Synthesis and structure of N-heterocyclic carbene complexes with tethered olefinic groups: Application of the ruthenium catalyst in olefin metathesis

Article abstract of DOI:10.1021/om0503242

Silver(I) and rhodium(I) complexes bearing the bisallyl-substituted N-heterocyclic carbene ligand (4R,5S)-4,5-diallyl-1,3-bis(2,4,6-trimethylphenyl) imidazolin-2-ylidene (allyl₂SIMes) have been prepared in a straightforward synthesis. The reaction of (4R,5S)-4,5-diallyl-1,3-bis(2,4,6- trimethylphenyl)-4,5-dihydro-3H-imidazol-1-ium tetrafluoroborate (1a) with Ag₂O affords the ionic biscarbene complex [(allyl₂SIMes) ₂Ag]⁺BF₄^- (2), while the reaction of (4R,5S)-4,5-diallyl-1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydro-3H-imidazol-1- ium chloride (1b) with Ag₂O leads to the monocarbene complex (allyl₂SIMes)AgCl (3). Sequential treatment of 1a with KOtBu and dimeric [RhCl(cod)]₂ (cod = cyclooctadiene) yields the rhodium carbene complex (allyl₂SIMes)RhCl(cod) (4). However, the reaction of 1a with the first-generation Grubbs catalyst (PCy₃) ₂Cl₂Ru=C(H)Ph (Cy = cyclohexyl) leads to ring-closing metathesis of the two allylic groups, yielding 1,3-bis(2,4,6-trimethylphenyl)- 3a,4,7,7a-tetrahydro-3H-benzimidazol-1-ium tetrafluoroborate (5). Subsequent reaction of this new imidazolium salt with KOtBu and 1 equiv of (PCy ₃)Cl₂Ru=C(H)(C₆H₄OiPr-2) forms [1,3-bis(2,4,6-trimethylphenyl)-3a,4,7,7a-tetrahydro-3H-benzimidazolin-2- ylidene]dichloro(2-isopropanolatobenzylidene)ruthenium(II) (8). All new complexes have been thoroughly characterized, including X-ray crystallographic analyses of 2, 3, and 8. The most intriguing feature of 8 is the presence of an innocent C=C bond that is part of a highly active olefin metathesis catalyst, which offers many options for further functionalization of the ligand backbone. The catalytic activity of complex 8 has been evaluated for the ring-closing metathesis of N,N-diallyl-4-toluenesulfonamide.

Full text of DOI:10.1021/om0503242

Organometallics 2005, 24, 4049-4056
4049
Synthesis and Structure of N-Heterocyclic Carbene
Complexes with Tethered Olefinic Groups: Application
of the Ruthenium Catalyst in Olefin Metathesis
Kerstin Weigl,† Katrin Ko¨hler,*,†,‡ Sebastian Dechert,# and Franc Meyer#
Merck KGaA, Frankfurter Strasse 250, D-64293 Darmstadt, Germany, and Institut fu¨r
Anorganische Chemie, Georg-August-Universita¨t Go¨ttingen, Tammannstrasse 4,
D-37077 Go¨ttingen, Germany
Received April 22, 2005
Silver(I) and rhodium(I) complexes bearing the bisallyl-substituted N-heterocyclic carbene
ligand (4R,5S)-4,5-diallyl-1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (allyl2SIMes)
have been prepared in a straightforward synthesis. The reaction of (4R,5S)-4,5-diallyl-1,3-
bis(2,4,6-trimethylphenyl)-4,5-dihydro-3H-imidazol-1-ium tetrafluoroborate (1a) with Ag2O
affords the ionic biscarbene complex [(allyl2SIMes)2Ag]+BF4- (2), while the reaction of (4R,5S)-
4,5-diallyl-1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydro-3H-imidazol-1-ium chloride (1b) with
Ag2O leads to the monocarbene complex (allyl2SIMes)AgCl (3). Sequential treatment of 1a
with KOtBu and dimeric [RhCl(cod)]2 (cod ) cyclooctadiene) yields the rhodium carbene
complex (allyl2SIMes)RhCl(cod) (4). However, the reaction of 1a with the first-generation
Grubbs catalyst (PCy3)2Cl2RudC(H)Ph (Cy ) cyclohexyl) leads to ring-closing metathesis of
the two allylic groups, yielding 1,3-bis(2,4,6-trimethylphenyl)-3a,4,7,7a-tetrahydro-3H-
benzimidazol-1-ium tetrafluoroborate (5). Subsequent reaction of this new imidazolium salt
with KOtBu and 1 equiv of (PCy3)Cl2RudC(H)(C6H4OiPr-2) forms [1,3-bis(2,4,6-trimeth-
ylphenyl)-3a,4,7,7a-tetrahydro-3H-benzimidazolin-2-ylidene]dichloro(2-isopropanolatoben-
zylidene)ruthenium(II) (8). All new complexes have been thoroughly characterized, including
X-ray crystallographic analyses of 2, 3, and 8. The most intriguing feature of 8 is the presence
of an innocent CdC bond that is part of a highly active olefin metathesis catalyst, which
offers many options for further functionalization of the ligand backbone. The catalytic activity
of complex 8 has been evaluated for the ring-closing metathesis of N,N-diallyl-4-toluene-
sulfonamide.
Introduction
The bulky groups R provide steric protection from
dimerization and carbene degradation pathways.
During the past decade, the use of N-heterocyclic
carbene (NHC) ligands derived from imidazolium ions
has emerged as an alternative to phoshine ligands in
the design of new organometallic compounds and cata-
lysts.1 N-Heterocyclic carbenes (type A), generated by
the abstraction of the proton at C-2 of an imidazolium
salt by a suitable base, show unique coordination
properties such as particularly strong σ-donor but poor
π-acceptor abilities. The interest in those nucleophilic
carbene ligands was low until Arduengo et al. discovered
in 1991 that the introduction of sterically demanding
groups R (adamantyl) in A enables the isolation and
crystallization of the free imidazol-2-ylidene carbene.2
N-Heterocyclic carbenes bound to metal complex
fragments (type B) are significantly less reactive than
Schrock and Fischer carbenes. They do not undergo
metathesis reactions, cyclopropanations, or many of the
other reactions attributed to metal carbenes.3 In recent
years the potential of N-heterocyclic carbenes as truly
useful ligands for catalysis, especially for ruthenium-
mediated olefin metathesis, has been shown by
Herrmann,4 Grubbs,5 Nolan,6 Hoveyda,7 Fu¨rstner,8
Blechert,9 and others.10 The key discovery was the
replacement of a phosphine with an NHC ligand in the
* To whom correspondence should be addressed. Fax: +49 551
3082510. E-mail: katrin.koehler@sartorius.com.
† Merck KGaA.
‡ New address: Sartorius AG, Weender Landstrasse 94-108, D-37075
Go¨ttingen, Germany.
# Georg-August-Universita¨t Go¨ttingen.
(1) (a) Herrmann, W. A.; Ko¨cher, C. Angew. Chem. 1997, 109, 2256;
Angew. Chem., Int. Ed. Engl. 1997, 36, 2162. (b) Bourissou, D.; Guerret,
O.; Gabbai, F. P.; Bertrand, G. Chem. Rev. 2000, 100, 39. (c) Herrmann,
W. A. Angew. Chem. 2002, 114, 1342; Angew. Chem., Int. Ed. 2002,
41, 1290. (d) Perry, M. C.; Burgess, K. Tetrahedron: Asymmetry 2003,
14, 951. (e) Peris, E.; Crabtree, R. H. Coord. Chem. Rev. 2004, 248,
2239. (f) Crudden, C. M.; Allen, D. P. Coord. Chem. Rev. 2004, 248,
2247.
(2) (a) Arduengo, A. J., III; Harlow, R. L.; Kline, M. J. J. Am. Chem.
Soc. 1991, 113, 361. (b) Arduengo, A. J., III; Dias, H. V. R.; Harlow, R.
