Xanthene-phosphole ligands: Synthesis, coordination chemistry, and activity in the palladium-catalyzed amine allylation

Article abstract of DOI:10.1021/om061172t

Two new xanthene-phosphole derivatives, 3 and 4, were synthesized through the nucleophilic substitution of the cyano group in 1-P-cyano-2,5- diphenylphosphole (1) and 1-P-cyano-3,4-dimethylphosphole (2) by the 4,5-dilithium salt of 9,9′-dimethylxanthene. For this, a new synthetic procedure was developed, allowing the synthesis of the required 1-P-cyano-2,5-diphenylphosphole from the 1,2,5-triphenylphosphole. Both ligands (DPP-Xantphos 3 for the diphenyl derivative and DMP-Xantphos 4 for the dimethyl derivative) react with [Pd(allyl)Cl]₂ to afford the corresponding cationic complexes 5Cl and 6Cl. Using AgOTf, stable triflate complexes 5OTf and 6OTf could be isolated. The chloride complexes, on the other hand, exhibit a limited stability in solution. The DPP-Xantphos derivative SCl eliminates allyl chloride to yield the dimeric palladium(O) complex 7 of general formula [Pd(3)]₂, in which each palladium is coordinated to the two phosphorus atoms of the same ligand and to one double bond of one phosphole unit of the second ligand. Decomposition of complex 6Cl furnished a mixture of compounds featuring a dimeric trinuclear species of general formula [Pd ₃(4)₂Cl₂]. This complex was also synthesized directly. Reaction of the DMP-Xantphos ligand 4 with 1 equiv of [Pd(COD)Cl ₂] and 2 equiv of [Pd(dba)₂] afforded dimer 8, which features one 18-VE Pd⁰ center and two Pd-Cl fragments, which are coordinated to the dienic system of the two phosphole ligands and connected through a single Pd-Pd bond. The catalytic activity of the triflate complexes 5OTf and 6OTf was evaluated in the allylation of aniline. Whereas the DMP-Xantphos derivative 6OTf exhibited a poor catalytic activity, very good conversion yields were obtained with the DPP-Xantphos complex 5OTf. On the basis of X-ray structure data and DFT calculations, it was concluded that the high catalytic activity of the DPP-Xantphos derivative complex [Pd(allyl)3]-[OTf] (6OTf) results from the combination of two effects: a large P-Pd-P bite angle, which enhances the reactivity of the allyl ligand, and the strong π-accepting capacity of the diphenylphosphole moiety, which allows the easy formation of a 14-VE complex.

Full text of DOI:10.1021/om061172t

1846
Organometallics 2007, 26, 1846-1855
Articles
Xanthene-Phosphole Ligands: Synthesis, Coordination Chemistry,
and Activity in the Palladium-Catalyzed Amine Allylation
Guilhem Mora, Bernard Deschamps, Steven van Zutphen, Xavier F. Le Goff,
Louis Ricard, and Pascal Le Floch*
Laboratoire “He´te´roe´le´ments et Coordination”, Ecole Polytechnique, CNRS,
91128 Palaiseau Ce´dex, France
ReceiVed December 22, 2006
Two new xanthene-phosphole derivatives, 3 and 4, were synthesized through the nucleophilic substitution
of the cyano group in 1-P-cyano-2,5-diphenylphosphole (1) and 1-P-cyano-3,4-dimethylphosphole (2)
by the 4,5-dilithium salt of 9,9′-dimethylxanthene. For this, a new synthetic procedure was developed,
allowing the synthesis of the required 1-P-cyano-2,5-diphenylphosphole from the 1,2,5-triphenylphosphole.
Both ligands (DPP-Xantphos 3 for the diphenyl derivative and DMP-Xantphos 4 for the dimethyl
derivative) react with [Pd(allyl)Cl]2 to afford the corresponding cationic complexes 5Cl and 6Cl. Using
AgOTf, stable triflate complexes 5OTf and 6OTf could be isolated. The chloride complexes, on the
other hand, exhibit a limited stability in solution. The DPP-Xantphos derivative 5Cl eliminates allyl
chloride to yield the dimeric palladium(0) complex 7 of general formula [Pd(3)]2, in which each palladium
is coordinated to the two phosphorus atoms of the same ligand and to one double bond of one phosphole
unit of the second ligand. Decomposition of complex 6Cl furnished a mixture of compounds featuring
a dimeric trinuclear species of general formula [Pd3(4)2Cl2]. This complex was also synthesized directly.
Reaction of the DMP-Xantphos ligand 4 with 1 equiv of [Pd(COD)Cl2] and 2 equiv of [Pd(dba)2] afforded
dimer 8, which features one 18-VE Pd0 center and two Pd-Cl fragments, which are coordinated to the
dienic system of the two phosphole ligands and connected through a single Pd-Pd bond. The catalytic
activity of the triflate complexes 5OTf and 6OTf was evaluated in the allylation of aniline. Whereas the
DMP-Xantphos derivative 6OTf exhibited a poor catalytic activity, very good conversion yields were
obtained with the DPP-Xantphos complex 5OTf. On the basis of X-ray structure data and DFT calculations,
it was concluded that the high catalytic activity of the DPP-Xantphos derivative complex [Pd(allyl)3]-
[OTf] (6OTf) results from the combination of two effects: a large P-Pd-P bite angle, which enhances
the reactivity of the allyl ligand, and the strong π-accepting capacity of the diphenylphosphole moiety,
which allows the easy formation of a 14-VE complex.
formylation,6 hydrocyanation,7 and alkylation or amination
reactions.8-11 In general, to investigate the ideal bite angle, one
can employ rigid aromatic backbones containing easily func-
tionalizable sites. Such a strategy has been nicely exploited by
Van Leeuwen and his group in the case of xanthene derivatives
(Scheme 1).12-20 Xantphos derivatives, consisting of a xanthene
skeleton with two acyclic or cyclic phosphine ligands, have thus
Introduction
The combination of electronic and steric effects plays a crucial
role in the fine-tuning of a catalyst’s activity and selectivity.
This is particularly true for phosphine-based ligands, widely
used in many catalytic transformations of synthetic relevance.
In the case of diphosphine ligands, a third parameter, the bite
angle, needs to be considered.1-5 Various recent studies have
unambiguously shown that even small variations of this
parameter often result in dramatic changes in a catalyst’s activity
and stereoselectivity. Illustrative examples are given by hydro-
(6) Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J. Organometallics 1995, 14,
3081-3089.
(7) Goertz, W.; Keim, W.; Vogt, D.; Englert, U.; Boele, M. D. K.; van
der Veen, L. A.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. J. Chem.
Soc., Dalton Trans. 1998, 2981-2988.
* Corresponding author. Tel: +33 1 69 33 45 70. Fax: +33 1 69 33 39
90. E-mail: lefloch@poly.polytechnique.fr.
(8) van Haaren, R. J.; Goubitz, K.; Fraanje, J.; van Strijdonck, G. P. F.;
Oevering, H.; Coussens, B.; Reek, J. N. H.; Kamer, P. C. J.; van Leeuwen,
P. W. N. M. Inorg. Chem. 2001, 40, 3363-3372.
(1) For a review on the effect of the ligand bite angle, see: van Leeuwen,
P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.; Dierkes, P. Chem. ReV. 2000,
100, 2741-2770.
(2) Casey, C. P.; Whiteker, G. T. Isr. J. Chem. 1990, 30, 299.
(3) Freixa, Z.; van Leeuwen, P. W. N. M. Dalton Trans. 2003, 1890-
1901.
(4) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H. Pure
Appl. Chem. 1999, 8, 1443.
(5) Dierkes, P.; van Leeuwen, P. W. N. M. J. Chem. Soc., Dalton Trans.
1999, 1519-1529.
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Am. Chem. Soc. 2006, 128, 1828-1839.
(10) Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M. Eur. J. Inorg. Chem. 1998, 155-157.
(11) Kranenburg, M.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. Eur.
J. Inorg. Chem. 1998, 25-27.
(12) Bronger, R. P. J.; Bermon, J. P.; Herwig, J.; Kamer, P. C. J.; van
Leeuwen, P. W. N. M. AdV. Synth. Catal. 2004, 346, 789-799.
