New highly fluorinated dirhodium(II) tetrakis(alkanecarboxylates) as catalysts for carbenoid C-H insertion reactions

Article abstract of DOI:10.1016/S0022-328X(01)01380-8

Six highly fluorinated dirhodium(II) tetrakis(alkanecarboxylates) [Rh₂(OOCR_F)₄, R_F = C₇F₁₅, CH₂C₆F₁₃, CH₂CH₂C₆F₁₃, CH₂CH₂C₈F₁₇, CH₂CH₂C₁₀F₂₁, and CH₂OCH₂CH₂C₁₀F₂₁] were prepared and characterized. Their suitability as catalysts for intermolecular carbenoid C-H insertion was investigated for the reaction of methyl diazoacetate with hexane. In the frame of fluorous synthesis, only Rh₂(OOCC₇F₁₅)₄ and Rh₂(OOCCH₂C₆F₁₃)₄ are interesting, since they are soluble in perfluoro(methylcyclohexane) and catalyze the C-H insertion reaction more effectively than all other catalysts, including Rh₂(OAc)₄. The same two catalysts were also used to achieve 1,5-cyclization of an α-diazo-β-keto ester by intramolecular C-H insertion. Unfortunately, deterioration of the catalysts occurs to a significant extent during all reactions, and therefore, the possibilities to recover and reuse them are rather limited.

Full text of DOI:10.1016/S0022-328X(01)01380-8

Journal of Organometallic Chemistry 643–644 (2002) 174–180
www.elsevier.com/locate/jorganchem
New highly fluorinated dirhodium(II) tetrakis(alkanecarboxylates)
as catalysts for carbenoid CꢀH insertion reactions
Andreas Endres, Gerhard Maas *
Abteilung Organische Chemie I, Uni6ersita¨t Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
Received 25 June 2001; accepted 9 October 2001
Dedicated to Franc¸ois Mathey at the occasion of his 60th birthday
Abstract
Six highly fluorinated dirhodium(II) tetrakis(alkanecarboxylates) [Rh2(OOCRF)4, RF=C7F15, CH2C6F13, CH2CH2C6F13,
CH2CH2C8F17, CH2CH2C10F21, and CH2OCH2CH2C10F21] were prepared and characterized. Their suitability as catalysts for
intermolecular carbenoid CꢀH insertion was investigated for the reaction of methyl diazoacetate with hexane. In the frame of
fluorous synthesis, only Rh2(OOCC7F15)4 and Rh2(OOCCH2C6F13)4 are interesting, since they are soluble in perfluoro(methylcy-
clohexane) and catalyze the CꢀH insertion reaction more effectively than all other catalysts, including Rh2(OAc)4. The same two
catalysts were also used to achieve 1,5-cyclization of an a-diazo-b-keto ester by intramolecular CꢀH insertion. Unfortunately,
deterioration of the catalysts occurs to a significant extent during all reactions, and therefore, the possibilities to recover and reuse
them are rather limited. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Rhodium complexes; Fluorous synthesis; Diazo compounds
fluorinated compounds (reagents, products, catalysts)
from a reaction mixture by extraction into perfluori-
nated solvents, such as perfluoro(methylcyclohexane)
(CF3ꢀC6F11, PFMC) and FC-75 which themselves are
not miscible at room temperature with common organic
solvents of low polarity [4]. Along these lines, we have
started to investigate the possibility to use highly fluori-
nated dinuclear rhodium(II) carboxylates as catalysts
for carbene transfer reactions and to recover and to
reuse them. In a preliminary communication [5], we
have shown that dimeric rhodium(II) perfluorooc-
tanoate and rhodium(II) 4-(perfluorohexyl)benzoate
[(Rh2(OOCR)4, R=C7F15 and C6H4-4-C6F13, respec-
tively) can be recycled several times with little loss of
material and activity in cyclopropanation reactions of
alkenes with methyl diazoacetate. In this paper, we
look at the performance of several ‘fluorous’ rhodium-
(II) alkanecarboxylates in an intermolecular aliphatic
CꢀH insertion reaction with methyl diazoacetate.
Transformations of this type are notorious for being
not highly efficient even with most rhodium catalysts
[1,2,6]. Furthermore, the intramolecular CꢀH insertion
reaction of an a-diazo-b-keto ester is described.
