Equilibrium studies of the binding of unsaturated fatty acid methyl esters to palladium(II)

Article abstract of DOI:10.1021/om049009q

Cationic palladium(II)-olefin complexes [CpPd(PR₃)(olefin)] BF₄ (PR₃ = PPh₃, PMePh₂, PEt ₃, PMe₃; olefin = methyl oleate (18:1), methyl linoleate (18:2), methyl linolenate (18:3)

Full text of DOI:10.1021/om049009q

Organometallics 2005, 24, 1725-1736
1725
Equilibrium Studies of the Binding of Unsaturated Fatty
Acid Methyl Esters to Palladium(II)
Kesete Y. Ghebreyessus, Arkady Ellern, and Robert J. Angelici*
Department of Chemistry, Iowa State University, Ames, Iowa 50011
Received December 14, 2004
Cationic palladium(II)-olefin complexes [CpPd(PR3)(olefin)]BF4 (PR3 ) PPh3, PMePh2,
PEt3, PMe3; olefin ) methyl oleate (18:1), methyl linoleate (18:2), methyl linolenate (18:3),
cis-3-hexene, 1,4-pentadiene) have been synthesized and characterized. (For 18:1, 18:2, and
18:3, the first number represents the chain length while the second indicates the number of
double bonds). The diene (1,4-pentadiene and 18:2) and triene (18:3) ligands also form
binuclear complexes {[CpPd(PR3)]2(olefin)}2+ containing two coordinated [CpPd(PR3)]+ units.
The crystal structure of {[CpPd(PMe3)]2(1,4-pentadiene)}(BF4)2 (5b) was determined by X-ray
crystallography. In all of the complexes, 1H and 13C{1H} NMR spectra establish the presence
of the η2-coordinated fatty acid methyl ester and alkene ligands. Equilibrium constants for
the formation of the [CpPd(PR3)(olefin)]+ complexes with 18:1, 18:2, 18:3, and cis-3-hexene
show that the binding abilities of the large unsaturated fatty acid methyl esters to [CpPd-
(PR3)]+ are similar to those of simple cis-olefins, such as cis-3-hexene and cis-2-butene. The
equilibrium constants for the binding of [CpPd(PR3)]+ to 18:1 and cis-3-hexene increase with
the increasing electron-donating ability and decreasing size of the phosphines: PPh3 <
PMePh2 < PEt3 < PMe3.
Chart 1
Introduction
One of the major challenges for the development of
vegetable oils into feedstocks for the synthesis of
chemicals1 now derived from petroleum is the separa-
tion of the different fatty acids that comprise these oils.2
Soybean oil, which is typical of such oils, consists of two
saturated fatty acids, palmitic (16:0, 10.6%) and stearic
(18:0, 4.7%), and three unsaturated fatty acids, oleic (18:
1, 24.3%), linoleic (18:2, 53.2%), and linolenic (18:3,
7.2%). (The first number in parentheses represents the
chain length, while the second indicates the number of
double bonds.) Their methyl esters are shown in Chart
1.
These methyl esters are obtained by transesterifica-
tion of the vegetable oils (triacylglycerols). This mixture
of fatty acid methyl esters (FAMEs) is produced com-
mercially and is known as biodiesel.3 Because of their
similar molecular weights and physical properties, it is
not possible to separate them by distillation. Consider-
ing the presence of cis-olefinic groups in 18:1, 18:2, and
18:3, one possible approach to their separation could
involve selective coordination of the double bonds to
transition-metal complexes. This has already been
demonstrated in widely used liquid- and gas-phase
chromatographic separations of these fatty acid methyl
esters on stationary phases that are impregnated with
AgNO3.4,5 Although highly effective for analytical ap-
plications, these methods are not economical for the
large-scale separation of the individual fatty acid esters.
To determine whether the binding abilities of 18:1,
18:2, and 18:3 are sufficiently different toward transi-
tion-metal complexes to allow them to be separated from
each other, we sought to determine equilibrium con-
stants for their coordination to [CpPd(PR3)]+, where Cp
) η5-C5H5. To our knowledge, no studies of transition-
metal binding to fatty acid derivatives have been
reported previously. The [CpPd(PR3)]+ system was
chosen because Kurosawa and co-workers6a had already
measured K values for the reactions in eq 1 for a variety
[CpPd(PR3)(o-MeC6H4CN)]BF4 + olefin h
[CpPd(PR3)(olefin)]BF4 + o-MeC6H4CN (1)
of simple olefins: e.g., ethylene, 1-butene, cis-2-butene,
(4) (a) Anderson, R. T.; Hollenbache, J. J. Lipid Res. 1965, 6, 577.
(b) Moriss, L. J. J. Lipid Res. 1966, 7, 717. (c) Momchilova, S.; Nikolova-
Damyanova, B. J. Sep. Sci. 2003, 26, 261.
(5) Lipid Chromatographic Analysis; Shibatomo, T.; Ed.; Marcel
Dekker: New York, 1994.
(6) (a) Kurosawa, H.; Majima, J.; Asada, N. J. Am. Chem. Soc. 1980,
102, 6996. (b) Miki, K.; Shiotani, O.; Kai, Y.; Kasai, N.; Kanatani, H.;
Kurosawa, H. Organometallics 1983, 2, 585. (c) Kurosawa, H.; Asada,
N.; Urabe, A.; Emoto, M. J. Organomet. Chem. 1984, 272, 321.
* To whom correspondence should be addressed. Phone: (515) 294-
2603. Fax: (515) 294-0105. E-mail: angelici@iastate.edu.
(1) Johnson, R. W.; Fritz, E. Fatty Acids in Industry; Marcel
Dekker: New York, 1989.
(2) Heidrich, J. F. J. Am. Oil Chem. Soc. 1984, 61, 271.
(3) Bechtold, R. L. Alternative Fuels Guidebook; Society of Automo-
tive Engineers: Warrendale, PA, 1997.
10.1021/om049009q CCC: $30.25 © 2005 American Chemical Society
Publication on Web 03/04/2005

1726 Organometallics, Vol. 24, No. 7, 2005
Ghebreyessus et al.
Scheme 1
Scheme 2
trans-2-butene, and styrene. During the course of the
equilibrium studies with 18:1, 18:2, and 18:3, it was
necessary to characterize the composition of the com-
plexes and the binding sites of the fatty acid methyl
esters with two and three double bonds. It is these
investigations of the [CpPd(PR3)(olefin)]+ and {[CpPd-
(PR3)]2(olefin)}2+complexes that we report herein.
Results and Discussion
Scheme 3
Synthesis and Characterization of the Com-
plexes. (a) CpPd(PR3)Cl (PR3 ) PMePh2 (1), PMe3
(2)). By a procedure used for the synthesis of CpPd-
(PR3)Cl (PR3 ) PPh3, PEt3, PBu3),6,7 compounds 1 and
2 were prepared by the reaction of the binuclear
chloride-bridged palladium(II) complexes (R3P)2Pd2Cl4
(PR3 ) PMePh2, PMe3) with cyclopentadienylthallium
in tetrahydrofuran at room temperature; the green air-
stable CpPd(PR3)Cl products were characterized by
their elemental analyses and 1H, 31P{1H}, and 13C{1H}
NMR spectra.
(b) [CpPd(PR3)(cis-3-hexene)]BF4 (PR3 ) PPh3
(3a), PMePh2 (3b), PMe3 (3c)). The complexes of cis-
3-hexene were prepared and characterized in order to
facilitate NMR assignments to the more complicated
spectra of the analogous complexes of 18:1. Reactions
of the CpPd(PR3)Cl complexes (0.11 mmol) with cis-3-
hexene (0.33 mmol) in chloroform-d/acetone-d6 in the
presence of silver tetrafluoroborate gave complexes
3a-c (Scheme 1). Coordination of the olefin to Pd(II)
was evidenced by a substantial upfield shift of the
olefinic protons from 5.34 ppm in free cis-3-hexene to
3.95, 4.02, and 4.40 ppm in 3a-c, respectively. Like the
other [CpPd(PR3)(olefin)]BF4 complexes, 3a-c were not
sufficiently stable to be isolated as pure solids.
(c) [CpPd(PR3)(1,4-pentadiene)]BF4 (4a,b) and
{[CpPd(PR3)]2(1,4-pentadiene)}(BF4)2 (5a,b, 6a,b).
These complexes were prepared and characterized as
relatively simple models of the 1,4-pentadiene unit in
the complexes of 18:2. The addition of 0.15-0.33 mmol
of 1,4-pentadiene and solid CpPd(PR3)Cl (0.11 mmol)
to a suspension of silver tetrafluoroborate in chloroform-
d/acetone-d6 (7:1) resulted in the formation of the three
types of complexes 4-6 (Scheme 2); in 4 the 1,4-
pentadiene is bonded to one [CpPd(PR3)]+ unit, while
two [CpPd(PR3)]+ units are bonded in the others (5 and
6). The relative abundances of complexes 4-6, as
determined from peak intensities in the 1H NMR
spectra, are dependent upon the amount of 1,4-penta-
diene used. When a large excess of the 1,4-pentadiene
ligand (3 equiv) is used, the mononuclear complexes
4a,b are formed as major products with only trace
amounts of 5a,b and 6a,b. On the other hand, when a
small amount (1.5 equiv) of the free 1,4-pentadiene is
used, the binuclear compounds 5a,b and 6a,b predomi-
nate. Therefore, the complexes 4-6 are in rapid equi-
librium, their relative amounts depending on the con-
centration of 1,4-pentadiene. Characterization of the
mononuclear (4a,b) and binuclear (5a,b and 6a,b)
complexes was established by means of 1H and 13C{1H}
NMR spectroscopy.
The 1H NMR spectrum of 4a shows three olefinic
resonances (instead of the six expected for an η2-
coordinated 1,4-pentadiene ligand) at 5.13 ppm (H3,6),
4.73 ppm (H2,7), and 4.31 ppm (H1,8), which are ap-
proximate averages of the chemical shifts of free 1,4-
pentadiene and the 1,4-pentadiene ligand with both
double bonds coordinated in 5a and 6a. For example,
the chemical shift for H3,6 in 4a is 5.13 ppm, while the
average for these protons in free 1,4-pentadiene (5.86
1
ppm) and 5a (4.14 ppm) is 5.00 ppm. These H NMR
results suggest that the two terminal CH2 and the two
internal CH protons are exchanging rapidly, as shown
in Scheme 3. The mechanism for this process could
involve Pd dissociation from one double bond and
coordination to the other or PR3 dissociation or Cp ring
slippage accompanied by coordination to the other
double bond. The resonance due to the Cp protons in
4a is a doublet at 5.88 ppm. The 31P{1H} NMR spectrum
shows a singlet at 35.51 ppm. The 13C{1H} NMR
spectrum of 4a is also consistent with this exchange
process. The olefinic carbon resonances appear as two
singlets at 116.80 ppm (C2,4) and 101.00 ppm (C1,5).
These chemical shifts are also approximate averages of
(7) Cross, R. J.; Wardle, R. J. Chem. Soc. A 1971, 2000.

