Reactions of tungsten acetylide-silylene complexes with pyridines: Direct observation of silylene/silyl migration in tungsten acetylide and carbyne/vinylidene frameworks

Article abstract of DOI:10.1021/om300772c

Reaction of acetylide-silylene complex Cp*(CO)₂W(SiPh ₂)(CC^tBu) (1a) with 4-(dimethylamino)pyridine (DMAP) gave an equilibrium mixture of DMAP-stabilized silylene acetylide complexes trans- and cis-Cp*(CO)₂W(SiPh₂·DMAP)(CC ^tBu) (trans-4 and cis-4). The corresponding reaction using Cp*(CO)₂W(SiPh₂)(CCSiMe₃) (2) produced the novel DMAP-coordinated silenylcarbyne/silylvinylidene complex Cp*(CO)₂W[CC(SiPh₂·DMAP)(SiMe₃)] (6a) as a major product, which was equilibrated with trans- and cis-Cp*(CO)₂W(SiPh₂·DMAP)(CCSiMe ₃) (trans-5a and cis-5a) via silylene/silyl migration. The novel structures of cis-4 and 6a were revealed by X-ray crystallography. A mixture of 2 and pyridine exhibited interesting temperature-dependent NMR spectral changes, indicating the formation of trans- and cis-Cp*(CO)₂W(SiPh ₂·py)(CCSiMe₃) (trans-5b and cis-5b) and Cp*(CO)₂W[CC(SiPh₂·py)(SiMe₃)] (6b) at low temperature, while a mixture of 1a and pyridine showed no such spectral changes.

Full text of DOI:10.1021/om300772c

Article
pubs.acs.org/Organometallics
Reactions of Tungsten Acetylide−Silylene Complexes with Pyridines:
Direct Observation of Silylene/Silyl Migration in Tungsten Acetylide
and Carbyne/Vinylidene Frameworks
Hiroyuki Sakaba,*,† Hiroyuki Oike,† Yasuhiro Arai,† and Eunsang Kwon‡
‡
†Department of Chemistry and Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku
University, Aoba-ku, Sendai 980-8578, Japan
S
* Supporting Information
ABSTRACT: Reaction of acetylide−silylene complex Cp*-
(CO)2W(SiPh2)(CCtBu) (1a) with 4-(dimethylamino)-
pyridine (DMAP) gave an equilibrium mixture of DMAP-
stabilized silylene acetylide complexes trans- and cis-Cp*-
(CO)2W(SiPh2·DMAP)(CCtBu) (trans-4 and cis-4). The
corresponding reaction using Cp*(CO)2W(SiPh2)(CCSiMe3) (2) produced the novel DMAP-coordinated silenylcarbyne/
silylvinylidene complex Cp*(CO)2W[CC(SiPh2·DMAP)(SiMe3)] (6a) as a major product, which was equilibrated with trans-
and cis-Cp*(CO)2W(SiPh2·DMAP)(CCSiMe3) (trans-5a and cis-5a) via silylene/silyl migration. The novel structures of cis-4
and 6a were revealed by X-ray crystallography. A mixture of 2 and pyridine exhibited interesting temperature-dependent NMR
spectral changes, indicating the formation of trans- and cis-Cp*(CO)2W(SiPh2·py)(CCSiMe3) (trans-5b and cis-5b) and
Cp*(CO)2W[CC(SiPh2·py)(SiMe3)] (6b) at low temperature, while a mixture of 1a and pyridine showed no such spectral
changes.
ecent extensive studies on transition-metal silylene
complexes have demonstrated their novel reactivity and
demonstrating the formation of novel donor-stabilized silylene
acetylide and silenylcarbyne/silylvinylidene complexes.
