Dirhodium(II) tetrakis(perfluoroalkylbenzoates) as partially recyclable catalysts for carbene transfer reactions with diazoacetates

Article abstract of DOI:10.1016/S0040-4020(02)00249-1

Three highly fluorinated dirhodium(II) tetrakis(benzoates), [Rh₂(O₂CR_F)₄, R_F=C₆H₄-4-C₆F₁₃ (3) and C₆H₃-3,5-di(C_nF_2n+1) (n=6: 4; n=8: 5)], have been prepared and characterized. Only 4 and 5 are suited for applications in fluorous synthesis due to their excellent solubility in fluorous solvents. They were found to catalyze the following carbenoid reactions of diazo compounds in the fluorous solvents 1,1,2-trichloro-1,2,2-trifluoroethane and perfluoro(methylcyclohexane): cyclopropanation of styrenes using methyl diazoacetate, intermolecular carbene C-H insertion into hexane with methyl diazoacetate, and intramolecular aromatic C-H insertion of an α-diazo-β-ketoester. Except for the second reaction type, the catalyst could be recovered to a high extent by a liquid-liquid extraction (fluorous solvent - dichloromethane) due to its preference for the fluorous solvent. For the cyclopropanation reactions, the recovered catalyst was used in four subsequent reaction/workup cycles without significant loss of activity. In contrast, the catalyst could not be recovered from the carbenoid C-H insertion reaction with hexane; apparently, some by-products of this sluggish reaction, such as carbene dimers and oligomers, caused the deactivation or destruction of the catalyst.

Full text of DOI:10.1016/S0040-4020(02)00249-1

TETRAHEDRON
Pergamon
Tetrahedron 58 %2002) 3999±4005
Dirhodium II) tetrakis per¯uoroalkylbenzoates) as partially
recyclable catalysts for carbene transfer reactions
with diazoacetates
Andreas Endres and Gerhard Maasp
È
Abteilung Organische Chemie I, Universitat Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
Received 9 November 2001; revised 22 December 2001; accepted 16 January 2002
AbstractÐThree highly ¯uorinated dirhodium%II) tetrakis%benzoates), [Rh2%O2CRF)4, RFˆC6H4-4-C6F13 %3) and C6H3-3,5-di%CnF2n11
)
%nˆ6: 4; nˆ8: 5)], have been prepared and characterized. Only 4 and 5 are suited for applications in ¯uorous synthesis due to their excellent
solubility in ¯uorous solvents. They were found to catalyze the following carbenoid reactions of diazo compounds in the ¯uorous solvents
1,1,2-trichloro-1,2,2-tri¯uoroethane and per¯uoro%methylcyclohexane): cyclopropanation of styrenes using methyl diazoacetate, inter-
molecular carbene C±H insertion into hexane with methyl diazoacetate, and intramolecular aromatic C±H insertion of an a-diazo-b-
ketoester. Except for the second reaction type, the catalyst could be recovered to a high extent by a liquid±liquid extraction %¯uorous
solventÐdichloromethane) due to its preference for the ¯uorous solvent. For the cyclopropanation reactions, the recovered catalyst was used
in four subsequent reaction/workup cycles without signi®cant loss of activity. In contrast, the catalyst could not be recovered from the
carbenoid C±H insertion reaction with hexane; apparently, some by-products of this sluggish reaction, such as carbene dimers and oligomers,
caused the deactivation or destruction of the catalyst. q 2002 Elsevier Science Ltd. All rights reserved.
1.Introduction
ideal catalyst for ¯uorous phase technology should have a
good absolute solubility in a ¯uorous solvent, should display
in ¯uorous±organic biphasic mixtures a high partition
coef®cient in favor of the ¯uorous solvent, and it should
not form adducts with organic components of the reaction
mixture so that the solubility in an organic solvent would
increase. Some empirical rules5h,6 can be observed in the
catalyst design in order to meet the ®rst two postulates
%e.g. a ¯uorine content of ca. 60%, appropriate length,
number, and spatial arrangement of per¯uoroalkyl chains).
