Isolation, X-ray crystal structure, and reactivity of a new C-H carbene complex of (5,10,15,20-tetraphenylporphyrinato)ruthenium(II)

Article abstract of DOI:10.1021/om800289v

The new (porphyrin)ruthenium(II) carbene complex 1 has been prepared by treating (TPP)Ru(CO)(EtOH) with excess 2,6-di-tert-butyl-4-methylphenyl diazoacetate and characterized by X-ray crystal structure analysis due to a kinetic stability. The reactivity of 1 toward axial ligands (CO, pyridine, dimethylphenylphosphine) and the asymmetric cyclopropanation of styrene with this bulky diazoacetate ester catalyzed by ruthenium Halterman porphyrin are also presented.

Full text of DOI:10.1021/om800289v

Organometallics 2008, 27, 3037–3042
3037
Isolation, X-ray Crystal Structure, and Reactivity of a New C-H
Carbene Complex of
(5,10,15,20-Tetraphenylporphyrinato)ruthenium(II)
Paul Le Maux,† Thierry Roisnel,‡ Ire`ne Nicolas,† and Ge´rard Simonneaux*,†
Inge´nierie Chimique et Mole´cules pour le ViVant, and Centre de Diffractome´trie, UMR 6226, UniVersite´ de
Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
ReceiVed April 1, 2008
The new (porphyrin)ruthenium(II) carbene complex 1 has been prepared by treating (TPP)Ru(CO)(EtOH)
with excess 2,6-di-tert-butyl-4-methylphenyl diazoacetate and characterized by X-ray crystal structure
analysis due to a kinetic stability. The reactivity of 1 toward axial ligands (CO, pyridine, dimethylphe-
nylphosphine) and the asymmetric cyclopropanation of styrene with this bulky diazoacetate ester catalyzed
by ruthenium Halterman porphyrin are also presented.
variety of porphyrin ruthenium complexes after our first X-ray
structure of a ruthenium porphyrin carbene complex in 1998.8
Remarkably, all of these structures contain a carbene carbon
center bearing two substituents different from hydrogen, due
to higher temperature stability. However, these carbene com-
plexes are rarely involved in cyclopropanation reaction. To
substantiate the existence of ruthenium carbenes and to more
fully characterize the Ru-C bonding, we report herein a
combined X-ray crystallographic and reactivity evaluation of
the first stable hydrogen carbon ruthenium porphyrin complex.
2,6-Di-tert-butyl-4-methylphenyl diazoacetate (DBA), a very
bulky diazo ester, previously reported by Doyle,14 was chosen
as diazo derivative due to an expected kinetic stabilization of
the resulting ruthenium carbene complex.15
Introduction
The cyclopropanation of olefins using transition metals as
catalysts for decomposition of diazo derivatives is one of the
best methods to create a carbon-carbon bond in organic
synthesis. The most exhaustively studied diazo reagents for
intermolecular cyclopropanation reactions are the R-diazoesters,
in particular ethyl diazoacetate.1–3 Generally, the mechanism
of the transition-metal-catalyzed decomposition of R-diazoesters
is believed to initially proceed via the formation of a metal
carbene complex. Thus several secondary carbene complexes
have been prepared and characterized in solution4 but very few
by X-ray crystallography,5 which can be considered as real
intermediates directly involved in the catalytic cycle.
Recent growth in the area of transition metal porphyrin
chemistry has also been driven by the increased interest
associated with ruthenium-catalyzed cyclopropanation. There
are two recent reviews on this topic.6,7 We8 and the groups of
Che,9 Berkessel,10 and Gross11 have found many different
ruthenium porphyrins that are active catalysts for cyclopropa-
nation of alkenes with diazo derivatives. To date, Che and
co-workers12,13 have reported the X-ray structures of a wide
Results
Synthesis. Reaction of the carbonyl compound (TPP)Ru(CO)
with excess of 2,6-di-tert-butyl-4-methylphenyl diazoacetate in
toluene (70 °C) results in the deplacement of the CO ligand
after 60 min (Scheme 1). The formation of the brown carbene
derivative 1 was observed and, then it was isolated in 91% yield.
This carbene is air stable in the solid state and soluble in
common polar organic solvents and can be purified by silica
gel chromatography. Microcrystals suitable for X-ray structure
analysis were obtained by recrystallization from CH2Cl2/pentane/
THF (1:5:0.01) (vide supra). This new product has been
characterized by conventional spectroscopic techniques. In
particular, its IR spectrum as a KBr pellet reveals the presence
of a single absorption at 1719 cm-1, attributed to the ester group,
and the absence of the CO absorption due to the axial ligand.