The reaction of 1a with DMAP in toluene at room
temperature resulted in the isolation of a yellow solid in 42%
yield (Scheme 2). X-ray analysis of crystals obtained by
R
important roles in metal-mediated reactions of organosilicon
compounds.1 The silylene center is highly electrophilic and
often forms a donor-stabilized silylene complex, typically with a
lone-pair donor. We previously reported the synthesis of
acetylide−silylene complexes (η5-C5Me4R)(CO)2W(SiPh2)-
Scheme 2. Reaction of Acetylide−Silylene Complex 1a with
DMAP
t
t
(CCR′) (1a: R = Me, R′ = Bu; 1b: R = Et, R′ = Bu; 2: R
= Me, R′ = SiMe3) (Scheme 1),2 whose unique charge transfer
Scheme 1. Reaction of Acetylide−Silylene Complex 2 with
Acetone
recrystallization from toluene/hexane showed the interesting
structure of DMAP-stabilized silylene acetylide complex cis-4,
which adopts a four-legged piano stool geometry with two cis-
arranged CO ligands (Figure 1). The W−Si bond distance
(2.5125(7) Å) is much shorter than that (2.567(2) Å) of
acetylide−silylene complex 1b2a and is in the range (2.45−2.51
Å) for the W−Si bonds of donor-stabilized silylene tungsten
complexes.4 The Si−C1 and Si−C2 interatomic distances
(2.436(3) and 3.141(3) Å, respectively) are significantly longer
than those (1.937(7) and 2.009(7) Å) of 1b.2a The W−C1−C2
angle (178.6(3)°) is linear, in contrast to the bent geometry
(CT) interactions between the acetylide and silylene ligands
have been disclosed by a theoretical study.3 Considering the
CT from the acetylide to the silylene, they can be viewed as an
intramolecularly π-bond-donor-stabilized silylene complex, and
the electrophilic nature of the silylene ligand has been recently
shown by the reaction of 2 with acetone to give the insertion
product Cp*(CO)2WCC(SiMe3)CMe2OSiPh2 (3).2b We
describe here the reactivity of 1a and 2 toward typical lone-pair
donors, pyridine and 4-(dimethylamino)pyridine (DMAP),
Received: August 10, 2012
© XXXX American Chemical Society
A
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Figure 1. Molecular structures of cis-4 showing thermal ellipsoids at
the 50% probability level. All hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg): W1−Si1, 2.5125(7);
W1−C1, 2.137(3); Si1−N1, 1.941(3); C1−C2, 1.213(4); Si1−W1−
C1, 62.59(7); Si1−W1−C26, 74.40(7); C26−W1−C27, 76.51(12);
C1−W1−C27, 83.50(11); W1−C1−C2, 178.6(3).
(153.8(5)°) of the corresponding moiety in 1b. The C1−C2
bond distance (1.213(4) Å) is shorter than that (1.270(9) Å) of
1b and comparable to a typical C−C triple bond distance.
These observations indicate considerably increased metal−
silylene and decreased acetylide−silylene interactions in cis-4
than in 1b. However, the following feature suggests that a weak
acetylide−silylene interaction may still exist in cis-4; the Si−
W−C1 angle (62.59(7)°) between two bulky DMAP-
coordinated silylene and tert-butylethynyl ligands is the smallest
among four basal interligand angles: Si−W−C26 = 74.40(7)°,
C1−W−C27 = 83.50(11)°, and C26−W−C27 = 76.51(12)°
for the other three angles. Also in comparison with the P−W−
Cα angle (75.1(2)°) and W−P distance (2.491(2) Å) of cis-
Cp(CO)2W(PPh3)(CαCPh),5 whose PPh3 ligand has a
bulkiness similar to the SiPh2·DMAP in cis-4, the Si−W−C1
angle is found to be fairly small.
1
Figure 2. Variable-temperature H NMR spectra in toluene-d8. (A)
tBu signals of trans-4 and cis-4. (B) SiMe3 signals of trans-5a, cis-5a,
X
and 6a. (C) SiMe3 signals of trans-5b, cis-5b, and 6b. Impurities.