L.; Kline, M. J. J. Am. Chem. Soc. 1992, 114, 5530. (c) Arduengo, A.
J., III; Goerlich, J. R.; Marshall, W. J. J. Am. Chem. Soc. 1995, 117,
11027.
(3) Collman, J. P., Hegedus, L. S., Norton, J. R., Finke R. G., Eds.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; Chapter 16.
10.1021/om0503242 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 07/06/2005

4050 Organometallics, Vol. 24, No. 16, 2005
Weigl et al.
ruthenium alkylidene complex C,11 leading to the
ruthenium catalyst D5a with improved robustness and
activity in metathesis of a wide range of olefins. Other
ruthenium-based metathesis catalysts are phoshine-free
and take advantage of chelating alkylidene fragments
(catalyst E) to achieve greater stability, recyclability,
and improved performance of the catalyst.7a
complexes B with functionalities (Cl, CH2OH, or others)
attached to the backbone of the heterocycle have been
reported, since the preparation of those ligands and
their complexes often requires lengthy and sophisticated
synthetic routes.14 The 4- and 5-positions of the hetero-
cycle, however, appear to be ideally suited for the
introduction of functional groups, since they are quite
remote from the catalytically active metal site; any
disturbing effect of those substituent groups on the
catalytic reaction should therefore be minimized. Proper
functionalization of the NHC ligand at its backbone C-4
and C-5 atoms hence is a promising approach with
respect to process improvements such as immobilization
of the catalyst to a solid support or biphasic liquid
catalysis.
In this contribution, we report on the synthesis and
properties of novel ruthenium(II), rhodium(I), and
silver(I) NHC complexes bearing one or two olefin
groups at the backbone of the heterocycle. We investi-
gated the catalytic behavior of the new ruthenium
complex in a ring-closing olefin metathesis reaction and
compared it to the related known catalyst E. For the
first time, the X-ray crystallographic investigation of an
olefin metathesis catalyst bearing itself an olefinic group
could be carried out.
In principle, N-heterocyclic carbenes with functional
groups bound to the N atoms of the heterocycle are
accessible using the synthetic sequence established for
type A molecules. Herrmann et al. described the intro-
duction of various functionalities such as ether, amino,
and phosphino groups tethered to the N atoms of the
N-heterocyclic carbene in order to generate potentially
chelating NHC ligands,12 and this area has seen much
progress in recent years.13 In contrast, relatively few
examples of NHC ligands A and NHC-bearing metal
Results and Discussion
(4) (a) Herrmann, W. A. Angew. Chem. 1998, 110, 2631; Angew.
Chem., Int. Ed. 1998, 37, 2490. (b) Ackermann, L.; Fu¨rstner, A.;
Weskamp, T.; Kohl, F. J.; Herrmann, W. A. Tetrahedron Lett. 1999,
40, 4787. (c) Weskamp, T.; Kohl, F. J.; Hieringer, W.; Gleich, D.;
Herrmann, W. A. Angew. Chem. 1999, 111, 2573; Angew. Chem., Int.
Ed. 1999, 38, 2416.
(5) (a) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999,
1, 953. (b) Sanford, M. S.; Love, J. A.; Grubbs, R. H. J. Am. Chem.
Soc. 2001, 123, 6543. (c) Love, J. A.; Sanford, M. S.; Day, M. W.;
Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 10103. (d) Trnka, T. M.;
Morgan, J. P.; Sanford, M. S.; Wilhelm, T. E.; Scholl, M.; Choi, T.-L.;
Ding, S.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 2546.
(e) Yun, J.; Marinez, E. R.; Grubbs, R. H. Organometallics 2004, 23,
4172. (f) Trnka, T. M.; Day, M. W.; Grubbs, R. H. Angew. Chem. 2001,
113, 3549; Angew. Chem., Int. Ed. 2001, 40, 3441. (g) Louie, J.; Grubbs,
R. H. Organometallics 2002, 21, 2153. (h) Seiders, T. J.; Ward, D. W.;
Grubbs, R. H. Org. Lett. 2001, 3, 3225.
(6) (a) Huang, J.; Stevens, E. D.; Nolan, S. P.; Petersen, J. L. J. Am.
Chem. Soc. 1999, 121, 2674. (b) Huang, J.; Schanz, H.-J.; Stevens, E.
D.; Nolan, S. P. Organometallics 1999, 18, 5375. (c) Jafarpour, L.;
Nolan, S. P. Organometallics 2000, 19, 2055. (d) Jafarpour, L.; Heck,
M.-P.; Baylon, C.; Lee, H. M.; Mioskowski, C.; Nolan, S. P. Organo-
metallics 2002, 21, 671.
(7) (a) Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H.
J. Am. Chem. Soc. 2000, 122, 8168. (b) Van Veldhuizen, J. J.;
Gillingham, D. G.; Garber, S. B.; Kataoka, O.; Hoveyda, A. H. J. Am.
Chem. Soc. 2003, 125, 12502. (c) Larsen, A. O.; Leu, W.; Oberhuber,
C. N.; Campbell, J. E.; Hoveyda, A. H. J. Am. Chem. Soc. 2004, 126,
11130.
Synthesis and Spectroscopic Characterization.
As previously described, 4,5-dihydroimidazolium salts
of type 1 with two allylic groups attached to the
backbone of the heterocycle can be obtained by double
allylation of glyoxalbis(2,4,6-trimethylphenyl)imine with
allylic Grignard reagents. Ring closure of the initially
formed vicinal diamine is then achieved by reaction with
HC(OEt)3 and NH4X.15
The study of silver(I) complexes containing N-hetero-
cyclic carbene ligands is becoming increasingly impor-
tant due to their ease of preparation, their function as
carbene transfer reagents, and their structural variety
that results from silver-silver interactions leading to
dimerization, oligomerization, or polymerization.16 An
elegant method to afford these silver carbene complexes
is the in situ deprotonation of imidazolium salts by
Ag2O. As the starting materials as well as the silver
carbene complex are air-stable, this reaction can be
carried out under aerobic conditions and gives a con-
venient entry into metal carbene chemistry. The reac-
(8) (a) Fu¨rstner, A.; Ackermann, L.; Gabor, B.; Goddard, R.; Leh-
mann, C. W.; Mynott, R.; Stelzer, F.; Thiel, O. R. Chem. Eur. J. 2001,
7, 3236. (b) Fu¨rstner, A.; Thiel, O. R.; Lehmann, C. W. Organometallics
2002, 21, 331. (c) Pru¨hs, S.; Lehmann, C. W.; Fu¨rstner, A. Organo-
metallics 2004, 23, 280.
(9) (a) Gessler, S.; Randl, S.; Blechert, S. Tetrahedron Lett. 2000,
41, 9973. (b) Randl, S.; Gessler, S.; Wakamatsu, H.; Blechert, S. Synlett
2001, 3, 430. (c) Wakamatsu, H.; Blechert, S. Angew. Chem. 2002, 114,
2509; Angew. Chem., Int. Ed. 2002, 41, 2403. (d) Zaja, M.; Connon, S.
J.; Dunne, A. M.; Rivard, M.; Buschmann, N.; Jiricek, J.; Blechert, S.
Tetrahedron 2003, 59, 6545. (e) Buschmann, N.; Wakamatsu, H.;
Blechert, S. Synlett 2004, 4, 667.
(10) See for example (a) Grela, K.; Kim, M. Eur. J. Org. Chem. 2003,
963. (b) Michrowska, A.; Bujok, R.; Harutyunyan, S.; Sashuk, V.;
Dolgonos, G.; Grela, K. J. Am. Chem. Soc. 2004, 126, 9318. (c) Krause,
J. O.; Nuyken, O.; Wurst, K.; Buchmeiser, M. R. Chem. Eur. J. 2004,
10, 777. (d) Krause, J. O.; Nuyken, O.; Buchmeiser, M. R. Chem. Eur.
