Weak η2-olefin bonding in palladium and platinum allyl cationic complexes containing chiral monodentate ligands with α-phenyl methyl amine side chains

Article abstract of DOI:10.1021/om8000636

Detailed NMR studies on a series of Pd and Pt allyl complexes containing phosphoramidite ligands with NCH(CH₃)Ph side chains are reported. When a coordination position becomes available, e.g., via abstraction of a chloride ligand, one double bond of the phenyl group of the side chain complexes to the metal, affording an η²-olefin structure. These allyl complexes exhibit a number of dynamic processes, and these have been elucidated via low-temperature NMR studies combined with 2D NOESY methods. DFT calculations confirm the ability of the amine side chain to coordinate to the metal almost without distortion, leading to a weak η²-arene-Pd bonding interaction (～13 kcal mol^-1). The latter result is supported by the NMR studies.

Full text of DOI:10.1021/om8000636

Organometallics 2008, 27, 2949–2958
2949
Weak η2-Olefin Bonding in Palladium and Platinum Allyl Cationic
Complexes Containing Chiral Monodentate Ligands with r-Phenyl
Methyl Amine Side Chains
Serena Filipuzzi, Paul S. Pregosin,* Maria Jose´ Calhorda,* and Paulo J. Costa
Laboratory of Inorganic Chemistry, ETH HCI, Ho¨nggerberg CH-8093 Zu¨rich, Switzerland, Departamento
de Qu´ımica e Bioqu´ımica, CQB, Faculdade de Cieˆncias, UniVersidade de Lisboa, Campo Grande,
1749-016 Lisboa, Portugal, and Departamento de Qu´ımica, CICECO, UniVersidade de AVeiro,
3810-193, AVeiro, Portugal
ReceiVed January 24, 2008
Detailed NMR studies on a series of Pd and Pt allyl complexes containing phosphoramidite ligands
with NCH(CH3)Ph side chains are reported. When a coordination position becomes available, e.g., via
abstraction of a chloride ligand, one double bond of the phenyl group of the side chain complexes to the
metal, affording an η2-olefin structure. These allyl complexes exhibit a number of dynamic processes,
and these have been elucidated via low-temperature NMR studies combined with 2D NOESY methods.
DFT calculations confirm the ability of the amine side chain to coordinate to the metal almost without
distortion, leading to a weak η2-arene-Pd bonding interaction (∼13 kcal mol-1). The latter result is
supported by the NMR studies.
have both been found to be capable of complexing a transition
metal. A number of related complexation modes have also been
reported.9
Introduction
There is an increasing interest in chiral monodentate
P-donors,1,2 as these have been found to be valuable in a variety
of organic transformations.1–4 Occasionally, one finds reports
suggesting that these ligands (and related bidentate phosphine
donors) are capable of coordinating a somewhat remote double
bond from the organic backbone. This is certainly the case for
the monodentate biaryl-based MOP5,6 and bidentate Binap7,8
An increasing number of papers concern themselves with the
use of phosphoramidite ligands, e.g., 1, in various homoge-
neously catalyzed reactions.10,11 Ligand 1 possesses three
stereogenic fragments, and a wide variety of differently
substituted phosphoramidite derivatives are now in use. Interest-
ingly, it has been recently reported12,13 that the π-system of
one of the amino-aryl fragments of 1 can interact with a Ru(II)
center, as indicated below, and thus stabilize an otherwise
reactive 16e species.
ligands. For MOP, the double bond adjacent to the R-group
and, for Binap, the double bond adjacent to the PPh2 moiety
* Corresponding author. E-mail: pregosin@inorg.chem.ethz.ch.
(1) Ansell, J.; Wills, M. Chem. Soc. ReV. 2002, 31 (5), 259–268.
(2) Jerphagnon, T.; Renaud, J.-L.; Bruneau, C. Tetrahedron: Asymmetry
2004, 15, 2101–2111.
(9) (a) Faller, J. W.; Sarantopoulos, N. Organometallics 2004, 23 (9),
2008–2014. (b) Kocovsky, P.; Vyskocil, S.; Cisarova, I.; Sejbal, J.; Tislerova,
I.; Smrcina, M.; Lloyd-Jones, G. C.; Stephen, S. C.; Butts, C. P.; Murray,
M.; Langer, V. J. Am. Chem. Soc. 1999, 121 (33), 7714–7715. (c) Wang,
Y.; Li, X.; Sun, J.; Ding, K. Organometallics 2003, 22 (9), 1856–1862.
(10) (a) Welter, C.; Dahnz, A.; Brunner, B.; Streiff, S.; Du¨bon, P.;
Helmchen, G. Org. Lett. 2005, 7 (7), 1239–1242. (b) Tissot-Croset, K.;
Polet, D.; Alexakis, A. Angew. Chem., Int. Ed. 2004, 43 (18), 2426–2428.
(c) Kiener, C. A.; Shu, C.; Incarvito, C.; Hartwig, J. F. J. Am. Chem. Soc.
2003, 125 (47), 14272–14273. (d) Imbos, R.; Minnaard, A. J.; Feringa,
B. L. J. Chem. Soc., Dalton Trans. 2003, (10), 2017–2023.
(3) (a) Polet, D.; Alexakis, A.; Tissot-Croset, K.; Corminboeuf, C.;
Ditrich, K. Chem.-Eur. J. 2006, 12 (13), 3596–3609. (b) Boele, M. D. K.;
Kamer, P. C. J.; Lutz, M.; Spek, A. L.; de Vries, J. G.; van Leeuwen, P.;
van Strijdonck, G. P. E. Chem.-Eur. J. 2004, 10 (24), 6232–6246. (c)
Hayashi, T. J. Organomet. Chem. 1999, 576 (1-2), 195–202. (d) Helmchen,
G.; Dahnz, A.; Duebon, P.; Schelwies, M.; Weihofen, R. Chem. Commun.
2007, (7), 675–691.
(4) Feringa, B. L. Acc. Chem. Res. 2000, 33, 346–353.
(5) Kumar, P. G. A.; Dotta, P.; Hermatschweiler, R.; Pregosin, P. S.;
Albinati, A.; Rizzato, S. Organometallics 2005, 24 (6), 1306–1314.
(6) Dotta, P.; Kumar, P. G. A.; Pregosin, P. S.; Albinati, A.; Rizzato, S.
Organometallics 2003, 22 (25), 5345–5349.
(11) (a) Arnold, L. A.; Imbos, R.; Mandoli, A.; de Vries, A. H. M.;
Naasz, R.; Feringa, B. L. Tetrahedron 2000, 56, 2865–2878. (b) Reetz,
M. T.; Ma, J. A.; Goddard, R. Angew. Chem., Int. Edit. 2005, 44, 412–
415.
