Conformational control of metallocene backbone by cyclopentadienyl ring substitution: A new concept in polyphosphane ligands evidenced by "through-space" nuclear spin-spin coupling. Application in heteroaromatics arylation by direct C-H activation

Article abstract of DOI:10.1021/om8012162

The present study deals with the conformational control of the metallocene backbone within ferrocenyl polyphosphane ligands and their performance in the highly topical palladium-catalyzed heteroaromatics arylation by direct C-H activation. New substituted

Full text of DOI:10.1021/om8012162

3152
Organometallics 2009, 28, 3152–3160
Conformational Control of Metallocene Backbone by
Cyclopentadienyl Ring Substitution: A New Concept in
Polyphosphane Ligands Evidenced by “Through-Space” Nuclear
Spin-Spin Coupling. Application in Heteroaromatics Arylation by
Direct C-H Activation
Radomyr V. Smaliy, Matthieu Beaupe´rin, He´le`ne Cattey, Philippe Meunier, and
Jean-Cyrille Hierso*
UniVersite´ de Bourgogne, Institut de Chimie Mole´culaire de l’UniVersite´ de Bourgogne UMR-CNRS 5260,
9 AVenue Alain SaVary, 21078 Dijon, France
Julien Roger and Henri Doucet
UniVersite´ de Rennes, Institut Sciences Chimiques de Rennes UMR-CNRS 6226, Campus de Beaulieu,
35042 Rennes, France
Yannick Coppel
Laboratoire de Chimie de Coordination du CNRS UPR-CNRS 8241, 205 Route de Narbonne,
31077 Toulouse Cedex 4, France
ReceiVed December 23, 2008
The present study deals with the conformational control of the metallocene backbone within ferrocenyl
polyphosphane ligands and their performance in the highly topical palladium-catalyzed heteroaromatics
arylation by direct C-H activation. New substituted cyclopentadienyl rings were synthesized, which
allowed the assembling of original tri- and diphosphanes. The bulky cyclopentadienyl lithium salts
diphenylphosphino-3-(triphenyl)methylcyclopentadienyllithium (4) and 1,2-bis(diphenylphosphino)-4-
(triphenyl)methylcyclopentadienyllithium (5) were prepared in excellent yield. The assembling of these
new hindered cyclopentadienyl salts (Cp) with other Cp fragments was performed in order to prepare
ferrocenyl ligands with controlled conformation. A comparison of conformations of 1,1′,2-tris(diphe-
nylphosphino)-3′,4-di-tert-butylferrocene (3) and 1,1′,2-tris(diphenylphosphino)-3′-(triphenyl)methyl-4-
tert-butylferrocene (6) allowed us to determine, for the first time, the conditions of an efficient control
of the orientation of the phosphino substituents on the ferrocene backbone in the absence of an ansa-
bridge. The characterization of these metallo-ligands, by multinuclear NMR in solution and by X-ray
diffraction in the solid state, focused on nonbonded JPP spin-spin couplings. These unusual couplings
are especially useful for assessing the conformation of the ferrocene backbone in solution. The palladium
complexes of the triphosphane ligand 6 and the diphosphane 1,1′-bis(diphenylphosphino)-3,3′-di(triph-
enyl)methylferrocene (7) were successfully used in the direct C-H activation of electron-rich
heteroaromatics for coupling to demanding aryl bromides, whether electron rich and/or sterically congested.
Products such as 2-butyl-5-(4-methoxyphenyl)furan (10), 2-butyl-5-o-tolylfuran (11), and thiophene
analogues (12 and 13) were obtained in yields higher than 90%. The NMR examination of the reaction
of [PdCl(η3-C3H5)]2 with ligands 6 and 7 allowed us to determine the coordination chemistry of the
precatalysts. The allylic palladium complexes 8 and 9 confirmed the unusual conformation present in 6.
As a consequence, the selective and “genuinely” tridentate bonding of a triphosphane to one palladium
center is reported. This seldom observed coordination mode is a direct consequence of the successful
ferrocene backbone conformation control.
features of ferrocene derivatives such as planar chirality,1
Introduction
reversible redox properties,2 high chemical stability, and a wide
array of substitution patterns3 have attracted intense interest both
The “sandwich” arrangement of metallocenes, such as fer-
rocene and its derivatives, is an important structural motif in
organometallic chemistry. The metallocenes have found ap-
plications in materials science and catalysis. Some attractive
in academic research and in industry.4 Recent ligand synthesis
by Santelli, De Meijere, and our group have provided several
examples of polyphosphane catalytic auxiliaries incorporating
(1) Arraya´s, R. G.; Adrio, J.; Carretero, J. C. Angew. Chem., Int. Ed.
2006, 45, 7674.
(2) Sakamoto, R.; Murata, M.; Nishihara, H. Angew. Chem., Int. Ed.
2006, 45, 4793.
* Corresponding author. E-mail: jean-cyrille.hierso@u-bourgogne.fr.
Phone: (+33) 3 80396106. Fax: (+33) 3 8039 3682.
10.1021/om8012162 CCC: $40.75
2009 American Chemical Society
Publication on Web 05/11/2009

Conformational Control of Metallocene Backbone
Organometallics, Vol. 28, No. 11, 2009 3153
A close spatial proximity of the phosphorus donor atoms of
1 and its derivatives, imposed by the blocked conformation of
the ferrocenyl backbone, has been evidenced.14-17 The signals
observed in the 31P NMR spectrum of 1 and its derivatives
revealed a collection of intense “through-space” JPP spin-spin
coupling constants.14 These
J result from the overlap of the
PP
TS
phosphorus lone-pairs having an appropriate orientation. Con-
versely, in the related triphosphane 2 (Figure 1),15,18 the
conformational “cis-orientation” of the phosphorus atoms is lost,
hypothetically because of the absence of the second tertiary-
butyl group. As a consequence, no 31P “through-space” spin
coupling between the magnetically nonequivalent phosphorus
atoms was observed for 2, as attested by the two 1:2 singlets
observed in the solution NMR spectrum.19 This discrepancy in
the conformational features of closely related ferrocene deriVa-
tiVes raises important questions about the conditions required
for a conformational control of metallocene backbones. We
anticipated that a specific ligand design might force three
substituents to adopt the same orientation within a metallocene
backbone (not only phosphorus donors). This controlled orienta-
tion would in turn provoke their close spatial proximity, which
could result in the emergence in chemical reactivity of coopera-
tive effects between the substituents. This proximity and its
associated effects can be a valuable feature in ferrocenyl
polyphosphanes from both a fundamental and an applied point
of view.10,13,14,19
Herein are presented our first investigations and results
devoted to the conformational control in ferrocenyl triphosphane
ligands. New substituted cyclopentadienyl rings, which allowed
the assembling of original tri- and diphosphanes, were synthe-
sized. Their characterization by multinuclear NMR in solution
focused on nonbonded JPP spin couplings. These couplings are
decisive indicators for assessing the conformation of the
ferrocene backbone. The present study aims to discuss and detail
the synthesis of polysubstituted metallocenes in which the
conformation of the backbone is controlled in solution. This
concept might find further applications in the rich chemistry of
sandwich complexes. The coordination behavior of the ligands
toward palladium confirms an unprecedented conformational
control. The activities of palladium complexes of the new
ligands were assessed in the highly topical palladium-catalyzed
arylation of substituted heteroaromatics via C-H bond activa-
tion. Such a reaction, which involves C-C bond formation, does
not result in the production of stoichiometric amounts of metallic
waste and therefore contribute to a more sustainable chemistry.
