PGSE NMR diffusion, overhauser, and DFT studies on the salts [Pd(η3-CH3CHCHCHPh)(dppe)](anion)

Article abstract of DOI:10.1021/om0505514

PGSE NMR diffusion, Overhauser and DFT studies on the salts [Pd(η³-CH₃CHCHCHPh)-(dppe)](anion) (dppe = 1,2-bis(diphenylphosphino)ethane, anion = BF₄^-, CF ₃SO₃^-, BArF^-, PF₆ ^-) are reported. In dichloromethane solution there is little or no ion pairing for the BArF derivative, whereas the other three anions show intermediate degrees of ion pairing. In chloroform solution the CF ₃SO₃^- and BArF^- salts show complete ion pairing. The ¹⁹F,¹H HOESY studies reveal a selective approach of the CF₃SO₃^- and PF₆ ^- anions with respect to the allyl ligand. The approach brings the anion somewhat closer to the allyl phenyl ring than to the allyl methyl group. Further, the anion approaches the Pd center from the side of the two terminal allyl protons. The anions are not attracted to the allyl ligand but rather are choosing both an electronically (allyl phenyl vs allyl methyl) and sterically (terminal allyl protons vs central allyl proton) preferred pathway toward the P and metal atoms. This result is partially rationalized via DFT calculations.

Full text of DOI:10.1021/om0505514

5710
Organometallics 2005, 24, 5710-5717
PGSE NMR Diffusion, Overhauser, and DFT Studies on
the Salts [Pd(η3-CH3CHCHCHPh)(dppe)](anion)
Daniele Schott and Paul S. Pregosin*
Laboratory of Inorganic Chemistry, ETHZ Ho¨nggerberg, CH-8093 Zu¨rich, Switzerland
Luis F. Veiros
Centro de Quı´mica Estrutural, Complexo I, Instituto Superior Te´cnico, Av. Rovisco Pais 1,
1049-001 Lisbon, Portugal
Maria Jose´ Calhorda
Departamento de Quı´mica e Bioqu´ımica, Faculdade de Cieˆncias, Universidade de Lisboa,
1749-016 Lisbon, Portugal
Received June 30, 2005
PGSE NMR diffusion, Overhauser and DFT studies on the salts [Pd(η3-CH3CHCHCHPh)-
-
-
(dppe)](anion) (dppe ) 1,2-bis(diphenylphosphino)ethane, anion ) BF4 , CF3SO3 , BArF-,
-
PF6 ) are reported. In dichloromethane solution there is little or no ion pairing for the BArF
derivative, whereas the other three anions show intermediate degrees of ion pairing. In
-
chloroform solution the CF3SO3 and BArF- salts show complete ion pairing. The 19F,1H
HOESY studies reveal a selective approach of the CF3SO3- and PF6- anions with respect to
the allyl ligand. The approach brings the anion somewhat closer to the allyl phenyl ring
than to the allyl methyl group. Further, the anion approaches the Pd center from the side
of the two terminal allyl protons. The anions are not attracted to the allyl ligand but rather
are choosing both an electronically (allyl phenyl vs allyl methyl) and sterically (terminal
allyl protons vs central allyl proton) preferred pathway toward the P and metal atoms. This
result is partially rationalized via DFT calculations.
Introduction
Pd-catalyzed reaction with reported enantioselectivities
in excess of 90% now being fairly routine.2-5
There is a continuing interest in the homogeneously
catalyzed allylic alkylation reaction. This reaction can
be promoted by several late transition metals, including
ruthenium,1 rhodium,2 and iridium;3 however, the ap-
plications involving palladium4,5 are still the most
numerous. A wide variety of phosphorus, sulfur, and
nitrogen chiral auxiliaries have been employed in this
The mechanism6 of the Pd-catalyzed allylic alkylation
reaction is thought to involve a Pd(0) olefin complex,7-10
e.g., 1, containing the substrate-bound leaving group,
LG. After oxidative addition, complex 1 (shown here as
containing a chelating ligand) affords a Pd(II) allyl
cationic complex, 2, with the leaving group as the anion.
