Congested ferrocenyl polyphosphanes bearing electron-donating or electron-withdrawing phosphanyl groups: Assessment of metallocene conformation from NMR spin couplings and use in palladium-catalyzed chloroarenes activation

Article abstract of DOI:10.1021/ic2015379

The synthesis of novel substituted cyclopentadienyl salts that incorporate both a congested branched alkyl group (tert-butyl, (triphenyl)methyl, or tri(4-tert-butyl)phenylmethyl) and a phosphanyl group is reported. The introduction of either electron-withdrawing or electron-donating substituents (furyl, i-propyl, cyclohexyl, tert-butyl) on P atoms was generally achieved in high yield. The modular synthesis of ferrocenyl polyphosphanes from an assembly of these cyclopentadienyl salts was investigated, leading to the formation of new triphosphanes (denoted as 9-12) and diphosphanes (denoted as 14-16). The resulting phosphanes are not sensitive to air or moisture, even when electron-rich substituents are present. This set of polyphosphanes displays varied conformational features, which are discussed in the light of their multinuclear NMR characterization in solution and of the X-ray solid state structure of the representative triphosphane 1,2-bis(diphenylphosphanyl)- 1′-(diisopropylphosphanyl)-3′-(triphenyl)methyl-4-tert-butyl ferrocene, 11. In particular, the existence of a range of significantly different nonbonded ("through-space", TS) spin-spin coupling constants between heteroannular P atoms, for the triphosphanes of this class, allowed their preferred conformation in solution to be appraised. The study evidences an unanticipated flexibility of the ferrocene platform, despite the presence of very congested tert-butyl and trityl groups. Herein, we show that, contrary to our first belief, the preferred conformation for the backbone of ferrocenyl polyphosphanes can not only depend on the hindrance of the groups decorating the cyclopentadienyl rings but is also a function of the substituents of the phosphanyl groups. The interest of these robust phosphanes as ligands was illustrated in palladium catalysis for the arylation of n-butyl furan with chloroarenes, using direct C-H activation of the heteroaromatic in the presence of low metal/ligand loadings (0.5-1.0 mol %). Thus, 4-chlorobenzonitrile, 4-chloronitrobenzene, 4-chloropropiophenone, and 4-(trifluoromethyl) chlorobenzene were efficiently coupled to n-butyl furan, using Pd(OAc) ₂ associated to the new diphosphane ligands 1,1′- bis(diisopropylphosphanyl)-3,3′-di(triphenyl)methyl ferrocene (15) or 1,1′-bis(dicyclohexylphosphanyl)-3,3′-di(triphenyl)methylferrocene (16), which respectively hold the electron-rich -Pi-Pr₂ and -PCy ₂ groups.

Full text of DOI:10.1021/ic2015379

ARTICLE
pubs.acs.org/IC
Congested Ferrocenyl Polyphosphanes Bearing Electron-Donating or
Electron-Withdrawing Phosphanyl Groups: Assessment of
Metallocene Conformation from NMR Spin Couplings and Use in
Palladium-Catalyzed Chloroarenes Activation
Sophal Mom,† Matthieu Beaupꢀerin,† David Roy,‡ Sylviane Royer,† Rꢀegine Amardeil,† Hꢀelꢁene Cattey,†
Henri Doucet,*,‡ and J.-C. Hierso*,†
†Institut de Chimie Molꢀeculaire de l’Universitꢀe de Bourgogne UMR-CNRS 5260, Universitꢀe de Bourgogne,
9 avenue Alain Savary 21078 Dijon, France
‡Institut Sciences Chimiques de Rennes UMR-CNRS 6226, Universitꢀe de Rennes I, Campus de Beaulieu 35042 Rennes, France
S Supporting Information
b
ABSTRACT:
The synthesis of novel substituted cyclopentadienyl salts that incorporate both a congested branched alkyl group (tert-butyl,
(triphenyl)methyl, or tri(4-tert-butyl)phenylmethyl) and a phosphanyl group is reported. The introduction of either electron-
withdrawing or electron-donating substituents (furyl, i-propyl, cyclohexyl, tert-butyl) on P atoms was generally achieved in high yield.
The modular synthesis of ferrocenyl polyphosphanes from an assembly of these cyclopentadienyl salts was investigated, leading to the
formation of new triphosphanes (denoted as 9ꢀ12) and diphosphanes (denoted as 14ꢀ16). The resulting phosphanes are not
sensitive toair or moisture, even whenelectron-richsubstituentsare present. This set of polyphosphanes displays variedconformational
features, which are discussed in the light of their multinuclear NMR characterization in solution and of the X-ray solid state structure of
the representative triphosphane 1,2-bis(diphenylphosphanyl)-10-(diisopropylphosphanyl)-30-(triphenyl)methyl-4-tert-butyl ferrocene,
11. In particular, the existence of a range of significantly different nonbonded (“through-space”, TS) spinꢀspin coupling constants
between heteroannular P atoms, for the triphosphanes of this class, allowed their preferred conformation in solution to be appraised.
The study evidences an unanticipated flexibility of the ferrocene platform, despite the presence of very congested tert-butyl and trityl
groups. Herein, we show that, contrary to our first belief, the preferred conformation for the backbone of ferrocenyl polyphosphanes
can not only depend on the hindrance of the groups decorating the cyclopentadienyl rings but is also a function of the substituents of
the phosphanyl groups. The interest of these robust phosphanes as ligands was illustrated in palladium catalysis for the arylation of n-
butyl furan with chloroarenes, using direct CꢀH activation of the heteroaromatic in the presence of low metal/ligand loadings
(0.5ꢀ1.0 mol %). Thus, 4-chlorobenzonitrile, 4-chloronitrobenzene, 4-chloropropiophenone, and 4-(trifluoromethyl)chlorobenzene
were efficiently coupled to n-butyl furan, using Pd(OAc)2 associated to the new diphosphane ligands 1,10-bis(diisopropylphosphanyl)-
3,30-di(triphenyl)methyl ferrocene (15) or 1,10-bis(dicyclohexylphosphanyl)-3,30-di(triphenyl)methylferrocene (16), which respec-
tively hold the electron-rich ꢀPi-Pr2 and ꢀPCy2 groups.
’ INTRODUCTION
a major role in modern metal-catalyzed organic reactions, and
many highly efficient catalytic procedures reported for CꢀC,
Ferrocene has emerged as an important motif in organome-
tallic chemistry, because of its useful applications within materials
science, electrochemistry, biomedical research, or ligand chem-
istry and homogeneous catalysis.1 Tertiary phosphanes play also
Received: July 19, 2011
Published: October 24, 2011
r
2011 American Chemical Society
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Scheme 1. Synthetic Pathways to Cyclopentadienyl (Cp)
Salts 4ꢀ8
Figure 1. Polyphosphane catalytic auxiliaries 1ꢀ3 built on a ferrocenyl
backbone.
CꢀN, or CꢀO bond formation by palladium-catalyzed cross-
coupling reactions are carried out in the presence of phosphane
auxiliary ligands.2 In addition to monodentate and bidentate
phosphane ligands, the high effectiveness of some polydentate
phosphanes (triphosphanes or tetraphosphanes) in the palla-
dium-catalyzed synthesis of fine chemicals has been recognized
in the past decade.2eꢀj As a part of our program that is directed
toward the development of air-stable efficient polydentate ligands
for cross-coupling reactions,3 we have showed that ferrocenyl
phosphanes—and especially triphosphanes (Figure 1)—can be
suitable ligands for CꢀH activation of heteroaromatic compounds.4
The relevant properties of these phosphanes prompted us to enlarge
the diversity of substituted ferrocenyl polyphosphanes with a search
for a controlled conformation of the ferrocene platform, possibly because
of congested branched alkyl substituents on the cyclopentadienyl
rings (see 2 and 3 in Figure 1). We were also interested in the
investigation of substantial changes in the electron-donating proper-
ties of P atoms and in the variation of the congested groups on
cyclopentadienyl (Cp) rings. The synthesis of several new con-
gested ferrocenyl diphosphane and triphosphane incorporating
groups of the (triphenyl)methyl type (trityl) is reported. Tertiary
phosphanes bearing electron-donor isopropyl and cyclohexyl
groups were also introduced with the view to promote oxidative
addition of haloarenes on metals. In addition, the synthesis of
phosphanes bearing an electron-withdrawing furyl group was also
achieved for the purpose of comparing ligand effects, and to possibly
promote the reductive elimination step in metal-catalyzed processes.
The analysis of the conformation adopted in solution by these new
polyphosphanes was assessed from multinuclear NMR and from the
X-ray structure of an original ferrocenyl triphosphane holding both a
tert-butyl and a (triphenyl)methyl congested group on different
cyclopentadienyl (Cp) rings. With the help of pertinent phosphorus
nuclear-spin coupling analysis in solution, the preferred conforma-
tion for these metallocene was estimated, indicating an unantici-
pated flexibility of the phosphanes. These new ligands were tested in
the direct arylation of n-butyl furan with chloroarenes to further
substantiate their interest in palladium-catalyzed CꢀC cross-cou-
plings and heteroarenes CꢀH activation.
cyclopentadienyl fragments and their assembly by reaction with
an iron halide in a final step is also a pertinent pathway to yield
polyfunctionalized ferrocenes. Following this way, ferrocenyl
phosphanes incorporating two different Cp rings (dissym-
metric ferrocenyl phosphanes) could be obtained and, some-
times, even preferentially formed than the expected symmetric
species.3c Usually, the structural differences between the sym-
metric and dissymmetric ferrocenes formed allow their easy
isolation by routine chromatography. Finally, the new Cp salts
formed throughout this methodology may be used for the
formation of other metallocene or hemimetallocene complexes
(Group 4, lanthanides, etc.).5,6 We have previously described the
synthesis of a Cp lithium salt bearing a (diphenyl)phosphanyl group
and the (triphenyl)methyl group starting from [Cp(trityl)Li].3g We
further extended this work to the synthesis of Cp lithium salt variants
4ꢀ8 that are presented in Scheme 1.
