Chiral monodentate phosphoramidite ligands control the absolute configuration at pseudotetrahedral ruthenium: Asymmetric catalytic cyclopropanation of olefins

Article abstract of DOI:10.1016/j.tetasy.2004.05.040

Piano-stool ruthenium complexes of the type [RuCl₂(p-cymene)(L)] (L=chiral phosphoramidite ligand) catalyse the asymmetric cyclopropanation of styrene and α-methylstyrene with ethyl diazoacetate after activation with TlPF₆ or (Et

Full text of DOI:10.1016/j.tetasy.2004.05.040

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 2193–2197
Chiral monodentate phosphoramidite ligands control the absolute
configuration at pseudotetrahedral ruthenium: asymmetric
catalytic cyclopropanation of olefins
Dominik Huber and Antonio Mezzetti*
Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, ETH H€onggerberg,
CH-8093 Z€urich, Switzerland
Received 30 April 2004; accepted 10 May 2004
Abstract—Piano-stool ruthenium complexes of the type [RuCl2(p-cymene)(L)] (L ¼ chiral phosphoramidite ligand) catalyse the
asymmetric cyclopropanation of styrene and a-methylstyrene with ethyl diazoacetate after activation with TlPF6 or (Et3O)PF6 as
halide scavengers. With a-methylstyrene, good enantioselectivities were observed (up to 86% and 87% ee for the cis-and trans-
cyclopropane derivative, respectively). However, total yields and diastereoselectivities were generally low.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
containing bidentate N-donors as catalysts for ketone
hydrogenation.6 The common feature of these systems is
the use of a bidentate chiral ligand. Our present
approach investigates the possibility of controlling the
absolute configuration at the metal by means of a
monodentate chiral ligand. To the best of our knowl-
edge, monodentate stereogenic ligands have not been
used yet––unless bound to the arene or cyclopentadienyl
ligand by a tether.7;8 The advantage of our approach is
that it allows us to vary freely two ligands of the
pseudotetrahedral coordination sphere. It also opens up
new potential applications for recently developed, bulky
chiral monodentate ligands.9
Pseudotetrahedral complexes containing stereogenic
metal atoms have been the object of extensive stereo-
chemical investigations over the last 30 years starting
with
Brunner’s
pioneering
investigations
of
[Mn(Cp)(CO)(PPh3)(NO)].1 Chiral bidentate ligands
have been extensively used to control the stereochemis-
try at the metal in complexes of the type [RuCl(Cp)(P–
PÃ)] (P–PÃ ¼ chiral diphosphine)2 or [RuX(g6-arene)(L–
L)]þ.3 As substitutions at 18-electron complexes are
generally assumed to occur dissociatively, the selectivity
observed implies that the chiral diphosphine controls the
geometry of the putative 16-electron intermediate and
the direction of attack of the incoming ligand.
2. Results and discussion
Despite their potential, the application of chiral half-
sandwich ruthenium complexes in asymmetric catalysis
has been mainly restricted to hydrogenation and Diels-
As a model reaction, we chose the asymmetric cyclo-
propanation of olefins, which requires the formation of
a diastereomerically enriched carbene intermediate, for
example, [RuCl(@CHR)(p-cymene)(PÃ)]þ (PÃ ¼ chiral
phosphoramidite). Brookhart has prepared the diaste-
reomerically pure iron analogues of the type
[Fe(Cp)(@C(H)CH3)(CO)(PÃ)]þ 5 containing a chiral
monodentate phosphine.10 Diastereo-and enantioselec-
tive stoichiometric carbene transfer reactions to olefins
have recently been reported by Hossain and co-work-
ers,11 whereas catalytic cyclopropanation of olefins
catalysed by iron and ruthenium half-sandwich com-
plexes is restricted to achiral systems, such as [RuCl
Alder reactions.3c For the latter, Kundig has devel-
€
oped complexes of the type [Ru(Cp)(OCMe2)(P–P)]þ
containing electron-poor chiral diphosphines (P–P).4
Davies, Oro, and Faller have independently studied
catalysts of the type [RuCl(p-cymene)(L–L)]þ (L–L ¼ P–
O-, P–N-, N–N- and P,S-hybrid ligands).5 Noyori et al.
