Catalytic cyclopropanation with iron(II) complexes

Article abstract of DOI:10.1021/om010513u

Iron(II) complexes of meso-tetra-p-tolylporphyrin (TTP), tetramethyldibenzotetraaza[14]-annulene (tmtaa), and trans-1,2-bis(salicylidene)cyclohexanediamine (saldach) catalyzed the cyclopropanation of styrene with aryldiazomethanes. When p-tolyldiazomethane was used as the carbene source, trans-cyclopropanes were the major products. Trans/cis ratios of up to 17:1 were obtained. However, using mesityldiazomethane resulted in a reversal of stereoselectivity, giving cis-cyclopropanes as the major product (cis/trans ratios of up to 2.9: 1). The stereoselectivity of iron(II) porphyrin-catalyzed cyclopropanation reactions was enhanced by performing the reactions at low temperature or by using bulky porphyrin ligands. Using trimethylsilyldiazomethane as the carbene source, trimethylsilylcyclopropanes were produced in excellent yields with (TTP)Fe. On treatment of (TTP)Fe with diazoreagents, carbene complexes were observed spectroscopically. These complexes transferred their carbene ligand to styrene to produce cyclopropanes stoichiometrically.

Full text of DOI:10.1021/om010513u

Organometallics 2001, 20, 5171-5176
5171
Ca ta lytic Cyclop r op a n a tion w ith Ir on (II) Com p lexes
Christopher G. Hamaker,† Gholam A. Mirafzal,‡ and L. Keith Woo*
Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111
Received J une 13, 2001
Iron(II) complexes of meso-tetra-p-tolylporphyrin (TTP), tetramethyldibenzotetraaza[14]-
annulene (tmtaa), and trans-1,2-bis(salicylidene)cyclohexanediamine (saldach) catalyzed the
cyclopropanation of styrene with aryldiazomethanes. When p-tolyldiazomethane was used
as the carbene source, trans-cyclopropanes were the major products. Trans/ cis ratios of up
to 17:1 were obtained. However, using mesityldiazomethane resulted in a reversal of
stereoselectivity, giving cis-cyclopropanes as the major product (cis/ trans ratios of up to 2.9:
1). The stereoselectivity of iron(II) porphyrin-catalyzed cyclopropanation reactions was
enhanced by performing the reactions at low temperature or by using bulky porphyrin
ligands. Using trimethylsilyldiazomethane as the carbene source, trimethylsilylcyclopropanes
were produced in excellent yields with (TTP)Fe. On treatment of (TTP)Fe with diazoreagents,
carbene complexes were observed spectroscopically. These complexes transferred their
carbene ligand to styrene to produce cyclopropanes stoichiometrically.
In tr od u ction
panes,8 3,5-diaryl-1,2-dioxolanes,9 3,5-diaryl-2-isoxazo-
lines,10 and cyclopropanecarboxylic acids.11 In addition,
arylcyclopropanes also possess useful photochemical
properties.12 Thus the catalytic production of arylcyclo-
propanes is an important synthetic goal.
Transition-metal-mediated cyclopropanation has re-
ceived much attention recently.1 The majority of cata-
lytic studies employ diazocarbonyl compounds as the
carbene source. Despite numerous reports of stoichio-
metric cyclopropanation with transition metal ben-
zylidene complexes,2 few reports exist on transition-
metal-catalyzed cyclopropanation using aryldiazometh-
anes.3,4 Moreover, production of arylcyclopropanes from
mixtures of aryldiazomethanes and olefins is typically
achieved by treatment with zinc halides5 or by photoly-
sis.6
Although silylcyclopropanes are also versatile syn-
thetic intermediates,13 very few reports exist on cyclo-
propanation reactions employing trimethylsilyldiazo-
methane as the carbene source.3e,14 Trimethylsilyldiazo-
methane is one of the most robust diazo compounds
known.15 In addition, its commercial availability16 makes
it an attractive reagent.
We recently reported that iron(II) porphyrin com-
plexes are efficient catalysts for the formation of cyclo-
propyl esters.17 Related complexes containing the readily
derivatized salen18 and tmtaa ligand systems (Figure
Arylcyclopropanes are reactive molecules and valu-
able synthetic intermediates. For example, they have
been used as starting materials in the synthesis of 1,3-
dihalo-1,3-diarylpropanes,7 1,3-dimethoxy-1,3-diarylpro-
(8) Shono, T.; Matsumura, Y. J . Org. Chem. 1970, 35, 4157.
(9) Mizuno, K.; Kamiyama, N.; Otsuji, Y. Chem. Lett. 1983, 477.
(10) Ichinose, N.; Mizuno, K.; Tamai, T.; Otsuji, Y. Chem. Lett. 1988,
233.
(11) Norsikian, S.; Marek, I.; Poisson, J .-F.; Normant, J . F. J . Org.
Chem. 1997, 62, 4898.
(12) (a) Hixson, S. S. J . Am. Chem. Soc. 1974, 96, 4866. (b) Ichinose,
N.; Mizuno, K.; Hiromoto, Z.; Otsuji, Y. Tetrahedron Lett. 1986, 27,
5619.
† Current Address: Department of Chemistry, Illinois State Uni-
versity, Normal, IL 61790-4160.
‡ Current Address: Department of Chemistry, Drake University,
2507 University Ave., Des Moines, IA 50311-4505.
(1) (a) Ye, T.; McKervey, M. A. In The Chemistry of the Cyclopropyl
Group; Rappoport, Z., Ed.; J ohn Wiley & Sons: New York, 1995; Vol.
2, p 657. (b) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds: From Cyclo-
propanes to Ylides; J ohn Wiley & Sons: New York, 1997. (c) Ye, T.;
McKervy, M. A. Chem. Rev. 1994, 94, 1091.