10.1021/om061172t CCC: $37.00 © 2007 American Chemical Society
Publication on Web 03/16/2007

Xanthene-Phosphole Ligands
Organometallics, Vol. 26, No. 8, 2007 1847
Scheme 1. General Formula of Xantphos Derivatives
Scheme 2. Synthesis of the Cyanophosphole 1
Scheme 3. Synthesis of DPP- and DMP-Xantphos
Derivatives 3 and 4
found important applications in processes, including the linear
hydroformylation of alkenes, where the selectivity was shown
to be highly dependent on the P-Rh-P bite angle.6,19
In the current work we report the synthesis of two new
xantphos derivatives featuring phospholes, their coordination
chemistry, including their palladium allyl complexes, and their
catalytic activities in amine allylation reactions. Phospholes,
unsaturated phosphorus-containing five-membered heterocycles,
exhibit a very rich chemistry, making them attractive building
blocks for a wide variety of purposes including serving as
ligands in catalysis.21,22 This study was motivated by two recent
findings. First, we found that phosphole derivatives can be
successfully applied to palladium-catalyzed allylation reactions
of primary amines.23 Using DFT calculations we proved that
the rate-limiting step in this catalysis is highly dependent on
the nature of the phosphine ligand and that the best results are
obtained with strong π-acceptor ligands such as phospholes.24
Second, Hartwig and co-workers showed that diphosphines with
a large bite angle surrounding a palladium allyl complex favor
nucleophilic attack of amines onto η3-allyl and η3-benzyl
complexes.9 We reasoned that xantphos derivatives featuring
phospholes would give rise to strongly π-accepting ligands with
a large bite angle and thus be of interest for the catalysis of
amine allylations.
dilithium salt of xanthene with the corresponding chlorophos-
phine. Although both chloro and bromo derivatives of 2,5-
diphenylphosphole and 3,4-dimethylphosphole are available,
they are very reactive and difficult to handle.25 We therefore
decided to use the corresponding P-cyano phospholes, 1-cyano-
2,5-diphenylphosphole (1) and 1-cyano-3,4-dimethylphosphole
(2). The synthesis of phosphole 2 has been described in the
literature, and it was easily prepared in high yield.26 On the
other hand, phosphole 1 had not been synthesized before. We
found that it could be readily prepared following the same
procedure, which consists of reacting the phospholide anion with
cyanogen bromide at low temperature in THF. After workup
and purification, phosphole 1 was recovered as a yellow powder
in 70% yield (Scheme 2).
Reaction of the 4,5-dilithium salt of 9,9′-dimethylxanthene
with phospholes 1 and 2 at low temperature in THF afforded
the corresponding DPP-Xantphos 3 and DMP-Xantphos 4 in
acceptable yields (>50%) (Scheme 3). The diphosphines 3 and
4 were isolated as an air-stable yellow and white solid,
respectively. They were fully characterized by conventional
Results and Discussion
1. Syntheses of DPP and DMP-Xantphos Ligands 3 and
4. Two differently substituted phospholes were selected for our
experiments: the readily available 2,5-diphenyl (DPP) and 3,4-
dimethyl (DMP) phospholes. Synthesis of xanthene derivatives
featuring phospholes is not unprecedented; two examples were
already reported by van Leeuwen and his group with tetraphe-
nylphosphole (TPP-Xantphos) and with dibenzophosphole
(DBP-xantphos).20 These were synthesized by reacting the 4,5-
1
NMR techniques (31P, H, and 13C), mass spectrometry, and
elemental analysis.
Additionally the structure of compound 3 was confirmed by
an X-ray crystal structure analysis. A view of one molecule of
3 is presented in Figure 1, and the most significant parameters
are listed in the corresponding legend. Crystal data and structural
refinement details are presented in Table 1. The structure of 3
deserves no further comments, with all bond lengths and bond
angles comparable to those of classical xantphos6 and 1-P-
substituted diphenylphosphole derivatives.27-30
2. Syntheses of Palladium(allyl) and Palladium(0) Com-
plexes of Ligands 3 and 4. Reactivity of 3 and 4 toward the
[Pd(allyl)Cl]2 dimer was investigated. In both cases a clean
reaction takes place in dichloromethane at room temperature
in the presence of AgOTf as chloride abstractor to afford
complexes 5OTf and 6OTf. The complexes were obtained as
yellow-green and white-gray powders, respectively (Scheme 4).
Both complexes were fully characterized by NMR techniques
(31P, 1H, 13C), mass spectrometry, elemental analysis, and X-ray
(13) Bronger, R. P. J.; Bermon, J. P.; Reek, J. N. H.; Kamer, P. C. J.;
van Leeuwen, P. W. N. M.; Carter, D. N.; Licence, P.; Poliakoff, M. J.
Mol. Catal. A Chem. 2004, 224, 145-152.
(14) Chen, R.; Bronger, R. P. J.; Kamer, P. C. J.; van Leeuwen, P. W.
N. M.; Reek, J. N. H. J. Am. Chem. Soc. 2004, 126, 14557-14566.
(15) Bronger, R. P. J.; Silva, S. M.; Kamer, P. C. J.; van Leeuwen, P.
W. N. M. Dalton Trans. 2004, 1590-1596.
(16) Bronger, R. P. J.; Silva, S. M.; Kamer, P. C. J.; van Leeuwen, P.
W. N. M. Chem. Commun. 2002, 3044-3045.
(17) Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Reek, J. N. H. Acc.
Chem. Res. 2001, 34, 895-904.
(18) Carbo, J. J.; Maseras, F.; Bo, C.; van Leeuwen, P. W. N. M. J. Am.
Chem. Soc. 2001, 123, 7630 -7637.
(19) van der Veen, L. A.; Keeven, P. H.; Schoemaker, G. C.; Reek, J.
N. H.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Lutz, M.; Spek, A. L.
Organometallics 2000, 19, 872-883.
(20) van der Veen, L. A.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.
Organometallics 1999, 18, 4765-4777.
(25) Charrier, C.; Bonnard, H.; Mathey, F.; Neibecker, D. J. Organomet.
Chem. 1982, 231, 361-367.
(26) Holand, S.; Mathey, F. Organometallics 1988, 7, 1796-1801.
(27) Mora, G.; van Zutphen, S.; Thoumazet, C.; Le Goff, X. F.; Ricard,
L.; Gru¨tzmacher, H.; Le Floch, P. Organometallics 2006, 25, 5528-5532.
(28) Thoumazet, C.; Ricard, L.; Grutzmacher, H.; le Floch, P. Chem.
Commun. 2005, 1592-1594.
(29) Thoumazet, C.; Melaimi, M.; Ricard, L.; Mathey, F.; le Floch, P.
Organometallics 2003, 22, 1580-1581.
(30) Melaimi, M.; Thoumazet, C.; Rocard, L.; le Floch, P. J. Organomet.
Chem. 2004, 689, 2988-2994.
(21) Quin, L. D. In Phosphorus-Carbon Heterocyclic Chemistry: The
Rise of a New Domain; Mathey, F., Ed.; Pergamon: Amsterdam, 2001; p
219.
(22) Mathey F. In Phosphorus-Carbon Heterocyclic Chemistry: The Rise
of a New Domain; Mathey, F.. Ed.; Pergamon: Amsterdam, 2001; p 753.
(23) Thoumazet, C.; Grutzmacher, H.; Deschamps, B.; Ricard, L.; le
Floch, P. Eur. J. Inorg. Chem. 2006, 19, 3911-3922.
(24) Piechaczyk, O.; Thoumazet, C.; Jean, Y.; le Floch, P. J. Am. Chem.
Soc. 2006, 128, 14306-14317.

1848 Organometallics, Vol. 26, No. 8, 2007
Mora et al.
Figure 1. View of one molecule of 3. The numbering is arbitrary
and different from that used in NMR spectra. Thermal ellipsoids
are drawn at the 30% probability level. Hydrogen atoms are omitted
for clarity. Selected bond distances (Å) and angles (deg): P(1)-
C(1), 1.808(2); C(1)-C(2), 1.364(2); C(2)-C(3), 1.433(2); C(3)-
C(4), 1.367(2); P(1)-C(4), 1.807(2); P(1)-C(5), 1.830(2); C(5)-
C(10), 1.401(2); O(1)-C(10), 1.377(2); O(1)-C(17), 1.386(2);
C(16)-C(17), 1.394(2); P(2)-C(16), 1.836(2); C(1)-P(1)-C(5),
107.02(7); C(4)-P(1)-C(5), 103.28(7); C(4)-P(1)-C(1), 91.88-
(7); C(2)-C(1)-P(1), 107.6(1); C(1)-C(2)-C(3), 115.6(2); C(4)-
C(3)-C(2), 114.9(2); C(3)-C(4)-P(1), 107.9(1); C(10)-C(5)-
P(1), 119.4(1); O(1)-C(10)-C(5), 114.6(1); C(10)-O(1)-C(17),
119.8(1); O(1)-C(17)-C(16), 114.7(1); C(17)-C(16)-P(2), 120.7-
(1).