and Ito et al. used half-sandwich ruthenium complexes
* Corresponding author. Tel.: +41-44-632-61-21; fax: +41-44-632-13-
10; e-mail: mezzetti@inorg.chem.ethz.ch
0957-4166/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.05.040

2194
D. Huber, A. Mezzetti / Tetrahedron: Asymmetry 15 (2004) 2193–2197
R
R
R
R
O
O
O
O
P
N
S
P
N
S
1b
1a
Chart 1.
(CO)2(C5Me5)] and [RuCl2(g3-allyl)(C5Me5)],12 [RuCl2
(g6-p-cymene)(P)] (P ¼ monodentate phosphine with a
pendant aryl group),13 [Ru(Cp)(MeCN)3]þ14 and [RuCl
(Cp)(PPh3)2].15 The latter catalyst, similar to [Fe(Cp)
(CO)2(THF)]þ,16 cyclopropanates styrene with moderate
to good cis-selectivity. As cis-selective catalysts for
asymmetric cyclopropanation are rare,17–20 we decided
to scrutinise the potential of half-sandwich complexes
of ruthenium of the type [RuCl2(p-cymene)(PÃ)]
(PÃ ¼ chiral monodentate P-containing ligand). Thus, we
tested O,O0-(S)-(1,10-dinaphthyl-2,20-diyl)-N,N0-bis[(R)-
1-phenylethyl]phosphoramidite 1a and O,O0-(S)-(1,10-
dinaphthyl-2,20-diyl-N,N0-bis[(R)-1-naphthylethyl]phos-
phoramidite 1b (Chart 1).21
Cl
Cl
Ru Ru
ꢀ
Figure 1. X-ray structure of 2a. Distances (A) and angles (deg): Ru–
C(1), 2.201(12); Ru–C(2), 2.218(9); Ru–C(3), 2.213(11); Ru–C(4),
2.197(11); Ru–C(5), 2.170(10); Ru–C(6), 2.206(10); Ru–Cl(1), 2.405(3);
Ru–Cl(2), 2.387(3); Ru–P, 2.317(3); P–Ru–Cl(1), 91.84(10); P–Ru–
Cl(2), 89.06(9); Cl(2)–Ru–Cl(1), 85.50(10).
1a or 1b
Cl
CH2Cl2
20oC
Cl
Ru
Cl
Cl
P*
2a (P* = 1a)
2b (P* = 1b)
Scheme 1.
22
Ligand 1a reacts readily with [RuCl2(p-cymene)]2
(1.1 equiv, CH2Cl2, room temperature, 1 h) to give
[RuCl2(p-cymene)(1a)] 2a (93% yield) (Scheme 1).23
X-ray structure determination of 2a24 showed that
the bulky phosphoramidite ligand effectively shields the
ruthenium atom (Figs. 1 and 2). Ruthenium arene
complexes containing chiral, monodentate P-donor
ligands are rare25 and, to the best of our knowledge,
have never been used for asymmetric catalytic reactions.
Complex 2a was activated by chloride abstraction with
the aim of obtaining the coordinatively unsaturated 16-
electron species [RuCl(p-cymene)(1a)]þ. Both (Et3O)PF6
and TlPF6 (1.1 equiv) react with 2a in CH2Cl2 within 0.5
and 2 h, respectively, to give the same orange complex
3a featuring a singlet at d 153.0 in the 31P NMR spec-
trum. Preliminary pulse gradient spin-echo (PGSE)
measurements26 suggest that 3a is a monomeric complex
based on the [RuCl(p-cymene)(1a)]þ fragment. Its
structure is currently under investigation.
Figure 2. Top view of complex 2a.