J. 2004, 10, 2029.
(11) Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R. H. Angew.
Chem. 1995, 107, 2179; Angew. Chem., Int. Ed. Engl. 1995, 34, 2039.
(12) Herrmann, W. A.; Ko¨cher, C.; Goossen, L. J.; Artus, G. R. J.
Chem. Eur. J. 1996, 2, 1627.
(13) See for example: (a) Fu¨rstner, A.; Krause, H.; Ackermann, L.;
Lehmann, C. W. Chem. Commun. 2001, 2240. (b) Danopoulos, A. A.;
Winston, S.; Gelbrich, T.; Hursthouse, M. B.; Tooze, R. P. Chem.
Commun. 2002, 482. (c) Broggini, D.; Togni, A. Helv. Chim. Acta 2002,
85, 2518. (d) Bolm, C.; Kesselgruber, M.; Raabe, G. Organometallics
2002, 21, 707.
(14) (a) Arduengo, A. J., III; Davidson, F.; Dias, H. V. R.; Goerlich,
J. R.; Khasnis, D.; Marshall, W. J.; Prakasha, T. K. J. Am. Chem. Soc.
1997, 119, 12742. (b) Mayr, M.; Buchmeiser, M. R.; Wurst, K. Adv.
Synth. Catal. 2002, 344, 712.
(15) Weigl, K.; Ko¨hler, K.; Wolmersha¨user, G. Adv. Synth. Catal.,
submitted.
(16) (a) Arduengo, A. J., III; Dias, H. V. R.; Calabrese, J. C.;
Davidson, F. Organometallics 1993, 12, 3405. (b) Wang, H. M. J.; Lin,
I. J. B. Organometallics 1998, 17, 972. (c) Tulloch, A. A. D.; Danopoulos,
A. A.; Winston, S.; Kleinhenz, S.; Eastham, G. J. Chem. Soc., Dalton
Trans. 2000, 4499. (d) Pytkowicz, J.; Roland, S.; Mangeney, P. J.
Organomet. Chem. 2001, 631, 157. (e) Ramnial, T.; Abernethy, C. D.;
Spicer, M. D.; McKenzie, I. D.; Gay, I. D.; Clyburne, J. A. C. Inorg.
Chem. 2003, 42, 1391. (f) Baker, M. V.; Brown, D. H.; Haque, R. A.;
Skelton, B. W.; White, A. H. Dalton Trans. 2004, 3756.

Ruthenium Catalyst in Olefin Metathesis
Organometallics, Vol. 24, No. 16, 2005 4051
Scheme 1. Synthesis of Silver Carbene Complexes 2 and 3
Scheme 2. Synthesis of 5a
tion of the allyl-substituted imidazolium salts 1a and
1b with 0.5 equiv of Ag2O gave the silver carbene
complex 2 or 3, respectively, in good yields (Scheme 1).
The synthesis of the silver carbene complex 2 could
even be carried out in water without hydrolysis of the
Ag-C bonds, while the silver chloride complex 3 was
prepared in THF. After stirring the reaction mixtures
for several hours at room temperature under the exclu-
sion of light, 2 and 3 were isolated as white solids by
simple filtration (2 is insoluble in water) or by filtration
and evaporation of the solvent (3 is soluble in THF).
Both compounds are stable as solids for several weeks
at room temperature under the exclusion of light. In
contrast, solutions of 2 and 3 gradually decompose at
25 °C within several hours with the formation of
elemental silver. Both compounds are soluble in polar
solvents such as THF or CH2Cl2. Crystals of 2 could be
grown from a saturated THF solution at room temper-
ature. Spectroscopic data corroborate the results of the
crystallographic analysis (see below) and confirm that
two N-heterocyclic carbene ligands are bound to one
silver atom, forming a cationic linear silver(I) species
with BF4 as the noncoordinating counterion. The H
and 13C NMR spectra of 2 and 3 in CDCl3 consist of the
expected sharp and well-resolved signals for each of the
organic groups. Formation of the carbene adducts 2 and
3 is accompanied by the loss of the proton signal of the
NC(H)N group in 1a (8.21 ppm) and 1b (10.40 ppm) and
a significant shift to higher frequency of the two protons
attached to the heterocycle. Carbene formation is also
clearly seen in the 13C NMR spectra: the signal of the
carbon atom of the NCN group is shifted from 158.2 ppm
in 1a to 206.5 ppm in 2 and from 160.4 ppm in 1b to
207.1 ppm in 3. These carbene carbon signals each
appear as two doublets with Ag-C coupling constants
of 170.4 and 196.3 Hz in 2 and 224.4 and 259.1 Hz in 3,
which is attributed to coupling with 107Ag and 109Ag,
respectively. The smaller coupling constants for 2
compared to 3 are consistent with values reported in
the literature for ionic [(NHC)Ag(NHC)]+(X-) (180-210
Hz)16a,b,f and neutral (NHC)AgX (230-270 Hz).16d,e
Interestingly, solutions of the new silver compounds 2
and 3 in H2O/MeCN (70:30) show similar ESI mass
spectra with a prominent peak for the [(NHC)2Ag+] ion
and minor peaks for [(NHC)Ag(NtCMe)+], [(NHC)Ag-
(H2O)+], and [(NHC)Ag+] ions. This might have been
expected for the biscarbene complex 2, but not for the
monocarbene complex 3. Strongly donating solvents
apparently promote the dissociation of (NHC)AgX com-
plexes to (NHC)2Ag+ and AgX2-, which has been also
found for Ag complexes with N-functionalized NHC
ligands.16c
a (i) KOtBu, THF, 25 °C, 45 min; (ii) [RhCl(cod)]2, toluene,
80 °C, 1 h.
To further explore the ability of the doubly allyl-
substituted carbene ligand derived from 1 to form
transition metal complexes, a rhodium(I) complex was
prepared according to Herrmann’s procedure.17 The
interest in rhodium NHC complexes has grown consid-
erably in recent years, since they have been shown to
catalyze various substrate transformations such as
hydrosilylation, hydroaminomethylation of olefins, or
diastereoselective carbocyclization reactions.18 Imida-
zolium salt 1b was treated with KOtBu in THF at 25
°C in order to generate in situ the doubly allyl-
substituted N-heterocyclic carbene adduct 4 (Scheme
2).15 In accordance with what is usually observed for
dihydroimidazolium salts that contain a saturated C-C
backbone (and in contrast to imidazolium salts with an
unsaturated CdC backbone),5d the parent carbene is not
isolated in its free form but forms an adduct with the
liberated HOtBu to finally give 4.
Upon heating to 80 °C for 1 h in toluene the carbene
adduct 4 eliminates HOtBu, and in the presence of
dimeric [RhCl(cod)]2 the doubly allyl-substituted (NHC)-
RhCl(cod) complex 5 is formed. After filtration and
purification by column chromatography 5 was obtained
as a yellow air-stable solid. It is soluble in polar aprotic
solvents such as THF or CH2Cl2, and no decomposition
of 5 could be observed over several days in solution
(NMR control). In the 1H and 13C NMR spectra of
complex 5 two diastereomers in a ratio of around 4:1
were observed at room temperature in CDCl3 solution.
This is most likely due to hindered rotation around the
carbene carbon-rhodium bond, assuming that the NHC
plane is perpendicular to the square planar rhodium
environment(asobservedpreviouslyinrelatedcomplexes),18d,19
and the two backbone allyl groups are cis-oriented.
-
1
(17) Denk, K.; Sirsch, P.; Herrmann, W. A. J. Organomet. Chem.
2002, 649, 219.
(18) (a) Enders, D.; Gielen, H.; Runsink, J.; Breuer, K.; Brode, S.;
Boehm, K. Eur. J. Inorg. Chem. 1998, 913. (b) Enders, D.; Gielen, H.
