Asymmetric inter- and intramolecular cyclopropanation of alkenes catalyzed by chiral ruthenium porphyrins. Synthesis and crystal structure of a chiral metalloporphyrin carbene complex

Article abstract of DOI:10.1021/ja001416f

Extensive investigations of asymmetric intermolecular cyclopropanation of terminal alkenes with diazoacetates catalyzed by ruthenium porphyrin [Ru(P*)(CO)(EtOH)] (1, H₂P* = 5,10,15,20-tetrakis-{(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8- dimethanoanthracene-9-yl}porphyrin) and the application of catalyst 1 to asymmetric intramolecular cyclopropanation of allylic or homoallylic diazoacetates are described. The intermolecular cyclopropanation of styrene and its derivatives with ethyl diazoacetate afforded the corresponding cyclopropyl esters in up to 98% ee with high trans/cis ratios of up to 36 and extremely high catalyst turnovers of up to 1.1 × 10⁴. Examination of the effects of temperature, diazoacetate, solvent, and substituent in the intermolecular cyclopropanation reveals that (i) both enantioselectivity and trans selectivity increase with decreasing temperature, (ii) sterically encumbered diazoacetates N₂CHCO₂R such as R = Bu^t, and donor solvents, such as diethyl ether and tetrahydrofuran, are beneficial to the trans selectivity, and (iii) electron-donating para substituents on styrene accelerate the cyclopropanations, with the log(k_x/k_H) vs σ⁺ plot for para-substituted styrenes p-X-C₆H₄CH=CH₂ (X = MeO, Me, Cl, CF₃) exhibiting good linearity with a small negative ρ⁺ value of -0.44 ± 0.09. In the case of intramolecular cyclopropanation, complex 1 promoted the decomposition of a series of allylic diazoacetates to form the cyclopropyl lactones in up to 85% ee, contributing the first efficient metalloporphyrin catalyst for an asymmetric intramolecular cyclopropanation. Both the inter- and intramolecular cyclopropanations were proposed to proceed via a reactive chiral ruthenium carbene intermediate. The enantioselectivities in these processes were rationalized on the basis of the X-ray crystal structures of closely related stable chiral carbene complexes [Ru(P*)(CPh₂)] (2) and [Ru(P*)(C(Ph)-CO₂CH₂CH=CH₂)] (3) obtained from reactions of complex 1 with N₂CPh₂ and N₂C(Ph)CO₂CH₂CH=CH₂, respectively.

Full text of DOI:10.1021/ja001416f

J. Am. Chem. Soc. 2001, 123, 4119-4129
4119
Asymmetric Inter- and Intramolecular Cyclopropanation of Alkenes
Catalyzed by Chiral Ruthenium Porphyrins. Synthesis and Crystal
Structure of a Chiral Metalloporphyrin Carbene Complex
Chi-Ming Che,* Jie-Sheng Huang, Fu-Wa Lee, Yan Li, Tat-Shing Lai, Hoi-Lun Kwong,†
Pang-Fei Teng,† Wing-Sze Lee,† Wai-Cheung Lo, Shie-Ming Peng,‡ and Zhong-Yuan Zhou§
Contribution from the Department of Chemistry, The UniVersity of Hong Kong, Pokfulam Road, Hong
Kong, Shanghai-Hong Kong Joint Laboratory on Chemical Synthesis, Shanghai Institute of Organic
Chemistry, Shanghai, China, Department of Biology and Chemistry, City UniVersity of Hong Kong, Tat
Chee AVenue, Kowloon Tong, Hong Kong, Department of Chemistry, National Taiwan UniVersity, Taipei,
Taiwan, and Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic
UniVersity, Hung Hom, Kowloon, Hong Kong
ReceiVed April 24, 2000
Abstract: Extensive investigations of asymmetric intermolecular cyclopropanation of terminal alkenes with
diazoacetates catalyzed by ruthenium porphyrin [Ru(P*)(CO)(EtOH)] (1, H2P* ) 5,10,15,20-tetrakis-
{(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene-9-yl}porphyrin) and the application of
catalyst 1 to asymmetric intramolecular cyclopropanation of allylic or homoallylic diazoacetates are described.
The intermolecular cyclopropanation of styrene and its derivatives with ethyl diazoacetate afforded the
corresponding cyclopropyl esters in up to 98% ee with high trans/cis ratios of up to 36 and extremely high
catalyst turnovers of up to 1.1 × 104. Examination of the effects of temperature, diazoacetate, solvent, and
substituent in the intermolecular cyclopropanation reveals that (i) both enantioselectivity and trans selectivity
increase with decreasing temperature, (ii) sterically encumbered diazoacetates N2CHCO2R, such as R ) But,
and donor solvents, such as diethyl ether and tetrahydrofuran, are beneficial to the trans selectivity, and (iii)
electron-donating para substituents on styrene accelerate the cyclopropanations, with the log(kX/kH) vs σ+ plot
for para-substituted styrenes p-X-C6H4CHdCH2 (X ) MeO, Me, Cl, CF3) exhibiting good linearity with a
small negative F+ value of -0.44 ( 0.09. In the case of intramolecular cyclopropanation, complex 1 promoted
the decomposition of a series of allylic diazoacetates to form the cyclopropyl lactones in up to 85% ee,
contributing the first efficient metalloporphyrin catalyst for an asymmetric intramolecular cyclopropanation.
Both the inter- and intramolecular cyclopropanations were proposed to proceed via a reactive chiral ruthenium
carbene intermediate. The enantioselectivities in these processes were rationalized on the basis of the X-ray
crystal structures of closely related stable chiral carbene complexes [Ru(P*)(CPh2)] (2) and [Ru(P*)(C(Ph)-
CO2CH2CHdCH2)] (3) obtained from reactions of complex 1 with N2CPh2 and N2C(Ph)CO2CH2CHdCH2,
respectively.
Introduction
selective catalyst for asymmetric intermolecular cyclopropana-
tion of terminal alkenes with diazoacetates (reaction 1 in Scheme
1). Currently, in the case of the cyclopropanation of styrene
with ethyl diazoacetate (EDA), a classical transformation for
determining the catalyst effectiveness for reaction 1,1 the
semicorrin- and bis(oxazoline)-copper catalysts feature excel-
lent enantioselectivity (ee up to 99%) but with a rather low trans
selectivity (trans/cis <4); the ruthenium-pybox catalysts result
in high enantioselectivity and trans selectivity (ee up to 91%,
trans/cis up to 16) but suffer from low catalyst turnover (∼100).
Despite a vast number of investigations on metal complex-
catalyzed asymmetric intermolecular cyclopropanations of alk-
enes with diazo compounds1 and the discovery of several types
of excellent catalysts for these transformations, such as semi-
corrin-2 and bis(oxazoline)3-copper and ruthenium-pybox
complexes,4,5a the challenge remains to develop a robust, highly
† City University of Hong Kong.
‡ National Taiwan University.
§ The Hong Kong Polytechnic University.
(1) Selected reviews: (a) Doyle, M. P.; Forbes, D. C. Chem. ReV. 1998,
98, 911. (b) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds; Wiley: New York,
1998. (c) Doyle, M. P.; Protopopova, M. N. Tetrahedron 1998, 54, 7919.
(d) Doyle, M. P. In ComprehensiVe Organometallic Chemistry II, Vol. 12;
Hegedus, L. S., Ed.; Pergamon: Oxford, 1995; p 387. (e) Togni, A.;
Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1994, 33, 497.
(2) (a) Fritschi, H.; Leutenegger, U.; Pfaltz, A. Angew. Chem., Int. Ed.
Engl. 1986, 25, 1005. (b) Fritschi, H.; Leutenegger, U.; Pfaltz, A. HelV.
Chim. Acta 1988, 71, 1553.
(3) (a) Lowenthal, R. E.; Abiko, A.; Masamune, S. Tetrahedron Lett.
1990, 31, 6005. (b) Evans, D. A.; Woerpel, K. A.; Hinman, M. M.; Faul,
M. M. J. Am. Chem. Soc. 1991, 113, 726. (c) Mu¨ller, D.; Umbricht, G.;
Weber, B.; Pfaltz, A. HelV. Chim. Acta 1991, 74, 232.
(4) (a) Nishiyama, H.; Itoh, Y.; Matsumoto, H.; Park, S.-B.; Itoh, K. J.
Am. Chem. Soc. 1994, 116, 2223. (b) Nishiyama, H.; Itoh, Y.; Sugawara,
Y.; Matsumoto, H.; Aoki, K.; Itoh, K. Bull. Chem. Soc. Jpn. 1995, 68,
1247. (c) Park, S.-B.; Sakata, N.; Nishiyama, H. Chem. Eur. J. 1996, 2,
303. (d) Nishiyama, H.; Aoki, K.; Itoh, H.; Iwamura, T.; Sakata, N.;
Kurihara, O.; Motoyama, Y. Chem. Lett. 1996, 1071.
(5) Abbreviations: (a) pybox ) 2,6-bis(oxazolinyl)pyridine. (b) P* )
5,10,15,20-tetrakis{(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimetha-
noanthracene-9-yl}porphyrinato dianion. (c) TPP ) meso-tetraphenylpor-
phyrinato dianion. (d) TMP ) meso-tetrakis(2,4,6-trimethylphenyl)por-
phyrinato dianion. (e) tmtaa ) 7,16-dihydro-6,8,15,17-tetramethyldibenzo-
[b,i]-[1,4,8,11]tetraazacyclotetradecinato(2-). (f) TTP ) meso-tetrakis(p-
tolyl)porphyrinato dianion.
10.1021/ja001416f CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/12/2001

4120 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
Che et al.
Scheme 1
complexes [Ru(P*)(CPh2)] (2) and [Ru(P*)(C(Ph)CO2CH2CHd
CH2)] (3). To our knowledge, complexes 2 and 3 contribute
the first isolated chiral metalloporphyrin carbene complexes and
the latter represents a unique metalloporphyrin carbene complex
whose carbene group bears a pendant alkene CdC bond.
We were impressed by the extremely high catalyst turnovers
of some metalloporphyrins in catalyzing alkene epoxidations
(up to 104).6 Exploring metalloporphyrin catalysts for asym-
metric alkene cyclopropanation, the carbon analogue of epoxi-
dation, would thus be of importance. In pioneering works by
Kodadek and co-workers,7 chiral rhodium(III) porphyrins
catalyze reaction 1 with thousands of turnovers and moderate
enantiocontrol (ee up to 60%). However, the trans/cis ratios
obtained are low (<1), which actually makes the rhodium
porphyrins unique catalysts for cis selectiVe cyclopropanations.