Figure 2. View of one molecule of 5OTf. The numbering is
arbitrary and different from that used in NMR spectra. Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and angles
(deg): C(48)-C(49), 1.3600(1); C(49)-C(50), 1.3600(2); Pd(1)-
C(48), 2.175(7); Pd(1)-C(49), 2.167(6); Pd(1)-C(50), 2.21(1); Pd-
(1)-P(1), 2.332(1); Pd(1)-P(2), 2.338(1); P(1)-C(18), 1.825(5);
P(2)-C(28), 1.820(5); P(1)-Pd(1)-P(2), 116.08(4); C(49)-Pd-
(1)-P(1), 121.4(2); C(49)-Pd(1)-P(2), 120.7(2); C(28)-P(2)-
Pd(1), 128.9(2); C(18)-P(1)-Pd(1), 128.3(2).
Scheme 4. Synthesis of Palladium Allyl Complexes 5OTf
and 6OTf
Table 1. Crystal Data and Structural Refinement
Details for 3
cryst size [mm]
empirical formula
molecular mass
cryst syst
space group
a [Å]
0.22 × 0.16 × 0.10
C47H36OP2
678.70
lemon yellow plate
P21/c
11.819(1)
b [Å]
17.351(1)
c [Å]
17.584(1)
R [deg]
90.00
101.065(1)
90.00
3538.9(4)
â [deg]
γ [deg]
V [Å]3
Scheme 5) differs greatly in the two structures. We can define
Θ as the angle between the plane P1 and the plane P2. Whereas
the Pd nearly lies in the same plane as the xanthene in the case
of complex 5OTf (Θ ) 175.7°), it is nearly perpendicular to
this plane in complex 6OTf (Θ ) 114.0°).
Z
4
calcd density [g‚cm-3
]
1.274
0.160
27.47
1424
abs coeff [cm-1
]
θ
max [deg]
F(000)
index ranges
-15 15; -22 20; -22 22
14 286/8085
5733
0.0267
0.9657 min., 0.9842 max.
454
12
0.0412/0.1163
1.030
0.286(0.045)/-0.287(0.045)
As illustrated in Figure 4, where a view of 5OTf and 6OTf
are presented, the relative distortions are the direct result of the
different substitution patterns of the phosphole rings. In 5OTf,
the “planar conformation” of the palladium allyl fragment
relative to the xanthene allows the reduction of steric crowding
between the phenyl groups on the adjacent phospholes. In 6OTf,
the ortho-positions of the phospholes are unsubstituted and the
phosphole rings can freely rotate around the xanthene-P bond
to adopt the most stable conformation, pushing the palladium
allyl out of the plane P1. Note that a similar distortion is
observed in other xantphos complexes: in the diphenylphos-
phino derivative, where steric crowding between the phenyl
groups is expected, though probably to a lesser extent than in
5OTf, Θ is found to be 137.9°.9 A direct consequence of the
distortion of 5OTf with respect to 6OTf is the widening of the
P-Pd-P bite angle (R) in complex 5OTf (R ) 116.08(4)°)
compared to 6OTf (R ) 103.39(3)°) or xantphos (R ) 108.11-
(1)° with OTf as counterion8). As will be discussed later, this
difference accounts for the relatively higher reactivity of 5OTf
toward nucleophiles.
no. of reflns collected/indep
no. of reflns used
Rint
abs corr
no. of params refined
refln/param
final R1a/wR2 [I > 2σ(I)]b
goodness-of-fit on F2
diff peak/hole [e‚Å-3
]
a R1 ) ∑|Fo| - |Fc||/∑|Fo|. b wR2 ) (∑w||Fo| - |Fc|| /∑w|Fo| )1/2
.
2
2
crystallography. Views of a single molecule of 5OTf and 6OTf
are presented in Figures 2 and 3, respectively, and the most
significant metric parameters are listed in the corresponding
legends. Crystal data and structural refinement details are
presented in Table 2.
In both structures, the palladium environment formed by the
two phosphorus atoms and the allyl fragment is square planar.
However, the orientation of this plane (P1, Scheme 5) relative
to the mean plane of the ligand defined by the two phosphorus
atoms and the two quaternary carbon atoms bearing them (P2,

Xanthene-Phosphole Ligands
Organometallics, Vol. 26, No. 8, 2007 1849
in dichloromethane at room temperature cleanly afforded
complexes 5Cl and 6Cl. Both complexes were isolated as yellow
and white powders, respectively, and characterized by 31P NMR
spectroscopy. Their chemical shifts were found to be similar to
that of their triflate counterparts, confirming their structural
similarity. However, both species exhibit a moderate stability
in solution, and within a few hours additional signals around
15 ppm appear in the 31P NMR spectra, which could not be
assigned directly. Several attempts were made to crystallize the
two chloride complexes. Whereas complex 6Cl, or its decom-
position products, could not be crystallized, diffusion of
petroleum ether into a dichloromethane solution of complex 5Cl
at room temperature afforded dark red crystals of complex 7
(Scheme 6, eq 1). A view of one molecule of complex 7 is
presented in Figure 5, and the most significant metric parameters
are listed in the corresponding legend. Crystal data and structural
refinement details are presented in Table 3.
Figure 3. View of one molecule of 6OTf. The numbering is
arbitrary and different from that used in NMR spectra. Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and angles
(deg): C(28)-C(29), 1.26(2); C(29)-C(30), 1.41(4); Pd(1)-C(28),
2.24(2); Pd(1)-C(29), 2.179(8); Pd(1)-C(30), 2.13(4); Pd(1)-P(1),
2.313(1); Pd(1)-P(2), 2.3247(8); P(1)-C(8), 1.830(3); P(2)-C(18),
1.815(3); C(29)-Pd(1)-P(1), 127.9(2); C(29)-Pd(1)-P(2), 127.3-
(2); P(1)-Pd(1)-P(2), 103.39(3); C(8)-P(1)-Pd(1), 113.1(1);
C(18)-P(2)-Pd(1), 114.8(1).
As can be seen, complex 7 is not the expected cationic
palladium allyl species, but a 32-VE dimeric palladium(0)
complex featuring two [(DPP-Xantphos)Pd0] fragments. Each
DPP-xantphos ligand (3) behaves as a six-electron donor. Four
electrons are donated by the two phosphorus atoms bound to
the same palladium atom, while two additional electrons are
donated to the second palladium atom by one double bond of
one phosphole ligand through η2-coordination. Each palladium
atom adopts a nearly trigonal planar geometry, as expected for
a d10 PdL3 complex. It is probably due to geometrical constraints
that the two phosphorus-palladium bond lengths are slightly
different (d(P1-Pd1) ) 2.309(1) Å and d(P2-Pd1) ) 2.335-
(1) Å). Another interesting piece of data is the CdC bond
lengths of the phosphole moieties. Indeed, a strong π-back-
bonding occurs with the [Pd(3)] fragment. As a result, the
coordinated double bond is significantly lengthened (1.435(4)
vs 1.343(5) Å for the uncoordinated bond).
Scheme 5. Out-of-Plane Displacement of the Ally Ligand in
Complexes 5 and 6
Complex 7 was also identified by elemental analysis, but its
1
high insolubility precluded the recording of 31P, H, and 13C
NMR spectra. The mechanism of formation of 7 could not be
established with accuracy, but one may propose that it relies
on the transient formation of a 14-VE [Pd(3)] complex, which
subsequently dimerizes. The only way to rationalize formation
of this unsaturated species is to consider that the chloride
counteranion behaves as a nucleophile onto the allyl fragment,
allowing the release of allyl chloride. To verify this hypothesis,
complex 5Cl was reacted with both lithium malonate dimethyl
ester and aniline at room temperature (Scheme 6, eqs 2 and 3).
