Synthesis and RCM activity of [(NHC)(NHCewg)RuCl 2(3-phenylindenylid-1-ene)] complexes

Article abstract of DOI:10.1021/om1002717

[(NHC)RuCl₂(3-phenylindenylid-1-ene)(py)] (1) serves as a convenient starting material for the synthesis of [(NHC)(NHC_ewg) RuCl₂(3-phenylindenylid-1-ene)] complexes 3a-3g utilizing [AgI(NHC_ewg)] complexes (2) as NHC transfer reagents. The respective complexes 3 display excellent activities in RCM reactions leading to tetrasubstituted olefins. The most active precatalyst, 3f, is characterized by 3,4-dichloro and N,N′-diethyl substituents and can be obtained in 94% isolated yield. The redox potentials of complexes 3 and the crystal structure of 3g (3,4-dichloro and N,N′-diisopropyl substituents) were determined.

Full text of DOI:10.1021/om1002717

Organometallics 2010, 29, 2761–2766 2761
DOI: 10.1021/om1002717
Synthesis and RCM Activity of
[(NHC)(NHCewg)RuCl2(3-phenylindenylid-1-ene)] Complexes
Lars H. Peeck and Herbert Plenio*
€
Organometallic Chemistry, Technische Universitat Darmstadt, Petersenstrasse 18, 64287 Darmstadt,
Germany
Received April 6, 2010
[(NHC)RuCl2(3-phenylindenylid-1-ene)(py)] (1) serves as a convenient starting material for the
synthesis of [(NHC)(NHCewg)RuCl2(3-phenylindenylid-1-ene)] complexes 3a-3g utilizing [AgI-
(NHCewg)] complexes (2) as NHC transfer reagents. The respective complexes 3 display excellent
activities in RCM reactions leading to tetrasubstituted olefins. The most active precatalyst, 3f, is
characterized by 3,4-dichloro and N,N0-diethyl substituents and can be obtained in 94% isolated
yield. The redox potentials of complexes 3 and the crystal structure of 3g (3,4-dichloro and N,N0-
diisopropyl substituents) were determined.
Introduction
is significantly reduced7 and that such ligands display
electron donation comparable to PCy3 or PEt3.7a,8 Conse-
quently, the replacement of PCy3 in Grubbs second-generation
complexes by NHCewg offered the chance to obtain more
active [(NHC)(NHCewg)RuCl2(CHPh)] species than
[(NHC)2RuCl2(CHPh)]. Indeed such complexes (H and I
in Scheme 1) turned out to be very useful in ring-closing
metathesis (RCM) reactions of sterically hindered sub-
strates, leading to tetra-substituted olefins.9 Complex H
(Scheme 1) with a tetranitro NHCewg ligand was the first
example of such a [(NHC)(NHCewg)RuCl2(CHPh)] com-
plex. However, in order to further improve the catalytic
performance of such complexes, more easily modifiable
NHCewg ligands were required. 3,4-Substituted N,N0-dialkyl
imidazolinium salts are useful precursors for NHCewg ligands
with variable electron donation (via the 3,4-substituents) as
well as steric bulk (via the N,N0-substituents). Optimization
of steric and electronic properties finally led to a modified
NHCewg ligand with 3,4-dichloro-N,N0-methyl, isopropyl
substituents. The respective [AgI(NHCewg)] complex was
reacted with C to generate the respective bisNHC complex
(I in Scheme 1) with further improved reactivity for RCM
reactions, leading to tetrasubstituted olefins.
Active (pre)catalysts of the Grubbs type for olefin metath-
esis reactions are often characterized by the presence of good
leaving groups trans to an N-heterocyclic carbene (NHC)
ligand.1 This is exemplified in Grubbs second-generation (A
in Scheme 1), Grubbs-Hoveyda (B), and Grubbs third-
generation complexes (C). Consequently, it was not surpris-
ing that complexes with a second NHC ligand in this position
are not ideal, since such ligands are bonded more tightly than
phosphines.2 Indeed, the [(NHC)2RuCl2(CHPh)] complexes
synthesized by Herrmann et al. (D,3 or Grubbs (E)4 turned
out to display only modest activities in olefin metathesis
reactions. Until recently bisNHC complexes were considered
to be less useful in olefin metathesis reactions, and this is why
only few such complexes (F and G in Scheme 1)5 have been
studied.6
In 2007 we realized that the donor ability of NHC ligands
substituted with electron-withdrawing substituents (NHCewg)
*To whom correspondence should be addressed. E-mail: plenio@
tu-darmstadt.de.
(1) Samojzowicz, C.; Bieniek, M.; Grela, K. Chem. Rev. 2009, 109,
3708.
(2) Hillier, A. C.; Sommer, W. J.; Yong, B. S.; Petersen, J. L.; Cavallo,
L.; Nolan, S. P. Organometallics 2003, 22, 4322.
(3) Weskamp, T.; Schattenmann, W. C.; Spiegler, M.; Herrmann,
Apart from the catalytic properties, the application of
complexes in catalysis also depends on the facile synthetic or
commercial availability and the stability of the precatalyst.
W. A. Angew. Chem., Int. Ed. 1998, 38, 2490.
(4) 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.
The indenylidene complexes introduced by Nolan et al.10
and Furstner et al. combine these properties12 and show
11
€
(5) (a) Rosen, E. L.; Sung, D. H.; Chen, Z.; Lynch, V. M.; Bielawski,
C. W. Organometallics 2009, 29, 250. (b) Ledoux, N.; Allaert, B.; Linden,
A.; Voort, P. V. D.; Verpoort, F. Organometallics 2007, 26, 1052.