Recently, Simonneaux and co-workers8 and our own group9
independently discovered that chiral ruthenium porphyrins
catalyze reaction 1 with high trans selectiVity. In our case, the
use of [Ru(P*)(CO)(EtOH)] (1) bearing the celebrated Halter-
man’s D4-symmetric sterically encumbered porphyrin P* 5b,10
gave rise to substantially higher enantio- and diastereocontrol
(ee 91%, trans/cis 24). Similar results were obtained subse-
quently by Berkessel and co-workers.11 In contrast to the detailed
mechanistic studies for rhodium porphyrin-catalyzed cyclopro-
panations,12 the mechanism for the ruthenium porphyrin-
catalyzed analogues is rarely studied,13 and in no case has the
observed enantioselectivity been rationalized.
In this paper, we report our extensive studies on the chiral
ruthenium porphyrin-catalyzed reaction 1 and the first applica-
tion of a ruthenium porphyrin catalyst to an asymmetric
intramolecular cyclopropanation (reaction 2 in Scheme 1), with
particular reference to the rationalization of the enantioselectivity
in these catalytic systems. Under modified conditions, complex
1 catalyzes the EDA cyclopropanation of styrene with high trans
selectivity (trans/cis ) 36) and excellent enantioselectivity (98%
ee for the trans diastereomer). Extremely high catalyst turnovers
(>1 × 104) could be obtained. The enantioselectivities observed
in complex 1-catalyzed reactions 1 and 2 are rationalized on
the basis of the crystal structures of closely related chiral carbene
Results
Asymmetric Intermolecular Cyclopropanation Catalyzed
by [Ru(P*)(CO)(EtOH)] (1). (i) Effects of Temperature and
Catalyst Loading. We inspected the reactions of a series of
terminal alkenes (4), mainly the monosubstituted, with various
diazoacetates (5) in the presence of catalytic amounts of complex
1.14 The results obtained in dichloromethane for the EDA (5a)
cyclopropanation of styrene (4a), 1,1-diphenylethene (4b),
R-methylstyrene (4c), and para-substituted styrenes p-X-C6H4-
CHdCH2 (X ) Cl, 4d; F, 4e; Me, 4f; MeO, 4g) are summarized
in Table 1 (loading of 1 ) 0.005 mol % for entry 4 and 0.05
mol % for the others). Note that all the reactions in Table 1
were performed at room temperature except for entries 2 (0 °C)
and 3 (-40 °C). As already described in the previous com-
munication,9 reaction 1 catalyzed by complex 1 (0.05 mol %)
at room temperature for alkenes 4a-d,f,g features high trans
selectivity and enantioselectivity. The catalyst turnovers are
generally >1000. Similar results were obtained for 4e (entry
8).
Examination of entries 1-3 discloses the temperature de-
pendence of the trans selectivity and enantioselectivity. Higher
enantiocontrol for the trans isomer 6a was achieved at lower
reaction temperature; the cyclopropanation at -40 °C afforded
6a in an ee as high as 98% (entry 3). The temperature
dependence of trans selectivity is impressive. By lowering the
reaction temperature from ∼20 to -40 °C, the trans/cis ratio
increased from 18 (entry 1) to 36 (entry 3). This contrasts with
the diazomethane cyclopropanation of alkenes catalyzed by
[Pd(OAc)2]3, whose trans/cis ratio decreases with decreasing
temperature.15 On the other hand, decreasing the loading of
complex 1 led to an increase of catalyst turnovers. When 0.005
mol % of 1 was employed, turnovers of 1.1 × 104 were obtained
(entry 4).
(6) (a) Traylor, P. S.; Dolphin, D.; Traylor, T. G. J. Chem. Soc., Chem.
Commun. 1984, 279. (b) Collman, J. P.; Wang, Z.; Straumanis, A.;
Quelquejeu, M.; Rose, E. J. Am. Chem. Soc. 1999, 121, 460. (c) Yu, X.-
Q.; Huang, J.-S.; Yu, W.-Y.; Che, C.-M. J. Am. Chem. Soc. 2000, 122,
5337.
(7) (a) O’Malley, S.; Kodadek, T. Tetrahedron Lett. 1991, 32, 2445. (b)
O’Malley, S.; Kodadek, T. Organometallics 1992, 11, 2299.
(8) (a) Galardon, E.; Le Maux, P.; Simonneaux, G. Chem. Commun. 1997,
927. (b) Galardon, E.; Roue´, S.; Le Maux, P.; Simonneaux, G. Tetrahedron
Lett. 1998, 39, 2333.
(9) Lo, W.-C.; Che, C.-M.; Cheng, K.-F.; Mak, T. C. W. Chem. Commun.
1997, 1205.
(10) (a) Halterman, R. L.; Jan, S.-T. J. Org. Chem. 1991, 56, 5253. (b)
Halterman, R. L.; Jan, S.-T.; Nimmons, H. L.; Standlee, D. J.; Khan, M.
A. Tetrahedron 1997, 53, 11257.
(11) Frauenkron, M.; Berkessel, A. Tetrahedron Lett. 1997, 38, 7175.
(12) (a) Maxwell, J. L.; Brown, K. C.; Bartley, D. W.; Kodadek, T.
Science 1992, 256, 1544. (b) Brown, K. C.; Kodadek, T. J. Am. Chem.
Soc. 1992, 114, 8336. (c) Bartley, D. W.; Kodadek, T. J. Am. Chem. Soc.
1993, 115, 1656.
(13) During the preparation of this manuscript, Simonneaux and co-
workers reported some mechanistic studies on the intermolecular cyclo-
propanations of alkenes with EDA catalyzed by nonchiral ruthenium
porphyrin [Ru(TPP)(CO)], see: Galardon, E.; Le Maux, P.; Simonneaux,
G. Tetrahedron 2000, 56, 615 and ref 5c.
(ii) Effect of Diazoacetate. Table 2 shows the results for
the cyclopropanation of styrene with a variety of other diazo-
(14) Nonterminal alkenes cis/trans-â-methylstyrene and trans-stilbene
were found to be almost unreactive toward the intermolecular cyclopropa-
nation with diazoacetates such as EDA in the presence of catalyst 1 under
the same conditions as those employed for terminal alkenes 4, with only
trace amounts of the corresponding cyclopropanes formed (but >95% yields
of dimerization products of EDA were detected).
(15) Vallgarda, J.; Hacksell, U. Tetrahedron Lett. 1991, 32, 5625.

Ru Porphyrin Catalyzed Cyclopropanation of Alkenes
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4121
Table 1. Asymmetric Cyclopropanation of Styrene and Its
Derivatives with Ethyl Diazoacetate (5a) Catalyzed by
[Ru(P*)(CO)(EtOH)] (1)a
selectivity. In this work, the trans selectivity is higher in diethyl
ether (trans/cis 29) than in tetrahydrofuran (trans/cis 23), a result
different from that of the iron porphyrin catalyst.16
Despite the solvent dependence of trans selectivity, the effect
of solvent on the enantioselectivity for the predominant, trans
isomer 6a is rather small, with the observed ee’s in a narrow
range of 87-91% for the six solvents examined. What is
different is the ee’s attained for the cis isomer 7a, which are
substantially higher in diethyl ether (18%) and tetrahydrofuran
(14%) than in other solvents (0-6%). As to the total yield of
6a and 7a, the highest (83%) was obtained in dichloromethane.
In diethyl ether, such a yield is lower (74%).
(iv) Effect of Para Substituent of Styrenes. The cyclopro-
panation rates of para-substituted styrenes p-X-C6H4CHdCH2
(X ) MeO, 4g; Me, 4f; Cl, 4d; CF3, 4h) relative to that of
styrene (4a) were estimated through competition experiments
for the EDA cyclopropanation in dichloromethane by employing
equimolar amounts of styrene and the para-substituted deriva-
tives. The relative rates kX/kH, defined as the molar ratio of
resultant cyclopropanes (6 + 7)/(6a + 7a), were found to be
3.20 (4g), 1.65 (4f), 1.44 (4d), and 0.84 (4h). Basically, electron-
donating para substituents accelerate, whereas electron-with-
drawing para substituents retard, the cyclopropanation reactions.
Attempts were made to correlate the above relative rates with
Hammett constants of the para substituents. Unlike the systems
catalyzed by nonchiral [Ru(TPP)(CO)]5c,13 or iron porphyrins,16
whose log(kX/kH) vs σ plots both give a good linearity, such a
plot for complex 1-catalyzed systems shows scattered data
points. Interestingly, plotting log(kX/kH) against σ+ resulted in
a good linearity (see Figure S1 in Supporting Information), with
a F+ value of -0.44 ( 0.09.
substrate (4)
(RL ) p-X-C6H4)
yield trans/cis
% eed
6e
(%)b
ratioc
turnovers
entry
RS
X
(6 + 7)
(6/7)
7
(1)
1
4a
4a
H
H
H
H
H
H
H
83
63
52
57
76
69
66
83
78
61
18
24
36
9.0
87
91
4
4
1.7 × 103
2f
H
H
H
1.3 × 103
3g 4a
4h 4a
98 nd 1.0 × 103
83
2
1.1 × 104
1.5 × 103
1.3 × 103
1.7 × 103
1.6 × 103
1.2 × 103
5
6
7
8
9
4b Ph
4c Me
81i
3.0
23
19
18
15
87 35 1.4 × 103
4d
4e
4f
H
H
H
H
Cl
F
Me
MeO
90
87
81
85
4
3
9
8
10
4g
a Reactions were performed in CH2Cl2 at room temperature for 20
h with a 1:5a:4 molar ratio of 1:2000:10000. b Isolated yields based
on 5a. c Determined by GC-MS. d Determined by chiral HPLC (chiral
column: Daicel OJ) for 6a,b,g and 7a,b,g, by chiral GC (chiral column:
J & W Scientific Cyclodex B, 30 m) for 6c,e and 7c,e, and by analyzing
the l-menthyl ester by Pfaltz’s method (ref 2b) for the others.
e Configuration: (1S,2S). f At 0 °C. g At -40 °C. h 1:5a:4 molar ratio
of 1:20000:100000 i (S)-Configuration.