(7) (a) Geldbach, T. J.; Pregosin, P. S. Eur. J. Inorg. Chem. 2002, 1907–
1918. (b) den Reijer, C. J.; Dotta, P.; Pregosin, P. S.; Albinati, A. Can.
J. Chem. 2001, 79, 693–704. (c) Geldbach, T. J.; Pregosin, P. S.; Rizzato,
S.; Albinati, A. Inorg. Chim. Acta 2006, 359 (3), 962–969.
(8) Costa, P. J.; Calhorda, M. J.; Pregosin, P. S. Collect. Czech. Chem.
Commun. 2007, 72 (5-6), 703–714.
(12) Huber, D.; Kumar, P. G. A.; Pregosin, P. S.; Mikhel, I. S.; Mezzetti,
A. HelV. Chim. Acta 2006, 89 (8), 1696–1715.
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10.1021/om8000636 CCC: $40.75
2008 American Chemical Society
Publication on Web 06/18/2008

2950 Organometallics, Vol. 27, No. 13, 2008
Filipuzzi et al.
Scheme 1
In order to further explore this possible bonding mode, as
well as the dynamics that might accompany such an interaction,
we have prepared a series of palladium(II) and, to a lesser extent,
platinum(II) allyl complexes using ligands 1-3 and describe
here their NMR characteristics. Compounds 2 and 3 are both
interesting and relevant as they (a) have been successfully used
as auxiliaries in enantioselective catalysis14,15 and (b) reduce
the complexity of the NMR analysis relative to that for 1. DFT
calculations confirm the ability of the amine side chain to
coordinate the metal almost without distortion, leading to a weak
η2-arene-Pd bonding interaction (∼13 kcal mol-1). The latter
result is supported by the NMR studies.
Results and Discussion
Table 1. 13C NMR Chemical Shifts for Allyl and Selected Allyl and
Aliphatic Resonances of the Chloro Compounds 4-14a
The cationic allyl complexes were prepared16 in a straight-
forward fashion, as indicated in Scheme 1, by first treating the
appropriate metal(allyl)chloro-bridged dinuclear species with 2
equiv of the P-donor, to afford the mononuclear chloro
compounds. Subsequent abstraction of the chloride ligand using
AgSbF6 affords the new cationic salts. Selected 13C NMR data
for the mononuclear chloro derivatives, 4-14, are given in Table
1, while the pertinent 13C NMR data for the various Pd and Pt
allyl cationic complexes, 15-25, are given in Tables 2 and 3.
In most of the salts the NMR spectra showed two isomeric
species, in almost equal quantities, due to the exo and endo
orientations of the allyl with respect to the chelating ligand.
Although we find about equal quantities of the two species, in
the tables these are always identified as “major” and “minor”.
We find only modest differences in the NMR characteristics of
these two isomers. Nevertheless, the presence of isomers results
in a significant complication of the proton spectroscopy, with
the result that a high-field instrument (700 MHz) was required
in order to (a) assign all of the various protons and then (b)
correlate these to their appropriate 13C signals. Table 4 gives
31P data for all of the cationic complexes, and an extensive list
of 1H chemical shifts can be found in the Supporting Informa-
tion. Except for one Pt complex, 24, the data were obtained at
low temperature in order to slow the various intramolecular
exchange processes.
complex
Ca Cb C1
C2 CA CC CC
[PdCl(C3H5)(S,S,S-1)], 4 major 55.2 21.4 142.1 129.0 79.5 119.1 58.4
minor 55.1 21.7 141.9 129.1 78.8 118.1 58.8
[PdCl(C4H7)(S,S,S-1)], 5 major 55.3 22.4 141.6 128.8 77.0 133.3 60.5
minor 55.3 22.3 141.4 128.4 78.1 133.8 58.7
[PdCl(C3H5)(S,R,R-1)], 6 major 53.9 20.3 143.1 128.5 78.5 nd 59.0
minor 54.2 20.6 143.2 128.3 79.6 nd 57.8
[PdCl(C4H7)(S,R,R-1)], 7 major nd 20.5 143.4 nd 76.6 133.7 nd
minor nd 19.7 142.8 nd 78.1 133.5 58.0
[PdCl(C3H5)(2)], 8
[PdCl(C4H7)(2)], 9
[PdCl(C3H5)(3)], 10
[PdCl(C4H7)(3)], 11
major 54.0 20.6 142.8 128.9 78.9 118.2 58.9
minor 54.3 21.0 142.7 128.6 79.3 119.1 57.7
major 54.0 20.6 142.8 128.9 78.4 133.6 58.8
minor 55.1 21.0 143.3 128.4 77.4 134.2 59.0
major nd nd
nd 128.8 78.4 116.6 66.8
minor nd 19.9 143.5 128.8 80.2 119.2 62.1
56.4 20.1 143.8 128.9 76.2 131.9 67.3
[PtCl(C3H5)(S,R,R-1)], 12 major 53.4 22.4 137.6 126.8 68.2 111.0 46.8
minor 53.8 22.7 138.1 126.9 68.8 111.2 45.7
[PtCl(C3H5)(2)], 13
[PtCl(C3H5)(3)], 14
major 54.2 20.4 142.8 128.6 67.9 110.2 46.1
minor 54.6 20.6 143.0 128.4 68.7 110.0 45.3
major 57.2 20.8 143.9 129.2 69.1 nd 51.9
minor 57.2 20.8 144.0 129.2 69.4 nd 49.2
The low-temperature NMR results are consistent with a
structure such as 26 for all of the cations; that is, one double
bond of the pendant phenyl ring, involving C1 and C2, is
complexed. This conclusion arises primarily from the 13C results
of Table 3. In this compilation the chemical shifts of the carbons
C1, C2, and C6 from the amine side chain are highlighted, and
it is convenient to start with the three Pt salts, 23-25. The
changes in the chemical shifts, ∆δ, are given with respect to
chloro complexes, as these represent better models than the free
a CD2Cl2, 500 or 700 MHz.
ligands. The substantial low-frequency shifts between ca. 15
and 40 ppm for carbons 1 and 2 in 23-25 are consistent with
an η2-olefin structure. For convenience we call these chemical
shift changes “relative chemical shifts” rather than coordination
chemical shifts. In some cases, e.g., for 24, the 195Pt satellites
are observed as broad shoulders on the proton resonance H2
(see Figure 1). Unfortunately, due to fast CSA-induced relax-
ation,17 this is not always the case. As expected the CH
(14) Palais, L.; Mikhel, I. S.; Bournaud, C.; Micouin, L.; Falciola, C. A.;
Vuagnoux-d’Augustin, M.; Rosset, S.; Bernardinelli, G.; Alexakis, A.