1
The H NMR spectrum of the isolated solid in toluene-d8
t
showed a single Bu signal at 20 °C (Figure 2A). When the
temperature was lowered, the signal broadened and then
decoalesced into two signals in 27:73 ratio at −50 °C. In the
29Si NMR spectrum at −50 °C, minor and major signals were
observed at 69.4 (JWSi = 111 Hz) and 41.4 ppm (JWSi = 93 Hz),
respectively. The minor component was characterized as trans-
DMAP-stabilized silylene complex trans-4 on the basis of the
29Si chemical shift and 183W satellites, which are in the ranges
(62−145 ppm and 70−132 Hz, respectively) for those of
donor-stabilized silylene tungsten complexes.4 The major
component was assigned to cis-4, and its 29Si resonance is
upfield-shifted by 28 ppm compared to that of trans-4. This
upfield shift may result from the weak acetylide−silylene
interaction suggested by the X-ray structure, considering the
characteristic upfield 29Si resonance (−48.1 ppm) of acetylide−
silylene complex 1a2a and the minor contribution of the
acetylide−silylene interaction in cis-4. These VT-NMR experi-
ments demonstrated an equilibrium between trans and cis
isomers of the DMAP-stabilized silylene complex in solution.
Treatment of 2 with DMAP gave a yellow solid in 48% yield,
and recrystallization from p-xylene/pentane gave single crystals,
the X-ray analysis of which revealed the three-legged piano-
stool structure 6a with a unique W−C1−C2−Si1 backbone
(Figure 3 and Scheme 3). A characteristic difference was found
for the two Si−C bonds. The Si1−C2 bond (1.813(2) Å) is
shorter by 2.5% than the Si2−C2 bond (1.859(2) Å). This
Figure 3. Molecular structure of 6a showing thermal ellipsoids at the
50% probability level. All hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg): W1−C1, 1.918(2); C1−
C2, 1.359(3); Si1−C2, 1.813(2); Si2−C2, 1.859(2); Si1−N1,
1.850(2); W1−C1−C2, 176.55(19); Si1−C2−Si2, 129.29(12); Si1−
C2−C1, 111.20(17); Si2−C2−C1, 117.65(17).
bond shortening suggests a weak multiple-bond character for
the Si1−C2 bond, although the Si1−C2 bond distance is
considerably longer than SiC bond distances (1.74−1.76 Å)
of nitrogen donor-stabilized silenes Do·R2SiCR2,6,7 and the
bond shortening is smaller than that (3.3%) in a typical
example, Me2EtN·Me2SiC(SiMe2Ph)2 (SiC = 1.761(4) Å
and Si−C = 1.822(4) Å for the average of two PhMe2Si−C
bonds).6b The Si1−N1 bond distance (1.850(2) Å) is
intermediate between the Si−N bond distance (1.988(4) Å)
of the Me2EtN-stabilized silene and a typical Si−N covalent
B
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Scheme 3. Reactions of Acetylide−Silylene Complex 2 with DMAP and Pyridine
bond distance (1.70−1.76 Å).8 The W−C1 bond distance
(1.918(2) Å) is longer than WC bond distances (1.81−1.82
Å) in tungsten carbyne complexes Cp(CO)2WCR (R = p-
Tol, SiPh3)9 and in the range (1.88−1.98 Å) of WC bond
distances in tungsten vinylidene complexes.10 However,
interesting differences were found in comparison of the W−
C1−C2 moiety of 6a with the WCC framework of
structurally closely related vinylidene complex 3. The W−C1
bond is 0.04 Å shorter than the WCC bond (1.957(3) Å)
of 3,2b whereas the C1−C2 bond (1.359(3) Å) is 0.05 Å longer
than the WCC bond (1.309(4) Å). These structural
features are attributable to a major contribution of vinylidene
form 6a accompanied by a minor contribution of DMAP-
stabilized silenylcarbyne form 6′a.
