Palladium(0)-alkene bis(triarylphosphine) complexes as catalyst precursors for the methoxycarbonylation of styrene

Article abstract of DOI:10.1021/om0506419

The fluorous complex [Pd(0)(P{C₆H₄-p-SiMe ₂(CH₂CH₂C₆F₁₃)} ₃)₂(MA)] (MA = maleic anhydride) was synthesized and characterized by its NMR spectra. Together with the nonfluorous complexes [Pd(0)(PPh₃)₂(alkene)] (alkene = C₂H ₄) (NC)₂C=C(CN)₂), NCC(H)= C(H)CN, MA, or benzoquinone) these were evaluated as catalyst precursors in the methoxycarbonylation of styrene. The nonfluorous C₂H₄ and MA complexes gave the highest conversions (the turnover number (TON) was 120; the (average) turnover frequency (TOF) amounted to 80 h^-1). The fluorous complex gave a significantly lower conversion (TON about 38; TOF 26 h^-1) than its nonfluorous counterpart, which is caused by a lower stability of the fluorous complex under the reaction conditions.

Full text of DOI:10.1021/om0506419

Organometallics 2005, 24, 6411-6419
6411
Palladium(0)-Alkene Bis(triarylphosphine) Complexes as
Catalyst Precursors for the Methoxycarbonylation of
Styrene
,#
Jeroen J. M. de Pater,†,§ D. S. Tromp,§ Duncan M. Tooke, Anthony L. Spek,
Berth-Jan Deelman,‡ Gerard van Koten,*,† and Cornelis J. Elsevier*,§
Debye Institute, Organic Synthesis 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 July 27, 2005
The fluorous complex [Pd(0)(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2(MA)] (MA ) maleic
anhydride) was synthesized and characterized by its NMR spectra. Together with the
nonfluorous complexes [Pd(0)(PPh3)2(alkene)] (alkene ) C2H4, (NC)2CdC(CN)2, NCC(H)d
C(H)CN, MA, or benzoquinone) these were evaluated as catalyst precursors in the
methoxycarbonylation of styrene. The nonfluorous C2H4 and MA complexes gave the highest
conversions (the turnover number (TON) was 120; the (average) turnover frequency (TOF)
amounted to 80 h-1). The fluorous complex gave a significantly lower conversion (TON about
38; TOF 26 h-1) than its nonfluorous counterpart, which is caused by a lower stability of
the fluorous complex under the reaction conditions.
Introduction
1,3-butadiene (DAB) and BIAN ligands, have proven to
be successful for the synthesis of a variety of palladium-
(0)-alkene complexes.6-10 Recently, Kluwer et al. re-
ported the synthesis of such complexes having mono-
dentate nitrogen ligands.5 The complexes with diimine
ligands are good catalysts for a number of reactions,
such as the selective hydrogenation of alkynes to Z-
alkenes.8,11
Palladium(0)-alkene complexes with phosphines as
ligands are also well known. Examples include com-
plexes with monophosphines such as [Pd(PPh3)2(alkene)],
in which alkene represents MA, tetracyanoethylene
(TCNE),7 or C2H4,12 [Pd(P{n-Bu}3)2(C2H4)],13 [Pd(1-
(Ph2P)C6H4-2-CHdNR)(alkene)],14 and [Pd(P{CH2Ph}3)2-
(C2H4)]15 as well as complexes with diphosphines such
as [Pd(bis{diphenylphosphino}ethane)(C2H4)],13 [Pd(bis-
{1,3-diisopropylphosphino}propane)(C2H4)],16 and [Pd-
Zerovalent palladium complexes with only alkenes are
well-established nowadays as starting materials in
modern organometallic chemistry. Examples include
homoleptic complexes such as [Pd2(dba)3‚dba],1 [Pd-
(COD)2],2 [Pd(ethene)3],2 and [Pd2(1,6-diene)3]3 and
mixed alkene complexes such as [Pd(1,6-diene)(ethene)],3
[Pd(norbornadiene)(MA)]4 (MA ) maleic anhydride),
and [Pd(COD)(MA)].5 These complexes, especially [Pd2-
(dba)3‚dba], serve as important starting materials for
the synthesis of zerovalent palladium complexes bearing
additional ligands such as phosphines and nitrogen
ligands. Their stability is usually governed by a subtle
interplay between the electron-donating and electron-
withdrawing properties of the ligands and the metal
center. Especially diimine ligands, such as the 1,4-diaza-
* Corresponding authors. (G.V.K.) Phone: +31-30-2533120. Fax:
+31-30-2523615. E-mail: g.vankoten@chem.uu.nl. (C.J.E.) Phone:
+31-20-5255653. Fax: +31-20-5256456. E-mail: else@science.uva.nl.
† Debye Institute, Organic Synthesis and Catalysis.
§ Van’t Hoff Institute for Molecular Sciences, Molecular Inorganic
Chemistry.
(6) Crociani, B.; Di Bianca, F.; Uguagliati, P.; Canovese, L.; Berton,
A. J. Chem. Soc., Dalton Trans. 1991, 71.
(7) Cavell, K. J.; Stufkens, D. J.; Vrieze, K. Inorg. Chim. Acta 1981,
47, 67-76.
(8) van Laren, M. W.; Elsevier, C. J. Angew. Chem., Int. Ed. 1999,
38, 3715.
‡ ARKEMA Vlissingen B.V.
Bijvoet Center for Biomolecular Research, Crystal and Structural
Chemistry.
(9) Klein, R. A.; Witte, P.; van Belzen, R.; Fraanje, J.; Goubitz, K.;
Numan, M.; Schenk, H.; Ernsting, J. M.; Elsevier, C. J. Eur. J. Inorg.
Chem. 1998, 319.
# Corresponding author for crystallographic data. Phone: +31-30-
2532538. Fax: +31-30-2523940. E-mail: a.l.spek@chem.uu.nl.
(1) Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J. J.; Ibers., J. A. J.
Organomet. Chem. 1974, 65, 253.
(10) Milani, B.; Anzilutti, A.; Vicentini, L.; Sessanta o Santi, A.;
Zangrando, E.; Geremia, S.; Mestroni, G. Organometallics 1997 16,
5064.
(2) (a) Green, M.; Howard, J. A. K.; Spencer, J. L.; Stone, F. G. A.
J. Chem. Soc., Chem. Commun. 1975, 449. (b) Green, M.; Howard, J.
A. K.; Spencer, J. L.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1977,
271.
(3) Krause, J.; Cestaric, G.; Haack, K.-J.; Seevogel, K.; Storm, W.;
Po¨rschke, K.-R. J. Am. Chem. Soc. 1999, 121, 9807.
(4) Itoh, K.; Ueda, F.; Hirai, K.; Ishii, Y. Chem. Lett. 1977, 877-
880.
(5) Kluwer, A. M.; Elsevier, C. J.; Bu¨hl, M.; Lutz, M.; Spek, A. L.
Angew. Chem., Int. Ed. 2003, 42, 3501.
(11) Kluwer, A. M.; Koblenz, T. S.; Jorischkeit, T.; Woelk, K.;
Elsevier, C. J. J. Am. Chem. Soc. 2005, 127, 15470.
(12) Visser, A.; van der Linde, R.; de Jongh, R. O. Inorg. Synth. 1976,
16, 127.
(13) Paonessa, R. S.; Prignano, A. L.; Trogler, W. C. Organometallics
1985, 4, 647.
(14) Scrivanti, A.; Matteoli, U.; Beghetto, V.; Antonaroli, S.; Scar-
pelli, R.; Crociani, B. J. Mol. Catal. A: Chem. 2001, 170, 51.
(15) Seligson, A. L.; Cowan, R. L.; Trogler, W. C. Inorg. Chem. 1991,
30, 3371.
10.1021/om0506419 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 11/19/2005

6412 Organometallics, Vol. 24, No. 26, 2005
de Pater et al.
