Ortho-Metalated dirhodium(II)-catalyzed α-diazocarbonyl transformation. Diastereoselective cyclopropanation of menthyl-α-diazo-β-keto ester and C-H insertion of α-diazo ester

Article abstract of DOI:10.1016/S0022-328X(00)00357-0

ortho-Metalated rhodium(II) compound (1d₁) containing two metalated P(C₆H₅)₂(C₆F₅) and two acetates has successfully catalyzed cyclopropanation of menthyl-2-diazo-3-oxo-6-heptanoate (4) to form cyclopropanes 6 and 7 with significant cis-trans (30:70) diastereoselectivity. An enhanced performance of methyl-2-diazoundecanoate (5) cyclization has been achieved mediated by 2d₁ and 2d₄ catalysts, obtaining 71 and 85%, respectively, of the 1,5-C-H insertion product, trans-2-pentylcyclopentanecarboxylate (8) versus 1,2-elimination product, (Z)-2-undecenoate (9) (29 and 15%, respectively). The three possible diastereomers of catalyst (1d) which possess two ortho-metalated P(C₆H₅)₂(C₆F₅) ligands in a head-to-tail configuration, with the two pentafluorophenyl groups in an endo-endo, endo-exo or exo-exo disposition have been separated by standard column chromatography. The X-ray structure analysis for two of these isomers 1d_3endo-exo and 1d_1endo-endo allows their structural assignment.

Full text of DOI:10.1016/S0022-328X(00)00357-0

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 612 (2000) 36–45
ortho-Metalated dirhodium(II)-catalyzed a-diazocarbonyl
transformation. Diastereoselective cyclopropanation of
menthyl-a-diazo-b-keto ester and CꢀH insertion of a-diazo ester
a
Pascual Lahuerta a,*1, Ine´s Pereira a, Julia Pe´rez-Prieto b,*2, Mercedes Sanau´ ,
Salah-Eddine Stiriba a,d,*3, Douglass F. Taber c,*4
a Departamento de Qu´ımica Inorga´nica, Facultad de Qu´ımicas, Dr Moliner 50, 46100 Burjassot, Valencia, Spain
b Departamento de Qu´ımica Orga´nica, Facultad de Farmacia, Vicent Andre´s Estelle´s s/n, 46100 Burjasot, Valencia, Spain
c Department of Chemistry and Biochemistry, Uni6ersity of Delaware, Newark, DE 19716, USA
d Laboratoire de Chimie Organome´tallique et de Catalyse, Institut le Bel, Uni6ersite´ Louis Pasteur, 4 rue Blaise Pascal,
67007 Strasbourg Cedex, France
Received 19 April 2000; received in revised form 2 June 2000
Abstract
ortho-Metalated rhodium(II) compound (1d1) containing two metalated P(C6H5)2(C6F5) and two acetates has successfully
catalyzed cyclopropanation of menthyl-2-diazo-3-oxo-6-heptanoate (4) to form cyclopropanes 6 and 7 with significant cis–trans
(30:70) diastereoselectivity. An enhanced performance of methyl-2-diazoundecanoate (5) cyclization has been achieved mediated
by 2d1 and 2d4 catalysts, obtaining 71 and 85%, respectively, of the 1,5-CꢀH insertion product, trans-2-pentylcyclopentanecar-
boxylate (8) versus 1,2-elimination product, (Z)-2-undecenoate (9) (29 and 15%, respectively). The three possible diastereomers of
catalyst (1d) which possess two ortho-metalated P(C6H5)2(C6F5) ligands in a head-to-tail configuration, with the two pen-
tafluorophenyl groups in an endo–endo, endo–exo or exo–exo disposition have been separated by standard column chromatogra-
phy. The X-ray structure analysis for two of these isomers 1d3endo–exo and 1d1endo–endo allows their structural assignment. © 2000
Elsevier Science B.V. All rights reserved.
Keywords: Rhodium; ortho-Metalated; Diazo compounds; Carbenoid; Selectivity
1. Introduction
trolling the relative and absolute chemistry around the
cyclopropane ring [3,4]. On other hand, only rhodium-
(II) tetracarboxylates have been investigated in catalytic
CꢀH insertion of a-diazo ester in which a b-hydride
elimination reaction occurred concomitantly [5]. In this
respect, the design of a rhodium(II) complex that itself
would cyclize such esters with high selectivity has not
yet been achieved.
Most recently, ortho-metalated dirhodium(II) com-
pounds of formula Rh2(OOCR)2(PC)2 [PC=ortho-
metalated phosphine, OOCR=carboxylate, head-to-
tail configuration] (1) (Chart 1) have been studied in
CꢀC bond formation mediated a-diazo ketone transfor-
mation, exhibiting good chemoselectivity and good to
excellent regioselectivity [6–8]. These compounds offer
interesting electronic and steric features, which make
them very attractive for rhodiumcarbenoid catalytic
purposes [9].
The rhodium(II)-mediated reactions of a-diazocar-
bonyl compounds onto appropriate substrates have
emerged as a powerful method in organic synthesis in
general and for the selective construction of carbocyclic
building blocks in particular, e.g. cyclopropanes and
cyclopentanes [1–3]. However, intramolecular cyclo-
propanation of a-diazocompounds catalyzed by Rh(II)
compounds is usually moderately diastereoselective [2].
Much less information is known, however, about con-
1 * Corresponding author. Tel.: +34-96-3864854; fax: +34-96-
3864322.
2 * Corresponding author.
3 * Corresponding author. E-mail: stiriba@chimie.u-strasbg.fr
4 * Corresponding author.