Table 2. Asymmetric Cyclopropanation of Styrene with Various
Diazoacetates (5) Catalyzed by [Ru(P*)(CO)(EtOH)] (1)
(v) Effect of Conjugation. Competition experiments of 1,1-
diphenylethene (4b), trans-2-methyl-1,3-pentadiene (4i), and
1-hexene (4j) vs styrene reveal a cyclopropanation rate order
4b > 4i > 4j (kX/kH ) 7.3 (4b), 3.3 (4i), 0.03 (4j)).17 This
order is parallel to that of the extent of conjugation 4b > 4i >
4j. A comparison of the kX/kH values among alkenes 4b,d,f-j
indicates that the alkene 4b is cyclopropanated most rapidly,
in agreement with a larger extent of conjugation in the transition
state expected for this alkene than for any of 4d,f-j.
Asymmetric Intramolecular Cyclopropanation Catalyzed
by [Ru(P*)(CO)(EtOH)] (1). The catalytic behavior of complex
1 toward reaction 2 for a series of allylic or homoallylic
diazoacetates was examined. The results obtained for several
allylic diazoacetates that lack substitution on the proximal
position of the CdC double bond (i.e., Rp ) H in Scheme 1)
are shown in Table 3. With diazoacetates N2CHCO2CH2CHd
CRcRt (8a-e) as substrates, the corresponding cyclopropyl
lactones 9a-e were obtained in moderate yields with up to 85%
ee.
N2CHCO2R (5)
% ee
yield (%) trans/cis ratio
entry
R
(6′+ 7′)
(6′+ 7′)
6′
7′
1
2
3
4
5
5b
Me
68
83
62
77
72
12
18
26
11
19
86
87
82
3
4
5a
5c
5d
5e
Et
But
11
l-menthyl
d-menthyl
67a 95a
64a 90a
a % de (diastereomeric excess).
acetates N2CHCO2R (R ) Me, 5b; But, 5c; l-menthyl, 5d;
d-menthyl, 5e) as compared with those obtained by using 5a.
In the cases of 5a-c (entries 1-3), increasing the steric
hindrance of R results in an increase of trans selectivity, with
the trans/cis ratio following the order Me < Et < But. This is
consistent with the results observed for other cyclopropanation
systems.2-4 However, the results obtained for 5d and 5e are
surprising (entries 4 and 5). First, contrary to the other
systems,2,3a,4 in which the cyclopropanations with 5d generally
give higher trans selectivity than those with 5a, the selectivity
obtained for 5d in this work is lower. Second, while the ee’s of
the trans cyclopropanes 6′ are much higher than those of their
cis counterparts 7′ for 5a-c, the de’s of 6′ are substantially
lower than those of 7′ in the cases of 5d and 5e.
(iii) Effect of Solvent. Running the cyclopropanation of
styrene with EDA in various solvents, including toluene,
dichloromethane, benzene, n-hexane, tetrahydrofuran, and di-
ethyl ether, disclosed a dependence of the trans selectivity on
the nature of the solvent, with trans/cis ratios rather similar for
the former four solvents (15-19) but considerably higher for
the ethers (23 and 29) (see Table S1 in Supporting Information).
For iron porphyrin-catalyzed cyclopropanation of styrene with
EDA,16 donor solvents were found to enhance the trans
A comparison of the results in Table 3 with those reported
for the dirhodium(II) carboxamidate catalyst18 reveals several
unusual features of catalyst 1. First, in the case of the dirhodium
catalyst, 8a,b are excellent substrates and afford considerably
higher ee’s than trans-cinnamyl diazoacetate (8d); however, 8d
has proven to be the best substrate for catalyst 1, affording a
much higher ee than 8a,b. Second, while the dirhodium catalyst
(16) Wolf, J. R.; Hamaker, C. G.; Djukic, J.-P.; Kodadek, T.; Woo, L.
K. J. Am. Chem. Soc. 1995, 117, 9194.
(17) The trans/cis ratio was found to be ∼1 and 1.3 for 4i and 4j,
respectively. In the case of 4i, only the terminal CdC bond was
cyclopropanated.
(18) Doyle, M. P.; Austin, R. E.; Bailey, A. S.; Dwyer, M. P.; Dyatkin,
A. B.; Kalinin, A. V.; Kwan, M. M. Y.; Liras, S.; Oalmann, C. J.; Pieters,
R. J.; Protopopova, M. N.; Raab, C. E.; Roos, G. H. P.; Zhou, Q.-L.; Martin,
S. F. J. Am. Chem. Soc. 1995, 117, 5763.

4122 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
Che et al.
Table 3. Asymmetric Intramolecular Cyclopropanation of Allylic
Diazoacetates (8) Catalyzed by [Ru(P*)(CO)(EtOH)] (1)a
Scheme 2
substrate (8)
entry
Rc
Rt
isolated yield of 9 (%)b
% ee of 9c
1
2
3
4
5
8a
8b
8c
8d
8e
H
Me
H
H
Ph
H
45
65
65
24 (1R,5S)
36 (1S,5R)
28 (nd)
85 (1S,5R)
53 (1S,5R)
Me
Me
Ph
H
60
24 (anti)d
a Reactions were performed in CH2Cl2 at room temperature for 18
h with a 1:8 molar ratio of 1:150. b On the basis of consumed substrates.
c Absolute configurations were assigned by comparing the elution orders
of the enantiomers as reported in ref 18. The ee’s were determined by
chiral GC (column: Chiraldex G-TA, 30 m). d The syn isomer was
formed in 18% yield and 24% ee.
generates the predominant enantiomer of the lactone 9d in
(1R,5S) configuration, catalyst 1 produces 9d predominantly in
(1S,5R) configuration. Finally, in the case of substrate 8e,
catalyst 1 gives rise to a mixture of lactones anti- and syn-9e
with the major product being the anti- rather than the expected
syn-isomer (see entry 5),19 different from the dirhodium catalyst,
which has not been reported to afford anti-9e.
Note that complex 1 was found to be ineffective in catalyzing
reaction 2 for the allylic diazoacetates with Rp ) methyl or
phenyl. Homoallylic diazoacetates such as 3-butenyl diazo-
acetate (10) appeared to be inferior to 8a-e. Under the same
conditions as indicated in Table 3, reaction 2 for 10 gave the
cyclopropyl lactone in only 10% yield with a rather low
enantiocontrol (29% ee).
ligands, [Ru(Por)(CRR′)] (13, Por ) TPP or TMP5d), from [Ru-
(TPP)]2 or [Ru(TMP)] precursors (reaction 5 in Scheme 2). The
synthesis of a ruthenium di(ethoxycarbonyl)carbene complex
bearing a sterically unencumbered porphyrin ligand, [Ru(TPP)-
(C(CO2Et)2)(MeOH)] (14), from the corresponding carbonyl
precursor and diazo compound was recently reported by
Simonneaux and co-workers (reaction 6 in Scheme 2),22 which
represents the first structurally characterized ruthenium por-
phyrin carbene complex.
Reactivity of [Ru(P*)(CO)(EtOH)] (1) toward Diazo-
acetates: Isolation of Chiral Carbene Complexes [Ru(P*)-
(CPh2)] (2) and [Ru(P*)(C(Ph)CO2CH2CHdCH2)] (3). Treat-
ment of complex 1 with excess diphenyldiazomethane (N2CPh2,
11) in benzene at room temperature readily gave rise to
analytically pure chiral ruthenium diphenylcarbene complex 2
as a dark red crystalline solid in 86% isolated yield (reaction 3
in Scheme 2). The reaction between 1 and an R-substituted
allylic diazoacetate, N2C(Ph)CO2CH2CHdCH2 (12), in dichlo-
romethane at room temperature afforded analytically pure chiral
ruthenium phenyl(allyloxycarbonyl)carbene complex 3 in a
similar isolated yield (reaction 4 in Scheme 2). Both the
monocarbene species 2 and 3 are rather stable, neither of which
was found to undergo stoichiometric inter- or intramolecular
cyclopropanation with an alkene. For instance, treating 2 with
styrene in benzene caused no detectable reaction even at the
boiling temperature of the solvent; refluxing a solution of 3 in
toluene overnight under nitrogen resulted in no appreciable
reaction (as revealed by UV-vis measurements and GC-MS).
Reactions 3 and 4 clearly provide precedents for the formation
of ruthenium carbene complexes bearing a sterically demanding
porphyrin macrocycle (such as P*) from reaction of a carbonyl
ruthenium porphyrin with a diazo compound.20 Previously,
Collman and co-workers21 pioneered the isolation of ruthenium
porphyrins with alkyl- and (alkoxycarbonyl)carbene axial
Spectral Features of [Ru(P*)(CPh2)] (2) and [Ru(P*)-
(C(Ph)CO2CH2CHdCH2)] (3). Both complexes 2 and 3 exhibit
a low-field 13C NMR signal that can be attributed to the
resonance of the coordinated carbene C atom (δ ) 315 (2),
285 (3)). Such resonances for other related ruthenium carbene
complexes are located in the range δ 271-306.4c,22,23 In the
FAB mass spectra of 2 and 3, the cluster peaks attributable to
the corresponding parent ions appear at m/z ) 1409 (2) and
1417 (3).
1
The H NMR spectra of 2 and 3 (Figures S2 and S3 in
Supporting Information) correspond to diamagnetic species, like
those of alkyl- or (alkoxycarbonyl)carbene complexes 1321 and
14.22 In contrast to the signals of the porphyrin pyrrole protons
for 13 and 14, which invariably appear as a singlet, such signals
for 2 and 3 appear as a multiplet centered at δ 8.26 (2) and
(20) Although our preliminary observations on the reaction between
1
complex 1 and EDA in benzene through H NMR and UV-vis measure-
ments suggest the formation of a ruthenium porphyrin carbene complex,
[Ru(P*)(CHCO2Et)], such a complex was not isolated or fully characterized
(see ref 9).
(21) (a) Collman, J. P.; Brothers, P. J.; McElwee-White, L.; Rose, E.;
Wright, L. J. J. Am. Chem. Soc. 1985, 107, 4570. (b) Collman, J. P.; Rose,
E.; Venburg, G. D. J. Chem. Soc., Chem. Commun. 1993, 934.
