Remarkably stable iron porphyrins bearing nonheteroatom-stabilized carbene or (alkoxycarbonyl)carbenes: Isolation, X-ray crystal structures, and carbon atom transfer reactions with hydrocarbons

Article abstract of DOI:10.1021/ja020391c

Reactions of [Fe(TPFPP)] (TPFPP = meso-tetrakis(pentafluorophenyl)porphyrinato dianion) with diazo compounds N₂C(Ph)R (R = Ph, CO₂Et, CO₂CH₂CH=CH₂) afforded [Fe(TPFPP)(C(Ph)R)] (R = Ph (1), CO₂Et (2), CO₂CH₂CH=CH₂ (3)) in 65-70% yields. Treatment of 1 with N-methylimidazole (Melm) gave the adduct [Fe(TPFPP)(CPh₂)(Melm)] (4) in 65% yield. These new iron porphyrin carbene complexes were characterized by NMR and UV-vis spectroscopy, mass spectrometry, and elemental analyses. X-ray crystal structure determinations of 1·0.5C₆H₆·0.5CH₂Cl₂ and 4 reveal Fe=CPh₂ bond lengths of 1.767(3) (1) and 1.827(5) A (4), together with large ruffling distortions of the TPFPP macrocycle. Complexes 2 and 4 are reactive toward styrene, affording the corresponding cyclopropanes in 82 and 53% yields, respectively. Complex 1 is an active catalyst for both intermolecular cyclopropanation of styrenes with ethyl diazoacetate and intramolecular cyclopropanation of allylic diazoacetates. Reactions of 2 and 4 with cyclohexene or cumene produced allylic or benzylic C-H insertion products in up to 83% yield.

Full text of DOI:10.1021/ja020391c

Published on Web 10/15/2002
Remarkably Stable Iron Porphyrins Bearing
Nonheteroatom-Stabilized Carbene or
(Alkoxycarbonyl)carbenes: Isolation, X-ray Crystal
Structures, and Carbon Atom Transfer Reactions with
Hydrocarbons
Yan Li, Jie-Sheng Huang, Zhong-Yuan Zhou,† Chi-Ming Che,* and Xiao-Zeng You‡
Contribution from the Department of Chemistry and Open Laboratory of Chemical Biology
of the Institute of Molecular Technology for Drug DiscoVery and Synthesis, The UniVersity of
Hong Kong, Pokfulam Road, Hong Kong
Received March 15, 2002
Abstract: Reactions of [Fe(TPFPP)] (TPFPP ) meso-tetrakis(pentafluorophenyl)porphyrinato dianion) with
diazo compounds N2C(Ph)R (R ) Ph, CO2Et, CO2CH2CHdCH2) afforded [Fe(TPFPP)(C(Ph)R)] (R ) Ph
(1), CO2Et (2), CO2CH2CHdCH2 (3)) in 65-70% yields. Treatment of 1 with N-methylimidazole (MeIm)
gave the adduct [Fe(TPFPP)(CPh2)(MeIm)] (4) in 65% yield. These new iron porphyrin carbene complexes
were characterized by NMR and UV-vis spectroscopy, mass spectrometry, and elemental analyses. X-ray
crystal structure determinations of 1‚0.5C6H6‚0.5CH2Cl2 and 4 reveal FedCPh2 bond lengths of 1.767(3)
(1) and 1.827(5) Å (4), together with large ruffling distortions of the TPFPP macrocycle. Complexes 2 and
4 are reactive toward styrene, affording the corresponding cyclopropanes in 82 and 53% yields, respectively.
Complex 1 is an active catalyst for both intermolecular cyclopropanation of styrenes with ethyl diazoacetate
and intramolecular cyclopropanation of allylic diazoacetates. Reactions of 2 and 4 with cyclohexene or
cumene produced allylic or benzylic C-H insertion products in up to 83% yield.
attention3-7 due mainly to the possible formation of carbene
complexes of cytochrome P-450 enzymes in reductive metabo-
Introduction
The fact that cytochrome P-450 enzymes in biological systems
bear iron porphyrin active sites makes iron porphyrins unique
candidates for model compounds of these enzymes. Numerous
efforts have been directed to oxoiron porphyrins and their
oxygen atom transfer reactions with alkenes or alkanes to afford
epoxidation or C-H insertion (i.e. hydroxylation) products,1
mainly to mimic the corresponding hydrocarbon oxidation
reactivity of the putative oxoiron species of cytochrome P-450
enzymes.2 The carbon analogues of oxoiron porphyrins, namely,
iron porphyrin carbene complexes, have also received much
lism of polyhalogenated compounds or oxidative metabolism
of benzodioxole derivatives3 and in the propylene epoxidation
by cytochrome P-450.6 However, the carbon atom transfer
reactions of iron porphyrin carbene complexes with alkenes to
form cyclopropanes are rarely studied,8,9 and no iron porphyrin
carbene complexes haVe been found to react with hydrocarbons
to form C-H insertion products.
Moreover, despite the report of a large number of iron
porphyrin carbene complexes in the literature (the predominant
of which are halocarbene complexes [Fe(Por)(CX2)], [Fe(Por)-
(C(X)X′)], or [Fe(Por)(C(R)X)] first prepared by Mansuy and
co-workers3), there are extremely few (if any) iron porphyrins
bearing nonheteroatom-stabilized carbenes CR2 and C(R)R′ or
* To whom correspondence should be addressed. E-mail: cmche@hku.hk.
† Department of Applied Biology and Chemical Technology, The Hong
Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
‡ Coordination Chemistry Institute and the State Key Laboratory of
Coordination Chemistry of Nanjing University, Nanjing 210093, P. R. China.
(1) For reviews on iron porphyrin-catalyzed epoxidation or hydroxylation
reactions that are generally believed to involve oxoiron porphyrin inter-
mediates, see: (a) Ellis, P. E., Jr.; Lyons, J. E. Coord. Chem. ReV. 1990,
105, 181. (b) Meunier, B. Chem. ReV. 1992, 92, 1411. (c) Collman, J. P.;
Zhang, X.; Lee, V. J.; Uffelman, E. S.; Brauman, J. I. Science 1993, 261,
1404. (d) Mansuy, D. Coord. Chem. ReV. 1993, 125, 129. For examples of
observed oxoiron porphyrins and their oxygen atom transfer reactions with
hydrocarbons, see: (e) Groves, J. T.; Haushalter, R. C.; Nakamura, M.;
Nemo, T. E.; Evans, B. J. J. Am. Chem. Soc. 1981, 103, 2884. (f) Tsuchiya,
S. J. Chem. Soc., Chem. Commun. 1991, 716. (g) Yamaguchi, K.; Watanabe,
Y.; Morishima, I. J. Chem. Soc., Chem. Commun. 1992, 1721. (h) Fujii,
H. J. Am. Chem. Soc. 1993, 115, 4641. (i) Groves, J. T.; Gross, Z.; Stern,
M. K. Inorg. Chem. 1994, 33, 5065. (j) Traylor, T. G.; Kim, C.; Richards,
J. L.; Xu, F.; Perrin, C. L. J. Am. Chem. Soc. 1995, 117, 3468. (k) Gross,
Z.; Nimri, S. J. Am. Chem. Soc. 1995, 117, 8021. (l) Goh, Y. M.; Nam, W.
Inorg. Chem. 1999, 38, 914.
(3) (a) Mansuy, D.; Lange, M.; Chottard, J.-C.; Guerin, P.; Morliere, P.; Brault,
D.; Rougee, M. J. Chem. Soc., Chem. Commun. 1977, 648. (b) Mansuy,
D.; Lange, M.; Chottard, J.-C.; Bartoli, J. F.; Chevrier, B.; Weiss, R. Angew.
Chem., Int. Ed. Engl. 1978, 17, 781. (c) Mansuy, D. Pure Appl. Chem.
1980, 52, 681. (d) Guerin, P.; Battioni, J. P.; Chottard, J.-C.; Mansuy, D.