0022-328X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00357-0

P. Lahuerta et al. / Journal of Organometallic Chemistry 612 (2000) 36–45
37
Table 1
List of ortho-metalated rhodium(II) catalysts a
Catalyst
R1
R2
R3
R4
R
Isomer
Ref.
1a1
1a2
1a3
1a4
1d1exo–exo
1d1endo–endo
1d1endo–exo
1d3endo–exo
1d4endo–exo
2a1
C6H5
C6H5
C6H5
C6H5
C6F5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6F5
C6F5
C6F5
C6F5
C6H5
C6F5
C6F5
C6H5
C6H5
C6H5
C6H5
C6H5
C6F5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6F5
C6H5
C6F5
C6F5
C6F5
CH3
CF3
C3F7
C(CH3)3
CH3
CH3
CH3
C3F7
C(CH3)3
CH3
[12]
[6b]
[6b]
This work
This work
This work
[7]
exo–exo
endo–endo
endo–exo
endo–exo
endo–exo
[7]
This work
[13a]
[7]
2d1
2d4
CH3
C(CH3)3
This work
a See (Chart 1) for catalysts structures.
cyclization with t-butyl-2-diazo-3-oxoundecanoate in
the presence of 1 and 2. Fortunately, all attempts
resulted in the formation of substantial amounts of the
cyclized product upon heating at 100°C5.
2.2. Diastereoselecti6e h-diazo-i-keto ester
cyclopropanation
As asymmetric synthesis can be accomplished by the
use of a chiral substrate, menthyl-2-diazo-3-oxo-6-hep-
tenoate (4) was used for face selecti6ity studies in
intramolecular cyclopropanation catalyzed by ortho-
metalated Rh(II) compounds. The chiral nature of the
ester group could induce stereoselection in its transfor-
mation [10]. In fact the carbene insertion reaction
would give rise to diastereoisomeric bicyclic cyclopen-
tanones (6) and (7) which could be easily separated by
silica gel chromatography. Several years ago, one of us
reported that copper bronze catalyzed the cyclization of
4, leading to a 1:1 mixture of the ketones 6 and 7,
respectively (Table 2) [10b]. Using Rh2(OOCCH3)4 we
observed an equimolar mixture of both ketones.
Chart 1.
We found of interest to assess the mixed carboxy-
late–phosphine complexes in the aforementioned cy-
clizations. In this report, we describe the finding that
intramolecular cyclopropanation with menthyl-2-diazo-
3-oxo-6-heptenoate (4) catalyzed by the complex 1 and
2 (Table 1) can be significantly diastereoselective and
competition between the 1,5-CꢀH insertion and the
b-elimination reaction with methyl-2-diazoundecanoate
(5) could be highly modulated. Results are compared
with those obtained with other catalysts.
We have found again, that the double-metalated
complexes 1a1 and 1a2 were not reactive on exposure to
the a-diazo-b-keto ester 4 at room temperature, but
they provided the cyclization products on heating at
100°C (sealed tube). We heretofore carried out all ex-
2. Results
2.1. Catalytic considerations
5 * All the ortho-metalated Rh(II) complexes, structure type 1 and
those of group 2, we have investigated, induce CꢀH insertion of an
a-diazo-b-keto ester, such as t-butyl-2-diazo-3-oxoundecanoate (i),
when the reaction is performed at 100°C. Only 2d1 lead to ii at room
temperature with high yield (89%).
Table 1 summarizes the structures of all the meta-
lated rhodium(II) compounds used in this report. The
catalytic reactions were performed as reported else-
where [7].
Our interest in ortho-metalated Rh(II) carbene-trans-
fer reactions has centered on intramolecular cyclo-
propanation and CꢀH insertion reactions [6,7]. We had
previously reported that the double-metalated com-
plexes 1a1 and 1a2 were unreactive with a-diazo-b-keto
esters in refluxing dichloromethane [7]. We initiated our
study by examining the possibility of effecting catalytic

38
P. Lahuerta et al. / Journal of Organometallic Chemistry 612 (2000) 36–45
Table 2
Ortho-metalated rhodium(II)-catalyzed reaction of a-diazo-b-keto ester (4)
a
Entry
Catalyst
Time (h)
Yield (%)
Relative ratio (%)
% De
6
7
1
2
3
4
5
6
7
8
Cu b
Rh2(OOCCH3)4
1a1
1d1mixture
1d1endo–endo
1d1endo–exo
1a2
1
1
1
2
2
2
2
1
61
56
49
66
74
64
54
68
50
50
50
35
37
40
40
43
50
50
50
65
63
60
60
57
0
0
0
30
26
20
20
14
2d1
a All the reactions were carried out in a sealed tube at 100°C.
b See Ref. [10b].
periments at this temperature (Table 2). For the ratio
measurement of the cyclopropane diastereomers, 13C-
NMR of the reaction mixtures have been used looking
at changes which occur in signals of the methine chem-
ical shifts at 74.60 and 74.87 ppm of 6 and 7, respec-
tively. The error bars of our ratios were in the range of
1–3%6. We observed a change in the diastereoselectiv-
ity of intramolecular cyclopropanation on changing the
transition metal complex used. Low yield and no
diastereomeric excess were obtained when the catalyst
1a1 was used. Increasing the electrophilicity of the
ligands (catalysts 1a2 and 1d1) resulted in a small im-
provement in the selectivity (20–30%) of these cata-
lysts. The three diastereoisomers 1d1 (endo–endo,
exo–endo and exo–exo) gave rise to quite similar re-
sults. The monometalated catalyst 2d1 was less selective.
important role in the cyclization of a-diazo esters
[5c,11]. We present here the results obtained with
methyl-2-diazoundecanoate (5) (Table 3).