0.10 ppm at 70 °C (Figure 2B). The latter behavior strongly
suggests the first direct observation of interconversion between
a metal acetylide and a metal carbyne/vinylidene by silylene/
silyl migration; the SiPh2·DMAP moiety in trans-5a, cis-5a, and
6a can be viewed as a resonance hybrid of DMAP-stabilized
silylene and 4-(dimethylamino)pyridiniumsilyl groups (Scheme
3). For the isomerization mechanism, the formation of 6a via
metallacyclopropene(η2-vinyl)/alkyne complex A, which is
derivable from cis-5a, might be also conceivable. However,
coordination of the η2-vinyl/alkyne-type ligand having two
bulky silyl substituents would cause steric repulsion toward the
metal fragment to favor the formation of 6a rather than that of
A from cis-5a. As a supportive example, it has been reported
that (η6-C6Me6)(CO)2CrCC(SiMe3)2 is thermodynami-
cally more stable than (η6-C6Me6)(CO)2Cr(η2-Me3SiC
CSiMe3).12 Considering also a recent theoretical study by
Koga et al. that the activation energy for 1,3-silyl migration is
considerably lower than those for 1,3-hydrogen and methyl
migrations in the conversion of the acetylide complex
(H3P)2ClRhR(CCH) to the vinylidene complex
(H3P)2ClRhCCHR (R = SiH3, 12.84; H, 18.71; CH3,
25.38 kcal mol−1),13 1,3-silylene/silyl migration seems to be
favored in the interconversion between cis-5 and 6a.
1
In the H NMR spectrum of the isolated solid in toluene-d8
at 20 °C, two SiMe3 signals were observed at 0.31 (major) and
0.08 ppm (minor) (Figure 2B).11 Although the shape of the
major signal did not change in low-temperature measurements,
the minor signal became broad at −10 °C and separated into
two signals at 0.20 and 0.11 ppm at −50 °C. At this
temperature, three components were observed in 70:18:12
ratio, based on the relative intensities of the SiMe3 signals at
0.41, 0.20, and 0.11 ppm, which were characterized as 6a, trans-
5a, and cis-5a, respectively. The 29Si NMR spectrum at −60 °C
showed three pairs of signals, which were assigned to trans-5a
(68.2 (SiPh2·DMAP) and −29.4 (SiMe3) ppm), cis-5a (50.5
(SiPh2·DMAP) and −27.9 (SiMe3) ppm), and 6a (−10.8
(SiPh2·DMAP) and −10.6 (SiMe3) ppm), judging from their
Reactivity of 1a and 2 toward pyridine was also investigated.
1
The room-temperature H NMR spectrum of a toluene-d8
solution of 1a and pyridine (3 equiv) showed their sharp signals
with no observable products, in contrast to the reaction with
DMAP, and slight signal broadening was observed only upon
cooling to −60 °C. Very interestingly, by contrast, the
treatment of 2 with pyridine (3.3 equiv) led to clear
temperature-dependent spectral changes. The 1H NMR
spectrum at 20 °C showed sharp signals of the starting
materials, involving one SiMe3 signal at −0.05 ppm (Figure 2C
and see also Supporting Information, Figure S5), whereas three
SiMe3 signals assigned to pyridine adducts 6b, trans-5b, and cis-
5b were observed at 0.32, 0.09, and −0.07 ppm in a 6:31:63
ratio at −50 °C (Figure 2C). This spectral change indicates that
the starting materials are equilibrated with the adducts and that
the equilibrium shifts toward the adducts at low temperature.