Binding of Unsaturated Fatty Acid Esters to Pd(II)
Organometallics, Vol. 24, No. 7, 2005 1727
Figure 2. ORTEP drawing of the {[CpPd(PMe3)]2(1,4-
pentadiene)}2+ cation in 5b showing the atom-numbering
scheme (50% probability thermal ellipsoids). Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å):
Pd(1)-C(9), 2.163(8); Pd(1)-C(10), 2.184(7); Pd(2)-C(12),
2.187(7); Pd(2)-C(13), 2.209(7); Pd(1)-P(2), 2.271(2); Pd-
(2)-P(1), 2.256(2); C(9)-C(10), 1.36(1); C(12)-C(13), 1.43-
(1). Selected bond angles (deg): C(10)-Pd(1)-P(2), 93.6(2);
C(9)-Pd(1)-P(2), 98.7(2); C(12)-Pd(2)-P(1), 94.5(2); C(13)-
Pd(2)-P(1), 100.1(1).
Figure 1. 1H NMR spectra of 5a and 6a in the Cp region
in CDCl3/acetone-d6: (a) 31P coupled; (b) 31P decoupled.
those for free 1,4-pentadiene and the 1,4-pentadiene
ligand with both double bonds coordinated in 5a and
6a. For example, the chemical shift for C2,4 in 4a is
116.80 ppm, while the average value of free 1,4-
pentadiene (135.5 ppm) and 5a (98.40 ppm) is 117.0
ppm. The resonance for the Cp carbons is observed as
a doublet at 103.88 ppm with a P-C coupling constant
of 2.0 Hz. To slow the exchange process and determine
if one of these compounds is favored at low temperature,
the 13C{1H} NMR spectrum of 4a-6a was recorded at
-80 °C. However, no additional peaks were observed,
suggesting that 4a remains fluxional at -80 °C. Also,
there was no significant change in the ratio of 4a-6a.
and 13C{1H} NMR shifts of the coordinated olefinic
protons and carbons compared to those of the free 1,4-
pentadiene. For instance, in the 13C{1H} NMR spectrum
of 5a, the olefinic signals at 98.46 ppm (C1,5) and 65.19
ppm (C2,4) are substantially upfield of those at 135.5
ppm (C2,4) and 115.5 ppm (C1,5) in the free 1,4-penta-
diene ligand. The 13C{1H} NMR spectrum of 5a also
displays a doublet at 103.30 ppm corresponding to the
Cp carbons. No significant change in the 13C{1H} NMR
spectra of 5a and 6a was observed when the tempera-
ture was lowered to -80 °C.
1
The H and 13C{1H} NMR spectra of 4b are similar to
those of 4a; they also indicate rapid migration of the
[CpPd(PMe3)]+ unit between the two double bonds.
The spectral features of the binuclear complexes
{[CpPd(PPh3)]2(1,4-pentadiene)}2+ (5a and 6a) are de-
scribed below. Figure 1 shows the 1H NMR spectrum of
the binuclear complexes 5a and 6a in the Cp region,
with and without 31P decoupling. Without 31P decou-
pling, the Cp protons of 5a and 6a give rise to two
doublet peaks at 5.94 and 5.93 ppm, while the 31P-
decoupled spectrum gives two singlets. The two Cp and
31P signals indicate that two binuclear compounds
{[CpPd(PPh3)2]2(1,4-pentadiene)}2+ (5a and 6a) are
present in solution. In the 31P{1H} NMR spectrum, 5a
displays a singlet resonance at 37.90 ppm, indicating
effective mirror symmetry of the molecule. Likewise, 6a
displays a singlet resonance at 37.40 ppm, indicating
the presence of two equivalent phosphorus atoms. The
two isomers 5a and 6a are proposed to have structures
that differ by the faces through which the [CpPd(PPh3)]+
units are coordinated to the 1,4-pentadiene. In one
isomer (5a) both [CpPd(PPh3)]+ units are on the same
side of the 1,4-pentadiene, when it is drawn (Scheme
2) in the planar conformation. In the other isomer (6a),
the [CpPd(PPh3)]+ units are on opposite sides of the
planar 1,4-pentadiene. It is not possible to interconvert
these isomers by rotating around any of the C-C single
bonds. NMR studies of 5b also show that it exists as
the two isomers 5b and 6b, but in this case it was
possible to obtain crystals of 5b, whose structure was
established by an X-ray diffraction analysis (see below).
It should be noted that when crystals of 5b were
dissolved in CD3NO2, the 1H NMR spectrum showed the
presence of 4b-6b, as expected for this rapidly equili-
brating mixture.
The 13C{1H} NMR spectrum of 6a displays signals at
94.40 ppm (C2,4) and 64.99 ppm (C1,5) for the olefinic
carbons; these compare to those at 135.5 ppm (C2,4) and
115.5 ppm (C1,5) in free 1,4-pentadiene. The 13C{1H}
NMR spectrum of 6a also displays a doublet at 104.23
ppm corresponding to the Cp carbons. Spectral data for
5b and 6b are quite similar to those of 5a and 6a
discussed above.
An ORTEP view, together with selected bond dis-
tances and angles, of 5b is given in Figure 2. Each
palladium is coordinated to cyclopentadienyl (Cp), PMe3,
and olefin ligands, and the [CpPd(PMe3)]+ groups are
on the same side of the 1,4-pentadiene. A similar
coordination geometry around the palladium atom was
found in the analogous [CpPd(PEt3)(CH2dCHC6H5)]-
6,8
BF4 and related complexes with substituted styrene
ligands.6b The Pd(1)-C(9) (2.163(8) Å), Pd(1)-C(10)
(2.184(7) Å), Pd(2)-C(12) (2.187(7) Å), and Pd(2)-C(13)
bond lengths (2.209(7) Å) are comparable to those in
[CpPd(PEt3)(CH2dCHC6H5)]BF4.6,8 The C(9)dC(10) bond
distance (1.36(1) Å) is well within the range of coordi-
nated carbon-carbon double bonds observed in [CpPd-
6,8
(PEt3)(CH2dCHC6H5)]BF4
and related substituted
styrene complexes,6b but the C(12)dC(13) bond distance
(1.43(2) Å) is longer than expected and probably reflects
the relatively large standard deviations for 5b.
(d) [CpPd(PR3)(18:1)]BF4 (PR3 ) PPh3 (7a), PMe-
Ph2 (7b), PMe3 (7c), PEt3 (7d)). The methyl oleate (18:
1) complexes [CpPd(PR3)(18:1)]BF4 (7a-d), though of
limited stability, were prepared from CpPd(PR3)Cl (0.11
The η2 coordination of the olefinic groups in 5a and
(8) Miki, K.; Yama, M.; Kai, Y.; Kasai, N. J. Organomet. Chem. 1982,
239, 417.
1
6a was also established by the pronounced upfield H

1728 Organometallics, Vol. 24, No. 7, 2005
Ghebreyessus et al.
Scheme 4
Figure 3. 1H NMR spectrum of 7a in CDCl3/acetone-d6:
mmol) and methyl oleate (0.33 mmol) in the presence
of silver tetrafluoroborate (Scheme 4). Attempted isola-
tion of the complexes as pure solids by precipitation and/
or crystallization was not successful. Washing the
resulting precipitate with hexanes to remove excess 18:1
(a) Cp; (b) free 18:1; (c) coordinated 18:1.
the methyl oleate in the 13C{1H} NMR spectra of 7a-d
were made on the basis of previous assignments for
those carbons in the free unsaturated fatty acid methyl
ester.12 The olefinic carbons in complexes 7a-d occur
as two peaks at 97.27 ppm (C9) and 97.40 ppm (C10) for
7a, at 95.54 ppm (C9) and 95.52 ppm (C10) for 7b, at
93.34 ppm (C9) and 93.47 ppm (C10) for 7c, and at 93.34
ppm (C10) and 93.19 ppm (C9) for 7d; these are upfield
of those at 129.72 ppm (C9) and 129.97 ppm (C10) for
free 18:1.12b The 13C{1H} NMR resonances for the Cp
ligand occur as doublets at 104.85 ppm (7a), 103.51 ppm
(7b), 102.38 ppm (7c), and 102.48 ppm (7d). The 13C-
{1H} resonance for the CdO group is observed at 173.35
ppm, while the OMe signal is observed at 51.05 ppm in
7a.
(e) [CpPd(PR3)(18:2)]BF4 (8a,b) and {[CpPd-
(PR3)]2(18:2)}(BF4)2 (9a,b). The methyl linoleate (18:
2) complexes [CpPd(PR3)(18:2)]BF4 (8a,b) and {[CpPd-
(PR3)]2(18:2)}(BF4)2 (9a,b) were prepared in the reaction
of CpPd(PR3)Cl (0.11 mmol) with methyl linoleate (0.33
mmol) in the presence of silver tetrafluoroborate, as
shown in Scheme 5. Like 7a,b, compounds 8 and 9 could
not be isolated in pure form, due to their limited
stability and gradual decomposition to [CpPd(PR3)2]2+
and free 18:2 as the main products. The synthesis of 8
and 9 in chloroform-d/acetone-d6 (7:1) produced a red
solution after filtration of the silver chloride precipitate.
1H and 13C{1H} NMR spectra of these solutions show
signals for the coordinated olefin protons and carbons
that are significantly upfield of the corresponding
signals in free 18:2. Assignments for protons H2, H8,
6a
led to the decomposition products [CpPd(PR3)2](BF4)2
and free 18:1. However, the relatively high stability of
the complexes in the presence of excess 18:1 was
exploited in their characterization and identification in
solution.
Coordination of methyl oleate (18:1) to the Pd(II)
center is clearly indicated by the 1H and 13C{1H} NMR
1
spectra. In the H NMR spectrum a large upfield shift
is observed for the coordinated olefinic protons in
complexes 7a-d relative to the uncoordinated olefin.
Such shielding of olefinic protons is common in η2-olefin
complexes of transition metals.9,10 The chemical shifts
of the coordinated olefinic protons occur at 4.08 ppm
(7a), 4.10 ppm (7b), 4.52 ppm (7c), and 4.38 ppm (7d).
The higher upfield chemical shifts observed for the PPh3
and PMePh2 complexes 7a,b are probably associated
with diamagnetic shielding by the phenyl rings. Since
1
distinct H NMR resonances for free (5.34 ppm) and
coordinated 18:1 (4.08 ppm) in 7a (Figure 3) are
observed, exchange between the free and coordinated
olefin is slow on the NMR time scale. The resonances
due to the Cp protons appear as doublets at 5.73, 5.77,
5.81, and 5.74 ppm for 7a-d, respectively, as a result
of coupling to phosphorus. These signals are shifted by
about 0.2 ppm downfield compared to those for the
corresponding CpPd(PR3)Cl complexes (∼5.56 ppm).
Assignments for protons H2, H8, H9,10, H11, H17, and H18
of methyl oleate in the complexes (see the Experimental
Section) are based on previous assignments for those
protons in the free unsaturated fatty acid methyl ester.11
Assignments for C1, C2, C8, C9, C10, C11, C17, and C18 of
H9,10, H11, H12,13, H14, H17, and H18 of methyl linoleate
in the complexes (see the Experimental Section) are
based on previous assignments for those protons in the
free unsaturated fatty acid methyl ester.11 Assignments
for C1, C2, C8, C9, C10, C11, C12, C13, C14, C17, and C18 of
the methyl linoleate in the 13C{1H} NMR spectra of 8
and 9 were made on the basis of previous assignments
for those carbons in the free unsaturated fatty acid
methyl ester.12 The methyl linoleate complexes present
(9) (a) Yamamoto, T.; Nakamura, Y.; Yamamoto, A. Bull. Chem. Soc.
Jpn. 1976, 49, 19. (b) Cheng, P.-T.; Cook, C. D.; Nyburg, S. C.; Wan,
K. Y. Inorg. Chem. 1971, 10, 2210. (c) Tolman, C. A.; English, A. D.;
Manzer, L. E. Inorg. Chem. 1975, 14, 2353. (d) Salmon, R. G.; Kochi,
J. K. J. Am. Chem. Soc. 1972, 94, 5087.
(10) (a) Thompson, J. S.; Whitney, J. F.; J. Am. Chem. Soc. 1983,
105, 5488. (b) Thompson, J. S.; Harlow, R. L.; Whitney, J. F. J. Am.
Chem. Soc. 1983, 105, 3522. (c) Thompson, J. S.; Whitney, J. F. Inorg.
Chem. 1984, 23, 2813. (d) Thompson, J. S.; Swiatek, R. M. Inorg. Chem.
1985, 24, 110.
(11) (a) Guille´n, M. D.; Ruiz, A. Eur. J. Lipid Sci. Technol. 2003,
105, 688. (b) Guille´n, M. D.; Ruiz, A. J. Sci. Food Agric. 2003, 83, 338.
(c) Miyake, Y.; Yokomizo, K.; Matsuzaki, N. J. Am. Oil Chem. Soc.
1998, 75, 1091. (d) Sacchi, R.; Addeo, F.; Paolillo, L. Magn. Reson.
Chem. 1997, 35, S133.
(12) (a) Batchelor, J. G.; Cushley, R. J.; Prestergard, J. H. J. Org.
Chem. 1974, 39, 1698. (b) Batchelor, J. G.; Prestegard, J. H.; Cushley,
R. J.; Lipsky, S. R. J. Am. Chem. Soc. 1973, 95, 6358. (c) Bus, J.; Sies,
I.; Marcel, S. F.; Jie, L. K. Chem. Phys. Lipids 1976, 17, 501. (d) ibid
1977, 18, 130. (e) Wollemberg, K. F. J. Am. Oil Chem. Soc. 1990, 61,
487. (f) Vlahov, G.; Chepkwony, P. K.; Ndalut, P. K. J. Agric. Food
Chem. 2002, 50, 970.

