Cyclopropanation and Diels-Alder reactions catalyzed by the first heterobimetallic complexes with bridging phosphinooxazoline ligands

Article abstract of DOI:10.1039/b206410n

The bimetallic complex trans-[(OC)₃Fe(μ-L^P,N)₂Cu]BF ₄(2), which contains two bridging phosphinooxazoline ligands, is the first metal-metal bonded six-membered ring system with P,N donors and its crystal structure shows a unique bimetallic cradle conformation. This complex is an efficient catalyst for the cyclopropanation of styrene by ethyl diazoacetate and for the Diels-Alder reaction between cyclopentadiene and methacrolein, these reactions being catalyzed for the first time by heterometallic complexes.

Full text of DOI:10.1039/b206410n

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Cyclopropanation and Diels–Alder reactions catalyzed by the first
heterobimetallic complexes with bridging phosphinooxazoline ligandsy
Pierre Braunstein, Guislaine Clerc and Xavier Morise
Laboratoire de Chimie de Coordination, UMR CNRS 7513, Universit e´ Louis Pasteur,
4
rue Blaise Pascal, F-67070, Strasbourg Cedex, France. E-mail: braunst@chimie.u-strasbg.fr
Received (in Montpellier, France) 1st July 2002, Accepted 10th September 2002
First published as an Advance Article on the web 25th October 2002
P,N
Fe(m-L
The bimetallic complex trans-[(OC)
3
2 4
) Cu]BF (2), which contains two bridging phosphinooxazoline
ligands, is the first metal–metal bonded six-membered ring system with P,N donors and its crystal structure
shows a unique bimetallic cradle conformation. This complex is an efficient catalyst for the cyclopropanation of
styrene by ethyl diazoacetate and for the Diels–Alder reaction between cyclopentadiene and methacrolein, these
reactions being catalyzed for the first time by heterometallic complexes.
Introduction
Heterometallic complexes are extensively studied in the search
for cooperative effects between metal centres of different nat-
ures, for metallosite selective reactions and/or chemical trans-
formations occurring at both metal centres in sequence or in a
1
concomitant manner. Special interest arises of course when
their reactivity is different from that of their homometallic or
mononuclear anologues. Such differences may be related to
the presence of a new chemical bond (direct metal–metal inter-
action), to changes in the coordination sphere of a metal centre
resulting from the stereoelectronic properties of an adjacent
metal, or to their combination.
Bi- or polyfunctional ligands, in particular functional phos-
phines, are often used as assembling ligands to stabilise bime-
tallic structures and have mostly led to the formation of five-
2
membered metallocycles. Metal–metal bonded systems with
larger bimetallic cycles have been less studied and in the case
3
of (P,N) ligands there appears to be no six-membered ring sys-
tem known and only one seven-membered macrocycle has
4
been very recently reported.
Although phosphinooxazoline ligands are being much inves-
5
tigated as P-monodentate or P,N-chelating ligands, there is no
reported example, to the best of our knowledge, of bridging
behaviour for such ligands. We have now investigated their
potential as assembling ligands to form metal–metal bonded
six-membered ring systems.
Fig. 1 View of the crystal structure of complex trans-
P,N
[
Fe(CO)
Selected bond lengths (A) and angles ( ): Fe–C(1) 1.763(9), Fe–C(2)
.78(1), Fe–C(3) 1.79(1), Fe–P(1) 2.197(3), Fe–P(2) 2.213(3), C(5)–
N(1) 1.28(1), C(21)–N(2) 1.28(1), N(1)–C(6) 1.48(1), N(2)–C(22)
.48(1), P(1)–C(4) 1.848(9), P(2)–C(20) 1.87(1), C(5)–O(4) 1.34(1),
3
(L
2
) ] (1). Ellipsoids are shown at the 50% probability level.
˚
ꢁ
1
1
C(21)–O(5) 1.34(1); C(1)–Fe–C(2) 118.7(4), C(1)–Fe–C(3) 120.4(5),
C(2)–Fe–C(3) 120.9(5), P(1)–Fe–P(2) 176.6(1), P(1)–C(4)–C(5)
Results and discussion
1
16.1(6), P(2)–C(20)–C(21) 115.2(7).