(13) (a) Paquette, L. A. Chem. Rev. 1986, 86, 733. (b) Reiâig, H.-U.
Top. Curr. Chem. 1988, 144, 73.
(2) Brookhart, M.; Studabaker, W. G. Chem. Rev. 1987, 87, 411.
(3) (a) Dull, M. F.; Abend, P. G. J . Am. Chem. Soc. 1959, 81, 2588.
(b) Doyle, M. P.; Griffin, J . H.; Bagheri, V.; Dorow, R. L. Organome-
tallics 1984, 3, 53. (c) Seitz, W. J .; Hossain, M. M. Tetrahedron Lett.
1994, 35, 7561. (d) Davies, H. M. L.; Bruzinski, P. R.; Fall, M. J .
Tetrahedron Lett. 1996, 37, 4133. (e) C¸ etinkaya, B.; O¨ zdemir, I.;
Dixneuf, P. H. J . Organomet. Chem. 1997, 534, 153. (f) Li, Y.; Huang,
J .-S.; Zhou, Z.-Y.; Che, C.-M. J . Am. Chem. Soc. 2001, 123, 4843-4844.
(4) An example using rhodium(II) acetate and dimethyl sulfide
exists. The rhodium precatalyst reacts with the diazoalkane and
dimethyl sulfide to generate a sulfur ylide. The ylide then transfers
the carbene fragment to an olefin to give cyclopropane. Aggarwal, V.
K.; Abdel-Rahman, H.; Thompson, A.; Mattison, B.; J ones, R. V. H.
Phosphorus, Sulfur Silicon Relat. Elem. 1994, 95/96, 283.
(5) Goh, S. H.; Closs, L. E.; Closs, G. L. J . Org. Chem. 1969, 34, 25.
(6) (a) Tomioka, H.; Ozaki, Y.; Koyabu, Y.; Izawa, Y. Tetrahedron
Lett. 1982, 23, 1917. (b) Oku, A.; Yokoyama, T.; Harada, T. J . Org.
Chem. 1983, 48, 5333.
(14) (a) Seyferth, D.; Menzel, H.; Dow, A. W.; Flood, T. C. J .
Organomet. Chem. 1972, 44, 279. (b) Haszeldine, R. N.; Scott, D. L.;
Tipping, A. E. J . Chem. Soc., Perkin Trans. 1 1974, 1440. (c) Daniels,
R. G.; Paquette, L. A. J . Org. Chem. 1981, 46, 2901. (d) Aoyama, T.;
Iwamoto, Y.; Nishigaki, S.; Shioiri, T. Chem. Pharm. Bull. 1989, 37,
253.
(15) Podlech, J . J . Prakt. Chem. 1998, 340, 679.
(16) Trimethylsilyl diazomethane is commercially available as a 2.0
M solution in hexanes from Aldrich Chemical Co., Milwaukee, WI.
(17) Wolf, J . R.; Hamaker, C. G.; Djukic, J .-P.; Kodadek, T.; Woo,
L. K. J . Am. Chem. Soc. 1995, 117, 9194.
(18) Abbreviations used: salen ) dianion of a generic bis(sali-
cylidene)diamine; saldach ) dianion of trans-1,2-bis(salicylidene)-
cyclohexanediamine; tmtaa ) dianion of tetramethyldibenzotetraaza-
[14]annulene; TTP ) dianion of meso-tetra-p-tolylporphyrin; TPP )
dianion of meso-tetraphenylporphyrin; TMP
) dianion of meso-
tetramesitylporphyrin; TDMPP ) dianion of meso-tetrakis(2,6-dimethox-
yphenyl) porphyrin; EDA ) ethyl diazoacetate; THF ) tetrahydrofu-
ran; TMS ) trimethylsilyl.
(7) Applequist, D. E.; Gdanski, R. D. J . Org. Chem. 1981, 46, 2502.
10.1021/om010513u CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/01/2001

5172 Organometallics, Vol. 20, No. 24, 2001
Hamaker et al.
Ta ble 1. Syn th esis of
1-p-Tolyl-2-p h en ylcyclop r op a n e fr om Styr en e a n d
N2CH(p-tolyl)
cyclopropane
time stilbene yield,a % yield,a %
addition 4,4-dimethyl-
trans/
entry
catalyst
cisa
1
2
3
(saldach)FeII b 50 min
33(4)c
84(7)
21(5)
18(4)c
16(7)
79(4)
4.0(4)c
1.9(4)
14(1)
b
(tmtaa)FeII
2 h
d
(TTP)FeII
25 min
a
Determined by GC analysis. b 1.5-1.7 mol % catalyst. c Values
in parentheses are standard deviations in the last digit based on
at least three catalytic runs. 0.8-0.9 mol % catalyst.
d
solvent-dependent trans/ cis ratio is consistent with
previous observations.17
Interestingly, when mesityldiazomethane was used
as the carbene source, the cis-cyclopropane isomer
became the major product (cis/ trans ) 2.0 ( 0.2). The
yield of 1-mesityl-2-phenylcyclopropane, 2b, was 60%
and the yield of 2,2′,4,4′,6,6′-hexamethylstilbene, 3b,
was 40% using a 30 min slow addition of a 48 mM
hexanes solution of mesityldiazomethane. Additionally,
trans-â-methylstyrene was converted to 1-mesityl-2-
methyl-3-phenylcyclopropane, 2c, in the presence of
(TTP)Fe and mesityldiazomethane. Compound 2c was
obtained in ca. 35% yield (unoptimized) and was de-
tected by GC/MS (m/z ) 250 [M]+). Using other diazo
reagents such as ethyl diazoacetate (EDA) and tri-
methylsilyldiazomethane, trans-â-methylstyrene was
not converted to cyclopropane when (TTP)Fe was used
as the catalyst.