These compounds were obtained in excellent yields, albeit
following different synthetic pathways. The lithium salts 4 and 5,
featuring the electron-withdrawing furyl groups, were obtained in
yields of >85% from the reaction of [Cp(trityl)Li] and [Cp(t-Bu-
trityl)Li] (t-Bu-trityl = [tri(4-tert-butyl)phenyl)methyl]) with
the appropriate bromophosphane (BrP(FuMe)2). Conversely,
the attempts of functionalization with electron-rich phosphanyl
groups of Cp lithium salts substituted by a trityl group failed.
Presumably, a trityl group on the Cp ring diminishes the global
nucleophilicity of the ring, in addition to the significant hin-
drance that it generates. As a consequence, chloro(dialkyl)phos-
phanes may have an electrophilic character that is too weak for
the reaction to proceed easily. Thus, to synthesize lithium salts 6
and 7, phosphanylation was first carried out on the nonsubsti-
tuted Cp ring, and the trityl group was introduced in a second step.
The introduction of ꢀP(t-Bu)2 fragments in place of ꢀP(i-Pr)2
or ꢀPCy2 groups was determined to be particularly difficult.
Lithium salts 6 and 7, which incorporated electron-donating alkyl
groups, were obtained in yields of >90% from the reaction of
[CpP(i-Pr)2Li] or [CpPCy2Li], with the chlorophosphane
ClCPh3. In contrast to the lack of reactivity found for [Cp-
(trityl)Li] and [Cp(t-Bu-trityl)Li] salts, we observed that, from
[Cp(t-Bu)Li], it is nevertheless possible to obtain the lithium salt
8 [Cp(t-Bu)P(i-Pr)2Li] via successive reaction with ClP(i-Pr2)
and n-BuLi, although a comparatively lower yield was obtained
(77%). The difference in NMR chemical shifts observed for the P
atoms in compounds 4ꢀ8, ranging between 0.21 and ꢀ60 ppm.
’ RESULTS AND DISCUSSION
Cyclopentadienyl (Cp) Functionalized with Congested
Groups and Electron-Rich or Electron-Poor Phosphanes.
The functionalization of cyclopentadienyl (Cp) rings is fairly
well-known and widely used.5,6 Yet, only a limited number of
metallocenic polyphosphanes of higher rank than diphosphanes
are available for use in synthetic chemistry and homogeneous
catalysis.7ꢀ9 Regarding the general methods available to yield
functionalized ferrocenes,3c some reactivity and selectivity pro-
blems may be encountered when a direct phosphanylation of the
ferrocene backbone is employed to produce polyfunctionalized
ferrocenes.10,11 Thus, the formation of adequately substituted
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ARTICLE
Figure 2. Triphosphanes 9ꢀ13 built on a ferrocenyl backbone.
70 ppm, attests the variety of steric and σ-electron-donating pro-
perties12 of the phosphanyl groups in the lithium salts synthesized.
Synthesis and Characterization of Congested Ferrocenyl
Triphosphanes. The Cp lithium salts 4ꢀ8 were engaged with
FeCl2 and [t-BuCp(PPh2)2Li] to form the dissymmetric triphos-
phanes 9ꢀ12 (see Figure 2). These compounds are worth compar-
ing with the triphosphane 13 previously reported (Figure 2),3g
especially regarding their structural and conformational features.
Table 1 gathers, for this set of triphosphanes, the P chemical
shifts and their specific JPP coupling constants in CDCl3. We have
established that constrained polyphosphanes may eventually
show very intense nuclear spinꢀspin couplings between P nuclei,
depending on their proximity in space and on a suitable orienta-
tion of their lone pairs.13 These through-space (TS) couplings
range from small values (i.e., 1ꢀ2 Hz) to very large values
(sometimes >100 Hz).14 They are frequently called “long-range”
couplings, since the nuclei involved are generally separated by at
least four covalent bonds. However, this term is misleading, since,
with the exception of rare fully conjugated systems, spinꢀspin
transmission does not occur through the many bonds that link
the two remote interacting atoms. The coupling is actually a
consequence of a scalar direct nuclearꢀnuclear nonbonded,
electron-mediated interaction. This scalar nonbonded spinꢀspin
coupling is directly observed between magnetically nonequiva-
lent nuclei experiencing lone-pairs overlap, independent of any
NMR pulse sequence.13 Several relevant structural features are
noticed for the electron-rich and electron-poor ferrocenyl triphos-
phanes 9ꢀ13, from the comparison of their solution NMR data.
Except for compound 11, three intense coupling constants
between PA, PB, and PM are detected, which lead to typical
multiplet signals. The detectable coupling constants for the
heteroannular P atoms pairs J(PAPM) and J(PBPM), which range
between 6 Hz and 22 Hz, indicate nonbonded spinꢀspin nuclear
coupling (TSJPP) operating via P lone-pair electrons rather than
spin couplings through four covalent bonds. The existence of
these spin couplings indicates the spatial proximity of the P
atoms concerned and, therefore, is informative on the conforma-
tion of the metallocene backbone in solution. The similarity of
J(PAPM) and J(PBPM) in 13 (11ꢀ12 Hz) had led us to propose,
for this compound, a conformation in solution averaged around
the one described in Figure 3a,3g in which the spatial distances
between PA PM and PB PM would range within a similar
and ꢀ3.7 ppm are obtained with the more electron-donating
cyclohexyl and isopropyl groups, respectively. Regarding the
electron-rich triphosphanes 11 and 12, based on the strong
differences found for the through-space (TS) J(PAPM) and
J(PBPM), the mutual distances between P atoms in solution are
expected to be strongly dissimilar. Substantially different J(PAPM)
and J(PBPM) were observed in each case with much weaker
J(PBPM) coupling constants found, compared to J(PAPM). This
suggests that the phosphorus PM is in a closer proximity to PA than
to PB (see Figure 3b), inducing a shorter PA PM TS distance,
3 3 3
and, thus, a more-efficient lone-pair overlap and a more-intense
spinꢀspin nuclear coupling. An extreme situation is observed with
phosphane 11, for which no J(PBPM) is detected, and a weaker
J(PAPM) coupling constant of 6 Hz is observed: this suggests a
conformation that is in better agreement with Figure 3c.
Our first idea of a fully controlled rigid conformation of the
ferrocene backbone by congested groups on Cp ring,3g which
had been deduced from the structural features of compound 13
solely, is clearly not consistent with these results. From the
different triphosphanes reported here, it is clearly observed that
the conformational control of the ferrocene backbone is not
systematically ensured by the introduction of congested trityl and
tert-butyl groups on Cp rings, despite the strong hindrance that is
created. Thus, several different metallocene conformations are
obtained in solution, even when a strictly identical functionalized
ferrocene platform is used. Herein, a ferrocene holding hetero-
annular trityl and tert-butyl groups constitutes the common
backbone of triphosphanes 9ꢀ13, yet their conformations, and
the mutual positions of P atoms in solution, differ significantly.
Thus, the nature of the substituents on the phosphanyl groups is
also critical in establishing the preferred averaged conformation
of these polyphosphanes.
X-ray structural characterization of a ferrocenyl polypho-
sphane incorporating a trityl group has never been reported until
now, since we previously failed to generate suitable single crystals
of compound 13. However, proper single crystals of compound
11 were obtained and analyzed by X-ray diffraction (XRD) (see
Figure 4, top). The solid-state structure determined is not in full
agreement with the 31P NMR observed in solution. The con-
formation found in the crystal (Figure 4, bottom) is different
from that which is predictable in solution from 31P31P NMR spin
couplings (see Figure 3c). The interaction evidenced in NMR
between PM and PA (J(PAPM) = 6 Hz) is not consistent with the
solid-state conformation obtained due to the orientation of P
lone pairs and the very long spatial distance between the nuclei
(dPA PM = 5.998 Å and dPB PM = 7.180 Å). Nevertheless,
3 3 3
3 3 3
value.
Thus, a similar time-averaged conformation is proposed for 9
and 10, which hold the electron-withdrawing furyl moieties, with
regard to their identical J(PAPM) and J(PBPM) of 17 and 23 Hz,
respectively. As a result of the electronic properties of furyl
groups, the pseudo-triplets corresponding to the resonance of
the shielded PM atoms in phosphanes 9 and 10 are observed
at ꢀ69.3 and ꢀ68.9 ppm, respectively, as expected, at much
higher field, compared to ꢀPPh2 groups (found between ꢀ17.0
and ꢀ25.0 ppm, depending on the atom environment). Consis-
tently, deshielded PM atoms with chemical shifts observed at ꢀ13.0
3 3 3
3 3 3
the change from the conformation in Figure 3c to the conforma-
tion at the bottom of Figure 4 may be achieved by a counter-
clockwise rotation of 72° of the upper Cp ring. This rotation
would not be hindered by the branched alkyl substituents on the
Cp rings, since they would not cross each other.
An alternative is a slight rotation of the CꢀPM and CꢀPA
bonds to allow overlapping of the P lone pairs of PA and PM,
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Table 1. 31P NMR Data for Triphosphanes 9ꢀ13
δ PA
δ PB
δ PM
triphosphane
(ppm)
signal
(ppm)
signal
(ppm)
signal
JPAPB (Hz)
JPAPM (Hz)
JPBPM (Hz)
(9)
ꢀ16.8
ꢀ19.3
ꢀ24.0
ꢀ24.0
ꢀ18.8
dd
dd
dd
dd
dd
ꢀ23.6
ꢀ24.3
ꢀ21.4
ꢀ21.9
ꢀ24.9
dd
dd
d
ꢀ69.3
ꢀ68.9
ꢀ3.7
ꢀ13.0
ꢀ21.7
p-t
p-t
d
56
72
59
63
41
17
23
6
17
23
a
(10)
(11)
(12)
(13)
dd
dd
dd
p-t
22
12
6
11
a Not detected (below 0.5 Hz).
Figure 3. Time-averaged conformations in solution proposed for 9, 10, 13 (left), 12 (middle), and 11 (right) from 31P31P NMR spinꢀspin couplings.