1
relative intensities and H−29Si HMBC correlations between
the SiMe3 and SiMe3 signals. The chemical shift of the
SiPh2·DMAP signal of trans-5a (68.2 ppm) is very close to that
of trans-4 (69.4 ppm), while the SiPh2·DMAP signal of cis-5a
(50.5 ppm) is 9 ppm downfield-shifted from that of cis-4 (41.4
ppm). This difference would be derived from stronger metal−
silylene and weaker acetylide−silylene interactions in 2 than in
1b observed in their molecular structures: W−Si = 2.5474(16)
Å and Si−Cβ(acetylide) = 2.059(6) Å for 2 and W−Si =
2.567(2) Å and Si−Cβ(acetylide) = 2.009(7) Å for 1b.2
Compared to these 29Si signals, the SiPh2·DMAP signal of 6a is
considerably upfield-shifted, and the vinylidene-type structure is
supported by 13C signals at 320.9 (Cα) and 87.4 (Cβ) ppm at
−70 °C. The low-temperature NMR measurements indicated
fast interconversion between trans-5a and cis-5a, similar to the
case for trans-4 and cis-4, and high-temperature measurements
demonstrated their slow interconversion with 6a, as evidenced
by coalescence of the SiMe3 signals to give a broad signal at
At −60 °C, three sets of 29Si signals were detected: 79.3 (JWSi
=
115 Hz, SiPh2·py) and −29.2 (SiMe3) ppm for trans-5b, 37.8
(vbr, SiPh2·py) and −25.5 (br, SiMe3) ppm for cis-5b, and −3.6
(SiPh2·py) and −10.3 (SiMe3) ppm for 6b (Figure 4A). Signal
assignments were performed on the basis of the 1H−29Si
HMBC spectrum and the similarity of their 29Si chemical shifts
to those of trans-4,5a, cis-4,5a, and 6a. The chemical shift and
C
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EXPERIMENTAL SECTION
■
General Procedures. All manipulations were carried out using
standard Schlenk, high-vacuum, and glovebox techniques. Hexane,
pentane, toluene, benzene-d6, and toluene-d8 were distilled from
sodium benzophenone ketyl. 4-(Dimethylamino)pyridine and triphe-
nylborane were purchased from Sigma-Aldrich. Cp*(CO)2W(SiPh2)-
(CCtBu) (1a),2a Cp*(CO)2W(SiPh2)(CCSiMe3) (2),2b Cp*(CO)2W-
(NCMe)Me,14 Ph2HSiCCtBu,2a and Ph2HSiCCSiMe3 were
2b
prepared according to the literature methods. NMR spectra were
recorded on a Bruker AV-400 or AV-600 spectrometer, and IR spectra
were obtained on a Shimadzu FTIR-8100 M spectrometer. High-
resolution mass spectra were recorded on a Bruker Daltonics solariX
9.4T FT-ICR mass spectrometer. Mass spectrometric analysis,
elemental analysis, and X-ray crystal analysis were performed at the
Research and Analytical Center for Giant Molecules, Tohoku
University.
Reaction of 1a with DMAP. An NMR tube was charged with 1a
(7.0 mg, 11 μmol), DMAP (1.3 mg, 11 μmol), and benzene-d6 (0.5
1
mL), and the tube was flame-sealed under vacuum. The H NMR
spectrum of the solution showed coalescent signals of trans-4 and cis-4
in 87% yield. 1H NMR (400 MHz, benzene-d6, rt): δ 1.11 (s, 9H, tBu),
2.03 (br, 6H, NMe2), 2.07 (s, 15H, Cp*), 5.82 (s, 2H, DMAP), 7.19−
7.27 (m, 2H, Ph), 7.27−7.37 (m, 4H, Ph), 8.00 (br, 2H, DMAP), 8.30
(br, 4H, Ph).
Figure 4. 29Si{1H} NMR spectra of trans-5b, cis-5b, and 6b in
toluene-d8 at −60 °C (A) and at −90 °C (B).
