 (major)
and 5.80 (minor) ppm. The 13C NMR spectrum displays the
imine carbon at 60.8 (major) and 57.2 (minor) ppm, an upfield
shift of ∼170 ppm from the iminoacyl carbon in complex 2a.
This significant change in the 13C chemical shift reflects the
sp3 character of the imine carbon in complex 3a. IR spectros-
copy of 3a in hexanes also indicates two isomers with carbonyl
CtO absorptions at 1904 and 1889 cm-1 (Figure 2). Addition
of a nucleophilic methyl group to 2a with MeMgBr as a reagent
produces W(CO)(acac)2(η2-MeNdCMePh) (4) (Scheme 3).
The X-ray structure of 4 (Figure 3) depicts the same
framework around the metal as is observed in the neutral nitrile
and cationic iminoacyl carbonyl complexes: two acetylacetonate
chelates and one carbon monoxide ligand surround tungsten with
an η2-NdC linkage in the remaining position. The chiral imine
Addition of Na[HB(OMe)3] to 2b appears to proceed like
1
the other addition reactions, but room temperature H NMR
spectroscopy does not indicate the presence of two diastereomers
in solution. In fact, signals due to the added hydrogen and the
methyl of the anticipated H-C-Me unit of the imine are absent
at room temperature. However, low-temperature 1H NMR
spectroscopy reveals that hydride addition indeed occurs to
produce W(CO)(acac)2(η2-MeNdCHMe) (3b). At 238 K, two
diastereomers are resolved and appear in a 1:1 ratio. The added
hydrogen atom is bound to the imine carbon and appears as a
quartet at either 4.55 or 5.11 ppm due to the presence of two
diastereomers. Variable-temperature NMR measurements focus-
ing on the two singlets for the methyl group bound to nitrogen
in the two diastereomers reveal a coalescence temperature of
263 K. By using the Gutowsky-Holm equation,48 this temper-
ature corresponds to a free energy barrier for diastereomer
interconversion of ∆Gq ) 13.2 kcal/mol. The fluxional process
observed at room temperature results from interconversion of
the two diastereomers on the NMR time scale. This dynamic
behavior is observed in the CHMe (3b) derivative, but not in
the CHPh (3a) or the CMePh (4) derivatives.
Figure 3. ORTEP diagram of W(CO)(acac)2(η2-MeNdCMePh) (4).
Thermal ellipsoids are drawn with 50% probability. Hydrogen atoms
are omitted for clarity.
For this interconversion process to occur, one of the two
stereocenters in the molecule must racemize. One possible
mechanism involves interconversion of chirality at the imine
carbon (Scheme 4, Pathway A). Dissociation of the carbon atom
from the tungsten center could form a 16-electron intermediate
species in which the imine is σ-bound through the nitrogen atom.
Once the imine assumes the planar geometry appropriate for
an N-bound ligand, the carbon can coordinate to tungsten
Figure 4. Expanded room temperature 1H NMR (CD2Cl2) spectrum
of W(CO)(acac)2(η2-EtNdCMeMe), 5, showing the ABX3 splitting
pattern attributed to the diastereotopic methylene protons on the
imine ligand.
(48) Gutowsky, H. S.; Holm, C. H. J. Chem. Phys. 1956, 25, 1228.

Reduction of π-Bound Nitriles to π-Bound Imines
Organometallics, Vol. 27, No. 6, 2008 1325
Table 2. Crystal Data and Refinement Parameters for 2a and 4
Scheme 4. Possible Mechanisms for Interconversion of Di-
astereomers in 3b
complex
2a
4
empirical formula
fw
color
tem p(K)
λ(Mo KR) (Å)
cryst syst
space group
a (Å)
C20H22F3NO8SW
677.29
burgundy
100(2)
0.71703
monoclinic
C2/c
28.4062(13)
7.6114(3)
22.3725(10)
90
98.730(3)
90
4781.1(4)
8
1.882
4.99
C20H25NO5W
543.26
dark red
100(2)
0.71703
monoclinic
P21/n
8.3192(3)
14.2955(4)
17.0591(6)
90
92.92
90
2026.15(12)
4
1.781
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
Vol. (Å3)
Z
Dcalc (Mg/m3)
µ (mm-1
F(000)
)
5.73
1064
Scheme 5. Synthetic Route To Generate Nonchiral Imine
Derivative 5
2638
cryst size (mm)
2θ range (deg)
no. of reflns collected
no. of independent reflns
0.20 × 0.05 × 0.01 0.10 × 0.10 × 0.10
5.00 to 50.00
30525
1.86 to 30.07
88084
4229
88084
[R(int) ) 0.0550]
4229/0/308
1.9382
[R(int) ) 0.0000]
88084/0/252
1.004
data/restraints/parameters
goodness-of-fit on F2
final R indices [I > 2σ(I)] R1 ) 0.040
R1 ) 0.0394
wR2 ) 0.1014
R1 ) 0.0530
wR2 ) 0.1065
wR2 ) 0.042
R indices (all data)
R1 ) 0.056
wR2 ) 0.044
etonate dechelation as a mechanism for accessing an interme-
diate with a mirror plane in this complex and makes it unlikely
that acac rearrangement is the dynamic process responsible for
diastereomer interconversion in complex 3b. Dissociation of the
imine ligand at carbon to form a κ1-N-imine with a chiral
tungsten center becomes the likely mechanism for the dynamic
process that interconverts diastereomers in 3b.
