Ion pairing and allyl dynamics in a series of [Pd(η3-allyl) (N, N-chelate)](anion) salts. On the influence of the BPh4 - anion

Article abstract of DOI:10.1021/om900697e

A series of BPh₄^- and other Pd-allyl salts of the form [Pd(η³-allyl)(N,N-chelate)](anion) (η³-allyl = CH₂C(Me)CH₂,3, and PhCHCHCHPh, 4) have been prepared and studied via PGSE diffusion and

Full text of DOI:10.1021/om900697e

Organometallics 2009, 28, 6489–6506 6489
DOI: 10.1021/om900697e
Ion Pairing and Allyl Dynamics in a Series of [Pd(η3-allyl)(N,N-
chelate)](anion) Salts. On the Influence of the BPh4- Anion
Aitor Moreno and Paul S. Pregosin*
€
€
Laboratory of Inorganic Chemistry, ETHZ, Honggerberg, CH-8093 Zurich, Switzerland
Beatriz Fuentes
IU CINQUIMA/Quimica Inorganica, Facultad de Ciencias, Universidad de Valladolid, E-47071 Valladolid, Spain
Luis F. Veiros*
´
ꢀ
Centro de Quımica Estrutural, Complexo I, Instituto Superior Tecnico, Avenida Rovisco Pais 1, 1049-001
Lisbon, Portugal
Alberto Albinati* and Silvia Rizzato
ꢁ
Dipartimento di Chimica Strutturale, Universita di Milano, Via G. Venezian 31, 20133 Milano, Italy
Received August 6, 2009
A series of BPh4- and other Pd-allyl salts of the form [Pd(η3-allyl)(N,N-chelate)](anion) (η3-allyl=
CH2C(Me)CH2, 3, and PhCHCHCHPh, 4) have been prepared and studied via PGSE diffusion and
other forms of NMR spectroscopy together with X-ray and DFT calculations. The diffusion data
reveal that the BPh4- salts show a very substantial amount of ion pairing in CD2Cl2 solution. Both
the solution Overhauser studies and the X-ray results are consistent with a BPh4- position that brings
one or more phenyl groups very close to the N,N-chelate, and this would facilitate phenylation
reactions. Variable-temperature and magnetization transfer NMR measurements reveal allyl and
ligand dynamics that fall under the general heading of “apparent rotation”. DFT calculations suggest
that this isomerization process in 3 and 4 is solvent assisted and proceeds with Pd-N bond breaking.
Introduction
homogeneous catalysis suggests that larger aluminum and
boron anions9 can sometimes afford faster reactions.10 Thus
the tetra phenyl borate derivative BArF- (= tetra(3,5-ditri-
fluoromethyl)phenyl borate) is a now often used to accom-
Although many transition metal salts are capable of
catalyzing organic transformations, the literature shows that
monocationic salts are frequently the catalysts of choice. The
selection of the accompanying anion is often restricted to
those that are thought to be incapable of competing as a
-
pany the cation. Interestingly, the parent BPh4 anion is
rarely selected. This may be related to observations in which
this anion can form an η6-arene complex11 (eq 1) or function
as a source of the phenyl anion12,13 (see eqs 2 and 3).
-
-
ligand, e.g., BF4 or PF6 rather than Cl-. However,
the recent literature concerned with anion effects1-8 in
*Corresponding authors. E-mail: pregosin@inorg.chem.ethz.ch.
(1) Smidt, S. P.; Zimmermann, N.; Studer, M.; Pfaltz, A.
Chem.;Eur. J. 2004, 10, 4685–4693.
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4138.
(3) Semeril, D.; Bruneau, C.; Dixneuf, P. H. Adv. Synth. Catal. 2002,
344, 585–595.
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286–287. (b) Martinez-Viviente, E.; Pregosin, P. S. Inorg. Chem. 2003, 42,
2209–2214. (c) Kumar, P. G. A.; Pregosin, P. S.; Schmid, T. M.; Consiglio, G.
Magn. Reson. Chem. 2004, 42, 795–800. (d) Macchioni, A. Chem. Rev.
2005, 105, 2039–2073.
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(8) Burckhardt, U.; Baumann, M.; Togni, A. Tetrahedron: Asymme-
try 1997, 8, 155.
PtHðNO ÞðPEt Þ þ NaðBPh Þ s PtðPh2ÞðPEt3Þ ð2Þ
f
3
3
4
2
2
MeOH
(11) (a) Aresta, M.; Quaranta, E.; Albinati, A. Organometallics 1993,
12, 2032–2043. (b) Torres, F.; Sola, E.; Martin, M.; Ochs, C.; Picazo, G.;
Lopez, J. A.; Lahoz, F. J.; Oro, L. Organometallics 2001, 20, 2716–2724.
(c) Note that BArF can also form an η6-complex: Douglas, T. M.; Molinos,
E.; Brayshaw, S. K.; Weller, A. S. Organometallics 2007, 26, 463–465.
(12) (a) Deeming, A. J.; Johnson, B. F. G.; Lewis, J. J. J. Chem. Soc.,
Dalton Trans. 1973, 1848. (b) Zheng, S.; Xu, L.; Xia, C. Appl. Organomet.
Chem. 2007, 21, 772–776.
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2090.
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Int. Ed. 1999, 38, 1220.
1989, 8, 2659–2664.
r
2009 American Chemical Society
Published on Web 10/19/2009
pubs.acs.org/Organometallics

6490 Organometallics, Vol. 28, No. 22, 2009
Moreno et al.
12a
these solution results with both X-ray crystallography and
DFT calculations. In addition to the question of ion pairing
we also consider aspects of the allyl dynamics in our salts.
PtHðNO ÞðPEt Þ þNaðBPh Þ s
f
3
3
4
2
MeOH
þ
Results and Discussion
ðPEt3Þ2HPtðμ-HÞPtðPhÞðPEt3Þ2
ð3Þ
13
Scheme 1 shows the two η3-allyl ligand types selected.
Several model salts contain either the BArF- or PF6- anions
in addition to those with the BPh4- anion. The new Pd-allyl
cationic complexes 3 and 4 were prepared using standard
methods (see Experimental Section) and were characterized
via NMR and microanalytical methods in addition to five
-
X-ray diffraction studies. Many of the BPh4 salts decom-
pose at room temperature, due to the phenylation reaction
mentioned above, so that the characterization for these salts
required low-temperature measurements.
Some time ago Crociani and co-workers14 reported on the
phenylation of palladium-allyl cationic complexes (see eq 4)
and suggested that the BPh4- anion might well be involved in
extensive ion pairing. In our NMR studies on cationic Mn-
(CO)3(η6-arene)þ complexes15 with several boron counter-
ions using pulsed gradient spin-echo (PGSE) NMR
diffusion methods16 we could show that, indeed, there was
Table 1 shows 13CNMR data for the allyl carbons of the
salts. These NMR parameters have been reported on a
number of occasions18,20-24 and used in discussions of both
bonding and reactivity. For the 2-methyl allyl cations, 3, the
terminal allyl 13C signals fall in the range δ=61-64, and we
do not find marked changes in their positions when the two
N-donors are different. The 1,3-diphenyl allyl cationic salts,
4, show the terminal allyl carbons in the range δ=78-81, in
agreement with the literature.18 In all of these complexes,
changing the anion has little or no effect on these allyl carbon
13C chemical shifts. Moreover, there are no noteworthy
changes in these terminal allyl 13C values when the chelating
ligands contain bulky groups in the ortho positions of the
Schiff base rings.
-
much more ion pairing with BPh4 than with BArF-.
A similar finding was reported for Ru(η6-arene) salts bearing
R-diimine ligands.17
Since we have a long-standing interest in palladium allyl
complexes,18 we have prepared some old and new salts of the
form [Pd(η3-allyl)(N,N)](anion) (see Scheme 1) and report
here studies concerned with the nature of the ionic interac-
tions and aspects of their dynamics in CD2Cl2 solutions. The
NMR approach to the subject of ion pairing follows that
used in our earlier studies.16,19 We separately measure the
diffusion constants (D values) for the cation and anion. If
these are identical and lead to relatively large hydrodynamic
radii, rH, we conclude that there is approximately 100% ion
pairing. This will often be the case for CDCl3 solutions;
however, for other solvents, for example, CD2Cl2, one
normally finds intermediate ion pairing. We then use
19F,1H (or 1H,1H) Overhauser measurements to provide
insight into the structure of the ion pair and try to support
1
Interestingly, a comparison of the H chemical shifts for
-
-
the PF6 and BPh4 salts shows that many protons in the
latter salts are shifted to lower frequency. Presumably this is
due to the local anisotropic effects associated with a proxi-
mate B(Ph) moiety (see Scheme 2 and Scheme S1). The
largest changes are found in the N,N-chelate rings, and the
-
same comparison using PF6 and BArF- (rather than
BPh4-) reveals only small differences, suggesting that the
-
BArF- is not as strongly ion paired as BPh4
.
X-ray Diffraction Studies. Five of the palladium salts
proved amenable for structural studies, and Table 2 provides
a list of the experimental details associated with these
measurements. Figure 1 shows ORTEP plots for the four
2-methyl allyl cations, 3a, 3b, 3f (as BPh4- salts) and 3h (as a
PF6- salt). Figure 2 gives the corresponding view for the 1,3-
diphenyl cation, 4g (as a PF6- salt). The immediate coordi-
nation spheres about the palladium atoms consist of the two
N-donors and the η3-allyl ligand. The complexed 2-methyl
allyl ligand is distorted such that the methyl group is tipped
(14) Crociani, B.; Antonaroli, S.; Dibianca, F.; Fontana, A.
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Munch, F.; Rose, E. Inorg. Chem. 2005, 44, 5941–5948.
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261–288. (b) Pregosin, P. S.; Kumar, P. G. A.; Fernandez, I. Chem. Rev.
2005, 105, 2977–2998. (c) Kumar, P. G. A. Aust. J. Chem. 2006, 59, 78–78.
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G.; Zuccaccia, C.; Clot, E.; Macchioni, A. Organometallics 2007, 26,
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Helmchen, G. Chem.-Eur. J. 2001, 7, 4913–4927. (c) Kollmar, M.;
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Article
Organometallics, Vol. 28, No. 22, 2009 6491
Scheme 1
away from the Pd center, in keeping with earlier measure-
ments on this type of ligand.25
The N-Pd-N chelate angles are all normal at ca. 78-79ꢀ.
The Pd-N bond lengths for the nitrogen ligands in the
complexed allyl salts fall in the relatively narrow range ca.
2.09-2.13 A. We note that in cation 4g, where some steric
crowding is unavoidable, the Pd-N(pyr) bond length, Pd-
(1)-N(10), 2.129(4) A, is slightly longer than that for the
Schiff base Pd-N interaction, Pd(1)-N(1), 2.091(4) A. For
the four 2-methyl allyl salts, the various Pd-C(terminal
allyl) separations do not vary much and mostly fall in the
range 2.10-2.15 A.
(25) For Pd(2-methyl allyl) structures, see: (a) Deeming, A. J.;
Rothwell, I. P.; Hursthouse, M. B.; Malik, K. M. A. J. Chem. Soc.,
Dalton Trans. 1979, 1899–1911. (b) Albinati, A.; Kunz, R. W.; Ammann,
C. J.; Pregosin, P. S. Organometallics 1991, 10, 1800–1806. (c) Ozawa, F.;
Son, T. I.; Ebina, S.; Osakada, K.; Yamamoto, A. Organometallics 1992, 11,
171–176. (d) Fernandez-Galan, R.; Manzano, B. R.; Otero, A.; Lanfranchi,
M.; Pellinghelli, M. A. Inorg. Chem. 1994, 33, 2309–2312. (e) Delis, J. G. P.;
Groen, J. H.; Vrieze, K.; van Leeuwen, P.; Veldman, N.; Spek, A. L.
Organometallics 1997, 16, 551–562. (f) Danopoulos, A. A.; Tsoureas, N.;
Macgregor, S. A.; Smith, C. Organometallics 2007, 26, 253–263. For
Pd(1,3-diphenyl allyl) structures, see: (g) Barbaro, P.; Pregosin, P. S.;
Salzmann, R.; Albinati, A.; Kunz, R. Organometallics 1995, 14, 5160–
5170. (h) Bastero, A.; Bella, A. F.; Fernandez, F.; Jansat, S.; Claver, C.;
Gomez, M.; Muller, G.; Ruiz, A.; Font-Bardia, M.; Solans, X. Eur. J. Inorg.
Chem. 2007, 132–139. (i) Ferioli, F.; Fiorelli, C.; Martelli, G.; Monari, M.;
Savoia, D.; Tobaldin, P. Eur. J. Org 2005, 1416–1426.
-
For 3a and 3b the positions of the BPh4 anions with
respect to the cation are informative, and these are shown in
-
Figure 3. There are a few short contacts between the BPh4
anions and the Pd cationic complexes in the range 2.7-2.9 A,
both in 3a(BPh4) and 3b(BPh4), the other packing distances
being longer than 3 A. It is interesting to notice that in both

