A new, highly active bimetallic Grubbs-Hoveyda-Blechert precatalyst for alkene metathesis

Article abstract of DOI:10.1021/om701242t

A new Grubbs-Hoveyda-Blechert alkene metathesis catalyst, in which the benzylidene ligand has been coordinated to a highly electron-withdrawing tricarbonylchromium moiety, is presented. The structure of the complex provides evidence for a so far unreported attractive interaction between the benzylidene hydrogen atom and one of the mesityl substituents at the Arduengo carbene ligand. Screening of the catalytic properties shows that the activity of the new catalyst in ring-closing, enyne, cross, and homo metathesis of alkenes is comparable and in some cases better than that of known catalysts.

Full text of DOI:10.1021/om701242t

1878
Organometallics 2008, 27, 1878–1886
A New, Highly Active Bimetallic Grubbs–Hoveyda–Blechert
Precatalyst for Alkene Metathesis
Nikolai Vinokurov,† José Ramon Garabatos-Perera,† Zhirong Zhao-Karger,†
Michael Wiebcke,‡ and Holger Butenschön*,†
Institut für Organische Chemie, Gottfried Wilhelm Leibniz UniVersität HannoVer, Schneiderberg 1B,
D-30167 HannoVer, Germany, and Institut für Anorganische Chemie, Gottfried Wilhelm Leibniz
UniVersität HannoVer, Callinstrasse 9, D-30167 HannoVer, Germany
ReceiVed December 12, 2007
A new Grubbs-Hoveyda-Blechert alkene metathesis catalyst, in which the benzylidene ligand has
been coordinated to a highly electron-withdrawing tricarbonylchromium moiety, is presented. The structure
of the complex provides evidence for a so far unreported attractive interaction between the benzylidene
hydrogen atom and one of the mesityl substituents at the Arduengo carbene ligand. Screening of the
catalytic properties shows that the activity of the new catalyst in ring-closing, enyne, cross, and homo
metathesis of alkenes is comparable and in some cases better than that of known catalysts.
catalyst properties to demands of practicability or asymmetric
catalysis. In this rapidly developing field the design of new
catalysts with improved application profiles continues to be an
important challenge (Chart 1).
Introduction
The development of efficient catalysts compatible with
numerous functional groups has caused metathesis to become
a powerful method for the construction of carbon-carbon
bonds.1–6 The metathesis catalysts frequently used predomi-
nantly include ruthenium and molybdenum carbene complexes,
the latter ones usually being more sensitive as compared to the
ruthenium systems. In addition to improvements in the efficiency
of the catalysts, a number of other variations such as catalyst
immobilization7,8 or the introduction of chirality9–18 adapted the
While 1 (Grubbs I) is among the first catalysts being routinely
used for alkene metathesis, ruthenium phosphane complexes 2
and 3 bearing Arduengo carbene ligands instead of one of the
phosphane ligands have been shown to be more efficient.19,20
Phosphane-free isopropoxy chelate complexes 4-6 and double
chelates 7 and 8, a group of catalysts introduced by Hoveyda,
Blechert, and Grela, show an expanded application profile
associated with enhanced catalytic activity and stability.21–24
Carbene complexes 6 and 8 show a significant increase in
catalytic activity as compared to 4, 5, and 7, because of a
weakened coordination of the oxygen atom positioned para to
the nitro group.
* Corresponding
mbox.oci.uni-hannover.de.
author.
E-mail:
holger.butenschoen@
† Institut für Organische Chemie.
‡ Institut für Anorganische Chemie.
(1) Grubbs, R. H. Handbook of Metathesis; Wiley-VCH: Weinheim,
2003; Vols. 1–3.
(2) Connon, S. J.; Blechert, S. Angew. Chem. 2003, 115, 1944–1968.;
Angew. Chem., Int. Ed. 2003, 42, 1900–1923.
The electron-withdrawing effect of the nitro substituent in 6
is mainly directed to the ortho and para positions, and
consequently the benzylidene carbon atom, which is coordinated
to ruthenium, should be comparatively less affected. This is
nicely reflected by inspection of the NMR properties of the
benzylidene moiety, indicating rather similar benzylidene proton
chemical shifts for 4 (δ ) 16.56 ppm) and for 6 (δ ) 16.42
ppm).24–26
(3) Fürstner, A.; Davies, P. W. Chem. Commun. 2005, 2307–2320.
(4) Grubbs, R. H. Angew. Chem. 2006, 118, 3845–3850.; Angew. Chem.,
Int. Ed. 2006, 45, 3760–3765.
(5) Schrock, R. R. Angew. Chem. 2006, 118, 3832–3844.; Angew. Chem.,
Int. Ed. 2006, 45, 3748–3759.
(6) Chauvin, Y. Angew. Chem. 2006, 118, 3824–3831.; Angew. Chem.,
Int. Ed. 2006, 45, 3741–3747.
(7) Clavier, H.; Grela, K.; Kirschning, A.; Mauduit, M.; Nolan, S. P.
Angew. Chem. 2007, 119, 6906–6922.; Angew. Chem., Int. Ed. 2007, 46,
6786–6801.
(Arene)tricarbonylchromium complexes have been known for
decades and are among the most important arene complexes
(8) Mulzer, J.; Öhler, E. Top. Organomet. Chem. 2004, 13, 269–366.
(9) Hoveyda, A. H. Catalytic Asymmetric Olefin Metathesis. In Hand-
book of Metathesis; Grubbs, R. H., Ed.; Wiley-VCH: Weinheim, 2003; Vol.
2, pp 128–150.
(19) Fürstner, A.; Ackermann, L.; Gabor, B.; Goddard, R.; Lehmann,
C. W.; Mynott, R.; Stelzer, F.; Thiel, O. R. Chem.-Eur. J. 2001, 7, 3236–
3253.
(10) La, D. S.; Sattely, E. S.; Ford, J. G.; Schrock, R. R.; Hoveyda,
A. H. J. Am. Chem. Soc. 2001, 123, 7767–7778.
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Hoveyda, A. H.; Schrock, R. R. J. Am. Chem. Soc. 1999, 121, 8251–8259.
(13) Cortez, G. A.; Baxter, C. A.; Schrock, R. R.; Hoveyda, A. H. Org.
Lett. 2007, 9, 2871–2874.
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1, 953–956.
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Angew. Chem., Int. Ed. 2002, 41, 2403–2405.
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G.; Grela, K. J. Am. Chem. Soc. 2004, 126, 9318–9325.
