Comparative oxidative addition of transition-metal iodocyclopentadienyl complexes (η5-C5H4-I)MLn, (M = Re, Mn, Fe) with a palladium(O) complex: Relevance to the efficiency of catalytic reactions

Article abstract of DOI:10.1021/om700302u

The rate constants of the oxidative addition of the transition-metal iodocyclopentadienyl complexes (η-C₅H₄-I)-MLn (ML _n = Mn(CO)₃ (1a), Re(CO)₃ (1b), CpFe (1c)) with Pd⁰(PPh₃)₄ have been determined in DMF. As expected, the oxidative addition is faster for the electron-acceptor groups Mn-(CO)₃ and Re(CO)₃ than for the electron-donor group FeCp, with the reactivity order 1a > 1b ? 1c. Comparison of the rate constants of the oxidative additions affords a new strategy for the evaluation of the electronic properties of transitionmetal units ligated to the iodocyclopentadienyl moiety with the following decreasing electron-acceptor properties: Mn(CO)₃ > Re(CO)₃ ? FeCp. The complexes formed in the oxidative addition are characterized as trans-[(η⁵- C₅H₄)PdI(PPh₃)₂]ML_n (ML_n = Mn(CO)₃ (2a), Re(CO)₃ (2b), CpFe (2c)) with the decreasing stability order in DMF: 2c ? 2b > 2a. The relevance to the efficiency of palladium-catalyzed Stille or Sonogashira reactions from related complexes 1 is discussed.

Full text of DOI:10.1021/om700302u

Organometallics 2007, 26, 3887-3890
3887
Comparative Oxidative Addition of Transition-Metal
Iodocyclopentadienyl Complexes (η5-C5H4-I)MLn (M ) Re, Mn, Fe)
with a Palladium(0) Complex: Relevance to the Efficiency of
Catalytic Reactions
Christian Amatore,† Be´atrice Godin,† Anny Jutand,*,† Benoit Ferber,‡ Siden Top,‡ and
Ge´rard Jaouen‡
De´partement de Chimie, Ecole Normale Supe´rieure, CNRS, 24 Rue Lhomond, 75231 Paris Cedex 5,
France, and Ecole Nationale Supe´rieure de Chimie de Paris, CNRS, 11 Rue Pierre et Marie Curie, 75231
Paris Cedex 5, France
ReceiVed March 28, 2007
Scheme 1. (MLn ) Mn(CO)3, Re(CO)3 FeCp)
Summary: The rate constants of the oxidatiVe addition of the
transition-metal iodocyclopentadienyl complexes (η5-C5H4-I)-
MLn (MLn ) Mn(CO)3 (1a), Re(CO)3 (1b), CpFe (1c)) with
Pd0(PPh3)4 haVe been determined in DMF. As expected, the
oxidatiVe addition is faster for the electron-acceptor groups Mn-
(CO)3 and Re(CO)3 than for the electron-donor group FeCp,
with the reactiVity order 1a > 1b . 1c. Comparison of the
rate constants of the oxidatiVe additions affords a new strategy
for the eValuation of the electronic properties of transition-
metal units ligated to the iodocyclopentadienyl moiety with the
following decreasing electron-acceptor properties: Mn(CO)3
> Re(CO)3 . FeCp. The complexes formed in the oxidatiVe
addition are characterized as trans-[(η5-C5H4)PdI(PPh3)2]MLn
(MLn ) Mn(CO)3 (2a), Re(CO)3 (2b), CpFe (2c)) with the
decreasing stability order in DMF: 2c . 2b > 2a. The
releVance to the efficiency of palladium-catalyzed Stille or
Sonogashira reactions from related complexes 1 is discussed.
close as possible to each other.2 For example, a catalytic reaction
may be not efficient, because the oxidative addition is too fast
in comparison to the rate of the transmetalation which follows
this first step. This may even be amplified whenever the products
formed after the fast oxidative addition are not stable. Indeed,
the overall catalytic reaction would not work, because a
transmetalation that is too slow will allow a significant
degradation of the accumulating intermediate. It is thus worth-
while to investigate the rate and mechanism of the oxidative
addition first.