Binding of Unsaturated Fatty Acid Esters to Pd(II)
Organometallics, Vol. 24, No. 7, 2005 1729
Scheme 5
olefinic signals for the coordinated and uncoordinated
double bonds in 8a indicates that the [CpPd(PPh3)]+
group is not rapidly migrating between the two double
bonds, as was observed in [CpPd(PPh3)(1,4-pentadiene)]-
(BF4) (4a). The long cis hydrocarbon chains on C9 and
C13 would be expected to prevent the two olefins from
achieving a parallel orientation that would allow a rapid
transfer of the [CpPd(PPh3)]+ unit from one olefin to
the other.
The electrospray ionization spectra (ESI) of chloroform/
acetone solutions of 8a and 9a and free 18:2 show peaks
at m/z 695 for [(Cp)Pd(PPh3)(18:2)]+, at m/z 903 for
[(Cp)Pd2(PPh3)(18:2)]2+, and at m/z 953 for [(Cp)Pd2(18:
2)]+. The isotopic pattern for the peaks is consistent with
the presence of two Pd atoms in the m/z 903 and 953
fragments. Treatment of a chloroform-d/acetone-d6 solu-
tion of 8a and 9a with equimolar [(n-Bu)4N]Cl led to
an instantaneous color change from red to green; the
1H NMR spectrum showed the products to be CpPd-
(PPh3)Cl and free 18:2.
The binuclear complex {[CpPd(PPh3)]2(18:2)}2+ (9a),
in solution contain either one coordinated [CpPd(PR3)]+
in which the [CpPd(PR3)]+ unit is coordinated to the
C
unit (8) or two (9). Identification of these compounds
9,10 and C12,13 sites shown in Scheme 5, is detected as
1
was achieved by comparison of their H, 31P{1H}, and
a minor product. The intensity ratio of the Cp protons
in the 1H NMR spectra of 8a and 9a was about 5:1. The
1H NMR spectrum of 9a exhibits doublet peaks at 5.87
and 5.86 ppm for the Cp protons; these resonances are
similar to those (5.94 ppm) observed for {[CpPd(PPh3)]2-
(1,4-pentadiene)}2+ (5a) (Scheme 2). Resonances for the
coordinated olefinic protons are observed as multiplets
at higher fields (4.00 and 3.89 ppm) as compared to
those for free 18:2 at 5.36 ppm. The 31P{1H} NMR
spectrum of 9a exhibits two separate singlet resonances
at 38.37 and 38.32 ppm with approximately equal
intensities due to the nonequivalent PPh3 ligands, as
expected for a molecule lacking mirror symmetry. These
resonances are similar to that (37.40 ppm) observed in
{[CpPd(PPh3)]2(1,4-pentadiene)}2+ (5a). The presence of
two nonequivalent 31P{1H} signals and two Cp groups
in the 1H NMR spectrum of 9a also indicates the
asymmetric nature of the methyl linoleate (18:2) ligand.
In the 13C{1H} NMR spectrum of 9a, resonances due to
the Cp carbons are observed as doublets at 103.54 and
103.65 ppm, which are similar to 103.30 ppm in {[CpPd-
(PPh3)]2(1,4-pentadiene)}(BF4)2 (5a). The coordinated
olefinic carbon resonances are observed at 94.92 ppm
(C9), 95.06 ppm (C10), 97.14 ppm (C12), and 97.28 ppm
(C13), which are considerably upfield of those (127.07
ppm (C9), 129.85 ppm (C10), 129.65 ppm (C12) and 130.20
ppm (C13)) in free 18:2. The 13C{1H} chemical shift
assignments for the coordinated olefinic carbons, high
field for C9,10 and low field for C12,13, are based on the
fact that the chemical shifts for C9,10 are at higher field
than those of C12,13 in free 18:2.12 For the binuclear
complex 9a, there is the possibility of forming two
isomers in which the [CpPd(PR3)]+ groups are coordi-
nated on either the same side or opposite sides of the
1,4-pentadiene unit, as observed for {[CpPd(PPh3)]2(1,4-
pentadiene)}(BF4)2 (5a,b and 6a,b) (Scheme 2). How-
ever, all the NMR data indicate the presence of only
13C{1H} NMR spectra with those of [CpPd(PR3)(18:1)]+
(7a,b) and {[CpPd(PR3)]2(1,4-pentadiene)}2+ (5a,b, 6a,b).
Since complexes 8b and 9b exhibit spectroscopic fea-
tures similar to those of 8a and 9a, a detailed discussion
of only 8a and 9a is presented here.
1
In H and 13C{1H} NMR spectra of the mixture of
complexes 8a and 9a are peaks that may be assigned
on the basis of their relative intensities to a complex
with the composition [CpPd(PPh3)(18:2)]+ (8a), whose
structure is proposed to be that shown in Scheme 5, in
which the [CpPd(PPh3)]+ unit is coordinated to C9 and
C10. The following 1H and 13C{1H} NMR data favor this
site for [CpPd(PPh3)]+ coordination rather than at C12
and C13, but they do not exclude the possibility of C12,13
coordination. However, there is no evidence for two
isomers of [CpPd(PPh3)(18:2)]+ in which [CpPd(PPh3)]+
is coordinated at C9,10 or C12,13. The 1H NMR spectrum
of 8a shows a broad multiplet centered at 4.06 ppm for
the coordinated olefinic protons, which is very similar
to that for H9,10 (4.08 ppm) in [CpPd(PPh3)(18:1)]+ (7a).
The uncoordinated olefinic protons in 8a occur as a
broad multiplet at 5.43 ppm, which is very similar to
H12,13 at 5.36 ppm in free 18:2. The 13C{1H} NMR
spectrum of 8a shows singlets at 94.87 and 94.90 ppm,
which are considerably upfield of C9 (127.88 ppm) and
C10 (128.01 ppm) in free 18:2 but are similar to those
for C9 (97.27 ppm) and C10 (97.40 ppm) in [CpPd(PPh3)-
(18:1)]+ (7a). The uncoordinated olefin carbons in 8a
give rise to peaks at 131.82 and 131.95 ppm, respec-
tively, which are close to those of C12 (129.99 ppm) and
C13 (130.16 ppm) in free 18:2. The assignment of [CpPd-
(PPh3)]+ bonding to C9,10 rather than C12,13 is based
primarily on the fact that the chemical shifts of C12,13
(131.82 and 131.95 ppm) of the uncoordinated olefin in
8a are more similar to those of C12,13 (129.99, 130.16
ppm) in free 18:2 than they are to C9,10 (127.88, 128.01
ppm) in free 18:2. Supporting the structural assignment
for 8a in Scheme 5 is the Cp doublet at 5.75 ppm, which
is similar to that (5.73 ppm) of [CpPd(PPh3)(18:1)]+ (7a)
and the 31P{1H} singlet at 37.87 ppm, which is similar
to that (38.51 ppm) in 7a. The observation of separate
1
one isomer. When the H and 13C{1H} NMR spectra of
the binuclear complex 9a are compared to those of
{[CpPd(PR3)]2(1,4-pentadiene)}(BF4)2 (5a,b and 6a,b),
the more likely structure is that shown in Scheme 5,