(6) (a) Piermattei, A.; Karthikeyan, S.; Sijbesma, R. P. Nature Chem.
2009, 1, 133. (b) Zhang, W.; Bai, C.; Lu, X.; He, R. J. Organomet. Chem.
2007, 692, 3563.
€
(8) Leuthausser, S.; Schwarz, D.; Plenio, H. Chem.;Eur. J. 2007, 13,
7195.
€
(9) (a) Vorfalt, T.; Leuthausser, S.; Plenio, H. Angew. Chem., Int. Ed.
2009, 48, 5191. (b) Sashuk, V.; Peeck, L. H.; Plenio, H. Chem.;Eur. J.
2010, 16, 3983.
(10) (a) Jafarpour, L.; Schanz, H.-J.; Stevens, E. D.; Nolan, S. P.
Organometallics 1999, 18, 5416. (b) F€urstner, A.; Thiel, O. R.; Ackermann,
L.; Schanz, H.-J.; Nolan, S. P. J. Org. Chem. 2000, 65, 2204.
€
(7) (a) Leuthausser, S.; Schmidts, V.; Thiele, C. M.; Plenio, H.
ꢀ
Chem.;Eur. J. 2008, 14, 5465. (b) Viciano, M.; Mas-Marza, E.; Sanaꢀu,
M.; Peris, E. Organometallics 2006, 25, 3063. (c) Khramov, D. M.; Lynch,
V. M.; Bielawski, C. W. Organometallics 2007, 26, 6042. (d) Siemeling, U.;
€
(11) Furstner, A.; Grabowski, J.; Lehmann, C. W. J. Org. Chem.
€
ꢀ
Farber, C.; Bruhn, C. Chem. Commun. 2009, 98. (e) Cesar, V.; Lugan, N.;
Lavigne, G. Eur. J. Inorg. Chem. 2010, 2010, 361. (f ) Hudnall, T. W.;
Bielawski, C. W. J. Am. Chem. Soc. 2009, 131, 16039.
1999, 64, 8275.
(12) Dorta, R.; Kelly, R. A.; Nolan, S. P. Adv. Synth. Catal. 2004,
346, 917.
r
2010 American Chemical Society
Published on Web 06/03/2010
pubs.acs.org/Organometallics

2762 Organometallics, Vol. 29, No. 12, 2010
Peeck and Plenio
Scheme 1. Grubbs Second- and Third-Generation (A, C), Grubbs-Hoveyda Complex (B), [(NHC)2RuCl2(CHPh)] (D, E, F, G), and
[(NHC)(NHCewg)RuCl2(CHPh)] (H, I) Complexes Utilized in Olefin Metathesis
Scheme 2. Synthesis of [(NHC)(NHCewg)RuCl2(3-phenylinde-
due to the significantly higher reaction temperatures (100 °C)
nylid-1-ene)] Complexes 3a-3g via Reactions of Complex 1 with
the Various [AgI(NHCewg)] Complexes 2a-2g
required for the pyridine versus NHCewg substitution. In the
case of complex 3a with hydrogen atoms in the 3,4-position,
the lower stability may have led to the loss of this complex in
the course of the chromatographic purification. However,
complexes 3b-3g are highly stable for extended periods of
time in the solid state and in solution, even when exposed to
air and moisture.
Crystal Structure of 3g. We determined the crystal
structure15 of a single member in the series of complexes
3a-3g to learn whether there are unusual structural features.
The diisopropyl-substituted complex 3g was chosen, since it
contains the most bulky NHCewg ligand. Single crystals were
obtained by slow evaporation of a CH2Cl2/iPrOH solution
of 3g under ambient atmosphere over the course of several
days. The practicability of such an approach provides evi-
dence for the high stability of complex 3g. The structure of
3g, featuring trans NHC groups and trans chloro substitu-
ents, is as expected (Figure 1). Moderate distortions from an
ideal trigonal-planar geometry appear to be due to the bulky
isopropyl groups. Despite the very different electronic and
steric properties of the two NHC ligands, the two Ru-
C(NHC) bond lengths in 3g are virtually identical (205.2(9)
and 205.7(9) pm). The similarity of the two Ru-C(NHC)
bonds in other Ru complexes with different NHC ligands
was observed previously. However, despite the considerable
steric bulk in the present complex, the respective Ru-
C(NHC) bonds in 3g are significantly shorter than in related
(NHC)(NHC0)Ru complexes [(207.2 and 207.8 pm)9b or
(211.2 and 213.2 pm)5a or (207.3 and 208.6 pm; 212.1 and
212.2 pm)]5b or in symmetrical bisNHC complexes, which
range from 210.3 to 211.7 pm.3,6b,16
excellent performance in various olefin metathesis reactions.13
This is why we initiated a study aimed at preparing and testing
the respective (NHC)(NHCewg)Ru complexes in RCM reac-
tions.
Synthesis of [(NHC)(NHCewg)RuCl2(3-phenylindenylid-1-
ene)] Complexes 3a -3g. Compared to our previous work,9
we have now considerably simplified the synthesis of
[(NHC)(NHCewg)RuCl2(CHR)] complexes. A one-step re-
action from the commercially available complex14 1 with a
[AgI(NHCewg)] complex (2a-2g) yields the respective com-
plexes 3a-3g, five of them (3b,c e,f,g) in excellent yields
(Scheme 2). Notably, the catalytically most active complex,
3f (Table 2), was obtained in 94% yield at 60 °C. The lower
yield (75%) for the cyano-substituted complex 3d is probably
(13) (a) Clavier, H.; Nolan, S. P. Chem.;Eur. J. 2007, 13, 8029.
