Carbonylation studies of Pd-methyl complexes modified with 1,4-Cs-symmetrical diphosphine ligands

Article abstract of DOI:10.1016/j.jorganchem.2006.06.038

Neutral palladium methyl chloride 2a-d [PdCH₃(P?P′)Cl] and cationic palladium methyl acetonitrile mono-triflate 3a-d [PdCH₃(P?P′)(CH₃CN)](CF₃ SO₃) complexes were synthesized and fully characterized (P?P′ = 1a-d). All the neutral and cationic complexes containing a C_s-symmetric diphosphine exist in solution as a mixture of geometric isomers. The carbonylation at atmospheric pressure of the neutral and cationic complexes revealed that migratory insertion of carbon monoxide is not stereospecific in these systems. The neutral and cationic acyl complexes were formed in situ as mixtures of stereoisomers, which were characterized by means of NMR spectroscopy. The crystal structures of [Pd(1a)Cl]₂(OTf)₂ and 2d are described.

Full text of DOI:10.1016/j.jorganchem.2006.06.038

Journal of Organometallic Chemistry 691 (2006) 4816–4828
www.elsevier.com/locate/jorganchem
Carbonylation studies of Pd-methyl complexes modified
with 1,4-Cs-symmetrical diphosphine ligands
a
b
a,
*
Antonella Leone , Sebastian Gischig , Giambattista Consiglio
a
Eidgeno¨ssische Technische Hochschule, Institut fu¨r Chemie und Bioingenieurwissenschaften, Ho¨nggerberg, Wolfgang-Pauli Strasse 10,
CH-8093 Zu¨rich, Switzerland
b
Eidgeno¨ssische Technische Hochschule, Laboratorium fu¨r Anorganische Chemie, Ho¨nggerberg, CH-8093 Zu¨rich, Switzerland
Received 25 April 2006; received in revised form 10 June 2006; accepted 27 June 2006
Available online 7 July 2006
Abstract
Neutral palladium methyl chloride 2a–d [PdCH3(P^P0)Cl] and cationic palladium methyl acetonitrile mono-triflate 3a–d
[PdCH3(P^P0)(CH3CN)](CF3SO3) complexes were synthesized and fully characterized (P^P0 = 1a–d). All the neutral and cationic com-
plexes containing a Cs-symmetric diphosphine exist in solution as a mixture of geometric isomers. The carbonylation at atmospheric
pressure of the neutral and cationic complexes revealed that migratory insertion of carbon monoxide is not stereospecific in these sys-
tems. The neutral and cationic acyl complexes were formed in situ as mixtures of stereoisomers, which were characterized by means of
NMR spectroscopy.
The crystal structures of [Pd(1a)Cl]2(OTf)2 and 2d are described.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Carbonylation; Palladium methyl complexes; Neutral; Cationic; 1,4-Cs-Symmetrical diphosphine ligands; Copolymerization
1. Introduction
[3]. More recently [4] the carbonylation reaction was
investigated in palladium(II) methyl complexes of C1-sym-
metrical Josiphos derivatives. In this series of ligands, the
fragment PCy2 was kept constant (Cy = cyclo-hexyl),
while the other PAr2 fragment was systematically varied.
The coordination of the acyl group trans to the PAr2 moi-
ety was favored. The selectivity for the trans location of
the acyl group to the PAr2 moiety was higher with the
increase of the p-acidity of the aryl fragment. Nozaki
and co-workers investigated the elementary steps (CO
and olefin insertion) of the copolymerization reaction
on the cationic complex [PdCH3{(R,S)-BINAPHOS}-
Carbon monoxide migratory insertion in transition
metal alkyl carbonyl complexes is a key step of the olefin
carbonylation and of the olefin-CO copolymerization reac-
tion. Several studies on CO migratory insertion into a tran-
sition metal–carbon r bond appeared for complexes
containing monodentate and bidentate C2-symmetrical
ligands [1,2].
Few examples of CO migratory insertion into palla-
dium(II) alkyl complexes of non-symmetrical diphos-
phines were reported. The CO migratory insertion was
investigated in palladium(II) and platinum(II) complexes
modified with 1-diphenylphosphino-2-tert-butyl-3-di-
cyclohexylphosphinoprop-1-ene. It was shown that the
insertion process of CO into metal-to-carbon r-bonds
involves a migration of the alkyl group to the CO ligand
(NCCD3)](BAr4)
(Ar = 3,5-bis(trifluoromethyl)phenyl);
{(R,S)-BINAPHOS = (R,S)-2-(diphenylphosphino)-1,10-
binaphthalen-20-yl-1,10-binaphthalene-2,20-diylphosphite [5].
13CO insertion (1 atm) into complex 1, which was present
as a single species (methyl group trans to the PPh2 moi-
ety), afforded the corresponding acyl complex [Pd13C(O)-
CH3(P^OP)(NCCD3)](BAr4) (P^OP = (R,S)-BINAPHOS)
as a single species, in which the acyl group was located
*
Corresponding author. Tel.: +41 44 63 23552; fax: +41 44 63 21162.
E-mail address: consiglio@chem.ethz.ch (G. Consiglio).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.038

A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
4817
trans to the PPh2 moiety. The same selectivity was found
P(cyclo-hexyl)2
in the next steps of the investigation, in which intermedi-
ates relevant to the copolymerization reaction were
obtained upon successive propene and carbon monoxide
migratory insertion reactions. Supported by theoretical
studies and crystallographic data, Nozaki proposed a
higher thermodynamic stability for the isomers bringing
alkyl or acyl groups trans to the phosphine moiety. This
was found in contrast with the trans influence concept,
according to which the phosphine is ranked at higher level
compared to phosphite [6,7].
In this paper the carbonylation at atmospheric pressure of
palladium methyl-chloride and methyl-solvento complexes
containing non-symmetrical diphosphines is described.
The isomer distribution following the CO migratory inser-
tion is explained on the basis of the non-equivalent electronic
properties of the ligand dentates.
PPh2
1a
PAr2
PAr2'
1b: Ar = C6H5 Ar' = 3-CF3C6H4
1c: Ar = 4-OCH3C6H4 Ar' = C6H5
1d: Ar = 4-CH3OC6H4 Ar' = 3-CF3C6H4
1b-d
Fig. 1. Cs-symmetric 1,4-diphosphine ligands 1a–d reacted with [PdCH3-
(COD)Cl].
and m (minor) (Table 1). The Cs-symmetric nature of the
ligand implies that the methyl group can be cis or trans
with respect to each phosphorus moiety (Fig. 2).
In the 1H NMR all the complexes 2a–d showed the char-
acteristic Pd–CH3 resonance as a doublet of doublets (dd),
2. Results
3
2.1. Synthesis of the model complexes
due to the JH–P coupling with the two non-equivalent
phosphorus atoms of the ligands. The Pd–CH3 shifts are
in the range 0.50–0.85 ppm. As far as the P–H coupling
is concerned, values around 7.5 Hz were found for the
The monocationic methyl solvento complexes were syn-
thesized according to the procedure illustrated in Scheme 1.
The palladium methyl chloride complexes were obtained
from [PdCH3(COD)Cl] by displacement of COD with the
diphosphine 1a–d (Fig. 1) [8,9]. Treatment of 1 equivalent
of the neutral palladium methyl chloride complexes with
1.1 equivalents of AgOTf in the presence of acetonitrile
afforded the corresponding methyl acetonitrile complex
by scavenging the halide with the silver salt. Neutral methyl
chloride palladium complexes [PdCH3(P^P0)Cl] and cat-
ionic methyl acetonitrile complexes [PdCH3(P^P0)-
CH3CN](OTf), containing Cs-symmetric 1,4-diphosphines,
were present as a mixture of geometric isomers.
3
3JH–P(trans), while the JH–P(cis) ranged between 3.2 and
4.3 Hz. These values are in agreement with those reported
for palladium methyl chloro complexes containing the C2v-
symmetrical diphosphines dppe, dppp, dppb [1].
The 31P{1H} NMR showed two pairs of doublets. Each
P is coupled through a 2JP–P with the other P of the diphos-
phine ligand. The resonances of the two phosphorus atoms
are separated by an interval of ca. 30 ppm. In each isomer,
the P signal observed downfield (i.e., around 30 ppm)
corresponded to Pcis to the alkyl group, while the one
upfield (i.e., around 0 ppm) to Ptrans. This assignment was
supported by similar observations for the complexes
[PdCH3(P^P)Cl] (where P^P = dppe, dppp, dppb, dppf
[1]) and by the assignment in analogous Pt complexes, in
which the phosphine with the lower frequency was identi-
fied as that trans to the R group [10].
2.2. Neutral methyl chloro complexes 2a–d
The Pd-methyl chloro complexes 2a–d (2a = [PdCH3-
(1a)Cl]; 2b = [PdCH3(1b)Cl]; 2c = [PdCH3(1c)Cl]; 2d =
[PdCH3(1d)Cl]) were isolated in high yield. All the
complexes were fully characterized by means of NMR
spectroscopy. Together with 1H, 31P{1H} NMR and
2.3. Cationic methyl solvento complexes 3a–d
1
1
1H–31P{1H}-correlation, H-TOCSY and H-NOESY cor-
relation experiments were necessary to achieve an unam-
biguous identification of the resonances observed in the
spectra. The neutral complexes 2a–d exist in solution as a
mixture of two geometric isomers, indicated as M (major)
The complexes 3a–d (3a = [PdCH3(1a)CH3CN](OTf);
3b = [PdCH3(1b)CH3CN](OTf); 3c = [PdCH3(1c)CH3CN]-
(OTf); 3d = [PdCH3(1d)CH3CN](OTf)) were obtained as
a mixture of isomers in solution (Table 1). As in the case
of the neutral complexes [PdCH3(P^P0)Cl] 2a–d
+
H3C
Cl
Pa
Pb
Pa
Pb
CH3
Cl
Pa^Pb
AgOTf
Pd
Pd
(OTf)-
Pd
- COD
CH2Cl2/CH3CN
- AgCl
CH3
NCCH3
Scheme 1. Synthetic pathway to neutral methyl chloro and to monocationic methyl acetonitrile palladium complexes. Only one of the two geometric
isomers is indicated in both cases. The stereochemistry has been arbitrarily assigned.