Chart 1. Palladium(0)-Alkene
The complex shows the Y-shaped trigonal-planar
geometry that has also been previously observed for
related complexes such as [palladium(0)(N,N′-diphenyl-
1,7,7-trimethylbicyclo[2.2.1]heptane-2,3-diimine-N,N′)-
(fumaronitrile)]20 and [palladium(II)(Me)2(2-(phenyl-
imino)-3-(2,6-dimethylphenylimino)-1,7,7-trimethyl-
bicyclo-[2.2.1]heptane-2,3-diylidene)].21 The Pd-N (2.153-
(5) Å) and Pd-C distances (2.045(5) Å) are also in
agreement with previously reported values.20 The N(1)-
Pd(1)-N(1)a bite angle of 76.32(12)° is somewhat smaller
than values known in the literature for related com-
plexes (values of 77.2-77.5° are reported20-22). As
expected, upon coordination of the alkene, an elongation
of the CdC bond distance (1.417(6) Å) when compared
with the free ligand (1.249(10) Å)23 and a concomitant
expected shortening of the C-CN bonds (1.435(7) Å)
when compared with the free ligand (1.480(8) Å) are
observed.23 Judging from the C-C-C angles in the
alkene ligand (119.1(5)°), the olefinic carbon atoms are
sp2 hybridized.
Bis(triphenylphosphine) Complexes 1-5a
a Legend: MA ) maleic anhydride; TCNE ) tetracyanoet-
hylene; FN ) fumaronitrile; BQ ) benzoquinone.
(4,5-bis{(diphenylphosphino)methyl}-2,2-dimethyl-1,3-
dioxolane)(C2H4)].17 They have been proposed as inter-
mediates in several catalytic reactions and are some-
times used as catalyst precursors. Well-known examples
of the latter use are the compounds [Pd(0)(P-N)-
(alkene)] (alkene ) fumaronitrile or dimethyl fumarate,
P-N ) 1-(Ph2P)C6H4-2-CHdNR (R ) CMe3 or C6H4-
OMe-4)), which have been used as precursor complexes
in the methoxycarbonylation of alkynes.14
We have recently investigated the use of [Pd(OAc)2-
(PAr3)2] complexes as precursors in the methoxycarbo-
nylation of styrene.18 In these studies one of the
complexes used was the so-called fluorous complex [Pd-
(OAc)2(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2]. One of the
problems with the fluorous complex is its low activity
and long induction period. We were therefore interested
in the development of other palladium phosphine com-
plexes that could give a more direct entry into the
catalytic cycle of the methoxycarbonylation process. A
viable option, we reasoned, would be the use of pal-
ladium(0)-alkene complexes. Here we report on the
synthesis of a number of palladium(0)-alkene complexes
with nonfluorous monodentate phosphines and one
complex with fluorous monodentate phosphines and
their application as catalyst precursors in the methoxy-
carbonylation of styrene.
NMR Studies on Palladium-Alkene Complexes
1, 3, and 5. Complexes 1 and 3 have been characterized
previously by 1H NMR spectroscopy and elemental
analysis, whereas 5 has been characterized only by
elemental analysis. In the present study we also re-
corded their 13C{1H} and 31P{1H} NMR spectra (for full
1
data see Experimental Section) and for 5 also its H
NMR spectrum. For complexes 1 and 3 the region of
the spectra where the alkene 13C resonances were
observed is given in Figure 2 (3 on the left side, 1 on
the right).
It is obvious from Figure 2 that the alkene carbon
region for 1 and 3 shows somewhat different patterns.
For both 1 and 3 the observed patterns are the X-part
of an AA′X system. For 3 simulation of these signals
(Figure 2, bottom left, using the WINDNMR program24)
showed that the observed multiplet structure corre-
sponds to the X part of an AA′X pattern (A ) 31P
nucleus, A′ ) 31P nucleus) with no exchange processes
involved.25 When the 13C{1H} NMR spectrum was
recorded while applying simultaneous 1H- and 31P-
decoupling, this multiplet pattern for the alkene carbon
atoms collapsed to a singlet. This confirms that coupling
of these alkene carbon atoms to phosphorus atoms,
which are at the cis- and trans-position, respectively,
causes the observed pattern. For complex 1 (with MA
as the alkene), a different pattern was observed for the
alkene carbon atoms in its 13C{1H} NMR spectrum
(Figure 2, top right). Simulation of this pattern (Figure
2, bottom right) showed that it is also the X part of an
AA′X pattern, but now with exchange present between
the A and A′ sites.26 Also for this compound application
Results
Synthesis of Palladium(0)-Alkene Complexes. A
number of palladium(0) complexes with different alk-
enes were synthesized (Chart 1). Known complexes 1,
2,7 4,19 and 512 were synthesized according to published
methods in good yields and purity. Known complexes 3
and 6 were prepared using the method depicted in eqs
1 and 2 (Scheme 1),7 which led to increased yields in
comparison with the literature method.6 Crystals suit-
able for single-crystal X-ray structure determination
were obtained from a concentrated solution of complex
6 in acetone. Its structure is given in Figure 1, and
the relevant bond lengths and angles are compiled in
Table 1.
(20) Ellis D. D.; Spek, A. L. Acta Crystallogr. C 2001, 57, 235.
(21) Schleis, T.; Heinemann, J.; Spaniol, T. P.; Mulhaupt, R.; Okuda,
J. Inorg. Chem. Commun. 1998, 1, 431.
(22) Ferrara, M. L.; Giordana, F.; Orabona, I.; Panunzi, A.; Ruffo,
F. Eur. J. Inorg. Chem. 1999, 1939.
(23) Britton, D.; Gleason, W. B. Cryst. Struct. Commun. 1982, 11,
1155.
(24) Reich, H. J. WINDNMR: NMR Spectrum Calculations, version
7.1.6; Department of Chemistry, University of Wisconsin: Madison,
WI, 2002.
(16) Perez, P. J.; Calabrese, J. C.; Bunel, E. E. Organometallics 2001,
20, 337.
(17) Hodgson, M.; Parker, D.; Taylor, R. J.; Ferguson, G. Organo-
metallics 1988, 7, 1761.
(25) The following values were used in the simulation of the alkene
region of 3: JAA′ ) 6.0 Hz, JAX ) -5.9 Hz (cis-phosphine), JA′X ) 36.5
Hz (trans-phosphine), KAA′ ) 0.
(18) de Pater, J. J. M.; Elsevier, C. J.; Deelman, B.-J.; van Koten,
G. Submitted for publication.
(19) Minematsu, H.; Takahashi, S.; Hagihara, N. J. Organomet.
Chem. 1975, 91, 389-398.
(26) For 1 the following values were used in the simulation of the
alkene region: JAA′ ) 11.0 Hz, JAX ) -6.1 Hz (cis-phosphine), JA′X
28.7 Hz (trans-phosphine), KAA′ ) 4.
)

Palladium(0)-Alkene Complexes
Organometallics, Vol. 24, No. 26, 2005 6413
Scheme 1. Synthetic Route for Complex 3a
a Legend: dba ) (1E,4E)-1,5-diphenylpenta-1,4-dien-3-one; t-BuDAB ) 3,6-diaza-2,2,7,7-tetramethyl-octa-3,5-diene.