Ca ta lytic Cyclop r op a n a tion w ith (tm ta a )F e. The
scope of cyclopropanation with catalytic amounts of
(tmtaa)Fe, 4, was also examined. Results using EDA as
the carbene source were poor. Generally, less than 20%
of EDA was converted to products in the presence of
complex 4 and an excess of styrene. However, complex
4 was an efficient catalyst for the decomposition of
aryldiazomethanes. Dropwise addition of a 39 mM
pentane/THF solution of p-tolyldiazomethane over 2 h
to a solution containing 14 equiv (relative to the diazo
reagent) of styrene and (tmtaa)Fe (1.5 mol %) in THF
produced cyclopropane 2a in 16% yield. The remaining
p-tolyldiazomethane was converted to olefin 3a (84%
yield). However, the trans/ cis ratio for cyclopropane 2a
was 1.9 ( 0.4, significantly lower than the 14:1 ratio
obtained using (TTP)Fe as the catalyst. When mesityl-
diazomethane was used as the diazoalkane, the yield
of cyclopropane 2b was 43% and the yield of olefin 3b
was 57% using a 60 min slow addition of diazo reagent.
As with (TTP)Fe, the major cyclopropane isomer was
cis-2b (cis/ trans ) 2.9 ( 0.3).
F igu r e 1. Iron complexes used in this study.18
1) seemed like a logical extension to our cyclopropana-
tion studies. J acobsen and others have used (salen)Mn-
(III) complexes extensively as epoxidation catalysts.19
Moreover, chiral salen ligands have been used in highly
enantioselective Mn(III)-catalyzed epoxidation19 and in
Co(III)-catalyzed cyclopropanation reactions.20 While no
reports exist, to our knowledge, on reactions between
(salen)Fe(II) complexes and diazo reagents, Floriani and
co-workers recently reported the isolation of (tmtaa)-
FedCPh2 by treatment of (tmtaa)Fe(II) with diphenyl-
diazomethane.21 Floriani also demonstrated that (tmtaa)-
Fe reacts with phenyldiazomethane to yield a carbene
complex which is only observable at low temperature.
At room temperature, the benzylidene complex decom-
posed to give (tmtaa)Fe and a mixture of cis- and trans-
stilbene.
Resu lts
Ca ta lytic P r od u ction of Ar ylcyclop r op a n es Us-
in g (TTP )F e. Since iron(II) porphyrins are efficient
catalysts for the production of cyclopropyl esters from
ethyl diazoacetate and olefins,17 an investigation of the
catalytic production of diarylcyclopropanes using (TTP)-
Fe was undertaken. Indeed, (TTP)Fe, 1, was an excel-
lent catalyst for the cyclopropanation of olefins with
aryldiazomethanes. Dropwise addition of a hexanes
solution of p-tolyldiazomethane to a THF solution
containing styrene (14 equiv) and (TTP)Fe (<1 mol %)
produced 1-(4-methylphenyl)-2-phenylcyclopropane, 2a ,
in 79% yield (trans/ cis ) 14 ( 1) as shown in eq 1. A
side product, 4,4′-dimethylstilbene, 3a , was obtained in
21% yield (Table 1). When the p-tolyldiazomethane was
added as a solution in diethyl ether, the trans/ cis ratio
for cyclopropane 2a increased slightly to 17:1. This
Ca ta lytic Cyclop r op a n a tion Usin g (sa ld a ch )F e.
An iron(II) salen complex, (saldach)Fe, 5, was also
investigated as a cyclopropanation catalyst. Cyclopro-
panation of styrene using EDA and catalytic amounts
of 5 gave less than 30% yield of diethyl maleate, diethyl
fumarate, and ethyl-2-phenylcyclopropane carboxylate,
6, combined. Unlike (tmtaa)Fe, changing the diazo
reagent to p-tolyldiazomethane did not improve product
yields. Only about 50% of the p-tolyldiazomethane was
(19) J acobsen, E. N. In Catalytic Asymmetric Synthesis; Ojima, I.,
Ed.; VCH: New York, 1993; p 159.
(20) (a) Fukuda, T.; Katsuki, T. Synlett 1995, 825. (b) Fukuda, T.;
Katsuki, T. Tetrahedron 1997, 53, 7201.
(21) Klose, A.; Solari, E.; Floriani, C.; Re, N.; Chiesi-Villa, A.; Rizzoli,
C. Chem. Commun. 1997, 2297.

Catalytic Cyclopropanation with Iron(II) Complexes
Organometallics, Vol. 20, No. 24, 2001 5173
Ta ble 2. Effect of P or p h yr in Str u ctu r e in th e
Cyclop r op a n a tion of Styr en e w ith EDA
in C6D6), while the protons on the R groups show large
upfield shifts, consistent with their position above the
porphyrin ligand. Complexes 8a and 8b slowly decom-
posed during recrystallization, preventing isolation of
pure samples. However, both complexes generated cy-
clopropanes from a stoichiometric reaction in the pres-
ence of excess styrene (eq 2).
entry
catalyst
solvent
trans/ cis
ref
1
2
3
4
5
(TTP)Fe
(TTP)Fe
(TMP)Fe
(TDMPP)Fe
(TDMPP)Fe
toluene
THF
toluene
toluene
THF
8.0:1
13:1
13:1
15:1
21:1
17
17
a
a
a
a
This work.
converted to cyclopropane 2a and olefin 3a in the
presence of excess styrene.