Using the ligand (2-oxazoline-2-ylmethyl)diphenylphosphine
P,N
6
P,N
(
L
), we have prepared trans-[Fe(CO)
it to form the Fe–Cu complex trans-[(OC)
2), with which the catalytic properties of heterometallic
3
(L
2
) ] 1 and used
P,N
3
Fe(m-L
2 4
) Cu]BF
(
Despite the ‘‘anti-type’’ spatial arrangement of the oxazo-
line groups in 1, which minimizes steric repulsion, the L
ligands can function as bridges and lead to two fused six-mem-
bered rings in 2. The n(C=N) vibration at 1643 cm is consis-
tent with the N-coordination of the oxazoline to Cu(I) and a
P,N
complexes have been examined for the first time in olefin cyclo-
propanation and Diels–Alder reactions. Complex 1, whose
structure has been determined by X-ray diffraction (Fig. 1),
was reacted with a stoichiometric amount of [Cu(NC-
ꢀ
1
3
1
1
Me) ][BF
4
4
] (Scheme 1) to afford the bimetallic complex 2 in
singlet is observed in the P{ H} NMR spectrum at d 71.71.
No signal characteristic of MeCN was observed, indicating
9
1% yield.
complete displacement from the precursor. The PCH carbon
2
1
3
1
atoms give rise in C{ H} NMR to an AA XX multiplet from
0
0
y Dedicated to Prof. R. Ugo on the occasion of his 65th birthday, with
2
which a JPP coupling constant of 34.8 Hz was extracted
our congratulations and best wishes.
6
8
New J. Chem., 2003, 27, 68–72
DOI: 10.1039/b206410n
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2003

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Scheme 1
(
reported in the literature for related trans-[Fe(CO) LL ] com-
gNMRV3.6 simulation). This value is similar to those
0
3
7
plexes (L ¼ tertiary phosphines). The n(CO) vibrations
Fig. 3 Perspective view of the structure of 2 along the P–Fe–P axis
showing the curvature generated by the two, mutually eclipsed assem-
bling phosphinooxazoline ligands. The Fe–Cu bond has been omitted
for clarity and only the ipso carbons of the phenyl groups are shown.
ꢀ
CH Cl ) at 1986(w), 1915(s) and 1882(vs) cm are consistent
2 2
1
(
with a meridional arrangement of the carbonyls around the Fe
centre. The structure of 2ꢂ1.5CH Cl was established by X-ray
2
2
diffraction (Fig. 2). The molecule contains a mirror plane
which includes the metals and the CO ligands. The coordina-
tion geometry about the Fe atom may be described as distorted
octahedral with the P atoms trans to one another and the CO
ligands in a mer arrangement. Alternatively, if one ignores the
Fe–Cu bond, it may be viewed as trigonal bipyramidal, as in 1,
a geometry consistent with a formally zero-valent Fe centre.
9a
or bridging dppm [2.497(2), 2.540(2) A ] or in a bis-seven-
˚
9b
˚
4
membered macrocyclic compound [2.4572(7) A], but is similar
to that in a complex with bridging N-(diphenylphosphino-
˚
10
methyl)morpholine [2.550(1) A]. The Fe–Cu distance in 2 is
equal to the sum of the atomic radii of iron and copper (2.54
˚
A). Owing to the presence of a mirror plane in the molecule,
the P, CH and oxazoline groups of one ligand are respectively
2
eclipsed with those of the other ligand. This creates a sort of
molecular cradle cavity (Fig. 3), which results from the ring
size and the ligand conformation and contrasts with the gener-
ally rather flat structures exhibited by dinuclear complexes
The Cu(I) atom exhibits a trigonal coordination involving
ligands.