Aspects of catalyst deactivation and reactivity are related to
the electronic situation at the catalytically active metal
center, and it may be necessary to place a spacer between
the metal and the strongly electron-withdrawing per¯uoro-
alkyl substituents by introducing a spacer between them and
the metal center.5b±g,7
Dinuclear rhodium%II) tetracarboxylates and amidates are
highly versatile catalysts for several effective transforma-
tions which involve carbene transfer from diazo compounds
to appropriate substrates.1,2 Although it was shown in a few
cases that 0.1 mol% and less of the catalyst are suf®cient
for high-yielding carbenoid reactions,3 the typical catalyst
loadings are 1±3 mol%. Taking into account the costs of
rhodium and its compounds, it could be desirable, at least
for reactions at a larger scale, to recover the catalyst from
the reaction mixture and to use it again. This can be
achieved by attaching the rhodium catalyst to a polymeric
support.4 Another approach is located in the emerging ®eld
of ¯uorous phase chemistry introduced by Horvath and
Â
5
Rabai in 1994. This technique takes advantage of the
preferred solubility of highly ¯uorinated molecules in
per¯uorinated %`¯uorous') solvents and of the temperature-
dependent miscibility of ¯uorous and common organic
solvents. In one of the applications of this concept, `¯uorous
biphase catalysis', it has been shown for several important
chemical transformations involving homogeneous catalysis
that catalysts with ¯uorous labels perform well and can be
recovered and reused.5c,d
In a preliminary communication,8 we have reported the use
of dinuclear rhodium%II) per¯uorooctanoate %1, Scheme 1)
and rhodium%II) 4-%per¯uorhexyl)benzoate %3) for the cyclo-
propanation of various alkenes. Both catalysts could be
recycled and reused several times without signi®cant drop
in the yields of cyclopropanes, but the less electrophilic
catalyst 3 gave distinctly higher yields. In another study,9
we pepared several highly ¯uorinated dirhodium%II)
tetrakis%alkanecarboxylates) [Rh2%OOCRF)4 RFˆCH2C6F13
%2), CH2CH2C6F13, CH2CH2C8F17, CH2CH2C10F21,
CH2OCH2CH2C10F21] and found that two CH2 groups
were necessary for complete electronic separation of
the per¯uoroalkyl chain from the rhodium centers.
Under the aspects of effectiveness and ease of recovery, the
Keywords: rhodium and compounds; ¯uorous synthesis; diazo compounds.
Corresponding author. Tel.: 149-731-5022790; fax: 149-731-5022803;
e-mail: gerhard.maas@chemie.uni-ulm.de
p
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020%02)00249-1

4000
A. Endres, G. Maas / Tetrahedron 58 )2002) 3999±4005
Scheme 1.
Unfortunately, however, all complexes with more than one
methylene spacer were insoluble in per¯uoro%methylcyclo-
hexane) %PFMC), in spite of their high ¯uorine content
%55.8±62.1%), and therefore not applicable for ¯uorous
biphase catalysis. The PFMC-soluble catalysts 1 and 2
performed fairly well in the carbenoid C±H insertion into
hexane with methyl diazoacetate %ca. 40% combined yield
of insertion products), a notoriously dif®cult reaction, but
only a minor fraction of the catalyst could be recovered by
extraction into PFMC after one reaction cycle. We reasoned
that the deterioration of 1 and 2 was related to their
enhanced electrophilicity as compared to Rh2%OAc)4, the
parent catalyst in rhodium carbenoid chemistry. We decided
to take rhodium benzoate complex 3 as a lead for the
development of ¯uorous rhodium catalysts which more
closely meet the criteria described above. In this paper,
we look at properties and performance of the two novel
¯uorous rhodium%II) benzoates 4 and 5.
Scheme 3.6a ˆ4-F13C6±C6H4COOH.
in Scheme 2. The latter compound was prepared on a
novel route from 3,5-diaminobenzoic acid by a Sandmeyer
reaction and converted into ester 8. Copper-mediated
coupling of 8 with the appropriate per¯uoroalkyl iodide,
using a known procedure,11 gave the ¯uorous esters 9 and
10, respectively, which were converted into the required
acids 6b and 6c.
The ¯uorous rhodium%II) benzoates were prepared by two
established procedures %Scheme 3). Complex 3 was
obtained from Rh2%OAc)4 and acid 6a by exchange of the
carboxylate ligands %method A) in boiling toluene and with
azeotropic removal of the liberated acetic acid. Using
method B,12 complexes 3±5 were obtained in moderate
yields from the sodium salts of 6a±c and rhodium%III)
chloride hydrate in ethanol. In the cases of 4 and 5, the
concomitant formation of some elemental rhodium was
observed which explains at least in part the incomplete
formation of the complexes. Separation of 4 and 5 from
most of the unreacted RFCO2Na was achieved by a simple
biphasic extraction with PFMC/THF which delivered the
complexes in the ¯uorous phase %97% purity according to
1H NMR) and the more polar sodium carboxylates in the
organic phase.
2.Results and discussion
2.1. Preparation and properties of complexes 3±5
The synthesis of rhodium complexes 3±5 requires the
%per¯uoroalkyl)benzoic acids 6a±c. 4-%Per¯uorohexyl)-
benzoic acid %6a) was prepared according to a published
procedure,10 the 3,5-bis%per¯uoroalkyl)benzoic acids 6b,c
were obtained from 3,5-diiodobenzoic acid %7) as shown
The IR and NMR spectra %1H and 13C) con®rmed the
absence of starting materials %Rh2%OAc)4, carboxylic
acids) from products 3±5. In addition, 3 and 4 were
characterized by laser desorption time-of-¯ight mass
spectrometry %positive ion mode). In both cases, the
molecular ion peak was observed; complex 4 gave
additional peaks corresponding to the successive loss of
C6F13 fragments. The IR spectra of the complexes %Table
1) exhibit three characteristic absorptions in the ranges
1564±1587, 1408±1412, and 1118±1242 cm21, corre-
sponding to the antisymmetric and symmetric stretching
Table 1. Characteristic IR absorptions of rhodium carboxylate complexes
Complex Rh2%OOCR)4
Rˆ
IR %KBr, cm21
)
n%CO)asym n%CO)sym
n%CF)
3
4
5
OOCC6H4-4-C6F13
1564
1588
1587
1551
1577
1409
1412
1408
1399
1413
1146/1203/1242
1146/1203/1242
1118/1209/1238
OOCC6H3-3,5-C6F13
OOCC6H3-3,5-C8F17
OOCPh
Scheme 2. %i) %1) NaNO2, H2SO4; %2) KI; 82%; %ii) %MeO)2SO2, K2CO3,
acetone; 82%; %iii) CnF2n11, Cu powder, DMSO, 120±1258C; 54/56%;
%iv) MeOH, KOH, H2O; 82/79%.