Angew. Chem., Int. Ed. 2007, 46 (39), 7462–7465.
(15) Alexakis, A.; Polet, D.; Benhaim, C.; Rosset, S. Tetrahedron:
Asymmetry 2004, 15 (14), 2199–2203.
(16) The compound [Pd(C3H5)(S,R,R-1)]SbF6, 17, was synthesized by
Mezzetti and co-workers. These authors have kindly provided the X-ray
data used in the DFT calculations. A manuscript from these authors
concerning related compounds has been submitted to Organometallics.
(17) Efficient CSA relaxation is favored by both large B0 fields
(necessary for sufficient 1H resolution) and low temperatures, which increase
the solution viscosity and thus the correlation time, thereby decreasing T1.
The latter phenomenon is known as thermal decoupling.

Weak η2 Olefin Bonding in Pd and Pt Allyl Cationic Complexes
Organometallics, Vol. 27, No. 13, 2008 2951
Table 2. 13C NMR Chemical Shifts and Relative Chemical Shifts for Selected Allyl Resonances of the Cationic Compounds 15-25a
complex
CA
∆δ
CB
∆δ
CC
∆δ
T (K)
[Pd(C3H5)(S,S,S-1)]SbF6, 15
[Pd(C4H7)(S,S,S-1)]SbF6, 16
[Pd(C3H5)(S,R,R-1)]SbF6, 17b
[Pd(C4H7)(S,R,R-1)]SbF6, 18
[Pd(C3H5)(2)]SbF6, 19
[Pd(C4H7)(2)]SbF6, 20
[Pd(C3H5)(3)]SbF6, 21
[Pd(C4H7)(3)]SbF6, 22
[Pt(C3H5)(S,R,R-1)]SbF6, 23
[Pt(C3H5)(2)]SbF6, 24
99.1, 95.4
98.0, 94.0
97.8, 96.6
96.2, 93.4
96.6, 97.8
96.0, 94.2
96.2, 94.0
93.6
18.1
18.4
18.2
17.4
18.0
17.3
15.6
17.4
17.6
22.0
18.0
120.9, 122.9
137.3,138.8
121.1, 122.3
137.7, 138.2
122.6, 121.3
138.0, 138.8
122.0, 119.6
135.6
3.3
4.5
58.8, 62.6
57.9, 62.3
57.4, 59.3
56.8, 60.1
59.4, 56.8
57.3, 59.9
65.5, 61.2
61.1
2.1
0.5
0.1
0.4
-0.2
0.3
-1.1
-6.3
7.3
0.2
2.6
173
173
203
203
193
193
213
213
298
253
243
4.4
3.3
4.5
1.9
3.7
7.4
6.3
85.9, 86.2
91.3, 89.4
87.2, nd
118.5
116.4,116.4
nd
55.3, 51.8
45.0, 46.8
53.2, nd
[Pt(C3H5)(3)]SbF6, 25
a ∆δ is relative to the chloro complexes. CD2Cl2 solutions, 500 or 700 MHz. b Synthesized by Mezzetti and co-workers (personal communication,
manuscript in preparation).
resonance for C2 usually18 experiences the largest change
relative to the ipso C1. The chemical shift of C6 in 23-25 is
only marginally affected.
palladium species, shown below.20 Our relative chemical shifts
tend to be smaller than the coordination chemical shifts for this
Moving to the Pd salts, Figure 2 shows low-temperature spectra
from two 13C,1H correlation spectra for Pd- salt 21. One needs
both the routine one-bond correlation to detect C2 and the long-
range correlation (using 3J(13C,1H) via the methyl groups) to locate
the ipso carbon, C1. The relative chemical shifts for these are not
as large as for the Pt salts. This is partially related to the difference
in back-bonding ability between Pt and Pd.
chelating phosphine model, supporting the idea that our salts
show only a weak interaction via the olefinic double bond. The
new olefinic bonds are comparable to those found for palladium/
MOP and ruthenium/phosphoramidites12,13 (see Scheme 2).
However, if the choice of temperature is not optimal,19 the
metal can slide across the π-donor and/or the olefin can
dissociate and rotate around the C1-C(Me)N bond. This results
1
The H spectra for all of the salts do contain a potentially
valuable hint with respect to the bonding. One observes two
3
very different J(31P,1H) values for the two amino side-chain
methine CH protons. A representative selection of values is
3
presented in Table 6. The unusually large J(31P,1H) value of
39-42 Hz is associated with the complexed arm and most
probably stems from an enforced conformation due to the olefin
complexation. Molecular models in addition to a solid-state
structure21 suggest that the P-N-C-H dihedral angle is close
to 180° (161° from DFT calculations; see the structure
in some averaging of the relative shifts over both C2 and C6
(see eq 1 and Figure 3), thus decreasing the magnitude of the
relative chemical shift for C2. This is clearly the case for almost,
but not quite all of the Pd salts; see entries 15, 16, and 21 of
fragment), so that the observed vicinal coupling constant
corresponds to about the maximum expected assuming a
literature Karplus relationship.22The changes in the values
3
for J(31P,1H) for the noncomplexed phenylethyl side chain
depend on the nature of the ligand (compare the values for
19 and 20 using ligand 2 as well as those for 18 and 23
using S,R,R-1).
The 13C chemical shifts for the terminal allyl positions are
presented in Tables 1 and 2. All of the neutral chloro-
palladium23 compounds 4-11 show chemical shifts in the range
(a) 76-80 ppm for the position pseudo-trans to the P-donor,
CA, and (b) 58-67 ppm for the allyl carbons pseudo-trans to
Table 3. For comparison, in Table 5, we show coordination
(18) For the salt containing the biphenol-based ligand, 2, this sequence
is reversed.
chemical shifts for η2-olefin ligands in a model cationic

2952 Organometallics, Vol. 27, No. 13, 2008
Filipuzzi et al.
chloride, CC. These chemical shifts are consistent with those of
the model compounds 27,24 28,25 and 29,26 containing phos-
phines or a carbene.
3a. Rotation around the C(phenyl)-CH(Me)N bond, which
process, e.g., after dissociation of the complexed olefin,
exchanges the H2 and H6 protons; see eq 1.
3b. The same net result, i.e., exchange of the ortho positions
on the phenyl ring, can be obtained if the metal “slides” or
“jumps” from C1-C2 to the neighboring C1-C6.