1730 Organometallics, Vol. 24, No. 7, 2005
Ghebreyessus et al.
Scheme 6
or two (12). Since complexes 10b-12b exhibit spectro-
scopic features similar to those of 10a-12a, a detailed
discussion of only 10a-12a is presented here.
In the reactions of CpPd(PPh3)Cl with 18:3, the three
species (10a-12a) shown in Scheme 6 were detected by
1
both their H and 13C{1H} NMR spectra. The relative
amounts of 10a-12a were about 3:1:1, as determined
1
from their H NMR spectra. Clearly, the coordination
behavior of 18:3 with CpPd(PPh3)Cl is considerably
more complicated than that observed for the analogous
complexes of 18:1 and 18:2, due to the presence of three
double bonds. However, analysis of the 1H and 13C{1H}
NMR spectra of the mixture shows peaks that cor-
respond to two, not three, monometalated complexes
with the composition [CpPd(PPh3)(18:3)]+ (10a and 11a)
whose structures are proposed to be those shown in
Scheme 6, in which the [CpPd(PPh3)]+ is coordinated
to C9,10, and C15,16, respectively. Compounds 10a and
11a have the same composition and very similar 1H and
13C{1H} NMR spectra. The only difference between
them is the coordination site of the [CpPd(PPh3)]+ unit
on the triene ligand. Assignments of the signals are
discussed separately for compounds 10a and 11a.
The 1H NMR spectrum of 10a shows a broad multiplet
at 4.09 ppm attributed to the coordinated olefinic
protons (H9,10) which is very similar to that for H9,10
(4.08 ppm) in [CpPd(PPh3)(18:1)]+ (7a). Resonances for
the uncoordinated olefinic protons in 10a are observed
as broad multiplets at 5.42 ppm (H12,13) and 5.48 ppm
(H15,16), which are close to those H12,13,15,16 (5.36 ppm)
in free 18:3. Supporting this structural assignment is
the doublet peak at 5.79 ppm assigned to the Cp
protons, which is similar to that (5.73 ppm) of [CpPd-
(PPh3)(18:1)]+ (7a). The 31P{1H} NMR spectrum of 10a
shows a singlet at 37.87 ppm which is similar to that
(38.51 ppm) in 7a. The 13C{1H} NMR spectrum of 10a
shows a doublet resonance at 104.72 ppm assigned to
the Cp carbons, which is similar to that (104.85 ppm)
for 7a. Resonances for the coordinated olefinic carbons
are observed at 94.56 ppm (C9) and 94.60 ppm (C10),
which are considerably upfield of those (127.05 ppm (C9)
and 127.67 ppm (C10)) in free 18:3 but similar to those
for C9 (97.27 ppm) and C10 (97.40 ppm) in [CpPd(PPh3)-
(18:1)]+ (7a). The 13C{1H} NMR spectrum of 10a also
shows resonances for the uncoordinated olefinic carbons,
C12,13 (131.14, 131.96 ppm) and C15,16 (132.35, 133.96
ppm), which are more similar to those for C12,13 (128.17,
128.20 ppm) and C15,16 (131.85, 130.17 ppm) than to
those for C9,10 (127.05, 127.67 ppm) in free 18:3.
Although the NMR data support the structure of 10a
shown in Scheme 6, they do not completely exclude the
possibility of [CpPd(PPh3)]+ coordination at one of the
other double bonds.
where the [CpPd(PR3)]+ groups are on the same side of
the 1,4-pentadiene unit, similar to that of {[CpPd-
(PMe3)]2(1,4-pentadiene)}(BF4)2 (5b), which was char-
acterized by an X-ray crystal structure analysis.
(f) [CpPd(PR3)(18:3)]BF4 (10a,b, 11a,b) and {[Cp-
Pd(PR )]2(18:3)}(BF4)2 (12a,b). The methyl linolenate
(18:3) c3omplexes 10-12 (Scheme 6) were prepared by
addition of 0.33 mmol of methyl linolenate and 0.11
mmol of CpPd(PR3)Cl to a chloroform-d/acetone-d6
(7:1) solution of silver tetrafluoroborate at 0 °C. Like 8
and 9, compounds 10-12 could not be isolated in pure
form, due to their limited stability and gradual decom-
position to [CpPd(PR3)2]2+ and free 18:3 as the main
products. The synthesis of 10-12 in chloroform-d/
acetone-d6 (7:1) produced a red solution after filtration
of the silver chloride precipitate. Assignments for
protons H2, H8, H9,10, H11, H12,13, H14, H15,16, H17, and
H18 of methyl linolenate in the complexes (see the
Experimental Section) are based on previous assign-
ments for those protons in the free unsaturated fatty
acid methyl ester.11 Assignments for C1, C2, C8, C9, C10,
C11, C12, C13, C14, C15, C16, C17, and C18 of the methyl
linolenate in the 13C{1H} NMR spectra of 10-12 were
made on the basis of previous assignments for those
carbons in the free unsaturated fatty acid methyl
ester.12 1H and 13C{1H} NMR spectra of these solutions
show signals for the coordinated olefin protons and
carbons that are shifted significantly upfield of the
corresponding signals in free 18:3. The relative abun-
dances of complexes 10a-12a, as determined by the
relative peak intensities, depends on the concentration
of the [CpPd(PPh3)]+ units. For example, when 0.33
mmol of the [CpPd(PPh3)(o-MeC6H4CN)]BF4 complex
was added instead of 0.11 mmol, the relative amounts
of 11a and 12a increased while that of 10a decreased.
Attempts to coordinate three [CpPd(PR3)]+ units by
using a 4-fold excess (0.44 mmol) of the CpPd(PR3)Cl
complexes gave no evidence for trimetalated 18:3. The
methyl linolenate complexes present in solution contain
either one coordinated [CpPd(PR3)]+ unit (10 and 11)
The spectral features of [CpPd(PPh3)(18:3)]+ (11a)
described below favor the C15,16 site for [CpPd(PPh3)]+
coordination rather than the C12,13 site, but they do not
exclude the possibility of C12,13 coordination. The 1H
NMR spectrum of 11a exhibits a broad multiplet at 4.06
ppm for the coordinated olefinic protons (H15,16) which
is considerably upfield of 5.36 ppm (H15,16) in free 18:
3.11 Resonances for the uncoordinated olefinic protons
in 11a are observed as broad multiplets at 5.38 ppm
(H9,10) and 5.44 ppm (H12,13), which are close to those of
1
H9,10,12,13 (5.36 ppm) in free 18:3. The H NMR signal

Binding of Unsaturated Fatty Acid Esters to Pd(II)
Organometallics, Vol. 24, No. 7, 2005 1731
for the Cp ligand is observed as a doublet at 5.81 ppm.
The 31P{1H} NMR spectrum displays a singlet at 35.33
ppm. In the 13C{1H} NMR spectrum of 11a, the Cp
carbons give rise to a doublet at 104.64 ppm with a P-C
coupling constant of 2.0 Hz. Resonances for the coordi-
nated olefinic carbons are observed at 97.14 ppm (C15)
and 98.92 ppm (C16), which are considerably upfield of
Previously Kurosawa and co-workers6a reported K1
values also in CDCl3 solvent at 23.0 °C for the binding
of simple olefins.
Scheme 7
[CpPd(PR3)(o-MeC6H4CN)]BF4 + olefinyK
1
\z
C15 (130.17 ppm) and C16 (131.85 ppm) in free 18:3. The
[CpPd(PR3)(olefin)]BF4 + o-MeC6H4CN
13C{1H} NMR spectrum of 11a also shows resonances
for the uncoordinated olefinic carbons C12,13 (128.88,
129.95 ppm), and C9,10 (125.60, 125.81 ppm), which are
more similar to C12,13 (128.17, 128.20 ppm) and C9,10
(127.05, 127.67 ppm) than to C15,16 (130.17, 131.85 ppm)
in free 18:3, which is the primary reason for assigning
[CpPd(PPh3)(o-MeC6H4CN)]BF4 +
K2
[CpPd(PPh3)(18:2)]BF4 y\z
{[CpPd(PPh3)]2(18:2)}(BF4)2 + o-MeC6H4CN
[CpPd(PPh3)(o-MeC6H4CN)]BF4 + 18:3 yK (10a)
z
[CpPd(PPh3)]+ coordination to C15,16 rather than C12,13
.
1
The dimetalated {[CpPd(PPh3)]2(18:3)}2+ (12a), in
which the [CpPd(PPh3)]+ unit is proposed to be coordi-
nated to the C9,10 and C15,16 positions, as shown in
Scheme 6, was detected as a minor product. While the
[CpPd(PPh3)(18:3)]BF
4 + o-MeC6H4CN
10a
[CpPd(PPh3)(o-MeC6H4CN)]BF4 + 18:3 yK (11a)
z
1
1
following H and 13C{1H} NMR spectra favor the C9,10
[CpPd(PPh3)(18:3)]BF
4 + o-MeC6H4CN
11a
[CpPd(PPh3)(o-MeC6H4CN)]BF4 +
4 yK (10a)
z
2
[CpPd(PPh3)(18:3)]BF
10a
{[CpPd(PPh3)]2(18:3)}(BF4)2 + o-MeC6H4CN
[CpPd(PPh3)(o-MeC6H4CN)]BF4 +
4 yK (11a)
z
2
[CpPd(PPh3)(18:3)]BF
11a
{[CpPd(PPh3)]2(18:3)]BF4 + o-MeC6H4CN
The equilibrium expressions shown in Scheme 7 are
defined as follows: K1 is the equilibrium constant for
the formation of the mononuclear complexes [CpPd-
(PR3)(olefin)]BF4 (olefin ) cis-3-hexene, 18:1, and
18:2). K2 is the equilibrium constant for the formation
of the binuclear methyl linoleate complex {[CpPd(PR3)]2-
(18:2)}(BF4)2 with two [CpPd(PR3)]+ units coordinated
at the C9-C10 and C12-C13 positions. K1(10a) is the
equilibrium constant for the formation of the mono-
nuclear methyl linolenate complex [CpPd(PPh3)(18:3)]-
BF4 (10a) with one [CpPd(PPh3)]+ unit coordinated at
the C9-C10 position, whereas K1(11a) is the equilibrium
constant for the formation of [CpPd(PPh3)(18:3)]BF4
(11a) with one [CpPd(PPh3)]+ unit coordinated at the
C15-C16 position. K2(10a) and K2(11a) are equilibrium
constants for the formation of the binuclear methyl
linolenate complex {[CpPd(PPh3)]2(18:3)}(BF4)2 (12a),
in which two [CpPd(PPh3)]+ units are coordinated at the
C9-C10 and C15-C16 positions.
The 1H NMR spectra of the reaction mixtures, re-
corded within 3-5 min of mixing, showed that the
reactions had already achieved equilibrium. The pres-
ence of well-separated resonances for the free and
coordinated olefins indicates that the exchange between
the free and coordinated olefin is slow on the NMR time
scale. Since 1H NMR signals were unambiguously
assignable to the o-tolunitrile and olefin species in
solution, integrations of the Cp and o-tolunitrile proton
signals using methyl â-naphthyl ether as an internal
standard gave concentrations of the reactants and