D. Huber, A. Mezzetti / Tetrahedron: Asymmetry 15 (2004) 2193–2197
2195
Table 1. Catalytic cyclopropanationa
R
R
R
CO2Et
N2CHCO2Et
+
2 (5 mol %)
MPF6
CO2Et
Ph
Ph
Ph
cis
trans
R = H, Me
Run
Ligand
R
MPF6
Mþ
Conv. (%)
Yield (%)
cis/trans
Ee (%)b
cis
trans
1
2
3
4
5
6
7
8
9
1a
1a
1a
1a
1b
1b
1b
1b
1b
H
Et3Oþ
Tlþ
Et3Oþ
Tlþ
Et3Oþ
Tlþ
Et3Oþ
Tlþ
Et3Oþc
37
30
31
31
6
25
15
31
29
5
42:58
40:60
60:40
61:39
45:55
46:54
57:43
57:43
60:40
8 (1R,2S)
2 (1R,2S)
rac
3 (1R,2R)
5 (1R,2R)
rac
H
Me
Me
H
8
rac
68 (1R,2R)
59 (1R,2R)
77 (1S,2R)
74 (1S,2R)
H
9
5
Me
Me
Me
19
19
13
19
19
9
)86
)83
)28
87
84
24
a Catalyst preparation: 2a (24 lmol) and TlPF6 or (Et3O)PF6 (26 lmol, 1.1 equiv) were dissolved in CH2Cl2 (1 mL) and stirred at room temperature
for 17 h. TlCl was filtered off with a syringe filter. With ligand 1b, the catalyst was prepared in situ from [RuCl2(p-cymene)]2 (12 lmol), 1b (48 lmol)
and the halide scavenger (26 lmol). Standard catalytic run: An internal standard and the olefin (0.48 mmol) were added to the solution of the
catalyst (24 lmol, 5 mol %). Ethyl diazoacetate (0.48 mmol, 1 equiv vs olefin) in CH2Cl2 (1 mL) was added over 6 h by a syringe pump. The total
reaction time was 20 h at room temperature in the dark. Results are the average of at least two experiments.
b The absolute configuration was determined for ethyl cis-and trans-phenylcyclopropane-1-carboxylate (as previously described)20a;28 but not for
ethyl cis-and trans-3-methyl-2-phenylcyclopropane-1-carboxylate.20b;29
c Two equivalents.
The 2a/MPF6 system (M ¼ Et3O or Tl) catalysed the
cyclopropanation of styrene by decomposition of ethyl
diazoacetate with low enantio-and diastereoselectivity
(8% ee and 42:58 cis/trans ratio) (Table 1, run 1). Similar
results were obtained with a-methylstyrene as the sub-
strate (8% ee and 61:39 cis/trans ratio) (run 4). In the
case of styrene, the formation of the trans-isomer was
slightly favoured, whereas with a-methylstyrene the cis-
isomer was predominant. This could be explained by the
sterically more demanding methyl group. The yields
were from low to moderate (15–31%), but increased
when going from styrene to a-methylstyrene.
of 1b (vs Ru) and the halide scavenger. The 31P NMR
spectrum of this reaction solution displayed the signal of
3b and that of the free ligand 1b, indicating that only
one ligand molecule bound to ruthenium. With this
procedure, the performance of the catalytic system is
stable at high enantioselectivity and is perfectly repro-
ducible. Thus, styrene can be cyclopropanated with
moderate enantioselectivity for both diastereoisomers
(cis: 77%; trans: 68% ee) with (Et3O)PF6 as the chloride
scavenger (Table 1, run 5). With a-methylstyrene, both
diastereoisomers were formed with good enantioselec-
tivity (cis: 86%; trans: 87% ee) with (Et3O)PF6 as the
chloride scavenger (Table 1, run 7). Comparable results
were obtained with TlPF6 as chloride scavenger (runs 6
and 8). Although yields were lower than with 1a, a sig-
nificant, similar increase was observed upon increasing
the substitution (styrene, 5%; a-methylstyrene, 19%
yield), which points to the predominance of electronic
factors over steric ones. The activation of 2b with
2 equiv of (Et3O)PF6, which probably caused the
abstraction of both chlorides, decreased both the yield
and enantioselectivity (run 9).
