A method for the synthesis of carbene precursors from aldehydes and the metalates (η5-C5H5)(CO)2Fe- and (η5-C9H7)(CO)2Fe-

Article abstract of DOI:10.1021/om970698y

Nucleophilic addition of the metalate Cp(CO)₂Fe^-M⁺ (M = Na, K) to aldehydes RCHO (R = Ph, CH₃, p-OCH₃Ph, p-ClPh, p-CH₃Ph, p-CF₃Ph, o-OCH₃Ph, and CH=C(CH₃)₂) and subsequent capture with ClSi(CH₃)₃ provided the (α-siloxyalkyl)iron complexes Cp(CO)₂FeCH(OSiMe₃)R in 42-79% yield. This new reaction was extended to the indenyl-ligated metalate In(CO)₂Fe^-Na⁺ with several aldehydes RCHO (R = Ph, CH₃, p-OCH₃Ph). Treatment of the (α-siloxyalkyl)iron complexes with trimethylsilyl triflate at between -25 and -78 °C, in the presence of alkenes, gave cyclopropanes through iron carbene complexes.

Full text of DOI:10.1021/om970698y

Organometallics 1998, 17, 1333-1339
1333
A Meth od for th e Syn th esis of Ca r ben e P r ecu r sor s fr om
Ald eh yd es a n d th e Meta la tes (η5-C5H5)(CO)2F e- a n d
(η5-C9H7)(CO)2F e-
Ronald D. Theys, Roy M. Vargas, Qinwei Wang, and M. Mahmun Hossain*
Department of Chemistry, University of WisconsinsMilwaukee, Milwaukee, Wisconsin 53201
Received August 11, 1997
Nucleophilic addition of the metalate Cp(CO)2Fe-M+ (M ) Na, K) to aldehydes RCHO (R
) Ph, CH3, p-OCH3Ph, p-ClPh, p-CH3Ph, p-CF3Ph, o-OCH3Ph, and CHdC(CH3)2) and
subsequent capture with ClSi(CH3)3 provided the (R-siloxyalkyl)iron complexes Cp(CO)2-
FeCH(OSiMe3)R in 42-79% yield. This new reaction was extended to the indenyl-ligated
metalate In(CO)2Fe-Na+ with several aldehydes RCHO (R ) Ph, CH3, p-OCH3Ph).
Treatment of the (R-siloxyalkyl)iron complexes with trimethylsilyl triflate at between -25
and -78 °C, in the presence of alkenes, gave cyclopropanes through iron carbene complexes.
In tr od u ction
Electrophilic iron carbene complexes have been and
continue to be of interest as highly reactive intermedi-
ates or potential intermediates for both stoichiometric1
and metal-catalyzed2 cyclopropanation reactions. Among
these iron carbenes, the complexes (η5-C5H5)(CO)(L)-
Fe+dCHR (L ) CO, PR3) have been found to be the most
effective in transferring their carbene ligands to alkenes,
forming cyclopropanes.1k Transfer frequently occurs
1
with nearly exclusive formation of the sterically more
crowded, thermodynamically less stable isomers of
cyclopropane. This, coupled with the relatively lower
cost of iron-type complexes, makes iron carbene com-
plexes attractive in cyclopropanation reactions. Due to
their lability, these carbene complexes are often gener-
ated in situ from their corresponding precursors by
treatment with Bronsted or Lewis acids. Synthesis of
these precursors to date has required use of the highly
nucleophilic (η5-C5H5)(CO)2Fe anion, commonly desig-
nated as Fp-, via SN2 substitution reactions with
organohalides. The earliest reaction utilized the toxic
and often difficult to prepare R-chloroalkyl methyl
ethers ClCH(OCH3)R (R ) H, Ph; eq 1).1a,b,c A variation
of this reaction uses R-chloroalkylmethyl/phenyl thio-
ethers ClCH(SR′)R (R ) H, R′) CH3, Ph; R ) CH3, CH2-
CH3, R′) Ph) to produce more stable precursors (eq
2).1h,j,l Both of these reactions have inherent limitations.
A more general reaction has been devised involving
hydride or alkyl anion reduction of a Fischer carbene
(eq 3).1d,f,i This procedure is lengthier than the previous
two.
Recently, we reported3 that the Fp anion acts as a
nucleophile in reactions with aldehydes RCHO to form
the alkoxides FpCH(O-)R, which were trapped with
chlorotrimethylsilane to provide the R-siloxyalkyliron
complexes FpCH(OSiMe3)R. These reactions represent
a simple and efficient method for synthesizing electro-
philic iron carbene precursors from readily available
starting materials. The new precursors were found to
be efficient reagents for stereoselective cyclopropana-
tion, presumably through in-situ-generated carbene
complexes. We wish to report on extension of this new
(1) (a) J olly, P. W.; Pettit, R. J . Am. Chem. Soc. 1966, 88, 5044. (b)
Brookhart, M.; Nelson, G. O. Ibid. 1977, 99, 6099. (c) Brookhart, M.;
Humphrey, M. B.; Kratzer, H. J .; Nelson, G. O. Ibid. 1980, 102, 7802.
(d) Brookhart, M.; Tucker, J . R.; Husk, G. R. Ibid. 1981, 103, 979. (e)
Kremer, K. A. M.; Kuo, G. H.; O’Connor, E. J .; Helquist, P.; Kerber, R.
C. Ibid. 1982, 104, 6119. (f) Brookhart, M.; Tucker, J . R.; Husk, G. R.
Ibid. 1983, 105, 258. (g) Casey, C. P.; Miles, W. H. Organometallics
1984, 3, 808. (h) Kremer, K. A. M.; Helquist, P. J . Organomet. Chem.
1985, 285, 231. (i) Casey, C. P.; Miles, W. H.; Tukada, H. J . Am. Chem.
Soc. 1985, 107, 2924. (j) O’Connor, E. J .; Brandt, S.; Helquist, P. Ibid.
1987, 109, 3739. (k) Brookhart, M.; Studabaker, W. B. Chem. Rev.