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A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
Table 1
Isomeric composition of neutral and cationic palladium methyl or palladium acetyl complexes
Neutral complexes
Cationic complexes
Ratio M:m before carbonylation
Ratio M0:m0 after carbonylationa
Ratio M:m before carbonylation
Ratio M0:m0 after carbonylation
2a: 16:1b
2b: 5.2:1c
2c: 1.2:1d
2d: 6.3:1e
a
4a: n.d.f
4b: 3.1:1c
4c: 1.3:1d
4d: 7:1e
3a: 1.5:1b
3b: 1.8:1c
3c: 1.5:1d
3d: 2.5:1e
5a: 1.8:1b
5b: 2.6:1c
5c: 1.8:1d
5d: 3.2:1e
Determined from high pressure NMR experiments.
Major isomer: CH3 or C(O)CH3 trans to PCy2.
Major isomer: CH3 or C(O)CH3 trans to P(3-CF3C6H4)2.
Major isomer: CH3 or C(O)CH3 trans to PPh2.
Major isomer: CH3 or C(O)CH3 trans to P(3-CF3C6H4)2.
Not determined.
b
c
d
e
f
PA
Cl
The ratio M:m presented only modest variations within
a range of ca. 80 K, when the isomer distributions M:m for
the cationic complexes 3a–d at 25 ꢁC (298 K) and at
ꢀ60 ꢁC (213 K) were compared (Table 2).
PA
CH3
Cl
Pd
Pd
PB
CH3
PB
The rate constant for the exchange process between the
major, M, and the minor, m, isomers is related to the relax-
ation time of the proton T1, which is in the magnitude of
order of 1 s. When an exchange reaction is detected
Fig. 2. Geometric isomerism in the complexes 2a–d.
(P^P0 = 1a–d), two Pd–CH3 signals (dd) were observed.
The coupling constants JH–P(trans) ranged from 6.5 to
1
3
through a H-NOESY experiment, the corresponding rate
3
constant would describe an exchange rate between 0.1
and 10 sꢀ1. The absence of exchange cross peaks shows
that the rate constant for the exchange M ꢀ m is slower
than 0.1 sꢀ1. The ratio of the isomeric mixture for the com-
plexes reported in Table 1 did not change over several days.
Therefore, it can be assumed that for each complex the two
isomers are in equilibrium, but the exchange rate between
them is rather slow (the 1H NMR spectrum presents sharp
peaks for the Pd–CH3 protons).
7.8 Hz, while the JH–P(cis) from 2.3 to 4.3 Hz. A good
agreement was observed with the values reported for palla-
dium methyl acetonitrile complexes containing dppe, dppp,
dppb [1]. The 31P{1H} NMR showed two pairs of doublets,
corresponding to each geometric isomer. The dd signal
arose from the coupling of each P with the other moiety
2
through a JP–P, which ranged between ca. 35.0 and
42.0 Hz [1]. The resonance of the Ptrans to the methyl
groups was detected around 0 ppm, while that of Pcis
around 30.0 ppm. Only the cyclo-hexyl groups produced
a shift downfield of the corresponding resonances for Ptrans
and Pcis in [PdCH3(1a)- CH3CN](OTf) at 11.0 (isomer M)
and 39.5 ppm (isomer m), respectively. Apparently, the
nature of the fourth ligand did not influence to a big extent
the chemical shift of the P resonances in this kind of com-
plexes. Due to the similar chemical shifts of the two non-
equivalent phosphorus moieties, 2D NMR experiments
were necessary for the assignment of the 31P resonances,
which resulted in many case overlapped.
In the cationic complexes the fourth coordination
position is occupied by CH3CN. While forming a r
bond with the metal, the CH3 group has a higher trans
influence than the donor ligand CH3CN. The nature of
the substituents at the phosphorus atoms as well as the
nature of the other ligands influence the isomer distribution
observed for the complexes 2a–d and 3a–d (Table 1).
The Pd–CH3 groups gave always one signal for each iso-
mer between 0.4 and 0.85 ppm. No exchange was detected
between the Pd–CH3 of the major and of the minor species
2.4. Carbonylation experiments of the neutral complexes
2a–d
The neutral complexes 2a–d were reacted with carbon
1
monoxide and their behavior was studied in situ by H
and 31P{1H} NMR spectroscopy, as well as with 2D
NMR experiments. Insertion of carbon monoxide into pal-
ladium methyl chloro complexes was slow. Carbon monox-
ide was bubbled through a needle with a gentle flow (40 ml/
min) for 40 min into a CDCl3 0.04 M solution of the com-
plex. Carbonylation did not occur quantitatively, as the Pd
methyl chloro could still be observed in the spectrum.
Insertion of carbon monoxide is reversible, but decarbony-
lation occurs slowly. The solutions of the partially car-
bonylated neutral complexes 4a–d released CO slowly
upon some days. The isomer distribution M0:m0 (M0, major
Table 2
Isomeric distribution for the cationic complex 3a–d at 25 and ꢀ60 ꢁC
1
from the H-NOESY, in the neutral and in the cationic
Ratio [PdCH3(P^P0)(CH3CN)](OTf)
3a
3b
3c
3d
complexes. A broadening of the Pd–CH3 signals was
observed for 2a when the temperature was raised to
40 ꢁC (313 K).
T = 25 ꢁC
T = ꢀ60 ꢁC
1.5:1
1.2:1
1.8:1
1.3:1
1.5:1
1.2:1
2.5:1
2.6:1