This allyl cation is attacked by a nucleophile, Nu-, to
regenerate a Pd(0) species plus the two usual organic
products (see eq 1). The regioselectivity of the reaction
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10.1021/om0505514 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/04/2005

[Pd(η3-CH3CHCHCHPh)(dppe)](anion)
Organometallics, Vol. 24, No. 23, 2005 5711
number of stable allyl complexes of Pd(II), which have
been isolated and characterized.4,5,7,11-13
have appeared. Specifically, Macchioni et al.20 and
Brintzinger and co-workers21 have both reported de-
tailed PGSE studies on model zirconium complexes with
relevance for polymerization catalysis. Further, we
have presented PGSE studies for model palladium23
(polymerization), iridium24 (hydrogenation), and ruthe-
nium25 (Diels-Alder) catalysts. For a routine PGSE
measurement, there are by and large no major instru-
mental or sample requirements (apart from a spectrom-
eter equipped with gradients) and 1-2 mM solutions
are readily measured.
The palladium complexes 2 are of special interest, in
that their structural distortions have been related to
the mechanism of this catalytic reaction.14 Further,
there has been some discussion as to whether the anion
in 2 ”remembers” from which carbon it originally came;
i.e., the anion formed from the leaving group is not
necessarily remote from the cation.15,16
Although conductivity measurements still represent
the accepted method of measuring how ions interact,
there is a growing literature which suggests that the
individual diffusion constants for the ions of a given salt
can provide a useful alternative. This is especially true
when taken together with HOESY (and/or NOESY)
measurements that allow an estimation of the relative
position(s) of the ions. Increasingly, one measures the
individual diffusion constants using pulsed gradient
spin-echo (PGSE) NMR methods17 and employs 19F and
1H probes for the individual anions and cations, respec-
tively.
As we have found no diffusion data for cationic allyl
complexes of Pd(II), we have prepared the relatively
-
simple salts 3, with BF4-, CF3SO3-, BArF-, and PF6
as anions, and report here our results from PGSE,
Overhauser NMR, and DFT experiments. The unsym-
The PGSE methodology stems from the relatively
early days of NMR; hence, a substantial literature exists
and the subject has been reviewed on several occa-
sions.17 The diffusion literature includes applications
from the fields of biology18 and polymers,19 among
others. Recently, studies on organometallic examples20-22
metrical phenyl/methyl allyl (rather than a symmetric
analogue, e.g., 1,3-diphenylallyl) was chosen in the hope
that the anion would express some choice with respect
to its position. The chelate 1,2-bis(diphenylphosphino)-
ethane was chosen so as to avoid the formation of “endo”
and “exo” isomers, i.e., isomeric complexes due to the
two possible positions of the central allyl proton, with
respect to the chelate, which are observed if the chelate
ligand is unsymmetrical.
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Organometallics 1997, 16, 579-590.
Results and Discussion
The complexes were prepared by treating the known
dinuclear Pd-allyl complex with the appropriate silver
or sodium salt in acetone solution, followed by the
addition of the chelating ligand (see eq 2). Details of
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A.; Pregosin, P. S.; Goicoechea, J. M.; Whittlesey, M. K. Organome-
tallics 2003, 22, 2956-2960. (c) Martinez-Viviente, E.; Pregosin, P. S.
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5418.

5712 Organometallics, Vol. 24, No. 23, 2005
Schott et al.
Table 1. 13C NMR Allyl Data (ppm) for Several of
the Pd Complexes
their characterization are given in the Experimental
Section.
