Cationic ruthenium alkylidene catalysts bearing phosphine ligands

Article abstract of DOI:10.1039/c5dt04506a

The discovery of highly active catalysts and the success of ionic liquid immobilized systems have accelerated attention to a new class of cationic metathesis catalysts. We herein report the facile syntheses of cationic ruthenium catalysts bearing bulky phosphine ligands. Simple ligand exchange using silver(i) salts of non-coordinating or weakly coordinating anions provided either PPh₃ or chelating Ph₂P(CH₂)_nPPh₂ (n = 2 or 3) ligated cationic catalysts. The structures of these newly reported catalysts feature unique geometries caused by ligation of the bulky phosphine ligands. Their activities and selectivities in standard metathesis reactions were also investigated. These cationic ruthenium alkylidene catalysts reported here showed moderate activity and very similar stereoselectivity when compared to the second generation ruthenium dichloride catalyst in ring-closing metathesis, cross metathesis, and ring-opening metathesis polymerization assays.

Full text of DOI:10.1039/c5dt04506a

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Cationic ruthenium alkylidene catalysts bearing
phosphine ligands†
Cite this: DOI: 10.1039/c5dt04506a
Koji Endo and Robert H. Grubbs*
The discovery of highly active catalysts and the success of ionic liquid immobilized systems have accele-
rated attention to a new class of cationic metathesis catalysts. We herein report the facile syntheses of
cationic ruthenium catalysts bearing bulky phosphine ligands. Simple ligand exchange using silver(I) salts of
non-coordinating or weakly coordinating anions provided either PPh3 or chelating Ph2P(CH2)nPPh2 (n = 2
or 3) ligated cationic catalysts. The structures of these newly reported catalysts feature unique geometries
caused by ligation of the bulky phosphine ligands. Their activities and selectivities in standard metathesis
reactions were also investigated. These cationic ruthenium alkylidene catalysts reported here showed
moderate activity and very similar stereoselectivity when compared to the second generation ruthenium
dichloride catalyst in ring-closing metathesis, cross metathesis, and ring-opening metathesis polymeri-
zation assays.
Received 16th November 2015,
Accepted 19th January 2016
DOI: 10.1039/c5dt04506a
www.rsc.org/dalton
exchange reactions which enabled highly enantioselective
asymmetric ring-opening cross metathesis (AROM) and cross
Introduction
Olefin metathesis is a convenient and powerful methodology metathesis (CM).8 We recently reported a family of NHC che-
for the construction of carbon–carbon double bonds.1 Due to lated catalysts which were produced by coordination of two
their high activity and functional group tolerance, ruthenium- pivalate ligands and subsequent intramolecular C–H bond
based catalysts have been utilized in a variety fields including activation.9 This family of catalysts has showed very high
natural product synthesis,2 biochemistry,3 green chemistry4 activity and Z-selectivity in a variety of metathesis reactions.10
and polymer chemistry.5 Along with the expansion of these
The formation of catalysts that are cationic at the metal
applications, the catalysts themselves have dramatically center or contain pendant positively charged groups has been
evolved. In particular, the introduction of an N-heterocyclic previously reported (1–6 in Fig. 1). One of the remarkable
carbene (NHC) ligand in place of a phosphine ligand led to a examples are ionic liquid tagged catalysts, like 1 and 2,11 that
large enhancement in catalyst activity and stability.6 These have an oligomeric tether capped with a cationic imidazolium
types of catalysts are widely used in both academic and indus- group. Due to their cationic charge, they can be immobilized
trial laboratories.
in an ionic liquid phase and behave as supported catalysts,
The modification of X-type ligands, which are generally achieving efficient catalyst recyclability. Several cationic cata-
chlorides in the original catalyst systems, is becoming a lysts, in which the ruthenium center is positively charged,
popular avenue of investigation because of their easy substi- have been also reported.12 Among these catalysts, 3 shows
tution and large impact on catalyst performance. Buchmeiser much higher activity in ring-opening metathesis polymeri-
et al. first utilized silver(I) salts to remove a chloride ligand and zation (ROMP) reactions of cyclooctene compared to standard
simultaneously introduce an anionic ligand in its place.7 They NHC-ligated catalyst.12a In ring-closing metathesis (RCM) reac-
expanded this methodology to form solid supported systems tions of a tetra-substituted olefin, which is one of the toughest
where a catalyst is bound to a monolith through a polymeric olefin metathesis transformations, 5 surpasses the second
X-type ligand.7a,b Additionally, Hoveyda et al. formed a bi- generation catalyst.12c
dentate chiral NHC ligated complex through similar ligand
Relying on the recent successes mentioned above, modifi-
cation of the X-type ligand to produce cationic ruthenium-
based catalysts is highly promising in improving catalyst
efficiency and expanding their applications. Therefore, the dis-
covery of facile methodologies to prepare these types of cata-
lysts is highly desired. Here we report the convenient syntheses
of cationic catalysts bearing bulky phosphine ligands, and
explore their reactivity in standard metathesis reactions.
Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry
and Chemical Engineering, California Institute of Technology, Pasadena, California
91125, USA. E-mail: rhg@caltech.edu
†Electronic supplementary information (ESI) available: NMR spectra and meta-
thesis data. CCDC 784488. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c5dt04506a
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Fig. 1 Examples of cationic ruthenium alkylidene catalysts.
Results and discussion
Catalyst syntheses
We chose [H2IMes2]RuCl2[vCH-o-(OiPr)C6H4] (7, H2I = imid-
azolidinylidene, Mes = mesityl) as a starting complex due to its
high activity in various metathesis reactions.13 It was pre-
viously reported that AgBF4 is capable of extracting a single
chloride ligand from complex 7.12d When 7 was reacted with
AgBF4 in the presence of PPh3, a cationic catalyst bearing a
bulky PPh3 ligand (8a) was obtained in high yield. In the same
manner, other silver salts of non-coordinating or weekly co-
ordinating anions also provided similar cationic catalysts (8b–d)
(Scheme 1). In the 1H NMR spectra of 8, signals for the methyl
groups of the two N-mesityl substituents appear as all inequi-
valent, suggesting that the bulky PPh3 ligand hinders rotation
of the NHC ligand at room temperature. X-ray quality crystals
of 8c were grown and the crystal structure indicates steric
Fig. 2 X-ray crystal structure of 8c. Displacement ellipsoids are drawn
at 50% probability. For clarity, hydrogen atoms and the counter anion
PF6 have been omitted. Selected bond length (Å) for 8c: C1–Ru1 2.0723
(15), C22–Ru1 1.8349(15), O1–Ru1 2.3442(10), Cl1–Ru1 2.3517(4), P1–
Ru1 2.2788(4).
repulsion between a phenyl group of the PPh3 ligand and the (Scheme 2). First, 9 was exposed to TMS(OTf) causing the sub-
N-mesityl group of the NHC ligand (Fig. 2). Compared to 7,13 stitution of one chloride ligand with an OTf anion, yielding
8c has smaller C1–Ru1–O1 angle (96.73(5)° versus 176.2(14)°) mono-triflate complex 10. Next, diphosphines DPPE and DPPP
and larger C1–Ru1–Cl1 angle (154.88(4)° versus 96.6(12)° and were added, subsequently replacing both the labile PPh3 and
90.9(12)°). The latter structural feature is also observed in pre- OTf ligands, and afforded cationic diphosphine chelated com-
viously reported complexes 4 12b and 5 12c (Fig. 1).
plexes 11a and 11b, respectively. As a result of coupling with
Next, we were able to synthesize cationic diphosphine che- two unequivalent phosphorus atoms, the signal of the benzyli-
1
lated catalysts derived from [H2IMes2]RuCl2(PPh3)(vCHPh) (9)14 dene proton appeared as doublet of doublets in the H NMR
Scheme 1
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Scheme 2
spectrum. Additionally, a large difference in the chemical showed moderate activities and the conversion to reach ∼90%
shifts of the two phosphorus atoms in the 31P NMR spectrum after 6 hours. The lower activity of PPh3-substituted complexes
suggests that the diphosphine ligand coordinates to the ruthe- 8a–c compared to 7 may be due to the steric bulkiness of the
nium center with one phosphorus atom at the equatorial posi- phosphine ligand that possibly hinders olefin coordination. It
tion and the other one at the axial position in the catalyst.
should be noted that no significant dependence of the counter
anions on metathesis activity was observed. The anions, which
potentially could coordinate to the ruthenium center and
compete with olefin coordination did not affect catalyst reactiv-
ity under the presented conditions. Alternatively, diphosphine-
substituted catalysts 11a–b exhibited poor activity, providing
significantly low to no conversion of 12. Considering the
mechanism of initiation, it is seemingly necessary to dis-
sociate one phosphorous arm from the ruthenium center in
order to make a vacant site for coordination of incoming
olefin (Fig. 4). Because the chelated form seems like a
dormant species, the high energy barrier of the dechelation of
the diphosphine ligand is thought to decelerate the catalyst
initiation and overall metathesis reaction.
Metathesis assays
Ring closing metathesis (RCM). First, the standard RCM
reaction of diethyldiallyl malonate (12)15 was carried out using
catalysts 8a–c and 11a–b in order to evaluate their activities
(Scheme 3). As shown in Fig. 3, mono-phosphine catalysts 8a–c
Cross metathesis (CM). In order to evaluate the activity and
stereoselectivity of these new catalysts, the standard CM reac-
tion of allylbenzene (14) and cis-1,4-diacetoxy-2-butene (15)15
was carried out (Scheme 4). Selected data for the cationic cata-
lysts are summarized in Table 1 and plotted in Fig. 5. Similar
to the RCM assay above, while 8a–b and 11a showed moderate
activities, no conversion was observed when 11b was used. It
has been reported that some asymmetric ruthenium-based
catalysts substituted with one bulky X-type ligand tend to give
lower E/Z ratio of the products compared to catalyst 7.16 In one
case, a ruthenium catalyst bearing a single bulky thiolate
ligand (18) provided an E/Z ratio of 0.20 in the homocoupling
of substrate 14 (Fig. 6).16b However, the E/Z ratio of product 16
formed by the cationic catalysts reported here are very similar
to the one by the dichloro analogue 7 (Fig. 5(b)). This possibly
indicates that the phosphine ligands are too far from the reac-
tion center to influence the stereoselectivity (Fig. 6).
