Synthesis of Ruthenium Complexes with a Nonspectator Si,O,P-Chelate Ligand: Interconversion between a Hydrido(η2-silane) Complex and a Silyl Complex Leading to Catalytic Alkene Hydrogenation

Article abstract of DOI:10.1021/om5011885

A ruthenium complex bearing a new phosphine(η²-silane) chelate ligand connected by a xanthene backbone, Ru{κ⁴(Si,H,O,P)-^tBu₂xantSiP(H)}(H)Cl(PPh₃) (2), was synthesized by a ligand substitution reaction of Ru(H)Cl(PPh₃)₃ with 2,7-di-tert-butyl-4-dimethylsilyl-5-diphenylphosphino-9,9-dimethylxanthene (1, ^tBu₂xantSiP(H)). Dehydrogenation reaction of 2 with styrene, a hydrogen acceptor, gave a 16-electron phosphine(silyl) complex Ru{κ³(Si,O,P)-^tBu₂xantSiP}Cl(PPh₃) (3) together with ethylbenzene. Complex 2 was reproduced quantitatively by exposure of 3 to H₂ (1 atm) at room temperature. Thus, hydrido(η²-silane) complex 2 and silyl complex 3 are interconvertible through alkene hydrogenation (from 2 to 3) and dihydrogen addition to the Ru-Si bond (from 3 to 2) in which ^tBu₂xantSiP functions as a nonspectator ligand by reversibly releasing and accommodating a hydrogen atom. Complex 2 was also found to catalyze hydrogenation of alkenes via this interconversion. (Chemical Presented).

Full text of DOI:10.1021/om5011885

Article
pubs.acs.org/Organometallics
Synthesis of Ruthenium Complexes with a Nonspectator Si,O,P-
2
Chelate Ligand: Interconversion between a Hydrido(η ‑silane)
Complex and a Silyl Complex Leading to Catalytic Alkene
Hydrogenation
Takashi Komuro, Takafumi Arai, Kei Kikuchi, and Hiromi Tobita*
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
*
S Supporting Information
2
ABSTRACT: A ruthenium complex bearing a new phosphine(η -silane)
chelate ligand connected by a xanthene backbone, Ru-
4
t
{
κ (Si,H,O,P)- Bu xantSiP(H)}(H)Cl(PPh ) (2), was synthesized by a ligand
2
3
substitution reaction of Ru(H)Cl(PPh ) with 2,7-di-tert-butyl-4-dimethylsil-
3
3
t
yl-5-diphenylphosphino-9,9-dimethylxanthene (1, Bu xantSiP(H)). Dehy-
2
drogenation reaction of 2 with styrene, a hydrogen acceptor, gave a 16-
3
t
electron phosphine(silyl) complex Ru{κ (Si,O,P)- Bu xantSiP}Cl(PPh ) (3)
2
3
together with ethylbenzene. Complex 2 was reproduced quantitatively by
2
exposure of 3 to H (1 atm) at room temperature. Thus, hydrido(η -silane)
2
complex 2 and silyl complex 3 are interconvertible through alkene hydrogenation (from 2 to 3) and dihydrogen addition to the
t
Ru−Si bond (from 3 to 2) in which Bu xantSiP functions as a nonspectator ligand by reversibly releasing and accommodating a
2
hydrogen atom. Complex 2 was also found to catalyze hydrogenation of alkenes via this interconversion.
INTRODUCTION
to a metal center, the target phosphine(silyl) ligand is also
expected to function as a hemilabile ligand that can take both
■
Transition-metal complexes with a chelate ligand containing at
least one silyl ligand moiety are attracting increasing interest
because of their unique reactivity and catalytic performance
arising from strong σ-donating ability and strong trans influence
3
2
4
κ (Si,O,P) and κ (Si,P) coordination modes. This hemilability
facilitates generation of coordinatively unsaturated species
during the reactions of complexes bearing this ligand. In this
work, we developed ruthenium complexes with a new
nonspectator Si,O,P-chelate ligand in which the silicon-
1
−3
of this moiety.
In this regard, multidentate ligands with not
only silyl ligand but also phosphine ligand moieties, e.g., P,Si,P-
chelate ligands, have particularly been developed and were
found to function as a supporting ligand for transition-metal
2
coordinating moiety can take both an η -silane ligand form
and a silyl ligand form, and they are interconvertible via H2-
addition and hydrogen transfer to alkene. We describe here the
synthesis and structures of these complexes, a reaction with
styrene, and application of this reaction to catalytic alkene
2
catalysts. These phosphine(silyl) multidentate ligands are
advantageous as a supporting ligand because firm coordination
of the phosphine ligand moieties as well as the chelate effect
inhibits effectively the dissociation of the silyl ligand moiety
from a metal center.
5
hydrogenation.
RESULTS AND DISCUSSION
■
Some recent studies on transition-metal complexes with
phosphine(silyl) chelate ligands revealed that these ligands can
function as a “nonspectator” ligand and participate in reactions
of the complexes via cleavage of the labile metal−silicon single
t
Synthesis of a Ligand Precursor (1, Bu xantSiP(H)). A
precursor of a new xanthene-based Si,O,P-chelate ligand was
synthesized by stepwise lithiation and substitution reactions of
,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene (A) (eq
2
6
7
3
4
1
bond. For instance, Montiel-Palma et al. have observed the
). Thus, one bromo group of A was lithiated with ca. 1
reversible addition/elimination of H on a ruthenium−silicon
bond of complexes with an Si,P,Si-chelate ligand, which leads to
the interconversion between a hydrido(η -silane)(silyl) com-
plex and a dihydridobis(η -silane) complex.
2
n
equiv of BuLi, and the resulting aryllithium was treated with
chlorodimethylsilane to give 4-bromo-2,7-di-tert-butyl-5-dime-
thylsilyl-9,9-dimethylxanthene (B). Subsequently, the reaction
2
2
3a
n
of isolated B with ca. 1 equiv of BuLi led to the lithiation of the
We have previously reported the synthesis and reactions of
metal complexes bearing a bis(silyl) chelate ligand, xantsil, in
which two silyl ligand moieties are connected by a xanthene
remaining bromo group, and the reaction mixture was then
treated with chlorodiphenylphosphine to give a ligand
precursor, 2,7-di-tert-butyl-4-dimethylsilyl-5-diphenylphosphi-
4
backbone. Along the same lines, we aimed at developing an
unsymmetrical chelate ligand with silicon- and phosphorus-
coordinating moieties on this backbone. Moreover, because the
ether oxygen in the xanthene backbone can weakly coordinate
Received: November 25, 2014
Published: March 25, 2015
©
2015 American Chemical Society
1211
DOI: 10.1021/om5011885
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Article
t
no-9,9-dimethylxanthene (1), abbreviated as Bu xantSiP(H) in
2
this paper.