(b) Clavier, H.; Urbina-Blanco, C. A.; Nolan, S. P. Organometallics 2009, 28,
2848. (c) Monsaert, S.; Canck, E. D.; Drozdzak, R.; Voort, P. V. D.; Verpoort,
F.; Martins, J. C.; Hendrickx, P. M. S. Eur. J. Org. Chem. 2009, 655.
(d) Bieniek, M.; Michrowska, A.; Usanov, D. L.; Grela, K. Chem.;Eur. J.
2008, 14, 806. (e) Boeda, F.; Clavier, H.; Nolan, S. P. Chem. Commun. 2008,
2726. (f) Boeda, F.; Bantreil, X.; Clavier, H.; Nolan, S. P. Adv. Synth. Catal.
Electrochemistry of [(NHC)(NHCewg)RuCl2(3-phenylinde-
nylid-1-ene)] Complexes. The redox potentials of complexes
3a-3g were determined by cyclic voltammetry in CH2Cl2
ꢀ
2008, 350, 2959. (g) Clavier, H.; Correa, A.; Escudero-Adan, E. C.; Benet-
(15) (a) Sheldrick, G. M. Acta Crystallogr. A 2008, 64, 112. (b)
Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(16) Conrad, J. C.; Yap, G. P. A.; Fogg, D. E. Organometallics 2003,
22, 1986.
Buchholz, J.; Cavallo, L.; Nolan, S. P. Chem.;Eur. J. 2009, 15, 10244.
(14) Burtscher, D.; Lexer, C.; Mereiter, K.; Winde, R.; Karch, R.;
Slugovc, C. J. Polym. Sci. A 2008, 46, 4630.

Article
Organometallics, Vol. 29, No. 12, 2010 2763
Table 1. Ru(II/III) Redox Potentials E of
[(NHC)(NHCewg)RuCl2(3-phenylindenylid-1-ene)] Complexes
3a-3ga
Figure 1. Crystal structure of 3g (CCDC 770090). Important
bond lengths (pm) and angles (deg): Ru-C(NHC) 205.2(9),
Ru-C(NHCewg) 205.7(9), Ru-C(indenylidene) 186.3(9), Ru-Cl
(239.3(3), 239.6(3), (NHC)C-Ru-C(NHCewg) 160.4(4), Cl-
Ru-Cl 162.6(1).
(Table 1) in order to learn about the influence of NHCewg
ligands on the Ru(II/III) redox potentials. In general, the
complexes studied here are characterized by a reversible elec-
trochemistry. The redox potentials range from E = þ0.458 V
(3a) to E = þ0.669 V for the cyano-substituted complex 3d.
The redox potentials in the series of complexes 3a-3d
accurately reflect the electron-donating ability of the various
17
X, Y substituents attached to the NHCewg and are con-
sistently (by ca. 30-50 mV) more cathodic than those of the
related benzylidene complexes.9b This points to a slightly
stronger electron-donating effect of the indenylidene group
compared to benzylidene. In the steric series 3b, 3e, 3f,
and 3g even subtle effects, such as the improved donation
of -CH(CH3)2 > -C2H5 > -CH3 groups, are evident in
the ordering of the redox potentials. There is, however, no
correlation of the redox potentials and the catalytic activity
of complexes 3.
a Conditions: solvent CH2Cl2 (0.1 M NBu4PF6) at 293 K; referenced
vs FcMe8 (E = -0.010 V); scan rate 100 mV s-1. ΔE is the difference of
the respective anodic and cathodic peak potentials.
Catalytic Activity of Complexes 3a-3g in RCM Reactions.
Various [(NHC)(NHCewg)RuCl2(CHPh)] complexes were
shown to be excellent catalysts for RCM reactions involving
sterically demanding substrates. Until recently such sub-
strates were considered to be difficult.18 We first screened
all of the precatalysts 3a-3g in two different olefin meta-
thesis reactions (Scheme 3).
Scheme 3. Test Reactions for Catalyst Evaluation
The screening results for substrates S1 and S2 are sum-
marized in Table 2. Indenylidene complexes normally re-
quire higher reaction temperatures than the corresponding
benzylidene complexes. For the complexes 3b-3g studied
here, 100 °C is necessary for efficient transformations. The
only exception is the less stable complex 3a, which gives
better results at 80 °C, but at the same time is the least effi-
cient one of the complexes studied here. For S1 at 0.5 mol %
loading (Table 1, entry 1) little discrimination between
3a-3g was observed; nonetheless 3f is the top performer,
with 77% conversion. At 0.2 mol % loading (Table 1, entry 2)
the superiority of 3f is more obvious. At this loading a
number of RCM reactions were carried out at 80 °C reaction
temperature, but significantly lower yields were observed.
With S2 all of the complexes tested gave nearly quantitative
yields of the RCM product at 0.5 mol % loading (Table 2,
entry 3). At 0.2 mol % loading (Table 2, entry 4) this still
holds true for 3b and 3f; at 0.1 mol % (Table 2, entry 5) the
80% conversion with 3f and 77% with 3b are impressive. The
effect of high substrate concentration on the RCM perfor-
mance was tested; however, neither 1 mol/L nor neat sub-
strate led to improvements.
(17) Hansch, C.; Leo, A.; Taft, R. W. Chem. Rev. 1991, 91, 165.
(18) (a) Chung, C. K.; Grubbs, R. H. Org. Lett. 2008, 10, 2693.