1
Figure 3 shows a set of variable-temperature H measure-
ments for 19. These spectra reveal that the allyl protons are
relatively sharp at ambient temperature. Exchange may still be
present, but it will most likely not be faster than a few per second
(i.e., close to the line widths). At ambient temperature one does
not easily find the side-chain CH signals, but these do become
relatively sharp at ca. 233 K and are found at δ ) 4.3 and 4.9
ppm. Clearly process 2 has a lower activation energy than the
allyl isomerization. Further, as indicated by the line shapes, the
“H2, H6” exchange (process 3) is still proceeding even at 213
K (see the shapes of the signals between 6.0 and 6.5 ppm). The
2D exchange map of the same compound, at 213 K, confirms
this assumption, as shown in Figure 4. Although most of the
aromatic protons are strongly overlapped, the ortho H2 reso-
nances are resolved and the cross-peaks for the exchange with
H6 readily visible. The figure also shows the exchange between
the meta protons, and these signals can be seen at higher
frequencies (see Figure 4, between 7.5 and 7.9 ppm). The
aliphatic part of the exchange map (not shown in the figure)
reveals that the exchange processes for the methyl and methine
groups of the ligand are slow at this temperature, but still
present, as suggested by the line shapes. Consequently, the
activation energies for processes 2 and 3a/3b, in 19, are not
very different, although the 3a/3b processes have a slightly lower
energy barrier.
For the palladium cationic series 15-22 (see Table 2), the
chemical shifts for CA fall in the range 93-99 ppm, while for
CC values lie between 57 and 66 ppm. Consequently, substitution
of the chloride by the η2-olefin results in a high-frequency
chemical shift of the carbon atom trans to the phosphorus ligand,
CA, while CC experiences no substantial change. These values
are somehow surprising, since one might have expected a larger
effect on the allyl carbon, CC, located in trans position to the
new ligating group. Perhaps the steric effects associated with
the complexed olefin help to weaken the bonding to CA.
This brings us to the various possible dynamics in these salts.
One can envision at least four intramolecular processes:
1. The frequently reported27 η3-η1-η3 isomerization mech-
anism, which can proceed by several mechanisms (only one of
which is shown in eq 2) and may be rather selective.
However, the exchange data from Figure 5 for 21 provide
support for the contention that both process 2 and process 3a/
3b can have similar activation energies. In this spectrum the
two amino-methyl phenyl rings are exchanging within both
isomers. The two, now equivalent, protons, Hc (from the
noncoordinated side chain of the two isomers), are exchanging
with the two ortho protons, Ha and Hb, from the coordinated
ring, due to rotation around the P-N bond. The protons Ha
and Hb are in exchange due to rotation of the complexed ring
2. Rotation around the P-N bond, as indicated in 30, which
will exchange the positions of the two amino side-chain phenyl
groups.
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(19) This is not a trivial choice since, at lower temperatures, one begins
to observe restricted rotation around the various C-C and, for the
SimplePhos, 3, P-C bonds, with the resultant loss of resolution and spectral
clarity. At higher temperatures, the dynamics of olefin exchange dominate.
Consequently, the temperatures indicated represent the most reasonable
compromise possible. On the basis of the observed temperature-dependent
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(15), 790–791.
(25) Krause, J.; Goddard, R.; Mynott, R.; Poerschke, K.-R. Organome-
tallics 2001, 20 (10), 1992–1999.
(26) Viciu, M. S.; Germaneau, R. F.; Navarro-Fernandez, O.; Stevens,
E. D.; Nolan, S. P. Organometallics 2002, 21 (25), 5470–5472.

Weak η2 Olefin Bonding in Pd and Pt Allyl Cationic Complexes
Organometallics, Vol. 27, No. 13, 2008 2953
Table 3. 13C Data and Relative Chemical Shifts for C1, C2, and C6 for the Saltsa
site
∆δ
complex
C1
∆δ
C2
C6
∆δ
T (K)
[Pd(C3H5)(S,S,S-1)]SbF6, 15
major
minor
major
minor
major
minor
major
minor
major
minor
major
minor
major
minor
131.9
133.3
131.3
131.5
132.9
131.8
131.4
133.3
133.4
134.1
128.9
128.4
133.1
132.9
133.7
113.8
116.0
122.9
125.7
122.6
nd
-10.1
-8.7
111.8
106.6
110.8
106.3
115.2
113.0
113.7
116.2
111.2
113.8
114.4
114.1
103.8
104.6
nd
-17.2
-22.4
-17.8
-22.3
-13.2
-15.4
-14.7
-12.2
-17.6
-15.0
-14.2
-14.6
-25.0
-24.2
123.9
127.4
125.0
127.8
121.0
117.5
118.0
117.7
122.6
119.1
119.5
117.8
127.8
127.4
nd
-5.2
-1.6
-3.6
-0.8
-7.4
-10.9
-10.4
-10.7
-6.2
-9.6
-9.2
-10.9
-1.0
-1.4
173
[Pd(C4H7)(S,S,S-1)]SbF6, 16
[Pd(C3H5)(S,R,R-1)]SbF6, 17b
[Pd(C4H7)(S,R,R-1)]SbF6, 18
[Pd(C3H5)(2)]SbF6, 19
-10.2
-10.0
-10.2
-11.4
-11.6
-9.8
173
203
203
193
193
213
-9.4
-8.6
[Pd(C4H7)(2)]SbF6, 20
-14.2
-14.6
-10.4
-10.6
-10.1
-24.0
-21.8
-21.0
-18.2
-21.4
[Pd(C3H5)(3)]SbF6, 21
[Pd(C4H7)(3)]SbF6, 22
[Pt(C3H5)(S,R,R-1)]SbF6, 23
213
298
major
minor
major
minor
major
minor
88.0
87.4
113.4
109.3
103.6
nd
-38.8
-39.4
-15.1
-19.2
-25.6
ca. 127
ca. 0.2
ca. 127
ca. 128
ca. 128
123.1
nd
ca. 0.2
ca. -0.5
ca. -0.5
-6.1
[Pt(C3H5)(2)]SbF6, 24
[Pt(C3H5)(3)]SbF6, 25
253
243
a ∆δ is relative to the chloro complexes. CD2Cl2 solutions, 500 or 700 MHz. b Synthesized by Mezzetti and co-workers (personal communication,
manuscript in preparation).
around the C(aryl)-CH(Me)N bond. Note that the two Hc
resonances are not in exchange with each other. Since the allyl
interconversion is slow at this temperature, the spectrum shows
two independent sets of cross-peaks, one for each allyl
arrangement.