±
±
OOCCH3

A. Endres, G. Maas / Tetrahedron 58 )2002) 3999±4005
4001
Scheme 4.
Table 2. Cyclopropanation of styrenes with methyl diazoacetate; see Scheme 4
Alkene
Catalyst
Yield of cyclopropane 11 %%, upper line) E/Z ratio %lower line)
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
Styrene
3a,b
4c
71
70
70
71
1.43
70.0
0.99
76.4
0.88
1.44
68.1
0.97
75.9
0.85
1.44
67.6
0.99
76.1
0.88
1.46
66.8
0.89
75.6
0.87
67.4
1.04
75.1
0.86
5c
a-Methyl-styrene
3a,b
4c
83
79
76
76
1.04
71.8
1.05
1.00
69.9
1.00
1.11
67.0
1.04
1.11
65.7
1.04
65.0
1.03
Yields and diastereomer ratios were determined by GC.
Ref. 8.
a
b
Solvent CH2Cl2.
Solvent FC-113.
c
modes of the carboxylate ligands12 and the C±F stretching
vibrations. The nasym%OOCR) vibration is a good indicator
for the electron-withdrawing effect of the ¯uorinated alkyl
chain. It can be expected from these data that complexes
3±5 are clearly more electrophilic at the metal centers
than the non-¯uorinated complexes Rh2%OOCPh)4 and
Rh2%OOCMe)4. While this property should raise the effec-
tiveness of the diazo decomposition step and the coordi-
nation of donor molecules at the free axial coordination
site at the rhodium center, it does not allow a simple predic-
tion of the selectivity for potentially competing carbene
transfer reactions.13
at the latest after addition of a few drops of the diazoester to
the reaction medium. Only when styrene was used as the
alkene, some of the catalyst remained undissolved during
the whole reaction. At the end of the cyclopropanation
reactions, the catalyst was recovered by extraction into
PFMC and was reused without further puri®cation. The
yield of 11 decreased only marginally over four reaction
cycles, although the recovery rate of catalyst after each
cycle was not quantitative %the percentage of available
catalyst after four cycles was 56, 27, 21, and 11% for the
cyclopropanation of styrene, 1-hexene, 2-methyl-2-propene
and a-methylstyrene, respectively).
Complex 3 was obtained as microcrystalline dark-green
needles, complexes 4 and 5 as dark-green waxy materials.
The ¯uorine contents of the three compounds are 50.3,
61.1, and 64.0%, respectively. While the solubility of 3
in per¯uoro%methylcyclohexane) %PFMC, C6F11±CF3),
per¯uorohexane, and 1,1,2-trichloro-1,2,2-tri¯uoroethane
%FC-113) is rather low, complexes 4 and 5 are highly soluble
in these media. Furthermore, 4 and 5 are insoluble in
standard organic solvents such as Et2O, CH2Cl2, CHCl3,
THF, toluene, and ethyl acetate; no visible leaching from
PFMC into heptane, CH2Cl2, toluene, and THF was noticed.
Based on these properties, the two complexes are expected
to be well suited for applications in ¯uorous phase
chemistry.
In contrast to 3, complexes 4 and 5 were found not to be
soluble in CH2Cl2-alkene mixtures. Therefore, cyclopropa-
nations of styrene and a-methylstyrene with these catalysts
were performed in the ¯uorous/organic hybrid solvent5d
FC-113. A tenfold excess of the alkene was applied to mini-
mize the formation of the formal carbene dimers, dimethyl
fumarate and maleate. At the end of the reaction, the solvent
was replaced by the biphasic system PFMC/CH2Cl2 which
allowed the extraction of the catalyst into the ¯uorous phase.
Again, the recovered catalyst was submitted to another
reaction cycle. Table 2 shows that the cyclopropane yields
remained almost the same over ®ve cycles. However, a
gravimetric determination of the amount of recovered
catalyst showed a signi®cant decrease after each cycle,
with a total loss of 51% of 4 and 38% of 5 after ®ve cycles
in the reaction with styrene. This loss cannot be attributed to
leaching of the intact ¯uorous catalyst into the organic phase
%see above); rather, it is associated with a partial deterio-
2.2. Cyclopropanation of styrenes with methyl
diazoacetate
1
We have already reported8 that complex 3 is well suited to
catalyze the formation of cyclopropanes 11 from alkenes
and methyl diazoacetate %Scheme 4, Table 2). These trans-
formations did not require a ¯uorous solvent, since the
catalyst dissolved in the alkene/dichloromethane phase or
ration or destruction of the complex. In fact, IR and H
NMR spectra of the recovered catalysts indicated the
presence of small amounts of the corresponding free acids
6b,c; furthermore, some elemental rhodium, separating as a
very ®ne black powder, was also observed.