J. Organomet. Chem. 1981, 218, 201. (e) Battioni, J. P.; Dupre, D.; Guerin,
P.; Mansuy, D. J. Organomet. Chem. 1984, 265, 53. (f) Mansuy, D. Pure
Appl. Chem. 1987, 59, 759. (g) Artaud, I.; Gregoire, N.; Battioni, J.-P.;
Dupre, D.; Mansuy, D. J. Am. Chem. Soc. 1988, 110, 8714. (h) Artaud, I.;
Gregoire, N.; Leduc, P.; Mansuy, D. J. Am. Chem. Soc. 1990, 112, 6899.
(4) (a) Ziegler, C. J.; Suslick, K. S. J. Am. Chem. Soc. 1996, 118, 5306. (b)
Ziegler, C. J.; Suslick, K. S J. Organomet. Chem. 1997, 528, 83.
(5) Hamaker, C. G.; Mirafzal, G. A.; Woo, L. K. Organometallics 2001, 20,
5171.
(6) Groves, J. T.; Avaria-Neisser, G. E.; Fish, K. M.; Imachi, M.; Kuczkowski,
R. L. J. Am. Chem. Soc. 1986, 108, 3837.
(7) Wolf, J. R.; Hamaker, C. G.; Djukic, J.-P.; Kodadek, T.; Woo, L. K. J.
Am. Chem. Soc. 1995, 117, 9194.
(2) Sono, M.; Roach, M. P.; Coulter, E. D.; Dawson, J. H. Chem. ReV. 1996,
96, 2841.
9
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J. AM. CHEM. SOC. 2002, 124, 13185-13193
13185

A R T I C L E S
Li et al.
Scheme 1
(alkoxycarbonyl)carbenes C(R)CO2R′ (R/R′ ) H, alkyl, or
aryl). These types of iron porphyrin carbene complexes, such
as the arylcarbene complex [Fe(TTP)(CH(2,4,6-Me3C6H2))]5,8
and the (alkoxycarbonyl)carbene complexes [Fe(Por)(CHCO2-
Et)],7 have been proposed by Kodadek, Woo, and their co-
workers to be the active cyclopropanating agents in the iron
porphyrin-catalyzed cyclopropanation of alkenes with aryldi-
azomethane or alkyl diazoacetate8 but are usually highly unstable
and in no cases have been isolated and fully characterized. In
particular, the putative (alkoxycarbonyl)carbene complexes
[Fe(Por)(CHCO2Et)] have not been observed directly,7 probably
owing to their extreme instability.
We report here several iron porphyrin R-phenyl-substituted
aryl- or (alkoxycarbonyl)carbene complexes [Fe(TPFPP)-
(C(Ph)R)] (R ) Ph (1), CO2Et (2), CO2CH2CHdCH2 (3);
TPFPP ) meso-tetrakis(pentafluorophenyl)porphyrinato dianion)
and [Fe(TPFPP)(CPh2)(MeIm)] (4, MeIm ) N-methylimida-
zole). These nonheteroatom-stabilized carbene or (alkoxycar-
bonyl)carbene complexes of iron porphyrins are remarkably
stable and can be isolated in spectroscopically and analytically
pure forms. Both the arylcarbene complexes 1 and 4 have been
characterized by X-ray crystallography, which are so far the
only examples of structurally characterized iron porphyrin
(nonhalo)carbene or nonheteroatom-stabilized carbene com-
plexes.10 In contrast to the isolable iron porphyrin halocarbene
complexes whose alkene cyclopropanations were reported by
Suslick and co-workers4,8 to occur only after photolytic cleavage
of their Fe-carbene bonds, complex 4 and the (ethoxycarbonyl)-
carbene complex 2 can react with styrenes to form cyclopro-
panes without photolysis, serving as the sole examples of
isolated iron porphyrin carbene complexes that can cyclopro-
panate alkenes under such conditions.8 Even more interesting
is that complexes 2 and 4 can react with cyclohexene and
cumene to selectively form allylic or benzylic C-H insertion
products, contributing the first isolated monocarbene metal
complexes that can undergo intermolecular carbon atom transfer
into saturated C-H bonds of unfunctionalized alkenes.11
Results and Discussion
Isolation and Spectral Features of [Fe(TPFPP)(C(Ph)R)]
(1-3) and [Fe(TPFPP)(CPh2)(MeIm)] (4). Reactions of
[Fe(TPFPP)] with diazo compounds N2C(Ph)R (R ) Ph,
(8) In 1995, Kodadek, Woo, and their co-workers reported that iron porphyrins
are active catalysts for cyclopropanation of alkenes with ethyl diazoacetate.
The active species in the catalytic carbon atom transfer reactions are
assumed to be iron porphyrin carbene complexes.7 Shortly after, Suslick
and co-workers demonstrated that photolysis of several halocarbene iron
porphyrins gives free halocarbenes, which can be trapped by alkenes to
form cyclopropanes.4 Recently, Woo and co-workers reported iron por-
phyrin-catalyzed alkene cyclopropanations with aryldiazomethane and
observed the carbene complexes [Fe(TTP)(CHR)] (R ) SiMe3, 2,4,6-
Me3C6H2; TTP ) meso-tetrakis(p-tolyl)porphyrinato dianion) by 1H NMR
spectroscopy; these two iron porphyrin carbene complexes, which were
contaminated by [Fe(TTP)], can react with alkenes to form cyclopropanes
without photolysis.5
CO2Et, CO2CH2CHdCH2) in benzene under an inert atmosphere
afforded complexes 1-3 in 65-70% yields (reaction 1 in
Scheme 1). All these complexes are stable enough to be handled
at room temperature and can be purified by chromatography
on silica gel column. The arylcarbene complex 1 even exhibits
a high stability toward attack by moist air and can crystallize
from solutions exposed to the atmosphere at room temperature.
However, the (alkoxycarbonyl)carbene complexes 2 and 3 are
unstable to moist air both in solution and in the solid state. For
example, when a dichloromethane solution of 2 exposed to the
atmosphere was stirred for 12 h at room temperature, the
(9) This contrasts with the case of non-porphyrin iron carbene complexes,
whose carbon atom transfer reactions with alkenes to form cyclopropanes
have been investigated extensively. See for example: Brookhart, M.;
Studabaker, W. B. Chem. ReV. 1987, 87, 411.
(10) Although many iron porphyrin carbene complexes have been isolated, only
the dichlorocarbene complex, [Fe(TPP)(CCl2)(H2O)] (TPP
) meso-
tetraphenylporphyrinato dianion), has been characterized by X-ray
crystallography.3b A few other iron porphyrins containing FedC double
bonds, such as vinylidene or µ2-carbide complexes, have also been
structurally characterized; see: (a) Goedken, V. L.; Deakin, M. R.;
Bottomley, L. A. J. Chem. Soc., Chem. Commun. 1982, 607. (b) Mansuy,
D.; Battioni, J. P.; Lavallee, D.; Fischer, J.; Weiss, R. Inorg. Chem. 1988,
27, 1052. (c) Beck, W.; Knauer, W.; Robl, C. Angew. Chem., Int. Ed. Engl.
1990, 29, 318.
(11) We previously isolated osmium porphyrin monocarbene complex [Os-
(TPFPP)(CPh2)(MeOH)] and bis(carbene) complex [Os(TPFPP)(CPh2)2].
Only the bis(carbene) complex can undergo carbon atom transfer into the
saturated C-H bonds of unfunctionalized alkenes; see: (a) Li, Y.; Huang,
J.-S.; Zhou, Z.-Y.; Che, C.-M. J. Am. Chem. Soc. 2001, 123, 4843. (b)
Che, C.-M.; Huang, J.-S. Coord. Chem. ReV. 2002, 231, 151.
9
13186 J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002

Iron Porphyrins Bearing Carbenes
A R T I C L E S
complex was converted to a mixture of [Fe(TPFPP)(OH)] and
{[Fe(TPFPP)]2O},12 accompanied by formation of the carbene
coupling product EtO2CC(Ph)dC(Ph)CO2Et and the ketone
PhCOCO2Et in 80 and 14% yields, respectively.