Table 1. Selected Bond Lengths, Bond Angles, and Torsion Angles for 6a
Bond Lengths (Å)
Pd(1)-N(1)
C(6)-C(6)a
C(6)-C(7)
N(1)-C(5)
2.153(5)
1.417(6)
1.435(7)
1.264(5)
Pd(1)-C(6)
C(5)-C(5)a
N(1)-C(4)
C(7)-N(2)
2.045(5)
1.462(6)
1.486(5)
1.140(7)
Bond Angles (deg)
N(1)-Pd(1)-C(6)
N(1)-Pd(1)-C(6)a
C(6)-Pd(1)-C(6)a
162.06(14)
121.55(14)
40.53(16)
N(1)-Pd(1)-N(1)a
Pd(1)-N(1)-C(4)
C(7)-C(6)-C(6)a
76.38(12)
125.6(2)
119.1(5)
Torsion Angles (deg)
N(1)a-Pd(1)-N(1)-C(4)
C(6)a-Pd(1)-N(1)-C(4)
N(1)a-Pd(1)-C(6)-C(7)
179.0(3)
-1.6(3)
N(1)a-Pd(1)-N(1)-C(5)
C(6)a-Pd(1)-N(1)-C(5)
C(6)a-Pd(1)-C(6)-C(7)
0.5(3)
179.8(3)
113.7(5)
-67.4(4)
a Symmetry operation a ) 1 - x, y, 1/2 - z.
complex. Therefore, the NMR solvents used (toluene-
d8 and CD2Cl2) were first saturated with ethene before
they were added to the complex. The 1H NMR spectrum
of this complex, when measured at ambient tempera-
ture, showed a broad signal due to exchange of free
ethene molecules present in solution with those that are
coordinated to the palladium complex. This exchange
process probably proceeds via an associative exchange
mechanism. When toluene-d8 was used as solvent,
assignment of the signals in the 13C{1H} NMR was
hampered by overlap of the signals from the carbon
atoms of PPh3 and those of toluene. This overlap was
not resolved by cooling of the sample to -40 °C. Lower
temperatures were not possible, because of the viscosity
of the solution, leading to very broad signals. Surpris-
ingly, the 13C signals for the CH2 groups of ethene were
not observed in the 13C{1H} NMR spectrum in this
solvent, neither at ambient temperature nor at lower
temperature down to -40 °C. In its 1H NMR spectrum
at -40 °C, two broad singlets were observed for the CH2
groups of ethene: one at 4.00 ppm and one at 5.30 ppm.
The former corresponds to coordinated ethene, while the
latter corresponds to free ethene in solution. In the 31P-
{1H} NMR spectra a singlet (δ ) 27.47 ppm) was
observed over the entire temperature range studied.
In CD2Cl2, complex 5 was less stable than in toluene-
d8, especially at ambient temperature. At low temper-
ature (-60 °C) again the 1H NMR spectrum showed two
signals corresponding to free and coordinated ethene,
respectively. These signals were still broad though,
indicating that intermolecular exchange is still taking
place at this temperature. In the aromatic region of the
13C{1H} NMR spectrum at -60 °C the signals corre-
sponding to the ipso-C and ortho-C of the PPh3 were
observed as the expected virtual triplets,29 whereas the
other two signals (meta-C and para-C of PPh3) were still
Figure 1. ORTEP plot of 6. Displacement ellipsoids are
drawn at the 50% probability level. Symmetry operation a
) 1 - x, y, 1/2 - z.
of both 1H- and 31P-decoupling resulted in a collapse of
the multiplet signal into a singlet, again showing that
the splitting is caused by coupling to phosphorus atoms
in cis- and trans-positions, respectively. The appearance
of such AA′X patterns has been reported previously for
related platinum complexes such as [Pt(0)(PPh3)2(trans-
{CH(CO2Et)dC(CO2Et)H})]27 and [Pt(0)(PPh3)2(H2Cd
C(CN)H)].28 For both 1 and 3 the signals for the ipso-,
ortho-, and meta-C atoms of PPh3 were observed as
virtual triplets due to virtual coupling.29-31
The instability of complex 5 in solution in the absence
of additional ethene hampered NMR studies on this
(27) Guedes da Silva, M. F. C.; Frau´sto, J. J. R.; Pombeiro, A. J. L.;
Bertani, R.; Michelin, R. A.; Mozzon, M.; Benetollo, F.; Bombieri, G.
Inorg. Chim. Acta 1993, 214, 85.
(28) Asaro, F.; Lenarda, M.; Pellizer, G.; Storaro, L. Spectrochim.
Acta Part A 2000, 56, 2167.
(29) The appearance of these triplets is due to virtual 31P-coupling.
Such a resonance pattern is observed for AA′X spins systems when
JAA′ . (νA - νA′) + (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 the complex [Pt(PPh3)2(trans-CH(CO2Et)dCH(CO2-
Et))]; see ref 27.
(30) For a more extensive review on the appearance of several
splitting patterns observed in [M(PR3)2X2] complexes, see: Verkade,
J. G. Coord. Chem. Rev. 1972/1973, 9, 1.
(31) With 31P-decoupling applied, also all the triplets observed in
the aromatic region collapsed to singlets, proving that the observed
patterns are due to coupling with 31P nuclei.

6414 Organometallics, Vol. 24, No. 26, 2005
de Pater et al.
Figure 2. 13C{1H} NMR (75.5 MHz) spectra, alkene region, for 3 (left) and 1 (right). Observed spectra at the top, calculated
spectra at the bottom.
Scheme 2. Synthesis of Complex 7, Starting from [Pd(0)(t-Bu-DAB)(MA)]
Scheme 3. Synthetic Route for Complex 7, Starting from [Pd(0)(MA)(norbornadiene)]
observed as singlets. The signals for ethene, either for
free or coordinated ethene, were not observed even at
this low temperature in the 13C{1H} NMR spectrum.
Decreasing the temperature beyond -60 °C was not
possible, because the complex precipitated from the
solution upon further cooling. Its 31P{1H} NMR spec-
trum showed in the whole temperature range two
signals: a large broad singlet at 26.95 ppm (which
sharpened at low temperatures), ascribed to complex
5,32 and a minor singlet at 33.85 ppm. The latter signal
could correspond to a zerovalent palladium complex
with three (or four) phosphines, formed from the reac-
tion of complex 5 with free PPh3, which is present
because complex 5 had partly decomposed.
yield of the complex resulted. The second method cleanly
removed the free t-BuDAB from the complex, but at the
same time induced appreciable decomposition of the
palladium complex, resulting in a low yield of the
desired complex.
Because of these problems, the route recently devel-
oped by Kluwer et al.,5 which allowed for the synthesis
of zerovalent palladium alkene complexes with mono-
dentate nitrogen ligands, was used to obtain pure 7 in
higher yields (eq 4, Scheme 3). Using this method, very
pure 7 was obtained in an acceptable yield indeed. Its
1H, 13C{1H}, and 31P{1H} NMR spectra showed the
expected signals for this compound, as well as those for
the perfluoroalkyl chain in its 13C{1H} and 19F NMR
spectra. Furthermore, because of the presence of the
fluorous phosphines in complex 7, it also shows ap-
preciably solubility (more than 20 mg/mL) in apolar
solvents such as n-hexane and Et2O.
The synthesis of [Pd(0)(P{C6H4-p-SiMe2(CH2CH2-
C6F13)}3)2(C2H4)] (8) was attempted following the same
synthetic procedure as that for 5.12 Although the
complex seemed to form, as judged by color changes of
the reaction mixture, isolation of the compound ap-
peared to be impossible. Precipitation by addition of
Et2O to the reaction mixture did not work, and neither
did the use of several other solvents. Rapid formation
of palladium black was observed once ethene was
removed. Further efforts to prepare this compound were
therefore abandoned.
Synthesis of Fluorous Pd(0)-Alkene Complexes.
After having tested the complexes 1-5 in the methoxy-
carbonylation of styrene (vide infra) we decided to
synthesize only the fluorous versions of the most active
complexes, i.e., the complexes with MA and ethene as
the alkene. The synthesis of [Pd(0)(P{C6H4-p-SiMe2(CH2-
CH2C6F13)}3)2(MA)] (7) was first attempted using the
same route as has been used for complex 1 (Scheme 2).