In terms of relative rates of the two processes as a function
of the P-donor, it seems that for phosphoramidite-type auxiliaries
(ligands 1 and 2) process 3 possesses the lowest activation
energy. On the other hand for aminophosphine-type ligand 3,
the exchange of the complexed and free side chains has a
relatively lower energy barrier. These observations are qualita-
tive and based on the relative intensities of the exchange cross-
peaks.
The chirality of phosphoramidites, as discussed in the
Introduction, arises from two modular elements: the atropoiso-
meric backbone and the stereogenic centers within the chiral
amine. From catalysis results4,18,28–30 it is known that only one
diastereomeric combination affords high enantioselectivities, the
so-called matched series, and it is assumed that the binaphthol
unit is imposing the absolute stereochemistry of the catalytic
product. When flexible binol backbones are used, the amine
alone is sufficient to induce atropoisomerism.28 Since the two
diastereomeric complexes from 1 should show different struc-
tures, we had hoped to detect differences in the olefin coordina-
tion via the 13C data. Unfortunately different temperatures were
necessary for the analysis of the two series of compounds
15-18, so that the 13C results are not readily interpreted. In
any case, it is not obvious that these relative chemical shifts
are very different.
DFT calculations were performed for the Pd complex
[Pd(C3H5)(S,R,R-1)]+ (using the crystallographic data from
17)16,21 and (given the interest in related ruthenium chemistry,
namely, the fact that a similar bond was observed in a Ru
complex bearing different chiral ligands) a model RuCl(p-
cymene) complex (Ru) depicted in Figure 6 (right side),12 where
the naphthyl group was replaced by the biaryl analogue.
The structures of the complexes were fully optimized, and
an energy partitioning analysis was carried out (see Experimental
Section for details). Two alternative structures, 17* and Ru*,
with enforced long distances between the metal and all phenyl
groups, were optimized as well, and all four structures are shown
in Figure 6. This methodology is similar to that described in an
earlier publication.8
A third structural possibility was considered in which the
phenyl groups of the amine side chain were kept far from the
metal, and a proximate double bond of the naphthyl fragment
was allowed to approach either the Ru or the Pd. No low-energy
structure with an η2-olefin could be obtained.
The calculated structure of the Pd complex 17 is very close
to the experimental one. Specifically, the Pd-C distances to
the weakly bound phenyl carbon atoms are 2.445 and 2.477 Å,
whereas the experimental values are 2.413 and 2.514 Å. The
agreement is not quite as good in the Ru complex (calculated:
2.497, 2.477 Å; experimental: 2.386, 2.378 Å), possibly because
the model complex chosen is different from the complex for
which one has X-ray data.
(28) Feringa, B. L.; Pineschi, M.; Arnold, L. A.; Imbos, R.; De Vries,
A. H. M. Angew. Chem., Int. Ed. Engl. 1997, 36 (23), 2620–2623.
(29) (a) Kno¨bel, A. K. H.; Escher, I. H.; Pfaltz, A. Synlett 1997, (12),
1429–1431. (b) Escher, I. H.; Pfaltz, A. Tetrahedron 2000, 56 (18), 2879–
2888.
In the alternative “nonbonded” structure containing Pd, 17*,
where no weak η2 interaction occurs, the shortest Pd-C distance
involving the amine phenyl groups is 3.617 Å. Interestingly, in
(30) Alexakis, A.; Rosset, S.; Allamand, J.; March, S.; Guillen, F.;
Benhaim, C. Synlett 2001, 9, 1375–1378.

2954 Organometallics, Vol. 27, No. 13, 2008
Filipuzzi et al.
Table 4. 31P NMR Data and Relative Chemical Shifts for the
Cationic Compounds (all of the data refer to CD2Cl2 solutions, 500
or 700 MHz)
isomer
complex
major
minor
∆δ
2.2
1.1
1.1
1.0
0.5
[Pd(C3H5)(S,S,S-1)]SbF6, 15
[Pd(C4H7)(S,S,S-1)]SbF6, 16
[Pd(C3H5)(S,R,R-1)]SbF6, 17
[Pd(C4H7)(S,R,R-1)]SbF6, 18
[Pd(C3H5)(2)]SbF6, 19
[Pd(C4H7)(2)]SbF6, 20
[Pd(C3H5)(3)]SbF6, 21
151.9
151.6
148.1
148.2
148.8
149.1
84.2
153.3
152.4
148.8
149.6
149.4
150.6
84.3
0.9
32.8
34.6
-4.9
6.0
[Pd(C4H7)(3)]SbF6, 22
84.8
[Pt(C3H5)(S,R,R-1)]SbF6, 23a
[Pt(C3H5)(2)]SbF6, 24b
137.8
141.6
82.1
138.0
141.7
82.2
[Pt(C3H5)(3)]SbF6, 25c
27.6
a 1J(Pt,P) ) 6827 Hz (major), 4655 Hz (minor); 195Pt δ ) -5101
(major), -5080 (minor). b 1J(Pt,P)
) 7114 Hz (major), 7056 Hz
(minor); 195Pt δ ) -4942 (major), -4988 (minor). c 1J(Pt,P) ) 4565
Figure 3. Series of variable-temperature 1H NMR spectra for
complex 19. Note that the side-chain CH and CH3 signals are broad
at ambient temperature, but that the allyl resonances are relatively
sharp.
Hz (major), 4655 Hz (minor).
Table 5. 13C NMR Data and Coordination Chemical Shifts for
Selected Olefins in a Model Complex35
olefin
CH2dCH2
MeCHdCH2
δ(dCH2) ∆δ(dCH2) δ(dCH) ∆δ(dCH)
88.0
86.4
77.2
-35.3
-29.6
-34.8
1
118.1
120.2
110.9
107.8
105.2
-16.5
-15.3
-14.4
-17.6
-30.5
Figure 1. Section of the H spectrum of Pt salt 24 showing the
PHCHdCH2
complexed two aryl C-H2 protons (from the two isomers) with their
(Z)-MeCHdCHMe
(E)-MeCHdCHMe
norbornene
broad 195Pt satellites.
Scheme 2
structures (and two tables of Supporting Information, S1 and
S2 provide more detail). These short contact distances for 17*
and Ru* are too long to be considered covalent bonds; however,
we shall use these results to represent the nonbonding coun-
terparts of complexes 17 and Ru, respectively.
Mayer indices (MI) were used as bond strength indicators to
confirm the trends given by the distances. In the Pd complex
17, the MIs for the η2-interactions are 0.249 and 0.296, while
for the three allyl Pd-C bonds they range from 0.254 (central)
to 0.437 and 0.568. The value for the Pd-P bond is 0.982. In
complex 17*, the strength of the bonds to the allyl carbon atoms
stays the same (central: 0.253) or becomes stronger (terminal
carbons: 0.441, 0.631). Although the Pd-P bond index barely
changes (0.967), the index for the long interaction (3.617 Å) is
very small (0.034). This value is ∼8-9 times smaller than the
effective Pd-C η2-interactions and can be neglected.