Figure 1. Ferrocenyl tetraphosphane 1 and triphosphane 2. 1 has a
blocked conformation with pseudoeclipsed phosphorus atoms at
internal positions for which JPP ) 60 Hz (down); for 2 an
unprecedented heteroannular JPC ) 5 Hz was observed with the
terminal methyl of t-Bu groups. The distances between NMR-active
atoms and the lone-pair orientation are essential for the intensity
of these spin-spin couplings and their mode of transmission.
three or four phosphorus atoms.5-9 These compounds exhibit
a high efficiency in stabilizing long-lived palladium-based
catalysts under substantially low metal/ligand loading conditions
(down to 10-6 mol % of palladium and polyphosphane ligand).7
For instance, the tetraphosphane metallo-ligand 1 (Figure 1) has
been found to be active in Heck and Suzuki cross-coupling
reactions with TONs up to 1 000 000. Under such conditions
of low catalyst loadings, classical mono- and diphosphanes are
ineffective.10 In our case, the ferrocene backbone is used as a
suitable robust platform for the introduction of three or four
phosphorus atoms in very close spatial proximity.11-13 One of
our goals is to study the unfamiliar influence of postulated
effects involving the multidentate nature of polyphosphane
ligands. The use in metal catalysis of this kind of polydentate
ligands, which include three or more donor atoms, might be
very pertinent. Indeed, very often in catalytic reactions an excess
of mono- or bidentate ligands with regard to the metal is
employed.7,10 A direct application of the chemistry of such
multidentate species is related to the development of more
sustainable catalytic systems based on the longeVity and the
stabilization of active intermediary species. This stability would
be attained via the enhancement of the coordination opportuni-
ties of the ligand to the metal center.7,12,13
Background
The analysis of the structure of the tetraphosphane metallo-
ligand 1 furthered our knowledge on the conformational control
of ferrocenyl-based phosphanes. The specific cis-orientation of
the four phosphorus atoms of the metallo-ligand 1, as depicted
in Figure 1, is a consequence of the cisoid conformation of the
(3) (a) Chen, W.; McCormack, P. J.; Mohammed, K.; Mbafor, W.;
Roberts, S. M.; Whittall, J. Angew. Chem., Int. Ed. 2007, 46, 4141. (b)
Iftime, G.; Daran, J.-C.; Manoury, E.; Balavoine, G. G. A. Organometallics
1996, 15, 4808.
(4) Blaser, H.-U. AdV. Synth. Catal. 2002, 344, 17.
(5) Doucet, H.; Santelli, M. Synlett 2006, 2001.
(6) Schill, H.; de Meijere, A.; Yufit, D. S. Org. Lett. 2007, 9, 2617.
(7) Hierso, J.-C.; Beaupe´rin, M.; Meunier, P. Eur. J. Inorg. Chem. 2007,
3767.
(14) Hierso, J.-C.; Fihri, A.; Ivanov, V. V.; Hanquet, B.; Pirio, N.;
Donnadieu, B.; Rebie`re, B.; Amardeil, R.; Meunier, P. J. Am. Chem. Soc.
2004, 126, 11077.
(8) Kondolff, I.; Feuerstein, M.; Doucet, H.; Santelli, M. Tetrahedron
2007, 63, 9514.
(9) Doucet, H.; Hierso, J.-C. Angew. Chem., Int. Ed. Engl. 2007, 46,
834.
(15) Hierso, J.-C.; Ivanov, V. V.; Amardeil, R.; Richard, P.; Meunier,
P. Chem. Lett. 2004, 33, 1296.
(16) Ivanov, V. V.; Hierso, J.-C.; Amardeil, R.; Meunier, P. Organo-
metallics 2006, 25, 989.
(17) Hierso, J.-C.; Evrard, D.; Lucas, D.; Richard, P.; Cattey, H.;
Hanquet, B.; Meunier, P. J. Organomet. Chem. 2008, 693, 574.
(18) Hierso, J.-C.; Fihri, A.; Amardeil, R.; Meunier, P.; Doucet, H.;
Santelli, M.; Ivanov, V. V. Org. Lett. 2004, 6, 3473.
(19) Jahel, A.; Vologdin, N. V.; Pirio, N.; Cattey, H.; Richard, P.;
Meunier, P.; Hierso, J.-C. Dalton Trans. 2008, 4206.
(10) Hierso, J.-C.; Fihri, A.; Amardeil, R.; Meunier, P.; Doucet, H.;
Santelli, M.; Donnadieu, B. Organometallics 2003, 22, 4490.
(11) Hierso, J.-C.; Smaliy, R.; Amardeil, R.; Meunier, P. Chem. Soc.
ReV. 2007, 36, 1754.
(12) Fihri, A.; Hierso, J.-C.; Meunier, P. Coord. Chem. ReV. 2007, 251,
2017.
(13) Evrard, D.; Lucas, D.; Mugnier, Y.; Meunier, P.; Hierso, J.-C.
Organometallics 2008, 27, 2643.

3154 Organometallics, Vol. 28, No. 11, 2009
Scheme 1. Synthesis of the Triphosphane 3 from Substituted Cyclopentadienyl Rings
Smaliy et al.
substituted cyclopentadienyl rings (Sb-Cp). A close spatial
proximity of the donor atoms is imposed by the blocked
conformation of the ferrocenyl backbone both in solution and
in the solid state. The intensity of nuclear spin-spin J couplings
between phosphorus atoms separated by at least four bonds
was found to increase exponentially with the decrease of
distances between the phosphorus atoms.14 Consequently, NMR
analysis on Pd(II)/1 precatalysts and electrochemistry studies
on analogous Pd(II)/Pd(0) species have revealed the involvement
of at least three phosphorus atoms in the coordination of
palladium.10,13 We additionally reported the synthesis and
properties of triphosphane 2,15,18 for which, conversely, the
phosphorus “orientation” was lost (Figure 1), hypothetically
because of the absence of the second tertiary-butyl group. As a
consequence, no “through-space” coupling between the mag-
netically nonequivalent phosphorus atoms was observed for 2
by solution 31P NMR.
The most usual way of exerting a conformational control on
metallocene backbones consists in bridging the cyclopentadienyl
rings.20 The resulting ansa-metallocenes display a number of
interesting properties often related to their rigidity. This kind
of conformation control by short interannular bridge bonding
clearly obviates any rotational flexibility.21 Additionally, as
demonstrated in some elegant syntheses,22 the introduction of
an interannular bridge in polysubstituted metallocenes together
with their ring functionalization may require several steps, some
potentially critical in terms of selectivity. To the best of our
knowledge, while a wide array of substitution patterns have been
applied in the preparation of substituted ferrocenes, including
1,1′- and 1,2-disubstituted, 1,1′,2-trisubstituted, and 1,1′,2,2′-
tetrasubstituted ferrocenes, the specific issue of gaining control
over a given conformation by means of the Cp substituents was
not addressed. This might in part be due to the dominant
development and applications of chiral diphosphanes, for which
the involvement of a third or fourth donor atom in their reaction
chemistry was seldom envisaged. Nevertheless, the catalytic
performances of ferrocenyl polyphosphanes make them worth-
while ligands, and the improvement of their design with the
control of their conformation in mind appeared to us a pertinent
issue.