Treatment of 5 with rhodium(II) tetracarboxylates
parallel previously reported results with similar diazo
derivatives.
Rhodium(II)
trifluoroacetate
in
dichloromethane at −78°C resulted in trace amounts
of the cyclization product, methyl trans-2-pentylcy-
clopentanecarboxylate (8). The major product, methyl
(Z)-2-undecenoate (9), was produced in 80% yield [11].
By using higher temperature or/and less electrophilic
catalysts, as Rh2(OOC(CH3)3)4, the 1,5-CꢀH insertion
reaction competed with the elimination reaction (Table
3).
We extended these studies to the ortho-metalated
complexes 1–2 (Table 3). Surprisingly, at room temper-
ature doubly metalated complexes, 1a1, 1d1 and 1a2 led
to only the b-elimination product in high yield. A less
electrophilic carboxylate ligand (as pivalate) was neces-
sary for a competitive 1,5-CꢀH insertion reaction, such
as 1a4 and 1d4 to appear.
2.3. Cyclization 6ersus elimination of an h-diazo ester
It has been reported that the type of ligand on the
dirhodium(II) catalyst and the temperature play an
In the case of monometalated Rh(II) complexes, one
actually obtains only the b-elimination product when
compound 2a1 (with triphenylphosphine and acetate as
ligands) is used. Surprisingly, the cyclization product
was favored using a catalyst with a less basic phos-
phine, P(C6F5)(C6H5)2. In this regard, it should be
noted that the excellent cyclization result was obtained
with catalysts possessing less electrophilic carboxylates
such as pivalates and the fluorinated metalated phos-
phine (see entry 10–12, Table 3).
6 The ratio of both diastereomers has been followed looking at
changes in 13C of CH.

P. Lahuerta et al. / Journal of Organometallic Chemistry 612 (2000) 36–45
39
Table 3
ortho-Metalated rhodium(II)-catalyzed reactions of a-diazo ester (5)
Entry
Catalyst
T (°C)
Yield (%)
Relative ratio (%)
8
9 a
100
b
1
2
3
5
6
7
8
9
Rh2(OOCCF3)4
Rh2(OOCCH3)4
−78
25
25
25
25
25
25
25
25
25
25
80
93
82
80
96
88
91
96
68
90
99
0
49
69
0
51
Rh2(OOCC(CH3)3)4
31(2/1) a
1a1
1a2
1a4
100
100
51(2/1) a
100
68(3/1) a
100
29
15
0
49
0
c
1d1
1d4endo–exo
2a1
2d1
32
0
10
11
12
71
85
2d4
a In the indicated cases the cis-9 was contaminated with the trans-9 (the relative ratio of both isomers appears into parentheses).
b See reference [11].
c All stereoisomers led to similar results.
2.4. Synthetic aspects of catalysts
The doubly metalated compound of formula Rh2
(OOCCH3)2[(C6H4)P(C6H5)2]2·2H2O (1a1), was pre-
pared according to the synthetic method described by
Cotton [12]. The monometalated compounds 2a1 [13a]
and 2d1 [7], were prepared according to reported meth-
ods. The doubly metalated compound of formula Rh2
(OOCCH3)2[(C6H4)P(C6F5)(C6H5)]2·2H2O (1d1) [7], was
also prepared by published methods. However, the
Fig. 1. The three possible configurations of diastereoisomers derived
photochemically-assisted ortho-metalation to obtain 1d1
isomers proved to be more efficient than the thermal
process, starting from 2d1 and P(C6H5)2(C6F5) in a 1:1
ratio in 3:1 chloroform–acetic acid solution by
irradiation.
from 1d.
Three diastereoisomers can be expected for com-
pound 1d1 depending on the relative disposition of the
C6F5 and C6H5 groups attached to both P atoms. These
three isomers labeled, exo–exo, exo–endo and endo–
endo are schematically depicted in Fig. 1. All the possi-
ble isomers were present in the crude reaction mixture,
they have been separated by the usual technique of
chromatography, the predominant one being (1d1endo–exo
)
which was isolated in yield of ꢀ90% [7] 1d1exo–exo and
1d1endo–endo were obtained in yields of 1.2 and 3%,
1
respectively. They have been characterized by H-, 13C-,
31P-, 19F-NMR and elemental analysis.
In order to confirm this structural assignment, we
carried out a crystal structure determination by X-ray
diffraction methods that we report here. The best crys-
Fig. 2. Perspective view and atom labeling scheme of compound
1d3endo–exo. Hydrogen atoms are omitted for clarity.

40
P. Lahuerta et al. / Journal of Organometallic Chemistry 612 (2000) 36–45
Table 4
NMR data for the three (1d1) isomers
Isomer
31P{1H}-NMR, l (ppm)
1JRhꢀP (Hz)
2JRhꢀP (Hz)
19F{1H}-NMR, l (ppm)
ortho
meta
para
1d1exo–exo
1d1endo–exo
14.4 (d)
14.5 (dd)
17.7 (dd)
19.4 (d)
170.8
173.3
175.3
175.3
−125.5 (br)
−126.6 (br)
−120.5 (br)
−122.6 (br)
−161.0 (m)
−162.4 (m)
−160.9 (m)
−162.5 (t)
−150.4 (t)
−151.2 (t)
−150.5 (t)
−151.5 (t)
9.5
7.4
1d1endo–endo
tal (Fig. 2) was obtained from the perfluorobutyrate
derivative (1d3endo–exo). The two remaining isomers, ob-
tained in much lower yield in the crude reaction mix-
ture, were also isolated as pure samples by
chromatography. As the NMR data (Table 4) do not
allow us to assign definitively the relative configuration
of each of these isomers, X-ray data were collected on
the best single crystal grown from the more polar of
these minor isomers.