1987, 87, 411. (l) Helquist, P. Adv. Met.-Org. Chem. 1991, 2, 143.
(2) (a) Seitz, W. J .; Saha, A. K.; Casper, D.; Hossain, M. M.
Tetrahedron Lett. 1992, 33, 7755. (b) Seitz, W. J .; Saha, A. K.; Hossain,
M. M. Organometallics 1993, 12, 2604. (c) Seitz, W. J .; Hossain, M.
M. Tetrahedron Lett. 1994, 35, 7561.
(3) A preliminary communication has appeared, see: Vargas, R. M.;
Theys, R. D. Hossain, M. M. J . Am. Chem. Soc. 1992, 114, 777.
S0276-7333(97)00698-5 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/06/1998

1334 Organometallics, Vol. 17, No. 7, 1998
Theys et al.
Sch em e 1
temperature of the reaction was later found to be very
critical. Recently, Yamashita6 reported that at room
temperature the Fp anion catalyzes the dimerization of
aromatic aldehydes to form esters via the alkoxides 3
(eq 4). This latest observation solidifies our findings of
nucleophilic addition of the Fp anion to the aldehydes.
Precendence exists for a proposed alkoxide intermedi-
ate with other transition metal moieties. Gladysz
proposed the existence of a related manganese alkoxide
anion (CO)5Mn(C6H5CHO-Li+) as a fleeting intermedi-
ate in the reduction of the manganese pentacarbonyl
acyl complex by trialkylborohydrides.7 Hegedus pro-
vided indirect evidence for the intermediacy of the
reaction to other aldehydes with the Fp anion and to
reaction of aldehydes with the indenyldicarbonyliron
anion (η5-C9H7)(CO)2Fe-.
chromium pentacarbonyl dianion (CO)5Cr-(NR2′CRO-)
2-
after nucleophilic addition of Cr(CO)5
to tertiary
amides.8
The possibility that either an insertion mechanism
or a substitution mechanism was involved in forming
the precursor was also dispelled. The (R-siloxybenzyl)-
manganese pentacarbonyl complex has been synthe-
sized via a proposed insertion mechanism between the
manganese silyl complex (CO)5Mn-SiMe3 and benzal-
dehyde (eq 5).9 No analogous reaction was observed
Resu lts a n d Discu ssion
The Fp anion 1 reacts with aldehydes 2 in THF to
form the alkoxides 3. The presumed alkoxides were
captured by chlorotrimethylsilane to provide the siloxy-
iron complexes 4 (Scheme 1).
Yields for the complexes 4 ranged from 42% to 79%.
Most of the complexes were formed by use of an excess
of aldehyde (3 equiv) and a limited amount of Fp anion
(1 equiv). Later, it was discovered that an excess of Fp
anion (2 equiv) actually could give a considerably higher
yield, as exemplified by 4d . With the aldehyde in
excess, a 40% yield was obtained, whereas with the Fp
anion in excess, a 79% yield was realized. In every case,
byproducts from this general reaction included the silyl
complex Fp-SiMe3 and the Fp dimer in varying
amounts.
Apparently, the reaction depicted in Scheme 1 rep-
resents the first successful nucleophilic addition of a
transition metal anion complex to an aldehyde. No
reaction was observed at room temperature between the
manganese pentacarbonyl anion and benzaldehyde.4
The greater nucleophilicity of the Fp anion may be one
reason for its successful addition to benzaldehyde.5 The
trapping agent is also critical. Treatment of the alkox-
ide intermediate with methyl iodide or trimethyloxo-
nium tetrafluoroborate only generated the methyl com-
plex (η5-C5H5)(CO)2Fe-CH3 and Fp dimer, [(η5-C5H5)-
(CO)2Fe]2. No Fp-CH(OCH3)R was formed, indicating
between the silyl complex (η5-C5H5)(CO)2Fe-SiMe3
10
and the aldehyde under the reaction conditions. We
also considered the possibility that chlorotrimethylsi-
lane and the aldehyde were reacting in situ to form
R-chloroalkyl silyl ethers. J ung11 reported that iodo-
trimethylsilane reacts exothermally at room tempera-
ture with aldehydes to form R-iodoalkyl silyl ethers. This
(6) Ohishi, T.; Shiotani, Y.; Yamashita, M. Organometallics 1994,
13, 4641.
(7) Selover, J . C.; Marsi, M.; Parker, D. W.; Gladysz, J . A. J .
Organomet. Chem. 1981, 206, 317.
(8) Imwinkelried, R.; Hegedus, L. S. Organometallics 1988, 7, 702.
(9) (a) J ohnson, D. L.; Gladysz, J . A. J . Am. Chem. Soc. 1979, 101,
6433. (b) J ohnson, D. L.; Gladysz, J . A. Inorg. Chem. 1981, 20, 2508.
(10) Piper, T. S.; Lemal, D.; Wilkinson G. Naturwissenschaften 1956,
43, 129.
(11) J ung, M. E.; Mossman, A. B.; Lyster, M. A. J . Org. Chem. 1978,
43, 3698.
that neither CH3I nor (CH3)3O+BF4 was an effective
-
trapping reagent for the alkoxide 3 intermediate. The
(4) Gladysz, J . A.; Selover, J . C.; Strouse, C. E. J . Am. Chem. Soc.
1978, 100, 6766.
(5) King, R. B. Acc. Chem. Res. 1970, 3, 417.

Synthesis of Carbene Precursors from Aldehydes
Organometallics, Vol. 17, No. 7, 1998 1335
Sch em e 2
clearly demonstrated that the mechanism shown in eq
7 is not the one in effect for formation of complexes 7.