4002
A. Endres, G. Maas / Tetrahedron 58 )2002) 3999±4005
Scheme 5.
Instead of using FC-113 as the reaction medium, the cyclo-
propanation of styrene catalyzed by 5 was also performed in
the vigorously stirred biphasic system PFMC/dichloro-
methane. This variation was operationally more simple,
because at the end of the reaction the PFMC phase, contain-
ing the ¯uorous catalyst, could be separated and reused
directly. While the yields of cyclopropanes 11 in the ®rst
two reaction cycles were nearly the same as for the reaction
performed in FC-113, they dropped considerably in the next
two cycles, with a concomitant increase in carbene dimers
%combined yields of 4 and 24%, respectively). After the
fourth cycle, no ¯uorous catalyst could be recovered.
Scheme 6.
study,9 we conclude that both the electrophilicity of 5 and
its high solubility in the reaction medium account for its
good performance in this reaction.
Table 3 also shows that the selectivity of the insertion reac-
tion is not in¯uenced markedly by the catalysts. The prefer-
ence for insertion into the C-2 methylene group of linear
alkanes has also been observed with all other rhodium
catalysts studied so far; insertion at the terminal CH3
position becomes more signi®cant only with very bulky
rhodium catalysts.1,16
2.3. Intermolecular carbenoid C±H insertion of methyl
diazoacetate
Carbenoid insertion of simple diazoacetate esters into the
non-activated C±H bonds of alkanes is sluggish with most
of the transition-metal catalysts investigated so far. The
best results are obtained with the highly electrophilic cata-
lyst dirhodium%II) tetrakis%tri¯uoroacetate), while simple
rhodium alkanoates such as Rh2%OAc)4 and Rh2%octanoate)4
are almost uneffective.14,15 Hence we investigated the inter-
molecular carbenoid C±H insertion of methyl diazoacetate
into hexane with catalysts 3 and 5 %Scheme 5). The reactions
were carried out in a large excess of hexane to reduce the
extent of dimerization and oligomerization of the carbenes.
While catalyst 3 was applied as a suspension in hexane, the
much more ¯uorophilic complex 5 was dissolved in the
solvent system PFMC±hexane which becomes homo-
geneous at ca. 408C. The results are given in Table 3. It
can be seen that catalyst 3 is not very effective, while
catalyst 5 provides a remarkably high combined yield of
insertion products 12±14 %ca. 64%), which is signi®cantly
better than with catalyst 2 investigated by us before. In
combination with the results obtained in this earlier
It is unfortunate that complex 5, which has now emerged as
a promising catalyst for carbenoid C±H insertion reactions
into alkanes, cannot be recovered ef®ciently in this environ-
ment: Formation of an olive-green solid was observed
already during the reaction, and after phase separation at
2188C, only a small fraction of the intact catalyst could
be recovered.
2.4. Intramolecular carbenoid C±H insertion
As a test case for an intramolecular C±H insertion, we
looked at the reaction of a-diazo-b-keto esters 15 and 18
catalyzed by 5 %Scheme 6). Ikegami et al.16 have shown that
the selectivity of the intramolecular carbenoid reactions
in these systems17 are more dependent on steric factors
operating in the catalyst than on its electrophilicity; rhodium
catalysts with bulky ligands strongly favored the aromatic
Table 3. C±H insertion of methyl diazoacetate into n-hexane; see Scheme 5
Catalyst
Solvent
Yield %%) of insertion at
Dimersa %%)
Relative yield of insertion
C-2
C-1
12
C-2
13
C-3
14
C-1
C-3
3
5
Hexane
PFMC±hexane
0.3
1.7
7.0
40.7
2.6
21.4
17.1
7.8
1
1
24.8
24.5
9.4
12.9
The product distribution was determined by GC.
Dimethyl fumarate and dimethyl maleate.
a

A. Endres, G. Maas / Tetrahedron 58 )2002) 3999±4005
4003
Table 4. Carbenoid intramolecular C±H insertion of 15 catalyzed by 5; see
Scheme 6
4.1.1. 3,5-Diiodobenzoic acid 7). To an ice-cooled, stirred
suspension of 3,5-diaminobenzoic acid %3.00 g, 19.7 mmol)
in 25% sulfuric acid %70 ml) was added dropwise a 2.5 M
aqueous solution of sodium nitrite %17.1 ml, 42.0 mmol).
The color of the originally red suspension changed to
orange. After 2 h, urea %3.0 g, 50 mmol) was added, and
then the solution was added slowly to an ice-cooled solution
of potassium iodide %16.4 g, 98.6 mmol) in water %15 ml).
