Olefin insertion in Pd-acyl complexes modified with 1,4-Cs-symmetrical diphosphine ligands

Article abstract of DOI:10.1016/j.jorganchem.2006.06.029

The insertion of ethene and propene was investigated in palladium(II) acyl complexes of the type [PdC(O)CH₃(P^∧P′)(CH₃CN)](OTf) modified with the C_s-symmetric diphosphines 2-4 and the parent ligand 1, described by C_2v-symmetry and taken as a reference. Ethene insertion was investigated for acyl complexes containing the ligands 2 and 3. Two insertion products formed in a ratio of approximately 1:1 for both systems, irrespective of the electronic properties of the ligands. Propene as an α-olefin can insert according to a 1,2- or 2,1-insertion mode into a palladium acyl bond, arising regioselectivity issues. Moreover, due to the C_s-symmetry of the ligands, two stereoisomers can result upon insertion, as the alkyl group of the formed five-membered metallacycle can be cis or trans to each non-equivalent moiety. Propene insertion was indeed neither stereo- nor regioselective in the cases of 3 and 4, in which the products arising from both 1,2- and 2,1-insertion were observed. 2 displayed total control of stereo- and regioselectivity, with the formation of one primary insertion product. Similar regioselectivity was observed for the reference ligand 1. The regioisomeric distribution was different from equimolar for propene insertion, where the ratio of the products might be controlled by a combination of steric and electronic factors.

Full text of DOI:10.1016/j.jorganchem.2006.06.029

Journal of Organometallic Chemistry 691 (2006) 4204–4214
www.elsevier.com/locate/jorganchem
Olefin insertion in Pd-acyl complexes modified with
1,4-Cs-symmetrical diphosphine ligands
*
Antonella Leone, Giambattista Consiglio
Eidgeno¨ssische Technische Hochschule, Institut fu¨r Chemie und Bioingenieurwissenschaften, Ho¨nggerberg, Wolfgang-Pauli Strasse 10,
CH-8093 Zu¨rich, Switzerland
Received 25 April 2006; received in revised form 27 May 2006; accepted 21 June 2006
Available online 30 June 2006
Abstract
The insertion of ethene and propene was investigated in palladium(II) acyl complexes of the type [PdC(O)CH3(PÙP0)(CH3CN)](OTf)
modified with the Cs-symmetric diphosphines 2–4 and the parent ligand 1, described by C2v-symmetry and taken as a reference.
Ethene insertion was investigated for acyl complexes containing the ligands 2 and 3. Two insertion products formed in a ratio of
approximately 1:1 for both systems, irrespective of the electronic properties of the ligands.
Propene as an a-olefin can insert according to a 1,2- or 2,1-insertion mode into a palladium acyl bond, arising regioselectivity issues.
Moreover, due to the Cs-symmetry of the ligands, two stereoisomers can result upon insertion, as the alkyl group of the formed five-
membered metallacycle can be cis or trans to each non-equivalent moiety. Propene insertion was indeed neither stereo- nor regioselective
in the cases of 3 and 4, in which the products arising from both 1,2- and 2,1-insertion were observed. 2 displayed total control of stereo-
and regioselectivity, with the formation of one primary insertion product. Similar regioselectivity was observed for the reference ligand 1.
The regioisomeric distribution was different from equimolar for propene insertion, where the ratio of the products might be controlled by
a combination of steric and electronic factors.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Ethene insertion; Propene insertion; 1,4-Cs-symmetrical diphosphines; Pd-acyl complexes; Regioisomeric distribution
1. Introduction
tion in the acyl complex [Pd13C(O)CH3(R,S)-BINA-
PHOS(CD3CN)]BAr4 (Ar = 3,5-(CF3)2C6H3), which exists
as a single stereoisomer with the acyl group trans to the
phosphine moiety, produced a mixture of two diastereoiso-
mers, in ratio 4:1 (where the major compound had the alkyl
group trans to the phosphine). The study reported by
Nozaki shows how non-symmetrical ligands bring about
issues of stereoselectivity upon insertion reaction in model
complexes. The stereo- and regiocontrol achieved by (R,S)-
BINAPHOS in the CO-propene copolymerization was
almost complete. Copolymerization experiments of CO
and propene with diphosphine ligands containing non-
equivalent ligating moieties showed a high degree of con-
trol as well, even in the presence of remarkable electronic
difference between the two dentates [43]. This NMR study
is an attempt to rationalize the high regio- and stereocon-
trol achieved in the copolymerization.
Olefin insertion into acyl palladium complexes is a fun-
damental step of the copolymerization of olefins and car-
bon monoxide [1–3]. The reaction has been investigated
independently [4–24] and in relation to the CO migratory
insertion [25–41]. Few reports have been published dealing
with propene insertion in acyl complexes modified with
non-symmetrical ligands [21,42], in particular with relation
to the catalysis.
Nozaki et al. reported the investigation of stepwise car-
bon monoxide and propene insertion in a palladium model
complex modified with the non-symmetrical phosphine
phosphite (R,S)-BINAPHOS [42]. Labeled dodecene inser-
*
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 Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.029

