Highly active catalysts in alkene metathesis: First observed transformation of allenylidene into indenylidene via alkenylcarbyne-ruthenium species

Article abstract of DOI:10.1002/anie.200352108

A cat. for all seasons: The transformation of the allenylidene-ruthenium complexes [RuCl(η⁶-arene) (=C=C=CR₂) (PR′ ₃)] [CF₃SO₃] into indenylidene species [RuCl(η⁶-arene) (indenylidene) (PR′

Full text of DOI:10.1002/anie.200352108

Communications
Active Catalysts in Alkene Metathesis
Highly Active Catalysts in Alkene Metathesis:
First Observed Transformation of Allenylidene
into Indenylidene via Alkenylcarbyne—
Ruthenium Species**
latter show impressive turn-over frequencies (TOFs) for the
polymerization of cyclooctene and cyclopentene under mild
conditions as well as RCM reactions.
In the course of our study on cyclooctene polymerization
promoted by allenylidene ruthenium(ii) complexes, we have
Ricardo Castarlenas and Pierre H. Dixneuf*
Dedicated to Professor Jean-Pierre Genet,
on the occasion of his 60th Birthday
observed that the addition of a strong acid to the initiator
6
= = =
[RuCl( C C CPh2)(PCy3)(h -p-cymene)][CF3SO3]
(1)
largely increases the rates of polymerization. Thus, when
five equivalents of HBF4 or CF3SO3H are added to catalytic
solutions of 1, TOF values increase by three orders of
magnitude (Table 1, entries 1–3). To understand the nature of
the catalytic species and control their synthesis, low temper-
Alkene metathesis has recently led to remarkable applica-
tions in organic synthesis as well as in polymer science
through ring-opening-metathesis polymerization (ROMP).[1]
Since the advent of functional group tolerant ruthenium
alkylidene catalysts,[2] this reaction
has reached a tremendous level of
development for the production of
a variety of macromolecules with
Table 1: Cyclooctene polymerisation at room temperature.[a]
Entry Cat. Ratio[b]
Acid[c]
Time
Yield 10ꢀ3 ”Mn
PDI[e] % cis[f] TOF[g]
[d]
¯
=
both C C bonds and functional
1
2
3
4
5
6
7
8
1
1
1
1
1
4
5
6
1.000
–
15 h
95% 143
1.9
1.7
1.6
1.5
1.4
1.8
1.9
1.6
27
40
38
28
35
25
22
26
63
groups regularly placed.[3] Ruthe-
nium catalysts for alkene metathe-
sis are not restricted to alkylidene
precursors of type LnRu CHR.
The ionic 18 electron ruthenium
allenylidene complexes [RuCl
1.000 HBF4 (5 equiv)
1.000 HOTf (5 equiv)
1 min 92% 224
1 min 95% 238
5 min 97% 387
55200
57200
116400
1096000
43800
312
10000
HOTf (5 equiv)
HOTf (100 equiv) 5 min 88% 857
HOTf (5 equiv)
HOTf (5 equiv)
HOTf (5 equiv)
100000
10000
10000
10000
=
10 min 73% 220
8 h 25% 107
5 min 92% 286
110000
= = =
( C C CAr2)(PR3)(p-cymene)]
[a] 4.5”10ꢀ3 mol of cyclooctene in 2.5 mL of PhCl. [b] [cyclooctene]/[Ru]. [c] Related to complex.
[d] determined by GPC in THF versus polystyrene standards. [e] Polydispersity index Mw/Mn.
[f] determined by 13C NMR. [g] Turnover frequency in moles per hour. Cat.=catalyst.
[X][4] (X = PF6, BPh4, CF3SO3) pro-
¯
¯
mote
ring-closing
metathesis
(RCM) of dienes and enynes[5] as
well as ROMP.[6] Indenylidene
derivatives of type RuCl2(PCy3)(L)(indenylidene) (L =
PCy3, imidazolylidene), expected to result from the corre-
sponding allenylidene although this has not been fully
demonstrated, have also shown good activity in RCM.[7]
Werner and co-workers reported that coordinatively unsatu-
rated ionic carbyne ruthenium precursors,[8] and especially
hydridocarbyne ruthenium complexes,[9] are active in ROMP
of cyclooctene and cross-metathesis.