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D.; Grela, K. J. Am. Chem. Soc. 2006, 128, 13652–13653.
(24) Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H. J. Am.
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(14) Deiters, A.; Martin, S. F. Chem. ReV. 2004, 104, 2199–2238.
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118, 7753–7757. Angew. Chem. Int. Ed. 2006, 45, 7591–7595.
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10.1021/om701242t CCC: $40.75
2008 American Chemical Society
Publication on Web 03/20/2008

Bimetallic Grubbs-HoVeyda-Blechert Precatalyst
Organometallics, Vol. 27, No. 8, 2008 1879
Chart 1. Alkene Metathesis Catalysts (Mes ) 2,4,6-trimethylphenyl)
with respect to organic synthesis. Among other features the
facial differentiation at the coordinated arene and the electron
withdrawal of the tricarbonylchromium moiety have been
exploited for stereoselective synthesis, dearomatization, and
many other reactions not possible in the absence of the
tricarbonylchromium group.27–45 The extent of its electron
withdrawal is comparable to that of a para nitro group, as
indicated by pKa comparison of the respective phenylacetic
acids.46
In contrast to an electron-withdrawing substituent such as a
nitro group at an arene, its coordination at tricarbonylchromium
causes the electron withdrawal to affect all six carbon atoms of
the arene ring and the groups attached to them. In order to reduce
the electron density in 6 not only at the chelating oxygen atom
but also at the benzylidene moiety, we envisaged the bimetallic
precatalyst 11 with a π-coordinated tricarbonylchromium group
at the benzylidene ligand.47 In addition to its electron withdrawal
the steric bulk of the tricarbonylchromium group due to its
proximity to the ruthenium atom in 11 might have some
influence in its catalytic properties. Here we present the synthesis
and full spectroscopic and structural characterization of 11 as
well as an investigation of the catalytic profile of this bimetallic
complex with respect to alkene metathesis.
complex 10 in racemic form in 58% yield as a bright yellow
powder after purification by column chromatography. The
constitution of 10 was confirmed by characteristic IR absorptions
1
at 1941 and 1837 cm-1 as well as by fully consistent H and
13C NMR spectra. The mass spectrum shows the molecular ion
peak and the fragmentation pattern typical for (arene)tricarbo-
nylchromium complexes. Reaction of 10 with Grubbs catalyst
3 in the presence of CuCl as a tricyclohexylphosphane scavenger
gave the racemic bimetallic complex 11 in 74% yield as a dark
red powder.48 Alternatively, 11 was obtained in 59% overall
yield by a one-pot procedure from the commercially available
Grubbs I catalyst 1: 1,3-dimesitylimidazolium tetrafluoroborate
(12) was treated with potassium tert-amylate, followed by
addition of 1 and then by addition of 10 and CuCl.
Results and Discussion
Treatment of ortho-isopropoxystryrene (9) with hexacarbo-
nylchromium in dibutyl ether/THF (10:1)34 afforded chromium
(27) Rosillo, M.; Dominguez, G.; Perez-Castells, J. Chem. Soc. ReV.
2007, 36, 1589–1604.
(28) Uemura, M. Top. Organomet. Chem. 2004, 7, 129–156.
(29) Semmelhack, M. F.; Chlenov, A. Top. Organomet. Chem. 2004,
7, 21–42.
11 was characterized spectroscopically. The 1H NMR chemi-
cal shift of the signal assigned to the benzylidene H atom is δ
) 15.49 ppm, a value considerably different from those of 4
and 6 (Vide supra). The effect of the tricarbonylchromium
moiety on the benzylidene part of the ligand system is also
reflected by the 13C NMR data of the benzylidene carbon atom.
While the respective resonance is observed at δ ) 297.3 ppm
for 4 and at δ ) 289.1 ppm for 6, it appears at δ ) 285.4 ppm
for 11 if measured in CD2Cl2 and at δ ) 283.5 ppm in C6D6.
Another unusual observation is the fact that in the 1H NMR
spectra the signals assigned to the mesityl protons appear as a
broadened singlet when the spectrum was recorded in CD2Cl2,
whereas there are two singlet signals when deuterated benzene
was used as the solvent. In addition, the signal assigned to the
ortho-methyl groups of the mesityl substituents is a sharp singlet
in CD2Cl2, whereas it is significantly broadened in C6D6 (Figure
(30) Semmelhack, M. F.; Chlenov, A. Top. Organomet. Chem. 2004,
7, 43–69.
(31) Schmalz, H.-G.; Gotov, B.; Böttcher, A. Top. Organomet. Chem.
2004, 7, 157–179.
(32) Muñiz, K. Top. Organomet. Chem. 2004, 7, 205–224.
(33) Minatti, A.; Doetz, K. H. Top. Organomet. Chem. 2004, 13, 123–
156.
(34) Kündig, E. P. Top. Organomet. Chem. 2004, 7, 3–20.
(35) Gibson, S. E.; Ibrahim, H. Chem. Commun. 2002, 2465–2473.
(36) Butenschön, H. Pure Appl. Chem. 2002, 74, 57–62.
(37) Pape, A. R.; Kaliappan, K. P.; Kündig, E. P. Chem. ReV. 2000,
100, 2917–2940.
(38) Semmelhack, M. F. J. Organomet. Chem. Library B 1976, 1, 361–
395.
(39) Uemura, M., Tricarbonyl(η6-arene)chromium Complexes in Organic
Synthesis. In AdVances in Metal-Organic Chemistry; Liebeskind, L. S., Ed.;
Jai Press, Ltd.: London, 1991; Vol. 2, pp 195–245.
(40) Davies, S. G.; Donohoe, T. J. Synlett 1993, 323–332.
(41) Davies, S. G.; McCarthy, T. D. Transition Metal Arene Complexes:
Side-chain Activation and Control of Stereochemistry. In ComprehensiVe
Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G.,
Eds.; Pergamon: Oxford, 1995; Vol. 12, pp 1039–1070.
(42) Dötz, K.-H.; Tomuschat, P. Chem. Soc. ReV. 1999, 28, 187–198.
(43) Butenschön, H. Synlett 1999, 680–691.
1
1). H NMR measurements in C6D6 do not show coalescence
up to 345 K.
(48) The synthesis of enantiomerically pure 11 would start from
enantiomerically pure 10, which might be obtained by resolution of 10 by
chiral HPLC. However, as the planar chiral (o-isopropoxybenzylidene)tri-
carbonylchromium moiety is separated from the catalytically active
ruthenium part in the catalytic cycle, we refrained from preparing 11 in
enantiomerically pure form.