Conformation Control by tert-Butyl Groups. Like 1, the
triphosphane ligand 3 was designed by incorporating two t-Bu
groups (one on each of the Sb-Cp rings), with the view to lead
to the desired conformation with three nearby phosphorus atoms
pointing in the same direction. 3 was obtained by reacting alkali
metal salts of adequately substituted cyclopentadienyl rings with
iron dichloride, following the method previously described for
producing dissymmetric ferrocenyl polyphosphanes (Scheme
1).16 The characterization of the new ligand revealed the failure
of this strategy since, as depicted in Figure 2, the X-ray structure
analysis reveals, in the solid state, a large spatial separation (>5.0
Å) between the third phosphorus atom and the 1,2-P chelating
pair (P1 · · · P2 ) 5.1098(2) Å, P1 · · · P3 ) 6.6591(2) Å). In
solution the 31P NMR consistently confirmed the absence of
spatial proximity between the heteroannular phosphorus nuclei.
For the chelating pair of phosphorus atoms an AB quartet
centered at -25.2 ppm is observed (JAB ) 98 Hz), while a
singlet at -20.7 ppm is attributed to the third one.23 The absence
of a coupling constant between AB and X resonances clearly
indicates the absence of a significant lone-pair overlap interac-
tion. The AB quartet is indicative of the slight difference of
environment between the two homoannular phosphorus atoms,
as illustrated in Scheme 1 (view from above). In the solid state,
an almost eclipsed conformation of the Sb-Cp rings is observed
for 3, which allows in fact a clear lessening of the steric
hindrance between the five substituents on the Sb-Cp rings.
The comparison of the preferred geometry observed in 2 and
3 (views from above in Figure 1 and Scheme 1) in the solid
state as well as in solution shows that the orientation of a third
phosphorus cannot be the result of only steric hindrance between
two tertiary-butyl groups. While 2 possess one t-Bu and 3 has
two t-Bu groups, their third phosphorus atoms display a
comparable orientation, away from the chelating pair. This
prevents de facto an easy cooperative coordination effect of the
three phosphorus nucleus in 3. Most probably the steric
hindrance of the phenyl groups attached to the phosphorus atoms
plays also a significant role in imposing the final conformation
in 2 and 3.
We subsequently envisioned that more bulky substituents than
tert-butyl groups might perturb the eclipsed conformation of
the Sb-Cp rings in ferrocenyl triphosphanes. Consequently, it
would be possible to reach a hindered conformation in which
three phosphorus atoms get a cis-conformation and come in
closer spatial proximity and eventually interact.
Conformation Control by a Trityl Group. Knowing the
role of tert-butyl groups in defining the conformation of 1, 2,
and 3, we explored whether a more hindered substituent might
induce a different effect on the conformation of triphosphane
ligands. To reach this goal, the (triphenyl)methyl group (trityl)
was chosen due to its easy access via ClCPh3. The lithium
salts diphenylphosphino-3-(triphenyl)methylcyclopentadienylli-
Results and Discussion
Different strategies were envisaged in order to prepare
ferrocenyl triphosphanes in which the orientation of the sub-
stituents would ensure a close spatial proximity of the phos-
phorus atoms as observed in the tetraphosphane 1 and contrary
to the case of triphosphane 2.
(20) Shapiro, P. J. Coord. Chem. ReV. 2002, 231, 67.
(21) Bridges containing three or more atoms are generally less rigid
and offer less stereochemical control, and they have received much less
attention; see ref 20.
(22) Liptau, P.; Tebben, L.; Kehr, G.; Fro¨hlich, R.; Erker, G.; Hollmann,
F.; Rieger, B. Eur. J. Org. Chem. 2005, 1909.
(23) A copy of the NMR spectrum is available in the Supporting
Information.

Conformational Control of Metallocene Backbone
Organometallics, Vol. 28, No. 11, 2009 3155
Figure 2. Plot of metallo-ligand 3 (30% probability). Hydrogen atoms are omitted for clarity. Selected bond distances (Å): Fe-Ct(1) )
1.6677(7), Fe-Ct(2) ) 1.6590(7). Selected internuclear distances (Å): P1 · · · P2 ) 5.1098(2), P1 · · · P3 ) 6.6591(2), P2 · · · P3 ) 3.4507(3).
Selected torsion angles (deg): P1-Ct(1)-Ct(2)-P2 ) -80.75(4), P1-Ct(1)-Ct(2)-P3 ) -149.68(4).
Scheme 2. Synthesis of Trityl-Substituted Cyclopentadienyl Rings 4 and 5
thium (4) and 1,2-bis(diphenylphosphino)-4-(triphenyl)methyl-
cyclopentadienyllithium (5) were obtained from [(Ph3C)-
CpLi] in 80% and 50% yield, respectively (Scheme 2).
Unfortunately, the second phosphorylation of the Cp ring
appears sluggish under our conditions, probably because of the
bulkiness of the Cp substituents.
The NMR characterization of the lithium salts 4 and 5 in
THF indicates proton shifts between 5.5 and 6.0 ppm and
phosphorus shifts at -19.4 ppm. The cyclopentadienyl fragment
4 was successfully used for assembling both dissymmetric and
symmetric new ferrocenyl phosphane ligands, following the
general methods previously reported.16 Curiously, the various
attempts to build ferrocenyl polyphosphanes from the fragment
5 were unsuccessful or suffered from a significant lack of
selectivity. The triphosphane 6 and the diphosphane 7 were
conversely obtained with fairly good yield of pure product
(g55%, Scheme 3).
the trityl group controls the global conformation of the ferrocene
backbone and consequently orients the third phosphorus atom
toward the chelating pair of phosphorus atoms. The trityl group
is certainly positioned far away enough from the homoannular
-PPh2 groups. This conformational constraint was not observed
for analogous ligands such as 2 and 3. In the absence of an X-ray
structure for 6, but based on related semiquantitative relationships,14,17
the proximity of phosphorus atoms (1-P, 1′-P) and (1′-P, 2-P) can
be predicted as less than 4.3 Å. The proposed conformation for
the triphosphane 6 is depicted in Figure 4. A complete attribution
was achieved by means of 13C and 1H with 31P broadband
1
decoupling and selective irradiation NMR (HMBC H/13C{31P},
HSQC 1H/13C{31P}).23
The proposed conformation should have substantial conse-
quences in the coordination to metals of 6; this hypothesis is
confirmed by the studies conducted with the palladium precursor
utilized in the catalytic applications and described below.