The enantioselectivity could be dramatically improved
upon increasing the steric bulk of the phosphoram-
idite. Ligand 1b reacts with [RuCl2(p-cymene)]2
(1.1 equiv, CH2Cl2, room temperature, 1 h) to give
[RuCl2(p-cymene)(1b)] 2b in 49% yield. We have not yet
been able to isolate pure 2b, which we attribute to the
facile dissociation of the bulky phosphoramidite. In-
deed, the 31P spectrum of isolated 2b exhibited a singlet
at d 145.0 for 2b along with the signal of the free ligand
1b (d 148.3, 10%).27 Either TlPF6 or (Et3O)PF6
(1.1 equiv) abstract chloride from 2b to give a new
complex 3b that shows a broadened singlet at d 166.5 in
the 31P NMR spectrum and is presently being charac-
terised.
Overall, some general trends can be recognised.
Increasing the steric bulk of either the monodentate
chiral ligand or of the substrate is beneficial to the
enantioselectivity of the reaction, but not to the activity
of the catalyst. The results with the naphthyl-substituted
ligand 1b and a-methylstyrene indicate that the system is
promising for 1,1-disubstituted olefins, which are more
difficult to cyclopropanate than styrene. A general
drawback of these catalysts is the low cyclopropane
yield (up to 37% for both diastereoisomers), which can
be partially explained by the competitive homocoupling
of the carbene. Indeed, after 20 h of reaction time, the
Preliminary cyclopropanation tests with the catalysts
prepared by reacting 2b (either prepared in situ or iso-
lated) with TlPF6 or (Et3O)PF6 (1.1 equiv), indicated
that ligand 1b gave higher enantioselectivities than 1a.
The results were not reproducible though, probably due
to the low stability of the catalyst. To suppress ligand
dissociation, [RuCl2(p-cymene)] was treated with 2 equiv

2196
D. Huber, A. Mezzetti / Tetrahedron: Asymmetry 15 (2004) 2193–2197
1H NMR spectrum of the reaction solution (run 9)
showed that, besides the cyclopropanation products
(9%), maleate and fumarate also formed (ca. 46% and
8% yield, respectively). However, as unreacted ethyl
diazoacetate is still present in the reaction solution (ca.
27% of starting amount), the homocoupling alone does
not account for the low yield (at least in this case).
Preliminary monitoring of the reaction course by gas
chromatography suggests that the catalyst stays active
during the whole reaction time. Thus, the most probable
explanation of the low cyclopropane yield is the intrinsic
low activity of the catalyst. Finally, the system did not
show the expected cis-selectivity so far. Present efforts
are being directed to improve the activity and stereo-
selectivity of the catalyst.
12. Simal, F.; Demonceau, A.; Noels, A. F.; Knowles, D. R.
T.; O’Leary, S.; Maitlis, P.; Gusev, O. J. Organomet.
Chem. 1998, 558, 163.
13. Simal, F.; Jan, D.; Demonceau, A.; Noels, A. F. Tetra-
hedron Lett. 1999, 40, 1653.
14. Matsushima, Y.; Kikuchi, H.; Uno, M.; Takahashi, S.
Bull. Chem. Soc. Jpn. 1999, 72, 2475.
15. Baratta, W.; Herrmann, W. A.; Kratzer, R. M.; Rigo, P.
Organometallics 2000, 19, 3664.
16. Mayer, M. M.; Hossain, M. M. J. Org. Chem. 1998, 63,
6839.
17. For a recent comprehensive review of the literature, see:
(a) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern
Catalytic Methods for Organic Synthesis with Diazo
Compounds: From Cyclopropanes to Ylides; New York:
Wiley, 1998, Chapter 4, pp 183–203; (b) Comprehensive
Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A.,
Yamamoto, H., Eds.; Springer: Berlin, 1999; pp 513–
603, Chapter 16.