In summary, stepwise conversion of π-bound nitriles to
π-bound imines has been accomplished. Single-crystal X-ray
structures have been determined for the cationic iminoacyl
complex [W(CO)(acac)2(η2-MeNdCPh)][OTf], 2a, and the
neutral imine complex W(CO)(acac)2(η2-MeNdCMePh), 4.
Complex 3b,W(CO)(acac)2(η2-MeNdCHMe), displays flux-
ionality, which interconverts diastereomers via dissociation of
the η2-imine carbon.
Table 1. Comparison of Salient Bond Distances, NMR, and IR Data
W-N
W-C
C-N
13C,
NtC (δ)
IR, νCO
(cm-1
complex
nitrile25
iminoacyl (2a) 1.977(7) 2.069(8) 1.283(10) 226.2
imine (4)
(Å)
(Å)
(Å)
)
2.018(5) 2.038(5) 1.270(7) 211.2
1895
1976
1.905(5) 2.274(2) 1.383(2) 59.3, 60.6 1881, 1885
through either face. Note that the geometry of the η2-coordinated
imine requires rotation of the CHMe fragment relative to the
CdNsMe plane of the κ1-N-imine upon binding the imine
carbon to tungsten.
Experimental Section
A second possibility for isomer interconversion involves
inversion of stereochemistry at tungsten via dissociation of an
acetylacetonate arm resulting in a 16-electron intermediate
species (Scheme 4, Pathway B). Reassociation of the chelate
arm on the opposite side of the metal atom inverts stereochem-
istry at the tungsten center.
General Information. Reactions were performed under a dry
nitrogen atmosphere with standard Schlenk techniques. Methylene
chloride, hexanes, and pentane were purified by passage through
an activated alumina column under a dry argon atmosphere.49 THF
was distilled from a sodium ketal suspension. Methylene chloride-
d2 was dried over CaH2 and degassed. All other reagents were
purchased from commercial sources and were used without further
purification.
To distinguish between these two possible mechanisms, an
imine derivative deprived of a chiral center at the imine carbon
was synthesized, and an ethyl substituent on the imine nitrogen
was used to probe chirality at the metal using the diastereotopic
methylene protons. W(CO)(acac)2[η2-EtNdCMe2], 5, was syn-
thesized by alkylation of 1b with EtOTf, follwed by subsequent
nucleophilic attack on the cationic complex with MeMgBr
(Scheme 5). At room temperature, the 1H NMR spectrum shows
one product, with a distinct ABX3 pattern corresponding to the
methylene protons on the nitrogen-ethyl substituent (Figure 4).
Detection of a chiral environment by the diastereotopic meth-
ylene protons at room temperature eliminates facile acetylac-
NMR spectra were recorded on Bruker DRX400, AMX400, or
AMX300 spectrometers. Infrared spectra were recorded on an ASI
Applied Systems React IR 1000 FT-IR spectrometer. Elemental
analysis was performed by Atlantic Mircrolab, Norcross, GA, and
Robertson Microlit, Madison, NJ. 1a and 1b were made in
accordance with a literature procedure.25
[W(CO)(acac)2(η2-MeNdCPh)][OTf] (2a). A 200-mL Schlenk
flask was charged with 1a (1.08 g) and the solid was dissolved in
(49) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

1326 Organometallics, Vol. 27, No. 6, 2008
Jackson et al.
methylene chloride (30 mL) resulting in a dark amber solution.