After 5 h at 208C, the suspension was cooled to 48C and the
brown solid was ®ltered off, washed with water, and dried. It
was decolorized by treatment with charcoal in boiling THF
%50 ml). Recrystallization from a large volume of toluene
gave a beige powder; yield: 6.04 g %82%); mp 2318C %lit.:18
Cycle
16 %%)
17 %%)
Catalyst %brought in/
recovered) %%)
1
2
67
59
3
3
100/96
96/91
C±H insertion product 16 over the aliphatic insertion
product 17, the best catalyst being Rh2%OOCCPh3)4. We
found that the treatment of diazo ester 15 with catalyst 5
in FC-113 also resulted in a high selectivity for 16 %Table 4).
The catalyst could be recovered by partioning of the product
mixture between PFMC and dichloromethane to the extent
of 96% in each of two reaction cycles. For comparison,
treatment of 15 with ¯uorous catalyst 2 was both lower-
yielding and less selective %16/17ˆ68:32, total yield 38%)
and could not be recovered by ¯uorous extraction. Thus,
complex 5 should also be considered as a candidate for
other intramolecular carbenoid reactions. We noticed,
however, that complex 5 was not able to decompose the
unsaturated diazo ester 18 effectively even after 2 weeks
at 458C in FC-113.
1
2338C). Rfˆ0.76 %THF). H NMR %[D6]-DMSO): dˆ8.17
%s, 2H, 2,6-H), 8.31 %s, 1H, 4-H). 13C NMR %[D6]-DMSO):
dˆ96.44 %C-3,5), 129.24 %C-1), 137.34 %C-2,6), 148.53
%C-4), 164.99 %CvO). IR %KBr): nˆ3649 %w), 3069 %m),
2830 %m), 2638 %m), 2516 %w), 1686 %s), 1275 %s) cm21
.
Anal. calcd for C7H4O2I2 %373.9): C 22.49, H 1.08; found:
C 22.42, H 1.13.
4.1.2. Methyl 3,5-diiodobenzoate 8). A suspension
consisting of acid 7 %1.00 g, 2.67 mmol), K2CO3 %437 mg),
and dimethyl sulfate %0.27 ml) in dry acetone %25 ml) was
re¯uxed for 8 h. After addition of water %6 ml) and stirring
for 12 h, the solvent was removed. The resulting beige resi-
due was extracted with dichloromethane %3£20 ml). The
combined organic phases were washed with brine %20 ml),
dried %Na2SO4), and evaporated. The residue was ®ltered
through a short bed of silica [petroleum ether/ether %7/3)].
The solution was concentrated, and the product separated as
colorless needles; yield: 846 mg %82%), mp 948C. Rfˆ0.93
%petroleum ether/ether, 7:3 v/v). 1H NMR %CDCl3): dˆ3.85
%s, 3H, OCH3), 8.15 %s, 1H, 4-H), 8.24 %s, 2H, 2,6-H). 13C
NMR %CDCl3): dˆ52.58 %OCH3), 94.28 %C-3,5), 133.13
%C-1), 137.63 %C-2,6), 149.09 %C-4), 164.09 %CvO). IR
%KBr): nˆ1741%s), 1240 %s), 1198 %s), 1142 %s) cm21. MS
%CI): m/zˆ389 [M11]1, 262 [M2I]1. Anal. calcd for
C8H6O2I2 %387.95): C 24.77, H 1.56; found: C 24.65, H 1.59.
3.Conclusion
This study has shown that the dirhodium tetrakis[3,5-
bis%per¯uoroalkyl)benzoates] 4 and 5, due to their excellent
solubility in ¯uorous solvents and their high ¯uorophilicity,
are promising candidates for reactions in ¯uorous phases
and for ¯uorous extraction procedures. However, when
they are applied to catalytic carbene transfer reactions
with diazoacetates, the possibilities to recover and to reuse
4 and 5 are limited because they are partly destroyed or
transformed into less ¯uorophilic species. There are indi-
cations that formal carbene dimers and oligomers are
involved in one of the deactivation pathways of these
catalysts. Therefore, the stability of these catalysts may be
higher when diazoesters are used that do not easily form
carbene dimers under rhodium catalysis, e.g. phenyl- and
vinyldiazoacetates.
4.1.3. Methyl 3,5-bis per¯uorohexyl)benzoate 9). A
mixture of a few iodine crystals and copper dust %3.00 g)
in acetone %20 ml) was stirred for 30 min. After removal of
the solvent, the copper was washed with aq. HCl %6N) in
acetone %20 ml, 2:3 v/v) and acetone %2£10 ml) and dried in
vacuo. The activated copper powder %819 mg, 12.9 mmol)
was mixed with ester 8 %500 mg, 1.29 mmol), per¯uoro-
hexyl iodide %0.6 ml, 2.71 mmol), and dry DMSO %9 ml).
The suspension was stirred for 6 h at 1258C. After cooling
down, water and ether %10 ml each) was added and stirred
for 10 min. Then the mixture was ®ltered through a BuÈchner
funnel. The residue was washed with ether %2£20 ml). The
combined ether phases were dried %Na2SO4) and evaporated.
