(Perfluoro)alkylsilyl-substituted 2-[bis(4-aryl)phosphino]pyridines: Synthesis and comparison of their palladium complexes in methoxycarbonylation of phenylacetylene in regular solvents and supercritical CO2

Article abstract of DOI:10.1021/om050479+

The synthesis and characterization of three new 2-[bis{4-(bromo)phenyl} phosphino]pyridine (8), 2-[bis{4-(trimethylsilyl)phenyl}phosphino]pyridine (9), and 2-[bis{4-((2-(perfluorohexyl)ethyl)dimethylsilyl)phenyl}phosphino]pyridine (10) ligands (L) is reported. The corresponding compounds trans-/cis-[PdCl ₂(L)₂] 11-13, trans-[PdCl(Me)(L)₂] 14-16, and maleic anhydride complexes [Pd(L)₂(cyclo-(-CH=CHC(O)OC(O)-)] 17 and 18 were synthesized and characterized. In the methoxycarbonylation of phenylacetylene in methanol catalysts derived from [Pd(OAc)₂] as the palladium source with either 9 or 10 as ligand showed the same activity (TON = 4000, 50 min reaction time) and selectivity (about 98% for the branched product) as the catalyst obtained from [Pd(OAc)₂] and 2-[diphenylphosphino] pyridine (2). Both 2 and 10 were also tested in this reaction using a 1:1 mixture of methanol and α,α′,α″-trifluorotoluene as solvent system: fluorous 10 generated a more active catalyst (TON = 3400 for 10 vs 3000 for 2). In supercritical CO₂ the use of 10 as ligand (with [Pd-(OAc)₂]) in this reaction gave a TON of 2000 (50 min reaction time) and a selectivity of >99% for the branched product. Nonfluorous [Pd(2)₂(cyclo-(CH=CHC(O)OC(O)-)] gave a particularly active catalyst for the methoxycarbonylation of phenylacetylene (TON of about 8000, 50 min reaction time, TOF₅₀ of about 30 000 mol phenylacetylene per mol Pd per hour in methanol) with no loss in selectivity (98% selectivity toward the branched product).

Full text of DOI:10.1021/om050479+

Organometallics 2005, 24, 5299-5310
5299
(Perfluoro)alkylsilyl-Substituted
2-[Bis(4-aryl)phosphino]pyridines: Synthesis and
Comparison of Their Palladium Complexes in
Methoxycarbonylation of Phenylacetylene in Regular
Solvents and Supercritical CO2
Jeroen. J. M. de Pater,†,§ C. Elizabeth P. Maljaars,† Elwin de Wolf,†
,#
Martin Lutz, Anthony L. Spek, Berth-Jan Deelman,*,†,‡
Cornelis J. Elsevier,*,§ and Gerard van Koten*,†
Debye Institute, Organic Chemistry and Catalysis, and Bijvoet Center for Biomolecular
Research, Crystal and Structural Chemistry, Utrecht University, Padualaan 8, NL-3584 CH
Utrecht, The Netherlands, Van’t Hoff Institute for Molecular Sciences, Molecular Inorganic
Chemistry, University of Amsterdam, Nieuwe Achtergracht 166, NL-1018 WV,
Amsterdam, The Netherlands, and ARKEMA Vlissingen B.V., P.O. Box 70,
NL-4380 AB Vlissingen, The Netherlands
Received June 10, 2005
The synthesis and characterization of three new 2-[bis{4-(bromo)phenyl}phosphino]-
pyridine (8), 2-[bis{4-(trimethylsilyl)phenyl}phosphino]pyridine (9), and 2-[bis{4-((2-
(perfluorohexyl)ethyl)dimethylsilyl)phenyl}phosphino]pyridine (10) ligands (L) is reported.
The corresponding compounds trans-/cis-[PdCl2(L)2] 11-13, trans-[PdCl(Me)(L)2] 14-16, and
maleic anhydride complexes [Pd(L)2(cyclo-(-CHdCHC(O)OC(O)-)] 17 and 18 were synthe-
sized and characterized. In the methoxycarbonylation of phenylacetylene in methanol
catalysts derived from [Pd(OAc)2] as the palladium source with either 9 or 10 as ligand
showed the same activity (TON ) 4000, 50 min reaction time) and selectivity (about 98%
for the branched product) as the catalyst obtained from [Pd(OAc)2] and 2-[diphenylphosphino]-
pyridine (2). Both 2 and 10 were also tested in this reaction using a 1:1 mixture of methanol
and R,R′,R′′-trifluorotoluene as solvent system: fluorous 10 generated a more active catalyst
(TON ) 3400 for 10 vs 3000 for 2). In supercritical CO2 the use of 10 as ligand (with [Pd-
(OAc)2]) in this reaction gave a TON of 2000 (50 min reaction time) and a selectivity of
>99% for the branched product. Nonfluorous [Pd(2)2(cyclo-(CHdCHC(O)OC(O)-)] gave a
particularly active catalyst for the methoxycarbonylation of phenylacetylene (TON of about
8000, 50 min reaction time, TOF50 of about 30 000 mol phenylacetylene per mol Pd per hour
in methanol) with no loss in selectivity (98% selectivity toward the branched product).
Introduction
way the reactivity and accessibility of the metal center
can be tuned. For instance, when in a bidentate ligand
the second donor atom coordinates weaker than the first
one, it can be replaced by incoming molecules and
substrates during a catalytic reaction while the ligand
remains monodentate-coordinated to the metal site. In
this way, it serves as a stabilizing co-ligand by occupying
a vacant site on the metal in the absence of substrate,
preventing decomposition of the metal catalyst. Al-
though several different donor atoms, such as O, S, C,
and N, have been used, especially the latter has been
employed extensively to make a variety of P,N-bidentate
ligands and transition metal complexes derived thereof
(Chart 1).2-5
The synthesis and application of phosphorus ligands
that besides the phosphorus atom contain a second
coordinating functionality is of considerable interest. For
instance, in the Shell Higher Olefin Process (SHOP) the
use of a bifunctional phosphine is necessary to obtain
high activity and selectivity.1 By introducing a second
donor atom in the ligand, it is possible to obtain
bidentate ligands that contain functionalities with dif-
ferent donor strengths and steric requirements. In this
* Corresponding authors. Phone: +31-30-2533120. Fax: +31-30-
2523615. E-mail: g.vankoten@chem.uu.nl. Phone: +31-20-5255653.
Fax: +31-20-5256456. E-mail: else@science.uva.nl. Phone: +31-113-
617225. Fax:
arkemagroup.com.
+31-113-612984. E-mail:
berth-jan.deelman@
† Debye Institute, Organic Chemistry and Catalysis.
§ Van’t Hoff Institute for Molecular Sciences, Molecular Inorganic
Chemistry.
(2) Rajender Reddy, K.; Surekha, K.; Lee, G.-H.; Peng, S.-M.; Liu,
S.-T. Organometallics 2001, 20, 5557.
(3) Drent, E. Eur. Patent Appl. EP-A-271144, 1988.
(4) Dekker, G. P. C. M.; Buijs, A.; Elsevier, C. J.; Vrieze, K.; van
Leeuwen, P. W. N. M.; Smeets, W. J. J.; Spek, A. L.; Wang, Y. F.; Stam,
C. H. Organometallics 1992, 11, 1937.
‡ ARKEMA Vlissingen B.V.
Bijvoet Center for Biomolecular Research, Crystal and Structural
Chemistry.
# Corresponding author for crystallographic data. Phone: +31-30-
2532538. Fax: +31-30-2523940. E-mail: a.l.spek@chem.uu.nl.
(1) Peuckert, M.; Keim, W. Organometallics 1983, 2, 594.
(5) Pfaltz, A.; Blankenstein, J.; Hilgraf, R.; Ho¨rmann, E.; McIntyre,
S.; Menges, F.; Scho¨nleber, M.; Smidt, S. P.; Wu¨stenberg, B.; Zimmer-
mann, N. Adv. Synth. Catal. 2003, 345, 33.
10.1021/om050479+ CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/27/2005