P,N
the Fe atom and the two nitrogen atoms from the L
˚
The Fe–Cu distance of 2.5441(7) A is longer than in a four-
membered cycle with a bridging aminosilyl ligand [2.530(2)
˚
8
A], in five-membered ring complexes with bridging 2-(diphe-
˚ ˚
nylphosphino)pyridine (Ph PPy) [2.501(2) A, 2.512(2) A],
2d
2
containing other types of assembling ligands, such as Ph PPy
2
ꢁ
or dppm. The C(1)–Fe–C(2) angle of 131.0(2) has opened
up compared to 1 owing to the presence of the Cu centre
˚
and this leads to a C(1)–Cu separation of 2.339(4) A and a
ꢁ
Fe–C(1)–O(1) angle of 174.32(1) .
Complex 2 is an efficient catalyst for the cyclopropanation
of styrene with ethyl diazoacetate [eqn. (1)]. The reaction
was carried out in 1,2-dichloroethane at room temperature (1
mol% of 2 based on ethyl diazoacetate), with an olefin/ethyl
diazoacetate ratio of 2:1. The ethyl diazoacetate was added
1
1
very slowly over a period of 35 h. Trans- and cis-ethyl 2-phe-
nyl-1-cyclopropanecarboxylates were obtained, in 91% iso-
lated yield in a 70:30 ratio, and complex 2 could still be
detected after complete consumption of the ethyl diazoacetate.
These results compare favourably with literature data for
1
2
mononuclear copper catalysts. However, we found that with
Cu(NCMe) ][BF ] as a catalyst under similar conditions,
trans- and cis-ethyl 2-phenyl-1-cyclopropanecarboxylates were
[
4
4
obtained in 97% isolated yield in a 64:36 ratio.
ð1Þ
For further comparison, we prepared the new mononuclear
Fig. 2 View of the crystal structure of complex 2. Ellipsoids are
˚
shown at the 50% probability level. Selected bond lengths (A) and
N,P,N
N,P,N
complex (CuL
)BF
4
[L
¼ bis(2-oxazoline-2-ylmethyl)-
ꢁ
13
angles ( ): Fe–Cu 2.5441(7), Fe–C(1) 1.795(4), Fe–C(2) 1.777(4), Fe–
C(3) 1.786(4), Fe–P 2.230(1), Cu–C(1) 2.339(4), Cu–C(2) 2.514(4),
Cu–N 1.939(2), C(17)–N 1.270(3); C(1)–Fe–C(2) 131.0(2), C(1)–Fe–
phenylphosphine)], in which the coordination sphere of the
Cu(I) ion contains two oxazoline ligands disposed similarly
to those in 2 (in which additionally the Fe centre behaves like
a metalloligand). With this complex as a catalyst, trans- and
cis-ethyl 2-phenyl-1-cyclopropanecarboxylates were obtained
in 91% isolated yield in a 68:32 ratio.
0
C(3) 108.1(2), C(2)–Fe–C(3) 121.0(2), P(1)–Fe–P(1 ) 173.75(4), Cu–
Fe–C(1) 62.4(1), Cu–Fe–C(2) 68.5(1), Cu–Fe–C(3) 170.5(1), Cu–Fe–P
0
9
1
0.16(2), Fe–Cu–N 113.33(7), N–Cu–N 132.7(1), Fe–C(1)–O(1)
74.32(1), Fe–C(2)–O(2) 178.32(1), Fe–C(3)–O(3) 178.96(1).
New J. Chem., 2003, 27, 68–72
69

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1
31
1
methods. The H and P{ H} NMR spectra were recorded
at 300.13 and 121.5 MHz, respectively, on a FT Bruker
1
3
AC300 instrument, C NMR spectra at 75.477 or 100.628
MHz on FT Bruker AC300 or AC400 instruments, respec-
tively, and the IR spectra in the 4000–400 cm range on a
ꢀ1
P,N
6
N,P,N 13
Bruker IFS66 FT spectrometer. The ligands (L ), (L
and (L
)
P,NPh 17
)
were prepared according to the literature.
Synthesis of the complexes
However, to the best of our knowledge, 2 is the first metal–
metal bonded heterometallic catalyst to be used in olefin cyclo-
propanation.