The preparation of iron porphyrin carbene complexes from
reactions of [Fe(Por)] with diazoacetates (such as reaction 1
for 2 and 3) is unprecedented in the literature. Previous methods
of preparing iron porphyrin carbene complexes include (i)
reaction of [Fe(Por)] with halo compounds in the presence of
reductants,3a-d,f (ii) reaction of [Fe(Por)] with iodonium ylide,3g
diazoketone,3g or diazoalkane,5 (iii) reaction of [Fe(Por)(C(R)-
Cl)] with alcohol or thiol,3e and (iv) reduction of an Fe-N-
bridged carbene complex with Zn-Hg,3h almost all of which
were developed by Mansuy and co-workers. The formation of
[Fe(TPFPP)(C(Ph)CO2Et)] (2) from [Fe(TPFPP)] and N2C(Ph)-
CO2Et provides support for the possible involvement of the [Fe-
(TPFPP)(CHCO2Et)] intermediate in [Fe(TPFPP)Cl]-catalyzed
cyclopropanation of alkenes with ethyl diazoacetate (EDA).7
Since the species [Fe(TPFPP)(CHCO2Et)] was not observed
directly,7 the stability of 1-3 might stem from the presence of
R-phenyl substituent in their carbene ligands. The electron-
deficient nature of the TPFPP macrocycle may also play a role
in stabilizing 1-3, because our attempts to extend reaction 1
to simple porphyrin ligands such as TPP10 did not result in
isolation of the corresponding iron porphyrin carbene complexes.
Previously we found that a bis(carbene)osmium complex with
TPFPP is also significantly stabler than its analogue with the
simple porphyrin ligand TTP.11
Like the halocarbene complex [Fe(TPP)(CCl2)]3a,10 which can
bind donor solvent or organic base (such as pyridine) to form
six-coordinate species [Fe(TPP)(CCl2)(L)],3b,c,10 complex 1
rapidly reacted with MeIm to afford 4 in 65% isolated yield
(reaction 2 in Scheme 1). This six-coordinate arylcarbene
complex is unstable toward moist air at room temperature,
suggesting that coordination of MeIm to 1 significantly desta-
bilizes its FedCPh2 bond. We have also examined the reactions
of 2 or 3 with MeIm and the reactions of 1-3 with pyridine,
but in these cases, the corresponding MeIm or pyridine adducts
were not isolated in pure form. A prolonged reaction (∼20 h)
of 2 with pyridine in dichloromethane led to formation of the
bis(pyridine) complex [Fe(TPFPP)(Py)2].13
The UV-vis spectra of 1-4 each show a Soret band at ∼403
nm and two Q-bands at about 522 and 556 nm, similar to the
Soret (408 nm) and Q-bands (525, 550 nm) of [Fe(TPP)-
(CCl2)].3a The mass spectra of 1-3 exhibit prominent cluster
peaks (M+) at m/z ) 1194, 1190, and 1202, respectively, which
can be attributed to the corresponding parent ions. Complex 4
gives no parent-ion peaks (M+) in its mass spectrum but shows
peaks attributable to M+ - MeIm, suggesting that the coordi-
nated MeIm ligand in 4 is rather labile under the mass
spectrometry conditions.
In the 13C NMR spectra of 1-4, the FedC(carbene) signals
are located at δ ) 358.98 (1), 327.47 (2), 325.67 (3), and 385.44
(4). These signals are substantially downfield from that of
[Fe(TPP)(CCl2)] (δ ) 224.7)3a but are comparable to those of
[Fe(TPP)(C(R)Cl)] (δ ≈ 310).3d Compared to the (alkoxycar-
bonyl)carbene complexes 2 and 3, the arylcarbene complexes
Figure 1. Mo¨ssbauer spectrum of [Fe(TPFPP)(CPh2)] (1) at 288 K.
1 and 4 give markedly downfield FedC(carbene) signals.
Notably, coordination of MeIm to 1 downfield shifts its
FedC(carbene) signal by ∼26 ppm.
A comparison of the 19F NMR spectra of 1-3 (see Experi-
mental Section) reveals that the influence of the carbene groups
CPh2, C(Ph)CO2Et, and C(Ph)CO2CH2CHdCH2 on the signals
of the meso-C6F5 groups in TPFPP is very small. For each of
1-3, two sets of signals were observed for either ortho- or meta-
fluorine atoms in the meso-C6F5 groups, in agreement with the
lack of equatorial plane symmetry in these five-coordinate iron
porphyrins.
1
With regard to the H NMR spectra, complex 1 shows the
pyrrole proton (Hâ) signal at δ ) 8.31 and the CPh2 phenyl
proton signals at δ ) 6.42 (Hp), 6.00 (Hm), and 3.13 (Ho).
Replacement of one of the CPh2 phenyl group in 1 by an
alkoxycarbonyl group to form 2 or 3 downfield shifts the above
signals to δ ≈ 8.56 (Hâ), 6.74 (Hp), 6.09 (Hm), and 3.40 (Ho).
When 1 binds MeIm to form 4, a slight upfield shift (∆δ e
0.08 ppm) was observed for the Hâ, Hp, and Hm signals. Note
that the spectrum of 4 was recorded in the presence of free MeIm
to prevent a significant dissociation of the complex in solution.
The signals of coordinated MeIm groups were not located,
probably arising from a rapid exchange between the coordinated
and free MeIm ligands on the NMR time scale, as similarly
rationalized for the absence of the signals of the coordinated
PriNHOH group in the 1H NMR spectrum of [Fe(TPP)(PriNO)-
(PriNHOH)].14
1
The appearance of the H NMR signals of 1-4 at normal
fields indicates that these iron porphyrin carbene complexes are
diamagnetic, like previously reported iron porphyrins bearing
other carbene groups.3,5 Consequently, these types of iron
porphyrins can be considered as low-spin iron(II) species.3 A
closely related diamagnetic non-porphyrin iron carbene complex,
[Fe(tmtaa)(CPh2)]15 (H2tmtaa ) tetramethyldibenzotetraazaan-
nulene), is also considered as an iron(II) species on the basis of
extended Hu¨ckel calculations and the correlation between the
out of plane distance of the metal and its dn configuration.
To provide further information about the electron density at
the iron nucleus in an iron porphyrin nonheteroatom-stabilized
carbene complex, we conducted Mo¨ssbauer studies on complex
1. Figure 1 shows the Mo¨ssbauer spectrum of this complex at
288 K, which features a symmetrical and well-resolved doublet.
Interestingly, the isomer shift and quadrupole splitting for 1 were
(12) (a) Cheng, R.-J.; Latos-Grazynski, L.; Balch, A. L. Inorg. Chem. 1982,
21, 2412. (b) Jayaraj, K.; Gold, A.; Toney, G. E.; Helms, J. H.; Hatfield,
W. E. Inorg. Chem. 1986, 25, 3516.
(14) Mansuy, D.; Battioni, P.; Chottard, J.-C.; Riche, C.; Chiaroni, A. J. Am.
Chem. Soc. 1983, 105, 455.
(15) Klose, A.; Solari, E.; Floriani, C.; Re, N.; Chiesi-Villa, A.; Rizzoli, C.
Chem. Commun. 1997, 2297.
(13) Moore, K. T.; Horva´th, I. T.; Therien, M. J. Inorg. Chem. 2000, 39, 3125.
9
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A R T I C L E S
Li et al.