(22) Galardon, E.; Le Maux, P.; Toupet, L.; Simonneaux, G. Organo-
metallics 1998, 17, 565.
(23) Klose, A.; Solari, E.; Floriani, C.; Geremia, S.; Randaccio, L. Angew.
Chem., Int. Ed. 1998, 37, 148.
(19) Currently, the cause of this phenomenon is not yet clear. Presumably,
the complex 1-catalyzed cyclopropanation of 8e proceeds via a stepwise
mechanism whose transition state features a broken PhCHdCH π-bond so
that the PhCH moiety can rotate about the remaining C-C σ-bond before
the lactone 9e is formed.

Ru Porphyrin Catalyzed Cyclopropanation of Alkenes
Table 4. Crystal Data and Structure Refinement for [Ru(P*)(CPh2)] (2)‚2CH2Cl2 and [Ru(P*)(C(Ph)CO2CH2CHdCH2)] (3)‚3CH2Cl2
complex 2 complex 3
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4123
empirical formula
formula weight
T, K
λ, Å
cryst syst
C97H86N4Ru‚2CH2Cl2
C95H86N4O2Ru‚3CH2Cl2
1578.62
1671.53
295(2)
0.710 73
orthorhombic
P212121
294(2)
0.710 73
monoclinic
P21
space group
a, Å
b, Å
c, Å
14.6870(3)
20.6491(3)
27.5075(2)
14.265(1)
18.125(1)
16.705(1)
â, deg
98.612(2)
4270.4(6)
V, Å3
8342.3(2)
Z
4
3296
1.257
0.366
2
1740
1.300
0.42
F(000)
density (calcd), Mg/m3
abs coeff, mm-1
index ranges
-18 e h e 19, -26 e k e 22, -35 e l e 35
49 593
19 115
SADABS
0.8313/0.6336
full-matrix least-squares on F2
19 115/0/964
R1 ) 0.081
1.017
0.00(4)
1.141 / -0.597
-17 e h e 18, -19 e k e 23, -21 e l e 21
28 653
15 800
SADABS
0.9512/0.9313
full-matrix least-squares on F2
15 800/14/949
R1 ) 0.061
0.960
-0.01(3)
0.918 / -0.769
no. of reflns collected
no. of independent reflns
abs correction
max/min transmission
refinement method
data/restraints/parameters
final R indices (I > 2σ(I))
goodness-of-fit on F2
absolute structure parameter
largest diff peak/hole, e Å-3
8.35 (3) with a pattern resembling that of an AB system. The
bridgehead protons of the norbornane moieties in the P* ligand
of either 2 or 3 give a total of eight signals (appearing as four
doublets) in equal intensity, different from the two singlets
observed for the corresponding protons in the dioxoruthenium-
(VI) complex bearing the same porphyrin macrocycle.24 The
signal patterns of the carbene phenyl groups in 2 and 3 are
normal. However, the OCH2 protons of the allyloxycarbonyl
group in 3 give two well-separated sets of double doublets,
dramatically different from the single doublet observed for these
protons in allyl diazoacetate 12.25
The UV-vis spectrum of 2 features two Soret bands located
at 397 and 432 nm, respectively. This resembles the alkylcarbene
complex [Ru(TTP)(CHCH3)] (13a) reported by Collman and
co-workers,21a whose UV-vis spectrum also shows two Soret
bands (395 and 421 nm). Metalloporphyrins having this property
are uncommon. In addition to complexes 2 and 13a, a few
nitrido- or nitrosylosmium porphyrins reported by Buchler,
Gouterman, and co-workers26 serve as additional examples. On
the other hand, compared with the alkylcarbene complex 13a,
the arylcarbene complex 2 shows an appreciably red-shifted â
band (13a, 527 nm; 2, 536 nm). It is worth noting that while
the â band of 2 is more similar to that of the di(alkoxycarbonyl)-
carbene complex 14 (531 nm),22 there is only one Soret band
in the UV-vis spectrum of 14. The UV-vis spectrum of 3,
which bears the C(Ph)CO2R group, shows a single Soret band
(402 nm) with an obvious shoulder (∼442 nm) on its red side,
in contrast to the double Soret bands observed for the CPh2
complex 2 and a single Soret band for the C(CO2R)2 complex
14.
Figure 1. ORTEP drawing of 2‚2CH2Cl2 with thermal ellipsoids drawn
at the 50% probability level. For clarity, the hydrogen atoms and solvent
molecules are omitted, and only the numbering scheme for the key
atoms is shown.
and 3 crystallized as 2‚2CH2Cl2 and 3‚3CH2Cl2, respectively,
from a dichloromethane solution mixed with acetonitrile (2) and
from dichloromethane/hexane exposed to the atmosphere (3).
Table 4 summarizes the crystal data and structure refinement
for both complexes; the structures are shown in Figures 1 and
2. Selected bond lengths (Å) and angles (deg) for 2 and 3 are
listed in Table 5.
X-ray Crystal Structure Determinations of [Ru(P*)(CPh2)]
(2) and [Ru(P*)(C(Ph)CO2CH2CHdCH2)] (3). Complexes 2
As shown in Figures 1 and 2 and Table 5, complexes 2 and
3 each contain a fiVe-coordinate ruthenium atom that is situated
in a slightly distorted square-pyramidal coordination sphere with
the carbene C atom at the vertex site. This is different from the
other structurally characterized metalloporphyrin carbene com-
plexes,22,27 which are exclusively six-coordinate. Further, of the
large number of structurally characterized mononuclear ruthe-
nium porphyrins,22,24,28 complexes 2 and 3 belong to the few
examples containing a five-coordinate ruthenium.
(24) Lai, T.-S.; Zhang, R.; Cheung, K.-K.; Kwong, H.-L.; Che, C.-M.
Chem. Commun. 1998, 1583.
(25) This striking feature probably arises from a significant steric
interaction in 3 between the allyl group in the carbene ligand and the adjacent
norbornane moiety in the P* ligand, which keeps the complex in conforma-
tions that lack an element of symmetry and prevents any dynamic process
to equalize these methylene protons (vide infra).
(26) Antipas, A.; Buchler, J. W.; Gouterman, M.; Smith, P. D. J. Am.
Chem. Soc. 1980, 102, 198.

4124 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
Che et al.
Table 5. Selected Bond Lengths (Å) and Angles (deg) for [Ru(P*)(CPh2)] (2) and [Ru(P*)(C(Ph)CO2CH2CHdCH2)] (3)
2
3
2
3
Ru-N(1)
Ru-N(2)
Ru-N(3)
Ru-N(4)
2.037(5)
2.046(5)
2.039(5)
2.053(5)
2.039(2)
2.031(2)
2.033(2)
2.047(2)
Ru-C(85)
1.860(6)
1.499(9)
1.496(9)
1.847(3)
1.460(4)
1.496(4)
C(85)-C(86)
C(85)-C(92)
C(86)-C(85)-C(92)
Ru-C(85)-C(92)
C(85)-Ru-N(2)
C(85)-Ru-N(4)
N(2)-Ru-N(3)
N(4)-Ru-N(1)
N(2)-Ru-N(4)
112.1(5)
123.7(5)
95.8(2)
97.1(2)
89.7(2)
89.5(2)
167.2(2)
114.3(2)
118.3(2)
94.8(1)
102.1(1)
89.57(7)
89.75(7)
163.09(9)
Ru-C(85)-C(86)
C(85)-Ru-N(1)
C(85)-Ru-N(3)
N(1)-Ru-N(2)
N(3)-Ru-N(4)
N(1)-Ru-N(3)
124.3(5)
95.1(2)
93.8(2)
89.4(2)
89.5(2)
171.2(2)
127.1(2)
93.5(1)
94.6(1)
89.57(8)
88.75(7)
171.95(8)
lies almost halfway between the adjacent Ru-N bonds (e.g.,
Ru-N(2) and Ru-N(3)), whereas the corresponding plane in
15 is almost parallel to diagonal Ru-N bonds. Second, the
C(86)-C(85)-C(92) angle of 112.1(5)° in 2 is appreciably
smaller than the corresponding angle in 15 (116.4(6)°). Third,
the two phenyl groups basically adopt a “face-to-face” confor-
mation in 2 but a “face-to-edge” conformation in 15.
The Ru-C(carbene) distances of 1.860(6) Å in 2 and
1.847(3) Å in 3 are similar to or slightly shorter than that in 15
(1.874(8) Å)23 but slightly longer than that in 14 (1.829(9) Å).22
The ruthenium atom is displaced from the mean plane of the
four pyrrole nitrogens toward the carbene C atom by ∼0.19 Å
in 2 and ∼0.22 Å in 3; both the displacements are larger than
those reported for the five-coordinate ruthenium porphyrin
alkyl28b or aryl28a complexes (∼0.11 Å) but smaller than that
reported for 15 (∼0.37 Å).23 As is evident from Figure 2 and
Figure S4 (see Supporting Information), the porphyrin ring of
either 2 or 3 exhibits an appreciable puckering distortion.
While the foregoing structural features of the diphenylcarbene
complex 2 and the phenyl(allyloxycarbonyl)carbene complex
3 are similar, there is a marked change in the orientations of
some meso phenyl groups of the P* ligand on going from 2 to
3, accompanied by a change in the orientation of the carbene
plane.30 Note the meso phenyl groups adjacent to the carbene
ligand in 3 (Figure 2), which are seVerely distorted from the
orientations basically perpendicular to the porphyrin ring
observed in 2 (see Figure S4), probably to keep the fused
norbornane moieties away from the carbene ligand. The C(85),
C(86), and C(92) plane in 3 rotates ∼10° toward the Ru-N(1)
bond from the position that bisects the N(1)-Ru-N(2) angle,
different from the orientation of the corresponding plane in 2
described above.
Figure 2. Ball and stick drawing of 3‚3CH2Cl2 with the atom-numbing
scheme (viewed along the C(6)-C(16) axis). The hydrogen atoms and
solvent molecules are not shown. For clarity, the core structure of 3 is
depicted in the inset.
In view of the presence of potentially coordinating acetonitrile
or water in the solution from which the crystals 2‚2CH2Cl2 and
3‚3CH2Cl2 grew, the formation of 2 and 3 with a vacant axial
site is astonishing. We note that a non-porphyrin ruthenium
tetraaza[14]annulene complex, [Ru(tmtaa)(CPh2)] (15),5e with
the same carbene group as in 2 recently reported by Floriani
and co-workers23 also has a five-coordinate ruthenium atom.