5300 Organometallics, Vol. 24, No. 22, 2005
de Pater et al.
Chart 2. Ligands Studied in This Paper.
Chart 1
Drent and co-workers have developed a palladium
system based on [Pd(OAc)2] and 2-[bis(aryl)phosphino]-
pyridine ligands, which shows high activity and selec-
tivity in the methoxycarbonylation of alkynes.3,6-8 In
particular the methoxycarbonylation of propyne, which
gives economically important products such as methyl
methacrylate, was studied in detail. This initial research
was followed by other studies by different authors
directed to the development of new ligands,9-12 the
elucidation of mechanistic details of the catalytic
cycle,13-15 and the use of well-defined precursor com-
plexes based on zerovalent palladium alkene com-
plexes.16 In these studies phenylacetylene was used as
the substrate, which showed a high selectivity (>98%)
toward the branched product. Therefore, the use of such
catalysts in the methoxycarbonylation of 4-(isobutyl)-
phenylacetylene and 2-ethynyl-6-methoxynaphthalene
is of high interest because it provides a short route to
Ibuprofen and Naproxen, respectively.
Recently, we have become interested in developing
fluorous palladium complexes that can be used to
perform methoxycarbonylation reactions in uncommon
media such as fluorous biphasic systems (FBS) and
supercritical carbon dioxide (scCO2). In scCO2 beneficial
effects on activity are expected, because of the possibility
to achieve complete miscibility of all reaction compo-
nents involved, including in this case gases such as CO
and H2. Indeed improved activities and selectivities have
been observed recently for several catalytic reactions in
scCO2, e.g., the Rh-catalyzed hydroformylation of
alkenes17-19 and the selective hydrogenation of alkynes
to Z-alkenes.20 Moreover, ample evidence exists that the
introduction of fluorous tails in known ligand systems
considerably increases the solubility of both ligands and
derived metal catalysts in fluorous solvents and scCO2.
Scheme 1. Synthetic Route for
2-[Bis{4-(bromo)phenyl}phosphino]pyridine 8a
a Legend: (i) 2 equiv Et2NH, Et2O, -75 °C; (ii) 1 equiv
n-BuLi, hexane/Et2O, 3:1, 20 °C; (iii) 0.5 equiv 5, Et2O, -75
°C; (iv) excess PCl3, reflux, 1 h; (v) 1 equiv n-BuLi, Et2O, -75
°C; (vi) 1 equiv 7, -75 °C.
In recent years some of us have successfully applied the
SiMe3-x(CH2CH2)x group as a useful spacer to attach
perfluoroalkyl chains to several mono- and bidentate
phosphine ligands.21,22 We report here the synthesis of
a fluorous 2-[bis(4-aryl)phosphino]pyridine ligand, which
is functionalized with SiMe2(CH2CH2C6F13) groups, and
derived palladium complexes. For comparison also the
-SiMe3-substituted ligand and palladium complexes
thereof were prepared. The catalytic activity of the
palladium complexes, derived from these new ligands,
has been compared with the catalytic activity of the
palladium complex derived from the nonfunctionalized
ligand 2 in the methoxycarbonylation of phenylacetylene
in both regular solvents and apolar solvents such as
scCO2.
(6) Drent, E.; Budzelaar, P. H. M.; Jager, W. W. Eur. Patent Appl.
EP-A-386833, 1990.
(7) Drent, E.; Budzelaar, P. H. M.; Jager, W. W.; Stapersma, J. Eur.
Patent Appl. EP-A-441447, 1991.
Results
(8) Drent, E.; Arnoldy, P.; Budzelaar, P. H. M. J. Organomet. Chem.
1993, 455, 247.
Synthesis of 2-[Bis{4-(trialkylsilyl)phenyl}phos-
phino]pyridines. In principle, the 2-[bis(aryl)phosphi-
no]pyridine ligand can be functionalized with perfluo-
roalkylsilyl chains in three ways, at either the phenyl
rings, the 2-pyridyl ring, or both. Following previously
developed routes we decided to explore the functional-
ization of the phenyl rings. In this paper the following
ligands were therefore considered (Chart 2). Ligand 2
is known, whereas 8, 9, and 10 are newly reported.
The starting compound, 2-[bis{4-(bromo)phenyl}phos-
phino]pyridine (8), was synthesized according to a four-
step route (Scheme 1). For 7 excess PCl3 instead of HCl-
(g) was used. This modified method had been reported
for the conversion of diisopropylamide-protected phos-
phines into chlorophosphines in high yields and purity.23
(9) Scrivanti, A.; Beghetto, V.; Zanato, M.; Matteoli, U. J. Mol. Cat
A: Chem. 2000, 160, 331.
(10) Scrivanti, A.; Beghetto, V.; Campagna, E.; Matteoli, U. J. Mol.
Cat A: Chem. 2001, 168, 75.
(11) Reetz, M. T.; Demuth, R.; Goddard, R. Tetrahedron Lett. 1998,
39, 7089.
(12) Clarke, M. L.; Cole-Hamilton, D. J.; Foster, D. F.; Slawin, A.
M. Z.; Derek Woollins, J. J. Chem. Soc., Dalton Trans. 2002, 1618.
(13) Scrivanti, A.; Beghetto, V.; Campagna, E.; Zanato, M.; Matteoli,
U. Organometallics 1998, 17, 630.
(14) Dervisi, A.; Edwards, P. G.; Newman, P. D.; Tooze, R. P.; Coles,
S. J.; Hursthouse, M. B. J. Chem. Soc, Dalton Trans. 1999, 1113.
(15) Dervisi, A.; Edwards, P. G.; Newman, P. D.; Tooze, R. P. J.
Chem. Soc, Dalton Trans. 2000, 523.
(16) Scrivanti, A.; Matteoli, U.; Beghetto, V.; Antonaroli, S.; Scar-
pelli, R.; Crociani, B. J. Mol. Catal. A: Chem. 2001, 170, 51.
(17) Koch, D.; Leitner, W. J. Am. Chem. Soc. 1998, 120, 13398.
(18) Meehan, N. J.; Sandee, A. J.; Reek, J. N. H.; Kamer, P. C. J.;
van Leeuwen, P. W. N. M.; Poliakoff, M. Chem. Commun. 2000, 1497.
(19) Wittmann, K.; Wisniewski, W.; Mynott, R.; Leitner, W.; Ludger
Kranemann, C.; Rische, T.; Eilbracht, P.; Kluwer, S.; Ernsting, J. M.;
Elsevier, C. J. Chem. Eur. J. 2001, 7, 4584.
(21) Richter, B.; de Wolf, E.; van Koten, G.; Deelman, B. J. J. Org.
Chem. 2000, 65, 3885.
(22) de Wolf, E.; Richter, B.; Deelman, B. J.; van Koten, G. J. Org.
Chem. 2000, 65, 5424.
(20) Kluwer, A. M. Ph.D. Thesis, University of Amsterdam, 2004,
Chapters 5 and 6.

Silyl-Substituted 2-[Bis(4-aryl)phosphino]pyridines
Organometallics, Vol. 24, No. 22, 2005 5301
Scheme 2a
Scheme 3. Synthetic Routes for the Various
Palladium Complexesa
a Legend: (i) 2 equiv n-BuLi, THF, -78 °C; (ii) 2 equiv
ClSiMe2R, THF, -78 °C.
All compounds were obtained pure after workup with 6
as a yellow oil, 7 as a light yellow solid, and 8 as a yellow
viscous oil, which slowly solidified upon standing. They
1
were characterized by H, 13C{1H}, and 31P{1H} NMR
a Legend: COD ) 1,5-cyclo-octadiene, TMEDA ) N,N,N′,N′-
tetramethylethylenediamine, t-BuDAB ) 1,4-bis(tert-butyl)-
1,4-diaza-1,3-butadiene, MA ) cyclo-(-CHdCHC(O)OC(O)-
).
spectroscopy as well as elemental analyses. The 31P{1H}
NMR resonance of 8 showed an upfield shift (δ ) -5.35
ppm) as compared to the resonance of parent 2-[diphe-
nylphosphino]pyridine (δ ) -2.89 ppm).
The key step in the synthesis of 8 is the last step in
Scheme 1. Both the lithiation of the 2-bromopyridine
and the addition of 7 have to be carried out at temper-
atures lower than -75 °C (preferentially between -75
and -80 °C). If the temperature is higher, especially
during the lithiation of 2-bromopyridine, formation of
large amounts of bi- and polypyridine compounds are
observed as a result of reaction of 2-lithiopyridine with
unreacted 2-bromopyridine or with another molecule of
2-lithiopyridine. This results in a significantly lower
yield of the final product. Furthermore both n-BuLi and
7 have to be slowly added to avoid excessive heating of
the solution, leading to the above-mentioned problems.
The functionalization of 8 with alkylsilyl groups was
carried out via the method shown in Scheme 2. This
synthetic route afforded both 9 and 10 in acceptable
yields (9, 30-60%; 10, 50-70%). NMR spectroscopic
analyses as well as their correct elemental analyses
confirmed the identity of 9 and 10. Their 1H NMR
spectra showed the same chemicals shifts for the signals
corresponding to the various pyridyl and phenyl protons,
as well as the expected resonance patterns for the
solvents, both polar (MeOH and acetone) and apolar (n-
pentane, n-hexane, and Et2O). Removal of impurities,
such as traces of phosphine-oxide, free pyridine, and
only partly substituted phosphine, could be achieved
only by washing at low temperatures. This meant that
the yield for 9 varied significantly from one reaction to
the other.
Synthesis of Palladium Complexes. To further
assess the properties of the new ligands 8-10, we
synthesized several of their palladium complexes (Scheme
3).
The [PdCl2(L)2] complexes 11-13 were obtained as
yellow solids in good yields. Complex 11 had already
been synthesized using [PdCl2(PhCN)2] as the palladium
precursor.24 The compounds showed the expected reso-
1
nance patterns in the H, 13C{1H}, and 31P{1H} NMR
spectra. All complexes were obtained as a mixture of
cis- and trans-isomers, with the trans-isomer being the
major isomer (trans:cis ratio is ca. 90:10), as was evident
from the distinctive signals observed in the 31P{1H}
NMR spectra for compounds 11-13 (singlet at about
23 ppm, indicative for a trans bis-phosphine complex,
and a second singlet at about 28 ppm, indicative for a
cis bis-phosphine complex). For compound 12 (with 8
as the ligand) crystals suitable for X-ray diffraction were
obtained by slow distillation of n-pentane into a solution
of the complex in CDCl3 in a standard 5 mm NMR tube
at -20 °C. In the crystal structure of 12 the Pd atoms
are located on inversion centers of space group P21/c.
The molecular structure of 12 in the crystal and the
relevant bond lengths and angles are given in Figure 1
and Table 1, respectively.
Only the trans-isomer of 12 was observed in the solid-
state structure. The palladium has a square-planar
coordination geometry with angles Cl(1)-Pd(1)-P(1)
(89.20(3)°) and Cl(1)-Pd(1)-P(1)i (90.80(4)°) close to 90°.
In the crystal structure of the related complex trans-
[PdCl2(PPh3)2]25,26 these values are 92.03° and 87.97°,
respectively. The bond lengths Pd(1)-Cl(1) (2.2828(9)
Å) and Pd(1)-P(1) (2.3240(10) Å) are slightly shorter
than the values reported for the complex [PdCl2(PPh3)2]
perfluoroalkyl chains for 10 in both its 13C{1H} and 19
F
NMR spectra. Likewise the chemical shifts in the 31P-
{1H} NMR spectra were almost identical (9, δ ) -2.89
ppm; 10, δ ) -2.85 ppm) and in good agreement with
the value found for parent 2-[diphenylphosphino]pyri-
dine (δ ) -2.89 ppm). This also indicates that the
introduction of a p-silyl (either fluorous or nonfluorous)
substituent in the phenyl phosphino grouping has little
electronic influence on the phosphorus atom. This is
desired indeed and is in agreement with previously
reported results for derivatives of PPh3 that employ the
perfluoroalkylated ethylsilyl spacer.21
The physical properties of 9 and 10 were quite
different from each other though. Whereas 9 was
initially isolated as a yellow oil, which only solidified
on prolonged standing, 10 was obtained as a light yellow
solid after washing with n-pentane. This difference in
appearance at ambient temperature also affected the
workup and final yield of both products. Because 10 is
a solid, it was quite easy to isolate this fluorous
compound in pure form and high yield by repeated
washing with n-pentane. Compound 9, however, dis-
played good to excellent solubility in a broad range of
(24) Xie, Y.; Lee, C.-L.; Yang, Y.; Rettig, S. J.; James, B. R. Can. J.
Chem. 1992, 70, 751.
(25) Ferguson, G.; McCrindle, R.; McAlees, A. J.; Parvez, M. Acta
Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1982, 38, 2679.
(26) Although in the Cambridge Crystal Structure Database an
entry is present for the complex trans-[PdCl2[2-(diphenylphosphino]-
pyridine)2], no 3D coordinates were reported.
(23) van der Veen, L. A.; Kamer, P. C. J.; van Leeuwen, P. W. N.
M. Organometallics 1999, 18, 4765.