6492 Organometallics, Vol. 28, No. 22, 2009
Moreno et al.
compounds a tetraphenyl borate anion is placed opposite the
η3-allyl moiety and close to the nitrogen chelate ring
(cf. Figure 3), in agreement with the solution NMR data
(see below); this may result, in part, from the partial positive
charges arising when the N atoms coordinated to the Pd
atom. We note that in 3a(BPh4) the anion intrudes much
more into the space occupied by the N,N-chelate than in
3b(BPh4). This observation seems to be related to a modest
distortion in the allyl bonding.
Table 1. 13C NMR Data for the Allyl Groups in Compounds 3 and
4 in CD2Cl2
cation
X
T/K
A
B
C
3a
PF6
298
298
298
298
298
298
213
253
213
263
263
263
263
263
223
193
193
223
223
263
263
263
203
61.1
61.1
61.4
61.0
61.0
60.1
64.3
62.2
61.9
61.8
61.5
61.6
61.8
62.1
61.6
81.2
81.2
80.1
79.6
80.5
80.5
80.6
80.6
136.9
136.7
137.5
136.7
136.6
135.5
136.8
136.4
135.9
136.6
136.5
137.6
137.2
137.4
137.4
108.4
108.1
106.8
106.8
106.8
106.3
106.2
106.3
BPh4
BArF
PF6
BPh4
BPh4
BPh4
BPh4
BPh4
PF6
BPh4
BArF
PF6
BPh4
BArF
PF6
3b
3c
3d
3e
3f
In 3a(BPh4) the allyl is slightly rotated with respect to the
N-Pd-N plane (indicated as a solid black line), whereas in
3b(BPh4) the two terminal allyl carbons are both slightly
below this plane. There is a similar modest rotation in the 1,3-
diphenyl salt 4g(PF6).
63.9
63.2
62.2
62.2
62.7
62.8
63.3
63.3
77.7
77.7
78.1
78.0
79.0
79.0
78.6
78.3
3g
3h
4e
4g
BPh4
PF6
BPh4
BArF
PF6
Summarizing these solid-state results, we find that the
“short” anion-cation interactions observed in the solid state
(e.g., e2.8 A for the BPh4 complexes and e2.6 A for the
4h
BPh4
BArF
-
-
PF6 anions) are consistent with the contacts found in
solution.
For the analogous salt 3a(BArF), D=12.32 for the cation
and D=8.48 for the anion with rHcorr =6.8 A; these data
suggest some but not much ion pairing since the corrected rH
for BArF is known to be ca. 6.6 A. Only three BPh4- salts,
3a-3c, are stable at ambient temperature, and once again the
diffusion data suggest intermediate ion pairing at 299 K. For
example, the D value for the cation of the 3a analogue is
12.32 and that for the anion 10.40.
Before discussing the 263 K D values for the more reactive
salts, three effects that drastically affect the measured
D values need to be considered: (a) possible convection,28
(b) solution viscosity29a (due to the change in temperature
from 299 to 263 K), and (c) solvent dielectric constant29b
(again due to the change in temperature). We have suggested
a method28 of suppressing convection and thereby obtaining
reliable D values at low temperature. This procedure requires
Diffusion Results. In addition to the new diffusion data for
the η3-allyl salts shown in Scheme 1 (see Table 3), we have
already collected a relatively large number of diffusion
constants (D values) for CD2Cl2 solutions of organic and
-
inorganic PF6 salts19a,b (including some with η3-allyl
ligands26). These data all arise from pulsed gradient
spin-echo (PGSE) NMR measurements. As noted above,
one normally finds intermediate ion pairing in this solvent,
but the hydrodynamic radii that are calculated from the
Stokes-Einstein equation27 suggest that the ions are larger
than what might be expected for acetone or aqueous solu-
tions. For example, the D values for the ions of 3a(PF6),
(13.02 for the cation and 13.54 for the anion) are not
identical, but the corrected hydrodynamic radius of 4.9
A for the anion is too large for a simple solvated PF6- anion.
Further, the D (and rH) values in 3a(PF6) for the cation and
anion in the more polar solvent acetone (15.64 (5.4 A) and
24.80 (4.4 A), respectively) confirm that the smaller anion is
indeed diffusing much faster than the cation. Therefore, the
larger rH value of 4.9 A for the anion in CD2Cl2 is consistent
with intermediate ion pairing.
(28) Martinez-Viviente, E.; Pregosin, P. S. Helv. Chim. Acta 2003, 86,
2364–2378.
(29) (a) Yaws, C. L. Chemical Properties Handbook; McGraw-Hill,
1999; pp 478-480. (b) Handbook of Chemistry & Physics, 89th ed.,
2008-2009 (online).
(30) (a) Ciancaleoni, G.; Zuccaccia, C.; Zuccaccia, D.; Clot, E.;
Macchioni, A. Organometallics 2009, 960–967. (b) Ciancaleoni, G.;
Zuccaccia, C.; Zuccaccia, D.; Macchioni, A. Magn. Reson. Chem. 2008,
46, S72–S79. (c) Bellachioma, G.; Ciancaleoni, G.; Zuccaccia, C.; Zuccaccia,
D.; Macchioni, A. Coord. Chem. Rev. 2008, 252, 2224–2238. (d) Rocchigiani,
L.; Zuccaccia, C.; Zuccaccia, D.; Macchioni, A. Chem.-Eur. J. 2008, 14,
6589–6592. (e) Zuccaccia, D.; Foresti, E.; Pettirossi, S.; Sabatino, P.; Zuccaccia,
C.; Macchioni, A. Organometallics 2007, 26, 6099–6105. (f) Ciancaleoni, G.;
Di Maio, I.; Zuccaccia, D.; Macchioni, A. Organometallics 2007, 26, 489–496.
(g) Zuccaccia, D.; Bellachioma, G.; Cardaci, G.; Zuccaccia, C.; Macchioni, A.
Dalton Trans. 2006, 1963–1971.
(26) Schott, D.; Pregosin, P. S.; Veiros, L. F.; Calhorda, M. J.
Organometallics 2005, 24, 5710–5717.
(27) The measured D value can be used to solve the Stokes-Einstein
relation, rH=kT/6πηD, for the hydrodynamic radius, rH. However, this
relation has been subject to criticism, in that the value 6 is often too large;
see: (a) Zuccaccia, D.; Macchioni, A. Organometallics 2005, 24,
corr
3476-3486. An empirical correction to afford rH
has been suggested;
see: (b) Macchioni, A.; Ciancaleoni, G.; Zuccaccia, C.; Zuccaccia, D. Chem.
Soc. Rev. 2008, 37, 479.