Tremendous efforts are currently made to produce more
efficient and stable catalysts to decrease the process cost and
the level of metal traces in fine chemicals and polymers.[10]
Herein we report the first observation that alkenylcarbyne
ruthenium intermediates, easily obtained from allenylidene
ruthenium arene complexes, are the key intermediates for
metal–indenylidene complex formation [Eq. (1)] and that the
ature NMR studies of protonated complex 1 have been
undertaken. The addition of 1.2 equivalents of triflic acid to
CD2Cl2 solutions of 1 at ꢀ408C led to a change from dark red
to dark orange, while a new 31P{1H} NMR signal appeared at
d = 78.6 ppm during the disappearance of that of 1 at d =
57.6 ppm. The conversion was completed in 20 min at ꢀ408C.
The 13C{1H} and 1H NMR data are consistent with the
6
ꢁ
=
alkenylcarbyne derivative [RuCl(h -p-cymene)( C-CH
CPh2)(PCy3)][CF3SO3]2 (2) resulting from protonation at the
Cb of the allenylidene ligand (Scheme 1). Indeed, the 13C{1H}
[*] Prof. Dr. P. H. Dixneuf, R. Castarlenas
Institut de chimie de Rennes, UMR 6509 CNRS
UniversitØ de Rennes
OrganomØtalliques et Catalyse
Campus de Beaulieu, 35042, Rennes (France)
Fax: (+33)2-2323-6939
E-mail: pierre.dixneuf@univ-rennes1.fr
[**] This work was supported by the CNRS, the Minist›re de la
recherche, the European Union within the EU network Polycat
(UPRN-CT-2000-10) and a Marie Curie Fellowship to RC, and the
RØgion Bretagne with the program PRIR (No.169 AOC).
Scheme 1. The formation of indenylidene species at low temperature.
DOI: 10.1002/anie.200352108 Angew. Chem. Int. Ed. 2003, 42, 4524 –4527
4524
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Angewandte
Chemie
NMR spectrum displays a doublet at 328.1ppm ( 2JP-C
=
before being quenched with ethyl vinyl ether (Table 1,
ꢁ
11 Hz) for the Ru C carbon and Cb (d = 130.5 ppm) and Cg
(d = 193.2 ppm) correlate with the olefinic proton (dH =
7.05 ppm) in 1H–13C HMQC and HMBC experiments,
entry 4). The isolation of low polydispersed polyoctenamer
showed a conversion of 97% corresponding to a calculated
TOF value of 116000 mol per hour. Indeed, a tremendous
increase in the TOF value to more than 1000000 mol per hour
was reached when 100000 equivalents of monomer were
loaded (entry 5). It was verified that polymerization does not
take place with CF3SO3H in the absence of the ruthenium
catalyst.
1
respectively. The H NMR spectrum of 2 also displays two
doublets at d = 6.75 and 6.61ppm showing the retention of the
coordinated p-cymene ligand.
When the temperature was raised to ꢀ208C a new signal
appeared at d = 48.3 ppm in the 31P{1H} spectrum. Complete
conversion was achieved in 30 min with a color change to
violet. The nature of this intermediate was consistent with the
indenylidene ruthenium complex [RuCl(h6-p-cymene)
Slight modifications of the starting allenylidene complex
were made by changing subtituents in the phenyl groups
6
= = =
[RuCl(h -p-cymene){ C C C(p-OMe-Ph)2}(PCy3)]
6
= ꢀ
=
= = =
CPh2)(PPh3)][CF3SO3] (5) or in the h6-arene ligand
{ CK CH C(Ph)CL H4}(PCy3)][CF3SO3] (3) containing both
[CF3SO3] (4), in the phosphane [RuCl(h -p-cymene)( C C
6
PCy3 and p-cymene groups (Scheme 1). Complex 3 results
from phenyl substitution by the electrophilic Ca carbon of 2,
thus a contribution of the canonical form 2B favors this
rearrangement.
6-
= = =
[RuCl)(h -1,2,4,5-tetramethylbenzene)( C C CPh2)(PCy3)]
[CF3SO3] (6). The addition of five equivalents of triflic acid to
solutions of 4–6 also promoted the formation of cycloocte-
namer (entries 6–8). Only precursor 6 led to similar results as
those of 1, thus showing that either the less electron-donating
phosphane PPh3 (5) or the introduction of electron releasing
groups in the phenyl rings (4) reduces catalytic activity.