J. Organomet. Chem. 2001, 617-618, 70. (c) Seayad, A. M.; Selvaku-
mar, K.; Ahmed, M.; Beller, M. Tetrahedron Lett. 2003, 44, 1679. (d)
Evans, P. A.; Baum, E. W.; Fazal, A. N.; Pink, M. Chem. Commun.
2005, 63.

4052 Organometallics, Vol. 24, No. 16, 2005
Weigl et al.
Scheme 3. Synthesis of 6a
Scheme 4. Synthesis of 8a
a (i) KOtBu, THF, 25 °C, 30 min, 1 equiv (PCy3)2Cl2RudC-
(H)Ph, toluene, 80 °C, 1 h; (ii) 0.1 mol % (PCy3)2Cl2RudC(H)Ph,
CH2Cl2, 25 °C, 17 h.
a (i) KOtBu, THF, 25 °C, 15 min; (ii) (PCy3)Cl2RudC(H)(C6H4-
OiPr-2), toluene, 80 °C, 1 h.
Hindered rotation around a carbene carbon-rhodium
bondwasalreadyfoundinchiralchloro(η4-cyclooctadiene)(tri-
azolinylidene)rhodium complexes.18a The 13C NMR spec-
trum of 5 shows the characteristic NCN carbon doublet
(1JRhC ) 48.2 Hz) at 214.7 ppm for the major isomer
and at 214.3 ppm for the minor isomer, which is similar
to the carbene carbon signal of the parent complex
Imidazolium salt 6 proved to be a valuable NHC
precursor for the synthesis of new catalysts that feature
an olefinic moiety in the ligand backbone. Similar to the
preparation of the carbene adduct 4 from 1b, imidazo-
lium salt 6 reacts with KOtBu in THF at 25 °C to give
the HOtBu adduct 7.15 Treatment of in situ prepared 7
with the first generation Hoveyda catalyst (PCy3)Cl2-
RudC(H)(C6H4OiPr-2) affords the new ruthenium com-
plex 8 (Scheme 4).
After purification of the crude product by column
chromatography (silica, CH2Cl2), 8 was isolated as an
air-stable green solid in 63% yield. Complex 8 is soluble
in most common polar and unpolar solvents, and
crystals suitable for X-ray crystallographic analysis
were grown at room temperature from a chloroform
solution that was layered with hexane. The benzylidene
ligand in the ruthenium complex 8 gives rise to 1H and
13C NMR absorptions that are very similar to those of
the parent complex (SIMes)Cl2RudC(H)(C6H4OiPr-2)
(E):7a the signal of the RudCH proton appears at 16.46
ppm in 8 (versus 16.56 ppm in E) and the carbon signal
of the RudC(H) group is observed at 298.3 ppm in 8
(versus 296.8 ppm in E). Although the NHC ligands are
different in 8 and E, the signals for the carbene-C of
the respective NHC ligands are alike and appear at
213.2 ppm in 8 versus 211.1 ppm in E.
Solid State Structure. The silver complexes 2 and
3 and the ruthenium complex 8 have been investigated
by X-ray crystallography in order to corroborate the
spectroscopic findings and to provide a solid foundation
for interpretation of the catalytic behavior. To the best
of our knowledge, this is the first structural information
about a ruthenium benzylidene complex incorporating
an olefinic group within the same molecule. The molec-
ular structures of 2, 3, and 8 are depicted in Figures
1-3, together with selected atom distances and bond
angles.
In 2 the silver atom is almost linearly coordinated by
the two NHC ligands (C-Ag-C 178.4(2)°) with Ag-C
distances of 2.082(4) and 2.087(4) Å. The planes of the
two NHC ligands defined by the N-C(carbene)-N
atoms intersect at 54.7(3)°. The related C2 symmetric
chloro complex 3 features a slightly shorter Ag-C
distance of 2.057(7) Å and a linearly coordinated silver
atom (Cl-Ag-C 180°). Chlorine, silver, and the carbene
carbon atom are located on a crystallographic 2-fold axis.
The Ag-Cl distance (2.305(2) Å) lies within the range
usually found for (NHC)Ag-Cl complexes (2.3-2.4
Å).16c,e,20 While 2 appears to be the first X-ray crystal-
1
(SIMes)RhCl(cod)17 (212.0 ppm, JRhC ) 48.2 Hz). Also
for the η4-bound cyclooctadiene ligand two sets of
doublets (due to rhodium-carbon coupling) could be
observed, the olefinic carbon atoms resonating at 67.2
(14.6 Hz) and 97.3 ppm (6.9 Hz) for the major isomer
and at 68.4 (14.7 Hz) and 97.0 ppm (7.2 Hz) for the
1
minor isomer. Variable-temperature H NMR spectra
in CD3CN did not reveal any dynamic process up to 70
°C, while spectra in D8-toluene indicate gradual decom-
position upon heating to even higher temperatures.
Fu¨rstner et al. had reported the successful isolation
of a ruthenium metathesis catalyst that bears an
unsaturated NHC ligand with terminal olefins attached
to one of the N atoms of the heterocycle.8a,13a In view of
those findings we set out to prepare a ruthenium
metathesis catalyst from the olefin-substituted satu-
rated imidazolium salt 1a. Upon reaction of 1a/KOtBu
with 1 equiv of the first-generation Grubbs catalyst
(PCy3)2Cl2RudC(H)Ph, however, gas formation (ethene)
due to ring-closing metathesis of the two proximate
allylic groups of the heterocycle was observed, but no
pure and stable product could be isolated (Scheme 3).
Under the reaction conditions employed, the present
saturated NHC ligand derived from 4 with two allylic
groups at the backbone C-4 and C-5 positions apparently
is not innocent in the presence of active Ru-benzylidene
catalysts. It should be noted that elevated temperatures
(80 °C) are required to liberate the carbene from its
adduct 4, as is usually the case for saturated NHC
systems. Since the Fu¨rstner ligands were of the unsat-
urated type, synthesis and isolation of the ruthenium
complexes with free terminal olefins tethered to the
NHC-N could be carried out at room temperature.
Upon heating to 80 °C, those complexes also metathe-
sized their own ligands, yielding metallacyclic species.8a
On the other hand, the present findings now offered
a convenient entry into NHC ligands with an annelated
cyclohexene moiety, since the imidazolium salt 1a can
be converted into the new imidazolium salt 6 in a
straightforward manner by treatment with catalytic
amounts of (PCy3)2Cl2RudC(H)Ph (0.1 mol %) in CH2-
Cl2 at 25 °C (Scheme 3).15
(19) Alcarazo, M.; Roseblade, S. J.; Alonso, E.; Ferna´ndez, R.;
Alvarez, E.; Lahoz, F. J.; Lassaletta, J. M. J. Am. Chem. Soc. 2004,
126, 13242.
(20) (a) Chen, W.; Wu, B.; Matsumoto, K. J. Organomet. Chem. 2002,
654, 233. (b) Simons, R. S.; Custer, P.; Tessier, C. A.; Youngs, W. J.
Organometallics 2003, 22, 1979.

Ruthenium Catalyst in Olefin Metathesis
Organometallics, Vol. 24, No. 16, 2005 4053
Figure 3. ORTEP plot (30% probability thermal ellipsoids)
of the molecular structure of 8. For the sake of clarity all
hydrogen atoms except those illustrating the stereochem-
istry have been omitted. Selected atom distances (Å) and
angles (deg): Ru1-C1 1.967(4), Ru1-C26 1.833(4), Ru1-
O1 2.250(3), Ru1-Cl1 2.345(1), Ru1-Cl2 2.333(1), C1-N1
1.358(5), C1-N2 1.354(5), C4-C5 1.336(8), C26-C27
1.444(5); C1-Ru1-C26 103.1(2), C1-Ru1-O1 177.0(1),
C1-Ru1-Cl1 94.6(1), C1-Ru1-Cl2 91.9(1), C26-Ru1-O1
79.6(1), C26-Ru1-Cl1 97.2(1), C26-Ru1-Cl2 98.3(1), O1-
Ru1-Cl1 86.34(8), O1-Ru1-Cl2 86.31(8), Cl1-Ru1-Cl2
161.41(4), Ru1-C26-C27 118.2(3), N1-C1-N2 106.0(3).