The resulting pale-brown solid was puri®ed by chroma-
tography [silica gel, petroleum ether/ether %7:3)]. Yield:
4.Experimental
4.1. General
All reactions were carried out under argon. Analytical grade
solvents were used. The petroleum ether used had a boiling
point range of 30±508C. Flash chromatography was per-
formed on silica gel %Merck silica gel 60 %0.040±0.063
mm)). NMR spectra were recorded on a Bruker AMX 400
instrument %1H: 400.1 MHz; 13C: 100.6 MHz; 19F: 376
MHz). Internal standards were used [1H: TMS or [D8]-
THF %dˆ1.73 and 3.58); 19F: CF2Cl±CFCl2 %dˆ268 and
273 ppm)]. IR spectra were recorded on Perkin±Elmer 883
and Bruker Vector 22 spectrometers. Laser desorption mass
spectra were obtained with a Bruker Re¯ex III instrument.
GC analyses were performed on a Varian 3800 instrument.
Elemental analyses were obtained on a `elementar vario EL'
instrumentÐPFMCˆper¯uoro%methylcyclohexane); FC-
113ˆ1,1,2-trichloro-1,2,2-tri¯uoroethane.
1
547 mg %55%); mp 598C. H NMR %CDCl3/FC-113): dˆ
4.02 %s, 3H, OCH3), 7.99 %s, 2H, 2,6-H), 8.50 %s, 1H, 4-H).
13C NMR %CDCl3/FC-113): dˆ52.8 %OCH3), 131.05
%C-2,6), 131.54 %C-3,5), 132.24 %C-4), 129.3, 136.8, 139.5
%m, C%RF)), 139.5 %C-1), 164.15 %CvO). 19F NMR %CDCl3/
FC-113): dˆ281.4 %t, 6F, CF3), 2112.5, 2121.8, 2122.1,
2123.2, 2126.6 %all m, CF2). IR %KBr): nˆ2965 %m), 1741
%s, CvO); 1240, 1198, 1142, 1122 %all s, C±F) cm21
.

4004
A. Endres, G. Maas / Tetrahedron 58 )2002) 3999±4005
4.1.4. Methyl 3,5-bis per¯uorooctyl)benzoate 10). The
compound was prepared, as described above for 9, from
copper dust %819 mg, 12.9 mmol), ester 8 %500 mg,
1.29 mmol), and per¯uorooctyl iodide %1.48 g, 2.71 mmol)
in dry DMSO %9 ml). Yield: 702 mg %56%); mp 62±638C.
1H NMR %CDCl3/FC-113): dˆ4.01 %s, 3H, OCH3), 7.98 %s,
2H, 2,6-H), 8.49 %s, 1H, 4-H). 13C NMR %CDCl3/FC-113):
dˆ53.7 %OCH3), 129.42 %C-2,6), 130.9 %C-3,5), 131.6 %C-4),
113.5±131.5 %m, C%RF)), 132.3 %C-1), 164.4 %CvO). 19F
NMR %CDCl3): dˆ282.2 %t, 3Jˆ10.8 Hz, 6F, CF3),
%m), 1286 %s), 1242 %s), 1203 %s), 1146 %s), 1122 %s), 1108
%m), 1094 %s) cm21. MS %LD-TOF): m/z: found 2409
%Rh2L5; calcd 2400.8) and 1962 %Rh2L4; calcd for
C52H16F52O8Rh2: 1961.8).
4.1.8. Tetrakis[m-3,5-bis per¯uorohexyl)benzoato-O:O0]
dirhodium 4). A solution of acid 6b %600 mg, 0.791 mmol)
and sodium hydroxide %31.5 mg, 0.791 mmol) in ethanol
%20 ml) was added to a stirred solution of RhCl3£3H2O
%52.3 mg, 0.198 mmol) in re¯uxing ethanol %15 ml). The
color of the solution changed from red to yellow and yellow
brown. After 7 h a green waxy solid precipitated. Then half
of the solvent was removed %408C/120 mbar) and after
cooling to 48C it was fully decanted. The dark-green residue
which contained some rhodium powder was dried %508C/
1 mbar), then dissolved in PFMC %2 ml). After ®ltration,
and liquid-liquid extraction with THF %2£1.5 ml), the
¯uorous solvent gave a solid which was subjected to ¯ash
chromatography [silica gel, petroleum ether/ether %7:3)] to
remove left-overs of 6b-sodium salt. Complex 4 was
obtained as a dark-green waxy solid; yield: 189 mg %61%).
Rfˆ0.97 %petroleum ether/ether, 7:3). 1H NMR %CDCl3/FC-
113): dˆ7.85 %s, 4H, 4-H), 8.41 %s, 8H, 2,6-H). 19F NMR
%CDCl3/FC-113): dˆ282.5 %m, 24F, CF3), 2112.3 %m, 16F,
CF2), 2122.7 %m, 32F), 2124.3 %m, 16F), 2127.7 %m, 16F).