(b) Kuhn, K. M.; Bourg, J.-B.; Chung, C. K.; Virgil, S. C.; Grubbs, R. H.
J. Am. Chem. Soc. 2009, 131, 5313. (c) Samojowicz, C.; Bieniek, M.;
Zarecki, A.; Kadyrov, R.; Grela, K. Chem. Commun. 2008, 6282.
The combination of facile, efficient synthesis and superior
RCM performance of 3f motivated us to study this complex
for a number of additional transformations (Table 3). At
0.5 mol % loading most substrates are converted in >90%

2764 Organometallics, Vol. 29, No. 12, 2010
Table 2. Catalyst Comparison: RCM Reactions Using Model Substrates S1 and S2a
Peeck and Plenio
loading/
mol %
entry
substrate
3a
3b
3c
3d
3e
3f
3g
1
2
S1
S1
0.5
0.2
50b
71
37/5b
58
28/22b
67
69
24/3b
77
58/37b
63
45/23b
22/36b
42/3b
22c/18d
98
3
4
5
S2
S2
S2
0.5
0.2
0.1
92b
75b
58b
98
97
77
97
93
60
96
91
72
98
98
80
99
85
66
81, 32d
45
a 0.2 mmol of olefinic substrate in 10 mL of toluene (0.02 M), T = 100 °C, 24 h; Ru complexes were added as a stock solution (3 mmol/L in toluene).
Substrate conversion determined by GC (conversions given in %). b Reactions carried out at 80 °C. c Substrate conc 1 mol/L. d Neat substrate.
Table 3. RCM Reactions Leading to Tetrasubstituted Olefins
Using Complex 3f a
Figure 2. RCM of substrate S1 in the electronic series of com-
plexes 3a-3d (T = 100 °C, 0.2 mol % cat., conversion after 24 h:
3a (22%), 3b (37%), 3c (28%), 3d (42%)).
Figure 3. RCM of substrate S1 in the electronic series of com-
plexes 3b,e,f,g (T = 100 °C, 0.2 mol % cat., conversion after
24 h: 3b (37%), 3e (24%), 3f (58%), 3g (45%)).
complexes related to I.9b For the RCM of diallyldiphenylsilane,
complex 3f shows unprecedented RCM activity (entry 10).9b
The conversion-time plots (Figures 2, 3) for the RCM of
diethyl dimethallyl malonate (S1) lend additional support to
the high stability of complexes 3 and the activation behavior,
which depends on the electronic and steric nature of the
imidazolium substituents. Complexes 3a and 3c initiate rela-
tivelyfast, butappeartohave decomposed afterca. 4 h since at
around this time product formation comes to an end. 3b and
3d are much slower, and after 8 h only 15% conversion was
a General conditions see Table 1.
observed, compared to 42% after 24 h reaction time.
Within the steric series (Figure 3), the fastest initiating
catalyst provides the lowest substrate conversion after
24 h. Notably, this complex carries the NHCewg substituents
(N,N0-Me, iPr, and 3,4-Cl,Cl) that were considered as the
“best” substituents in the previously reported benzylidene
yield into the respective RCM products. The comparison
with previously published complexes reveals that complexes
3a-3g are more efficient than the tetranitro-NHC complex
H and comparable to the corresponding benzylidene

Article
Organometallics, Vol. 29, No. 12, 2010 2765
precatalysts.9b However, in the indenylidene series of com-
plexes 3 the same substituents result in a less efficient pre-
catalyst. The “best” precatalyst in the present study is
characterized by N,N0-Et, Et, and 3,4-Cl,Cl substituents,
while this pattern had been one of the poorest performers
in the previous benzylidene study.9b
performed using silica gel 60 F 254 (0.2 mm) on aluminum plates.
Preparative chromatography was performed using E. Merck silica
60 (0.063-0.02 mesh). GC experiments were run on a Clarus
500 GC with autosampler and FID detector. Column: Varian CP-
Sil 8 CB (l=15 m, di=0.25 mm, dF=1.0 μm), N2 (flow: 17 cm s-1
;
split 1:50); injector temperature: 270 °C, detector temperature:
350 °C. The following compounds were prepared according to
literature procedures: AgI(NHC) complexes,9b diethyl 2,2-bis-
(2-methylallyl)malonate,22 N,N-dimethallylsulfonamide.9b (NHC)-
(py)RuCl2(3-phenylindenylid-1-ene) (1) was provided by Umicore.
General Procedure for the Synthesis of [(NHC)(NHCewg)-
RuCl2(3-phenylindenylid-1-ene)] Complexes 3a-3g. [(NHC)(py)-
RuCl2(3-phenylindenylid-1-ene)] (100 mg, 0.14 mmol) and the
appropriatesilvercomplex(0.20mmol)weredissolvedin10mLof
toluene. The reaction mixture was heated to 60-100 °C (chosen
temperature depending on the silver complex). The reaction was
monitored via TLC. After 30 min, the solvent was evaporated in
vacuo and the crude product purified by column chromatography
(silica, cyclohexane/ethyl acetate, 2:1, v/v). The obtained product
was washed with cold pentane (-10 °C) to provide complexes
3a-3g as microcrystalline red solids (yields: 75-95%).