Figure 1. ORTEP plot (30% probability thermal ellipsoids)
of the molecular structure of 2. For the sake of clarity the
BF4-, all hydrogen atoms except those illustrating the
stereochemistry, and the disorder have been omitted.
Selected atom distances (Å) and angles (deg): Ag1-C1
2.087(4), Ag1-C28 2.082(4), C1-N1 1.330(5), C1-N2
1.323(5), C28-N3 1.332(5), C28-N4 1.320(5); C1-Ag1-
C28 178.4(2), N1-C1-N2 109.0(4), N3-C28-N4 109.8(4).
of 2 or 3 and some silver(I) complexes featuring a single
NHC ligand based on 1,3-dimethyl- or 1,3-dibenzyl-
substituted (4R,5R)-4,5-di-tert-butylimidazolin-2-ylidene
reveals no significant differences ((1,3-(CH3)2-NHC)-
Ag-I: 108.8(7)°, (1,3-(CH2C6H5)2-NHC)Ag-Br: 109.5-
(15)°).16d
The overall structure of 8 is as anticipated and is
analogous to those of the parent complex (SIMes)Cl2-
RudC(H)(C6H4OiPr-2) (E)7a with the ether-O trans to
the NHC ligand and an almost linear C1-Ru-O1
arrangement (177.0(1)°). The Ru1-C26 distance is in
the expected range for ruthenium benzylidene com-
plexes, while the combination of a rather weak O donor
and a strong trans-influence of the NHC gives rise to a
long Ru1-O1 bond of 2.250(3) Å and a Ru1-C1 bond
(1.967(4) Å) that is considerably shorter than in the case
of second-generation Grubbs catalysts with a phosphine
trans to the NHC (where d(Ru-CNHC) is usually found
in the range 2.05-2.09 Å).5c,f,g,6a,8a,13a All values for 8
are in good accordance with what has been observed for
other complexes of the Hoveyda type characterized
crystallographically.7a,10c,22
The most intriguing feature of 8 is the presence of an
innocent CdC bond that is part of a highly active olefin
metathesis catalyst. Very few ruthenium NHC com-
plexes with functional substituents at the backbone C
atoms of the NHC ligand have been reported,8a and this
appears to be the first such compound of the Hoveyda
type and the first with a free olefinic functional group.
Second-generation Grubbs catalysts with a long-chain
terminal olefin tethered to the NHC-N were shown to
undergo internal metathesis to form a metallacycle at
elevated temperatures (i.e., at temperatures used for the
synthesis of 8), as already mentioned above.8a
Figure 2. ORTEP plot (30% probability thermal ellipsoids)
of the molecular structure of 3. For the sake of clarity all
hydrogen atoms except those illustrating the stereochem-
istry and the disorder have been omitted. Selected atom
distances (Å) and angles (deg): Ag1-Cl1 2.305(2), Ag1-
C1 2.057(7), C1-N1 1.336(6); C1-Ag1-Cl1 180.0, N1-C1-
N1′ 109.3(6). Symmetry transformation used to generate
equivalent atoms: (′) -x+1, y, -z+1/2.
lographic structure of a silver(I) biscarbene complex
with saturated NHC ligands, the molecular structure
of 2 closely resembles that of bis(1,3-dimesitylimidazol-
2-ylidene)silver(I) triflate (C-Ag-C 176.3(2)°; d(Ag-C)
2.067(4) and 2.078(4) Å),16a as well as several other
silver(I) complexes with two unsaturated NHC
ligands.16c,f,21 A notable distinction are the values of the
N-C-N angles in 2 and 3 (2: 109.0(4) and 109.8(4)°;
3: 109.3(6)°), which are larger than those in related
complexes with unsaturated NHC backbone (e.g.,
103.6(4)° and 104.8(4)° in bis(1,3-dimesitylimidazol-2-
ylidene)silver(I) triflate16a and 104.4(5)° in 1,3-di-
mesitylimidazol-2-ylidene-silver(I) chloride16e). This can
be attributed to the different ring geometries of the
NHC ligands derived from either imidazoles or 4,5-
dihydroimidazoles. A comparison of the N-C-N angles
Ring-Closing Olefin Metathesis. Ring-closing me-
tathesis (RCM) has become a very popular method for
the formation of unsaturated cyclic compounds from
terminal diolefins and is now widely used in organic
chemistry.23 With the described efficient route for the
(21) (a) Bildstein, B.; Malaun, M.; Kopacka, H.; Wurst, K.; Mitter-
bo¨ck, M.; Ongania, K.-H.; Opromolla, G.; Zanello, P. Organometallics
1999, 18, 4325. (b) Gerrison, J. C.; Simons, R. S.; Talley, J. M.;
Wesdemiotis, C.; Tessier, C. A.; Youngs, W. J. Organometallics 2001,
20, 1276. (c) Nielsen, D. J.; Cavell, K. J.; Skelton, B. W.; White, A. H.
Inorg. Chim. Acta 2002, 327, 116. (d) Hu, X.; Tang, Y.; Gantzel, P.;
Meyer, K. Organometallics 2003, 22, 612.
(22) Van Veldhuizen, J. J.; Garber, S. B.; Kingsbury, J. S.; Hoveyda,
A. H. J. Am. Chem. Soc. 2002, 124, 4954.

4054 Organometallics, Vol. 24, No. 16, 2005
Weigl et al.
Scheme 5. Ring-Closing Metathesis
ently causes a slightly decreased productivity of the new
complex in comparison to parent E is not clear at
present.
Conclusion
Table 1. RCM of N,N-Diallyl-4-toluenesulfonamide
Silver and rhodium complexes of a functionalized
NHC ligand bearing two allyl groups at the NHC
backbone have been prepared via routes previously
established for the nonfunctionalized analogues. The
X-ray crystal structure of 2 appears to the first for a
biscarbene silver(I) complex with two saturated imida-
zolin-2-ylidene ligands. In the presence of Grubbs
catalyst, however, the backbone allyl groups of imida-
zolium salt 1 are readily metathesized to give a new
imidazolium salt, 6, with an annelated cyclohexene
moiety. The NHC derived from 6 can be smoothly
transferred onto ruthenium carbene complexes via the
usual phosphine substitution reaction, as has been
confirmed by the structural characterization of the new
Hoveyda-type ruthenium metathesis catalyst 8. A par-
ticularly attractive feature of 8 is the presence of an
internal olefinic group as part of the NHC ligand
backbone, which remains innocent with respect to olefin
metathesis even at elevated temperatures. It should be
noted that unstrained cycloolefins such as cyclohexenes
usually do not participate in any ROMP or ROM
reactions in the presence of Grubbs or Hoveyda type
catalysts.25 This provides many options for further
functionalization of the new NHC ligand via, inter alia,
dihydroxylation, cyclopropanation, hydroalkoxysilyla-
tion, etc. in order to create catalysts that are applicable
under various process conditions, for example, in im-
mobilized or biphasic liquid catalysis. The position of
this internal olefinic group in 8 appears to be ideally
suited for functionalization, since it is quite remote from
the catalytically active metal site; any disturbing effect
on the catalytic reaction should therefore be minimized.