Table 1. Crystal Data and Structure Refinements for
[Fe(TPFPP)(CPh2)] (1) and [Fe(TPFPP)(CPh2)(MeIm)] (4)
param
1‚0.5C H ‚0.5CH Cl2
4
6
6
2
empirical formula
C57H18F20N4Fe‚
0.5C6H6‚0.5CH2Cl2
1276.12
C61H24F20N6Fe
fw
1276.71
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/n
14.962(3)
16.406(3)
23.782(5)
90.00
106.844(3)
90.00
5587(2)
rhombohedral
R3h
42.299(4)
42.299(4)
17.367(2)
90.00
90.00
120.00
26911(5)
18
R, deg
â, deg
γ, deg
V, Å3
Z
4
F(000)
2544
1.517
0.429
-19 e h e 19,
-10 e k e 21,
-30 e l e 30
37 229
11 484
1.418
0.358
-54 e h e 54,
-41 e k e 54,
-22 e l e 22
61 815
D(calcd), Mg/m3
abs coeff, mm-1
index ranges
no. of reflcns collcd
no. of indepdt reflcns
abs corr
max/min transm
data/restraints/params
final R indices (I > 2σ(I))
12 809
13 740
SADABS
0.9584/0.9268
12809/92/780
R1 ) 0.077,
wR2 ) 0.167
1.09
SADABS
0.9651/0.9383
13740/361/1000
R1 ) 0.069,
wR2 ) 0.159
1.10
goodness-of-fit
largest diff peak/hole, e Å-3 0.658/-0.559
0.681/-0.486
Figure 2. Ball and stick drawings of the structures of (a) [Fe(TPFPP)-
(CPh2)]‚0.5C6H6‚0.5CH2Cl2 (1‚0.5C6H6‚0.5CH2Cl2) and (b) [Fe(TPFPP)-
(CPh2)(MeIm)] (4). The solvent molecules and/or hydrogen atoms are not
shown.
out of the mean porphyrin plane toward the carbene group,
whereas that in [Fe(TPP)(CCl2)(H2O)] is not significantly
displaced from the porphyrin plane. Despite the above differ-
ences in the structures of 1 and [Fe(TPP)(CCl2)(H2O)], the
average Fe-N(pyrrole) distances in these two complexes (1.966-
(3) and 1.984(4) Å, respectively) are similar.
Notice that the FedCPh2 bond in 1 is even shorter than
that in the five-coordinate non-porphyrin carbene complex
[Fe(tmtaa)(CPh2)]‚PhCH3, which is reported to show a particu-
larly short Fe-C(carbene) bond of 1.794(3) Å.15 Both 1 and
[Fe(tmtaa)(CPh2)] have a distorted square pyramidal FeN4C
core. The displacement of the iron atom from the mean N4 plane
in 1 is 0.238 Å, smaller than that of 0.335 Å in [Fe(tmtaa)-
(CPh2)].15
The coordination of MeIm to 1 to form six-coordinate aryl-
carbene complex 4 (Figure 2b) lengthens the FedCPh2 bond
of 1 to 1.827(5) Å, which is now similar to the Fe-CCl2 dis-
tance in [Fe(TPP)(CCl2)(H2O)]. The Fe-N(MeIm) distance of
2.168(4) Å and the C-Fe-N(MeIm) angle of 176.6(2)° in 4
are also similar to the Fe-O(H2O) distance (2.13(3) Å) and
the C-Fe-O(H2O) angle (177.1(1.5)°) in [Fe(TPP)(CCl2)-
(H2O)], respectively. Furthermore, complex 4 exhibits a con-
siderably smaller displacement of the iron atom from the
mean plane of the porphyrin ring (0.122 Å toward the CPh2
group), along with slightly longer Fe-N(pyrrole) bonds (average
1.973(4) Å), than complex 1. However, the porphyrin ring in 4
shows a more severe ruffling distortion (Figure 3, inset): the
mean deviation of the 24 component atoms from their mean
plane reaches 0.198 Å.
found to be 0.03 and 2.34 mm/s, respectively, similar to those
observed for iron(IV) rather than low-spin iron(II) porphyrins.16
Prior to this work, Mo¨ssbauer studies on iron porphyrin carbene
complexes were reported only for the diamagnetic halocarbene
species [Fe(TPP)(CCl2)],16 whose isomer shift (0.10 mm/s) and
quadrupole splitting (2.28 mm/s) also fall in the region of iron-
(IV) porphyrins.
X-ray Crystal Structures of [Fe(TPFPP)(CPh2)] (1) and
[Fe(TPFPP)(CPh2)(MeIm)] (4). Upon obtaining diffraction-
quality crystals of 1‚0.5C6H6‚0.5CH2Cl2 and 4 (see Experimental
Section), we determined their structures by X-ray crystal-
lography, which are depicted in Figure 2. The crystal data and
structure refinements for the two crystals are summarized in
Table 1, whereas the selected bond lengths and angles are given
in Table 2.
As shown in Figure 2a, the arylcarbene complex 1 contains
a five-coordinate iron center, unlike the structurally characterized
halocarbene complex [Fe(TPP)(CCl2)(H2O)] (whose iron atom
is six-coordinate).3b A comparison of the metrical parameters
of 1 and [Fe(TPP)(CCl2)(H2O)] reveals several interesting
structural features of the arylcarbene complex. First, the
Fe-C(carbene) distance of 1.767(3) Å in 1 is considerably
shorter than that in [Fe(TPP)(CCl2)(H2O)] (1.83(3) Å). Second,
the porphyrin ring of 1 exhibits a marked ruffling distortion
(Figure 3, inset) with a mean deviation of 0.138 Å from the
mean plane of the 24 component atoms, in contrast to the
essentially planar porphyrin ring (mean deviation: ∼0.03 Å)
of [Fe(TPP)(CCl2)(H2O)]. Third, the iron atom in 1 is 0.294 Å
The large ruffling distortions of the porphyrin macrocycle in
the iron porphyrins 1 and 4 are unusual. In the crystal structure
of {[Fe(TPFPP)]2O},17a the porphyrin ring displays a moderate
doming distortion with a mean deviation of 0.0721 Å from the
mean porphyrin plane. Although [Fe(TPP)(CO)(MeIm)] also has
(16) English, D. R.; Hendrickson, D. N.; Suslick, K. S. Inorg. Chem. 1983, 22,
368.
9
13188 J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002

Iron Porphyrins Bearing Carbenes
A R T I C L E S
Table 2. Selected Bond Lengths (Å) and Angles (deg) for [Fe(TPFPP)(CPh2)] (1) and [Fe(TPFPP)(CPh2)(MeIm)] (4)
1
4
1
4
Fe-N1
Fe-N2
Fe-N3
Fe-N4
1.961(3)
1.967(3)
1.964(3)
1.973(3)
1.972(3)
1.963(4)
1.987(3)
1.970(4)
Fe-C45
C45-C46
C45-C52
Fe-N5
1.767(3)
1.482(4)
1.484(5)
1.827(5)
1.489(6)
1.499(7)
2.168(4)
Fe-C45-C46
C46-C45-C52
C45-Fe-N1
C45-Fe-N3
N1-Fe-N2
N3-Fe-N4
N1-Fe-N3
126.1(3)
124.8(4)
Fe-C45-C52
C45-Fe-N5
C45-Fe-N2
C45-Fe-N4
N2-Fe-N3
N4-Fe-N1
N2-Fe-N4
122.3(2)
124.2(4)
176.6(2)
91.5(2)
92.4(2)
89.6(2)
89.8(1)
176.1(2)
111.5(3)
96.0(1)
99.4(1)
89.5(1)
88.8(1)
164.6(1)
111.0(4)
92.8(2)
94.8(2)
89.9(2)
90.2(2)
172.4(2)
95.6(1)
96.9(1)
89.6(1)
88.8(1)
167.5(1)
Scheme 2
between the Ph-C(carbene) bonds and the closest Fe-N(pyr-
role) bonds.
The structure determinations on both the five- and six-
coordinate iron complexes 1 and 4 bearing the same carbene
and porphyrin ligands make it practical to directly assess the
influence of a trans donor ligand on the metal-carbene bond.
Prior to this work, quite a few other metalloporphyrin carbene
complexes have been structurally characterized (some are five-
coordinate;18d the others are six-coordinate3b,11,18a-c) but no pair
of these five- and six-coordinate complexes contain the same
[M(Por)(carbene)] entity. The considerable lengthening of the
Fe-C(carbene) bond of 1 upon coordination with MeIm is
parallel to the decreased stability obserVed for 4 as mentioned
aboVe and to the higher reactiVity of 4 than 1 described below.