Although formation of the desired complex was ob-
served, as was evident from 31P{1H} and 1H NMR
spectra of the crude product after the same workup as
1
for 1, its H NMR spectrum also showed the presence
of free t-BuDAB. Because of similar solubilities of
t-BuDAB and palladium complex 7 in the washing
solvent (Et2O), its removal was not possible. Several
other methods, i.e., extraction with methanol and n-
pentane at both ambient and low temperatures as well
as removal of the t-BuDAB by sublimation, were tried.
The first method gave some improvement in purity after
several extractions (ca. 10% free t-BuDAB was left).
However, because of the appreciable solubility of 7 in
these solvents, even at low temperatures, a very low
Catalysis. The compounds 1-5 were tested as pre-
cursors in the catalytic methoxycarbonylation of styrene
(Scheme 4). To allow for comparison with our data on
the use of [Pd(OAc)2(PPh3)2] as the catalyst precursor,18
the same reaction conditions (such as palladium con-
centration, Pd:styrene, Pd:acid, and Pd:H2O ratios) were
applied in the present study with the palladium(0)
precursors. The data for 1-5 and [Pd(OAc)2(PPh3)2] are
presented in Table 2.
(32) In toluene-d8 the 31P NMR spectrum of 5 showed one singlet
at 27.47 ppm.

Palladium(0)-Alkene Complexes
Organometallics, Vol. 24, No. 26, 2005 6415
Table 3. Results for Methoxycarbonylation of
Scheme 4. General Reaction Scheme for
Methoxycarbonylation of Styrene
Styrene with 1, 5, and [Pd(OAc)2(PPh3)2] at 60 °Ca
entry
complex
conversion (%)
i:n
1
2
3
1
5
54
63
45
62:38
63:37
65:35
[Pd(OAc)2(PPh3)2]b
a General conditions: [Pd] ) 2 µmol/mL, Pd:styrene:HO3SC6H4-
p-Me (p-tsaH):H2O ) 1:150:30:600, solvent ) MeOH/R,R′,R′′-
trifluoro toluene, 1:1 (v/v), reaction time ) 90 min, 30 bar CO.
b Data taken from ref 18.
Table 2. Results for Methoxycarbonylation of
Styrene with 1-5 and [Pd(OAc)2(PPh3)2]a
when they were dissolved in the reaction medium
comprising MeOH/R,R′,R′′-trifluorotoluene, p-toluene-
sulfonic acid, water, and styrene. Whereas for complexes
1 and 5 the color of the solution immediately turned
orange-red, for 3 the solution became only slightly
orange colored. For precursors 2 and 4 the solution
stayed light yellow. This could indicate that from the
different complexes different intermediates are formed
in varying concentrations.
entry
complex
conversion (%)
i:n
1
2
3
4
5
6
1
2
3
4
5
80
2
41:59
42:58
40:60
41:59
41:59
40:60
40
27
80
>95
[Pd(OAc)2(PPh3)2]b
a General conditions: [Pd] ) 2 µmol/mL, Pd:styrene:HO3SC6H4-
p-Me (p-tsaH):H2O ) 1:150:30:600, solvent ) MeOH/R,R′,R′′-
trifluorotoluene, 1:1 (v/v), reaction time ) 90 min, T ) 80 °C, 30
bar CO. b Data taken from ref 18.
To see if a palladium-hydride species is indeed
formed, we conducted a NMR experiment. A solution
of p-toluenesulfonic acid (3 equiv with respect to pal-
ladium) in MeOH-d4 was added to complex 5. The initial
gray suspension became a clear dark red solution in
Scheme 5. Formation of a Palladium(II)-Hydride
Species from a Palladium(0) Alkene Complex
1
about 1 min. After transfer to a NMR tube a H NMR
spectrum (at 500 MHz, ambient temperature) was
recorded, showing the presence of a broad doublet
centered at -6.88 ppm (2J(1H-31P) ) 175 Hz). This
indicates that a palladium-hydride complex is formed
with a cis bis-phosphine configuration.30,37 In its 31P-
{1H} NMR spectrum a broad singlet at 28.43 ppm was
visible. When a 1H{31P} NMR spectrum was measured,
Several observations can be made. The first one is
that the conversion after 90 min is dependent on the
nature of the alkene in the precursor and increases in
the order TCNE < BQ < FN < MA, C2H4 < [Pd(OAc)2-
(PPh3)2]. With [Pd(OAc)2(PPh3)2] as precursor the high-
est conversion is obtained, while the results with either
complex 1 or 5 as precursor compare quite favorably
with the results obtained with the palladium(II) precur-
sor. Apparently the i:n ratio is the same (within
experimental error) for every complex used and inde-
pendent of the nature of palladium starting precursor.
This provides evidence that probably in all cases the
same catalytic species is generated and present as the
active species in solution. Although conclusive evidence
is not available yet, a viable species that could be the
starting point for catalysis is the palladium(II) hydride
compound [Pd(H)(O3SC6H4-p-Me)(PPh3)2]. Such a spe-
cies has been proposed by others to be the actual
precatalyst for this reaction33 and is formed from the
palladium(0) complexes via the reaction of the added
acid with the palladium(0) complex (Scheme 5).34-36
It is interesting to note that differences in color
between the different catalyst precursors were observed
1
the broad doublet in the H NMR spectrum collapsed
to one broad singlet centered at -6.89 ppm.
For complexes 1 and 5 we observed that, after ca. 70
min reaction time, extensive decomposition of the
catalyst to palladium black took place. Hence, we also
performed catalysis with these two complexes at 60 °C
instead of 80 °C, under otherwise identical conditions.
Performing catalysis at a lower temperature would
hopefully lead to less decomposition of the palladium
complex and might also have a beneficial effect on the
i:n ratio, as has already been shown previously.38,39 For
comparison we also used the catalyst precursor [Pd-
(OAc)2(PPh3)2] at 60 °C. The results of the experiments
are given in Table 3.
For all three complexes we see that the conversion is
significantly decreased at this lower temperature. The
two zerovalent palladium complexes, however, show a
smaller decrease in activity when compared with [Pd-
(OAc)2(PPh3)2] (ca. 20-25% decrease for 1 and 5 vs 55%
decrease in conversion for [Pd(OAc)2(PPh3)2]. Further-
more, upon opening the autoclave after reaction the
presence of palladium black was not observed. This
indicates that at these lower temperatures the catalyst
is much more stable.40 The i:n ratio in all three experi-
(33) Seayad, A.; Jayasree, S.; Damodaran, K.; Toniolo, L.; Chaudahri,
R. V. J. Organomet. Chem. 2000, 601, 100.
(34) The formation of hydrido-palladium complexes from the reaction
of palladium(0) complexes with an acid can be regarded either as the
protonation of the basic palladium(0) (when strong acids are used such
as HBF4 and HO3SC6H4-p-Me) or as an oxidative addition (when weak
acids are used). In the former reaction the formed palladium complex
can be considered as either Pd(0) ligated by a proton or Pd(II) ligated
by a hydride. Since the Pd-H signal is observed at very negative ppm
values, indicative of a palladium-hydride, this first reaction is therefore
usually also considered as an oxidative addition reaction. See: Ama-
tore, C.; Jutand, A.; Meyer, G.; Carelli, I.; Chiarotto, I. Eur. J. Inorg.
Chem. 2000, 1855, and references therein.
(37) For values of 1H NMR shifts for the palladium-hydride reso-
nance, see: (a) Reference 34. (b) Reference 36. (c) Perez, P. J.;
Calabrese, J. C.; Bunel, E. E. Organometallics 2001, 20, 337.
(38) Girones, J.; Duran, J.; Polo, A.; Real, J. J. Mol. Catal. A: Chem.
2002, 1.
(39) Seayad, A.; Kelkar, A. A.; Chaudhari, R. V.; Toniolo, L. Ind.
Eng. Chem. Res. 1998, 37, 2180.