Either reaction occurred readily, leading to the formation of
complex 7 as a dark red powder. The formulation of these
powders was confirmed by elemental analysis and X-ray
analysis. Indeed slow diffusion of a solution of aniline in hexane
into a dichloromethane solution of complex 5Cl yielded crystals
of 7 (analogous to those recorded previously). Note that the
same results were obtained when reactions were carried out on
the 5OTf derivative.
Scheme 6. Three Syntheses of Dimer 7
In pursuing our investigations we found that complex 6Cl
exhibited a totally different reactivity when carrying out the
same reaction under the same experimental conditions. Addition
of lithium malonate dimethyl ester to a solution of 6Cl yielded
a complex mixture of compounds whose structures could not
be established on the sole basis of the 31P NMR spectrum.
Careful examination of the spectrum of this crude mixture,
however, revealed the presence of a major compound, 8, which
exhibited a AA′BB′ spin system pattern. Fortunately single
crystals of this complex could be grown by slow diffusion of
petroleum ether into the crude mixture. A view of complex 8
Additional experiments were carried out to synthesize cationic
complexes of ligands 3 and 4 with different counteranions. A
surprising result was obtained when no chloride abstractor was
used. Reaction of ligands 3 and 4 with the [Pd(allyl)Cl]2 dimer

1850 Organometallics, Vol. 26, No. 8, 2007
Mora et al.
Figure 4. Views of complexes 5OTf (left) and 6OTf (right) showing the relative position of the palladium allyl fragments toward the
mean plane of the complex.
Table 2. Crystal Data and Structural Refinement Details for 5OTf and 6OTf
5OTf
6OTf
cryst size [mm]
empirical formula
molecular mass
cryst syst
space group
a [Å]
0.16 × 0.04 × 0.04
0.40 × 0.12 × 0.02
2(C50H41OP2Pd)2(CF3O3S)CH2Cl2
C30H33OP2PdCF3O3S2(CH2Cl2)
2120.33
monoclinic
P21/c
11.186(1)
896.83
orthorhombic
Pbca
15.022(1)
b [Å]
55.192(1)
20.250(1)
c [Å]
15.304(1)
24.550(1)
R [deg]
90.00
97.412(1)
90.00
9369.4(11)
90.00
90.00
90.00
7468.0(7)
â [deg]
γ [deg]
V [Å]3
Z
4
8
calcd density [g‚cm-3
]
1.503
0.681
1.595
0.976
abs coeff [cm-1
]
θ
max [deg]
F(000)
26.37
4320
27.48
3632
index ranges
-13 11; -63 68; -14 19
-19 15; -24 24; -25 31
no. of reflns collected/indep
no. of reflns used
Rint
51 275/17 259
28 071/8226
13 013
0.0345
5573
0.0370
abs corr
0.8988 min., 0.9733 max.
0.6962 min., 0.9807 max.
no. of params refined
reflection/param
final R1a/wR2 [I > 2σ(I)]b
goodness-of-fit on F2
1138
11
0.0614/0.2128
1.132
434
12
0.0429/0.1241
1.005
diff peak/hole [e‚Å-3
]
0.966(0.132)/-1.083(0.132)
1.221(0.084)/-0.618(0.084)
2
2
a R1 ) ∑|Fo| - |Fc||/∑|Fo|. b wR2 ) (∑w||Fo| - |Fc|| /∑w|Fo| )1/2
.
is presented in Figure 6, and the most relevant metric parameters
are reported in the corresponding legend. Crystal data and
structural refinement details are presented in Table 3.
units.31 In this complex each cobalt is coordinated to the two
double bonds of one phosphole ring and to the phosphorus atom
of the second ring. Complex 8 on the other hand is, to the best
of our knowledge, the first complex where two metal atoms
are sandwiched between two phospholes coordinated exclusively
through the π system.
This particular arrangement raises a problem for the electron
counting in 8. If eight electrons are given by the four phosphorus
atoms to the central palladium atom and four electrons to the
two [PdCl] fragments, complex 8 is a 50-electron complex that
features one zerovalent palladium atom and a dimeric PdI unit.
In this unit, each palladium atom is surrounded by 16 electrons,
six donated by the ligands and one electron residing in a Pd2-
Pd2′ bond. Not surprisingly, this Pd2-Pd2′ (2.5759(8) Å) bond
is significantly shorter than the Pd2-Pd1 and Pd2′-Pd1 bonds
As can be seen, the structure of 8 is totally different from
that of dimer 7. Complex 8 is a trinuclear palladium complex
that features two DMP-xantphos units. Each unit behaves as
an eight-electron donor. The two phosphorus atoms are η1-
coordinated on the central palladium atom, whereas one of the
two phospholes also behaves as a four-electron donor through
its two double bonds, which are η2-coordinated to two different
Pd-Cl fragments. Thus, two Pd-Cl fragments are encapsulated
by two phosphole rings that lie in two perpendicular planes.
Mathey and co-workers already reported the ability of the 3,4-
dimethylphospholyl unit to coordinate a metal atom through both
the phosphorus and the diene system in the synthesis of a
dinuclear cobalt complex containing two 3,4-dimethylphospholyl
(31) Holand, S.; Mathey, F.; Fischer, J.; Mitschler, A. Organometallics
1983, 2, 1234-1238.

Xanthene-Phosphole Ligands
Organometallics, Vol. 26, No. 8, 2007 1851
Table 4. Allylation of Aniline Using Catalysts 5, 6, and 7
entry
catalyst (mol %)a
additive
time (h)
conversion (%)
1
2
3
4
5
6
5OTf (1 mol %)
6OTf (1 mol %)
5OTf (0.1 mol %)
5OTf (0.1 mol %)
7 (0.05 mol %)
7 (0.05 mol %)
no
no
no
MgSO4
no
1
1
2
1
5
5
100
15
73
95
54
75
NH4Br
a Reactions conditions: 2 mmol of C3H6O, 4 mmol of PhNH2, toluene
(4 mL). After the reaction time indicated, conversions were determined by
GC with internal standard and correction factors.
Scheme 7. Synthesis of Dimer 8
Figure 5. View of one molecule of 7. The numbering is arbitrary
and different from that used in NMR spectra. Thermal ellipsoids
are drawn at the 30% probability level. Hydrogen atoms and phenyl
groups on phosphole have been omitted for clarity. Selected bond
distances (Å) and angles (deg): P(1)-C(17), 1.829(3); P(2)-C(28),
1.865(3); P(1)-C(10), 1.818(3); C(9)-C(10), 1.353(5); C(8)-C(9),
1.442(5); C(7)-C(8), 1.360(5); P(1)-C(7), 1.822(3); Pd(1)-P(1),
2.309(1); Pd(1)-P(2), 2.335(1); P(2)-C(38), 1.844(3); C(38)-
C(39), 1.343(5); C(39)-C(40), 1.462(5); C(40)-C(41), 1.435(4);
P(2)-C(41), 1.826(3); Pd(1)-C(40), 2.151(3); Pd(1)-C(41), 2.234-
(3); Pd(1)-Pd(2), 4.03(1); C(17)-P(1)-Pd(1), 128.5(1); C(28)-
P(2)-Pd(1), 123.1(1); C(10)-P(1)-C(7), 91.3(2); C(41)-P(2)-
C(38), 90.9(2); P(1)-Pd(1)-P(2), 120.60(4); C(40)-Pd(1)-P(1),
95.3(1); C(41)-Pd(1)-P(1), 129.6(1); C(40)-Pd(1)-P(2), 143.9-
(1); C(41)-Pd(1)-P(2), 108.6(1).
Scheme 8. Energetic Variation of the LUMO of a
PdL2(allyl) Complex as a Function of the L-Pd-L Angle
No mechanism accounting for the formation of 8 can be
proposed at this stage. In order to devise a more straightforward
approach to this interesting species, a new synthetic procedure
was developed. Since one can reason that complex 8 formally
results from the reaction of 2 equiv of ligand 2 with two
palladium(0) and one palladium(II), 2 equiv of [Pd(dba)2] and
1 equiv of [Pd(COD)Cl2] were reacted with 2 equiv of 2 in
THF at room temperature. After stirring for 10 h, complex 8
was the sole species detected in the 31P NMR spectrum of the
reaction mixture. By removing the solvent in Vacuo and washing
the resulting solid with diethyl ether, 8 was isolated in 85%
yield as a brown solid, which could be fully characterized
by means of NMR spectroscopy and elemental analysis
(Scheme 7).