Treatment with 1.5 equiv of methyl trifluoromethylsulfonate
(MeOTf) caused a color change to burgundy. In situ IR spectroscopy
revealed a single CO absorbance at ∼1985 cm-1after 30 min of
stirring. The solvent volume was reduced in vacuo and hexanes
(50 mL) were added to precipitate the cationic product. Excess
solvent was removed via cannula filtration yielding a burgundy
powder (1.32 g, 93%). A portion of the isolated burgundy powder
2a was dissolved in methylene chloride and layered with hexanes
in an inert atmosphere at -30 °C. Small burgundy needles of 2a
suitable for X-ray analysis formed overnight. IR (KBr): νCO ) 1976
cm-1, νCN ) 1627 cm-1. 1H NMR (CD2Cl2, 298 K, δ): 7.88–7.90
(m, 2H, o-C6H5), 7.80–7.84 (m, 2H, m-C6H5), 7.69–7.73 (m, 1H,
p-C6H5), 5.95, 5.94 (each a s, each 1H, acac C–H), 4.97 (s, 3H,
N-CH3), 2.58, 2.38, 2.37, 2.16 (each a s, each 3H, acac CH3).
13C{1H} NMR (CD2Cl2, 298 K, δ): 25.4, 26.3, 26.6, 28.4 (acac
CH3), 42.3 (N-CH3), 101.6, 104.3 (acac CH), 128.0 (ipso-C6H5),
130.1 (m-C6H5), 132.1 (o-C6H5), 136.7 (p-C6H5), 187.8, 188.9,
193.3, 199.0 (acac CO), 220.8 (CtO), 226.2 (NtC). Anal. Calcd
for WC20H22O8NSF3: C, 35.46; H, 3.28; N, 2.07. Found: C, 35.14;
H, 3.14; N, 1.99.
2.13, 2.09, 2.03 (each a s, each 3H, acac CH3). 13C{1H} NMR
(CD2Cl2, 298 K, δ, major diastereomer): 26.0, 26.3, 27.7, 27.9 (acac
CH3), 43.6 (N-CH3), 60.8 (N-C), 99.4, 101.0 (acac CH), 127.4
(m-C6H5), 127.6 (p-C6H5), 127.9 (o-C6H5), 148.1 (ipso-C6H5), 184.3,
186.3, 187.0, 193.8 (acac CO), 233.4 (CtO). 13C{1H} NMR
(CD2Cl2, 298 K, δ, minor diastereomer): 25.7, 26.9, 27.5, 28.1 (acac
CH3), 43.8 (N-CH3), 57.2 (N-C), 99.4, 101.5 (acac CH), 126.6
(m-C6H5), 126.7 (o-C6H5), 127.0 (p-C6H5), 147.2 (ipso-C6H5), 185.5,
185.6, 188.1, 194.7 (acac CO), 235.3 (CtO). Anal. Calcd for
WC19H23O5N: C, 43.11; H, 4.39; N, 2.65. Found: C, 43.10; H, 4.34;
N, 2.66.
W(CO)(acac)2(η2-MeNdCHMe) (3b). Under an inert atmo-
sphere, 2b (30 mg) was placed in a 100-mL Schlenk flask. The
flask was cooled to -78 °C and THF (15 mL) was added. In a
separate flask a solution containing Na[HB(OMe)3] (7 mg) and
THF (5 mL) was prepared and cannula transferred to the flask
containing 2b resulting in a color change from green to red.
After 30 min of stirring, the solvent volume was reduced in vacuo
and hexanes (20 mL) were added to precipitate residual salts.
The red supernatant was cannula filtered to a separate flask and
the remaining solvent was removed in vacuo yielding a red-
brown solid (17 mg, 75%). 1H NMR (CD2Cl2, 240 K, δ, 1:1
diastereomers): 5.64, 5.46, 5.43 (each a s, 2:1:1, acac CH), 5.11,
4.55 (each a q, 1H, N-C-H, 2JH-H ) 4.9 Hz), 3.64, 3.57 (each
a s, 3H, N-CH3), 2.46, 2.45, 2.20, 2.06, 2.05, 2.00, 1.98 (each
a s, 3:3:6:3:3:3:3, acac CH3), 2.23, 1.96 (each a d, each 3H,
[W(CO)(acac)2(η2-MeNdCMe)][OTf] (2b). A 200-mL Schlenk
flask was charged with 1b (0.74 g) and the solid was dissolved in
CH2Cl2 (20 mL) resulting in a dark amber solution. Treatment with
1 equiv of MeOTf caused a color change to olive green. In situ IR
spectroscopy revealed a single CO absorbance at ∼1985 cm-1after
30 min of stirring. The solvent volume was reduced in vacuo and
hexanes (50 mL) were added to precipitate the cationic product.