Scheme 3
Ring opening metathesis polymerization (ROMP). Next, the
ROMP of norbornene (19) was tested with the presented cat-
ionic catalysts (Scheme 5). In all cases, an immediate increase
in the viscosity of the reaction solution was observed after
stirring substrate 19 with the catalysts, indicating rapid
Fig. 3 Plots for conversion vs. time for RCM of 12. All reactions were
carried out using 0.080 mmol of 12 and 0.80 μmol of catalyst in 0.8 ml
of CD2Cl2 at 30 °C. Data for 7 is from ref. 15. a Conversion of 12 to 13
determined by 1H NMR analysis.
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Fig. 4 One plausible mechanism of catalyst initiation for 11a.
Scheme 4
Table 1 Selected data for the CM of 14 and 15 a
16
17
Cat. loadb,
mol%
Time,
min
Entry
Cat.
7
Solvent
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Conv.c, %
E/Zd
8.4
Conv.c, %
E/Zd
1e
2
2.5
2
30
30
120
30
120
30
120
30
120
75
72
34
74
28
73
6.2
34
0.0
0.0
4.0
5.0
0.0
2.5
0.0
2.8
0.0
0.0
0.0
0.0
4.40
5.9
10.1
3.3
6.1
3.2
5.7
2.2
3.2
8a
2.5
(NA) f
(NA) f
(NA) f
(NA) f
(NA) f
(NA) f
(NA)f
(NA)f
3
8b
2.5
4
11a
11b
5.0
5
5.0
(NA)f
(NA)f
a All reactions were carried out using 0.20 mmol of 14, 0.40 mmol of 15 and 0.10 mmol of tridecane (internal standard for GC analysis) in 1.0 ml
of solvent at 23 °C. b Based on 14. c Conversion of 14 to the product determined by GC analysis. d Molar ratio of E isomer and Z isomer of the
product determined by GC analysis. e Ref. 15. f GC signal of the product was too small to quantify.
polymerization. The conversion and E/Z ratio of the product
Materials. [H2IMes2]RuCl2[vCH-o-(OiPr)C6H4] (7, H2I = imid-
poly-norbornene 20 are summarized in Table 2. 8a–b and 11a azolidinylidene, Mes = mesityl) was obtained from Materia,
were able to complete the reaction within 30 min at the pre- Inc. [H2I(Mes)2]RuCl2(PPh3)(vCHPh) (9) was synthesized
sented condition. Even 11b, which showed negligible activity according to the literature procedure.14 Diethyldiallyl malonate
in the RCM and CM reactions above, provided 70% yield of 20 (12), allylbenzene (14), cis-1,4-diacetoxy-2-butene (15) and tri-
after 30 min.
decane were distilled over CaH2 and stored under nitrogen in
Schlenk flasks. Norbornene (19) was purified by sublimation
before use. All the other commercially available reagents were
used as received without further purification.
Experimental section
General information
Instruments. 1H, 13C and 31P NMR spectra were recorded on
a Varian 500 MHz spectrometer or a Varian 300 MHz spectro-
Atmosphere. All reactions were carried out in dry glassware meter. High-resolution mass spectra were provided by the Cali-
under an argon atmosphere using standard Schlenk tech- fornia Institute of Technology Mass Spectrometry Facility
niques or in a Vacuum Atmospheres Glovebox under a nitro- using JEOL JMS-600H High Resolution Mass Spectrometer.
gen atmosphere unless otherwise specified.
X-ray crystallographic data were collected by the California
Solvents. CD2Cl2 was dried over CaH2 and vacuum trans- Institute of Technology Beckman Institute X-ray Crystallo-
ferred to a dry Schlenk flask and subsequently degassed with graphy Facility using Bruker KAPPA APEXII X-ray diffractometer.
argon. Ethyl vinyl ether and isopropyl alcohol were used as Gas chromatography data were obtained using Agilent 6850
received. All the other solvents were purified by passage through FID gas chromatograph equipped with a DB-Wax polyethylene
solvent purification columns and further degassed with argon.18 glycol capillary column (Agilent).
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Table 2 Data for the ROMP of 19 a
20
Conv.c, %
Cat. loadb,
mol%
Time,
min
Entry
Cat.