1. Introduction
Dinuclear rhodium complexes (Rh2L4) with carboxy-
late, amidate, and related ligands are highly versatile
catalysts for carbene transfer from diazo compounds to
a range of substrates via rhodium carbene intermediates
[1,2]. These catalysts are not only efficient, but can also
be applied to a broad range of carbene transfer reac-
tions, and the choice of an appropriate ligand often
allows to influence the chemo-, regio-, and diastereose-
lectivity of a transformation. One disadvantage of
rhodium catalysts is the high price of the metal. In spite
of this, efforts to recover the catalysts have rarely been
made. One notable exception is Doyle’s polyethylene-
bound dirhodium(II) pyrrolidin-2-one-5(S)-carboxylate
[3]. Another possibility is suggested by the recent pro-
gress in fluorous phase synthesis. Among other applica-
tions, this methodology allows to separate highly
* Corresponding author. Tel.: +49-731-5022790; fax: +49-731-
5022803.
E-mail address: gerhard.maas@chemie.uni-ulm.de (G. Maas).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01380-8

A. Endres, G. Maas / Journal of Organometallic Chemistry 643–644 (2002) 174–180
175
Table 1
Yields, fluorine content, and solubilities of complexes 2–7 [PFMC=perfluoro(methylcyclohexane)]
Rh2(OOCR)4 R=
Yield (%) method a
Fluorine content (%)
Solubility in PFMC
2
3
4
5
6
7
C7F15
CH2C6F13
CH2CH2C6F13
CH2CH2C8F17
CH2CH2C10F21
CH2O(CH2)2C10F21
77 (A), 32 (B)
74 (A)
53 (B)
57 (B)
68 (B)
61.4
57.7
55.9
59.6
62.1
59.3
Soluble
Soluble
Insoluble
Insoluble
Insoluble
Insoluble
30 (B)
r\30 (B)ca=‘‘D’’\\59.3\Insoluble
a See Scheme 1 for methods A and B.
2. Results and discussion
the corresponding acids and rhodium(III) chloride hy-
drate in refluxing ethanol according to a standard
procedure [12] (Scheme 1, method B). The moderate
yields (Table 1) are due at least in part to the formation
of elemental rhodium under the reaction conditions, in
particular in the case of 7. While 2 was also obtained by
method B in modest yield, the ligand exchange method
A was not suited to prepare 4, probably, because the
pKa value of 3-(perfluorohexyl)propionic acid was not
sufficiently low. We found it difficult to remove the last
solvent traces from the complexes. In particular, tolu-
ene could not be removed completely even by heating
the complexes at 60 °C/1 mbar for 12 h. While, com-
plexes 4–7 are green microcrystalline solids, 2 and 3
were obtained as dark-green, waxy materials which
were not easy to isolate from the reaction vessel. How-
ever, they formed solid purple bis(acetonitrile) com-
plexes on exposure to CH3CN which could be handled
conveniently and from which the solvent-free complexes
could be recovered by treatment at 60 °C/1 mbar for 5
h.
2.1. Preparation and characterization of rhodium
complexes 2–7
As a rule of thumb, a compound with a good solubil-
ity in a perfluorinated solvent should have a fluorine
content of ca. 60% or higher. This requirement is
fulfilled by dirhodium(II) tetrakis(perfluorooctanoate)
(2, 61.4% F). However, it is clear that the four strongly
electron-withdrawing ligands affect the electronic prop-
erties of the rhodium core of the complex and enhance
its electrophilicity. In fact, the related rhodium per-
fluorobutyrate [Rh2(pfb)4] has been used in diazo de-
composition and carbene transfer reactions when a
much more electrophilic catalyst than the standard
catalyst Rh2(OAc)4 was needed [1,7], and it is also
known for its high p-coordination of olefins [8].
Complexes 2 and 3 are soluble in PFMC, but unfor-
tunately with respect to fluorous synthesis, 4–7 are
completely insoluble in PFMC, in spite of the fact that
their fluorine content is between 55.8% (4) and 62.1%
(6). It appears that due to the presence of the spacer
groups, the perfluoroalkyl segments do no longer shield
the polar carboxylate moieties efficiently enough to
prevent repulsive interactions between the latter and the
perfluorinated solvent molecules. It should be kept in
mind that the fluorous rhodium carboxylates presented
here differ from most other fluorous catalysts by their
polar carboxylate head groups; typically, fluorous cata-
(Formula 1)
In order to create fluorous rhodium catalysts that
still resemble Rh2(OAc)4 in their electronic properties,
we prepared complexes 3–7 (Table 1) where spacer
groups [CH2, (CH2)2 and (CH2)2OCH2] have been in-
troduced to isolate the metal atoms from the strongly
electron-withdrawing perfluoroalkyl segments of the lig-
ands. The spacer concept has been widely used in the
design of compounds bearing long perfluoroalkyl
chains [4,9–11].