The quality of the data was not completely satisfac-
tory, and the presence of disordered molecules of sol-
vent in the asymmetric unit resulted in a high residual
R value (11%). Multiple attempts to form better crys-
tals were unsuccessful. However, the important struc-
tural features of the molecule (Fig. 3) were
unambiguously established and an endo–endo structure
was assigned for this isomer. These data proved that
the order of isomer elution from the column chro-
matography was: exo–exo (minor), endo–exo (major)
and endo–endo (minor).
The bridge involving the metalated phosphine shows an
‘envelope’ conformation that is normal in this type of
rhodium compounds [12]. The two RhꢀP bond dis-
,
tances, Rh(1)ꢀP(1) 2.210(6) and Rh(2)ꢀP(2) 2.213(6) A,
are comparable to those found in other doubly meta-
lated compounds [12,13]. The four equatorial RhꢀO
bond distances are within the experimental error,
,
2.17(12)–2.18(2) A. The longest RhꢀO bond distance
corresponds to the axial water molecules, Rh(1)ꢀO(2)
,
2.337(12) and Rh(2)ꢀO(1) 2.35(2) A, and is indicative of
the high trans influence of the metal–metal bond. The
RhꢀRhꢀOaxial angles, 163.7(4) and 160.7(6)° deviate
from linearity, most likely due to steric interactions
between the non-metalated phenyl rings and the axial
ligands. This deviation is among the highest observed
for this type of rhodium dimer [16].
The angles around the two phosphorus atoms show
some significant differences, reflecting the different
configurations of the two P atoms. It is remarkable that
the value for the angle Rh(1)ꢀP(1)ꢀC(41) 107.9(7)° is
considerably smaller than the average of the other three
angles 118.5(6)°. This small angle can probably be
traced back to a hydrogen bridge between O(2)ꢀ
H···F(46).
The exchange of acetate groups with other carboxy-
lates such as trifluoroacetates, heptafluorobutyrates and
pivalates in compounds 1d1, 2a1 and 2d1 using the
method described by Doyle [14], afforded the rest of the
products used in these studies.
2.5.2. Rh2(OOCCH3)2[(C6H4)P(C6H5)(C6F5)]2·2H2O
2.5. Crystal structural aspects
(1d1endo–endo)
Relevant crystallographic data are summarized in
2.5.1. Rh2(O2CC3F7)2[(C6H4)P(C6H5)(C6F5)]2·2H2O
Table 5. Selected bond distances and angles are listed in
(1d3endo–exo
)
Relevant crystallographic data for 1d3endo–exo are
summarized in Table 5. A view of the molecule is
shown in Fig. 2.
Important bond distances and angles are listed in
Table 6. In the molecular structure two Rh atoms are
bridged by two perfluorobutyrate groups and by two
P(C6H5)2(C6F5) ligands, in a head-to-tail conformation,
each one metalated in one phenyl ring. The two phos-
phorus atoms have different configurations, as is shown
in Fig. 2. Two water molecules, occupying the axial
positions, complete the slightly distorted octahedral
coordination around the metals [angles in the range
84.5(5)–95.5(5)°]. The value of the RhꢀRh bond dis-
,
tance, 2.530(2)A, falls within the range reported for
dirhodium compounds of similar structures [12,13,15].
Fig. 3. Perspective view and atom labeling scheme of compound
1d1endo–endo. Hydrogen atoms are omitted for clarity.

P. Lahuerta et al. / Journal of Organometallic Chemistry 612 (2000) 36–45
41
Table 5
Rh(II) compounds with a tertiary phosphine, but we
can not recall any example with a C6F5 group in the
phosphine being used.
Crystallographic data and structure refinement for (1d3endo–exo) and
(1d1endo–endo
a
)
1d3endo–exo
1d1endo–endo
Formula
Formula weight
Crystal system
Temperature (K)
Space group
Unit cell dimensions
C44H22F24O6P2Rh2
1370.38
Triclinic
C40H28F10O6P2Rh2
1062.39
Monoclinic
293 (2)
3. Discussion
It is remarkable to note that a-diazo-b-keto esters
can react with ortho-metalated complexes 1 at 100°C.