Phosphino(silyl)xanthene 1 was characterized by spectro-
scopic analysis. The H NMR spectrum of 1 shows a septet
1
Figure 1. Molecular structure of 2 (50% probability ellipsoids).
2
Hydrogen atoms except the η -Si−H hydrogen (H1) and the hydrido
signal for the Si−H proton and a doublet signal for the SiMe
protons at δ 4.83 and 0.51, respectively. Four signals assignable
to the aromatic protons of the xanthene backbone are also
observed, one of which is especially upfield-shifted and appears
as a doublet of doublets at δ 6.90 due to the couplings with a
hydrogen (H2) are omitted for clarity. Since the methyl carbons of
t
t
one Bu group in the Bu xantSiP(H) ligand are disordered with the
2
occupancy factors 0.67:0.33, a set of the disordered atoms with the
major occupancy factor is depicted. Selected bond distances (Å) and
angles (deg): Ru−Si 2.3929(16), Ru−P1 2.4132(14), Ru−P2
2.2278(13), Ru−Cl 2.4486(14), Ru−O 2.272(3), Ru−H1 1.51(6),
Ru−H2 1.59(6), Si−H1 1.81(6), Si−H2 2.01(6); Si−Ru−P1
123.43(6), Si−Ru−P2 99.79(5), Si−Ru−Cl 140.44(6), P1−Ru−P2
105.91(5), P1−Ru−Cl 87.63(5), P2−Ru−Cl 93.16(5), Si−Ru−O
80.65(9), P1−Ru−O 77.46(9), P2−Ru−O 175.34(10), Cl−Ru−O
3
4
phosphorus atom and an aromatic proton ( J = 4.6 Hz, J
PH
HH
2
9
31
=
−
2.4 Hz). The Si and P NMR chemical shifts for 1 (δSi
17.1 and δ −15.0) are close to the corresponding values of
P
4a,b
bis(dimethylsilyl)xanthene (xantsilH ) (δ −21.3)
bis(diphenylphosphino)xanthene (xantphos) (δP −16.2),
respectively.
and
2
Si
8
8
3.69(10), Si−Ru−H1 49(2), Si−Ru−H2 56(2), Ru−H1−Si 92(3).
Synthesis of a (Hydrido)ruthenium Complex 2
2
t
11
Bearing a Phosphine(η -silane) Ligand Bu xantSiP(H).
2
2.01(6) Å) are somewhat different. The Si−H1 distance is in
2
Reaction of phosphino(silyl)xanthene 1 with chlorido(hydrido)
ruthenium complex Ru(H)Cl(PPh ) at 40 °C in toluene gave
the range of the corresponding distances of the (η -silane)-
2
3
3
ruthenium complexes RuH {(η -HSiMe ) X}(PCy ) (X =9
2
2 2
3 2
4
t
Ru{κ (Si,H,O,P)- Bu xantSiP(H)}(H)Cl(PPh ) (2) in 68%
2
3
C H , (CH ) , OSiMe O, and NH) (1.73(3)−1.93(5) Å),
6
4
2 2
2
yield (eq 2). In this reaction, two PPh ligands of Ru(H)Cl-
3
and the Ru−H1−Si angle (92(3)°) is also close to the
2
2
(
PPh3) were replaced by a phosphine(η -silane) ligand
3
corresponding angles of σ-complexes RuH {(η -HSiMe ) X}-
2
2 2
t
Bu xantSiP(H).
2
(PCy ) (X = C H , (CH ) , and OSiMe O) (86.6(15)−
3
2
6
4
2 2
2
9b,c
9
5.1(14) Å). These data support that the Ru−H1−Si bond
in 2 is a three-center−two-electron (3c-2e) bond. On the other
hand, the Si−H2 distance is in the range (1.9−2.4 Å) of SISHA
(
secondary interactions between silicon and hydrogen atoms)
9a,12
proposed by Sabo-Etienne et al.
1
NMR Spectroscopic Analysis of Complex 2. In the H
NMR spectrum of 2 in C D at room temperature, two broad
6
6
signals appear in the hydridic region at −12.29 and −4.45 ppm,
2
which are assignable to the hydrogen of the η -Si−H and the
2
Crystal Structure of Hydrido(η -silane) Complex 2.
Single-crystal X-ray analysis revealed that complex 2 adopts a
distorted pentagonal bipyramidal geometry containing a
hydrido hydrogen, respectively (vide infra). The broadening of
these signals implies the existence of a dynamic behavior
2
involving the exchange of chemical environments of the η -Si−
4
t
2
κ (Si,H,O,P)- Bu xantSiP(H) ligand with η -silane, ether-oxy-
gen, and phosphine ligand moieties (Figure 1). The Ru−Si
bond distance (2.3929(16) Å) is comparable to those of (η -
H and Ru−H hydrogens. This was further confirmed by the
2
2
change of the shapes of the η -Si−H and Ru−H signals in
2
1
variable-temperature H NMR spectra (700 MHz): On cooling
2
1
silane)ruthenium complexes RuH {(η -HSiMe ) X}(PCy ) (X
the solution, these H signals sharpened, and, at 233 K, they
2
2 2
3 2
9
=
C H , (CH ) , OSiMe O, and NH) (2.395(2)−2.484(1) Å).
were observed as two sharp doublets of doublets (δ −12.34 and
−4.24) (see Figure S1 in the Supporting Information). On the
other hand, when the solution was heated from room
6
4
2 2
2
The Ru−P1 distance (2.4132(14) Å) is longer than the Ru−
P(xantphos) distances for Ru(xantphos)(PPh )HCl (2.3037(8)
3
2
and 2.3060(8) Å; xantphos = 9,9-dimethyl-4,5-bis-
diphenylphosphino)xanthene) probably due to strong trans
temperature up to 353 K, the broad η -Si−H and Ru−H
10
(
signals further broadened, and, at 353 K, these signals almost
2
influence of the hydrido ligand (H2) located at the site trans to
P1 in 2. Two hydrogen atoms on ruthenium were found in the
difference Fourier map, and their positions were refined
isotropically. The Ru−H distances (Ru−H1 = 1.51(6) Å and
Ru−H2 = 1.59(6) Å) are almost identical, whereas the Si−H
interatomic distances (Si−H1 = 1.81(6) Å and Si−H2 =
disappeared. Although it was not clear whether the η -Si−H
1
and Ru−H signals attain the coalescence or not by the H
NMR measurement with a 700 MHz spectrometer, the
coalescence was confirmed by measuring the variable-temper-
1
ature (301−353 K) H NMR spectra with a 400 MHz
2
spectrometer in which the η -Si−H and Ru−H signals were
1
212
DOI: 10.1021/om5011885
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Article
1
coalesced into a single broad signal (δ ca. −8.6) at 353 K
ethylbenzene, identified by H NMR spectroscopy, was formed
as a main product together with 3. It is noteworthy that
insertion of styrene into the Ru−Si bond of 3 as an undesirable
side-reaction, which is normally observed in stoichiometric
(
coalescence temperature: ca. 338 K). Therefore, a plausible
mechanism of the dynamic behavior of 2 involves the exchange
2
of the η -Si−H and Ru−H hydrogens. Related dynamic
2
16
behavior has been reported for several hydrido(η -silane)
reactions of silyl complexes with alkenes, did not occur in the
reaction of 2 with excess styrene.