Tem p er a tu r e Effects in th e Cyclop r op a n a tion of
Styr en e w ith EDA Ca ta lyzed by (TTP )F e. In our
studies of catalytic cyclopropanation reactions, it was
possible to vary slightly the stereoselectivity by chang-
ing the solvent. Additionally, the reaction temperature
had a dramatic effect on the trans/ cis ratio. When a
dichloromethane solution of (TTP)Fe and excess styrene
was treated with EDA at -78 °C for 3 h, cyclopropane
6 was obtained in 92 ( 7% yield with a trans/ cis ratio
of 29 ( 2. This is significantly greater than the 8.8:1
ratio for the same reaction in dichloromethane at 25
°C.17
The stoichiometric reaction between (TTP)FedCH-
(mesityl) and styrene was followed by H NMR spec-
1
troscopy. The reaction was monitored by following the
disappearance of the â-pyrrole signal of the porphyrin
and the o-methyl signal of the mesityl group. In the
presence of excess styrene, the reaction followed pseudo-
first-order kinetics (Supporting Information Figure S1).
The half-life at 25 °C was approximately 41 min in the
presence of 12 equiv of styrene and approximately 17
min in the presence of 18 equiv of styrene.
Effect of P or p h yr in Str u ctu r e in Ir on (II) P or -
p h yr in -Ca ta lyzed Cyclop r op a n a tion . The structure
of the porphyrin also had an effect on the diastereose-
lectivity of iron(II) porphyrin-catalyzed cyclopropanation
reactions. At ambient temperature in toluene, the
cyclopropanation of styrene with EDA produced prima-
rily trans-6. When the porphyrin was TTP, the trans/
cis ratio was 8.0:1. With TMP, methyl groups occupy
all of the ortho positions of the aryl substituents, and
the trans/ cis ratio increased to 13:1. Moreover, using
the bulky TDMPP ligand with o-methoxy substituents
increased the trans/ cis ratio to 15:1 (Table 2).
Ca ta lytic Syn th esis of 1-P h en yl-2-Tr im eth ylsi-
lylcyclop r op a n e, 7. Since trimethylsilyl diazomethane
is commercially available, its use as a carbene source
in catalytic cyclopropanation reactions was also inves-
tigated. Using 0.6 mol % of (TTP)Fe and approximately
a 10-fold excess (relative to N2CHTMS) of styrene,
1-phenyl-2-trimethylsilylcyclopropane, 7, was obtained
in 89 ( 4% yield with trimethylsilyl diazomethane as
the carbene source. Unlike previously reported cyclo-
propanation reactions using (trimethylsilyl)diazomethane,
no evidence for formation of 1,2-bis(trimethylsilyl)-
ethene byproducts from carbene coupling was observed.
The trans/ cis ratio for cyclopropane 7 was 10 ( 1 when
the reaction was performed in toluene and 13 ( 1 when
the reaction was performed in THF. Neither (tmtaa)Fe
nor (saldach)Fe produced any detectable quantities of
cyclopropane 7 under similar conditions.
Discu ssion
Liga n d Effects in Ir on (II)-Ca ta lyzed Cyclop r o-
p a n a tion . Given the efficiency of iron(II) porphyrins
as cyclopropanation catalysts, iron(II) complexes of the
related saldach and tmtaa ligand systems were inves-
tigated. Both (TTP)Fe and (tmtaa)Fe were efficient
catalysts for the catalytic cyclopropanation of olefins
with aryldiazomethanes. The cyclopropane stereoselec-
tivities derived from (TTP)Fe were greater than those
obtained using (tmtaa)Fe, when using p-tolyldiazo-
methane. Steric differences in the metal complexes may
influence these observed stereoselectivities. The iron
atom in complex 4 is displaced 0.114 Å above the N4
plane of the tmtaa ligand,23 while the iron atom in
(TPP)Fe lies within the N4 plane of the porphyrin
ligand.24 Moreover, in the structurally characterized
complex (tmtaa)FedCPh2, the iron atom lies 0.355(1)
Å above the N4 plane toward the carbene ligand.21 As a
result, the carbene ligand encounters little steric en-
cumbrance from the benzo rings of the tmtaa ligand.
Presumably, the carbene carbon in (tmtaa)FedCHR is
more accessible compared to the carbene carbon of
(TTP)FedCHR. Thus, the less crowded environment at
the active site in (tmtaa)FedCHR leads to lower ste-
reoselectivities compared to that of (TTP)FedCHR.
Further evidence for the steric influence of the macro-
cyclic ligand on diastereoselectivities was derived from
studies in which the size of the ortho-substituents of
the tetraarylporphyrin was varied. This served to
modify the size of the pocket around the active site. As
the ortho-group increased in steric bulk [R ) H (TTP),
Me (TMP), and OMe (TDMPP)], the trans/ cis ratio for
cyclopropane 6 increased sequentially from 8.0:1, to 13:
1, and to 15:1, respectively (Table 2).
Sp ectr oscop ic Id en tifica tion of Ca r ben e Com -
p lexes of (TTP )F e. Treatment of a solution of (TTP)-
Fe with a solution of N2CHR (R ) mesityl, trimethyl-
silyl) led to the formation of carbene complexes (TTP)Fed
CHR (R ) mesityl, 8a ; R ) trimethylsilyl, 8b). Samples
of the carbene complexes were usually contaminated
1
with ca. 5% of unreacted (TTP)Fe as evidenced by H
(22) (a) Woo, L. K.; Smith, D. A. Organometallics 1992, 11, 2344.
(b) Djukic, J .-P.; Smith, D. A.; Young, V. G.; Woo, L. K. Organometallics
1994, 13, 3020.
(23) Goedken, V. L.; Pluth, J . J .; Peng, S.-M.; Bursten, B. J . Am.