With this information in mind, we evaluated the change
in diastereoselectivity of catalytic intramolecular cyclo-
propanation reaction of 4 using ortho-metalated Rh(II)
568 (2)
(
P1
P21/c
,
a (A)
12.2216(11)
13.9965(12)
15.6232(14)
94.7230 (10)
102.8360(10)
90.2770(10)
2596.1(4)
2
13.2990(14)
23.625(3)
14.758(2)
90
110.962(2)
90
4330.0(8)
4
1.631
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
Table 6
3
,
Selected bond distances (A) and angles (°) for (1d3endo–exo
)
,
V (A )
Z
Dcalc (mg m−3
)
1.753
0.3×0.3×0.6
0.828
Bond lengths
Rh(1)ꢀRh(2)
Rh(1)ꢀP(1)
Rh(2)ꢀP(2)
Rh(2)ꢀC(61)
Rh(1)ꢀC(16)
Rh(1)ꢀO(3)
2.530(2)
2.210(6)
2.213(6)
2.01(2)
1.98(2)
2.175(13)
Rh(2)ꢀO(4)
Rh(2)ꢀO(5)
Rh(2)ꢀO(1)
Rh(1)ꢀO(6)
Rh(1)ꢀO(2)
2.18(2)
2.182(14)
2.35(2)
2.172(12)
2.337(12)
Crystal size (mm)
Absorption
0.15×0.05×0.05
0.923
coefficient (mm−1
F (000)
)
1340
2108
Index ranges
−115h511,
−125k512,
−145l512
−145h56,
−265k57,
−155l516
1.64–23.30
Bond angles
Rh(2)ꢀRh(1)ꢀO(2) 163.7(4)
Rh(2)ꢀRh(1)ꢀP(1)
Rh(2)ꢀRh(1)ꢀC(16) 95.4(7)
Rh(2)ꢀRh(1)ꢀO(3)
Rh(2)ꢀRh(1)ꢀO(6)
P(1)ꢀRh(1)ꢀO(3)
P(1)ꢀRh(1)ꢀO(6)
P(1)ꢀRh(1)ꢀC(16)
O(3)ꢀRh(1)ꢀO(6)
Rh(1)ꢀP(1)ꢀC(41) 107.9(7)
Rh(1)ꢀP(1)ꢀC(51) 120.4(8)
C(41)ꢀP(1)ꢀC(51) 105.2(10)
Theta range for data 1.46–18.84
collection (°)
Reflections collected 3922
Unique data
Absorption
correction
Rh(1)ꢀRh(2)ꢀO(1) 160.7(6)
89.71(15) Rh(1)ꢀRh(2)ꢀP(2) 89.8(2)
9533
Rh(1)ꢀRh(2)ꢀC(61) 95.5(6)
3309 (Rint=0.0417)
None
5905 (Rint=0.0599)
SADABS
88.0(4)
85.9(2)
176.0(4)
92.1(3)
97.0(6)
84.4(5)
Rh(1)ꢀRh(2)ꢀO(4)
Rh(1)ꢀRh(2)ꢀO(5)
P(2)ꢀRh(2)ꢀO(4)
P(2)ꢀRh(2)ꢀO(5)
P(2)ꢀRh(2)ꢀC(61)
O(4)ꢀRh(2)ꢀO(5)
Rh(2)ꢀP(2)ꢀC(21)
Rh(2)ꢀP(2)ꢀC(31)
C(21)ꢀP(2)ꢀC(31)
84.7(4)
87.1(4)
96.8(4)
177.0(4)
92.1(6)
83.0(6)
118.0(7)
117.0 (6)
102.2(11)
Data/restraints/
parameters
3906/28/644
1.109
5905/0/578
Goodness-of-fit on
0.766
F2
Final R indices
[I\2|(I)]
R indices (all data)
R1=0.0968,
wR2=0.2427
R1=0.1140,
R1=0.1160,
wR2=0.2810
R1=0.2021,
wR2=0.2597
1.468 and −0.900
wR2=0.3587
4.569 and −1.407
Largest difference
Table 7
peak and hole
,
Selected bond distances (A) and angles (°) for (1d1endo–endo
)
−3
,
(e A
)
Bond lengths
a Both external water molecules are not considered in the molecular
formula.
Rh(1)ꢀRh(2)
Rh(1)ꢀP(2)
Rh(2)ꢀP(1)
Rh(2)ꢀC(46)
Rh(1)ꢀC(16)
Rh(1)ꢀO(4)
2.496(2)
2.210(5)
2.203(5)
1.97(2)
2.05(2)
2.131(12)
Rh(2)ꢀO(1)
Rh(2)ꢀO(6)
Rh(1)ꢀO(5)
Rh(2)ꢀO(3)
Rh(1)ꢀO(2)
2.168(12)
2.367(13)
2.31(2)
2.134(13)
2.112(13)
Table 7. The molecular structure of 1d1endo–endo is
closely related to that described for the 1d3endo–exo iso-
mer with the two ortho-metalated P(C6H5)2(C6F5) lig-
ands in a head-to-tail arrangement. Nevertheless the
perfluorobutyrate groups have been replaced by two
acetate groups and the two pentafluorophenyl groups
are now an endo–endo disposition. So the two phos-
phorus atoms have the same configurations as is shown
in Fig. 3. The important RhꢀL distances for 1d3endo–exo
and 1d1endo–endo isomers are equal within the standard
errors. The relatively high standard deviations do not
allow a detailed comparative discussion of the struc-
tural features in these isomers.
Bond angles
Rh(2)ꢀRh(1)ꢀO(4)
Rh(1)ꢀRh(2)ꢀP(1)
Rh(1)ꢀRh(2)ꢀC(46) 95.6(6)
Rh(1)ꢀRh(2)ꢀO(6) 170.3(4)
Rh(1)ꢀRh(2)ꢀO(1)
P(1)ꢀRh(2)ꢀO(6)
P(2)ꢀRh(1)ꢀO(4)
P(2)ꢀRh(1)ꢀ O(5)
O(3)ꢀRh(2)ꢀO(1)
Rh(2)ꢀP(1)ꢀC(21)
Rh(2)ꢀP(1)ꢀC(31)
C(11)ꢀP(1)ꢀC(31)
83.8(3)
Rh(2)ꢀRh(1)ꢀO(2)
87.1(3)
88.21(14)
87.63(14) Rh(2)ꢀRh(1)ꢀP(2)
Rh(1)ꢀRh(2)ꢀC(46) 95.6(6)
Rh(1)ꢀRh(2)ꢀO(1)
Rh(1)ꢀRh(2)ꢀO(6) 170.3(4)
P(1)ꢀRh(2)ꢀO(3)
P(2)ꢀRh(1)ꢀO(2)
82.6(3)
82.6(3)
95.4(3)
95.0(4)
98.7(6)
80.5(5)
116.9(6)
114.5(7)
105.0(8)
174.3(4)
175.3(3)
C(46)ꢀRh(2)ꢀO(1) 173.7(7)
O(2)ꢀRh(1)ꢀO(5)
Rh(2)ꢀP(1)ꢀC(11)
Rh(1)ꢀP(2)ꢀC(41)
85.7(6)
111.3(6)
111.1(7)
These types of structures are not new, they were
reported a long time ago [12,13,16] for ortho-metalated

42
P. Lahuerta et al. / Journal of Organometallic Chemistry 612 (2000) 36–45
behavior appears with doubly metalated compounds
containing pivalate carboxylates 1a4 and 1d4.