Exposure of 3 to dihydrogen gas (1 atm) in C D at room
temperature for 5 min led to quantitative reproduction of
1
e,3a,9,12−14
⧧
ruthenium complexes.
The activation energy (ΔG )
for the dynamic behavior of 2 at the coalescence temperature
ca. 338 K) is calculated to be ca. 58 kJ mol .
The JPH coupling constants (27 and 22 Hz) for the H NMR
6
6
−1
(
1
2
hydrido(η -silane) complex 2 (eq 3). This result and that in the
signal at −12.34 ppm observed at 233 K indicate that the
hydrogen is located cis to both phosphorus atoms. On the other
hand, those (100 and 23 Hz) for the signal at −4.24 ppm are
consistent with the position of hydrogen cis to one phosphorus
reaction of 2 with styrene (eq 3) clearly show that complexes 2
and 3 are interconvertible via addition of dihydrogen to the
Ru−Si bond (from 3 to 2) and alkene hydrogenation (from 2
to 3).
Characterization of Silyl Complex 3. Single-crystal X-ray
analysis revealed that complex 3 adopts a square-pyramidal
geometry in which the silyl silicon atom with strong trans
influence is located at the apical position (Figure 2). The Ru−
1
atom and trans to another phosphorus atom. Therefore, the H
2
signals at −12.34 and −4.24 ppm are assignable to the η -Si−H
hydrogen (H1 in the crystal structure of 2 (see Figure 1)) and
the Ru−H hydrogen (H2), respectively. To determine the J
SiH
coupling constant for these signals, the phosphorus-decoupled
1
31
H{ P} NMR spectrum was measured at 233 K, which exhibits
two singlets at the corresponding chemical shifts (Figure S1).
Only the former signal bears the definite satellite signals from
which the JSiH coupling constant was determined to be 34 Hz.
This constant is much smaller than 65 Hz, the lower limit for a
secure criterion of a Ru−H−Si 3c-2e bond proposed by Sabo-
Etienne and Lachaize: for example, the corresponding constant
2
9a
for RuH {(η -HSiMe ) C H }(PCy ) is 65 Hz. However, it
2
2 2
6
4
3 2
is still larger than a common lower limit (20 Hz) for M−H−Si
15
nonclassical interactions and is also close to the J value (28
SiH
Hz) for the agostic Si−H hydrogens in the bis-
2
(
phosphinobenzylsilane)ruthenium complex RuH {η -HSi-
2
13
Me CH (o-C H )PPh } . Therefore, based on the above
2
2
6
4
2 2
discussion and the previously mentioned discussion on the X-
ray analysis of 2, complex 2 can be best formulated as a
2
hydrido(η -silane) complex rather than a dihydrido(silyl)
complex.9
The 2 Si{ H} NMR spectrum of 2 at room temperature
shows a doublet signal at 13.9 ppm (JSiP = 7 Hz), which is
coupled with only one of two phosphorus atoms located at cis
1
Figure 2. Molecular structure of 3 (50% probability ellipsoids).
Hydrogen atoms are omitted for clarity. Selected bond distances (Å)
and angles (deg): Ru−Si 2.3317(15), Ru−P1 2.2538(13), Ru−P2
2.2528(13), Ru−Cl 2.3812(13), Ru−O 2.234(4); Si−Ru−P1
2
positions. This chemical shift is close to those for (η -
2
silane)ruthenium complexes RuH {(η -HSiMe ) C H }(PR )
(
2
2 2
6
4
3 2
98.87(5), Si−Ru−P2 99.44(5), Si−Ru−Cl 98.43(5), P1−Ru−P2
98.32(5), P1−Ru−Cl 153.35(5), P2−Ru−Cl 98.66(5), Si−Ru−O
82.41(11), P1−Ru−O 80.10(10), P2−Ru−O 177.75(11), Cl−Ru−O
82.28(10).
9
b
4.77−8.80 ppm, R = Cy, Ph, and pyl; pyl = pyrrolyl) but is
substantially shifted downfield in comparison with that of 1
−17.1 ppm).
Dehydrogenation Reaction of Hydrido(η -silane)
Complex 2. To remove a hydrido ligand and an η -Si−H
hydrogen atom on ruthenium in 2, a reaction with styrene, a
hydrogen acceptor, was examined: Heating a mixture of 2 with
excess styrene in toluene at 100 °C afforded a dehydrogenation
(
2
2
Si bond distance (2.3317(15) Å) is shortened from that of 2
2.3929(16) Å), consistent with the common trend that a
(
metal−silicon bond of a silyl complex is stronger than that of an
η -silane complex. This distance for 3 is also similar to those for
2
3
t
product, Ru{κ (Si,O,P)- Bu xantSiP}Cl(PPh ) (3), which was
isolated in 90% yield from the reaction mixture (eq 3). The H
2
3
the five-coordinate 16-electron bis(silyl)ruthenium complex
1
3
Ru{κ (Si,O,Si)-xantsil}(PCy )(CO) (2.2870(16) and
3
.3584(16) Å, xantsil = (9,9-dimethylxanthene-4,5-diyl)bis-
4d
Si,O,P-chelate ligand of 3 is much narrower than the
corresponding angle of 2 (123.43(6)°). In accordance with
this narrowing, the puckered angle between the least-squares
planes of two aromatic rings of the xanthene backbone in 3
(
55.5(2)°) is substantially larger than that for 2 (28.6(2)°).
The 29Si NMR spectrum exhibits a pseudotriplet signal at
4
8.0 ppm, which is shifted downfield in comparison with that
2
NMR spectrum of the product shows neither η -Si−H nor Ru−
for 2 (13.9 ppm) but is almost identical to that for
Ru{κ (Si,O,Si)-xantsil}(PCy )(CO) (48.6 ppm).