5302 Organometallics, Vol. 24, No. 22, 2005
de Pater et al.
triplet, arising from coupling to both 31P nuclei. For all
complexes, however, cooling of the samples to -10 °C
led to the appearance of the expected triplet for the Pd-
Me signal (3JH,P ) 6.2 Hz), due to coupling with the two
P atoms. The appearance of this triplet, along with only
one signal in the 31P{1H} NMR spectra, also showed that
complexes 14-16 have the trans bis-phosphine config-
uration. These results point to the presence of an
exchange process at ambient temperature. One pos-
sibility could be the displacement of the chloride by the
nitrogen of the pyridyl ring, which has been shown to
occur by others in complexes such as [PdCl(Me)(N-N-
N)] (N-N-N ) 2-(2-((2′-pyridylmethylene)amino)ethyl)-
pyridine (MAP)28 or 2,6-bis(pyrimidin-2-yl)pyridine (bp-
py)29). We therefore performed 15N NMR measurements
(using the DEPT sequence) with both the free ligand 2
and complex 14 in order to study this process in more
detail. For 2, a triplet at -51 ppm (relative to ni-
tromethane) was observed.30 Unfortunately, for complex
14 no signal could be observed, despite several attempts
and variation of several parameters.31 Apparently, the
N-H coupling, needed for the DEPT measurement, is
lost upon coordination of the ligand to palladium. This
has also been reported for complexes of the type [PdCl-
(Me)(N-N-N)].28
Figure 1. Displacement ellipsoid plot of 12, drawn at the
50% probability level. All hydrogen atoms, except H(12) and
H(12)i, have been omitted for clarity. Only one orientation
of the disordered bromophenyl groups is shown. Symmetry
operation i: -x, -y, -z.
The zerovalent palladium complex 17 was obtained
as a yellow solid in good yield following a literature
method published for the corresponding triphenylphos-
phine complex.32 In its room-temperature 1H NMR
spectrum (in CD2Cl2) the signal for the olefinic CH of
MA was observed as a broad singlet instead of the
expected doublet. In the aromatic region some signals
for the pyridyl protons as well as the aryl protons were
overlapping. The 13C{1H} NMR spectrum (20 °C) showed
broad signals in the aromatic region. When the sample
was cooled to -30 °C, the signal in the 1H NMR
spectrum for the CH’s of MA became a doublet with a
3J(1H-31P) of 5.5 Hz. Also the overlapping signals in
the aromatic region for the pyridyl protons sharpened
into distinct doublets and triplets.
(2.2905 and 2.3366 Å respectively). A large anisotropy
was observed for the 4-(bromo)phenyl rings, but not for
the pyridyl ring. In the crystal structure of 12 the
distance H(12)-Pd(1) (2.87 Å) is significantly shorter
than the sum of the van der Waals radii (3.50 Å),
2
indicating an additional interaction with the dz orbital
of palladium. Such an interaction has also been observed
in the complex trans-[PdCl2(PPh3)2] (a distance of 2.91
Å was reported).25 In the latter complex also a short
intramolecular Cl-Haryl interaction (2.81 Å) was ob-
served, which is not present in the structure of 12 (Cl-
(1)-H(12) is 3.36 Å). This therefore leads to a situation
for 12 where one of the phenyl rings (C(7)-C(8)-C(9)-
C(10)-C(11)-C(12)) is almost perpendicular to the
P(1)-P(1)i-Pd(1)-Cl(1)-Cl(1)i coordination plane, as
was evident from the value of 88.2(3)° for the angle
between the least-squares planes of P(1)-P(1)i-Cl(1)-
Cl(1)i and C(7)-C(8)-C(9)-C(10)-C(11)-C(12). For
trans-[PdCl2(PPh3)2] the angle between the least-
squares plane of P(1)-P(1)i-Cl(1)-Cl(1)i and C(7)-
C(8)-C(9)-C(10)-C(11)-C(12) has a value of 69.99°
(Figure 2). Furthermore, in complex 12 an intermolecu-
lar hydrogen bond is present between H(16) and the
chloride of a neighboring palladium complex (2.76 Å,
angle of 132°).
The 13C{1H} NMR spectrum at -40 °C revealed the
dCH resonance of maleic anhydride as a multiplet
pattern (Figure 3, top left), similar to that observed for
[Pd(PPh3)2(cyclo-(-CHdCHC(O)OC(O)-))].33 As was
shown for that complex also for 17 the observed pattern
is the X part of an AA′X pattern (A ) 31P, A′ ) 31P, for
the simulated spectrum (using WINDNMR34) see Figure
3, bottom left35) with exchange between the A and A′
nuclei.
(28) Ru¨lke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(29) Groen, J. H.; van Leeuwen, P. W. N. M.; Vrieze, K. J. Chem.
Soc., Dalton Trans. 1998, 113.
The palladium methyl chloride complexes 14-16,
which were synthesized following the same route as
reported for the triphenylphosphine complex,27 were
isolated as light yellow solids. They were characterized
(30) For the 15N NMR measurement of 2 a value of 2J(15N-1H) of
11 Hz was used.
1
by their H, 13C{1H}, and 31P{1H} NMR spectroscopic
(31) Measurements with 14 were carried out at -15 °C. Different
values of 2J(15N-1H), namely, 3, 9, and 11 Hz, were tried, as well as
longer delay times (d1) and longer acquisition periods (up to 72 h).
(32) Cavell, K. J.; Stufkens, D. J.; Vrieze, K. Inorg. Chim. Acta 1980,
47, 67.
data and elemental analysis and, for 16, also by 19F
NMR, which showed the expected signals for the C6F13
tail. Unfortunately, for complex 15 no good elemental
analyses could be obtained, due to the presence of
impurities, which could not be removed. In all 1H NMR
spectra at ambient temperature, the signal for Pd-Me
was observed as a broad singlet instead of the expected
(33) de Pater, J. J. M.; Tromp, D. S.; Tooke, D. M.; Lutz, A. L.;
Deelman, B. J.; van Koten, G.; Elsevier, C. J. Organometallics,
submitted.
(34) Reich, H. J. WINDNMR: NMR Spectrum Calculations, version
7.1.6; Department of Chemistry, University of Wisconsin: Madison,
WI, 2002.
(35) The following values were used in the simulation of this
pattern: VAA′ ) 0.3 Hz, JAA′ ) 12.0 Hz, JAX ) -7.5 Hz (cis-phosphine),
JA′X ) 29.4 Hz (trans-phosphine), KAA′ ) 5.0.
(27) Byers, P. K.; Canty, A. J.; Jin, H.; Kruis, D.; Markies, B. A.;
Boersma, J.; van Koten, G. Inorg. Synth. 1998, 32, 162.

Silyl-Substituted 2-[Bis(4-aryl)phosphino]pyridines
Organometallics, Vol. 24, No. 22, 2005 5303
Table 1. Selected Bond Lengths, Bond Angles, and Torsion Angles for
trans-[PdCl2(P{C6H4-p-Br}2{C5H4N-2})2] (12)a
Bond Lengths (Å)
Pd(1)-P(1)
2.3240(8)
90.80(3)
Pd(1)-Cl(1)
2.2827(8)
89.20(3)
Bond Angles (deg)
Cl(1)-Pd(1)-P(1)i
Cl(1)-Pd(1)-P(1)
Torsion Angles (deg)
Cl(1)-Pd(1)-P(1)-C(1)
Cl(1)-Pd(1)-P(1)-C(13)
Cl(1)i-Pd(1)-P(1)-C(7)
-32.15(13)
Cl(1)-Pd(1)-P(1)-C(7)
Cl(1)i-Pd(1)-P(1)-C(1)
Cl(1)i-Pd(1)-P(1)-C(13)
88.70(13)
147.85(13)
27.64(15)
-152.36(15)
-91.30(13)
a Symmetry operation i: -x, -y, -z.
{1H} NMR spectra showed in the whole temperature
range a singlet at 30.06 ppm.
We also attempted the synthesis of complex 18, based
on the fluorous ligand 10. Although complex formation
did indeed take place, as confirmed by the expected 1H
and 31P{1H} NMR resonance patterns, purification of
18 was not possible due to the presence of free tert-butyl
DAB. For 17, this ligand could be removed by washing
with Et2O at room temperature, but for 18 the complex
and the free tert-butyl DAB have similar solubility
properties, making separation difficult. Other methods,
such as removal of tert-butyl DAB at low temperature
or by sublimation, did indeed lower the amount of free
DAB in the final product. This procedure led to very
low product yields and did not result in a completely
pure product.
Catalysis. We applied in situ prepared palladium
catalysts based on [Pd(OAc)2] with 2 and the new
ligands 9 and 10 as well as the zerovalent palladium
complex 17 in the methoxycarbonylation of pheny-
lacetylene. The in situ catalysts were prepared accord-
ing to the conditions as described by Scrivanti (Scheme
4).10 The results are presented in Table 2.
All in situ prepared catalysts afforded complete
conversion of the substrate (Pd:substrate ) 1:4000, 50
min reaction time, 50 °C) when the solvent used was
pure methanol. If a 1:1 mixture of methanol and R,R′,R′′-
trifluorotoluene was used, the catalyst derived from the
new ligand 10 showed a higher activity than the one
with 2. In both solvents catalyst systems with 10 also
gave a selectivity toward the branched product similar
to those with 2, indicating that para-substitution of the
phenyl rings with either a fluorous or a nonfluorous
alkylsilyl moiety did not affect the catalysis. For 2 and
10 it was observed that when a 1:1 mixture of MeOH
and R,R′,R′′-trifluorotoluene was used, a slight decrease
in the selectivity toward the branched product was
obtained.
The catalytic system with ligand 10 was also tested
in the methoxycarbonylation of phenylacetylene in
scCO2. A slight modification of the above experiments
was adopted to ensure that the total volume of the
organic phase was approximately 5 mL (note that the
total volume of the autoclave used is 50 mL). Therefore,
phenylacetylene and methanol were added in a 1:2 ratio,
whereas all other ratios were the same as given in
Scheme 4 and Table 2. Confirmation that the mixture
was indeed supercritical and homogeneous was achieved
by visual inspection of the autoclave interior after
heating and pressurization.39 It was observed that a
Figure 2. Crystal structure of 12 (left) and trans-[PdCl2-
(PPh3)2] (right), showing the tilting of one of the phenyl
rings. For 12 the pyridyl ring and all hydrogen atoms not
involved have been omitted; for trans-[PdCl2(PPh3)2] one
of the phenyl rings and all hydrogen atoms not involved
have been omitted.
In the aromatic region, multiplet signals correspond-
ing to the carbon atoms of the phenyl ring as well as
the ipso-C of the pyridyl ring were observed. For the
ortho- and meta-PPh2 carbon atoms the expected virtual
triplet pattern was observed,36,37 but they were observed
as two sets of separate signals. For the ipso-C PPh2
carbon atom a more complicated multiplet pattern was
observed (see Figure 3, top right). This multiplet pattern
could be simulated (using WINDNMR34), which showed
that this pattern is the X-part of an AA′X pattern (A )
31P, A′ ) 31P, Figure 3, bottom right).38 When the 13C
NMR spectrum was measured with simultaneous de-
1
coupling of H and 31P, the spectrum simplified. The
resonance for dCH (MA) became a singlet, while the
multiplets in the aromatic region became two sets of
singlets. This proves that the multiplet structure was
caused by coupling to 31P, while the observation of two
sets of signals for the phenyl rings under simultaneous
1H and 31P decoupling indicates that the phenyl rings
of the phosphorus ligand are nonequivalent. The 31P-
(36) The appearance of these triplets is due to virtual 31P-coupling.
Such a resonance pattern is observed for AA′X spins systems when
JAA′ . (VA - VA′) + (JAX + JA′X)/2, see: Wiberg, K. B., Nist, B. J., Eds.
Interpretation of NMR Spectra; W. A. Benjamin, Inc.: New York, 1962;
pp 21-27. The appearance of such virtual triplets is not uncommon
for PPh3 ligands when coordinated to metal centers. It has for instance
been observed for [Pt(PPh3)2(trans-CH(CO2Et)dCH(CO2Et))], see:
Guedes da Silva, M. F. C.; Frau´sto, J. J. R.; Pombeiro, A. J. L.; Betani,
R.; Michelin, R. A.; Mozzon, M.; Benetollo, F.; Bombieri, G. Inorg. Chim.
Acta 1993, 214, 85.
(37) Verkade, J. G. Coord. Chem. Rev. 1972/73, 9, 1.
(38) The following values were used in the simulation of this
pattern: VAA′ ) 3.4 Hz, JAA′ ) 17.2 Hz, JAX ) 2.3 Hz (cis-phosphine),
JA′X ) 34.1 Hz (trans-phosphine), KAA′ ) 2.2.
(39) This autoclave was built in-house at the University of Amster-
dam. For a detailed technical description, see ref 20, chapter 2.