Article
Organometallics, Vol. 28, No. 22, 2009 6493
Scheme 2. Two Examples of Differences in 1H Chemical Shifts (Δδ (PF6- - BPh4)) between PF6- and BPh4- Salts (Δδ values, given
in ppm)
Table 2. Experimental Data for the X-ray Diffraction Study of Compounds 3a(BPh4), 3b(BPh4), 3f(BPh4), 3h(PF6), and 4g(PF6) (Et2O)
3
4g [PF6] (Et2O)
3a [BPh4]
3b [BPh4]
3f [BPh4]
3h [PF6]
3
formula
mol wt
C
636.89
150(2)
38H35BN2Pd
C40H35BN2Pd
660.91
150(2)
C41H39BN2OPd
692.95
295(2)
C22H29 F6N2PPd
572.84
150(2)
C32H34F6N2O0.5PPd
705.98
295(2)
data coll T, K
diffractometer
cryst syst
space group (no.)
a, A
b, A
c, A
R, deg
β, deg
Bruker APEX II CCD
monoclinic
P21/n (14)
9.7435(6)
24.092(2)
14.5385(9)
70.635(1)
79.001(1)
77.229(1)
3391.5(4)
4
monoclinic
C2/c (15)
21.526(1)
13.4110(6)
22.919(1)
90.
110.205(1)
90.
6209.2(5)
8
1.363
triclinic
P1 (2)
orthorhombic
P212121 (19)
8.2983(6)
10.1408(7)
28.891(2)
90.
90.
90.
2431.2(3)
4
1.565
triclinic
P1 (2)
11.341(1)
12.287(1)
13.584(2)
115.187(1)
112.844(1)
90.092(1)
1546.5(3)
2
10.5449(9)
15.848(1)
19.611(2)
79.266(1)
85.419(1)
81.359(1)
3179.0(5)
4
γ, deg
V, A3
Z
F
(calcd), g cm-3
1.419
0.632
1.357
0.582
1.475
0.695
μ, mm-1
radiation
0.627
0.887
Mo KR (graphite monochromated, λ=0.71073 A)
1.87 e θ e 27.23
18 083
6845
4428
θ range, deg
1.82 e θ e 28.32
36 973
7704
2.20 e θ e 28.39
41 790
8421
2.13 e θ e 29.28
14 203
5869
5597
1.83 e θ e 28.37
39 805
15 461
no. data collected
no. indep data
no. obsd reflns (no)
[|Fo|2 > 2.0σ(|F|2) ]
no. of params refined (nv)
absolute struct param
[Flack param]
Rint
5748
5859
10 356
484
442
430
301
0.01(2)
757
0.0575
0.0381
0.0762
1.045
P
0.0546
0.0276
0.0860
1.003
P
0.0433
0.0368
0.0859
0.999
0.0225
0.0260
0.0584
1.022
0.0278
0.0625
0.1763
1.019
R (obsd reflns)
Rw2 (obsd reflns)
GOFd
P
P
P
P
P
a Rint
=
|Fo - ÆFo2æ|/ Fo
.
b R= (|Fo - (1/k)Fc|)/ |Fo|. c Rw2 ={ [w(Fo - (1/k)Fc
]/ w|Fo
]}1/2
.
d GOF=[ w(Fo - (1/k)Fc2)2/
2
2
2
2 2
)
2 2
|
2
(no - nv)]1/2
.
placing the sample solution in a capillary surrounded by
another (or no) solvent. Given the relatively small amount of
CD2Cl2 solution measured, there is a significant reduction in
the signal-to-noise with the result that higher concentrations
are often necessary. It is well known30 that increasing the
sample concentration (in our case from 2 to 10 mM) will
result in some salt aggregation. The dependence of both
viscosity and dielectric constant on temperature is known,29
and we have corrected for the first in the calculations of the
rH values. It is important for this discussion to realize that
CD2Cl2 and other solvents are more polar at lower tempera-
ture so that one might expect less ion pairing.
263 K (entries 14-19), at which temperature the BPh4- salts
are stable for prolonged periods. The D values are now all
markedly smaller (primarily due to the change in viscosity);
however, once again, the two D values for the cation and
anion within any one salt are not identical.
Entries 20-30 show the diffusion data for the 10 mM
solutions of the BPh4- salts at 263 K. For the two stable salts,
3a(BPh4) and 3c(BPh4), entries 20 and 21, the two D values
for the cation and anion are not identical. However, for the
more reactive salts, entries 22-30, the two D values are either
very much closer or identical within the experimental error.
Even allowing for the possibility that, by coincidence, the
To obtain an idea of the effect on the D values of changing
from 2 to 10 mM solutions, we show data in Table 3 for three
salts (entries 11-13) at this higher concentration at 299 K.
For 3a(PF6) the 10 mM D values are now 12.65 and 13.32,
whereas previously these were 13.02 and 13.54, for the cation
and anion, respectively. The table also shows a set of model
measurements for 10 mM solutions of PF6- and BArF- at
cation and anion might have similar sizes, the much larger
corr
rH
values, 6.3-6.9 A, confirm that there is now a very
substantial amount of ion pairing. Indeed, in some cases the
ion pairing appears to be 100% despite the increase in
dielectric constant due to the lower temperature. To support
this conclusion, we have made a few (time-consuming) low-
temperature measurements at 2 mM (entries 31-37) and find

6494 Organometallics, Vol. 28, No. 22, 2009
Moreno et al.
Figure 1. ORTEP plots for the four 2-methyl allyl cations, 3a and 3b. Ellipsoids are drawn at 50% probability. Selected bond lengths
(A) and bond angles (deg) for the cations in 3a: Pd-N(1), 2.089(2); Pd-N(10), 2.107(2); Pd-C(1L), 2.126(3); Pd-C(2L), 2.133(3);
Pd-C(3L), 2.112(3); N(1)-Pd-N(10) 78.72(7). The average B-C separation is 1.650(5). 3b: Pd-N(1), 2.099(3); Pd-N(10), 2.102(3);
Pd-C(1L), 2.118(5); Pd-C(2L), 2.146(4); Pd-C(3L), 2.091(5); N(1)-Pd-N(10) 79.1(1). The average B-C separation is 1.645(4). 3f:
Pd-N(10), 2.108(2); Pd-N(1), 2.127(2); Pd-C(1L), 2.108(3); Pd-C(2L), 2.143(2); Pd-C(3L), 2.111(3); N(10)-Pd-N(1), 78.28(8). The
average B-C separation is 1.644(5). 3h: Pd-N(1), 2.100(2); Pd-N(10), 2.108(2); Pd-C(1L), 2.115(3); Pd-C(2L), 2.149(3); Pd-C(3L),
2.119(3); N(1)-Pd-N(10) 78.63(8).
Figure 2. ORTEP plot for the 1,3-diphenyl cation, 4g. Ellip-
soids are drawn at 50% probability; hydrogen atoms omitted for
clarity. Selected bond lengths (A) and bond angles (deg) for one
of the two independent cations in 4g: Pd(1)-N(1), 2.091(4);
Pd(1)-N(10), 2.129(4); Pd(1)-C(1L); 2.159(5); Pd(1)-C(2L),
2.138(5); Pd(1)-C(3L), 2.160(5); N(1)-Pd(1)-N(10), 77.8(1).
that the reactive BPh4- salts are still very strongly ion paired.
For example, for the 1,3-diphenyl allyl salt 4g(BPh4), the two
Figure 3. Positions of the BPh4- anions in 3a(BPh4) (top) and
3b(BPh4) (bottom).
D values are (5.67 and 5.72 for the anion and cation,
respectively) now identical within the experimental error.
-
We conclude that several of the BPh4 salts do indeed
show more ion pairing in CD2Cl2 solution relative to, for
example, the BArF- analogues, in agreement with Crocia-
ni’s suggestion. Further, the X-ray studies suggest that the
BPh4- anion is indeed quite close to the Pd atom, and it now
remains to consider the interaction of the ions in solution.
Anion/Cation Interactions. The 19F,1H HOESY spectra for
the allyl complexes 3 and 4 with PF6- as model anion show
an interesting general picture. There are a relatively large
number of interionic contacts (five or more in every salt), and
both the allyl and the N,N-chelate are involved.
For all of the 2-methyl allyl salts, 3, one observes modest to
strong contacts to all of the allyl protons including the
methyl group, with the syn allyl proton the strongest within
this ligand. In these simple allyl salts the various contacts to