Solvent
E/Zd
1
2
3
4
5
7
8a
8b
11a
11b
1.0
1.0
1.0
1.0
1.0
CD2Cl2
CD2Cl2
CD2Cl2
CD2Cl2
CD2Cl2
30
30
30
30
30
100
100
100
100
70
0.69
0.70
0.69
0.68
0.65
a All reactions were carried out using 0.20 mmol of 19 and 0.002 mmol
of catalyst in 0.8 ml of solvent at 23 °C. b Based on 19. c Conversion of
19 to 20 determined by 1H NMR analysis. d Molar ratio of E isomer and
Z isomer of 20 determined by 1H NMR analysis.
Catalyst syntheses
General procedure for the synthesis of {[H2IMes2]RuCl(PPh3)-
[vCH-o-(OiPr)C6H4]}X (8). In a glove box, 7, the corresponding
silver salt, triphenylphosphine and dichloromethane were
added into a 20 ml screw-cap vial equipped with a magnetic
stir bar. The reaction mixture was stirred at room temperature
for 2 h under dark. The resulting slurry was filtered and the
filtrate was evaporated. The crude product was recrystallized
from CH2Cl2–pentane or THF at −20 °C.
{[H2IMes2]RuCl(PPh3)[vCH-o-(OiPr)C6H4]}BF4 (8a). Starting
from 7 (300 mg, 479 μmol), AgBF4 (103 mg, 527 μmol) and tri-
phenylphosphine (151 mg 575 μmol) in 10 ml of CH2Cl2, 8a
was obtained as a red-orange crystalline solid (397 mg,
422 μmol, 88.1% yield based on 7). 1H NMR (500 MHz,
CD2Cl2): δ/ppm 15.16 (d, J = 7.0 Hz, 1H), 8.0–6.3 (br, 15H),
7.55–7.51 (m, 1H), 7.24 (d, J = 8.5 Hz, 1H), 7.17 (br s, 1H),
6.95–6.92 (m, 1H), 6.69–6.67 (m, 1H), 6.53 (br s, 1H), 6.42
(br s, 1H), 6.04 (br s, 1H), 5.74 (sep, J = 6.7 Hz, 1H), 4.20 (br s,
1H), 4.05 (br s, 1H), 3.97 (br s, 1H), 3.63 (br s, 1H), 2.93 (br s,
3H), 2.35 (br s, 3H), 2.07 (br s, 3H), 1.97 (br s, 3H), 1.88–1.86
(br m, 6H), 1.59 (d, J = 6.7 Hz, 3H), 1.30 (br s, 3H). 13C{1H}
NMR (125.7 MHz, CD2Cl2): δ/ppm 289.4 (d), 208.9 (d), 154.1,
142.0, 141–140 (br m), 137–136 (br m), 136.0 (br s), 135.1
(br s), 135–134 (br m), 133–132 (br m), 132.7, 132–131 (br m),
130.0 (br s), 130–128 (br m), 126.9, 122.9, 118.0, 81.8, 23.4,
22.8, 22–21 (br, m), 20.7 (br s), 20–19 (br m), 17.7 (br s).
31P{1H} NMR (121.4 MHz, CD2Cl2): δ/ppm 53.6. HRMS (FAB+):
Calculated for {[H2IMes2]RuCl(PPh3)[vCH-o-(OiPr)C6H4]}+:
853.2628, Found: 853.2617.
Fig. 5 Plots for (a) conversion vs. time and (b) E/Z ratio vs. conversion
for CM of 14 and 15. a Conversion of 14 to 16 determined by GC analy-
sis.17 b Molar ratio of E isomer and Z isomer of 16 determined by GC
analysis.
{[H2IMes2]RuCl(PPh3)[vCH-o-(OiPr)C6H4]}OTf (8b). Start-
ing from 7 (300 mg, 479 μmol), AgOTf (135 mg, 527 μmol) and
triphenylphosphine (151 mg 575 μmol) in 10 ml of CH2Cl2, 8b
was obtained as a red-orange crystalline solid (277 mg,
276 μmol, 57.6% yield based on 7). 1H NMR (500 MHz,
CD2Cl2): δ/ppm 15.15 (d, J = 7.3 Hz, 1H), 8.0–6.3 (br, 15H),
7.54–7.51 (m, 1H), 7.22 (d, J = 8.2 Hz, 1H), 7.17 (br s, 1H),
6.94–6.91 (m, 1H), 6.68–6.66 (m, 1H), 6.53 (br s, 1H), 6.42
(br s, 1H), 6.04 (br s, 1H), 5.74 (sep, J = 6.7 Hz, 1H), 4.19 (br s,
1H), 4.04 (br s, 1H), 3.96 (br s, 1H), 3.64 (br s, 1H), 2.92 (br s,
3H), 2.35 (br s, 3H), 2.07 (br s, 3H), 1.97 (br s, 3H), 1.87–1.86
(br m, 6H), 1.58 (d, J = 6.7 Hz, 3H), 1.30 (br s, 3H). 13C{1H}
Fig. 6 Plausible intermediates for (a) 18 and (b) 8.