Due to the high activity of the indenylidene complex, 3,
for the ROMP of cyclooctene, the polymerization of the less
reactive cyclopentene was evaluated. A Schlenk tube was
charged with allenylidene complexes (1, 4, or 6), 1000 equiv-
alents of cyclopentene (2.33m), PhCl, and 5 equivalents
of triflic acid at 08C (Figure 1). To make a comparison of
+
+
ꢁ
ꢀ
=
=
ꢀ
=
[Ru C CH CPh2 (2A)$Ru C CH CPh2 (2B)].
The 13C{1H} NMR spectrum shows a doublet (2JP-C
=
=
10 Hz) at d = 334.1ppm corresponding to Ru C carbon
atom as well as signals for every carbon of indenylidene
group (see experimental section). The 1H spectrum displays a
singlet at d = 6.88 ppm that correlates with C2 (d = 143.1 ppm)
in a HMQC experiment and with C1 and C3 (d = 154.6 ppm) in
a HMBC experiment. Indeed, the unambiguous presence of
the indenylidene ligand arises from the correlation of C1 and
H8 of the indenylidene ligand in the HMBC experiment,
which is not observed for its alkenylcarbyne precursor 2. Four
doublets between d = 6.36 and 6.15 ppm were observed for
the four arene protons of the coordinated p-cymene ligand.
Attempts to isolate complex 3 were unsuccessful because of
slow decomposition of the complex at room temperature by
loss of p-cymene ligand and formation of [HPCy3][CF3SO3] as
observed in H and 31P{1H} NMR spectra.
1
Whereas alkenylcarbyne osmium[11] complexes have been
fully described, only two types of unstable dicationic alke-
nylcarbyne ruthenium intermediates were recently reported
on the protonation of the corresponding allenylidene ruthe-
2
ꢁ
=
nium
complexes,
[RuCl( CCH CPh2)(k -P,O-
Figure 1. Cylopentene polymerization with different catalysts and moni-
tored by 1H NMR experiments. Conv. = conversion
Cy2PCH2CH2OCH3)(k-P-Cy2PCH2CH2OCH3)][BF4,PF6] by
ꢁ
=
Werner
et al.[12]
and
[Cp*Ru(dippe)( CCH CPh2)]
[B(ArF)4]2 by Valerga and co-workers.[13] No formation of
related indenylidene complexes was observed in these
examples. It is noteworthy that the formation of indenylidene
ruthenium derivatives [RuCl2(PR3)2(indenylidene)] was
observed while attempting to produce the corresponding
allenylidene ruthenium complex.[7c] However, the rearrange-
ment of allenylidene into the indenylidene ligand was never
directly observed.[7] Thus, the above results show for the first
time the direct intramolecular transformation of an allenyli-
dene ruthenium species into an indenylidene species on
protonation via an alkenylcarbyne intermediate.
the activity of these catalysts, experiments with the
well-known
stable
ruthenium
alkylidene
catalysts
=
(7)[2c]
and RuCl2( CHPh)-
=
RuCl2( CHPh)(PCy3)2
[2a]
=
(PCy3)2{ CNK (Mes)CH2CH2NL (Mes)} (8) were carried out
at room temperature. The analysis of calculated TOF values
clearly demonstrates the excellent catalytic performance of
in situ generated indenylidene species from 1, 4, or 6 with
TOF values lying between 540 and 670, eight times more than
those observed for the catalyst 8 (Table 2). In addition, when
five equivalents of triflic acid were added to vessel containing
8, even lower yields and lower TOF values were observed,
which is in agreement with the previous observation that the
addition of HCl does not increase activity of pure 8.[14] It was
described that with Schrock-type initiators of such as
The activity in ROMP of the in situ prepared species 3 was
thus evaluated. To quickly generate species 3, complex 1 was
first treated with CF3SO3H at room temperature. When
10000 equivalents of cyclooctene (1.46m) in PhCl were
added, complete gelatification was observed within
1minute, but the reaction was stirred for a further 5 min
=
[W( CHtBu)(OtBu)2(NAr)], the polymerization of cyclo-
pentene took place at temperatures below ꢀ408C ([cata-
Angew. Chem. Int. Ed. 2003, 42, 4524 –4527
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Communications
6
= = =
Table 2: Cyclopentene polymerization with the catalytic system RuCl(h -p-cymene)( C C CR2)(PR’3)]
The above results show for the first
time that the direct intramolecular trans-
formation of an allenylidene ruthenium
complex into an indenylidene ruthenium
derivative, on protonation via an alkenyl-
carbyne compound. Moreover they show
the birth of a new in situ generated
18 electron, ionic arene indenylidene
ruthenium catalytic species, highly active
for ROMP of cyclooctene and cyclopen-
tene, RCM or ADMET reactions even
operating at 08C and arising from easily
made allenylidene complexes.