On other hand, the observation that catalysts 2d1 and
2d4 with P(C6H5)2(C6F5) (entry 11 and 12, Table 3) are
efficient for a cyclization reaction, is certainly of impor-
tance in several ways. This appears to be unexpected,
since such a fluorinated phosphine will increase the
electrophilicity of the rhodium–carbenoid. To explain
this result, we propose the intermediate shown in (Fig.
4).
Fig. 4. Proposed Rh–carbenoid intermediate stabilization in 2d1. The
three carboxylates ligands completing the lantern structure are incom-
pletely drawn to provide better overview.
We suggest that the fluorine atom can stabilize the
Rh–carbenoid, making the elimination process slower
and favoring the cyclization reaction. This idea can be
supported by comparison with the recognized charge
distribution of hexafluorobenzene. In this case the elec-
tron charge density is contained in the plane of the
carbon ring pointing toward the fluorine atoms due to
their strong electronegativity [17]. However, in the case
of doubly metalated compounds, the presence of a
second metalated phosphine provides a more encum-
bered face of the Rh center and prevents the stabiliza-
tion of the carbocationic intermediate. These findings
reflect that the combination of both steric and elec-
tronic features is critical.
compounds. In this respect, Taber has used only Cu
dust for the same study [10b]. This prompted us to
reinvestigate this reaction, and we found that the chiral
auxiliary in the keto ester 4 does not provide any
induction of asymmetry in its cyclization when the
reaction is mediated by dirhodium tetraacetate (Table
2). Similarly, doubly-metalated 1a1 (with acetate and
triphenylphosphine as bridging ligands) also leads to an
equimolar ratio of both stereoisomers 6 and 7. Surpris-
ingly, more acidic ortho-metalated complexes such as
1d isomers that would give rise to cyclization through
an early transition state provided some diastereoselec-
tivity. One interesting feature of these ortho-metalated
Rh(II) catalysts is that they react with bulky a-diazo-b-
keto esters such as 4 and permit a preference for the
occurrence of 7 over 6. We can just point out that
Rh2(OOCCH3)4 gave 6 and 7 in equal ratio. The forma-
tion of the cyclopropanation product with significant
diastereoselectivity is certainly an interesting result.
On the other hand, in the competition between b-
elimination and 1,5-CꢀH insertion (Table 3) our results
demonstrate that monometalated catalysts 2d1 and 2d4
with P(C6H5)2(C6F5) are substantially more selective to
give cyclized product than doubly-metalated catalysts
with PPh3 and even with P(C6H5)2(C6F5). To provide
some explanation to these results, we recall that this
type of a-diazo ester transformation with rhodium(II)
carboxylates involving a competitive reaction between
elimination and 1,5-insertion has been previously re-
ported by Taber [5a,c,d]. He postulated that [5c]; the
selective occurrence of one or the other of these pro-
cesses might be dominated by their respective entropy
of activation. Hence, b-hydride elimination with a
smaller entropy of activation might take place readily
instead of carbocycle formation and more exclusively at
−78°C, such an explanation appears to be in accor-
dance with the use of very reactive catalysts such as
Rh2(OOCCF3)4.
4. Conclusions
In summary, the Rh(II) compounds described herein
exhibit interesting catalytic properties. Thus, ortho-
metalated dirhodium(II) offered unprecedented high
diastereocontrol when employed for cyclopropanation
of 4. Furthermore, the use of the appropriate ortho-
metalated Rh(II) catalyst playing on the nature of the
OOCR group and the metalated phosphine, e.g. steric
and electronic features, lead to further improvements in
the selectivity of 1,5-CꢀH insertion of the a-diazo ester
5. In particular 2d4 was found to be a suitable and
efficient catalyst for the extremely sensitive cyclization
of 5 since it provides mainly the cyclized product 8. The
synthesis and characterization details of the novel
ortho-metalated Rh(II) complexes based upon
P(C6F5)(C6H5)2 and PPh3 with structure types 1 and 2
have been reported. Two isomers (endo–exo and endo–
endo) of 1d have been analyzed by X-ray diffraction.
5. Experimental
It would seem likely that Taber’s report and the
present instances are fully in agreement that a less
electron-withdrawing group lead to the cyclization reac-
tion, thereby, rendering the rhodium carbenoid less
electrophilic. This allows the cyclization reaction to
occur when the elimination reaction is slowing. This
5.1. General data
The general procedures and instrumentation have
been described previously [7]. Photochemical reactions
were carried out in a photochemical reactor equipped
with a mercury vapor lamp (Osram-125). Column chro-

P. Lahuerta et al. / Journal of Organometallic Chemistry 612 (2000) 36–45
43
matography for organic compounds was performed on
TLC-mech silica gel, as described elsewhere [18].