The isolated yields are slightly higher for the indenyl-
ligated anion than with the Fp anion when using
benzaldehyde and p-anisaldehyde. By using a larger
excess of p-anisaldehyde, the yield of 7c was improved
from 52% to 62%. A major byproduct in the synthesis
of 7c was the dimer [In(CO)2Fe]2.13,15 Minor byproducts
included the silyl complex In(CO)2Fe-SiMe3 and the
pinacol silyl ether [(p-OCH3Ph)CH-(OSiMe3)]2,9b the
latter is thought to be formed by decomposition of the
product 7c.16
method was used by Gladysz to make (CO)5MnCH2(OSi-
(CH3)3) via a proposed SN2 mechanism (eq 6).12 In our
The isolated yield of the acetaldehyde-generated
precursor 7b (31%) from the indenyl-ligated anion was
much lower than that from the Fp anion (70%). The
reason for this lower yield is not yet understood. The
major byproducts of the synthesis of 7b were the dimer
[In(CO)2Fe]2, the silyl complex In(CO)2Fe-SiMe3, and,
interestingly, the hydride complex In(CO)2Fe-H.17
To order to determine the potential synthetic utility
of the (R-siloxyalkyl)iron complexes 4 as precursors in
the generation of electrophilic iron carbene complexes
for cyclopropanation, each was separately treated with
1.1-1.7 equiv of trimethylsilyl triflate at -78 °C in the
presence of 2-4 equiv of an olefin (Scheme 3).
The yields and stereochemistry for the products of
these cyclopropanation reactions are summarized in
Table 1. It is readily apparent from these unoptimized
results that the new precursors 4a ,b,e,g are efficient.
They also exhibit high cis selectivity when reacted with
acyclic alkenes. In addition, precursor 4a shows very
high endo selectivity with cyclopentene. Reaction of
styrene with precursor 4c provided the cis isomer as
the major product, exhibiting higher selectivity (4:1)
than the related R-methoxy complex Cp(CO)2Fe-CH-
(OCH3)(p-OCH3C6H5) with propene (2:1).18 Precursor
4d also provided the only cis isomer with styrene.
Precursor 4h preferred the trans isomer when reacted
with styrene. This is consistent with the related
R-methoxy complex Cp(CO)2Fe-CH(OCH3)(CHdC-
(CH3)2), reported previously.1g
case, we observed no reaction between ClSiMe3 and
benzaldehyde at room temperature or low temperature,
discounting a similar SN2 mechanism. Therefore, the
mechanistic pathways illustrated in eqs 5 and 6 do not
appear to be involved in forming 4.
To expand the scope of our new reaction to related
organometallic nucleophiles, we evaluated the reactivity
of the (η5-indenyl)iron metalate 513 and several alde-
hydes 2 under similar reaction conditions to the Fp
analogues. Treatment with chlorotrimethylsilane cap-
tured the presumed alkoxide intermediate to produce
the indenyl-ligated (R-siloxyalkyl)iron complexes 7
(Scheme 2).
As mentioned previously, we saw no reaction between
the silyl complex containing the η5-C5H5 (Cp) ligand and
aldehydes. However, with the indenyl (In) complexes,
it is well-known that this ligand can undergo η5- to η3-
ring slippage to bind incoming nucleophiles. For this
reason, an alternative mechanism is possible involving
η5- to η3-ring slippage with ligation of the aldehyde
followed by insertion (eq 7). To discount this mecha-
14
nism, In(CO)2Fe-SiMe3 and the aldehydes 2 were
stirred in THF under similar conditions to those used
for formation of the precursors 7. After workup of the
reaction mixtures, no (R-siloxyalkyl)iron complexes were
detected, only starting materials were isolated. This
(15) Hallam, B. F.; Pauson, P. L. J . Chem. Soc. 1958, 646.
(16) The cyclopentadienyl analogue 4c decomposes to the same silyl
pinacol ether, see: Vargas, R.; Hossain, M. M. Tetrahedron Lett. 1993,
34, 2727.
(17) Ahmed, H.; Brown, D. A.; Fitzpatrick, N. J .; Glass, W. K. Inorg.
Chim. Acta 1989, 164, 5.
(12) Brinkman, K. C.; Vaughn, G. D.; Gladysz, J . A. Organometallics
1982, 1, 1056.
(13) Forschner, T. C.; Cutler A. R. Inorg. Chim. Acta 1985, 102, 113.
(14) Pannell, K. H.; Lin, S.-H.; Kapoor, R. N.; Cervantes-Lee, F.;
Pinon, M.; Parkanyi, L. Organometallics 1990, 9, 2454.
(18) Broom, M. B. H. Ph.D. Dissertation, University of North
Carolina, 1982.

1336 Organometallics, Vol. 17, No. 7, 1998
Theys et al.
Sch em e 3
Sch em e 4
Ta ble 1. Cyclop r op a n es fr om P r ecu r sor s 4
Ta ble 2. Cyclop r op a n es fr om P r ecu r sor s 7
precursor
4a (R ) Ph)
olefin
yield (%)
precursor
7a (R ) Ph)
olefin
yield (%)
styrene
68
62
88
72
38
30
81
87
(all cis)a,b
(all endo)a,b
(all cis)a,b
(all cis)b,d
(4:1)a-c
cyclopentene
2-methyl-2-butene
styrene
styrene
61
95
95
64
89
(all cis)a,b
(all endo)a,b
(all cis)a,b
(all cis)b,d
(4:1)a-c
cyclopentene
2-methyl-2-butene
styrene
4b (R ) CH3)
4c (R ) p-OCH3Ph) styrene
7b (R ) CH3)
7c (R ) p-OCH3Ph)
4d (R ) p-ClPh)
styrene
styrene
styrene
(all cis)a,b
(all cis)a,b
(12:1)a,b
styrene
4e (R ) p-CH3Ph)
4g (R ) o-OCH3Ph)
a
b
Isolated, unoptimized yield. Ratios were determined by GC
d
and/or 1H NMR spectroscopy. c cis:trans ratio. Determined by GC
1,1-diphenylethene 61a
with results calibrated against an internal standard.
4h (R ) CHCMe2)
styrene
44
(1:2)a,b,c
a
b
Isolated, unoptimized yield. Ratios were determined by GC
precursor 4c was used. This yield may again be related,
in part, to the longer reaction times used for 7c.