Chem. Soc. 1976, 98, 8014.
(24) Li, N.; Su, Z.; Coppens, P.; Landrum, J . J . Am. Chem. Soc. 1990,
112, 7294.
NMR. Unlike (TTP)Fe, the iron carbene complexes are
diamagnetic and have NMR spectra that are similar to
the known osmium(II) complexes, (TTP)OsdCHR.22 The
R-protons of the carbene ligands show large downfield
shifts (δ ) 19.71 ppm for 8a and δ ) 24.86 ppm for 8b

5174 Organometallics, Vol. 20, No. 24, 2001
Hamaker et al.
F igu r e 3. Olefin approach to the iron carbene intermedi-
ate as viewed down the CdFe bond (Fe atom not shown
beneath the carbene carbon). The plane of the olefin is
parallel to the plane defined by the FedCH fragment.
When the carbene substituent is mesityl (right), the
o-methyl groups prevent the olefin from approaching from
the same direction as when the substituent is p-tolyl (left).
F igu r e 2. Olefin approach to the iron carbene intermedi-
ate when the carbene substituent is small. The trans/cis
ratio of the product cyclopropane is determined by the
approach of the styrene molecule and a late transition state
along the reaction path.
The complex (saldach)Fe was not an efficient catalyst
for cyclopropanation. This may be due to activation of
the imine bonds of the salen ligand25 and complications
arising from side reactions involving these functional
groups.
Effect of Dia zo Rea gen t Str u ctu r e on Cyclop r o-
p a n e Ster eoselectivity. Catalytic production of cis-
substituted cyclopropanes is rare. Rhodium(III) porphy-
rins give slight excesses of cis-substituted cyclopropanes
using diazo esters as the carbene source.26 Doyle and
co-workers showed that catalysis using rhodium(II)
acetate gave primarily cis-substituted cyclopropanes
when phenyldiazomethane was used as the carbene
source (cis/ trans ) 3.3 for 1,2-diphenylcyclopropane),
but the yields are often low (38% for 1,2-diphenyl-
cyclopropane).3b Additionally, Seitz and Hossain re-
ported that 10 mol % of the iron complex [(η5-C5H5)Fe-
(CO)2(THF)][BF4] catalyzed the production of cis-
substituted cyclopropanes (cis/ trans g 24:1) using phenyl
diazomethane as the carbene source.3c
Using either ca. 0.8 mol % (TTP)Fe or ca. 1.8 mol %
(tmtaa)Fe and p-tolyldiazomethane, primarily trans-
cyclopropanes were obtained with styrene (trans/ cis )
14:1 for 1 and 1.9:1 for 4). However, by changing the
diazo reagent to mesityldiazomethane, cis-cyclopropanes
became the major product. A mechanistic analysis
rationalizes these phenomena. As proposed previously
for (TTP)Fe,17 the preferred olefin approach for cyclo-
propanation arises from a parallel, side-on orientation
of the CdC-C alkene plane relative to the FedCHCR
plane (Figure 2). When the substituent on the carbene
ligand is 2,4,6-mesityl, this side-on approach is impeded
by the methyls in the 2,6-positions of the mesityl group
(Figure 3). Consequently, the only available product-
forming olefin approach with the mesitylmethylidene
intermediate is from above the iron mesitylmethylidene
complex. The preference for the cis-product is presum-
ably due to a π-π interaction between the arenes in the
transition state (Figure 4).
F igu r e 4. Illustration of styrene approach toward (TTP)-
FedCH(mesityl). Arene π-π interactions presumably pro-
mote formation of the cis-cyclopropane.
as the carbene source. The side-on approach shown in
Figure 2 is not available to 1,2-substituted olefins due
to unfavorable steric interactions with the porphyrin (or
tmtaa) ligand.
Use of Low -Tem p er a tu r e To Im p r ove Ster eose-
lectivity in (TTP )F e-Ca ta lyzed Cyclop r op a n a tion
Rea ction s. A common method used to increase the
trans/ cis ratio for catalytic cyclopropanation of olefins
with diazo esters is to increase the size of the alkyl
group on the diazo ester.27 However, most of these diazo
reagents are not commercially available. Consequently,
it would be synthetically useful to improve diastereo-
selectivities with commercially available reagents. At
ambient temperature in methylene chloride solvent,
catalytic amounts of (TTP)Fe produce cyclopropane from
EDA and styrene with a trans/ cis ratio of 8.8:1.17 By
lowering the reaction temperature to -78 °C, the trans/
cis ratio for cyclopropane 6 was dramatically increased
to 29 ( 2 when methylene chloride was used as the
solvent. This increase in stereoselectivity is consistent
with the late transition state for (TTP)Fe-catalyzed
cyclopropanation reactions proposed previously.17
Cyclopr opan ation with Tr im eth ylsilyldiazom eth -
a n e. In the few documented cases of cyclopropanation
using trimethylsilyldiazomethane as the carbene source,
yields were generally low. A 46% yield of cyclopropane
7 with a trans/ cis ratio of 4.8 was obtained using
catalytic amounts of copper(I) chloride,14c and only a 2%
yield of cyclopropane 7 was obtained using a ruthenium-
(II) carbene complex as the catalyst.3e Also, significant
amounts of bis(trimethylsilyl)ethene were produced.
When (TTP)Fe was used as the catalyst, styrene was
The change in olefin approach with the mesityldiazo-
methane system is supported by the observation that
trans-â-methylstyrene was converted to cyclopropane 2c
using mesityldiazomethane as the carbene source and
(TTP)Fe as the catalyst. In comparison, trans-â-meth-
ylstyrene was not cyclopropanated when EDA, p-tolyl-
diazomethane, or trimethylsilyldiazomethane were used
(25) Diltz, S.; Aguirre, G.; Ortega, F.; Walsh, P. J . Tetrahedron:
Asymmetry 1997, 8, 3559.