As indicated by the molecular structure of 1 described below,
the carbene complex exists as a six-coordinate, diamagnetic 18-
electron species in the solid state. In solution, 1H NMR studies
show that the ligated THF is weakly bound and is in rapid
exchange with free THF. For example, broad signals for THF
appear at 2.20 and 1.15 ppm at 298 K, whereas at 178 K, these
* Corresponding author. E-mail: gerard.simonneaux@univ-rennes1.fr.
† Inge´nierie Chimique et Mole´cules pour le Vivant.
‡ Centre de Diffractome´trie.
(1) Brookhart, M.; Studabaker, W. B. Chem. ReV. 1987, 87, 411–432.
(2) Doyle, M. P.; Forbes, D. C. Chem. ReV. 1998, 98, 911–935.
(3) Lebel, H.; Marcoux, J. F.; Molinaro, C.; Charette, A. B. Chem. ReV.
2003, 103, 977–1050.
(4) Lee, H. M.; Bianchini, C.; Jia, G.; Barbaro, P. Organometallics 1999,
18, 1961–1966.
(5) Werner, H.; Stu¨er, W.; Wolf, J. R.; Laubender, M.; Weberndo¨rfer,
B.; Herbst-Irmer, R.; Lehmann, C. Eur. J. Inorg. Chem. 1999, 1889–1897.
(6) Simonneaux, G.; Le Maux, P. Coord. Chem. ReV. 2002, 228, 43–
60.
(7) Che, C. M.; Huang, J. S. Coord. Chem. ReV. 2002, 231, 151–164.
(8) Galardon, E.; Le Maux, P.; Toupet, L.; Simonneaux, G. Organo-
metallics 1998, 17, 565–569.
(9) Lo, W. C.; Che, C. M.; Cheng, K. F.; Mak, T. C. W. J. Chem. Soc.,
Chem. Commun. 1997, 1205–1206.
(10) Frauenkron, M.; Berkessel, A. Tetrahedron Lett. 1997, 38, 7175–
7176.
(13) Li, Y.; Huang, J. S.; Xu, G. B.; Zu, N.; Zhou, Z. Y.; Che, C. M.;
Wong, K. Y. Chem.-Eur. J. 2004, 10, 3486–3502.
(11) Gross, Z.; Galili, N.; Simkhovich, L. Tetrahedron Lett. 1999, 40,
1571–1574.
(14) Doyle, M. P.; Bagheri, V.; Wandless, T. J.; Harn, N. K.; Brinker,
D. A.; Eagle, C. T.; Loh, K. L. J. Am. Chem. Soc. 1990, 112, 1906–1912.
(15) Park, S. B.; Sakata, N.; Nishiyama, H. Chem.-Eur. J. 1996, 2,
303–306.
(12) Che, C. M.; Huang, J. S.; Lee, F. W.; Li, Y.; Lai, T. S.; Kwong,
H. L.; Teng, P. F.; Lee, W. S.; Lo, W. C.; Peng, S. M.; Zhou, Z. Y. J. Am.
Chem. Soc. 2001, 123, 4119–4129.
10.1021/om800289v CCC: $40.75
2008 American Chemical Society
Publication on Web 05/31/2008

3038 Organometallics, Vol. 27, No. 13, 2008
Le Maux et al.
Scheme 1
Table 1. 1H NMR Selected Data for Complexes 1-5a
porphyrin carbene ligand
complex Hpyrrole HHCd Hph CH3
Table 2. Crystal Data and Structure Refinement for 1
L
empirical formula
fw
C65H60N4O3Ru
1046.24
t-Bu
14.70 6.59 2.04 0.09
Ho,m, p
CH3
temperature
100(2) K
1
2
3
8.53
1.15, 2.20
wavelength
cryst syst, space group
unit cell dimens
0.71073 Å
triclinic, P1j
j
8.42, 8.35 15.18 6.54 2.03 0.07, 0.10
8.16
4.34, 6.55,
6.84
2.33
a ) 11.0476(16) Å, R ) 95.986(8)°
b ) 11.5485(18) Å, ꢀ ) 90.096(9)°
c ) 23.183(4) Å, γ ) 116.905(8)°
2619.2(7) Å3
4
5
8.15
7.95
4.52, 6.49, 2.14,
6.62
2.37, 5.33,
5.92
2.30
volume
Z, calcd density
absorp coeff
F(000)
2, 1.327 Mg/m3
0.351 mm-1
1092
a L ) THF (1), P Me2Ph (3, 4), pyridine (5).
cryst size
θ range for data collection
limiting indices
0.33 × 0.24 × 0.12 mm
two resonances appear at -0.2 and -1.1 ppm. Thus, the
positions of these signals are strongly shifted upfield relative
to those of free THF (3.55 and 1.41 ppm) due to the ring current,
this effect being increased at low temperature due to the
increased fraction of ligated THF. However, no significant
changes of the porphyrin or carbene resonances are observed.