Synthesis of trans-[Fe(CO)
3
{(2-oxazoline-2-ylmethyl)diphe-
nylphosphine}
added over 5 min to a stirred mixture of L
mmol) and NaBH (0.271 g, 7.11 mmol) in 150 mL of n-
2 5
] (1). [Fe(CO) ] (0.942 mL, 7.11 mmol) was
P,N
(6.15 g, 22.9
Furthermore, 2 was found to catalyze the Diels–Alder reac-
tion of methacrolein with cyclopentadiene [eqn. (2)]. The reac-
tion reached 76% convertion after stirring for 162 h at
4
BuOH. Vigourous gas evolution occurred and a yellow solu-
tion resulted. The reaction mixture was refluxed for 2 h (longer
reaction times did not increase the yield), and cooled to room
temperature. A yellow precipitate was already observed after
ꢁ
14
ꢀ
20 C.
1
5 min under reflux. After concentration of the solution and
addition of hexane, large quantities of crystals formed upon
cooling the mixture in a freezer for 12 h. The precipitate was
collected by filtration and washed with cold methanol (3 ꢃ 10
ml) to remove the borate salts. The solid product was dried
ð2Þ
3
1
1
under vacuum. The IR and P{ H} NMR spectra showed
the isolated product to be exclusively trans-[Fe(CO) (L ) ]
1 15
The exo:endo ratio of 74/26 (determined by H NMR) com-
pares favourably with the best copper systems reported in the
P,N
3
2
(
4.82 g, 90%). IR (CH
2
Cl
2
): n(CO) 1974 (w), 1886 (vs),
1
4
literature, amongst which we could not find any Cu(I) sys-
tem. For a better comparison, we therefore evaluated [Cu(NC-
Me) ][BF ] as a catalyst for this reaction under the same
ꢀ1
n(C=N) 1661(m) cm ; (KBr): n(CO) 1973 (vw), 1931 (sh),
ꢀ1
1
1
876 (vs), n(C=N) 1658 (ms) cm
K): d 7.78–7.42 (m, 20H, aromatics), 4.06 (t, 4H, J
.
H NMR (CDCl
3
, 298
¼ 9.0
3
4
4
HH
conditions. The reaction reached 70% convertion after stirring
ꢁ
3
J
Hz, OCH
4
(
2
), 3.75 (t, 4H,
HH ¼ 9.0 Hz, NCH
2
), 3.60 (m,
for 162 h at ꢀ20 C and the exo:endo ratio was 85/15 (deter-
13
1
H, JPH ¼ 7.9 Hz, PCH ). C{ H} NMR (CD Cl ): d 213.2
1
minedby HNMR). Incontrast, (CuL
N,P,N
2
2
2
1
)BF
4
didnotcatalyze
2
t, 3CO, JPC ¼ 22 Hz), 162.7 (s, C=N), 137.0 (d, JPC ¼ 22
this reaction, although the utilization of phosphinoox-
azoline ligands and Cu(I) salts has been reported for the cata-
lytic enantioselective aza-Diels–Alder reaction of imines.
Hz, ipso-aryl), 132.8 (s, m-aryl), 130.6 (s, p-aryl), 128.6 (s,
), 55.2 (s, NCH
o-aryl), 67.9 (s, OCH
2
2 2
), 34.1 (m, PCH ).
1
6
31
1
P{ H} NMR (CDCl , 298 K): d 78.4 (s) Anal. Calcd. for
3
C
35 2 5 2
H32FeN O P : C, 61.94; H, 4.76; N, 4.13. Found: C,
6
1.81; H, 5.01; N, 3.89%.
Conclusion
P,N
The complex trans-[Fe(CO)
3
(L
)
precursor for the construction of new bimetallic complexes
2
] 1 is a readily available
Synthesis of 2. Solid [Cu(NCMe) ]BF (0.464 g, 1.47 mmol)
4 4
was added to a solution of 1 (0.997 g, 1.47 mmol) in CH
2
Cl
2
at
ꢁ
with phosphinooxazoline assembling ligands, as exemplified
P,N
with the formation of trans-[(OC)
25 C. The mixture was stirred vigorously for 20 min, the yel-
low solution became deeper almost immediately. The mixture
was concentrated and slow diffusion of pentane afforded yel-
3
Fe(m-L
2 4
) Cu]BF (2), a
formally Fe(0) ! Cu(I) complex. The latter appears to be the
first metal–metal bonded heterometallic complex successfully
tested in olefin cyclopropanation and Diels–Alder reactions.