A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
4819
insertion product, m0, minor insertion product), as of
2.5. Carbonylation experiments of the cationic complexes
3a–d
Table 1, was obtained from high pressure NMR experi-
ments, in which complete carbonylation occurred [11].
The species 2a was not investigated by means of high pres-
sure NMR, so no data about the final isomer distribution
after CO insertion are available. M0 should be regarded
as the major species observed after bubbling CO for
40 min at room pressure.
The insertion reaction was studied by bubbling CO
through a metallic needle in a 0.04 M solution of the com-
plex in CDCl3 or CD2Cl2 at ꢀ60 or ꢀ80 ꢁC, respectively.
The reaction was completed within 5–10 min. The insertion
products [PdC(O)CH3(P^P0)(CH3CN)](OTf) 5a–d (5a =
[PdC(O)CH3(1a)(CH3CN)](OTf); 5b = [PdC(O)CH3(1b)-
In the 1H NMR the insertion of carbon monoxide
caused a shift downfield of the resonance of the methyl
group; the acyl group was found in the region 1.80–
2.65 ppm. The proximity of the cyclo-hexyl groups seemed
to induce a greater shift downfield of the acyl resonance.
(CH3CN)](OTf);
5c = [PdC(O)CH3(1c)(CH3CN)](OTf);
5d = [PdC(O)CH3(1d)(CH3CN)](OTf)) were characterized
by means of 1D and 2D NMR spectroscopy. Upon carbon-
ylation the doublet of doublets of the Pd–CH3 group disap-
peared. A broad singlet was detected in the region 1.60–
2.60 ppm, corresponding to the acyl group. As already
observed in the carbonylation of the neutral complexes,
the acyl group cis to the cyclo-hexyl rings in 5a underwent
a considerable shift downfield with respect to the other spe-
cies with no alkyl groups at the phosphorus moieties. No
4JH–P, describing the coupling with the non-equivalent Pcis
and Ptrans of the two fragments (cis and trans are referred to
the position with respect to the acyl group), was observed
in any of the cases investigated. The phosphorus reso-
nances underwent a shift upfield (up to 2 ppm for the Ptrans
and 11–14 ppm for the Pcis). For instance, in 3c Ptrans was
observed at 1.0 ppm and Pcis at 31.0 ppm for the major iso-
mer. Upon carbonylation, for the isomer with the same
stereochemistry (i.e., the same moieties cis and trans to
the acyl group) Ptrans and Pcis were detected at 0.9 and
4
In all the cases, no JH–P was observed in the C(O)CH3
1
signals of the Pd acyl complexes. The H resonance for
the acyl group appeared as a broad singlet. The reso-
nances assigned to the Ptrans underwent a shift upfield of
ca. 2–5 ppm upon carbonylation, while those of the Pcis
a bigger shift, from 28–32 to 15–18 ppm for the aryl
groups and from 36.5 to 27.5 ppm for the cyclo-hexyl
2
groups. The coupling constants JP–P increased on going
from the methyl complexes 2a–d to the acetyl complexes
4a–d from ca. 37–41 to 66–70 Hz. The values obtained
for the neutral complexes are comparable with that found
for
[PdC(O)CH3(dppb)Cl]
(dppb = 1,4-bis(diph-
enylphosphino)butane), forming a seven-membered ring
with the metal (2JP–P of 39 Hz) [1].
The insertion products showed exchange peaks in the
1H-NOESY (Fig. 3). This suggests that after the insertion
the two isomers are in equilibrium.
2
17.5 ppm, respectively. The coupling constants JP–P
increased from ca. 36–42 to ca. 66–71 Hz. As the carbon
backbone and the geometric properties of the ligands are
very similar, no big differences among the values of the
2JP–P for the cationic palladium methyl and the acetyl com-
plexes are expected.
3c was also treated with 1 atm of 13CO; the species
[Pd(13C(O)CH3)(1c)(CH3CN)](OTf) was formed as a mix-
ture of two isomers with the same distribution obtained
2
with non-labelled CO. The JC–P coupling constants for
the acetyl carbon were 103 Hz with Ptrans and 9.6 Hz with
the Pcis, respectively. These values are in good agreement
with the data reported by Nozaki [5] for [Pd(13C(O)CH3)-
2
(BINAPHOS)CD3CN](OTf), in which JC–P for the acetyl
carbon was 94 Hz with the phosphine and 20 Hz with the
phosphite. They are also comparable with those reported
by Elsevier [12] for [Pd(13C(O)CH3)(13CO){(2S,4S)-2,4-
2
bis(diphenylphosphinopentane)}], where JC–P for the ace-
tyl carbon was 79 Hz with the trans phosphorus atom and
19.8 Hz with the cis phosphorus atom. In [Pd(13C(O)CH3)-
(1c)(CH3CN)](OTf) no displacement of acetonitrile by
13CO was observed at 1 atm. A similar result was already
found by Nozaki [5] for the complex [Pd(13C(O)CH3)-
(BINAPHOS)CD3CN](OTf). However, this contrasted
2
what observed by Elsevier [12], who reported the JC–P
between phosphorus and 13CO in [Pd(13C(O)CH3)(13CO)-
{(2S,4S)-2,4-bis(diphenylphosphinopentane)}](BF4). The
ligand 1c is rather basic, as it contains the 4-CH3OC6H4
Fig. 3. 1H-NOESY (d ppm, CDCl3; T = 298 K) for the isomeric mixture
of 4a: exchange peaks between the acyl groups of the major and minor
isomers.

4820
A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
substituents at one phosphorus moiety. The complex 3c
should then display strong affinity for the acid CO. Ther-
modynamic considerations may explain the stability of
the palladium acyl complex 5c without the displacement
of CH3CN. Carbonylation studies on Pd complexes modi-
fied with (R)-(S)-Josiphos derivatives [4] showed that the
acetonitrile ligand is not replaced by carbon monoxide
upon complete conversion to the palladium acyl
complexes.
On the basis of what observed for the neutral complexes,
the isomer distribution reported for the cationic carbonyl-
ation products should correspond to the equilibrium com-
position of the system.
3. Discussion
The neutral palladium methyl chloride and cationic pal-
ladium methyl acetonitrile complexes synthesized in this
work exist as a mixture of isomers in solution. The deriva-
tives 2b–d showed the prevalence of the geometric isomer in
which the methyl group occupies the position trans to the
more electron-withdrawing group present at the P moieties.
A bigger difference in the isomer distribution is observed
when a bigger differentiation between the two moieties is
present, as in the case of 1b and 1d. Conversely, in case
of 2c, the electronic differentiation of the two phosphorus
was modest and the ratio between the geometric isomers
resulted close to 1. These three examples are consistent
with the trans influence order, which is based on the follow-
ing magnitude scale: CH3 > PCy2 > PAr2 >> Cl [14,15].
The methyl group prefers the coordination trans to the
more electron poor fragment, which has weaker r-induc-
tive effect. The distribution of geometric isomers observed
in the case of 2a contradicts the ‘‘trans influence’’ concept
and can rather be explained in terms of steric effects. The
methyl group adopts a trans position to the PCy2 fragment
to minimize the steric repulsions. Apparently, this effect is
remarkable, as the bigger isomer distribution in the series
(16:1) is observed for 2a. A similar trend has already been
reported for chloro methyl Pt complexes modified with (R)-
(S)-Josiphos derivatives [16]. The methyl Pd chloro com-
plex derived by (R,S)-BINAPHOS [5] showed the preva-
lence of the geometric isomer with the methyl trans to the
phosphite moiety (ratio M:m = 5:1), reflecting the less trans
influence of the P(OAr)2 group over PAr2.
2.6. X-ray crystallography
Efforts to obtain the cationic complex [PdCH3(1a)CH3-
CN]OTf) resulted in the neutral dinuclear dichloride spe-
cies [PdCl(1a)]2(OTf)2. The methyl group exchanged with
the chloride in the chlorinated solvent CHCl3 [13] and a
dimerization occurred. Moreover, the non-coordinated
solvent was replaced by the chloride. Four molecules of
CHCl3 co-crystallizes in the asymmetric unit, as well as
two triflate counterions. Two molecules of the complex
crystallize in the asymmetric unit. The complex crystal-
ꢀ
lized in the triclinic space group P1. Fig. 4 shows the
molecular structure of the dinuclear complex together
with the atom numbering scheme (limited to one subunit
[Pd(1a)Cl]+).
Single crystals suitable for X-ray analysis were obtained
for the neutral derivative 2d by layering a CHCl3 solution
of the complex with n-pentane. Fig. 5 shows the molecular
structure of the complex with the atom numbering scheme.
2d crystallizes in the orthorhombic space group Pbca as
white platelets.
The ratio between the isomers is more similar for the
cationic than for the neutral complexes. The bigger elec-
tronic differentiation between the fragments in 1b and 1d
increases the ratio M:m. 3a exists as a mixture of stereoiso-
Fig. 4. ORTEP plot of the cation of [Pd(1a)Cl]2(OTf)2. Thermal ellipsoids are set at the 30% probability level. Hydrogen atoms are omitted for clarity.