Complexes 2 and 3 were prepared from Rh2(OAc)4
(1) by exchange of the acetate ligands (Scheme 1,
method A). By reaction of Rh2(OAc)4 with four equiva-
lents of perfluorooctanoic acid and (perfluoro-
hexyl)acetic acid, respectively, in boiling toluene and
with azeotropic removal of the liberated acetic acid, the
complexes were obtained in good yields (77 and 74%).
Complexes 4–7 were prepared from the sodium salts of
Scheme 1.

176
A. Endres, G. Maas / Journal of Organometallic Chemistry 643–644 (2002) 174–180
Table 2
As expected due to their D4h symmetry, 2–6 have
very simple 1H-NMR spectra. As already noted by
Brunner for other rhodium(II) carboxylate complexes
[15], the resonances of the alkyl protons of the carboxy-
late ligand in 3–6 show a high-field shift compared with
the free carboxylic acids (Dl:0.2 ppm). The 19F-NMR
spectra of the complexes are remarkably similar for
complexes with the same length of the perfluorinated
chain. The IR spectra of the complexes (Table 3)
exhibit three characteristic absorptions in the ranges
1575–1663, 1414–1445, and 1104–1263 cm−1, corre-
sponding to the antisymmetric and symmetric stretch-
ing modes of the carboxylate ligands [12] and the CꢀF
stretching vibrations. The wasym(OOCR) vibration is a
good indicator for the electron-withdrawing effect of
the fluorinated alkyl chain [12]. The comparison with
Rh2(OAc)4 suggests that the (CH2)2 and CH2O(CH2)2
spacers are sufficient to suppress the electronic influence
of the perfluoroalkyl segments on the RhꢀRh core of
the complex.
Distribution of catalysts 2 and 3 in the two-phase system PFMC –
organic solvent, determined gravimetrically
K=cPFMC/cSolv
Et2O
CH2Cl2
Hexane
Toluene
2
3
4.9
0.6
18.7
8.5
29.4
28.7
18.9
25.7
Table 3
Characteristic IR absorptions of complexes 1–7
Rh2(OOCR)4 R=
IR (KBr, cm−1
)
w(CO)asym
w(CO)sym
w(CF)
1
2
3
4
5
6
7
CH3
C7F15
CH2C6F13
CH2CH2C6F13
CH2CH2C8F17
CH2CH2C10F21
1577
1663
1611
1579
1575
1581
1413/1428
1424
–
1207/1244
1206/1241
1188/1249
1147/1206
1104/1263
1146/1242
1414/1428
1422/1444
1422/1445
1421/1443
1414
Since, we did not characterize 2–7 by elemental
analysis, we verified the absence of any starting mate-
rial by IR and NMR spectroscopy. In addition, the
complexes were characterized by laser desorption time-
of-flight mass spectrometry (positive ion mode). For
2–5, main peaks corresponding to the units Rh2L4 and
Rh2L5 could be observed, while complexes 6 and 7,
yielded only unspecific particle patterns.
CH2O(CH2)2C10F21 1599
2.2. Catalytic intermolecular CꢀH insertion with
methyl diazoacetate
Intermolecular CꢀH insertion into alkanes by di-
azoacetate esters is significantly more effective with
dirhodium(II) tetrakis(trifluoroacetate) than with sim-
ple rhodium alkanoates such as Rh2(OAc)4 and
Rh2(octanoate)4 [6,16]. Hence, we investigated the inter-
molecular CꢀH insertion into hexane by methyl dia-
zoacetate with catalysts 2–4, 7, and Rh2(OAc)4 (1) in
order to disclose the effect of the spacer groups
(Scheme 2). The reactions were carried out in a large
excess of hexane to reduce the extent of dimerization
and oligomerization of the carbenes. In the case of 2
and 3, a small volume of PFMC was added to the
hexane kept at 40 °C; at this temperature, the two
liquids form a homogeneous phase in which the catalyst
is completely soluble. Yields and product distributions
were determined by GC (see Section 4). The results are
listed in Table 4. They confirm the earlier observations
(see above) that the more electrophilic catalysts (2 and
3) are also more effective at CꢀH insertion. The unef-
fectiveness of Rh2(OAc)4, 4, and 7 can be attributed to
both their similarly low electrophilicity and their insolu-
bility in the reaction medium. The selectivity of the
insertion reaction is not influenced markedly by the
catalysts used in this study, and it is also rather similar
Scheme 2.
lysts contain phosphane or amine ligands with per-
fluoroalkyl segments but no other polar function. Low
solubility in perfluorocarbons was also noticed for re-
lated highly fluorinated cobalt(II) [13] and mangane-
se(II) [14] carboxylates.