(44) Bolm, C.; Muñiz, K. Chem. Soc. ReV. 1999, 28, 51–59.
(45) Kamigawa, K.; Uemura, M. Synlett 2000, 938–949.
(46) Nicholls, B.; Whiting, M. C. J. Chem. Soc. 1959, 551–556.
(47) Zaja, M.; Connon, S. J.; Dunne, A. M.; Rivard, M.; Buschmann,
N.; Jiricek, J.; Blechert, S. Tetrahedron 2003, 59, 6545–6558.

1880 Organometallics, Vol. 27, No. 8, 2008
VinokuroV et al.
1
Figure 1. H NMR spectra (400 MHz) of 11 in CD2Cl2 (top) and in C6D6 (bottom). Selected signal assignments: (A) benzylidene proton,
(B) mesityl protons, (C) mesityl ortho-methyl protons, (S) residual solvent signal.
These observations indicate a hindered rotation of one of the
mesityl substitutents around the C-N bond in 11 in deuterated
benzene, whereas this appears not to be the case in deuterated
dichloromethane. Such an observation has not been reported
for 424,25 or for 626 and suggests that the molecular dynamics
is reduced in C6D6 as compared to CD2Cl2, a trend opposing
that reported by Fürstner19 and Grela.49
Crystallization by slow evaporation from a solvent mixture
(2:1) of hexane and tert-butyl methyl ether (TBME) afforded
crystals suitable for a single-crystal X-ray structure analysis
(Figure 2). 11 displays a strongly distorted trigonal bipyramidal
Figure 2. Structure of 11 in the crystal. Only one enantiomer is
shown. Selected bond lengths [pm], angles [deg], and dihedral
angles [deg]: Ru-C1 180.7(5), Ru-C14 195.9(6), Ru-O4 229.8(4),
Ru-Cl1 231.8(2), Ru-Cl2 233.7(2), C14-N1 136.1(7), C14-N2
137.1(6), Cr-C2 224.9(6), Cr-C3 218.9(6), Cr-C4 218.6(7),
Cr-C5 218.5(6), Cr-C6 222.9(6), Cr-C7 226.3(5); C1-Ru-O4
79.5(2), C1-Ru1-C14 101.9(2), C14-Ru-O4 178.38(18), Cl1-
Ru-Cl2 160.16(6); N1-C14-Ru-C1 3.5(6), N2-C14-Ru-C1
-177.8(5), C14-Ru-C1–C2 -179.3(5); C-H · · · π hydrogen bond
(M denotes the centroid of the mesityl substituent): C1 · · · M 344.9,
C1-H1 93, H1 · · · M 253, C1-H1 · · · M 170.
coordination geometry at ruthenium with the isopropoxy ligand
in an axial position and the chlorine atoms as well as the
benzylidene ligand in equatorial positions. One face of the
benzylidene ligand moiety is efficiently blocked by the tricar-
bonylchromium group, which, for obvious steric reasons, adopts
a staggered conformation with one carbonyl ligand pointing
away from the chlororuthenium part of the complex. Compared
to the Hoveyda-Grubbs catalyst 4,24 a decreased Ru-C14 bond
length is observed in 11 [198.1(5) vs 195.6(5) pm]. As the
heterocyclic carbene ligand is identical in both compounds, its
σ-donor or π-acceptor properties are unlikely to be the reason
for the observed difference. Instead, the Cr(CO)3 coordination
makes the benzylidene ligand a stronger acceptor ligand, thereby
leading to a stronger and shorter Ru-C14 bond. The Ru-O4
bond, which is decoordinated in metathesis catalysis, is slightly
longer than in 4 [229.8(3) vs 226.1(3) pm],24 possibly indicating
(49) Grela, K. Preparation and Applications of Tunable Catalysts for
Alkene and Alkyne Metathesis Reaction. In Wissenschaftsforum Chemie
2007; Gesellschaft Deutscher Chemiker: Ulm, 2007.

Bimetallic Grubbs-HoVeyda-Blechert Precatalyst
Organometallics, Vol. 27, No. 8, 2008 1881
a somewhat weaker bond in 11 as a result of a reduced donor
ability of the isopropoxy group.
observed as a singlet at δ ) 15.72 ppm, a value that compares
very well with the corresponding absorption in 11.
Another interesting observation is the short distance between
the benzylidene proton H1 and the center of the mesityl ring
attached at N1 (253 pm), suggesting an interaction with the π
system (C-H · · · π hydrogen bond),50 which is in line with the
differentiation of the mesityl groups by 1H NMR. It is interesting
to note that the location of the benzylidene proton directly below
the mesityl ring in Hoveyda-Grubbs type precatalysts has
previously been observed,19,51–54 but for 11 this distance is
shorter, presumably as a result of the strongly electron-
withdrawing Cr(CO)3 group rendering H1 more electrophilic.
Recently, the precedent of a π-π stacking of the two perpen-
dicularly arranged aromatic rings in Grubbs-type complexes has
been documented.19
In addition to 11 two related complexes were prepared.
Treatment of Grubbs I catalyst 1 with tricarbonyl(ortho-isoprop-
oxystyrene)chromium(0) (10) in the presence of copper(I)
chloride afforded the bimetallic derivative 13 in 48% yield as
a brown-red powder after purification by column chromatog-
raphy. While the presence of a phosphane ligand was confirmed
by 31P NMR, the resonance assigned to the benzylidene proton
appears as a doublet at δ ) 16.58 ppm (3JP,H ) 4.2 Hz). This
contrasts with the corresponding resonance of the respective
catalyst not coordinated at tricarbonylchromium, which is
observed at δ ) 17.44 ppm (3JP,H ) 4.4 Hz)55 with similar
coupling constants, indicating a similar dihedral angle.56 In the
13C NMR spectrum the benzylidene carbon atom resonates at
δ ) 274.5 ppm as compared to δ ) 280.63 ppm for the
corresponding chromium-free complex.55
As complex 11 was the least sensitive and best characterized
one in the series, we decided to screen the catalytic properties
of this compound. Indeed, 11 proved to be stable in air at 25
°C for at least two months without significant loss of catalytic
activity. The results of ring-closing metathesis experiments are
listed in Table 1 in comparison to corresponding reactions with
catalysts 3-6 and 8, which are among the most advanced
catalysts known today.