Introduction
In a study of the molecular recognition of planar chiralities
by the R form of the estrogen receptor, the formyl-substituted
transition-metal iodocyclopentadienyl complexes (R)- and (S)-
[η5-C5H3-1-I-2-(CHO)]MLn (MLn ) Mn(CO)3, Re(CO)3, CpFe)
have been engaged in palladium-catalyzed reactions with alkynyl
derivatives of estradiol: Stille reactions (R ) SnBu3) and
Sonogashira reactions (R ) H) (Scheme 1).1
We wish therefore to report here kinetic data on the reactivity
of the related iodocyclopentadienyl complexes (η5-C5H4-I)MLn
(MLn ) Mn(CO)3 (1a), Re(CO)3 (1b), CpFe (1c); Chart 1) in
their oxidative addition with Pd0(PPh3)4 in DMF.
The ferrocenyl products (MLn ) CpFe) were mainly obtained
in a Sonogashira reaction, whereas the cyrhetrenyl (MLn ) Re-
(CO)3) and cymantrenyl (MLn ) Mn(CO)3) products were
mainly formed in a Stille reaction.1 All reactions involve a
common first step: the oxidative addition of (R)- or (S)-[η5-
C5H3-1-I-2-(CHO)]MLn with a Pd(0) complex. In a first
approach, the difference in reactivity seems to depend on the
type of reaction, Stille versus Sonogashira: i.e., on the nucleo-
philic attack (transmetalation) on σ-cyclopentadienyl-Pd(II)
complexes formed in the oxidative addition of the iodocyclo-
pentadienyl derivatives. However, the effective rates of the
successive steps in a catalytic cycle are not independent from
each other. Indeed, catalytic reactions are more efficient if the
rates of the different steps of the catalytic cycle are made as
Results and Discussion
Kinetics of the Oxidative Addition. The reactivity of 1a
with Pd0(PPh3)4 (C0 ) 2.2 mM) in DMF containing nBu4NBF4
(0.3 M) was followed by means of electrochemical techniques,3,4
on the basis of the fact that the oxidation current of Pd0(PPh3)3
(the major complex generated from Pd0(PPh3)4) must decrease
after addition of 1a, due to a decay of its concentration in the
oxidative addition (eq 1 in Scheme 2). This analytical technique
can be used only if the Pd(0) complex is more easily oxidized
than the reagents involved in the oxidative addition. The
electrochemical properties of complexes 1a-c were first
investigated to compare their oxidation potentials with that of
Pd0(PPh3)3. The oxidation peaks of 1a-c were all located at
* To whom correspondence should be addressed. Tel: 33144323872.
Fax: 33144323325. E-mail: Anny.Jutand@ens.fr.
† Ecole Normale Supe´rieure.
(2) Amatore, C.; Jutand, A. J. Organomet. Chem. 1999, 576, 254-278.
(3) Fauvarque, J. F.; Pflu¨ger, F.; Troupel, M. J. Organomet. Chem. 1981,
208, 419-427.
(4) Amatore, C.; Jutand, A.; Khalil, F.; M’Barki, M. M.; Mottier, L.
Organometallics 1993, 12, 3168-3178.
‡ Ecole Nationale Supe´rieure de Chimie de Paris.
(1) Ferber, B.; Top, S.; Vessie`res, A.; Welter, R.; Jaouen, G. Organo-
metallics 2006, 25, 5730-5739.