Complexes 2 and 3 are also soluble at ambient
temperature in organic media such as THF and diethyl
ether (good solubility), dichloromethane, chloroform
(intermediate), and toluene (low). In the two-phase
systems PFMC–organic solvent, with the exception of
PFMC–hexane, a leaching into the organic phase can
be noticed visually by the green color of the latter. As
Table 2 shows, the distribution coefficients of mixtures
with hexane, toluene and CH2Cl2 are sufficiently far on
the side of PFMC to allow an efficient extraction of the
catalysts into the perfluorocarbon solvent.

A. Endres, G. Maas / Journal of Organometallic Chemistry 643–644 (2002) 174–180
177
Table 4
Products and yields of the reaction of methyl diazoacetate with hexane catalyzed by 1–7
Catalyst Rh2(OOCR)4 R=
Yield (%)
Relative yield of insertion
8
9
10
1.1
12.3
2.9
11.9
1.0
0.8
11 (E+Z)
C-1/C-2/C-3
1
2
CH3
0.3
2.5
0.4
2.8
26.0
5.7
24.9
2.2
2.6
24.9
8.8
20.6
8.7
19.9
14.9
1/14.0/5.5
1/15.6/7.4
C7F15
a
3
4
7
CH2C6F13
CH2CH2C6F13
CH2O(CH2)2C10F21
2.6
1/14.4/6.9
B0.2
:0.2
a Yields of a second reaction cycle in which the amount of catalyst recovered from the first cycle was used.
to other rhodium carboxylate catalysts such as
Rh2(OOCCF3)4 and Rh2(octanoate)4 [1,16].
tion into PFMC at the end of the reaction. Complex
formation of the highly electrophilic catalysts with the
b-diketonate moieties of 13 and 14 — either at the
open coordination site of the rhodium atoms or by
exchange of the bridging ligands under the forcing
reaction conditions — could explain both the deactiva-
tion of the catalysts and the loss of solubility in
fluorous solvents.
We have also checked whether the catalysts can be
recovered and reused. In the case of the insoluble
complexes 4, 7, and Rh2(OAc)4, green sticky solids were
obtained at the end of the reaction, which are a mixture
of catalyst (IR) and organic material consisting most
likely of carbene oligomers (based on the very broad
NMR absorptions in the range for COOMe protons).
Obviously, efforts to recover the catalysts from these
mixtures are not meaningful. A color change of cata-
lysts 2 and 3 from green to olive-yellow at the end of
the reaction indicated at least a partial alteration. In the
case of 2, only 32% of the catalyst could be recovered
by extraction into the fluorinated solvent (i.e. by phase
separation of the hexane–PFMC mixture at −18 °C).
When this material was applied to a second cycle of the
CꢀH insertion reaction with the same concentration of
diazoacetate as before, a strong decrease of the inser-
tion reaction and a simultaneous increase of carbene
dimer formation was noted. This result can be at-
tributed to the lower concentration of catalyst in the
second cycle; we know from other experiments that
carbene dimer formation becomes more important
when the catalyst drops below a certain threshold.
3. Conclusion
This study has revealed that the applicability of the
concept of fluorous synthesis to rhodium-catalyzed car-
bene transfer reactions is limited. The widely used
catalyst Rh2(OAc)4 can be made fluorous by replacing
the acetate ligands with alkanecarboxylate ligands bear-
ing long perfluoroalkyl segments (C6F13, C8F17, C10F21).
In order to suppress the electron-withdrawing effect of
the latter on the RhꢀRh core of the complex, at least
two methylene groups are required as spacers between
these segments and the carboxylate head group. How-
ever, only catalysts 2 and 3, i.e. those without a spacer
or with only one methylene spacer are soluble in the
perfluorinated solvent PFMC, this solubility being a
2.3. Intramolecular CꢀH insertion
As a test case for an intramolecular CꢀH insertion,
we looked at the reaction of a-diazo-b-keto ester 12
catalyzed by 2 and 3, respectively, in benzotrifluoride as
solvent (Scheme 3). In line with previous studies using
Rh2(OAc)4 [17] and other rhodium catalysts [18], both
the aromatic CꢀH insertion product 13 and the methyl-
ene insertion product 14 were formed. The preference
for 13 is higher than in the case of Rh2(OAc)4 (54:46
mixture) but
a bit lower than in the case of
Rh2(O2CCF3)4 [18]. We observed, however, that cataly-
sis by 2 and 3 required harsher conditions than with all
other rhodium catalysts reported so far and that the
combined yield of insertion was lower. Furthermore,
none of the two catalysts could be recovered by extrac-
Scheme 3.