3
4c,d
H signal, which confirms that abstraction of the corresponding
hydrogens in 2 occurred. The same reaction conducted in an
NMR tube using C D as a solvent at 60−80 °C revealed that
The cou-
3
pling constant of the silicon with both phosphorus nuclei of
t
Bu xantSiP and PPh (J = 21 Hz) is larger than those for
6
6
2
3
SiP
1
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Article
1
8
complex 2 (7 Hz and nearly zero), which is possibly caused by
the stronger Ru−Si(silyl) bond for 3 in comparison with the
have already been investigated, to the best of our knowledge,
this is the first example of catalytic hydrogenation of alkenes
that proceeds through interconversion between a well-
2
Ru−Si(η -silane) bond for 2.
2
Catalytic Hydrogenation of Alkenes Promoted by
Complex 2. To apply the finding of the interconversion
between 2 and 3, we examined the hydrogenation of styrene
characterized hydrido(η -silane) complex and a silyl complex.
CONCLUSION
■
2
using hydrido(η -silane) complex 2 as a catalyst. Thus, reaction
We have synthesized two ruthenium complexes bearing a new
xanthene-based Si,O,P-chelate ligand ( Bu xantSiP), i.e.,
hydrido(phosphine)(η -silane) complex 2 and phosphine(silyl)
complex 3. These complexes are interconvertible via dehydro-
genation/hydrogenation on the Ru−Si bond. Hydrogen
transfer from hydrido(η -silane) complex 2 to alkene affords
of styrene with 1 atm of H in the presence of 5 mol% of 2 in
t
2
2
C D at 60 °C for 2 days afforded ethylbenzene quantitatively
2
6
6
(
ca. 100% NMR yield) (eq 4). This catalytic hydrogenation was
2
silyl complex 3, while addition of dihydrogen to the Ru−Si
t
bond of 3 reproduces 2. In this interconversion, the Bu xantSiP
2
ligand turned out to be a nonspectator ligand that took two
2
interconvertible forms, i.e., an η -silane form and a silyl form.
1
monitored by H NMR spectroscopy, mainly at the region of
SiMe signals, revealing that complex 2 exists as the major Ru
complex during the course of the reaction. Complex 2 was also
found to catalyze the hydrogenation of 4-methoxystyrene and
This interconversion has been applied to the construction of a
catalytic alkene hydrogenation reaction. Further studies on
reactivity and catalytic activity of complexes 2 and 3 are
currently under way.
3
,3-dimethylbut-1-ene under similar conditions (eq 4, see
Experimental Section for details): 4-Methoxystyrene was
converted to 4-ethylanisole in 95% NMR yield based on the
conversion of the alkene (91%) after 2 days, while 3,3-
dimethylbut-1-ene was converted to 2,2-dimethylbutane in ca.
EXPERIMENTAL SECTION
General Procedures. All manipulations were carried out under
dry nitrogen or argon in a glovebox or using a high-vacuum line and
standard Schlenk techniques.
■
1
00% NMR yield based on the conversion (88%) after 8 days.
Possible Mechanism for the Alkene Hydrogenation
Materials. Hexane, toluene, THF, benzene-d , and toluene-d were
6
8
dried over CaH and vacuum-transferred. All the solvents were stored
2
Catalyzed by 2. A possible mechanism for the catalytic alkene
hydrogenation promoted by 2 is illustrated in Scheme 1.
under argon over 4 Å molecular sieves in a glovebox. 1,2-
Dimethoxyethane (DME) (dehydrated, Kanto Chemical Co., Inc.)
was used as received. Chlorodimethylsilane (ClSiMe H) and
2
Scheme 1. Possible Mechanism for Hydrogenation of
Alkenes Catalyzed by Hydrido(η -silane)ruthenium
Complex 2
chlorodiphenylphosphine (ClPPh ) were distilled before use. Styrene,
2
2
4
-methoxystyrene, and 3,3-dimethylbut-1-ene were distilled, degassed,
and stored under argon over 4 Å molecular sieves in a glovebox. Flash
1
9
chromatography was performed using silica gel 60N (Kanto
Chemical Co., Inc., 40−50 μm, spherical, neutral). 4,5-Dibromo-2,7-
7
20
di-tert-butyl-9,9-dimethylxanthene (A) and Ru(H)Cl(PPh ) were
3
3
prepared according to the literature methods.
1
1
31
13
1
29
1
Spectroscopic Measurements. H, H{ P}, C{ H}, Si{ H},
and 31P{ H} NMR spectra in solution were recorded on a Bruker
AVANCE III 400, Bruker AVANCE 300, or JEOL JNM-ECA 700
Fourier transform spectrometer. Chemical shifts are reported in parts
per million, and coupling constants (J) and line widths at half-height
1
2
9
1
(
Δν1/2) are given in Hz. Si{ H} NMR measurements were
performed using the DEPT pulse sequence or using an inverse gate
decoupling (IG) pulse sequence. The residual proton (C D H, 7.15
6
5
ppm; C D CD H, 2.09 ppm) and the carbon resonances (C D , 128.0
6
5
2
6
6
1
ppm) of deuterated solvents were used as internal references for H
and 13C resonances, respectively. Aromatic proton and carbon are
29
1
31
1
abbreviated as ArH and ArC, respectively. Si{ H} and P{ H} NMR
chemical shifts were referenced to SiMe (0 ppm) and 85% H PO (0
4
3
4
ppm) as an external standard, respectively. The NMR data were
collected at room temperature unless indicated otherwise. Infrared
spectra were measured on a KBr pellet using a Horiba FT-720
spectrometer. UV−visible absorption spectra were acquired on a
Shimadzu MultiSpec-1500 spectrometer at room temperature. Mass
spectra and high-resolution mass spectra (HRMS) were recorded on a
Bruker Daltonics solariX 9.4T spectrometer operating in the
electrospray ionization (ESI) mode or the atmospheric pressure
chemical ionization (APCI) mode, on a JEOL JMS-T100GCV
spectrometer operating in the field desorption (FD) mode, or on a
Shimadzu QP5050 spectrometer operating in the electron impact (EI)
mode. Elemental analyses were carried out using a J-Science Lab JM11
microanalyzer. Measurements of some NMR and mass spectra and
elemental analysis were performed at the Research and Analytical
Center for Giant Molecules, Tohoku University.