RCM (entries 1–4) was performed starting from dienes 17,
19, 21, and 23 with monosubstituted double bonds at 25 and at
0 °C with 1 mol % of catalyst 11, giving cyclic products 18,
20, 22, and 24 in very good yields. The new catalyst showed a
catalytic activity comparable to that of Hoveyda-Grubbs
catalysts 5 and 6. In addition, experiments with a 10-fold
reduced catalyst loading of 0.1 mol % of 11 showed that RCM
works even at this low catalyst concentration, albeit with
somewhat reduced yields, as indicated by GC. RCM with more
highly substituted alkenes (entries 5–7) was possible with
substrates 25 and 27, giving 26 and 28 in 99% and 49% yield,
respectively, which is again comparable to the efficiency of the
best catalysts known today. However, the experiment with 29
failed, and the known catalysts also gave very poor yields of
RCM product 30.
rac-13 performed very well in enyne metatheses (Table 2),
the reaction of enyne 31 afforded 32 in almost quantitative yield,
and even with 0.1 mol % of catalyst 86% yield was achieved
(entry 1). The reaction of enyne 33 to diene 34 showed a
significantly higher activity of 11 as compared to the other
catalysts, as indicated by a much higher yield, lower catalyst
loading, and lower reaction temperature (entry 2). When
performed in benzene instead of dichloromethane as the solvent,
however, the yield dramatically decreased to 8%. As a possible
explanation, we consider the reduced molecular dynamics in
11 in benzene as compared to dichloromethane, which has been
indicated by NMR (Vide supra). This might render conforma-
tions favorable for the metathesis catalysis less accessible.
CM catalyses (Table 3) were performed with 11 using 35,
38, and 48 as coupling partners for R,ꢀ-unsaturated ester 36,
ketone 40, sulfone 42, nitrile 44, and phosphane oxide 46. The
yields are very high and compare very well to those of the other
catalysts. The selectivity of cross-metathesis reactions with vinyl
phosphaneoxide 46 and sulfone 42 led exclusively to E-isomers;
only experiments involving methyl acrylate (36, entries 1, 2)
or acrylonitrile (44, entry 5) showed a tendency toward increased
amounts of the Z-isomer. 11 is active even over extended heating
in dichloromethane, as indicated by the reaction of 48 giving
49 in 83% yield (entry 7). Overall the experiments show that
not only a nitro group as in catalyst 6 but also coordination at
an electron-withdrawing tricarbonylchromium group gives a
metathesis catalyst of good stability and extremely high catalytic
activity.
Next we attempted to synthesize the 3-methoxy-substituted
analogue of 11. The chromium-free catalyst had earlier been
prepared and investigated by Blechert.47,57 Complexation of
2-isopropoxy-2-methoxystyrene (14) with Cr(CO)6 under stan-
dard reaction conditions afforded complex 15 in 51% yield as
a yellow powder. Subsequent treatment with 3 in the presence
of CuCl afforded 16 in 43% yield as a brown-red powder. 16
is rather sensitive, difficult to purify, and unfortunately under-
went partial decomposition. However, the IR and 1H NMR data
obtained clearly identify the product obtained as 16. IR
absorptions at 1955 and at 1874 (br) cm-1 indicate the Cr(CO)3
1
group, and the H NMR signal of the benzylidene proton is
(50) Braga, D.; Grepioni, F.; Tedesco, E. Organometallics 1998, 17,
2669–2672.
(51) Ledoux, N.; Allaert, B.; Linden, A.; Van Der Voort, P.; Verpoort,
F. Organometallics 2007, 26, 1052–1056.
(52) Fürstner, A.; Krause, H.; Ackermann, L.; Lehmann, C. W. Chem.
Commun. 2001, 2240–2241.
(53) Ledoux, N.; Linden, A.; Allaert, B.; Vander Mierde, H.; Verpoort,
F. AdV. Synth. Catal. 2007, 349, 1692–1700.
(54) Barbasiewicz, M.; Bieniek, M.; Michrowska, A.; Szadkowska, A.;
Makal, A.; Wozniak, K.; Grela, K. AdV. Synth. Catal. 2007, 349, 193–203.
(55) Kingsbury, J. S.; Harrity, J. P. A.; Peter, J.; Bonitatebus, J.;
Hoveyda, A. H. J. Am. Chem. Soc. 1999, 121, 791–799.
(56) Nguyen, S. T.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1993,
115, 9858–9859.
Recently we reported the homometathesis of the P-chiral
phosphane oxide (SP)-50, which gave trans product (SP,SP)-51
in 80% yield in the presence of 5 mol % of nitro-substituted
(57) Maechling, S.; Zaja, M.; Blechert, S. AdV. Synth. Catal. 2005, 347,
1413–1422.

1882 Organometallics, Vol. 27, No. 8, 2008
VinokuroV et al.
Table 1. Ring-Closing Metathesis Catalyzed by 11 in Comparison to Other Catalysts [solvent CH2Cl2, yields of isolated product unless
otherwise indicated]
a Identified by comparison of 1H and 13C NMR data with literature data. b Yield determined by gas chromatography without product isolation.
catalyst 6 in dichloromethane at 40 °C over 24 h.59 We now
were pleased to find that replacement of 6 by 11 under otherwise
unchanged reaction conditions afforded (SP,SP)-51 in an im-
proved yield of 91%.
2-(boranatomethylphenyl)phosphanylethyl methanesulfonate
(53) in 86% yield,62 to 55 was also tried. However, no
metathesis was observed with 6 as the catalyst, nor were any
other products obtained. Presumably the electron withdrawal
of the borane moiety reduces the electron density of the vinyl
group to an extent precluding a complexation at ruthenium. Most
recently Gouverneur reported related findings using 3 as the
catalyst.63
Conclusions
11 proved to be an air-stable precatalyst for ring-closing,
enyne, cross, and homo metathesis with an efficiency that very
well compares to those of the most advanced catalysts for these
reactions. In particular, in the homometathesis of P-chiral
vinylphosphane oxide (SP)-50 catalyst 11 came out to be
significantly more efficient that the so far best catalyst 6. The
In order to open a different pathway to P-chiral diphosphanes
by homometathesis of vinyl derivatives, the homometathesis of
borane-stabilized methylphenylvinylphosphane 54, which was
prepared either from methylphenylvinylphosphane60,61 (52) by
reaction with borane in 46% yield or alternatively from

Bimetallic Grubbs-HoVeyda-Blechert Precatalyst
Organometallics, Vol. 27, No. 8, 2008 1883
Table 2. Enyne Metathesis Catalyzed by 11 in Comparison to Other Catalysts [solvent CH2Cl2 unless otherwise indicated, yields of isolated
product]
a Identified by comparison of 1H and 13C NMR data with literature data.