Complex 3a: reaction temperature 60 °C; dark red crystals,
yield 78 mg (75%). 1H NMR (500 MHz, CDCl3, 300 K): δ 8.60
(1H, d, J=7.4 Hz, indenylidene-H), 7.75 (2H, m, PhH), 7.49
(1H, tt, J=7.4, 1.2 Hz, indenylidene-H), 7.37 (2H, m, PhH), 7.25
(1H, td, J=7.4, 1.2 Hz, indenylidene-H), 7.21 (1H, s, indenyl-
idene-H ), 7.15 (1H, td, J=7.5, 1.0 Hz, PhH ), 7.12 (1H, d, J=7.4
Hz, indenylidene), 7.06 (2H, s, mesityl-H ), 6.56 (1H, d, J=1.8
Hz), 6.50 (1H, d, J=1.8 Hz, HC=CH ), 6.44 (1H, s, mesityl-H),
6.14 (1H, s, mesityl-H ), 4.09 (2H, m, NCH2CHAHBN), 3.94
(1H, m, NCH2CHAHBN), 3.84 (1H, m, NCH2CHAHBN), 3.27
(3H, s NCH3), 2.77 (3H, s, ArCH3), 2.70 (3H, s NCH3), 2.68
(3H, s, ArCH3), 2.36 (3H, s, ArCH3), 2.32 (3H, s, ArCH3), 1.99
(3H, s, ArCH3), 1.79 (3H, s, ArCH3). 13C NMR (126 MHz,
CDCl3, 300 K): δ 291.5, 221.7, 181.8, 143.6, 140.6, 140.4 (2
signals), 139.0, 137.3, 137.2, 137.1 (2 signals), 136.8 (2 signals),
136.7, 135.5, 129.7 (2 signals), 129.2, 129.0, 128.5, 128.4, 127.6,
127.3, 126.6, 123.3, 121.9, 116.4, 52.5, 51.8, 36.7, 36.2, 21.2, 21.1,
20.5, 18.8, 18.5. HRMS (EI): m/z calcd for C41H44N4Cl2Ru
764.1978, found 764.2003.
But why are the (NHC)(NHCewg)Ru complexes more effi-
cient than Grubbs second-generation or Grubbs-Hoveyda
complexes? We have shown before that the initiation reaction
of the [(NHC)(NHCewg)RuCl2(CHPh)] complexes involves
the dissociation of the NHCewg ligand.9b Consequently, all
of the complexes utilized here should finally generate the
same active species, which in turn should be the same as the
one generated from Grubbs-Hoveyda and Grubbs second-
generation complexes. Nonetheless, complexes 3 are much
more efficient for RCM reactions of sterically demanding
substrates. We therefore believe that the stability of the pre-
catalyst and the rate at which the active species is generated
from this precatalyst make the difference. When this rate
corresponds to the rate at which a certain substrate is con-
verted into the respective product (here tetrasubstituted
olefins) with the aid of the active catalyst, efficient substrate
conversion is observed.19
Summary and Conclusions
We have synthesized a series of easily available [(NHC)-
(NHCewg)RuCl2(CHR)] complexes in excellent yields from
easily available precursors. The activity of such precatalysts
in various RCM reactions leading to tetrasubstituted olefins
was studied and found to be superior to that of the previously
reported [(NHC)(NHC-tetranitro)RuCl2(CHPh)] complex
H. One of the main lessons learned from this study is that
the nature of the substituents at the NHCewg enables the fine-
tuning of the initiation rate and its adaption to the needs of
certain substrates.
Complex 3b: reaction temperature 60 °C; red crystals, yield
108 mg (95%). 1H NMR (500 MHz, CDCl3, 300 K): δ 8.56 (1H,
d, J=7.4 Hz, indenylidene-H ), 7.74 (2H, m, PhH ), 7.50 (1H, tt,
J=7.4, 1.2 Hz, indenylidene-H ), 7.38 (2H, t, J=7.6 Hz, PhH ),
7.26 (1H, td, J=7.4, 1.2 Hz, indenylidene-H ), 7.11-7.07 (2H,
overlapped signals, PhH þ indenylidene-H ), 7.11 (1H, d, J=
7.4 Hz, indenylidene-H ), 7.08 (2H, s, mesityl-H ), 6.44 (1H, s,
mesityl-H ), 6.17 (1H, s, mesityl-H ), 4.10 (2H, m, NCH2CHA-
HBN), 3.94 (1H, m, NCH2CHAHBN), 3.84 (1H, m, NCH2-
CHAHBN), 3.25 (3H, s, NCH3), 2.76 (3H, s, ArCH3), 2.71 (3H,
s, NCH3), 2.67 (3H, s, ArCH3), 2.38 (3H, s, ArCH3), 2.32 (3H, s,
ArCH3), 1.98 (3H, s, ArCH3), 1.79 (3H, s, ArCH3). 13C NMR
(126 MHz, CDCl3, 300 K): δ 295.2, 220.0, 183.6, 143.5, 140.5,
140.4 (2 signals), 139.2, 138.1, 137.5, 137.0, 136.8, 136.7
(2 signals), 135.2, 129.8, 129.7, 129.2, 129.1 (2 signals), 128.8,
128.4, 127.9, 127.8, 126.6, 117.5, 116.5, 52.5, 51.7, 34.8, 33.7,
21.2, 21.0, 20.5, 18.7, 18.4. HRMS (EI): m/z calcd for
C41H42N4Cl4Ru 832.1190, found 832.1187.