Excess solvent was removed via cannula filtration yielding an olive
2
NdCsCH3, JH-H ) 4.9 Hz). 13C{1H} NMR (CD2Cl2, 240 K,
δ, 1:1 diastereomers): 19.4–28.1 (acac CH3, NdC-CH3), 41.2,
43.2 (N-CH3), 56.4, 56.7 (NdC), 99.4, 99.5, 100.8, 100.9 (acac
CH), 183.7, 184.1, 184.8, 185.4, 186.0, 186.1, 193.7, 194.1 (acac
CO), 231.3, 231.9 (CtO).
green powder (740 mg, 75%). IR (KBr): νCO ) 1968 cm-1, νCN
)
1657 cm-1. H NMR (CD2Cl2, 298 K, δ): 5.88, 5.87 (each a s,
each 1H, acac CH), 4.79 (s, 3H, N-CH3), 4.11 (s, 3H, NdCsCH3),
2.53, 2.13 (each a s, each 3H, acac CH3), 2.32 (s, 6H, acac CH3);
13C{1H} NMR (CD2Cl2, 298 K, δ): 20.3 (NtCsCH3), 25.2, 26.1,
26.4, 28.1 (acac CH3), 41.3 (N-CH3), 101.7, 104.0 (acac CH),
187.5, 188.8, 193.3, 198.8 (acac CO), 219.7 (CtO), 233.1 (NtC).
Anal. Calcd for WC15H20O8NSF3: C, 29.28; H, 3.28; N, 2.28.
Found: C, 29.06; H, 3.01; N, 1.96.
1
W(CO)(acac)2(η2-MeNdCMePh) (4). Under an inert atmo-
sphere, 2a (50 mg) was placed in a 100-mL Schlenk flask. The
flask was cooled to -78 °C and THF (10 mL) was added. A
solution of methyl magnesiumbromide, MeMgBr (30 µL, 3 M
in Et2O), was added to the flask. After 10 min of stirring, in
situ IR spectroscopy indicated the presence of one CO absor-
bance at 1866 cm-1. The solvent was removed in vacuo and
the resulting red solid was dissolved in a minimal amount of
CH2Cl2. Hexanes were added to precipitate the residual mag-
nesium salt and the red liquid was cannula filtered to another
flask, where the solvent was removed in vacuo to yield a red
solid. Column chromatography on silica with methylene chloride
eluted a red band (24 mg, 60%). Complex 4 was dissolved in
hexanes and placed in a freezer at -30 °C. Dark red crystals
suitable for X-ray analysis formed after a few days. IR (hexanes):
[W(CO)(acac)2(η2-EtNdCMe)][OTf] (2c). A Schlenk flask was
charged with 1b (50 mg) and CH2Cl2 (20 mL). Ethyl triflate (30
µL) was added at 0 °C and the solution was stirred overnight at
room temperature. The green solution was reduced and washed with
1
hexanes to afford a green-brown powder (55 mg, 79%). H NMR
(CD2Cl2, 298 K, δ): 5.92, 5.87 (each a s, each 1H, acac CH), 5.17
(m, 2H, N-CH2-CH3), 4.13 (s, 3H, NtCsCH3), 2.52, 2.32, 2.30,
2.14 (each a s, each 3H, acac CH3), 1.46 (t, 3H, N-CH2-CH3).
13C{1H} NMR (CD2Cl2, 298 K, δ): 15.0 (N-CH2-CH3), 20.6
(NtCsCH3), 25.4, 26.2, 26.4, 28.2 (acac CH3), 51.8
(NsCH2sCH3), 101.6, 104.1 (acac CH), 187.7, 188.9, 193.2, 198.9
(acac CO), 219.5 (CtO), 232.0 (NtC).
