Synthesis and catalytic evaluation of ruthenium-arene complexes generated using imidazol(in)ium-2-carboxylates and dithiocarboxylates

Article abstract of DOI:10.1021/om9002363

The ability of five imidazol(in)ium-2-carboxylates and dithiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms to act as NHC precursors for in situ catalytic applications was probed in ruthenium-promot

Full text of DOI:10.1021/om9002363

4056 Organometallics 2009, 28, 4056–4064
DOI: 10.1021/om9002363
Synthesis and Catalytic Evaluation of Ruthenium-Arene Complexes
Generated Using Imidazol(in)ium-2-carboxylates and Dithiocarboxylates
Lionel Delaude,*,† Xavier Sauvage,† Albert Demonceau,† and Johan Wouters‡
†Center for Education and Research on Macromolecules (CERM), Institut de Chimie (B6a),
Universite de Liege, Sart-Tilman par 4000 Liege, Belgium, and ‡Department of Chemistry,
University of Namur (FUNDP), 61 Rue de Bruxelles, 5000 Namur, Belgium
ꢀ
ꢁ
ꢁ
Received March 30, 2009
The ability of five imidazol(in)ium-2-carboxylates and dithiocarboxylates bearing cyclohexyl,
mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms to act as NHC precursors for
in situ catalytic applications was probed in ruthenium-promoted ring-opening metathesis and atom
transfer radical polymerizations. Results obtained with 1:2 mixtures of [RuCl2( p-cymene)]2 and
NHC CO2 adducts were in line with those reported previously starting from preformed [RuCl2-
( p-cymene)(NHC)] complexes, whereas the NHC CS2 zwitterions were almost completely inactive.
3
3
To account for this dichotomy, the preparation of preformed ruthenium-arene complexes from
[RuCl2( p-cymene)]2 and NHC CX2 inner salts was thoroughly investigated. As expected, imidazo-
lium-2-carboxylates lost their CO2 moiety and afforded [RuCl2( p-cymene)(NHC)] complexes in high
3
yields, whereas the NHC CS2 betaines retained their zwitterionic nature and led to cationic
complexes of the [RuCl( p-cymene)(NHC CS2)]PF6 type. These stable, 18-electron species are
3
3
the first examples of well-defined transition-metal complexes bearing chelating NHC CS2 ligands.
3
They were characterized by various analytical techniques, and the molecular structure of [RuCl-
( p-cymene)(IMes CS2)]PF6 was determined by X-ray diffraction analysis.
3
Introduction
(Scheme 1). Due to the high sensitivity of the free carbenes
toward oxygen and moisture, this reaction is often carried
out in situ. Therefore, imidazol(in)ium salts serve de facto as
stable NHC ligand precursors in various catalytic systems.4
An equally important strategy to obtain transition-metal-
NHC complexes involves the reaction of an imidazol(in)ium
salt with a silver(I) source. The intermediate Ag(I)-NHC
complex formed can readily transfer its carbene ligand to
another late transition metal via transmetalation, thereby
affording the desired final product (Scheme 1).5 Although
very general, this method is not exempt from failure, and
Ag-induced oxidative degradation of imidazolium precur-
sors bearing alkyl groups on C2 may lead to unexpected
reactions.6 Thus, new synthetic paths that would allow the
convenient and efficient delivery of NHC ligands to transi-
tion-metal catalytic centers are highly desirable.
Stable N-heterocyclic carbenes (NHCs) have become
ubiquitous ligands in organometallic chemistry and homo-
geneous catalysis.1 They have already afforded an impressive
range of transition-metal complexes that have found numer-
ous applications in organic synthesis and polymer chemis-
try.2 Currently, the NHCs most commonly encountered are
imidazolin-2-ylidene and imidazolidin-2-ylidene derivatives
(with or without a formal double bond between C4 and C5,
respectively).3 They are usually obtained by deprotonation
of the corresponding imidazol(in)ium salts with a strong base
*To whom correspondence should be addressed. E-mail: l.delaude@
ulg.ac.be.
(1) For monographs, see: (a) Carbene Chemistry: From Fleeting
Intermediates to Powerful Reagents; Bertrand, G., Ed.; Marcel Dekker:
New York, 2002. (b) N-Heterocyclic Carbenes in Synthesis; Nolan, S. P.,
Ed.; Wiley-VCH: Weinheim, 2006. (c) N-Heterocyclic Carbenes in
Transition Metal Catalysis; Glorius, F., Ed.; Topics in Organometallic
Chemistry, Vol. 21; Springer: Berlin, 2007.
(2) For reviews, see: (a) Herrmann, W. A.; Kocher, C. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 2162–2187. (b) Jafarpour, L.; Nolan, S. P. Adv.
Organomet. Chem. 2001, 46, 181–222. (c) Herrmann, W. A. Angew. Chem.,
(4) For selected examples, see: (a) Viciu, M. S.; Grasa, G. A.; Nolan,
S. P. Organometallics 2001, 20, 3607–3612. (b) Grasa, G. A.; Viciu, M. S.;
Huang, J.; Nolan, S. P. J. Org. Chem. 2001, 66, 7729–7737. (c) Lee, S.;
Hartwig, J. F. J. Org. Chem. 2001, 66, 3402–3415. (d) Ma, Y.; Song, C.;
Jiang, W.; Wu, Q.; Wang, Y.; Liu, X.; Andrus, M. B. Org. Lett. 2003, 5,
3317–3319. (e) Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F. J.
Am. Chem. Soc. 2004, 126, 15195–15201. (f) Fleckenstein, C.; Roy, S.;
€
€
Int. Ed. 2002, 41, 1290–1309. (d) Herrmann, W. A.; Weskamp, T.; Bohm,
€
V. P. W. Adv. Organomet. Chem. 2002, 48, 1–69. (e) Perry, M. C.; Burgess, K.
Leuthausser, S.; Plenio, H. Chem. Commun. 2007, 2870–2872. (g) Kantchev,
ꢀ
Tetrahedron: Asymmetry 2003, 14, 951–961. (f) Cesar, V.; Bellemin-
E. A. B.; O'Brien, C. J.; Organ, M. G. Angew. Chem., Int. Ed. 2007, 46,
2768–2813.
(5) For reviews, see: (a) Lin, I. J. B.; Vasam, C. S. Comments Inorg.
Chem. 2004, 25, 75–129. (b) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005,
105, 3978–4008. (c) Lin, I. J. B.; Vasam, C. S. Coord. Chem. Rev. 2007, 251,
642–670.
Laponnaz, S.; Gade, L. H. Chem. Soc. Rev. 2004, 33, 619–636. (g) Crudden,
C. M.; Allen, D. P. Coord. Chem. Rev. 2004, 248, 2247–2273. (h) Scott,
N. M.; Nolan, S. P. Eur. J. Inorg. Chem. 2005, 1815–1828. (i) Hahn, F. E.;
Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122–3172.
(3) For reviews, see: (a) Bourrisou, D.; Guerret, O.; Gabbaı, F. P.;
Bertrand, G. Chem. Rev. 2000, 100, 39–91. (b) de Fremont, P.; Marion, N.;
ꢀ
(6) Chianese, A. R.; Zeglis, B. M.; Crabtree, R. H. Chem. Commun.
Nolan, S. P. Coord. Chem. Rev. 2009, 253, 862–892.