Article
Organometallics, Vol. 28, No. 22, 2009 6495
a
3
Table 3. D (10-10 m2 s-1) and rH (A) Values for [Pd(η -allyl)(N-N)](X) in CD2Cl2 at 299 and 263 K, Respectively
˚
corr
rH
corr
fragment
D
Dc/Da
rH
D
Dc/Da
rH
rH
2 mM, 299 K
PF6
BArF
1. 3ab
2. 3b
3. 3g
4. 3h
5. 4e
6. 4g
7. 4h
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
13.02
13.54
12.58
13.50
10.84
12.63
10.73
12.79
10.33
13.06
10.13
12.98
9.49
0.96
0.93
0.86
0.84
0.79
0.78
0.73
4.1
3.9
4.2
3.9
4.9
4.2
4.9
4.1
5.1
4.1
5.2
4.1
5.6
4.1
5.0
12.32
8.48
1.45
4.3
6.2
5.2
6.8
4.9
5.1
4.9
5.6
5.1
5.7
5.1
5.8
5.0
5.9
5.0
6.2
5.0
10.40
8.40
9.94
8.35
1.24
1.19
5.1
6.3
5.3
6.3
5.8
6.8
6.0
6.9
9.45
8.35
8.92
8.25
1.13
1.08
5.6
6.3
5.9
6.4
6.2
6.9
6.5
7.0
12.95
2 mM, 299 K, BPh4
8. 3a
9. 3b
10. 3c
cation
anion
cation
anion
cation
anion
12.32
10.40
11.68
10.00
12.24
10.08
1.18
4.3
5.1
4.5
5.3
4.3
5.2
5.2
5.8
5.3
6.0
5.2
5.9
1.17
1.21
10 mM, 299 K
11. 3a
12. 3a
13. 3c
BPh4
PF6
cation
anion
cation
anion
cation
anion
10.84
9.65
12.65
13.32
11.22
9.89
1.12
0.95
1.13
4.9
5.5
4.2
4.0
4.7
5.4
5.6
6.1
5.1
4.9
5.5
6.0
BPh4
10 mM, 263 K
PF6
4.4
4.0
4.4
4.1
5.5
4.6
5.4
4.5
5.6
4.5
6.0
5.2
BArF
14. 3a
15. 3b
16. 3h
17. 4e
18. 4g
19. 4h
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
7.40
8.08
7.37
7.78
5.82
6.95
5.94
7.22
5.70
7.16
5.39
6.24
0.92
0.95
0.84
0.82
0.80
0.86
5.2
4.9
5.2
5.1
6.2
5.4
6.1
5.3
6.3
5.3
6.6
5.9
6.99
5.12
1.37
1.19
4.6
6.3
5.4
6.8
5.72
4.81
5.6
6.7
6.3
7.2
4.77
4.44
5.04
5.47
1.07
0.92
6.8
7.3
6.4
5.9
7.3
7.4
6.9
6.5
10 mM, 263 K, BPh4
1.14
20. 3a
21. 3c
22. 3d
23. 3e
24. 3e
25. 3f
26. 3g
27. 3h
28. 4e
29. 4g
30. 4h
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
6.09
5.34
6.34
5.34
5.60
5.50
5.72
5.32
5.35
5.03
5.65
5.42
5.38
5.09
5.38
5.23
5.33
5.28
5.12
5.16
5.45
5.32
5.3
6.0
5.1
6.0
5.8
5.9
5.6
6.1
6.0
6.1
5.7
5.9
6.0
6.3
6.0
6.2
6.0
6.1
6.3
6.2
5.9
6.1
6.0
6.5
5.8
6.6
6.4
6.5
6.3
6.6
6.6
6.9
6.3
6.5
6.6
6.9
6.6
6.7
6.6
6.7
6.8
6.8
6.5
6.6
1.19
1.02
1.08
1.05
1.04
1.06
1.03
1.01
0.99
1.02

6496 Organometallics, Vol. 28, No. 22, 2009
Moreno et al.
Table 3. Continued
2 mM, 263 K
31. 3a
32. 3a
33. 3a
34. 3g
35. 3h
36. 4g
37. 4h
BPh4
PF6
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
cation
anion
6.89
6.53
7.54
8.17
7.82
5.33
5.91
5.53
5.86
5.65
5.67
5.72
5.38
5.52
1.06
4.7
4.9
4.3
3.9
4.0
6.0
5.5
5.8
5.5
5.7
5.7
5.6
6.0
5.8
5.5
5.7
5.2
4.9
5.1
6.6
6.1
6.4
6.1
6.3
6.3
6.3
6.6
6.4
0.92
1.47
1.07
1.04
0.99
0.97
BArF
BPh4
BPh4
BPh4
BPh4
a rH was calculated using the Stokes-Einstein relation; rH
was calculated using a semiempirical estimation of c (one iteration step).63 For the
corr
calculation of rH, the viscosity of CH2Cl2 at 299 and 263 K was used, respectively (η(299 K)=0.46 ꢀ 10-3 kg s-1 m-1, η(263 K)=0.60 ꢀ 10-3 kg s-1 m-1).
b D values for 3a(PF6) for the cation/anion in acetone-d6 (15.64/24.80) and methanol-d4 (10.88/15.96) solution.
Scheme 3
the N,N ligands change somewhat (see Scheme 3 for the most
important in three examples). The solid arrows indicate the
stronger, the dotted arrows the weaker interactions. The
strong contacts are comparable to;or stronger than;those
-
to the allyl ligand. The overall picture suggests that the PF6
anion sits above the N-Pd-N coordination plane, in
a pseudocoordination position, and for asymmetric N,N
ligands preferably on the side close to the pyridine. This
latter point arises from (a) the stronger contact to the syn
allyl proton as opposed to the anti allyl proton and (b) the
fact that for the mesityl Schiff base shown, the anion seems to
be placed somewhat closer to the pyridine moiety; that is, it is
not in a classical fifth coordination position. Figure 4 shows
the 19F,1H HOESY spectrum for salt 3g(PF6) at 263 K in
CD2Cl2.
The selective cross-peaks indicate that the anion chooses
Figure 4. 19F,1H HOESY spectrum of 3g(PF6) at 263 K in
to occupy a specific position, close to the Schiff base CHdN
CD2Cl2 (10 mM). Strong contacts to the R-diimine ligand pro-
moiety and aryl proton H30 (as indicated by the arrow),
tons 30, 7’, 8, and 9 suggest an approach of the anion as indicated
rather than move randomly around the exterior of the cation.
This type of positional preference for the PF6 anion has
been observed previously.17
by the arrow. Interestingly, there is also a contact to proton 60.
-
between δ 6.8 and 7.4 are indicated with a star) reveal
cross-peaks to aryl protons H30 and H3 as well as Schiff
base proton H70 among others. These data suggest that the
For the 1,3-diphenyl allyl salts, 4, a similar picture emerges
with the PF6- anion occupying a pseudocoordination posi-
tion. However, for these ligands, the anion resides on the side
of the allyl ligand close to the two anti protons, but remote
from the central allyl proton, in keeping with expected steric
effects due to the two relatively large phenyl groups.
-
BPh4 anion is positioned close to the bidentate ligand
and that the solution structure is related to that of the solid
state.
Summarizing, the Overhauser solution data support the
idea that the BPh4- anion prefers to be located close to the
chelating nitrogen ligands. Moreover, taken together with
the NMR diffusion and crystallographic results, it is reasonable
-
Turning to the BPh4 anion, Figure 5 shows a 2-D
ROESY spectrum for salt 4e(BPh4) at 193 K in CD2Cl2.
-
The three sets of BPh4 1H resonances (those located

Article
Organometallics, Vol. 28, No. 22, 2009 6497
Figure 5. 700 MHz 1H,1H ROESY spectrum of 4e(BPh4) at 193 K in CD2Cl2 (10 mM). The anion shows contacts to protons 3, 30, and
70, respectively (see marks in the upper part of the spectrum; the resonances of the BPh4 anion are labeled with an asterisk).
Additionally, there are weak contacts to the allyl protons “a” and “c” (not shown). The single circle cross-peaks of the exchanging
phenyl resonances are due to the apparent allyl rotation.
that (assuming an open coordination position becomes
available) phenyl anion transfer will be a facile process.
Allyl Dynamics. Palladium allyl complexes are well
known31-37 to exhibit various dynamic processes including
η3 to η1 isomerization, syn/anti H atom exchange (within the
complexed allyl ligand), and “apparent” allyl rotation.
According to the literature, these allyl isomerization pro-
cesses may occur via different mechanisms and may be under
(31) Vrieze, K. Fluxional Allyl Complexes. In Dynamic Nuclear
Magnetic Resonance Spectroscopy; Jackman, L. M.; Cotton, F. A., Eds.;
Academic Press: New York, 1975; pp 441-483.
(32) Faller, J. W. In Dynamic NMR Spectroscopy in Organometallic
Chemistry, Comprehensive Organometallic Chemistry III; Crabtree, R. H.;
Mingos, D. M. P., Eds.; Elsevier: Oxford, 2006; pp 407-428.
(33) (a) Cesarotti, E.; Grassi, M.; Prati, L.; Demartin, F. J. Organo-
met. Chem. 1989, 370, 407–419. (b) Cesarotti, E.; Grassi, M.; Prati, L.;
Demartin, F. J. Chem. Soc., Dalton Trans. 1991, 2073.
(34) (a) Fernandez-Galan, R.; Jalon, F. A.; Manzano, B. R.; Rodri-
guez de la Fuente, J.; Vreahami, M.; Jedlicka, B.; Weissensteiner, W.;
Jogl, G. Organometallics 1997, 16, 3758–3768. (b) Montoya, V.; Pons, J.;
Garcia-Anton, J.; Solans, X.; Font-Bardia, M.; Ros, J. Organometallics
2007, 26, 3183–31990.
(35) (a) Wassenaar, J.; van Zutphen, S.; Mora, G.; Le Floch, P.;
Siegler, M. A.; Spek, A. L.; Reek, J. N. H. Organometallics 2009, 28,
2724–2734. (b) Deng, W.; You, S.; Hou, X.; Dai, L.; Xia, W.; Sun, J. J. Am.
Chem. Soc. 2001, 123, 6508–6519.
(36) Breutel, C.; Pregosin, P. S.; Salzmann, R.; Togni, A. J. Am.
Chem. Soc. 1994, 116, 4067.
(37) Gogoll, A.; Ornebro, J.; Grennberg, H.; Backvall, J. E. J. Am.
€
Chem. Soc. 1994, 116, 3631.