The HMQC spectrum shows a typical low-field signal for the
carbene carbon at 281.3 ppm. The 1H NMR spectrum reveals a
low-field signal for the hydrogen bound to the carbene carbon
at 14.70 ppm (Table 1) and resonances at 6.59 (H Ph), 2.04
(Me), and 0.09 (t-Bu) ppm. These three resonances are shifted
upfield relative to those of the diazoester, 7.15, 2.35, and 1.4
ppm, respectively, because of the ring current effect. In UV-vis
spectroscopy, the coordination of the carbene species slightly
modifies the absorption spectrum of the starting carbonyl
complex; the Soret band undergoes a 2 nm blue shift when the
Q-band becomes broad and appears at 482 nm. All these
spectroscopic properties are in agreement with previous data
for porphyrin ruthenium carbene complexes.
3.13 to 27.48°
-14 e h e 14, -14 e k e 14,
-30 e l e 30
no. of reflns collected/unique
completeness to θ ) 27.48
absorp corr
max. and min. transmn
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
42 022/11 934 [R(int) ) 0.0517]
99.4%
semiempirical from equivalents
0.959 and 0.885
full-matrix least-squares on F2
11 934/0/666
1.255
R1 ) 0.0666, wR2 ) 0.1287
R1 ) 0.0728, wR2 ) 0.1311
2.285 and -2.011 e Å-3
largest diff peak and hole
Table 3. Selected Bond Distances (Å) and Angles (deg) for 1
Ru(1)-C(31)
Ru(1)-N(1)
Ru(1)-N(2)
Ru(1)-N(3)
1.839(4)
2.042(3)
2.053(3)
2.057(3)
Ru(1)-N(4)
Ru(1)-O(51)
C(31)-C(32)
C(31)-H(31)
2.054(3)
2.376(3)
1.480(5)
0.9500
C(31)-Ru(1)-N(1)
C(31)-Ru(1)-N(2)
C(31)-Ru(1)-N(3)
C(31)-Ru(1)-N(4)
94.40(14)
96.39(14)
92.52(14)
90.02(14)
N(3)-Ru(1)-O(51)
N(4)-Ru(1)-O(51)
N(1)-Ru(1)-N(3)
N(2)-Ru(1)-N(4)
88.43(10)
85.47(10)
173.08(12)
173.58(12)
This method was also found effective for chiral ruthenium
porphyrins. Using the Halterman porphyrin,16 it was possible
to isolate the carbene ruthenium porphyrin 2 as a dark brown
C(31)-Ru(1)-O(51) 175.38(13) C(32)-C(31)-Ru(1) 127.6(3)
1
N(1)-Ru(1)-O(51)
N(2)-Ru(1)-O(51)
84.69(11)
88.13(10)
C(32)-C(31)-H(31) 116.2
Ru(1)-C(31)-H(31) 116.2
compound with 93% yield. The H NMR data for 1 and 2 are
summarized in Table1.
Crystal and Molecular Structure of 1. Details of the
structure obtained for 1 are given in the Experimental Section.
Table 2 lists crystallographic data for 1; selected bond distances
and bond angles are given in Table 3. The carbene complex 1
forms as dark brown crystals in the triclinic space group P1
j
(16) Halterman, R. L.; Jan, S. T. J. Org. Chem. 1991, 56, 5253–5254.
(17) Kawai, M.; Yuge, H.; Miyamoto, T. K. Acta Crystallogr. Sect. C
2002, 58, m581–m582.
with two molecules per unit cell. Figure 1 illustrates the
molecular structure and atom labeling. As indicated in the
structure, the carbene complex exists as a six-coordinate
compound, with a THF molecule as axial ligand. As expected
for such a complex, the porphyrin ligand is nearly planar.
However, the ruthenium atom is slightly out of the mean plane
of the porphyrin plane, 0.10 Å toward the carbene ligand. A
similar situation has been previously observed with other
(18) Harada, T.; Wada, S.; Yuge, H.; Miyamoto, T. K. Acta Crystallogr.
Sect. C 2003, 59, m37–m39.
(19) Wada, S.; Yuge, H.; Miyamoto, T. K. Acta Crystallogr. Sect. C
2003, 59, m369–m370.
(20) Scheidt, W. R. Systematics of the Stereochemistry of Porphyrins
and Metalloporphyrins. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: San Diego, CA, 2000; Vol. 3,
pp 49-112.

C-H Carbene Complex of (5,10,15,20-tetraphenylporphyrinato)ruthenium(II)
Organometallics, Vol. 27, No. 13, 2008 3039
perpendicular to the plane formed by Ru(1)-C(31)-C(32)-H(31).
This presumably decreases the intramolecular strain of the two
tert-butyl groups pointing toward the porphyrin ring. Thus the
orientation of the phenyl ring of the ester group is such that it
renders difficult the nucleophilic attack of any substrate onto
the electrophilic carbene center. This situation explains the
kinetic stabilization of complex 1.