2004, 2176–2177.
r
pubs.acs.org/Organometallics
Published on Web 07/02/2009
2009 American Chemical Society

Article
Scheme 1. Formation of Transition-Metal Complexes from
Various NHC Precursors
Organometallics, Vol. 28, No. 14, 2009 4057
Scheme 2. Imidazol(in)ium-2-carboxylates (X=O) and Dithio-
carboxylates (X=S) Used in This Work
Recently, we7,8 and others9,10 have shown that imidazol(in)-
ium-2-carboxylates readily lost their CO2 moiety upon heating
or dissolution and could serve as efficient carbene precursors in
organocatalytic processes10,11 or for the synthesis of various
transition-metal-NHC complexes (Scheme 1).12 We have
already taken advantage of this lability to generate active
species in the palladium-catalyzed Suzuki-Miyaura cross-
coupling of aryl halides with trans-2-phenylvinylboronic acid.8
In ruthenium-promoted olefin metathesis and cyclopropana-
tion reactions, we have also shown that a 1:2 mixture of
Results and Discussion
Catalytic Tests. To begin this study, we wanted to compare
the ability of NHC CO2 and NHC CS2 betaines to act as
3
3
catalyst modifiers toward ruthenium complexes for in situ
catalytic applications. Zwitterionic adducts of five represen-
tative saturated or unsaturated NHCs bearing mesityl (Mes),
2,6-diisopropylphenyl (Dip), or cyclohexyl (Cy) substituents
on their nitrogen atoms were elected as starting materials for
these investigations (Scheme 2).
[RuCl2(p-cymene)]2 dimer and IMes CO2 displayed the same
3
level of activity as the preformed [RuCl2(p-cymene)(IMes)]
complex (IMes is 1,3-dimesitylimidazolin-2-ylidene, p-cymene
is 1-isopropyl-4-methylbenzene).7 In sharp contrast with these
results, preliminary experiments carried out with imidazol-
(in)ium-2-dithiocarboxylates indicated that these adducts
compared poorly with their NHC HCl or NHC CO2 counter-
To complement the data obtained previously with NHC
3
CO2 adducts,7 we first carried out the ring-opening metath-
esis polymerization (ROMP) of cyclooctene, a standard test-
reaction used in our laboratory for assessing the metathetical
activity of ruthenium-arene complexes.13,14 Reactions were
carried out in chlorobenzene at 60 °C using a 1:2 mixture of
3
3
parts for activating palladium(II) acetate in Suzuki-Miyaura
reactions.8
In this contribution, we further investigate the ability of
NHC CO2 and NHC CS2 betaines to serve as carbene
[RuCl2(p-cymene)]2 dimer and NHC CS2 adducts. The
3
3
3
monomer-to-ruthenium molar ratio was 250, and an ordin-
ary neon tube placed 10 cm away from the Pyrex reaction
flasks complemented the experimental setup. This device
ensured a strong, reproducible visible light illumination
required to convert saturated ruthenium-(p-cymene) com-
plexes bearing NHC ligands into metathetically active spe-
cies, most likely via total or partial decoordination of the
η6-arene ligand.15,16
ligand precursors for transition-metal complexes. Both
types of zwitterions were first employed to generate in situ
catalytic species in ruthenium-promoted polymerization
reactions. To account for the differences of reactivity ob-
served, we also compared the thermal stabilities of imidazol-
(in)ium-2-carboxylates and dithiocarboxylates by thermo-
gravimetric analysis. A second part of this work involved
the isolation and characterization of ruthenium-arene
Despite this photochemical activation, no polymers were
isolated in the present study, and only oligomers accounted
for the low conversions observed (Table 1). These results
complexes obtained from various NHC CX2 adducts
3
(X=O, S) in order to validate the assumptions derived from
the in situ experiments.
sharply contrast with those obtained previously with NHC
3
CO2 adducts sporting aryl groups on their nitrogen atoms.7
Almost quantitative conversions of the starting material and
high yields of polyoctenamer were attained within 2 h with
(7) Tudose, A.; Demonceau, A.; Delaude, L. J. Organomet. Chem.
2006, 691, 5356–5365.
ꢀ
(8) Tudose, A.; Delaude, L.; Andre, B.; Demonceau, A. Tetrahedron
Lett. 2006, 47, 8529–8533.
(9) Duong, H. A.; Tekavec, T. N.; Arif, A. M.; Louie, J. Chem.
Commun. 2004, 112–113.
(10) Zhou, H.; Zhang, W.-Z.; Liu, C.-H.; Qu, J.-P.; Lu, X.-B. J. Org.
Chem. 2008, 73, 8039–8044.
(13) (a) Jan, D.; Delaude, L.; Simal, F.; Demonceau, A.; Noels, A. F.
J. Organomet. Chem. 2000, 606, 55–64. (b) Maj, A.; Delaude, L.; Demonceau,
A.; Noels, A. F. J. Organomet. Chem. 2007, 692, 3048–3056. (c) Sauvage,
X.; Borguet, Y.; Noels, A. F.; Delaude, L.; Demonceau, A. Adv. Synth.
Catal. 2007, 349, 255–265. (d) Sauvage, X.; Borguet, Y.; Zaragoza, G.;
Demonceau, A.; Delaude, L. Adv. Synth. Catal. 2009, 351, 441–455.
(14) Delaude, L.; Demonceau, A.; Noels, A. F. Curr. Org. Chem.
2006, 10, 203–215.
(11) (a) Kayaki, H.; Ikarija, T. JP 2006-137733, 2006; Chem. Abstr.
2006, 145, 27996. (b) Bantu, B.; Pawar, G. M.; Decker, U.; Wurst, K.;
Schmidt, A. M.; Buchmeiser, M. R. Chem.;Eur. J. 2009, 15, 3103–
3109. (c) Bantu, B.; Pawar, G. M.; Wurst, K.; Decker, U.; Schmidt, A.
M.; Buchmeiser, M. R. Eur. J. Inorg. Chem. 2009, 1970–1976.
(12) (a) Voutchkova, A. M.; Appelhans, L. N.; Chianese, A. R.;
Crabtree, R. H. J. Am. Chem. Soc. 2005, 127, 17624–17625. (b) Voutch-
kova, A. M.; Feliz, M.; Clot, E.; Eisenstein, O.; Crabtree, R. H. J. Am. Chem.
Soc. 2007, 129, 12834–12846.
(15) Delaude, L.; Demonceau, A.; Noels, A. F. Chem. Commun. 2001,
986–987.
ꢀ
(16) Ahr, M.; Thieuleux, C.; Coperet, C.; Fenet, B.; Basset, J.-M.
Adv. Synth. Catal. 2007, 349, 1587–1591.

4058 Organometallics, Vol. 28, No. 14, 2009
Delaude et al.
Table 1. ROMP of Cyclooctene Catalyzed by Various Ruthenium-NHC Complexes Generated In Situ from [RuCl2(p-cymene)]2 and
Imidazol(in)ium-2-(dithio)carboxylates
NHC CS2
conversion (%)a
NHC CO2
conversion (%)a,b
isolated yield (%)b
3
3
ICy CS2
IMes CS2
9
10
4
14
0
ICy CO2
IMes CO2
30
100
79
100
89
0
91
64
85
77
3
3
3
3
IDip CS2
SIMes CS2
SIDip CS2
IDip CO2
SIMes CO2
SIDip CO2
3
3
3
3
3
3
a Determined by GC using cyclooctane as internal standard. b Data from ref 7.
Table 2. ATRP of MMA Catalyzed by Various Ruthenium-
NHC Complexes Generated In Situ from [RuCl2(p-cymene)]2 and
Imidazol(in)ium-2-(dithio)carboxylates
a
a
NHC CX2
isolated yield (%)
Mn
Mw/Mn
3
b
b
ICy CS2
IMes CS2
<5
<5
88
64
86
-
-
3
44 000
145 000
25 000
31 000
26 000
1.68
2.06
1.27
2.01
1.65
3
ICy CO2
IMes CO2
3
3
IDip CO2
SIMes CO2
3
74
3
a Determined by SEC with PMMA calibration. b Oligomeric pro-
Figure 1. Comparison of the TGA curves for mesityl-substi-
tuted NHC CO2 and NHC CS2 adducts.
ducts.