5304 Organometallics, Vol. 24, No. 22, 2005
de Pater et al.
Figure 3. 13C{1H} NMR spectrum, alkene region (top left) and part of the aromatic region (top right) of complex 17, in
CD2Cl2 at -40 °C. Bottom left and right are simulations of these patterns.
Scheme 4. Palladium-Catalyzed
Methoxycarbonylation of Phenylacetylene
Scheme 5. Conditions for Methoxycarbonylation
of Phenylacetylene with
[Pd(2)2(cyclo-(CHdCHC(O)OC(O)-))] (17)
Table 2. Results for Methoxycarbonylation of
Phenylacetylene with Catalysts Derived from 2, 9,
or 10a
Table 3. Results for the Methoxycarbonylation of
Phenylacetylene with 17 as the Precursora
i:nb
entry Pd:substrate
solvent
conversion (%)
i:nb
entry
ligand
solvent
conversion (%)
1
2
3
4
5
2
MeOH
100
100
100
75
97.8:2.2
98.2:1.8
98.3:1.7
96.5:3.5
96.8:3.2
1
2
3
4
5
1:4000
1:8000
1:20000
1:4000
1:8000
MeOH
100
99
98.4:1.6
98.5:1.5
98.2:1.8
98.8:1.2
97.6:2.4
9
MeOH
MeOH
10
2
10
MeOH
MeOH
40
MeOH/BTFc
MeOH/BTFc
MeOH/BTFc
MeOH/BTFc
100
75
85
a General conditions: Pd:substrate ) 1:4000, [phenylacetylene]
) 1.4 mmol/mL, stirrer ) 400 rpm. b Estimated error in the i- and
n-values: (0.1. c BTF ) C6H5CF3.
a General conditions: [phenylacetylene] ) 1.4 mmol/mL, stirrer
) 400 rpm, Pd:ligand ) 1:10. b Estimated error in the i- and
n-values: (0.1. c BTF ) C6H5CF3.
homogeneous solution was obtained at P(total) ) 140
bar (P(CO) ) 40 bar). Initial catalytic tests performed
at P(total) ) 150 bar gave a conversion of 50% (turnover
number (TON) ) 2000) in 50 min and a selectivity for
the branched product of more than 99%. The presence
of perfluoroalkyl chains in the palladium catalyst
provided an enormous improvement, since application
of nonfluorous 2 as ligand under identical conditions
gave a suspension and only 3% conversion (TON ) 120)
in 50 min time.
It has been reported that for the in situ prepared
catalysts a certain ligand-to-palladium ratio is needed
to convert the palladium precursor into the actual
catalytic species.13,14 In this process some ligand is
sacrificed and oxidized to the corresponding phosphine
oxide. Furthermore, only a small amount (15-20%) of
the starting palladium compound is transformed into
an active species, the bulk being present as unidentified
polynuclear species.13 We were therefore interested to
see if we could apply a more well-defined palladium(0)
complex as a catalyst precursor for the methoxycarbo-
nylation of phenylacetylene. The use of palladium(0)-
alkene complexes as precursors for this reaction has
been reported.16 We therefore applied 17 as a precursor
complex using the conditions given in Scheme 5. The
results of these catalytic reactions using 17 are given
in Table 3.
From this table one can see that the zerovalent
complex 17 is an excellent precursor for the methoxy-
carbonylation reaction, giving complete conversion for
substrate-to-palladium ratios of 4000:1 and 8000:1 in
MeOH. At higher substrate-to-palladium ratios incom-
plete conversion is observed in 50 min. A conversion of
40% (corresponding to a TON of 8000, see entry 3 in
Table 3) is then reached. In a 1:1 mixture of methanol
and R,R′,R′′-trifluorotoluene the activity is somewhat
lower (TON of ca. 6000), although it is still about twice
as high when compared to the in situ prepared catalyst
from [Pd(OAc)2] and 2 (compare entry 5 in Table 3 with
entry 4 in Table 2). Furthermore, the selectivity to the
branched ester is not affected and remained in all
experiments above 97%. For 17 in MeOH a time-versus-
conversion profile was established by sampling the
reaction at regular intervals and plotting the results
(Figure 4). As is clearly seen, the activity is very high
in the first 5 to 10 min and then starts to level off. Using
the data from Figure 4 we can see that after about 10
min 50% of the substrate has been consumed. This

Silyl-Substituted 2-[Bis(4-aryl)phosphino]pyridines
Organometallics, Vol. 24, No. 22, 2005 5305
The 13C{1H} NMR spectrum of 17 at -40 °C showed
some very special features in the aromatic region. Not
only were the signals for the ipso-C PPh3 carbon atoms
observed as complicated multiplet patterns instead of
the expected virtual triplets, but also all the signals for
the PPh2 carbon atoms were split into two sets. The
presence of these multiplet signals for the ipso-C as well
as the observed multiplet for the alkene carbon atoms
are the result of an AA′X spin system with exchange
between A and A′, as was shown when these patterns
1
were simulated. Since simultaneous decoupling of H
and 31P resulted in the disappearance of the multiplet
patterns, but not the splitting of the aromatic signals
into two sets, this provides evidence that the phosphorus
centers are diastereotopic; that is, the molecule does not
have an apparent symmetry plane containing the
phosphorus centers. This can be caused by the fact that
there is no free rotation around the Pd-P bond at this
low temperature. When the 13C{1H} NMR spectrum of
17 was measured at ambient temperature, we observed
that these multiplet patterns had disappeared and that
all signals were observed as broad singlets. Apparently
the interchange process between two different isomers
of the complex, possibly caused by alkene rotation
around the palladium(CdC) bond, dissociation/reasso-
cation reaction of the alkene, or Pd-P rotation, becomes
fast at room temperature.40
Catalytic methoxycarbonylation of phenylacetylene
using the in situ prepared catalysts has demonstrated
that the influence of funtionalization of the P,N-ligand
with a fluoroalkyl group is especially evident when
catalysis was performed in a 1:1 (v/v) mixture of
methanol and R,R′,R′′-trifluorotoluene, where the use of
10 led to a higher conversion compared to 2. A possible
explanation might be that the actual catalyst is formed
with different rates and efficiency. Ligand 10, with its
perfluoroalkyl silyl groups attached, might be more
compatible with the more apolar medium. Subtle influ-
ences such as more favorable formation of mononuclear
species of the type [Pd(OAc)2({2-pyridyl}PAr2)2] might
play a role here. The effect of perfluoralkyl functional-
ization was even more pronounced when the reaction
was performed in scCO2. An in situ prepared catalyst
that has 10 as the ligand gave a homogeneous solution
and a good activity, whereas with 2 a suspension was
obtained and only a low activity. In scCO2 also a higher
selectivity toward the branched product was observed
when compared with the reactions in methanol and
methanol:R,R′,R′′-trifluorotoluene 1:1 (v/v). These results
therefore show that the methoxycarbonylation of phe-
nylacetylene and other alkynes in scCO2 clearly has
potential, which warrants further investigations.
The distinct difference in activity when zerovalent
palladium complex 17 is used instead of the in situ
prepared catalyst can be explained by considering the
crucial steps in the proposed catalytic cycle (Scheme 6).13
As mentioned earlier, the in situ catalyst first proceeds
through several steps before the actual catalytically
Figure 4. Conversion (TON) versus time plot for complex
17. General conditions: Pd:substrate ) 1:10173, [pheny-
lacetylene] ) 1.4 mmol/mL, 50 °C, 40 bar CO, solvent )
MeOH.
Table 4. Influence of Ligand-to-Palladium Ratio
on Activity of 17 in Methoxycarbonylation of
Phenylacetylenea
entry
ligand:palladium
conversion (%)
i:nb
1
2
3
4
5
6
10
8
98
99
98.0:2.0
98.5:1.5
98.3:1.7
98.4:1.6
98.5:1.5
98.5:1.5
6
>99
>99
85
4
3
2
35
a General conditions: Pd:substrate:MeSO3H ) 1:8000:20, 40 bar
CO, 50 °C, 50 min, stirrer ) 400 rpm, [phenylacetylene] ) 1.4
mmol/mL, solvent ) MeOH. b Estimated error in the i- and
n-values: (0.1.
corresponds to a TOF50 value of about 30 000 mol
substrate per mol palladium per hour.
Furthermore, application of a zerovalent palladium
alkene complex as a precursor might allow lower ligand-
to-palladium ratios, since in principle no ligand will be
sacrificed to form the catalytically active species.14 To
study the best ligand-to-palladium ratio without lower-
ing the activity and selectivity of the catalyst, the
experiments shown in Table 4 were performed. For a
ligand:Pd(0) ratio of 2, i.e., when complex 17 itself was
used, the conversion was only 35% after 50 min (entry
6, Table 4). Addition of one extra equivalent of ligand
(entry 5 in Table 4) gave a dramatic increase in the
catalytic activity to 85% conversion in the same time.
With two extra equivalents added (total ligand-to-
palladium ratio is 4, entry 4 in Table 4) complete
conversion is observed within the reaction time (50 min).
Further increase of the ligand:Pd(0) ratio had no further
beneficial effect and beyond a certain point appeared
to cause a small decrease in catalyst activity.
Discussion
The new ligands 9 and 10 display a coordination
behavior similar to that of the unsubstituted ligand
2-[diphenylphosphino]pyridine (2). This was not unex-
pected, since the introduced funtionalities at the para-
positions are expected not to introduce significant steric
hindrance at the metal center. Moreover, the 31P{1H}
NMR chemical shifts observed for the different com-
plexes showed similar values, which indicated that the
electron-withdrawing effect of the perfluoroalkyl chains
on the phosphorus atom is attenuated by the silicon
atom.
(40) These processes have been observed in other palladium(0)-
alkene complexes as well, see: (a) Go´mez-de la Torre, F.; Jalo´n, F. A.;
Lo´pez-Agenjo, A.; Manzano, B. R.; Rodr´ıguez, A.; Sturm, T.; Wassen-
steiner, W.; Mart´ınez-Ripoll, M. Organometallics 1998, 17, 4634. (b)
Manzano, B. R.; Jalo´n, F. A.; Go´mez-de la Torre, F.; Lo´pez-Agenjo, A.
M.; Rodr´ıguez, A. M.; Mereiter, K.; Weissensteiner, W.; Sturm, T.
Organometallics 2002, 21, 789. (c) van Asselt, R.; Elsevier, C. J. Inorg.
Chem. 1994, 33, 1521.