A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
4821
Fig. 5. ORTEP plot of 2d. Thermal ellipsoids are set at the 30% probability level. Hydrogen atoms and CF3 disorder are omitted for clarity.
mers in the ratio 1.5:1. Steric factors may explain the loca-
tion of the methyl trans to the cyclo-hexyl groups. The
complex modified with 1c was the less sensitive to variation
of the fourth ligand in the coordination sphere. The isomer
ratios obtained for neutral and cationic complexes were
comparable.
dium (Scheme 2). This is supported by the following
observation. First, no coordination of 13CO was observed
in contrast to what was reported for [Pd(CH3){(S,S)-
BDPP}(S)] ((S,S)-BDPP = {(2S,4S)-2,4-bis(diphenylphos-
phinopentane)}) [12] and for [PdCH3(dppp)(OEt2)](BAr04)
(dppp = 1,3-bis-(diphenylphosphino)propane) [18]. The
peak of the acetonitrile group could be still observed in
Studies on square planar 16-electron complexes of
palladium(II) and platinum(II) containing diphosphine
ligands revealed that insertion of carbon monoxide occurs
preferentially from a four coordinate complex, formed by
substitution of a phosphine ligand by CO [9,17]. When
neutral and cationic complexes of the kind [PdCH3-
(P^P)Y]n+ are considered (Y = Cl or CH3CN; n+ = 0,
1), the fourth ligand of the coordination sphere, i.e.,
chloro or acetonitrile, should play an active role in the
migratory insertion. In the neutral complexes the r-donor
nature of the chloride makes its dissociation less likely
than in the case of the dative weak r-donor CH3CN.
One can propose the pathway for the carbonylation of
the neutral complexes illustrated in Scheme 2. For the
minor isomer m the migratory insertion would proceed
through an equivalent mechanism.
In the case of cationic palladium alkyl complexes the
dissociation of acetonitrile should be more likely, since it
is a weak r-donor. The dissociation of the acetonitrile
would create a vacancy that CO could readily occupy.
The CO and the methyl would be cis to each other and
the migratory insertion could occur. Alternatively, one
could think about a similar mechanism as described for
the neutral complexes, where one moiety of the diphos-
phine and not the acetonitrile dissociates from the palla-
1
the H NMR of the carbonylated product between 2 and
2.20 ppm in all the systems investigated. As a second point,
the half-life times for the CO insertion of 3b and 3d were
much larger than the values found for more basic diphos-
phine investigated [11]. This may be consistent with a
strong bonding of the acetonitrile to the metal in this kind
of complexes, particularly enhanced in the case of ligands
with electron-withdrawing substituents.
As the ratio between the major and the minor isomer is
different for the reagents and the products of the migratory
insertion (Table 1), an isomerization step should be taken
into account. One cannot say if it occurs before or after the
migratory insertion or in both cases. Before the migratory
insertion, the coordinated CO and the methyl group have
two possible stereochemical arrangements for the non-
equivalence of the P moieties of the ligands. In a similar
way, after the migratory insertion, two stereochemical alter-
natives, cis or trans to each P, are available for the acyl group.
Two species with comparable but slightly different energy
should be present in the transition state of the migratory
insertion step. However, one cannot exclude that the Pd-
methyl complex and the Pd-acyl complex are flipping at their
own ground state between two different stereochemical
arrangements (Scheme 2) according to their relative stability.

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A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
PA
CH3
PA
CH3
X
CH3
X
PA
PB
Preequilibrium
Isomerization
+ CO
- CO
Pd
Pd
Pd
X
M
PB
PB
PA
CO
PA
Migratory insertion
CH3
Pd
Pd
X
X
CH3
CO
PB
PB
PA
PB
PA
PB
X
PA
PB
X
PA
C(O)CH3
X
Isomerization
Pd
Pd
Pd
Pd
X
PB
C(O)CH3
C(O)CH3
m
C(O)CH3
M
Scheme 2. Proposed mechanism for the CO insertion in the neutral complexes 2a–d. The stereochemistry has been arbitrarily assigned. The arrows in
brackets denote the possibility of an isomerization prior or after the CO migratory insertion (X = Cl or CH3CN).
Regardless to the details of the mechanism, each complex
has two non-equivalent fragments with different stability
and different reactivity with respect to CO. Van Leeuwen
reported that both [PdCH3(P^P0)(solvent)](OTf) and
[PdC-(O)CH3(P^P0)(solvent)](OTf) are in rapid equilibrium
between their cis/trans isomers (P^P0 = 1-diphenylphosph-
ino-2-tert-butyl-3-dicyclohexylphosphinoprop-1-ene) [3].
Nozaki proposed a similar cis/trans isomerization for the
Pd-(R,S)-BINAPHOS system, although it was not directly
observed [5]. Supported by some evidences for Pt com-
plexes, it was proposed that the methyl group in
[PdCH3(CO){(R,S)-BINAPHOS}](BAr4), which exists as
a single isomer, migrates from trans to the phosphine to
cis to the phosphine prior to the migration to the coordi-
nated CO. With this isomerization, the methyl group may
become more activated in trans to the phosphite than at
the original position. In this way, the migration to the coor-
dinated CO should be accelerated to give the acyl complex
[19,20]. In the present work such high degree of stereospec-
ificity is not observed, probably because the two moieties
were not as electronically different as in the case of (R,S)-
BINAPHOS. One may assume that the activation mecha-
nism proposed by Nozaki occurs also for the present
systems [5]. When the single complex is considered, the
major isomer M has the methyl group occupying the posi-
tion trans to the more acid moiety, with the exception of
systems derived from 1a. This isomer is the more thermody-
namically stable (Table 1). In the conditions of the experi-
ment the intermediate [PdCH3CO(P^P0)](OTf) cannot be
observed. One may assume that the methyl group migrates
[5] from trans to cis to the more acid dentate of the ligand
prior to the migration of the coordinated CO. This isomer-
ization has the effect of activating the methyl group. The
migration of the alkyl to the coordinated CO should be
accelerated to give the major final insertion product M0
(acyl group trans to the acid moiety, see Table 1). At the
same time, the other isomer exists, where the methyl group
is trans to the more basic moiety. These two intermediates
should have different energy and reactivity. The intermedi-
ate [PdCH3CO(P^P0)] originating from the minor isomer,
where the methyl is trans to the more basic moiety, might
insert CO directly without isomerization, following Noza-
ki’s assumptions [5]. A similar isomerization of an alkyl
platinum complex prior to the migration of the alkyl group
to the coordinated CO is well known in monodentate phos-
phine complexes [21,22].
Effects on the reactivity of two different isomeric species
have been recently reported [23]. The rate of reductive elim-
ination for palladium aryl amido complexes was measured.
The work suggested that ground state effects, the ‘‘trans
influence’’ effects, dominate the control of the rate. The
determination of the half-life times for these complexes
[11] suggests that there are differences in reactivity not only
in the series 3b–d, due to overall donating properties of the
ligands, but also within the same species for the non-equiv-
alence of the dentates (the major, M, and minor, m, iso-
mers insert CO with unlike rate).
4. Conclusions
Insertion of carbon monoxide into Pd methyl complexes
modified with 1,4-Cs-symmetric diphosphines is not stereo-
specific. The entire synthetic pathway for the generation of
these complexes, from the neutral methyl chloride to the