TS
which may lead to the small
J
PP
observed in solution. The
of furans and thiophenes with bromoarenes, but was useless for
chloroarenes activation.3g Modified versions of 17-bearing elec-
tron-enriched phosphanyl groups were synthesized as ferroce-
nylphosphanes 14ꢀ16. This class of diphosphanes 14ꢀ17
usually forms mixtures of rac and meso diastereomers, since no
asymmetric control is exerted during synthesis; eventually, upon
purification, only the major diastereomer may be obtained, as has
been the case for 17.16
The P chemical shifts for 14ꢀ16 (Table 2, column 2) are
found to be significantly deshielded, compared to 17, because of
the electron-donating properties of alkyl groups attached to the P
nuclei. Similar to diphosphane 17, 15 was obtained as a single
diastereomer after workup, with a P signal shift at ꢀ2.4 ppm, and
three signals for Cp protons at 3.99, 3.68, and 3.52 ppm.
Phosphanes 14 and 16 were obtained showing two sets of
signals, corresponding to the presence of two diastereomers.
Compound 14 (rac+meso) is characterized by a major P signal
at ꢀ0.2 ppm (85%) and a minor signal at ꢀ1.4 ppm. In agree-
ment, two sets of three proton signals from Cp rings are found at
4.09, 3.96, and 3.93 ppm (major) and 4.01, 3.99, and 3.98 ppm
(minor). Compound 16 (rac+meso) is characterized by a major P
signal at ꢀ8.7 ppm (70%) and a minor signal at ꢀ10.7 ppm. Broad
signals for protons of the cyclopentadienyl rings are observed at
3.84, 3.65, and 3.45 ppm.
rotational ability of the ꢀP(i-Pr2) group in 11 is also supported
by a JPC coupling constant of 5 Hz observed in 13C NMR
between the P-atom-bearing isopropyl groups and the methyl
groups of t-Bu. Such rare JPC coupling constants have been
already observed in a parent compound and in other
polyphosphanes.2h,13c They are explained as a TS (P,C) nuclear
spin transmission between the P lone-pair electrons and the
pairing electrons of the CꢀC bonds of the t-Bu methyl groups.
The conformation displayed in the X-ray structure determined
for 11 (Figure 4) is in good agreement with this interaction,
evidenced in 13C NMR, from an adequate orientation of P3 lone
pair toward the t-Bu group.
JPP and JPC TS spinꢀspin couplings observed for the phos-
phanes 9ꢀ13 indicate an unforeseen flexibility of their backbone,
despite the presence of tert-butyl and trityl congested groups.
Another important element of the ferrocenylphosphane flexi-
bility is indicated by the molecular structure of 11 with the
dihedral angle of the two Cp ring planes. This angle would be
normally expected to be close to zero with strictly parallel Cp ring
planes; however, as visible from Ortep in Figure 4, a fairly open
dihedral angle of 7.55(7)° is found. In the related ferrocenylpho-
sphane bearing two t-Bu groups instead of one t-Bu and one trityl
group,4c the corresponding dihedral angle was found to be
3.89(15)°.15
In order to check the electron-donating ability of the novel
77
polyphosphanes, we measured the 31Pꢀ Se coupling constants for
Synthesis and Characterization of Congested Electron-
Rich Ferrocenyl Diphosphanes. Lithium salts 4ꢀ8 were em-
ployed to form the new electron-rich ferrocenyl diphosphanes
14ꢀ16 (see Figure 5) using our Cp assembly method. The
diphosphane 17 has been previously determined to be an
effective ligand to promote palladium-catalyzed direct coupling
the diselenide derivatives of 14ꢀ17 (reported in Table 2). For
comparison purposes, we also measured the 1JP,Se coupling constant
for the diselenide derivative of the ferrocenyl diphosphane analogue
1,10-bis[di(5-methyl-2-furyl)phosphanyl]ferrocene, Fc[P(FuMe)2]2,
incorporating furyl moieties. An increase in these coupling constants
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Figure 4. ORTEP views (top) and drawing (bottom) of the molecular structure determined in the solid state for 11 (H atoms are omitted for the sake of
clarity, ellipsoids with 30% probability).
Figure 5. Diphosphanes 14ꢀ17 and their stereoisomeric properties (planar chirality).
indicates an increase in the scharacter of the P lone-pair orbital (i.e., an
electron-withdrawing effect of the phosphane on the selenium
Table 2. 31P NMR Data for Diphosphanes 14ꢀ17 and
Corresponding Phosphane Selenides
1
(Se)).12 As a benchmark, the JP,Se value for triphenylphosphine
δ ꢀPR2 (ppm) meso
and/or rac
δ ꢀP(dSe)R2
1JP,Se
selenide (SedPPh3) and for 1,10-bis[diphenylphosphanyl]ferrocene
selenide have been reported to be 730 and 737 Hz, respectively.12a,c
The 1JP,Se values determined from 14, 15, and 16 (710, 696, and 688
Hz, respectively), compared to 1JP,Se from 17 (741 Hz), confirmed
the expected electron-donating properties of the phosphanes. Con-
sistently, the electron-withdrawing properties induced at phosphorus
by the presence of methylfuryl groups were supported by the 1JP,Se of
787 Hz found for Fc[SedP(FuMe)2]2, which is among the highest
(P,Se) coupling constants reported to date for such types of tertiary
phosphanes.12
diphosphane
(ppm)
(Hz)
(14)
(15)
ꢀ0.2 (85%) / ꢀ1.3 (15%)
58.9 / 58.5
50.6
41.8a
710 / 712
696
ꢀ2.4
ꢀ8.7 (70%) / ꢀ10.7 (30%)
ꢀ24.0
(16)
688
(17)
Fc[P(FuMe)2]2
31.4
741
b
ꢀ64.9
ꢀ8.1
787
a For the major isomer. b Data taken from refs 3a and 3b.
heteroaromatics by direct CꢀH activation. Compared to aryla-
tion reactions using organometallic reagents (for example,
boronic acids, or zinc or tin organometallics) the direct regiose-
lective coupling of heteroaromatics with aryl halides via CꢀH
bond activation/functionalization is an interesting synthetic
Arylation of Heteroaromatics with Chloroarenes via CꢀH
Bond Activation. With this set of new diphosphanes and
triphosphanes in hand, which are built by following the ligand
design that we choose, we examined their influence in palladium
catalysis in the activation of chloroarenes for arylation of
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Table 3. Palladium-Catalyzed Direct 5-Arylation of n-Butylfuran with Ligands 15 or 16
a Pd(OAc)2, ligands 14ꢀ17 or dppf, aryl halide (1 mmol), 2-n-butylfuran (2 mmol), KOAc (2 mmol), Bu4NBr (1 mmol), DMAc, 150 °C, 16 h,
under argon.
strategy. Significant advantages are provided by this type of CꢀH
activation, in terms of clean chemistry, with the formation of a
halide salt as the main side-product and no stoichiometric
metallic waste.17,18
and for which the large bite angle that is associated to 1,10-
bidentate coordination may facilitate reductive elimination at
palladium.1a,11 A comparison with the Pd(OAc)2/dppf (at 1
mol %) system was also conducted, and the results for the dipho-
sphanes 14 and 17 were also checked, showing mainly that a
catalyst loading below 1 mol % is not suited in their case. Table 3
summarizes the results obtained in the coupling of various
chloroarenes with n-butylfuran. In the presence of the electron-
deficient aryl chlorides (4-chlorobenzonitrile, 4-chloronitroben-
zene, 4-chloropropiophenone, or 4-(trifluoromethyl)chloroben-
zene) and 0.5ꢀ1.0 mol % Pd(OAc)2, associated with 0.5ꢀ1.0
mol % of ligand 15 or 16, the 5-arylation products 18, 19, 21, and
22 were obtained in very high yields (entries 2, 3, 7, 8, 12, 13, 14,
and 16), with the catalysts incorporating dppf (entries 5 and 15)
being less efficient. On the other hand, the reaction toward the
ester 20 was difficult (entry 10, 37% yield). In the presence of
2-chlorobenzonitrile, which is more congested, a modest yield of
34% in 23 was obtained, because of partial conversion of this aryl
chloride (entry 17). An electron-rich aryl bromide, 4-bromo-N,N-
dimethylaniline was also found to have a moderate reactivity in the
presence of these catalysts, and 24 was obtained in yields of 38%
ꢀ44% (entries 19, 20, and 21). Diphosphanes 14 and 17 may give
satisfactory results, albeit at 1 mol % catalyst (entries 1, 4, 6, 9, 11,
and 18). Therefore, this catalytic system tolerates substrates that
incorporate useful functional groups such as nitriles, nitro, or keto
Ligand-less palladium catalysts, and classical systems for CꢀH
activation combining palladium and monophosphanes or dipho-
sphanes (Pd(OH)2ꢀC*, Pd(OAc)2, Pd(PPh3)4, PdCl2ꢀPCy3,
Pd(OAc)2/P(o-tolyl)3, [PdCl2(dppf)] (where dppf = bis-
(diphenylphosphanyl)ferrocene)) are not efficient for the activa-
tion of demanding bromoarenes and of chloroarenes for direct
arylation of furans.4a,17,18 This was confirmed by our preliminary
screening experiments, and, in addition, we observed that triphos-
phanes 9 and 10 were not well-suited for direct arylation of
heteroaromatics with aryl chlorides under our conditions (see
Table 3). Their electron-poor character possibly disfavored one
or several steps of the catalytic cycle, in particular, the oxidative
addition of organic chlorides may be difficult, because of the low
electronic density at P. We also observed that the catalytic
performances of triphosphanes 11ꢀ13 in direct arylation of
heteroaromatics with chloroarenes and hindered bromoarenes, if
better than 9 and 10, unfortunately did not match the perfor-
mances previously obtained with related ferrocenyl tripho-
sphanes.4 Therefore, we focused our catalytic investigations on
the diphosphanes 15 and 16, which hold two electron-rich pho-
sphanyl groups to promote the oxidative addition of chloroarenes,
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groups, which can be manipulated for accessing more-sophisti-
cated heterocyclic molecules.
all of the 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%, <100
ppm H2O). All catalytic reactions were performed using analytical-grade
DMAc that was not distilled prior to use. Potassium acetate (99%+) was
used. Commercial aryl halides and 2-n-butylfuran were used without
purification. Flash chromatography was performed on silica gel
The results obtained illustrate the potential of air-stable,
moisture-insensitive electron-rich diphosphanes 15 and 16 in
this specific arylation reaction. Assuming that these new phos-
phanes effectively promote oxidative addition, because of elec-
tron-enriched P donors, our study suggests that, to go further in
the scope of these direct arylation reactions, and especially in
using lower catalyst loadings, the oxidative addition of chloroar-
enes is probably not the single chemical step to facilitate. The
design of ligands more specifically assisting the CꢀH activation
of heteroarenes and arenes, which remains a catalytic step subject
of much questioning,19 might be of much interest. To extend the
scope of this attractive reaction, our ongoing research is currently
directed toward this goal.