Stoichiometric Cyclopropanation of Alkenes by [Fe-
(TPFPP)(C(Ph)CO2Et)] (2) and [Fe(TPFPP)(CPh2)(MeIm)]
(4). Treatment of 2 with excess styrene in benzene at 60 °C for
15 h afforded 1,2-diphenylcyclopropanecarboxylic acid ethyl
ester19 in 82% yield with a trans:cis ratio of 2.0:1 (reaction 320
in Scheme 2). This serves as a good evidence for [Fe(TPFPP)-
(CHCO2Et)] as a cyclopropanating agent in [Fe(TPFPP)Cl]-
catalyzed cyclopropanation of styrene with EDA,7 since the
CHCO2Et complex is expected to be more reactive than 2 due
to the lack of R-phenyl substituent in the carbene ligand. The
lower diastereoselectivity in reaction 3 compared to that in the
catalytic reaction (trans:cis ) 6.07) probably results from a
smaller difference in steric bulk between the phenyl and
Figure 3. Orientations of the carbene axial ligands in [Fe(TPFPP)(CPh2)]
(1) and [Fe(TPFPP)(CPh2)(MeIm)] (4) with respect to the porphyrin ligands.
The inset shows the perpendicular displacements of the porphyrin ring
carbon atoms from the mean plane of the 24 component atoms (including
four pyrrole nitrogens) observed for 1, 4, and the closely related osmium
analogue [Os(TPFPP)(CPh2)(MeOH)] reported in ref 11, together with the
side views of the porphyrin rings in these monocarbene complexes. The
perpendicular displacements of the porphyrin ring nitrogen atoms from the
mean plane of the 24 component atoms average 0.058 Å for 1, 0.049 Å for
4, and 0.041 Å for [Os(TPFPP)(CPh2)(MeOH)].
a substantially puckered porphyrin ligand in its crystal structure,17b
the porphyrin macrocycle in this carbonyl complex exhibits a
saddle rather than ruffling distortion, and the mean deviation
from the mean porphyrin plane is 0.147 Å, smaller than that
found in 4. The large ruffling distortion of the TPFPP macro-
cycle in 1 and 4 also contrasts with the small saddle distortion
of the same porphyrin ligand (mean deviation: 0.0382 Å) in
the monocarbene osmium porphyrin [Os(TPFPP)(CPh2)(MeOH)]11
(Figure 3, inset) but is comparable to the ruffling distortion in
the bis(carbene)osmium porphyrin [Os(TPFPP)(CPh2)2] (mean
deviation: 0.197 Å).11
For both 1 and 4, the sum of the angles at the coordinated
carbene carbon (1, 359.9(3)°; 4, 360.0(4)°) is almost identical
to 360°, consistent with the sp2 hybridization of this carbon
atom. In the structure of either 1 or 4, the carbene plane lies
close to a pair of diagonal Fe-N(pyrrole) bonds, as depicted
in Figure 3, with dihedral angles of about 14° (1) and 19° (4)
(18) (a) Boschi, T.; Licoccia, S.; Paolesse, R.; Tagliatesta, P.; Pelizzi, G.; Vitali,
F. Organometallics 1989, 8, 330. (b) Djukic, J.-P.; Smith, D. A.; Young,
V. G., Jr.; Woo, L. K. Organometallics 1994, 13, 3020. (c) Galardon, E.;
Le Maux, P.; Toupet, L.; Simonneaux, G. Organometallics 1998, 17, 565.
(d) 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.
(17) (a) Gold, A.; Jayaraj, K.; Doppelt, P.; Fischer, J.; Weiss, R. Inorg. Chim.
Acta 1988, 150, 177. (b) Salzmann, R.; Ziegler, C. J.; Godbout, N.;
McMahon, M. T.; Suslick, K. S.; Oldfield, E. J. Am. Chem. Soc. 1998,
120, 11323.
(19) Huisgen, R.; Sustmann, R.; Bunge, K. Chem. Ber. 1972, 105, 1324.
(20) The iron porphyrin product from the reaction is extremely air-sensitive.
Workup of the reaction mixture only led to isolation of {[Fe(TPFPP)]2O}
contaminated by [Fe(TPFPP)(OH)].
9
J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002 13189

A R T I C L E S
Li et al.
Table 3. Intermolecular Cyclopropanation of Alkenes with EDA
Catalyzed by [Fe(TPFPP)(CPh2)] (1)a
alkene
conversn of
EDA (%)
yield (%)b
(trans + cis)
ratio of
trans:cisc
entry
R
X
1
H
H
H
H
H
H
Me
Cl
H
100
91
100
100
100
83
97
85
86
54
6.6:1
7.0:1
4.5:1
6.3:1
1.5:1
2d
3
4
5
Me
a Reaction conditions: CH2Cl2, rt, 5 h; 1:EDA:alkene molar ratio )
1:1000:20 000. bBased on consumed EDA. cDetermined by GC-MS. dEDA
was added over 20 h; 1:EDA:alkene molar ratio ) 1:5000:100 000.
Figure 4. Plot of log(kX/kH) vs σ+ for the reactions of [Fe(TPFPP)(C(Ph)-
CO2Et)] (2) with p-XC6H4CHdCH2 (X ) MeO, Me, H, Cl, CF3).
CO2Et groups in C(Ph)CO2Et than that between the H and
CO2Et groups in CHCO2Et,7,18d which leads to a smaller
difference in energy between the transition states corresponding
to the trans and cis cyclopropyl esters in reaction 3.
The activation of coordinated carbene groups by trans donor
ligands has also been proposed in the cases of osmium21 and
ruthenium18d porphyrins. However, in those cases, this remains
to be proved owing to the lack of well-identified five- and six-
coordinate complexes of the same [M(Por)(carbene)] entities.
Taking into account the dramatically enhanced reactivity of
4 (relative to that of 1) toward alkene cyclopropanations, the
coordination of donor solvents to putative [Fe(Por)(CHCO2Et)]
species described above may also promote their cyclopropana-
tion of alkenes and result in a lower diastereoselectivity in the
catalytic reactions. Such an effect of donor solvents may
compete with an opposite effect proposed in the literature;7 that
is, the coordination of donor solvents to [Fe(Por)(CHCO2Et)]
to form [Fe(Por)(CHCO2Et)(solv)] adducts would render the
carbene group less electrophilic and thus retard their cyclopro-
panation of alkenes (which would enhance the diastereoselec-
tivity in the catalysis). The answer to the question about which
of the two effects is dominating should depend on the electronic/
steric properties of both the carbene ligands and the solvents
involved.
Catalytic Cyclopropanations by [Fe(TPFPP)(CPh2)] (1).
(i) Intermolecular Cyclopropanation of Alkenes with EDA.
Although complex 1 was unable to cyclopropanate styrene
stoichiometrically, it can catalyze intermolecular cyclopropa-
nation of styrenes with EDA (reaction 5 in Table 3), pro-
viding a precedent for alkene cyclopropanation catalyzed
by iron porphyrin carbene complex. The reactions were
performed under the conditions similar to those employed for
the [Fe(TPFPP)Cl]-catalyzed cyclopropanations.7 The trans:cis
ratios observed for the cyclopropanation of styrene (6.6:1) and
R-methylstyrene (1.5:1) (see entries 1 and 5 in Table 3) by
employing 0.1 mol % 1 are similar to those (6.0:1 and 1.1:1,
respectively) found for the cyclopropanation of the same alkenes
catalyzed by [Fe(TPFPP)Cl].7 With a lower loading of 1 (0.02
mol %) and a slower addition of EDA, the cyclopropanation of
styrene afforded a slightly higher trans:cis ratio of 7.0:1 (entry
2 in Table 3) and a high catalyst turnover number of 4410; the
latter is similar to the 4200 catalyst turnovers reported for the
[Fe(TPFPP)Cl]-catalyzed cyclopropanations.7
When 2 was treated with a 1:1 (molar ratio) mixture of styrene
and its derivative p-XC6H4CHdCH2 at 60 °C for 15 h, the molar
ratios of the cyclopropyl esters derived from p-XC6H4CHdCH2
and styrene were found to be 2.6 (X ) MeO), 1.6 (X ) Me),
1.2 (X ) Cl), and 0.69 (X ) CF3). These ratios can be taken as
the kX/kH ratios,18d i.e., the ratios between the cyclopropanation
rates of p-XC6H4CHdCH2 and styrene. Plotting log(kX/kH)
values against the Hammett constants (σ+) of the para-
substituents gave a linearity with R ) 0.98 and F ) -0.41 (
0.05 (Figure 4).