Figure 2. Sections of two 13C,1H correlations for 21: (left) the one-
bond correlation showing the two aryl C2 CH resonances of both
isomers at ca. 104 ppm and (right) the result from the long-range
correlation (using the methyl groups and their 3J(C,H) values)
showing the positions of the four C1 phenyl ipso carbons. Two of
these C1 signals, at ca. 133 ppm, are shifted to lower frequency by
ca. 8 ppm.
the Ru model complex, Ru*, there is a short contact (3.315 Å)
and it involves the biaryl (binol) group of the phosphine. Figure
6 also provides the relevant M-C distances for these four

Weak η2 Olefin Bonding in Pd and Pt Allyl Cationic Complexes
Organometallics, Vol. 27, No. 13, 2008 2955
Table 6. 3J(P,H) Values for the Phenylethyl Groups of Selected
ligand. The [Pd(allyl)]+ moiety is slightly less stable (0.03 kcal
mol-1) when the CdC bond is not coordinated, the opposite
taking place for Ru. When the differences for the other
contributions in both geometries (17 and 17*) are examined
for the Pd complex, the electrostatic and Pauli terms practically
cancel each other (-15.38, 17.21), with the binding energy ∆E
(-12.66 kcal mol-1) being almost the same as the orbital term
(∆Eorb) -12.94 kcal mol-1).
Complexes
3J(31P,1H)
complex
complexed arm
free arm
[Pd(C3H5)(S,S,S-1)]SbF6, 15
[Pd(C4H7)(S,S,S-1)]SbF6, 16
[Pd(C4H7)(S,R,R-1)]SbF6, 18
[Pd(C3H5)(2)]SbF6, 19
[Pd(C4H7)(2)]SbF6, 20
[Pd(C4H7)(3)]SbF6, 22
41
41, 42
41
40
41
nd
The situation is different for the Ru complex. The electrostatic
term ∆Eelec drops by 85.46 kcal mol-1 when varying the
coordination sphere of the metal and is accompanied by a large
loss of orbital interaction (56.06 kcal mol-1). As the Pauli
repulsion (∆Epauli) decreases by a relatively large amount
(103.64), the global result reveals a large interaction energy
between the CdC bond of the amine phenyl and the Ru
fragment (30.13 kcal mol-1).
ca. 19
ca. 7
ca. 14
ca. 13
nd
39
39
[Pt(C3H5)(S,R,R-1)]SbF6, 23
ca. 7
The situation is similar in the Ru model complexes. In Ru,
the relevant MIs are as follows: Ru-Cl (0.824), Ru-P (1.057),
Ru-C1 (0.326), Ru-C2 (0.267). For Ru* these change to
Ru-Cl (0.869), Ru-P (0.817), and Ru-C(arene carbon at 3.315
Å) 0.008. The Ru-C bonds to the carbon atoms in the p-cymene
ring become stronger in Ru* (0.334, 0.351, 0.401, 0.418, 0.448,
0.454, compared to 0.309, 0.335, 0.365, 0.415, 0.440, 0.461 in
Ru). Again, the strength of the presumed Ru-C weak interac-
tion in Ru* is negligible compared to the two existing
interactions in the initial structure of Ru. Interestingly the Ru-P
bond also weakens, probably because of the distortion imposed
to the ligand. The metal makes stronger bonds only to Cl and
the ring in p-cymene. Wiberg indices can be used for the same
purpose (these are given in Tables S1 and S2) and give the
same qualitative information with respect to the bond strengths.
In order to estimate the strength of the Pd-C η2-interactions,
we carried out an energy decomposition analysis (see Experi-
mental Section for details), and the results are collected in Table
7. The first surprising result concerns the strength of the η2-
arene interaction (30.13 kcal mol-1) for the Ru complex 17.
Comparing this situation with the one described earlier for
[CpRu(Binap)]+, one finds that the major difference involves
the ready ability of the amine side chain in the Ru complex to
approach the metal; that is, this fragment does not need to distort
in order to complex. This fact is reflected in the low change of
reorganization energy, 6.02 kcal mol-1. This was not the case
in [CpRu(Binap)]+, where the reorganization energy of Binap
was 19.45 kcal mol-1, a factor that largely contributed to the
weak η2-arene interaction (the lower Mayer indices confirm this
aspect). Notice that a similar approach of the naphthyl fragment
in the ligand is almost impossible in Ru, owing to the presence
of the oxygen atom. In the absence of large preparation energies,
the η2-arene interaction cannot even be called weak. The
distances and MIs involved are comparable to those observed
between Ru and the p-cymene carbon atoms.
In the known 16-electron species [CpMo(CO)2(PPh3)]+, the
interaction with a CdC bond helps to decrease the electronic
unsaturation (large ∆Eorb); on the other hand, the coordination
number rises to seven and other effects compensate, leading to
a very weak interaction.
The corresponding value in the Pd complex (12.94 kcal mol-1
)
The calculated change in 13C chemical shifts associated with
the relevant carbon atoms also shows clearly a different behavior
exhibited by the carbon atoms involved in the weak bond (Table
S3).
approaches the values calculated in a previous study involving
[CpMo(CO)2(PPh3)]+ (8.58 kcal mol-1) and [CpRu(Binap)]+
(13.74 kcal mol-1).8
The reorganization energies of the two fragments between
the two geometries are small, close to 0 for the metal fragment
[Pd(allyl)]+ or [Ru(p-cymene)Cl]+, and not much larger for the
Conclusions
Incorporation of two chiral R-phenethyl amine side chains
into the P-donor ligands places one of the two phenyl groups
in a position to interact with the Pd and Pt centers in our cationic
allyl complexes. Both the NMR data and the DFT calculations
suggest that the binding energies in the η2-olefin cationic
complexes that form are relatively low (∼13 kcal mol-1), in
agreement with the fluxional behavior observed. However this
type of weak bond is interesting in that it may be sufficient to
briefly stabilize a coordinatively unsaturated metal complex and/
or a reactive transition state.
Experimental Section
General Procedures. All reactions and manipulations were
performed under a N2 atmosphere using standard Schlenk tech-
niques. The palladium precursors [Pd(C3H5)Cl]2 and [Pd(C4H7)Cl]2
and the silver salts were purchased from commercial sources and
used as received from the producer. Silver salts were stored in a
glovebox. Phosphoramidite ligands 1, 2, and SimplePhos,3 3, and
complexes of the type [Pd(allyl)(phosphoramidite)Cl]4 were syn-
thesized according to published procedures. Solvents were dried
Figure 4. 2D exchange spectrum for 19 showing the “H2, H6”
exchange for the two isomers. The H6 resonances are strongly
overlapped.