1
(230ꢀ400 mesh). H NMR (300.13, 500.13, or 600.13 MHz), 31P
NMR (121.49, 202.46, or 242.93 MHz), and 13C NMR (75.47, 125.77,
or 150.92 MHz), including low-temperature, 13C J modulation APT,
13C-dept 135 NMR experiments were performed in our laboratories (on
Bruker Model 300, 600 or DRX 500 equipment) in CDCl3 at 293 K,
unless stated otherwise. The exact mass was measured on a Bruker
MicrOTOF Q system.
Synthesis of Cyclopentadienyl Lithium Salts. The starting
halide reagents 1-[bis(4-tert-butylphenyl)(chloro)methyl]4-tert-butyl-
benzene (4-t-Bu-Ph)3CCl20 and bis(5-methyl-2-furyl)bromophosphane
BrP(FuMe)2,3b and the lithium salts (triphenyl)methylcyclopentadienyl
lithium [Ph3CCpLi], (tert-butyl)cyclopentadienyl lithium [t-BuCpLi],
1-diphenylphosphanyl-3-tert-butylcyclopentadienyl lithium [1-PPh2-3-
t-Bu-CpLi], and 1,2-bis(diphenylphosphanyl)-4-tert-butylcyclopenta-
dienyl lithium [1,2-(PPh2)2-3-t-BuCpLi], were synthesized following
procedures described in the literature.3g,c,21 The protocols for the
synthesis of [P(i-Pr)2CpLi] and [PCy2CpLi] salts were modified from
the literature.2g,22,23
Di-(5-methyl-2-furyl)phosphanyl-3-[(triphenyl)methyl]cy-
clopentadienyl Lithium (4). To a stirred suspension of [CPh3CpLi]
(3.19 g, 10.15 mmol) in 40 mL of toluene at ꢀ80 °C was added, dropwise,
a solution of BrP(FuMe)2 (2.52 g, 9.23 mmol) in 10 mL of toluene. The
reaction mixture was stirred for 2 h, which allowed the temperature to
slowly rise up to 0 °C, and was then stirred for 18 h at room temperature.
The solution was filtered over Celite, to remove the LiCl precipitate, which
was washed with 15 mL of toluene. The filtrate was evaporated almost to
dryness, and 50 mL of heptane was added to the residue. The resulting
colorless solution was treated at ꢀ40 °C with n-BuLi (7.15 mL, 1.6 M in
hexane, 11.44 mmol). The reaction mixture was stirred for 18 h at room
temperature. The air-sensitive white precipitate formed was filtered, washed
with heptane, and dried under vacuum to give 4.03 g of 4 (yield 86%).
1H NMR (THF-d8): δ 2.19 (s, 6H, CH3 furyl), 5.85 (d, 2H, 3J =
1 Hz, H-furyl), 5.94, 6.01, 6.15 (m, 1H each, H-Cp), 6.24 (d, 2H, 3J =
1 Hz, H-furyl), 7.02ꢀ7.33 (m, 15H, Ph). 31P{1H} NMR (THF-d8):
δ ꢀ60.70 (s).
’ CONCLUSION
Ferrocene-based diphosphane and triphosphane ligands for
metal catalysis were synthesized from new cyclopentadienyl
(Cp) salts substituted with both congested branched alkyl groups
and phosphanyl groups, with the P atoms bearing either electron-
donor isopropyl and cyclohexyl groups or electron-withdrawing
furyl groups. The triphosphanes 9ꢀ13 formed present, in
solution, a set of “through-space” (TS) spinꢀspin nuclear
31P31P couplings due to the proximity of the P atoms. The
diversity of JPP collected for compounds 9ꢀ13 (from 0 to 23 Hz)
arises from their conformational differentiation and highlight the
flexibility of their ferrocene backbone via Cp rings rotation. Thus,
different conformations in solution are evidenced for these
ferrocenyl triphosphanes, despite their identical ferrocene back-
bone, which incorporates very congested tert-butyl and
(triphenyl)methyl groups. The X-ray structure determination
of the triphosphane 11 also indicates that preferred conforma-
tions in the solid state and in solution can be different for the
same species, since the long P P distances obtained in the
3 3 3
TS
X-ray molecular structure are not consistent with the
J
PP
observed in solution. In addition, in the molecular structure of
11, we observe that the ferrocene backbone can adapt itself to the
congested environment by a significant deviation of parallelism
of the Cp rings with a dihedral angle deviation above 7°. The
cyclopentadienyl lithium salts 4ꢀ8 were also employed to form
the electron-rich ferrocenyl diphosphanes 14ꢀ16 using the Cp
assembly method. The effect of the diphosphane and tripho-
sphane ligands was compared in the arylation of n-butyl furan, via
CꢀH activation, with aryl chlorides catalyzed by palladium. To
date, ligand-less palladium catalysts and classical systems for
CꢀH activation combining palladium and monophosphanes or
diphosphanes (such as Pd(OH)2ꢀC*, Pd(OAc)2, [Pd(PPh3)4],
PdCl2ꢀPCy3, Pd(OAc)2/P(o-tolyl)3, [PdCl2(ddpf)] are not
efficient for the activation of demanding bromoarenes and of
chloroarenes for direct arylation of furans. The results obtained
demonstrate the higher performance of the electron-rich dipho-
sphanes 15 and 16 in the arylation of substituted furans with
functionalized electron-deficient aryl chlorides, such as 4-chlor-
obenzonitrile, 4-chloronitrobenzene, 4-chloropropiophenone,
or 4-(trifluoromethyl)chlorobenzene.
Di-(5-methyl-2-furyl)phosphanyl-3-[tri-(4-tert-butylphe-
nyl)methyl]cyclopentadienyl Lithium (5). The precursor [tri(4-
tert-butylphenyl)methyl]cyclopentadienyl lithium was first synthesized
following this protocol. To a stirred suspension of Cp lithium (1.2 g,
15 mmol) in 20 mL of toluene at ꢀ20 °C was added, dropwise, a
suspension of 1-[bis(4-tert-butylphenyl)(chloro)methyl]4-tert-butyl-
benzene (2.6 g, 5.8 mmol) in 30 mL of toluene. The mixture was stirred
for 24 h at room temperature under argon. The solution was filtered over
Celite, to remove the LiCl precipitate. The filtrate was evaporated almost
to dryness, and 20 mL of hexane was added to the residue. The resulting
colorless solution was treated with n-BuLi (9 mL, 1.6 M in hexane,
14.4 mmol) at ꢀ20 °C. The reaction mixture was stirred for 24 h at room
temperature. The air-sensitive white precipitate formed was filtered,
washed with hexane, and dried under vacuum to give 3.26 g of lithium
salt [(4-t-Bu-Ph)3CCpLi] (yield 83%).
1H NMR (THF-d8): δ 1.28 (s, 27H, t-Bu), 5.43 (t, 2H, J = 4 Hz,
H-Cp), 5.62 (t, 2H, J = 4 Hz, H-Cp), 7.05ꢀ7.15 (m, 12H, Ph).
To a stirred suspension of [(4-t-Bu-Ph)3CCpLi] (2.78 g, 5.76 mmol)
in 30 mL of toluene at ꢀ80 °C was added, dropwise, a solution of
BrP(FuMe)2 (1.57 g, 5.76 mmol) in 15 mL of toluene. The reaction
mixture was stirred for 24 h at room temperature. The solution was
filtered over Celite to remove the LiCl precipitate, which was washed
’ EXPERIMENTAL SECTION
The reactions were carried out in oven-dried glassware (115 °C)
under an argon atmosphere using Schlenk and vacuum-line techniques.
For the synthesis and characterization of lithium salts and phosphanes,
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with 15 mL of toluene. The filtrate was treated with n-BuLi (4.3 mL,
1.6 M in hexane, 6.91 mmol) at ꢀ80 °C. The reaction mixture was
stirred for 24 h at room temperature. The solution was evaporated
almost to dryness, and 20 mL of heptane were added to the residue. The
resulting mixture was filtered and the solid was washed with 15 mL of
heptane and dried under vacuum to give 3.52 g of 5 (yield 90%).
1H NMR (THF-d8): δ 1.34 (s, 27H, t-Bu), 2.29, 2.21 (s, 1H each,
CH3 furyl), 5.48 (s, 1H, H-Cp), 5.90 (s, 2H, H-furyl), 6.09 (m, 2H,
H-Cp), 6.31 (s, 2H, H-furyl), 7.05ꢀ7.15 (m, 12H, Ph). 31P{1H} NMR
(THF-d8): δ ꢀ60.60 (s).
was evaporated almost to dryness, and 60 mL of heptane were added to
the residue. The resulting reddish solution was treated with n-BuLi
(9.50 mL, 1.6 M in hexane, 15.2 mmol) at ꢀ80 °C. The reaction mixture
was stirred for 18 h at room temperature. The air-sensitive purple red
precipitate that formed was filtered, washed with heptane, and dried
under vacuum to give 7.04 g of 7 (yield = 96%).
1H NMR (THF-d8): δ 0.50ꢀ1.90 (m, 22H, Cy), 5.6ꢀ6.5 (m, 3H,
H-Cp), 6.8ꢀ7.8 (m, 15H, Ph). 31P{1H} NMR (THF-d8): δ ꢀ11.60 (s).