The diphosphane 7 displays a more classical 31P NMR
The solution multinuclear NMR spectrum of 6 is very
informative.23 From 31P NMR measurements a set of multiplets
in agreement with the existence of an intense interaction between
the three phosphorus atoms was observed (Figure 3).
1
spectrum with one singlet detected at -20.50 ppm. In the H
The analysis of the spectrum can be done at first order (ABC
spin system). The signals corresponding to the phosphorus of
the chelating pair, 1-P and 2-P, are centered at -18.8 and -24.9
ppm. They appear as a doublet of doublets, due to a strong but
classical coupling constant, 3JPP ) 41 Hz, but also due to more
intriguing coupling constants with the phosphorus atom 1′-P,
of the other cyclopentadienyl ring. The signal for the third
phosphorus is a pseudotriplet due to the JPP ) 11 and 12 Hz
with 1-P and 2-P. It is now recognized that this kind of intense
spin-spin coupling (herein 4JPP > 10 Hz) between heteroannular
phosphorus atoms operates “through-space” (TSJPP) and results
from a close spatial proximity of the spin-active nucleus.14
Therefore, we were delighted to find that the introduction of
Figure 3. 31P NMR spectrum of metallo-ligand 6 in toluene-d8.

3156 Organometallics, Vol. 28, No. 11, 2009
Smaliy et al.
Figure 4. 31P and 13C NMR attribution of metallo-ligand 6 with ensuing conformation.
Scheme 3. Synthesis of Triphosphane 6 (racemic) and Diphos-
phane 7 from Trityl-Substituted Cyclopentadienyl Rings
Scheme 4. Coordination Behavior of Triphosphanes 6 and
7 with [PdCl(η3-C3H5)]2
shows the immediate and quantitative coordination of the three
phosphorus donors to the metal center (Figure 5). The three
multiplets around -20 ppm are replaced by three broad signals
downfield shifted to -9.1, 24.0, and 29.8 ppm. These chemical
shifts indicate the bonding of all the phosphorus donors to the
metal center and show also that the chelating pair is certainly
more tightly bonded than the third heteroannular phosphorus
atom (signal at -9.1 ppm). The broadness of the signals suggests
a possible fluxional character of this bonding; however variable-
temperature measurement between -5 and 45 °C did not
produce a significant modification of the spectrum. This “true”
tridentate coordination (triligation) is unprecedented in the
NMR spectrum, three signals are observed for the protons of
the cyclopentadienyl rings at 3.45, 3.92, and 4.05 ppm. The
13C NMR spectrum displays typical quaternary signals from a
trityl group attached to Cp (C[CPh3] at 58.32 ppm and
C-C[CPh3] at 103.38 ppm). Thus, multinuclear NMR experi-
ments at room temperature indicate a symmetrical structure for
the ligand. Compound 7 is stable in the solid state but undergoes
phosphorus oxidation in solution if no precaution is taken (inert
atmosphere and deoxygenated solvent): a signal attributed to
PdO at a chemical shift of 26.83 ppm is observed, and the
signals for Cp protons appeared slightly shifted to higher field.
This behavior is rather uncommon for ferrocenic triarylphos-
phanes of this family and might be a sign of electron enrichment
of the phosphorus atoms.
Coordination Chemistry of 6 and 7 to Palladium. Due to
its inherent stability and solubility, as well as easiness of
reduction to Pd(0), the dimeric complex of palladium [PdCl-
(η3-C3H5)]2 is a convenient source of Pd(II) in various catalytic
cross-coupling reactions.10,18,24 It was used in the present study
as a palladium source for the catalytic arylation of heteroaro-
matics, and it was also employed to determine the coordination
behavior of complexes 6 and 7 toward palladium. The com-
plexes 8 and 9, depicted in Scheme 4, were quantitatively
obtained in NMR tubes from stoichiometric mixtures of
[PdCl(η3-C3H5)]2/2L (L ) 6 or 7) in CD2Cl2 at room temperature
(31P NMR in Figures 5 and 6).
The 31P NMR spectrum, recorded 5 min after the addition of
a solution of palladium allyl dimer to a solution of 6 in CD2Cl2,
Figure 5. 31P NMR spectrum of palladium complex 8 in CD2Cl2
at 318 K (10 min after Pd/2L addition).
(24) Hierso, J.-C.; Fihri, A.; Amardeil, R.; Meunier, P.; Doucet, H.;
Santelli, M. Tetrahedron 2005, 61, 9759.

Conformational Control of Metallocene Backbone
Organometallics, Vol. 28, No. 11, 2009 3157
downfield from 3.05, 4.11, and 5.51 ppm to 3.60, 4.22, and
5.83 ppm, respectively. These modified ferrocenyl phosphane
ligands and their complexes were tested in cross-coupling
reactions between aryl halides and heterocyclic compounds, in
order to evaluate their potential in palladium-catalyzed C-H
activation.
Direct C-H Activation in Heteroaromatics Arylation
Catalyzed by 8 and 9. The pallado-catalyzed formation of aryl/
heteroaryl coupling products via direct C-H activation is a
relatively recently reported reaction.26 This synthetic strategy
is attractive in terms of green chemistry and atom economy
when compared to alternative coupling methods that involve
organometallic heteroaryl or aryl reagents, the metallic groups
being either ZnX,27 SnR3,28 or B(OR)2.29 Such coupling
reactions lead to the subsequent formation of metallic waste in
stoichiometric amounts. Table 1 summarized the catalytic
coupling reactions that have been explored. The selection of
demanding substrates, such as the electron-rich bromoanisole
or congested 2-bromotoluene and 2-bromo-m-xylene, was made
on purpose since it was recently shown that the influence of
the ligand is decisive in these cases.26f-h Conversely, with less
challenging substrates such as electron-deficient aryl bromides
ligand-free couplings are achievable. Ligands 6 and 7 associated
with 0.5 mol % of [PdCl(η3-C3H5)]2 were found to give very
efficient catalysts for the coupling between 2-n-butylfuran or
2-n-butylthiophene and 4-bromoanisole or 2-bromotoluene. Both
ligands gave target products 10-13 in good yields (70 to 100%)
and high selectivity (Table 1, entries 5, 6, 8, 9, and 12-15).
For such reactions, other previously reported catalytic systems,26
such as Pd(PPh3)4, Pd(OH)2/C, PdCl2/2PCy3, or Pd(OAc)2, gave
very low to moderate yields (Table 1, entries 1-4 and 7). The
coupling of 2-n-propylthiazole with highly congested 2-bromo-
m-xylene gave 14 with moderate conversion and yields (Table
1, entries 11 and 16). Nevertheless, it should be noted that the
ligand-free Pd(OAc)2 catalyst did not produce 14 from this very
challenging aryl bromide (Table 1, entry 10).
Figure 6. Temperature dependence of the 31P NMR spectrum of
palladium complex 9 in CD2Cl2.