3. Catalytic Activity of Complexes 5, 6, 7, and 8. The
catalytic activity of complexes 5-8 was evaluated in the
palladium-catalyzed allylation of primary amines using aniline
as nucleophile (commonly employed to test the activity of a
catalyst in this process24,32). In a first series of experiments,
catalytic amounts of complexes 5OTf and 6OTf (1%) were
reacted with allyl alcohol (1 equiv) in the presence of aniline
(2 equiv) in toluene at room temperature. Under these conditions,
a complete conversion was observed with complex 5OTf in
1 h, whereas complex 6OTf exhibited a low activity (15%
Figure 6. View of one molecule of 8. The numbering is arbitrary
and different from that used in NMR spectra. Thermal ellipsoids
are drawn at the 30% probability level. Hydrogen atoms are omitted
for clarity. Selected bond distances (Å) and angles (deg): Pd(1)-
P(1), 2.317(1); Pd(1)-P(2), 2.397(1); Pd(1)-Pd(2), 2.8499(7);
P(1)-C(1), 1.789(4); C(1)-C(2), 1.419(5); C(2)-C(3), 1.452(6);
C(3)-C(4), 1.403(5); P(1)-C(4), 1.795(4); Pd(2)-C(1), 2.159(3);
Pd(2)-C(2), 2.321(3); Pd(2)-C(3), 2.329(3); Pd(2)-C(4), 2.149-
(3); Pd(2)-Cl(1), 2.406(1); Pd(2)-Pd(2′), 2.5759(8); P(2)-C(22),
1.787(3); C(22)-C(23), 1.350(5); C(23)-C(24), 1.479(6); C(24)-
C(25), 1.364(5); P(2)-C(25), 1.783(4); P(1)-Pd(1)-P(1), 129.56-
(5); P(2)-Pd(1)-P(2), 99.00(5); Pd(2′)-Pd(1)-Pd(2), 53.73(2);
Pd(2′)-Pd(2)-Pd(1), 63.13(1).
(2.8499(7) Å). This led us to conclude that no bonding occurs
between the central palladium atom and the two [Pd-Cl]
fragments.
(32) Ozawa, F.; Okamoto, H.; Kawagishi, S.; Yamamoto, S.; Minami,
T.; Yoshifuji, M. J. Am. Chem. Soc. 2002, 124, 10968-10969.

1852 Organometallics, Vol. 26, No. 8, 2007
Table 3. Crystal Data and Structural Refinement Details for Complexes 7 and 8
Mora et al.
7
8
cryst size [mm]
empirical formula
molecular mass
cryst syst
space group
a [Å]
0.14 × 0.12 × 0.06
0.16 × 0.10 × 0.10
C94H72O2P4Pd24(CH2Cl2)
C54H56Cl2O2P4Pd3C4H8O
954.95
triclinic
P1h
13.057(1)
697.59
monoclinic
C2/c
17.642(1)
b [Å]
13.211(1)
19.869(1)
c [Å]
15.355(1)
16.475(1)
R [deg]
94.885(1)
111.473(1)
117.498(1)
2080.1(13)
90.00
92.641(1)
90.00
5769(3)
â [deg]
γ [deg]
V [Å]3
Z
2
8
calcd density [g‚cm-3
]
1.525
0.818
1.606
1.176
abs coeff [cm-1
]
θ
max [deg]
F(000)
26.37
972
28.70
2832
index ranges
-15 16; -16 16; -19 19
-23 23; -23 26; -22 22
no. of reflns collected/indep
no. of reflns used
Rint
25 609/8483
12 426/7423
6347
0.0439
5369
0.0216
abs corr
0.8940 min., 0.9525 max.
0.8341 min., 0.8914 max.
no. of params refined
refln/param
516
12
0.0402/0.0402
1.026
300
17
final R1a/wR2 [I > 2σ(I)] b
0.0421/0.1249
1.034
1.231(0.115)/-0.983(0.115)
goodness-of-fit on F2
diff peak/hole [e‚Å-3
]
1.007(0.081)/-0.797(0.081)
2
2
a R1 ) ∑|Fo| - |Fc||/∑|Fo|. b wR2 ) (∑w||Fo| - |Fc|| /∑w|Fo| )1/2
.
Scheme 9. Activation Energies Needed for the Dissociation of the Phenylallylammonium Ligand to Produce [Pd(3)] and
[Pd(dppe)] Complexes (energies in kcal/mol)
conversion after 1 h and 30% after 5 h) (see Table 4, entries 1
and 2). Further experiments were carried out with complex 5OTf
where the catalyst load was reduced to 0.1% (entry 3). Even at
such low catalyst loading, the activity of 5OTf remained very
good. Even more satisfying results were obtained when a water
scavenger, such as MgSO4, was used with 0.1% of catalyst. In
this case a near complete conversion was obtained after 1 h at
room temperature (entry 4), which compares favorably with the
best catalytic systems developed so far.32 On the basis of the
fact that we recently demonstrated a 14-VE PdL2 complex to
be the active species,24 additional experiments were carried out
using dimer 7. In solution this dimer may dissociate to give
two 14-VE [Pd(DPP)] monomers. Results of these experiments
are also reported in Table 4. Experiments were conducted with
0.05% of 7 under the same experimental conditions. As
expected, 7 was found to be less active than its allyl precursor.
Clearly, dissociation into a monomeric form is not favored.
Nevertheless, a conversion of 54% was obtained after 5 h (entry
5). Interestingly, we found that the presence of NH4Br
(5 mol %) as cocatalyst yielded better conversion yields. This
observation is in good agreement with the proposed mechanism,
showing that the allylammonium produced during the reaction
assists the elimination of water from a transient [L2Pd(η2-
allylalcohol)] complex.24 In the presence of NH4Br, a 75%
conversion yield was obtained after 5 h at room temperature
(entry 6). Experiments conducted with dimer 8 under the same
experimental conditions lead to poor conversions. The
in-situ formation of complex 8 during catalysis with complex
6 may help explain why complex 6 displays such poor
activity.

Xanthene-Phosphole Ligands
Organometallics, Vol. 26, No. 8, 2007 1853
Two factors explain the remarkable activity of complex 5:
the strong π-accepting capacity of the diphenylphosphole unit
and the wide P-Pd-P bite angle. Both effects work in the same
direction. In 1996, on the basis of computational results, Szabo
concluded that nucleophilic attack at the terminal carbon atom
of the allyl is favored by an increase of the bite angle.33 These
conclusions were experimentally confirmed by Kamer and co-
workers, who evaluated a series of diphosphines in the pal-
ladium-catalyzed allylation,11 and further confirmed very re-
cently by Hartwig and co-workers for a comparable catalytic
transformation.9 There is a vacant antibonding MO resulting
from the combination of a vacant nonbonding dxy orbital of the
metal with the nπ MO of the allyl ligand, featuring important
contributions at the terminal carbons. Increasing the bite angle
of a ligand surrounding the palladium results in the stabilization
of this antibonding MO (Scheme 8). The presence of strong
π-accepting ligands further contributes to lowering the energy
of the vacant nonbonding dxy orbital. Therefore, both the bite
angle and the π-accepting capacity of the ligand reduces the
palladium-allyl bond strength and favors nucleophilic attack
at the terminal carbon.
of 6Cl. Examination of the X-ray data of 5OTf and 6OTf
suggests that the reactivity of both complexes is mainly governed
by the substitution pattern of the phosphole units, dictating the
structure of the complexes. The presence of phenyl substituents
at the 2-positions of the phospholes forces the complex to adopt
a geometry with a relatively large P-Pd-P bite angle. In good
agreement with previous studies, this leads complex 5OTf to
be highly reactive toward nucleophilic attacks at the allyl ligand
by C and N nucleophiles. Therefore, complex 5OTf exhibits
high catalytic activity in the allylation of aniline. This high
catalytic activity results from the combination of two effects:
a large bite angle at palladium, which enhances the reactivity
of the allyl ligand, and the strong π-accepting capacity of the
diphenylphosphole units, which favors the formation of a 14-
VE palladium(0) complex. Further experiments, which are
currently underway in our laboratories, will now focus on a
systematic investigation of the coordination chemistry of these
new ligands and their use in catalytic processes of synthetic
relevance.