Experimental Section
All chemicals were purchased as reagent grade from commer-
cial suppliers and used without further purification, unless other-
wise noted. All reactions involving ruthenium complexes were
performed under an atmosphere of argon. Toluene, CH2Cl2, and
pentane were dried by using a column purification system.20 1
H
and 13C NMR spectra were recorded on a Bruker DRX 500 at
500 MHz (1H) and 126 MHz (13C), respectively. The chemical
shifts are given in ppm on the delta scale (δ) and are referenced to
tetramethylsilane (1H, 13C NMR 0 ppm) or the residual peak of
CHCl3 (1H NMR 7.26 ppm) or CDCl3 (13C NMR 77.16 ppm).21
Abbreviations for NMR data: s=singlet; d=doublet; t=triplet;
q = quartet; m = multiplet; bs = broad signal; Ar = aromatic
protons. Cyclic voltammograms were recorded in dry CH2Cl2
under an argon atmosphere at ambient temperature using an
EG&G 263A-2 potentiostat. A three-electrode configuration was
employed. The working electrode was a Pt disk (diameter 1 mm)
sealed in soft glass with a Pt wire as counter electrode. The pseudo
reference electrode was an Ag wire. Potentials were calibrated
internally against the formal potential of octamethylferrocene
(-10 mV (CH2Cl2) vs Ag/AgCl). NBu4PF6 (0.1 mol/L) was used
as supporting electrolyte. Thin-layer chromatography (TLC) was
Complex 3c: reaction temperature 80 °C; dark red crystals,
yield 99 mg (90%). Two isomers (ratio 1:0.45). H NMR (500
1
MHz, CDCl3, 300 K): δ 8.57 (isomer 1, 1H, dd, J=0.83, 7.5 Hz,
indenylidene-H ), 8.48 (isomer 2, 1H, d, J = 7.4 Hz, 1H,
indenylidene-H ), 7.75-7.70 (overlapped signals, isomer 1, 2H,
PhH; isomer 2, 2H, PhH ), 7.60 (isomer 2, 1H, s, indenylidene-
H ), 7.55-7.48 (o s, isomer 1, 2H, indenylidene-H; isomer 2, 1H,
indenylidene-H ), 7.41-7.36 (o s, isomer 1, 2H, PhH; isomer
2, 2H, PhH ), 7.29-7.23 (o s, isomer 1, 1H, PhH; isomer 2, 1H,
(19) We are currently studying this problem in detail; our results will
be reported in due course.
(20) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(21) Gottlieb, H. E.; Kotlyar, V.; Nudelmann, A. J. Org. Chem. 1997,
62, 7512.
(22) Stewart, I. C.; Ung, T.; Pletnev, A. A.; Berlin, J. M.; Grubbs,
R. H.; Schrodi, Y. Org. Lett. 2007, 9, 1589.

2766 Organometallics, Vol. 29, No. 12, 2010
Peeck and Plenio
PhH ), 7.20-7.04 (o s, isomer 1, 2H, mesityl-H þ 2H indenyli-
dene-H þ 1H, NCHC(NO2)N; isomer 2, 2H, mesityl-H þ 2H
indenylidene-H þ 1H, NCHC(NO2)N), 6.45 (isomer 2, s, 1H,
mesityl-H), 6.44 (isomer 1, s, 1H, mesityl-H), 6.18 (isomer 2, s,
1H, mesityl-H), 6.16 (isomer 1, s, 1H, mesityl-H), 4.14-4.03 (o s,
isomer 1, 2H, NCH2CH2N; isomer 2, 2H, NCH2CH2N),
3.96-3.80 (o s, isomer 1, 2H, NCH2CH2N; isomer 2, 2H,
NCH2CH2N), 3.63 (isomer 1, 3H, s, NCH3), 3.36 (isomer 2,
3H, s, NCH3), 3.06 (isomer 2, 3H, s, NCH3), 2.79 (isomer 1,
3H, s, NCH3), 2.76 (isomer 2, 3H, s, ArCH3), 2.75 (isomer 1,
3H, s, ArCH3), 2.65 (os, isomer 1, 3H, s, ArCH3, isomer 2, 3H, s,
ArCH3), 2.39 (isomer 1, 3H, s, ArCH3), 2.36 (isomer 2, 3H, s,
ArCH3), 2.33 (isomer 2, 3H, s, ArCH3), 2.31 (isomer 1, 3H, s,
ArCH3), 1.97 (isomer 1, 3H, s, ArCH3), 1.96 (isomer 2, 3H, s,
ArCH3), 1.80-1.77 (o s, isomer 1, 3H, s, ArCH3, isomer 2, 3H, s,
ArCH3). 13C NMR (126 MHz, CDCl3, 300 K): δ 298.1, 297.1,
218.9, 218.8, 194.0, 192.7, 143.5, 143.2, 140.5 (2 signals), 140.4,
140.3, 139.5, 139.2, 139.0, 138.4, 137.7, 137.6, 136.9, 136.8,
136.7, 136.4, 136.3, 135.2, 135.0, 129.8 (2 signals), 129.7, 129.2
(2 signals), 129.1, 129.0, 128.4, 128.3, 128.1 (2 signals), 126.7,
126.6, 125.5, 116.8, 116.7, 52.5, 51.7, 38.1, 37.4, 37.2, 35.3, 21.2,
21.1, 21.0, 20.4 (2 signals), 18.6, 18.4 (2 signals). HRMS (EI):
m/z calcd for C41H42N5O2Cl2Ru [M - H]þ 808.1751, found
808.1776.
