Ruthenium Catalyst Initiation Processes
A R T I C L E S
Reaction of [1-EtCy2]/([1-EtCy2])2 Mixture with Excess
Ethene at 225 K. The compound was generated at room temper-
ature in a J-Young tube in CD2Cl2 containing 0.0062 M
Me3SiOSiMe3 as an internal standard, after which the sample was
quickly immersed in a dry ice/acetone (-78 °C) bath. The
temperature in the NMR probe was calibrated to 225 K using a
methanol thermometer, and the NMR tube was quickly transferred
from the dry ice/acetone bath to the precooled NMR probe.
Concentrations of monomer and dimer were followed over time as
described above. After equilibration, the sample was quickly
reimmersed in a dry ice/acetone bath, and three freeze-pump-thaw
cycles were performed, keeping the temperature at or below -78
°C. An excess (6 and 11 equiv relative to [Ru]total) of ethene was
transferred into the tube at -196 °C, after which the tube was
thawed at -78 °C and carefully shaken at this temperature. The
tube was reinserted into the NMR probe at 225 K, and concentra-
tions of monomer () 0) and dimer were followed over time as
described above.
in materials chemistry and fine chemical synthesis due to the
mild conditions under which they can initiate metathesis
reactions.
Experimental Section
General. Argon-filled VAC dryboxes were used to store air-
and moisture-sensitive compounds and for manipulation of air-
sensitive materials. Reactions were performed under an argon
atmosphere in the drybox. Internal standards 1,3,5-trimethoxyben-
zene and hexamethyldisiloxane were purchased from Aldrich.
B(C6F5)3 was purchased from Strem and was sublimed before use.
Ethylene was purchased from Matheson and dichloromethane-d2
was purchased from Cambridge Isotope Laboratories. o-Isopro-
poxystyrene was synthesized by published procedures.73 All
ruthenium-containing starting materials were synthesized by pub-
lished procedures29,51,74 or procedures provided in Supporting
Information. Where applicable, cooling baths consisting of dry ice/
acetone (195 K) were used to maintain low temperature conditions.
1H, 31P{1H} NMR experiments were performed on Bruker 400 MHz
spectrometers. Data are given in ppm relative to residual solvent
signals for 1H and 31P spectra was referenced to 85% H3PO4.
Temperature calibration for low temperature NMR experiments was
Reaction of [1-MeCy2]/([1-MeCy2])2 Mixture with Excess
Ethene. The compound was generated at room temperature in a
J-Young tube in CD2Cl2 containing 0.0062 M Me3SiOSiMe3 as an
internal standard. Three freeze-pump-thaw cycles were performed,
and the NMR tube was transferred to the NMR probe at 245 K
and allowed to equilibrate for 1 h to obtain a ca. 20:1 dimer/
monomer mixture. The tube was taken out of the probe, quickly
immersed in a dry ice/acetone bath, and an excess (ca. 10 equiv)
of ethene was added to the tube as described above. The temperature
in the NMR probe was calibrated using a methanol thermometer.
The tube was reinserted into the NMR probe, and concentrations
of monomer () 0) and dimer were followed over time as described
above. This analysis was performed at four temperatures in the range
235-254 K.
1
achieved by monitoring the H NMR spectrum of pure methanol
before and after changing the temperature. For quantitative experi-
ments 16 scans were collected for every spectrum. T1 measurements
were performed on the resonances of interest, and a delay (d1) of
5*T1 between single acquisitions was used, taking as a reference
the longest relaxation time. In the case of the initiation kinetics of
the ruthenium phosphonium alkylidene complexes, 5*T1 cor-
responded to 6 s. Electrospray ionization mass spectrometry was
performed on the Bruker Esquire 3000 (positive mode, 3200V
capillary voltage, 7 psi nebulizer, 5.0 L/min dry gas, 573 K dry
temperature, 0.10 ms accumulation time, and target mass set
between 150-400 m/z depending on the phosphonium salt byprod-
uct).
Measurement of Equilibrium Constants for [1-MeCy2]+/
([1-MeCy2]+)2. The compound was generated in CD2Cl2 containing
0.0062 M Me3SiOSiMe3 as an internal standard. The temperature
in the NMR probe was calibrated using a methanol thermometer.
The integrations of the H2IMes NCH2CH2N backbone protons were
used in the analysis, since they are distinct and do not overlap with
each other or with other peaks. The equilibrium constant K ()
[dimer]eq/[monomer]2eq) was then determined in the temperature
range 295-245 K, in intervals of ca. 5 K. At the lower temperatures,
the sample was given 1 h to allow it to fully equilibrate before K
was measured.
Generation of II from 1-R3-A (30 equiv of o-isopropoxy-
styrene; R3
) Cy3, Cyp3; A ) ClB(C6F5)3, B(C6F5)4).