10.1021/om700302u CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/14/2007

3888 Organometallics, Vol. 26, No. 15, 2007
Notes
Chart 1
Scheme 2
potentials more positive than that of Pd0(PPh3)3 (Ep ) +0.083
V vs SCE (irrev)): Ep ) +0.47 V (irrev), Ep ) +0.55 V
1a
1b
(irrev), Ep1c ) +0.72 V (rev). Consequently, the kinetics of the
oxidative addition of 1a with Pd0(PPh3)3 could be monitored
by recording the decay versus time of the oxidation current of
Pd0(PPh3)3 at a rotating-gold-disk electrode polarized at
+0.1 V.
The oxidative addition was performed in the presence of n
) 1, 5, and 10 equiv of 1a. The use of correct kinetic laws was
required, taking into account the variation of the concentration
of the phosphine released in the course of the oxidative addition
(see mechanism in Scheme 2). x is the molar fraction of the
Pd(0) at t: x ) [Pd(0)t]/[Pd(0)0] ) ioxt/iox
.
0
Figure 1. Kinetics of the oxidative addition of Pd0(PPh3)4 (C0 )
2.2 mM) in DMF at 25 °C. (a) For 1a, plot of Xn (see text) versus
time: n ) 1 (0), 5 (b), 10 equiv ([) of 1a. (b) For 1b (3 equiv),
plot of X3 ) lnx - 2 ln[(2 + x)/3] versus time. (c) For 1c (10
equiv), plot of X10 (see text) versus time.
n ) 1: X1 ) 2 - ln x - 2/x ) -kKt
n ) 5: X5 ) {ln x - 3 ln[(4 + x)/5]}/2 ) -kKt (b)
n ) 10: X10 ) (2 ln x - x + 1)/10 ) -kKt (c)
(a)
classification of the electronic properties of MLn groups as
Within this formulation, plotting Xn (n ) 1, 5, 10) against
time gave the same straight line irrespective of n, thus attesting
to first-order reactions for both 1a and Pd0(PPh3)4 (Figure 1a).
The value of kK, which characterizes the reactivity of 1a, was
determined from the slope of the common regression line. The
same reactions were performed with 1b (Figure 1b) and 1c
(Figure 1c). The reactivity order is displayed in Chart 2. Just
for comparison, let us recall that the oxidative addition of
iodobenzene, performed under the same conditions at 20 °C, is
electron-acceptor groups onto
(Chart 3).
a cyclopentadienyl ring
Chart 3. Decreasing Electron-Acceptor Properties of MLn
Mn(CO)3 > Re(CO)3 . FeCp
Pd(II) Complexes Formed in the Oxidative Addition. The
complexes trans-[(η5-C5H4)PdI(PPh3)2]MLn (2a-c), generated
in the oxidative addition, were characterized by 1H and 31P NMR
spectroscopy. All complexes exhibited a 31P NMR singlet
indicative of a trans coordination of the two PPh3 ligands on
the Pd(II) center (Chart 4). One related complex has been
reported by Basset et al. in the oxidative addition of Pd0(PPh3)4
with a phenyl chloride whose phenyl group was η6-coordinated
to the electron-acceptor group Cr(CO)3.6
characterized by kK ) 0.05 s-1 4
.
Chart 2 (DMF, 25 °C)
1a (kK ) 0.04 s-1) > 1b (kK ) 0.03 s-1) .
1c (kK ) 0.000019 s-1)
Complex 1a is slightly more reactive than complex 1b, and
both are considerably more reactive than complex 1c (Chart
2). The oxidative addition of aryl halides with Pd0(PPh3)4 is
faster when the aryl group is substituted by an electron-acceptor
group5 (Hammett correlation with a positive slope).3 The kinetic
results established here are in full agreement with this rule, since
Mn(CO)3 and Re(CO)3 are electron-acceptor groups, whereas
the Fe(Cp) group is an electron-donor group. Comparison of
the rate constants of the oxidative addition allows an easy
Complexes 2a,b were not as stable and underwent ligand
scrambling at long reaction times, according to the reactions
reported in Scheme 3.