Experimental Section
Recent DFT calculations have also demonstrated that the rate-
limiting step in this coupling process is the release of the
η2-allylammonium ligand, formed by nucleophilic attack of
the amine onto the allyl ligand, resulting in the formation of a
14-VE PdL2 fragment.24 In order to get further insight into
the reactivity of complex 5, DFT calculations were carried
out to estimate the activation energy needed for this decom-
plexation process. A comparison was made with the corre-
sponding [Pd(dppe)] (dppe ) 1,2-bis-diphenylphosphinoethane)
complex, which is known to act as a relatively poor catalyst
(20% conversion yield after 24 h using 1% of catalyst23). These
calculations were carried out within the framework of DFT
with the Gaussian 03W set of programs. Due to the size of the
system, the ONIOM method combining the B3PW91 with the
UFF force field was employed. The phenyl groups of the
phosphole ligands, those of the dppe ligand, and that of the
aniline were computed at the molecular mechanic level, but
single-point calculations on the optimized structure were carried
out at the DFT level using the polarized continuum model
(PCM) (solvent ) THF). Further details (used basis sets)
regarding this computational part of the study are presented in
the Experimental Section. As expected, these calculations
revealed that decomplexation of the allylammonium moiety is
by far easier (∆G( ) 5.9 kcal/mol) in the case of complex 5
than in the corresponding dppe complex (∆G( ) 22.0 kcal/
mol) (Scheme 9). This important difference is accounted for
by the stronger π-accepting capacity of the DBP-xantphos ligand
with regard to dppe.
Computational Details. Calculations were performed with the
GAUSSIAN 03 series of programs.34 Geometries were optimized
with the ONIOM method using a combination of the B3PW91
functional35,36 with the UFF force field.37 Phenyl groups of the
phosphole ring in DPP-Xantphos and aniline, as well as phenyl
groups of the dppe ligands, were calculated at the molecular
mechanics level. The other atoms were calculated at the quantum
level of theory. The standard 6-31G* basis set was used for all
atoms (H, C, N, O, and P). The basis set used for metals (Pd) is
the Hay and Wadt38 small-core quasi-relativistic effective core
potential with the double-ú valence basis set (441s/2111p/311d)
augmented with a f-polarization function (exponent ) 1.472).39
Minima were characterized by frequencies calculation. Single-point
calculations were performed on all optimized geometries at the
quantum level for all atoms using the PCM-UFF model.40-43
Synthesis. All reactions were routinely performed under an inert
atmosphere of argon or nitrogen using Schlenk and glovebox
techniques and dry, deoxygenated solvents. Dry hexanes were
(34) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.;
Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels,
A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. GAUSSIAN 03,
Revision B.04; Gaussian, Inc.: Pittsburgh, PA, 2003.
(35) Becke, A. D. J. J. Phys. Chem. 1993, 98, 5648-5662.
(36) Perdew, J. P.; Wang, Y.; Phys. ReV. B 1992, 45, 13244-13249.
(37) Rappe, A. K.; Kasewit, C. J.; Colwell, K. S.; Goddard, W. A., III;
Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024.
(38) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299-310.
(39) Ehlers, A. W.; Bo¨hme, M.; Dapprich, A.; Gobbi, A.; Ho¨llwarth,
A.; Jonas, V.; Ko¨hler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
Chem. Phys. Lett. 1993, 208, 111-114.
(40) Miertus, S.; Scrocco, E.; Tomasi, J. Chem. Phys. 1981, 55, 117.
(41) Barone, V.; Cammi, R.; Tomasi, J. Chem. Phys. Lett. 1996, 255,
327.
Conclusions
Two new phosphole-xanthene derivatives, DPP-Xantphos 3
and DMP-Xantphos 4, have been synthesized. Although, both
ligands can behave as a chelator for a [Pd(allyl)] fragment, their
respective stability strongly depends on the nature of the
counteranion employed. Whereas triflate derivatives, 5OTf and
6OTf, were found to be stable, decomposition occurs when
chloride is used as counteranion. As a result, two unusual
structures could be characterized, a dimeric 32-VE palladium-
(0) complex resulting from the decomposition of 5Cl and a
trinuclear species featuring two 16-VE palladium(I) and one
18-VE palladium(0) fragment resulting from the decomposition
(42) Cossi, M.; Scalmani, G.; Rega, N.; Barone, V. J. Chem. Phys. 2002,
117, 43-54.
(43) Barone, V.; Improta, R.; Rega, N. Theor. Chem. Acc. 2004, 111,
237-245.
(33) Szabo, K. J. Organometallics 1996, 15, 1128-1133.

1854 Organometallics, Vol. 26, No. 8, 2007
Mora et al.
obtained by distillation from Na/benzophenone. Dry dichlo-
romethane was distilled on P2O5, dry triethylamine on KOH, and
dry toluene on metallic Na. Nuclear magnetic resonance spectra
were recorded on a Bruker AC-300 SY spectrometer operating at
was filtered off and dissolved in dichloromethane, and the solution
was filtered off on silica gel. The solvent was removed and the
compound recrystallized from Et2O to afford a white solid (1.0-
1.15 g, 55%). Anal. Calcd for C27H28OP2: C, 75.34; H, 6.56.
Found: C, 75.26; H, 6.60. 31P{1H} NMR (CD2Cl2): δ -9.5 (s).
1
300.0 MHz for H, 75.5 MHz for 13C, and 121.5 MHz for 31P.
4
1H NMR (CD2Cl2): δ 1.51 (s, 6H, C(CH3)2), 2.02 (d, JHP ) 3.4
Solvent peaks are used as internal reference relative to Me4Si for
1H and 13C chemical shifts (ppm); 31P chemical shifts are relative
to a 85% H3PO4 external reference. Coupling constants are given
in hertz. The following abbreviations are used: s, singlet; d, doublet;
t, triplet; m, multiplet. 1,2,5-Triphenylphosphole is easily available
on a multigram scale from the simple reaction of dichlorophe-
nylphosphine with 1,4-diphenyl-1,3-butadiene.44 All other reagents
and chemicals were obtained commercially and used as received.
Elemental analyses were performed by the “Service d’analyse du
CNRS”, at Gif sur Yvette, France. The GC yields were determined
on a Perichrom 2100 gas chromatograph equipped with a Perichrom
column (silicone OV1, CP-SIL 5 CB), 30 m × 0.22 mm.
2
Hz, 12H, CdCCH3), 6.78 (d, 4H, JHP ) 36.4 Hz, HR-phosphole),
3
6.88 (t, JHH ) 7.7 Hz, 2H, CHxanthene), 7.03 (m, ∑J ) 13.3 Hz,
3
4
2H, CHxanthene), 7.20 (dd, JHH ) 7.8 Hz, JHH ) 1.3 Hz, 2H,
CHxanthene). 13C NMR (CD2Cl2): δ 16.0 (vt, ∑J ) 3.4 Hz,
CdCCH3), 30.5 (C(CH3)2), 32.5 (C(CH3)2), 121.0 (m, ∑J ) 15.9
Hz, CP), 122.0 (CHxanthene), 124.5 (CHxanthene), 125.5 (d, JC-P
1
)
2.1 Hz, CR-phosphole), 128.5 (CC(CH3)2), 128.5 (CHxanthene), 147.0
(m, ∑J ) 22.5 Hz, Câ-phosphole), 149.0 (m, ∑J ) 15.3 Hz, CO).
Synthesis of Complex 5, [Pd(C3H5)(3)][OTf]. To a solution of
DPP-Xantphos 3 (100 mg, 0.15 mmol) in dichloromethane (3 mL)
was added [Pd2(µ-Cl)2(C3H5)2] (27 mg, 0.075 mmol) at room
temperature. The solution was stirred for 5 min. Completion of the
reaction was confirmed by 31P NMR. Silver triflate salt (38 mg,
0.15 mmol) was then added to the solution at room temperature.