(40) The orange-red solution collected from the autoclave quickly
turned dark-red/brown and gave palladium black deposition when
exposed to air for a few minutes.
(35) Oxidative addition of acids to palladium(0) alkene complexes
has been reported earlier in the literature, see refs 15 and 17.
(36) For a review on several methods of synthesizing palladium-
hydride complexes as well as their reactions, see: Grushin, V. V. Chem.
Rev. 1996, 96, 2011, and references therein.

6416 Organometallics, Vol. 24, No. 26, 2005
Table 4. Results for Methoxycarbonylation of Styrene with 7 and
de Pater et al.
[Pd(OAc)2(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2] as the Precursor Complexesa
entry
complex
time (min)
conversion (%)
i:n
1
2
3
4
5
6
7
8
7
7
7
7
60
120
180
180
60
120
180
180
25
42
45
17b
17
45
68
20b
53:47
53:47
51:49
72:28
54:46
53:47
53:47
70:30
[Pd(OAc)2(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2]c
[Pd(OAc)2(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2]c
[Pd(OAc)2(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2]c
[Pd(OAc)2(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2]c
a General conditions: [Pd] ) 2 µmol/mL, Pd:styrene:HO3SC6H4-p-Me (p-tsaH):H2O ) 1:150:30:600, solvent ) MeOH/trifluoro toluene,
1:1 (v/v), 30 bar CO, T ) 80 °C. b At 60 °C. c Data taken from ref 18.
ments is different from those obtained in the experi-
ments at 80 °C and displays a slightly higher selectivity
toward the branched (i) product.
The new fluorous complex 7 was also tested as a
possible precursor complex for the methoxycarbonyla-
tion of styrene, using the same conditions as described
above. For comparison reasons results obtained previ-
ously with the complex [Pd(OAc)2(P{C6H4-p-SiMe2-
(CH2CH2C6F13)}3)2] are also given in Table 4.
Discussion
The 13C{1H} NMR data of the different palladium-
(0)-alkene complexes show distinct differences. For both
1 and 3 the patterns observed for the signals of the
alkene carbon atoms correspond to the X part of an AA′X
pattern, as was shown by simulations. The two patterns
differed, however, from each other. From the observed
13C{1H} NMR data of complex 3 and the simulation
thereof we can conclude that no interconversion process
is occurring. Since both dCH carbon atoms experience
coupling to a cis- and a trans-phosphorus atoms, we
observe their signal as the X part of an AA′X pattern,
which in the absence of exchange processes gave the
pattern as observed in the left side of Figure 2. For
complex 1, with maleic anhydride as the alkene, we
have shown by simulation of the alkene part of the 13C-
{1H} NMR spectrum that this is the X part of an AA′X
pattern with an exchange process present. With the
current data, however, we cannot say which process is
occurring.41 The exchange process leads to the observa-
tion of a more complicated multiplet pattern (right side
of Figure 2).
This difference between complexes 1 and 3 is remark-
able, since in the literature is has been reported that
fumaronitrile and maleic anhydride have similar electron-
withdrawing abilities, so that their coordinating strength
is also the same.22,42,43 We would therefore expect
similar resonance patterns for the alkene carbon atoms
in their 13C{1H} NMR spectra. A reason could be that
for maleic anhydride, which is a cis-alkene, rotation of
the alkene around the palladium(CdC) bond is easier
than for fumaronitrile (a trans-alkene). It has been
reported by several researchers that rotation of the
alkene around the metal(CdC) bond depends among
others on the steric bulk at the metal center.41a,c,d It has
been shown that in certain cases only the complexes
having a cis-alkene in their coordination sphere show
rotational behavior of the alkene around the metal(Cd
It is obvious that although 7 can be used as a
precursor for this catalytic reaction, the activity ob-
tained was quite low, especially compared to the conver-
sions obtained with complexes 1 and 5. When we
compare the data acquired for 7 with the results
obtained for the complex [Pd(OAc)2(P{C6H4-p-SiMe2(CH2-
CH2C6F13)}3)2],18 in the first hour with complex 7 a
higher conversion is obtained as compared to [Pd(OAc)2-
(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2]. After 2 h reaction
time conversion and selectivity are the same for both
complexes. Complex 7, however, only shows a marginal
increase in conversion (from 42 to 45%) after 3 h of
reaction when compared with the fluorous palladium
acetate complex (68% conversion after 180 min) at 80
°C. The selectivity for both complexes was the same
within margin of error. This lower activity with 7 after
more than 2 h reaction time is probably caused by
extensive catalyst decomposition, which is also evident
when the reaction mixture was visually inspected dur-
ing catalysis. The initial orange-red solution present
gradually lost its color during the progress of the
reaction and the formation of palladium black was
observed. When the autoclave contents were collected
afterward, likewise a large amount of palladium black
was present. Although this was also observed for the
catalysts with PPh3 as ligand, decoloration of the
reaction medium and deposition of palladium black was
only observed at the late stages of the reaction (after
ca. 70 min). This means that the catalyst with the
fluorous phosphines is less stable than the catalyst with
PPh3 under these conditions.
(41) In the literature several exchange processes for such complexes
have been reported. One route is the dissociation/reassociation route,
whereby the alkene dissociates from the metal center and then
reassociates again; see ref 22. The other route is the rotation of the
alkene around the palladium(CdC) bond. For some examples in the
literature, see: (a) Go´mez-de la Torre, F.; Jalo´n, F. A.; Lo´pez-Agenjo,
A.; Manzano, B. R.; Rodr´ıguez, A.; Sturm, T.; Wassensteiner, 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. (d) Albright, T. A.; Hoffmann, R.; Thibeault, J. C.; Thorn, D. L.
J. Am. Chem. Soc. 1979, 101, 3801.
When catalysis with 7 was performed at 60 °C instead
of 80 °C, some conversion was observed (entry 4 in Table
4), but this was low when compared to 1 and 5. The
catalyst, however, appeared to be more stable at this
lower temperature: no decoloration of the reaction
medium was observed and no palladium black formation
was initially present when the autoclave was opened
afterward.40 When the reaction was performed at 60 °C,
both 7 and [Pd(OAc)2(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2]
had almost the same activity and selectivity after 180
min reaction time.
(42) Canovese, L.; Visentin, F.; Uguagliati, P.; Crociani, B. J. Chem.
Soc., Dalton Trans. 1996, 1921.
(43) Ito, Ts.; Hasegawa, S.; Takahashi, Y.; Ishii, Y. J. Organomet.
Chem. 1974, 73, 401.

Palladium(0)-Alkene Complexes
Organometallics, Vol. 24, No. 26, 2005 6417
Scheme 6. Catalytic Cycle for
Methoxycarbonylation of Styrene Using a
[Pd(0)(PAr3)2(alkene)] Complex as the Precursora
C) bond. This could very well apply here as well, but
further investigations would be necessary in order to
be certain.
1
In the H NMR spectrum (at ambient temperature)
of the palladium ethene complex 5 we observed broad
singlets for the alkene signal as well as for the signals
of the PPh3 groups. This is caused by the intermolecular
exchange between free ethene in solution and coordi-
nated ethene on the palladium center, as has been
previously observed for the complex [Pd(diop)(ethene)].17
At low temperature the exchange broadened signal in
the 1H NMR spectrum is split up into separate signals
for free and coordinated ethene. These signals are still
broad singlets at -60 °C, showing that the exchange
proces is rapid, even at such a low temperature. This
was further corroborated by the observation that at
ambient temperature as well as at -60 °C no signal for
the alkene carbon atoms could be detected in the 13C-
{1H} NMR spectrum.