A. Leone, G. Consiglio / Journal of Organometallic Chemistry 691 (2006) 4204–4214
4205
2. Results
CH3
CH3
2.1. Olefin insertion in acyl complexes
O
O
CH3
CH3
Olefin insertion into an acyl complex results in an alkyl
complex, in which the ketone oxygen coordinates to the
metal to form a five-membered ring [22,25,26]. In this
study, the acyl complexes [PdC(O)CH3(PÙP0)(CH3CN)]-
(OTf) (where PÙP0 = 1–4, Fig. 1) were generated in situ
by bubbling CO or 13CO through a metallic needle for 5–
10 min into a CDCl3 0.04 M solution of the cationic com-
plexes [PdCH3(PÙP0)(CH3CN)](OTf) at ꢀ60 °C. 25–28
equivalents of the olefin (ethene, propene) were then added
through a gastight syringe to the solution of the complex.
At ꢀ60 °C no insertion of the olefin was observed even
after several hours. Insertion occurred when the solution
was warmed up to ꢀ20 °C. The NMR spectra for the char-
acterization of the insertion products were recorded at this
temperature. The low temperature was necessary to avoid
the decomposition of the insertion product via b-H elimina-
tion [8].
From the point of view of regiochemistry the insertion
of an a-olefin such as propene into a palladium acyl bond
can occur either by primary (1,2) or secondary (2,1) mode.
Additionally, the formed alkyl group can be located trans
or cis to each moiety of the Cs-symmetric ligand, thus
forming two products for each insertion mode (Fig. 2)
[42]. The insertion modes of the olefin are competitive.
However, in most of the cases one mode was preferred to
the other. The identification of the isomers resulting from
the prevailing insertion mode was achieved through multi-
nuclear 1D and 2D NMR experiments. The isomers result-
ing from the less preferred insertion mode were generally
present in small amount and their resonances were often
overlapping those of the other pair of isomers. Their iden-
tification and partial characterization was possible only by
employing labeled 13CO.
Ar2'P Pd
Ar2P
Pd
PAr2
PAr'2
CH3
CH3
O
O
Ar2'P Pd
Ar2P Pd
PAr'2
CH
CH3
PAr2
Fig. 2. Possible products resulting from the primary and secondary
insertion of propene into the acyl complex [PdC(O)CH3(PÙP0)(CH3C-
N)](OTf). PÙP0: Cs-symmetrical diphosphine (Ar ¼ Ar0, 2–4).
Insertion of ethene in the species [PdC(O)CH3(2)(CH3C-
N)](OTf), which exists as a mixture of two isomers in a
ratio 2.6:1 [44], led to a mixture of two stereoisomers in
ratio ca. 1:1 (ratio of the acyl group signals in the 1H
NMR spectrum). The 31P{1H} NMR spectrum showed
two pairs of doublets. The signals of the methylene group
PdCH2 (Ha) appeared quite broadened and were observed
at 1.64–1.65 ppm, while the methylene group in the b posi-
tion with respect to the metal, CH2C(O) (Hb), gave a broad
singlet in the region 3.00–3.20 ppm. b-H elimination
seemed to be less relevant than in the case of the alkyl com-
plexes resulting from the propene insertion (see below). The
ratio of the stereoisomers was changed to approximately
equimolar when compared to the acyl precursors. The most
relevant NMR data are reported in Tables 1 and 2.
Ethene insertion was also studied for the system
[PdC(O)CH3(3)(CH3CN)](OTf). The complex was gener-
ated in situ by bubbling CO in a CDCl3 solution of the pal-
ladium methyl complex for ca. 5 min at ꢀ60 °C. The acyl
complex was formed as a mixture of isomers in ratio
1.8:1 [44]. In the major isomer M the acyl group occupies
the position trans to the PPh2 moiety, according to the
trans influence concept. Upon insertion of ethene the five-
membered ring, in which the ketone oxygen coordinates
to the metal, was formed. Two products were formed after
the ethene insertion in a ratio 1:1. Also in this case the
31P{1H} NMR spectrum showed two pairs of doublets.
The phosphorus signals resulted both shifted downfield
with respect to those measured for the acyl complex. The
shift observed for the Pcis to the alkyl group was in the
order of 14 ppm and was bigger than that observed for
the Ptrans (2–4 ppm). The peaks of the ring protons
appeared quite broad but distinctly at 253 K. The protons
of the PdCH2 group (Ha) were found in the range 1.20–
1.55 ppm, while those of the CH2C(O)CH3 (Hb) were
shifted downfield between ca. 3.10 and 3.50 ppm.
2.2. Insertion of ethene in [PdC(O)CH3-
(PÙP0)(CH3CN)](OTf) (PÙP0 = 2, 3)
Ethene insertion was studied for the acyl complexes of
the ligands 2 and 3. Regiochemical issues are not involved.
PPh2
PPh2
1
PAr2
2: Ar = C6H5
Ar' = 3-CF3C6H4
Ar' = C6H5
PAr2'
3: Ar = 4-CH3OC6H4
4: Ar = 4-CH3OC6H4
Ar' = 3-CF3C6H4
2- 4
In the region between 4.00 and 4.50 ppm the
1H–31P{1H} correlation spectrum showed the cross peaks
Fig. 1. Diphosphine ligands used.