183W satellites for the SiPh2·py signal of trans-5b are reasonable
for the typical donor-stabilized silylene complex,4 and the
SiPh2·py signal of cis-5b is upfield-shifted relative to it, similar
to the case for cis-4 and cis-5a, supporting its cis-donor-
stabilized silylene structure. Notably, only the signals of cis-5b
were broad at −60 °C and sharpened at −90 °C (Figure 4). In
In a preparative reaction, toluene (3 mL) was vacuum transferred to
a mixture of Cp*(CO)2W(NCMe)Me (100 mg, 0.23 mmol) and
Ph2HSiCCtBu (64 mg, 0.24 mmol) with cooling in a liquid nitrogen
bath. The mixture was thawed at −70 °C and warmed to room
temperature with stirring. After 30 min at room temperature, the
solvent was removed under vacuum to leave crude 1a, to which DMAP
(30 mg, 0.25 mmol) and toluene (2.5 mL) were added. The mixture
was stirred at room temperature for 50 min. After removal of the
volatiles, the residual solid was washed with hexane (4 × 2 mL) to give
an air-sensitive yellow solid (74 mg, 42% yield based on Cp*-
(CO)2W(NCMe)Me). The room-temperature spectrum of the solid
was the same as that of the NMR tube reaction, and variable-
temperature NMR measurements were performed using toluene-d8 as
a solvent. 1H NMR (600 MHz, toluene-d8, −60 °C): δ 1.06 (s, tBu, cis-
1
the H NMR spectrum at −60 °C, the coordinated pyridine
signals of trans-5b were clearly detected at 8.67, 6.48, and 6.08
ppm (see Supporting Information, Figure S6). On the other
hand, the corresponding signals of cis-5b were observed as
coalescent signals with free pyridine at 8.46, 6.89, and 6.55 ppm
at −60 °C, and they considerably broadened at −80 °C (see
Supporting Information, Figures S6 and S7). These observa-
tions imply that the dissociation equilibrium of pyridine is
much more facilitated in cis-5b than in trans-5b, most likely
due to the weak acetylide−silylene interaction remaining in the
cis isomer. Dissociation of the coordinated donor in the DMAP
system is also demonstrated by the reaction of a mixture of
trans-5a, cis-5a, and 6a with BPh3 (1 equiv) in benzene-d6,
leading to the rapid and clean formation of 2 and DMAP·BPh3.
From the above results, important substituent effects of
SiMe3 vs CMe3 group on the reactivity of acetylide−silylene
complexes are derived as follows. The SiMe3 substituent
increases the reactivity of an acetylide−silylene complex toward
a nitrogen base, as shown by the reactivity of 1a and 2 toward
pyridine. This is ascribed to the stronger metal−silylene and
weaker acetylide−silylene interactions in 2 than in 1a, as
evidenced by X-ray structural comparison of 2 and 1b. The
reactions of 1a and 2 with DMAP demonstrate that the SiMe3
group favors the formation of silylvinylidene/silenylcarbyne
complex 6a, and a similar stabilization effect for a vinylidene-
type structure has been observed in their reactions with
acetone.2b The strength of bases also affects the product
distribution. In the reactions of 2, the weaker base pyridine
favors the formation of cis-donor-stabilized silylene acetylide
complex cis-5b over trans isomer trans-5b, while the stronger
base DMAP overcomes the acetylide−silylene interaction to
favor trans isomer trans-5a over cis isomer cis-5a, although the
most favorable product is silylvinylidene/silenylcarbyne com-
plex 6a. Further studies of the acetylide−silylene complexes are
in progress to uncover their novel property and reactivity.
t
4), 1.23 (s, Bu, trans-4), 1.62 (s, NMe2, trans-4), 1.71 (s, NMe2, cis-
4), 2.08 (s, Cp*, overlapped with a C6D5CD2H signal), 2.15 (s, Cp*,
cis-4), 5.12 (m, DMAP, cis-4), 5.18 (m, DMAP, trans-4), 7.22−7.26
(m, Ph), 7.32−7.38 (m, Ph), 7.54 (m, Ph), 7.63 (m, DMAP, cis-4),
8.14−8.19 (m, Ph), 8.27 (m, DMAP, trans-4), 8.35 (m, Ph). 13C{1H}
NMR (150 MHz, toluene-d8, −70 °C): δ 11.5 (C5Me5, trans-4), 11.7
(C5Me5, cis-4), 30.2 (CMe3, trans-4), 30.6 (CMe3, cis-4), 31.5 (CMe3,
cis-4), 32.7 (CMe3, trans-4), 38.2 (NMe2, trans- and cis-4), 86.5
(WCC, cis-4), 89.3 (WCC, trans-4), 100.0 (C5Me5, cis-4), 100.1
(C5Me5, trans-4), 104.8 (DMAP, cis-4), 105.1 (DMAP, trans-4),
127.3, 130.2, 132.5, 135.0, 135.5 (Ph), 136.5 (WCC, trans-4), 142.9
(Ph), 145.7 (DMAP, cis-4), 146.2 (WCC, cis-4), 147.4 (DMAP, trans-
4), 153.9 (DMAP, cis-4), 154.7 (DMAP, trans-4), 221.1 (CO, trans-
4), 238.2 (CO, cis-4), 249.0 (CO, cis-4). Several acetylide and
aromatic carbon signals were not assigned due to their poor intensities
or overlap with solvent signals. 29Si{1H} NMR (118 MHz, toluene-d8,
−70 °C): δ 69.4 (1JWSi = 111 Hz, trans-4), 41.4 (1JWSi = 93 Hz, cis-4).