Table 3. Cross Metathesis Catalyzed by 11 in Comparison to Other Catalysts [solvent CH2Cl2, yields of isolated product unless otherwise noted]
a Identified by comparison of 1H and 13C NMR data with literature data. b Yield determined by gas chromatography without product isolation.

1884 Organometallics, Vol. 27, No. 8, 2008
VinokuroV et al.
Hz, J ) 1.1 Hz, arom. H), 4.22 (d, 1H, J ) 6.8 Hz, arom. H), 4.14
(t, 1H, J ) 6.3 Hz, arom. H), 2), 3.71 [sept, 1H, J ) 6.1 Hz,
CH(CH3)2], 1.09 (d, 3H, J ) 6.2 Hz, CH3), 0.77 (d, 3H, J ) 6.0
Hz, CH3) ppm. 13C NMR (100.6 MHz, C6D6): δ 233.8 (CO), 139.9
(COiPr), 129.7 (-CHdCH2), 114.9 (dCH2), 94.7 (CCHdCH2),
93.8 (arom. CH), 92.7 (arom. CH), 84.8 (arom. CH), 75.8 (arom.
CH), 72.0 [CH(CH3)2], 22.1 (CH3), 21.5 (CH3) ppm. MS (EI): m/z
(%) 298 (42) [M+], 242 (19) [M+ - 2CO], 215 (28), 214 (89)
[M+ - 3 CO], 173 (8), 172 (29), 171 (98) [M+ - 3 CO -
H3CCHdCH2], 162 (6), 145 (7), 143 (22) [M+ - 3 CO -
H3CCHdCH2 - HCCH], 120 (20), 91 (14), 52 (100) [Cr+]. HR-
MS (EI): (C14H14O452Cr) calcd 298.0297, found 298.0297. Anal.
(C14H14O4Cr) Calcd: C 56.38, H 4.73. Found: C 56.43, H 4.61.
Precatalyst 11. 10 (88 mg, 0.3 mmol) in 3 mL of dichlo-
romethane was added dropwise via syringe to benzylidene complex
3 (250 mg, 0.3 mmol) and CuCl (30 mg, 0.3 mmol) in 5 mL of
dichloromethane. The mixture was heated at reflux for 1 h, the
reaction progress being monitored by TLC (Rf ) 0.13, hexane/
EtOAc, 5:2). After solvent removal at reduced pressure the residue
was dissolved in 35 mL of benzene and carefully filtered under
argon through silica gel to remove residual 10. Subsequent elution
with hexane/TBME (2:1) gave 168 mg (0.2 mmol, 74%) of 11 as
an air-stable dark red solid (mp 176 °C, dec).
structure of 11 indicates an attractive benzylidene C-H · · · π
interaction to one of the mesityl substituents. Further investiga-
tions directed to broadening the application profile of bimetallic
precatalysts of this type are underway in our laboratories.
Experimental Section
General Procedures. All operations involving air-sensitive
materials were performed under argon using standard Schlenk
techniques. Diethyl ether, THF, and benzene were dried over Na/
K-benzophenone; petroleum ether (PE) and tert-butyl methyl ether
(TBME) were dried over CaCl2; dibutyl ether and dichloromethane
were dried over CaH2 and distilled under Ar prior to use. Starting
materials were either purchased or prepared according to literature
procedures. IR: Perkin-Elmer 2000, FT 1170 (ATR). 1H NMR:
Bruker AVS 400 (400.1 MHz), AVB 500 (500.1 MHz). Chemical
shifts refer to δTMS ) 0 ppm or to residual solvent peaks. br: broad,
unresolved signal. 13C NMR: Bruker AVS 500 (125 MHz).
Chemical shifts refer to δTMS ) 0 ppm or to residual solvent peaks.
MS (EI, LSIMS): AMD 604 Inectra, Finnigan MAT 112, MAT
312, 70 eV. HRMS (ESI): Finnigan MAT 312, VG Autospec.
Melting points: Electrothermal IA 9200. GC: Hewlett-Packard
HPGC, SE-54 capillary column, FID detector 19231 D/E. Each
metathesis experiment was checked at least two times.
IR (KBr): ν˜ 2925 (w) cm-1, 2847 (w), 2052 (w), 1963 (s, CO),
1903 (s, CO), 1867 (s, CO), 1739 (w), 1605 (w), 1484 (w), 1448
(w), 1382 (w), 1296 (w), 1260 (s), 1208 (w), 1098 (w), 1016 (b),
1
928 (w), 854 (w), 822 (w), 674 (w), 661 (w), 620 (w). H NMR
(400 MHz, C6D6): δ 15.49 (s, 1H, RudCH), 7.00 (s, 2H, mesityl-
CH), 6.88 (s, 2H, mesityl-CH), 4.97 (dd, 1H, J ) 6.5 Hz, J ) 1.2
Hz, RudCHCCH), 4.68 (dt, 1H, J ) 7.0 Hz, J ) 1.2 Hz,
RudCHCCHCHCH), 4.10 (d, 1H, J ) 6.9 Hz, RuCHCCHCH-
CHCH), 4.01 [sept, 1H, J ) 6.2 Hz, OCH(CH3)2], 3.74 (t, 1H, J )
6.2 Hz, RudCHCCHCH), 3.36 (s, 4H, CH2), 2.54 (bs, 12H, o-CH3),
2.25 (s, 6H, p-CH3), 1.21 (d, 3H, J ) 6.2 Hz, OCHCH3), 1.08 (d,
3H, J ) 6.0 Hz, OCHCH3). 1H NMR (400 MHz, CD2Cl2): δ 15.49
(s, 1H, RudCH), 7.03 (4H, br, mesityl-CH), 5.65 (1H, dt, J ) 7.0
Hz, J ) 1.2 Hz, RudCHCCHCHCH), 5.23 (1H, d, J ) 6.9 Hz,
RuCHCCHCHCHCH), 5.18 (1H, dd, J ) 6.5 Hz, J ) 1.2 Hz,
RudCHCCH), 4.79 (1H, t, J ) 6.2 Hz, RudCHCCHCH), 4.62
[sept, J ) 6.2 Hz, 1H, OCH(CH3)2], 4.15 (4H, s, CH2), 2.37 (18H,
br, o-CH3, p-CH3), 1.26 (d, J ) 6.2 Hz, 3H, OCHCH3), 1.14 (d, J
) 6.0 Hz, 3H, OCHCH3). 13C NMR (100.6 MHz, C6D6): δ 285.6
(RudCH), 233.0 (CrCO), 210.7 (RudCNN), 138.6 (arom. C-O),
138.4 (N-Cq), 137.2 (mesityl-o-Cq), 135.5 (mesityl-p-Cq), 129.9
(mesityl-m-CH), 129.5 (p-Cq), 107.3 (RudCHCq), 91.6 (RudCHCC-
HCHCH), 91.5 (RudCHCCH), 83.8 (RuCHCCHCH), 77.2 (OCH),
76.1 (RudCHCCHCHCHCH), 51.2 (br, CH2), 21.6 (CHCH3), 21.4
(CHCH3), 21.1 (o-CH3), 17.9 (p-CH3). 13C NMR (100.6 MHz,
CD2Cl2): δ 285.4 (RudCH), 232.7 (CrCO), 208.8 (RudCNN),
138.7 (arom. C-O), 138.6 (N-Cq), 136.8 (mesityl-o-Cq), 129.3
(mesityl-m-CH), 128.5 (mesityl-p-Cq), 107.3 (RudCHCq), 92.3
(RudCHCCHCHCH), 92.2 (RudCHCCH), 85.2 (RuCHCCHCH),
77.7 (OCH), 77.05 (RudCHCCHCHCHCH), 51.5 (br, CH2), 21.4
(CHCH3), 21.4 (CHCH3), 21.0 (br, o-CH3 + p-CH3). ESI-HRMS
(CH3CN, C36H41ClCrN3O4Ru [M - Cl + CH3CN]+): calcd
768.1234, found 768.1250.