The only slightly lower activity of 8 in RCM of N,N-
diallyltoluene-4-sulfonamide as compared to the bench-
mark system E underlines its potential to serve as an
entry point into advanced metathesis catalysts. Inves-
tigations in this regard are in progress.
by 8 and E (reaction time 17 h)
catalyst (mol %) conversion with 8 (%) conversion with E (%)
0.05
100.0
80.6
19.7
13.8
100.0
97.2
52.0
33.9
0.02
0.005
0.002
synthesis of the ruthenium complex 8 and in view of
the fact that 8 bears itself an olefinic group at the ligand
backbone, our focus turned to the evaluation of its
catalytic activity in olefin metathesis. So far, only few
reports have been given about the synthesis and testing
of second-generation ruthenium catalysts bearing sub-
stituents at the NHC backbone: Grubbs’ complexes F
and G5a,h or Fu¨rstner’s complexes H and I.8a
We could not find any reports about Hoveyda type
catalysts with substituents at the NHC backbone,
except of Blechert’s work concerning type E catalysts
covalently bound on solid supports via the NHC back-
bone.24 The olefin-substituted catalyst 8 was probed in
ring-closing olefin metathesis in comparison to the
parent ruthenium catalyst (SIMes)Cl2RudC(H)(C6H4-
OiPr-2) (E), using N,N-diallyltoluene-4-sulfonamide as
a standard RCM substrate (Scheme 5).
When using 0.1 mol % of 8, the ring-closing metath-
esis reaction was complete after 165 min in CH2Cl2 at
45 °C, indicating high activity. Under identical condi-
tions the benchmark catalyst E showed complete con-
version after 105 min. We also explored the productivity
of 8 in comparison to E by decreasing the catalyst
amounts from 0.1 to 0.002 mol % (Table 1). Metathesis
reactions were again carried out in CH2Cl2 at 45 °C over
17 h.
At very low catalyst loadings of less than 0.05 mol %,
the benchmark catalyst E showed somewhat higher
productivities in the RCM reaction of N,N-diallyltolu-
ene-4-sulfonamide than the backbone-substituted 8.
However, values for 8 are still in a viable range and
are clearly adequate for use of the novel system in RCM
applications, bearing in mind that a different catalyst
may be optimal for each individual substrate. The subtle
influence of the remote olefinic group in 8 that appar-
Experimental Section
General Details. All operations were carried out under an
inert atmosphere of argon using standard vacuum and Schlenk
techniques or in a glovebox under an atmosphere of argon
(Labmaster 130, MBraun, Germany). All solvents were dried
and purified by passing through suitable drying columns or
by employing standard drying agents.26,27 N,N-Diallyltoluene-
4-sulfonamide was prepared from diallylamine, tosyl chloride,
and triethylamine in CH2Cl2. (SIMes)Cl2RudC(H)(C6H4OiPr-
2) was prepared according to the literature procedure.7a Ag2O
(Merck), 1 M KOtBu/THF (Aldrich), [RhCl(cod)]2 (Aldrich), and
(PCy3)Cl2RudC(H)(C6H4OiPr-2) (Aldrich) were used as re-
1
ceived. H and 13C NMR spectra were recorded on a Bruker
DPX 250 Advance or Bruker AMX 300 at ambient tempera-
ture. Data are given in ppm relative to solvent signals for 1H
and 13C NMR spectra. IR spectra were recorded on a Bruker
(23) (a) Armstrong, S. K. J. Chem. Soc., Perkin Trans. 1998, 1, 371.
(b) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413. (c) Fu¨rstner,
A. Top. Organomet. Chem.1998, 37. (d) Fu¨rstner, A. Angew. Chem.
2000, 112, 3140; Angew. Chem., Int. Ed. 2000, 39, 3012. (e) Astruc, D.
New J. Chem. 2005, 29, 42.
(24) (a) Schu¨rer, S. C.; Gessler, S.; Buschmann, N.; Blechert, S.
Angew. Chem. 2000, 112, 4062. (b) Randl, S.; Buschmann, N.; Connon,
S. J.; Blechert, S. Synlett 2001, 10, 1547.
(25) Connon, S. J.; Blechert, S. Angew. Chem. 2003, 115, 1944;
Angew. Chem., Int. Ed. 2003, 42, 1900.
(26) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: New York, 1988.
(27) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.

Ruthenium Catalyst in Olefin Metathesis
Organometallics, Vol. 24, No. 16, 2005 4055
Equinox 55 FT-IR instrument as KBr pellets. Bands are
characterized as broad (br), strong (s), medium (m), and weak
(w). Elemental analyses were measured using a Vario EL. The
temperature of the combustion tube was 1150 °C and of the
reducing tube 850 °C. He (99.996%) and O2 (99.995%) were
used as supply gases. Melting points were obtained on a Bu¨chi
B-540 capillary apparatus. Mass spectra were collected using
a Thermo LCQ-DECA (ESI, H2O/MeCN ) 70:30) and Waters
VG AutoSpec (EI). HPLC chromatograms were recorded on a
Merck Hitachi Elite LaChrom. All silica gel column chroma-
tography was driven with argon and performed with silica gel
60 (0.040-0.063 mm, pH (10% suspension) 6.5-7.5, surface
area 480-540 m2/g; pore volume 0.74-0.84 mL/g).
Chloro(η4-1,5-cyclooctadiene)-[(4R,5S)-4,5-diallyl-1,3-
bis(2,4,6-trimethylphenyl)-4,5-dihydro-3H-imidazolin-2-
ylidene]rhodium(I) (5). A flask was charged with the
imidazolium salt 1b (205 mg, 0.48 mmol) and 5 mL of THF.
KOtBu solution (1 M) in THF (0.5 mL, 0.48 mmol) was added,
and the reaction solution was stirred for 45 min at room
temperature. Dimeric [RhCl(cod)]2 (100 mg, 0.20 mmol) in 3
mL of toluene was added and stirred at 80 °C for 1 h. After
filtration all volatiles were removed under vacuum. The
resulting solid was purified by column chromatography (silica,
CH2Cl2/MeOH ) 20:1). After removal of the solvent under
vacuum the solid was washed with hexane. The resulting
yellow solid was dried under vacuum. Yield: 77 mg, 0.13 mmol,
1
31%. Mp: 154 °C. H NMR (250 MHz, CD3CN): δ 1.39-1.89
Bis[(4R,5S)-4,5-diallyl-1,3-bis(2,4,6-trimethylphenyl)-
4,5-dihydro-3H-imidazolin-2-ylidene]silver(I) tetrafluo-
roborate (2). To a suspension of silver(I) oxide (15.4 mg, 0.11
mmol) in 20 mL water was added the imidazolium salt 1a (100
mg, 0.21 mmol), and the reaction mixture was stirred for 2
days at room temperature. The precipitate was isolated and
resolved in THF. After filtration the solvent was removed
under vacuum and the resulting colorless solid was dried
under vacuum. Yield: 91 mg, 0.09 mmol, 85%. Mp: 186 °C.