1732 Organometallics, Vol. 24, No. 7, 2005
Ghebreyessus et al.
Table 1. Equilibrium Constants for the Formation
of [CpPd(PR3)(olefin)]BF4 and
Hoff plot (-ln(K1) vs 1/T) of these data are ∆H° ) -16.7
( 1 kJ mol-1, ∆G° ) +2.3 kJ mol-1 at 5 °C, and ∆S° )
-68.5 ( 4 J mol-1 K-1. The relatively small ∆H° value
implies that the Pd-olefin and Pd-nitrile bond energies
are very similar. The negative entropy (∆S°) value for
this reaction is consistent with a greater loss in degrees
of freedom when the large 18:1 coordinates to palla-
dium(II) in place of o-tolunitrile.
In the case of 18:2 (Scheme 5), an equilibrium mixture
of complexes involving coordination to one or two double
bonds was observed. The major observed product was
the mononuclear [CpPd(PPh3)(18:2)]BF4 species, while
the {[CpPd(PPh3)]2(18:2)}(BF4)2 binuclear species was
produced as a minor product. In this system, K1 (0.22)
is 2 times larger than K2 (0.11).
In the reactions of [CpPd((PPh3)(o-MeC6H4CN)](BF4)
with 18:3, equilibrium mixtures contain two isomeric
mononuclear [CpPd(PPh3)(18:3)]+ complexes (10a and
11a) and the binuclear [CpPd(PPh3)]2(18:3)]2+ (12a).
The K1(10a) value (0.17) for the formation of isomer 10a
is very similar to that of K1 (0.19 ( 0.01) for the binding
of 18:1 in [CpPd(PPh3)(18:1)]+. The K2(10a) value for
the binding of the second [CpPd(PPh3)]+ to 10a to give
12a is essentially the same as K1(10a), which indicates
that the presence of the first [CpPd(PPh3)]+ on 18:3 does
not reduce the binding to the second [CpPd(PPh3)]+ unit.
The K1(11a) value (0.072) for the formation of isomer
11a is about half of the value (0.17) of K1(10a). Although
the difference between K1(10a) and K1(11a) is not large,
it is not obvious why on the basis of their structures
(Scheme 6) there would be a significant difference in
K1(10a) and K1(11a) values. The low stability of 11a is
also evident in the relatively high value of K2(11a) (0.47)
for the addition of the second [CpPd(PPh3)]+ unit to 11a.
Perhaps the most significant result of these studies
is that the K1 values for cis-3-hexene (0.43), 18:1 (0.19),
18:2 (0.22), and 18:3 (0.17) (for the major isomer) are
all very similar; the slightly higher value for cis-3-
hexene may reflect the overall smaller size of this olefin.
In addition, the K2 values for 18:2 (0.11) and 18:3 (0.20)
for the major isomer 10a are also similar, which
indicates that the binding of one [CpPd(PPh3)]+ unit
does not substantially reduce the binding ability of the
diene or triene to the second [CpPd(PPh3)]+ unit.
{[CpPd(PR3)]2(olefin)}(BF4)2 in CDCl3 at 25 °C
According to Scheme 7
compd
PR3
olefin
K1
K2
3a
3b
3c
7a
7b
7d
7c
8
PPh3
cis-3-hexene 0.43 ( 0.02
PMePh2 cis-3-hexene 3.2 ( 0.1
PMe3
PPh3
PMePh2 18:1
PEt3
PMe3
PPh3
PPh3
cis-3-hexene 21.1 ( 0.1
18:1
0.19 ( 0.01
1.64 ( 0.05
2.50 ( 0.05
5.52 ( 0.06
0.22 ( 0.02
0.17 ( 0.02
(10a)
18:1
18:1
18:2
18:3
0.11 ( 0.01
0.20 ( 0.02
(10a)
10
10
PPh3
18:3
0.072 ( 0.009 0.47 ( 0.04
(11a)
(11a)
7a
7a
7a
7a
PPh3
PPh3
PPh3
PPh3
18:1
18:1
18:1
18:1
0.56 ( 0.11a
0.43 ( 0.11b
0.37 ( 0.11c
0.30 ( 0.11d
a At -10.0 ( 0.1 °C. b At -5.0 ( 0.1 °C. c At 5.0 ( 0.1 °C. d At
10.0 ( 0.1 °C.
products which allowed the equilibrium constants to be
calculated. The equilibrium constants for cis-3-hexene
and the fatty acid methyl esters (18:1, 18:2, and 18:3)
determined by this method are presented in Table 1.
The K1 values for the cis-3-hexene complexes [CpPd-
(PR3)(cis-3-hexene)]BF4 increase with the phosphines in
the order: PPh3 (0.43) < PMePh2 (3.21) < PMe3 (21.1).
A similar trend in the K1 values was observed for the
methyl oleate [CpPd(PR3)(18:1)]BF4 complexes: PPh3
(0.19) < PMePh2 (1.64) < PEt3 (2.50) < PMe3 (5.52). The
cone angles and the pKa values13 for these phosphines
are PPh3 (145°, 2.73), PMePh2 (136°, 4.57), PEt3 (132°,
8.69), and PMe3 (118°, 8.65). Since PMe3 and PEt3 have
very similar basicities and, therefore, electron-donating
abilities, the lower K1 for the PEt3 complex (2.50) as
compared with that (5.52) for the PMe3 complex is
probably due to the greater steric effect of PEt3. The
PEt3 and PMePh2 ligands have similar cone angles (132
vs 136°), but 18:1 binds more strongly to the PEt3
complex, as indicated by the K1 values (2.50 vs 1.64).
This difference in K1 values suggests that the more
strongly donating PEt3 ligand promotes strong olefin
coordination by back-bonding. Thus, both electronic and
steric effects of the phosphine ligand appear to play a
role in the observed trend in K1 values. It should be
noted that PPh3 is both the most bulky and least basic
of the phosphines, which results in its complex having
the lowest K1 value.
K1 values for the formation of the [CpPd(PPh3)(olefin)]-
BF4 complexes are nearly the same (within a factor of
2) for cis-3-hexene, 18:1, and 18:2. Moreover, these
values are similar to those reported6a previously for cis-
2-butene (0.22 ( 0.05); however, they are significantly
larger than those of trans-olefins, e.g., trans-2-butene
(0.04), but smaller than those of terminal olefins, e.g.,
1-butene (1.14), styrene (0.63), and ethylene (13.5 (
0.6).6a
The equilibrium constant (K1) for the formation of
[CpPd(PPh3)(18:1)]+ was also measured at 10.0 ( 0.1,
5.0 ( 0.1, -5.0 ( 0.1, and -10.0 ( 0.1 °C (Table 1).
The thermodynamic parameters calculated from a van’t
Conclusions
Cationic Pd(II)-olefin complexes of the type [CpPd-
(PR3)(olefin)]BF4 (PR3 ) PPh3, PMePh2, PEt3, PMe3;
olefin ) 18:1, 18:2, 18:3, cis-3-hexene, 1,4-pentadiene)
and {[CpPd(PR3)]2(olefin)}2+ (olefin ) 1,4-pentadiene,
18:2, 18:3) have been characterized by 1H, 13C{1H}, and
31P{1H} NMR spectroscopy in solution. Equilibrium
constants for the formation of these complexes have led
to the following observations. (a) Olefin binding in-
creases significantly with the PR3 ligand in the com-
plexes in the order PPh3 < PMePh2 < PEt3 < PMe3. (b)
Equilibrium constants (K1) for the binding of all of the
cis-olefins to [CpPd(PPh3)]+ are similar. Since this is
also true for 18:1, 18:2, and 18:3, it will be difficult to
separate these fatty acid methyl esters from each other
on the basis of their ability to coordinate to one [CpPd-
(PPh3)]+ unit. (c) Equilibrium constants (K2) for the
binding of a second [CpPd(PPh3)]+ unit to the diene (18:
2) and triene (18:3) are also similar to each other and
(13) Liu, H.-Y.; Eriks, K.; Prock, A.; Giering, W. P. Organometallics
1990, 9, 1758.

Binding of Unsaturated Fatty Acid Esters to Pd(II)
Organometallics, Vol. 24, No. 7, 2005 1733
1
3a: H NMR (400 MHz, CDCl3/acetone-d6, 25 °C) δ 7.40-
7.50 (m, 15H, Ph), 5.65 (d, JPH ) 2.8 Hz, 5H, C5H5), 3.95 (m,
to their K1 values, which shows that the binding of one
[CpPd(PPh3)]+ unit does not significantly reduce the
ability of a 1,4-diene or 1,4-triene to bind to a second
[CpPd(PPh3)]+ unit.
3
2H, H3,4), 2.04 (m, 4H, H2,5), 0.88 (t, JHH ) 7.6 Hz, 6H, H1,6).
1
3b: H NMR (400 MHz, CDCl3/acetone-d6, 25 °C) δ 7.30-
7.50 (m, 10H, Ph), 5.71 (d, JPH ) 2.4 Hz, 5H, C5H5), 4.02 (m,
2
2H, H3,4), 2.17 (d, JPH ) 11.6 Hz, 3H, PMePh2) 2.05 (m, 4H,
3
Experimental Section
H
2,5), 0.92 (t, JHH ) 7.5 Hz, 6H, H1,6).
3c: 1H NMR (400 MHz, CDCl3/acetone-d6, 25 °C) δ 5.71 (d,
All of the reactions were carried out under an argon
atmosphere. Diethyl ether, methylene chloride, hexanes, and
tetrahydrofuran were purified on alumina using a Solv-Tek
solvent purification system, as described by Grubbs and co-
workers.14 Acetone was refluxed over and distilled from
CaSO4.15 [CpPd(PPh3)(o-MeC6H4CN)]BF4,6a CpPd(PPh3)Cl,7
CpPd(PEt3)Cl,7 and (PR3)2Pd2Cl416 were synthesized by litera-
ture procedures. All other chemicals were reagent grade and
were used as received. 1H, 13C{1H}, and 31P{1H} NMR spectra
were recorded on a Bruker DRX-400 spectrometer. Proton and
carbon chemical shifts were measured relative to internal
deuterated solvents, while 85% H3PO4 (aqueous) was the
external reference for phosphorus chemical shifts; positive
values are downfield of the respective reference. See H and C
JPH ) 2.4 Hz, 5H, C5H5), 4.40 (m, 2H, H3,4), 2.11 (m, 4H, H2,5),
1.53 (d, 3JPH ) 12.4 Hz, 9H, 3CH3), 0.99 (t, 3JHH ) 7.6 Hz, 6H,
H1,6).
Syntheses of [CpPd(PR3)(1,4-pentadiene)]BF4 (4a,b)
and {[CpPd(PR3)]2(1,4-pentadiene)}(BF4)2 (5a,b and 6a,b).
The same procedure as for the synthesis of 3a-c above was
followed for the synthesis of 4-6.
4a (PR3 ) PPh3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 7.50 (m, 15H, Ph), 5.88 (d, JPH ) 2.8 Hz, 5H, C5H5),
5.13 (m, 2H, H3,6), 4.73 (m, 2H, H2,7), 4.31 (m, 2H, H1,8), 3.21
3
4
(dd, JHH ) 7.6 Hz, JHH ) 2.8 Hz, 2H, H4,5); 13C{1H} NMR
2
(100.6 MHz, CDCl3, 25 °C) δ 133.30 (d, JPC ) 11.6 Hz, Co),
4
3
132.08 (d, JPC ) 2.8 Hz, Cp), 129.17 (d, JPC ) 11.2 Hz, Cm),
128.06 (d,1JPC ) 50.0 Hz, Ci), 116.80 (C2,4), 103.88 (d, JPC
)
1
labels in the schemes for the H and 13C NMR assignments.
2.0 Hz, C5H5),101.00 (C1,5), 44.12 (C3); 31P{1H} NMR (162 MHz,
CDCl3, 25 °C) δ 35.51 (PPh3).
In the 31P{1H} spectra of the [CpPd(PR3)(olefin)]BF4 complexes,
small amounts of the [CpPd(PR3)2]BF4 complexes were often
detected.6a
4b (PR3 ) PMe3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 5.94 (d, JPH ) 2.4 Hz, 5H, C5H5), 5.64 (m, 2H, H3,6),
Syntheses of the Complexes CpPd(PR3)Cl (PR3
)
3
5.05 (m, 2H, H2,7), 4.78 (m, 2H, H1,8), 3.59 (d, JHH ) 8.0 Hz,
PMePh2 (1), PMe3 (2)). The complexes were synthesized by
following the literature method for CpPd(PPh3)Cl.6,7 Thallium
cyclopentadienyl (0.31 g, 1.10 mmol) was suspended in 100
mL of tetrahydrofuran (THF), and (PR3)2Pd2Cl4 (0.50 g, 0.57
mmol) was added. The mixture immediately changed color to
green and was stirred at room temperature for 1 h. The
resulting solution was filtered to remove thallium chloride. The
solvent was removed under reduced pressure to leave a dark
green solid. The solid was dissolved in a minimum amount of
benzene and layered with hexane to yield dark green needles
of the desired products in 60-70% yield. Anal. Calcd for C18H18-
PPdCl (1): C, 53.09; H, 4.45. Found: C, 52.99; H, 4.45. Anal.
Calcd for C8H14PPdCl (2): C, 33.94; H, 4.98. Found: C, 34.26;
H, 5.06.
2H, H4,5), 1.64 (d, JPH ) 12.8 Hz, 9H, 3CH3); 13C{1H} NMR
2
(100.6 MHz, CDCl3/acetone-d6, 25 °C) δ 116.06 (C2,4), 101.61
1
(d, JPC ) 2.4 Hz, C5H5), 99.04 (C1,5), 37.64 (C3), 18.13 (d, JPC
) 32.2 Hz, CH3); 31P{1H} NMR (162 MHz, CDCl3/acetone-d6,
25 °C) δ 5.45 (PMe3).
5a (PR3 ) PPh3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 7.31-7.70 (m, 30H, 2PPh3), 5.94 (d, JPH ) 2.1 Hz,
10H, C5H5), 4.86 (m, 2H, H3,6), 3.86 (m, 4H, H1,2,7,8), 2.93 (dd,
3JHH ) 7.6 Hz, JHH ) 2.8 Hz, 2H, H4,5); 13C{1H} NMR (100.6
4
2
MHz, CDCl3, 25 °C) δ 133.44 (d, JPC ) 10.8 Hz, Co), 131.93
(Cp), 129.35 (d,3JPC ) 9.0 Hz, Cm), 128.10 (d, JPC ) 48.9 Hz,
1
Ci), 104.23 (d, JPC ) 1.6 Hz, C5H5), 98.46 (C2,4), 65.19 (C1,5),
37.58 (C3); 31P{1H} NMR (162 MHz, CDCl3, 25 °C) δ 37.90.
1
5b (PR3 ) PMe3): H NMR (400 MHz, CD3NO2, 25 °C) δ
1: 1H NMR (400 MHz, CDCl3, 25 °C) δ 7.40-7.65 (m, 10H,
Ph), 5.57 (d, JPH ) 2.4 Hz, 5H, C5H5), 2.15 (d, 2JPH ) 11.6 Hz,
3H, PMePh2); 13C{1H} NMR (100.6 MHz, CDCl3, 25 °C) δ
6.08 (d, JPH ) 2.4 Hz, 10H, C5H5), 4.87 (m, 1H, H3,6), 4.62 (m,
4H, H1,2,7,8), 3.73 (dd, 3JHH ) 7.6 Hz, 3JHH ) 2.0 Hz, 2H, H4,5),
1.71 (d 2JPH ) 12.4 Hz, 9H, 3CH3); 13C{1H} NMR (100.6 MHz,
CD3NO2, 25 °C) δ 102.95 (d, JPC ) 1.5 Hz, C5H5), 94.66 (C2,4),
1
2
134.59 (d, JPC ) 49.2 Hz, Ci), 132.11 (d, JPC ) 11.9 Hz, Co),
4
3
130.71 (d, JPC ) 2.7 Hz, Cp), 128.73 (d, JPC ) 10.9 Hz, Cm),
1
67.89 (C1,5), 42.90 (C3), 17.62 (d, JPC ) 33.1 Hz, CH3); 31P-
1
100.94 (d, JPC ) 2.6 Hz, C5H5), 15.41 (d, JPC ) 33.3 Hz,
{1H} NMR (162.0 MHz, CD3NO2, 25 °C) δ 5.88 (PMe3).
6a (PR3 ) PPh3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 7.31-7.70 (m, 30H, 2PPh3), 5.93 (d, JPH ) 2.1 Hz,
10H, C5H5), 4.14 (m, 2H, H3,6), 3.72 (m, 2H, H1,2,7,8), 2.85 (dd,
PMePh2); 31P{1H} NMR (162 MHz, CDCl3, 25 °C) δ 23.44
(PMePh2).
2: 1H NMR (400 MHz, CDCl3, 25 °C) δ 5.71 (d, JPH ) 2.4
Hz, 5H, C5H5), 1.61 (d, JPH ) 12.0 Hz, 9H, PMe3); 13C{1H}
2
4
3JHH ) 7.6 Hz, JHH ) 2.8 Hz, 2H, H4,5); 13C{1H} NMR (100.6
NMR (100.6 MHz, CDCl3, 25 °C) δ 99.48 (d, JPC ) 2.7 Hz,
2
MHz, CDCl3, 25 °C) δ 133.35 (d, JPC ) 10.8 Hz, Co), 131.22
C5H5), 18.68 (d, JPC ) 32.1 Hz, PMe3); 31P{1H} NMR (162
1
3
(Cp), 129.09 (d, JPC ) 9.0 Hz, Cm), 104.23 (d, JPC ) 1.6 Hz,
MHz, CDCl3, 25 °C) δ 0.47 (PMe3).
C5H5), 94.40 (C2,4), 64.99 (C1,5), 37.17 (C3); 31P{1H} NMR (162
MHz, CDCl3, 25 °C) δ 37.40 (PPh3).
Syntheses of [CpPd(PR3)(cis-3-hexene)]BF4 (PR3
)
PPh3 (3a), PMePh2 (3b), PMe3 (3c)). A suspension of AgBF4
(0.10 mmol) in a chloroform/acetone (1:1) (10.0 mL) solvent
mixture was treated with 0.33 mmol of cis-3-hexene. To this
mixture was added solid CpPd(PR3)Cl (0.10 mmol) with
stirring at 0 °C. After it was stirred for 15 min, the red solution
was filtered to remove AgCl. The filtrate was layered with
hexane to yield a red-brown precipitate of the complexes.
Attempted purification to remove the excess olefin resulted
in gradual decomposition of the products. Hence, the complexes
were prepared in situ and characterized in chloroform-d/
acetone-d6 (7:1) solvent mixtures.
1
6b (PR3 ) PMe3): H NMR (400 MHz, CD3NO2, 25 °C) δ
6.07 (d, JPH ) 2.4 Hz, 10H, C5H5), 5.13 (m, 2H, H3,6), 4.76 (m,
4H, H1,2,7,8), 3.68 (dd, 3JHH ) 7.6 Hz, 2JHH ) 2.0 Hz, 2H, H4,5),
1.71 (d, 2JPH ) 12.4 Hz, 9H, 3CH3); 13C{1H} NMR (100.6 MHz,
CD3NO2, 25 °C) δ 102.80 (d, JPC ) 2.1 Hz, C5H5), 97.50 (C2,4),
1
67.89 (C1,5), 47.50 (C3), 17.60 (d, JPC ) 33.0 Hz, CH3); 31P-
{1H} NMR (162 MHz, CD3NO2, 25 °C) δ 5.86 (PMe3).
Syntheses of [CpPd(PR3)(18:1)]BF4 (PR3 ) PPh3 (7a),
PMePh2 (7b), PMe3 (7c), PEt3 (7d)). As described for the
synthesis of the cis-3-hexene complexes, the complexes [CpPd-
(PR3)(18:1)]BF4 (PR3 ) PPh3 (7a), PMePh2 (7b), PMe3 (7c),
PEt3 (7d)) were all synthesized by the following method. To a
suspension of AgBF4 (0.11 mmol) in a chloroform/acetone (1:
1) (10.0 mL) solvent mixture was added 0.33 mmol of methyl
oleate (18:1). To this solution was added solid CpPd(PR3)Cl
(0.11 mmol) with stirring at 0 °C. After it was stirred for 15
(14) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(15) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon: New York, 1980.
(16) Chatt, J.; Venanzi, L. M. J. Chem. Soc. 1957, 2351