Coordination of alkene on ruthenium accompanied by
dissociation of the labile xanthene oxygen in 2 occurs to give
2
η -alkene complex C. Migratory insertion of the coordinated
alkene into the metal−hydrido bond in C leads to the
formation of alkyl complex D. The alkane is subsequently
eliminated from D accompanied by Si−H bond cleavage and
C−H bond formation, which can be driven by the σ-CAM (σ-
complex-assisted metathesis) mechanism proposed by Perutz
17
and Sabo-Etienne, to give silyl complex 3. Finally, as
illustrated in eq 3, complex 2 is regenerated by the reaction
of 3 with H . Although catalytic and stoichiometric hydro-
2
Synthesis of 4-Bromo-2,7-di-tert-butyl-5-dimethylsilyl-9,9-dime-
thylxanthene (B). In a 500 mL three-necked round-bottomed flask,
genation reactions of alkenes with metal−silicon complexes
1
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DOI: 10.1021/om5011885
Organometallics 2015, 34, 1211−1217

Organometallics
Article
solution): m/z calcd for [ C 71H4616O Si P] ([M + H] ) 565.3050,
1
2
28 31
+
+
4
,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene (A) (5.06 g, 10.5
3
mmol) was suspended into toluene (100 mL) and DME (150 mL).
found 565.3049. Anal. Calcd for C H OSiP: C, 78.68; H, 8.03.
37
45
The mixture was cooled at −90 °C using a MeOH/liquid N bath, and
Found: C, 78.64; H, 8.14.
Synthesis of Ru{κ (Si,H,O,P)- Bu xantSiP(H)}(H)Cl(PPh ) (2). Ru-
2
n
4
t
BuLi (7.1 mL, 1.65 M hexane solution, 12 mmol) was added dropwise
2
3
via a syringe. After stirring at −90 °C for 1 h, the mixture was allowed
(H)Cl(PPh ) (0.079 g, 0.085 mmol) and 1 (0.051 g, 0.090 mmol)
3 3
to warm to −40 °C using a CH CN/liquid N bath and stirred at −40
were dissolved in toluene (5 mL). The solution was stirred at 40 °C
for 22 h. The resulting mixture was filtered through a Whatman PTFE
syringe filter (pore size: 0.45 μm), and the brown filtrate was
3
2
°
C for a further 2 h. The resulting mixture was cooled again at −70 °C
using a MeOH/liquid N bath, and chrolodimethylsilane (1.10 g, 11.6
2
mmol) was added dropwise via a syringe. The mixture was then
allowed to warm to room temperature and was stirred for 20 h. After
removal of volatiles under vacuum, the residue was extracted with
hexane. The hexane extract was filtered to remove LiCl, and the filtrate
was evaporated under vacuum to give a colorless solid (5.60 g). This
crude solid was purified by flash chromatography using hexane as an
eluent. An eluate containing the title compound was collected and
evaporated to dryness. Compound B was obtained as a colorless
evaporated under vacuum. To the residue was added Et O and then
2
pentane, leading to precipitation of a pale yellow solid. The mother
liquor was removed using a Pasteur pipet, and the solid was dried
4
t
under vacuum to give Ru{κ (Si,H,O,P)- Bu xantSiP(H)}(H)Cl(PPh )
2
3
1
(2) as a pale yellow powder (0.056 g, 0.058 mmol, 68%). H NMR
19
2
(400 MHz, rt, C D ): δ −12.29 (br s, Δν = 86 Hz, 1H, η -Si−H),
6
6
1/2
2
−4.45 (br d, J = ca. 100 Hz, 1H, Ru−H), 0.08 (br s, 3H, SiMe),
PH
t
t
0.43 (br s, 3H, SiMe), 1.09 (s, 9H, Bu), 1.32 (s, 9H, Bu), 1.597 (br s,
1
powder (4.29 g, 9.34 mmol, 89%). H NMR (300 MHz, C D ): δ 0.72
3H, 9-CMe), 1.603 (br s, 3H, 9-CMe), 6.80−7.12 (m, 15H,
6
6
3
t
t
4
(
(
d, J = 3.8 Hz, 6H, SiMe), 1.12 (s, 9H, Bu), 1.30 (s, 9H, Bu), 1.47
s, 6H, 9-CMe), 5.06 (sept with satellites, J = 190 Hz, J = 3.8
Hz, 1H, SiH), 7.28 (d, J = 2.3 Hz, 1H, ArH), 7.47 (d, J = 2.4
Hz, 1H, ArH), 7.53 (d, J = 2.3 Hz, 1H, ArH), 7.69 (d, J = 2.4
C{ H} NMR (75.5 MHz, C D ): δ −3.3 (s with
satellites, J = 52 Hz, SiMe), 31.3, 31.7 (CMe ), 32.8 (9-CMe), 34.4,
ArH(PPh)), 7.36 (d, J = 2.2 Hz, 1H, ArH(xanthene)), 7.36−
HH
HH
1
3
4
SiH
HH
7.48 (m, 2H, ArH(PPh)), 7.45 (d,
J
HH
= 2.2 Hz, 1H, ArH-
4
4
4
HH
HH
(xanthene)), 7.62 (d, J = 2.2 Hz, 1H, ArH(xanthene)), 7.74−7.85
HH
4
4
21
1
HH
HH
(m, 6H, ArH(PPh)), 8.05−8.14 (m, 2H, ArH(PPh)). H NMR (700
MHz, 233 K, toluene-d , hydridic region): δ −12.34 (dd, J = 27, 22
21
13
1
Hz, 1H, ArH).
6
6
8
PH
1
2
2
SiC
3
Hz, 1H, η -Si−H), −4.24 (dd,
J
= 100, 23 Hz, 1H, Ru−H).
PH
3
1
4.6 (CMe ), 35.3 (9-CMe), 110.7, 122.2, 124.9, 125.0, 128.9, 131.4,
1
31
3
H{ P} NMR (700 MHz, 233 K, toluene-d ): δ −12.34 (s with
8
21
31.6, 145.8, 146.1, 146.8, 152.9 (ArC). An ArC signal was not
2
satellites, JSiH = 34 Hz, 1H, η -Si−H), −4.24 (s), 0.00 (s, 3H, SiMe),
29
1
observed due to overlap with the signal of C D . Si{ H} NMR (59.6
t
t
6
6
0.44 (s, 3H, SiMe), 1.11 (s, 9H, Bu), 1.35 (s, 9H, Bu), 1.57 (s, 3H, 9-
−1
MHz, DEPT, C D ): δ −14.8. IR (KBr pellet, cm ): 2962 (s, νCH),
6
6
CMe), 1.59 (s, 3H, 9-CMe), 6.77−7.08 (m, 15H, ArH(PPh)), 7.16 (d,
2
1
904 (w, ν ), 2869 (w, ν ), 2119 (m, ν ), 1565 (w), 1479 (m),
4
CH
CH
SiH
J
= 2.1 Hz, 1H, ArH(xanthene)), 7.30−7.34 (m, 2H, ArH(PPh)),
HH
427 (s), 1363 (m), 1269 (s), 1244 (m), 1207 (w), 1188 (w), 1109
4
7
.37 (d, J = 2.2 Hz, 1H, ArH(xanthene)), 7.39−7.43 (m, 2H,
HH
(
(
6
w), 899 (s), 885 (s), 868 (m), 773 (w), 737 (w). MS (EI): m/z 460
4
ArH(PPh)), 7.46 (d, J = 2.1 Hz, 1H, ArH(xanthene)), 7.65 (d,
+
+
HH
M , 10), 445 (M − Me, 100). Anal. Calcd for C H OSiBr: C,
4
25
35
JHH = 2.2 Hz, 1H, ArH(xanthene)), 7.80 (br, 6H, Δν = ca. 100 Hz,
1/2
13
5.34; H, 7.68. Found: C, 65.35; H, 7.54.