(26) (a) Callot, H. J .; Metz, F.; Piechocki, C. Tetrahedron 1982, 38,
2365. (b) Maxwell, J .; O_Malley, S.; Brown, K.; Kodadek, T. Organo-
metallics 1992, 11, 645.
(27) (a) 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. (b) Evans, D. A.; Woerpel, K. A.; Hinman, M. M.; Faul, M. M. J .
Am. Chem. Soc. 1991, 113, 726. (c) Ichiyanagi, T.; Shimizy, M.;
Fujisawa, T. Tetrahedron 1997, 53, 9599.

Catalytic Cyclopropanation with Iron(II) Complexes
Organometallics, Vol. 20, No. 24, 2001 5175
Modified procedures as described below were used for the
preparation of (tmtaa)Fe35 and (saldach)Fe.36
converted to cyclopropane 7 in 89 ( 4% yield with no
bis(trimethylsilyl)ethene production. Additionally, the
stereoselectivity for the reaction was excellent, providing
up to a 13-fold excess of trans-7.
Syn th esis of (tm ta a )F e, 4. In a round-bottom flask, 271
mg (0.790 mmol) of H2tmtaa and 474 mg (2.20 mmol) of FeBr2
were dissolved in ca. 5 mL of 2:1 (v/v) toluene/THF. To the
stirred reaction was added approximately 1 mL of triethyl-
amine, and the reaction mixture changed from orange to red-
purple in color. After 19 h, the solvent was removed in vacuo
and the product dissolved in 5 mL of toluene. The mixture was
filtered through a pad of Celite to remove excess FeBr2 and
triethylammonium bromide. Recrystallization at -25 °C from
toluene/hexanes (1:5 (v/v)) afforded 213 mg (68%) of complex
4 as a purple solid in two crops. The complex (tmtaa)Fe was
paramagnetic with no observable signals in the 1H NMR.
However, sharp signals for the complex (tmtaa)Fe(py)2 were
observed upon addition of an excess of pyridine. 1H (C6D6, 300
MHz): 7.03 (m, 12 H, HAr + Hpy-3,5); 6.56 (d, 4H, Hpy-2,6); 4.27
(s, 2H, methine); 2.42 (s, 12H, HMe). The pyridine H-4 triplet
was not observed. These data match the literature values in
which (tmtaa)Fe was synthesized from H2tmtaa and Fe(py)4-
(NCS)2.
Con clu sion s
Iron(II) porphyrins are among the most efficient
catalysts reported for the catalytic cyclopropanation of
olefins with diazo reagents. Using iron(II) complexes of
tmtaa and porphyrins, the stereochemistry of product
cyclopropanes can be controlled by varying the reaction
temperature, solvent, macrocyclic substituents, or diazo
reagent. For example, at -78 °C, trans/ cis ratios of up
to 29:1 were possible in the cyclopropanation of styrene
with EDA using (TTP)Fe. The complex (TDMPP)Fe gave
higher trans/ cis ratios than (TTP)Fe. Additionally,
(TTP)Fe and (tmtaa)Fe were efficient catalysts for the
production of diarylcyclopropanes from aryldiazometh-
anes and styrene. Significantly, a reversal of stereose-
lectivity was observed with mesityldiazomethane. Cy-
clopropane cis/ trans ratios of 2.9:1 were achieved using
mesityldiazomethane and (tmtaa)Fe. The complex (TTP)-
Fe was also an excellent catalyst for the production of
silylcyclopropanes using (trimethylsilyl)diazomethane
as the carbene source. When styrene was employed as
the olefin, 1-phenyl-2-trimethylsilylcyclopropane was
obtained in 89% yield.
Syn th esis of (sa ld a ch )F e, 5. A round-bottom flask was
charged with Na2(saldach) (440 mg, 1.20 mmol), FeBr2 (270
mg, 1.25 mmol), and 12 mL of toluene. THF (3 mL) was added
to the brown-orange slurry which immediately changed color
to a bright purple. The reaction was stirred for 10 min and
then passed through a pad of Celite. The solvent was removed
from the filtrate in vacuo, the residue was dissolved in a min-
imum of toluene and diluted with hexanes (4:1 (v/v) toluene/
hexanes). Cooling to -25 °C produced microcrystalline 6 on
filtration and washing with hexanes (230 mg, 51%). The
complex (saldach)Fe was paramagnetic with no observable
Exp er im en ta l Section
1
signals in the H NMR spectrum. Addition of pyridine or tert-
butyisocyanide did not yield any species observable by 1H
NMR. The UV/vis data were similar to those reported for the
complex (salen)Fe which was synthesized from either H2salen
and iron(II) sulfate or iron(II) acetate in DMF or ethanol or
from H2(salen) and Fe3(CO)12 in DMF. UV/vis (toluene): 350,
533 nm. Anal. Calcd (found) for C20H20FeN2O2: C, 63.85 (63.40);
H, 5.36 (5.65); N, 7.45 (6.59). MS{ESI}: m/z ) 376 [M]+.
Ca ta lytic Cyclop r op a n a tion Rea ction s Usin g Ar yld ia -
zom eth a n es. To a round-bottom flask was added 1.0 mL (8.7
mmol) of styrene, a known amount (typically on the order of
30 mg) of hexamethylbenzene (internal standard for GC), the
appropriate iron catalyst, and 5 mL of THF. To the stirred
reaction mixture was slowly added a solution of aryldiazo-
methane in 15 mL of 2:1 (v/v) petroleum ether/THF (ca. 580
µmol for reactions using p-tolyldiazomethane and ca. 600 µmol
for reactions using mesityldiazomethane). The reaction was
analyzed by GC to determine product yields. Products were
identified by co-injection with authentic samples.