1734 Organometallics, Vol. 24, No. 7, 2005
Ghebreyessus et al.
2
min, the red solution was filtered to remove AgCl. The filtrate
was layered with hexane to yield a red-brown precipitate.
Subsequent purification attempts to remove the excess 18:1
resulted in decomposition. Hence, further reactions and char-
acterizations of the complexes were conducted in chloroform-
d/acetone-d6 (7:1) solution.
1.54 (d, JPH ) 12.4 Hz, 9H, 3PMe3), 1.50 (m, 2H, H17), 1.26
(m, 14H, H3,15), 0.87 (t, 3JHH ) 7.2 Hz, 3H, H18); 13C{1H} NMR
(100.6 MHz, CDCl3/acetone-d6, 25 °C) δ 173.80 (CdO), 131.95
(C13), 131.83 (C12), 102.38 (d, JPC ) 1.4 Hz, C5H5), 91.22 (C10),
91.18 (C9), 50.95 (OMe), 33.57 (C2), 33.48 (C11), 32.64 (C8), 30.95
(C14), 30.80-24.37 (C3,15), 21.92 (C17), 17.17 (d 1JPC ) 32.8 Hz,
PMe3), 13.49 (C18); 31P{1H} NMR (162 MHz, CDCl3/acetone-
d6, 25 °C) δ 4.84 (PMe3).
7a: 1H NMR (400 MHz, CDCl3/acetone-d6, 25 °C) δ 7.51 (m,
15H, Ph), 5.73 (d, JPH ) 2.8 Hz, 5H, C5H5), 4.08 (m, 2H, H9,10),
3
3.51 (s, 3H, OMe), 2.31 (m, 2H, H11), 2.23 (t, JHH ) 7.2 Hz,
9a (PR3 ) PPh3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 7.49-7.52 (m, 15H, Ph), 5.87 (d, JPH ) 1.6 Hz, 5H,
C5H5), 5.86 (d, JPH ) 1.6 Hz, 5H, C5H5), 5.43 (m, 2H, H12,13),
4.00 (m, 2H, H12,13), 3.89 (m, 2H, H9,10), 3.60 (s, 3H, OMe), 3.01
(m, 2H, H11), 2.65 (m, 2H, H8), 2.20 (t, 3JHH ) 6.4 Hz, 2H, H2),
2.12 (m, 2H, H14), 1.52 (m, 2H, H17), 1.22 (m, 14H, H3,15), 0.82
(t, 3JHH ) 7.2 Hz, 3H, H18); 13C{1H} NMR (100.6 MHz, CDCl3/
acetone-d6, 25 °C) δ 173.64 (CdO), 133.41 (d, 1JPC ) 20.4 Hz,
Ci), 132.36 (d, JPC ) 13.2 Hz, Co), 132.20 (d, JPC ) 2.1 Hz,
Cp), 125.94 (d, JPC ) 8.0 Hz, Cm), 101.38 (d, JPC ) 1.5 Hz,
C5H5), 101.30 (d, JPC ) 1.5 Hz, C5H5), 97.28 (C13), 97.14 (C12),
94.91 (C10), 94.87 (C9), 50.91 (OMe), 33.54 (C2), 33.48 (C11),
32.60 (C8), 30.93 (C14), 30.84-21.98, (C3,15), 13.49 (C18); 31P-
{1H} NMR (162 MHz, CDCl3/acetone-d6, 25 °C) δ 38.37, (PPh3),
38.32 (PPh3).
2H, H2), 2.11 (m, 2H, H8), 1.34 (m, 2H, H17), 1.20 (m, 20H,
3
H
3,12), 0.85 (t, JHH ) 7.0 Hz, 3H, H18); 13C{1H} NMR (100.6
MHz, CDCl3/acetone-d6, 25 °C) δ 173.69 (CdO), 133.25 (d, 2JPC
) 11.5 Hz, Co), 132.22 (d, 4JPC ) 2.7 Cp), 129.4 (d, 1JPC ) 20.7
Hz, Ci), 128.05 (Cm), 104.85 (d, JPC ) 1.9 Hz, C5H5), 97.40 (C10),
97.27 (C9), 50.96 (OMe), 35.52 (C2), 32.47 (C11), 31.41 (C8),
31.30-24.38, (C3,12), 22.26 (C17), 13.66 (C18); 31P{1H} NMR (162
MHz, CDCl3/acetone-d6, 25 °C) δ 38.51 (PPh3).
2
4
3
1
7b: H NMR (400 MHz, CDCl3/acetone-d6, 25 °C) δ 7.40-
7.65 (m, 10H, Ph), 5.77 (d, JPH ) 2.4 Hz, 5H, C5H5), 4.10 (m,
2H, H9,10), 3.52 (s, 3H, OMe), 2.32 (m, 2H, H11), 2.25 (t, 3JHH
)
2
7.2 Hz, 2H, H2), 2.15 (d, JPH ) 11.6 Hz, 9H, PMePh2), 2.13
(m, 2H, H8), 1.57 (m, 2H, H17), 1.21 (m, 20H, H3,12), 0.83 (t,
3JHH ) 7.0 Hz, 3H, H18); 13C{1H} NMR (100.6 MHz, CDCl3/
acetone-d6, 25 °C) δ 173.53 (CdO), 134.59 (d, 1JPC ) 49.2 Hz,
1
9b (PR3 ) PMe3): H NMR (400 MHz, CDCl3/acetone-d6,
2
4
Ci), 132.11 (d, JPC ) 11.9 Hz, Co), 130.71 (d, JPC ) 2.7 Hz,
25 °C) δ 5.84 (d, JPH ) 2.4 Hz, 5H, C5H5), 5.82 (d, JPH ) 2.3
3
Cp), 128.73 (d, JPC ) 10.9 Hz, Cm), 103.51 (d, JPC ) 1.8 Hz,
Hz, 5H, C5H5), 4.32 (m, 2H, H12,13), 4.30 (m, 2H, H9,10), 3.31 (s,
3H, OMe), 3.09 (m, 2H, H11), 2.63 (m, 2H, H8), 2.22 (t, 3JHH
)
C5H5), 95.54 (C10), 95.52 (C9), 51.94 (OMe), 35.52 (C2), 32.47
(C11), 31.41 (C8), 31.30-24.33 (C3,12), 22.24 (C17), 15.41 (d, 1JPC
) 33.3 Hz, PMePh2), 13.66 (C18); 31P{1H} NMR (162 MHz,
CDCl3/acetone-d6, 25 °C) δ 38.41 (PMePh2).
2
6.5 Hz, 2H, H2), 2.17 (m, 2H, H14), 1.57 (d, JPH ) 12.4 Hz,
9H, 3PMe3), 1.55 (d, 2JPH ) 12.4 Hz, 9H, 3PMe3), 1.50 (m, 2H,
H17), 1.19 (m, 14H, H3,15), 0.80 (t, 3JHH ) 7.0 Hz, 3H, H18); 13C-
{1H} NMR (100.6 MHz, CDCl3/acetone-d6, 25 °C) δ 173.75
(CdO), 102.76 (d, JPC ) 1.5 Hz, C5H5), 102.74 (d, JPC ) 1.5
Hz, C5H5), 93.27 (C13), 93.11 (C12), 91.22 (C10), 91.18 (C9), 51.0
(OMe), 33.48 (C2), 33.38 (C11), 32.60 (C8), 30.93 (C14), 30.82-
7c: 1H NMR (400 MHz, CDCl3/acetone-d6, 25 °C) δ 5.81 (d,
JPH ) 2.4 Hz, 5H, C5H5), 4.52 (m, 2H, H9,10), 3.58 (s, 3H, OMe),
2
2.17 (m, 4H, H8,11), 1.92 (m, 2H, H2), 1.63 (d, JPH ) 12.4 Hz,
9H, 3CH3), 1.54 (m, 2H, H17), 1.24 (m, 20H, H3,12), 0.87 (t, 3JHH
) 7.0 Hz, 3H, H18); 13C{1H} NMR (100.6 MHz, CDCl3/acetone-
d6, 25 °C) δ 173.66 (CdO), 102.38 (d, JPC ) 2.1 Hz, C5H5), 93.47
(C10), 93.34 (C9), 50.93 (OMe), 33.49 (C2), 33.39 (C11), 33.02
(C8), 31.44-24.39 (C3,12), 22.22 (C17), 17.12 (d, 1JPC ) 32.90 Hz,
PMe3), 13.63 (C18); 31P{1H} NMR (162 MHz, CDCl3/acetone-
d6, 25 °C) δ 4.85 (PMe3).
1
1
21.94 (C3,15), 17.15 (d JPC ) 32.7 Hz, PMe3), 17.13 (d, JPC
)
32.6 Hz, PMe3), 13.49 (C18); 31P{1H} NMR (162 MHz, CDCl3/
acetone-d6, 25 °C) δ 4.26 (PMe3), 4.08 (PMe3).
Syntheses of [CpPd(PR3)(18:3)]BF4 (10a,b and 11a,b)
and {[CpPd(PR3)]2(18:3)}(BF4)2 (12a,b). The same proce-
dure as for the synthesis of complexes 7a-c was followed for
the synthesis of 10-12.
7d: 1H NMR (400 MHz, CDCl3/acetone-d6, 25 °C) δ 5.74 (d,
JPH ) 2.4 Hz, 5H, C5H5), 4.38 (m, 2H, H9,10), 3.48 (s, 3H, OMe),
1.97 (m, 4H, H8,11), 1.83 (m, 6H, 3CH2), 1.72 (m, 2H, H2), 1.42
(m, 2H, H17), 1.11 (m, 20H, H3,12), 0.95 (m, 9H, 3CH3), 0.70
(t,3JHH ) 7.0 Hz, 3H, H18); 13C{1H} NMR (100.6 MHz, CDCl3/
acetone-d6, 25 °C) δ 173.51 (CdO), 102.48 (d, JPC ) 2.2 Hz,
C5H5), 93.34 (C10), 93.19 (C9), 50.83 (OMe), 33.39 (C2), 33.35
(C11), 33.05 (C8), 31.44-24.30 (C3,12), 19.12 (C17), 17.00 (d, 1JPC
1
10a (PR3 ) PPh3): H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 7.48-7.50 (m, 15H, Ph), 5.79 (d, JPH ) 2.4 Hz, 5H,
C5H5), 5.42 (m, 2H, H15,16), 5.29 (m, 2H, H12,13), 4.09 (m, 2H,
H
9,10), 3.66 (s, 3H, OMe), 3.08 (m, 1H, H11), 2.80 (m, 1H, H14),
2.21 (t, 3JHH ) 6.5 Hz, 2H, H2), 2.15 (m, 2H, H8), 1.52 (m, 2H,
H17), 1.22 (m, 10H, H3), 0.84 (t, JHH ) 7.2 Hz, 3H, H18); 13C-
3
{1H} NMR (100.6 MHz, CDCl3/acetone-d6, 25 °C) δ 173.57
2
) 28.2 Hz, PEt3), 13.40 (C18), 7.91 (d, JPC ) 19.3, PEt3); 31P-
2
(CdO), 133.96 (C16), 132.52 (C15), 133.20 (d, JPC ) 11.3 Hz,
{1H} NMR (162 MHz, CDCl3/acetone-d6, 25 °C) δ 42.52 (PEt3).
Syntheses of [CpPd(PR3)(18:2)]BF4 (8a,b) and {[CpPd-
(PR )]2(18:2)}(BF4)2 (9a,b). The same procedure as for the
synt3hesis of complexes 7a-c was followed for the synthesis
of 8 and 9.
4
Co), 132.10 (d, JPC ) 2.2 Hz, Cp), 132.18 (C15), 131.96 (C13),
3
130.30 (C12), 127.50 (d, JPC ) 4.0 Hz, Cm), 104.72 (d, JPC
)
2.20 Hz, C5H5), 94.60 (C10), 94.50 (C9), 50.97 (OMe), 33.67 (C2),
32.60 (C11), 31.26 (C8), 30.84 (C14), 27.27-24.35 (C3), 21.98
(C17), 13.72 (C18); 31P{1H} NMR (162 MHz, CDCl3/acetone-d6,
25 °C) δ 35.27 (PPh3).
8a (PR3 ) PPh3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 7.49-7.52 (m, 15H, Ph), 5.75 (d, JPH ) 2.4 Hz, 5H,
C5H5), 5.43 (m, 2H, H12,13), 4.06 (m, 2H, H9,10), 3.60 (s, 3H,
10b (PR3 ) PMe3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 5.75 (d, JPH ) 2.4 Hz, 5H, C5H5), 5.35 (m, 2H, H15,16),
5.33 (m, 2H, H12,13), 4.35 (m, 2H, H9,10), 3.52 (s, 3H, OMe), 3.05
3
OMe), 3.01 (m, 1H, H11), 2.65 (m, 1H, H8), 2.20 (t, JHH ) 6.4
3
Hz, 2H, H2), 2.12 (m, 2H, H14), 1.52 (m, 2H, H17), 1.22 (m, 14H,
(m, 1H, H11), 2.90 (m, 1H, H14), 2.27 (t, JHH ) 6.7 Hz, 2H,
3
2
H
3,15), 0.80 (t, JHH ) 7.2 Hz, 3H, H18); 13C{1H} NMR (100.6
H2), 2.18 (m, 2H, H8), 1.61 (d, JPH ) 12.3 Hz, 9H, 3PMe3),
3
MHz, CDCl3/acetone-d6, 25 °C) δ 173.64 (CdO), 133.41 (d, 1JPC
) 20.4 Hz, Ci), 132.36 (d, JPC ) 13.2 Hz, Co), 132.20 (d, JPC
) 2.1 Hz, Cp), 129.25 (C13), 129.14 (C12), 125.94 (d, JPC ) 8.0
1.58 (m, 2H, H17), 1.20 (m, 10H, H3), 0.91 (t, JHH ) 7.2 Hz,
3H, H18); 13C{1H} NMR (100.6 MHz, CDCl3/acetone-d6, 25 °C)
δ 173.83 (CdO), 133.63 (C16), 132.18 (C15), 126.54 (C13), 126.25
(C12), 102.33 (d, JPC ) 2.0 Hz, C5H5), 90.70 (C10), 90.40 (C9),
50.96 (OMe), 33.66 (C2), 32.63 (C11), 31.30 (C8), 30.94 (C14),
27.37-24.31 (C3), 21.92 (C17) 17.19 (d, 1JPC ) 32.7 Hz, PMe3),
15.50 (C18); 31P{1H} NMR (162 MHz, CDCl3/acetone-d6, 25 °C)
δ 5.22 (PMe3).
2
4
3
Hz, Cm), 104.75 (d, JPC ) 2.0 Hz, C5H5), 94.94 (C10), 94.87 (C9),
50.91 (OMe), 33.54 (C2), 33.48 (C11), 32.60 (C8), 30.93 (C14),
30.84-24.35 (C3,15), 21.98 (C17), 13.49 (C18); 31P{1H} NMR (162
MHz, CDCl3/acetone-d6, 25 °C) δ 33.69 (PPh3).
1
8b (PR3 ) PMe3): H NMR (400 MHz, CDCl3/acetone-d6,
1
25 °C) δ 5.74 (d, JPH ) 2.4 Hz, 5H, C5H5), 5.34 (m, 2H, H12,13),
4.45 (m, 2H, H9,10), 3.67 (s, 3H, OMe), 3.03 (m, 1H, H11), 2.63
(m, 1H, H8), 2.25 (t, 3JHH ) 6.6 Hz, 2H, H2), 2.15 (m, 2H, H14),
11a (PR3 ) PPh3): H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 7.48-7.50 (m, 15H, Ph), 5.81 (d, JPH ) 2.8 Hz, 5H,
C5H5), 5.33 (m, 2H, H12,13), 5.29 (m, 2H, H9,10), 4.01 (m, 2H,