6498 Organometallics, Vol. 28, No. 22, 2009
Moreno et al.
Figure 6. 700 MHz 1H NMR variable-temperature spectra of 3h(BPh4) in CD2Cl2 (10 mM) from 253 to 278 K. The resonances of the
allyl protons and the isopropyl groups have identical line broadening; that is, the dynamic processes responsible for their broadening
are coupled.
either electronic or steric control.36 Further, these dynamics
may be associated with Pd-N bond breaking.37 Given that
“anion effects”1 on various reactions are now fairly com-
monplace, we were curious as to the effect of our various
anions on the dynamics associated with 3 and 4 and, speci-
fically, if the BPh4- anion was in any way unusual.
4h represents the most sterically crowded of all of our Pd
cations.38
Figure 8 shows a section of the phase-sensitive 2-D
ROESY for 3e(BPh4) at 213 K in CD2Cl2. The open cross-
peaks have the same sign as the diagonal and arise from
exchange. For both 3 and 4 an analysis of these 2-D data
reveals selective syn/syn0 and anti/anti0 allyl proton exchange
in all cases. We do not find syn/anti exchange.39 There are
many reports of this type of selective syn/syn0 and anti/anti0
exchange in Pd-allyl chemistry.32,34b
Figures 6 and 7 show variable-temperature 1H NMR
-
studies for 3h and 4h, respectively, as BPh4 salts. Clearly,
in both figures, lowering the temperature causes the various
broad lines observed at ambient temperature to sharpen. In
Figure 6 the four allyl and nonequivalent methine and
methyl i-Pr resonances sharpen at the same rate. This is the
case for most of our salts except for the three 1,3-diphenyl
allyl analogues, 4h(anion), and the behavior for one of these,
4h(BPh4), is illustrated in Figure 7. Here one sees that the two
anti allyl protons, “a” and “c”, found between δ=4.7 and δ=
5.1, are quite sharp at 233 K, whereas the i-Pr resonances are
still relatively broad. It would seem that for the cations 4h we
may have two different dynamic processes, perhaps because
(38) The observed line broadening between two exchanging sites of
equal population will depend on the difference in the frequencies, Δν, so
that a direct comparison of, for example, the line shapes of two ex-
changing allyl protons with those for two exchanging methyl protons
from the Schiff base is only valid if the Δν values are identical.
(39) For examples of syn/anti exchange see: Kumar, P. G. A.; Dotta,
P.; Hermatschweiler, R.; Pregosin, P. S.; Albinati, A.; Rizzato, S.
Organometallics 2005, 24, 1306-1314, and Filipuzzi, S.; Pregosin,
P. S.; Albinati, A.; Rizzato, S. Organometallics 2008, 27, 437-444. See
also ref 32 for a review in which the subject is mentioned.

Article
Organometallics, Vol. 28, No. 22, 2009 6499
1
Figure 7. 700 MHz H NMR variable-temperature spectra of 4h(BPh4) in CD2Cl2 (10 mM) from 213 to 273 K. The two anti allyl
protons, “a” and “c”, found between δ=4.7 and δ=5.1, are quite sharp at 233 K, whereas the i-Pr resonances are still relatively broad. It
would seem that for the cations 4h we may have two different dynamic processes.
for the three anions BPh4-, PF6-, and BArF- of the
Scheme 4
catalytically more relevant 1,3-diphenyl cations 4g and
4h and show these results in Table 4. These values fall in
the range ca. 10-13 kcal/mol and, assuming an error of
(1 kcal/mol, are not very different. The values for the
salts 3 are on the order of 10 kcal/mol. We conclude that
(consistent with the terminal allyl carbon 13C chemical
shifts of Table 1) the anion does not play an important
role in these dynamics. Similar activation energies
have been reported in earlier studies on Pd-allyl comp-
lexes.34b
The question of the mechanism of the dynamics remains
open. An η3 to η1 isomerization to afford a three-coordinate
species is possible and would result in syn/anti exchange if
the η1-complex undergoes a rotation around the C-C bond
(arrow 2 of A in Scheme 4). However, this is not observed in
our salts. Nevertheless, if the η1-complex undergoes a
rotation around the Pd-C bond (arrow 1 in Scheme 4)
Using magnetization transfer methods we have deter-
mined the activation energies involved in these dynamics

6500 Organometallics, Vol. 28, No. 22, 2009
Moreno et al.
Figure 8. 700 MHz 1H,1H ROESY spectrum of 3e(BPh4) at 213 K in CD2Cl2 (10 mM). The single circle cross-peaks represent syn/syn0
and anti/anti0 proton exchange due to the apparent allyl rotation. Multi-circles show NOE contacts between corresponding syn/anti
protons. Note the absence of syn/anti exchange.
and then isomerizes further;39 this would shift the two R1
groups into different positions with respect to a salt having
two different L-donor ligands. Alternatively, “apparent”
allyl rotation as suggested by B in the scheme affords the
same result. Continuing, an L dissociation34,37 to afford a
three-coordinate η3-allyl species, such as C, or a possible
five-coordinate complex (not shown) has also been dis-
cussed as a possible pathway for the observed syn/syn0
and anti/anti0 allyl isomerization.
CH3CN to solutions of two of our salts, 3h(PF6) and 4h-
(PF6). In this fashion we had hoped to find evidence for a
possible η1-complex such as 5. For the 2-methyl allyl cation,
3h(PF6), we find no evidence for a new species; however,
based on the new dependence of the line shapes, the isomer-
ization rate increases. This rate increase is also observed in
CD3CN solution. For the larger 1,3-diphenyl allyl
cation, 4h(PF6), we find no change at all upon addition of
CH3CN (see Figure S1). It would seem that an η1-complex is
not likely to be a major contributor; however, the addition of
the nitrile seems to play some role for the salts of 3, again
In an effort to clarify the issue we have carried out
experiments in which we have added from 1 to 10 equiv of

Article
Organometallics, Vol. 28, No. 22, 2009 6501
Table 4. Activation Energies for the Dynamics of the 1,3-Diphenyl
Cations in 4g and 4h
the Cl atom from CH2Cl2, the allyl ligand (η3-coordinated), and
the imine N atom. The angle between the plane defined by the
two terminal Callyl atoms and the Cl-Pd-Nimine plane in I3g is
β=6ꢀ. In the calculated path, the solvent molecule, CH2Cl2,
assists allyl rotation in complex 3g by providing an intermediate
(I3g) stabilized by a square-planar environment around the
metal, in the middle of the rotation process. In the transition
state TS13g the angle R, between the Pd-allyl plane and the
Pd-N,N plane, is already 55ꢀ, indicating, once more, that TS13g
is a late transition state.
Ea/kcal mol-1
structure
anion
allyl
4g
4g
4g
4h
4h
4h
BPh4
PF6
BArF
BPh4
PF6
12.5
11.2
12.1
12.0
10.2
9.7
11.6
13.2
12.2
13.8
10.4
11.2
10 mM, 263 K
BArF
In the second step depicted in Figure 9, from I3g to 3g0, allyl
rotation continues and the CH2Cl2 molecule is expelled from
the coordination sphere. The product of this step, 3g0,
represents the enantiomer of the initial complex, 3g, and
results from a 180ꢀ rotation of the allyl ligand. In the
transition state associated with the second step, TS23g,
regeneration of the Pd-Npy bond is already evident, with a
distance of 2.278 A and an associated Wiberg index of 0.142.
The second half of the mechanism, represented on the
right side of the profile in Figure 9, is completely equivalent
to the first one, described above, and thus, no further
discussion is warranted. It is the asymmetry present in the
N,N ligand that causes the difference between the two halves
of the profile. In the first half of the profile, the methyl
substituent on allyl goes over the aryl group in the imine,
while in the second half of the mechanism, as allyl rotation
occurs the methyl substituent on allyl is brought to the side of
the pyridine ring.
The rate-limiting step of the calculated mechanism is the
second one, with an overall energy barrier of 13.1 kcal/mol.
This value agrees reasonably well with the experimen-
tal activation energies (see Table 4) and is similar to the
values calculated for complexes 4g (12.7 kcal/mol) and 4h
(12.3 kcal/mol). The energy profiles obtained for these two
species (see Supporting Information) are essentially equiva-
lent to the one calculated for 3g.
suggesting that the allyl structure is an important factor in
the dynamics.
DFT Studies. The mechanism of the dynamic process
described above for the allyl complexes 3g, 4g, and 4h was
investigated by means of DFT calculations.40 The energy
profile calculated for complex 3g is represented in Figure 9.
The corresponding profiles obtained for the complexes 4g
and 4h are provided as Supporting Information.
In the reagent, 3g, the metal coordination environment
comprises the η3-allyl ligand, formally occupying two adja-
cent coordination positions, and the two N atoms of the
chelating ligand, occupying the remaining two positions of
the square-planar geometry. In the first step of the calculated
path, there is addition of one solvent molecule (via TS13g)
with formation of intermediate I3g. In this intermediate, I3g,
the solvent molecule coordinates the metal through one Cl
atom, and as a consequence, the Pd-Npy bond is broken. In
I3g the Pd-Npy distance is long (2.607 A) and the corre-
sponding Wiberg index (WI)41 is small (0.059). These values
differ considerably from those calculated for 3g, where the
Pd-Npy bond is well established: d=2.136 A and WI=0.223.
I3g is a rather unstable intermediate, with an energy of 7.5
kcal/mol higher than the reactants, and, thus, should corre-
spond to a short-lived species. The transition state associated
with the first step, TS13g, can be thought of as rather a late
one, with both the formation of the Pd-Cl bond (d=2.720
A, WI=0.110) and the breaking of the Pd-Npy interaction
(d=2.450 A, WI=0.085) well advanced. For comparison
purposes, in intermediate I3g the Pd-Cl distance is 2.588 A
and the Wiberg index is 0.150.
An important structural change, occurring along the first
step, involves the relative position of the allyl ligand. In 3g,
the coordination plane of the complex is defined by the allyl
ligand and the two N-atoms of the chelating ligand. The
angle between the plane defined by the metal and the two
terminal Callyl atoms, and the N-Pd-N plane is R=0ꢀ. In
the intermediate, I3g, the equivalent angle is R=73ꢀ, indicat-
ing a strong rotation of the allyl ligand with respect to the
N-Pd-N plane. In I3g, the metal coordination sphere includes
Alternative pathways involving allyl slippage from η3 to
η1, induced for example by solvent coordination, were
thoroughly tested. However, no such species could be opti-
mized for complexes 4g and 4h, while in the case of 3g the
corresponding species, [Pd(η1-allyl)(CH2Cl2)(N,N)]þ, is19kcal/
mol less stable than the reagents, thereby precluding its
participation in the mechanism.
A rotation of the aryl substituent about the Nimine-Caryl
bond of the N,N ligand was also investigated by means of
DFT calculations. This process was rather difficult to calcu-
late due to the proximity between the aryl group and the allyl
ligand in the complex. As a consequence, the resulting
mechanisms involved strong disruption of the molecule
structure and, thus, high energy barriers. The profile repre-
sented in Figure 10 was calculated for complex 3g and
corresponds to the most favorable mechanism obtained.
In the mechanism calculated for mesityl rotation in com-
plex 3g there is also participation of one CH2Cl2 molecule in
a similar fashion to that described for allyl rotation. In the
first step of the mechanism, from 3g to III3g, there is coordi-
nation of the solvent molecule, with formation of one Pd-Cl
bond, with simultaneous breaking of the Pd-Nimine bond.
Cleavage of the Pd-Nimine bond proved essential in this
mechanism, in order to increase the separation between the
aryl group and the coordinated allyl ligand, thus reducing the
unfavorable steric interactions.
(40) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and
Molecules; Oxford University Press: New York, 1989.
(41) (a) Wiberg, K. B. Tetrahedron 1968, 24, 1083. (b) Wiberg indices
are electronic parameters related to the electron density between atoms. They
can be obtained from a natural population analysis and provide an indication
of the bond strength.
However there is an important difference in intermediate
III3g, relative to those present in the mechanism of allyl