IR (KBr): νCO 1892, 1806 cm−1. Anal. Calcd for C37H44N2O2SiW: C,
58.42; H, 5.83; N, 3.68. Found: C, 58.15; H, 6.03; N, 3.42.
Reaction of 2 with DMAP. An NMR tube was charged with 2
(9.5 mg, 16 μmol), DMAP (2.0 mg, 16 μmol), and benzene-d6 (0.5
1
mL), and the tube was flame-sealed under vacuum. The H NMR
spectrum of the solution showed the coalescent signals of trans-5a and
cis-5a and the signals of 6a in 37% (trans-5a + cis-5a) and 63% (6a)
1
yields, respectively. H NMR (400 MHz, benzene-d6, rt): δ 0.13 (s,
SiMe3, trans- and cis-5a), 0.39 (s, SiMe3, 6a), 1.84 (s, NMe2, 6a), 1.90
(br, NMe2, trans- and cis-5a), 2.03 (s, Cp*, trans- and cis-5a), 2.24 (s,
Cp*, 6a), 5.36−5.66 (br, DMAP, trans- and cis-5a), 5.66−5.90 (br,
DMAP, 6a), 7.18−7.28 (m, Ph, trans- and cis-5a + 6a), 7.28−7.39 (m,
Ph, trans- and cis-5a + 6a), 7.75−8.13 (br, Ph, trans- and cis-5a + 6a),
8.14−8.33 (m, DMAP, trans- and cis-5a + 6a).
D
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In a preparative reaction, toluene (2.5 mL) was vacuum transferred
to a mixture of Cp*(CO)2W(NCMe)Me (100 mg, 0.23 mmol) and
Ph2HSiCCSiMe3 (69 mg, 0.24 mmol) with cooling in a liquid
nitrogen bath. The mixture was thawed at −70 °C and warmed to
room temperature with stirring. After 30 min at room temperature, the
volatiles were removed under vacuum to leave crude 2, to which
DMAP (29 mg, 0.24 mmol) and toluene (2.2 mL) were added. The
mixture was stirred at room temperature for 2 h. After removal of the
volatiles, the residual solid was washed with hexane (4 mL) and then
with hexane/toluene (5 × 3.7 mL/0.3 mL) to give an air-sensitive
yellow solid (86 mg, 48% yield based on Cp*(CO)2W(NCMe)Me).
The room-temperature spectrum of the powder was the same as that
of the NMR tube reaction, and variable-temperature NMR measure-
structures were solved by direct methods using SHELXS9715 for cis-
4·0.5hexane and SIR200416 for 6a, and structural refinements were
performed by full-matrix least-squares using SCHLXL97 for cis-
4·0.5hexane and CRYSTALS17 for 6a. The non-hydrogen atoms were
refined anisotropically, and the hydrogen atoms were refined using the
riding model. Selected crystallographic data are summarized in Table
S1 in the Supporting Information.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C{1H} NMR spectra and selected crystallographic
data (PDF and CIF). This material is available free of charge via
the Internet at http://pubs.acs.org.