Binding of Unsaturated Fatty Acid Esters to Pd(II)
Organometallics, Vol. 24, No. 7, 2005 1735
Table 2. Crystal Data and Structure Refinement
Details for 5b
H
15,16), 3.68 (s, 3H, OMe), 3.08 (m, 1H, H11), 2.85 (m, 1H, H14),
2.20 (t, 3JHH ) 6.4 Hz, 2H, H2), 2.12 (m, 2H, H8), 1.52 (m, 2H,
H17), 1.22 (m, 10H, H3), 0.80 (t, JHH ) 7.2 Hz, 3H, H18); 13C-
3
a
empirical formula
C21H36B2F8O4.5P2Pd2
{1H} NMR (100.6 MHz, CDCl3/acetone-d6, 25 °C) δ 173.82
formula wt
808.86
1
2
(CdO), 133.41 (d, JPC ) 20.4 Hz, Ci), 132.36 (d, JPC ) 13.2
Hz, Co), 132.20 (d, 4JPC ) 2.1 Hz, Cp), 127.01 (C13), 126.91 (C12),
125.94 (d, 3JPC ) 8.0 Hz, Cm), 125.81 (C10), 125.60 (C9), 102.40
(d, JPC ) 2.1 Hz, C5H5), 98.92 (C16), 97.14 (C15), 51.03 (OMe),
33.65 (C2), 32.60 (C11), 30.61 (C8), 30.30 (C14), 27.12-24.35 (C3),
21.98 (C17), 15.72 (C18); 31P{1H} NMR (162 MHz, CDCl3/
acetone-d6, 25 °C) δ 37.87 (PPh3).
temp
180(2) K
0.710 73 Å
monoclinic
C2/c
wavelength
cryst syst
space group
unit cell dimens
a
21.919(5) Å
19.441(4) Å
16.339(4) Å
90°
b
c
11b (PR3 ) PMe3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 5.74 (d, JPH ) 2.4 Hz, 5H, C5H5), 5.26 (m, 2H, H12,13),
5.23 (m, 2H, H9,10), 4.37 (m, 2H, H15,16), 3.31 (s, 3H, OMe), 3.06
R
â
104.285(4)°
90°
γ
6747(3) Å3
8
3
V
Z
(m, 1H, H11), 2.80 (m, 1H, H14), 2.23 (t, JHH ) 6.5 Hz, 2H,
2
H2), 2.13 (m, 2H, H8), 1.59 (d, JPH ) 12.4 Hz, 9H, 3PMe3),
density (calcd)
abs coeff
F(000)
cryst size
θ range for data collecn
index ranges
h
k
l
no. of rflns collected
no. of indep rflns
completeness to θ ) 26.37°
abs cor
max, min transmissn
refinement method
1.592 Mg/m3
1.230 mm-1
3216
3
1.54 (m, 2H, H17), 1.21 (m, 10H, H3), 0.88 (t, JHH ) 7.2 Hz,
3H, H18); 13C{1H} NMR (100.6 MHz, CDCl3/acetone-d6, 25 °C)
δ 173.81 (CdO), 132.02 (C13), 130.56 (C12), 125.81 (C10), 125.60
(C9), 102.40 (d, JPC ) 2.1 Hz, C5H5), 93.17 (C16), 90.91 (C15),
51.03 (OMe), 33.65 (C2), 32.62 (C11), 31.28 (C8), 30.89 (C14),
27.17-24.37 (C3), 21.88 (C17), 17.16 (d, 1JPC ) 32.9 Hz, PMe3),
13.72 (C18); 31P{1H} NMR (162 MHz, CDCl3/acetone-d6, 25 °C)
δ 5.13 (PMe3).
0.30 × 0.15 × 0.08 mm3
2.46-26.37°
-26 to +27
-24 to +24
-20 to +20
27 365
12a (PR3 ) PPh3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 7.48-7.50 (m, 15H, Ph), 5.92 (d, JPH ) 2.2 Hz, 5H,
C5H5), 5.91 (d, JPH ) 2.2 Hz, 5H, C5H5), 5.33 (m, 2H, H12,13),
4.03 (m, 2H, H15,16), 4.01 (m, 2H, H9,10), 3.69 (s, 3H, OMe), 3.19
6889 (R(int) ) 0.0459)
99.7%
semiempirical from equivalents
1, 0.72
3
full-matrix least squares on F2
(m, 2H, H14), 3.04 (m, 2H, H11), 2.40 (t, JHH ) 7.0 Hz, 2H,
H2), 2.15 (m, 2H, H8), 1.52 (m, 2H, H17), 1.22 (m, 10H, H3),
no. of data/restraints/params 6889/1/402
goodness of fit on F2
1.041
0.86 (t, JHH ) 7.2 Hz, 3H, H18); 13C{1H} NMR (100.6 MHz,
3
final R indices (I > 2σ(I))b
1
CDCl3/acetone-d6, 25 °C) δ 173.78 (CdO), 133.41 (d, JPC
20.4 Hz, Ci), 132.36 (d, JPC ) 13.2 Hz, Co), 132.20 (d, JPC
)
)
2
4
R1
0.0636
0.1714
wR2
3
2.1 Hz, Cp), 126.41 (C13), 126.25 (C12), 125.94 (d, JPC ) 8.0
Hz, Cm), 102.78 (d, JPC ) 2.0 Hz, C5H5), 102.70 (d, JPC ) 2.1
Hz, C5H5), 94.82 (C16), 94.80 (C15), 94.65 (C10), 94.55 (C9), 51.07
(OMe), 33.58 (C2), 32.60 (C11), 29.15 (C8), 28.91 (C14), 28.61
(C8), 27.14-24.37 (C3), 21.96, (C17), 15.78 (C18); 31P{1H} NMR
(162 MHz, CDCl3/acetone-d6, 25 °C) δ 38.07 (PPh3), 38.03
(PPh3).
R indices (all data)b
R1
wR2
0.0915
0.1955
largest diff peak, hole
2.211, -1.165 e Å-3
a H atoms of 4.5 water solvent are not included. b R1 ) ∑||Fo|
- |Fc||/∑|Fo| and wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo2)2]}1/2
.
2
2
12b (PR3 ) PMe3): 1H NMR (400 MHz, CDCl3/acetone-d6,
25 °C) δ 5.79 (d, JPH ) 2.4 Hz, 5H, C5H5), 5.77 (d, JPH ) 2.4
Hz, 5H, C5H5), 5.14 (m, 2H, H12,13), 4.44 (m, 2H, H15,16), 4.33
(m, 2H, H9,10), 3.54 (s, 3H, OMe), 3.03 (m, 1H, H11), 2.83 (m,
signals for the free and coordinated nitrile ligand against the
methoxy signal (3.90 ppm) of the internal reference. These
concentrations were used to calculate the equilibrium constant
K:
3
1H, H14), 2.24 (t, JHH ) 6.6 Hz, 2H, H2), 2.15 (m, 2H, H8),
2
1.57 (d, JPH ) 12.4 Hz, 9H, 3PMe3), 1.55 (m, 2H, H17), 1.24
[CpPd(PR3)(olefin)+][o-MeC6H4CN]
K )
(m, 10H, H3), 0.90 (t, JHH ) 7.2 Hz, 3H, H18); 13C{1H} NMR
3
(100.6 MHz, CDCl3/acetone-d6, 25 °C) δ 173.78 (CdO), 129.95
(C13), 126.91 (C12), 102.78 (d, JPC ) 2.0 Hz, C5H5), 102.70 (d,
JPC ) 1.9 Hz, C5H5), 95.02 (C16), 93.12 (C15), 90.86 (C10), 90.54
(C9), 51.05 (OMe), 33.69 (C2), 32.64 (C11), 31.28 (C8), 30.86 (C14),
27.30-24.45 (C3), 22.01 (C17), 17.15 (d, 1JPC ) 32.6 Hz, PMe3),
13.76 (C18); 31P{1H} NMR (162 MHz, CDCl3/acetone-d6, 25 °C)
δ 5.07 (PMe3), 5.08 (PMe3).
Determination of the Equilibrium Constants. Equilib-
rium constants for the binding of the unsaturated fatty acid
methyl esters and cis-3-hexene to [CpPd(PR3)]+ were deter-
mined according to Scheme 7 by 1H NMR analysis (400 MHz)
at 25.0 ( 0.1 °C. The initial concentration of the [CpPd(PR3)-
(o-MeC6H4CN)]BF4 complexes was 5.24 × 10-2 M. The K values
shown in Table 1 are averages of at least three measurements
using different concentrations ((5.24-1.10) × 10-2 M) of the
alkenes. The errors reported in Table 1 are standard deviations
of three different K values calculated from each measurement.
Solutions for the equilibrium measurements were prepared in
air by adding CDCl3 to [CpPd(PPh3)(o-MeCH3C6H4CN)]BF4
and methyl â-naphthyl ether (internal reference) in an NMR
tube. Then the free fatty acid methyl ester or cis-3-hexene was
added at room temperature. The relative concentrations of the
complexes were then calculated by integrating the Cp signals
of the Pd-olefin and Pd-nitrile complexes and the methyl
[CpPd(PR3)(o-MeC6H4CN)+][olefin]
The equilibrium constant for the formation of [CpPd(PPh3)-
(18:1)]+ was also measured at 10.0 ( 0.1, 5.0 ( 0.1, -5.0 (
0.1, and -10.0 ( 0.1 °C, from which the thermodynamic
parameters were calculated from a plot of 1/T vs -ln(K1).
To ensure equilibration of the olefins with the {CpPd(PR3)-
(o-MeC6H4CN)]BF4 complexes, a 1H NMR spectrum was
recorded within 3-5 min after each solution was prepared. A
second 1H NMR spectrum was recorded 15 min later. A third
1
1H NMR spectrum was recorded
/ h later. No significant
2
difference was observed among the first, second, and third 1H
NMR spectra. This indicates, for all the olefins examined, that
equilibrium was established by the time the first spectrum was
recorded (less than 10 min from solution preparation).
Crystallographic Structural Determination of 5b.
Single crystals of the title compound, suitable for X-ray
analysis, were obtained from a concentrated solution in
chloroform-d/acetone-d6 containing an excess of the 1,4-pen-
tadiene. A crystal selected under ambient conditions (Table
2) was covered with epoxy glue under a layer of solvent,
mounted, and centered in the X-ray beam by using a video
camera. The crystal evaluation and data collection were
performed at 180 K on a Bruker CCD-1000 diffractometer with