The mixture was stirred 15 min, filtered, and concentrated, to afford
a yellow-green solid (140 mg, 95%). Anal. Calcd for C51H41F3O4P2-
PdS: C, 62.81; H, 4.24. Found: C, 62.68; H, 4.23. 31P{1H} NMR
(CD2Cl2): δ -0.5 (s). 1H NMR (CD2Cl2): δ 1.58 (s, 3H, C(CH3)2),
Synthesis of Cyanophosphole 1. To a solution of 1,2,5-
triphenylphosphole (5.0 g, 16 mmol) in tetrahydrofuran (100 mL)
cooled to 0 °C was added lithium wire (0.25 g, 65 mmol), and the
mixture was stirred at 0 °C for 2 h. AlCl3 (0.35 g, 2.65 mmol) was
added, and the mixture was stirred at 0 °C for 1 h and cannulated
on a solution of BrCN (3.4 g, 32 mmol) in tetrahydrofuran
(50 mL) at -78 °C. The mixture was then allowed to warm slowly
to room temperature. The solvent was removed and replaced by
dichloromethane. The solution obtained was filtered off on silica
gel, dichloromethane was removed, and the solid obtained was
triturated with Et2O to afford a yellow powder (2.1-2.4 g, 70%).
Anal. Calcd for C17H12NP: C, 78.15; H, 4.63. Found: C, 78.00;
H, 4.73. 31P{1H} NMR (CDCl3): δ -49.0 (s). 1H NMR (CDCl3):
δ 7.18-7.32 (m, 8H, Haromatic and Hâ-phosphole), 7.47 (d, 3JHH ) 7.9
Hz, 4H, Hortho-phenyl). 13C NMR (CDCl3): δ 116.5 (d, 2JCP ) 74.4
Hz, CCN), 126.5 (d, 3JCP ) 9.2 Hz, Cortho-phenyl), 128.5 (Cpara-phenyl),
3
4
1.63 (s, 3H, C(CH3)2), 3.30 (dd, 2H, JHH ) 13.4 Hz, JHP ) 7.8
3
Hz, Hallyl), 3.95 (d, JHH ) 7.1 Hz, 2H, Hallyl), 5.50 (vsept, ∑J )
41.3 Hz, 1H, Hallyl), 7.13-7.32 (m, 16H, Haromatic), 7.48-7.63 (m,
14H, Haromatic). 13C NMR (CD2Cl2, 25 °C): δ 27.0 (C(CH3)2), 27.5
(C(CH3)2), 37.5 (C(CH3)2), 82.5 (vt, ∑J ) 23.7 Hz, CHallyl), 111.0
(CHallyl), 122.5 (Caromatic), 126.5 (Caromatic), 127.1 (Caromatic), 127.3
(Caromatic), 129.3 (Caromatic), 129.5 (Caromatic), 129.7 (Caromatic), 129.8
(Caromatic), 129.9 (Caromatic), 130.0 (Caromatic), 133.4 (vt, ∑J ) 14.6
Hz, CP), 135.0 (vt, ∑J ) 12.2 Hz, Câ-phosphole), 135.4 (vt, ∑J )
12.2 Hz, Câ-phosphole), 136.6 (vt, ∑J ) 4.6 Hz, Caromatic), 148.2
(AXX′, ∑J ) 57.9 Hz, CR-phosphole), 149.5 (AXX′, ∑J ) 57.9 Hz,
CR-phosphole), 157.1 (vt, ∑J ) 9.5 Hz, CO).
Synthesis of Complex 6, [Pd(4)(C3H5)2][OTf]. To a solution
of DMP-Xantphos 4 (100 mg, 0.23 mmol) in dichloromethane (3
mL) was added [Pd2(µ-Cl)2(C3H5)2] (43 mg, 0.12 mmol) at room
temperature. The solution was stirred for 5 min. Completion of the
reaction was confirmed by 31P NMR. Silver triflate salt (60 mg,
0.23 mmol) was then added to the solution at room temperature.
The mixture was stirred 15 min, filtered, and concentrated, to afford
a white-gray solid (160 mg, 92%). Anal. Calcd for C31H33F3O4P2-
PdS: C, 51.21; H, 4.58. Found: C, 51.13; H, 4.57. 31P{1H} NMR
(CD2Cl2): δ 4.45 (s). 1H NMR(CD2Cl2): δ 1.65 (s, 6H, C(CH3)2),
2
129 (Cmeta-phenyl), 133.5 (d, JCP ) 16.8 Hz, Cipso-phenyl), 136.5 (d,
2JCP ) 16.8 Hz, Câ-phosphole), 142.5 (CR-phosphole).
Synthesis of DPP-Xantphos 3. To a solution of 9,9′-dimeth-
ylxanthene (1.0 g, 4.8 mmol) and TMEDA (2.1 mL, 14 mmol) in
Et2O (45 mL) at -78 °C was added a 1.4 M solution of
sec-butyllithium in cyclohexane (10 mL, 14 mmol). The reaction
mixture was stirred at room temperature for 20 h. Two equivalents
of cyanophosphole 1 (2.6 g, 9.6 mmol) was added slowly at
-78 °C. The mixture was allowed to warm to room temperature
and was stirred for 3 h. The title compound, which precipitated,
was filtered off and dissolved in dichloromethane, and the solution
was filtered off on silica gel. The solvent was removed and the
compound recrystallized from Et2O to afford a yellow solid (1.6-
2.1 g, 65%). Anal. Calcd for C47H36OP2: C, 83.17; H, 5.35.
Found: C, 83.13; H, 5.36. 31P{1H} NMR (CD2Cl2): δ -17.0 (s).
1H NMR (CD2Cl2): δ 1.42 (s, 6H, CH3), 6.71 (m, 2H, CHxanthene),
3
3
2.24 (s, 12H, CdCCH3), 3.11 (dd, 2H, JHH ) 13.4 Hz, JHP ) 9
3
4
Hz, Hallyl), 4.78 (dd, JHH ) 7.2 Hz, JHP ) 2.8 Hz, 2H, Hallyl),
5.27 (vsept, ∑J ) 41.6 Hz, 1H, Hallyl), 6.77 (d, 2JHP ) 7.8 Hz, 2H,
6.80 (t, 3JHH ) 7.6 Hz, 2H, CHxanthene), 7.03-7.19 (m, 12H, Haromatic),
2
HR-phosphole), 6.80 (d, JHP ) 7.8 Hz, 2H, HR-phosphole), 7.19-7.29
3
7.22-7.32 (m, 6H, Haromatic and Hâ-phosphole), 7.63 (d, 8H, JHH
)
3
3
(m, 4H, CHxanthene), 7.57 (dd, 2H, JHH ) 6.0 Hz, JHH ) 2.0 Hz,
CHxanthene). 13C NMR (CD2Cl2, 25 °C): δ 18.3 (vt, 3JCP ) 6.1 Hz,
CdCCH3), 27.4 (C(CH3)2), 27.6 (C(CH3)2), 37.0 (C(CH3)2), 72.9
(vt, ∑J ) 28.0 Hz, CHallyl), 117.3 (dd, 1JCP ) 23.0 Hz, 3JCP ) 21.7
7.3 Hz, Hortho-phenyl). 13C NMR (CD2Cl2): δ 32.0 (CH3), 36.0
(C(CH3)2), 118.5 (vt, ∑J ) 11.6 Hz, CP), 124.5 (CHxanthene), 127.0
(vt, ∑J) 5.0 Hz, Caromatic), 128.0 (Caromatic), 128.5 (CHxanthene), 129.5
(Caromatic), 132.5 (Caromatic), 132.5 (CHxanthene), 133.5 (vt, ∑J ) 5.1
Hz, Câ-phosphole), 137.0 (vt, ∑J ) 8.5 Hz, Caromatic), 154.5 (CR-phosphole),
155.0 (vt, ∑J ) 11.5 Hz, CO).
3
1
Hz, CP), 120.6 (t, JCP ) 4.8 Hz, CHallyl), 123.0 (dd, JCP ) 25.0
3
1
3
Hz, JCP ) 22.4 Hz, CR-phosphole), 123.6 (dd, JCP ) 20.9 Hz, JCP
) 18.3 Hz, CR-phosphole), 126.0 (vt, ∑J ) 7.8 Hz, CHxanthene), 128.5
(CHxanthene), 129.2 (CHxanthene), 135.4 (vt, ∑J ) 4.2 Hz, CC(CH3)2),
155.1 (vt, ∑J ) 10.0 Hz, Câ-phosphole), 155.4 (vt, ∑J ) 10.0 Hz,
Câ-phosphole), 155.6 (vt, ∑J ) 4.2 Hz, CO).