Although the ruthenium atom in 2 has a coordination
geometry similar to that in 15, the coordinated diphenylcarbene
groups in 2 and 15 are considerably different in the following
aspects.29 First, the carbene C(85), C(86), and C(92) plane in 2
Asymmetric Intermolecular Cyclopropanation Catalyzed
by [Ru(P*)(CPh2)] (2). Under conditions identical to those
indicated in note a of Table 1, except using 2 instead of 1 as
the catalyst, the results obtained for the cyclopropanation of
terminal alkenes 4a-g with EDA are shown in Table 6. As
shown in this table, for all these alkene substrates, the complex
2-catalyzed cyclopropanations afforded cyclopropyl esters 6 and
7 in moderate to good yields (36-75%). The trans/cis ratios
(29) This probably stems from different steric interactions of the carbene
group with the porphyrin and tetraaza[14]annulene ligands.
(27) (a) Mansuy, D.; Lange, M.; Chottard, J. C.; Bartoli, J. F.; Chevrier,
B.; Weiss, R. Angew. Chem., Int. Ed. Engl. 1978, 17, 781. (b) Boschi, T.;
Licoccia, S.; Paolesse, R.; Tagliatesta, P.; Pelizzi, G.; Vitali, F. Organo-
metallics 1989, 8, 330. (c) Djukic, J.-P.; Smith, D. A.; Young, V. G., Jr.;
Woo, L. K. Organometallics 1994, 13, 3020.
(28) (a) Ke, M.; Rettig, S. J.; James, B. R.; Dolphin, D. J. Chem. Soc.,
Chem. Commun. 1987, 1110. (b) Alexander, C. S.; Rettig, S. J.; James, B.
R. Organometallics 1994, 13, 2542. (c) Sun, X.-R.; Huang, J.-S.; Cheung,
K.-K.; Che, C.-M. Inorg. Chem. 2000, 39, 820 and references therein. (d)
Au, S.-M.; Huang, J.-S.; Yu, W.-Y.; Fung, W.-H.; Che, C.-M. J. Am. Chem.
Soc. 1999, 121, 9120. (e) Huang, J.-S.; Sun, X.-R.; Leung, S. K.-Y.; Cheung,
K.-K.; Che, C.-M. Chem. Eur. J. 2000, 6, 334. (f) Huang, J.-S.; Leung, S.
K.-Y.; Cheung, K.-K.; Che, C.-M. Chem. Eur. J. 2000, 6, 2971.
(30) We think that these orientation changes are due to the steric
interaction in 3 between the allyl group (rather than the phenyl group) of
the carbene ligand and the adjacent norbornane moiety of the P* ligand,
since the orientations of the carbene plane and meso phenyl groups in the
diphenylcarbene complex 2 are quite normal. Indeed, inspection of the space
filling model of 3 reveals that the rotations of the allyloxycarbonyl group
about any of the C(93)-O(2), O(2)-C(92), and C(92)-C(85) bonds are
rather limited whereas the rotation of the carbene phenyl group about the
C(85)-C(86) bond is relatively free. This finding, together with the lack
of symmetry in the structure of 3 (Figure 2), should account for the unusual
OCH2 but normal phenyl signal patterns described earlier for the C(Ph)-
1
CO2CH2CHdCH2 group in the H NMR spectrum of 3.

Ru Porphyrin Catalyzed Cyclopropanation of Alkenes
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4125
Table 6. Asymmetric Cyclopropanation of Styrene and Its
Derivatives with Ethyl Diazoacetate (5a) Catalyzed by
[Ru(P*)(CPh2)] (2)a
utilized as catalysts for asymmetric intermolecular cyclopropa-
nation reactions, as already described in the Introduction.
On the other hand, the asymmetric intramolecular cyclopro-
panation depicted as reaction 2 in Scheme 1 was investigated
extensively in recent years.1,4b,18,35-37 Currently, the most
selective catalyst for this reaction is the dirhodium(II) carboxa-
midate complex developed by Doyle and co-workers.18,35
Despite the advantage that such intramolecular reactions usually
afford only one diastereomer because of geometric constraints18
(unlike the intermolecular reaction 1 in which diastereocontrol
is an important issue), prior to this work the use of a
metalloporphyrin catalyst for an intramolecular alkene cyclo-
propanation remains essentially unexplored.38
Following our preliminary work that demonstrates the ef-
ficiency of the chiral carbonylruthenium(II) porphyrin complex
1 in catalyzing reaction 1 for a series of terminal alkenes,9 the
present one addresses a number of issues including the effects
of temperature, catalyst loading, solvent, diazoacetate, and
alkene on the reaction. Moreover, it demonstrates the feasibility
of using complex 1 as an efficient catalyst for reaction 2.
Although the enantioselectivity in reaction 2 obtained for catalyst
1 is not superior to that for the foregoing dirhodium(II)
carboxamidate catalyst, the present work first demonstrates the
efficiency of a chiral metalloporphyrin in catalyzing asymmetric
intramolecular cyclopropanations.
The results shown in entry 3 of Table 1 (ee 98%, trans/cis
ratio 36) represent the highest selectivity yet obtained for
complex 1-catalyzed reaction 1, which to our knowledge also
represent the highest diastereocontrol ever attained for metal
complex-catalyzed cyclopropanation of styrene with EDA,
whose trans product 6a is a critical precursor for the synthesis
of tranylcypromine (an oral MAOI-type antidepressant).39 The
unusual robustness of catalyst 1 is reflected by the 1.1 × 104
turnovers shown in entry 4 of Table 1, a value unprecedentedly
high for metal complex-catalyzed cyclopropanations.
On the Nature of the Active Intermediates in [Ru(P*)-
(CO)(EtOH)] (1)-Catalyzed Inter- and Intramolecular Cy-
clopropanations. In the literature, it is widely believed that the
active intermediates in metal-catalyzed inter- and intramolecular
cyclopropanations of alkenes are electrophilic metal carbene
complexes,1 a few of which have eventually been isolated in
the case of intermolecular systems by treating the catalysts with
the respective diazoacetates in the absence of alkenes.4c,d,32 The
isolation of carbenoid intermediates in the intramolecular
systems seems more challenging owing to the required coexist-
ence of the carbene moiety and the pendant alkene group, and
has not been realized so far.
substrate (4)
(RL ) p-X-C6H4)
% ee
yield (%) trans/cis ratio
turnovers
entry
RS
X
(6 + 7)
(6/7)
6
7
(2)
1
2
3
4
5
6
7
4a
4b Ph
4c Me
4d
4e
4f
H
H
H
H
Cl
F
Me
MeO
36
63
72
61
71
62
75
11
83 7 7.2 × 102
70
1.3 × 103
5.6
5.2
8.4
4.1
12
66 25 1.4 × 103
88 40 1.2 × 103
85 12 1.4 × 103
71 nd 1.2 × 103
71 9 1.5 × 103
H
H
H
H
4g
a Reaction conditions and the configurations of 6 are the same as
indicated in Table 1.
(up to 12) and the enantiocontrol (up to 88% ee for the trans
isomers 6) are relatively high. However, compared with complex
1, complex 2 is a less selective catalyst for reaction 1, especially
in terms of trans selectivity (cf. Tables 1 and 6).
To our knowledge, 2 is the first structurally characterized
chiral metal carbene complex that acts as an efficient catalyst
for asymmetric cyclopropanation of alkenes. Prior to this work,
Nishiyama and co-workers demonstrated that a structurally
characterized chiral carbene complex [Ru(pybox)Cl2(C(CO2-
Et)2)] undergoes stoichiometric asymmetric alkene cyclopro-
panation at 110 °C.4d
The fact that the monocarbene complex 2 can efficiently
catalyze reaction 1 but is inert toward stoichiometric alkene
cyclopropanation spurred our interest in examining the catalytic
process in some detail. When the cyclopropanation of styrene
with EDA in the presence of a catalytic amount of 2 was
monitored by UV-vis spectroscopy and GC-MS, we found
complex 2 sustained not less than 200 turnovers, suggesting
that the monocarbene entity remains intact during this period
in the catalytic reaction.
Discussion
Development of Metalloporphyrin Cyclopropanation Cata-
lysts. The utilization of metalloporphyrins as catalysts for
intermolecular alkene cyclopropanation is traced back to 1980,
when Callot and co-workers31 reported that rhodium(III) por-
phyrins catalyze the EDA cyclopropanation of common alkenes
in 60-71% yields with an intriguing cis selectivity, contrary
to the trans selectivity generally observed for the classical non-
porphyrin cyclopropanation catalysts. Trans-selective metal-
loporphyrin cyclopropanation catalysts were first developed by
Woo and co-workers for osmium porphyrins32 and later by
Kodadek and Woo for iron porphyrins.16 However, since the
porphyrin macrocycles in these catalysts bear no chiral auxil-
iaries, the resultant cyclopropanation reactions are not enantio-
selective.33
(34) Collman, J. P.; Zhang, X.; Lee, V. J.; Uffelman, E. S.; Brauman, J.
I. Science 1993, 261, 1404.
(35) (a) Doyle, M. P.; Pieters, R. J.; Martin, S. F.; Austin, R. E.; Oalmann,
C. J.; Mu¨ller, P. J. Am. Chem. Soc. 1991, 113, 1423. (b) Doyle, M. P.;
Zhou, Q.-L.; Dyatkin, A. B.; Ruppar, D. A. Tetrahedron Lett. 1995, 36,
7579. (c) Doyle, M. P.; Peterson, C. S.; Zhou, Q.-L.; Nishiyama, H. Chem.
Commun. 1997, 211. (d) Doyle, M. P.; Davies, S. B.; Hu, W. Org. Lett.
2000, 2, 1145. (e) Doyle, M. P.; Hu, W.; Chapman, B.; Marnett, A. B.;
Peterson, C. S.; Vitale, J. P.; Stanley, S. A. J. Am. Chem. Soc. 2000, 122,
5718.
(36) (a) Martin, S. F.; Oalmann, C. J.; Liras, S. Tetrahedron Lett. 1992,
33, 6727. (b) Martin, S. F.; Oalmann, C. J.; Liras, S. Tetrahedron 1993,
49, 3521.