1736 Organometallics, Vol. 24, No. 7, 2005
Ghebreyessus et al.
Mo KR (λ ) 0.710 73 Å) radiation and a detector-crystal
distance of 5.03 cm. The data were collected using a full-sphere
routine and were corrected for Lorentz and polarization effects.
The absorption correction was based on fitting a function to
the empirical transmission surface, as sampled by multiple
equivalent measurements17 using SADABS software.18 Posi-
tions of the heavy atoms were found by direct methods. The
remaining non-hydrogen atoms, including water solvent, were
located in an alternating series of least-squares cycles and
difference Fourier maps. All non-hydrogen atoms were refined
in a full-matrix anisotropic approximation. All hydrogen atoms
were placed in the structure factor calculation at idealized
positions and were allowed to ride on the neighboring atoms
with relative isotropic displacement coefficients. The H atoms
of water solvent were not assigned or included in the calcula-
two halves), and 4.5 water molecules were found in the
asymmetric unit in a c-centered monoclinic cell. Two halves
of the anion lay on a c-glide and lead to highly disordered
spherically shaped moieties.
Acknowledgment. This project was supported by
the National Research Initiative of the USDA Coopera-
tive State Research, Education and Extension Service,
Grant No. 2003-35504-12846.
Supporting Information Available: A figure giving a
van’t Hoff plot of -ln(K1) vs 1/T for [CpPd(PPh3)(o-MeC6H4-
CN)]+ + 18:1 ) [CpPd(PPh3)(18:1)]+ + o-MeC6H4CN (7a) and
tables of crystal data and structural refinement details, atomic
coordinates, isotropic and anisotropic displacement param-
eters, bond lengths and angles, and hydrogen coordinates for
5b (these crystallographic data are also available as CIF files).
This material is available free of charge via the Internet at
http://pubs.acs.org.
-
tions. One organometallic cation, two BF4 anions (one plus
(17) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.
(18) All software and sources of the scattering factors are contained
in the SHELXTL (version 5.1) program library (G. Sheldrick, Bruker
Analytical X-ray Systems, Madison, WI).
OM049009Q