Tricarbonyl(2-isopropoxystyrene)chromium(0) (10). 2-Iso-
propoxystyrene24 (9, 1.000 g, 6.2 mmol) in 3 mL of THF was added
to Cr(CO)6 (1.765 g, 8.0 mmol) in 440 mL of Bu2O/THF (10:1),
and the mixture was heated at reflux for 42 h. In the first 2 h the
color of the reaction mixture turned to orange. The reaction mixture
was cooled to 25 °C and filtered under argon through silica gel.
Solvent evaporation at reduced pressure gave an orange residue,
which was purified by column chromatography [SiO2, PE/TBME
(2:1), Rf ) 0.42] to give 1.050 g (3.5 mmol, 58%) of 10 as a yellow
powder (mp 63.5–64.0 °C).
One-Pot Synthesis of 11 from Grubbs I (1). At 25 °C 0.23
mL (0.39 mmol, 1.7 M in toluene) of potassium tert-amylate was
(58) Grela, K.; Kim, M. Eur. J. Org. Chem. 2003, 963–966.
(59) Vinokurov, N.; Michrowska, A.; Szmigielska, A.; Drzazga, Z.;
Wojciuk, G.; Demchuk, O. M.; Grela, K.; Pietrusiewicz, K. M.; Butenschön,
H. AdV. Synth. Catal. 2006, 348, 931–938.
IR (KBr): ν˜ 2981 (w) cm-1, 1941 (s, CO), 1837 (s, CO), 1626
(w), 1532 (w), 1461 (s), 1424 (s), 1375 (w), 1335 (w), 1280 (w),
1249 (s), 1157 (w), 1107 (s), 993 (w), 949 (w), 918 (s), 816 (w),
667(s), 625 (s). 1H NMR (400 MHz, C6D6): δ 6.64–6.71 (dd, 1H,
J ) 17.6 Hz, J ) 11.1 Hz, CHdCH2), 5.32 (d, 1H, J ) 17.6 Hz,
-CHdCHH), 5.27 (dd, 1H, J ) 6.6 Hz, J ) 1.2 Hz, arom. H),
4.92 (d, 1H, J ) 11.1 Hz, CHdCHH), 4.75–4.78 (dt, 1H, J ) 7.0
(60) Singh, S.; Nicholas, K. M. Chem. Commun. 1998, 149–150.
(61) Kabachnik, M. I.; Chang, C.-Y.; Tsvetkov, E. N. Dokl. Akad. Nauk
SSSR 1960, 135, 603–605.
(62) Ohashi, A.; Kikuchi, S.-i.; Yasutake, M.; Imamoto, T. Eur. J. Org.
Chem. 2002, 2535–2546.
(63) Dunne, K. S.; Lee, S. E.; Gouverneur, V. J. Organomet. Chem.
2006, 691, 5246–5259.

Bimetallic Grubbs-HoVeyda-Blechert Precatalyst
Organometallics, Vol. 27, No. 8, 2008 1885
added to 158 mg (0.4 mmol) of 1,3-dimesitylimidazolinium
tetrafluoroborate in 7 mL of hexane, and the mixture was stirred
for 1 h. Then 300 mg (0.36 mmol) of Grubbs I catalyst (1) was
added as a solid, and the reaction mixture was heated at reflux for
40 min, being monitored by TLC (hexane/EtOAc, 9:1). Thereafter
the reaction mixture was cooled to 25 °C, and 37 mg (0.38 mmol)
of CuCl and 113.3 mg (0.37 mmol) of 10 in 7 mL of dichlo-
romethane were added. After stirring the reaction mixture at reflux
for 1 h, solvents were removed at reduced pressure and the residue
was purified as described previously. Yield: 161 mg (0.21 mmol,
59%) of 11.
Bimetallic Complex 13. Tricarbonyl(2-isopropoxystyrene)chro-
mium(0) (10) (145.0 mg, 0.49 mmol) in dichloromethane (6 mL)
was added via syringe to benzylidene complex 1 (200 mg, 0.25
mmol) and CuCl (24.1 mg, 0.24 mmol) in dichloromethane (12
mL). The reaction mixture was heated at 40 °C for 1 h, the reaction
progress being monitored by TLC (Rf ) 0.13, hexane/TBME,
15:1). After solvent removal at reduced pressure the residue was
purified by column chromatography under argon, leading to 13 as
a brown-red powder, 85.6 mg (0.11 mmol, 48%).
(5 mL). The reaction mixture was heated at 40 °C for 1 h. After
solvent removal at reduced pressure the residue was dissolved in
benzene (10 mL) and carefully filtered under argon through silica
gel to remove residual 15. Subsequent elution with diethyl ether
afforded 40.1 mg (0.05 mmol, 43%) of 16 as a purple solid, which
decomposed during the NMR measurement. Mp ) 109–110 °C.