178
A. Endres, G. Maas / Journal of Organometallic Chemistry 643–644 (2002) 174–180
prerequisite for recovery of the catalyst. Thus, there is
the dilemma that those catalysts, which are electroni-
cally similar to rhodium acetate (5–7), cannot be used
under homogeneous catalysis conditions and are, there-
fore, not suited for the intermolecular CꢀH insertion
into alkanes. On the other hand, the soluble and more
electrophilic catalysts 2 and 3 promote the CꢀH inser-
tion into hexane with methyl diazoacetate in a com-
bined yield of ca. 40% but are altered and deactivated
in the course of the reaction and can be recovered only
to a low extent (ca. 30%) by extraction into PFMC. In
combination with our earlier studies on cyclopropana-
tion of alkenes and of toluene with methyl diazoacetate
[5], it can be concluded that high recovery of catalyst 2
can only be expected (a) if the carbene transfer reaction
is sufficiently fast to prevent the formation of carbene
dimers or oligomers which appear to deactivate the
catalyst or (b) if the catalysts are not too electrophilic,
in order to prevent product inhibition to occur. We are
now investigating rhodium (perfluoroalkyl)benzoates,
which appear to qualify better for fluorous synthesis
due to their higher and more selective solubility in
fluorous phases.
within 10 min. After the ethanol had distilled off, the
temperature was raised to 110 °C. In order to remove
the acetic acid liberated in the ligand exchange reaction,
four portions of toluene (4×10 ml) were added subse-
quently and were allowed to distill off each time. The
mixture was refluxed during 11 h, then about half of the
solvent was removed. By cooling to 4 °C a dark green,
a waxy solid separated which was dissolved in hot
1,1,2-trichlorotrifluoroethane–toluene (1:1). On cool-
ing, complex 2 separated again as a waxy solid, which
was subjected to flash column chromatography [silica
gel, petroleum ether–pentane (7:3)] to remove traces of
acid. Yield: 97 mg (77%). Treatment of the dark green
waxy product with acetonitrile yielded the bis(acetoni-
trile) complex 2×(CH3CN)2 as a pink solid, melting
point (m.p.) 71 °C, which was more convenient to
handle and from which the solvent-free complex 2
could be regenerated by heating at 60 °C 1 mbar for 5
h. Rf=0.89 (petroleum ether–ether, 7:3). 19F-NMR
(CDCl3): l= −81.64 (m, 12 F, CF3), −117.11 (m, 8
F), −122.92 (m, 8 F), −123.55 (m, 8 F), −124.31 (m,
16 F), −127.77 (m, 8 F). IR (KBr): w=2314 (w), 1739
(w), 1663 (s), 1424 (m), 1365 (m), 1319 (w), 1244 (s),
1207 (s), 1148 (s), 1018 (m), 669 (m) cm−1. MS (LD-
TOF): m/z=1857.7 (Rh2L4), 2268.2 (Rh2L5); Calc.
1856.7, 2270.6. C32F60O8Rh2 (M=1856.7 g mol−1).
4. Experimental
All reactions were carried out under argon. Analyti-
cal grade solvents were used. The petroleum ether used
had a boiling point range of 30–50 °C. Flash chro-
matography was performed on silica gel (Merck silica
gel 60 (0.040–0.063 mm). NMR spectra were recorded
on an Bruker AMX 400 instrument (1H: 400.1 MHz;
13C: 100.6 MHz; 19F: 376 MHz). Internal standards
were used [1H: TMS or THF-d8 (l=1.73 and 3.58);
19F: CF2ClꢀCFCl2 (l= −68 and −73 ppm). IR spec-
tra were recorded on Perkin–Elmer 883 and Bruker
Vector 22 spectrometers. LD mass spectra were ob-
tained with a Bruker Reflex III instrument. GC analy-
ses were performed on a Varian 3800 instrument.
(1H,1H,2H,2H-perfluorododecyl)oxyacetic acid [19], 2-
4.1.2. Tetrakis[v-2-(perfluorohexyl)acetato-O:O%]
dirhodium, Rh2(OOCCH2C6F13)4 (3)
The complex was prepared and purified analogously
to 2, described above, from 41.2 mg (0.11 mmol) (per-
fluorohexyl)acetic acid in toluene (25 ml) and
Rh2(OAc)4 in ethanol (12 ml). Yield: 35 mg (74%) of a
waxy material. Treatment with acetonitrile yields an
adduct 3×(CH3CN)2 as a pink solid, m.p. 73 °C,
which is more convenient to handle and from which the
original complex 3 can be regenerated as described for
2. Rf=0.59 (petroleum ether–ether, 7:3). 1H-NMR
3
(CDCl3–THF-d8): l=3.17 (t, 8 H, J(H,F)=17.9 Hz,
CH2). 19F-NMR (CDCl3–THF-d8): l= −82.15 (m, 12
F, CF3), −113.34 (m, 8 F), −123.01 (m, 8 F), −
124.04 (m, 8 F), −124.26 (m, 8 F), −127.34 (m, 8 F).