1
The reactions were followed by 31P and H NMR, focusing
on the protons of the cyclopentadienyl moieties. To an NMR
tube containing Pd0(PPh3)4 in acetone-d6 was added a stoichio-
1
metric amount of 1a. The first H NMR recorded after 8 min
displayed the signals of 2a (5.64 (d, J ) 2 Hz, 2H) and 5.74
(6) Dufaud, V.; Thivole-Cazat, J.; Basset, J. M.; Mathieu, R.; Jaud, J.;
Waissermann, J. Organometallics 1991, 10, 4005-4015.
(5) Fitton, P.; Rick, E. A. J. Organomet. Chem. 1971, 28, 287-288.

Notes
Organometallics, Vol. 26, No. 15, 2007 3889
Chart 4
A similar scrambling reaction was also observed from
complex 2b, after addition of a stoichiometric amount of 1b to
Pd0(PPh3)4 in an NMR tube containing acetone-d6. The first 1H
NMR recorded after 24 min displayed the signals of 2b at 6.18
(d, J ) 2 Hz, 2H) and 6.07 ppm (d, J ) 2 Hz, 2H), along with
those of unreacted 1b. After 67 min, the signals of 1b were no
longer detected, attesting to the completion of the oxidative
addition. In addition to the signals of complex 2b, the singlet
of the complex CpRe(CO)3 (5b; δ 5.49 ppm (s)) was observed
as well as the signals of the dimer complex 4b (δ 5.94 (br
s, 2H) and 6.05 ppm (br s, 2H)). PdI2(PPh3)2 was also detected
on the 31P NMR spectrum. Complex 2b gave complex 4b with
time. After 4 h, the 1H MNR spectrum exhibited the singlet of
5b and the two sets of signals of complexes 2b and 4b (ratio
1:1). The signals of the intermediate complex 3b were hardly
detected due to low stationary concentration.
Scheme 3
Upon comparing the evolution of complexes 2a,b with time,
one concludes that 2a is less stable than 2b. No scrambling
reaction was observed from complex 2c generated in the slowest
oxidative addition (Chart 5).
ppm (d, J ) 2 Hz, 2H)) and those of unreacted 1a. After 35
min, the signals of 1a were no longer detected, attesting to the
completion of the oxidative addition. The complex CpMn(CO)3
(5a; δ 4.8 ppm (s)) was observed, as well as a new intermediate
complex at 4.35 (br s, 2H) and 4.49 ppm (br s, 2H), associated
with a 31P NMR singlet at 22.72 ppm. The latter disappeared
with time as well as 2a, leading to PdI2(PPh3)2, CpMn(CO)3
(5a), and the dimer complex 4a (δ 5.94 (br s, 2H) and 6.06
ppm (br s, 2H)). PdI2(PPh3)2 was isolated as red crystals and
characterized by an X-ray structure analysis and a 31P NMR
singlet at δ 12.93 ppm. After 4 h 15 min, the 1H NMR spectrum
only exhibited the signals of CpMn(CO)3 (5a) and the dimer
complex 4a. The signals of the intermediate complex were
assigned to complex 3a. Ligand scrambling from 2a gave 3a,
which must undergo reductive elimination, leading to the dimeric
complex 4a and Pd0(PPh3)2 (Scheme 3). Complex 5a may be
formed from 2a or 3a by a reaction with protons or by H•
abstraction (Scheme 3). The scrambling reaction was also
observed when investigating the kinetics of the reaction of 1a
with Pd0(PPh3)4 under the condition of a relatively slow
oxidative addition: i.e., n ) 1 equiv of 1a. One indeed notices
that the oxidation current at a rotating-gold-disk electrode of
the Pd(0) complex (proportional to its concentration) did not
drop to zero but decreased and then increased to a fixed value
equal to 80% of the initial value. Upon further addition of 1
equiv of 1a, the oxidation current dropped again and then
increased. The oxidation current dropped to zero upon addition