6502 Organometallics, Vol. 28, No. 22, 2009
Moreno et al.
Figure 9. Energy profile calculated for the rotation of the 2-methyl allyl ligand in complex 3g, with participation of one molecule of
CH2Cl2. The minima and the transition states were optimized (PBE1PBE/VDZP), and the structures obtained are indicated next to
their respective energies. The energy values (kcal/mol) are with respect to the reactants (3g plus one molecule of CH2Cl2, lower left in the
figure), and the values in italics represent energy barriers. The allyl ligand is shown with darker circles, the chelate ligand is shown in
gray, and the chloride atoms in CH2Cl2 are shown in green.
rotation, I3g and II3g. In the mechanism of allyl rotation
cleavage of the Pd-Npy bond followed solvent coordination
with the N,N ligand maintaining a cisoid conformation of the
central NCCN frame; that is, in the corresponding inter-
mediates, I3g and II3g, both N atoms were on the same side,
pointing to the metal. Equivalent intermediates, with both
N atoms pointing toward the metal, but with cleavage of the
Pd-Nimine bond (while maintaining the Pd-Npy bond)
could not be optimized for any of the complexes investigated,
3g, 4g, and 4h. All attempts made for the optimization of
such species resulted in CH2Cl2 loss and regeneration of the
initial complex.
The only way that an intermediate with a dissociated
Pd-Nimine bond could be obtained was through the rotation
of the central NC-CN frame of the N,N ligand, and this is
shown in the first step of the calculated mechanism, repre-
sented in Figure 10. In intermediate III3g, the NCCN dihe-
dral angle is 176ꢀ, indicating that the two N atoms are on
opposite sides of the N,N ligand: the N atom of the pyridine
ring is coordinated to Pd, while the imine N atom points
away from the metal. In the transition state associated with
the first step, TS53g, the NCCN dihedral angle (84ꢀ) is
intermediate between the one present in III3g and that
observed in the reactant, 3g (2ꢀ). Once the Pd-Nimine is
broken in III3g, the rotation of the aryl group proceeds
smoothly along two comparatively small barriers, TS63g
and TS73g. Each of these barriers corresponds to the passage
of the 2,6-substituents in the ring (methyl groups in the case
of mesityl, in complex 3g) over each of the other ligands
attached to the metal. Thus, in the first barrier (TS63g) the
mesityl ring goes over the solvent molecule (CH2Cl2), while
in the second transition state (TS73g) the aryl ring crosses the
η3-allyl ligand. Overcoming the two previous barriers corre-
sponds to a complete revolution of the aryl ring (360ꢀ), and
thus, III3g is regenerated. Complex 3g is obtained via a step
equivalent to the first one, but going in the reverse sense:
from III3g to 3g, with restoration of the Pd-Nimine bond and
loss of CH2Cl2.
The rate-limiting steps of the entire process are the break-
ing and the formation of the Pd-Nimine bond, that is, the first
and the last steps in the calculated mechanism. The activa-
tion energy calculated (21.1 kcal/mol) indicates that this
mechanism is considerably less favorable than the one
described above for allyl rotation. This same conclusion
holds for complexes 4g and 4h, where the overall activation
energy values calculated for aryl rotation were 17.9 and 20.5 kcal/
mol, respectively. The corresponding mechanisms are
equivalent to the one obtained for 3g, and the energy profiles
are presented as Supporting Information.
Conclusions
-
The diffusion NMR data reveal that the BPh4 salts do
show a very substantial amount of ion pairing in dichlor-
omethane solution, in keeping with Crociani’s original sug-
gestion. Both the solution Overhauser studies and the X-ray
results are consistent with a BPh4- position that brings one
or more phenyl groups very close to the N,N-chelate, and
this would facilitate phenyl transfer. Despite this, and the
observed local anisotropic effects that result in a low-fre-
quency shift of several of the chelate 1H resonances, there is
little or no effect of this anion on the 13C chemical shifts of
these complexed allyl ligands.
The observed allyl and ligand dynamics fall under the
general heading of “apparent rotation”. We do not find any
syn/anti isomerism. Although there are several mechanistic
possibilities to account for this, the DFT calculations suggest
that this isomerization process in 3 and 4 is solvent assisted
and proceeds with Pd-Npyr bond breaking. Both the experi-
mental and calculated activation energies are in good agree-