Scheme 5
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NMR (125.7 MHz, CD2Cl2): δ/ppm 209.1 (d), 154.2, 154.2, amount of CH2Cl2. The solution was added dropwise with
142.0, 141–140 (br m), 137–136 (br m), 136.0 (br s), 135.1 vigorous stirring into a large amount of pentane (for 11a) or
(br s), 135–134 (br m), 133–132 (br m), 132.7, 132–131 (br m), Et2O (for 11b). The appeared precipitate was corrected on a
130.1 (br s), 130–128 (br m), 127.0, 122.9, 118.0, 81.8, 23.5, filter, washed with appropriate solvent, and dried under
22.8, 22–21 (br, m), 20.7 (br s), 20–19 (br m), 17.8 (br s). reduced pressure.
31P{1H} NMR (121.4 MHz, CD2Cl2): δ/ppm 53.5. HRMS (FAB+):
Calculated for {[H2IMes2]RuCl(PPh3)[vCH-o-(OiPr)C6H4]}+: Starting from 9 (100 mg, 120 μmol), TMS(OTf) (24.0 μl,
853.2628, Found: 853.2666. 29.5 mg, 133 μmol) and DPPE (57.5 mg 144 μmol) in 5.0 ml of
{[H2IMes2]RuCl[Ph2P(CH2)2PPh2](vCHPh)}(OTf) (11a).
{[H2IMes2]RuCl(PPh3)[vCH-o-(OiPr)C6H4]}PF6 (8c). Starting CH2Cl2, 11a was obtained as a yellow-brown solid (76.7 mg,
from 7 (300 mg, 479 μmol), AgPF6 (133 mg, 527 μmol) and tri- 71.0 μmol, 53.4% yield based on 9). 1H NMR (500 MHz,
phenylphosphine (151 mg 575 μmol) in 10 ml of CH2Cl2, 8c CD2Cl2): δ/ppm 16.23 (dd, J = 26.9 Hz, J = 1.2 Hz, 1H),
was obtained as a red-orange crystalline solid (406 mg, 7.87–7.76 (m, 5H), 7.69–7.56 (m, 1H), 7.53–7.19 (m, 12H), 7.04
406 μmol, 84.7% yield based on 7). 1H NMR (500 MHz, (s, 1H), 6.92–6.88 (m, 2H), 6.85–6.76 (m, 2H), 6.62–6.59
CD2Cl2): δ/ppm 15.16 (d, J = 7.3 Hz, 1H), 8.0–6.3 (br, 15H), (m, 4H), 6.43 (s, 1H), 5.60 (s, 1H), 4.06–4.00 (m, 1H), 3.93–3.87
7.55–7.51 (m, 1H), 7.23 (d, J = 8.5 Hz, 1H), 7.18 (br s, 1H), (m, 1H), 3.81–3.70 (m, 2H), 2.76 (s, 3H), 2.42 (s, 3H), 2.28
6.95–6.92 (m, 1H), 6.69–6.68 (m, 1H), 6.53 (br s, 1H), 6.42 (s, 3H), 2.19–2.13 (br m, 1H), 2.10–2.03 (br m, 1H), 1.94
(br s, 1H), 6.05 (br s, 1H), 5.74 (sep, J = 6.7 Hz, 1H), 4.18 (br s, (s, 3H), 1.82 (s, 3H), 1.40–1.34 (br m, 1H), 1.17 (s, 3H),
1H), 4.03 (br s, 1H), 3.96 (br s, 1H), 3.63 (br s, 1H), 2.93 (br s, 0.68–0.64 (br m, 1H). 13C{1H} NMR (125.7 MHz, CD2Cl2):
3H), 2.35 (br s, 3H), 2.07 (br s, 3H), 1.98 (br s, 3H), 1.88–1.86 δ/ppm 213.1 (dd), 149.0, 141.5, 140.0, 139.6, 139.4, 138.3,
(br m, 6H), 1.59 (d, J = 6.7 Hz, 3H), 1.30 (br s, 3H). 13C{1H} 137.7, 136.8, 135.9, 135.6, 135.3, 135.2, 135.0, 133.9, 133.9,
NMR (125.7 MHz, CD2Cl2): δ/ppm 289.5 (d), 209.0 (d), 154.2, 133.7, 133.3, 132.5–132.4 (m), 132.0, 131.9, 131.9, 131.3–131.2
154.2, 142.0, 141–140 (br m), 137–136 (br m), 136.0 (br s), (m), 130.9, 130.8–130.8 (m), 130.6–130.6 (m), 130.5, 130.4,
135.2 (br s), 135–134 (br m), 133–132 (br m), 132.7, 132–131 130.2–130.2 (m), 129.9, 129.0, 128.9, 128.9, 128.9, 128.5, 128.5,
(br m), 130.0 (br s), 130–128 (br m), 127.0, 122.9, 118.0, 81.8, 128.4, 128.2, 41.4–41.0 (m), 21.8–21.4 (m), 21.0–20.9 (m),
23.5, 23.4, 22.8, 22–21 (br, m), 20.7 (br s), 20–19 (br m), 17.7 20.6–20.5 (m), 18.9–18.9 (m), 18.0–18.0 (m), 15.9. 31P{1H} NMR
(br s). 31P{1H} NMR (121.4 MHz, CD2Cl2): δ/ppm 53.5. HRMS (121.4 MHz, CD2Cl2): δ/ppm 53.4 (d), 52.4 (d). HRMS (FAB+):
(FAB+): Calculated for {[H2IMes2]RuCl(PPh3)[vCH-o-(OiPr) Calculated for {[H2IMes2]RuCl[Ph2P(CH2)2PPh2](vCHPh)}+:
C6H4]}+: 853.2628, Found: 853.2647.