3
3
mesityl- or 2,6-diisopropylphenyl-substituted carbene
precursors, whereas the cyclohexyl-bearing imidazolium-
2-carboxylate led to a 30% conversion and afforded only
soluble oligomers and no high molecular weight polymer
(Table 1). The patent superiority of NHCs bearing aryl
groups on their nitrogen atoms over 1,3-dialkyl derivatives
was already recognized when [RuCl2(p-cymene)(NHC)]
complexes, either preformed or generated in situ from imi-
dazol(in)ium chlorides and a base, were investigated in
ROMP reactions.15 Earlier studies had also shown that the
C4-C5 double bond in the imidazole ring was not crucial to
achieve high catalytic efficiencies.17
In a second series of experiments, we have investigated the
ruthenium-promoted atom transfer radical polymerization
(ATRP) of methyl methacrylate (MMA) with selected re-
presentative carboxylate or dithiocarboxylate adducts bear-
ing alkyl or aryl groups on their nitrogen atoms (Table 2).
Ethyl 2-bromo-2-methylpropionate served as initiator, and
the reactions were carried out for 16 h in toluene at 85 °C
under the exclusion of oxygen. The initial monomer/initia-
tor/ruthenium molar proportions were 800:2:1. Under these
conditions, the two imidazolium-2-dithiocarboxylates tested
obtained with ICy CO2 and IMes CO2 using the same
3
3
experimental protocol (Table 2). The former inner salt did
not afford a controlled polymerization, but the latter one
displayed a satisfactory activity. It is noteworthy that
molecular weights and polydispersities reached with the in
situ catalytic systems based on these two NHC CO2 adducts
3
were in line with those obtained previously with preformed
[RuCl2(p-cymene)(NHC)] complexes bearing the ICy or
IMes ligand.18 Further modifications of the carbene moiety
were accomplished by replacing the mesityl groups of IMes
with diisopropylphenyl substituents in IDip or by removing
the heterocyclic C4-C5 double bond in SIMes. Yet, none of
these alterations resulted in a better control of the polymer-
ization (Table 2).
Thermogravimetric Analysis. In order to rationalize the
large discrepancy observed between NHC CO2 and NHC
3
3
CS2 zwitterions in terms of catalytic activity, we probed their
thermal stabilities in the solid state by thermogravimetric
analysis (TGA). Decomposition profiles shown in Figure 1
for mesityl-substituted derivatives provide graphic evidence
for the greater lability of carboxylate inner salts compared to
their dithio analogues, even if clean loss of the CX2 moiety
was not detected in this series. Thus, imidazol(in)ium-2-
carboxylates are more likely to release carbene ligands when
heated to 60 °C (ROMP experiments) or 85 °C (ATRP
conditions) in the presence of the [RuCl2(p-cymene)]2 dimer,
a requisite for generating catalytically active species in situ.
were almost completely inactive. With ICy CS2 only oligo-
mers were isolated, whereas with IMes CS2 a small amount
of polymer precipitated. Yet, molecular weight determina-
tion by size-exclusion chromatography (SEC) indicated that
the initiation efficiency was very low and the polydispersity
rather broad. These results sharply contrasted with those
3
3
(17) Delaude, L.; Szypa, M.; Demonceau, A.; Noels, A. F. Adv.
Synth. Catal. 2002, 344, 749–756.
(18) Delaude, L.; Delfosse, S.; Richel, A.; Demonceau, A.; Noels, A.
F. Chem. Commun. 2003, 1526–1527.

Article
Organometallics, Vol. 28, No. 14, 2009 4059
Scheme 3. Synthesis of Ruthenium-Arene Complexes Bearing
NHC Ligands from [RuCl2(p-cymene)]2 and Imidazolium-2-car-
boxylates
IMes CS2 in THF or toluene failed. In all cases, 13C NMR
3
analysis of the crude reaction mixtures revealed the persis-
tence of signals in the 195-225 ppm region, thereby showing
that elimination of CS2 had not occurred, even after pro-
longed heating under a slow stream of argon. In view of the
great stability displayed by NHC CS2 adducts in solution or
3
in the solid state (cf. Figure 1), this observation is
not surprising. Indeed, a survey of the literature confirmed
that none of the various reactions of diaminocarbenium-
dithiocarboxylate species reported thus far involved the
regeneration of diaminocarbenes.25 Unlike the CO2 adducts,
which readily dissociate and can be viewed as convenient
surrogates for free NHCs, the CS2 betaines retain their
zwitterionic nature throughout chemical transformations.
Thus, their reactivity is determined mainly by the presence of
a Lewis acid center in the imidazol(in)ium ring, while the
CS-2 group acts as a Lewis or Brønsted base. To the best of
our knowledge, this dual behavior has been exploited in two
organocatalytic applications so far, namely, the cyanosilyla-
tion of aldehydes with trimethylsilyl cyanide26 and the
Staudinger reaction of ketenes with imines.27
Similar TGA curves were recorded for the cyclohexyl- and
2,6-diisopropylphenyl-based adducts (not shown). As pre-
viously noted, the presence or the absence of a heterocyclic
C4-C5 double bond did not significantly alter the onset of
the degradation process.7,19
In light of the above considerations, we decided to apply
the experimental procedure originally devised by Miguel
et al. for the preparation of [RuCl(arene)(PR3 CS2)]PF6
3
complexes (arene=benzene, p-cymene, or hexamethylben-
zene, PR3 = PiPr3 or PCy3) to the reaction of [RuCl2-
Synthesis of Ruthenium-Arene Complexes. Because imi-
dazol(in)ium-2-dithiocarboxylates obviously behaved very
differently from the corresponding carboxylate adducts in
catalytic systems generated in situ, we have investigated in
more detail the formation of preformed ruthenium-arene
complexes from these two types of precursors. In a first series
of experiments, the [RuCl2(p-cymene)]2 dimer was refluxed
for 2 h in THF with 2 equiv of ICy CO2, IMes CO2, or
(p-cymene)]2 with NHC CS2 adducts.28 Thus, the two
3
partners were refluxed in ethanol for 3 h in the presence of
excess carbon disulfide and potassium hexafluorophosphate
under a slow stream of argon, followed by filtration and
evaporation of the volatiles. Under these conditions, the
dithiocarboxylate anions cleaved the μ-chloro bridges of the
ruthenium dimer to afford new cationic complexes with the
3
3
IDip CO2. A slow stream of argon was applied on top of the
3
generic formula [RuCl(p-cymene)(NHC CS2)]PF6 in high
yields. Because TGA analyses had shown that NHC CS2
3
condenser to help displace carbon dioxide. After workup and
purification by column chromatography, the corresponding
[RuCl2(p-cymene)(NHC)] complexes (1-3) were isolated
in ca. 70-90% yields (Scheme 3). These neutral, 18-electron
species are well-known catalyst precursors for several ruthe-
nium-mediated organic transformations,14,20 including
ROMP15 and ATRP.18 Their synthesis from [RuCl2(p-cym-
ene)]2 and free NHCs has already been reported in the
literature.21-24 From a practical point of view, the recourse
3
betaines were far more stable than the phosphonium dithio-
caboxylates employed by the Spanish team,19 we reasoned
that they might as well react with the ruthenium dimer under
less stringent conditions. To test this hypothesis, a stream-
lined protocol involving the use of stoichiometric amounts of
[RuCl2(p-cymene)]2 (1 equiv), NHC CS2 adducts, and KPF6
3
(2 equiv each) was devised. No carbon disulfide was added,
and the whole transformation was carried out in ethanol at
60 °C under normal atmosphere (Scheme 4). Gratifyingly,
the reactions proceeded very cleanly, and full conversions
were atttained within 1 h.29 The inorganic byproduct (KCl)
was removed by filtration through Celite to afford almost
quantitative yields of ruthenium-arene complexes bearing
imidazol(in)ium-2-dithiocarboxylate ligands (4-8). These
compounds were further purified by recrystallization from
chloroform/cyclohexane. It should be noted that losses of
materials occurred mainly during this final step, but we did
not attempt to optimize it.
to NHC CO2 adducts as carbene transfer agents provides a
3
convenient alternative to the use of air- and moisture-sensitive
carbene reagents, while ensuring high yields of organometallic
products. The potential of this strategy was already under-
lined by Crabtree et al., who successfully isolated a variety of
late transition metal-NHC complexes by reacting 1,3-di-
methylimidazolium-2-carboxylate with suitable metal precur-
sors, including the dichloro(p-cymene)ruthenium(II) dimer.12
Attempts to prepare the [RuCl2(p-cymene)(IMes)] com-
plex (2) by refluxing [RuCl2(p-cymene)]2 with 2 equiv of
Products 4-8 were isolated as dark solids that did not
show any sign of decomposition after more than two years of
(19) Delaude, L.; Demonceau, A.; Wouters, J. Eur. J. Inorg. Chem.