3
1
ArH(PPh)), 8.09 (d, J = 7.6 Hz, 2H, ArH(PPh)). C{ H} NMR
HH
Synthesis of 2,7-Di-tert-butyl-4-dimethylsilyl-5-diphenylphosphi-
t
(101 MHz, rt, C D ): δ 8.1 (d, J = 7 Hz, SiMe), 12.1 (SiMe), 22.7
no-9,9-dimethylxanthene ( Bu xantSiPH) (1). To a solution of 4-
6
6
PC
2
(
9-CMe), 31.4, 31.9 (CMe ), 33.8 (9-CMe), 34.7, 34.8 (CMe ), 36.3
bromo-2,7-di-tert-butyl-5-dimethylsilyl-9,9-dimethylxanthene (B)
3
3
1
n
(9-CMe), 120.9, 123.7, 125.0 (d, JPC = 32 Hz), 127.4 (ArC-
(
0.31 g, 0.67 mmol) in Et O (4 mL) was added BuLi (0.50 mL,
2
(
(
xanthene)), 128.4−129.4 (ArC(xanthene) + ArC(PPh)), 129.4, 130.7
1
.60 M hexane solution, 0.80 mmol) dropwise via a syringe at 0 °C.
2
ArC(PPh)), 132.0 (ArC(xanthene)), 132.5 (d,
J
= 12 Hz)
PC
The mixture was allowed to warm to room temperature and then was
stirred for 4 h. The resulting mixture was evaporated under vacuum to
give a colorless solid. The residue was suspended in hexane (4 mL),
and chlorodiphenylphosphine (0.20 g, 0.91 mmol) was added via a
syringe. The mixture was heated at 60 °C with stirring overnight. The
resulting colorless suspension was filtered through a membrane filter
(
J
ArC(PPh)), 134.4−135.7 (ArC(xanthene) + ArC(PPh)), 137.8 (d,
1
1
3
= 50 Hz), 140.1 (d, J = 36 Hz) (ArC(PPh)), 147.5 (d, J = 4
PC PC
PC
2
21
Hz), 148.3, 156.9 (d, JPC = 15 Hz), 157.3 (ArC(xanthene)). Some
ArC signals in the range 128.4−129.4 and 134.4−135.7 ppm could not
be assigned, and coupling constants (JPC values) were also not
(
Nihon Millipore, Omnipore membrane, pore size 0.2 μm, 25 mm in
determined. Due to overlap with the signal of C
6
D
6
, some ArC signals
were not observed. Si{ H} NMR (79.5 MHz, IG, rt, C D ): δ 13.9
6 6
29
1
diameter). The filtrate was evaporated, and a residual colorless oil was
recrystallized with hexane at −30 °C. The title compound 1 was
(d, JSiP = 7 Hz). 31P{ H} NMR (162 MHz, rt, C
1
D ): δ 18.7 (d, JPP =
2
6
6
1
2
obtained as a colorless solid (0.122 g, 0.216 mmol, 32%). H NMR
13 Hz, PPh (xanthene)), 75.7 (d, J = 13 Hz, PPh ). IR (KBr pellet,
2
PP
3
3
−1
(
400 MHz, C D ): δ 0.51 (d, J = 3.8 Hz, 6H, SiMe), 1.14 (s, 9H,
cm ): 3055 (w, νCH), 2962 (s, νCH), 2904 (w, νCH), 2870 (w, νCH),
2094 (vw, νRuH), 1963 (br w, νRuH), 1481 (m), 1435 (s), 1419 (s),
6
6
HH
t
t
Bu), 1.30 (s, 9H, Bu), 1.61 (s, 6H, 9-CMe), 4.83 (sept with satellites,
JSiH = 194 Hz, J = 3.8 Hz, 1H, SiH), 6.90 (dd, J = 4.6 Hz, J
2.4 Hz, 1H, ArH), 7.01−7.11 (m, 6H, o- and p-Ph), 7.45 (dt, J
.5 Hz, J = 1.7 Hz, 4H, m-Ph), 7.50 (dd, J = 2.4 Hz, J = 0.6
Hz, 1H, ArH), 7.52 (d, J = 2.4 Hz, 1H, ArH), 7.58 (d, J = 2.4
C{ H} NMR (101 MHz, C D ): δ −3.21, −3.15
SiMe), 31.4, 31.7 (CMe ), 33.1 (9-CMe), 34.5, 34.6 (CMe ), 34.9 (9-
1
3
3
4
1392 (w), 1362 (w), 1254 (w), 1184 (m), 1092 (m), 806 (m), 744
HH
PH
HH
1
3
(
m), 694 (s), 652 (w), 540 (s), 509 (m). UV−vis (λ , nm (ε, M−
=
7
=
max
HH
4
4
5
−1
+
cm ), THF): 274sh (13 000), 355sh (1600). MS (FD): m/z 962 (M
PH
HH
PH
4
4
− 2 H, 100). Anal. Calcd for C55
H
61OSiP
xantSiP}Cl(PPh
3
ClRu: C, 68.48; H, 6.37.
HH
HH
2
21
13
1
Hz, 1H, ArH).
(
Found: C, 68.40; H, 6.43.