Di-isopropylphosphanyl-3-tert-butylcyclopentadienyl
Lithium (8). To a stirred suspension of [t-BuCpLi] (4.11 g, 32.1
mmol) in 30 mL of toluene at ꢀ80 °C was added dropwise ClP(i-Pr)2
(5.15 mL, 32.1 mmol). The mixture was stirred for 16 h overnight, which
allowed the temperature to slowly increase to room temperature. The
solution was filtered over Celite, to remove the LiCl formed, which was
washed twice with 15 mL of toluene. The filtrate was concentrated to
∼15 mL and was treated with n-BuLi (27.5 mL, 1.6 M in hexane,
44.0 mmol) at ꢀ40 °C. The temperature was allowed to increase slowly
to room temperature, and stirring was continued for 16 h. The filtrate
was evaporated almost to dryness, and 15 mL of heptane was added to
the residue. This mixture was vigorously stirred for 4 h, and the white
solid formed was filtered, washed with 15 mL of heptane, and dried
under vacuum to give 6.01 g of 8 (yield 77%).
Di-isopropylphosphanyl-3-[(triphenyl)methyl]cyclopen-
tadienyl Lithium (6). The precursor [CpP(i-Pr)2Li] was first synthe-
sized following this protocol. To a stirred suspension of CpLi (3.17 g,
44.0 mmol) in 60 mL of toluene at ꢀ80 °C was added, dropwise,
ClP(i-Pr)2 (6.71 g, 44.0 mmol). The reaction mixture was stirred for 2 h,
which allowed the temperature to slowly rise up to 0 °C, and was then
stirred for 18 h at room temperature. Twenty milliliters (20 mL) of
heptane were added to the mixture, and after 10 min, it was filtered over
Celite to remove LiCl. The filtrate was evaporated almost to dryness and
30 mL of heptane were added to the residue. The resulting colorless
solution was treated with n-BuLi (27.5 mL, 1.6 M in hexane, 44.0 mmol)
at ꢀ40 °C. The reaction mixture was stirred for 18 h at room temperature.
The air-sensitive white precipitate formed was filtered, washed with heptane,
and dried under vacuum to give 7.99 g of [CpP(i-Pr)2Li] (yield = 94%).
1H NMR (THF-d8): δ 0.92 (m, 12H, CH(CH3)2), 1.86 (m, 2H,
CH(CH3)2), 5.85, 5.92 (m, 2H each, H-Cp). 31P{1H}(THF-d8):
δ ꢀ3.40 (s).
1H NMR (THF-d8): δ 0.97ꢀ1.13 (m, 12H, CH(CH3)2), 1.21 (s, 9H,
t-Bu), 1.97 (m, 2H, CH(CH3)2), 5.85, 5.94, 6.02 (m, 1H each, H-Cp).
31P{1H} NMR (THF-d8): δ 0.21 (s).
Ferrocenyl Phosphanes Synthesis. 1,2-Bis(diphenylphosphanyl)-
10-di(5-methyl-2-furyl)phosphanyl-30-tri(4-tert-butylphenyl) methyl-4-tert-
butyl Ferrocene (9). To a stirred suspension of FeCl2 (0.51 g, 4.1 mmol) in
15 mL of THF was added, dropwise, by cannula, a solution of [t-BuCp-
(PPh2)2Li] (1.98 g, 4.0 mmol) in 20 mL of THF at ꢀ40 °C. After the
addition, the cooling bath was removed, which allowed the temperature to
slowly increase to room temperature. After 1 h of stirring, a solution of [(t-
BuPh)3CCp(P(FuMe)2)Li] (2.4 g, 3.6 mmol) in 25 mL of THF at ꢀ10 °C
was added to the reaction mixture. The mixture was refluxed for 24 h. After
filtration of the brown-red suspension and evaporation of the filtrate, 4.3 g of
an oily residue was obtained. Compound 9 was isolated in a pure form as an
orange powder (1.5 g, 35% yield) from column chromatography on silica
(toluene/heptane 7:3).
To a stirred suspension of [CpP(i-Pr)2Li] (10.1 g, 53.1 mmol) in
50 mL of toluene at ꢀ80 °C was added, dropwise, a suspension of
ClCPh3 (14.5 g, 52.0 mmol) in 40 mL of toluene. The mixture was
stirred overnight, which allowed the temperature to slowly rise to room
temperature. The solution was filtered over Celite, to remove the LiCl
precipitate, which was washed with 15 mL of toluene. The filtrate was
evaporated almost to dryness, and 50 mL of heptane were added to the
residue. The resulting reddish solution was treated with n-BuLi
(36.5 mL, 1.6 M in hexane, 58.4 mmol) at ꢀ80 °C. The reaction
mixture was stirred for 18 h at room temperature. The air-sensitive
purple red powder that formed was filtered, washed with heptane, and
dried under vacuum to give 21.1 g of 6 (yield = 92%).
1H NMR (CDCl3): δ(ppm) = 0.67 (s, 9H, t-BuCp), 1.27 (s, 27H,
(CH3)3CPh), 2.26, 2.07 (s, 3H each, CH3-furyl), 4.12 (s broad, 2H, Cp),
4.17 (m, 2H, Cp), 4.24 (m, 1H, Cp), 5.80, 5.88, 6.32, 6.36 (m, 1H each,
H-furyl), 6.85ꢀ7.45 (m, 32H, Ph). 31P{1H}(CDCl3): δ (ppm) = ꢀ16.8
1H NMR (THF-d8): δ 0.60ꢀ1.3 (m, 12H, CH(CH3)2), 1.90 (m, 2H,
CH(CH3)2), 5.40ꢀ6.70 (m, 3H, H-Cp), 6.70ꢀ7.70 (m, 15H, Ph).
31P{1H} NMR (THF-d8): δ ꢀ3.22 (s).
(dd, 1P, 3JPP = 56 Hz, TSJPP = 17 Hz, PPh2), ꢀ23.6 (dd, 1P, 3JPP = 56 Hz,
Dicyclohexylphosphanyl-3-[(triphenyl)methyl]cyclopentad-
ienyl Lithium (7). The precursor dicyclohexylphosphanylcyclopenta-
dienyl lithium was first synthesized following this protocol. To a stirred
suspension of Cp lithium (0.64 g, 8.9 mmol) in 15 mL toluene at ꢀ80 °C
was added, dropwise, ClPCy2 (2.07 g, 8.88 mmol). The reaction mixture
wasstirredfor1h, whichallowedthetemperaturetoslowlyincreaseto0°C,
and was then stirred for 18 h at room temperature. The mixture was filtered
over Celite, to remove the LiCl precipitate, which was washed with 10 mL of
toluene. The filtrate was evaporated almosttodrynessand20mLofheptane
were added to the residue. The resulting colorless solution was treated with
n-BuLi (6.11 mL, 1.6 M in hexane, 9.77 mmol) at ꢀ40 °C. The reaction
mixture was stirred for 18 h at room temperature. The air-sensitive white
precipitate that formed was filtered, washed with heptane, and dried under
vacuum to give 2.23 g of [CpPCy2Li] (yield = 94%).
TS
J
= 17 Hz, PPh2), ꢀ69.3 (p-t, 1P, TSJPP = 17 Hz, P(FuMe)2). 13
C
PP
NMR (CDCl3): δ (ppm) = 156.4, 155.7 (s, 1C each, OCMe), 152.0 (d,
1C, 1JPC = 15 Hz, PCO), 149.4 (d, 1C, 1JPC = 22 Hz, PCO), 148.3 (s, 3C,
p-Ph-trityl), 144.3 (s, 3C, ipso-Ph-trityl), 140.5 (d, 1C, 1JPC = 12 Hz, ipso-
PhP), 138.8, (d, 1C, 1JPC = 15 Hz, ipso-PhP), 138.3 (d, 1C, 1JPC = 12 Hz,
ipso-PhP), 137.7, (d, 1C, 1JPC = 12 Hz, ipso-PhP), 136.0 (d, JPC = 20 Hz,
Ph-P), 134.6 (d, JPC = 5 Hz, Ph-P), 134.4 (d, JPC = 4 Hz, Ph-P), 133.6 (d,
J
PC = 20 Hz, Ph-P), 132.9 (d, JPC = 20 Hz, Ph-P), 130.5 (s, 6C, o-Ph-
trityl), 128.8 (s, Ph-P), 128.3 (d, JPC = 9 Hz, Ph-P), 128.0 (s, Ph-P),
127.7 (d, JPC = 6 Hz, Ph-P), 127.4 (d, JPC = 6 Hz, Ph-P), 127.3 (d, JPC = 8
Hz, Ph-P), 127.2 (s, Ph-P), 124.0 (s, 6C, m-Ph-trityl), 123.2 (d, 1C, 2JPC
= 28 Hz, CH-furyl), 119.9 (d, 1C, 2JPC = 19 Hz, CH-furyl), 108.1 (s, 1C,
4-Fc), 106.7 (m, 2C, 3JPC = 5 Hz, CH-furyl), 104.2 (s, 1C, 30-Fc), Cp
quaternary C (1-Fc, 2-Fc, 10-Fc) obscured, 75.0 (s, 1C, HC-Cp), 74.9
(m, 1C, HC-Cp), 73.2 (m, 1C, HC-Cp), 72.6 (m, HC-Cp), 72.5 (m, HC-
Cp), 58.0 (s, 1C, CPh3), 34.3 (s, 3C, PhC-t-Bu), 31.4 (s, 9C, PhC-
(CH3)3), 31.3 (s, 3C, CpC(CH3)3), 30.0 (s, 1C, CpC-t-Bu) 14.0, 13.8 (s,
1C each, CH3-furyl). C79H83FeO2P3 (1213.29). Exact mass [M+Na]+:
m/z = 1235.48379, simulated = 1235.48501, σ = 0.0427, err[ppm] = 0.8.
1,2-Bis(diphenylphosphanyl)-10-di(5-methyl-2-furyl)phosphanyl-
30-(triphenyl)methyl-4-tert-butyl Ferrocene (10). To a stirred suspension
1H NMR (THF-d8): δ 0.80ꢀ2.00 (m, 22H, Cy), 5.83 (m, 2H,
H-Cp), 5.89 (m, 2H, H-Cp). 31P{1H} NMR (THF-d8): δ ꢀ12.28 (s).