The selectivities for precursors 4a -c and 7a -c were
identical when comparing their counterpart. This was
a little surprising since we anticipated some variation
in the selectivities owing to the greater steric bulk of
the indenyl ligand. Since the indenyldicarbonyliron
dimer is not commercially available, use of the readily
available cyclopentadienyldicarbonyliron dimer would
be more advantageous for preparation of the (R-siloxy-
alkyl)iron precursors and, in turn, for cyclopropanation.
However, unlike the Cp-ligated complexes, the indenyl-
ligated complexes 7a ,c have been shown to undergo
direct carbonylation under mild reaction conditions to
form their acyl analogues.19
and/or 1H NMR spectroscopy. c Cis:trans ratio. Determined by
d
GC with results calibrated against an internal standard.
To order to verify that these complexes could indeed
1
generate the carbene in situ, low-temperature H and
13C NMR studies were undertaken using the (R-siloxy-
benzyl)iron complex 4a as a representative example.
Treatment of complex 4a , at -40 °C in CD2Cl2 with
trimethylsilyl triflate, generated a distinctive peak in
the proton NMR at 16.79 ppm, characteristic of the
carbene Cp(CO)2Fe+dCHPh (8a ). By monitoring this
reaction using 13C NMR under the same conditions, a
peak at 342.4 ppm was detected as an absorption, which
is also characteristic of 8a . The location of these peaks
in the 1H and 13C NMR are in agreement with data
observed for formation of 8a from the (R-methoxybenz-
yl)iron complex Cp(CO)2Fe-CH(OCH3)Ph.1b
Con clu sion
The indenyl-ligated precursors 7 also provided cyclo-
propanes in an efficient and selective manner (Scheme
4 and Table 2). The reaction conditions for 7 were
similar to those conditions outlined for precursors 4,
with the exception that the reaction times were ex-
tended for 7b,c. In comparison to the Cp-ligated
precursor 4a , the phenyl-substituted precursor 7a gave
a slightly lower cyclopropane yield with styrene. On the
other hand, the yields were excellent with both cyclo-
pentene and 2-methyl-2-butene, which are higher, in the
bicyclic case significantly higher, than for precursor 4a .
This may be partly due to the extended reaction times
for precursor 7a . It was discovered later that longer
reaction times gave higher yields for precursors 7. No
extended reaction times were evaluated for precursors
4. For the methyl-substituted precursor 7b, a lower
yield was obtained with styrene than for precursor 4b.
For the p-methoxyphenyl precursor 7c, a significantly
higher yield was obtained with styrene than when
A simple route to the synthesis of secondary electro-
philic iron carbene precursors from readily available
aldehydes and iron metalates has been devised. This
route works well with both saturated and unsaturated
aldehydes. The cyclopentadienyl-ligated anion Cp(CO)2-
Fe- and the indenyl-ligated anion In(CO)2Fe- were
nucleophilically added to aldehydes in an efficient
manner. The (R-siloxyalkyl)iron complexes produced,
upon treatment with chlorotrimethylsilane, were found
to be effective starting materials for in situ generation
of carbene complexes, which generally produced cyclo-
propanes in a stereoselective fashion in high yields.
Future work on this project will focus on extension of
this method to other metalates. In addition, application
of these reactions to asymmetric synthesis of cyclopro-
panes is in progress.20
(19) Theys, R. D.; Hossain, M. M. Organometallics 1994, 13, 866.
(20) Theys, R. D.; Hossain, M. M. Tetrahedron Lett. 1995, 36, 5113.

Synthesis of Carbene Precursors from Aldehydes
Organometallics, Vol. 17, No. 7, 1998 1337
1 h at -78 °C, after which 1.2-3 mmol of chlorotrimethylsilane
was added and stirred for an additional 1 h at -78 °C. The
solvent was removed under reduced pressure, and the residue
was dissolved in a small amount of THF for transfer to a water-
jacketed chromatography column containing silica gel (40-
140 mesh) in pentane. 4b was eluted with pentane in 70%
yield as a reddish-brown oil containing 10% of the iron silyl
complex Fp-SiMe3.10 For 4a , initial elution with pentane gave
5% Fp-SiMe3 and subsequent elution with a 5% THF/pentane
mixture gave 4a in 78% yield as a yellow-brown oil. The
following spectral characteristics were obtained. 4a : 1H NMR
(CDCl3, 250 MHz) δ 7.19 (m, 5H, Ph), 6.56 (s, 1H, FeCH), 4.50
(s, 5H, C5H5), 0.00 (s, 9H, Si(CH3)3); 13C NMR (CDCl3, 62.9
MHz) δ 217.4 (CO), 155.9 (Cipso), 127.6, 123.8, 123.2 (Ph), 87.0
(C5H5), 86.0 (FeCH), 0.0 (Si(CH3)3); IR (CH2Cl2) νCO 1948, 2004
cm-1; MS(EI) 357 (M)+ (not observed), 240, 212, 179, 149, 121.
Anal. Calcd for FeC17H20O3Si: C, 57.17; H, 5.60. Found: C,
57.48; H, 5.49. 4b: 1H NMR (CDCl3, 250 MHz) δ 5.66 (q, 1H,
J ) 6 Hz, FeCH), 4.71 (s, 5H, C5H5), 1.66 (d, 3H, J ) 6 Hz,
CH3), 0.07 (s, 9H, Si(CH3)3); 13C NMR (CDCl3, 62.9 MHz) δ
217.8, 216.9 (CO), 86.2 (C5H5), 81.7 (FeCH), 35.9 (CH3), 0.2
(Si(CH3)3); IR (CH2Cl2) νCO 1944, 2000 cm-1. CH analysis was
attempted, but the precursor was too air-sensitive to analyze
in this fashion.
Exp er im en ta l Section
Gen er a l In for m a tion . All reactions and manipulations
of transition metal complexes were performed under a dry
nitrogen atmosphere using standard Schlenk line and/or
drybox techniques. All glassware required for the above was
either flamed under vacuum or dried in an oven prior to use.