2009, 1882–1891.
(20) Dragutan, V.; Dragutan, I.; Delaude, L.; Demonceau, A. Coord.
(25) For reviews, see: (a) Kirmse, W. Eur. J. Org. Chem. 2005, 237–
260. (b) Delaude, L. Eur. J. Inorg. Chem. 2009, 1681–1699.
(26) Blanrue, A.; Wilhelm, R. Synlett 2004, 2621–2623.
(27) Sereda, O.; Blanrue, A.; Wilhelm, R. Chem. Commun. 2009,
1040–1042.
Chem. Rev. 2007, 251, 765–794.
€
(21) Herrmann, W. A.; Kocher, C.; Goossen, L. J.; Artus, G. R. J.
Chem.;Eur. J. 1996, 2, 1627–1636.
(22) Jafarpour, L.; Huang, J.; Stevens, E. D.; Nolan, S. P. Organo-
metallics 1999, 18, 3760–3763.
ꢀ
(28) (a) Cuyas, J.; Miguel, D.; Perez-Martınez, J. A.; Riera, V.
ꢀ
(23) Lo, C.; Cariou, R.; Fischmeister, C.; Dixneuf, P. H. Adv. Synth.
Catal. 2007, 349, 546–550.
(24) Ledoux, N.; Allaert, B.; Verpoort, F. Eur. J. Org. Chem. 2007,
5578–5583.
Polyhedron 1992, 11, 2713–2716. (b) Alvarez, B.; Miguel, D.; Perez-
Martìnez, J. A.; Riera, V. J. Organomet. Chem. 1994, 474, 143–147.
(29) We thank one of the anonymous reviewers for encouraging us to
probe this simple aerobic route.

4060 Organometallics, Vol. 28, No. 14, 2009
Delaude et al.
Scheme 4. Synthesis of Ruthenium-Arene Complexes Bearing
Imidazol(in)ium-2-dithiocarboxylate Ligands
Figure 2. Molecular conformation (ORTEP diagram) of [RuCl-
(p-cymene)(IMes CS2)]PF6 (5) with thermal ellipsoids drawn at
3
the 50% probability level. Hydrogen atoms and the PF-6 coun-
terion were omitted for the sake of clarity.
storage at room temperature under normal atmosphere.
Their high stability was also evidenced by the fact that
identical UV/visible spectra were recorded in acetonitrile,
whether the solutions were freshly made or kept with no
particular precautions in a closed vessel for more than two
weeks. Analytical and spectroscopic data supported the
structures depicted in Scheme 4. 1H NMR analysis showed
the presence of two doublets at ca. 5.5 and 5.7 ppm,
respectively, assigned to the aromatic protons of the η6-
(p-cymene) ligand, while 13C NMR spectra displayed a
strongly deshielded signal at 212-218 ppm, due to the CS2-
group coordinated as a κ2S,S0 chelate to the ruthenium
center. The catalytic activity of cationic complexes 4-7
was probed in the ROMP of cyclooctene for 2 h at 60 °C,
but, as expected, they did not afford any polymer. The
metathetical activity of compound 8 was further screened
in RCM and ROMP reactions using the standard character-
ization system proposed by Grubbs and co-workers.30 Yet,
for both the ring-closing metathesis of diethyl diallylmalo-
nate and the ring-opening metathesis polymerization of
cyclooctadiene, no sign of evolution was detected by NMR
spectroscopy after 15 h in CD2Cl2 at 30 °C using 1 mol % of
catalyst 8. We are currently investigating other ruthenium-
catalyzed processes that might benefit from the use of stable
cationic complexes such as compounds 4-8, and we shall
report on them in due course.
κ1S, κ2S,S0, or κ3S,C,S0 ligands in mono- and binuclear metal
complexes for several decades,33 the coordination chemistry
of NHC CS2 betaines is still a largely uncharted territory.
3
Preliminary experiments in this field were conducted by Borer
et al., who showed that 1,3-dimethylimidazolium-2-dithiocar-
boxylate formed stable complexes with a range of transition
metal halides or nitrates.34 The products obtained were
characterized by IR and UV/visible spectroscopies only.
Measurements of electrical conductivity, magnetic suscept-
ibility, or cyclic voltammetry complemented the analyses in
some cases, but no NMR or XRD analyses were reported.
Thus, the accurate structure of the products obtained and the
mode of binding of the zwitterionic ligand remained highly
speculative. This prompted us to further investigate the
structural features of complexes 4-8.
X-ray Diffraction Analysis. Crystals of [RuCl(p-cymene)-
(IMes CS2)]PF6 (5) suitable for X-ray diffraction analysis
3
were grown from acetonitrile. Their molecular structure is
depicted in Figure 2 and compared with those reported
previously for the related ruthenium-arene complex
[RuCl2(p-cymene)(IMes)] CHCl3 (9)23 and the free IMes
3
3
CS2 ligand (10)19 in Figure 3. This figure also shows the
common atom-numbering system adopted to label the
selected bond lengths and angles listed in Table 3. As
expected, complex 5 displayed the distinctive three-legged
piano stool geometry already observed in complex 9 and
in many other ruthenium-arene species.35 Chelation of
ruthenium with the betaine adduct via its CS-2 moiety led
to a reduction of the S1-C6-S2 bite angle from 129.1(4)° to
112.3(2)° but did not significantly affect the C-S bond
distances that remained close to 1.67 A in both complexed
and uncomplexed structures. Within each molecule, the
C6-S1 and C6-S2 distances were very similar, indicating
that the negative charge was equally spread over the two
sulfur atoms. It should be pointed out that in the case of
Whereas phosphine-carbon disulfide adducts31 and other
1,1-dithiolate species,32 including dithiocarbamate, xanthate,
and thioxanthate anions, have been widely employed as
(30) Ritter, T.; Hejl, A.; Wenzel, A. G.; Funk, T. W.; Grubbs, R. H.
Organometallics 2006, 25, 5740–5745.
(31) For a review, see: Galindo, A.; Miguel, D.; Perez, J. Coord.
Chem. Rev. 1999, 193-195, 643–690.
(32) For reviews, see: (a) Coucouvanis, D. Prog. Inorg. Chem. 1970,
11, 233–371. (b) Eisenberg, R. Prog. Inorg. Chem. 1970, 12, 295–369.
(c) Coucouvanis, D. Prog. Inorg. Chem. 1979, 26, 301–469. (d) Burns, R. P.;
McCullough, F. P.; McAuliffe, C. A. Adv. Inorg. Chem. Radiochem. 1980,
23, 211–280. (e) Hogarth, G. Prog. Inorg. Chem. 2005, 53, 71–561.
(33) For recent examples, see: (a) Knight, E. R.; Cowley, A. R.;
Hogarth, G.; Wilton-Ely, J. D. E. T. Dalton Trans. 2009, 607–609.
(b) Macgregor, M. J.; Hogarth, G.; Thompson, A. L.; Wilton-Ely, J. D. E. T.