2956 Organometallics, Vol. 27, No. 13, 2008
Filipuzzi et al.
Figure 5. 2D NOESY spectrum of 21 showing that the two amino-methyl phenyl rings are exchanging in both isomers. The two equivalent
protons, Hc (from the two isomers), are exchanging with the two ortho protons, Ha and Hb, from the other ring due to rotation around the
P-N bond. The protons Ha and Hb are in exchange due to processes 3a,b. The two Hc resonances are not in exchange with each other,
as the allyl interconversion is slow at this temperature.
Figure 6. DFT-optimized structures for the complexes 17, 17*, Ru, and Ru*, emphasizing the shortest M-C contacts with phenyl groups.
and distilled under standard procedures and stored under nitrogen.
NMR spectra were recorded with Bruker DPX-250, 300, 400, 500,
and 700 MHz spectrometers at room temperature, unless otherwise
stated. Chemical shifts are given in ppm; coupling constants (J) in
hertz. Elemental analyses and mass spectroscopic studies were
performed at the ETHZ. Extensive lists of detailed NMR data can
be found in supplementary tables S4-S14.
Synthesis of [PdCl(allyl)(phosphoramidite)]. A solution of the
P-donor ligand (0.180 mmol, 2.0 equiv) in CH2Cl2 (5 mL) is slowly
added, under stirring, to a solution of the suitable dinuclear species
[Pd(µ-Cl)(allyl)]2 (0.090 mmol, 1.0 equiv) in CH2Cl2 (5 mL). After
the addition is finished, the solution is stirred for 15 min, then the
solvent is removed under reduced pressure, giving a solid, which
is washed with diethyl ether and dried under vacuum.

Weak η2 Olefin Bonding in Pd and Pt Allyl Cationic Complexes
Organometallics, Vol. 27, No. 13, 2008 2957
Table 7. Energy Decompositiona for the Interaction between L and
[Pd(µ-Cl)(C3H5)]2 (0.090 mmol, 1.05 equiv) in CH2Cl2 (10 mL).
After the addition is finished, particles of platinum dimer are still
visible in suspension. The mixture is stirred until it clears up (about
30 min), then it is filtered to remove the excess platinum precursor.
The solvent is removed under reduced pressure, giving a solid,
which is washed with diethyl ether and dried under vacuum.
[PtCl(C3H5)(S,R,R-1)], 12: yellowish-white solid, yield 73%.
Anal. Calcd for C39H35ClNO2PPt · CD2Cl2: C, 53.63; H, 4.13; N,
1.56. Found: C, 53.35; H, 3.82; N, 1.33. MALDI MS: 1317 (M+
- Cl + 1), 875 (M+ - Cl - C3H5 + HPA).
M in [Pd(C3H5)(1)]+ (17) and a Model of [Ru(p-cymene)Cl(1)]+ (Ru)
17
8.89
2.66
17* ∆ (17-17*) Ru
Ru* ∆ (Ru-Ru*)
Eprep(L)
Eprep(M)
∆Eprep
∆Eelec
11.03
2.63
-2.14
0.03
19.76 13.74
11.10 10.36
6.02
0.74
6.76
-85.46
103.64
-56.06
-36.89
-30.13
11.55
13.66
-2.11
-15.38
17.21
30.86 24.10
-150.83 -135.45
167.21 150.00
-107.83 -95.17
-91.45 -80.62
-174.11 -89.65
228.19 124.55
-147.91 -91.85
-93.83 -56.94
-62.97 -32.84
∆Epauli
∆Eorb
∆Eint
-12.66
-10.83
-12.94
∆E ) -De -79.90 -66.96
[PtCl(C3H5)(2)], 13: whitish solid, yield 85%. Anal. Calcd for
C31H31ClNO2PPt: C, 52.36; H, 4.39; N, 1.97. Found: C, 52.03; H,
4.32; N, 1.95. MALDI MS: 1114 (M+ - Cl + 2), 675 (M+ - Cl),
668 (M+ - C3H5), 633 (M+ - Cl - C3H5).
[PtCl(C3H5)(3)], 14: whitish solid, yield 80%. MALDI MS: 645
(M+ - Cl), 603 (M+ - Cl - C3H5). Although from the 31P NMR
spectrum only the desired product can be detected, the elemental
analysis data are poor.
a Values in kcal mol-1; L ) ligand 1 and M ) [Pd(allyl)]+ (17, 17*)
or L ) small ligand 1(1′) and M ) [Ru(p-cymene)Cl]+ (Ru, Ru*).
[PdCl(C3H5)(S,S,S-1)], 4: white solid, yield 90%. Anal. Calcd
for C39H35ClNO2PPd: C, 64.83; H, 4.88; N, 1.94. Found: C, 63.95;
H, 4.92; N, 1.90. MALDI MS: 1184 (M+ - Cl - C3H5 + L), 686
(M+ - Cl), 645 (M+ - Cl - C3H5), 538 (M+ - Cl - C3H5 -
Pd).
[PdCl(C4H7)(S,S,S-1)], 5: yellowish-white solid, yield 95%.
Anal. Calcd for C40H37ClNO2PPd: C, 65.23; H, 5.06; N, 1.90.
Found: C, 64.42; H, 5.16; N, 1.90. MALDI MS: 700 (M+ - Cl),
644 (M+ - Cl - CH2CCH3CH2), 538 (M+ - Cl - CH2CCH3CH2
- Pd).
Synthesis of [Pt(allyl)(phosphoramidite)]SbF6 (NMR sample).
A solution of the suitable [PtCl(C3H5)(phosphoramidite)] complex
(0.030 mmol, 1.0 equiv) in CD2Cl2 (1 mL) is transferred via cannula
into a Schlenk tube containing solid AgSbF6 (0.030 mmol, 1.0
equiv). A white precipitate of AgCl forms immediately. The
suspension is then stirred for 10 min, and the solution is filtered
through Celite directly into a NMR tube equipped with a J. Young-
type valve.