of iodobenzene (10 equiv), establishing that the species which
appeared while the oxidative addition proceeded was a Pd(0)
complex or a species in equilibrium with the initial reactive
Pd(0) complex and that this Pd(0) complex was regenerated
through spontaneous evolution of 2a (2a f 3a f 4a in Scheme
3). The scrambling reaction was thus followed by cyclic
voltammetry performed at a stationary-gold-disk electrode. The
oxidation peak of Pd0(PPh3)3 (2.2 mM in DMF) at EP ) +0.083
V vs SCE disappeared upon addition of 1a (1 equiv), but a
new oxidation peak appeared at less positive potential at +0.029
V. It disappeared upon addition of PhI. Consequently, the new
oxidation peak characterized Pd0(PPh3)3, whose oxidation peak
had been shifted because the concentration of the free PPh3 had
varied upon oxidative addition (see mechanism in Scheme 2)
due to the formation of PdI2(PPh3)2. Furthermore, the reduction
Chart 5. Decreasing Stability Order of Complexes 2a-c
[(η5-C5H4)PdI(PPh3)2]FeCp . [(η5-C5H4)PdI(PPh3)2]Re(CO)3 >
[(η5-C5H4)PdI(PPh3)2]Mn(CO)3
Therefore, the stability order of complexes 2a-c is opposite
to the reactivity order of 1a-c in their oxidative addition. The
slowest oxidative addition gave the most stable complex and
vice versa.
In conclusion, the complexation of the iodocyclopentadienyl
ligand by transition-metal complexes in (η5-C5H4-I)MLn (MLn
) Mn(CO)3, Re(CO)3, CpFe) affects the rate of its oxidative
addition with Pd0(PPh3)4 in DMF. As expected, iodocyclopen-
tadienyl moieties ligated to the electron-acceptor groups (Mn-
(CO)3, Re(CO)3) give a faster oxidative addition than these
moieties ligated to an electron-donor group (FeCp) (Chart 2).
Therefore, investigation of the rate of the oxidative addition of
a Pd(0) complex affords a new strategy which allows the
classification of the electronic properties of transition-metal
groups as ligands of the iodocyclopentadienyl moiety7 with the
decreasing electron-acceptor properties: Mn(CO)3 > Re(CO)3
. FeCp.
The most stable complex, trans-[(η5-C5H4)PdI(PPh3)2]FeCp,
is the one which is formed in the slowest oxidative addition
with the decreasing stability order
[(η5-C5H4)PdI(PPh3)2]FeCp . [(η5-C5H4)PdI(PPh3)2]Re(CO)3 >
[(η5-C5H4)PdI(PPh3)2]Mn(CO)3
In palladium-catalyzed reactions, once the complexes trans-
[(η5-C5H4)PdI(PPh3)2]MLn (2) are generated in the oxidative
addition, their decomposition competes with their reaction with
the nucleophiles of Stille or Sonogashira reactions (transmeta-
(7) Since their structures strongly differ, their electronic properties cannot
be compared by IR spectroscopy, which is restricted to CO vibrations. The
1H NMR shifts of the protons of the Cp-I group in the complexes 1a-c
could be compared and used to estimate the electronic properties of Mn-
(CO)3, Re(CO)3, and FeCp. In CDCl3 the chemical shifts are 4.67 and 5.00
ppm for complex 1a,8 4.70 and 5.00 ppm for complex 1b,8 and 4.15 and
4.41 ppm for 1c.9 From these data, we conclude that the FeCp group is
less electron accepting than Mn(CO)3 and Re(CO)3, but the latter two cannot
be distinguished and classified. A comparison of the rate constants of the
oxidative addition provides a better classification for the three organometallic
moieties (see text).
peak of PdI2(PPh3)2 at Ep ) -0.95 V was observed when
red
the cyclic voltammetry was performed first toward reduction
potentials, giving support to the formulation in Scheme 3.