1H NMR (250 MHz, CDCl3): δ 1.85 (s, 12 H, o-C6H2(CH3)2),
1.92 (s, 12 H, o-C6H2(CH3)2), 2.10-2.21 (m, 4 H, CH2CdC),
2.38 (s, 12 H, p-C6H2CH3), 2.41-2.52 (m, 4 H, CH2CdC), 4.36
(m, 8 H, cod-CH2, isomer 1 + 2), 2.29, 2.34, 2.40, 2.56, 2.68 (s,
18 H, C6H2(CH3)3, isomer 1 + 2), 2.59 (m, 2 H, CH2CdC, isomer
1 + 2), 3.07-3.13 (m, 2 H, cod-CHdCH, isomer 1), 3.37-3.43
(m, 2 H, cod-CHdCH, isomer 2), 4.17-4.29 (m, 2 H, NCHCHN,
isomer 1 + 2), 4.42-4.54 (m, 2 H, cod-CHdCH, isomer 1 + 2),
4.94-5.04 (m, 4 H, CHdCH2, isomer 1 + 2), 5.44-5.73 (m, 2
H, CHdCH2, isomer 1 + 2), 6.94, 6.96, 6.98, 7.04 (s, 4 H, Aryl
C6H2Me3, isomer 1 + 2) (the second signal of CH2CdC is
covered by the signal of C6H2(CH3)3). 13C NMR (75.5 MHz,
CDCl3): δ major isomer, 19.2, 21.0, 21.9 (C6H2(CH3)3), 28.0,
31.9, 32.6 (cod-CH2, CH2CdC), 66.1 (NCHCHN), 67.2 (d, 1JRhC
1
) 14.6 Hz, cod-CHdCH), 97.3 (d, JRhC ) 6.9 Hz, cod-CHd
3
2
(m, 4 H, NCHCH2), 4.84 (dd, J ) 10.2 Hz, J ) 1.3 Hz, 4 H,
CH), 117.1 (CHdCH2), 128.7, 130.3 (Aryl C3,5), 134.6 (CHd
CdC(H)H), 4.90 (dd, 3J ) 17.2 Hz, 2J ) 1.3 Hz, 4 H, CdC(H)-
1
CH2), 135.1, 135.7, 137.7, 139.4 (Aryl C1,2,4,6), 214.7 (d, JRhC
3
3
3
H), 5.35 (ddt, J ) 16.8 Hz, J ) 10.4 Hz, J ) 6.4 Hz, 4 H,
CHdCH2), 6.81 (s, 4 H, C6H2Me3), 6.85 (s, 4 H, C6H2Me3). 13
) 48.2 Hz, NCN); δ minor isomer, 20.0, 20.3, 21.6 (C6H2(CH3)3),
28.1, 31.7, 32.7 (cod-CH2, CH2CdC), 65.4 (NCHCHN), 68.4 (d,
C
NMR (75.5 MHz, CDCl3): δ 17.7, 18.5 (o-C6H2(CH3)2), 21.1 (p-
C6H2CH3), 32.1 (CH2CdC), 65.2 (NCHCH2), 117.6 (CHdCH2),
1
1JRhC ) 14.7 Hz, cod-CHdCH), 97.0 (d, JRhC ) 7.2 Hz, cod-
CHdCH), 117.1 (CHdCH2), 128.4, 130.2 (Aryl C3,5), 134.4
129.5, 129.7 (Aryl C3,5), 133.2 (CHdCH2), 134.3 (Aryl C4),
1
(CHdCH2), 136.5, 138.5 (Aryl C1,2,4,6), 214.3 (d, JRhC ) 48.2
1
135.5, 135.8 (Aryl C2,6), 138.5 (Aryl C1), 206.5 (AgC, J107Ag
)
Hz, NCN). IR (KBr, cm-1): 2920 (s), 2872 (w), 2826 (w), 1640
(m), 1609 (m), 1478 (s), 1448 (w), 1428 (w), 1402 (vs), 1378
(w), 1262 (vs), 1244 (w), 1151 (w), 1101 (w), 1014 (m), 933 (w),
955 (w), 911 (m), 850 (m), 815 (w), 801 (w), 730 (m), 653 (w),
574 (w). MS (EI, m/z (%)): 632 (40) [M+], 597 (12) [M+ - Cl],
488 (55) [M+ - Cl - cod], 387 (100) [M+ - Cl - cod - Rh].
Anal. Calcd for C35H46ClN2Rh (mol wt 633.11): C, 66.4; H, 7.3;
N, 4.4. Found: C, 66.7; H, 7.6; N, 4.4.
170.4 Hz, 1J109Ag ) 196.3 Hz). IR (KBr, cm-1): 3078 (w), 2978
(w), 2920 (m), 2861 (w), 1634 (m), 1609 (w), 1483 (s), 1377 (w),
1309 (w), 1274 (m), 1231 (w), 1054 (vs), 911 (w), 856 (w), 573
(w), 520 (w). MS (ESI, m/z (%)): 881 (100) [M+ - BF4], 799
(22) [M+ - BF4 - 2 C3H5], 534 (39) [M+ - BF4 - C27H34N2 +
MeCN], 511 (70) [M+ - BF4 - C27H34N2 + H2O], 495 (18) [M+
- BF4 - C27H34N2]. Anal. Calcd for C54H68N4AgBF4 (mol wt
967.85): C, 67.0; H, 7.1; N, 5.8. Found: C, 67.3; H, 7.4; N,
5.8.
(1,3-Bis(2,4,6-trimethylphenyl)-3a,4,7,7a-tetrahydro-
3H-benzimidazolin-2-ylidene)dichloro(2-isopropanolato-
benzylidene)ruthenium(II) (8). A flask was charged with
the imidazolium salt 6 (89 mg, 0.2 mmol) and 5 mL of THF.
KOtBu solution (1 M) in THF (200 µL, 0.2 mmol) was added,
and the reaction solution was stirred for 15 min at room
temperature. The resulting suspension was added to a solution
of (PCy3)Cl2RudC(H)C6H4OiPr-2 (100 mg, 0.17 mmol) in 3 mL
of toluene. After stirring for 1 h at 80 °C all volatiles were
removed in a vacuum. To the resulting residue was added 4
mL of CHCl3, and the mixture was stirred for an additional
16 h at room temperature. After removal of the volatiles under
vacuum the residue was purified by column chromatography
(silica, CH2Cl2). The green fraction was isolated, and the
solvent was removed under vacuum. The resulting green solid
was dried under vacuum. Yield: 71 mg, 0.11 mmol, 63%. Mp:
[(4R,5S)-4,5-Diallyl-1,3-bis(2,4,6-trimethylphenyl)-4,5-
dihydro-3H-imidazolin-2-ylidene]silver(I) chloride (3).
To a suspension of silver oxide (8.3 mg, 0.04 mmol) in 5 mL of
THF was added the imidazolium salt 1b (30 mg, 0.07 mmol),
and the reaction mixture was stirred for 16 h at room
temperature. After filtration the product was precipitated by
adding pentane. The resulting colorless solid was filtered,
washed with pentane, and dried under vacuum. Yield: 35 mg,
1
0.07 mmol, 94%. Mp: 226 °C. H NMR (250 MHz, CDCl3): δ
2.26 (s, 6 H, o-C6H2CH3), 2.29 (s, 6 H, o-C6H2CH3), 2.34 (m, 2
H, CH2CdC), 2.36 (s, 6 H, p-C6H2CH3), 2.54-2.64 (m, 2 H,
CH2CdC), 4.44 (m, 2 H, NCHCH2), 4.94 (dd, 3J ) 10.2 Hz, 2J
) 1.3 Hz, 2 H, CdC(H)H), 4.98 (dd, 3J ) 17.1 Hz, 2J ) 1.5 Hz,
3
3
3
2 H, CdC(H)H), 5.46 (ddt, J ) 17.1 Hz, J ) 10.3 Hz, J )
6.7 Hz, 2 H, CHdCH2), 6.91, 6.93 (s, 4 H, C6H2Me3). 13C NMR
(75.5 MHz, CDCl3): δ 18.2, 19.3 (o-C6H2(CH3)2), 21.0 (p-
C6H2CH3), 32.0 (CH2CdC), 65.4, 65.5 (NCHCH2), 117.7 (CHd
CH2), 130.0, 130.1 (Aryl C3,5), 133.5 (CHdCH2), 134.5 (Aryl
C4), 135.2, 136.1 (Aryl C2,6), 138.7 (Aryl C1), 207.1 (AgC, 1J107Ag
) 224.4 Hz, 1J109Ag ) 259.1 Hz). IR (KBr, cm-1): 3073 (w), 2977
(w), 2918 (m), 2854 (w), 1639 (m), 1610 (m), 1482 (vs), 1464
(vs), 1377 (m), 1311 (w), 1288 (m), 1277 (m), 995 (m), 913 (m),
852 (m), 793 (w), 633 (w), 572 (w), 513 (w). MS (ESI, m/z (%)):
881 (100) [2 M+ - Ag - 2 Cl], 799 (20) [2 M+ - Ag - 2 Cl -
2 C3H5], 534 (30) [M+ - Cl + MeCN], 511 (87) [M+ - Cl +
H2O], 494 (19) [M+ - Cl]. Anal. Calcd for C27H34N2AgCl (mol
wt 529.88): C, 61.2; H, 6.5; N, 5.3. Found: C, 60.6; H, 6.6; N,
5.1.