Complex 3d: reaction temperature 100 °C; red crystals, yield
78 mg (70%). 1H NMR (500 MHz, CDCl3, 300 K): δ 8.44 (1H, d,
J=7.4 Hz, indenylidene-H ), 7.71 (2H, d, J=7.8 Hz, PhH ), 7.53
(1H, t, J=7.4 Hz, indenylidene-H ), 7.40 (2H, t, J=7.8 Hz, PhH ),
7,28 (1H, t, J=7.4 Hz, indenylidene-H ), 7.17 (1H, t, J=7.8 Hz,
PhH ), 7.11 (1H, d, J = 7.4 Hz, indenylidene-H ), 7.09 (2H, s,
mesityl-H ), 7.06 (1H, s, indenylidene-H ), 6.44 (1H, s, mesityl-
H ), 6.19 (1H, s, mesityl-H ), 4.08 (2H, m, NCH2CHAHBN), 3.94
(1H, m, NCH2CHAHBN), 3.84 (1H, m, NCH2CHAHBN), 3.46
(3H, s, NCH3), 2.93 (3H, s, NCH3), 2.75 (3H, s, ArCH3), 2.64
(3H, s, ArCH3), 2.39 (3H, s, ArCH3), 2.32 (3H, s, ArCH3), 1.94
(3H, s, ArCH3), 1.78 (3H, s, ArCH3). 13C NMR (126 MHz,
CDCl3, 300 K): δ 299.6, 217.8, 197.0, 143.2, 140.6, 140.5, 140.3,
139.6 (2 signals), 137.9, 137.0, 136.7 (2 signals), 136.6, 136.0,
134.9, 129.9, 129.8, 129.3, 129.2 (2 signals), 128.7, 128.4 (2
signals), 126.7, 117.1, 116.2, 115.2, 106.9, 106.8, 52.6, 51.7, 36.9,
35.9, 21.2, 21.0, 20.5, 20.4, 18.6, 18.3. HRMS (EI): m/z calcd for
C43H41N6Cl2Ru [M - H]þ 813.1805, found 813.1809.
139.3, 138.8, 138.0, 137.6, 137.4, 137.3, 137.1 (2 signals), 137.0,
136.9, 136.0, 135.4, 130.2, 129.8 (2 signals), 129.2, 129.1, 129.0,
128.9, 128.6, 128.5, 128.4, 127.9 (2 signals), 127.8, 127.7, 126.6,
126.5, 119.4, 118.3, 116.4, 116.2, 115.4, 114.0, 57.0, 52.4, 52.3,
52.2, 51.8, 34.8, 33.7, 21.4, 21.3 (2 signals), 21.2 (2 signals), 21.1,
20.5, 20.3, 18.8, 18.7, 18.6, 18.5. HRMS (EI): m/z calcd for
C43H46N4Cl4Ru 860.1503, found 860.1533.
Complex 3f: reaction temperature 60 °C; red crystals, yield
110 mg (94%). 1H NMR (500 MHz, CDCl3, 300 K): δ 8.67 (1H,
d, J=7.4 Hz, indenylidene-H ), 7.75 (2H, m, PhH ), 7.50 (1H, tt,
J=7.4, 1.2 Hz, indenylidene-H ), 7.38 (3H, overlapped signals,
PhH þ indenylidene-H ), 7.26 (1H, td, J=7.4, 1.2 Hz, indenyl-
idene-H ), 7.19 (1H, td, J=7.6, 1.2 Hz, PhH ), 7.11-7.08 (3H,
overlapped signals, indenylidene-H þ mesityl-H ), 6.46 (1H, s,
mesityl-H ), 6.08 (1H, s, mesityl-H ), 4.06 (2H, t, J=10.3 Hz,
NCH2CHAHBN), 3.91 (1H, J=10.3 Hz, NCH2CHAHBN), 3.82
(1H, q, J=10.3 Hz, NCH2CHAHBN), 3.58 (2H, m, NCH2CH3),
3.22 (2H, m, NCH2CH3), 2.71 (3H, s, ArCH3), 2.68 (3H, s,
NCH3), 2.39 (3H, s, ArCH3), 2.27 (3H, s, ArCH3), 2.04 (3H, s,
ArCH3), 1.84 (3H, s, ArCH3), 1.31 (3H, t, J = 7.0 Hz,
NCH2CH3), 0.54 (3H, t, J = 7.1 Hz, NCH2CH3). 13C NMR
(126 MHz, CDCl3, 300 K): δ 293.4, 219.8, 183.4, 143.9, 140.6,
140.0, 138.9, 137.5, 137.3, 137.2, 137.0, 136.9 (2 signals), 136.8,
135.5, 130.0, 129.2, 129.1, 129.0, 128.9, 128.6, 127.8, 127.6,
126.6, 117.6, 116.3, 116.2, 52.5, 52.0, 44.8, 43.6, 21.3, 21.1,
20.20.4, 18.7 (2 signals), 16.5, 15.6. HRMS (EI): m/z calcd for
C43H46N4Cl4Ru 860.1503, found 860.1530.