The Ru-C distance of 1.839(4) Å is slightly longer than the
ruthenium-carbon double bond (1.829(9) Å) for (TPP)Ru-
[C(CO2Et][MeOH] reported by us8 some years ago and similar
to those reported by Che13 and Miyamoto.13,17–19 The Ru-O
(THF) distance 2.376(3) Å is shorter than the axial Os-O bond
(THF, 2.43(2) Å) in a similar carbene osmium complex, reported
by Woo et al.,21 as expected from the different size of the two
metal atoms.
Ligand-Exchange Reactions. We decided to investigate the
reaction of 1 and 2 with stronger σ-donor ligands, such as
dimethylphenylphosphine. The titration curve is shown in Figure
3. Modification of the wavelength of the Soret band reveals the
presence of an intermediate (λmax 412 nm) that appears after
addition of 1 equiv of ligand. This intermediate is probably the
mixed phosphine-carbene complex.8 Addition of a large excess
of phosphine results in the formation of the symmetric bis-
ligated derivative, as identified bu UV-vis and 1H NMR
(Table 1).
Figure 1. ORTEP drawing and atom labeling of 1.
We also investigated the interaction of 1 and CO. During
slow bubbling of carbon monoxide in a solution of toluene, the
carbene ligand is completely displaced after 8 h at 100 °C. Thus
the reaction mixture progressively turns red and a precipitate
appears, which is easily characterized by IR and NMR as a
mixture of (TPP)Ru(CO) and (TPP)Ru(CO)2.22
Treatment of 1 with excess of pyridine did not allow isolation
of the corresponding six-coordinate ruthenium porphyrin carbene
complex. For example, addition of an excess of pyridine to a
solution of 1 in dichloromethane afforded (TPP)Ru(Pyr)2, which
was isolated in 78% yield. This contrast with the reactivity of
the ruthenium porphyrin bis-phenyl carbene complex toward
pyridine; in this case the mixed ligated complex was obtained.13
Catalytic Carbene Transfer Reactions. To determine if the
increase of the bulkiness of the diazo derivative occurs with
changes in reactivity, catalytic experiments were first performed
without olefins to obtain formerly the dimerization of the
carbenes. In contrast to results obtained with ethyl diazoacetate
leading mainly to maleate, no dimerization was observed in the
presence of a catalytic amount of (TPP)Ru(CO) at 100 °C.
Then, we examined the possibility of the bulky carbene
transfer reaction to styrene, although the carbene complex is
quite stable. The addition of 2,6-di-tert-butyl-4-methylphenyl
diazoacetate to styrene catalyzed by TPPRuCO was carried out
to give in 70% yield the corresponding 2-phenylcyclopropane-
1-carboxylate with pure trans geometry (Scheme 2, Table 4).
The reaction conditions were quite drastic since it was necessary
to heat at 100 °C for 12 h.
Figure 2. Figure showing the dihedral angle ꢁ (between the plane
of the ligand and the plane defined by a porphyrinato nitrogen atom,
the metal, and the carbene ligand carbon atom).
porphyrin ruthenium complexes.8 The Ru-N distances of
2.042(3)-2.054(3) Å all fall within the range previously
reported for diamagnetic ruthenium porphyrin complexes.8,13,17–19
The geometry of the coordination sphere is close to an octahedral
geometry. Bond angles at ruthenium are in the range 90.02(14)-
96.39(14)° for cis angles and 173.08(12)-173.58 (12)° for trans
angles. The O-Ru-C(carbene) angle is 175.38(13)°. Such
values, which are significantly different from expected values
for an ideal octahedral geometry, are probably related to steric
interactions between the bulky ester group and the phenyl groups
of the porphyrin. The carbene fragment is distorted, since the
angle formed by C(32)-C(31)-H(31) is 116.2°, a value that is
significantly smaller than 120°, the angle expected for ideal sp2
hybridization.
The stereochemical constraints that result from the steric
interaction of the axial ligand atoms with atoms of the
porphyrinato core have recently been discussed in a review
reported by Scheidt.20 The orientation of the ligand can be
specified by the dihedral angle ꢁ between the plane of the ligand
and a plane defined by a porphyrinato nitrogen atom, the metal
atom (Ru), and the ligand carbon (carbene) atom. Minimum
steric interaction will occur for a dihedral angle of 45°. For
complex 1, this angle is 45.15° (Figure 2), showing the
importance of the steric interaction due to to the large ester
group. In addition, the phenyl of the carbene ligand has its plane
The asymmetric version was also tested using Halterman
porphyrin as chiral ligand (Schemes 1 and 2). To evaluate the
reactivity of the bulky diazoacetate, its ruthenium-catalyzed
decomposition was examined in the presence of styrene in
toluene at 65 °C by using 2 as catalyst (Table 4). The diazo
derivatives were added slowly to the reaction mixture over 1 h,
and the reaction was stopped after 12 h. The cyclopropane was
(21) Djukic, J. P.; Smith, D. A.; Young, V. G.; Woo, L. K. Organo-
metallics 1994, 13, 3020–3026.