To a stirred suspension of [CpPCy2Li] (3.71 g, 13.83 mmol) in
40 mL of toluene at ꢀ80 °C was added, dropwise, a suspension of
ClCPh3 (3.64 g, 13.07 mmol) in 40 mL of toluene. The mixture was
stirred overnight, which allowed the temperature to slowly increase to
room temperature. The solution was filtered over Celite, to remove the
LiCl precipitate, which was washed with 15 mL of toluene. The filtrate
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of FeCl2 (0.30 g, 2.3 mmol) in 10 mL of THF was added, dropwise, by
cannula, a solution of [t-BuCp(PPh2)2Li] (1.15 g, 2.3 mmol) in 20 mL of
THF at ꢀ40 °C. After the addition, the cooling bath was removed, which
allowed the temperature to slowly increase to room temperature. After 1 h
of stirring, a solution of [Ph3CCp(P(FuMe)2)Li] (1.13 g, 2.3 mmol) in
20 mL of THF at ꢀ10 °C was added to the reaction mixture. The mixture
was refluxed for 24 h. After filtration and evaporation of the filtrate, a brown-
red oil (1.92 g) was obtained, and 0.79 g of 10 was isolated as an orange
powder (33% yield) from column chromatography on silica (toluene/
heptane 7:3).
Ph-P), 127.2 (s, Ph-P), 127.1 (d, JPC = 8 Hz, Ph-P), 126.9 (d, JPC = 8 Hz,
Ph-P), 126.8 (s, Ph-P), 126.3 (m, Ph-P), 126.1 (s, 6C, m-Ph-trityl), 124.9
(s, 3C, p-Ph-trityl), 106.5 (s, 1C, 4-Fc), 102.6 (s, 1C, 30-Fc), 82.3 (dd,
1C, JPC = 26 and 14 Hz, 1-or 2-Fc), 80.3 (d, 1C, JPC = 23 Hz, 10-Fc), 77.3
(p-t, 1C, 2 JPC = 14 Hz, 1- or 2-Fc), 74.9, 74.8, 71.6, 70.7, 69.8 (s, 1C
each, CH-Cp), 58.2 (s, 1C, CPh3), 30.8 (d, 3C, TSJPC = 5 Hz, CH3-t-Bu),
30.1 (s, 1C, C(CH3)3-t-Bu), 23.1 (d, 1C, 1JPC = 18 Hz, CH-i-Pr), 22.1 (d,
1C, 1JPC = 16 Hz, CH-i-Pr), 20.8 (d, 1C, 2JPC = 21 Hz, CH3-i-Pr), 19.6
(d, 1C, 2JPC = 14 Hz, CH3-i-Pr), 19.4 (d, 1C, 2JPC = 14 Hz, CH3-i-Pr),
18.8 (d, 1C, 2JPC = 6 Hz, CH3-i-Pr). C63H63FeP3 (968.94). Exact mass
[M+Na]+: m/z = 991.34134, simulated = 991.33859, σ = 0.5952,
err[ppm] = ꢀ2.7.
1H NMR (CDCl3): δ(ppm) = 0.68 (s, 9H, t-BuCp), 2.27, 2.07 (s, 3H
each, CH3-furyl), 4.19 (s broad, 3H, Cp), 4.14 (s, 1H, Cp), 4.05 (s, 1H,
Cp), 5.78, 5.89 (s large, 1H each, H-furyl), 6.33, 6.36 (m, 1H each,
H-furyl), 6.83ꢀ7.41 (m, 35H, Ph). 31P{1H}(CDCl3): δ (ppm) = ꢀ19.3
(dd, 1P, 3JPP = 72 Hz, TSJPP = 23 Hz, 1-PPh2), ꢀ24.3 (dd, 1P, 3JPP = 72
Hz, TSJPP = 23 Hz, 2-PPh2), ꢀ68.9 (p-t, 1P, TSJPP = 23 Hz, 10-P(FuMe)2).
13C NMR (CDCl3): δ (ppm) = 155.5, 154.9 (s, 1C each, OCMe), 150.8
(d, 1C, 1JPC = 15 Hz, PCO), 148.2 (d, 1C, 1JPC = 22 Hz, PCO), 146.1 (s,
3C, ipso-Ph-trityl), 139.0 (d, 1C, 1JPC = 11 Hz, ipso-Ph), 137.4 (d, 1C,
1JPC = 14 Hz, ipso-Ph), 137.0 (d, 1C, 1JPC = 11 Hz, ipso-Ph), 136.6 (d,
1,2-Bis(diphenylphosphanyl)-10-(dicyclohexylphosphanyl)-30-
(triphenyl)methyl-4-tert-butyl Ferrocene (12). To a stirred suspension
of FeCl2 (0.57 g, 4.6 mmol) in 20 mL of THF at ꢀ40 °C was added,
dropwise, by cannula, a solution of 1,2-bis(diphenylphosphanyl)-4-tert-
butylcyclopentadienyl lithium (2.21 g, 4.5 mmol) in 25 mL of THF. The
reaction mixture was allowed to slowly warm to room temperature and
was stirred for 2 h. The reaction mixture was then cooled to ꢀ40 °C and
a solution of 1-dicyclohexylphosphanyl-3-(triphenyl)methylcyclopen-
tadienyllithium 7 (2.26 g, 4.4 mmol) in 25 mL of THF was added. After
the addition, the reaction mixture was allowed to slowly warm to room
temperature, and then it was stirred for 1 h. The THF solvent was
removed, the residue was dissolved in 50 mL of toluene, and the
resulting solution was refluxed for 24 h. The brown solution was then
filtered through silica to yield a mixture of ferrocenyl phosphanes. This
mixture was purified by column chromatography (alumina gel, column
height = 30 cm, column diameter = 5.5 cm), using a 2:1 toluene/heptane
mixture to separate, as the first fraction, the symmetric ferrocenyl
tetraphosphane (3.35 g); then, as the last fraction, 1.21 g of phosphane
12 was obtained (26%).
1C, 1JPC = 10 Hz, ipso-Ph), 134.9 (d, JPC = 24 Hz, Ph-P), 133.1 (d, JPC
=
20 Hz, Ph-P), 133.0 (d, JPC = 20 Hz, Ph-P), 132.0 (d, JPC = 20 Hz, Ph-P),
129.9 (s, 6C, o-Ph-trityl), 127.8 (s, Ph-P), 127.3 (d, JPC = 9 Hz, Ph-P),
127.0 (s, Ph-P), 126.9 (m, Ph-P), 126.4 (m, Ph-P), 126.2 (s, 6C, m-Ph-
trityl), 125.0 (s, 3C, p-Ph-trityl), 122.1 (d, 1C, 2JPC = 28 Hz, CH-furyl),
119.2 (d, 1C, 2JPC = 20 Hz, CH-furyl), 107.0 (s, 1C, 4-Fc), 105.7 (d, 2C,
3JPC = 8 Hz, CH-furyl), 102.6 (s, 1C, 30-Fc), 79.5 (m, 2C, 1,2-Fc), Cp
quaternary C (10-Fc) obscured, 75.0 (m, 1C, HC-Cp), 74.4 (s, 1C, HC-
Cp), 73.4 (s, 1C, HC-Cp), 72.0 (s, 1C, HC-Cp), 71.7 (m, 1C, HC-Cp),
58.2 (s, 1C, CPh3), 30.2 (s, 3C, C(CH3)3), 29.1 (s, 1C, C(CH3)3), 13.0,
12.7 (s, 1C each, CH3-furyl). C67H59FeO2P3 (1044.95). Exact mass [M
+Na]+: m/z = 1067.29636, simulated = 1067.29714, σ = 0.039, err-
[ppm] = 0.6.
1H NMR (CDCl3): δ (ppm) = 0.95 (s, 9H, tBu), 1.09ꢀ1.29 (m, 11H,
H-Cy), 1.43ꢀ1.95 (m, 11H, H-Cy), 3.71, 3.98, 4.12, 4.14, 4.32 (s, 1H
each, H-Cp), 6.69ꢀ7.55 ppm (m, 35H, H-Ph). 31P{1H}(CDCl3): δ
1,2-Bis(diphenylphosphanyl)-10-(diisopropylphosphanyl)-30-(tri-
phenyl)methyl-4-tert-butyl Ferrocene (11). To a stirred suspension of
FeCl2 (0.30 g, 2.4 mmol) in 15 mL of THF at ꢀ40 °C was added,
dropwise, by cannula, a solution of 1,2-bis(diphenylphosphanyl)-4-tert-
butylcyclopentadienyl lithium (1.16 g, 2.3 mmol) in 20 mL of THF. The
reaction mixture was allowed to slowly warm to room temperature and
was stirred for 2 h. The reaction mixture was then cooled to ꢀ40 °C, and
a solution of 1-diisopropylphosphanyl-3-(triphenyl)methylcyclopentad-
ienyl lithium 6 (1.00 g, 2.3 mmol) in 20 mL of THF was added. After the
addition, the reaction mixture was allowed to slowly warm to room
temperature, and then it was stirred for 18 h overnight. The THF solvent
was removed, the residue was dissolved in 50 mL of toluene, and the
resulting solution was refluxed for 18 h. The brown solution was then
filtered through silica to yield a mixture of ferrocenyl phosphanes. This
mixture was purified by column chromatography (alumina gel, column
height = 30 cm, column diameter = 5.5 cm), using a 2:1 toluene/heptane
mixture to separate, as the first fraction, the symmetric ferrocenyl
tetraphosphane (0.63 g), then a 1:1 toluene/heptane solution was used
to separate 0.27 g of the dissymmetric triphosphane 1,2-bis(dip-
henylphosphanyl)-10-(diisopropylphosphanyl)-30-(triphenyl)methyl-4-
tert-butylferrocene 11 (12% yield).