Complex 3g: reaction temperature 60 °C; red crystals, yield
109 mg (90%). 1H NMR (500 MHz, CDCl3, 300 K): δ 8.60 (1H,
dd, J=7.4, 1.2 Hz, indenylidene-H ), 7.74 (2H, m, PhH ), 7.50
(1H, tt, J=7.4, 1.2 Hz, indenylidene-H ), 7.39 (2H, m, PhH ),
7.33 (1H, s, indenylidene-H ), 7.26 (1H, td, J=7.4, 1.2Hz, indenyl-
idene-H ), 7.21 (1H, td, J=7.5, 1.2 Hz, PhH ), 7.12-7.08 (3H,
overlapped signals, indenylidene-H þ mesityl-H ), 6.46 (1H, s,
mesityl-H ), 6.07 (1H, s, mesityl-H ), 4.89 (1H, sep, J=6.8 Hz,
NCH(CH3)2), 4.01-3.70 (5 H, overlapped multiplets, NCH-
(CH3)2 þ NCH2CH2N), 2.73 (3H, s, ArCH3), 2.70 (3H, s, NCH3),
2.39 (3H, s, ArCH3), 2.24 (3H, s, ArCH3), 2.02 (3H, s, ArCH3),
1.87 (3H, s, ArCH3), 1.35 (3H, d, J=6.8 Hz, NCH(CH3)2), 1.29
(3H, d, J = 6.8 Hz, NCH(CH3)2), 0.86 (3H, d, J = 6.8 Hz,
NCH(CH3)2), 0.56 (3H, d, J=6.8 Hz, NCH(CH3)2). 13C NMR
(126 MHz, CDCl3, 300 K): δ 294.8, 219.2, 184.2, 143.9, 140.6,
139.5, 138.8, 137.6, 137.4, 137.3 (2 signals), 137.2, 137.1, 136.8,
136.2, 130.3 (2 signals), 129.2, 129.1, 129.0, 128.6 (2 signals),
127.8, 127.6, 126.5, 117.1, 116.0, 115.8, 56.9, 53.4, 52.4, 52.3, 21.3,
21.2 (2 signals), 21.1, 20.4, 20.2, 18.8 (2 signals). MS (EI): m/z
calcd for C45H50N4Cl4Ru 888.2, found 888.5.
Complex 3e: reaction temperature 60 °C; red crystals, yield
109 mg (93%). Two isomers (ratio 1:0.45). 1H NMR (500 MHz,
CDCl3, 300 K): δ 8.61 (isomer 1, 1H, dd, J = 0.83, 7.5 Hz,
indenylidene-H ), 8.57 (isomer 2, 1H, d, J=7.4 Hz, 1H, indenyl-
idene-H ), 7.76 (isomer 2, m, 2H, PhH ), 7.71 (isomer 1, m, 2H,
PhH ), 7.53-7.48 (overlapped signals, isomer 1, 1H, indenyli-
dene-H; isomer 2, 1H, indenylidene-H ), 7.41-7.36 (o s, isomer
1, 2H, PhH; isomer 2, 2H, PhH ), 7.30-7.22 (o s, isomer 1, 2H,
indenylidene-H, isomer 2, 2H, indenylidene-H ), 7.22-7.15 (o s,
isomer 1, 1H, PhH; isomer 2, 1H, PhH ), 7.13-7.05 (overlapped
signals, isomer 1, 1H, indenylidene-H þ 2H, mesityl-H; isomer
2, 1H, indenylidene-H þ 2H, mesityl-H ), 6.44 (o s, isomer 1, 1H,
mesityl-H, isomer 2, 1H, mesityl-H), 6.14 (isomer 1, s, 1H,
mesityl-H), 6.08 (isomer 2, s, 1H, mesityl-H), 4.72 (isomer 2,
1H, sept, NCH(CH3)2, J=6.9 Hz), 4.12-3.71 (o s, isomer 1, 1H,
NCH(CH3)2, 4H, NCH2CH2N, isomer 2, 4H, NCH2CH2N),
3.26 (isomer 1, s, 3H, NCH3), 2.75 (isomer 2, s, 3H, ArCH3),
2.73 (isomer 1, s, 3H, ArCH3), 2.71 (isomer 2, s, 3H, NCH3),
2.70 (isomer 2, s, 3H, ArCH3), 2.68 (isomer 1, s, 3H, ArCH3),
2.40 (isomer 2, s, 3H, ArCH3), 2.37 (isomer 1, s, 3H, ArCH3),
2.26 (o s, isomer 1, s, 3H, ArCH3, isomer 2, s, 3H, ArCH3), 2.03
(isomer 1, s, 3H, ArCH3), 1.99 (isomer 2, s, 3H, ArCH3), 1.85
(isomer 1, s, 3H, ArCH3), 1.84 (isomer 2, s, 3H, ArCH3), 1.34
(isomer 2, 3H, d, J=7.0 Hz, NCH(CH3)2), 1.32 (isomer 2, 3H, d,
J = 7.0 Hz, NCH(CH3)2), 0.88 (isomer 1, 3H, d, J =7.0 Hz,
General Protocol for Catalyst Screening. All reactions were
carried out in closed 25 mL Schlenk tubes under an atmosphere
of argon at 80 or 100 °C. To a 25 mL Schlenk tube was added
substrate (0.2 mmol) dissolved in dry toluene (10 mL, substrate
conc 0.02 M) under an atmosphere of argon. This solution was
heated to 80 or 100 °C, and catalyst (0.05-0.5 mol %) from a
stock solution (3 mmol/L) in toluene was added. For the
determination of substrate conversion, samples were taken
every hour under a stream of argon and were injected into GC
vials containing 150 μL of 25% ethyl vinyl ether solution in
toluene. A final sample was taken after 24 h.
Acknowledgment. This work was supported by the
DFG via grant 178/13-1. We wish to thank Dipl.-Ing.
F. Stober for the X-ray data collection. We wish to thank
Dr. Winde/Umicore for a generous gift of complex 1.
1
Supporting Information Available: Copies of H, 13C NMR
spectra of complexes 3a-3g, cyclic voltammograms, and a
CIF file providing information on the crystal structure
of complex 3g are available free of charge via the Internet at
http://pubs.acs.org.
NCH(CH3)2, 0.62 (isomer 1, 3H, d, J=7.0 Hz, NCH(CH3)2. 13
C
NMR (126 MHz, CDCl3, 300 K): δ 296.2, 293.8, 220.2, 219.1,
184.3, 183.6, 144.0, 143.6, 140.6, 140.5, 140.4 (2 signals), 139.5,