6
6
3
t
Synthesis of Ru{κ (Si,O,P)- Bu
) (3). In a Pyrex tube
3
3
2
1
CMe), 124.0, 124.5 (d, JPC = 17 Hz), 124.88, 124.93, 128.6
with a Teflon valve, 2 (0.020 g, 0.021 mmol) and styrene (0.020 g,
0.19 mmol) were dissolved in toluene (5 mL). The Teflon valve was
closed, and the solution was stirred at 100 °C for 2 days. The orange
reaction mixture was filtered to remove insoluble materials, and the
filtrate was evaporated under vacuum. The residue was washed with
(
1
ArC(xanthene)), 128.69 (d, 3J = 5 Hz), 128.73 (ArC(PPh )),
P
C
2
2
29.3, 130.3, 131.3 (ArC(xanthene)), 134.4 (d, J = 20 Hz), 138.1
PC
1
(
d, J = 13 Hz) (ArC(PPh )), 145.5 (ArC(xanthene) × 2), 151.3 (d,
PC 2
21
2
JPC = 17 Hz), 153.2 (ArC(xanthene)). Although the reason that two
13
1
3
t
inequivalent SiMe signals are observed in the C{ H} NMR spectrum
is not elucidated, a possible explanation for this observation is that 1
may exist as a mixture of two rotamers in solution due to hidered
pentane and evaporated to dryness. Ru{κ (Si,O,P)- Bu
2
xantSiP}Cl-
(PPh ) (3) was obtained as an orange powder (0.018 g, 0.019 mmol,
3
1
90%). H NMR (400 MHz, rt, C D ): δ −0.30 (br s, 3H, SiMe), 0.94
6 6
t
29
1
t
rotation around the Si−C(xanthene) bond. Si{ H} NMR (79.5
(br s, 3H, SiMe), 1.06 (s, 9H, Bu), 1.25 (s, 9H, Bu), 1.72 (br s, 3H, 9-
31
1
MHz, IG, C D ): δ −17.1. P{ H} NMR (162 MHz, C D ): δ −15.0.
CMe), 1.94 (br s, 3H, 9-CMe), 5.58−5.68 (m, 2H, ArH(PPh)), 6.45
6
6
6
6
−1
3
4
3
IR (KBr pellet, cm ): 3051 (w, ν ), 2962 (s, ν ), 2929 (m, ν ),
(dt, JHH = 7.8 Hz, JPH = 1.7 Hz, 2H, ArH(PPh)), 6.66 (dt, JHH = 7.7
CH
CH
CH
4
2
902 (m, νCH), 2868 (m, νCH), 2150 (m, νSiH), 1475 (m), 1458 (m),
Hz, JPH = 1.7 Hz, 2H, ArH(PPh)), 6.75−6.89 (m, 2H, ArH(PPh)),
3
4
1421 (s), 1398 (m), 1392 (m), 1362 (m), 1263 (s), 1246 (s), 1211
6.86 (dd, J = 8.0 Hz, J = 2.0 Hz, 1H, ArH(xanthene)), 6.93−
4
PH
HH
(
(
m), 1146 (w), 1115 (w), 1099 (w), 895 (m), 883 (m), 862 (w), 833
w), 773 (w), 741 (m), 696 (m), 505 (w). HRMS (ESI, a THF
7.08 (m, 9H, ArH(PPh)), 7.38 (d, J = 2.1 Hz, 1H, ArH(xanthene)),
4
7.53−7.61 (m, 2H, ArH(PPh)), 7.58 (d, J = 2.0 Hz, 1H,
1
215
DOI: 10.1021/om5011885
Organometallics 2015, 34, 1211−1217

Organometallics
Article
4
ArH(xanthene)), 7.64 (d, J = 2.1 Hz, 1H, ArH(xanthene)), 7.93−8.07
mg, 3 μmol) and 3,3-dimethylbut-1-ene (5 mg, 0.06 mmol) in C D
6
6
21
13
1
(
m, 6H, ArH(PPh)).
C{ H} NMR (101 MHz, rt, C D ): δ 4.5 (d,
JPC = 5 Hz, SiMe), 11.0 (SiMe), 22.2, 30.9 (9-CMe), 31.5, 31.9
(0.6 mL) in the presence of Cp Fe (internal standard, less than 1 mg)
6
6
2
3
at 60 °C under 1 atm of H . After 2 days for 4-methoxystyrene (91%
2
(
CMe ), 34.86, 34.88 (CMe ), 38.6 (9-CMe), 120.7, 123.6, 125.4 (d,
conversion) or 8 days for 3,3-dimethylbut-1-ene (88% conversion), 4-
ethylanisole or 2,2-dimethylbutane was formed in 95% (TON = 17) or
∼100% (TON = 18) NMR yield, respectively, based on the conversion
3
3
1
JPC = 40 Hz), 126.5 (ArC(xanthene)), 126.8 (ArC(PPh)), 127.5 (d,
2J = 10 Hz) (ArC(xanthene)), 128.4−129.7 (ArC(xanthene) +
PC
1
2
of the alkene. The products were identified by comparing the H and
ArC(PPh)), 128.9, 132.0 (d, J = 10 Hz) (ArC(PPh)), 134.4−134.7
PC
2
1
13
(
ArC(xanthene) + ArC(PPh)), 134.8 (d, J = 10 Hz), 135.2 (d, J
C NMR spectroscopic data with those from the literature for 4-
PC
PC
=
1
3
22
=
5
44 Hz), 136.2 (d, J = 35 Hz) (ArC(PPh)), 136.4, 138.6 (d, J
Hz) (ArC(xanthene)), 139.9 (d, J = 44 Hz) (ArC(PPh)), 147.9,
48.8 (d, JPC = 4 Hz), 159.08 (d, JPC = 14 Hz), 159.09
ethylanisole or those of the authentic sample for 2,2-dimethylbutane.
PC
PC
1
X-ray Crystal Structure Analysis. X-ray quality single crystals
were obtained from DME/pentane at −30 °C (for 2·0.5pentane as
pale yellow block crystals) and from DME/hexane at room
temperature (for 3 as orange plate crystals). Intensity data for the
analysis were collected on a Rigaku RAXIS-RAPID imaging plate
diffractometer with graphite-monochromated Mo Kα radiation (λ =
0.710 69 Å) under a cold nitrogen stream (T = 150 K). Numerical
absorption corrections were applied to the data. The structures were
PC
3
2
1
21
(
ArC(xanthene)). Some ArC(xanthene or PPh) signals in the
range 128.4−129.7 and 134.4−134.7 ppm could not be assigned, and
coupling constants (J values) were also not determined. Due to
overlap with the signal of C D , some ArC(PPh) signals were not
observed. Si{ H} NMR (79.5 MHz, IG, rt, C D ): δ 48.0 (t, J =
2
6
PC
6
6
2
9
1
2
6
6
SiP
1 Hz). 3 P{ H} NMR (162 MHz, rt, C D ): δ 57.4 (d, J = 32 Hz),
1.5 (d, J = 32 Hz). IR (KBr pellet, cm ): 3055 (w, νCH), 2962 (s,
1
1
2
6
6
PP
2
−1
23
PP
solved by the Patterson method using the DIRDIF-2008 program
νCH), 2904 (w, νCH), 2870 (w, νCH), 1481 (w), 1435 (s), 1419 (m),
(for 2·0.5pentane) or by direct methods using the SHELXS-97
2
4
1
5
(
392 (w), 1176 (w), 1092 (m), 795 (w), 744 (m), 694 (s), 656 (w),
program (for 3) and refined by full matrix least-squares techniques
24
−1
−1
2
40 (m), 517 (s). UV−vis (λmax, nm (ε, M cm ), THF): 355
on all F data with SHELXL-97. In the case of 2·0.5pentane, one tert-
t
3500), 412 (3700). HRMS (APCI): m/z calcd for
butyl group in the Bu xantSiP(H) ligand shows rotational disorder
2
1
2
C551H6016O Si P Cl Ru] ([M + H] ) 963.2615, found
28 31 35 102
+
+
[
with the occupancy factors 0.67:0.33, and the pentane molecule was
disordered over two sites related to each other by an inversion center.