3890 Organometallics, Vol. 26, No. 15, 2007
Notes
carried out in a three-electrode thermostated cell (25 °C) connected
to a Schlenk line. The reference was a saturated calomel electrode
(Radiometer) separated from the solution by a bridge filled with 3
mL of DMF containing nBu4NBF4 (0.3 M). The counter electrode
was a platinum wire of ca. 1 cm2 apparent surface area. A 13.5
mL portion of DMF containing nBu4NBF4 (0.3 M) was introduced
into the cell followed by 34.7 mg (0.03 mmol) of Pd0(PPh3)4. Cyclic
voltammetry was performed at a stationary-gold-disk electrode
(diameter 2 mm) at a scan rate of 0.2 V s-1. The kinetic
measurements for the oxidative addition of 1a were performed at
a rotating-gold-disk electrode (Radiometer, EDI 65109, diameter
2 mm, angular velocity 105 rad s-1) polarized at +0.1 V vs SCE.
A 99 mg portion (0.3 mmol) of 1a dissolved in 0.2 mL of DMF
was added, and the decrease of the oxidation current of Pd0(PPh3)3
was recorded versus time until total conversion. Cyclic voltammetry
and 31P NMR spectroscopy were performed just afterward.
Characterization of [(η5-C5H4)PdI(PPh3)2]Mn(CO)3 (2a). To
5.6 mg (4.8 µmol) of Pd0(PPh3)4 in 500 µL of acetone-d6 was added
4.4 mg (13.5 µmol) of 1a. After 30 min, the acetone solution was
poured into 100 mL of diethyl ether. A red precipitate of 2a was
formed, contaminated by some CpMn(CO)3, which was separated
and isolated as light yellow crystals by dissolution of the crude
lation steps). Catalytic reactions are more efficient if the rates
of the different steps of the catalytic cycle are made as close as
possible to each other.2 One can thus predict that (i) slow
transmetalation steps will favor the efficiency of catalytic
reactions involving (η5-C5H4-I)FeCp (slowest oxidative addition)
and (ii) fast transmetalation steps will favor the efficiency of
catalytic reactions of (η5-C5H4-I)Mn(CO)3 or (η5-C5H4-I)Re-
(CO)3 involved in fast oxidative additions, bypassing decom-
position of the Pd(II) complexes formed in the oxidative
addition. The high stability of complex 2c (FeCp) formed in
the slowest oxidative addition must be more compatible with
the slow nucleophilic attack of RCtCCu (present at catalytic
concentration) in Sonogashira reactions. This is why the
Sonogashira reaction appeared to be more efficient with the
coordinated FeCp reagent in Scheme 1.1 The faster nucleophilic
attack of RCtC-SnBu3 (present at stoichiometric concentra-
tion) in Stille reactions is more adapted to the fast oxidative
additions of complexes 1a,b. Moreover, the complexation of
the active Pd(0) complex by the CtC bond of RCtC-SnBu3
should occur, as established for CH2dCH-SnBu3 and RCt
CH derivatives.10 This complexation would slow down the
oxidative addition of 1a,b and thus favor the efficiency of the
catalytic Stille reaction by bringing the rate of the oxidative
addition closer to that of the transmetalation step. This affords
an educated explanation of the fact that the Stille reactions
were found to be more efficient with the coordinated Mn(CO)3
and Re(CO)3 reagents than with the coordinated Fe(Cp)
(Scheme 1).1
1
precipitate into chloroform. Its H NMR in CDCl3 was similar to
that of an authentic sample (see text). The red solid 2a was isolated
and characterized. 1H NMR (250 MHz, acetone-d6, TMS): δ 5.64
(d, J ) 2 Hz, 2H), 5.74 (d, J ) 2 Hz, 2H), 7.22 (m, 4H), 7.38 (m,
2H), 7.49 (m, 4H), 7.79 (m, 4H), 7.93 (m, 8H), 7.98 (m, 4H), 8.05
ppm (m, 4H). 13C NMR (62.9 MHz, acetone-d6, TMS): δ 206.16
ppm (CO), instead of 225 ppm in 1a. 31P NMR (101 MHz, acetone-
d6): δ 20.65 ppm (s).