In d ep en d en t Syn th esis of 1-Mesityl-2-p h en ylcyclop r o-
p a n e, 2b. An authentic sample of compound 2b was synthe-
sized using the method of Applequist and Gdanski from
mesitaldehyde and acetophenone.7 The yield was 900 mg
(12.2%) of a tan, viscous oil having a trans/ cis ratio of 1.5:1.
1H NMR (CDCl3, 400 MHz) of cis-isomer, 5c: 7.02 (m, 3H,
C6H5), 6.72 (s, 2H, C6H2(CH3)2), 6.44 (m, 2H, C6H5), 2.21 (s,
6H, CH3), 2.19 (s, 3H, CH3), 2.02 (m, 1H, C3H4), 1.97 (m, 1H,
C3H4), 1.40 (m, 1H, C3H4), 1.04 (m, 1H, C3H4). 1H NMR
(CDCl3). 1H NMR (CDCl3, 400 MHz) of trans-isomer, 5c: 7.32
(t, 2H, C6H5, J HH ) 7.6 Hz), 7.20 (m, 3H, C6H5), 6.86 (s, 2H,
Gen er a l Meth od . All reactions were carried under dry
nitrogen or argon using a Vacuum/Atmospheres glovebox
equipped with a MO40H DriTrain gas purification system or
on a vacuum line using standard Schlenk techniques. All
solvents were dried using standard methods.28 Olefins were
dried over activated 4 Å molecular sieves and degassed prior
to use. All slow additions were performed with a dropping
1
funnel. H NMR spectra were recorded on Varian VXR300 or
1
Bruker DRX400 spectrometers. H NMR peak positions were
referenced against residual proton resonances of deuterated
solvents (δ, ppm: CDCl3, 7.24; C6D6, 7.15). Gas chromatogra-
phy was performed using a HP 5890 Series II29 and GC/MS
data was obtained from a Finnegan Magnum GC-MS.30 Elec-
trospray mass data was obtained on a Finnigan TSQ 700 in
the positive ion mode. Elemental analyses (C, H, N) were
performed by Iowa State University Instrument Services.
Hexamethylbenzene (aryldiazomethane reactions) or dodecane
(EDA or N2CHTMS reactions) were used as the internal
standard for GC yield determinations. Aryldiazomethanes
were prepared from the corresponding tosylhydrazones ac-
cording to a literature procedure,31 except that diethlyene
glycol methyl ether was used rather than triethylene glycol
as the solvent. The tetraazaannulene ligand, H2tmtaa, was
synthesized using a literature procedure.32 The ligand H2-
(saldach) was synthesized by treating 2 equiv of salicylalde-
hyde with trans-1,2-diaminocyclohexane in refluxing ethanol
for 1 h.33 The disodium salt, Na2(saldach) was synthesized
according to a literature procedure.32 A procedure published
by Reed on the reduction of either (TTP)FeCl or [(TTP)Fe]2-
(µ-O) with Zn/Hg amalgam was used to synthesize (TTP)Fe.34
(33) Solari, E.; DeAngelis, S.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,
C. J . Chem. Soc., Dalton Trans. 1991, 2471.
(34) Reed, C. A.; Kouba, J . K.; Grimes, C. J .; Cheung, S. K. Inorg.
Chem. 1978, 17, 2666.
(35) Goedkin, V. L.; Park, Y.-A. J . Chem. Soc., Chem. Commun.
1975, 214.
(36) (a) Earnshaw, A.; King, E. A.; Larkworth, L. F. J . Chem. Soc.
A 1968, 1048. (b) Calderazzo, F.; Floriani, C.; Henzi, R.; L_Eplattenier,
F. J . Chem. Soc. A 1969, 1378. (c) Floriani, C.; Calderazzo, F. J . Chem.
Soc. A 1971, 3665.
(28) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon Press: New York, 1980.
(29) DB-5 capillary column (30 m, 0.32 mm i.d., 0.25 µm film
thickness).
(30) Varian gas chromatograph coupled to an ITS 40 ion trap mass
spectrometer (capillary column DB-5MS (30 m, 0.25 mm i.d., 0.25 µm
film thickness)).
(31) Closs, G. L.; Moss, R. A. J . Am. Chem. Soc. 1964, 86, 4042.
(32) Goedken, V. L.; Weiss, M. C. Inorg. Synth. 1980, 20, 115.

5176 Organometallics, Vol. 20, No. 24, 2001
Hamaker et al.
C6H2(CH3)2), 2.37 (s, 3H, CH3), 2.27 (s, 6H, CH3), 1.84 (m, 1H,
C3H4), 1.76 (m, 1H, C3H4), 1.17 (m, 1H, C3H4), 1.02 (m, 1H,
C3H4). 13C NMR (CDCl3, 100.8 MHz) trans- and cis-isomers:
143.23, 141.03, 138.95, 138.62, 135.85, 135.52, 135.28, 130.78,
128.72, 128.70, 128.34, 127.29, 126.31, 125.53, 125.42, 124.93,
25.85, 24.86, 23.42, 22.90, 20.82, 20.81, 20.79, 20.67, 19.50,
17.77.37 MS{EI} m/z (rel intens): 236 [M]+ (100), 222 (24), 133
(24), 117 (20), 63 (70), 53 (31).