A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
4823
cationic methyl acetonitrile palladium complexes to the
acyl palladium complexes shows that thermodynamic and
kinetic factors are affecting the isomer distribution at every
step.
and were all used as received. Silver trifluoromethansulfo-
nate was purchased from Fluka. Dichloromethane, and
acetonitrile used for the synthesis were of ‘‘puriss.’’ grade,
dried over molecular sieves (‘‘crown cap’’) and were pur-
chased from Fluka. All the solvents used for recrystalliza-
tion were of ‘‘puriss.’’ quality, purchased from Fluka or
J.T. Baker and purified according to standard procedures.
CDCl3 was purchased from Merck and was used without
further purification. Elemental analysis (EA) was per-
Complexes [Pd(P^P0)(H2O)2](OTf)2 were used as catalyst
precursors for the CO propene copolymerization, affording
materials with high degree of regio- and stereoregularity.
Complexes [Pd(P^P0)(H2O)2](OTf)2 (P^P0 = 1a–c) showed
good activity, while [Pd(1d)(H2O)2](OTf)2 achieved a quite
unsatisfactory performance [24]. However, the stereo- and
regiocontrol was high in all the cases considered. The cata-
lytic behavior may be related to the different reactivity of
these complexes with carbon monoxide. According to the
model study described in this paper, the carbon monoxide
insertion is never stereospecific. The ratio between the ster-
eoisomers depends on the ligand. Considerations related to
electronic factors may suggest that the single fragments
have different reactivity, not only with respect to the CO
insertion but also relatively to the following steps of the
copolymerization reaction.
The olefin insertion seems to be the rate-determining
step of the copolymerization [25]. With achiral Cs-sym-
metric ligands, the enantioface selection should be
chain-end controlled. Highly isotactic copolymers imply
a high enantioface control in the coordination and then
in the insertion of the olefin. The insertion of carbon
monoxide creates two isomers that can lead to four Pd-
alkyl complexes after the insertion of the olefin. These
considerations show that a big number of pathways are
potentially available. However, among them, one should
be working effectively in transmitting the stereochemical
information in the copolymerization process. Even
though some polymerization pathways may start, some
of the intermediates are probably ‘‘sleeping’’ in the fur-
ther steps of the catalytic cycle. Alternatively, an isomer-
ization process should probably take place during the
growth of the polymer chain, which develops eventually
at the more reactive/stable moiety. This is reasonable,
as the Pd has unsymmetrical electron contributions from
the two different dentates. At the stage of the CO inser-
tion one cannot suggest which the more reactive moiety
is, as this reaction is not stereospecific in all the cases
examined. These differences probably remain in the cata-
lytic cycle.
formed by the service of ‘‘Laboratorium fur Organische
¨
Chemie’’ of the ETH Zurich.
5.2. NMR spectroscopy
The 1H, 31P{1H} and the 2D spectra were recorded on a
1
Bruker Avance 500 (frequency in MHz: H, 500.13; 31P,
202.45). 19F{1H} NMR spectra were recorded on a Bruker
Avance 200 (frequency in MHz: 19F, 188.31). Chemical
shifts are given in parts per million (ppm) relative to
TMS (internal standard) or to the solvent residual peak
1
for H NMR, and relative to 85% H3PO4 (external stan-
dard) for 31P{1H} NMR. 19F NMR spectra are calibrated
to CCl3F as the internal standard.
The coupling constants J are given in hertz. The multi-
plicity is denoted by the following abbreviations: s, singlet;
d, doublet; t, triplet; q, quartet; qt, quintet; sx, sextet; sp,
septet; m, multiplet; dd, doublet of doublets; dq, doublet
of quartets; br, broad.
NMR probe temperature was measured by means of a
thermocouple. Standard pulse sequences were employed
for 31P–1H, 1H-COSY, 1H-TOCSY and 1H-NOESY corre-
1
lation studies. H-TOCSY spectra were recorded using a
1
0.2 s mixing time. H-NOESY spectra were recorded using
a 0.8 s mixing time.
5.3. X-ray crystallography
X-ray structures were measured on a Bruker CCD dif-
fractometer (Bruker SMART PLATFORM, with CCD
detector, graphite monocromator, Mo Ka radiation).
The program SMART served for the data collection. Inte-
gration was performed with SAINT. The structure solution
and refinement on F2 were accomplished with SHELXTL
97. Model plots were made with ORTEP32. All non-hydro-
gen atoms were refined freely with anisotropic displace-
ments. The hydrogen atoms were refined at calculated
positions riding on their carrier atoms. Weights are opti-
mized in the final refinement cycles. Table 3 gives the
crystallographic data for the compounds [Pd(1a)-
Cl]2(OTf)2 and 2d.
5. Experimental part
5.1. General remarks
All manipulations with air- or moisture-sensitive com-
pounds were carried out under nitrogen or argon using
standard Schlenk techniques or a glove box. Trans-[PdCl2-
(NCPh)2] [26], [Pd(COD)Cl2] [8] and [PdCH3(COD)Cl] [27]
were prepared according to published procedures. The syn-
thesis of the ligands 1a–d has been previously published
[24]. PdCl2 was purchased from Johnson Matthey, benzo-
nitrile, COD and Sn(CH3)4 were purchased from Fluka,
5.4. Synthesis of palladium methyl chloro complexes 2a–d
5.4.1. General procedure
To a solution of [PdCH3(COD)Cl] (1 equivalent) in
CH2Cl2 the diphosphine ligand 1a–d (1.1–1.2 equivalents)
in CH2Cl2 was added. The mixture was stirred for 3 h at

4824
A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
Table 3
Crystal data, measurement and refinement parameters for [Pd(1a)Cl]2(OTf)2 and 2d
Identification code
Empirical formula
Formula weight
Temperature (K)
[Pd(1a)Cl]2(OTf)2
C34.75H41Cl7F3O3P2PdS
1012.23
200(2)
0.71073
2d
C37H33ClF6O2P2Pd
827.42
298(2)
0.71073
˚
Wavelength (A)
Crystal system
Space group
Triclinic
Orthorhombic
Pbca
ꢀ
P1
Unit cell dimensions
˚
a (A)
14.4236(10)
18.002(2)
˚
b (A)
14.5509(10)
21.6669(15)
15.1104(17)
26.847(3)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
82.2550(10)
84.8970(10)
72.1660(10)
4283.9(5)
90
90
90
3
˚
Volume (A )
7302.6(14)
Z
4
8
Density (calc.) (mg cmꢀ3
)
1.569
1.040
2046
1.505
0.732
3344
Absorption coefficient (mmꢀ1
F(000)
)
Crystal size (mm)
H range for data collection (ꢁ)
Limiting indices
1.00 · 0.46 · 0.31
1.67–26.37
0.40 · 0.20 · 0.13
1.52–24.71
ꢀ18 6 h 6 17, ꢀ18 6 k 6 18, ꢀ27 6 l 6 27
ꢀ21 6 h 6 21, ꢀ17 6 k 6 17, ꢀ26 6 l 6 31
Reflections collected
38968
39894
Independent reflections (Rint
Completeness to h
Refinement method
Data/restrains/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
)
17452 (0.0178)
26.37ꢁ 99.6%
6224 (0.0472)
24.71ꢁ 100.0%
Full-matrix least-squares on F2
6224/24/494
1.290
R1 = 0.0703
Full-matrix least-squares on F2
17452/18/993
1.052
R1 = 0.0424
wR2 = 0.1182
wR2 = 0.1344
R indices (all data)
R1 = 0.0500
R1 = 0.0775
wR2 = 0.1248
1.606 and ꢀ1.097
wR2 = 0.1375
0.681 and ꢀ1.070
ꢀ3
˚
Largest diff. peak and hole (e A
)
room temperature. The solution was then evaporated to ca.
0.5 ml of CH2Cl2 and the product was precipitated by
adding n-pentane, washed with n-pentane and dried under
HV.
In the labeling of the carbon backbone protons (Ha, Hb,
Hc, Hd) syn and anti are referred to the position with
respect to each non-equivalent moiety of the ligand. Ptrans
and Pcis are referred to the position with respect to the
methyl group.
5.4.2.2. Minor isomer, CH3 trans to PPh2. 1H NMR
(500 MHz, CDCl3, 25 ꢁC): d 0.84 (dd, 3 H, CH3,
3
3JH–P(trans) = 7.16 Hz; JH–P(cis) = 3.77 Hz), 1.18–1.44 (m,
11H, Cy, overl. with isomer M), 1.58–1.90 (m, 11H, Cy,
overl. with isomer M), 2.52 (br, 2H, CH2PCy2), 3.42 (br,
2H, CH2PPh2), 6.10 (m, 1H, Hd syn to PPh2), 6.85 (m,
1H, Hc), 7.10 (m, 1H, Hb), 7.17 (m, 1H, Ha syn to PCy2),
7.40–7.55 (m, 5H, Ph, overl. with isomer M), 7.66–7.80
(m, 5H, Ph, overl. with isomer M).
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 0.6 (d,
2
2
5.4.2. Synthesis of [PdCH3(1a)Cl] (2a)
PPh2; JP–P = 37.0 Hz), 36.5 (d, PCy2; JP–P = 36.3 Hz).
Anal. Calc. for C33H43P2ClPd (643.52): C, 61.59; H,
6.73. Found: C, 61.98; H, 6.81.
Yield: 98%, white solid. The compound exists as a mix-
ture of two isomers in solution (M, major isomer, and m,
minor isomer). M:m = 16:1.
5.4.3. Synthesis of [PdCH3(1b)Cl] (2b)
5.4.2.1. Major isomer, CH3 trans to PCy2. 1H NMR
Yield: 83%, light-brown solid. The compound exists as a
mixture of two isomers in solution (M, major isomer, and
m, minor isomer). M:m = 5.2:1
(500 MHz, CDCl3, 25 ꢁC):
d 0.48 (dd, 3H, CH3,
3JH–P(trans) = 7.16 Hz; JH–P(cis) = 3.77 Hz), 1.18–1.44 (m,
11H, Cy, overl. with isomer m), 1.58–1.90 (m, 11H, Cy,
overl. with isomer m), 3.24 (br, 2H, CH2PCy2), 3.69 (br,
2H, CH2PPh2), 6.03 (m, 1H, Hd syn to PPh2), 6.82 (m,
1H, Hc), 7.11 (m, 1H, Hb), 7.26 (m, 1H, Ha syn to PCy2),
7.40–7.55 (m, 5H, Ph, overl. with isomer m), 7.66–7.80
(m, 5H, Ph, overl. with isomer m).
3
5.4.3.1. Major isomer, CH3 trans to P(3-CF3C6H4)2. 1H
NMR (500 MHz, CDCl3, 25 ꢁC): d 0.72 (dd, 3 H, CH3,
3
3JH–P(trans) = 7.80 Hz; JH–P(cis) = 4.05 Hz), 3.79–3.91 (br,
4H, CH2P(3-CF3C6H4)2 and CH2PPh2), 6.04 (m, 1H,
C6H4, Hd syn to P(3-CF3C6H4)2), 6.14 (m, 1H, C6H4, Ha
syn to PPh2), 6.79–6.83 (m, 2H, C6H4, Hb and Hc, overl.
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 9.6 (d,
2
2
PCy2; JP–P = 38.5 Hz), 29 (d, PPh2; JP–P = 39.3 Hz).