Article
Organometallics, Vol. 28, No. 22, 2009 6503
Figure 10. Energy profile calculated for the rotation of the mesityl group around the C-Nimine bond, in complex 3g, with participation
of one molecule of CH2Cl2. The minima and the transition states were optimized (PBE1PBE/VDZP), and the structures obtained are
indicated next to their respective energies. The energy values (kcal/mol) are referred to the reactants (3g plus one molecule of CH2Cl2),
and the values in italics represent energy barriers.
-
ment, and we do not find a significant effect of the BPh4
anion on these dynamics. On the basis of the calculations, the
bulky substituents in the ortho positions of the Schiff base
prevent rotation about the N-C bond so that the two
nonequivalent methyl (or isopropyl) groups exchange only
when the apparent allyl rotation occurs.
hybrid generalized gradient approximation (GGA), including
25% mixture of Hartree-Fock43 exchange with DFT40 exchan-
ge-correlation, given by the Perdew, Burke, and Ernzerhof
functional (PBE).44 The optimized geometries were obtained
with a VDZP basis set (basis b1) consisting of the LanL2DZ
basis set45 augmented with an f-polarization function,46 for Pd,
and a standard 6-31G(d,p)47 for the remaining elements. Tran-
sition-state optimizations were performed with the synchronous
transit-guided quasi-Newton method (STQN) developed by
Schlegel et al.48 Frequency calculations were performed to
confirm the nature of the stationary points, yielding one ima-
ginary frequency for the transition states and none for the
minima. Each transition state was further confirmed by follow-
ing its vibrational mode downhill on both sides and obtaining
Experimental Section
The reactions were carried out with magnetic stirring and
without special precautions against light or atmospheric moist-
ure and oxygen, unless otherwise stated. Solvents were dried and
distilled following standard procedures and stored under N2.
Deuterated dichloromethane was distilled over CaH2 and de-
gassed using two freeze-pump-thaw cycles and stored under
N2. All commercially available starting materials were pur-
chased from commercial sources and used as received unless
otherwise stated. NMR spectra were recorded with Bruker
Avance 400 and 700 MHz spectrometers. Elemental analyses
and mass spectroscopic studies were performed at ETHZ.
Computational Details. All calculations were performed using
the GAUSSIAN 03 software package42 and the PBE1PBE func-
tional, without symmetry constraints. That functional uses a
(43) Hehre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. Ab Initio
Molecular Orbital Theory; John Wiley & Sons: New York, 1986.
(44) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997,
78, 1396. (b) Perdew, J. P. Phys. Rev. B 1986, 33, 8822.
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(46) Ehlers, A. W.; Bohme, M.; Dapprich, S.; Gobbi, A.; Hollwarth,
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Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin,
A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A.Gaussian 03, Revision C.02; Gaussian, Inc.:
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6504 Organometallics, Vol. 28, No. 22, 2009
Moreno et al.
the minima presented on the energy profiles. A natural popula-
tion analysis (NPA)49 and the resulting Wiberg indices41 were
used to study the electronic structure and bonding of the
optimized species.
atoms of the cation were located from difference Fourier maps
and their coordinates was refined with isotropic temperature
factors fixed at B(H)=1.2B(Cbonded). The contribution of the
remaining hydrogens, in their calculated positions (C-H=0.96
A, B(H)=1.2B(Cbonded) (A2)), was included in the refinement
using a riding model.
Structural Study of 3b(BPh4). The space group was assumed
to be P1 (no. 2), and the centrosymmetric choice was confirmed
by the successful refinement. The cell constants at 150 K were
obtained by least-squares fit, at the end of the data collection,
using reflections up to θmax e 20.9ꢀ. The least-squares refine-
ment was carried out using anisotropic displacement parameters
for all non-hydrogen atoms, while the H atoms were included in
the refinement as described above.
Structural Study of 3f(BPh4). The space group was deter-
mined from the systematic absences, and the cell constants were
refined by least-squares, at the end of the room-temperature
data collection, using reflections up to θmax e 23.6ꢀ.
The least-squares refinement was carried out using anisotro-
pic displacement parameters for all non-hydrogen atoms. The
contribution of the hydrogen atoms, in their calculated posi-
tions (C-H=0.96 A, B(H)=aB(Cbonded) (A2) with a=1.5 for the
hydrogen atoms of the methyl groups, 1.2 for the others), was
included in the refinement using a riding model.
The energy profiles reported result from single-point energy
calculations using a VTZP basis set (basis b2), and the geome-
tries were optimized at the PBE1PBE/b1 level. Basis b2 con-
sisted of a standard 3-21G50 with an added f-polarization
function46 for Pd and standard 6-311þþG(d,p)51 for the
remaining elements. Solvent (dichloromethane) effects were
considered in the PBE1PBE/b2//PBE1PBE/b1 energy calcula-
tions using the polarizable continuum model (PCM) initially
devised by Tomasi and co-workers52 as implemented in Gaus-
sian 03,53 and thus, the energy values can be taken as free
energy.54 The molecular cavity was based on the united atom
topological model applied on UAHF radii, optimized for the
HF/6-31G(d) level.
Crystallography. Crystals of 3a(BPh4), 3b(BPh4), 3f(BPh4),
3h(PF6), and 4g(PF6) were mounted on a Bruker APEX II CCD
diffractometer for the unit cell and space group determinations
and for the data collections. For the low-temperature data
collections crystals were cooled using a cold nitrogen stream.
Selected crystallographic and other relevant data are listed in
Table 2 and in the Supporting Information.
Data were corrected for Lorentz and polarization factors
with the data reduction software SAINT55 and empirically for
absorption using the SADABS program.56
Structural Study of 3h(PF6). Space group and cell constants
were determined at 150 K. The values of the cell parameters were
refined at the end of the data collection using reflections up to
θmax e 29.2ꢀ. In the Fourier difference maps two different
orientations for one of the two isopropyl groups (that bonded
to C3) were clearly shown; therefore, two carbon atoms were
used to model this disorder and refined isotropically (site
occupancy factor 0.5). The least-squares refinement was carried
out using anisotropic displacement parameters for all non-
hydrogen atoms not affected by disorder.
The H atoms of the allyl ligand were found from difference
Fourier maps and their coordination was refined with isotropic
temperature factors kept fixed at B(H) = 1.2B(Cbonded); the
contribution of the remaining hydrogen atoms, in their calcu-
lated positions (C-H=0.96 A, B(H)=aB(Cbonded) (A2) with a=
1.5 for the hydrogen atoms of the methyl groups, 1.2 for the
others), was included in the refinement using a riding model.
Refining the Flack parameter tested the handedness of the
structure.61
Structural Study of 4g[PF6]. Unfortunately only low-quality,
poorly diffracting crystals (see below) could be found. The space
group was assumed to be P1 (no. 2), and the centrosymmetric
choice was later confirmed by the successful refinement. The cell
constants were refined by least-squares, at the end of the RT
data collection, using reflections up to θmax e 23.5ꢀ. There are
two independent molecules in the asymmetric unit; however,
there are no chemically significant differences in the immediate
coordination spheres of the Pd atoms or in the bond distances
and angles of both the anions and the cations.
The structures were solved by direct and Fourier methods and
refined by full matrix least-squares57 (the function minimized
P
being [w(|Fo|2 - 1/k|Fc |)2]). For all structures, no extinction
2
correction was deemed necessary. The scattering factors used,
corrected for the real and imaginary parts of the anomalous
dispersion, were taken from the literature.58 All calculations and
plotting were carried out by using the PC version of SHELX-
97,57 WINGX, ORTEP,59 and Mercury programs60
Structural Study of 3a(BPh4). The space group was unam-
biguously determined from the systematic absences, while the
cell constants (at 150 K) were refined by least-squares, at the end
of the data collection, using reflections up to θmax e 22.2ꢀ. The
least-squares refinement was carried out using anisotropic
displacement parameters for all non-hydrogen atoms. The H
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1980, 102, 939. (b) Gordon, M. S.; Binkley, J. S.; Pople, J. A.; Pietro, W. J.;
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The PF6- counterions are very disordered, as can be judged
from the large ADPs. One of the PF6- moieties showed clearly,
in the Fourier difference maps, positional disorder of the four
equatorial fluorine atoms that could be modeled assuming three
different orientations for each of the F atoms; the disordered
atoms were refined isotropically (leading to occupancy factors
of 0.5, 0.3, and 0.2, respectively). No reasonable model could be
found for the other counterion, where rotational disorder,
unhindered by any short contact with the cation, is present.
The ADPs of the F atoms, allowed to refine anisotropically,
show the situation clearly. Toward the end of the refinement a
Fourier difference map revealed a disordered clathrated diethyl
ether molecule that was included in the refinement, using
isotropic temperature factors and a slack-constraint for the
ꢁ
(52) (a) Cances, M. T.; Mennucci, B.; Tomasi, J. J. Chem. Phys. 1997,
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Article
Organometallics, Vol. 28, No. 22, 2009 6505
C-C bond distances. The poor high-angle diffraction is a
consequence of the disorder.
equipped with a multinuclear inverse probe. The concentration
of the sample was 10 mM unless otherwise stated. A spin-lock
pulse of 400 ms duration was used. The number of scans per
increment was 32, and 1K experiments were acquired in the