The catalytic systems based on the ferrocenyl phosphane
ligands 6 and 7 efficiently complement the few systems reported
to date for direct C-H activation of heteroaromatics.26 Accord-
ing to these preliminary results, they are of particular interest
for the coupling of electron-rich heteroaromatics to demanding
aromatic substrates. In particular, their robustness to temperature
in solution as well as to air and moisture in the solid state make
these compounds of rather easy and convenient use. Under our
conditions, however, only a slight difference in activity (in favor
of the diphosphane 6) is observed. Therefore, in the absence of
kinetic data on the Pd0 intermediaries of the catalytic cycle,13
coordination chemistry of ferrocenyl triphosphanes (such as 2,
for which only the chelating pair has been found to coordinate
palladium).25 The corresponding H NMR spectrum recorded
1
in CD2Cl2 confirms the structure proposed for 8 (and the
formation of only one species), with a clear shift of the five
resonances attributed to cyclopentadienyl protons from 3.93,
4.25, 4.28, 4.33, and 4.37 ppm to 3.51, 4.03, 4.67, 4.77, and
4.85 ppm, respectively.23 The characteristic multiplet of allylic-
CH is also shifted from 5.51 to 5.88 ppm.
The coordination of ligand 7 to palladium was found to be
fast with a complete disappearance of the signal at -20.50
ppm.23 Upon coordination, two signals of a nearby chemical
shift are observed at 298 K: 21.06 and 21.51 ppm (middle
spectrum in Figure 6). The variable-temperature experiments
confirmed that the signals are due to the formation of a single
dissymmetric species for which only one 31P NMR signal is
found at higher temperature (rapid exchange at 318 K, top
spectrum in Figure 6). At 278 K, the exchange between the
anisochronous phosphorus is slower and a typical AB pattern
is found for compound 9 (centered at 21.2 ppm, JAB ) 46 Hz).
The formulation proposed in Scheme 4 for 9 was confirmed by
1H NMR analysis, the shift of the three resonances attributed
to cyclopentadienyl protons (from 3.45, 3.92, and 4.05 ppm in
CD2Cl2 to 3.80, 4.39, and 4.56 ppm) being clearly observed.
The characteristic signals of allylic protons are also shifted
(26) (a) Ohta, A.; Akita, Y.; Ohkuwa, T.; Chiba, M.; Fukunaga, R.;
Miyafuji, A.; Nakata, T.; Tani, N.; Aoyagi, Y. Heterocycles 1990, 31, 1951.
(b) Parisien, M.; Valette, D.; Fagnou, K. J. Org. Chem. 2005, 70, 7578. (c)
Lavenot, L.; Gozzi, C.; Ilg, K.; Orlova, I.; Penalva, V.; Lemaire, M. J.
Organomet. Chem. 1998, 567, 49. (d) McClure, M. S.; Glover, B.; McSorley,
E.; Millar, A.; Osterhout, M. H.; Roschangar, F. Org. Lett. 2001, 3, 11. (e)
Okazawa, T.; Satoh, T.; Miura, M.; Nomura, M. J. Am. Chem. Soc. 2002,
124, 5286. (f) Pozˇgan, F.; Roger, J.; Doucet, H. ChemSusChem 2008, 1,
404, and references therein. (g) Battace, A.; Lemhadri, M.; Zair, T.; Doucet,
H.; Santelli, M. Organometallics 2007, 26, 472. (h) Battace, A.; Lemhadri,
M.; Zair, T.; Doucet, H.; Santelli, M. AdV. Synth. Catal. 2007, 349, 2507.
(i) For reviews on C-H activation of aryl groups see: Ritleng, V.; Sirlin,
C.; Pfeffer, M. Chem. ReV. 2002, 102, 1731. Campeau, C.; Fagnou, K.
Chem. Commun. 2006, 1253.
(27) Brandao, M. A. F.; de Oliveira, A. B.; Snieckus, V. Tetrahedron
Lett. 1993, 34, 2437, and references therein.
(28) For recent examples see: (a) Schneider, S.; Bannwarth, W. Angew.
Chem., Int. Ed. 2000, 39, 4142. (b) Su, W.; Urgaonkar, S.; McLaughlin,
P. A.; Verkade, J. G. J. Am. Chem. Soc. 2004, 126, 16433.
(29) Kondolff, I.; Doucet, H.; Santelli, M. Synlett 2005, 2057, and
references therein.
(25) Boudon, J.; Hierso, J.-C. Unpublished results.

3158 Organometallics, Vol. 28, No. 11, 2009
Smaliy et al.
Table 1. Heteroaromatics Arylation from Various Pd/L Systems
expansion of a more sustainable chemistry. The heteroaromatic/
aromatic products are potential building blocks in the synthesis
of natural and biologically active compounds. Ongoing studies
are dedicated to a better comprehension of the relationship
between the structure and catalytic potential of the designed
polyphosphanes.
Experimental Section
The reactions were carried out in oven-dried glassware (115 °C)
under an argon atmosphere using Schlenk and vacuum-line
techniques. Solvents, including deuterated solvents used for NMR
spectroscopy, were dried and distilled prior to use. FeCl2 from a
commercial source was used (Aldrich anhydrous beads, 99.9%, H2O
cat.
yield
entry
heteroaryl
aryl bromide
precursors product (%)
1
< 100 ppm). H (300.13, 500.13, or 600.13 MHz), 31P (121.49,
a
1
2
3
4
5
6
7
8
9
2-n-butylfuran
2-n-butylfuran
2-n-butylfuran
2-n-butylfuran
2-n-butylfuran
2-n-butylfuran
2-n-butylthiophene 4-bromoanisole
2-n-butylthiophene 4-bromoanisole
2-n-butylthiophene 2-bromotoluene
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-bromoanisole
4-bromoanisole
2-bromotoluene
Pd(PPh3)4
0
Pd(OH)2/Cb
PdCl2/2PCy3
10
10
10
10
11
12
12
13
40
14
202.46, or 242.93 MHz), and 13C NMR (75.47, 125.77, or 150.92
MHz), including low-temperature, 13C J modulation APT, COSY
1H-1H, HMQC, and HMBC NMR experiments were performed
in our laboratories (on Bruker 300, 600, or DRX 500), in CDCl3 at
293 K unless otherwise stated. Elemental analyses and mass spectra
were performed by the analytical service of the CSM of the
“Universite´ de Bourgogne”.
c
d
Pd(OAc)2
33 (12)
86 (81)
71 (66)
60 (50)
100 (90)
80 (74)
0
8
8
d
Pd(OAc)2
8
8
d
10 2-n-propylthiazole 2-bromo-m-xylene Pd(OAc)2
11 2-n-propylthiazole 2-bromo-m-xylene 8
14
10
11
12
13
14
37 (32)
95
96 (90)
91
95
48
1,1′,2-Tris(diphenylphosphino)-3′,4-di-tert-butylferrocene (3).
To a suspension of FeCl2 (500 mg, 3.93 mmol) in 50 mL of THF
was added at -40 °C a solution of diphenylphosphino-3-tert-
butylcyclopentadienyllithium (1.08 g, 3.45 mmol) in 15 mL of THF.