A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
4825
with isomer m), 7.45–7.55 (m, 6H, Ph), 7.55–7.59 (m, 2H,
3-CF3C6H4), 7.70–7.84 (m, 4H, Ph, overl. with isomer
m), 7.89–7.97 (br, 4H, 3-CF3C6H4, overl. with isomer m),
8.03–8.13 (br, 2H, 3-CF3C6H4 overl. with isomer m).
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 1.1 (d,
2 2
P(4-OCH3C6H4)2, JP–P = 39.0 Hz), 28.9 (d, PPh2, JP–P
=
39.0 Hz).
Anal. Calc. for C35H35O2P2ClPd (691.48): C, 60.79; H,
5.10. Found: C, 61.23; H, 5.26.
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC):
d 1.9
2
(d, P(3-CF3C6H4)2; JP–P = 38.5 Hz), 30.9 (d, PPh2;
2JP–P = 38.5 Hz).
5.4.5. Synthesis of [PdCH3(1d)Cl] (2d)
19F NMR (188 MHz, CDCl3, 25 ꢁC): d 62.5 (s,
Yield: 91%, light-brown solid. The compound exists as a
mixture of two isomers in solution (M, major isomer, and
m, minor isomer). M:m = 6.3:1
CF3).
5.4.3.2. Minor isomer, CH3 trans to PPh2. 1H NMR
5.4.5.1. Major isomer, CH3 trans to P(3-CF3C6H4)2. 1H
NMR (500 MHz, CDCl3, 25 ꢁC): d 0.71 (dd, 3H, CH3,
(500 MHz, CDCl3, 25 ꢁC):
d 0.62 (dd, 3H, CH3,
3JH–P(trans) = 7.50 Hz; JH–P(cis) = 4.30 Hz), 3.72–3.82 (br,
4H, CH2P(3-CF3C6H4)2 and CH2PPh2), 6.10 (m, 1H,
C6H4, Hd syn to P(3-CF3C6H4)2), 6.22 (m, 1H, C6H4, Ha
syn to PPh2), 6.79–6.83 (m, 2H, C6H4, Hb and Hc, overl.
with isomer M), 7.43–7.49 (m, 6H, Ph), 7.65–7.69 (m,
2H, 3-CF3C6H4), 7.80–7.85 (m, 4H, Ph, overl. with isomer
M), 7.89–7.97 (br, 4H, 3-CF3C6H4, overl. with isomer M),
8.03–8.13 (br, 2H, 3-CF3C6H4 overl. with isomer M).
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 0.6 (d,
3
3
3JH–P(trans) = 7.50 Hz; JH–P(cis) = 3.50 Hz), 3.71 (br, 2H,
CH2P(3-CF3C6H4)2 overl. with isomer m), 3.79 (br, 2H,
CH2P(4-OCH3C6H4)2), 3.90 (s, 6H, OCH3), 6.06 (m, 1H,
C6H4, Hd syn to P(3-CF3C6H4)2), 6.25 (m, 1H, C6H4, Ha
syn to P(4-OCH3C6H4)2), 6.80–6.92 (m, 2H, C6H4, Hb
and Hc, overl. with isomer m), 6.99–7.04 (m, 4H, 4-
OCH3C6H4), 7.55–7.62 (m, 2H, 3-CF3C6H4), 7.66–7.73
(m, 4H, 4-OCH3C6H4, overl. with isomer m), 7.73–7.79
(m 2H, 3-CF3C6H4), 7.90–8.00 (br, 2H, 3-CF3C6H4, overl.
with isomer m), 8.05–8.16 (br, 2H, 3-CF3C6H4, overl. with
isomer m).
2
2
PPh2, JP–P = 39.3 Hz), 31.5 (d, P(3-CF3C6H4)2, JP–P
39.3 Hz).
=
19F NMR (188 MHz, CDCl3, 25 ꢁC): d 62.6 (s, CF3).
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 2.2 (d, P(3-
Anal. Calc. for C35H29F6P2ClPd (767.42): C, 54.78; H,
3.81. Found: C, 54.85; H, 3.86.
2
CF3C6H4)2; JP–P = 38.7 Hz), 28.5 (d, P(4-OCH3C6H4)2;
2JP–P = 38.7 Hz).
5.4.4. Synthesis of [PdCH3(1c)Cl] (2c)
19F NMR (188 MHz, CDCl3, 25 ꢁC): d 62.5 (s, CF3).
Yield: 88%, white solid. The compound exists as a mix-
ture of two isomers in solution (M, major isomer, and m,
minor isomer). M:m = 1.2:1.
5.4.5.2. Minor isomer, CH3 trans to P(4-OCH3C6H4)2. 1H
NMR (500 MHz, CDCl3, 25 ꢁC): d 0.58 (dd, 3H, CH3,
3
3JH–P(trans) = 7.50 Hz; JH–P(cis) = 3.50 Hz), 3.66 (s, 2H,
5.4.4.1. Major isomer, CH3 trans to PPh2. 1H NMR
CH2P(4-OCH3C6H4)2), 3.70 (br, 2H, CH2P(3-CF3C6H4)2,
overl. with isomer M), 3.89 (s, 6H, OCH3), 6.10 (m, 1H,
C6H4, Hd syn to P(3-CF3C6H4)2), 6.29 (m, 1H, C6H4, Ha
syn to P(4-OCH3C6H4)2), 6.80–6.92 (m, 2H, C6H4, Hb
and Hc, overl. with isomer M), 6.94–6.99 (m, 4H, 4-
OCH3C6H4), 7.66–7.73 (m, 4H, 4-OCH3C6H4, overl. with
isomer M), 7.82–7.86 (m, 2H, 3-CF3C6H4), 7.90–8.00 (br,
4H, 3-CF3C6H4, overl. with isomer M), 8.05–8.16 (br, 2H,
3-CF3C6H4, overl. with isomer M).
(500 MHz, CDCl3, 25 ꢁC):
d 0.61 (dd, 3H, CH3,
3
3JH–P(trans) = 7.60 Hz; JH–P(cis) = 3.80 Hz), 3.69 (s, 2H,
2
CH2PPh2), 3.76 (d, 2H, CH2P(4-OCH3C6H4)2; JH–P
=
12.70 Hz), 3.90 (s, 6H, OCH3), 6.15 (m, 1H, C6H4, Hd
syn to PPh2), 6.20 (m, 1H, C6H4, Ha syn to P(4-OCH3-
C6H4)2), 6.84–6.89 (m, 2H, C6H4, Hb and Hc, overl. with
isomer m), 6.98–7.02 (m, 4H, 4-OCH3C6H4), 7.41–7.47
(m, 6H, Ph), 7.68–7.74 (m, 4H, 4-OCH3C6H4), 7.80–7.87
(m, 4H, Ph).
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d ꢀ1.6 (d,
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d ꢀ1.4 (d,
P(4-OCH3C6H4)2; JP–P = 40.7 Hz), 31.6 (d, P(3-CF3-
2
2
2
2
PPh2, JP–P = 39.3 Hz), 31.5 (d, P(4-OCH3C6H4)2, JP–P
=
C6H4)2; JP–P = 40.7 Hz).
39.3 Hz).
19F NMR (188 MHz, CDCl3, 25 ꢁC): d 62.6 (s, CF3).
Anal. Calc. for C37H33O2F6P2ClPd (827.48): C, 53.71;
H, 4.02. Found: C, 53.92; H, 4.15.
5.4.4.2. Minor isomer, CH3 trans to P(4-OCH3C6H4)2. 1H
NMR (500 MHz, CDCl3, 25 ꢁC): d 0.64 (dd, 3H, CH3,
3
3JH–P(trans) = 7.60 Hz; JH–P(cis) = 3.80 Hz), 3.67 (s, 2H,
5.5. Synthesis of palladium methyl acetonitrile complexes
2
CH2P(4-CH3OC6H4)2), 3.82 (d, 2H, CH2PPh2; JH–P
=
10.73 Hz), 3.86 (s, 6H, OCH3), 6.10–6.14 (m, 1H, C6H4,
Hd syn to PPh2), 6.21–6.25 (m, 1H, C6H4, Ha syn to
P(4-OCH3C6H4)2), 6.78–6.84 (m, 1H, C6H4, Hb), 6.84–
6.88 (m, 1H, C6H4, Hc, overl. with isomer M), 6.95–6.98
(m, 4H, 4-OCH3C6H4), 7.47–7.56 (m, 6H, Ph), 7.71–7.78
(m, 4H, 4-OCH3C6H4), 7.75–7.81 (m, 4H, Ph).
5.5.1. General procedure [1]
To a solution of 2a–d (1 equivalent) in CH2Cl2 AgOTf
(1.1 equivalents) in a mixture of CH2Cl2 and CH3CN
(v/v ca. 20:1) was added. The solution was stirred at room
temperature for 2 h and then filtered through Celite to
remove AgCl. The filtrate was concentrated under reduced