Prior to this work, no Hammett plots were reported for the
reactions of isolated iron porphyrin carbene complexes with
alkenes. The F value obtained for the reactions between the
isolated carbene complex 2 and p-XC6H4CHdCH2 (X ) H,
MeO, Me, Cl, CF3) is comparable to that of -0.68 ( 0.07 found
for the [Fe(TTP)]-catalyzed cyclopropanation of the same
alkenes with EDA.7 This further supports the intervention of
the [Fe(Por)(CHCO2Et)] species in the EDA cyclopropanation
of alkenes catalyzed by iron porphyrins and is consistent with
the proposed electrophilic nature of these transient carbene
species and some carbocationic character of the alkene carbons
in the transition states.7
The arylcarbene complex 1 is inactive toward stoichiometric
styrene cyclopropanations. We once treated 1 with excess sty-
rene in benzene at 80 °C for 24 h but detected no cyclopropa-
nation products in the reaction mixture. Interestingly, when a
solution of 1 and styrene in benzene containing ∼2 equiv of
2,6-dichloropyridine (2,6-Cl2Py) was stirred at 80 °C for 10 h,
1,1,2-triphenylcyclopropane11 was obtained in 56% yield. We
speculated that 2,6-Cl2Py and other donor reagents (L) can
activate the coordinated CPh2 group in 1 by formation of six-
coordinate complex [Fe(TPFPP)(CPh2)(L)]. This is the main
reason we studied the binding behavior of 1 toward donor
reagents such as MeIm and pyridine, which eventually led to
the isolation of the MeIm adduct 4.
(ii) Intramolecular Cyclopropanation of Allylic Diazoac-
etates. Because there are much less reports on intramolecular
Indeed, 4 has a considerably longer FedCPh2 bond and is
less stable than 1, as described above. Treatment of 4 with
excess styrene at 80 °C for 12 h gave 1,1,2-triphenylcyclopro-
pane in 53% yield (reaction 420 in Scheme 2).
(21) Collman, J. P.; Rose, E.; Venburg, G. D. J. Chem. Soc., Chem. Commun.
1993, 934.
9
13190 J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002

Iron Porphyrins Bearing Carbenes
A R T I C L E S
Table 4. Intramolecular Cyclopropanation of Allylic Diazoacetates
Catalyzed by [Fe(TPFPP)(CPh2)] (1)a
Table 5. Stoichiometric C-H Insertion Reactions of
[Fe(TPFPP)(C(Ph)CO2Et)] (2) or [Fe(TPFPP)(CPh2)(MeIm)] (4)
with Alkenes or Tetrahydrofuran
substrate
conversn yieldb
c
t
entry
R
R
additive
(%)
(%)
1
2
3
4
Ph
Ph
Me
Et
H
H
Me
H
21
100
100
100
84
49
76
92
62
73
58
2,6-Cl2Py
2,6-Cl2Py
2,6-Cl2Py
2,6-Cl2Py
5c Me2CdCH(CH2)2 Me
b
a A mixture of two diastereomers in a molar ratio of 1.2:1. A mixture
6
Me
Me2CdCH(CH2)2 2,6-Cl2Py
100
of two diastereomers in a molar ratio of 2:1.
a Reaction conditions: CH2Cl2, 40 °C, 13 h; 1:substrate ) 1:200 or 1:2,6-
Cl2Py:substrate ) 1:1:200 (molar ratio). bBased on consumed substrate.
cMolar ratio of 1:2,6-Cl2Py:substrate ) 1:1:1000.
cyclohexene at 80 °C for 24 h to form allylic C-H insertion
product 3-(diphenylmethyl)cyclopentene or -cyclohexene in
∼80% yield.11 In this work, we found that reaction of the
monocarbene iron porphyrin 2 with cyclohexene under similar
conditions afforded the corresponding allylic C-H insertion
product as a 1.2:1 mixture of two diastereomers23 in 64% yield
(entry 1 in Table 5). Complex 4 can also react with cyclohexene
at 80 °C, but the reaction gave the 3-(diphenylmethyl)cyclo-
hexene in a lower yield of 24% after 36 h (entry 2 in Table 5).
Treatment of 2 with tetrahydrofuran at 65 °C for 24 h resulted
in a regiospecific insertion of the C(Ph)CO2Et carbene group
into the R-C-H bond of tetrahydrofuran, similar to the C-H
insertion reaction of tungsten arylcarbene (CHPh and CH(p-
C6H4Me)) complexes with the same organic substrate.24 The
C-H insertion product25 was isolated in 88% yield as a 2:1
mixture of two diastereomers (entry 3 in Table 5), and the major
and minor diastereomers show their CH(Ph)CO2Et proton
resonance at δ ) 2.52 and 2.62, respectively. Such a diaste-
reoselectivity is the inverse of that observed for the rhodium
complex-catalyzed C-H insertion of C(Ph)CO2Me into the
R-C-H bond of tetrahydrofuran,26 which features a diastereo-
selectivity of 1:2.3 (the major diastereomer shows the CH(Ph)-
CO2Me proton resonance at δ ) 2.62).
It is interesting that both 2 and 4 are reactive toward cumene
at 80 °C, leading to transfer of their carbene groups into a
benzylic C-H bond, with 3-methyl-2,3-diphenylbutyric acid
ethyl ester and cumyldiphenylmethane27 obtained in 83 and 59%
yields, respectively (entries 4 and 7 in Table 5). The yield of
the C-H insertion product markedly decreased whereas that
of the carbene coupling product increased when the reaction
was carried out at lower temperatures. For example, treating 2
with cumene at 60 and 25 °C gave 3-methyl-2,3-diphenylbutyric
acid ethyl ester in 67 and 15% yields (entries 5 and 6),
accompanied by formation of EtO2CC(Ph)dC(Ph)CO2Et in 23
and 67% yields, respectively (at 80 °C, the yield of EtO2CC-
(Ph)dC(Ph)CO2Et was 12%).
cyclopropanation of alkenes catalyzed by metalloporphyrins than
by non-porphyrin metal complexes,18d we tested the catalytic
behavior of 1 toward an intramolecular alkene cyclopropanation
by examining the decomposition of a series of allylic diazoac-
etates N2CHCO2CH2CHdCRcRt in the presence of 0.5 or 0.1
mol % complex 1.
When a solution of the allylic diazoacetate with Rc ) Ph
and Rt ) H in dichloromethane was slowly added to a solution
of 1 in the same solvent at 40 °C, the corresponding bicyclic
lactone22 (see reaction 6 in Table 4) was obtained in 49% yield
with substrate conversion of 21% (entry 1 in Table 4).
Remarkably, addition of 2,6-Cl2Py increased the yield of the
lactone to 76% and resulted in complete substrate conversion
(entry 2 in Table 4).
Treatment of other allylic diazoacetates with 1 in the presence
of 2,6-Cl2Py gave the respective lactones22 in good-to-excellent
yields (entries 3-6). The best result was obtained for N2CHCO2-
CH2CHdCMe2, whose decomposition afforded the correspond-
ing lactone in 92% yield with 100% substrate conversion (entry
3 in Table 4).
The above decomposition of allylic diazoacetates catalyzed
by 1 constitutes the first intramolecular alkene cyclopropanation
catalyzed by iron porphyrin. Previously, we reported enantio-
selective intramolecular cyclopropanations of several allylic or
homoallylic diazoacetates catalyzed by a chiral ruthenium
porphyrin,18d which afford bicyclic lactones in up to 65% yield.
Stoichiometric C-H Insertion Reaction of [Fe(TPFPP)-
(C(Ph)CO2Et)] (2) or [Fe(TPFPP)(CPh2)(MeIm)] (4) with
Hydrocarbons. We examined the reactions of 2 or 4 with
saturated C-H bonds of several types of hydrocarbons, includ-
ing cyclohexene, cumene, and tetrahydrofuran (which can be
considered as an activated hydrocarbon). All these reactions
were found to effect insertion of the carbene group of 2 or 4
into a C-H bond of the organic substrates (reaction 720 in
Table 5). The major byproducts in the reactions are the re-
spective carbene coupling product EtO2CC(Ph)dC(Ph)CO2Et
or Ph2CdCPh2.