The reaction mixture was allowed to slowly rise to room temper-
ature and was stirred for 2 h. The reaction mixture was then cooled
to -40 °C, and a solution of 1,2-bis(diphenylphosphino)-4-tert-
butylcyclopentadienyllithium (1.71 g, 3.45 mmol) in 15 mL of THF
was added. After addition, the reaction mixture was allowed to
slowly rise to room temperature and was stirred for 2 h. THF was
removed, the residue was dissolved in 100 mL of toluene, and the
resulting solution was refluxed for 15 h. The brown solution was
then filtrated through silica to yield 2 g of a mixture of ferroce-
nylphosphanes 3 and 1. This mixture was difficult to purify, and
several preparative chromatography steps using hexane with 5%
of ethyl acetate as eluent were necessary to finally separate 550
mg (20%) of 3. 1H NMR (CDCl3): δ (ppm) 0.71, 0.93 (s, 9H each,
t-Bu), 3.63, 4.30, 4.32, 4.40, 4.62 (s, 1H each, H-Cp), 6.60-7.80
ppm (m, 30H, H-Ph). 31P{1H} (CDCl3): δ (ppm) -20.65 (s, 1′-P),
-25.00 (AB q, JAB ) 98 Hz, 1,2-P). 13C NMR (CDCl3): δ (ppm)
127.0-143.0 (m, 36 C, C6H5), 107.4 (s, 1C, 4-Fc), 107.0 (s, 1C,
12 2-n-butylfuran
13 2-n-butylfuran
14 2-n-butylthiophene 4-bromoanisole
15 2-n-butylthiophene 2-bromotoluene
4-bromoanisole
2-bromotoluene
9
9
9
9
16 2-n-propylthiazole 2-bromo-m-xylene 9
a Conditions: [PdCl(η3-C3H5)]2 0.005 mmol, L ) 6 or 7 0.01 mmol,
heteroaryl 2 mmol, aryl bromide 1 mmol, KOAc 2 mmol, DMAc, 150
°C, 20 h. GC yields and yields in parentheses are isolated. The
following systems have been employed for heteroaryl/aryl halide
couplings:26 1 mol % with AcONa in DMF 110 °C. b 1 mol % with
AcOK in DMAc, 150 °C. c 1 mol % with KOAc/Bu4NBr in DMF 110
°C. d 1 mol % Pd(OAc)2 as catalyst.
the relationship between their activity and their very different
coordination modes toward palladium (as evidenced with the
PdII complexes 8 and 9) remains to be clarified.
Summary
The design of ligands is of paramount importance for the
development of metal catalysis, in keeping with an ever more
sustainable approach of chemistry. The present work shows for
the first time that a conformational control of the metallocenes
backbone is possible in solution by substituting the cyclopen-
tadienyl ring with a very hindered substituent, such as the
(triphenyl)methyl group. For instance, the ferrocenyl ligand 6
in the absence of any ansa-bridge between its Cp rings displays
a cis-orientation of its three phosphorus donors. This unprec-
edented conformation leads to the bonding of the three
phosphorus atoms to the same metal center in palladium
complexes. This was demonstrated in solution by the presence
of intense “through-space” Jpp couplings between phosphorus
atoms separated by at least four bonds and confirmed by studies
concerning palladium coordination. The nuclear spin-spin
couplings of proximate phosphorus atoms are key indicators
for assessing the conformation of the ferrocene backbone. The
activity of the new ligands was tested with success in the
palladium-catalyzed arylation of substituted electron-rich aro-
matic heterocycles via C-H bond activation. Demanding
substrates such as electron-rich and/or hindered aryl bromides
were quantitatively coupled to thiophenes and furans. This kind
of C-C bond forming, which does not result in stoichiometric
metallic waste production, is in conformity with the necessary
1
1
3′-Fc), 82.0 (d, 1C, 1-Fc, JCP ) 20 Hz), 80.1(d, 1C, 2-Fc, JCP
)
1
15 Hz), 76.8 (d, 1C, 1′-Fc, JCP ) 13.5 Hz), 76.0 (dd, 1C, 3-Fc,
3
2JCP ) 28 Hz, JCP ) 4.5 Hz), 72.5 (s, 1C, 5′-Fc), 70.9 (s, 1C,
4′-Fc), 70.35 (dd, 1C, 5-Fc, 2JCP 4.5 Hz, 3JCP e 1 Hz), 68.5 (d, 1C,
2′-Fc, 2JCP 4.5 Hz), 31.9, 31.7 (s, 3C each, C(CH3)3), 30.4, 30.0 (s,
1C each, C(CH3)3). C54H53FeP3 (850.76): calcd C 76.2, H 6.28;
found C 75.80, H 6.82. Exact mass: m/z 850.268 (M+), simulated
850.271, (σ) 0.043.
X-ray Analysis of 3. Intensity data were collected on a Nonius
Kappa CCD at 115 K. The structures were solved by direct methods
(SIR92)30 and refined with full-matrix least-squares methods based
on F2 (SHELXL-97)31 with the aid of the WINGX program.32 All
non-hydrogen atoms were refined with anisotropic thermal param-
eters. Hydrogen atoms were included in their calculated positions
and refined with a riding model. Crystallographic data are reported
in Supporting Information.
(30) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl.
Crystallogr. 1993, 26, 343.
(31) Sheldrick, G. M. SHELXL-97; Institu¨t fu¨r Anorganische Chemie
der Universita¨t: Go¨ttingen, Germany, 1998.
(32) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.

Conformational Control of Metallocene Backbone
Organometallics, Vol. 28, No. 11, 2009 3159
Diphenylphosphino-3-(triphenyl)methylcyclopentadienyllithi-
um (4). A 15 g (53.8 mmol) amount of degassed trityl chloride
were dissolved in 35 mL of tetrahydrofuran.33 This solution was
added by cannula at -20 °C to a suspension of 4.1 g (56.9 mmol)
of cyclopentadienyllithium in 15 mL of THF. The reaction mixture
was stirred 10 min at low temperature and then heated at reflux for
3 h. After solvent evaporation, the residue was triturated with 100
mL of 40% aqueous EtOH for 20 min. The solvent was removed
by decantation, and the residue was dissolved in 60 mL of toluene.