(22) Eaton, G. R.; Eaton, S. S. J. Am. Chem. Soc. 1975, 97, 235–236.

3040 Organometallics, Vol. 27, No. 13, 2008
Le Maux et al.
Figure 3. UV-vis titration curves of a solution of 1 in CH2Cl2 (10 mg, 10.2 µM) with PMe2Ph.
Scheme 2
balt,28 and iron29–32 porphyrins as catalysts have been reported.
Rhodium catalysts produce synthetically useful excesses of cis
cyclopropyl esters using ethyl diazoacetate as the carbene source,
whereas, in the same conditions, osmium and iron catalysts
mainly provide the trans product. Despite the relationship
between ruthenium, iron, and osmium and the synthesis of
different carbene complexes of ruthenium porphyrins, nicely
developed by Collman et al.,33 it is more recently that
cyclopropanation9,10,34 and ethyl diazoacetate insertion into
heteroatom bond reactions35 were observed using ruthenium
porphyrins as catalysts. This renewal of interest in reactions
catalyzed by ruthenium(II) porphyrin complexes is related to
the simultaneous development of new chiral ruthenium por-
phyrins. However, the preparation of transition metal carbene
complexes that lack direct heteroatom stabilization of the
Table 4. Cyclopropanation of Styrene with
2,6-Di-tert-butyl-4-methylphenyl Diazoacetate Catalyzed by Ru
Porphyrins 1 and 2a
c
catalyst
temperature (°C)
yieldb (%)
trans (%)
eetrans (%)
1
2
100
65
70
62
100
100
60
a Reactions were performed in toluene for 12 h with a catalyst:
diazo:substrate molar ratio of 1:200:1000. b Yields were based on
isolated cyclopropane. c Determined by chiral HPLC using a Chiralcel
OD column.
formed with 62% yield and 60% enantioselectivity for the trans
isomer (Table 4). The formation of the cis isomer was not
detected.
Then, we investigated the potential of 1 as a catalyst for the
cyclopropanation of styrene by EDA. The diazo derivatives were
added slowly to the reaction mixture over 1 h, and the reaction
was stopped after 12 h. The cyclopropane was formed with 95%
yield and 13:1 trans:cis ratio.
(26) Smith, D. A.; Reynolds, D. N.; Woo, L. K. J. Am. Chem. Soc.
1993, 115, 2511–2513.
(27) Hamaker, C. G.; Djukic, J. P.; Smith, D. A.; Woo, L. K.
Organometallics 2001, 20, 5189–5199.
(28) Huang, L.; Chen, Y.; Gao, G. Y.; Zhang, X. P. J. Org. Chem. 2003,
68, 8179–8184.
Discussion
(29) Wolf, J. R.; Hamaker, C. G.; Djukic, J. P.; Kodadek, T.; Woo,
L. K. J. Am. Chem. Soc. 1995, 117, 9194–9199.
(30) Hamaker, C. G.; Mirafzal, G. A.; Woo, L. K. Organometallics 2001,
20, 5171–5176.
The use of metalloporphyrins as cyclopropanation catalysts
has been proposed by Callot et al., who first reported that
rhodium porphyrins provided a cis preference for the cyclo-
propanation of styrene with ethyl diazoacetate.23 Since then,
numerous examples involving rhodium,24,25 osmium,26,27 co-
(31) Li, Y.; Huang, J. S.; Zhou, Z. Y.; Che, C. M.; You, X. Z. J. Am.
Chem. Soc. 2002, 124, 13185–13193.
(32) Tagliatesta, P.; Pastorini, A. J. Mol. Catal. A: Chem. 2003, 198,
57–61.
(33) Collman, J. P.; Brothers, P. J.; McElwee-White, L.; Rose, E.;
Wright, L. J. J. Am. Chem. Soc. 1985, 107, 4570–4571.
(34) Galardon, E.; Le Maux, P.; Simonneaux, G. J. Chem. Soc., Chem.
Commun. 1997, 927–928.
(23) Callot, H. J.; Piechocki, C. Tetrahedron Lett. 1980, 21, 3489–3492.
(24) Maxwell, J. L.; Brown, K. C.; Bartley, D. W.; Kodadek, T. Science
1992, 256, 1544–1547.
(25) Maxwell, J. L.; O’Malley, S.; Brown, K. C.; Kodadek, T.
Organometallics 1992, 11, 645–652.