1
ments were performed using toluene-d8 as a solvent. H NMR (600
MHz, toluene-d8, −60 °C): δ 0.12 (s, SiMe3, cis-5a), 0.21 (s, SiMe3,
trans-5a), 0.42 (s, SiMe3, 6a), 1.733 (s, NMe2, 6a), 1.735 (s, NMe2,
trans-5a), 1.78 (s, NMe2, cis-5a), 2.03 (s, Cp*, trans-5a), 2.09 (s, Cp*,
cis-5a, overlapped with a C6D5CD2H signal), 2.30 (s, Cp*, 6a), 5.20
(br m, DMAP, trans-5a), 5.23 (br m, DMAP, cis-5a), 5.61 (m, DMAP,
6a), 7.0−7.6 (br m, Ph), 7.53 (m, DMAP, trans-5a), 8.15 (m, DMAP,
6a), 8.2−8.5 (br, Ph). 13C NMR (100 MHz, toluene-d8, −70 °C): δ
1.1 (SiMe3, cis-5a), 1.8 (SiMe3, trans-5a), 2.7 (SiMe3, 6a), 11.3
(C5Me5, trans-5a), 11.5 (C5Me5, cis-5a), 12.0 (C5Me5, 6a), 38.1
(NMe2, trans-5a), 38.3 (NMe2, cis-5a), 38.5 (NMe2, 6a), 87.4 (WCC,
6a), 100.4 (C5Me5, trans-5a and cis-5a), 101.7 (C5Me5, 6a), 105.2
(DMAP, cis-5a), 106.3 (DMAP, trans-5a), 106.4 (DMAP, 6a), 133.9,
134.6, 135.3, 136.7, 145.4, 145.9, 146.9, 154.7, 155.4 (Ph), 234.4
(CO), 237.2 (CO), 237.5 (CO), 247.6 (CO), 320.9 (WCC, 6a).
Several acetylide and aromatic carbon signals were not assigned due to
overlap with solvent signals. 29Si NMR (79 MHz, toluene-d8, −60 °C):
δ −29.4 (SiMe3, ↔ δH 0.21, trans-5a), −27.9 (SiMe3, ↔ δH 0.12, cis-
5a), −10.8 (SiPh2·DMAP, 6a), −10.6 (SiMe3, ↔ δH 0.42, 6a), 50.5
(SiPh2·DMAP, cis-5a), 68.2 (SiPh2·DMAP, trans-5a); 29Si−1H HMBC
correlations are indicated by ↔. IR (KBr): νCO 1869, 1767 cm−1.
HRMS: calcd for C36H44N2O2Si2W 776.24503, found 776.25060.
Reaction of 2 with Pyridine. An NMR tube was charged with 2
(40 mg, 0.061 mmol), pyridine (0.20 mmol, 3.3 equiv), and toluene-d8
(0.6 mL). The tube was flame-sealed under vacuum, and variable-
AUTHOR INFORMATION
Corresponding Author
*E-mail: sakaba@m.tohoku.ac.jp.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by Grants-in-Aid for Scientific
Research (No. 22550051) from the Ministry of Education,
Culture, Sports, Science and Technology of Japan.
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■
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MHz, toluene-d8, −60 °C): δ −0.07 (s, SiMe3, cis-5b), 0.10 (s, SiMe3,
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(SiMe3, 6b), 11.2 (C5Me5, trans-5b), 11.4 (C5Me5, cis-5b), 11.9
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SiPh2·py, cis-5b), 79.3 (JWSi = 115 Hz, SiPh2·py, trans-5b). 29Si−1H
HMBC correlations are indicated by ↔.
Reaction of a Mixture of cis-5a, trans-5a, and 6a with BPh3.
BPh3 (3.3 mg, 13 μmol) was added into an NMR tube containing a
mixture of cis-5a, trans-5a, and 6a (10 mg, 13 μmol) in benzene-d6
(0.5 mL), and the tube was flame-sealed under vacuum. The 1H NMR
spectrum showed their quantitative conversion into 2 and
DMAP·BPh3.
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dx.doi.org/10.1021/om300772c | Organometallics XXXX, XXX, XXX−XXX