4826
A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
pressure to ca. 0.5 ml and then collected in 30 ml of cold
(0 ꢁC) pentane with rapid stirring. The complex was recov-
ered by filtration, washed with cold pentane and dried
under vacuum.
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 1.9 (d, P(3-
2 2
CF3C6H4)2; JP–P = 38.5 Hz), 30.9 (d, PPh2; JP–P
=
38.5 Hz).
19F NMR (188 MHz, CDCl3, 25 ꢁC): d ꢀ78.7 (free tri-
flate), 62.5 (s, CF3).
5.5.2. Synthesis of [PdCH3(1a)(CH3CN)](OTf) (3a)
Quantitative yield of a yellow powder. The compound
exists as a mixture of two isomers in solution (M, major
isomer, and m, minor isomer). M:m = 1.5:1.
5.5.3.2. Minor isomer, CH3 trans to PPh2. 1H NMR
(500 MHz, CDCl3, 25 ꢁC):
d 0.62 (dd, 3H, CH3,
3JH–P(trans) = 7.50 Hz; JH–P(cis) = 4.30 Hz), 1.90–2.10 (br,
3H, CH3CN overl. with isomer M), 4.00 (br, 2H,
CH2PPh2), 4.03 (br, 2H, CH2P(3-CF3C6H4)2), 6.04 (m,
1H, C6H4, Hd syn to P(3-CF3C6H4)2), 6.53 (m, 1H, C6H4,
Ha syn to PPh2), 6.83–6.88 (m, 1H, C6H4, Hc), 6.94–6.99
(m, 1H, C6H4, Hb), 7.53–7.68 (m, 6H, Ph overl. with isomer
M), 7.69–7.82 (m, 4H, Ph overl. with isomer M), 7.83–7.84
(m, 4H, 3-CF3C6H4 overl. with isomer M), 7.89 (m, 2H,
3-CF3C6H4), 8.03–8.11 (m, 2H, 3-CF3C6H4 overl. with
isomer M).
3
5.5.2.1. Major isomer, CH3 trans to PCy2. 1H NMR
(500 MHz, CDCl3, 25 ꢁC): d 0.44 (dd, 3H, CH3, 3JH–P(trans)
=
6.50 Hz; JH–P(cis) = 2.50 Hz), 1.08–1.96 (m, 22H, Cy overl.
3
with isomer m), 2.55 (br, 3H, CH3CN), 3.32 (d, 2H,
2
CH2PCy2; JH–P = 10.40 Hz), 3.68 (br, 2H, CH2PPh2),
6.00 (m, 1H, C6H4, Hd syn to PPh2), 6.86 (m, 1H, C6H4,
Hc), 7.12–7.20 (m, 1H, C6H4, Hb, overl. with isomer m),
7.25 (m, 1H, C6H4, Ha syn to PCy2), 7.36–7.86 (m, 10H,
Ph, overl. with isomer m).
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 0.6 (d,
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 11.0 (d,
PPh2; JP–P = 40.0 Hz), 30.9 (d, P(3-CF3C6H4)2; JP–P =
2
2
2
2
PCy2; JP–P = 40.0 Hz), 32.4 (d, PPh2; JP–P = 40.0 Hz).
19F NMR (188 MHz, CDCl3, 25 ꢁC): d ꢀ78.7 (free
triflate).
40.0 Hz).
19F NMR (188 MHz, CDCl3, 25 ꢁC): d ꢀ78.7 (free
triflate), 62.6 (s, CF3).
Anal. Calc. for C38H32NO3F9P2SPd (922.09): C, 49.50;
H, 3.50. Found: C, 49.82; H, 3.59.
5.5.2.2. Minor isomer, CH3 trans to PPh2. 1H NMR
(500 MHz, CDCl3, 25 ꢁC):
d 0.68 (dd, 3H, CH3,
3JH–P(trans) = 6.50 Hz; JH–P(cis) = 2.50 Hz), 1.08–1.96 (m,
22H, Cy overl. with isomer M), 2.15 (br, 3H, CH3CN),
3.39 (br, 2H, CH2PCy2), 3.49 (br, 2H, CH2PPh2), 6.39
(m, 1H, C6H4, Hd syn to PPh2), 6.96 (m, 1H, C6H4, Hc),
7.12–7.20 (m, 1H, C6H4, Hb overl. with isomer M), 7.30
(m, 1H, C6H4, Ha syn to PCy2), 7.36–7.86 (m, 10H, Ph,
overl. with isomer M).
3
5.5.4. Synthesis of [PdCH3(1c)(CH3CN)](OTf) (3c)
Yield: 88%, yellow powder. The compound exists as a
mixture of two isomers in solution (M, major isomer,
and m, minor isomer). M:m = 1.5:1.
5.5.4.1. Major isomer, CH3 trans to PPh2. 1H NMR
(500 MHz, CDCl3, 25 ꢁC):
d 0.45 (dd, 3H, CH3,
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d ꢀ1.0 (d,
3JH–P(trans) = 6.90 Hz; JH–P(cis) = 2.30 Hz), 2.14 (br, 3H,
CH3CN, overl. with isomer m), 3.75 (br, 2H, CH2P-
(4-OCH3C6H4)2), 3.84 (br, 2H, CH2PPh2), 3.89 (s, 6H,
OCH3), 6.13 (m, 1H, C6H4, Ha syn to P(4-OCH3C6H4)2),
6.52 (m, 1H, C6H4, Hd syn to PPh2), 6.86–6.91 (m, 1H,
C6H4, Hc), 6.92–6.99 (m, 1H, C6H4, Hb), 7.01–7.10 (m,
4H, 4-OCH3C6H4, overl. with isomer m), 7.48–7.62 (m,
4H, 4-OCH3C6H4, overl. with isomer m), 7.55–7.62 (m,
8H, Ph, overl. with isomer m), 7.65–7.71 (m, 2H, Ph, overl.
with isomer m).
3
2
2
PPh2; JP–P = 35.7 Hz), 39.5 (d, PCy2; JP–P = 35.7 Hz).
19F NMR (188 MHz, CDCl3, 25 ꢁC): d ꢀ78.7 (free
triflate).
Anal. Calc. for C36H46NO3F3P2SPd (798.20): C, 54.17;
H, 5.81. Found: C, 54.68; H, 6.02.
5.5.3. Synthesis of [PdCH3(1b)(CH3CN)](OTf) (3b)
Yield: 88%, light-brown powder. The compound exists
as a mixture of two isomers in solution (M, major isomer,
and m, minor isomer). M:m = 1.8:1.
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 1.0 (d, PPh2;
2JP–P = 39.3 Hz), 31.0 (d, P(4-OCH3C6H4)2; JP–P
=
2
5.5.3.1. Major isomer, CH3 trans to P(3-CF3C6H4)2. 1H
NMR (500 MHz, CDCl3, 25 ꢁC): d 0.72 (dd, 3H, CH3,
39.3 Hz).
19F NMR (188 MHz, CDCl3, 25 ꢁC): d ꢀ78.7 (free
3
3JH–P(trans) = 7.80 Hz; JH–P(cis) = 4.00 Hz), 1.90–2.10 (br,
triflate).
3H, CH3CN, overl. with isomer m), 4.07 (br, 2H,
CH2PPh2), 4.12 (br, 2H, CH2P(3-CF3C6H4)2), 6.08 (m,
1H, C6H4, Hd syn to P(3-CF3C6H4)2), 6.23 (m, 1H, C6H4,
Ha syn to PPh2), 6.75–6.83 (m, 2H, C6H4, Hb and Hc),
7.53–7.68 (m, 6H, Ph, overl. with isomer m), 7.69–7.82
(m, 4H, Ph, overl. with isomer m), 7.73 (m, 2H, 3-
CF3C6H4), 7.83–7.84 (m, 4H, 3-CF3C6H4, overl. with iso-
mer m), 8.03–8.11 (br, 2H, 3-CF3C6H4, overl. with isomer
m).
5.5.4.2.
Minor
isomer,
CH3
trans
to
P(4-
OCH3C6H4)2. 1H NMR (500 MHz, CDCl3, 25 ꢁC): d
3
3
0.41 (dd, 3H, CH3, JH–P(trans) = 6.90 Hz; JH–P(cis)
=
2.30 Hz), 2.15 (br, 3H, CH3CN, overl. with isomer M),
3.77 (br, 2H, CH2P(4-OCH3C6H4)2), 3.82 (br, 2H,
CH2PPh2), 3.88 (s, 6H, OCH3), 6.04 (m, 1H, C6H4, Hd
syn to PPh2), 6.48 (m, 1H, C6H4, Ha syn to P(4-OCH3-