IR (KBr): w=2961 (m), 1719 (m), 1611 (s), 1428 (s),
1414 (s), 1365 (m), 1317 (m), 1241(s), 1206 (s), 1145 (s),
1123 (m), 1064 (m), 748 (m), 738 (m), 709 (m), 683 (m)
cm−1. MS (LD-TOF): m/z=1712.8 (Rh2L4), 2089.6
(Rh2L5); Calc. 1712.7, 2090.7. C32H8F52O8Rh2 (M=
1712.7 g mol−1).
(perfluorohexyl)acetic
acid
[20],
3-(perfluoro-
hexyl)propionic acid [21], 3-(perfluorooctyl)propionic
acid [21] and 3-(perfluorodecyl)propionic acid [21] were
prepared according to literature procedures.
4.1. Preparation of the dirhodium
tetrakis(alkanecarboxylates)
4.1.1. Tetrakis(v-perfluorooctanoato-O:O%) dirhodium
(2)
4.1.3. Tetrakis[v-3-(perfluorohexyl)propionato-O:O%]
dirhodium, Rh2(OOCCH2CH2C6F13]4 (4)
A solution of perfluorooctanoic acid (112 mg, 0.27
mmol) in toluene (15 ml) was placed in a reaction vessel
equipped with a dropping funnel and a Dean-Stark trap
and was heated at 100 °C. A solution of Rh2(OAc)4
(30.0 mg, 0.07 mmol) in EtOH (15 ml) was added
A solution of 3-(perfluorohexyl)propionic acid (80.0
mg, 0.20 mmol) and sodium hydroxide (8.2 mg, 0.20
mmol) in ethanol (15 ml) was added to a stirred solu-
tion of RhCl3·3H2O (13.4 mg, 0.05 mmol) in refluxing
ethanol (5 ml). The color of the solution changed from

A. Endres, G. Maas / Journal of Organometallic Chemistry 643–644 (2002) 174–180
179
red to yellow and yellow brown. A green solid precipi-
4.1.6. Tetrakis[v-(1H,1H,2H,2H-perfluorododecyloxy)-
acetato-O:O%] dirhodium (7)
tated, leaving a colorless mother liquor. The solid was
isolated by filtration, dissolved in hot EtOH, and
filtered hot to remove traces of a grey powder
(rhodium). The solution was concentrated and cooled at
4 °C to furnish the complex 4 together with a small
amount of sodium 3-(perfluorohexyl)propionate. Re-
crystallization from THF yielded pure 4 as a pale green
microcrystalline solid; m.p. \280 °C; yield: 24 mg
(53%). Rf=0.31 (petroleum ether–ether, 7:3). 1H-NMR
(CD3OD–1,1,2-trichlorotrifluoroethane): l=2.40–2.48
(m, 16 H, (CH2)2). 19F-NMR (CD3OD–1,1,2-trichloro-
trifluoroethane): l= −82.10 (t, 12 F, 3J=10.3 Hz,
CF3), −115.73 (m, 8 F, CF2), −122.59 (m, 8 F, CF2),
−123.59 (m, 8 F, CF2), −124.38 (m, 8 F, CF2),
−126.99 (m, 8 F, CF2). IR (KBr): w=2966 (w), 1579
(s), 1534 (m), 1444 (s), 1422, 1375, 1366, 1300 (all m),
1249, 1211, 1188 (all s), 1138 (s), 1120, 1107, 1039, 1077
(all m), 703, 651, 641 (all m) cm−1. MS (LD-TOF):
m/z=1768.8 (Rh2L4), 2159.8 (Rh2L5); Calc. 1768.8,
2159.8. C36H16F52O8Rh2 (M=1768.8 g mol−1).
The complex was prepared analogously to 4, de-
scribed above, from 2-(1H,1H,2H,2H-perfluorododecy-
loxy)acetic acid (61.0 mg, 0.10 mmol), sodium
hydroxide (4 mg, 0.10 mmol), and RhCl3·3H2O (6.5 mg,
0.025 mmol). After a reaction time of 5 h, a dark grey
solid had separated which was filtered off, treated with
boiling THF (20 ml), and filtered hot to remove a small
amount of a grey powder (rhodium). The filtered solu-
tion was concentrated and cooled at 4 °C to furnish 7
as a pale green microcrystalline solid. m.p. 162 °C;
1
yield: 10 mg (30%). H-NMR (THF-d8–1,1,2-trichloro-
trifluoroethane): l=1.54 (t, 8 H, 3J=6.6 Hz, Rf10CH2),
2.39–2.49 (m, 8 H, Rf10CH2CH2), 3.82 (s, 8 H, Ha).