CF3SO3
BArF
PF6
C1
C2
C3
86.8
118.1
89.6
85.9
117.5
89.0
86.6
118.0
89.6
-
Table 2. Detailed NMR Data for the PF6 Salt 3da
assignt assignt
ortho arom
13C 132.3 ortho arom
δ
δ
1H 6.85
7.45
dppe ring A
ortho arom
dppe ring B
ortho arom
dppe ring C
ortho arom
dppe ring D
meta arom
dppe ring A
meta arom
dppe ring B
meta arom
dppe ring C
meta arom
dppe ring D
para arom
dppe ring A
131.8 ortho arom
dppe ring B
7.31
7.65
132.4 ortho arom
dppe ring D
The assignment of the 1H NMR spectra for the three
allyl protons of 3 was straightforward. The terminal
allyl dCH resonance, close to the methyl group, HA, was
identified via its COSY and NOESY contacts. The
central allyl proton, HB, is readily assigned, as its
associated 13C resonance appears in a characteristic26-28
region at ca. 118 ppm (see Chart 1). The 31P,1H correla-
7.24
7.62
7.54
7.71
7.46
Chart 1
dppe ring A
para arom
7.66
dppe ring D
ortho arom allyl
CH3
7.02
1.73
4.35
6.18
5.06
18.7 CH3
CHMe allyl HA
CHCHCH allyl HB
CHPh allyl HC
86.6 CHMe allyl
118.0 CHCHCH allyl
89.6 CHPh allyl
28.8 CH2CH2 dppe
28.2 CH2CH2 dppe
2.46-2.68 CH2CH2 dppe
31P 46.3
PA, 2JPP ) 39.9 Hz
49.0
PB, 2JPP ) 39.9 Hz
PF6, 2JFP ) 710 Hz
tion can then be used to assign the nonequivalent 31P,
PA and PB, spins. Specifically, one can use the relatively
large 3J(31P,1H(allyl))trans value to connect a specific
terminal allyl proton to the P atom in a pseudo-trans
position (see Figure 1).26 Moreover, the 31P,1H correla-
tion allows the recognition and partial assignment of
the four sets of P-phenyl ortho protons (also in Figure
1). These assignments are important for the discussion
-143.2
19F -73.7
PF6, 1JPF ) 710 Hz
a 1H (700 and 500 MHz), 13C (125 MHz), 31P (202 MHz), and
19F (376 MHz) NMR spectra were recorded in CD2Cl2 at 299 K.
δ 46.3 and 49.0, as well as the two terminal allyl 13C
chemical shifts, δ 86.6 and 89.6, are rather similar (see
Table 1), suggesting that there is little imbalance in the
bonding of the allyl group to the palladium atom.
Detailed NMR data for 3d are given in Table 2.
of the 19F,1H HOESY results. It is worth noting that
-
the two 31P chemical shifts, e.g. for the anion PF6
,
Diffusion Data. PGSE diffusion data for the four
salts 3 are shown in Table 3. In the following discussion,
we will refer to a hydrodynamic radius, rH, which we
derive from the Stokes-Einstein relation (eq 3). Use of
D ) (kT)/(6ηπrH)
(3)
k ) Boltzmann constant, T ) temperature, η )
viscosity of the solvent
the rH value allows one to circumvent the effect of
viscosity on the D values, while introducing a more
readily understood structural aspect.
(26) Pregosin, P. S.; Salzmann, R. Coord. Chem. Rev. 1996, 155, 35-
68.
(27) Malet, R.; Moreno-Manas, M.; Pajuelo, F.; Parella, T.; Pleixats,
R. Magn. Reson. Chem. 1997, 35, 227-236. Malet, R.; Moreno-Manas,
M.; Parella, T.; Pleixats, R. Organometallics 1995, 14, 2463-2469.
(28) A° kermark, B.; Krakenberger, B.; Hansson, S.; Vitagliano, A.
Organometallics 1987, 6, 620.
Figure 1. 31P,1H correlation for 3d showing the geometry-
dependent spin-spin interactions from the P atoms to their
pseudo-trans terminal allyl protons, HA and HC (CD2Cl2).