Synthesis of DMP-Xantphos 4. To a solution of 9,9′-dimeth-
ylxanthene (1.0 g, 4.8 mmol) and TMEDA (2.1 mL, 14 mmol) in
Et2O (45 mL) at -78 °C was added a 1.4 M solution of
sec-butyllithium in cyclohexane (10 mL, 14 mmol). The reaction
mixture was stirred at room temperature for 20 h. Two equivalents
of cyanophosphole 2 (1.3 g, 9.6 mmol) was added slowly at
-78 °C. The mixture was allowed to warm to room temperature
and was stirred for 3 h. The title compound, which precipitated,
Synthesis of Complex 7, [Pd2(3)2]. To a solution of DPP-
Xantphos 3 (100 mg, 0.147 mmol) in dichloromethane (3 mL) was
added [Pd2(µ-Cl)2(C3H5)2] (27 mg, 0.074 mmol) at room temper-
ature. The solution turned from yellow to orange and was stirred
for 5 min. Completion of the reaction was confirmed by 31P NMR.
Aniline (100 µL, 1.1 mmol) was then added to the solution at room
temperature. A red-brown, insoluble solid appeared, which was
(44) Campbell, I. G.; Cookson, R. C.; Hocking, M. B.; Hughes, A. N. J.
Chem. Soc. 1965, 2184-2193.

Xanthene-Phosphole Ligands
Organometallics, Vol. 26, No. 8, 2007 1855
filtered, washed with dichloromethane, and dried (105 mg, 91%).
Anal. Calcd for C94H72O2P4Pd2: C, 71.90; H, 4.62. Found: C,
71.77; H, 4.62. Insolubility of the compound prevented NMR
studies.
1, 2, and 3. The crystal structures were solved using SIR 9745 and
SHELXL97.46 ORTEP drawings were made using ORTEP III for
Windows.47
General Procedure for the Allylation of Aniline. The catalyst
(19 mg of 5, 15 mg of 6 for 1% (Table 4, entries 1 and 2); 1.9 mg
of 5 for 0.1% (Table 4, entries 3 and 4); 1.6 mg of 7 for 0.05% of
dimer (Table 4, entries 5 and 6)) was placed in a Schlenck tube
with or without an additive as indicated in Table 4 (0.50 g of
MgSO4, entry 4; 10 mg of NH4Br, entry 6) and THF (2 mL). The
Schlenck tube was then filled with aniline (364 µL, 4 mmol) and
allyl alcohol (136 µL, 2 mmol). The mixture was stirred at room
temperature, and the progress of the reaction was monitored by
GC. The mixture was filtered to remove the MgSO4 and the solvent
evaporated in Vacuo. The product was then isolated by column
chromatography on alumina (hexanes).
Crystallographic data can be obtained free of charge at www.c-
cdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK;
fax: (internat.) +44-1223/336-033; e-mail: deposit@ccdc.cam.ac.uk]
with the deposition numbers CCDC 631901-631905.
Synthesis of Complex 8, [Pd3(4)2Cl2]. To a solution of [Pd-
(COD)Cl2] (33 mg, 0.12 mmol) and [Pd(dba)2] (130 mg, 0.24
mmol) in tetrahydrofuran (2 mL) was added the DMP-Xantphos 4
(100 mg, 0.23 mmol). After 10 h stirring, the solvent was removed
and 10 mL of diethyl ether was added. The resultant brown solid
was filtered off and again washed with diethyl ether (120 mg, 85%).
Anal. Calcd for C54H56Cl2O2P4Pd3: C, 51.84; H, 4.51. Found: C,
2
51.74; H, 4.51. 31P{1H} NMR (CD2Cl2): δ -8.5 (t, JPP ) 27.9
2
1
Hz), -4.5 (t, JPP ) 27.9 Hz). H NMR (CD2Cl2): δ 1.29 (s, 6H,
CdCCH3), 1.38 (s, 6H, C(CH3)2), 1.89 (s, 6H, C(CH3)2), 1.92 (s,
6H, CdCCH3), 1.95 (s, 6H, CdCCH3), 2.00 (s, 6H, CdCCH3),
4.59 (AA′MM′XX′, ∑J ) 36.6 Hz, 2H, HR-phosphole), 5.15 (AA′M-
M′XX′, ∑J ) 31.8 Hz, 2H, HR-phosphole), 5.59 (AA′MM′XX′, ∑J
) 31.8 Hz, 2H, HR-phosphole), 6.36 (ddd, 3JHH ) 7.8 Hz, 2JHP ) 6.6
4
Hz, JHH ) 1.2 Hz, 2H, Haromatic), 6.65 (AA′MM′XX′, ∑J ) 36.6
3
Hz, 2H, HR-phosphole), 6.84 (t, 2H, JHH ) 7.8 Hz, Haromatic), 7.14-
3
4
7.23 (m, 4H, Haromatic), 7.38 (dd, JHH ) 7.8 Hz, JHH ) 1.2 Hz,
2H, Haromatic), 7.56 (dd, 3JHH ) 7.5 Hz, 4JHH ) 1.8 Hz, 2H, Haromatic).
13C NMR (CD2Cl2, 25 °C): δ 17.0 (CdCCH3), 17.8 (d, JCP ) 3.7
Hz, CdCCH3), 18.0 (d, JCP ) 4.2 Hz, CdCCH3), 23.7 (C(CH3)2),
32.2 (C(CH3)2), 37.1 (C(CH3)2), 65.2 (vt, ∑J ) 29.6 Hz, CR-phosphole),
70.0 (vt, ∑J ) 27.8 Hz, CR-phosphole), 103.7 (vt, ∑J ) 12.0 Hz,
Câ-phosphole), 106.0 (vt, ∑J ) 13.2 Hz, Câ-phosphole), 124.3 (Caromatic),
124.9 (Caromatic), 125.4 (vt, ∑J ) 6.9 Hz, CR-phosphole), 127.2
(Caromatic), 127.8 (Caromatic), 128.9 (Caromatic), 129.5 (Caromatic), 130.8
(m, CR-phosphole), 134.2 (m, CC(CH3)2), 135.9 (m, CC(CH3)2), 145.3
(vt, ∑J ) 11.1 Hz, Câ-phosphole), 149.8 (vt, ∑J ) 10.2 Hz,
Câ-phosphole), 155.8 (vt, ∑J ) 10.8 Hz, Caromatic), 157.0 (vt, ∑J )
9.9 Hz, Caromatic).
Acknowledgment. The authors thank the CNRS (Centre
National de la Recherche Scientifique) and the Ecole Polytech-
nique for the financial support of this work and IDRIS for the
allowance of computer time (project no. 060616).
Supporting Information Available: Computed Cartesian co-
ordinates, thermochemistry, and PCM energies of complexes [Pd-
(DBP-xantphos)(η2-phenylallylammonium)], [Pd(DBP-xantphos)],
[Pd(dppe)(η2-phenylallylammonium)], and [Pd(dppe)]. CIF files and
tables giving crystallographic data for 3, 5OTf, 6OTf, 7, and 8
(including atomic coordinates, bond lengths and angles, and
anisotropic displacement parameters) and computational details.
This material is available free of charge via the Internet at
http://pubs.acs.org.
X-ray Crystallography for 3, 5, 6, 7, and 8. Yellow needles
of 3 and 5, white needles of 6, and red-brown blocks of 8
crystallized by slow diffusion of hexanes into a saturated dichlo-
romethane solution of respectively 3, 5, 6, and 8. Dark red needles
of complex 7 were obtained by diffusing a solution of aniline in 1
mol/L hexanes at 4 °C into a dichloromethane solution of complex
5. Data were collected on a Nonius Kappa CCD diffractometer using
a Mo KR (λ ) 0.71073 Å) X-ray source and a graphite mono-
chromator at 150 K. Experimental details are described in Tables
OM061172T
(45) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. SIR97, an
integrated package of computer programs for the solution and refinement
of crystal structures using single-crystal data.
(46) Sheldrick, G. M. SHELXL-97; Universita¨t Go¨ttingen: Go¨ttingen,
Germany, 1997.
(47) Farrugia, L. J. ORTEP-3; Department of Chemistry, University of
Glasgow: Scotland.