(ppm) = ꢀ13.0 (dd, TSJPP = 22 and 6.0 Hz, 10-PCy2), ꢀ21.9 (dd, 3JPP
=
63 Hz, TSJPP = 6 Hz, 1-PPh2), ꢀ24.0 (dd, 3JPP = 63 Hz, TSJPP = 22 Hz,
2-PPh2). 13C NMR (CDCl3): δ (ppm) = 146.3 (s, 3C, ipso-Ph-trityl),
139.2 (d, 1C, 1JPC = 11 Hz, ipso-Ph), 137.8 (m, 1C, ipso-Ph), 137.5 (m,
1C, ipso-Ph), 137.3 (m, 1C, ipso-Ph), 135.2 (d, JPC = 23 Hz, Ph-P), 133.9
(d, JPC = 21 Hz, Ph-P), 132.4 (d, JPC = 20 Hz, Ph-P), 132.2 (d, JPC = 21
Hz, Ph-P), 129.7 (s, 6C, o-Ph-trityl), 127.5 (s, Ph-P), 127.4 (s, Ph-P),
126.9 (m, Ph-P), 126.5 (s, Ph-P), 126.4 (m, Ph-P), 126.0 (s, 6C, m-Ph-
trityl), 125.0 (s, 3C, p-Ph-trityl), 106.94 (s, 1C, 4-Fc), 102.32 (s, 1C, 30-
Fc), 80.1(dd, 1C, JPC = 20 and 14 Hz, 1-Fc), 79.5 (d, 1C, JPC = 25 Hz, 10-
Fc), 79.1 (d, 1C, JPC = 15 Hz, 2-Fc), 73.6 (s, 1C, CH-Cp), 73.3 (s, 1C,
CH-Cp), 72.9 (m, 1C, CH-Cp), 72.6 (s, 1C, CH-Cp), 72.3 (m, 1C, CH-
Cp), 58.2 (s, 1C, CPh3), 34.2, 32.7 (d, 1C each, 1JPC = 15 Hz, CH-Cy),
30.49 (s, 3C, CH3-t-Bu), 30.1 (d, 1C, JPC = 15 Hz, CH2ꢀCy), 29.7 (s,
1C, C(CH3)3-t-Bu), 28.8 (d, 1C, JPC = 9 Hz, CH2ꢀCy), 28.7 (d, 1C, JPC
= 8 Hz, CH2ꢀCy), 26.5 (m, 5C, CH2ꢀCy), 25.7 (s, 1C, CH2ꢀCy), 25.3
(s, 1C, CH2ꢀCy). C69H71FeP3 (1049.07). Exact mass [M+H]+: m/z =
1049.418, simulated = 1049.419, σ = 0.5939, err[ppm] = 1.1. Despite
repeated work-up procedures, and a good exact-mass analysis, additional
peaks are observed in the 31P NMR spectrum, possibly due to
conformers of 12 being present in trace amounts (<10%).
1H NMR (CDCl3): δ(ppm) = 0.65 (dd, 3H, 3JPH, JHH = 13 and 8 Hz,
3
3
CH3-i-Pr), 0.79 (dd, 3H, 3JPH, JHH = 13 and 8 Hz, CH3-i-Pr), 0.86 (m,
1,10-Bis(diisopropylphosphanyl)-3,30-di-tert-butyl Ferrocene (14).
To a stirred suspension of FeCl2 (0.60 g, 4.7 mmol) in 15 mL of THF
at ꢀ80 °C was added a solution of diisopropylphosphanyl-3-tert-
butylcyclopentadienyl lithium 8 (2.30 g, 9.4 mmol) in 20 mL of THF.
The reaction mixture was allowed to slowly warm to room temperature,
and then it was stirred for 2 h. The THF solvent was removed, the
residue was dissolved in 20 mL of toluene, and the resulting solution was
refluxed for 3 h. The brown solution was then filtered through silica to
give an orange oil. This crude product was purified by column chro-
6H, CH3-i-Pr), 1.15 (s, 9H, tBu), 1.53 (m, 2H, JHH = 5 and 2.5 Hz, CH),
3.76, 4.01, 4.16, 4.23, 4.54 (s, 1H each, H-Cp), 6.73ꢀ7.55 (m, 35H, H-
TS
Ph). 31P{1H}(CDCl3): δ (ppm) = ꢀ3.7 (d,
J
= 6 Hz, 10-PiPr2),
PP
ꢀ21.4 (d, 3JPP = 59 Hz, 1-PPh2), ꢀ24.0 (dd, 3JPP = 59 Hz, TSJPP = 6 Hz,
2-PPh2). 13C NMR (CDCl3): δ (ppm) = 146.31 (s, 3C, ipso-Ph-trityl),
138.9 (d, 1C, 1JPC = 10 Hz, ipso-Ph), 137.6 (m, 3C, ipso-Ph), 135.0 (d,
JPC = 24 Hz, Ph-P), 133.6 (d, JPC = 21 Hz, Ph-P), 132.8 (d, JPC = 21 Hz,
Ph-P), 131.8 (d, JPC = 21 Hz, Ph-P), 129.8 (s, 6C, o-Ph-trityl), 127.8 (s,
11600
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Inorganic Chemistry
ARTICLE
matography (alumina gel, column height = 30 cm, column diameter =
5.5 cm), using first a 3:2 (toluene/heptane) mixture and then a 1:1
(toluene/heptane) mixture to give 1.05 g of diphosphane 14 (yield = 42%).
H NMR (CDCl3, rac+meso): δ(ppm) = 0.65 (p-t, 6H, 3JPH, 3JHH = 10
Hz, i-PrꢀCH3, minor isomer), 0.98 (dd, 6H, 3JPH, 3JHH = 15 and 5 Hz, i-
7.13ꢀ7.27 (m, 30 H, Ph); the signals for the minor isomer are obscured.
31P{1H}(CDCl3): δ (ppm) = ꢀ8.7 (s, 2PCy2, major isomer 70%),
ꢀ10.7 (s, 2PCy2, minor isomer 30%). 13C NMR (CDCl3): δ (ppm) =
146.8 (s, 6C, ipso-Ph-trityl, major isomer 70%), 146.4 (s, 6C, ipso-Ph-
trityl, minor isomer 30%), 130.0 (s, 12C, o-Ph-trityl, minor isomer),
129.5 (s, 12C, o-Ph-trityl, major isomer), 126.2 (s, 12C, m-Ph-trityl,
major isomer), 126.1 (s, 12C, m-Ph-trityl, minor isomer), 125.1 (s, 6C,
p-Ph-trityl, major isomer), 125.0 (s, 6C, p-Ph-trityl, minor isomer), 99.5
(s, 2C, 3,30-Fc), 79.5 (m, 2C, 1,10-Fc), 74.7 (m, 2C, Cp-CH), 72.6 (m,
4C, Cp-CH), 58.4 (s, 2C, CPh3, minor isomer), 58.0 (s, 2C, CPh3, major
isomer), 33.8, 33.7, 31.1, 29.2 (m, 1C each, CH-Cy, rac+meso),
29.6ꢀ25.2 (m, 20C, CH2ꢀCy, rac+meso). C72H80FeP2 (1063.20).
Exact mass [M+H]+: m/z = 1063.51861, simulated = 1063.51596, σ =
0.135, err[ppm] = ꢀ2.5.
3
PrꢀCH3, minor isomer), 1.16 (dd, 6H, JPH, 3JHH = 15 and 10 Hz, i-
PrꢀCH3, major isomer), 1.22 (s, 18H, t-Bu, major isomer 85%), 1.23 (s,
18H, t-Bu, minor isomer 15%), 1.40 (dd, 6H, 3JPH, 3JHH = 18 and 8 Hz, i-
PrꢀCH3, major isomer), 1.71 (hept, 2H, 3JHH = 5 Hz, i-PrꢀCH), 2.16
(hept, 2H, 3JHH = 5 Hz, i-PrꢀCH), 3.93, 3.96, 4.09 (m, 2H each, H-Cp,
major isomer), 3.99 (m, H-Cp, minor isomer). 31P{1H}(CDCl3): δ
(ppm) = ꢀ0.2 (s, 2P-i-Pr2, major isomer 85%), ꢀ1.4 (s, 2P-i-Pr2, minor
isomer 15%). 13C NMR (CDCl3): δ (ppm) = 104.0 (s, 2C, CpC-t-Bu,
minor isomer 85%), 103.9 (s, 2C, CpC-t-Bu, major isomer 85%), 76.4
(d, 2C, 1JPC = 20 Hz, CpC-Pi-Pr2), 72.2 (d, 2C, JPC = 24 Hz, Cp-CH,
major isomer), 70.9 (d, 2C, JPC = 23 Hz, Cp-CH, minor isomer), 69.1 (s,
2C, Cp-CH, minor isomer), 69.0 (s, 2C, Cp-CH, major isomer), 68.0 (s,
1
Synthesis of Phosphorus Selenides for JPdSe Measurement. The
diphosphanes 14ꢀ17 or 1,10-bis[di(5-methyl-2-furyl)phosphanyl]-
3a,b
ferrocene Fc[P(FuMe)2]2 (0.028 mmol, <30 mg) were dissolved in
3 mL of toluene, and selenium powder was added (4.4 mg, 0.056 mmol).
The mixture was stirred at room temperature overnight. The solution
was filtered over Celite to remove the selenium in excess and was directly
analyzed by 31P NMR.
2C, Cp-CH, minor isomer), 67.3 (s, 2C, Cp-CH, major isomer), 32.1 (s,
TS
6C, t-Bu-(CH3)3, minor isomer), 31.9 (d, 6C,
J
= 3 Hz, t-
PC
Bu-(CH3)3, major isomer), 30.7 (s, 2C, C(CH3)3, major isomer), 29.7
(s, 2C, C(CH3)3, minor isomer), 24.4 (d, 2C, 1JPC = 16 Hz, CH-i-Pr),
22.7 (d, 2C, 1JPC = 19 Hz, CH-i-Pr), 22.8, 22.7 (m, 2C each, CH-i-Pr,
General Procedure for Catalytic Experiments. In a typical experi-
ment, the aryl halide (1.00 mmol), heteroaromatic derivative (2.00
mmol), KOAc (2.00 mmol), and Bu4NBr (1.00 mmol) were introduced
in a Schlenk tube that was equipped with a magnetic stirring bar. The
Pd(OAc)2/ligand 15 or 16 catalyst (ratio 1:1) and DMAc (5 mL) were
added, and the Schlenk tube was purged several times with argon. The
Schlenk tube was placed in a preheated oil bath at 150 °C, and reactants
were subjected to stirring for 16 h. The reaction mixture then was
analyzed by gas chromatography to determine the conversion of the aryl
halide. 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.
minor isomer), 22.6 (d, 2C, 1JPC = 11 Hz, CH3-i-Pr), 20.8 (d, 2C, 1JPC
20 Hz, CH3-i-Pr), 19.7 (d, 2C, 1JPC = 9 Hz, CH3-i-Pr), 18.2 (d, 2C, 1JPC
=
=
5 Hz, CH3-i-Pr), 22.2, 20.7, 19.8, 18.1 (m, 2C each, CH3-i-Pr, minor
isomer). C30H52FeP2 (530.53). Exact mass [M+H]+: m/z = 531.29661,
simulated = 531.29664, σ = 0.1495, err[ppm] = 0.1.