The reaction of 5 with p-toluenesulfonic acid under
controlled conditions has shown that a palladium-
hydride complex is indeed formed and that its formation
is rapid. We can assume that for the different complexes
such a palladium-hydride species is also formed when
the catalyst precursor is dissolved in the reaction
medium (which contains among others p-toluenesulfonic
acid). The data from Table 2 show, however, that there
is a big influence of the alkene present in the precursor
complex on the observed activity of the catalyst. The
complexes with the alkene that is relatively weakly
bonded (ethene) show the highest activity, whereas the
complex with a strongly binding alkene (TCNE) showed
almost no activity. The other alkenes fall nicely between
these two extremes. Maleic anhydride is an exception
here, since it gave the same activity as the ethene
complex, although it is reported to have the same
coordination strength as fumaronitrile. These observa-
tions suggest that the presence of different alkenes
influences the rate-determining step (or the preceding
step) of the reaction.
What exactly the rate-determining step is we cannot
say. There are, however, several likely possibilities. The
first one is that when the palladium(0)-alkene com-
plexes are used, the rate-determining step is the forma-
tion of the palladium-hydride complex, which is the
actual active species. When a strongly coordinated
alkene is present, the formation of a [PdL2] species (by
dissociation of the alkene), which is supposed to react
with the acid in a next step to give the palladium(II)-
hydride complex, is hindered. In this way, only a varying
amount of precatalyst is converted into an active species,
depending on the alkene palladium bonding, leading for
the stronger binding alkenes to the low conversion
observed. This does not explain, however, why complex
1 gave such a high activity, while complex 3 gave a
much lower activity, despite that maleic anhydride and
fumaronitrile have a similar coordinating strength.
The second reason could be that in all cases the active
species is formed quickly, regardless of which precata-
lyst is used, but the alkene released competes with
styrene for coordination to the palladium center in the
rate-determining step of the catalytic cycle itself. For
alkenes that have a higher coordinating strength, we
would then expect a lower conversion (in the same
reaction time). Although such a trend is clearly visible
a Legend: L ) MeOH or CO.
from the current data, again maleic anhydride does not
show the behavior that we would expect based on coor-
dinating strength only. More detailed investigations into
the behavior of the complexes, and especially that of
complex 1, are necessary to obtain a full understanding.
When we compare the results for the palladium(0)-
alkene complexes with those for [Pd(OAc)2(PPh3)2] as
the precursor, we see that the best palladium(0)-alkene
complexes (1 and 5) compare quite favorably with this
complex, in terms of both activity and selectivity. We
can presume therefore that for the palladium(0)-alkene
complexes the same catalytic cycle as proposed for [Pd-
(OAc)2(PPh3)2] is operational (Scheme 6).33
Fluorous precursor palladium(0) complex 7 gave a
lower conversion when compared with its nonfluorous
analogue 1. A similar effect was already observed in a
previous study, where we compared the complexes [Pd-
(OAc)2(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2] and [Pd-
(OAc)2(PPh3)2].18 Apparently, the introduction of fluo-
rous phosphines into catalysts for the methoxycar-
bonylation of styrene has a negative effect on the
activity. However, for 7 a slightly higher selectivity
toward the branched product was observed when com-
pared with 1, which is again in line with the observa-
tions made when the complexes [Pd(OAc)2(PAr3)2] were
used as catalyst precursors.
Between palladium(0) complex 7 and [Pd(OAc)2-
(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2] as the catalyst pre-
cursor differences were also observed. During the first
2 h of catalysis there is no difference between the use
of 7 and [Pd(OAc)2(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2],
but after that time period 7 gave almost no further
activity, whereas with [Pd(OAc)2(P{C6H4-p-SiMe2(CH2-
CH2C6F13)}3)2] still appreciable activity was observed
until about 3 h reaction time. For the palladium(II)
complex we have already shown that there is an
equilibrium between [Pd(OAc)2(P{C6H4-p-SiMe2(CH2-
CH2C6F13)}3)2] and the dimeric complex [Pd(OAc)2-
(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)]2 and free phosphine
in solution. This dimeric complex is slowly converted
into active species during the reaction time. This makes
sure that fresh catalyst is present in solution, also after

6418 Organometallics, Vol. 24, No. 26, 2005
de Pater et al.
otherwise. Chemical shifts are referenced internally against
residual solvent signal (1H, 13C) or externally against CFCl3
(19F) or 85% H3PO4 (31P). Abbreviations used: s ) singlet, d )
doublet, t ) triplet, vt ) virtual triplet, m ) multiplet. GC
analyses were performed on a Varian 3300 gas chromatograph
equipped with a 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.
Elemental analyses were carried out by H. Kolbe Mikroana-
lytisch Laboratorium, Mu¨llheim an der Ruhr.
Autoclaves. Two autoclaves were employed for all catalytic
reactions. One was a normal Hastelloy autoclave with a
volume of 100 mL. Stirring was achieved with a magnetic
stirring bar, and heating was accomplished with a heating
mantle. To exclude contamination with metallic palladium or
other residues from the inner wall, a glass insert was employed
in all reactions. The second autoclave was a home-built
stainless steel (Hastelloy) autoclave with a volume of 50 mL.45
It is equipped with a pressure transducer (Kulite), thermo-
couples in the wall and interior of the autoclave, four heating
rods drilled into the mantle, a rupture disk assembly (set at
250 bar), an injection port, and two borosilicate (Maxos 200)
windows to allow visual inspection of the contents. The
temperature was controlled for both autoclaves to be (2 °C of
the desired reaction temperature.
2 h of catalysis. For 7 such an equilibrium reaction is
not present; here the catalyst precursor is converted
straightaway into catalytically active species. We can
therefore assume, also because we observe extensive
formation of palladium black with 7 as the precursor,
that after 2 h most of the catalyst is destroyed.
Conclusions
A series of zerovalent palladium(0)-alkene bis(triph-
enylphosphine) complexes was synthesized and char-
acterized. In the 13C{1H} NMR spectra of the complexes
it was observed that the alkene carbon signals of
coordinated fumaronitrile and maleic anhydride show
different patterns. The complexes were tested as cata-
lyst precursors for the methoxycarbonylation of styrene
at 80 °C, from which the following ranking in activity
was observed: ethene ≈ maleic acid anhydride >
fumaronitrile > benzoquinone > tetracyanoethylene.
Catalysis at lower temperatures gave a moderate drop
in conversion, but a higher selectivity toward the
1
branched product. H NMR experiments with the pal-
ladium-ethene complex showed that the starting alkene
complex reacts with p-toluenesulfonic acid to give a
palladium-hydride complex. The complex [Pd(0)(P{C6H4-
p-SiMe2(CH2CH2C6F13)}3)2(maleic anhydride)] was also
synthesized, characterized, and tested as a catalyst
precursor for this reaction. It was found to be less active
than its nonfluorous counterpart and to rapidly decom-
pose to palladium black under reaction conditions (80
°C). This decomposition could be prevented by lowering
the reaction temperature, which also has a beneficial
effect on selectivity toward the branched product.
The results presented here show that palladium(0)-
alkene complexes are viable precursors for the meth-
oxycarbonylation of styrene and that the fluorous
derivatives could be successfully synthesized and ap-
plied as precursors as well. Before application in FBS
is feasible, issues concerning catalyst stability under
reaction conditions and recycling should be further
investigated. Also, further investigations on the catalytic
cycle are worthwhile, for instance by examining the
kinetics, order in styrene, and the influence of alkene
released from the precursor complex.
[Palladium(0)(PPh3)2(maleic anhydride)] (1). Following
the procedure as described by Vrieze et al.,7 the title compound
was prepared from [Pd(0)(t-BuDAB)(MA)] 1 (0.71 g, 1.90 mmol)
and triphenylphosphine (1.30 g, 4.94 mmol) and obtained as
a yellow-green solid (0.96 g, 1.90 mmol, 100% based on [Pd(0)-
(t-BuDAB)(MA)]). 1H NMR data were in accordance with those
reported.