(m, 3H, C6H5), 1.74 (m, 1H, C3H4), 0.89 (m, 1H, C3H4), 0.77
(m, 1H, C3H4), -0.03 (m, 10H, C3H4 + Si(CH3)3). 1H (C6D6, 300
MHz) of the cis-isomer: 0.85 (m, 1H, C3H4), -0.19 (s, 9H, Si-
(CH3)3). All other signals for the cis-cyclopropane were ob-
scured by those of the trans-isomer.
(TTP )F edCH(m esityl), 8a . A round-bottom flask was
charged with 9 mg (13 µmol) of (TTP)Fe and ca. 2 mL of THF.
To this solution was added 120 µL of a 136 mM solution of
N2CH(mesityl) (16.3 µmol) in pentane. The reaction mixture
was stirred vigorously for 3 min, and then the solvent was
removed in vacuo. The resulting complex was dissolved in
Low -Tem p er a tu r e P r ep a r a tion of Eth yl-2-p h en ylcy-
clop r op a n eca r boxyla te, 3. In a glovebox, 18 mg (25 µmol)
of (TTP)Fe, 22 µL of dodecane (GC standard), and 9.13 mmol
of styrene were placed into a round-bottom flask and dissolved
in 15 mL of dichloromethane. The flask was capped with a
rubber septum and removed from the glovebox. The flask was
cooled to -78 °C with a dry ice/acetone bath, and EDA (108
µmol) was added via syringe. The reaction was stirred at -78
°C for 3 h and then allowed to warm to room temperature.
The reaction was analyzed by gas chromatography. The yield
of cyclopropane was 92 ( 7% with a trans/ cis ratio of 29:1.
1-P h en yl-2-(tr im eth ylsilyl)cyclop r op a n e, 7. In a typical
reaction, 8.5 mmol of styrene, 3.5 mg of (TTP)Fe (4.8 µmol,
0.6 mol %), and 20 µL of dodecane (GC standard) were
dissolved in 3 mL of solvent. Trimethylsilyldiazomethane (400
µL of a 2.0 M solution in hexanes, 800 µmol) in 12 mL of
solvent was added dropwise over approximately 1 h. The
reaction mixture was stirred vigorously and analyzed by GC
after ca. 18 h. Unlike cyclopropanation with other diazo
reagents, the slow addition was not necessary, as no carbene
dimer, 1,2-bis(trimethylsilyl)ethene, was ever detected in the
reactions performed using (TTP)Fe as a catalyst. Therefore,
subsequent reactions were performed by adding all of the
trimethylsilyldiazomethane at once, rather than dropwise. The
yield of cyclopropane was 89 ( 4%. The trans/ cis ratio was 10
( 1 using toluene as the solvent and 13 ( 1 using THF as the
solvent. The cyclopropane could be isolated by removing all of
the solvent and excess styrene in vacuo, dissolving the residue
in hexanes, passing the solution through a plug of neutral
alumina (2 × 5 cm), and eluting with hexanes. The cyclopro-
pane was isolated after removal of the hexane from the
combined filtrate and washings by rotary evaporation. 1H
(C6D6, 300 MHz) of the trans-isomer: 7.13 (m, 2H, C6H5), 7.03
1
C6D6, and its 1H NMR spectrum was recorded. H (C6D6, 400
MHz): 19.71 (s, 1H, dCHAr), 8.72 (s, 8H, â-H), 7.84 (br, 8H,
C6H4CH3), 7.23 (d, 8H, C6H4CH3, J HH ) 7.6 Hz), 5.54 (s, 2H,
C6H2(CH3)3), 2.34 (s, 12H, C6H4CH3), 1.70 (s, 3H, p-C6H2-
(CH3)3), -1.12 (s, 6H, o-C6H2(CH3)3). Contamination of the
sample with ca. 5% (TTP)Fe precluded the isolation of pure
material for elemental analysis.
(TTP )F edCH(TMS), 8b. To a solution of 24 mg (TTP)Fe
(33 µmol) in 5 mL of toluene was added 51.5 µL of a 2.0 M
solution of N2CH(TMS) (1.0 × 102 µmol) in hexanes. The
mixture was stirred for 3 h, and the solvent was removed at
reduced pressure. The residue was dissolved in C6D6, and its
1
1H NMR spectrum was recorded. H (C6D6, 300 MHz): 24.86
(s, 1H, dCHTMS), 8.69 (s, 8H, â-H), 7.92 (d, 8H, C6H4CH3,
J HH ) 7.8 Hz), 7.17 (d, 8H, C6H4CH3, partially obscured by
C6D6), 2.31 (s, 12H, C6H4CH3), -1.80 (s, 9H, Si(CH3)3).
Contamination of the sample with ca. 5% (TTP)Fe precluded
the isolation of pure material for elemental analysis.
Ack n ow led gm en t. Funding for this work was pro-
vided by the Proctor and Gamble Corp., through a
fellowship to C.G.H.; the National Science Foundation;
and the donors of the Petroleum Research Fund, ad-
ministered by the American Chemical Society. We thank
Mr. Glen Post for the synthesis of the ligand H2(tmtaa).
G.A.M. appreciates support from Drake University for
a sabbatical leave.
Su p p or tin g In for m a tion Ava ila ble: Plot of kinetic data
for the reaction between (TTP)FedCH(mesityl) and styrene.
This information is available free of charge via the Internet
at http://pubs.acs.org.
(37) The 13C resonances of the C3 ring carbons were reported, but
no other spectroscopic data was given. Leonova, T. V.; Shapiro, I. O.;
Ranneva, Y. I.; Subbotin, O. A.; Kudryavtsev, R. V.; Shabarov, Y. S.;
Shatenshtein, A. I. J . Org. Chem. USSR (Engl. Transl.) 1976, 12, 570;
Zh. Org. Khim. 1976, 12, 579.
OM010513U