5306 Organometallics, Vol. 24, No. 22, 2005
de Pater et al.
Scheme 6. Proposed Catalytic Cycle for the
Methoxycarbonylation of Alkynesa
palladium center and in the right geometry, will be
increased, thus enhancing the activity. When the ligand-
to-palladium ratio is too high, on the other hand, the
phosphine ligand competes with CO and/or methanol
for coordination to the metal center, thus slowing down
the catalyst somewhat. In the range of ligand-to-
palladium ratio we studied, however, this is only a
marginal effect.
Conclusions
In conclusion, we have developed a new route toward
2-[bis(4-substituted aryl)phosphino]pyridines. These com-
pounds were readily made from a convenient starting
compound, the p-bromo-functionalized phosphine 8,
which itself was obtained in high yield via a four-step
route. A number of palladium complexes were made
with these new P,N-ligands and it was shown that they
displayed a coordination behavior similar to that of the
nonfunctionalized ligand 2.
Testing of the new ligands 9 and 10 in both methanol
and a 1:1 (v/v) mixture of methanol and R,R′,R′′-
trifluorotoluene showed that 4-(perfluoroalkyl)ethylsilyl
functionalization has a beneficial effect on activity when
compared with 2 (a TON of about 3400 was reached
with 10 in MeOH/R,R′,R′′-trifluorotoluene, 1:1, compared
to 3000 with 2 as the ligand), while selectivity was not
affected (about 97-98% toward the branched ester). For
the methoxycarbonylation of phenylacetylene in scCO2
the use of [Pd(OAc)2] with 10 as the ligand afforded an
active catalyst (TON of about 2000), which showed a
significantly higher selectivity (>99%) for the branched
ester than in regular solvents. The use of complex 17
afforded a catalyst that is twice as active (TON of about
6000 in MeOH/R,R′,R′′-trifluorotoluene, 1:1, 8000 in
MeOH) as the in situ prepared catalysts in regular
solvents. These results allow the further development
of new catalysts that combine high activity and selectiv-
ity with excellent compatibility with apolar solvents
such as scCO2.
a R ) methyl or phenyl.
active species, presumably a palladium(0) complex, is
formed. In this process only a small part of the starting
compound is converted into a catalytically active spe-
cies.13,14 When the zerovalent palladium complexes are
used, these initial reactions are not required, because
the catalyst precursor in this case will closely resemble
the actual catalytically active species. The only step
required is a replacement of the coordinated alkene by
an alkyne, which is a facile process. It can be assumed
that a larger part of the precursor complex is directly
available to play a role in the catalytic cycle.
Variation of the ligand-to-palladium ratio with the
zerovalent palladium complex as precursor showed that
a certain excess of ligand is needed to obtain good
conversions. This can be explained in the following
manner. It has been proposed that one of the key steps
in the catalytic cycle of Scheme 6 is the transfer of H+
from the N atom of the pyridine ring to the coordinated
alkyne (whether this goes via a palladium hydride will
not be discussed here41). When a low ligand-to-pal-
ladium ratio is used (lower than 4), we can assume that
there is a competition between the phosphine ligand,
CO, and also methanol to coordinate to the palladium
center. This might lead to a situation where only one
phosphine ligand is coordinated to palladium and in the
trans-position to the alkyne. Furthermore, it is known
in the literature that with this type of ligand formation
of polynuclear species is a feasible process,13,42 and we
expect that this is especially favorable at low ligand-
to-palladium ratios. When more than 2 equiv of ligand
is present, this formation of polynuclear species will be
disfavored and the concentration of mononuclear spe-
cies, with at least two phosphines coordinated to the
Experimental Section
General Procedures. All reactions were performed using
standard Schlenk techniques under N2 atmosphere. Diethyl
ether and THF were distilled from Na/benzophenone, acetone
was distilled from B2O3, benzene, n-pentane, and n-hexane
were distilled from sodium wire, methanol was distilled from
Mg(OMe)2, and CH2Cl2 was distilled from CaH2. R,R′,R′′-
Trifluorotoluene was degassed via freeze-pump-thaw cycles
(3 times) and stored on molecular sieves. C6D6 (Cambridge
Isotopes Laboratories, CIL) was degassed and stored under
nitrogen on Na. CDCl3 and CD2Cl2 (CIL) were degassed and
stored under nitrogen on molecular sieves. PCl3 was refluxed
to expel dissolved HCl and subsequently distilled.43 Pheny-
lacetylene (98%, Acros) was flashed over a short column
(neutral alumina (Merck)) prior to use. All other reagents
(Acros, Aldrich, Lancaster) were used as received. 1H, 13C{1H},
19F, and 31P{1H} NMR spectra were recorded on a Varian
Unity-INOVA 300 MHz, a Varian Unity-INOVA 500 MHz, a
Varian Mercury-VxWorks 300 MHz, or a Varian Mercury 200
MHz spectrometer at 25 °C unless stated otherwise. Additional
1H-1H COSY-45 and 13C-1H HETCOR spectra were recorded
on a Varian Unity-INOVA 500 MHz to assign 1H and 13C
signals for compounds 8, 9, 10, and 17. The COSY measure-
(41) The route where a direct transfer of the H+ from the pyridyl N
atom to the coordinated alkyne takes place seems more plausible, since
this route can explain all the results acquired from several experiments
as described in the literature. See: (a) Ref 13. (b) Trost, B. M.; Schmidt,
T. J. Am. Chem. Soc. 1988, 110, 2301.
(42) Newkome, G. R. Chem. Rev. 1993, 93, 2067, and references
therein.
(43) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: Oxford, 1988; p 336.