18. (a) Uchida, T.; Irie, R.; Katsuki, T. Synlett 1999, 1793; (b)
Uchida, T.; Irie, R.; Katsuki, T. Tetrahedron 2000, 56,
3501.
19. (a) Niimi, T.; Uchida, T.; Irie, R.; Katsuki, T. Adv. Synth.
Catal. 2001, 343, 79; (b) Niimi, T.; Uchida, T.; Irie, R.;
Katsuki, T. Tetrahedron Lett. 2000, 41, 3647; (c) Fukuda,
T.; Katsuki, T. Tetrahedron 1997, 53, 7201.
Acknowledgements
We thank Mr. P. G. Anil Kumar for the PGSE NMR
experiments and the Swiss National Science Foundation
for financial support to D.H. (grant 200020-101357).
20. (a) Bachmann, S.; Furler, M.; Mezzetti, A. Organometal-
lics 2001, 20, 2102; (b) Bachmann, S.; Mezzetti, A. Helv.
Chim. Acta 2001, 84, 3063; (c) Bonaccorsi, C.; Bachmann,
S.; Mezzetti, A. Tetrahedron: Asymmetry 2003, 14, 845.
21. The phosphoramidites 1a and 1b were synthesised accord-
ing to the procedure of Feringa: Arnold, L. A.; Imbos, R.;
Mandoli, A.; de Vries, A. H. M.; Naasz, R.; Feringa, B. L.
Tetrahedron 2000, 56, 2865; See also: Boiteau, J. G.;
Minnaard, A. J.; Feringa, B. L. J. Org. Chem. 2003, 68,
9481.
References and notes
1. (a) Brunner, H. Z. Anorg. Allg. Chem. 1969, 368, 120; (b)
Brunner, H. Adv. Organomet. Chem. 1980, 18, 151.
2. (a) Consiglio, G.; Morandini, F. Chem. Rev. 1987, 87, 761;
(b) Morandini, F.; Consiglio, G.; Lucchini, V. Organo-
metallics 1985, 4, 1202; (c) For seminal papers concerning
[RuCl(Cp)(P–PÃ)] complexes, see also: Morandini, F.;
Consiglio, G.; Straub, B.; Ciani, G.; Sironi, A. J. Chem.
Soc., Dalton Trans. 1983, 2293; (d) Consiglio, G.; Mor-
andini, F. J. Organomet. Chem. 1986, 310, C66.
22. Bennett, M. A.; Smith, A. K. J. Chem. Soc., Dalton Trans.
1974, 233.
3. (a) Bennett, M. A. Coord. Chem. Rev. 1997, 166, 225; (b)
For their application as stoichiometric reagents in organic
chemistry, see: Pigge, F. C.; Coniglio, J. J. Curr. Org.
Chem. 2001, 5, 757; (c) Ganter, C. Chem. Soc. Rev. 2003,
32, 130.
23. RuCl2(p-cymene)]2 (387 mg, 0.632 mmol) and 1a (750 mg,
1.39 mmol, 1.1 equiv) were dissolved in dry CH2Cl2
(20 mL) under an Ar atmosphere, with the resulting
solution stirred at room temperature for 1 h. 2-Propanol
(15 mL) was added and CH2Cl2 evaporated. The precip-
€
4. (a) Kundig, E. P.; Saudan, C. M.; Alezra, V.; Viton, F.;
Bernardinelli, G. Angew. Chem., Int. Ed. 2001, 40, 4481;
itate was filtered off and dried in vacuum to give 2a as an
23
D
orange solid. Yield: 992 mg (93%). ½aŠ ¼ þ65 (c 0.125,
(b) Viton, F.; Bernardinelli, G.; Kundig, E. P. J. Am.
Chem. Soc. 2002, 124, 4968.