[Pd(η3-CH3CHCHCHPh)(dppe)](anion)
Organometallics, Vol. 24, No. 23, 2005 5713
Table 3. 1H (Cations) and 19F (Anions) Diffusion Resultsa for the Pd-Allyl Complexes
a 10-10 m2 s-1 2 mM solutions. Estimated using the diffusion coefficient of HDO in D2O as reference. D values are (2%. b Viscosity, η
(299 K) for CH2Cl2: 0.414 kg s-1 m-1
.
On the basis of earlier measurements,29 one now
expects almost identical D values for the cation and
anion in CDCl3 solutions: i.e., >90% ion pairing. Indeed,
in this solvent, the anion and cation of 3b are moving
at about the same rate, on the basis of their respective
D values (see Figure 2), suggesting that a tight ion pair
represents the correct description for these CF3SO3- and
BArF- salts. The BArF ion pair is, as expected, consid-
erably larger, on the basis of its rH value. For compari-
son we show related data for the salts 4a,b in the same
Figure 2. Diffusion data for the chloroform solution of 3b,
showing identical slopes for the cation and anion.
two anions. Interestingly, there are five phenyl rings
in 3 and five “rings” in 4 and, as we have shown,22e the
presence of such rings strongly affects translation. In
any case, the rH values provide an estimation of the size
of these salts in CDCl3.
table and note that, perhaps by coincidence, the two
In dichloromethane solution, the anions and cations
of 3 are moving at very different rates, on the basis of
their respective D values; consequently, the ion pairing
is not 100%. However, the D (and rH) values for the
anions suggest substantial partial ion pairing for the
salts have almost the same D and rH values for these
(29) (a) Pregosin, P. S.; Martinez-Viviente, E.; Kumar, P. G. A.
Dalton Trans. 2003, 4007-4014. (b) Valentini, M.; Ruegger, H.;
Pregosin, P. S. Helv. Chim. Acta 2001, 84, 2833-2853. (c) Valentini,
M.; Pregosin, P. S.; Ru¨egger, H. Organometallics 2000, 19, 2551-2555.

5714 Organometallics, Vol. 24, No. 23, 2005
Schott et al.
-
three anions BF4-, CF3SO3-, and PF6 but little or no
ion pairing for the BArF- anion. Reasonable estimates
for the rH values of the solvated anions in methanol
solution are 2.5-2.8 Å for BF4 and PF6 and 3.0-3.3 Å
for CF3SO3: i.e., much smaller than the values observed
for 3 in dichloromethane solution. For BArF in metha-
nol, 5.8-6.1 Å represents a reasonable range. Therefore,
an observed value of 4.8 Å for the triflate of 3b indicates
-
substantial ion pairing. This rH value for the CF3SO3
anion of 4.8 Å is somewhat large: e.g., for 4a the
analogous value in dichloromethane is 4.3 Å.30 The
translation of the cation is not strongly affected by the
anion, and an rH value of ca. 5.6 Å seems a reasonable
estimate for this solvated ion.
Overhauser Data. Using 19F,1H HOESY31,32 or
NOESY methods, several groups have reported that
external anions tend to take up positions remote from
the coordinated anionic ligands. For example, in the
oxazoline33 and bipyridine34 Ir(III) hydride cationic
complexes containing fairly large ligands, L, the exter-
nal anion avoids the relatively small hydride and
chooses to approach the metal via the oxazoline, as in
5, or via the bipy, as in 6. Moreover, there are additional
Figure 3. 19F,1H HOESY for 3d, showing a relatively large
number of selective contacts from the anion to the cation
(10 mM, CD2Cl2). Only half of the 19F doublet is shown.
reports which suggest that the anion makes only a
selective approach toward the cation, i.e., the anion does
not move freely around the periphery of the cation.
Chart 2
-
Consequently, it was of interest to see how the CF3SO3
-
and PF6 anions behaved in 3.