1
3
105 °C dec. H NMR (250 MHz, CDCl3): δ 1.25 (d, J ) 6.1
Hz, 6 H, OCH(CH3)2), 2.06-2.17 (m, 2 H, NCHCH2), 2.31-
2.41 (m, 2 H, NCHCH2), 2.40 (s, 12 H, o-C6H2(CH3)2), 2.48 (s,
3
6 H, p-C6H2CH3), 4.74 (s, 2 H, NCHCHN), 4.86 (septet, J )
6.2 Hz, 1 H, OCH(CH3)2), 6.00 (m, 2 H, CHdCH), 6.77 (d, 1 H,
3J ) 8.3 Hz, C6H4), 6.80-6.87 (m, 1 H, C6H4), 6.90 (dd, 1 H, 3J
4
) 7.5 Hz, J ) 1.9 Hz, C6H4), 7.07 (s, 4 H, C6H2Me3), 7.42-
7.52 (m, 1 H, C6H4), 16.46 (s, 1 H, RudCH). 13C NMR (75.5
MHz, CDCl3): δ 21.0, 21.2 (OCH(CH3)2, C6H2(CH3)3), 25.6
(NCHCH2), 62.2 (NCHCHN), 74.8 (OCH(CH3)2), 112.9, 122.2,
122.7, 127.4, 129.5 129.6, 129.9 (C6H4 C2,3,4, CHdCH, C6H2-
Me3 C3,5), 138.6, 140.0, 145.6, 152.1 (C6H4 C1,6, C6H2Me3 C1,2,4,6),
213.2 (NCN), 298.3 (RudCH). IR (KBr, cm-1): 2972 (m), 2919
(s), 2854 (w), 1607 (w), 1589 (s), 1575 (s), 1476 (vs), 1452 (vs),

4056 Organometallics, Vol. 24, No. 16, 2005
Table 2. Crystal Data and Refinement Details for 2, 3, and 8
Weigl et al.
2
3
8
-
empirical formula
fw
C
54H68AgN4+, BF4
967.80
C
27H34AgClN2
C35H42Cl2N2ORu
678.70
529.88
cryst size [mm]
cryst syst
0.48 × 0.41 × 0.36
orthorhombic
Pccn (No. 56)
18.3537(6), 90
23.3319(8), 90
23.5876(12), 90
10100.8(7)
1.273
0.27 × 0.23 × 0.21
monoclinic
C2/c (No. 15)
8.4002(11), 90
16.1489(13), 100.859(9)
19.953(2), 90
2658.3(5)
0.27 × 0.18 × 0.15
triclinic
space group
a [Å], R [deg]
b [Å], â [deg]
c [Å], γ [deg]
V [Å3]
P1h (No. 2)
9.1068(7), 89.870(6)
11.6390(9), 79.381(6)
15.9346(12), 74.296(6)
1596.1(2)
F
calcd [g cm-3
]
1.324
1.412
Z
8
4
2
F(000)
4064
0.453
1096
704
µ [mm-1
]
0.874
0.689
Tmax/Tmin
hkl range
0.8838/0.7611
(21, -24 to +27, -27 to +25
1.41-24.82
39 184
8677 [0.0406]
5727
0.8812/0.7472
(9, (18, -23 to +22
2.08-24.78
13 084
2279 [0.0509]
1902
0.9266/0.7515
-9 to +10, (13, (18
1.82-24.81
16 290
5470 [0.0369]
4627
θ range [deg]
no. of measd reflns
no. of unique reflns [Rint
no. of obsd reflns I > 2σ(I)
no. of refined params
goodness-of-fit
]
679
1.004
141
1.034
378
1.034
R1, wR2 (I>2σ(I))
R1, wR2 (all data)
0.0476, 0.1347
0.0743, 0.1468
1.043/-0.577
0.0497, 0.1348
0.0606, 0.1419
0.788/-0.710
0.0412, 0.1055
0.0526, 0.1103
2.060 (near Ru)/-0.389
resid el dens [e Å-3
]
1418 (s), 1384 (vs), 1312 (w), 1261 (vs), 1236 (vs), 1198 (w),
1155 (m), 1139 (m), 1113 (vs), 1098 (w), 1034 (m), 938 (s), 877
(w), 851 (m), 841 (m), 798 (m), 746 (s), 679 (m), 663 (w), 577
(m). MS (EI, m/z (%)): 678 (53) [M+], 600 (10) [M+ - C3H7Cl],
563 (23) [M+ - C3H7Cl - Cl], 494 (45) [(C25H30N2)RuCl+], 458
(50) [(C25H30N2)Ru+], 359 (45) [C25H30N2+], 41 (100) [C3H5+].
Anal. Calcd for C35H42Cl2N2ORu (mol wt 678.70 g/mol): C,
61.9; H, 6.2; N, 4.1. Found: C, 61.8; H, 6.2; N, 4.1.
General Procedure for Ring-Closing Metathesis Reac-
tion (RCM). N,N-Diallyl-4-toluenesulfonamide was purified
by Kugelrohr distillation (4.2 × 10-1 mbar, 300 °C) shortly
before use in the RCM reaction. The RCM reaction was
performed under argon in a Carousel Reaction Station (Dis-
covery Technologies). A 0.05 M solution of N,N-diallyl-4-
toluenesulfonamide in CH2Cl2 was stirred under reflux for 30
min. A solution of the Ru catalyst 8 or (SIMes)Cl2RudC(H)-
(C6H4OiPr-2) in toluene was then added to the substrate
solution, and the reaction mixture was stirred at 45 °C for 17
h. Product formation was monitored by HPLC.
of the non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were placed in calculated positions and
assigned to an isotropic displacement parameter of 0.08 Å2.
-
The BF4 anion in 2 is positioned on two distinct 2-fold axes
with half-occupancy and is disordered in one case. DFIX (dB-F
) 1.365 Å) and SADI restraints were applied to model the
disorder. The atoms were refined isotropically. Parts of the
carbene ligands in 2 are disordered about two positions
(occupancy factors C5-C6: 0.756(17)/0.244(17); C29>C36:
0.683(6)/0.317(6)). DFIX (dCdC ) 1.30 Å), SADI (N3-C29, N4-
C30), and SAME (C29>C36) restraints were applied to model
the disorder. The carbon atoms were refined anisotropically
by use of DELU and SIMU restraints. Parts of the carbene
ligand (C2>C9) in 3 are disordered about a 2-fold axis. DFIX
(dCdC ) 1.30 Å, dC-C ) 1.50 (-C-Cd) and 1.53 Å (-C-C-))
and DANG (dCd(C)-C) ) 2.5 Å) restraints were applied to model
the disorder. The atoms were refined isotropically. Face-
indexed absorption corrections were performed numerically
with the program X-RED.29
X-ray Crystal Structure of 2, 3, and 8. X-ray data were
collected on a STOE IPDS II diffractometer (graphite mono-
chromated Mo KR radiation, λ ) 0.71073 Å) by use of ω scans
at -140 °C for 2 and 8 (Table 2). After crystal decomposition
was observed at -140 °C, X-ray data for 3 were collected at
-50 °C (Table 2). The structures were solved by direct methods
and refined on F2 using all reflections with SHELX-97.28 Most
Acknowledgment. K.K. and K.W. thank the ana-
lytical department of Merck KGaA for NMR, IR, and
MS measurements and C,H,N analyses.
Supporting Information Available: X-ray data of 2, 3,
and 8 as a CIF file. This material is available free of charge
via the Internet at http://pubs.acs.org.
(28) Sheldrick, G. M. SHELXL-97 Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997. Sheld-
rick, G. M. SHELXS-97 Program for Crystal Structure Solution;
Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997.
OM0503242
(29) X-RED; STOE & CIE GmbH: Darmstadt, Germany, 2002.