Tetrahydrofuran (Baker, reagent grade) and diethyl ether
(EM Science, reagent grade) were freshly distilled under a
nitrogen atmosphere from sodium benzophenone ketyl. Dichlo-
romethane (Baker, HPLC grade) was distilled under nitrogen
from phosphorus pentoxide. Pentane (technical grade) was
purified by sequential stirring overnight with concentrated
sulfuric acid, washing with water, drying over Na2SO4 (anhy-
drous), distilling, and redistilling prior to use from sodium
under nitrogen.
The aromatic aldehydes (benzaldehyde, p-anisaldehyde,
p-chlorobenzaldehyde, p-tolualdehyde, and trifluoro-p-tolual-
dehyde) were sequentially extracted with saturated sodium
bicarbonate, washed with water, stored over MgSO4 (anhy-
drous), and freshly distilled under vacuum. Acetaldehyde was
stirred twice over NaHCO3, dried with CaSO4 (anhydrous), and
then distilled at atmospheric pressure. 3-Methyl-2-butenal
was dried over anhydrous CaSO4 and distilled twice under
vacuum with the receiver flask cooled to -78 °C. o-Anisalde-
hyde (Lancaster) was used without purification. Chlorotrim-
ethylsilane was distilled at atmospheric pressure and then
stored in a desiccator. Indenyliron dicarbonyl dimer was
synthesized according to the literature procedure.13 Cyclo-
pentadienyliron dicarbonyl dimer, styrene, cyclopentene, and
2-methyl-2-butene were obtained from Aldrich Chemical Co.
and used without further purification unless stated otherwise.
Trimethylsilyl triflate (CF3SO3SiMe3) was obtained from Lan-
caster and used without treatment. Chlorotrimethylsilane and
all of the aldehydes were obtained from Aldrich Chemical Co.
Deuterated chloroform (Isotec) was refluxed over phosphorus
pentoxide, degassed several times with liquid nitrogen, dis-
tilled under vacuum from P2O5 using a Schlenk flask and
stored under nitrogen.
1H and 13C spectra were obtained in CDCl3 on a Bruker 250
and 62.9 MHz NMR spectrometer, respectively. Chemical
shifts for the 1H NMR spectra were determined by utilizing
residual CHCl3 (δ 7.24) as an internal reference. 13C NMR
resonances were measured from CDCl3 (77.0 ppm). Infrared
spectra were recorded using a Nicolet MX-1 FTIR spectrom-
eter. Mass spectra were determined on a Hewlett-Packard
5985B (H/P) GC/MS system, operated in DIP (direct insertion
probe) EI-70 eV, and HR-MS were determined on a GC/MS
VG-AUTOSPEC-3000. For the CH microanalyses, a Perkin-
Elmer 240c elemental analyzer was employed. A Varian
Aerograph GC Series 1700 with a 3% SE-30 column (6 ft ×
1/4 in.) or a Varian Aerograph GC Series 1200 with a 5% SE-
52, 80/100 A/W column (8 ft × 1/8 in.) was used to analyze
the isomeric purity of the cyclopropanes generated from the
Cp-ligated complexes 4. A Hewlett-Packard 5880A GC with
a cross-linked 5% PhMe silicone high-performance capillary
column was used to analyze for the isomeric purity of the
cyclopropanes generated from the indenyl-ligated complexes
7.
Cp (CO)2F e-CH(OSiMe3)R, 4a ,b (R ) P h , CH3). Gen -
er a l P r oced u r e. A 0.6-1.5 mmol sample of iron dimer [Cp-
(CO)2Fe]2 was dissolved in 20-50 mL of degassed THF and
added to 6-12 mmol of sodium metal in a 1% Na-Hg amalgam
at 0 °C.21 After addition, the mixture was warmed to room
temperature and stirred for 1 h. The Fp anion which formed
was transferred to another flask using a filter stick. The Fp
anion solution was cooled to -78 °C, and 1.2-12 mmol of the
aldehyde was added dropwise. This mixture was stirred for
Cp (CO)2F e-CH(OSiMe3)R, 4c-g (R ) p-OCH3P h , p-
ClP h , p-CH3P h , p-CF 3P h , o-OCH3P h ). Gen er a l P r oce-
d u r e. A 1.0-1.6 mmol sample of FpK22 was dissolved in 25-
50 mL of THF and cooled to -78 °C, and 0.5 (R ) p-ClPh,
p-CH3Ph) to 4.8 mmol of aldehyde was added dropwise. After
the reaction mixture was stirred for 1-3 h at -78 °C, 0.5-1.6
mmol of chlorotrimethylsilane was added. Stirring was con-
tinued for 1 h, and the temperature was maintained at -78
°C. The solvent was removed under reduced pressure, and
separation with a water-jacketed column was achieved on
silica gel (40-140 mesh) using a 2-5% THF/pentane mixture
(4d ) or a 2% ether/pentane mixture (4e). 4d (79%) was
isolated as yellow crystals and 4e (68%) as a cream-colored
solid. For complexes 4c, 4f, and 4g separation was achieved
on neutral Al2O3 (activity 2) using a 2% THF/pentane mixture.
Isolation of 4c (57%) as a cream-colored solid, 4f (42%) as
yellow crystals, and 4g (79%) as an orange viscose oil resulted.
The following spectral characteristics were obtained. 4c: 1H
NMR (CDCl3, 250 MHz) δ 7.14 (d, 2H, J ) 9 Hz, Ph), 6.73 (d,
2H, J ) 9 Hz, Ph), 6.58 (s, 1H, FeCH), 4.50 (s, 5H, C5H5), 3.77
(s, 3H, OCH3), -0.01 (s, 9H, Si(CH3)3); IR (CH2Cl2) νCO 1945,
2002 cm-1; MS(EI) 386 (M)+ (not observed), 209, 177, 149, 121.