A section of the 2-D HOESY spectrum for 3d in
dichloromethane solution is shown in Figure 3. There
are a number of medium-to-strong contacts involving
the allyl protons, and these arise primarily from the two
terminal allyl protons and the two ortho phenyl allyl
resonances (see arrows). One finds a weak cross-peak
from the central allyl proton, a weak interaction to the
CH2-CH2 backbone, and another weak contact to the
methyl group. Of the two terminal allyl protons, that
closest to the phenyl reveals the strongest interaction.
The strongest contact in the spectrum arises from a
series of overlapping phenyl protons at ca. 7.7 ppm.
From the diffusion data, we know that there is incom-
plete ion pairing, so that the strongest cross-peak could
arise from the anion floating around the periphery of
the phenyl array. This would explain the weak interac-
tions with the ethylene backbone and the allyl methyl
group. However, the selectivity observed with respect
to the terminal allyl protons suggests (a) a steric
preference in which the anion approaches the allyl
ligand preferentially from the side containing the two
terminal allyl protons (see 7a in Chart 2) (and not the
two syn allyl substituents) and (b) that the approach
seems to favor the phenylsrather than the methylsside
of the allyl anion (see 7b in Chart 2). The pathway
moves the anion toward the Pd atom, as we shall show
on the basis of the DFT results.
The same pattern of cross-peaks is observed in the
2-D HOESY of the triflate analogue 3b in dichlo-
romethane solution, although the intensities are sig-
nificantly weaker, since the triflate CF3 group is slightly
more remote from the cation. We show in Figure 4 the
HOESY spectrum for the triflate salt 3b in CDCl3, a
solvent which affords 100% ion pairing (see Table 3).
Although this solvent is not routinely used in allylic
alkylation chemistry, it was of interest to seek possible
(30) Martinez-Viviente, E.; Pregosin, P. S. Inorg. Chem. 2003, 42,
2209-2214.
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Organometallics 2005, 24, 1315-1328. (b) Macchioni, A. Chem. Rev.
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Chem. 2003, 27, 80-87.

[Pd(η3-CH3CHCHCHPh)(dppe)](anion)
Organometallics, Vol. 24, No. 23, 2005 5715
Figure 5. Optimized geometry of the cation [Pd(η3-
PhCHCHCHCH3)](Me2PCH2CH2PMe2)]+ with the calcu-
lated NPA charges indicated for the heavy atoms. The
Pd-C(allyl) bond distances (Å) are represented in bold and
italics. The Pd (dark gray) and the P atoms (light gray)
are shaded.
agreement with the observed 13C data from the terminal
allyl carbons. Also, the two Pd-C bonds stemming from
the two terminal allyl carbon atoms are equivalent from
the electronic point of view, as shown by the corre-
sponding Wiberg indices:38 0.28 for Pd-C16 and 0.30
for Pd-C18.
The atomic charges, calculated by means of natural
population analysis (NPA),39 are also shown in Figure
5, along with a numbering scheme, for the relevant
atoms. The charges on the terminal allyl carbons,
-0.290 for C16 and -0.291 for C18, do not differ much;
however, the negative charge for the phenyl ipso carbon,
-0.086 for C10, is much smaller than that found on the
allyl methyl carbon, -0.696 for C19. Still, one should
not overlook the fact that the P atoms carry a great deal
of the positive charge (ca. +1.04 for each atom). Con-
sequently, it would seem that the approach of the anion
via a pathway closer to the allyl phenyl ring arises from
electronic and not steric considerations and involves the
differing allyl substituents rather than the allyl carbons
themselves. The anions are not attracted to the allyl
ligand but rather are choosing both an electronically
(allyl phenyl vs allyl methyl) and sterically (terminal
allyl protons vs. central allyl proton) preferred pathway
toward the P and metal atoms.