A. Leone et al. / Journal of Organometallic Chemistry 691 (2006) 4816–4828
4827
C6H4)2), 6.79-6.84 (m, 1H, C6H4, Hb), 6.92–6.99 (m, 1H,
C6H4, Hc), 7.01–7.10 (m, 4H, 4-OCH3C6H4, overl. with
isomer M), 7.48–7.62 (m, 4H, 4-OCH3C6H4, overl. with
isomer M), 7.55–7.62 (m, 8H, Ph, overl. with isomer M),
7.65–7.71 (m, 2H, Ph, overl. with isomer M).
Anal. Calc. for C40H36NO5F9P2SPd (982.17): C, 48.92;
H, 3.69. Found: C, 49.10; H, 3.88.
5.6. Carbonylation of the neutral complexes 2a–d
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d ꢀ1.0 (d,
CO was bubbled (ca. 40 ml/min) through a metallic nee-
dle into a solution of 20–25 mg of the complex in 5 ml of
CDCl3 for ca. 40 min. The sample was then introduced into
the probe and the first spectrum acquired after 5 min.
2
2
P(4-OCH3C6H4)2; JP–P = 40.7 Hz), 33.7 (d, PPh2; JP–P
=
40.7 Hz).
19F NMR (188 MHz, CDCl3, 25 ꢁC): d ꢀ78.7 (free
triflate).
5.7. Carbonylation of the cationic complexes 3a–d
Anal. Calc. for C38H38NO5F3P2SPd (846.15): C, 53.94;
H, 4.53. Found: C, 54.50; H, 4.95.
The complex (20–25 mg) was dissolved in 0.5 ml of
CDCl3 and the solution cooled down to ꢀ60 ꢁC. CO was
bubbled for 5–10 min through a metallic needle. The sam-
ple was then introduced into the precooled (ꢀ60 ꢁC) probe
and the first spectrum recorded after 5 min.
5.5.5. Synthesis of [PdCH3(1d)(CH3CN)](OTf) (3d)
Yield: 81%, light-brown powder. The compound exists
as a mixture of two isomers in solution (M, major isomer,
and m, minor isomer). M:m = 2.5:1.
5.5.5.1. Major isomer, CH3 trans to P(3-CF3C6H4)2. 1H
NMR (500 MHz, CDCl3, 25 ꢁC): d 0.61 (dd, 3H, CH3,
Acknowledgement
3
3JH–P(trans) = 7.10 Hz; JH–P(cis) = 2.30 Hz), 2.13-2.25 (br,
The authors thank Dr. Heinz Ruegger (Laboratory for
Inorganic Chemistry, ETH Zurich) for the support in the
¨
NMR measurements and for a lot of helpful discussions.
¨
3H, CH3CN, overl. with isomer m), 3.90 (s, 6H, OCH3,
overl. with CH2P(4-OCH3C6H4)2 of isomer m), 3.91 (br,
2H, CH2P(4-OCH3C6H4)2), 4.03 (br, 2H, CH2P(3-CF3-
C6H4)2, overl. with isomer m), 6.16 (m, 1H, C6H4, Ha syn
to P(4-OCH3C6H4)2), 6.27 (m, 1H, C6H4, Hd syn to
P(3-CF3C6H4)2), 6.81–6.88 (m, 2H, C6H4, Hb and Hc,
overl. with isomer m), 7.02–7.10 (m, 4H, 4-OCH3C6H4,
overl. with isomer m), 7.62–7.69 (m, 4H, 4-OCH3C6H4,
overl. with isomer m), 7.69–7.74 (m, 2H, 3-CF3C6H4),
7.78–7.86 (m, 4H, 3-CF3C6H4, overl. with isomer m),
7.96–8.00 (br, 2H, 3-CF3C6H4, overl. with isomer m).
31P{1H} NMR (202 MHz, CDCl3, 25 ꢁC): d 2.9 (d, P(3-
Appendix A. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC Nos. 281609 (2d) and 281610 ([Pd(1a)Cl]2-
(OTf)2). These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, by e-mailing to
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033. Supple-
mentary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2006.06.038.
2
CF3C6H4)2; JP–P = 40.6 Hz), 30.5 (d, P(4-OCH3C6H4)2;
2JP–P = 40.6 Hz).
19F NMR (188 MHz, CDCl3, 25 ꢁC): d ꢀ78.7 (free tri-
flate), 62.5 (s, CF3).
5.5.5.2. Minor isomer, CH3 trans to P(3-CF3C6H4)2. 1H
NMR (500 MHz, CDCl3, 25 ꢁC): d 0.47 (dd, 3H, CH3,
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