Silyl-Substituted 2-[Bis(4-aryl)phosphino]pyridines
Organometallics, Vol. 24, No. 22, 2005 5307
3
ments were performed with a relaxation delay of 1 s, an
acquisition time of 193 ms, 8 scans per FID, and 512 incre-
ments. This gave a 2K × 2K data matrix, which was further
processed with the VNMR software package. For the HETCOR
measurements a relaxation delay of 2 s and an acquisition time
of 81 ms were used. Per FID 48 scans were performed and a
total of 128 increments were used. This gave a 4K × 1K data
matrix, which was further processed with the VNMR software
package. 15N NMR measurements were performed using the
1H NMR (CDCl3, 300.1 MHz): δ 0.96 (t, JH,H ) 7.0 Hz, 6
3
3
H, CH3), 3.05 (dq, JH,P ) 2.6 Hz, JH,H ) 7.0 Hz, 4 H, CH2),
7.25 (t, 3JH,H ) 7.2 Hz, H-aryl), 7.47 (d, 3JH,H ) 6.9 Hz, H-aryl).
13C{1H} NMR (CDCl3, 75.5 MHz): δ 14.8 (d, JC,P ) 3.2 Hz,
3
2
4
CH3), 44.5 (d, JC,P ) 15.7 Hz, CH2), 123.2 (d, JC,P ) 1.2 Hz,
3
2
p-C C6H4), 131.5 (d, JC,P ) 5.9 Hz, m-C C6H4), 133.7 (d, JC,P
1
) 20.7 Hz, o-C C6H4), 139.2 (d, JC,P ) 16.2 Hz, ipso-C C6H4).
31P{1H} NMR (CDCl3, 81.0 MHz): δ 59.8 (s). Anal. Calcd for
C16H18Br2NP: C 46.29, H 4.37, N 3.37, P 7.46. Found: C 46.42,
H 4.48, N 3.31, P 7.41.
1
DEPT sequence on a Bruker DRX-300 spectrometer. H and
13C{1H} NMR spectra were referenced to the residual solvent
peak (1H: CHCl3 δ ) 7.26 ppm, C6HD5 δ ) 7.16 ppm, CHDCl2
δ ) 5.35 ppm; 13C: CDCl3 δ ) 77.16 ppm, C6D6 δ ) 128.06
ppm, CD2Cl2 δ ) 54.00 ppm), 31P{1H} NMR spectra externally
Synthesis of Chlorobis(4-(bromo)phenyl)phosphine
(7). To a sample of 6 (6.64 g, 16.0 mmol) was added 15 mL of
PCl3. The mixture was stirred at 75 °C for 2 h. After cooling
to room temperature the excess PCl3 and formed Et2NPCl2
were distilled off by flame distillation under reduced pressure.
The yellow-orange solid residue was extracted twice with
n-pentane and Et2O. After removing the volatiles in vacuo a
light yellow solid was obtained (5.86 g, 15.5 mmol, 99%).
1H NMR (CDCl3, 300.1 MHz): δ 7.43 (t, J ) 7.8 Hz), 7.56
(t, J ) 8.4 Hz). 13C{1H} NMR (CDCl3, 75.5 MHz): δ 125.8 (s,
to H3PO4 (85%), 19F NMR spectra externally to CFCl3, and 15
N
NMR spectra externally to nitromethane. Abbreviations
used: s ) singlet, d ) doublet, t ) triplet, vt ) virtual triplet,
q ) quartet, m ) multiplet. Elemental analyses were carried
out by H. Kolbe Mikroanalytisch Laboratorium, Mu¨llheim an
der Ruhr. GC analyses were performed on a Varian 3300 gas
chromatograph, equipped with J&W Scientific Inc. DB-5
column (30 m, 0.320 mm internal diameter) and a FID detector
(280 °C), using N2 as the carrier gas and attached to a Varian
4400 integrator. The compounds [RhCl(PPh3)3],44 2-[diphe-
nylphosphino]pyridine (2),45 Et2NPCl2 (5),46 [PdCl2(COD)],47
[PdCl(Me)(TMEDA)],27 and [Pd(t-BuDAB)(cyclo-(-CHdCHC-
(O)OC(O)-))]32 were synthesized as reported.
3
2
p-C C6H4); 132.3 (d, JC,P ) 6.7 Hz, m-C C6H4); 133.2 (d, JC,P
1
) 24.6 Hz, o-C C6H4); 137.3 (d, JC,P ) 33.8 Hz, ipso-C C6H4).
31P{1H} NMR (CDCl3, 81.0 MHz): δ 78.6 (s). Anal. Calcd for
C12H8Br2ClP: C 38.09, H 2.13, P 8.18. Found: C 38.15, H 2.04,
P 8.28.
Autoclaves. Standard catalytic runs were performed by
using two different autoclaves, except for the experiments in
scCO2, where only the second autoclave described was used.
One was a stainless steel autoclave with a total volume of 100
mL, equipped with a pressure gauge, a rupture disk assembly,
and a connection to the high-pressure system. To avoid
contamination from the autoclave walls, a glass insert was
used with this autoclave. The second autoclave was an
in-house built stainless steel autoclave (V ) 50 mL),39 equipped
with two borosilicate (Maxos 200) windows to allow visual
inspection of the interior of the autoclave, a pressure trans-
ducer, temperature gauges inside the autoclave and the wall,
a rupture disk assembly (set at 250 bar), and four heating
elements in the wall for heating. For both autoclaves the
contents were stirred via magnetic stirring bars at 400 rpm.
Synthesis of Chlorodimethyl(3,3,4,4,5,5,6,6,7,7,8,8,8-
tridecafluoro-octyl)silane. To a solution of [RhCl(PPh3)3]
(0.19 g, 0.21 mmol) in benzene (20 mL) were added 3,3,4,4,5,5,-
6,6,7,7,8,8,8-tridecafluoro-1-octene (11.47 g, 33.1 mmol) and
HSiMe2Cl (7.5 mL, 66.2 mmol). The resulting light yellow
solution was refluxed for 2 h. After cooling the excess HSiMe2-
Cl and benzene were distilled off at ambient pressure. The
final product was obtained by flame distillation at reduced
pressure as a colorless liquid (12.47 g, 28.0 mmol, 85% based
on 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octene). All NMR
data were in accordance with literature values.48
Synthesis of Bis(4-(bromo)phenyl) N,N-Diethylphos-
phoramidite (6). To a stirred solution of 1,4-dibromobenzene
(9.11 g, 38.6 mmol) in a 3:1 (v/v) mixture of hexane and Et2O
was added a 1.6 M solution of n-BuLi in hexane (24.3 mL, 38.9
mmol). The mixture was stirred for 15 min at room temper-
ature, during which a white suspension was formed. This
suspension was cooled to -75 °C, and Et2NPCl2 (3.51 g, 21.9
mmol) was added. The resulting yellowish suspension was
allowed to reach room temperature during overnight stirring.
The suspension was centrifuged and all volatiles of the liquid
layer were removed in vacuo, yielding the desired product as
a yellow oil (7.90 g, 19.2 mmol, 99%).
Synthesis of 2-[Bis{4-(bromo)phenyl}phosphino]pyri-
dine (8). To a solution of 2-bromopyridine (1.42 g, 8.99 mmol)
in Et2O at -75 °C was added dropwise a 1.6 M solution of
n-BuLi in hexane (5.8 mL, 9.28 mmol). The resulting dark red
solution was stirred for 1 h at -75 °C, after which 7 (3.42 g,
8.99 mmol) in Et2O was added dropwise. The resulting orange
suspension was allowed to reach room temperature overnight.
To the yellow-orange suspension was added degassed H2O (20
mL). After phase separation the aqueous layer was extracted
twice with Et2O. The combined organic fractions were dried
on MgSO4 and filtered and the volatiles removed in vacuo. The
resulting orange oil (crude product) was extracted twice with
n-pentane. After combining the pentane layers the solvent was
evaporated. The final product was obtained as a yellow solid
(2.63 g, 6.29 mmol, 70%).
1H NMR (C6D6, 300.1 MHz): δ 7.12 (d, J ) 7.5 Hz, 2 H,
H-pyridyl), 7.24 (m, H-aryl and H-pyridyl), 7.48 (d, J ) 8.4
Hz, H-aryl), 7.58 (t, J ) 4.5 Hz, H-pyridyl), 8.71 (d, J ) 3.9
Hz, H-pyridyl). 13C{1H} NMR (C6D6, 75.5 MHz): δ 122.39 (s,
C(2)); 124.16 (s, C(9)); 128.26 (d, 3JC,P ) 23.9 Hz, C(3)); 132.02
(d, 3JC,P ) 7.2 Hz, C(8); 135.41 (d, 2JC,P ) 4.5 Hz, C(4)); 135.96
1
2
(d, JC,P ) 12.8 Hz, C(6)); 136.06 (d, JC,P ) 20.6 Hz, C(7));
150.62 (d, 3JC,P ) 10.6 Hz, C(1)); 163.13 (d, 1JC,P ) 1.9 Hz, C(5)).
31P{1H} NMR (CDCl3, 81.0 MHz): δ -5.34 (s). Anal. Calcd for
C17H12Br2NP: C 48.49, H 2.87, Br 37.95, N 3.33, P 7.36.
Found: C 48.52, H 2.87, Br 37.69, N 3.26, P 7.39.
Synthesis of 2-[Bis{4-(trimethylsilyl)phenyl}phosphino]-
pyridine (9). A solution of 8 (1.04 g, 2.47 mmol) in THF was
cooled to -80 °C with an ethanol/liquid N2 bath. Subsequently,
a 1.6 M solution of n-BuLi in hexane (3.15 mL, 5.02 mmol)
was added. The resulting red solution was stirred for 1 h at
-80 °C, after which Me3SiCl (0.58 g, 5.34 mmol) in THF (5
mL) was added. The mixture was slowly warmed to room
temperature overnight, after which a saturated degassed
NaHCO3 solution (10 mL) was added to the light yellow
suspension. The organic layer was separated, and the aqueous
layer was extracted once with Et2O. The organic layers were
combined, dried on MgSO4, and filtered, and the volatiles were
(44) Osborn, J. A.; Wilkinson, G. Inorg. Synth. 1990, 28, 88.
(45) Schmidbaur, H.; Inoguchi, Y. Z. Naturforsch. B Anorg. Chem.
Org. Chem. 1980, 35, 1329.
(46) Perich, J. W.; Johns, R. B. Synthesis 1988, 143.
(47) Drew, D.; Doyle, J. R. Inorg. Synth. 1990, 28, 346.
(48) Ame´duri, B.; Boutevin, B.; Nouiri, M.; Talbi, M. J. Fluorine
Chem. 1995, 74, 191.