(35) Galardon, E.; Le Maux, P.; Simonneaux, G. J. Chem. Soc., Perkin
Trans. 1 1997, 2455–2456.

C-H Carbene Complex of (5,10,15,20-tetraphenylporphyrinato)ruthenium(II)
Organometallics, Vol. 27, No. 13, 2008 3041
gel column chromatography under argon (CH2Cl2/pentane, 1:4) to
give 120 mg of a dark brown product (91%). Microcrystals suitable
for X-ray structure analysis were obtained by recrystallization from
electrophilic carbene carbon center is still of interest owing to
the high reactivity of these species in comparison with that of
heteroatom-stabilized systems and the relevance of these com-
plexed divalent species as possible intermediates in the catalytic
mechanism.
1
CH2Cl2/pentane/THF (1:5:0.01). H NMR (CDCl3, ppm): δ 8.53
(s, 8Η); 8.12 (m, 8H); 7.73 (m, 12H); 6.59 (s, 2H); 2.04 (s, 3H);
1
0.09 (s, 18H). HMQC: H, 14.70 (s, HCd); 13C, 281.30 (HCd).
The stability of the carbene complex 1 is in marked contrast
with its congener resulting from reaction of (TPP)Ru(CO) with
ethyl diazoacetate, which is stable only at very low temperature
(-70 °C). This important increase in thermal stability is
associated with a large steric effect of the ester substituent. Thus
the most interesting feature of the structure of complex 1 is the
steric congestion due to the presence of the bulky ester group
on the carbene ligand. An interesting structural feature is the
orientationofthecarbeneligand,thevalueofthecarbene-porphyrin
dihedral angle being (ꢁ ) 45.15°) (Figure 2). Importantly, the
steric constraints also appear to limit access to the electrophilic
carbene center and prevent substrate approach. The two tert-
butyl groups and the phenyl group of the carbene ligand seem
to form a “cap” above the plane of the porphyrin ring and protect
the carbene center from reacting species. As a second conse-
quence of the bulkiness of the diazo ester compound, higher
temperatures are needed for the cyclopropanation reaction,
which gave the trans isomer as the sole product. A similar
conclusion was also obtained using the same diazo derivatives
but with two different catalytic systems.14,15 As expected, no
dimerization of the carbene was observed.
UV-vis (CH2Cl2) λmax/nm (log ꢀ): 408 (5.22); 482 (3.98). IR (KBr,
cm-1): 1719. HRMS: calcd for C61H53N4O2Ru 975.3212 (M + H)+,
found 975.3230.
Synthesis of (Halt)Ru[:CH(CO2-2,6-di-tert-butyl-4-methylphe-
nyl)](THF), 2. A solution of 2,6-di-tert-butyl-4-methylphenyl
diazoacetate (34 mg, 0.117 mmol, in 5 mL of dry toluene) was
added to a solution of (Halt)Ru(CO) (100 mg, 0.078 mmol) in 30
mL of dry toluene at 70 °C under argon. The reaction was monitored
by thin-layer chromatography, and after 30 min, the solvent was
removed under vacuum. The crude product was purified by a silica
gel column under argon (CH2Cl2/pentane, 1:4) to give 110 mg of
a dark brown product (93%). 1H NMR (CDCl3, ppm): 8.42 (d,4H,
J ) 4.8 Hz); 8.35 (d, 4H, J ) 4.8 Hz); 7.36 (s, 4H); 6.54 (s, 2H);
3.60 (d, 4H, J ) 2.4 Hz); 3.53 (d,4H, J ) 2.7 Hz); 3.10 (d, 4H, J
) 2.8 Hz); 2.41 (d, 4H, J ) 2.8 Hz); 2.03 (s, 3H); 1.89-2.02 (m,
16H); 1.22-1.49 (m,24H); 0.92 (t, 8H, J ) 7.0 Hz); 0.10 (s, 9H);
0.07 (s,9H). HMQC: 1H, 15.18 (s, HCd); 13C, 278.39 (Cd).
UV-vis (CH2Cl2): λmax/nm (log ꢀ) 409 (5.15); 480 (3.58). IR (KBr,
cm-1): 1723. HRMS: calcd for C101H101N4O2Ru 1503.6968 (M +
H)+, found 1503.6992.
Ligand-Exchange Reaction of 1 with PMe2Ph. Synthesis of
(TPP)Ru(PMe2 Ph)2, 3. To a solution of 1 (10 mg, 10.2 µmol) in
1 mL of CH2Cl2 was added via syringe 6 equiv of PMe2Ph. The
titration was monitored by UV-vis spectroscopy (Figure 3). The
bis-phosphine complex 3 was purified by silica gel column
chromatography (CH2Cl2/pentane, 1:4) to give 9 mg of a red-brown
product (90%). 1H NMR (CDCl3, ppm): δ 8.16 (s, 8Η); 7.94-7.98
(m, 8H); 7.65-7.71 (m, 12H); 6.84 (t, 2H, J ) 6 Hz); 6.55 (t, 4H,
J ) 6 Hz); 4.29-4.38 (m, 4H); 2.33 (t, 6H, J ) 4 Hz). 31P NMR
(CDCl3, ppm): 2.12. UV-vis (CH2Cl2): λmax/nm (log ꢀ) 433 (5.12);
522 (4.01).