The resulting solution was dried on MgSO4 and filtered through
silica. After evaporation of the toluene, the oily residue was
crystallized from a mixture of n-octane/toluene (3:1) kept one night
at 5 °C in a refrigerator. The product was filtrated on a glass filter,
washed with 30 mL of cold ether, and dried to give 10 g of pale
yellow crystals (yield 60%). To a suspension of 10 g (32.42 mmol)
of this diene in 60 mL of hexane was added dropwise 21 mL of
n-BuLi (1.6 M, 33.60 mmol) at -20 °C. The temperature was
slowly raised to room temperature, and stirring was continued
overnight. During this time the initially almost colorless suspension
turned pink. The resulting mixture was filtrated, and the solid was
washed with 30 mL of hexane (or toluene/hexane for further
purification) and dried under vacuum to yield 10 g of [(Ph3C)CpLi]
brown-red mixture and evaporation of the filtrate, 1.14 g of pure
product was isolated in 55% yield from column chromatography
on silica (eluent toluene/hexane, 1:2). The attribution of the nucleus
(except for Ph groups) was done from NMR experiments (spectra
available as Supporting Information or upon request to the authors):
13C and 1H with 31P broadband decoupling and selective irradiation,
1
1
1
HMBC H/13C{31P}, HSQC H/13C{31P}, HMBC H/31P, COSY
1
45{31P}. H NMR (toluene-d8): δ 0.77 (s, 9H, t-Bu), 3.94 (s, 1H,
2′-Cp), 4.28 (s, 1H, 4′-Cp), 4.29 (s, 1H, 3-Cp), 4.32 (s, 1H, 5′-Cp),
4.35 (s, 1H, 5-Cp), 6.70-7.39 (m, 45H, Ph). 13C{1H} NMR: δ 30.22
(s, 1C, C(CH3)3), 31.24 (s, 3C, C(CH3)3), 59.24 (s, 1C, CPh3), 73.21
2
3
(dd, 1C, JPC ) 16.4, JPC ) 2.5 Hz, 3-Fc), 73.28 (s, 1C, 4′-Fc),
2
75.06 (s, 1C, 2′-Fc), 75.08 (s, 1C, 5′-Fc), 75.86 (dd, 1C, JPC
)
3
1
15.1, JPC ) 5.0 Hz, 5-Fc), 79.90 (d, 1C, JPC ) 13.8 Hz, 1′-Fc),
80.65 (dd, 1C, JPC ) 23.9, 2JPC ) 18.2 Hz, 2-Fc), 81.61 (dd, 1C,
1
1JPC ) 11.3, JPC ) 17.6 Hz, 1-Fc), 103.72 (s, 1C, 3′-Fc), 108.65
2
3
(d, 1C, JPC ≈ 3.8 Hz, 4-Fc), 126.14 (s, Ph), 127.26-128.28 (m,
CPh3), 128.73 (s, Ph), 128.93 (s, Ph), 130.78 (s, Ph), 133.03 (d,
Ph), 133.07 (d, JPC ) 7.2 Hz, Ph), 134.13 (d, Ph), 134.18 (dd, Ph),
135.17 (d, Ph), 136.22 (dd), 137.53 (dd, JPC ) 12.5. and 1.2 Hz,
1C, ipso-PhP), 138.07 (d, JPC ≈ 13.8 Hz, 1C, ipso-Ph), 138.42 (dd,
1C, JPC ≈ 2.9 Hz, ipso-PhP), 138.66 (d, 1C, JPC ) 15.0 Hz, ipso-
PhP), 140.41 (d, 1C, JPC ) 12.6 Hz, ipso-PhP), 141.46 (d, 1C, JPC
1
(yield 98%). H NMR (THF-d8): δ (ppm) 5.40, 5.60 (t, J ) 2.8
Hz, 2H each, H-Cp), 6.70-7.40 (m, 15H, H-Ph).
) 17.6 Hz, ipso-PhP). 31P{1H} NMR: δ -24.9 (dd, JPP ) 41.0
3
TS
TS
Hz,
J
) 11.0 Hz, 2-PPh2), -21.7 (p-t,
J
) 11.0 and 12.0
To a stirred suspension of [(Ph3C)CpLi] (10 g, 31.81 mmol) in
60 mL of toluene was added dropwise a solution of Ph2PCl (6 mL,
33.45 mmol) in 20 mL of toluene at -80 °C. The mixture was
stirred overnight, allowing the temperature to slowly rise to room
temperature. The solution was filtrated over Celite, to remove the
LiCl precipitate, which was washed two times with 15 mL of
toluene. The filtrate was reduced to approximately 30 mL. The
concentrated solution was treated with 22 mL of n-BuLi (1.6 M,
35.20 mmol) at -20 °C and then evaporated almost to dryness; 60
mL of hexane was added to the residue, and this mixture was
vigorously stirred overnight. The resulting suspension was filtrated,
and the desired product was recovered as a white solid and washed
two times with 30 mL of hexane before drying under vacuum. The
lithium salt 4 was obtained pure in 80% yield (12.70 g). 1H NMR
(THF-d8): δ (ppm) 5.45, 5.65, 5.95 (m, 1H, H-Cp), 6.80-7.40 (m,
25H, H-Ph). 31P NMR (THF-d8): δ (ppm) -19.35 ppm.
1,2-Bis(diphenylphosphino)-4-(triphenyl)methylcyclopentadi-
enyllithium (5). To a stirred solution of 4 (5 g, 10.03 mmol) in a
mixture of 30 mL of toluene and 15 mL of THF was added
dropwise Ph2PCl (2.3 mL, 13.04 mmol) at room temperature. The
mixture was stirred for 48 h under argon and evaporated almost to
dryness. The residue was triturated with toluene (45 mL), the
resulting solution was filtrated over Celite, the precipitate of LiCl
was washed with toluene (two times 10 mL), and the filtrate was
reduced to 20 mL. This solution was treated with 9 mL of n-BuLi
(1.6 M, 14. 00 mmol) at -20 °C and evaporated almost to dryness.
After addition of 30 mL of hexane and vigorous stirring for 8 h a
pink precipitate was formed. It was filtered off, washed with hexane,
and dried under vacuum to yield 3.6 g of 5 (52%). 1H NMR (THF-
d8): δ (ppm) 5.57 (s, 2H, H-Cp), 6.80-7.40 (m, 35H, H-Ph). 31P
NMR (THF-d8): δ (ppm) -19.40 ppm.
PP
PP
3
TS
Hz, 1′-PPh2), -18.8 (dd, JPP ) 41 Hz,
J
) 12.0 Hz, 1-PPh2).
PP
C69H59FeP3 (1036.97): calcd C 79.92, H 5.73; found C 79.87, H
5.66. Exact mass: m/z 1036.313 (M+), simulated 1036.318, (σ)
0.059.
1,1′-Bis(diphenylphosphino)-3,3′-di(triphenyl)methylferrocene (7).
To a stirred suspension of 0.2 g of FeCl2 (1.58 mmol) in 10 mL of
THF was added dropwise by cannula a solution of 4 (0.8 g, 1.6
mmol) in 20 mL of THF at -10 °C. After THF addition the cooling
bath was removed, and 45 mL of toluene was added. Reflux was
carried out until completion of the reaction as followed by 31P NMR.
7 was isolated pure by column chromatography using a mixture of
1
toluene/hexane (1:1) (1.09 g, 65% yield). H NMR (CD2Cl2): δ
3.45 (s, 2H, Cp), 3.92 (s, 2H, Cp), 4.05 (s, 2H, Cp), 6.88-7.75
(m, 50H, Ph). 13C{1H} NMR: 125.77 MHz: δ 58.32 (s, 2C, CPh3),
72.74, 74.50, 79.01 (w, 2C each), 86.71 (w, 2C, 1-1′-Fc); due to
coupling to phosphorus, cyclopentadienyl CH and quaternary signals
were of weak intensity except for 103.38 (s, 2C, 3,3′-Fc), 125.30
(s, Ph), 126.25 (s, Ph), 127.05 (m, Ph), 127.92 (s, Ph), 129.85 (s,
Ph), 131.71 (d, Ph), 133.09 (d, Ph), 146.18 (s, ipso-Ph). 31P{1H}
NMR: δ -20.50 (s, PPh2). C72H56FeP2 (1039.03): calcd C 83.23,
H 5.43; found C 83.09, H 5.28. Exact mass: m/z 1039.325 (M+),
simulated 1038.320, (σ) 0.198.