(37) Rogers, D. H.; Yi, E. C.; Poulter, C. D. J. Org. Chem. 1995, 60,
941.
There are a wide variety of chiral metalloporphyrins known
in the literature,34 whose catalytic behavior toward asymmetric
alkene epoxidation has been examined. Yet few of them were
(31) Callot, H. J.; Piechocki, C. Tetrahedron Lett. 1980, 21, 3489.
(32) Smith, D. A.; Reynolds, D. N.; Woo, L. K. J. Am. Chem. Soc. 1993,
115, 2511.
(33) Gross and co-workers recently reported that nonchiral iron, ruthe-
nium, osmium, and rhodium porphyrins can catalyze asymmetric cyclo-
propanation of styrene with a chiral carbenoid, see: Gross, Z.; Galili, N.;
Simkhovich, L. Tetrahedron Lett. 1999, 40, 1571.
(38) Kodadek and co-workers investigated the rhodium porphyrin-
catalyzed reaction 2 for cis-5-methyl-2-hexenyl diazoacetate, which afforded
the cyclopropyl lactone in 10% ee. The yield of the product was not reported.
See: Maxwell, J. L.; O’Malley, S.; Brown, K. C.; Kodadek, T. Organo-
metallics 1992, 11, 645.
(39) Csuk, R.; Schabel, M. J.; von Scholz, Y. Tetrahedron: Asymmetry
1996, 7, 3505.

4126 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
Che et al.
Concerning metalloporphyrin-catalyzed alkene cyclopropa-
nations, previous studies on rhodium,7,12,31 osmium,32 iron,16 and
ruthenium13 catalysts all support the intermediacy of the
respective metalloporphyrin carbene complexes in the processes.
Notably, Woo and co-workers successfully isolated a nonchiral
osmium porphyrin monocarbene complex that can undergo
catalytic alkene cyclopropanation reactions.32
The active intermediates in complex 1-catalyzed reactions 1
and 2 have not been isolated and clearly identified despite
multiple attempts. However, insight into the nature of these
intermediates can be obtained from the foregoing results on the
solvent and substitutent effects on complex 1-catalyzed reaction
1, from the observed reactivity of complex 1 toward diazo-
acetates, and from the catalytic behavior of complex 2 toward
reaction 1.
The solvent effect reflects some similarity between the active
intermediates in the complex 1- and iron porphyrin-catalyzed
intermolecular cyclopropanations. In the latter system, the
putative monocarbene active intermediate [Fe(Por)(CHCO2Et)]
capable of binding donor solvents in an axial site accounts for
the increase of trans selectivity with increasing donating
capability of the solvent.16 However, the opposite trends of trans
selectivity from diethyl ether to tetrahydrofuran for the iron
porphyrin- and complex 1-catalyzed cyclopropanations may
imply that the active intermediates in complex 1-catalyzed
reaction 1 are not simply a ruthenium counterpart of [Fe(Por)-
(CHCO2Et)], i.e., the five-coordinate monocarbene species [Ru-
(P*)(CHCO2R)].
The substituent effect suggests a more rapid cyclopropanation
for more electron rich alkenes, a phenomenon typical for the
cyclopropanations via electrophilic metal carbene intermediates.1
The linear correlation between log(kX/kH) and σ+ with a small
negative F+ value (-0.44 ( 0.09) implies that the vinyl carbons
of the styrenes in the rate-limiting transition state come into
direct resonance interaction with the para substituents and may
have some carbocationic character, which, however, should be
far from a well-developed carbonium ion, since for reactions
that involve a carbocation intermediate a large negative F+ value,
such as the F+ of -4.54 found for the solvolysis of tert-cumyl
chloride,40 is expected.
The reaction of complex 1 with diazoacetates 11 and 12 to
form the respective five-coordinate carbene complexes [Ru-
(Por*)(CPh2)] (2) and [Ru(P*)(C(Ph)CO2CH2CHdCH2)] (3),
together with reaction 6 which forms the six-coordinate complex
1422 (see Scheme 2), reveals the possible formation of a chiral
ruthenium carbene porphyrin, [Ru(P*)(CHX)] or [Ru(P*)-
(CHX)(L)] (X ) CO2R 16, CO2(CH2)nC(Rp)dCRcRt 17), in the
catalytic systems “1 + diazoacetate 5 + alkene 4” or “1 +
diazoacetate 8 or 10”. The inertness of the isolated five-
coordinate complexes 2 and 3 toward stoichiometric inter- or
intramolecular alkene cyclopropanation at even >100 °C
suggests that either (i) the five-coordinate monocarbene species
[Ru(P*)(CHX)] are not the active intermediates in complex
1-catalyzed reactions 1 and 2 (which can be conducted at
temperatures of -40 to ∼20 °C) or (ii) complexes 2 and 3 are
much less reactive than [Ru(P*)(CHX)].
The catalytic behavior of complex 2 toward reaction 1 (i.e.,
significantly lower diastereocontrol than catalyst 1, cf. Tables
1 and 6) signifies the functioning of different active intermedi-
ates in the complex 1- and 2-catalyzed intermolecular cyclo-
propanations. Both catalysts, however, feature trans selectivity
and have roughly comparable enantiocontrol. In view of the
inertness of 2 toward stoichiometric cyclopropanation of styrene
and the sustentation of >200 turnovers for 2 in the correspond-
ing catalytic process, the [Ru(P*)(CPh2)(CHCO2Et)] (18) active
intermediate bearing mixed carbene ligands is suggested in the
complex 2-catalyzed cyclopropanations. Owing to Ru-C mul-
tiple bonding, the carbene group CPh2 in 18 would have a strong
trans effect, leading to weakening and hence increasing the
reactivity of the RudCHCO2Et bond. Previously, Woo and co-
workers41 proposed osmium analogues of 18 as intermediates
in the formation of alkenes catalyzed by nonchiral osmium
porphyrins.
On the basis of these observations, we propose that the active
intermediates in complex 1-catalyzed reactions 1 and 2 could
be the respective ruthenium porphyrin carbene complexes [Ru-
(P*)(CHX)(L)] (16 or 17), where L is a ligand with a
considerable trans effect, such as the carbene group CHX.42 We,
however, cannot exclude the possibility of the five-coordinate
complexes [Ru(P*)(CHX)] and their adducts with solvent
molecules acting as an active intermediate in these reactions.
The lower trans selectivity and enantioselectivity in the EDA
cyclopropanation of styrenes catalyzed by complex 2 than by
complex 1 may be ascribed to different L ligands trans to the
CHCO2Et group of the active intermediates in the two cases.
Currently, it is uncertain how the intermediates 16 interact with
donor solvents, such as ethers, to afford higher trans selectivity.
Bearing in mind the hitherto unrealized isolation of metal
carbene intermediates in metal-catalyzed reaction 2, the isolation
of complex 3, which contains a carbene group with a pendant
CdC bond and closely resembles the proposed intermediates
17 in complex 1-catalyzed reaction 2, is of interest. We know
of no other examples of metalloporphyrin carbene complexes
that have this property.
Scheme 3 shows the mechanism we propose here for the
intermolecular cyclopropanation catalyzed by complex 1, in
which the transition states for carbene transfer 19a and 19b are
presumed to be late and have parallel CdC and RudC bonds,
analogous to their iron counterparts proposed by Kodadek, Woo,
and co-workers.16 Apparently, the transition state 19a would
be more stable than 19b due to the lack of steric interaction
between the larger group (RL) on the alkene and the CO2R group
on the carbene. Therefore, trans cyclopropanes are preferentially
formed.43 It can be expected that a smaller R group in CO2R or
a smaller difference in size between RL and RS groups would
result in a lower trans/cis ratio, which is indeed the case in view
of the trans selectivity order 5b < 5a < 5c (Table 2) and the
much lower trans/cis ratio obtained for R-methylstyrene (4c)
than for the other styrenes (Table 1). Moreover, probably since
it is difficult for nonterminal alkenes to reach a transition state
similar to 19a and 19b, such alkenes are found to be inferior
(41) Woo, L. K.; Smith, D. A. Organometallics 1992, 11, 2344.
(42) Although we were unable to directly observe any of the bis(carbene)
species [Ru(P*)(CHX)2], the formation of such species in the corresponding
catalytic systems is not impossible. Previous work by Woo and co-workers
indicates that a monocarbene osmium porphyrin [Os(TTP)(C(p-C6H4Me)2)]
can react with diaryldiazomethane N2C(p-C6H4Me)2 to form a biscarbene
complex [Os(TTP)(C(p-C6H4Me)2)2] (refs 5f and 41). This implies that
similar phenomenon may also occur with ruthenium owing to the analogy
between the chemistry of osmium and ruthenium, which is to some extent
supported by the possible formation of [Ru(P*)(CPh2)(CHCO2Et)] (18) in
complex 2-catalyzed reaction 1. Moreover, Simonneaux and co-workers
(ref 22) observed that the EDA cyclopropanations of styrene catalyzed by
nonchiral complexes [Ru(TPP)(C(CO2Et)2)(MeOH)] (14) and [Ru(TPP)-
(CO)(EtOH)] afford similar trans/cis ratios and in the former case the final
ruthenium-containing products are basically the original carbene complex.
In our opinion this observation, together with the fact that the C(CO2Et)2
group in 14 is rather inert but the CO group in [Ru(TPP)(CO)(EtOH)] labile
toward the attack by EDA to form [Ru(TPP)(CHCO2Et)], possibly implies
the intermediacy of [Ru(TPP)(C(CO2Et)2)(CHCO2Et)] in the case of catalyst
14 (although this possibility is not mentioned in that paper).
(40) Brown, H. C.; Okamoto, Y. J. Am. Chem. Soc. 1958, 80, 4979.

Ru Porphyrin Catalyzed Cyclopropanation of Alkenes
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4127
Scheme 3
Figure 3. Top-view space-filling model for the [Ru(P*)(CHCO2R)]
moiety (R ) Et) of the proposed active species 16 on the basis of the
X-ray structure of complex 2 and the interaction of its carbene group
with styrene placed (a) above and (b) below the carbene plane.