5308 Organometallics, Vol. 24, No. 22, 2005
de Pater et al.
Table 5. Crystallographic Data for the Crystal
Structure Determination of 12
removed in vacuo. The crude product was washed with
n-pentane and MeOH at low temperatures to give the product
as a yellow oil (0.60 g, 1.50 mmol, 60%), which slowly solidified
to a yellow solid.
formula
mol wt
cryst syst
space group
a (Å)
C34H24Br4Cl2N2P2Pd
1019.43
1H NMR (C6D6, 499.8 MHz): δ 0.26 (s, 18 H, SiMe3), 6.53
(m, 1H, H(2)), 6.87 (m, 1H, H(4)), 7.12 (m, 1 H, H(3)), 7.36 (d,
monoclinic
P21/c (no. 14)
13.5697(1)
7.5837(1)
19.7320(2)
117.1114(4)
1807.47(3)
1.873
3
3JH,H ) 7.5 Hz, 4 H, H(8)), 7.57 (t, JH,H ) 7.5 Hz, 4 H, H(7)),
8.52 (d, 3JH,H ) 4.0 Hz, 1 H, H(1)). 13C{1H} NMR (C6D6, 125.7
MHz): -0.83 (s, SiMe3), 122.38 (s, C(2)), 128.72 (d, 3JC,P ) 20.2
b (Å)
c (Å)
â (deg)
3
3
Hz, C(3)), 134.11 (d, JC,P ) 6.4 Hz, C(8)), 134.44 (d, JC,P
)
V (Å3)
19.0 Hz, C(7)), 135.58 (d, 2JC,P ) 3.5 Hz, C(4)), 138.52 (d, 1JC,P
Dcalcd (g cm-1
Z
)
3
) 11.6 Hz, C(6)), 141.51 (s, C(9)), 150.85 (d, JC,P ) 11.6 Hz,
2
C(1)), 164.98 (d, JC,P ) 2.3 Hz, C(5)). 31P{1H} NMR (CDCl3,
1
F(000)
984
µ(Mo KR) (mm-1
cryst color
)
5.199
81.0 MHz): δ -2.89 (s). Anal. Calcd for C23H30NPSi2: C 67.76,
H 7.42, N 3.44, P 7.60. Found: C 67.95 H 7.56, N 3.12, P 7.80.
Synthesis of 2-[Bis{4-((2-(perfluorohexyl)ethyl)dimeth-
ylsilyl)phenyl}phosphino]pyridine (10). The procedure
followed was the same as for compound 9. To a solution of 8
(1.15 g, 2.73 mmol) in THF at -80 °C was added a 1.6 M
solution of n-BuLi in hexane (3.4 mL, 5.46 mmol) and after 1
h tridecafluorooctyldimethyl chlorosilane (2.45 g, 5.50 mmol)
in THF. After workup as described for 9 the crude product
was washed with n-pentane at -40 °C to afford compound 10
as an off-white solid (1.48 g, 1.37 mmol, 51%).
yellow
cryst size (mm)
θmin, θmax (deg)
data set (hkl)
-9 to +9,
abs corr range
total no. of data,
0.15 × 0.15 × 0.15
1.69, 27.49
-17 to +17,
-25 to +25
0.42-0.46
32 263, 4151
no. of unique data
Rint
0.0444
no. of refined params,
no. of restraints
R1/wR2 (I > 2σ(I))
R1/wR2 (all data)
goodness of fit
295, 138
0.0393, 0.0928
0.0509, 0.1000
1.077
1H NMR (C6D6, 300.1 MHz): δ 0.02 (s, 12 H, Si(Me)2), 0.84
(m, 4 H, SiCH2CH2), 1.90 (m, 4 H, SiCH2CH2), 6.56 (t, 3JH,H
)
3
3
7.5 Hz, 1 H, H(2)), 6.92 (tt, JH,H ) 7.5 Hz, JH,P ) 1.8 Hz,
w-1 a
σ2(Fo2) + (0.0372P)2 + 4.0289P
-1.51, 1.48
3
3
H(4)), 7.13 (d, JH,H ) 7.5 Hz, 1 H, H(3)), 7.23 (d, JH,H ) 6.5
Hz, 4 H, H(8)), 7.54 (t, 3JH,H ) 7.5 Hz, 4 H, H(7)), 8.52 (d, 3JH,H
) 4.8 Hz, H(1)). 13C{1H} NMR (C6D6, 125.7 MHz): δ -4.04 (s,
min., max. residual
density (e/Å3)
2
2
a P ) (Fo + 2Fc )/3.
2
Si(Me)2), 5.04 (s, SiCH2CH2), 26.00 (t, JC,F ) 20.7 Hz,
SiCH2CH2), 120-107 (multiple m, C6F13 tail), 122.10 (s, C(2)),
128.30 (d, 3JC,P ) 22.6 Hz, C(3)), 133.64 (d, 3JC,P ) 6.7 Hz, C(8)),
134.06 (d, 2JC,P ) 19.5 Hz, C(7)), 135.13 (d, 2JC,P ) 4.3 Hz, C(4)),
diffractometer with rotating anode and Mo KR radiation
(graphite monochromator, λ ) 0.71073 Å) at a temperature of
150(2) K. An absorption correction based on multiple measured
reflections was applied. The structure was solved with direct
methods49 and refined with SHELXL-9750 on F2 of all reflec-
tions. Non-hydrogen atoms were refined freely with anisotropic
displacement parameters. Hydrogen atoms were introduced
in calculated positions and refined as rigid groups. The
bromophenyl groups were disordered over two positions in a
50% ratio, respectively, to avoid close intermolecular contacts.
Geometry calculations, drawings, and checking for higher
symmetry were performed with the PLATON package.51
[PdCl2(2-[bis{4-(trimethylsilyl)phenyl}phosphino]pyr-
idine)2] (13). Starting from 9 (0.22 g, 0.54 mmol) and [PdCl2-
(COD)] (79.0 mg, 0.27 mmol) after normal workup, the final
product was obtained by washing of the crude product with
n-pentane. The product was isolated as a yellow solid (0.19 g,
0.19 mmol, 70%).
1
138.06 (s, C(9)), 138.71 (d, JC,P ) 12.2 Hz, C(6)), 150.44 (d,
3JC,P ) 10.3 Hz, C(1)), 163.78 (d, 1JC,P ) 4.0 Hz, C(5)). 19F NMR
(C6D6, 282.4 MHz): δ -93.91 (s, 6 F, CF3), -128.27 (m, 4 F,
CF2), -134.68 (s, 4 F, CF2), -135.75 (s, 8 F, CF2), -138.99 (s,
4 F, CF2). 31P{1H} NMR (CDCl3, 81.0 MHz): δ -2.85 (s). Anal.
Calcd for C37H32F26NPSi2: C 41.46, H 3.01, F 46.09, N 1.31, P
2.89. Found: C 41.26, H 2.88, F 45.98, N 1.29, P 2.81.
General Procedure for Synthesis of [PdCl2(2-[bis-
(aryl)phosphino]pyridine)2] Complexes 11-13. A proce-
dure previously reported for 11 was followed,25 but instead of
[PdCl2(PhCN)2] [PdCl2(COD)] was used as the palladium
precursor complex.
[PdCl2(2-[diphenylphosphino]pyridine)2] (11). Starting
from 2-[diphenylphosphine]pyridine (0.43 g, 1.62 mmol) and
[PdCl2COD] (0.23 g, 0.81 mmol) the desired compound was
obtained as a yellow solid (0.57 g, 0.81 mmol, 99%). NMR
spectroscopic data were in accordance with those reported in
the literature.25
1H NMR (CDCl3, 300.1 MHz): δ 0.24 (s, 36 H, SiMe3), 7.32-
7.83 (br m, 24 H, H-aryl and H-pyridyl). 13C{1H} NMR (CDCl3,
75.5 MHz, 0 °C): δ -0.65 (s, SiMe3), 124.89 (s), 128.23 (s),
132.81 (s), 132.95 (s), 133.65 (s), 133.83 (s), 134.22 (s), 144.63
(s), 149.14 (s). 31P{1H} NMR (CDCl3, 121.5 MHz): δ 22.61 (s,
trans-isomer), 27.93 (s, cis-isomer). Anal. Calcd for C46H60-
Cl2N2P2PdSi4: C 55.66, H 6.09, P 6.24, Pd 10.72. Found: C
56.01, H 6.21, P 6.18, Pd 10.65.
General Procedure for Synthesis of trans-[PdCl(Me)-
(2-[bis(aryl)phosphino]pyridine)2] Complexes 14-16.28
To a solution of the appropriate ligand in CH2Cl2 was added
0.5 equiv of [PdCl(Me)(TMEDA)]. The resulting red solution
was stirred at ambient temperature for 45 min, after which
all volatiles were removed in vacuo. The resulting solid was
washed twice with n-pentane to afford the final product.
trans-[PdCl(Me)(2-[diphenylphosphino]pyridine)2] (14).
Starting from 2 (0.27 g, 1.03 mmol) and [PdCl(Me)(TMEDA)]
[PdCl2(2-[bis{4-(bromo)phenyl}phosphino]pyri-
dine)2] (12). Starting from 8 (0.47 g, 1.12 mmol) and [PdCl2-
(COD)] (158.5 mg, 0.56 mmol) after normal workup, the final
product was obtained by recrystallization from CH2Cl2/Et2O
(0.50 g, 0.49 mmol, 88%). Crystals suitable for X-ray analysis
were obtained after 2 weeks by slow distillation of n-pentane
into a solution of 12 in CDCl3 in a 5 mm NMR tube at -20 °C.
1H NMR (CDCl3, 300.1 MHz): δ 7.30-8.74 (br m, 24 H,
H-aryl and pyridyl). 13C{1H} NMR (CDCl3, 75.5 MHz):
δ
124.83 (br s, p-C aryl), 126.59 (br s, C-pyridyl), 127.77 (t, ipso-C
aryl), 128.91 (s, p-C pyridyl), 131.69 (br s, C-aryl), 136.02 (br
s, C-pyridyl), 136.84 (br s, C-aryl), 150.28 (br s, C-pyridyl). 31P-
{1H} NMR (CDCl3, 81.0 MHz): δ 22.39 (s, trans-isomer), 28.72
(s, cis-isomer). Anal. Calcd for C34H24Br4Cl2N2P2Pd: C 40.06,
H 2.37, P 6.08, Pd 10.44. Found: C 39.70, H 2.52, P 6.18, Pd
10.49.
X-ray Crystal Structure Determination of Compound
12. Pertinent data for the structure determination are given
in Table 5. Data were measured on a Nonius KappaCCD
(49) Sheldrick, G. M. SHELXS-86, Program for crystal structure
solution; Universita¨t Go¨ttingen: Germany, 1986.
(50) Sheldrick, G. M. SHELXL-97, Program for crystal structure
refinement; Universita¨t Go¨ttingen: Germany, 1997.
(51) Spek. A. L. J. Appl. Crystallogr. 2003, 36, 7.