second dimension. The total experimental times were approxi-
mately 12 h.
Magnetization transfer experiments were performed by using
the selective inversion-exchange/recovery monitoring scheme
according to the literature.65 For fitting the monitored data of
the magnetization transfer experiments the CIFIT program
package was used.66
Preparation of the r-Diimines. Bipy, phenanthroline, and
TMEDA were purchased from commercial sources and used
as received. The symmetric R-diimine d67 and the pyridine-2-
carbaldimines e,68 f,69 g,70 and h70 were prepared by published
methods.
The least-squares refinement was carried out using anisotro-
pic displacement parameters for all atoms not affected by
disorder, while the contribution of the hydrogen atoms, in their
calculated positions (C-H=0.96 A, B(H)=aB(Cbonded) (A2)
with a=1.5 for the hydrogen atoms of the methyl groups, 1.2 for
the others), was included using a riding model.
NMR Measurements. All the PGSE diffusion measurements
were performed using the standard stimulated echo pulse
sequence on a 400 MHz Bruker Avance spectrometer equipped
with a microprocessor-controlled gradient unit and an inverse
multinuclear probe with an actively shielded Z-gradient coil.
The shape of the gradient pulse was rectangular, its duration
δ was 1.75 ms, and its strength varied automatically in the course
of the experiments. The calibration of the gradients was carried
out via a diffusion measurement of HDO in D2O at ambient
temperature. The data obtained were used to calculate the
D values of the samples, according to the literature.62
PGSE Measurements at Ambient Temperature. Samples of 2
and 10 mM, respectively, were prepared in 0.5 mL of deuterated
dichloromethane in a 5 mm diameter NMR tube. In the
1H-PGSE experiments, Δ16 was set to 117.75 and 167.75 ms,
respectively. The number of scans was 16 per increment with a
recovery delay of 12 to 25 s. Typical experimental times were
2-6 h. For 19F, Δ was set to 117.75 and 167.75 ms, respectively.
Sixteen scans were taken with a recovery delay of 18 to 25 s and a
total experimental time of ca. 2.5-6 h.
Preparation of [Pd(η3-allyl)(N,N0)]X. The allylic chloro-
bridged dimers3 (allyl = 2-Me-C3H4, 1,3-diphenylallyl) were
prepared by published methods. The mostly new cationic
complexes 3a, 3g, 3h, 4g, 4h (X) (X=BPh4, PF6, BArF), 3b, 4e
(X = BPh4, PF6), and 3c-f (X = BPh4) were synthesized
following a slightly modified literature procedure:71 The suita-
ble allylic chloro-bridged dimer (32 mg, 0.081 mmol) and the
ligand (25 mg, 0.162 mmol) were mixed together in methanol
(3 mL). After the solution was cooled to 0 ꢀC, dropwise addition
of the suitable sodium salt (54.7 mg, 0.162 mmol), dissolved in
MeOH/H2O (3 mL, 2:1 v/v), caused the immediate precipitation
of a yellow solid, which was stirred for 5 min and filtered off.
Repeated washings with H2O and MeOH/H2O (2:1, v/v) gave
the pure product, which was dried in vacuo (40 mg, 78%).
[Pd(η3-2-MeC3H4)(bipy)]BPh4 (3a(BPh4)),72 [Pd(η3-2-MeC3H4)-
(py-2-CHdNC6H4OMe-4)]BPh4 (3f(BPh4)), and [Pd(η3-2-
MeC3H4)(-C(Me)dN NC6H4OMe-4)2]BPh4 (3d(BPh4))71 were de-
scribed elsewhere some time ago.
PGSE Measurements at 263 K. Samples of 2 and 10 mM,
respectively, were prepared in 0.07 mL of deuterated dichlor-
omethane. In order to overcome the convection problem in low-
temperature PGSE diffusion measurements, a coaxial insert
(with a diameter of 1.5 mm) inside a normal 5 mm NMR tube
was employed as described earlier.28
1H and 13C NMR chemical shift data for the new salts can be
found in Table S1 in the Supporting Information.
In the 1H-PGSE experiments, Δ16 was set to 117.75 and
167.75 ms, respectively. The number of scans varied between
24 and 64 scans per increment with a recovery delay of 12 to 25 s.
Typical experimental times were 4-10 h. For 19F, Δ was set to
117.75 and 167.75 ms, respectively; 24-64 scans were taken with
a recovery delay of 18 to 25 s and a total experimental time of ca.
6-10 h.
All the spectra were acquired using 32K points and processed
with a line broadening of 1 Hz (1H) and 2 Hz (19F). The slopes of
the lines, m, were obtained by plotting their decrease in signal
intensity versus G2 using a standard linear regression algorithm.
Normally, 14-20 points were used for regression analysis, and all
of the data leading to the reported D values afforded lines whose
correlation coefficients were >0.999. The gradient strength was
incremented in 3-4% steps from 3 to 4% to 60-80%.
A measurement of 1H and 19F T1 was carried out before each
diffusion experiment, and the recovery delay set to 5 times T1.
We estimate the experimental error in D values at (2%. The
hydrodynamic radii, rH, were estimated using the Stokes-Einstein
equation (c = 6) or by introducing a semiempirical estimation of
the c factor.63
[Pd(η3-2-MeC3H4)(bipy)]PF6 (3a(PF6)): white solid, yield
82%. Anal. Calcd for C14H15F6N2PdP: C, 36.34; H, 3.27; N,
6.05. Found: C, 36.43; H, 3.26; N, 5.94.
[Pd(η3-2-MeC3H4)(bipy)]BArF (3a(BArF)): white solid, yield
81%. Anal. Calcd for C46H27N2BF24Pd: C, 46.79; H, 2.30; N,
2.37. Found: C, 46.76; H, 2.52; N, 2.33.
[Pd(η3-2-MeC3H4)(phen)]PF6 (3b(PF6)): white solid, yield
76%. Anal. Calcd for C16H15N2F6PPd: C, 39.49; H, 3.11; N,
5.76. Found: C, 39.45; H, 3.13; N, 5.58.
[Pd(η3-2-MeC3H4)(phen)]BPh4 (3b(BPh4)): white solid, yield
86%. Anal. Calcd for C40H35N2BPd: C, 72.69; H, 5.34; N, 4.24.
Found: C, 71.79; H, 5.41; N, 4.21.
[Pd(η3-2-MeC3H4)(TMEDA)]BPh4 (3c(BPh4)): white solid,
yield 60%. Anal. Calcd for C34H43N2BPd: C, 68.41; H, 7.26; N,
4.69. Found: C, 68.32; H, 7.22; N, 4.63.
[Pd(η3-2-MeC3H4)(py-2-CHdNC6H4Me-4)]BPh4 (3e(BPh4)):
yellow solid, yield 74%. Anal. Calcd for C41H39N2BPd: C,
72.74; H, 5.81; N, 4.14. Found: C, 72.27; H, 5.69; N, 3.96.
The 19F,1H HOESY measurements were acquired using the
standard four-pulse sequence64 on a 400 MHz Bruker Avance
spectrometer equipped with a doubly tuned (1H, 19F) TXI
probe. A mixing time of 800 ms was used. The number of scans
was 8-16 and the number of increments in the F1 dimension
512. The delay between the increments was set to 0.8 s. The
concentration of the sample was 10 mM.
(65) Led, J. J.; Gesmar, H. J. Magn. Reson. 1982, 49, 444–463.
(66) (a) The CIFIT program package was used for the simulations
and data evaluation: Bain, A. D.; Cramer, J. A. J. Magn. Reson. 1996,
118, 21-27. (b) Muhandiramm, D. R.; McClung, R. E. D. J. Magn. Reson.
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473.
1
The H,1H ROESY measurements were acquired on a 400
and 700 MHz Bruker Avance spectrometer, respectively, both
(70) Diez, V.; Cuevas, J. V.; Garcia-Herbosa, G.; Aullon, G.;
Charmant, J. P. H.; Carbayo, A.; Munoz, A. N. Inorg. Chem. 2007,
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6506 Organometallics, Vol. 28, No. 22, 2009
Moreno et al.
[Pd(η3-2-MeC3H4)(py-2-CHdNMes)]PF6 (3g(PF6)): yellow
solid, yield 53%. Anal. Calcd for C19H23N2F6PPd: C, 42.99;
H, 4.37; N, 5.28. Found: C, 42.90; H, 4.33; N, 5.20.
[Pd(η3-1,3-DiphenylC3H3)(py-2-CHdNC6H4(i-Pr)2-2,6)]PF6
(4h(PF6)): yellow solid, yield 67%. MALDI MS: 565.2 (Mþ).
[Pd(η3-1,3-DiphenylC3H3)(py-2-CHdNC6H4(i-Pr)2-2,6)]BPh4
(4h(BPh4)): yellow solid, yield 83%. Anal. Calcd for
C57H55N2BPd: C, 77.33; H, 6.26; N, 3.16. Found: C, 76.79; H,
6.54; N, 3.23.
[Pd(η3-2-MeC3H4)(py-2-CHdNMes)]BPh4 (3g(BPh4)): yel-
low solid, yield 81%. Anal. Calcd for C43H43N2BPd: C, 73.25;
H, 6.15; N, 3.97. Found: C, 72.68; H, 6.38; N, 3.96.
[Pd(η3-2-MeC3H4)(py-2-CHdNMes)]BArF (3g(BArF)): yel-
low solid, yield 84%. Anal. Calcd for C51H38N2BF24Pd: C,
48.92; H, 3.06; N, 2.24. Found: C, 49.14; H, 2.85; N, 2.21.
[Pd(η3-2-MeC3H4)(py-2-CHdNC6H4(i-Pr)2-2,6)]PF6 (3h(PF6)):
yellow solid, yield 64%. Anal. Calcd for C22H29N2F6PPd: C,
46.13; H, 5.10; N, 4.89. Found: C, 46.33; H, 5.13; N, 4.83.
[Pd(η3-2-MeC3H4)(py-2-CHdNC6H4(i-Pr)2-2,6)]BPh4 (3h-
(BPh4)): yellow solid, yield 92%. Anal. Calcd for C46H49N2BP-
d: C, 73.95; H, 6.61; N, 3.75. Found: C, 73.36; H, 6.91; N, 3.71.
[Pd(η3-2-MeC3H4)(py-2-CHdNC6H4(i-Pr)2-2,6)]BArF (3h-
(BArF)): yellow solid, yield 57%. Anal. Calcd for
C63H47N2BF24Pd: C, 53.85; H, 3.37; N, 1.99. Found: C, 54.12;
H, 3.18; N, 2.12.
[Pd(η3-1,3-DiphenylC3H3)(py-2-CHdNC6H4(i-Pr)2-2,6)]BArF
(4h(BArF)): yellow solid, yield 62%. Anal. Calcd for
C65H47N2BF24Pd: C, 54.62; H, 3.31; N, 1.96. Found: C, 54.66;
H, 3.38; N, 2.11.
Acknowledgment. P.S.P. thanks the Swiss National
Science Foundation and the ETH Zurich for support,
as well as the Johnson Matthey Company for the loan of
palladium salts. The support and sponsorship by COST
Action D24 “Sustainable Chemical Processes: Stereose-
lective Transition Metal-Catalysed Reactions” is kindly
acknowledged. A.A. thanks MIUR for support (PRIN
[Pd(η3-1,3-DiphenylC3H3)(py-2-CHdNC6H4Me-4)]PF6 (4e-
(PF6)): yellow solid, yield 65%. MALDI MS: 495.0 (Mþ),
299.0 (Mþ - R-diimine).
ꢀ
2007). B.F. thanks Ministerio de Ciencia y Tecnologı
´
a of
Spain (CTQ: 2004-07667) for studentships.
[Pd(η3-1,3-DiphenylC3H3)(py-2-CHdNC6H4Me-4)]BPh4
(4e(BPh4)): yellow solid, yield 81%. Anal. Calcd for
C52H45N2BPd: C, 76.62; H, 5.56; N, 3.44. Found: C, 75.89; H,
5.58; N, 3.40.
Supporting Information Available: Scheme S1, Table S1,
Figure S1, and Figures S2-5 with the energy profiles calcu-
lated for allyl rotation and for aryl rotation in complexes 4g
and 4h, respectively, and Table S2 with atomic coordinates
of all optimized structures. Experimental details and a full
listing of crystallographic data, including tables of posi-
tional and isotropic equivalent displacement parameters,
anisotropic displacement parameters, calculated positions
of the hydrogen atoms, bond distances, bond angles, and
torsional angles, are listed in the CIF file. This material is
available free of charge via the Internet at http://pubs.acs.
org.
[Pd(η3-1,3-DiphenylC3H3)(py-2-CHdNMes)]PF6 (4g(PF6)):
yellow solid, yield 45%. MALDI MS: 523.1 (Mþ).
[Pd(η3-1,3-DiphenylC3H3)(py-2-CHdNMes)]BPh4 (4g(BPh4)):
yellow solid, yield 71%. Anal. Calcd for C54H49N2BPd: C,
76.92; H, 5.86; N, 3.32. Found: C, 76.34; H, 6.08; N, 3.34.
[Pd(η3-1,3-DiphenylC3H3)(py-2-CHdNMes)]BArF (4g(BArF)):
yellow solid, yield 56%. Anal. Calcd for C63H47N2BF24Pd: C,
53.85; H, 3.37; N, 1.99. Found: C, 54.12; H, 3.18; N, 2.12.