Hydrogen atoms are not shown except those in styrene and the indicated
methano and ethano bridges.
substrates for the ruthenium porphyrin-catalyzed intermolecular
cyclopropanation.14
Rationalization of the Enantioselectivity in [Ru(P*)(CO)-
(EtOH)] (1)-Catalyzed Inter- and Intramolecular Cyclopro-
panations. The understanding of enantiocontrol in complex
1-catalyzed reactions 1 and 2 is of fundamental importance for
the further development of this type of catalyst. Suppose that
16 or 17 are really the active intermediates in these processes,
a key step for rationalizing the observed enantioselectivity is
to determine the conformation of the sterically demanding P*
ligand and the orientation of the carbene plane with respect to
the macrocycle in these chiral intermediates. Since intermediates
16 and 17 bear the same D4-symmetric porphyrin ligand in the
same absolute configuration as complexes 2 and 3 and all the
species 16, 17, 2, and 3 are ruthenium porphyrin carbene
complexes, the structural information on 2 and 3 serves as a
useful basis for rationalizing the enantioselectivity in complex
1-catalyzed reactions 1 and 2.44
built a model for the key moiety [Ru(P*)(CHCO2R)] (R ) Et)
of the proposed active intermediate 16 (Figure 3) by employing
the CS Chem 3D 4.5 software package, with the P* geometry
and carbene plane orientation the same as those in the structure
of the ruthenium carbene complex 2. A styrene molecule
oriented as in the transition state 19a (Scheme 3) was placed
above (Figure 3a) and below (Figure 3b) the carbene plane
(corresponding to the transition states that produce the trans
cyclopropane in (1S,2S) and (1R,2R) configuration, respectively).
Evidently, the interaction between the styrene phenyl group and
the sterically demanding ethano bridge of the norbornane moiety
in Figure 3b will provoke a severe strain. Therefore, the
transition state corresponding to Figure 3a is greatly preferred
over that corresponding to Figure 3b. This accounts for the high
ee’s attained for 6a with its predominant enantiomer in the
(1S,2S) configuration (see note e in Table 1).
Similar rationalization may be applicable to the cases of the
substrates 4c-g in Table 1. Worthy of note is the good
enantiocontrol for substrate 1,1-diphenylethene (4b). If the
terminal CdC bond of 4b is fully parallel to the RudC bond
in the transition state, the resulting cyclopropanation is expected
to be nonenantioselective according to the above rationalization,
which is contrary to the results shown in Table 1. We think
that for this alkene, to ease the steric interaction between the
alkene phenyl group and the carbene ethoxycarbonyl group, the
terminal CdC bond may preferably tilt toward the methano
bridge indicated in Figure 3a, thus accounting for the observed
predominant (S)-configuration.
(ii) Intramolecular Cyclopropanation. The results of com-
plex 1-catalyzed reaction 2 manifest that allylic diazoacetates
N2CHCO2CH2CHdCRcRt (8a-d) are superior substrates for
this catalytic system. Since for substrate 8c the absolute
configuration of the resultant cyclopropyl lactone 9c was not
determined, the enantioselectivity rationalization here will be
confined to substrates 8a,b,d. In these cases, the proposed
intermediates are [Ru(P*)(CHCO2CH2CHdCRcRt)(L)].44
As described earlier, the structure of 3 features an appreciable
distortion of the C(85), C(86), and C(92) plane from the position
bisecting the N(1)-Ru-N(2) angle and a severe distortion of
some meso phenyl rings from being perpendicular to the
porphyrin ring, probably due to a considerable steric interaction
between the allyl group and the adjacent norbornane moiety.30
A similar phenomenon most likely occurs with the [Ru(P*)-
(CHCO2CH2CHdCRcRt)] moieties.
(i) Intermolecular Cyclopropanation. As shown in Table
1, complex 1-catalyzed reaction 1 for styrene (substrate 4a)
affords the predominant, trans isomer 6a in high enantioselec-
tivity. To rationalize the enantiocontrol for this substrate, we
(43) As one reviewer pointed out, although the steric inspection
rationalizes the trans selectivity for catalyst 1, the electronic factor, i.e.,
the ruthenium metal, may be primarily responsible for the extraordinary
trans selectivity for the ruthenium catalyst. This is reflected in the proposed
late transition states (19a,b) in Scheme 3, which contrast with the early
transition state in rhodium porphyrin catalysts. Indeed, in addition to the
ruthenium-pybox and ruthenium porphyrin catalysts described in the text,
other reported ruthenium cyclopropanation catalysts also exhibit a trans
selectivity, see for example: (a) Simal, F.; Demonceau, A.; Noels, A. F.
Tetrahedron Lett. 1998, 39, 3493. (b) Simal, F.; Jan, D.; Demonceau, A.;
Noels, A. F. Tetrahedron Lett. 1999, 40 1653. (c) Stoop, R. M.; Bauer, C.;
Setz, P.; Wo¨rle, M.; Wong, T. Y. H.; Mezzetti, A. Organometallics 1999,
18, 5691. (d) Bianchini, C.; Lee, H. M. Organometallics 2000, 19, 1833,
and references in these papers. An obvious exception is the ruthenium-
salen catalyst reported by Katsuki and co-workers (Uchida, T.; Irie, R.;
Katsuki, T. Tetrahedron 2000, 56, 3501), which shows a cis selectivity.
(44) Since the identity of L in [Ru(P*)(CHX)(L)] (16 and 17) remains
open, the following are to be considered about the structures of these
proposed intermediates. When L * CHX, 16/17 are monocarbene species
and would have a [Ru(P*)(CHX)] moiety similar to complex 2/3. If L )
CHX, i.e., 16/17 are biscarbene species [Ru(P*)(CHX)2], then it may not
always be the case that both the carbene ligands coordinate to the ruthenium
center in the same manner as those in 2/3. However, according to theoretical
studies on trans-biscarbene complexes (see for example: Albright, T. A.;
Burdett, J. K.; Whangbo, M. H. In Orbitals Interactions in Chemistry;
Wiley: New York, 1985; p 286. Cauchy, D.; Jean, Y.; Eisenstein, O.;
Volatron, F. Organometallics 1988, 7, 829), the two carbene planes will
preferentially be orthogonal to each other. In this case, the rationalization
of enantioselectivity on the basis of either of the CHX groups gives the
same results owing to the D4-symmetric nature of the P* macrocycle.

4128 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
Che et al.
with the bulkier ethano bridge in II and IV, it is expected that
transition state I (or III) is more stable than transition state II
(or IV).
As depicted in Figure 4, I and IV result in formation of the
lactones 9 in a configuration opposite to that of 9 formed from
II and III. The predominant configuration observed for 9 would
depend on which of the transition states I-IV prevail in the
catalytic processes.
In the cases of small Rc and Rt groups (such as H and Me),
I and II are apparently preferred over III and IV as a result of
the smaller steric interaction between the allyloxycarbonyl group
and the porphyrin ring. Because II is less stable than I, the
prevailing transition state in such cases should be the latter.
This is consistent with the predominant configuration observed
for 9a,b (entries 1 and 2, Table 3).
However, when Rc is H and Rt becomes a sterically
demanding phenyl group (8d), modeling studies reveal that there
is an extremely severe steric interaction between the phenyl
group and the porphyrin ring in I and II, and only III and IV
can accommodate the phenyl group. Accordingly, the prevailing
transition state for this substrate should be III (as described
above, IV is less stable than III), which accounts for the
predominant configuration of (1S,5R) found for 9d (entry 4,
Table 3).
To achieve an excellent enantiocontrol, the energy difference
between I and II (or between III and IV) should be sufficiently
large. This requires the Rc or Rt groups to have a proper size so
that their orientation toward the norbornane ethano bridge is
effectively prohibited due to steric hindrance but their orientation
toward the methano bridge experiences little strain. Evidently,
H or Me groups are too small to meet this requirement, which
rationalizes the low enantioselectivity observed for substrates
8a,b. The high enantioselectivity achieved for substrate 8d can
be attributed to its desirably large Rt (Rt ) phenyl) group, whose
interaction with the norbornane methano (III) and ethano bridge
(IV) resembles that depicted in Figure 3.
Figure 4. Schematic structure of the [Ru(P*)(CHCO2CH2CHdCRcRt)]
moiety in the transition states that result in formation of the lactones
9. The orientation of the carbene plane (H-C-X) is based on the X-ray
structure of complex 3. Note that only the norbornane moieties at the
same side as the carbene group are shown.
Conclusions
The following conclusions can be drawn from this work. First,
chiral carbonyl ruthenium porphyrin [Ru(P*)(CO)(EtOH)] (1)
is one of the most trans-selective metal catalysts currently
available for asymmetric intermolecular cyclopropanation of
styrenes with diazoacetates N2CHCO2R. The EDA cyclopro-
panation of styrene catalyzed by complex 1 affords excellent
enantioselectivity with unprecedentedly high trans/cis ratio and
catalyst turnovers. Second, complex 1 represents the hitherto
most efficient metalloporphyrin catalyst for an asymmetric intra-
molecular cyclopropanation process, catalyzing the cyclopro-
panation of several allylic diazoacetates N2CHCO2CH2CHd
CRcRt in up to 85% ee. Third, the active intermediates in the
complex 1-catalyzed inter- and intramolecular cyclopropanations
could be the respective chiral electrophilic ruthenium carbene
complexes [Ru(P*)(CHX)(L)] (X ) CO2R, CO2CH2CHd
However, it should be noted that as [Ru(P*)(CHCO2CH2-
CHdCRcRt)(L)] approach the transition states for the formation
of lactones 9 the allyloxycarbonyl groups CO2CH2CHdCRcRt
in the carbene complexes must fold to allow the CdC bonds to
be close enough to the carbene groups. This would relieve the
original steric interaction between the allyl groups and respective
norbornane moieties. Consequently, the carbene plane would
rotate back to the position almost bisecting the angle between
adjacent Ru-N bonds (as in complex 2) and both of the severely
tilted meso-phenyl rings would recover to their normal orienta-
tions (i.e., close to being perpendicular to the porphyrin ring).
If this is the case, the [Ru(P*)(CHCO2CH2CHdCRcRt)] moieties
in the transition states should have the structure schematically
shown in Figure 4.