Silyl-Substituted 2-[Bis(4-aryl)phosphino]pyridines
Organometallics, Vol. 24, No. 22, 2005 5309
(0.14 g, 0.52 mmol) a light yellow solid was obtained as the
final product (0.30 g, 0.44 mmol, 85% based on [PdCl(Me)-
(TMEDA)]).
JC,P ) 14.0 Hz, C(7)), 134.60 (vt, JC,P ) 14.0 Hz, C(7)), 135.61
(s, C(4)), 150.04 (vt, JC,P ) 15.0 Hz, C(1)), 158.56 (m, JC,P
)
60.7 Hz, C(5)), 170.43 (s, CdO cyclo-(-CHdCHC(O)OC(O)-
)). 31P{1H} NMR (CD2Cl2, 121.5 MHz): δ 30.06 (s). Anal. Calcd
for C37H30N2O3P2Pd: C 62.42, H 4.14, N 3.83, P 8.47, Pd 14.55.
Found: C 62.30, H 4.19, N 3.75, P 8.36, Pd 14.38.
1H NMR (CD2Cl2, 499.8 MHz): δ -0.01 (s, 3 H, Pd-Me), 7.34
(t, J ) 5.7 Hz, 2H, H-pyridyl), 7.46 (m, 12 H, H-aryl), 7.75 (t,
J ) 7.5 Hz, 2 H, H-pyridyl), 7.85 (d, J ) 5.0 Hz, 8 H, H-aryl),
8.06 (d, J ) 6.0 Hz, 2 H, H-pyridyl), 8.78 (d, J ) 4.0 Hz, 2 H,
H-pyridyl). 13C{1H} NMR (CD2Cl2, 125.7 MHz): δ 4.43 (br s,
Pd-Me), 124.39 (s, C(2)), 128.57 (vt, JC,P ) 9.8 Hz, C(8)), 130.83
Attempted Synthesis of [Pd(2-[bis{4-((2-(perfluoro-
hexyl)ethyl)dimethylsilyl)phenyl}phosphino]pyridine)2-
(cyclo-(-CHdCHC(O)OC(O)-))] (18). Starting from 10 (0.52
g, 0.49 mmol) and [Pd(t-BuDAB)(cyclo-(-CHdCHC(O)OC(O)-
))] (72.3 mg, 0.19 mmol) a yellow oil was obtained after workup
as described above. After several washings with n-pentane at
-50 °C a light yellow oil was obtained (0.49 g), which contained
the desired product together with about 25% of free t-BuDAB.
1H NMR (CD2Cl2, 300.1 MHz): δ 0.34 (s, 24 H, SiMe2), 1.01
(m, 8 H, SiCH2CH2), 1.25 (s, CMe3 of t-BuDAB), 2.08 (m, 8 H,
SiCH2CH2), 4.15 (br s, 2 H, CH of cyclo-(-CHdCHC(O)OC-
(O)-)), 7.11 (br m, 4 H, H-pyridyl), 7.42 (m, 18 H, H-aryl and
H-pyridyl), 8.51 (br s, 2 H, H-pyridyl). 31P{1H} NMR (CD2Cl2,
121.5 MHz): δ 29.72 (br s).
Catalytic Methoxycarbonylation of Phenylacetylene.
For catalysis employing the in situ prepared catalysts the
following procedure was used.10 [Pd(OAc)2] was weighed under
N2 in a Schlenk vessel. In a second Schlenk vessel were
subsequently added the appropriate amounts of ligand, meth-
ane sulfonic acid, n-decane (GC internal standard), phenyl-
acetylene, and solvents (pure methanol or methanol and
R,R′,R′′-trifluoro toluene, 1:1 (v/v)). After mixing, this solution
was transferred to the first Schlenk vessel via syringe. The
resulting solution was charged to the autoclaves under N2 flow.
After sealing the autoclaves three vacuum-nitrogen cycles were
performed, followed by three times flushing with CO (15 bar).
The autoclaves were heated to the desired temperature and
pressurized with CO. After the desired reaction time the
autoclaves were cooled and carefully vented. A sample of the
autoclave content was analyzed by GC after filtration over
basic alumina and dilution with diethyl ether.
(s, C(9)), 131.73 (vt, JC,P ) 45.0 Hz, C(6)), 132.42 (vt, JC,P
)
27.8 Hz, C(3)), 135.93 (vt, JC,P ) 12.2 Hz, C(7)), 150.44 (vt,
JC,P ) 13.8 Hz, C(1)), 157.45 (vt, JC,P ) 64.6 Hz, C(5)). 31P-
{1H} NMR (CD2Cl2, 121.5 MHz): δ 30.33 (s). Anal. Calcd for
C35H31ClN2P2Pd: C 61.51, H 4.57, P 9.06, Pd 15.57. Found: C
61.40, H 4.68, P 9.42, Pd 15.23.
trans-[PdCl(Me)(2-[bis{4-(bromo)phenyl}phosphino]-
pyridine)2] (15). Starting from 8 (0.52 g, 1.24 mmol) and
[PdCl(Me)(TMEDA)] (168.2 mg, 0.62 mmol) a yellow solid was
obtained as the final product (0.50 g, 0.50 mmol, 81% based
on [PdCl(Me)(TMEDA)]).
1H NMR (CDCl3, 300.1 MHz): δ -0.03 (s, 3 H, Pd-Me), 7.28
(d, JH,H ) 7.2 Hz, 2 H, H-pyridyl), 7.52 (d, JH,H ) 7.5 Hz, 8 H,
H-aryl), 7.67 (m, 10 H, H-aryl + H-pyridyl), 7.96 (d, JH,H
)
6.0 Hz, 2 H, H-pyridyl), 8.74 (s, 2 H, H-pyridyl). 31P{1H} NMR
(CDCl3, 81.0 MHz): δ 29.37 (br s). No good elemental analyses
could be obtained for this compound.
trans-[PdCl(Me)(2-[bis{4-((2-(perfluorohexyl)ethyl)-
dimethylsilyl)phenyl}phosphino]pyridine)2] (16). Start-
ing from 10 (0.30 g, 0.28 mmol) and [PdCl(Me)(TMEDA)] (38.1
mg, 0.14 mmol) a light yellow solid was obtained as the final
product (0.26 g, 0.11 mmol, 81% based on [PdCl(Me)(T-
MEDA)]).
1H NMR (CD2Cl2, 499.8 MHz): δ -0.01 (s, 3 H, Pd-Me), 0.38
(s, 24 H, SiMe2), 1.05 (m, 8 H, SiCH2CH2), 2.09 (m, 8 H,
SiCH2CH2), 7.34 (t, J ) 6.0 Hz, 2 H, H-pyridyl), 7.59 (d, J )
7.5 Hz, 8 H, H-aryl), 7.75 (t, J ) 7.0 Hz, 2 H, H-pyridyl), 7.85
(m, 8 H, H-aryl), 8.04 (br s, 2 H, H-pyridyl), 8.78 (d, J ) 4.0
Hz, 2 H, H-pyridyl). 13C{1H} NMR (CD2Cl2, 125.7 MHz): δ
-3.35 (s, SiMe2), 4.40 (br s, Pd-Me), 5.50 (s, SiCH2CH2), 26.41
For catalysis experiments employing the zerovalent pal-
ladium complex 17 the same procedure as above was followed,
except that now the palladium complex instead of [Pd(OAc)2]
was weighed in the first Schlenk vessel.
2
(t, JC,F ) 23.6 Hz, SiCH2CH2), 108.68-120.90 (several m,
C6F13-tail), 124.51 (s, C(2)), 132.60 (m), 133.63 (vt, JC,P ) 8.6
Hz, C(8)), 135.24 (vt, JC,P ) 11.6 Hz, C(7)), 136.03 (br s), 141.08
For experiments in scCO2 the 50 mL home-built autoclave
was utilized. After charging the autoclave with the reaction
mixture, three vacuum-nitrogen cycles were performed, fol-
lowed by flushing three times with CO (15 bar). The autoclave
was heated to the desired temperature (50 °C) and subse-
quently pressurized with CO (40 bar). Then, CO2 was pumped
into the autoclave using an ISCO DM-100 high-pressure pump
to achieve a total pressure of 150 bar, after which stirring was
initiated by a magnetic stirring bar. During the reaction the
pressure dropped from 150 to 145 bar. After the reaction the
autoclave was cooled to -20 °C and the excess CO and CO2
were carefully vented via a cold trap cooled to -60 °C. Note:
when working with supercritical fluids, the user should never
be directly exposed to the autoclave. The use of suitable
polycarbonate shielding between the autoclave and the user is
therefore strongly recommended.
For the catalytic experiments which were sampled during
the reaction a 100 mL in-house built autoclave was used, using
the same procedures as described earlier for the in situ
prepared catalysts. This autoclave was equipped with a motor-
driven top-stirrer, thermocouples inside the autoclave and
heating mantle, water-cooling of the interior of the autoclave,
a rupture-disk assembly (set at 80 bar), a pressure transducer,
and appropriate control devices for the temperature. Sampling
at regular intervals was achieved via a piece of 1/16 in.
stainless steel tubing inside the autoclave, equipped with a
valve at the end.
(s, C(9)), 150.49 (vt, JC,P ) 13.8 Hz, C(1)), 157.23 (vt, JC,P
)
63.4 Hz, C(5)). 31P{1H} NMR (CD2Cl2, 121.5 MHz): δ 29.79
(s). Anal. Calcd for C75H67ClN2P2PdSi4: C 39.16, H 2.94, P 2.69,
Pd 4.63. Found: C 39.54, H 3.31, P 2.74, Pd 4.30.
General Procedure for the Synthesis of [Pd(2-[bis-
(aryl)phosphino]pyridine)2(cyclo-(-CHdCHC(O)OC(O)-
))] Complexes.32 To a solution of the appropriate phosphine
in acetone was added 0.5 equiv of [Pd(t-BuDAB)(cyclo-(-CHd
CHC(O)OC(O)-))]. The resulting orange solution was stirred
at ambient temperature for 30 min, after which the volume of
the solution was reduced to about 2 mL. Et2O was added, and
the formed precipitate was collected by decantation of the
liquids and drying of the residue in vacuo.
[Pd(2-[diphenylphosphino]pyridine)2(cyclo-(-CHdCH-
C(O)OC(O)-))] (17). Starting from 2 (0.26 g, 0.99 mmol) and
[Pd(t-BuDAB)(cyclo-(-CHdCHC(O)OC(O)-))] (0.14 g, 0.37
mmol) the desired product was isolated as a yellow solid (0.21
g, 0.29 mmol, 76% based on [Pd(t-BuDAB)(cyclo-(-CHdCHC-
(O)OC(O)-))]) after workup as above and washing with
n-pentane.
3
1H NMR (CD2Cl2, 499.8 MHz, -30 °C): δ 4.14 (d, JH,P
)
5.5 Hz, 2 H, CHdCH), 6.92 (d, 3JH,H ) 6.5 Hz, 2 H, H(3)), 7.13
(t, 3JH,H ) 6.0 Hz, 2 H, H(2)), 7.30 (t, 3JH,H ) 6.0 Hz, 8 H, H(8)),
7.37 (m, 12 H, H(7 + 9), 7.47 (t, 3JH,H ) 7.8 Hz, H(4)), 8.49 (d,
3JH,H ) 4.5 Hz, 2 H, H(1)). 13C{1H} NMR (CD2Cl2, 125.7 MHz,
-40 °C): δ 55.05 (m, JC,P ) 21.9 Hz, JC,P ) 21.4 Hz, CHd
CH), 123.22 (s, C(2)), 127.63 (vt, JC,P ) 20.2 Hz, C(3)), 128.35
(m, C(8)), 130.06 (s, C(9)), 130.27 (s, C(9)), 131.75 (m, JC,P
2
2
After every catalytic run the autoclaves were cleaned by
rinsing with aqua regia, water, and acetone, respectively,
followed by drying in vacuo.
)
72.2 Hz, C(6)), 132.85 (m, JC,P ) 72.6 Hz, C(6)), 133.83 (vt,

5310 Organometallics, Vol. 24, No. 22, 2005
de Pater et al.
Supporting Information Available: CIF file of crystal
data collection and refinement parameters, atomic coordinates,
bond lengths and angles, and anisotropic displacement pa-
rameters for 12. This material is available free of charge via
the Internet at http://pubs.acs.org.
Acknowledgment. The authors thank D. S. Tromp
for the gift of [Pd(t-BuDAB)(cyclo-(-CHdCHC(O)OC-
(O)-))] and M. Mittelmeijer for help with the setup of
the autoclave for the sampling experiments. This work
was supported by the Council for Chemical Sciences
from the Dutch Organization for Scientific Research
(CW-NWO).
OM050479+