The benzylic C-H bond of cumene is apparently more
reactive than the allylic C-H bonds of cyclohexene toward the
carbene group of 2 or 4 (compare entries 1 and 4 or 2 and 7 in
Our previous work demonstrates that the bis(carbene)osmium
porphyrin [Os(TPFPP)(CPh2)2] reacts with cyclopentene or
(23) Yadav, V. K.; Balamurugan, R.; Parvez, M.; Yamdagni, R. J. Chem. Soc.,
Perkin Trans. 1 2001, 323.
(24) Fischer, H.; Schmid, J.; Ma¨rkl, R. J. Chem. Soc., Chem. Commun. 1985,
572.
(22) 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.
(25) Kruse, C. G.; Janse, A. C. V.; Dert, V.; van der Gen, A. J. Org. Chem.
1979, 44, 2916.
(26) Davies, H. M. L.; Hansen, T. J. Am. Chem. Soc. 1997, 119, 9075.
(27) Okamoto, A.; Snow, M. S.; Arnold, D. R. Tetrahedron 1986, 42, 6175.
9
J. AM. CHEM. SOC. VOL. 124, NO. 44, 2002 13191

A R T I C L E S
Li et al.
visible spectra were recorded on a HP 8453 diode array spectropho-
tometer; IR spectra on a Bio-Rad FTS165 spectrometer. FAB and ES
(electrospray) mass spectra were measured on a Finnigan MAT 95 and
a Finnigan LCQ quadrupole ion trap mass spectrometer, respectively.
1H, 13C, and 19F NMR spectra were obtained on a Bruker DPX-300
FT-NMR spectrometer; chemical shifts were recorded relative to
tetramethylsilane (1H and 13C) or CF3COOH (19F, δ -76.5). Mo¨ssbauer
spectrum was measured on an Austin S-600 Mo¨ssbauer spectrometer
at 288 K by placing the sample in a 57Co radiation source, with the
transmittances of the 14.4 keV γ-ray collected continuously over >48
h. GC-MS measurements were conducted on a HP G1800C GCD Series
II spectrometer. Elemental analyses were carried out by the Institute
of Chemistry, the Chinese Academy of Sciences.
Preparation of [Fe(TPFPP)(C(Ph)R)] (R ) Ph, CO2Et, CO2-
CH2CHdCH2). To a solution of [Fe(TPFPP)] (0.05 mmol) in benzene
(100 mL) was added a solution of N2C(Ph)R (0.10 mmol) in the same
solvent (10 mL). The mixture was stirred for 10 h at room temperature
and then evaporated to dryness in vacuo. The residue was purified by
chromatography on a silicon gel column with benzene-hexane (1:1,
v/v) as eluent, affording the desired product as a red solid.
Table 5). However, it is surprising that no significant amounts
of C-H insertion products were detected in the reaction of 2
or 4 with ethylbenzene, which also contains benzylic C-H
bonds. This reflects a high substrate selectivity (cumene vs
ethylbenzene) in the C-H insertion reactions of 2 and 4.28 To
our knowledge, besides complexes 2 and 4, no other isolated
metal carbene complexes have been reported to undergo benzylic
C-H insertion reactions with unfunctionalized alkenes.
Conclusion
We have isolated and fully characterized a remarkably stable
iron porphyrin nonheteroatom-stabilized carbene complex [Fe-
(TPFPP)(CPh2)] (1) and its MeIm adduct [Fe(TPFPP)(CPh2)-
(MeIm)] (4). The X-ray crystal structure determinations of 1
and 4 provide a direct measure of the trans influence of the
MeIm ligand on the FedCPh2 bond. We have also isolated and
well characterized two additional iron porphyrin carbene
complexes, [Fe(TPFPP)(C(Ph)CO2Et)] (2) and [Fe(TPFPP)-
(C(Ph)CO2CH2CHdCH2)] (3); these R-phenyl-substituted (alkoxy-
carbonyl)carbene complexes are far more stable than the putative
[Fe(TPFPP)(CHCO2Et)] intermediates in iron porphyrin-
catalyzed cyclopropanation of alkenes with ethyl diazoacetate.
The formation of 2 and 3 from [Fe(TPFPP)] and respective
diazoacetates represents a convenient route to iron porphyrin
(alkoxycarbonyl)carbene complexes. Our observations that
reactions of [Fe(TPFPP)] with diazo compounds N2C(Ph)R (R
) Ph, CO2Et) form the carbene complexes 1 and 2 and that 2
and 4 can react with styrenes to form cyclopropanes provide
support for the intervention of [Fe(Por)(CHR)] or [Fe(Por)-
(CHCO2Et)] in the iron porphyrin-catalyzed cyclopropanations
reported by Kodadek, Woo, and their co-workers.5,7 The
reactions of 2 and 4 with cyclohexene and cumene to form C-H
insertion products create precedents for iron porphyrin-mediated
carbon atom transfer into C-H bonds of hydrocarbons. More-
over, this work contributes the first examples of (i) structurally
characterized iron porphyrin (nonhalo)carbene or nonhetero-
atom-stabilized carbene complexes, (ii) isolated and fully
characterized iron porphyrin carbene complexes that can cy-
clopropanate alkenes without photolysis, (iii) iron porphyrin
carbene complexes that can catalyze alkene cyclopropanations,
(iv) iron porphyrins that can catalyze intramolecular cyclopro-
panations, and (v) isolated monocarbene metal complexes that
can undergo intermolecular carbon atom transfer into saturated
C-H bonds of unfunctionalized alkenes.
[Fe(TPFPP)(CPh2)] (1). Yield: 70%. Anal. Calcd for C57H18F20N4-
Fe‚0.5C6H14: C, 58.23; H, 2.04; N, 4.53. Found: C, 58.28; H, 2.37;
1
N, 4.44. H NMR (CDCl3): δ 8.31 (s, 8H), 6.42 (t, J ) 7.4 Hz, 2H),
6.00 (t, J ) 7.7 Hz, 4H), 3.13 (d, J ) 7.5 Hz, 4H). 13C NMR (CDCl3):
δ 358.98 (FedC). 19F NMR (CDCl3): δ -135.53 (dd), -136.16 (dd),
-151.50 (t), -160.95 (dt), -161.03 (dt). UV-vis (1.12 × 10-5 M,
CH2Cl2): λmax (log ꢀ) 404 (5.07), 524 (4.00), 557 nm (4.14). FAB
MS: m/z 1194 (M+), 1028 ([M - CPh2]+).
[Fe(TPFPP)(C(Ph)CO2Et)] (2). Yield: 67%. Anal. Calcd for
C54H18F20N4O2Fe‚0.5CH2Cl2 (a product recrystallized from CH2Cl2/
C6H14): C, 53.09; H, 1.55; N, 4.54. Found: C, 52.83; H, 1.53; N, 4.94.
1H NMR (CDCl3): δ 8.56 (s, 8H), 6.74 (t, J ) 7.3 Hz, 1H), 6.09 (t, J
) 7.6 Hz, 2H), 3.40 (d, J ) 7.9 Hz, 2H), 2.62 (q, J ) 7.1 Hz, 2H),
0.28 (t, J ) 7.1 Hz, 3H). 13C NMR (CDCl3): δ 327.47 (FedC). 19F
NMR (CDCl3): δ -136.34 (dd), -137.00 (dd), -151.92 (t), -161.56
(dt), -161.66 (dt). UV-vis (5.97 × 10-6 M, CH2Cl2): λmax (log ꢀ)
402 (5.11), 521 (4.02), 555 nm (4.12). FAB MS: m/z 1190 (M+), 1028
([M - C(Ph)CO2Et]+).
[Fe(TPFPP)(C(Ph)CO2CH2CHdCH2)] (3). Yield: 65%. Anal.