Although our preliminary catalytic results do not demonstrate
a clear advantage of the bimetallic system over a well-chosen
mononuclear Cu(I) catalyst, we had to resort to different
Cu(I) precursors to observe catalysis in each reaction. We
expect further developments in the context of bimetallic effects
in catalysis and of enhanced selectivity properties associated
with the unique ‘‘bimetallic cavity-like’’ shape of complex 2.
Current extensions include the use of chiral systems and we
have already prepared the Fe–Cu complex 2* (see Experimen-
low crystals (1.11 g, 91%). IR (CH
1
2
Cl
2
): n(CO) 1986 (mw),
ꢀ
1 1
915 (s) 1882 (vs), n(C=N) 1643 (m) cm . H NMR (CDCl ,
3
2
98 K): d 7.58–7.52 (m, 20H, aromatics), 4.46 (t, 4H,
3
3
JHH ¼ 9.7 Hz, OCH ), 4.17 (t, 4H, J
¼ 9.7 Hz, NCH ),
2
HH
2
0 0
3
.56 (appearance of ‘‘filled-in d’’ analyzed as an AA XX spin
2
+4
2
system (X ¼ P), 4H,
JPH ¼ 9.1, JPP ¼ 34.8 Hz, PCH ).
2
1
3
1
C{ H} NMR (CD
2
2
Cl
2
): d 210.0 (t, 3CO
J
PC ¼ 25 Hz),
1
68.7 (s, C N), 133.9–128.9 (aromatics), 68.6 (s, OCH ),
=
1
5
2
0
0
5.3 (s, NCH
JPC ¼ 19.6, JPP ¼ 34.8 Hz, PCH ).
2
), 31.6 (m, AA XX spin system (X ¼ P),
2
+3
31
1
P{ H} NMR
32BCuF Fe-
2
(
CDCl
3
, 298 K): d 71.7 (s). Anal. Calcd. for C35
H
4
P,NPh 17
N O P ꢂ1.5CH Cl ꢂ0.5MeCN: C, 46.12; H, 3.77; N, 3.59.
tal) containing the enantiopure ligand L .
in catalysis will be the subject of further studies.
Its evaluation
2
5
2
2
2
Found: C, 46.15; H, 3.57; N, 3.87%.
N,P,N
Synthesis of [Cu(L
g, 2.48 mmol) was added to a solution of L
)]BF
4
. Solid [Cu(NCMe)
4
]BF
4
(0.781
N,P,N
(0.686 g, 2.48
CN at 25 C. The mixture was stirred vigorously
ꢁ
mmol) in CH
for 20 min and a white precipitate formed after hexane was
3
ꢀ
1 1
added (1.04 g, 98%). IR (KBr): n(C=N) 1644 (vs) cm . H
NMR (CD Cl ): d 1.97 (s, 3H, CH CN), 3.17 (m, 2 H, part
2
2
3
A of an ABX system (A ¼ B ¼ H, X ¼ P), PCH
A
H
B
), 3.45
m, 2 H, part B of an ABX system, PCH H ), 3.74 (m, 2 H,
(
part
A
B
A
of an ABFG system (A ¼ B ¼ F ¼ G ¼ H),
NCH H ), 3.89 (m, 2 H, part G of an ABFG system,
B
Experimental
A
NCH
A
H
B
), 4.48 (m, 2 H, part F of an ABFG system, OCH
F
-
All reactions were performed under purified nitrogen. Solvents
were purified and dried under nitrogen by conventional
H ), 4.55 (m, 2H, part B of an ABFG system, OCH H ),
G F G
7.58–7.89 (m, 5 H, aromatics), P{ H} NMR (DMSO-d ):
6
3
1
1
7
0
New J. Chem., 2003, 27, 68–72

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.
2 2
Crystallographic analysis of 1 and 2 1.5CH Cl
d ꢀ22.3 (s). Anal. Calcd. for C14
C, 41.11; H, 4.32; N, 8.99. Found: C, 40.57; H, 4.30; N,
.00%. At this stage, we cannot state whether the molecule
of acetonitrile found in solution and in the solid (elemental
analysis) corresponds to a molecule of solvation or to a
Cu(I)-bound ligand.