Anal. Calcd for FeC18H22O4Si: C, 55.96; H, 5.74. Found: C,
55.74; H, 5.45. 4d : 1H NMR (CDCl3, 250 MHz) δ 7.13 (s, 4H,
Ph), 6.50 (s, 1H, FeCH), 4.51 (s, 5H, C5H5), 0.00 (s, 9H,
Si(CH3)3); IR (CH2Cl2) νCO 1948, 2006 cm-1. Anal. Calcd for
FeC17H19O3SiCl: C, 52.26; H, 4.90. Found: C, 52.57; H, 4.84.
4e: 1H NMR (CDCl3, 250 MHz) δ 7.01 (m, 4H, Ph), 6.57 (s,
1H, FeCH), 4.50 (s, 5H, C5H5), 2.25 (s, 3H, CH3), 0.00 (s, 9H,
Si(CH3)3); IR (CH2Cl2) νCO 1946, 2003 cm-1. Anal. Calcd for
FeC18H22O3Si: C, 58.38; H, 5.99. Found: C, 58.77; H, 6.08.
4f: 1H NMR (CDCl3, 250 MHz) δ 7.44 (d, 2H, J ) 8 Hz, Ph),
7.30 (d, 2H, J ) 8 Hz, Ph), 6.54 (s, 1H, FeCH), 4.54 (s, 5H,
C5H5), 0.03 (s, 9H, Si(CH3)3); 13C NMR (CDCl3, 62.9 MHz) δ
216.6 (CO), 160.1 (Cipso), 123.0, 124.7, 127.7 (Ph), 102.7 (CF3),
87.0 (C5H5), 69.0 (FeCH), 0.0 (Si(CH3)3); IR (CH2Cl2) νCO 1951,
2007 cm-1. 4g: 1H NMR (CDCl3, 250 MHz) δ 7.52 (d, 1H, J )
7 Hz, Ph), 7.01 (t, 1H, J ) 7 Hz, Ph), 6.89 (t, 1H, J ) 7 Hz,
Ph), 6.76 (s, 1H, FeCH), 6.69 (d, 1H, J ) 7 Hz, Ph), 4.60 (s,
5H, C5H5), 3.80 (s, 3H, OCH3), 0.00 (s, 9H, Si(CH3)3); 13C NMR
(CDCl3, 62.9 MHz) δ 216.7, 215.5 (CO), 150.7 (Cipso), 144.5,
125.7, 124.5, 120.4, 109.1 (Ph), 86.4 (Cp), 62.9 (FeCH), 54.5
(OCH3), 0.0 (Si(CH3)3); IR (CH2Cl2) νCO 1943, 1999 cm-1. We
are unable to obtain analytically pure samples of 4f and 4g
for acceptable CH analysis.
Cp (CO)2F e-CH(OSiMe3)(CHdC(CH3)2), 4h . Sp ecific
P r oced u r e. To a solution of 1.4 mmol of FpK in 20 mL of
(21) Piper, T. S.; Wilkinson, G. J . Inorg. Nucl. Chem. 1956, 3, 104.
(22) Plotkin, J . S.; Shore, S. G. Inorg. Chem. 1981, 20, 284.

1338 Organometallics, Vol. 17, No. 7, 1998
Theys et al.
THF at -78 °C, 4.1 mmol of 3-methyl-2-butenal in 10 mL of
THF was added dropwise. After 1 h of stirring at -78 °C, 1.4
mmol of chlorotrimethylsilane was added. Stirring was con-
tinued for an additional 1 h at -78 °C. Due to the thermal
instability of this complex, it was not purified by column
chromatography. Instead, the solvent was removed under
reduced pressure and quickly cooled to -78 °C. Complex 4h
was isolated in 63% yield as a reddish-brown oil after extrac-
tion of the crude reaction mixture with pentane at -78 °C and
subsequent removal of the solvent under reduced pressure. The
isolated complex 4h contained small impurities of Fp dimer
and starting aldehyde. 4h : 1H NMR (CDCl3, 250 MHz, -40
°C) δ 6.35 (d, 1H, J ) 10 Hz, FeCH), 5.69 (d, 1H, J ) 10 Hz,
CCHdC), 4.68 (s, 5H, C5H5), 1.60 (s, 3H, CH3), 1.55 (s, 3H,
CH3) 0.01 (s, 9H, Si(CH3)3); 13C NMR (CDCl3, 62.9 MHz, -40
°C) δ 216.8 (CO), 118.2, 139.1 (CHdC), 86.1 (C5H5), 66.9
(FeCH), 25.6 (CH3), 18.2 (CH3), 0.1 (Si(CH3)3); IR (CH2Cl2) νCO
on the perceived stability of the generated carbene. The
solution was stirred for 10 min with complexes 4a ,c,7a and
for 1 h with complexes 4d ,e, all at -78 °C. The solution was
stirred for 1 h at -78 °C and then warmed to room temper-
ature over 0.5 h for complex 7c. Sixty-seventy milliliters of
pentane was added to precipitate all of the iron salts. Neu-
tralization of the decanted liquid by a saturated NaHCO3
solution, separation, and passing of the neutralized organic
layer through a short column of neutral alumina (activity 1
or 3) gave a colorless liquid. The eluant was dried over MgSO4
(anhydrous) or used as is for distillation. The solvent was
removed by simple distillation under atmospheric pressure or
by rotary evaporation (7c) under reduced pressure. In most
cases, this mixture was directly analyzed by 1H NMR to
determine the isomeric (cis/trans or endo/exo) ratios or by gas
chromatography. cis-1,2-Diphenylcyclopropane,23 endo-6-
phenylbicyclo[3.1.0]hexane,23 and cis-1,3,-trimethyl-2-phenyl-
cyclopropane23 generated from 4a or 7a and the corresponding
alkenes were isolated by Kugelrohr distillation or by column
chromatography on silica or alumina (activity III). cis- and
trans-1-(p-methoxyphenyl)-2-phenylcyclopropanes24 generated
from 4c or from 7c and styrene were isolated by Kugelrohr
distillation or by column chromatography on alumina (activity
III). cis-1-(p-Methylphenyl)-2-phenylcyclopropane25 and cis-
1-(p-chlorophenyl)-2-phenylcyclopropane25 generated from sty-
rene and 4d and 4e, respectively, were isolated by Kugelrohr
distillation. The yields and isomeric ratios are listed in Tables
1 and 2.