Organometallics 2009, 28, 197–208. (c) Knight, E. R.; Leung, N. H.;
Thompson, A. L.; Hogarth, G.; Wilton-Ely, J. D. E. T. Inorg. Chem. 2009,
48, 3866–3874. (d) Knight, E. R.; Leung, N. H.; Lin, Y. H.; Cowley, A. R.;
Watkin, D. J.; Thompson, A. L.; Hogarth, G.; Wilton-Ely, J. D. E. T. Dalton
Trans. 2009, 3688–3697.
(34) (a) Borer, L. L.; Kong, J. V. Inorg. Chim. Acta 1986, 122, 145–
148. (b) Borer, L. L.; Kong, J. V.; Keihl, P. A.; Forkey, D. M. Inorg. Chim.
Acta 1987, 129, 223–226.
(35) For reviews, see: (a) Le Bozec, H.; Touchard, D.; Dixneuf, P. H.
Adv. Organomet. Chem. 1989, 29, 163–247. (b) Bennett, M. A. Coord.
Chem. Rev. 1997, 166, 225–254. (c) Therrien, B. Coord. Chem. Rev. 2009,
253, 493–519.

Article
Organometallics, Vol. 28, No. 14, 2009 4061
Figure 3. Atom-numbering system and molecular structures of [RuCl(p-cymene)(IMes CS2)]PF6 (5), [RuCl2(p-cymene)(IMes)]
CHCl3 (9), and IMes CS2 (10). Hydrogen atoms and cocrystallized counterions or solvent molecules were omitted for clarity.
3
3
3
˚
Table 3. Selected Bond Lengths (A) and Angles (deg) Derived from Crystal Structures of [RuCl(p-cymene)(IMes CS2)]PF6 (5), [RuCl2(p-
3
cymene)(IMes)] CHCl3 (9),a and IMes CS2 (10)b
3
3
compound
C6-S1
C6-S2
C2-C6
N1-C2
N3-C2
N1-C1a
C4-C5
5
9
1.680(3)
1.673(2)
1.464(3)
1.351(3)
1.370(3)
1.387(6)
1.374(6)
1.342(3)
1.376(3)
1.387(6)
1.374(6)
1.460(3)
1.449(5)
1.461(6)
1.456(6)
1.324(4)
1.312(3)
1.318(11)
1.341(10)
10c
1.667(3)
1.669(3)
1.667(3)
1.669(3)
1.483(8)
1.489(7)
compound
S1-C6-S2
N1-C2-N3
N1-C2-C6-S1
N1-C2-C6-S2
-136.2(2)
C1b-C1a-N1-C2
5
9
112.3(2)
107.3(1)
102.0(2)
107.2(4)
106.4(5)
48.1(2)
77.8(2)
87.2(3)
104.9(6)
106.6(6)
10c
129.1(4)
129.1(4)
-65.3(2)
-62.1(2)
118.0(5)
114.7(5)
a Data from ref 23. b Data from ref 19. c Two molecules are present in the asymmetric unit.
IMes CS2 (10) equivalence of both C-S distances resulted
imidazol(in)ium-2-carboxylates9,11c,38 and their dithio19,39,40
or diseleno40 analogues investigated so far by XRD analysis.
The distortion was, however, less pronounced in complex 5
3
from C2 symmetry in the crystal structure. Thus, only half of
the molecule formed the asymmetric unit, while the other
half was generated by symmetry. Moreover, the lengths of
the two C-S bonds were much closer to the distances
reported for common CdS double bonds (1.67 A) than those
of single C-S bonds (1.75 A).36
than in free IMes CS2. This could result from less favorable
3
Coulombic interactions between the carbenium ion carbon
and the lone pair of electrons on the sulfur atoms.40 The
C2-C6 exocyclic bond was also significantly shorter in
The imidazolium ring and the dithiocarboxylate unit were
not coplanar (see torsion angles N1-C2-C6-S in Table 3).
Nearly orthogonal conformations were observed in acyclic
carbenium dithiocarboxylates37 and in all but one of the other
[RuCl(p-cymene)(IMes CS2)]þ when compared to the free
3
betaine. This indicates greater electron delocalization from
the dithiocarboxylate unit to the imidazolium ring in the
presence of the positively charged Ru cation, as further
evidenced by shorter N1-C2 and N3-C2 bonds in the
(36) Allen, F. H.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor,
R. In International Tables for Crystallography; Prince, E., Ed.; Springer:
Berlin, 2006; Vol. C, pp 790-811.
(37) (a) Ziegler, M. L.; Weber, H.; Nuber, B.; Serhadle, O. Z.
Naturforsch., Teil B 1987, 42, 1411–1418. (b) Nagasawa, A.; Akiyama,
I.; Mashima, S.; Nakayama, J. Heteroat. Chem. 1995, 6, 45–49. (c) Fujihara,
T.; Ohba, T.; Nagasawa, A.; Nakayama, J.; Yoza, K. Acta Crystallogr., Sect.
C 2002, 58, o558–o559.
€
(39) (a) Sheldrick, W. S.; Schonberg, A.; Singer, E.; Eckert, P. Chem.
Ber. 1980, 113, 3605–3609. (b) Borer, L. L.; Kong, J. V.; Oram, D. E. Acta
Crystallogr., Sect. C 1989, 45, 1169–1170. (c) Kuhn, N.; Bohnen, H.;
Henkel, G. Z. Naturforsch., Teil B 1994, 49, 1473–1480. (d) Kuhn, N.;
Niquet, E.; Steimann, M.; Walker, I. Z. Naturforsch., Teil B 1999, 54, 1181–
1187. (e) Akkurt, M.; Ozt€urk, S.; K€uc-€ukbay, H.; Orhan, E.; B€uy€ulg€ungor, O.
::
€
Acta Crystallogr., Sect. E 2004, 60, o219–o221.
(40) Nakayama, J.; Kitahara, T.; Sugihara, Y.; Sakamoto, A.; Ishii,
(38) Kuhn, N.; Steimann, M.; Weyers, G. Z. Naturforsch., Teil B
1999, 54, 427–433.
A. J. Am. Chem. Soc. 2000, 122, 9120–9126.

4062 Organometallics, Vol. 28, No. 14, 2009
Delaude et al.
Table 4. Wavenumbers of IR Stretching Vibrations Bands (cm-1
presence of the metal. Interestingly, the geometry of the
heterocyclic ring suffered more distortions in complex 5
involving IMes CS2 than in complex 9, containing the IMes
)
in [RuCl(p-cymene)(NHC CS2)]PF6 Complexes (4-8) and the
3
Corresponding NHC CS2 Free Ligands
3
3
carbene. Besides, the relative orientation of the p-cymene
ligand was different in the two complexes (see Figure 3), but
the distance between the centroid of the arene and the metal
center remained almost the same in the crystal structures
νasym
νasym
free
ligand
νasym
νasym
h
h
h
h
complex
(N2Cþ)
(CS-2 )
(N2Cþ)a
(CS-2 )a
4
5
6
7
8
1474
1485
1470
1559
1549
1029
1025
1010
1032
1058
ICy CS2
IMes CS2
1474
1488
1469
1531
1524
1058
1052
1058
1064
1080
3
3
of [RuCl(p-cymene)(IMes CS2)]PF6 (1.710 A) and [RuCl2-
(p-cymene)(IMes)] CHCl3 (1.716 A).
IDip CS2
SIMes CS2
SIDip CS2
3
3
3
3
In all three structures under scrutiny, the N1-C2 and
N3-C2 bond distances were (nearly) equal (Table 3) and
indicated a significant CdN double-bond character, consis-
tent with electronic conjugation within the N2Cþ motif.