1,10-Bis(diisopropylphosphanyl)-3,30-di(triphenyl)methyl Ferrocene
(15). To a stirred suspension of FeCl2 (0.74 g, 5.8 mmol) in 20 mL of
THF at ꢀ80 °C was added a solution of diisopropylphosphanyl-
3-(triphenyl)methylcyclopentadienyl lithium (6) (5.02 g, 11.7 mmol)
in 25 mL of THF. The reaction mixture was allowed to slowly warm to
room temperature, and then it was stirred for 2 h. The THF solvent was
removed, the residue was dissolved in 30 mL of toluene, and the
resulting solution was refluxed for 3 h. The brown solution was then
filtered through silica to give an orange oil. This crude product was
purified by column chromatography (silica gel, column height = 30 cm,
column diameter = 5.5 cm), using, first, a 2:1 heptane/acetone mixture
and then methanol (MeOH) to obtain 0.54 g of diphosphane 15 (10%).
1H NMR (CDCl3): δ (ppm) = 0.87ꢀ1.11 (m, 24H, i-PrꢀCH3), 1.51
(m, 2H, CH), 2.03 (m, 2H, i-PrꢀCH), 3.52, 3.68, 3.99 (m, 2H each, H-
Cp), 7.09ꢀ7.27 (m, 30H, Ph-trityl). 31P{1H}(CDCl3): δ (ppm) = ꢀ2.4
(s, 2P-i-Pr2). 13C NMR (CDCl3): δ (ppm) = 146.5 (s, 6C, ipso-Ph-
trityl), 129.5 (s, 12C, o-Ph-trityl), 126.2 (s, 12C, m-Ph-trityl), 125.1
(s, 6C, p-Ph-trityl), 100.2 (s, 2C, 3,30-Fc), 80.1 (m, 2C, 1,10-Fc), 73.8,
73.4, 72.8 (m, 2C, Cp-CH), 58.0 (s, 2C, CPh3), 22.8 (m, 2C, CH-i-Pr),
22.7 (m, 2C, CH-i-Pr), 21.0 (d, 2C, 2JPC = 24 Hz, CH3-i-Pr), 20.6 (d, 2C,
2JPC = 18 Hz, CH3-i-Pr), 19.7 (m, 2C, CH3-i-Pr), 19.0 (m, 2C, CH3-i-
Pr). C60H64FeP2 (902.94). Exact mass [M+H]+: m/z = 903.38899,
simulated = 903.39069, σ = 0.0232, err[ppm] = 1.7.
2-n-Butyl-5-(4-cyanophenyl)furan (18).24 The combination
of 4-chlorobenzonitrile (0.138 g, 1 mmol), 2-n-butylfuran (0.248 g,
2 mmol), AcOK (0.196 g, 2 mmol), Bu4NBr (0.322 g, 1.00 mmol),
Pd(OAc)2 (2.24 mg, 0.01 mmol), and ligand 16 (10.1 mg, 0.01 mmol)
affords 18 in 90% yield (0.202 g). Anal. Calcd for C15H15NO: C, 79.97;
H, 6.71. Found: C, 80.06; H, 6.67.
2-n-Butyl-5-(4-nitrophenyl)furan (19).24 The combination
of 4-bromonitrobenzene (0.158 g, 1 mmol), 2-n-butylfuran (0.248 g,
2 mmol), AcOK (0.196 g, 2 mmol), Bu4NBr (0.322 g, 1.00 mmol),
Pd(OAc)2 (2.24 mg, 0.01 mmol), and ligand 15 (9.03 mg, 0.01 mmol)
affords 19 in 90% yield (0.221 g). Anal. Calcd for C14H15NO3: C, 68.56;
H, 6.16. Found: C, 68.70; H, 6.07.
Methyl 4-(5-butylfuran-2-yl)-benzoate (20).25 The combina-
tion of methyl 4-chlorobenzoate (0.171 g, 1 mmol) 2-n-butylfuran
(0.248 g, 2 mmol), AcOK (0.196 g, 2 mmol), Bu4NBr (0.322 g, 1.00
mmol), Pd(OAc)2 (2.24 mg, 0.01 mmol), and ligand 15 (9.03 mg, 0.01
mmol) affords 20 in 37% yield (0.095 g). Anal. Calcd for C16H18O3: C,
74.39; H, 7.02. Found: C, 74.45; H, 7.18.
1,10-Bis(dicyclohexylphosphanyl)-3,30-di(triphenyl)methyl Ferro-
cene (16). To a stirred suspension of FeCl2 (0.44 g, 3.5 mmol) in 20 mL
of THF at ꢀ80 °C was added a solution of dicyclohexylphosphanyl-
3-(triphenyl)methylcyclopentadienyl lithium (7) (2.73 g, 5.4 mmol) in
25 mL of THF. The reaction mixture was allowed to slowly warm to
room temperature, and then it was stirred for 1 h. The THF solvent was
removed, the residue was dissolved in 20 mL of toluene, and the
resulting solution was refluxed for 24 h. The brown solution was then
filtered through silica to yield an orange oil. This crude product was
purified by column chromatography (alumina gel, column height =
30 cm, column diameter = 5.5 cm), using a 2:1 toluene/heptane mixture,
to give 0.185 g of diphosphane 16 (5%).
2-n-Butyl-5-(4-propionylphenyl)furan (21).4b The combina-
tion of 4-chloropropiophenone (0.169 g, 1 mmol), 2-n-butylfuran
(0.248 g, 2 mmol), AcOK (0.196 g, 2 mmol), Bu4NBr (0.322 g, 1.00
mmol), Pd(OAc)2 (1.12 mg, 0.005 mmol), and ligand 16 (5.03 mg,
0.005 mmol) affords 21 in 94% yield (0.240 g). Anal. Calcd for
C17H20O2: C, 79.65; H, 7.86. Found: C, 79.71, H, 7.98.
2-n-Butyl-5-(4-trifluoromethylphenyl)furan (22).25 The
combination of 4-(trifluoromethyl)chlorobenzene (0.181 g, 1 mmol),
2-n-butylfuran (0.248 g, 2 mmol), AcOK (0.196 g, 2 mmol), Bu4NBr
(0.322 g, 1.00 mmol), Pd(OAc)2 (2.24 mg, 0.01 mmol), and ligand 16
(10.1 mg, 0.01 mmol) affords 22 in 90% yield (0.241 g). Anal. Calcd for
C15H15F3O: C, 67.16; H, 5.64. Found: C, 66.99; H, 5.67.
1H NMR (CDCl3, rac+ meso): δ(ppm) = 1.10ꢀ1.33 (m, 22 H,
H-Cy), 1.48ꢀ1.72 (m, 22 H, H-Cy), 3.45, 3.64, 3.84 (m, 2H each, H-Cp),
11601
dx.doi.org/10.1021/ic2015379 |Inorg. Chem. 2011, 50, 11592–11603

Inorganic Chemistry
ARTICLE
2-(5-n-Butylfuran-2-yl)benzonitrile (23).24 The combination
of 2-chlorobenzonitrile (0.138 g, 1 mmol), 2-n-butylfuran (0.248 g, 2
mmol), AcOK (0.196 g, 2 mmol), Bu4NBr (0.322 g, 1.00 mmol),
Pd(OAc)2 (2.24 mg, 0.01 mmol), and ligand 15 (9.03 mg, 0.01 mmol)
affords 23 in 34% yield (0.077 g). Anal. Calcd for C15H15NO: C, 79.97;
H, 6.71. Found: C, 79.69; H 6.96.
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2-n-Butyl-5-(4-N,N-dimethylaminophenyl)-furan (24).26
The combination of 4-bromo-N,N-dimethylaniline (0.200 g, 1 mmol),
2-n-butylfuran (0.248 g, 2 mmol), AcOK (0.196 g, 2 mmol), Bu4NBr
(0.322 g, 1.00 mmol), Pd(OAc)2 (1.12 mg, 0.005 mmol), and ligand 16
(5.03 mg, 0.005 mmol) affords 24 in 44% yield (0.107 g). Anal. Calcd for
C16H21NO: C, 78.97; H, 8.70. Found C, 78.95; H, 8.72.
’ ASSOCIATED CONTENT
1
Supporting Information. H, 13C, and 31P NMR spectrum
S
b
for polyphosphanes 9ꢀ12 and 14ꢀ16, and X-ray data for 11,
with the corresponding CIF file. This material is available free of
charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel.: +33 2 23 23 83 84 (H.D.), +33 3 80 39 61 06 (J.-C.H.).
Fax: +33 2 23 23 69 39 (H.D.), +33 3 80 39 36 82 (J.-C.H.).
E-mail: henri.doucet@univ-rennes.fr (H.D.), jean-cyrille.hierso@
u-bourgogne.fr (J.-C.H.).
’ ACKNOWLEDGMENT
Support provided from CNRS, Rꢀegion Bourgogne, and the
Universitꢀe de Bourgogne (through 3MIM program and project
PARI SMT08) is gratefully acknowledged. S.M. and D.R. were
granted a Ph.D. fellowship by the ANR program for Sustainable
Chemistry Development (No. ANR-09-CP2D-03 CAMELOT).
We thank D. Armspach and D. Matt (University of Strasbourg)
for providing tris(t-Bu-trityl)chloride.
’’ DEDICATION
This paper is dedicated to Dr. Christian Bruneau on the occasion
of his 60th birthday.
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