In conclusion, we have substantiated the mechanism of the
asymmetric cyclopropanation of olefins with diazoacetates
catalyzed by ruthenium porphyrins by isolation and X-ray
structure determination of the corresponding carbene complexes
as active intermediates.
Experimental Section
General Experiments. All reactions were performed under argon
and were magnetically stirred. Solvents were distilled from ap-
propriate drying agent prior to use: toluene from sodium and
benzophenone, CH2Cl2 from CaH2, CHCl3 from P2O5. Com-
mercially available reagents were used without further purification
unless otherwise stated. All reactions were monitored by TLC with
Merck precoated aluminum foil sheets (silica gel 60 with fluorescent
indicator UV254). Compounds were visualized with UV light at 254
and 365 nm. Column chromatographies were carried out using silica
Ligand-Exchange Reaction of 2 with PMe2Ph. Synthesis of
(Halt)Ru(PMe2 Ph)2, 4. To a solution of 2 (90 mg, 60 µmol) in 1
mL of CH2Cl2 was added via syringe 2.5 equiv of PMe2Ph. The
reaction was monitored by UV-vis spectroscopy and TLC. The
bis-phosphine complex 4 was purified by silica gel column
chromatography (CH2Cl2/pentane, 1:4) to give 80 mg of a red-
brown product (89%). 1H NMR (CDCl3, ppm): δ 8.15 (s, 8Η);
7.30 (s, 4H); 6.62 (t, 2H); 6.49 (t, 4H); 4.52 (m, 4H); 3.54 (s, 8H);
2.63 (s,8H); 1.83-1.99 (m, 16H); 1.31-1.43 (m, 24H); 0.89-0.96
(m, 8H), 2.14 (s, 6H); 2.30 (s,6H). 31P NMR (CDCl3, ppm): -3.03.
UV-vis (CH2Cl2): λmax/nm (log ꢀ) 433 (5.34); 524 (3.94).
Ligand-Exchange Reaction of 1 with Pyridine. Synthesis of
(TPP)Ru(pyridine)2, 5. To a solution of 1 (10 mg, 10.2 µmol, in
1 mL of CH2Cl2) was added via syringe 100 equiv of pyridine.
The titration was monitored by UV-vis spectroscopy. The bis-
pyridine complex 5 was purified by a silica gel column chroma-
tography (CH2Cl2/pentane, 1:4) to give 7 mg of a yellow-brown
product (78%). 1H NMR (CDCl3, ppm): δ 7.95 (s, 8Η); 7.67, 7.58
(2m, 20H); 5.92 (t, 2H, J ) 6.2 Hz); 5.33 (t, 4H, J ) 6.4 Hz); 2.37
(d, 4H, J ) 5.2 Hz). UV-vis (CH2Cl2): λmax /nm (log ꢀ) 409 (5.13);
505 (4.42).
1
gel from Merck (0.063-0.200 mm). H NMR and 13C NMR in
CDCl3 were recorded using Bruker (Advance 500dpx and 300dpx)
spectrometers at 500 and 75 MHz, respectively. UV-visible spectra
were recorded on a UVIKON XL from Biotech. Infrared spectra
were performed in KBr disks in a IFS 28 Bruker. The enantiomeric
excess of the cyclopropane was determined on a Varian Prostar
218 system equipped with a Chiralcel OD-H column.
The porphyrins were synthesized by literature methods: meso-
tetrakis-5,10,15,20-phenylporphyrin (TPPH2) and [(1S,4R,5R,8S)-
1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene-9-yl]por-
phyrin (HaltH2).16 The corresponding ruthenium carbonyl complexes,
(TPP)Ru(CO) and (Halt)Ru(CO), were obtained by refluxing the
porphyrins in o-dichlorobenzene with Ru3CO12 at 180 °C.6 The
2,6-di-tert-butyl-4-methylphenyl diazoacetate was obtained accord-
ing to the procedure of Doyle.14 Methanesulfonyl azide was
prepared from methanesulfonyl chloride and sodium azide.