IR (ATR): ν˜ 2924 (w) cm -1, 2845 (w), 2363 (w), 2052 (w),
1955 (s, CO), 1874 (s, br, CO), 1479 (w), 1443 (w), 1262 (s), 1173
1
(w), 1099 (w), 887 (w), 851 (w), 806 (w), 674 (w), 657 (w). H
NMR (400 MHz, C6D6): δ ) 1.35 (d, J ) 6.0 Hz, 6H, 2 CHCH3),
2.71 (br, 18H, mesityl-CH3), 3.42 [sept, 1H, CH(CH3)2], 2.79 (s,
3H, OCH3), 3.68 (s, 4H, CH2), 3.88 (t, 1H, RudCHCCHCH), 4.25
(d, 1H, RudCHCCH or RuCHCCHCHCH), 4.69 (d, 1H,
RudCHCCH or RuCHCCHCHCH), 7.05 (s, 4H, mesityl-CH),
15.72 (s, 1H, RudCH) ppm.
Methylphenylvinylphosphane Borane Adduct (53). (a) Potas-
sium tert-butoxide (30 mg, 0.3 mmol) was added as a powder to a
stirred solution of 2-(boranatomethylphenyl)phosphanylethyl meth-
anesulfonate62 (60 mg, 0.2 mmol) in toluene (2 mL). The mixture
was stirred for 1 h at 25 °C. After quenching the reaction by addition
of water the organic layer was separated, and the aqueous layer
was extracted with ethyl acetate (3 × 10 mL). The combined
organic extracts were washed with aqueous NaHCO3 (20 mL) and
brine (30 mL) and dried with MgSO4, and the solvents were
removed at reduced pressure. The crude product was purified by
flash chromatography (SiO2, 25 × 4 cm, ethyl acetate) to afford
pure product as an oil, 37.9 mg (0.20 mmol, 86%). To prevent
decomposition, 53 was stored as a solution in dichloromethane at
-25 °C.
IR (ATR): ν˜ 2922 (w) cm -1, 2849 (w), 1957 (s, CO), 1882 (s,
br, CO), 1518 (w), 1444 (w), 1261 (w), 1102 (w), 949 (w), 801
1
(w), 725 (w), 658 (w), 622 (w). H NMR (400 MHz, CDCl3): δ
1.7–2.24 (m, 33H, PCy3; d, J ) 6.0 Hz, 3H, CHCH3; d, J ) 6.0
Hz, 3H, CHCH3), 4.90 (t, J ) 6.1 Hz, 1H, RudCHCCHCH), 5.02
[sept, J ) 6.0 Hz, 1H, CH(CH3)2], 5.47 (d, J ) 6.9 Hz, 1H,
RudCHCCHCHCHCH), 5.74 (dt, J ) 6.9 Hz, J ) 1.0 Hz, 1H,
RudCHCCHCHCH), 5.97 (dd, J ) 6.5 Hz, J ) 1.2 Hz, 1H,
RudCHCCH), 16.58 (d, J ) 4.2 Hz, 1H, 1-H) ppm. 13C NMR
(100.6 MHz, BB, DEPT, CDCl3): δ 21.9 (CHCH3), 22.7 (CHCH3),
26.2 (PCHCH2CH2CH2), 27.6 (d, 2JPC ) 12.3 Hz, PCHCH2), 29.9
(d, 1JPC ) 31.1 Hz, PCH), 35.6 (d, 3JPC ) 25.6 Hz, PCHCH2CH2),
77.2 (RudCHCCHCHCHCH), 77.8 [CH(CH3)2], 84.3 (Rud
CHCCHCH), 91.8 (RudCHCCH), 91.9 (RudCHCCHCHCH),
105.7 (RudCHC), 137.5 (RudCHCCO), 232.2 (CO), 274.01
(RudC) ppm. 31P NMR (CDCl3, 161 MHz): δ +64.1 ppm. ESI-
(b) To a stirred solution of methylphenylvinylphosphane60,61 (52,
200 mg, 1.3 mmol) in THF (2 mL) was added at 0 °C BH3 (115
mg, 1.4 mL, 1.4 mmol, 1.0 M in THF). The mixture was allowed
to reach 20 °C over 2 h. The reaction was quenched by addition of
2 N HCl (3 mL). The organic layers were separated, and the aqueous
layer was extracted with ethyl acetate (3 × 20 mL). The combined
extracts were washed with aqueous NaHCO3 (20 mL) and brine
(30 mL) and dried with MgSO4, and the solvents were removed
under reduced pressure. The crude product was purified by flash
chromatography (SiO2, 25 × 4 cm, ethyl acetate/cyclohexane, 2:5)
to afford pure product as a colorless viscous oil, 101 mg (0.6 mmol,
46%). To prevent decomposition, 127 was stored as a solution in
dichloromethane at -25 °C.
HRMS (CH3CN, C33H4837Cl52CrNO4P102Ru [M
CH3CN]+): calcd 742.1458, found 742.1459.
- Cl +
Tricarbonyl(η6-2-isopropoxy-3-methoxystyrene)chromi-
um(0) (15). 2-Isopropoxy-3-methoxystyrene47 (0.470 g, 2.4 mmol)
in THF (3 mL) was added to Cr(CO)6 (0.59 g, 2.7 mmol, 1.1 equiv)
in Bu2O/THF (10:1, 175 mL) and heated at reflux for 42 h. In the
first 2 h the color of the reaction mixture turned orange. The reaction
mixture was cooled to 25 °C and filtered under argon through silica
gel. Solvent evaporation at reduced pressure gave a yellow residue,
which was purified by column chromatography (SiO2, PE/TBME,
2:1) to give 0.46 g (1.3 mmol, 51%) of 15 as a light yellow powder.
Mp ) 99 °C.