Toluene and chloroform were dried and degassed,
methylene chloride was distilled from CaH2 under ar-
gon atmosphere and filtered over K2CO3 immediately
before use in catalytic reactions. Tetrahydrofuran
(THF) was distilled from sodium–benzophenone under
argon atmosphere. Acetic acid was only degassed. The
preparation of Rh2(OOCCH3)4 [19], Rh2(OOCCF3)4
[20], Rh2(OOC(CH3)3)4 [21], was prepared as described
in the literature. Diazo compounds 4 [10b] and 5 [11]
were prepared as described. Compounds 6, 7 [10b], 8
and 9 [12] were fully characterized as reported.
ing pivalate), 38.88 (s, C(CH3)3, axial pivalate), 114.55–
154.24 (m, aromatics), 167.03–167.18 (m), 178.99
(s, OCO), 182.02 (s, OCO). Anal. Calc. for
C56H66O8P2Rh2: C, 59.25; H, 5.86. Found: C, 59.62; H,
6.31%.
5.4. Synthesis of Rh2(OOCCH3)2[(C6H4)P(C6F5)-
(C6H5)]2·2H2O (1d1exo–exo) and (1d1endo–endo
)
Rh2(OOCCH3)3[(C6H4)P(C6H5)(C6F5)]·2H2O
(2d1)
(0.300 g, 0.389 mmol) and P(C6H5)2(C6F5) (0.164 g,
0.467 mmol) were dissolved in 30 ml of degassed
CHCl3. After stirring for 10 min, 10 ml of acetic acid
were added and the mixture was irradiated for 3 h. The
resulting solution was evaporated to dryness under
vacuum and the residue was transferred to a chro-
matography column and was washed with acetone col-
lecting a single band, which was concentrated and
transferred to a new column. The column was washed
with 5:1 hexane–acetone and a minor purple band was
collected, concentrated and crystallized from CH2Cl2–
ethyl acetate–hexane to give a purple solid 5 mg (1.2%
yield) of Rh2(OOCCH3)3)2((C6H4)P(C6F5)(C6H5))2·
2H2O: (exo–exo) (1d1exo–exo). 1H-NMR (CDCl3): l
1.35 (s, 6H, bridging acetate), 6.67–7.75 (m, 18H, aro-
5.2. X-ray diffraction analysis
X-ray diffraction experiments were carried out on a
Siemens Smart diffractometer with a CCD detector
using MoꢀKa radiation. All calculations were done
using SMART software for data collection [22]. The
structures were solved by direct methods, and refined
on F2 with the program SHELXTL [23]. Scattering fac-
tors for neutral atoms and anomalous dispersion cor-
rections were taken from the International Tables for
X-Ray Crystallography [24]. The positions of the re-
maining non-hydrogen atoms were located after an
alternating series of least-squares cycles and difference
Fourier maps and were refined anisotropically. Hydro-
gen atoms were placed in geometrically generated posi-
tions and refined riding on the carbon atom to which
they are attached.
1
matics). 31P{1H}-NMR (CDCl3): l 14.4 (d, J=170.8
Hz). 13C{1H}-NMR (CDCl3): l 24.0 (s, CH3, bridging
acetate), 122.0–148.0 (m, aromatics), 162.5 (m, RhC),
182.5 (s, OCO). 19F{1H}-NMR (CDCl3): l −161.0 (m,
2F, meta), −150.4 (t, 1F, para), −125.5 (br, 2F,
ortho). Anal. Calc. for C40H28F10O6P2Rh2: C, 45.22; H,
2.66. Found: C, 45.66; H, 2.31%.
Owing to the poor quality of the crystals we could
not refine the structures further. This fact, together with
the existence of some remaining, and also disordered,
solvent water molecules made it impossible to reach
lower R values.
After elution with 5:3 hexane–ethyl acetate a violet
band was separated corresponding to the previously
described 1d1endo–exo isomer [7]. Immediately with the
same eluent a minor purple band was isolated, concen-
trated and crystallized from a mixture of ethyl acetate–
hexane–CH2Cl2 to give 11.1 mg (3% yield) of Rh2-
(OOCCH3)2[(C6H4)P(C6H5)(C6F5)]2·2H2O (1d1endo–endo).
1H-NMR (CDCl3): l 1.30 (s, 3H, bridging acetate),
6.80–7.84 (m, 18H aromatics). 31P{1H}-NMR (CDCl3):
5.3. Synthesis of Rh2[OOCC(CH3)3]2[(C6H4)P(C6H5)2]2·
2HOOCC(CH3)3 (1a4)
1
l 19.4 (d, J=175.3 Hz). 13C{1H}-NMR (CDCl3): 23.2
Rh2(OOC(CH3)3)4·2H2O (100 mg, 0.167 mmol) and
P(C6H5)3 (0.0965 g, 0.36 mmol) were reacted in 3:1
toluene–pivalic acid at reflux for 1 h. Pivalic acid was
removed by distillation under vacuum and the dark-
violet crude was chromatographed. Elution with 1:1
CH2Cl2–hexane gave a purple band which was col-
lected and concentrated and the purple crude was redis-
solved in CH2Cl2. Addition of hexane, precipitated a
purple solid (0.020 g) of Rh2(OOCC(CH3)3)2-
((C6H4)P(C6H5)2)2·2HOOCC(CH3)3 (1a4) at −20°C.
1H-NMR (CDCl3): l 0.57 (18H, s, bridging pivalate),
1.25 (18H, s, axial pivalate), 6.49–7.78 (28H, m, aro-
matics), 11.43 (br, HOOCC(CH3)3). 31P{1H}-NMR
(CDCl3): l 20.5 (d, 1J RhꢀP=171.03 Hz). 13C{1H}-
NMR (CDCl3): l 27.07 (s, CH3, bridging pivalate),
27.28 (s, CH3, axial pivalate), 38.85 (s, C(CH3)3, bridg-
(s, CH3, bridging acetate), 122.0–136.8 (m, aromatics),
167.2 (m, RhC), 182.5 (s, OCO). 19F{1H}-NMR
(CDCl3): l −162.5 (t, 2F, meta), −151.5 (t, 1F,
para), −122.6 (b, 2F, ortho). Anal. Calc. for
C40H28F10O6P2Rh2: C, 45.22; H, 2.66. Found: C, 44.88;
H, 3.05%.