931.2651, Found: 931.2671.
{[H2IMes2]RuCl[Ph2P(CH2)3PPh2](vCHPh)}(OTf) (11b).
{[H2IMes2]RuCl(PPh3)[vCH-o-(OiPr)C6H4]}SbF6 (8d). Start-
ing from 7 (300 mg, 479 μmol), AgSbF6 (181 mg, 527 μmol) Starting from 9 (100 mg, 120 μmol), TMS(OTf) (24.0 μl,
and triphenylphosphine (151 mg 575 μmol) in 10 ml of 29.5 mg, 133 μmol) and DPPP (59.6 mg 144 μmol) in 5.0 ml of
CH2Cl2, 8d was obtained as a red-orange crystalline solid CH2Cl2, 11b was obtained as a yellow solid (78.7 mg,
(490 mg, 450 μmol, 93.9% yield based on 7). 1H NMR 71.9 μmol, 59.7% yield based on 9). 1H NMR (500 MHz,
(500 MHz, CD2Cl2): δ/ppm 15.17 (d, J = 7.3 Hz, 1H), 8.0–6.3 CD2Cl2): δ/ppm 16.83 (dd, J = 26.5 Hz, J = 1.2 Hz, 1H),
(br, 15H), 7.55–7.51 (m, 1H), 7.22 (d, J = 8.5 Hz, 1H), 7.18 (br s, 7.68–7.60 (m, 7H), 7.50–7.44 (m, 3H), 7.39–7.36 (m, 2H),
1H), 6.95–6.92 (m, 1H), 6.69–6.67 (m, 1H), 6.54 (br s, 1H), 6.42 7.32–7.28 (m, 3H), 7.17–7.14 (m, 3H), 7.11–7.08 (br m, 2H),
(br s, 1H), 6.05 (br s, 1H), 5.74 (sep, J = 6.7 Hz, 1H), 4.16 (br s, 6.87–6.84 (m, 2H), 6.67–6.64 (br m, 2H), 6.62 (s, 1H), 6.48
1H), 4.02 (br s, 1H), 3.96 (br s, 1H), 3.62 (br s, 1H), 2.92 (br s, (s, 1H), 6.41–6.37 (br m, 2H), 5.73 (s, 1H), 4.02–3.95 (m, 1H),
3H), 2.35 (br s, 3H), 2.07 (br s, 3H), 1.98 (br s, 3H), 1.87–1.86 3.84–3.78 (m, 1H), 3.71–3.66 (m, 2H), 2.83 (s, 3H), 2.42 (s, 3H),
(br m, 6H), 1.59 (d, J = 6.7 Hz, 3H), 1.31 (br s, 3H). 13C{1H} 2.31–2.19 (br m, 3H), 2.12 (s, 3H), 1.95 (s, 3H), s1.89 (s, 3H),
NMR (125.7 MHz, CD2Cl2): δ/ppm 289.5 (d), 209.1 (d), 154.2, 1.78–1.73 (br m, 1H), 1.57–1.50 (br m, 1H), 1.15 (s, 3H),
154.2, 142.0, 141–140 (br m), 137–136 (br m), 136.0 (br s), 0.93–0.80 (br m, 1H). 13C{1H} NMR (125.7 MHz, CD2Cl2):
135.2 (br s), 135–134 (br m), 133–132 (br m), 132.7, 132–131 δ/ppm 211.0 (dd), 150.2, 150.2, 141.5, 140.1, 139.4, 139.0,
(br m), 130.1 (br s), 130–128 (br m), 127.0, 122.9, 118.0, 81.8, 138.3, 138.1, 137.5–137.5 (m), 137.2–137.2 (m), 137.1, 136.0,
23.5, 23.4, 22.8, 22–21 (br, m), 20.7 (br s), 20–19 (br m), 17.7 135.9, 135.6, 134.7, 134.7, 133.7, 133.5, 133.4, 133.2, 133.1,
(br s). 31P{1H} NMR (121.4 MHz, CD2Cl2): δ/ppm 53.5. HRMS 131.7–131.7 (m), 131.6–131.6 (m), 131.3, 131.2, 131.0, 130.6,
(FAB+): Calculated for {[H2IMes2]RuCl(PPh3)[vCH-o-(OiPr)C6H4]}+: 130.6, 130.2, 130.1, 130.0, 129.8, 129.8, 129.4, 129.0, 128.7.