H
17BCuF
4
N
2
O
2
PꢂCH
3
CN:
Single crystals were selected and mounted on a Kappa CCD
diffractometer. Data were collected using phi-scans and the
structure was solved using direct methods and refined against
9
2
18,19
F using SHELX 97 software.
No absorption correction
was used. All non-hydrogen atoms were refined anisotropically
with H atoms introduced as fixed contributors (dC–H ¼ 0.95 A˚ ,
U11 ¼ 0.04).
P,NPh
Synthesis of trans-[Fe(CO)
3
(L
2
) ] (1*). To a stirred mix-
P,NPh
ture of L (5.33 g, 15.4 mmol) and NaBH (0.181 g, 4.76
4
mmol) in 150 mL of n-BuOH, [Fe(CO)
Crystal data for 1: C H FeN O P , M ¼ 678.45, orthor-
3
5
32
2
5 2
5
] (0.630 mL, 4.76
˚
˚
˚
hombic, a ¼ 41.966(1) A, b ¼ 34.575(1) A, c ¼ 9.741(1) A,
3
mmol) was added over 5 min. Vigourous gas evolution
occurred and a yellow solution resulted. The reaction mixture
was refluxed for 2 h (longer reaction times did not increase the
yield), and cooled to room temperature. After concentration of
the solution and addition of hexane, a yellow powder formed
upon cooling the reaction mixture in a freezer for 12 h. The
precipitate was filtered and washed with cold methanol
˚
V ¼ 14 133(2) A , T ¼ 173 K, space group: Fdd2, Z ¼ 16,
ꢀ
1
˚
m(Mo-Ka) ¼ 0.559 mm (l ¼ 0.71073 A), 17 857 reflections
measured, 2614 reflections with I > 3s(I), R ¼ 0.046 and
Rw ¼ 0.079.
For 2ꢂ1.5CH
2
Cl
2
:
C
35
H
32BCuF
4
FeN
2
O
5
P
2
ꢂ1.5CH
2 2
Cl ,
˚
˚
M ¼ 956.2, monoclinic, a ¼ 24.4623(7) A, b ¼ 14.3872(6) A,
˚
ꢁ
˚
3
c ¼ 12.4708(4) A, b ¼ 111.598(4), V ¼ 4080.9(5) A , T ¼
ꢀ
1
(
dried under vacuum. Both IR and P NMR spectra showed
3 ꢃ 10 ml) to remove the borate salts. The solid product was
1
(
73 K, space group C2/m, Z ¼ 2, m(Mo-Ka) ¼ 1.213 mm
˚
3
1
l ¼ 0.71073 A), 13 114 reflections measured, 4571 reflections
P,NPh
the isolated product to be exclusively trans-[Fe(CO)
(
3
(L
2
) ]
with I > 3s(I), R ¼ 0.046 and Rw ¼ 0.057.
0.382 g, 9.70%). IR (CH Cl ): n(CO) 1970 (w), 1882 (vs),
n(C=N) 1657 (m) cm . H NMR (CDCl
, 298 K): d 8.10–
2
2
CCDC reference numbers 177707 and 177708.
See http://www.rsc.org/suppdata/nj/b2/b206410n/ for crys-
tallographic data in CIF or other electronic format.
ꢀ
1 1
3
6
.90 (m, 30H, aromatics), 5.09 (dd, 2H, A part of an AB spin
2
3
system J(H
A
H
B
) ¼ 9.8 Hz, J(H
A
H) ¼ 8.6 Hz, OCH
A
H
B
),
) ¼ 9.8
), 3.89 (t, 2H, J(H
H) ꢄ
H) ¼ 8.6 Hz, NCH), 3.75 (m, 2H, A part of an AB spin
system, PCH ), 3.64 (m, 2H, B part of an AB spin system,
2
4
A B
.45 (dd, 2H, B part of an AB spin system J(H H
3
3
Hz, J(H
B
H) ¼ 8.6 Hz, OCH
A
H
B
A
3
J(H
B
Acknowledgements
A
H
B
3
1
1
This work was supported by the CNRS and the Minist e` re de la
Recherche and we are also grateful to the COST D-17 pro-
gramme of the European Commission (DG-XII). We are
grateful to Ms. N. Gruber and Dr. A. DeCian for the X-ray
structure determinations.