Cyclop r op a n a tion s fr om Com p lexes 4b a n d 7b. Gen -
er a l P r oced u r e. Due to the air sensitivity of these precur-
sors, the cyclopropanation reactions were carried out imme-
diately after purification. A 0.15-0.27 mmol (1 equiv) sample
of the precursor was dissolved in 4-8 mL of CH2Cl2, and 0.34-
0.54 mmol (ca. 2 equiv) of styrene was added. The solution
was cooled to -78 °C, and 0.16-0.33 mmol (ca. 1.1 equiv) of
trimethylsilyl triflate was introduced. The color of the solution
immediately changed from yellow-orange to purple. With
complex 4b, this mixture was stirred for 10 min at -78 °C
and an internal standard (dodecane) added. With complex 7b,
the reaction mixture was stirred for 0.5 h at -78 °C and
n-decane added as an internal standard. Subsequently, 50-
60 mL of pentane was added, the decanted solution neutralized
with saturated NaHCO3 in water solution and the organic
layer passed through a short column of neutral alumina
(activity 1). Gas chromatographic analysis and comparison
with an authentic sample indicated that only cis-1-methyl-2-
phenylcyclopropane23 was produced in 72% and 68% yields
from 4b and 7b, respectively.
1945, 2012 cm-1
.
In (CO)2F e-CH (OSiMe3)R , 7a -c, (RdP h , CH3, p -O-
CH3P h . Gen er a l P r oced u r e. A 0.25-0.45 mmol sample of
13
iron dimer [In(CO)2Fe]2 was dissolved in 20-45 mL of THF.
This solution was degassed and added to 2.0-6.0 mmol of
sodium metal in a 1% Na-Hg amalgam at room temperature.
This mixture was stirred for 2-3 h, cooled to -78 °C,
transferred via cannula to another sidearm flask, and cooled
to -78 °C, and 0.50-2.0 mmol (for R ) Ph, p-OCH3Ph, 1 equiv,
for R ) CH3, all 4 equiv added at one time) of aldehyde was
added. The reaction mixture was allowed to stir for 1 h (2 h
for R ) CH3) at -78 °C, then an additional 1.5-3.0 mmol of
aldehyde was added and stirring was continued for 2 h more
at -78 °C. A 0.60-1.0 mmol amount of chlorotrimethylsilane
was added dropwise over 5 min and allowed to stir for an
additional 1 h. The solvent was removed under reduced
pressure, and the product was separated with a water-jacketed
chromatography column on neutral Al2O3 (activity 3) using a
1-2% CH2Cl2/pentane mixture for 7a ,c or pentane for 7b.
Isolation of 7a (99%), 7b (31%), and 7c (52%) as orange oils
was achieved. The following spectral characteristic were
obtained. 7a : 1H NMR (CDCl3, 250 MHz) δ 7.04-7.26 (m,
9H, In and Ph), 6.30 (s, 1H, Fe-CH), 5.25 (br s, 1H, In, H1 or
H3), 4.90 (br s, 1H, In, H3 or H1), 4.84 (t, 1H, J ) 3 Hz, In, H2),
0.02 (s, 9H, Si(CH3)3); 13C NMR (CDCl3, 62.9 MHz) δ 216.5,
216.8 (CO), 154.8 (Cipso), 123.2, 124.0, 124.1, 124.4, 126.0,
126.3, 127.6 (In, benzo C’s and Ph), 105.9 (In, C2), 104.0, 105.4
(In, C3a,7a), 73.7, 74.0 (In, C1,3), 70.2 (Fe-CH), 0.0 (Si(CH3)3);
IR (CH2Cl2) νCO 1999, 1942 cm-1. 7b: 1H NMR (CDCl3, 250
MHz) δ 7.39 (m, 2H, In, benzo), 7.08 (m, 2H, In, benzo), 5.40
(br s, 1H, In, H1 or H3), 5.31 (br s, 1H, In, H3 or H1), 5.14 (q,
1H, J ) 6 Hz, Fe-CH), 4.90 (t, 1H, J ) 3 Hz, In, H2), 1.59 (d,
3H, J ) 6 Hz, Fe-C-CH3), 0.06 (s, 9H, Si(CH3)3); 13C NMR
(CDCl3, 62.9 MHz): δ 216.3, 217.4 (CO), 123.9, 124.4, 125.9,
126.2 (In, benzo C’s), 105.1, 106.3 (In, C3a,7a), 101.9 (In, C2),
72.8, 73.2 (In, C1,3), 70.6 (Fe-CH), 35.3 (Fe-C-CH3), 0.2
(Si(CH3)3); IR (CH2Cl2): νCO 1999, 1938 cm-1. 7c: 1H NMR
(CDCl3, 250 MHz) δ 7.32 (m, 2H, In, benzo), 7.16 (d, J ) 9 Hz,
2H, Ph), 7.04 (m, 2H, In, benzo), 6.76 (d, J ) 9 Hz, 2H, Ph),
6.32 (s, 1H, FeCH), 5.25 (br s, 1H, In, H1 or H3), 4.97 (br s,
1H, In, H3 or H1), 4.80 (t, J ) 3 Hz, 1H, In, H2), 3.79 (s, 3H,
OCH3), 0.01 (s, 9H, Si(CH3)3); 13C NMR (CDCl3, 62.9 MHz) δ
216.6, 216.9 (CO), 156.0 (Cipso), 147.2 (Cpara), 112.7, 123.9,
124.3, 125.9, 126.1 (In, benzo C’s and Ph), 106.1 (In, C2), 105.5,
104.3 (In, C3a,7a), 73.6, 73.9 (In, C1,3), 70.2 (Fe-CH), 55.1
Cyclop r op a n a tion fr om Com p lex 4g. The cyclopropant-
ion reaction was carried out in the similar manner as previ-
ously described for complex 4c. An 87% yield of a 12:1 cis:
trans ratio of 1-(o-methoxyphenyl)-2-phenylcyclopropane was
prepared from complex 4c and styrene. These cyclopropanes
were characterized by spectroscopic methods. cis-1-(o-Meth-
oxyphenyl)-2-phenylcyclopropane: 1H NMR (CDCl3, 250 MHz)
δ 7.02-6.86 (m, Ph), 6.71 (t, 1H, J ) 7.8 Hz, Ph), 6.62 (d, 1H,
J ) 8.1 Hz, Ph), 3.61 (s, 3H, OCH3), 2.48 (t, 2H, J ) 7.4 Hz,
CH), 1.39 (t, 2H, J ) 7.4 Hz, CH2); 13C NMR (CDCl3, 62.9 MHz)
δ 159.0, 139.1, 129.4, 128.2, 127.2, 127.0, 126.8, 125.2, 119.8,
110.0, (Ph), 55.3 (OCH3), 23.4, 20.4 (CH), 10.1 (CH2). Anal.