CHCl3). 1H NMR (300 MHz, CDCl3):
d
1.19 (d,
€
J ¼ 6:9 Hz, 3H, cymene-CH(CH3)2); 1.30 (d, J ¼ 6:9 Hz,
3H, cymene-CH(CH3)2); 1.71 (d, J ¼ 6:9 Hz, 6H,
CH(Ph)(CH3); 2.11 (s, 3H, cymene-CH3); 2.85 (hept,
J ¼ 6:9 Hz, 1H, cymene-CH(CH3)2); 4.38 (d, J ¼ 4:8 Hz,
1H, cymene-Harom); 4.99 (d, J ¼ 6:0 Hz, 1H, cymene-
Harom); 5.10–5.16 (m, 2H, NCH); 5.19 (d, J ¼ 6:0 Hz, 1H,
cymene-Harom); 5.24 (d, J ¼ 6:0 Hz, 1H, cymene-Harom);
6.66–8.02 (m, 22H, Harom). 31P NMR (121.5 MHz, CDCl3):
d 141.0 (s). MS (HiRes MALDI): m=z 676 ([M)(p-
cymene))Cl]þ, 100). Anal. Calcd for C46H44Cl2NO2PRu:
C, 65.32; H, 5.24; N, 1.67. Found: C, 65.44; H, 5.40; N,
1.67.
5. (a) Davies, D. L.; Fawcett, J.; Garratt, S. A.; Russell, D.
R. Chem. Commun. 1997, 1351; (b) Carmona, D.; Cativ-
iely, C.; Elipe, S.; Lahoz, F. J.; Lamata, M. P.; de Viu,
L. R.; Oro, L. A.; Vega, C.; Viguri, F. Chem. Commun.
1997, 2351; (c) Faller, J. W.; Grimmond, B. J.; D’Alliessi,
D. G. J. Am. Chem. Soc. 2001, 123, 2525; (d) Faller, J. W.;
Grimmond, B. J. Organometallics 2001, 20, 2454.
6. (a) Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008; (b)
Ito, M.; Hirakawa, M.; Murata, K.; Ikariya, T. Organo-
metallics 2001, 20, 379.
€
7. Butenschon, H. Chem. Rev. 2000, 100, 1527.
8. Trost, B. M.; Vidal, B.; Thommen, M. Chem. Eur. J. 1999,
5, 1055.
9. Tang, W.; Zhang, X. Chem. Rev. 2003, 103, 3029; See also:
Lagasse, F.; Kagan, H. B. Chem. Pharm. Bull. 2000, 48,
315.
10. Brookhart, M.; Liu, Y. M.; Goldman, E. W.; Timmers, D.
A.; Williams, G. D. J. Am. Chem. Soc. 1991, 113, 927.
11. (a) Theys, R. D.; Hossain, M. M. Tetrahedron Lett. 1995,
24. Orange crystals of 2a were grown from 2-propanol.
Crystal data: monoclinic, P21, 0.30 · 0.06 · 0.03 mm,
ꢀ
a ¼ 12:3128ð11Þ, b ¼ 13:9824ð12Þ, c ¼ 12:3910ð11Þ A,
3
ꢀ
b ¼ 112:163ð2Þꢁ, V ¼ 1975:6ð3Þ A , Z ¼ 2, F ð000Þ ¼ 872,
Dcalcd ¼ 1:422 Mg cmꢀ3, l ¼ 0:612 mmꢀ1. Data were col-
lected at room temperature on a Bruker AXS SMART
APEX platform in the h range 2.30–20.81ꢁ. The structure
was solved with SHELXTL using direct methods. Of the
7619 measured (ꢀ11 6 h 6 12, ꢀ13 6 k 6 13, ꢀ12 6 l 6 12),
4121 unique reflections were used in the refinement (full-
matrix least squares on F 2 with anisotropic displacement
€
36, 5113; (b) Wang, Q.; Fosterling, F. H.; Hossain, M. M.
Organometallics 2002, 21, 2596, and references cited
therein.