Figure 4. 19F,1H HOESY for 3b (10 mM in CDCl3),
showing a larger number of stronger (relative to 3d)
selective contacts from the triflate anion to the allyl cation.
changes in the relative position of the anion. The
spectrum clearly shows that (a) there are more cross-
peaks than for 3b in dichloromethane, but about the
same number as in Figure 3, for the PF6 in dichlo-
romethane, (b) the allyl selectivity, in terms of the
relative intensities, is still present, i.e., the cross-peaks
to the two terminal allyl protons are more intense, and
(c) there are now no interactions with the CH2CH2
phosphine moiety. We conclude that the increased ion
pairing in CDCl3 has compensated for the more remote
triflate CF3 group but that little else has changed.
DFT Results. DFT studies on allyl complexes have
proven to be informative in describing asymmetric allyl
bonding of the η3-PhCHCHCH2 anionic ligand in Cp
complexes of ruthenium.35 Consequently, we have car-
ried out DFT/B3LYP calculations36 on the model cationic
complex [Pd(η3-PhCHCHCHCH3)](Me2PCH2CH2PMe2)]+,
which contains methyl, rather than phenyl, substituents
on the phosphine. The optimized geometry is repre-
sented in Figure 5 and corresponds to a typical37 Pd(II)
square-planar complex.
Comment. These results suggest that the anions
associated with the relatively simple η3-CH3CHCHCHPh
palladium cation do indeed partially occupy a preferred
position. The anion approaches via a pseudo-fifth coor-
(37) See, for example the Cambridge Structural Database (CSD):
Allen, F. H. Acta Crystallogr., Sect. B 2002, 58, 380.
(38) (a) Wiberg, K. B. Tetrahedron 1968, 24, 1083. (b) Wiberg indices
are electronic parameters related with the electron density between
two atoms. They can be obtained from a natural population analysis
and provide an indication of the bond strength.
(39) (a) The absolute values of the calculated charges may be
overestimated; however, the trends obtained should be reliable. (b)
Carpenter, J. E.; Weinhold, F. J. Mol. Struct. (THEOCHEM) 1988,
169, 41. (c) Carpenter, J. E. Ph.D. Thesis, University of Wisconsin,
Madison, WI, 1987. (d) Foster, J. P.; Weinhold, F. J. Am. Chem. Soc.
1980, 102, 7211. (e) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1983,
78, 4066. (f) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1983, 78, 1736.
(g) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985,
83, 735. (h) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988,
88, 899. (i) Weinhold, F.; Carpenter, J. E. The Structure of Small
Molecules and Ions, Plenum: New York, 1988; p 227.
The calculated Pd-C(allyl) separations (see Figure 5)
do not suggest significant distortion and thus are in
(35) Hermatschweiler, R.; Ferna´ndez, I.; Pregosin, P. S.; Watson,
E. J.; Albinati, A.; Rizzato, S.; Veiros, L. F.; Calhorda, M. J. Organo-
metallics 2005, 24, 1809-1812.
(36) (a) Parr, R. G.; Yang, W. Density Functional Theory of Atoms
and Molecules; Oxford University Press: New York, 1989. (b) Becke,
A. D. J. Chem. Phys. 1993, 98, 5648. (c) Miehlich, B.; Savin, A.; Stoll,
H.; Preuss, H. Chem. Phys. Lett. 1989, 157, 200. (d) Lee, C.; Yang, W.;
Parr, G. Phys. Rev. B 1988, 37, 785.

5716 Organometallics, Vol. 24, No. 23, 2005
Schott et al.
atom, and the same basis set augmented with a d-polarization
function44 was used for the P atom; the remaining elements
were described by a standard 4-31G(d)45 basis set. The
optimization was performed without symmetry constraints. A
natural population analysis (NPA)39 and the resulting Wiberg
indices38 were used to study the electronic structure and
bonding of the optimized species.
dination position but chooses to come from the direction
associated with the two terminal allyl hydrogen atoms,
rather than approach the allyl via the central allyl
proton. There is no evidence that the anion is positioned
behind the plane of the allyl, remote from the palladium,
in an area where a nucleophile might possibly approach
a coordinated allyl ligand. Of course, the preparation
and subsequent study of 3 allows ample time for
equilibration of the various positions occupied by the
anion(s). In a catalytic allylic alkylation reaction, it is
possible that the leaving group, as the anion, does not
migrate far before the nucleophile, Nu-, which is
present in large excess, attacks the allyl. Consequently,
one cannot extrapolate our results to catalysis. Never-
theless, the combined PGSE, NOE, DFT approach
provides a fairly clear qualitative picture of how the ions
interact in these palladium salts.