Synthesis of (TPP)Ru [:CH(CO2-2,6-di-tert-butyl-4-meth-
ylphenyl)](THF), 1. A solution of 2,6-di-tert-butyl-4-methylphenyl
diazoacetate (58 mg (0.202 mmol) in 5 mL of dry toluene) was
added to a solution of (TPP)Ru(CO) (100 mg, 0.134 mmol) in 30
mL of dry toluene at 70 °C under argon. The reaction was monitored
by thin-layer chromatography, and after 1 h, the solvent was
removed under vacuum. The crude product was purified by silica
Ligand-Exchange Reaction of 1 with CO. Carbon monoxide
was bubbled through a solution of 10 mg (10.2 µmol) of 1 in 1
mL of toluene at 100 °C for 8 h. A red precipitate appeared, and
after isolation the product was identified by its IR spectrum as a
mixture of (TPP)Ru(CO) and (TPP)Ru(CO)2, 1953 and 2015 cm-1
,
respectively, as previously reported.22
Catalytic Cyclopropanation of Styrene by Catalyst 1. The
diazo compound 2,6-di-tert-butyl-4-methylphenyl diazoacetate (57.6
mg, 0.2 mmol) dissolved in 0.2 mL of toluene was added at a

3042 Organometallics, Vol. 27, No. 13, 2008
Le Maux et al.
controlled rate over a 1 h period to a stirred solution of 104 mg (1
mmol) of styrene and 0.74 mg (1 µmol) of the catalytic precursor
(TPP) Ru CO in 1 mL of toluene at 100 °C. After it was stirred at
100 °C for 12 h, the reaction solution was passed through a short
silica gel column (pentane/CH2Cl2, 4:1) to remove the catalyst and
excess styrene. After evaporation of solvents, the cyclopropane
product (45 mg, 70%) was characterized by 1H NMR as trans-
2,6-di-tert-butyl-4-methylphenyl-2-phenylcyclopropane-1-carboxy-
Catalytic Cyclopropanation of Styrene by Catalyst 1 with
Ethyl Diazoacetate. The ethyl diazoacetate (22.8 mg, 0.2 mmol)
dissolved in 0.2 mL of toluene was added at a controlled rate over
a 1 h period to a stirred solution of 104 mg (1 mmol) of styrene
and 0.97 mg (1 µmol) of the catalyst 1 in 1 mL of toluene at ambient
temperature. After it was stirred for 12 h, the reaction solution was
analyzed by GC (95%, trans/cis 13:1).
X-ray Crystallographic Structure Determination of 1. Inten-
sity data were collected on a Bruker-AXS diffractometer at T )
100(2) K. The structure was solved by direct methods using the
SIR97 program36 and then refined with full-matrix least-squares
methods based on F2 (SHELX-97)37 with the aid of the WINGX
program.38 All non-hydrogen atoms were refined with anisotropic
thermal parameters. H atoms were finally included in their
calculated positions. A final refinement on F2 with 11 934 unique
intensities and 666 parameters converged at σR(F2) ) 0.1287 (R(F)
) 0.0666) for 11 199 observed reflections with I > 2σ(I).
1
late. H NMR (CDCl3, ppm): 7.22-7.45 (m, 5H); 7.17 (s, 2H);
2.70-2.80 (m,1H); 2.37 (s, 3H); 2.18-2.28 (m, 1H); 1.53-1.63
(m,1H); 1.41 (s, 9H); 1.40 (s, 9H).
Catalytic Cyclopropanation of Styrene by Catalyst 2. The
diazo compound 2,6-di-tert-butyl-4-methylphenyl diazoacetate (57.6
mg, 0.2 mmol) dissolved in 0.2 mL of toluene was added at a
controlled rate over a 1 h period to a stirred solution of 104 mg (1
mmol) of styrene and 1.2 mg (1 µmol) of the catalytic precursor
(Halt) Ru CO in 1 mL of toluene at 65 °C. After it was stirred at
65 °C for 12 h, the reaction solution was passed through a short
silica gel column (pentane/CH2Cl2, 4:1) to remove the catalyst and
excess styrene. After evaporation of solvents, the cyclopropane
product (45 mg, 62%) was characterized by 1H NMR as trans-
2,6-di-tert-butyl-4-methylphenyl-2-phenylcyclopropane-1-carboxy-
late. The ee ()60%) was determined by chiral HPLC using a
Chiralcel OD column, n-hexane/iPrOH ) 99:1, flow rate ) 0.2
mL/min, wavelength ) 220 nm, tR ) 13.96 min for the minor
Supporting Information Available: Tables of atomic coordi-
nates, bond lengths and angles, anisotropic displacement parameters,
and torsional angles. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM800289V
isomer, tR ) 15.98 min for the major isomer. [R]23 ) +120
D
(CH2Cl2).
(37) Sheldrick, G. M. SHELX97, Programs for Crystal Structure Analysis
(Release 97-2); Institu¨t fu¨r Anorganische Chemie der Universita¨t: Go¨ttingen,
Germany, 1998.
(36) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115–119.
(38) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.