IR %KBr): nˆ1627 %m), 1588 %m), 1412 %s), 1364 %s), 1322
%s), 1240 %vs), 1203 %vs), 1146 %vs), 1124 %s), 1103 %s), 1061
%m) cm21. MS %LD-TOF): m/z: 3236.9 %Rh2L4; calcd for
C76H12F104O8Rh2: 3234.2); further fragments at M2n£318
[nˆ1,2,3,¼; M%C6F13)ˆ319.0].
4.1.9. Tetrakis[m-3,5-bis per¯uorooctyl)benzoato-O:O0]
dirhodium 5). The complex was prepared and puri®ed,
as described above for 4, from a solution of acid 6c
%100 mg, 0.104 mmol) and sodium hydroxide %4.1 mg,
0.104 mmol) in ethanol %20 ml) and a solution of RhCl3£3
H2O %9.00 mg, 34.6 mmol) in re¯uxing ethanol %15 ml).
Yield: 44 mg %63%) of a dark-green waxy solid. Rfˆ0.97
%petroleum ether/ether, 7:3). 1H NMR %CDCl3/FC-113):
dˆ7.83 %s, 1H, 4-H), 8.37 %s, 2H, 2,6-H). 13C NMR
%CDCl3/FC-113): dˆ182.64 %OCO). 19F NMR %CDCl3/FC-
113): dˆ282.5 %t, 24F, 3Jˆ10.3 Hz, CF3), 2112.3 %m, 16F,
CF2), 2122.5 %m, 16F, CF2), 2122.7 %m, 16F, CF2), 2123.3
%m, 32F, CF2), 2124.1 %m, 16F, CF2), 2127.7 %m, 16F,
CF2). IR %KBr): nˆ3097 %w), 1626 %m), 1587 %s), 1463
%m), 1408 %s), 1369 %s), 1314 %s); 1238 %vs, broad), 1209
%vs, broad), 1150 %vs), 1118 %s) cm21. C92H12F136O8Rh2:
Mˆ4034.4 g/mol.
3
2112.4 %t, Jˆ14.3 Hz, 4F), 2122.4 %m, 4F), 2123.2 %m,
16F), 2124.1 %m, 2F), 2127.4 %m, 2F).
4.1.5. 3,5-Bis per¯uorohexyl)benzoic acid 6b). Ester 9
%250 mg, 0.32 mmol) was suspended in methanol %2 ml)
and water %4 ml) and potassium hydroxide %130 mg,
2.32 mmol) was added. After heating at 1008C for 15 h,
the solvents were removed and the solid residue was neutra-
lized with 6 N hydrochloric acid. After extraction with
ether %3£20 ml), drying of the combined ethereal phases
%Na2SO4) and evaporation of the solvent, the residue was
recrystallized from toluene to give a white powder. Yield:
1
201 mg %82%); mp 1038C. H NMR %CDCl3): dˆ7.97 %s,
1H, 4-H), 8.47 %s, 2H, 2,6-H). 19F NMR %CDCl3): dˆ281.3
%m, 6H, CF3), 2111.6, 2121.9, 2122.2, 2123.3, 126.7 %all
m, CF2). IR %KBr): nˆ3442 %m), 3099 %m), 1710 %s), 1614
%m), 1281 %s), 1238 %s), 1198 %s), 1144 %s) cm21
.
4.1.6. 3,5-Bis per¯uorooctyl)benzoic acid 6c). The acid
was prepared, as described above for 6b, from ester 10
%250 mg, 0.257 mmol) and potassium hydroxide %130 mg,
2.32 mmol) in methanol %2 ml) and water %4 ml). Yield:
1
205 mg %83%); mp 1178C. H NMR %CDCl3): 7.97 %s, 1H,
4-H), 8.47 %s, 2H, 2,6-H). IR %KBr): nˆ3443 %m), 1712 %s),
1204 %s), 1149 %s) 1118 %m) cm21
.
4.1.7.
Tetrakis[m-4- per¯uorohexyl)benzoato-O:O0]
dirhodium 3). A solution of 4-%per¯uorohexyl)benzoic
acid10 %6a) %80 mg, 181 mmol) in toluene %25 ml) was placed
in a reaction vessel equipped with a dropping funnel and a
Dean±Stark trap and was heated at 1008C. A solution of
Rh2%OAc)4 %20 mg, 45.3 mmol) in EtOH %15 ml) was
added within 10 min. After the ethanol had distilled off,
the temperature was raised to 1108C. In order to remove
the acetic acid liberated in the ligand exchange reaction,
four portions of toluene %4£15 ml) were added subsequently
and were allowed to distill off each time. The mixture was
re¯uxed during 11 h, then about half of the solvent was
removed. By cooling to 48C a pale green solid separated,
which was ®ltered off and dried. The pale green powder was
boiled in ethanol %10 ml) and ®ltered hot. The resulting solid
was boiled in THF %40 ml). ®ltration about 3/4 of the THF
were removed. The product precipitated at 48C as a green
®nely crystalline solid; yield: 68 mg %77%); mp 1218C
%dec.). By slow evaporation of a solution in THF/FC-113,
the complex was obtained as dark green needles. Rfˆ0.66
4.1.10. Cyclopropanation of styrene with methyl diazo-
acetate. A solution of methyl diazoacetate %100 mg, 1.00
mmol) in FC-113 %0.5 ml) was added with the aid of a
syringe pump within 8 h to a stirred solution of the catalyst
%4 or 5, 1 mol%) and a tenfold excess of styrene %1.13 ml,
10.0 mmol) in FC-113 %1.5 ml). After an additional reaction
time of 4 h at 208C, the solvent was removed and the residue
was stirred with PFMC %0.7 ml) and dichloromethane
%2.5 ml) for 20 min. After the phase separation, the ¯uorous
phase was evaporated and the recovered catalyst so obtained
was used in an additional reaction cycle. Cyclopropane 11
%RˆH) was found in the dichloromethane phase, and after
addition of dibenzyl ether as an internal standard the yield
and E/Z ratio was determined by GC %Table 2).