[Pd(η3-Me(CH)3Ph)(dppe)][PF6]. To 1 equiv of [Pd(µ-Cl)-
(η3-Me(CH)3Ph)]2 (64 mg, 545.8 g mol-1, 1.18 × 10-4 mol) was
added 2 equiv of the AgPF6 salt (59.1 mg, 252 g mol-1, 2.35 ×
10-4 mol). The mixture of solids was placed under vacuum and
purged with nitrogen three times. Then 2-4 mL of acetone
was added, and the yellow mixture was stirred under nitrogen
for ca. 2 h. After this time, the dark yellow solution was filtered
through Celite and 2 equiv of dppe in CH2Cl2 (94 mg, 398 g
mol-1, 2.36 × 10-4 mol) added to the filtrate (still under
nitrogen). The solution was then stirred for 1 h. The yellow
solution that resulted was filtered over Celite and the solid
rinsed with CH2Cl2. The solvent was removed under vacuum
to yield a bright yellow solid. Yield: 144 mg, 1.85 × 10-4 mol,
78.7%. MS (ESI; m/z): M+ 634.9, M - allyl+ 504.9.
Experimental Section
[Pd(η3-Me(CH)3Ph)(dppe)][CF3SO3]. To
1 equiv of
General Procedure (NMR). 1H, 31P, 13C, and 19F NMR
spectra were recorded on Bruker Avance 250, 300, 400, 500,
and 700 NMR spectrometers. Chemical shifts are quoted in
parts per million (ppm) downfield of TMS. Deuterated solvents
were dried by distillation over molecular sieves and stored in
the presence of molecular sieves under N2.
Diffusion. All the measurements were performed on a
Bruker Avance spectrometer, 400 MHz, equipped with a
microprocessor-controlled gradient unit and a multinuclear
inverse probe with an actively shielded Z-gradient coil. In
general, the gradient shape is rectangular and its length was
1.75 ms. Its strength was increased by steps of 4% during the
course of the experiment. The time between midpoints of the
gradients was 167.75 ms for all experiments. The experiments
were carried out at a set temperature of 299 K within the NMR
probe. However, these parameters were altered for the 1H
diffusion measurement of the BArF compound in CD2Cl2,
where the gradient shape length was set to 2.00 ms and the
time between midpoints of the gradients was 68 ms.
[Pd(µ-Cl)(η3-Me(CH)3Ph)]2 (60 mg, 545.8 g mol-1, 1.1 × 10-4
mol) was added 2 equiv of the AgCF3SO3 salt (58 mg, 256.9 g
mol-1, 2.3 × 10-4 mol). Both solids were placed under vacuum
and purged with nitrogen three times. Then, 2-4 mL of
acetone was added, and the yellow mixture was stirred under
nitrogen for ca. 2 h. After this time, the yellow solution was
filtered through Celite and 2 equiv of dppe in CH2Cl2 (94 mg,
398 g mol-1, 2.36 × 10-4 mol) was added to the filtrate (still
under nitrogen). The solution was then stirred for 2 h. The
resulting pale yellow solution was filtered over Celite and the
filtrate rinsed with CH2Cl2. The solvent was removed under
vacuum to yield a pale yellow solid. Yield: 128 mg, 1.63 ×
10-4 mol, 74.1%. MS (MALDI; m/z): M+ 635, M - allyl+ 505,
M- 149. Anal. Calcd: C, 56.6; H, 4.49. Found: C, 55.9; H, 4.54.