1H NMR (400 MHz, CDCl3): δ 0.48 (m, 3H, BH3), 1.61 (d,
2JPH ) 10.3 Hz, 3H, CH3), 6.04 (m, 2H, P-CHdCH2), 6.29 (m,
1H, P-CHd), 7.43 (m, 3H, m-, p-H), 7.66 (m, 2H, o-H) ppm. 13
C
NMR (100.6 MHz, CDCl3): δ 11.1 (d, 1JPC ) 40.8 Hz, CH3), 128.7
(d, 3JPC ) 9.9 Hz, m-CH), 129.1 (d, 1JPC ) 57.3 Hz, P-Cq), 129.3
(d, 1JPC ) 52.2 Hz, P-CHdCH2), 131.1 (d, 4JPC ) 2.3 Hz, p-CH),
2
2
IR (ATR): ν˜ 2978 (w) cm -1, 1950 (s, CO), 1869 (s, CO), 1844
(s, CO), 1518 (w), 1411 (w), 1376 (w), 1276 (w), 1205 (w), 1097
(w), 1047 (w), 996 (w), 916 (w), 855 (w), 797 (w), 735 (w), 708
131.3 (d, JPC ) 9.4 Hz, o-CH), 133.1 (d, JPC ) 3.8 Hz,
P-CHdCH2) ppm. 31P NMR (162 MHz, CDCl3): δ 7.1–8.2 (m)
ppm.
1
General Procedure for Ring-Closing (Table 1) and Enyne
Metathesis (Table 2). A solution of 11 in dichloromethane [0.00050
mmol (0.1%), 0.00500 mmol (1%), or 0.02500 mmol (5%)] was
added to a solution of the substrate (0.5 mmol, 0.02 M) in
dichloromethane at 0 or at 25 °C. The mixture was stirred at this
temperature, and the reaction was monitored by TLC (hexane/ethyl
acetate). After the reaction was complete cold vinyl ethyl ether (0.5
mL, 2 M in CH2Cl2) was added to the reaction mixture. The solvent
was removed at reduced pressure, and the product was isolated by
column chromatography (SiO2, hexane/ethyl acetate). Product
identification was based on literature data.19,21–23,58
General Procedure for Cross Metathesis (Table 3). 11 in
dichloromethane [(0.00500 mmol (1%), 0.0125 mmol (2.5%), or
0.02500 mmol (5%)] was added to the substrate (0.5 mmol, 0.125
or 0.2 M) at 25 °C. The mixture was stirred at this temperature or
at 40 °C, and the reaction was monitored by TLC (hexane/ethyl
(w), 665 (w), 628 (s). H NMR (400 MHz, C6D6): δ 1.09 (d, J )
6.2 Hz, 3H, 1-H), 1.23 (d, J ) 6.1 Hz, 3H, 2-H), 2.97 (s, 3H, 13-
H), 4.11 (m, 1H, 6-H), 4.28 (sept, J ) 6.1 Hz, 1H, 3-H), 4.51 (m,
2H, 7-H; 8-H), 5.08 (d, J ) 11.0 Hz, 1H, 11′-H), 5.29 (d, J ) 17.8
Hz, 1H, 11-H), 6.52–6.78 (dd, J ) 17.8 Hz, J ) 11.0 Hz, 1H,
10-H) ppm. 13C NMR (100.6 MHz, BB, DEPT, HMQC, HMBC,
C6D6): δ 22.5 (C-2), 22.3 (C-1), 55.9 (C-13), 74.2 (C-6), 79.6 (C-
3), 81.9 (C-8), 90.2 (C-7), 104.5 (C-9), 117.4 (C-11), 127.1 (C-5),
130.4 (C-10), 136.8 (C-4), 234.3 (C-12) ppm. MS (EI) m/z (%):
328 (31) [M+], 272 (12), 244 (92), 216 (26), 202 (82), 186 (82),
150 (11). Anal. (C15H16O5Cr) Calcd: C 54.88, H 4.91. Found: C
54.81, H 5.21.
Bimetallic Complex 16. Tricarbonyl(2-isopropoxy-3-methoxy-
styrene)chromium(0) (15) (38.6 mg, 0.12 mmol) in dichloromethane
(2 mL) was added via syringe to benzylidene complex 3 (100 mg,
0.12 mmol) and CuCl (11.6 mg, 0.12 mmol) in dichloromethane

1886 Organometallics, Vol. 27, No. 8, 2008
VinokuroV et al.
the mesityl group attached to N2 treated as 2-fold positionally
disordered rigid group (Figure 3), anisotropic displacement param-
eters for all non-H atoms with the exception of the C atoms of the
disordered mesityl group, for which isotropic displacement param-
eters were used, H atoms geometrically placed and allowed to ride
on the respective C atoms, H atoms of the disordered mesityl group
were not considered, 294 parameters in final refinement, R1 ) 0.044
(I > 2σI, 2594 reflections), wR2 ) 0.072 (all reflections), largest
peak (hole) in final difference electron density map 0.43 (-0.50) e
Å-3
.
Figure 3. ORTEP diagram of 11 illustrating the two orientations
of the trimethylphenyl group attached to N2.
Acknowledgment. This research was kindly supported by
the Gottlieb Daimler- and Karl Benz-Foundation (doctoral
fellowship to N.V.) and by the Deutsche Forschungsgemein-
schaft. We thank Solvay Pharmaceuticals GmbH for the
donation of chemicals.
acetate). After the reaction was complete cold vinyl ethyl ether (0.5
mL, 1 M in CH2Cl2) was added. The solvent was removed at
reduced pressure, and the product was isolated by column chro-
matography (SiO2, hexane/ethyl acetate). Product identification was
based on literature data.21–23,59
Crystal Structure Analysis of 11.64 Crystals were obtained by
slow evaporation from hexane/TBME (2:1) under argon. Empirical
formula C34H27Cl2CrN2O4Ru, formula weight 751.54 g/mol, crystal
system monoclinic, space group P21/c (14), unit cell dimensions a
) 9.996(4) Å, b ) 23.873(8) Å, c ) 15.218(6) Å, ꢀ ) 99.64(5)°,
Supporting Information Available: NMR spectra of new
compounds and the .cif file of 11. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM701242T
V ) 3580(2) Å3, Z ) 4, dcalc ) 1.394 g/cm3, µ ) 0.911 mm-1
,
crystal size 0.33 × 0.07 × 0.07 m3, STOE IPDS one-axis
diffractometer with imaging plate detector, T ) 298 K, Mo KR
radiation (λ ) 0.71073 Å), θmax ) 25.90°, 51 080 (6712) measured
(unique) reflections, R(int) ) 0.076, direct methods, full-matrix
least-squares refinement on F2 including all data (SHELXL-97),65
(64) Crystallographic data (without structure factors) have been deposited
as supplementary publication no. CCDC 635880 at the Cambridge Crystal-
lography Data Centre. Copies can be obtained free of charge by contacting
the CCDC: deposit@ccdc.cam.ac.uk.
(65) Sheldrick, G. M. SHELX97, Programs for Crystal Structure
Analysis; University of Göttingen: Germany, 1997.