Calcd for C55H18F20N4O2Fe‚1.5C6H6‚0.5CH2Cl2 (a product recrystallized
from benzene/CH2Cl2/C6H14): C, 56.87; H, 2.07; N, 4.11. Found: C,
1
56.91; H, 2.23; N, 3.86. H NMR (CDCl3): δ 8.55 (s, 8H), 6.75 (t, J
) 7.4 Hz, 1H), 6.08 (t, J ) 7.9 Hz, 2H), 4.92-4.81 (m, 1H), 4.64-
4.60 (dd, J ) 10.4, 1.1 Hz, 1H), 4.45-4.39 (dd, J ) 17.1, 1.4 Hz,
1H), 3.39 (d, J ) 7.5 Hz, 2H), 3.04 (d, J ) 5.9 Hz, 2H). 13C NMR
(CDCl3): δ 325.67 (FedC). 19F NMR (CDCl3): δ -136.22 (dd),
-137.00 (dd), -151.88 (t), -161.53 (dt), -161.65 (dt). UV-vis (7.98
× 10-6 M, CH2Cl2): λmax (log ꢀ) 402 (5.03), 521 (3.91), 555 nm (4.01).
ES MS: m/z 1202 (M+), 1028 ([M - C(Ph)CO2CH2CHdCH2]+).
Preparation of [Fe(TPFPP)(CPh2)(MeIm)] (4). A solution of 1
(50 mg, 0.04 mmol) in dichloromethane (5 mL) containing MeIm (8.2
mg, 0.1 mmol) was stirred for 15 min at room temperature. Addition
of hexane (15 mL) to the solution followed by evaporation of the
mixture in vacuo led to formation of a red precipitate. The precipitate
was collected by filtration, washed with hexane, and dried. Yield: 65%.
Anal. Calcd for C61H24F20N6Fe: C, 57.39; H, 1.89; N, 6.58. Found:
C, 57.67; H, 1.95; N, 6.14. 1H NMR (CDCl3): δ 8.23 (s, 8H), 6.36 (t,
J ) 7.4 Hz, 2H), 6.06 (t, J ) 7.7 Hz, 4H), 3.13 (d, J ) 7.3 Hz, 4H)
(measured in the presence of free MeIm). 13C NMR (CDCl3): δ 385.44
(FedC) (measured in the presence of free MeIm). UV-vis (8.85 ×
10-6 M, CH2Cl2): λmax (log ꢀ) 403 (5.24), 524 (4.20), 557 nm (4.29).
FAB MS: m/z 1194 ([M - MeIm]+).
Experimental Section
General Methods. All reactions were performed under an argon
atmosphere unless otherwise specified. [Fe(TPFPP)Cl], pyridine, 2,6-
dichloropyridine, and ethyl diazoacetate were purchased from Aldrich.
The solvents (AR grade) were predried according to standard proce-
dures. Styrene, 4-methylstyrene, 4-chlorostyrene, 4-methoxystyrene,
4-trifluoromethylstyrene, cyclohexene, cumene, and N-methylimidazole
(all from Aldrich) were purified by distillation. N2C(Ph)R (R ) Ph,29
CO2Et, CO2CH2CHdCH222,30) and other allylic diazoacetates22 were
prepared by literature methods. [FeII(TPFPP)] was prepared in situ by
reduction of [FeIII(TPFPP)Cl] with Zn/Hg amalgam in benzene.7 UV-
(28) The higher reactivity of cumene than that of ethylbenzene toward the C-H
insertion reactions might stem from a higher activity of the tertiary benzylic
C-H bond in the former than the secondary benzylic C-H bonds in the
latter.
(29) Miller, J. B. J. Org. Chem. 1959, 24, 560.
(30) Corey, E. J.; Myers, A. G. Tetrahedron Lett. 1984, 25, 3559.
Stoichiometric Cyclopropanation of Styrene by [Fe(TPFPP)-
(C(Ph)CO2Et)] (2) or [Fe(TPFPP)(CPh2)(MeIm)] (4). A solution of
2 or 4 (0.015 mmol) and styrene (1.0 g, 9.6 mmol) in benzene (2 mL)
was stirred at 60 °C for 15 h (2) or at 80 °C for 12 h (4). The resultant
9
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Iron Porphyrins Bearing Carbenes
A R T I C L E S
mixture was then evaporated to dryness in vacuo. The crude cyclo-
propanation product thus obtained was purified by chromatography on
a silica gel plate with ethyl acetate/hexane (1:9, v/v).
evaporated to dryness in vacuo. The products were separated by
chromatography on a silica gel plate with ethyl acetate/hexane (1:9,
v/v).
Competitive Cyclopropanation of Styrene and Para-Substituted
Styrene by [Fe(TPFPP)(C(Ph)CO2Et)] (2). A mixture of 2 (18.0 mg,
0.015 mmol), styrene (416.6 mg, 4.0 mmol), and para-substituted
styrene (4.0 mmol) was stirred at 60 °C for 15 h. The mixture was
then evaporated to dryness in vacuo. After chromatography of the
residue on a silica gel plate with ethyl acetate/hexane (1:9, v/v), the
ratio of the cyclopropyl esters derived from para-substituted styrene
X-ray Crystal Structure Determinations. A diffraction-quality
crystal of 1 in the form 1‚0.5C6H6‚0.5CH2Cl2 (0.10 × 0.16 × 0.18
mm, red prism) was grown from a slow evaporation of a solution of 1
in dichloromethane/benzene/hexane exposed to the atmosphere at room
temperature, whereas that of 4 (0.10 × 0.12 × 0.18 mm, dark red prism)
was grown from a solution of 4 in dichloromethane/hexane at -5 °C
under nitrogen. The data were collected at 294(2) K in the θ range of
1.7-27.5° (1‚0.5C6H6‚0.5CH2Cl2) or 1-27.5° (4) on a Bruker CCD
SMART system by using graphite-monochromatized Mo KR source
(λ ) 0.710 73 Å). The structures were refined by full-matrix least
squares on F2 by employing the SHELXL programs.
1
and styrene was determined by GC-MS and H NMR spectroscopy.
Intermolecular Cyclopropanation of Alkenes with EDA Cata-
lyzed by [Fe(TPFPP)(CPh2)] (1). Complex 1 (3.0 mg, 2.5 µmol) and
alkene (50.4 mmol) were dissolved in dichloromethane (1 mL). To
this solution was added a solution of ethyl diazoacetate (287.4 mg,
2.52 mmol) in dichloromethane (10 mL) using a syringe pump over 4
h at room temperature. The reaction mixture was stirred for 1 h and
then evaporated to dryness in vacuo. The crude cyclopropyl esters thus
obtained were purified by chromatography on a silica gel column with
diethyl ether/hexane (1:5, v/v) as eluent.
Intramolecular Cyclopropanation of Allylic Diazoacetates Cata-
lyzed by [Fe(TPFPP)(CPh2)] (1). Complex 1 (3.0 mg, 2.5 µmol) and
2,6-dichloropyridine (0.37 mg, 2.5 µmol) were dissolved in dichlo-
romethane (1 mL). To this solution was added a solution of allylic
diazoacetate (0.50 mmol) in dichloromethane (10 mL) using syringe
pump over 12 h at 40 °C. The reaction mixture was stirred for 1 h and
then evaporated to dryness in vacuo. The bicyclic lactone thus obtained
was purified by chromatography on a silica gel column with diethyl
ether/hexane (1:5, v/v) as eluent.
Acknowledgment. This work was supported by the Generic
Drug Research Program of The University of Hong Kong, the
Hong Kong University Foundation, the Hong Kong Research
Grants Council, and the University Grants Committee of the
Hong Kong SAR of China (Area of Excellence Scheme, AoE/
P-10/01). C.-M.C. thanks for the NSFC Young Researcher
Award administrated by the NSF of China.
Supporting Information Available: Text providing charac-
terization of cyclopropanation and C-H insertion products,
tables of final coordinates, bond lengths, bond angles, and
anisotropic displacement parameters for 1‚0.5C6H6‚0.5CH2Cl2
and 4, and ORTEP drawings of 1‚0.5C6H6‚0.5CH2Cl2 and 4
with the atom-numbering schemes (Figures S1 and S2). This
material is available free of charge via the Internet at
http://pubs.acs.org.
Typical Procedures of Stoichiometric C-H Insertion Reaction
of [Fe(TPFPP)(C(Ph)CO2Et)] (2) or [Fe(TPFPP)(CPh2)(MeIm)] (4)
with Hydrocarbons. A mixture of 2 or 4 (0.015 mmol) and cumene
(1.0 mL) was stirred at 80 °C for 15 or 20 h. The mixture was then
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