19F-NMR (400.1 MHz, [d8] THF–1,1,2-trichlorotriflu-
oroethane): l= −82.29 (t, 12 F, 3J=8.9 Hz, CF3),
−114.45 (m, 8 F, CF2), −122.69 (m, 40 F, CF2),
−123.7 (m, 8 F, CF2), −124.68 (m, 8 F, CF2), −
127.29 (m, 8 F, CF2). IR (KBr): w=2904 (w), 1599 (s),
1414, 1373, 1343 (all m), 1211 (s), 1151 (s), 663, 644 (all
m) (w) cm−1. C56H24F84O12Rh2 (M=2690.5 g mol−1).
4.1.4. Tetrakis[v-3-(perfluorooctyl)propionato-O:O%]
dirhodium, Rh2(OOCCH2CH2C8F17]4 (5)
4.2. Rh-catalyzed reaction of methyl diazoacetate with
n-hexane
The complex was prepared analogously to 4, de-
scribed above, from 3-(perfluorooctyl)propionic acid
(90.0 mg, 0.18 mmol), sodium hydroxide (7.3 mg, 0.18
mmol) and RhCl3·3H2O (12 mg, 0.46 mmol). M.p.
\220 °C; yield: 28 mg (57%). Rf=0.4 (petroleum
The catalyst (1 mol%) was dissolved (2 and 3) or
suspended (4–7) in perfluoro(methylcyclohexane) (0.5
ml). After addition of hexane (4 ml), the temperature
was raised to 40 °C. 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, 40 °C) dibenzylether was added as
an internal standard, and the yield and product distribu-
tion was determined by gas chromatography (column:
fused silica, CP-WAX 52 CB as stationary phase, 25
m×0.32 mm; variable temperature 50“250 °C). The
mixtures of the insertion products were not separated on
a preparative scale; rather, the components were iden-
tified by GC–MS and by characteristic 13C-NMR sig-
nals.
1
ether–ether, 7:3). H-NMR ([d8] THF–1,1,2-trichloro-
trifluoroethane): l=2.23–2.34 (m, 8 H, Hb), 2.38–2.41
(t, 8 H, 3J=6.7 Hz, Ha). 19F-NMR (THF-d8–1,1,2-
trichlorotrifluoroethane): l= −82.32 (t, 12 F, 3J=10.3
Hz, CF3), −116.07 (m, 8 F, CF2), −122.4 (m, 8 F,
CF2), −122.94 (m, 16 F, CF2), −123.78 (m, 8 F, CF2),
−124.72 (m, 8 F, CF2), −127.30 (m, 8 F, CF2). IR
(KBr): w=2944 (w), 1575 (s), 1445, 1422, 1372, 1335 (all
m), 1206, 1147, 1107 (all s), 705 (m), 660 (m) cm−1. MS
(LD-TOF): m/z=2169.9 (Rh2L4); Calc. 2169.3.
C44H16F68O8Rh2 (M=2169.3 g mol−1).
4.2.1. Methyl octanoate (8)
4.1.5. Tetrakis[v-3-(perfluorodecyl)propionato-O:O%]
dirhodium, Rh2(OOCCH2CH2C10F21)4 (6)
Prepared independently by esterification of octanoic
acid. 13C-NMR (CDCl3): l=13.96, 22.53, 24.91, 28.86,
29.06, 31.59, 34.04, 51.31 (OMe), 173.01 (CꢁO).
MS(EI): m/z=158 [M]+, 87 [H2CꢁCHCO2Me+H]+,
74.
The complex was prepared analogously to 4, de-
scribed above, from 3-(perfluorodecyl)propionic acid
(60.0 mg, 0.10 mmol), sodium hydroxide (4 mg, 0.10
mmol), and RhCl3·3H2O (6.7 mg, 0.025 mmol). Pale
green microcrystals were obtained by crystallization
from hot ethanol; m.p. \220 °C; yield: 22 mg (68%).
Due to the insolubility in common solvents at room
temperature (r.t.), no NMR spectra could be recorded.
IR (KBr): w=3434 (m), 1581(s), 1443 (m), 1421 (m),
1376 (m), 1346 (m), 1213 (s), 1152 (s), 1108 (m), 664 (m),
644 (m) cm−1. C52H16F84O8Rh2 (M=2570.4 g mol−1).
4.2.2. Methyl 3-methylheptanoate (9)
13C-NMR (CDCl3, partial): l=30.44 (CH), 172.81
(CꢁO). MS(EI): m/z=158 [M]+, 143 [M−Me]+, 101
[M−Bu]+, 74.