Electronic effects of the N-substituting aromatic rings were
not transferred to the imidazolium ring motif. This was
underlined by rather long N-C inter-ring distances, closer
to a single N-C bond (1.47 A) than to a double NdC bond
(1.34 A),36 and by a perpendicular orientation of the mesityl
groups versus the central heterocycle (cf. torsion angle C1b-
C1a-N1-C2 in Table 3). Deviation from orthogonality was
more pronounced in complex 5 (77.8(2)°) than in complex
9 (87.2(3)°) and in the free zwitterionic ligand 10 (ca. 106°),
probably due to steric effects.
3
a Data from ref 19.
Examination of the UV/visible spectra of [RuCl(p-
cymene)(NHC CS2)]PF6 complexes 4-7 dissolved in
3
acetonitrile revealed the presence of weak absorption
bands in the visible domain (NHC = ICy: 489 and
580 nm, IMes: 518 nm, IDip: 550 nm, SIMes: 513 nm)
due to nfπ* transitions within the dithiocarboxylate
group, which are responsible for the dark colors of these
compounds. Several other absorption maxima leading to
well-shaped peaks or poorly defined shoulders were also
detected in the UV part of the spectra. They are most
likely caused by πfπ* transitions within the CS-2 group,
the phenyl rings, and the aromatic imidazolium hetero-
cycles,34,42 but we have not investigated in more detail
their exact assignments.
IR and UV/Visible Spectroscopies. The FT-IR spectra of
complexes 4-8 were recorded in KBr pellets. In all cases, the
two strongest signals were due to the P-F stretching
and bending vibrations of the PF-6 anion located at 842 and
558 cm-1, respectively.41 Changes brought to the coordina-
Conclusion
tion sphere of ruthenium by varying the NHC CS2 ligand had
3
The ability of imidazol(in)ium-2-carboxylates and dithio-
carboxylates to act as NHC precursors for in situ catalytic
applications was probed in ruthenium-promoted ring-open-
ing metathesis and atom transfer radical polymerizations.
no influence on the position of these peaks. In addition to the
various C-C and C-H stretching vibration bands, two
remarkable absorptions originated from the organic subunits
of the molecules, namely, the asymmetric stretching vibra-
tions of the N2Cþ and CS2- groups (Table 4). The former
amidinium unit gave rise to a medium-intensity band located
at ca. 1475 cm-1 for aromatic imidazolium cycles and at ca.
1555 cm-1 in complexes 7 and 8 sporting an imidazolinium
ring. A second characteristic absorption of medium intensity
was present in the 1010-1060 cm-1 region and assigned to the
asymmetric stretching of the dithiocarboxylate group. We
failed to identify the corresponding symmetric stretching
vibration bands in the experimental spectra of complexes
4-8. On the basis of theoretical calculations performed
on 1,3-dimethylimidazolium-2-dithiocarboxylate, they are
Results obtained with the NHC CO2 adducts were in line
with those reported previously starting from preformed
3
[RuCl2(p-cymene)(NHC)] complexes, whereas 1:2 mixtures
of [RuCl2(p-cymene)]2 dimer and NHC CS2 zwitterions
3
were almost completely inactive in the reactions under
consideration. Comparison of TGA curves recorded for
both types of adducts showed that NHC CO2 betaines were
3
more labile than their CS2 analogues and therefore more
likely to release carbene ligands upon thermal activation.
To further rationalize the difference of catalytic activities
observed, we have investigated thoroughly the preparation
of preformed ruthenium-arene complexes from [RuCl2-
expected to be very weak and located below 900 cm-1 40
.
Comparison of the νasym(N2Cþ) and νasym(CS2-) wave-
numbers recorded for [RuCl(p-cymene)(NHC CS2)]PF6
(p-cymene)]2 and NHC CX2 inner salts. In a first series of
3
h
h
experiments, the ruthenium dimer was refluxed for 2 h in
THF with 2 equiv of ICy CO2, IMes CO2, or IDip CO2. As
3
3
complexes 4-6 and the corresponding NHC CS2 free
3
3
3
expected, the corresponding [RuCl2(p-cymene)(NHC)] com-
plexes (1-3) were isolated in high yields. From a practical
point of view, this procedure is particularly attractive
because it does not involve the manipulation of air- and
moisture-sensitive free carbenes. When similar reactions
ligands showed that the imidazolium moiety of these zwit-
terions was not affected by complexation. Indeed, almost
identical frequencies were obtained for the N-CdNþ
stretching vibrations in both complexed and uncomplexed
betaines (Table 4). On the other hand, the absorption bands
for the SdC-S- asymmetric stretching were significantly
shifted to lower energy upon coordination, in good agree-
ment with the formation of a chelate between the dithiocar-
boxylate unit of the ligand and the metal center. In the case of
imidazolinium-based ligands SIMes CS2 and SIDip CS2,
were carried out with IMes CS2, 13C NMR spectroscopy
3
revealed that the dithiocarboxylate unit was not cleaved off.
Thus, in a second series of experiments, the reaction between
[RuCl2(p-cymene)]2 and NHC CS2 adducts was performed
3
in the presence of potassium hexafluorophosphate for 1 h at
60 °C. Ethanol acted as solvent, and no particular precau-
tions were taken to exclude air and moisture. Under these
conditions, new cationic complexes (4-8) with the generic
3
3
both the νasym(N2Cþ) and νasym(CS-2 ) stretching vibrations
h
underwent changes upon coordination, although they were
h
shifted in opposite directions.
formula [RuCl(p-cymene)(NHC CS2)]PF6 were isolated in
3
(41) Syed Mohamed, K.; Padma, D. K. Spectrochim. Acta, Part A
1985, 41, 725–728.
(42) Furlani, C.; Luciani, M. L. Inorg. Chem. 1968, 7, 1586–1592.

Article
Organometallics, Vol. 28, No. 14, 2009 4063
high yields. These stable, 18-electron species are the first
examples of well-defined transition-metal complexes bearing
NHC CS2 ligands. They were characterized by various
analytical techniques, and the molecular structure of com-
pound 5 was determined by X-ray diffraction analysis. As
expected from the in situ catalytic screening, they did not
show any metathetical activity in ROMP or RCM reactions,
but we are currently assessing their potentials in other
ruthenium-catalyzed transformations.
under nitrogen. The reaction mixture was heated for 16 h in an
oil bath at 85 °C. After cooling to room temperature, it was
diluted with THF (5 mL) and poured in n-heptane (600 mL)
under vigorous stirring. The precipitated polymer was filtered
with suction, dried overnight under dynamic vacuum, and
characterized by SEC.
3
Preparation of Ruthenium-Arene Complexes Using Carboxy-
late Precursors. A 250 mL round-bottom flask equipped with a
magnetic stirring bar and a reflux condenser topped with an oil
bubbler was charged with [RuCl2(p-cymene)]2 (0.5 g, 0.82 mmol)
and an imidazol(in)ium-2-carboxylate (1.71 mmol, 2.1 equiv).
The reactor was purged of air by applying three vacuum/argon
cycles before dry and degassed THF (100 mL) was added. The
resulting suspension was refluxed for 2 h under a slow stream of
argon, leading to the formation of a dark brown solution. The
reaction mixture was brought back to room temperature, and
the solvent was removed under reduced pressure to afford a dark
brown residue, which was washed with n-pentane (2ꢀ20 mL).
The remaining solid was dissolved in dichloromethane (10 mL).
Neutral alumina (0.2 g) was added to the solution, and the
solvent was removed under reduced pressure. The resulting free-
flowing powder was dry-loaded on a short plug of neutral
alumina (0.2 g). This column was eluted using a gradient of
hexanes/dichloromethane from 1:0 to 0:1 v/v. The initial frac-
tions containing p-cymene traces were discarded. In some cases,
a small amount of methanol (2%) was added to dichloro-
methane in order to improve the recovery of product from the
column. The resulting brown solution was washed with water to
remove the last traces of imidazolium salt. It was evaporated on
a rotary evaporator and dried under high vacuum.