Calcd for C16H16O: C, 85.68; H, 7.19. Found: C, 86.00; H, 7.11.
trans-1-(o-Methoxyphenyl)-2-phenylcyclopropane: 1H NMR
(CDCl3, 250 MHz) δ 7.33-7.14 (m, 7H, Ph), 7.05 (t, 1H, J )
7.8 Hz, Ph), 6.62 (d, 1H, J ) 8.1 Hz, Ph), 3.61 (s, 3H, OCH3),
2.14 (m, 2H, CH), 1.34-1.47 (m, 2H, CH2); 13C NMR (CDCl3,
62.9 MHz) δ 158.3, 143.0, 128.2, 127.4, 126.6, 126.2, 125.6,
(OCH3), 0.0 (Si(CH3)3); IR (CH2Cl2) νCO 1998, 1940 cm-1
.
Cyclop r op a n a tion s fr om Com p lexes 4a -e a n d 7a ,c.
Gen er a l P r oced u r e. A 0.15-1.5 mmol (1 equiv) sample of
the precursor was dissolved in 4-10 mL of CH2Cl2 and 0.3-
3.0 mmol (2 equiv) of the alkene added. The solution was
cooled to -78 °C, and 0.21-1.6 mmol (1.1 equiv) of trimeth-
ylsilyl triflate was introduced. In general, the color of the
reaction mixture changed from yellow-orange to purple. The
solution was then stirred for varied amounts of time depending
(23) Casey, C. P.; Polichnowski, S. W.; Shusterman, A. J .; J ones, C.
R. J . Am. Chem. Soc. 1979, 101, 7282.
(24) Hixson, S. S.; Garrett, D. W. J . Am. Chem. Soc. 1974, 96, 4872.
(25) Hoffmann, J . M.; Graham, K. J .; Rowell, Ch. F. J . Org. Chem.
1975, 40, 3005.

Synthesis of Carbene Precursors from Aldehydes
Organometallics, Vol. 17, No. 7, 1998 1339
125.2, 120.5, 110.5 (Ph), 55.5 (OCH3), 26.5, 21.6 (CH), 16.9
(CH2). HR-MS calcd for C16H16O 224.120115, found 224.124643.
A white solid sample of 1-(o-methoxyphenyl)-2,2-diphenylcy-
clopropane in 61% yield was also prepared from complex 4g
and 1,1-diphenylethene and characterized by the following
spectroscopic methods: 1H NMR (CDCl3, 250 MHz) δ 7.55-
6.64 (m, 14H, Ph), 3.91 (s, 3H, OCH3), 3.06 (m, 1H, CH), 2.03
(m, 1H, CH2), 1.58 (m, 1H, CH2); 13C NMR (CDCl3, 62.9 MHz)
δ 158.9, 147.5, 141.4, 129.9, 128.7, 128.2, 127.7, 127.3, 127.2,
126.9, 125.9, 125.7, 119.9, 109.7 (Ph), 55.30 (OCH3), 38.3
(CPh2), 26.3 (CH), 17.8 (CH2). Anal. Calcd for C22H20O: C,
87.96; H, 6.71. Found: C, 87.92; H, 6.62.
Cyclop r op a n a tion fr om Com p lex 4h . Sp ecific P r oce-
d u r e. Due to the instability of precursor 4h , the cyclopropa-
nation reaction was carried out immediately after purification.
A 1.25 mmol (1 equiv) sample of 4h was dissolved in 5 mL of
CH2Cl2, cooled to -60 °C, and treated with 6.0 mmol (ca. 5
equiv) of styrene. To this solution, 2.2 mmol (ca. 1.5 equiv) of
trimethylsilyl triflate was added. An immediate change in
color from reddish-yellow to reddish-orange occurred. The
reaction was stirred for 30 min at -60 °C, and the solvent
was removed under reduced pressure. The resulting reddish
oil was cooled to -60 °C, and a solution of 2.0 mmol of NaI in
5 mL of acetone was transferred to the oil. Stirring was
continued for 20 min at room temperature, and the acetone
was removed by rotary evaporation. Pentane was then added
to the residue and transferred to a saturated NaHCO3 solution.
The neutralized mixture was dried over anhydrous Na2SO4
and filtered through a small plug of sea sand. The solvent
was removed by rotary evaporation, and the crude product was
eluted from a silica gel column with a 1-5% mixture of ethyl
acetate in pentane.
1-Phenyl-2-(2-methyl-1-propenyl)cyclopropane1i,26 was ob-
tained in an isolated yield of 44%. This mixture was analyzed
by both 1H NMR and gas chromatography (column tempera-
ture 140 °C; Rt (cis) 4.35 min, Rt (trans) 5.15 min). A 1:2 cis:
trans ratio of isomers was indicated.
Ack n ow led gm en t is made to the donors of the
Petroleum Research Fund, administered by the Ameri-
can Chemical Society, for partial support of this re-
search. We also thank Frank Laib and Keith Krumnow
for their technical assistance.
OM970698Y
(26) Kuo, G. H.; Helquist, P.; Kerber, R. C. Organometallics 1984,
3, 806.