[CF3SO3] + HOSO2CF3.[a]
[c]
¯
Entry
Complex
T [8C]
Acid[b]
Time
Yield
10ꢀ3 ”Mn
PDI[d]
% cis[e]
TOF[f]
1
2
3
4
1
4
6
7
8
1
0
0
0
5 equiv
5 equiv
5 equiv
–
1 h
1 h
1 h
3 h
3 h
15 min
67%
54%
60%
12%
24%
91%
106
90
88
31
60
–
1.5
1.8
1.7
1.5
1.6
–
15
18
16
21
19
–
670
540
600
40
80
20
20
ꢀ40
5
–
6[h]
5 equiv
44444
[a] 7.3”10ꢀ3 mol of cyclopentene in 2.5 mL of PhCl [cyclopentene]/[Ru]=1000. [b] Related to Ru
complex. [c] determined by GPC in THF versus polystyrene standards. [d] Polydispersity index Mw/Mn.
[e] determined by 13C NMR. [f] Turnover frequency in moles per hour. [g] bulk polymerization,
[cyclopentene]/[Ru]=10000.
¯
¯
lyst]:[monomer] = 1:200, 4 h, 95% conversion).[15] At this Experimental Section
Preparation of 2: A dark-red solution of 1 (40 mg, 0.045 mmol) in
temperature, the in situ generated complex 3 was able to
polymerize in fifteen minutes up to 90% of cyclopentene in
bulk conditions with extremely low loading of the catalyst
(1:10000) showing even better activity (Table 2, entry 6). The
above experiments constitute the first evidence of an
indenylidene–metal catalyst precursor for ROMP.
The indenylidene species 3 is also an active catalyst
precursor in other typical alkene metathesis reactions.
Monitoring the RCM of diallyltosylamide with the catalytic
system made from 1 and five equivalents of CF3SO3H was
carried out in an NMR tube. Initially, the mixture was cooled
to ꢀ408C. The formation of 2 was observed by 31P{1H} NMR
but no RCM product was formed after 1hour at ꢀ408C. At
08C the formation of 3 was observed and the RCM reaction
took place at 08C reaching 99% of conversion in 30 min.
Other typical alkene metathesis reactions like acyclic diene
metathesis (ADMET) of decadiene and ring closing meta-
thesis of allylpropargyltosylamide were carried out, thus
showing versatility of catalyst 3 (Table 3). Therefore, the
CD2Cl2 (0.5 mL) in an NMR tube under argon atmosphere at 233 K
was treated with triflic acid (5 mL 0.056 mmol). The solution
immediately turned dark orange and after sealing the NMR tube
under argon atmosphere measurements were made. 1H NMR
(300 MHz, CD2Cl2, 233 K): d = 8.12 (vt, JH-H = 7.0 Hz, 2H, Hmeta-Ph),
ꢁ
ꢀ
=
7.8–7.3 (m, 6H, HPh), 7.05 (s, 1H, Ru C CH ), 6.92 (vt, JH-H
=
7.5 Hz, 2H, Hmeta-Ph), 6.75 and 6.61(both d, JH-H = 6.0 Hz, 4H, h6-p-
i
cymene), 2.9–2.6 (m, 4H, Pr and PCH), 2.28 (s, 3H, CH3), 2.1–
0.9 ppm (m, 36H, Cy and iPr). 13C{1H} NMR + DEPT, HMQC and
ꢁ
HMBC (75.4 MHz, CD2Cl2, 233 K): d = 328.1(d, JC-P = 11 Hz, Ru C),
=
193.2 (s, CH CPh2), 140.5 and 137.6 (both s, Cipso-Ph), 136.0, 134.8,
ꢁ
ꢀ
=
134.2, 130.3, 129.4, and 127.8 (all s, CPh), 130.5 (s, Ru C CH ), 128.2
and 125.8 (both s, Cipso-p-cymene), 120.4 (c, JC-F = 320.0 Hz, CF3), 111.8,
108.7 (both s, Cp-cymene), 33.3 (s, CHiPr), 31–24 (br, Cy), 25.1, 22.2 (s,
CH3-iPr), 19.9 ppm (s, CH3). 31P{1H} NMR (121.4 MHz, CD2Cl2,
233 K): d = 78.6 ppm (s).
Preparation of 3: A dark-red solution of 1 (40 mg, 0.045 mmol) in
CD2Cl2 (0.5 mL) in an NMR tube under argon atmosphere at 253 K
was treated with triflic acid (5 mL 0.056 mmol). The tube was sealed
under argon and reaction was monitored by 31P NMR. The formation
of 2 was first observed and a new species, 3, was progressively formed.