D. Huber, A. Mezzetti / Tetrahedron: Asymmetry 15 (2004) 2193–2197
2197
parameters). The absolute structure parameter refined to
)0.03(5). R1 ¼ 0:0557 [3578 data with Fo > 2rðFoÞ],
wR2 ¼ 0:1091 (all 4121 data). Max. and min. difference
CDCl3): d 1.17 (d, J ¼ 6:9 Hz, 3H, cymene-CH(CH3)2);
1.21 (d, J ¼ 6:6 Hz, 3H, cymene-CH(CH3)2); 2.00 (s, 3H,
cymene-CH3); 2.05 (d, J ¼ 5:7 Hz, 6H, CH(Ph)(CH3); 2.88
(hept, J ¼ 6:9 Hz, 1H, cymene-CH(CH3)2); 4.89–5.93 (m,
4H, cymene-Harom and NCH); 5.07 (d, J ¼ 8:7 Hz, 1H,
cymene-Harom and NCH); 5.35 (d, J ¼ 6:0 Hz, 1H, cym-
ene-Harom and NCH); 6.93–8.20 (m, 26H, Harom). 31P
NMR (121.5 MHz, CDCl3): d 145.0 (s, 90%, complex 2b);
148.3 (s, 10%, free ligand 1b).
peaks were +0.417 and )0.598 e Aꢀ3. Crystallographic
ꢀ
data (excluding structure factors) for 2a have been
deposited with the Cambridge Crystallographic Data
Centre as supplementary publication numbers CCDC
234351. Copies of the data can be obtained, free of charge,
on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [fax: +44(0)-1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk].
28. Achiral GC analysis: Optima, 25 m, He carrier (100 kPa).
Temperature programme: 50 ꢁC isotherm for 5 min, then
to 200 ꢁC at 5 ꢁC minꢀ1. tR (min): styrene, 8.5; decane
(internal standard), 12.8; ethyl-cis-2-phenyl-cyclopropane
carboxylate, 26.5; ethyl-trans-2-phenyl-cyclopropane car-
boxylate, 27.9. Chiral GC analysis: Supelco Beta Dex 120,
1.4 mL He minꢀ1; temperature programme: 120 ꢁC iso-
therm. tR (min): cis-(1R,2S), 52.8; cis-(1S,2R), 55.5; trans-
(1R,2R), 62.7; trans-(1S,2S), 64.6.
25. (a) Salvadori, P.; Pertici, P.; Marchetti, F.; Lazzaroni, R.;
Vitulli, G.; Bennett, M. A. J. Organomet. Chem. 1989, 370,
155; (b) Pertici, P.; Pitzalis, E.; Marchetti, F.; Rosini, C.;
Salvadori, P. J. Organomet. Chem. 1994, 466, 221; (c)
Faller, J. W.; Patel, B. P.; Albrizzio, M. A.; Curtis, M.
Organometallics 1999, 18, 3096; (d) Arena, C. G.; Calamia,
S.; Faraone, F.; Graiff, C.; Tiripicchio, A. J. Chem. Soc.,
Dalton Trans. 2000, 3149.
26. (a) Pregosin, P. S.; Martinez-Viviente, E.; Kumar, P. G. A.
Dalton Trans. 2003, 4007; (b) Binotti, B.; Macchioni, A.;
Zuccaccia, C.; Zuccaccia, D. Comments Inorg. Chem.
2002, 23, 417.
29. Achiral GC analysis: as for styrene. tR (min): a-methyl-
styrene, 12.0; dodecane (internal standard) 19.6; ethyl
(cis)-2-methyl-phenylcyclopropane-1-carboxylate,
26.3;
ethyl (trans)-2-methyl-phenylcyclopropane-1-carboxylate,
27.6. Chiral GC analysis: Supelco Beta Dex 120, 1.4 mL
He minꢀ1; temperature programme: 120 ꢁC isotherm. tR
(min) (cis)-I, 39.3; (cis)-II, 41.3; (trans)-I, 49.7; (trans)-II,
50.9. Positive ee values mean that II is the major isomer.
27. Synthesis as for 2a from [RuCl2(p-cymene)]2 (196 mg,
0.320 mmol) and 1b (451 mg, 0.705 mmol, 1.1 equiv).
Yield: orange solid, 260 mg (49%). 1H NMR (300 MHz,