4.2.3. Methyl 3-ethylhexanoate (10)
13C-NMR (CDCl3, partial): l=36.42 (CH), 172.55

180
A. Endres, G. Maas / Journal of Organometallic Chemistry 643–644 (2002) 174–180
(CꢁO). MS(EI): m/z=158 [M]+, 129 [M−Et]+, 127
[M−OCH3]+, 115 [M−Pr]+, 74.
[4] Reviews: (a) I.T. Horva´th, J. Ra´bai, Science 266 (1994) 72;
(b) A. Studer, S. Hadida, R. Ferritto, S.-Y. Kim, P. Jeger, P.
Wipf, D.P. Curran, Science 275 (1997) 823;
(c) Curran D.P.; Angew. Chem. 110 (1998) 1230; Angew. Chem.
Int. Ed. Engl. 37 (1998) 1174;
In an effort to recover catalyst 2, PFMC (1.5 ml) was
added to the reaction mixture after the reaction was
over. At −18 °C, complete separation of the hexane
and PFMC phases took place. From the green-colored
PFMC phase, 32% of the original amount of 2 were
recovered.
(d) I.T. Horva´th, Acc. Chem. Res. 31 (1998) 641;
(e) R.H. Fish, Chem. Eur. J. 5 (1999) 1677;
(f) E. de Wolff, G. van Koten, B.-J. Deelman, Chem. Soc. Rev.
28 (1999) 37;
(g) M. Cavazzini, F.Montanari, G. Pozzi, S. Quici, J. Fluorine
Chem. 94 (1999) 183;
(h) L.P. Barthel-Rosa, J.A. Gladysz, Coord. Chem. Rev. 190–
192 (1999) 587;
4.3. Intramolecular CꢀH insertion of 12
(i) B. Betzemeier, P. Knochel, Top. Curr. Chem. 206 (1999) 61;
(j) A. Endres, G. Maas, Chem. Unserer Zeit. 34 (2000) 382.
[5] A. Endres, G. Maas, Tetrahedron Lett. 40 (1999) 6365.
[6] H.M.L. Davies, T. Hansen, M.R. Churchill, J. Am. Chem. Soc.
122 (2000) 3063.
[7] Rh2(pfb)4-catalyzed decomposition of a-silyl-a-diazoacetates: (a)
G. Maas, M. Gimmy, M. Alt, Organometallics 11 (1992) 3813;
(b) M. Alt, G. Maas, Chem. Ber. 127 (1994) 1537;
(c) V. Gettwert, F. Krebs, G. Maas, Eur. J. Org. Chem. (1999)
1213.
[8] (a) M.P. Doyle, S.N. Mahapatro, A.C. Caughey, M.S. Chinn,
M.R. Colsman, N.K. Harn, A.E. Redwine, Inorg. Chem. 26
(1987) 3070;
(b) V. Schurig, Inorg. Chem. 25 (1986) 945.
[9] V. Herrera, P.J.F. de Rege, I.T. Horva´th, T. Le Husebo, R.P.
Hughes, Inorg. Chem. Commun. 1 (1998) 197.
[10] E.G. Hope, A.M. Stuart, J. Fluorine Chem. 100 (1999) 75.
[11] C. Rocaboy, W. Bauer, J.A. Gladysz, Eur. J. Org. Chem. (2000)
2621.
A solution of diazo ester 12 [17] (65 mg, 0.25 mmol)
in benzotrifluoride (0.5 ml) was added during 1 h via a
syringe pump to a solution of catalyst 2 (7.0 mg, 1.5
mol%) or 3 (6.7 mg, 1.5 mol%) in benzotrifluoride (1.5
ml) and heated at 45 °C for 6 h, then at 80 °C for 8 h.
With catalyst 2, the reaction solution turned greenish-
brown, with catalyst 3 it kept the original green color.
The solvent was replaced by CDCl3 and after addition
of dibenzyl ether as a standard, the composition of the
mixture was determined by 1H-NMR spectroscopy. The
chemical shifts of products 13 and 14 agreed with
literature values [17], yields are given in Scheme 3.
Acknowledgements
[12] G. Winkaus, P. Ziegler, Z. Anorg. Allg. Chem. 350 (1967) 51.
[13] G. Pozzi, M. Cavazzini, S. Quici, S. Fontana, Tetrahedron Lett.
38 (1997) 7605.
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Chem. (1997) 109 1997 2438; Angew. Chem. Int. Ed. Engl.
(1997) 36, 2346.
We thank Dr M. Wunderlin and Dr R. Heinrich
(University of Ulm) for recording of the LD-TOF mass
spectra.
[15] H. Brunner, H. Kluschanzoff, K. Wutz, Bull. Soc. Chim. Belg.
98 (1989) 63.
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