Characterization of [(η5-C5H4)PdI(PPh3)2]Re(CO)3 (2b). To
7.5 mg (6.8 µmol) of Pd0(PPh3)4 in 500 µL of acetone-d6 was added
8.9 mg (19.4 µmol) of 1b. After 30 min, the acetone solution was
poured into 100 mL of diethyl ether. A red precipitate of 2b was
Experimental Section
General Considerations. 31P NMR spectra were recorded on a
Bruker spectrometer (101 MHz) with H3PO4 as an external
reference. 1H NMR spectra were recorded on a Bruker spectrometer
(250 MHz, TMS). Cyclic voltammetry and amperometry were
performed at gold-disk electrodes with a homemade potentiostat
and a Tacussel GSTP4 waveform generator. The voltammograms
were recorded on a Nicolet 301 oscilloscope. All experiments were
performed under an argon atmosphere.
1
formed. H NMR (250 MHz, acetone-d6): δ 6.18 (d, J ) 2 Hz,
2H), 6.07 (d, J ) 2 Hz, 2H), 7.35 (m, 4H), 7.51 (m, 6H), 7.83 (m,
12H), 8.12 ppm (m, 8H). 31P NMR (101 MHz, acetone-d6): δ 19.86
ppm (s).
Characterization of [(η5-C5H4)PdI(PPh3)2]FeCp (2c). To 6 mg
(5.2 µmol) of Pd0(PPh3)4 in 500 µL of acetone-d6 was added 3 mg
(9.3 µmol) of 1c. After 12 h, the acetone solution was poured into
100 mL of diethyl ether. A brown precipitate of 2c was isolated
and characterized. 1H NMR (250 MHz, acetone-d6): δ 4.16 (s, 5H),
4.67 (d, J ) 2 Hz, 2H), 4.92 (d, J ) 2 Hz, 2H), 7.42 (m, 12H),
7.65 (m, 6H), 7.72 ppm (m, 12H). 31P NMR (101 MHz, acetone-
d6): δ 26.04 ppm (s).
Chemicals. DMF was distilled from calcium hydride under
vacuum and kept under argon. The complexes 1a,8 1b,8 1c,9 and
11
Pd0(PPh3)4 were synthesized as detailed in the literature.
General Procedure for the Kinetics of the Oxidative Addition
of (η5-C5H4-I)MLn (1a-c) with Pd0(PPh3)4. Experiments were
Acknowledgment. This work has been supported in part
by the Centre National de la Recherche Scientifique (UMR
CNRS-ENS-UPMC 8640, UMR-CNRS 7576), the Ministe`re de
la Recherche (Ecole Normale Supe´rieure and Ecole Nationale
Supe´rieure de Chimie de Paris), and ANR FerVect (ANR-06-
blanc-0387-01). We thank Johnson Matthey for a loan of
palladium salt.
(8) Lynch, T. J.; Diminguez, R.; Helvenston, M. C. Organometallics
1988, 7, 2566-2567.
(9) Guillaneux, D.; Kagan. H. B. J. Org. Chem. 1995, 60, 2502-2505.
(10) (a) For the complexation of Pd(0) by alkynes, see: Amatore, C.;
Bensalem. S.; Ghalem, S.; Jutand, A.; Medjour, Y. Eur. J. Org. Chem.
2004, 366-371. (b) For the complexation of Pd(0) by vinylstannanes, see:
Amatore, C.; Bucaille, A.; Fuxa, A.; Jutand, A.; Meyer, M.; Ndedi Ntepe,
A. Chem. Eur. J. 2001, 7, 2134-2142. (c) For a review see: Jutand, A.
Pure Appl. Chem. 2004, 76, 565-576.
(11) Rosevear, D. T.; Stone, F. G. A. J. Chem. Soc. A 1968, 164-167.
OM700302U