DFT Calculations. Density functional theory (DFT) calcula-
tions31 were carried out with the Amsterdam Density Functional
(ADF2006) program.32 Gradient-corrected geometry optimizations33
without symmetry constraints were performed using the local
density approximation of the correlation energy (Vosko, Wilk,
Nusair)34 andtheexchange-correlationsfunctionalsofPerdew-Wang
(PW91).35 Relativistic effects were taken into account with the
ZORA approximation.36 A triple-ꢀ Slater-type orbital (STO) basis
set augmented by two polarization functions was used for Pd, Ru,
P, O, C, N, and H. A frozen core approximation was used to treat
the core electrons: (1s) for C, O, and N, (1s, 2p) for P, ([1-3]s,
[2-3]p, 3d) for Pd and Ru. Mayer indices37 were used as bond
strength indicators.
[PdCl(C4H7)(S,R,R-1)], 6: white solid, yield 91%. Anal. Calcd
for C40H37ClNO2PPd · H2O: C, 63.64; H, 5.20; N, 1.86. Found: C,
63.34; H, 5.19; N, 2.01. MALDI MS: 700 (M+ - Cl), 645 (M+
-
Cl - CH2CCH3CH2), 538 (M+ - Cl - CH2CCH3CH2 - Pd).
[PdCl(C3H5)(2)], 8: white solid, yield 92%. Anal. Calcd for
C31H31ClNO2PPd · H2O: C, 58.14; H, 5.19; N, 2.18. Found: C,
58.70; H, 5.09; N, 2.21. MALDI MS: 984 (M+ - Cl - C3H5 +
L), 586 (M+ - Cl), 545 (M+ - Cl - C3H5), 440 (M+ - Cl -
C3H5 - Pd).
[PdCl(C4H7)(2)], 9: white solid, yield 93%. Anal. Calcd for
C32H33ClNO2PPd: C, 60.39; H, 5.23; N, 2.20. Found: C, 60.40; H,
5.19; N, 2.40. MALDI MS: 600 (M+ - Cl), 545 (M+ - Cl -
CH2CCH3CH2), 438 (M+ - Cl - CH2CCH3CH2 - Pd).
[PdCl(C3H5)(3)], 10: pale green solid, yield 90%. Anal. Calcd
for C31H33ClNO2PPd · H2O: C, 60.99; H, 5.77; N, 2.29. Found:
C, 60.72; H, 5.49; N, 2.25. MALDI MS: 556 (M+ - Cl), 515 (M+
- Cl - C3H5), 410 (M+ - Cl - C3H5 - Pd).
The energy decomposition analysis (EDA) developed by Ziegler
and Rauk38 was applied to the PW91-optimized geometries to
analyze the interactions between the metals and the C-C bonds.
The bond dissociation energy (∆E ) -De) between two fragments
is taken as the sum of two contributions, ∆E ) ∆Eprep + ∆Eint,
where ∆Eprep is the energy required to reorganize the fragments
from their equilibrium geometry to the geometry of the complex;
∆Eint is the interaction energy between the two fragments in the
complex and can be divided into three components: ∆Eelec + ∆Epauli
[PdCl(C4H7)(3)], 11: pale green solid, yield 92%. Anal. Calcd
for C32H35ClNO2PPd · H2O: C, 61.54; H, 5.97; N, 2.24. Found: C,
60.80; H, 5.71; N, 2.24. MALDI MS: 570 (M+ - Cl), 515 (M+
-
Cl - CH2CCH3CH2), 410 (M+ - Cl - CH2CCH3CH2 - Pd).
Synthesis of [Pd(allyl)(phosphoramidite)]SbF6 (NMR
sample). A solution of the suitable [PdCl(C3H5)(phosphoramidite)]
complex (0.030 mmol, 1.0 equiv) in CD2Cl2 (1 mL) is transferred
via cannula into a Schlenk tube containing solid AgSbF6 (0.030
mmol, 1.0 equiv). A white precipitate of AgCl forms immediately.
The suspension is stirred for ca. 2 h, then the solution is filtered
through Celite directly into a NMR tube equipped with a J. Young-
type valve.
In some cases the product was isolated by evaporating the solvent
and washing the resulting solid with Et2O. The elemental analyses
for these complexes are poor, since they are coordinatively
unsaturated and tend to absorb water.
+ ∆Eorb
.
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[Pd(C4H7)(S,S,S-1)]SbF6, 15: yellowish-white solid, yield 75%.
MALDI MS: 1184 (M+ - C3H5 + L), 686 (M+), 646 (M+
-
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C3H5), 540 (M+ - C3H5 - Pd).
[Pd(C3H5)(2)]SbF6, 19: yellowish-white solid, yield 65%.
MALDI MS: 600 (M+), 546 (M+ - CH2CCH3CH2), 438 (M+
CH2CCH3CH2 - Pd).
-
(35) Perdew, J. P.; Chevary, J. A.; Vosko, S. H.; Jackson, K. A.;
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MALDI MS: 927 (M+ - C3H5 + L), 556 (M+), 518 (M+ - C3H5),
410 (M+ - C3H5 - Pd).
Synthesis of [PtCl(allyl)(phosphoramidite)]. A solution of the
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2958 Organometallics, Vol. 27, No. 13, 2008
Filipuzzi et al.
The ∆Eelec term corresponds to the electrostatic interaction energy
between the fragments; ∆Epauli is the repulsive interaction between
the fragments as a result of the fact that two electrons with the
same spin are unable to occupy the same region in space; ∆Eorb is
associated with the orbital interaction energy (covalent bond
formation).
the Gaussian03 implementation of the gauge-independent atomic
orbital (GIAO) method.44
Acknowledgment. P.S.P. thanks the Swiss National Sci-
ence Foundation and the ETH Zurich for support, as well as
the Johnson Matthey Company for the loan of palladium
salts. We also thank Prof. Alex Alexakis (Geneva) for the
gift of ligands 2 and 3 as well as Prof Antonio Mezzetti
(ETHZ) and Dr. Igor Mikhel for helpful discussions. P.J.C.
acknowledges the FCT for grant SFRH/BPD/27082/2006.
M.J.C. and P.J.C. thank FCT, POCI, and FEDER for funding
(project POCI/QUI/58925/2004).
Single-point DFT/B3LYP39 calculations using the previously
optimized geometries (ADF/PW91) were also performed with
Gaussian0340 using the standard LanL2DZ basis set with the
associated ECP41 for Ru and Pd, and a standard 6-311G** basis
set for the remaining elements. Wiberg Indices42 were obtained
from a natural population (NPA) analysis43 and were also used as
bond strength indicators. NMR chemical shifts were calculated using
Supporting Information Available: Distances, Mayer indices
and Wiberg indices for the two Pd complexes 17 and 17* are given
in Table S1, and for the two Ru complexes Ru and Ru* in Table
S2. Table S3 gives DFT calculated 13C relative* chemical shifts
for complexes 17, 17*, Ru, and Ru*. This material is available
free of charge via the Internet at http://pubs.acs.org.
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