The formation of 3 was completed in 20 min. 1H NMR (300 MHz,
CD2Cl2, 233 K): d = 8.33 (m, 1H, H8-ind), 7.84 (d, JH-H = 7.5 Hz, 2H,
Table 3: Alkene metathesis with in situ prepared catalyst 3 from RuCl(h6-
Horto-Ph), 7.75 (t, JH-H = 7.5 Hz, 1H, Hpara-Ph), 7.60 (vt, JH-H = 7.5 Hz,
[a]
= = =
p-cymene)( C C CPh2)(PCy3)][CF3SO3] (1) + HOSO2CF3 at 08C.
2H, Hmeta-Ph), 7.42 (m, 2H, H7-ind and H6-ind), 7.13 (m, 1H, H5-ind), 6.88
Substrate
Product
Time
12 h
Yield TOF[b]
94%
= ꢀ
=
(s, 1H, Ru C CH ), 6.36, 6.31, 6.19, and 6.15 (all d, 4H, JH-H
=
6.0 Hz, h6-p-cymene), 2.83 (m, 1H, Pr), 2.78 (m, 3H, PCH), 2.31(s,
i
3H, CH3), 2.1–0.9 ppm (m, 36H, Cy and iPr). 13C{1H} NMR + DEPT,
ADMET
RCM
4
HMQC and HMBC (75.4 MHz, CD2Cl2, 233 K): d = 334.1(d, JC-P
10 Hz, Ru = C), 154.6 (s, C3-ind), 146.8 (s, C9-ind), 143.1 (d, JC-P = 2 Hz,
2-ind), 136.5 (s, C4-ind), 134.7 (s, C7-ind), 133.4 (s, C8-ind), 132.7 (s, C6-ind),
132.5 (s, Cpara-Ph), 131.7 (s, Cipso-Ph), 130.0 (s, Cmeta-Ph), 127.8 (s, Corto-Ph),
126.3 and 125.3 (both s, Cipso-p-cymene), 121.2 (s, C5-ind), 120.4 (c, JC-F
=
C
30 min 99% 98
=
320.0 Hz, CF3), 103.6 and 99.7 (both s, Cp-cymene), 33.8 (s, CHiPr); 30–24
(br, Cy); 24.2 and 22.8 (both s, CH3-iPr); 19.6 ppm (s, CH3). 31P{1H}
NMR (121.4 MHz, CD2Cl2, 233 K): d = 48.3 ppm (s).
Enyne
metathesis
3 h
75% 12.5
Polymerisation of cyclolefins: 1 (8 mg 9 mmol) was dissolved in
PhCl (0.5 mL) at 253 K and 4 mL (45 mmol) of triflic acid was added.
After 30 min at this temperature desired amount of freshly prepared
catalyst was transferred to a vessel at chosen temperature containing
PhCl (2.5 mL) and monomer (500 mg; 4.5 mmol of cyclooctene,
1.46m; 7.3 mmol of cyclopentene 2.33m). After the reaction had
finished, the resulting viscous mixture was dissolved with CHCl3
containing 0.1% of 2,6-di-tert-butyl-4-methylphenol (BHT; 20 mL)
and vinyl ethyl ether (0.3 mL). This solution was poured into
methanol (300 mL) to precipitate the polymer, which was collected
by filtration, dried under vacuum, and characterized by 1H and
13C NMR. Average molecular weights were determined using gel-
[a] 4.5”10ꢀ6 mol of 1 + 22.5”10ꢀ6 mol of HOSO2CF3 in 0.5 mL of
CD2Cl2 [substrate/[Ru]=50. [b] Turnover frequency in moles per hour.
activity of 18 electron, ionic indenylidene-arene complex 3
seems higher than that of previously reported 16 electron,
neutral diphosphane indenylidene or phosphane imidazolyl-
idene indenylidene ruthenium complexes[7] probably because
the p-cymene ligand is easily released, thus generating active
initiators.
4526
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Angew. Chem. Int. Ed. 2003, 42, 4524 –4527

Angewandte
Chemie
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Received: June 10, 2003 [Z52108]
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Keywords: carbenes · carbyens · heterogeneous catalysis ·
metathesis · ring-opening polymerization · ruthenium
.
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