The carbon atoms of the tert-butyl group and the pentane molecule
were isotropically refined, and no hydrogen atoms on the carbon
atoms were included. Except for the disordered carbon atoms,
anisotropic refinements were applied to all non-hydrogen atoms. The
2
9
63.2621. Anal. Calcd for C H OSiP ClRu: C, 68.62; H, 6.18.
55 59 2
Found: C, 68.86; H, 6.34. A reaction of complex 2 with styrene (ca. 2
equiv) in an NMR tube with a J-Young Teflon valve (5 mm o.d.) was
1
31
1
monitored by H and P{ H} NMR spectroscopy using C D as a
6
6
solvent under heating at 60 °C for 6.5 days and then at 80 °C for 6
days. After heating, 2 was completely consumed, and complex 3 and
ethylbenzene were formed as the main products. During the
monitoring, complex 3 and ethylbenzene were observed as the
predominant products in the reaction mixture. Although some ArH
2
Ru−H and η -Si−H hydrogen atoms of 2 (H1 and H2) were found on
the difference Fourier map and was refined isotropically. Other
hydrogen atoms except for the hydrogens on the disordered carbon
atoms in 2·0.5pentane were put at calculated positions. All calculations
1
signals of ethylbenzene in the H NMR spectrum of the final reaction
25
were carried out using Yadokari-XG 2009. CCDC reference
mixture were not clearly resolved due to the overlap with other signals,
the chemical shifts of the observed signals of ethylbenzene are in good
agreement with those of the authentic sample.
numbers: 1049529 (2) and 1049530 (3). Crystallographic data are
available in the Supporting Information as a CIF file, and selected
crystallographic data are also listed in Table S1.
NMR Monitoring of a Reaction of Complex 3 with
Dihydrogen. Complex 3 (2 mg, 2 μmol) and Cp Fe (internal
standard, less than 1 mg; Cp = η -C H ) were dissolved in C D (0.5
mL). The solution was transferred to an NMR tube with a J-Young
Teflon valve (5 mm o.d.). A H NMR spectrum of the mixture was
measured to determine the ratio of the intensities of signals of 3 and
Cp Fe. The NMR tube was evacuated briefly to degas, and 1 atm of H2
was subsequently applied to the tube. The tube was shaken well and
allowed to stand at room temperature for 5 min, and then a H NMR
spectrum of the reaction mixture was measured. Complex 2 was
formed quantitatively (∼100% NMR yield). The product 2 was
identified by comparing the H and P{ H} NMR spectra with those
of the authentic sample synthesized by the procedure described above.
Hydrogenation of Styrene Catalyzed by Complex 2. 2 (2 mg,
2
5
ASSOCIATED CONTENT
5
5
6
6
■
1
*
S
Supporting Information
1
A figure depicting variable-temperature H NMR spectra and a
1
31
H{ P} NMR spectrum of 2 (Figure S1), a table giving
2
selected X-ray crystallographic data for 2 and 3 (Table S1), a
text describing the result of DFT calculation (a geometry
optimization) of a simplified model complex for 2, and a CIF
file giving X-ray crystallographic data for 2 and 3. This material
is available free of charge via the Internet at http://pubs.acs.org.
1
1
31
1
2
μmol), styrene (4 mg, 0.04 mmol), and Cp Fe (internal standard,
2
AUTHOR INFORMATION
■
less than 1 mg) were dissolved in C D (0.5 mL). The solution was
transferred to an NMR tube with a J-Young Teflon valve (5 mm o.d.).
A H NMR spectrum of the mixture was measured to determine the
ratio of the intensities of the signals of styrene and the signal of Cp Fe.
The NMR tube was evacuated briefly to degas and then was charged
with 1 atm of H gas. The tube was shaken well and then heated at 60
6
6
Corresponding Author
*E-mail: tobita@m.tohoku.ac.jp.
1
2
Notes
The authors declare no competing financial interest.
2
1
°C, and the conversion of styrene was monitored by H NMR
spectroscopy. After heating for 2 days, the alkene was completely
consumed, and ethylbenzene was formed quantitatively (∼100% NMR
yield, TON = 20). During the reaction, the tube was shaken well
several times to dissolve dihydrogen gas in the solution, and after 1 day
ACKNOWLEDGMENTS
■
This work was supported by Grants-in-Aid for Scientific
Research (Grant Numbers 25410058 and 23750053) from the
Japan Society for the Promotion of Science (JSPS). We are
grateful to Mr. Shinichiro Yoshida (Tohoku University) for
assistance with the VT NMR and H{ P} NMR spectroscopic
measurements of complex 2. We also acknowledge the
Research and Analytical Center for Giant Molecules, Tohoku
University, for spectroscopic measurements and elemental
analyses.
of the reaction, the tube was charged again with 1 atm of H gas. The
2
1
product (ethylbenzene) was identified by comparing the H and
1
3
1
C{ H} NMR spectra with those of the authentic sample.
1
31
Hydrogenation Reactions of 4-Methoxystyrene and 3,3-
Dimethylbut-1-ene Catalyzed by Complex 2. The title reactions
were monitored by a procedure similar to that for the above-
mentioned hydrogenation of styrene using 2 (2 mg, 2 μmol) and 4-
methoxystyrene (6 mg, 0.04 mmol) in C D (0.5 mL) or using 2 (3
6
6
1
216
DOI: 10.1021/om5011885
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Organometallics
Article
(
10) Ledger, A. E. W.; Moreno, A.; Ellul, C. E.; Mahon, M. F.;
REFERENCES
■
Pregosin, P. S.; Whittlesey, M. K.; Williams, J. M. J. Inorg. Chem. 2010,
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11) According to a comment from a reviewer, we examined DFT
(
1) Selected recent reports dealing with ruthenium complexes
4
(
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2
1
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H interatomic distances are 1.93 Å for the η -Si−H hydrogen and 2.14
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compounds B and 1−3 at room temperature were confirmed by
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5
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13
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H− C HMQC and H− C HMBC spectra.
(
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(
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DOI: 10.1021/om5011885
Organometallics 2015, 34, 1211−1217