5.5. Synthesis of Rh2[OOCC(CH3)3]2[(C6H4)-
P(C6H5)(C6F5)]2·2HOOCC(CH3)3 (1d4endo–exo
)
To 0.100 (0.073 mmol) of Rh2(OOCC3F7)2-
g
[(C6H4)P(C6H5)(C6F5)] 2·2H2O and 10 ml of pivalic acid
were mixed with vigorous stirring. The solution was
refluxed for 24 h. The excess pivalic acid was distilled
off under vacuum, the residue was dissolved in

44
P. Lahuerta et al. / Journal of Organometallic Chemistry 612 (2000) 36–45
CH2Cl2–hexane and was then chromatographed on
silica gel. Elution with 20:1 hexane–acetone separated a
dark-green band that was collected. The solvent was
evaporated and the product was crystallized from
factors) for the structures reported in this paper have
been deposited with the Cambridge Crystallographic
Data Centre as supplementary publications nos. CCDC
142825 for the compound 1d3endo–exo and CCDC 142826
for the compound 1d1endo–endo. Copies of this informa-
tion may be obtained free of charge from: The Direc-
tor, CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK (Fax: +44-1223-336033; e-mail: deposit@ccdc.
cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
1
CH2Cl2–hexane at 0°C. Yield: 0.055 g (60%). H-NMR
(CDCl3): l 0.65 (s, 9H, bridging pivalate), 0.75 (s, 9H,
bridging pivalate), (s, 18H, axial pivalate), 6.45–7.78
(m, 28H, aromatics). 31P{1H}-NMR (CDCl3): l 16.4 (d,
1JRhꢀP=53.02 Hz), 17.89 (d, 1JRhꢀP=58.13 Hz).
13C{1H}-NMR (CDCl3): l 26.94 (s, axial pivalate),
29.30 (s, bridging pivalate), 29.64 (s, bridging pivalate),
39.02 (s, C(CH3)3), 39.74 (s, C(CH3)3), 121.51–150.0
(m, aromatics), 161.5 (m, RhC), 186.59 (OCO), 189.22
(s, OCO), 189.836 (s, OCO). 19F{1H}-NMR (CDCl3): l
−124.54 (br, 2F, ortho), −122.91 (br, 2F, ortho),
−152.21–(−152.49) (m, 2F, para), −161.69 (t, J=
18.9 Hz, 2F), −162.54 (t, J=19.2 Hz, 2F). Anal. Calc.
for C56H56O8F10P2Rh2: C, 51.14; H, 4.29. Found: C,
51.68; H, 3.99%.
Acknowledgements
We are grateful to the Direccio´n General de Inves-
tigacio´n Cient´ıfica y Te´cnica (DGICYT) (Project PB94-
0988) and the EC (Project TMR Network ERBF-
MRXCT 60091) for financial support. S.-E.S. is a
CNRS fellow.
5.6. Synthesis of Rh2[OOCC(CH3)3]3[(C6H4)P(C6H5)-
(C6F5)]·2HOOCC(CH3)3 (2d4)
References
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To 0.100 g (0.11 mmol) of Rh2(OOCCF3)3[(C6H4)-
P(C6H5)(C6F5)]·2H2O (2d1) and 10 ml of pivalic acid
were mixed with vigorous stirring. The solution was
refluxed for 24 h. The excess pivalic acid was distilled
off under vacuum and the residue was dissolved in
CH2Cl2–hexane and was chromatographed on silica
gel. Elution with 20:1 hexane–acetone separated a
dark-blue band that was collected. The solvent was
evaporated and the product was crystallized from
CH2Cl2–hexane. Yield: 0.074
g
(55%). 1H-NMR
(CDCl3): l 0.5 (s, cis bridging pivalate), 0.65 (s, cis
bridging pivalate), 1.35 (s, trans bridging pivalate), 1.45
(s, axial pivalate), 6.7–7.65 (m, aromatics), 8.45 (br,
HOOCC(CH3)3). 13C{1H}-NMR (CDCl3): l 27.20 (s,
(CH3)3, trans bridging), 28.10 (s, (CH3)3, cis bridging),
39.54 (s, C(CH3)3), 40.67 (s, C(CH3)3), 122.25 (d, J=9
Hz, aromatic), 128.10 (d, J=2.57 Hz, aromatic),
128.66 (d, J=11 Hz, aromatic), 130.90 (s, aromatic),
132.91 (d, J=49 Hz, aromatic), 134.9 (d, J=12 Hz,
aromatic), 139.9 (d, J=16 Hz, aromatic), 147 (d, J=
26 Hz), 162 (m, RhC); 188,83 (s, OCO); 197.49 (s,
OCO), 197.69 (s, OCO). 31P{1H}-NMR (CDCl3): l
14.67 (dd, 1J=160.1, 2J=5.6 Hz). 19F{1H}-NMR
(CDCl3): l −125.21 to −125.0 (m, 2F, meta), −
114.02 (t, J=20.5 Hz, 1F, para), −90.45 (d, JPF=20.1
Hz, para). Anal. Calc. for C43H56O10F5PRh2: C, 51.14;
H, 5.30. Found: C, 50.64; H, 5.65%.
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46. Supplementary material
Experimental details for the preparation of i and ii
(2 pages). Crystallographic data (excluding structure

P. Lahuerta et al. / Journal of Organometallic Chemistry 612 (2000) 36–45
45
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