(H2IMes)(Cl3)RudC(H)PR3 (6-7 mg, 0.0083 mmol, R ) Cy, Cyp)
and B(C6F5)3 (5 mg, 0.0098 mmol) or [(H2IMes)-
(Cl2)RudC(H)PCy3]+[B(C6F5)4]- (12 mg, 0.0083 mmol) were
charged into an NMR tube along with 0.4 mL of CD2Cl2. In a
gastight syringe, 200 µL of a stock solution containing o-
isopropoxystyrene (41 mg, 0.250 mmol) and 1,3,5-trimethoxyben-
zene internal standard (2.8 mg, 0.017 mmol) was added. The NMR
tube was placed in an acetone/dry ice bath for transporting to the
precooled NMR probe (243 K) where the stock solution was added
at (195 K) before insertion into the probe. The reaction progress
was monitored by both 1H and 31P{1H} NMR spectroscopy through
cycling experiments, at various intervals (depending on the half-
life of the conversion), until essentially all of the starting material
catalyst was converted to II (δ ∼16 ppm). Integration of the starting
complex alkylidene peak (δ ∼18 ppm) against the internal standard
(δ ) 6.1 ppm) was used for the first-order treatment of the data.
31P{1H} NMR of 1-Cy3 phosphonium byproduct (CD2Cl2, 161.8
MHz, 238 K): δ 28.22 ([(Ar)HCdC(H)PCy3]+[B(C6F5)4]-), 27.41
([H2CdC(H)PCy3]+[B(C6F5)4]-); δ 28.15 ([(Ar)HCdC(H)PCy3]+
[ClB(C6F5)3]-), 27.34 ([H2CdC(H)PCy3]+[ClB(C6F5)3]-). ESI MS of
1-Cy3 phosphonium byproduct C20H36P+: 307 m/z ([H2CdC-
(H)PCy3]+); C29H46OP+: 441 m/z ([(Ar)HCdC(H)PCy3]+);
C18F15BCl-: 547 m/z; C24F20B-: 679 m/z. 31P{1H} NMR of 1-Cyp3
phosphonium byproduct (CD2Cl2, 161.8 MHz, 238 K): δ 36.48
([(Ar)HCdC(H)PCyp3]+[ClB(C6F5)3]-), 35.98 ([H2CdC(H)PCyp3]+
[ClB(C6F5)3]-). ESI MS of 1-Cyp3 phosphonium byproduct C17H30P+:
265 m/z ([H2CdC(H)PCyp3]+); C26H40OP+: 399 m/z ([(Ar)HCd
C(H)PCyp3]+); C18F15BCl-: 547 m/z.
Measurement of Equilibration and of Equilibrium Con-
stants for [1-EtCy2]/([1-EtCy2])2. The compound was generated
at room temperature in CD2Cl2 containing 0.0062 M Me3SiOSiMe3
as an internal standard, after which the sample was quickly
immersed in a dry ice/acetone (-78 °C) bath. The temperature in
the NMR probe was calibrated using a methanol thermometer, and
the NMR tube was quickly transferred from the dry ice/acetone
bath to the precooled NMR probe. Concentrations of monomer and
dimer were followed over time until equilibrium was attained
(except at 207 and 213 K, for which equilibrium was not attained
after >14 h). The integrations of the alkylidene (RudCH) protons
were used in the analysis. K was determined after equilibriation,
in the temperature range 225-260 K in intervals of ca. 7 K.
Generation of II from 1-R3 (1 equiv of o-isopropoxy-
(72) It is not clear why the o-isopropoxystyrene gives 35% of the
stryrenylphosphonium salt, but the donor properties of the o-isopropyl
group may play a role in this observation directing the OR group
towards the R3P+ moiety.
(73) Krause, J. O.; Nuyken, O.; Wurst, K.; Buchmeiser, M. R. Chem. Eur.
J. 2004, 10, 777–784.
(74) Dubberley, S. R.; Romero, P. E.; Piers, W. E.; McDonald, R.; Parvez,
M. Inorg. Chim. Acta 2006, 359, 2658–2664.
i
styrene; R3 ) Pr3, EtCy2, EtiPr2, MeCy2, MeiPr2). (H2IMes)-
i
(Cl3)RudC(H)PR3 (6-7 mg, 0.0083 mmol, R3 ) Pr3, EtCy2,
MeCy2, MeiPr2) and B(C6F5)3 (5 mg, 0.0098 mmol) were charged
into an NMR tube along with 0.4 mL of CD2Cl2. In a gastight
syringe 200 µL of a stock solution containing o-isopropoxystyrene
(1.3 mg, 0.0083 mmol) and 1,3,5-trimethoxybenzene internal
9
J. AM. CHEM. SOC. VOL. 132, NO. 8, 2010 2793