PCH
Calcd. for C47
Found: C, 67.99; H, 4.86; N, 3.39%.
A
H
B
). P{ H} NMR (CDCl
3
, 298 K): d 77.7 (s). Anal.
H
40FeN : C, 67.94; H, 4.86; N, 3.37.
2 5 2
O P
P,NPh
Synthesis of trans-[(OC)
Cu(NCMe) ]BF (0.145 g, 0.46 mmol) was added to a solution
3
Fe(l-L
2 4
) Cu]BF (2*). Solid
[
of trans-[Fe(CO)
4
4
P,NPh
3
(L
2 2 2
) ] (1*) (0.382 g, 0.46 mmol) in CH Cl
ꢁ
at 25 C. The yellow solution became deeper almost immedi-
ately and the mixture was stirred vigorously for 20 min. Con-
centration and slow diffusion of pentane afforded a yellow
References
1
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X. Morise, Organometallics, 1998, 17, 540; (c) P. Braunstein and
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powder (0.411 g, 91%). IR (CHCl ): n(CO) 1988 (mw), 1919
3
ꢀ
1 1
(
s) 1885 (vs), n(C=N) 1640 (m) cm . H NMR (CDCl
K): d 8.00–6.70 (m, 30H, aromatics), 4.68 (br, 4H, OCH
.11 (br, 2H, NCH), 3.45 (m, 2H, A part of an AB spin system,
3
, 298
),
2
4
PCH
PCH
Calcd. for C47
A
A
H
B
), 3.61 (m, 2H, B part of an AB spin system,
, 298 K): d 69.65 (s). Anal.
CN: C, 57.58; H, 4.24;
3
1
1
H
B
). P{ H} NMR (CDCl
40BCuF FeN
N, 4.11. Found: C, 58.00; H, 4.07; N, 4.03%.
3
2
000, 19, 854; ( f ) P. Braunstein, J. Durand, M. Knorr and C.
H
4
2
O
5
P
2
ꢂCH
3
Strohmann, Chem. Commun., 2001, 211; (g) P. Braunstein, M.
Chetcuti and R. Welter, Chem. Commun., 2001, 2508; (h) P.
Braunstein, G. Clerc and X. Morise, Organometallics, 2001, 20,
5
036
Catalytic reactions
2
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Cyclopropanation. The reaction was carried out in 1.5 mL of
,2-dichloroethane at room temperature using 1 mol% catalyst
1
(
(
based on ethyl diazoacetate), activated with phenylhydrazine
0.2 mL of a 1% solution in 1,2-dichloroethane). In order
1
1
to minimize the formation of diethyl fumarate and maleate
which result from carbene dimerization), an olefin:ethyldiazo-
3
4
5
(
acetate ratio of 2:1 was used and the ethyl diazoacetate was
added very slowly over a period of 35 h. The yields and diaster-
eoselectivities were determined by H NMR analysis after total
1
consumption of ethyl diazoacetate.
Diels–Alder reaction. The Diels–Alder addition of methacro-
lein to cyclopentadiene was performed in 4 mL of CH Cl with
6
7
2
2
2
pentadiene freshly cracked, and 5 mol% catalyst. The reaction
.0 mmol (0.168 mL) dienophile, 2.4 mmol (0.20 mL) cyclo-
ꢁ
mixture was stirred at ꢀ20 C for 162 h and then filtered
through silica gel with Et O elution to give after concentration
2
(
(
exo)-2-methylbicyclo[2.2.1]hept-5-ene-2-carboxaldehyde and
endo)-2-methyl bicyclo[2.2.1]hept-5-ene-2-carboxaldehyde as
a clear colourless oil.
8
P. Braunstein, C. Stern, C. Strohmann and N. Tong, Chem. Com-
mun., 1996, 2237.
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7
2
New J. Chem., 2003, 27, 68–72