853.2628, Found: 853.2643.
128.5, 128.4, 127.6, 127.5, 36.5–36.2 (m), 23.4, 23.2, 21.5–21.0
General procedure for the synthesis of {[H2IMes2]RuCl- (m), 19.4–19.4 (m), 18.3, 18.0–18.0 (m), 16.8. 31P{1H} NMR
[Ph2P(CH2)nPPh2](vCHPh)}(OTf) (11). In a glove box, 9 and (121.4 MHz, CD2Cl2): δ/ppm 18.9 (d), 3.5 (d). HRMS (FAB+):
CH2Cl2 were added into a 20 ml screw-cap vial equipped with a Calculated for {[H2IMes2]RuCl[Ph2P(CH2)3PPh2](vCHPh)}+:
magnetic stir bar. With stirring, trimethylsilyl trifluoromethane- 945.2808, Found: 945.2801.
sulfonate was added slowly. After stirring at room temperature
for 1 h, the corresponding diposphine was added. Then the
Crystal structure determination of 8c
reaction solution was stirred at room temperature for 2 h, and Single crystals of 8c were recrystallised by diffusion of pentane
evaporated. The crude product was dissolved in a small into a saturated CH2Cl2 solution of 8c; a suitable crystal was
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mounted on a hand-crafted glass fiber with Paratone oil The sample was heated at 50 °C for 30 min, cooled to room
(Exxon) and transferred to the 100 K cold gas stream of an temperature, passed through a pad of silica gel using CH2Cl2
OxfordCryosystems 700 Series Cryostream Cooler on the as eluent and then analyzed by GC. GC response factor and
Bruker KAPPA APEXII 02B diffractometer.
retention time for each substrate were summarized in
Crystal data. C52H59Cl7F6N2OP2Ru, M = 1253.17, monocli- Table S6.† The amounts of the substrates in each sample were
nic, a = 10.1739(4), b = 23.3587(10), c = 23.0472(9) Å, U = 5463.3 determined by previously reported method using response
(4) Å3, T = 100 K, space group P21/n (no. 14), Z = 4, 160 797 factors.15
reflections measured, 21 852 unique (Rint = 0.056), which were
Representative procedure for ROMP of norbornene (19). A
2 ml volumetric flask was charged with 19 (125 mg,
used in all calculations. Refinement of F2 against all reflec-
2
tions (except the omitted (0 1 1)) with the weights w = 1/σ2(Fo ). 1.33 mmol), and CD2Cl2 was added to prepare 2.0 ml of stock
All non-hydrogen atoms were refined anisotropically. The solution (0.665 M). In a glove box, 8a (1.9 mg, 2.0 μmol) and
cation and solvent hydrogen atoms were treated differently. All CD2Cl2 (500 μl) were added into an NMR tube with a screw-cap
hydrogen atoms in the cation were freely refined with four septum top. The stock solution (300 μl; 19: 18.8 mg, 200 μmol)
parameters, three positional and one isotropic displacement. was added via syringe and the sample was vigorously shaken
The six hydrogen atoms on the three dichloromethane mole- for 30 seconds. Then the sample was allowed to stand for
1
cules were included into the model at geometrically calculated 30 min at 23 °C and analyzed by H NMR. The conversion of
positions and refined using a riding model. The isotropic dis- 19 to 20 was determined by comparing the ratio of the inte-
placement parameters of these hydrogen atoms were fixed to grals of the olefinic protons in the starting material with those
1.2 times the Ueq value of the carbon atoms to which they are in the product in the 1H NMR spectrum.
bonded. The final wR(F2) was 0.059 (all data).
Metathesis assays
Conclusion
Representative procedure for RCM of diethyldiallyl malonate
(12).15 In a glove box, a 1.0 ml volumetric flask was charged
While aiming to discover a convenient methodology for the
with 8a (7.5 mg, 8.0 μmol) and CD2Cl2 was added to prepare
preparation of cationic ruthenium alkylidene catalysts, simple
1.0 ml of stock solution (0.008 M). CD2Cl2 (700 μl) and the
ligand exchange using silver(I) salt of non-coordinating or
stock solution (100 μl, 0.80 μmol) were added into an NMR
weakly coordinating anion was investigated. When NHC-sub-
tube with a screw-cap septum top. The sample was equili-
stituted catalyst 7 was reacted with a variety of silver(I) salt in
brated at 30 °C in the NMR probe before 12 (19.3 μl, 19.2 mg,
the presence of PPh3, cationic catalysts bearing a single PPh3
80 μmol) was added via syringe. Data points were collected
ligand 8a–d were afforded selectively in good yield. Catalysts
over an appropriate period of time using the Varian array func-
8a–d were shown to exhibit moderate activity in the standard
tion. The conversion of 12 to 13 was determined by comparing
metathesis reactions. In contrast to reported neutral catalysts
the ratio of the integrals of the methylene protons in the start-
bearing a single bulky ligand, the stereoselectivities of 8a–d
ing material with those in the product in the 1H NMR spectra.
were very similar to that of dichloride substituted catalyst 7.