On the basis of the indicated orientation of the carbene plane
(H-C-X), four possible transition states of [Ru(P*)(CHCO2CH2-
CHdCRcRt)(L)] are to be considered, i.e., the transition states
I-IV depicted in Figure 4,45 which are interconvertible via
rotations about the C-C or C-O bonds in the (allyloxy-
carbonyl)carbene group. The major difference between I and
II (or between III and IV) lies in the interaction of their Rc
and Rt groups with the norbornane moiety A or the interaction
of the carbene methylene group directly bonded to the oxygen
atom with the norbornane moiety B′/B. Since these groups
interact with the norbornane methano bridge in I and III but
(45) The roughly orthogonal orientation of the CdC and RudC bonds
in I-IV (which contrasts with the parallel orientation in 19a,b shown in
Scheme 3 for terminal alkenes) should be favored for substrates bearing
nonterminal alkene moieties, such as all the allylic diazoacetates 8 examined
in this work except 8a, since for the CdC bond of a nonterminal alkene it
is hard to reach a position both parallel to the RudC bond and sufficiently
close to the carbene C atom as a result of the steric interaction between the
porphyrin ring and the substituents on the CdC bond. For substrate 8a
(which contains a terminal alkene moiety), the forgoing parallel orientation
may be favored over any of the orientations in I-IV. If such is the case,
a rationalization of the rather low enantioselectivity for 8a can be made on
the basis of model structures shown in Figures 3a and 3b by replacing the
styrene phenyl groups in the figures with hydrogen.

Ru Porphyrin Catalyzed Cyclopropanation of Alkenes
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4129
signal at δ 3.11). 13C NMR (300 MHz, CDCl3): δ 285 (RudC). UV/
vis (6.08 × 10-6 M, CH2Cl2): λmax (log ꢀ) 402 (5.26), 442 sh (4.72),
533 nm (4.20). FAB-MS: m/z 1417 (M+).
CRcRt), where L is a ligand with a considerable trans effect.
Fourth, reaction of complex 1 with diazo compounds N2CPh2
and N2C(Ph)CO2CH2CHdCH2 affords stable five-coordinate
chiral ruthenium monocarbene complexes [Ru(P*)(CPh2)] (2)
and [Ru(P*)(C(Ph)CO2CH2CHdCH2)] (3), respectively, which
constitute the first isolated chiral metalloporphyrin carbene
complexes.
Intermolecular Cyclopropanation Catalyzed by Complexes 1 and
2. A Typical Procedure. A solution of complex 1 (3.3 mg, 2.5 µmol)
and styrene (2.65 g, 25 mmol) in dichloromethane (10 mL) was stirred
at room temperature for 30 min. EDA (0.57 g, 5.0 mmol) was added
via a syringe pump over 8 h, and the mixture was stirred for an
additional 12 h. The trans/cis ratio was determined by GC-MS with an
Ultra 2 cross-linked 5% phenyl-methyl silicone column (25 m × 0.2
mm × 0.33 µm). After the desired products were purified by flash
chromatography, their enantiomeric excesses were determined by chiral
GC with a Cyclodex B column (J & W Scientific, 30 m) or chiral
HPLC with a Daicel OJ column.
Experimental Section
General. All manipulations were carried out under a nitrogen
atmosphere unless stated otherwise. Solvents were purified according
to standard procedures. Ethyl diazoacetate (Aldrich) was used as
received. The chiral D4-symmetric Halterman’s porphyrin (H2P*),10
complex 1,9,46 allyl18 and other alkyl diazoacetates,2b and diphenyl-
diazomethane47 were prepared by the literature methods. Various
alkenes purchased from Aldrich were purified by being passed through
Competitive Cyclopropanations Catalyzed by Complex 1. In a
typical experiment, equimolar amounts of each alkene (1.5 mmol each)
and complex 1 (0.5 mg) were dissolved in dichloromethane (2 mL) at
room temperature. A solution of EDA (0.3 mmol) in dichloromethane
(1 mL) was added over a period of 6 h. The cyclopropyl esters formed
were analyzed by GC-MS.
1
alumina or by distillation over CaH2. H and 13C{1H} NMR spectra
were recorded on a Bruker DPX-300 or DRX-500 FT-NMR spectrom-
eter. Chemical shifts were referenced to tetramethylsilane. Fast atom
bombardment (FAB) mass spectra were obtained on a Finnigan MAT
95 mass spectrometer with 3-nitrobenzyl alcohol as the matrix. UV-
visible spectra were recorded on a Perkin-Elmer Lambda 19 spectro-
photometer. GC-MS measurements were performed on a HP G1800C
GCD Series II spectrometer. Elemental analyses were performed by
the Butterworth Laboratories Ltd., Teddington, UK.
Intramolecular Cyclopropanation Catalyzed by Complex 1. To
a well-stirred solution of complex 1 (2.2 mg, 0.0017 mmol) in CH2Cl2
(2 mL) was added dropwise allylic diazoacetate (0.25 mmol) in CH2-
Cl2 (2 mL) at room temperature. The reaction mixture was stirred for
18 h. The desired products were purified by flash column chromatog-
raphy with a suitable mixture of ethyl acetate and petroleum ether (bp
40-60 °C) as the eluent.
X-ray Crystal Structure Determination of 2‚2CH2Cl2 and 3‚
3CH2Cl2. Single crystals of 2‚2CH2Cl2 and 3‚3CH2Cl2 were obtained
from slow evaporation of a solution of 2 in dichloromethane/acetonitrile
at -20 °C and a solution of 3 in dichloromethane/hexane at 5 °C. For
2‚2CH2Cl2, a crystal of the dimensions 0.40 × 0.20 × 0.05 mm was
mounted on a glass fiber and diffraction data were collected in the θ
range of 1.23-27.49° at 295(2) K on a Siemens SMART CCD
diffractometer; for 3‚3CH2Cl2, a crystal of the dimensions 0.20 × 0.16
× 0.14 mm was mounted on a glass fiber and diffraction data were
collected in the θ range of 1.67-27.60° at 294(2) K on a Bruker
SMART CCD diffractometer. In both cases, graphite monochromatized
Mo KR radiation (λ ) 0.71073 Å) was used. The structures of 2‚2CH2-
Cl2 and 3‚3CH2Cl2 were solved by the heavy atom method and refined
by full-matrix least squares on F2 by using the SHELXL programs.
Preparation of [Ru(P*)(CPh2)] (2). A solution of diphenyldiazo-
methane (20 mg, 0.10 mmol) in benzene (15 mL) was added to a
solution of complex 1 (50 mg, 0.038 mmol) in benzene (15 mL) under
an argon atmosphere. The resulting mixture was stirred for 3 h. After
removal of all the volatiles in vacuo, the product was extracted into
n-pentane and the filtrate was evaporated to dryness. The residue was
then recrystallized from dichloromethane/acetonitrile and dried in vacuo.
Yield: 86%. Anal. Calcd for C97H86N4Ru: C, 82.70; H, 6.15; N, 3.98.
1
Found C, 82.99; H, 6.34; N, 3.72. H NMR (500 MHz, CDCl3. For
labeling of various protons, see Figure S2): δ Hâ 8.26 (m, 8H), Hp′
7.28 (s, 4H), Ha, Ha′, Hb, Hb′ 3.57 (d, 4H), 3.47 (d, 4H), 2.89 (d, 4H),
2.39 (d, 4H), CH2 0.79-2.04 (m, 48H); CPh2: Hp 6.32 (t, 2H), Hm
6.11 (t, 4H), Ho 3.41 (d, 4H). 13C NMR (300 MHz, CDCl3): δ 315
(RudC). UV/vis (7.54 × 10-6 M, CH2Cl2): λmax (log ꢀ) 397 (5.19),
432 (5.06), 536 nm (4.29). FAB-MS: m/z 1409 (M+).
Preparation of [Ru(P*)(C(Ph)CO2CH2CHdCH2)] (3). To an ice
bath-cooled solution of complex 1 (50 mg, 0.038 mmol) in dichloro-
methane (5 mL) under argon was added a solution of allyl R-diazo-
phenylacetate (40 mg, 0.20 mmol) in dichloromethane (10 mL) by
syringe over 10 h. The reaction mixture was then treated with methanol
(2 mL) and evaporated to dryness under vacuum at room temperature.
Column chromatography of the residue on basic alumina with dichloro-
methane/hexane (1:5 v/v) as eluent gave the desired product as a dark
red solid in 85% yield. Anal. Calcd for C95H86N4O2Ru‚MeOH: C,
Acknowledgment. This work was supported by The Uni-
versity of Hong Kong, the Hong Kong Research Grants Council,
the Hong Kong University Foundation, and the Croucher
Foundation.
Supporting Information Available: Results of complex
1-catalyzed cyclopropanation of styrene with EDA in various
solvents (Table S1), log(kX/kH) vs σ+ plot for complex 1-cat-
alyzed cyclopropanation of para-substituted styrenes (Figure S1),
1H NMR spectra of complexes 2 and 3 in CDCl3 (Figures S2
and S3), and side views of the structure of complex 2 (Figure
S4), along with ORTEP drawings with the atom-numbering
schemes, tables of final coordinates, bond lengths, bond angles,
and anisotropic displacement parameters of 2‚2CH2Cl2 and
3‚3CH2Cl2 (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
1
79.58; H, 6.26; N, 3.87. Found C, 79.85; H, 6.09; N, 4.08. H NMR
(500 MHz, CDCl3. For labeling of various protons, see Figure S3): δ
Hâ 8.35 (m, 8H), Hp′ 7.30 (s, 4H), Ha, Ha′, Hb, Hb′ 3.56 (d, 4H), 3.48
(d, 4H), 3.11 (d, 4H), 2.43 (d, 4H), CH2 0.87-2.02 (m); carbene
Ph: Hp 6.59 (t, 1H), Hm 6.16 (t, 2H), Ho 3.70 (d, 2H); CO2CH2CHd
CH2: CH 4.92 (m, 1H), CHdCH2 4.49 (d, 1H), 4.28 (d, 1H), OCH2
3.38 (dd, 1H), ∼3.1 (dd, 1H, note that only one of the two doublets is
discernible owing to a partial overlap of this signal with the intense
(46) (a) Berkessel, A.; Frauenkron, M. J. Chem. Soc., Perkin Trans. 1
1997, 2265. (b) Lai, T.-S.; Kwong, H.-L.; Zhang, R.; Che, C.-M. J. Chem.
Soc., Dalton Trans. 1998, 3559.
(47) Miller, J. B. J. Org. Chem. 1959, 24, 560.
JA001416F