νCO ) 1881, 1885 cm-1 1H NMR (CD2Cl2, 298 K, δ, both
.
diastereomers): 7.23–7.30 (m, 4H, m-C6H5), 7.13–7.15 (m, 2H,
o-C6H5), 6.98–7.03 (m, 2H, p-C6H5), 6.75–6.77 (m, 2H, o-C6H5),
5.61, 5.55, 5.54, 5.52 (each a s, each 1H, acac CH), 3.85, 3.79
(each a s, each 3H, N-CH3), 2.46, 2.43, 2.26, 2.17, 2.14, 2.10,
2.09, 2.06 (each a s, each 3H, acac CH3), 2.45, 1.96 (each a s,
each 3H, NdCsCH3). 13C{1H} NMR (CD2Cl2, 298 K, δ, both
diastereomers): 23.2, 24.6 (NdCsCH3), 25.7, 26.0, 26.3, 26.8,
27.5, 27.6, 28.0, 28.1 (acac CH3), 40.0, 40.7 (NsCH3), 59.3,
60.6 (NsC), 99.4, 99.6, 101.1, 101.5 (acac CH), 126.2, 126.4
(p-C6H5), 126.3, 127.1, 127.2, 127.3 (o/m-C6H5), 149.7, 150.6
(ipso-C6H5), 185.2, 185.7, 185.7, 186.3, 186.4, 187.7, 193.9,
194.3 (acac CO), 234.6, 236.5 (CtO). Anal. Calcd for
C20H25O5NW: C, 44.21; H, 4.65; N, 2.58. Found: C, 44.03 H,
4.49; N, 2.02.
W(CO)(acac)2(η2-MeNdCHPh) (3a). Under an inert atmo-
sphere, 2a (200 mg) was combined with sodium trimethoxyboro-
hydride, Na[HB(OMe)3] (40 mg), in a 200-mL Schlenk flask. The
flask was cooled to -78 °C and THF (20 mL) was added. A color
change from burgundy to cherry red occurred and in situ IR
spectroscopy revealed a new CO absorbance at 1883 cm-1 after
10 min of stirring. The solvent was removed in vacuo and the
resulting red solid was chromatographed on silica with CH2Cl2 to
elute a red band (75 mg, 48%). IR (hexanes): νCO ) 1904 cm-1
(major diastereomer), νCO ) 1889 cm-1 (minor diastereomer). 1H
NMR (CD2Cl2, 298 K, δ, major diastereomer): 7.24–7.32 (m, 3H,
m and p-C6H5), 7.14–7.16 (m, 2H, o-C6H5), 5.48, 5.72 (each a s,
each 1H, acac CH), 5.56 (s, 1H, N-C-H), 3.71 (s, 3H, N-CH3),
2.57, 2.25, 2.16, 2.03 (each a s, each 3H, acac CH3). 1H NMR
(CD2Cl2, 298 K, δ, minor diastereomer): 7.01–7.07 (m, 3H, m and
p-C6H5), 6.80–6.83 (m, 2H, o-C6H5), 5.80 (s, 1H, N-C-H), 5.58,
5.56 (each a s, each 1H, acac CH), 3.83 (s, 3H, N-CH3), 2.49,
W(CO)(acac)2(η2-EtNdCMe2) (5). A 200-mL Schlenk flask
was charged with 2c (50 mg) and THF (25 mL). The resulting green
solution was cooled to -78 °C. A solution of methylmagnesium-
bromide (40 µL, 3 M in Et2O) was added to the flask yielding a
red-brown solution. Solvent was removed in vacuo after 1 h and
the product was extracted with hexanes. Removal of solvent gave

Reduction of π-Bound Nitriles to π-Bound Imines
Organometallics, Vol. 27, No. 6, 2008 1327
a red-brown powder (30 mg, 69%). 1H NMR (CD2Cl2, 298 K, δ):
5.58, 5.46 (each a s, each 1H, acac CH), 3.94 (m, 2H,
N-CH2-CH3), 2.40, 2.15, 2.07, 1.99 (each a s, each 3H, acac CH3),
2.20, 2.03 (each a s, each 3H, N-C(CH3)-CH3). 13C{1H} NMR
(CD2Cl2, 298 K, δ): 16.4 (N-CH2-CH3), 26.1, 26.4, 27.3, 28.0
(acac CH3), 30.0, 31.9 (N-C(CH3)-CH3), 49.6 (N-CH2-CH3),
59.8 (N-C), 99.5, 101.0 (acac CH), 185.6, 185.7, 186.2, 194.0 (acac
CO), 233.6 (C≡O).
Acknowledgment. We thank the National Science Foun-
dation (CHE-0717086) for financial support.
Supporting Information Available: Full details of the crystal
structure analyses for 2a and 4 in CIF format and NMR spectra of
2c, 3b, and 5. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM7009039