Representative procedure for CM of allylbenzene (14) and
Additionally, diphosphines DPPE or DPPP were reacted with
cis-1,4-diacetoxy-2-butene (15).15
complex 9, causing formation of cationic diphosphine-che-
Preparation of a substrate mixture. In a glove box, tridecane
lated catalysts 11a–b. 11a–b exhibited poor activity in the stan-
(92.0 μl, 69.6 mg, 377 μmol), 14 (100 μl, 89.2 mg, 755 μmol)
dard RCM and CM compared to 8a–d, most likely due to slow
and 15 (240 μl, 259 mg, 1.51 mmol) were combined in a 5 ml
initiation derived from the high energy barrier of dechelation
vial with a screw-cap septum top and a magnetic stir bar; this
of the diphosphine ligand. Modification of the charge of
mixture was allowed to stir for 5 min.
ruthenium alkylidene catalyst is a promising avenue of investi-
Preparation of reaction solution and CM of 14 and 15. In a
gation in improving catalyst efficiency and expanding their
glove box, a 5 ml vial with a screw-cap septum top and a mag-
applications. The simple methods presented in this report will
netic stir bar was charged with 8a (4.7 mg, 5.0 μmol) and
enable easy access to similar cationic catalysts and facilitate
CH2Cl2 (1.0 ml). The catalyst solution was removed from the
further investigations.
glove box and then stirred at 23 °C under argon. To the catalyst
solution, the substrate mixture (115 μl; tridecane: 24.5 μl,
18.5 mg, 100 μmol; 14: 26.6 μl, 23.7 mg, 201 μmol; 15: 63.9 μl,
69.0 mg, 401 μmol) was added via syringe. The reaction solu-
tion was allowed to stir at 23 °C and reaction aliquots
Acknowledgements
(ca. 40 μl) were taken at the specific time points.
We thank Dr M. B. Herbert for helpful discussions and sugges-
GC analysis. Samples for GC analysis were obtained by tions for this work, Materia, Inc. for the generous donation of
adding the reaction aliquot to 400 μl of a 3 M solution of ethyl catalysts and Dr M. W. Day and Mr L. M. Henling for X-ray crys-
vinyl ether in isopropyl alcohol. The sample was shaken and tallography. The Bruker KAPPA APEXII X-ray diffractometer
allowed to stand for 10 min. 100 μl of 1 M slurry of tris was purchased via an NSF CRIF:MU award to the California
(hydroxymethyl)phosphine in isopropyl alcohol was added.19 Institute of Technology, CHE-0639094. This work was finan-
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cially supported by NIH (NIH 5R01GM031332), NSF
(CHE-0410425 and CHE-0809418) and Mitsui Chemicals, Inc.
A. Fedorov and R. H. Grubbs, J. Am. Chem. Soc., 2012, 134,
2040; (c) M. B. Herbert, V. M. Marx, R. L. Pederson and
R. H. Grubbs, Angew. Chem., Int. Ed., 2013, 52, 310;
(d) V. M. Marx, M. B. Herbert, B. K. Keitz and R. H. Grubbs,
J. Am. Chem. Soc., 2013, 135, 94; (e) H. Miyazaki,
M. B. Herbert, P. Liu, X. Dong, X. Xu, B. K. Keitz, T. Ung,
G. Mkrtumyan, K. N. Houk and R. H. Grubbs, J. Am. Chem.
Soc., 2013, 135, 5848; (f) L. E. Rosebrugh, V. M. Marx,
B. K. Keitz and R. H. Grubbs, J. Am. Chem. Soc., 2013, 135,
10032; (g) J. Hartung and R. H. Grubbs, J. Am. Chem. Soc.,
2013, 135, 10183; (h) J. S. Cannon and R. H. Grubbs, Angew.
Chem., Int. Ed., 2013, 52, 9001; (i) J. Hartung and
R. H. Grubbs, Angew. Chem., Int. Ed., 2014, 53, 3885;
( j) S. L. Mangold, D. J. O’Leary and R. H. Grubbs, J. Am.
Chem. Soc., 2014, 136, 12469; (k) J. Hartung, P. K. Dornan
and R. H. Grubbs, J. Am. Chem. Soc., 2014, 136, 13029;
(l) M. B. Herbert and R. H. Grubbs, Angew. Chem., Int. Ed.,
2015, 54, 5018; (m) P. K. Dornan, Z. K. Wickens and
R. H. Grubbs, Angew. Chem., Int. Ed., 2015, 54, 7134.
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