2
13C{1H} NMR (CD2Cl2, 75.5 MHz): δ 56.2 (m, JC,P ) 20.2
2
Hz (t), JC,P ) 22.7 MHz (d), CH of MA), 128.8 (vt, JC,P ) 9.4
Hz, m-C PPh3), 130.0 (s, p-C PPh3), 132.3 (vt, JC,P ) Hz, ipso-C
PPh3), 134.1 (vt, JC,P ) 14.2 Hz, o-C PPh3), 170.5 (s, CdO of
MA). 31P{1H} NMR (CD2Cl2, 121.5 MHz): δ 27.37 (s).
[Palladium(0)(PPh3)2(tetracyanoethylene)] (2). Follow-
ing the experimental procedure as described by Vrieze et al.,7
the title compound was synthesized from [Pd(0)(t-BuDAB)-
(TCNE)] (0.72 g, 1.79 mmol) and triphenylphosphine (1.22 g,
4.65 mmol) and isolated as a green solid (1.36 g, 1.79 mmol,
100% based on [Pd(0)(t-BuDAB)(TCNE)]). 1H NMR data were
in accordance with those reported.
2
13C{1H} NMR (CDCl3, 75.5 MHz): δ 26.11 (vt, JC,P ) 22.5
3
Hz, CdC TCNE), 113.79 (vt, JC,P ) 3.7 Hz, CN), 129.39 (vt,
JC,P ) 10.8 Hz, m-C PPh3), 131.56 (s, p-C PPh3), 134.08 (vt,
JC,P ) 12.8 Hz, o-C PPh3). The signal for ipso-C of PPh3 was
not observed. 31P{1H} NMR (CDCl3, 121.5 MHz): δ 23.86 (s).
[Palladium(0)(PPh3)2(fumaronitrile)] (3). A procedure
similar to the one used for 1 and 2 was used.7 To a solution of
6 (1.73 mmol) in a Schlenk vessel in dry acetone (20 mL) was
added triphenylphosphine (1.20 g, 4.50 mmol). After stirring
for 2 h the reaction mixture was filtered on Celite and
evaporated to dryness to give an off-white solid in quantitative
yield (1.23 g, 1.73 mmol, 100% based on 6). 1H NMR data were
in accordance with previously reported values.
Experimental Section
General Procedures. All experimental work was carried
out in Schlenk type vessels under a N2 atmosphere unless
stated otherwise. Diethyl ether, n-pentane, n-hexane, THF,
and toluene were dried and distilled from sodium. Acetone was
distilled from B2O3. MeOH was distilled from Mg(OMe)2.
R,R′,R′′-Trifluorotoluene was degassed via freeze-pump-
thaw cycles (3 times) and stored on molecular sieves. [Pd2-
(dba)3‚dba],1 [Pd(PPh3)2(MA)],7 [Pd(PPh3)2(TCNE)],7 [Pd-
(PPh3)2(BQ)],19 [Pd(PPh3)2(C2H4)],12 and P{C6H4-p-SiMe2(CH2-
2
13C{1H} NMR (CD2Cl2, 75.5 MHz): δ 34.6 (dd, JC,P ) 6.6
2
44
Hz, JC,P ) 36.8 Hz, CH(CN)), δ 121.6 (t, CH(CN)), 128.8 (m,
CH2C6F13)}3 were synthesized as reported. PPh3, [AlEt2-
C-aryl PPh3), 130.3 (s, p-C PPh3), 134.0 (m, C-aryl PPh3). 31P-
{1H} NMR (CD2Cl2, 121.5 MHz): δ 27.04 (s).
(OEt)]2 (Aldrich), n-decane, p-toluenesulfonic acid monohy-
drate (Acros), and [Pd(acetylacetonato)2] (Strem) were used as
received. Styrene (Acros) was purified by flash chromatography
(neutral Alumina, Fluka) prior to use. C2H4 (Praxair, grade
4.0) and CO (Praxair, >99.9%) were used as received. CDCl3,
CD2Cl2, C6D6, and toluene-d8 (Cambridge Isotope Laboratories)
[Palladium(0)(PPh3)2(p-benzoquinone)] (4). A proce-
dure for related complexes was used.19 To a suspension of
tetrakistriphenylphosphinepalladium(0) (120 mg, 0.10 mmol)
in dry benzene (1 mL) was added a solution of benzoquinone
(10.8 mg, 0.13 mmol) in dry benzene (0.4 mL). The reaction
mixture was stirred for 30 min. The clear solution was
concentrated to 0.2 mL, and a mixture of ether/hexane (2:1)
was added to obtain a red to orange solid in quantitative yield
(76.9 mg, 0.10 mmol, 100% based on [Pd(PPh3)4]).
1
were degassed and stored on molecular sieves under N2. H,
13C{1H}, 19F, and 31P{1H} NMR spectra were recorded on a
300 MHz Varian Mercury-VxWorks, a Varian-INOVA 500, and
a Bruker DRX300 at ambient temperature unless stated
(44) Richter, B.; de Wolf, A. C. A.; van Koten, G.; Deelman, B.-J. J.
Org. Chem. 2000, 65, 3885.
(45) For a detailed description see: ref 11, Chapter 2.

Palladium(0)-Alkene Complexes
Organometallics, Vol. 24, No. 26, 2005 6419
3
2
1H NMR (C6D6, 300.1 MHz): δ 5.39 (d, JH,P ) 6.6 Hz, 4H,
BQ), 6.94 (m, 18H, H-aryl PPh3), 7.35 (m, 12H, H-aryl PPh3).
13C{1H} NMR (C6D6, 75.5 MHz): δ 104.81 (vt, 3JC,P ) 1.5 Hz,
CH BQ), 128.43 (vt, JC,P ) 9.4 Hz, m-C PPh3), 130.02 (s, p-C
PPh3), 133.99 (vt, JC,P ) 14.4 Hz, o-C PPh3), 185.89 (s, CdO
BQ). 31P{1H} NMR (C6D6, 121.5 MHz): δ 30.64 (s).
(0.0328P)2 + 5.2766P] where P ) (Fo + 2Fc2)/3. Residual
electron density: between -1.19 and 0.72 e/Å3. The drawings,
structure calculations, and checking for higher symmetry were
performed with the program Platon.52
[Palladium(0)(P{C6H4-p-SiMe2(CH2CH2C6F13)}3)2-
(maleic anhydride)] (7). In a Schlenk vessel was weighed
P{C6H4-p-SiMe2(CH2CH2C6F13)}3 (0.89 g, 0.60 mmol), which
was subsequently dissolved in THF (10 mL). [Palladium(0)-
(maleic anhydride)(norbornadiene)] (89.4 mg, 0.30 mmol) was
added, and the resulting yellow solution was stirred for 30 min
at ambient temperature. The solution was filtered through
Celite to remove metallic palladium, and the filter cake was
washed with THF (2 × 5 mL). The combined organic layers
were evaporated to dryness. The remaining yellow oil was
washed with n-pentane at -40 °C (3 times). The final product
was obtained as a light yellow solid (0.51 g, 0.16 mmol, 54%
based on [palladium(0)(maleic anhydride)(norbornadiene)]).
1H NMR (300.1 MHz, CD2Cl2): δ 0.33 (s, 36H, SiMe2), 0.98
[Palladium(0)(PPh3)2(ethene)] (5). Following the proce-
dure as described by de Jongh et al.12 the title compound was
synthesized from [Pd(acetylacetonate)2] (1.00 g, 3.28 mmol),
triphenylphosphine (1.72 g, 6.56 mmol), and [Al(Et)2(OEt)]2
(4.8 mL, 6.50 mmol) and isolated as a light gray solid (0.78 g,
1.18 mmol, 36% based on [Pd(acetylacetonate)2]). Because of
the high instability of the complex in solution when no
additional ethene is present, NMR spectra were recorded in
ethene-saturated toluene-d8 and CD2Cl2.