Reaction of the Palladium Allyl Chloride Dimer with 2
equiv of Ligands 6 and 7. A solution of the allyl dimer [PdCl-
(η3-C3H5)]2 in 0.3 mL of CD2Cl2 (3.5 mg, 0.97 × 10-5 mole) was
added to a solution of 6 or 7 (20 mg, 1.93 × 10-5 mole) in 0.3 mL
of CD2Cl2 under an argon atmosphere at room temperature. The
resulting orange-red solution was immediately monitored by NMR
(600 MHz) at variable temperature between 268 and 318 K. With
the view to check the stability of the formed species, measurements
were conducted for several hours (2-6 h) and the solutions were
also checked after reflux in the NMR solvent.
Preparation of the Pd/L Catalysts. An oven-dried Schlenk tube
equipped with a magnetic stirring bar, under argon atmosphere,
was charged with [Pd(η3-C3H5)Cl]2 (18.3 mg, 0.05 mmol) and 6
or 7 (104 mg, 0.1 mmol). Then 5 mL of anhydrous DMAc was
added, and the solution was stirred at room temperature for 20 min.
The appropriate amount of catalyst solution was transferred to the
catalytic experiments.
1,1′,2-Tris(diphenylphosphino)-3′-(triphenyl)methyl-4-tert-bu-
tylferrocene (6). To a stirred suspension of 0.26 g of FeCl2 (2.05
mmol) in 10 mL of THF was added dropwise by cannula a solution
of [(t-Bu)Cp(PPh2)2Li] (1.0 g, 2.01 mmol) in 20 mL of THF at
-40 °C. After addition the cooling bath was removed, allowing
the temperature to slowly rise to room temperature. After 1 h
stirring, a solution of [(Ph3C)Cp(PPh2)Li] (2.00 mmol, 1.0 g) in
20 mL of THF was added at -10 °C to the reaction mixture. The
mixture was then evaporated to dryness, and 45 mL of toluene was
added to the residue and refluxed for 24 h. After filtration of the
Catalytic Experiments. In a typical experiment, the aryl bromide
(1 mmol), heteroaryl derivative (2 mmol), and KOAc (2 mmol)
were introduced in an oven-dried Schlenk tube, equipped with a
(33) Hoch, M.; Duch, A.; Rehder, D. Inorg. Chem. 1986, 25, 2907.

3160 Organometallics, Vol. 28, No. 11, 2009
Smaliy et al.
magnetic stirring bar. The palladium catalyst solution (1 mol %)
and DMAc (4 mL) were added, and the Schlenk tube was purged
five times with argon. The mixture in the Schlenk tube was stirred
for 20 h at 150 °C. Then, the reaction mixture was analyzed by
gas chromatography to determine the conversion of the aryl
bromide. The solvent was removed by heating of the reaction vessel
under vacuum, and the residue was charged directly onto a silica
gel column. The products were eluted, using an appropriate ratio
of diethyl ether and pentane.
2-Butyl-5-(o-tolyl)thiophene (13).26h The reaction of 2-bromo-
toluene (0.171 g, 1 mmol), 2-n-butylthiophene (0.280 g, 2 mmol),
and KOAc (0.196 g, 2 mmol) with the palladium complex (0.01
mmol) using ligand 6 affords the corresponding product 13 in 74%
(0.170 g) isolated yield.
5-(2,6-Dimethylphenyl)-2-propylthiazole (14). The reaction of
2-bromo-m-xylene (0.185 g, 1 mmol), 2-n-propylthioazole (0.254
g, 2 mmol), and KOAc (0.196 g, 2 mmol) with the palladium
complex (0.01 mmol) using ligand 6 affords the corresponding
1
2-Butyl-5-(4-methoxyphenyl)furan (10).26g The reaction of
4-bromoanisole (0.187 g, 1 mmol), 2-n-butylfuran (0.248 g, 2
mmol), and KOAc (0.196 g, 2 mmol) with the palladium complex
(0.01 mmol) using ligand 6 affords the corresponding product 10
in 81% (0.187 g) isolated yield.
product 14 in 32% (0.074 g) isolated yield. H NMR (CDCl3): δ
(ppm) 1.05 (t, J ) 7.4 Hz, 3H), 1.89 (sext, J ) 7.4 Hz, 2H), 2.46
(s, 6H), 3.02 (t, J ) 7.4 Hz, 2H), 7.05-7.25 (m, 3H), 7.36 (s, 1H).
13C NMR (CDCl3): δ (ppm) 13.7, 20.9, 23.3, 35.5, 127.4, 128.5,
130.4, 134.3, 138.6, 140.4, 171.8. C14H17NS (231.36): calcd C
72.68, H 7.41; found C 72.60, H 7.61.
2-Butyl-5-o-tolylfuran (11). The reaction of 2-bromotoluene
(0.171 g, 1 mmol), 2-n-butylfuran (0.248 g, 2 mmol), and KOAc
(0.196 g, 2 mmol) with the palladium complex (0.01 mmol) using
ligand 7 affords the corresponding product 11 in 90% (0.193 g)
Acknowledgment. This work was supported by CNRS,
the “Conseil Re´gional de Bourgogne” (postdoctoral grant for
R.V.S.) and the “Rennes Metropole”, which are sincerely
acknowledged. The authors wish to thank D. Armspach
(Strasbourg L. P. University) for his help and S. Royer for
technical assistance. J.R. is grateful to French MEN for a
grant. Dr. A. Battace is also thanked for some cross-coupling
reactions performed by employing literature reported systems.
1
isolated yield. H NMR (CDCl3): δ (ppm) 0.98 (t, J ) 7.4 Hz,
3H), 1.41 (sext., J ) 7.4 Hz, 2H), 1.70 (quint., J ) 7.4 Hz, 2H),
2.51 (s, 3H), 2.72 (t, J ) 7.4 Hz, 2H), 6.11 (d, J ) 3.2 Hz, 1H),
6.46 (d, J ) 3.2 Hz, 1H), 7.20-7.40 (m, 3H), 7.71 (d, J ) 7.9 Hz,
1H). 13C NMR (CDCl3): δ (ppm) 13.9, 22.0, 22.3, 27.8, 30.3, 106.6,
109.3, 125.9, 126.5, 126.8, 130.6, 131.1, 134.1, 151.7, 155.9.
C15H18O (214.30): calcd C 84.07, H 8.47; found C 84.01, H 8.60.
2-Butyl-5-(4-methoxyphenyl)thiophene (12).26f The reaction of
4-bromoanisole (0.187 g, 1 mmol), 2-n-butylthiophene (0.280 g, 2
mmol), and KOAc (0.196 g, 2 mmol) with the palladium complex
(0.01 mmol) using ligand 6 affords the corresponding product 12
in 90% (0.222 g) isolated yield.
Supporting Information Available: Crystal structure data for
3 as a CIF file, NMR spectra corresponding to ref 23, and exact
mass ES analysis of 3, 6, and 7. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM8012162