[Pd(η3-Me(CH)3Ph)(dppe)][BF4]. To 1 equiv of [Pd(µ-Cl)-
(η3-Me(CH)3Ph)]2 (32 mg, 545.8 g mol-1, 5.86 × 10-5 mol) was
added 2 equiv of the AgBF4 salt (23 mg, 195 g mol-1, 1.17 ×
10-4 mol). Both solids were evacuated under vacuum and
purged with nitrogen three times. Then, 2 mL of acetone was
added, and the yellow mixture was stirred under nitrogen for
about 1 h. After this time, the yellow solution was filtered
through Celite and 2 equiv of dppe (94 mg, 398 g mol-1, 2.35
× 10-4 mol) was added to the filtrate (still under nitrogen).
The solution was then stirred for another 1 h. The resulting
solution was filtered through Celite and the filtrate rinsed with
CH2Cl2. The solvent was removed under vacuum to yield a
pale yellow solid. Yield: 38.7 mg, 5.36 × 10-5 mol, 45.7%.
[Pd(η3-Me(CH)3Ph)(dppe)][BArF]. To 1 equiv of [Pd(µ-Cl)-
(η3-Me(CH)3Ph)]2 (30 mg, 545.8 g mol-1, 5.5 × 10-5 mol) was
added 2 equiv of the NaBArF salt (59 mg, 534.99 g mol-1, 1.1
× 10-4 mol). Both solids were evacuated under vacuum and
purged with nitrogen three times. Then, 4 mL of acetone was
added, and the yellow mixture was stirred under nitrogen for
about 1 h. After this time, the dark yellow solution was filtered
over Celite and 2 equiv of dppe (44 mg, 398 g mol-1, 1.1 ×
10-4 mol) was added to the filtrate (still under nitrogen). Then
As indicated in Table 3, the diffusion values were measured
using 2 mM CDCl3 and CD2Cl2 solutions. Cation diffusion rates
1
were measured using the H signal from the ortho proton of
the aromatic, whereas the anion D values were obtained from
the 19F and 1H resonances (where available) of the boron
substituent. The error coefficient for the D values is (0.06.
HOESY. 19F,1H HOESY spectra were measured using 10
mM solutions in CD2Cl2, at 299 K with mixing times of 0.8 s.
Computational Details. The calculations were performed
using the Gaussian 98 software package40 and the B3LYP
hybrid functional. This functional includes a mixture of
Hartree-Fock41 exchange with DFT36a exchange correlation,
given by Becke’s three-parameter functional36b with the Lee,
Yang, and Parr correlation functional, which includes both
local and nonlocal terms.36c,d The LanL2DZ basis set42 aug-
mented with an f-polarization function43 was used for the Pd
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Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
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Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
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[Pd(η3-CH3CHCHCHPh)(dppe)](anion)
Organometallics, Vol. 24, No. 23, 2005 5717
the solution was stirred for another 1 h. The resulting yellow
solution was filtered through Celite and the filtrate rinsed with
CH2Cl2. The solvent was removed under vacuum to yield a
dark yellow solid. Yield: 149 mg, 1.0 × 10-4 mol, 90.4%. MS
(m/z): M+ 635, M - allyl+ 505, M- 863.
lyzed Reactions” is kindly acknowledged. P.S.P. also
thanks the Swiss National Science Foundation and the
ETH Zurich for support and the Johnson Matthey Co.
for the loan of metal salts.
The palladium salts were stored under nitrogen in the
refrigerator.
Supporting Information Available: Atomic coordinates
for the optimized structure of [Pd(η3-PhCHCHCHCH3)]-
(Me2PCH2CH2PMe2)]+. This material is available free of charge
via the Internet at http://pubs.acs.org.
Acknowledgment. The support and sponsorship of
this research by COST Action D24 “Sustainable Chemi-
cal Processes: Stereoselective Transition Metal-Cata-
OM0505514