Experimental Section
General Comments. Unless otherwise specified, all the synth-
eses were carried out under a dry argon atmosphere using
standard Schlenk techniques. Solvents were distilled from
appropriate drying agents and deoxygenated prior to use.
Imidazol(in)ium-2-carboxylates7 and dithiocarboxylates19 were
synthesized according to published procedures. The [RuCl2-
(p-cymene)]2 dimer43 was purchased from Strem. Anhydrous
neutral alumina W200 was obtained from Woelm, Eschwege
(Germany). All the other chemicals were obtained from Aldrich.
1H and 13C NMR spectra were recorded at 298 K with a Bruker
DRX 400 spectrometer operating at 400.13 and 100.62 MHz,
respectively. Chemical shifts are listed in parts per million
downfield from TMS and are referenced from the solvent peaks
or TMS. Infrared spectra were recorded with a Perkin-Elmer
Spectrum One FT-IR spectrometer. UV/visible spectra were
recorded with a Hewlett-Packard HP 8453 spectrophotometer.
Thermogravimetric analyses were performed with a TA Q500
instrument using a 5 °C/min ramp. Gas chromatography was
carried out with a Varian 3900 instrument equipped with a flame
ionization detector and a WCOT fused silica column (stationary
phase: CP-Sil 5CB, column length: 15 m, inside diameter:
0.25 mm, outside diameter: 0.39 mm, film thickness: 0.25 μm).
Size-exclusion chromatography (SEC) was performed in THF
at 45 °C with a SFD S5200 autosampler liquid chromato-
graph equipped with a SFD 2000 refractive index detector
and a battery of 4 PL gel columns fitted in series (particle size:
5 μm; pore sizes: 105, 104, 103, and 102 A; flow rate: 1 mL/min).
The molecular weights (not corrected) are reported versus
monodisperse PMMA standards used to calibrate the instru-
ment. Elemental analyses were carried out in the Laboratory of
RuCl2(p-cymene)ICy (1): brown solid (0.79 g, 89% yield);
NMR data were in accord with literature values.21
RuCl2(p-cymene)IMes (2): brown solid (0.85 g, 85% yield);
NMR data were in accord with literature values.22-24
RuCl2(p-cymene)IDip (3): brown solid (0.81 g, 71% yield);
NMR data were in accord with literature values.22
Preparation of Ruthenium-Arene Complexes with Dithiocar-
boxylate Ligands. A 50 mL round-bottom flask equipped with a
magnetic stirring bar was charged with [RuCl2(p-cymene)]2
(0.1225 g, 0.2 mmol), an imidazol(in)ium-2-dithiocarboxylate
(0.4 mmol), and potassium hexafluorophosphate (0.0736 g,
0.4 mmol). Reagent grade, denaturated ethanol (20 mL) taken
straight from the bottle was added, and the reaction mixture was
heated for 1 h under normal atmosphere in an oil bath at 60 °C.
After cooling to room temperature, the volatiles were evapo-
rated under vacuum. The residue was taken up with dichloro-
methane (10 mL) and filtered through a short plug of
Celite. The inorganic salts were rinsed with dichloromethane
(2ꢀ5 mL), and the filtrate was evaporated on a rotary evapora-
tor. The crude product was recrystallized from chloroform/
cyclohexane and dried under high vacuum.
ꢁ
Pharmaceutical Chemistry at the University of Liege.
ROMP of Cyclooctene. A 25 mL round-bottom flask
equipped with a magnetic stirring bar and capped with a
three-way stopcock was charged with [RuCl2(p-cymene)]2
(9.2 mg, 0.015 mmol) and an imidazol(in)ium-2-(dithio)carbox-
ylate (0.03 mmol). Air was expelled by applying three vacuum/
argon cycles before dry chlorobenzene (5 mL) and cyclooctene
(1 mL, 7.5 mmol) were added with dried syringes under argon.
The reaction mixture was stirred for 2 h in an oil bath at 60 °C. It
was irradiated with a 40 W “cold white” fluorescent tube placed
10 cm away from the Pyrex reaction flask. The conversion was
monitored by gas chromatography using the cyclooctane im-
purity of cyclooctene as internal standard. The resulting gel was
diluted with chloroform (20 mL) and slowly poured into metha-
nol (500 mL) under vigorous stirring. The precipitated poly-
octenamer was filtered with suction, dried overnight under
dynamic vacuum, and characterized by SEC and NMR.
[RuCl(p-cymene)(ICy CS2)]PF6 (4): dark green, microcrys-
3
talline powder (0.23 g, 80% yield). 1H NMR (400 MHz, CDCl3):
δ 1.22-1.45 (m, 6 H, Cy), 1.32 (d, 3JHH=6.8 Hz, 6 H, p-cym CH-
(CH3)2), 1.60-1.74 (m, 6 H, Cy), 1.86 (br d, 4 H, Cy), 2.04 (br d,
4 H, Cy), 2.37 (s, 3 H, p-cym CH3), 2.87 (sept, 3JHH=6.8 Hz, 1 H,
p-cym CH(CH3)2), 4.52 (m, 2 H, CHN), 5.72 (d, 3JHH=5.8 Hz,
2 H, p-cym CHar), 5.97 (d, 3JHH=5.8 Hz, 2 H, p-cym CHar), 7.53
(s, 2 H, Im-C4,5) ppm. 13C NMR (100 MHz, CDCl3): δ 19.6,
22.9, 23.0, 25.0, 32.6, 33.6, 59.1, 85.7, 85.9, 105.5, 107.0, 120.0,
ATRP of MMA. A 25 mL glass tube containing a magnetic
stirring bar and capped with a three-way stopcock was charged
with [RuCl2(p-cymene)]2 (3.6 mg, 0.006 mmol) and an imidazol-
(in)ium-2-(dithio)carboxylate (0.012 mmol). Air was expelled by
applying three vacuum/nitrogen cycles before methyl methacry-
late (1 mL, 9.35 mmol) and ethyl 2-bromo-2-methylpropionate
(0.1 M in toluene, 0.25 mL) were added with dried syringes
141.3, 218.1 (CS2) ppm. IR (KBr): ν 2933, 2859, 1564, 1474,
h
1452, 1202, 1029, 841, 710, 558 cm-1. UV/vis (MeCN): λ (ε) 217
(25 200), 238 (22 900), 291 (9300), 371 (5000), 489 (2300), 580
(1400) nm (M-1 cm-1). Anal. Calcd for C26H38ClF6N2PRuS2
(724.22): C, 43.12; H, 5.29; N, 3.87; S, 8.86. Found: C, 43.31; H,
5.35; N, 4.17; S, 8.16.
[RuCl(p-cymene)(IMes CS2)]PF6 (5): dark purple, micro-
crystalline powder (0.24 g, 75% yield). H NMR (400 MHz,
3
1
CDCl3): δ 1.07 (d, 3JHH=6.4 Hz, 6 H, p-cym CH(CH3)2), 2.04
(s, 12 H, ortho-CH3), 2.14 (s, 3 H, p-cym CH3), 2.38 (s, 6 H,
(43) Bennett, M. A.; Smith, A. K. J. Chem. Soc., Dalton Trans. 1974,
233–241.

4064 Organometallics, Vol. 28, No. 14, 2009
Delaude et al.
3
para-CH3), 2.53 (sept, 1 H, p-cym CH(CH3)2), 5.46 (d, 3JHH
=
CDCl3): δ 1.03 (d, JHH = 6.8 Hz, 6 H, p-cym CH(CH3)2),
1.30 (d, 3JHH=6.4 Hz, 12 H, SIDip CH(CH3)2), 1.34 (d, 3JHH
6.4 Hz, 12 H, SIDip CH(CH3)2), 2.04 (s, 3 H, p-cym CH3), 2.43
(sept, 3JHH=6.8 Hz, 1 H, p-cym CH(CH3)2), 2.94 (sept, 3JHH
6.4 Hz, 4 H, SIDip CH(CH3)2), 4.42 (s, 4 H, CH2N), 5.40
3
5.6 Hz, 2 H, p-cym CHar), 5.65 (d, JHH=5.6 Hz, 2 H, p-cym
CHar), 7.03 (s, 4 H, meta-CH), 7.57 (s, 2 H, dCHN) ppm.