1H NMR (toluene-d8, 300.1 MHz): δ 4.09 (br s, CH2 of
ethene), 7.17 (m, 18H, PPh3), 7.65 (br s, 12H, PPh3). 13C{1H}
NMR (CD2Cl2, 75.5 MHz, -60 °C): δ 127.84 (s, C-aryl PPh3),
128.62 (s, C-aryl PPh3), 133.27 (vt, JC,P ) 15.0 Hz, o-C PPh3),
137.20 (vt, JC,P ) 27.4 Hz, ipso-C PPh3). The signal for CH2 of
ethene was not observed. 31P{1H} NMR (toluene-d8, 121.5
MHz, -40 °C): δ 27.47 (s).
[Palladium(0)(tert-butylDAB)(fumaronitrile)] (6). A
procedure similar to the one used for 1 and 2 was used.7 To a
solution of [Pd2(dba)3‚dba] (2.94 mmol) and tert-butylDAB (6.45
mmol) in a Schlenk vessel in dry acetone (20 mL) was added
fumaronitrile (0.50 g, 6.45 mmol). After stirring overnight at
room temperature, the reaction mixture was filtered over
Celite and evaporated to dryness. The resulting yellow solid
was washed with n-pentane and dried under vacuum to give
a yellow solid (1.74 g, 4.94 mmol, 84% yield based on [Pd2-
(dba)3‚dba]). Crystals suitable for single-crystal X-ray deter-
mination were obtained by slow evaporation of the solvent from
a solution of the complex in acetone. Its 1H NMR data were in
accordance with those reported earlier in the literature.
13C{1H} NMR (CD2Cl2, 75.5 MHz): δ 156.8 (CdN imine),
123.4 (CN fumaronitrile), 62.6 (CH(CN)), 29.7 (C(CH3)3), 18.3
(CH3). FAB MS: M+ ) 353.1.
Crystal Structure Determination of [palladium(0)-
(tert-butylDAB)(fumaronitrile)] (6). C14H22N4Pd, fw )
352.76, yellow block, 0.04 × 0.10 × 0.40 mm3, monoclinic, space
group C2/c (no. 15), a ) 11.812(5) Å, b ) 14.33(3) Å, c ) 10.703-
(5) Å, â ) 120.42(5)°, V ) 1562(4) Å3, Z ) 4, F ) 1.500 g/cm3,
F(000) ) 720. A total of 12 527 reflections were measured up
to a resolution of (sin θ/λ) ) 0.63 Å-1 on a Nonius Kappa CCD
diffractometer with rotating anode and Mo KR radiation
(graphite monochromator, λ ) 0.71073 Å) at a temperature of
150(2) K. A multiscan absorption correction was applied using
SADABS.46 The unit cell was obtained using DIRAX,47 and
data were collected using Collect Software48 and integrated
using EvalCCD.49 A total of 1786 reflections were unique (Rint
) 0.065). The structure was solved with DIRDIF9950 and
refined using SHELXL97.51 Non-hydrogen atoms were refined
freely. H(6) was located in a difference map refined isotropi-
cally. All other hydrogen atoms were placed in idealized
3
(m, 12H, SiCH2CH2), 2.03 (m, 12H, SiCH2CH2), 4.15 (d, JH,P
) 4.8 Hz, CH MA), 7.18 (t, 10H, P-C6H4), 7.37 (d, 10H, P-C6H4).
13C{1H} NMR (CD2Cl2, 125.7 MHz): δ -3.64 (s, SiMe2), 5.28
2
(s, SiCH2), 26.08 (t, JC,F ) 23.5 Hz, SiCH2CH2), 131.38 (s,
C-aryl phosphine), 133.48 (m, C-aryl phosphine), 140.36 (s,
C-aryl phosphine). 19F NMR (CD2Cl2, 282.4 MHz): δ -124.61
(s, 12F, CF2), -121.62 (s, 12F, CF2), -121.34 (s, 12F, CF2),
-120.46 (s, 12F, CF2), -114.43 (s, 12F, CF2), -79.54 (s, 18F,
CF3). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 28.50 MHz (s).
Due to instability of the complex, no satisfactory elemental
analyses could be obtained.
Catalytic Studies. The following description for [Pd(0)-
(PPh3)2(MA)] is illustrative for all catalysis runs using the
zerovalent Pd alkene complexes. In a Schlenk vessel was
weighed the starting palladium complex (27.0 mg, 0.037
mmol). A second Schlenk vessel was charged with styrene
(580.7 mg, 5.58 mmol, 151 equiv with respect to Pd), p-
toluenesulfonic acid monohydrate (209.7 mg, 1.10 mmol, 30
equiv with respect to Pd), H2O (0.38 mL, 600 equiv with respect
to Pd), n-decane (22 mg, 0.15 mmol), MeOH (8.7 mL), and
R,R′,R′′-trifluorotoluene (8.7 mL). The resulting clear solution
was mixed and then transferred via syringe to the Schlenk
vessel containing the palladium complex. This mixture was
divided equally over the two autoclaves. After sealing they
were evacuated three times and refilled with N2, followed by
flushing three times with CO (15 bar). The autoclaves were
heated to the desired temperature and subsequently pressur-
ized with CO (30 bar), which was taken as the starting point.
After the desired reaction time had passed, the autoclaves were
cooled and carefully vented and their contents collected.
Analysis was performed via GC using n-decane as an internal
standard. The autoclaves were cleaned by washing with aqua
regia, water, and acetone, respectively.
NMR Study on the Reaction of [Pd(0)(PPh3)2(C2H4)]
with 3 equiv of p-Toluenesulfonic Acid in MeOH-d4. In
a Schlenk vessel the starting palladium complex (77.0 mg, 0.12
mmol) was weighed. To this was added a solution of p-
toluenesulfonic acid (66.9 mg, 0.35 mmol, 3 equiv) in MeOH-
d4 (0.5 mL). After about 1 min, when the initial gray suspen-
sion had turned into a clear dark red solution, this solution
was transferred via syringe to a 5 mm NMR tube. The NMR
tube was placed in the NMR spectrometer and shimmed, and
the 1H (500 MHz), 1H{31P}, and 31P{1H} NMR spectra were
recorded. For the 1H{31P} NMR experiment, 31P decoupling was
performed using the GARP-1 sequence.
positions and constrained to ride on their parent atoms (Uiso
-
(H) ) 1.2Uiso(C) for aromatic H atoms and Uiso(H) ) Uiso(C)
for all other hydrogen atoms). Refined parameters: 94. R (I >
2σ(I)): R1 ) 0.0325, wR2 ) 0.0720. R (all data): R1 ) 0.0434,
2
wR2 ) 0.0753. S ) 1.1. Weighting scheme w ) 1/[σ2(Fo ) +
(46) Bruker. SADABS; Bruker AXS GmbH: Karlsruhe, Germany,
2002.
(47) Duisenberg, A. J. M. J. Appl. Crystallogr. 1992, 25, 92.
(48) Collect Software; Nonius B.V.: Delft, The Netherlands, 1998.
(49) Duisenberg, A. J. M.; Kroon-Batenburg, L. M. J.; Schreurs, A.
M. M J. Appl. Crystallogr. 2003, 36, 220.
(50) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Garc´ıa-Granda,
S.; Gould, R. O.; Israel, R.; Smits, J. M. M. The DIRDIF99 Program
System; Technical Report of the Crystallography Laboratory, Univer-
sity of Nijmegen: The Netherlands, 1999.
(51) Sheldrick, G. M. SHELXL97, Program for crystal structure
refinement; University of Go¨ttingen: Germany, 1997.
Supporting Information Available: CIF files of crystal
structure data collection and refinement parameters, atomic
coordinates, bond lengths and angles, and anisotropic dis-
placement parameters for 6. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM0506419
(52) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.