1
%petroleum ether/ether, 7:3). H NMR %400.1 MHz, [D8]-
THF/FC-113): dˆ7.44 and 7.95 %d, 16H, 3Jˆ8.2 Hz,
AA0BB0 system). 13C NMR %100.6 MHz, [D8]-THF/FC-
113): dˆ184.55 %OCO). 19F NMR %[D8]-THF/FC-113):
3
dˆ281.4 %t, 12F, J%F,F)ˆ8.0 Hz, CF3), 2111.0 %m, 8F),
2121.4 %m, 8F), 2122.1 %m, 8F), 2122.9 %m, 8F), 2126.4
%m, 8F). IR %KBr): nˆ1604 %m), 1564 %s), 1409 %s), 1363

A. Endres, G. Maas / Tetrahedron 58 )2002) 3999±4005
4005
911±935. %d) Maas, G. Top. Curr. Chem. 1987, 137, 77±253.
%e) Doyle, M. P. Chem. Rev. 1986, 86, 919±939.
The cyclopropanation of a-methylstyrene was done analog-
ously. The cyclopropanes gave 1H NMR spectra which were
in agreement with published data.
3. See, for example: %a) Doyle, M. P.; van Leusen, D.; Tamblyn,
W. H. Synthesis 1981, 787±789. %b) Davies, H. M. L.;
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4.1.11. Rh-catalyzed reaction of methyl diazoacetate
with n-hexane. The catalyst %1 mol%) was dissolved %5)
or suspended %3) in PFMC %0.5 ml). After addition of hex-
ane %4 ml), the temperature was raised to 408C. A solution of
methyl diazoacetate %100 mg, 1.0 mmol) in hexane %0.5 ml)
was added with the aid of a syringe pump within 6 h. After
an additional reaction time %2 h/408C) dibenzyl ether was
added as an internal standard, and the yield and product
distribution was determined by gas chromatography
%column: fused silica, CP-WAX 52 CB as stationary
phase, 25 m£0.32 mm; variable temperature 50!2508C).
The insertion products 12±14 were not separated on a
preparative scale; rather, the components were identi®ed
by GC-MS and by characteristic 13C NMR signals, see lit.9
Â
Â
5. %a) Horvath, I. T.; Rabai, J. Science 1994, 266, 72±75.
%b) Studer, A.; Hadida, S.; Ferritto, R.; Kim, S.-Y.; Jeger, P.;
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4.1.12. Intramolecular carbenoid C±H insertion of 15. A
solution of diazo ester 1517 %65 mg, 0.25 mmol) in FC-113
%0.5 ml) was added during 1 h via a syringe pump to a
solution of catalyst 5 %8.0 mg, 1.0 mol%) in FC-113. After
additional 12 h, the solvent was removed and a mixture of
dichloromethane/PFMC %1.4 ml, 1:1) was added and stirred
for 30 min. The catalyst collected in the PFMC phase was
used for a further cycle. The dichloromethane was replaced
by CDCl3 and after addition of dibenzyl ether as a standard,
the composition of the mixture was determined by 1H NMR
spectroscopy; yields are given in Table 4. The chemical
shifts of products 16 and 17 agreed with the published
data.16
Â
6. Kiss, L. E.; Kovesdi, I.; Rabai, J. J. Fluorine Chem. 2001, 108,
È
95±109.
7. Rocaboy, C.; Bauer, W.; Gladysz, J. A. Eur. J. Org. Chem.
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Acknowledgements
13. Pirrung, M. C.; Morehead, Jr., A. T. J. Am. Chem. Soc. 1994,
116, 8991±9000.
We thank Dr. Markus Wunderlin and Robert Heinrich
%University of Ulm) for recording of the LD-TOF mass
spectra. This work was supported ®nancially by the Fonds
der Chemischen Industrie.
14. Davies, H. M. L.; Hansen, T.; Churchill, M. R. J. Am. Chem.
Soc. 2000, 122, 3063±3070.
Â
15. %a) Demonceau, A.; Noels, A. F.; Hubert, A. J.; Teyssie, P.
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