13C NMR (100 MHz, CDCl3): δ 17.6, 19.3, 21.4, 22.6, 32.3,
86.4, 86.6, 106.7, 106.8, 126.3, 130.1, 130.4, 136.8, 142.3, 212.4
=
=
3
3
(CS2) ppm. IR (KBr): ν 3171, 3145, 2962, 2922, 1608, 1552,
(d, JHH =6.0 Hz, 2 H, p-cym CHar), 5.57 (d, JHH =6.0 Hz,
2 H, p-cym CHar), 7.25 (d, 3JHH=7.6 Hz, 4 H, meta-CH), 7.49
h
1485, 1384, 1233, 1025, 842, 720, 558 cm-1. UV/vis (MeCN):
λ (ε) 197 (81 900), 313 (10 700), 396 (4000), 518 (3300) nm
(M-1 cm-1). Anal. Calcd for C32H38ClF6N2PRuS2 (796.28):
C, 48.27; H, 4.81; N, 3.52; S, 8.05. Found: C, 48.14; H, 4.59; N,
3.71; S, 8.24.
(t, JHH=7.6 Hz, 2 H, para-CH) ppm. 13C NMR (100 MHz,
3
CDCl3): δ 19.6, 22.8, 23.8, 25.8, 29.6, 32.2, 54.1, 87.8, 87.9,
105.9, 109.2, 125.2, 125.6, 130.0, 131.8, 146.4, 153.4, 211.8 (CS2)
ppm. IR (KBr): ν 3175, 2968, 2928, 2870, 1591, 1549, 1504, 1466,
1445, 1389, 1360, 1323, 1285, 1083, 1058, 844, 805, 758, 687,
558 cm-1. Anal. Calcd for C38H52ClF6N2PRuS2 (882.45): C,
51.72; H, 5.94; N, 3.17; S, 7.27. Found: C, 51.23; H, 5.94; N,
3.42; S, 7.05.
X-ray Crystal Structure Determination. Data were collected at
room temperature on a Gemini diffractometer (Oxford Diffrac-
tion Ltd.) equipped with a Ruby CCD detector using an
Enhance (Mo) X-ray source. Data collection program: CrysAlis
CCD (Oxford Diffraction Ltd.), data reduction: CrysAlis
RED (Oxford Diffraction Ltd.), structure solution: SHELXS,
structure refinement (on F2): SHELXL-97,44 data analysis:
PLATON.45 A multiscan procedure was applied to correct for
absorption effects. Hydrogen atom positions were calculated
and refined isotropically using a riding model. Disorder of the
PF-6 ion was refined.
h
[RuCl(p-cymene)(IDip CS2)]PF6 (6): dark blue, microcrys-
3
talline powder (0.24 g, 69% yield). 1H NMR (400 MHz, CDCl3):
3
δ 1.06 (d, JHH =5.6 Hz, 6 H, p-cym CH(CH3)2), 1.19-1.24
(m, 24 H, IDip CH(CH3)2), 2.09 (s, 3 H, p-cym CH3), 2.32 (sept,
3JHH=6.0 Hz, 4 H, IDip CH(CH3)2), 2.48 (sept, 3JHH=6.6 Hz,
1 H, p-cym CH(CH3)2), 5.41 (d, JHH = 5.0 Hz, 2 H, p-cym
3
CHar), 5.58 (d, 3JHH=5.0 Hz, 2 H, p-cym CHar), 7.36 (d, 3JHH
=
6.8 Hz, 4 H, meta-CH), 7.62 (t, 3JHH=7.2 Hz, 2 H, para-CH),
7.71 (s, 2 H, dCHN) ppm. 13C NMR (100 MHz, CDCl3): δ
19.5, 22.8, 23.1, 24.9, 29.6, 32.3, 81.1, 87.3, 106.4, 107.5, 125.6,
127.7, 130.1, 132.8, 136.8, 145.2, 211.8 (CS2) ppm. IR (KBr):
ν 3175, 2966, 2930, 2872, 1549, 1471, 1389, 1368, 1207, 1061,
h
1010, 843, 804, 756, 722, 558 cm-1. UV/vis (MeCN): λ (ε)
193 (88 000), 238 (22 800) shoulder, 328 (11 600), 550 (4200)
nm (M-1 cm-1). Anal. Calcd for C38H50ClF6N2PRuS2 (880.45):
C, 51.84; H, 5.72; N, 3.18; S, 7.28. Found: C, 51.09; H, 5.71; N,
3.42; S, 7.01.
Crystal Data for [RuCl(p-cymene)(IMes CS2)]PF6 (5): dark
3
purple crystals (from MeCN), triclinic, P1, a=8.126(1) A, b=
14.560(1) A, c=16.441(1) A, R=77.9(1)°, β=80.5(1)°, γ=77.2
(1) °, V=1841.0(1) A3, Z=2, Fcalc=1.436 g cm-3, F000=812,
λ(Mo KR)=0.71073 A, θmax =28.20°, 52 973 total measured
reflections, 8363 independent reflections (Rint =0.0288), 5698
observed reflections (I > 2σ(I)), μ = 0.710 mm-1, 451 para-
meters, R1 (all data) = 0.0554, R1 (observed data) = 0.0340,
[RuCl(p-cymene)(SIMes CS2)]PF6 (7): dark purple, micro-
3
1
crystalline powder (0.22 g, 69% yield). H NMR (400 MHz,
CD2Cl2): δ 0.96 (d, 3JHH=6.8 Hz, 6 H, p-cym CH(CH3)2), 2.09
(s, 3 H, p-cym CH3), 2.33 (s, 18 H, mesityl CH3), 2.40 (m, 1 H,
p-cym CH(CH3)2), 4.32 (s, 4 H, CH2N), 5.44 (d, 3JHH=6.0 Hz,
2 H, p-cym CHar), 5.63 (d, 3JHH=6.0 Hz, 2 H, p-cym CHar), 6.98
(s, 4 H, meta-CH) ppm. 13C NMR (100 MHz, CD2Cl2): δ 17.9,
19.1, 21.0, 22.4, 32.2, 51.0, 86.1, 86.8, 107.4, 107.6, 130.1, 130.3,
S=GooF=1.049, Δ/s.u.=0.002, residual Fmax=0.872 e A-3
min=-0.349 e A-3
,
F
.
135.8, 141.3, 156.2, 213.1 (CS2) ppm. IR (KBr): ν 2963, 2922,
h
Acknowledgment. We thank Ms. A. Richel and Ms. P.
ꢀ
Wrzesniak for the ATRP catalytic tests and Mrs B.
Norberg for the XRD analyses.
1610, 1559, 1511, 1466, 1382, 1355, 1291, 1213, 1088, 1032, 842,
741, 689, 575, 558 cm-1. UV/vis (MeCN): λ (ε) 195 (85 700), 513
(2400) nm (M-1 cm-1). Anal. Calcd for C32H40ClF6N2PRuS2
(798.30): C, 48.15; H, 5.05; N, 3.51; S, 8.03. Found: C, 48.08; H,
4.98; N, 3.69; S, 8.02.
Supporting Information Available: CIF file with crystallo-
graphic data for complex 5. This material is available free of
charge via the Internet at http://pubs.acs.org.
[RuCl(p-cymene)(SIDip CS2)]PF6 (8): dark brown, micro-
crystalline powder (0.31 g, 89% yield). H NMR (400 MHz,
3
1
(44) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
€
(45) Speck, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht (The Netherlands), 2005.
€
Crystal Structures; University of Gottingen: Gottingen (Germany), 1997.