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A. Leone, G. Consiglio / Journal of Organometallic Chemistry 691 (2006) 4204–4214
Table 1
1
Relevant H NMR data (d ppm, CDCl3; T = 298 K) for the ethene insertion products of [PdC(O)CH3(2)(CH3CN)](OTf)
Ethene insertion
PdCHa
(ppm)
d
PdCHa
(ppm)
d
CHbC(O) d
(ppm)
CHbC(O) d
(ppm)
C(O)CH3
(ppm)
d
Ratioa
M0:m0
M0, Pd–CH2 bond trans to P(3-CF3C6H4)2
m0, Pd–CH2 bond trans to PPh2
1.64
1.65
1.64
1.65
3.10
3.20
3.10
3.20
2.26
2.28
ca. 1:1
ca. 1:1
a
Ratio between the isomers calculated from the integration of the acyl groups in the 1H NMR spectrum.
Table 2
Relevant 31P{1H} NMR data (d ppm, CDCl3; T = 298 K) for the ethene insertion products of [PdC(O)CH3(2)(CH3CN)](OTf)
Ethene insertion
Ptrans d (ppm)
Pcis d (ppm)
2JP–P (Hz)
Ratioa M0: m0
M0, Pd–CH2 bond trans to P(3-CF3C6H4)2
m0, Pd–CH2 bond trans to PPh2
4.5
4.9
34.7
34.5
40.7
41.5
ca. 1:1
ca. 1:1
Pcis and Ptrans describe the phosphorus atom cis and trans to the alkyl group, respectively.
a
Ratio between the isomers calculated from the integration of the acyl groups in the 1H NMR spectrum.
between the phosphorus atoms and the benzylic methylene
groups of the ligand. The signals in the 1H NMR spectrum
were broad and overlapped, but the cross peaks were
observed distinctly. Tables 3 and 4 summarize the relevant
NMR data for the ethene insertion products of [PdC(O)-
CH3(3)(CH3CN)](OTf).
plex. In the 31P{1H} NMR (Fig. 3) one could recognize two
pairs of doublets corresponding to the primary insertion
products. Upon insertion of the olefin all the phosphorus
resonances underwent a shift downfield (i.e., from d 0.9
and 17.5 ppm for Ptrans and Pcis, respectively, in the major
isomer of [PdC(O)CH3(3)(CH3CN)](OTf) to 3.3 and 32.3
for Ptrans and Pcis, respectively, in MI); the shift was bigger
for the Pcis to the alkyl group than for the Ptrans. Part of the
acyl complex underwent decarbonylation, so that the alkyl
palladium complex could be still observed in spectrum
(indicated with D). The phosphorus resonances for the sec-
ondary insertion products were overlapped with those of
the primary insertion products.
2.3. Insertion of propene in [PdC(O)CH3(3)(CH3-
CN)](OTf)
Upon propene insertion in [PdC(O)CH3(3)(CH3C-
N)](OTf) four stereoisomers were formed, as one could
immediately see from the number of the acyl peaks in the
region 2.05–2.35 ppm. The four products formed in a ratio
MI:mI:MII:mII = 7:4.7:1:1 (overall ratio normalized to mII).
The main products resulted from a preferred primary inser-
tion of propene (MI and mI: major and minor isomers),
while the minor products MII and mII originated from
the secondary insertion. The assignment of the regiochem-
istry of the insertion was possible by combining the infor-
For the isomer MI the Ptrans to the alkyl group was
found at 3.3 ppm and the Pcis at 32.3 ppm, while for the
isomer mI Ptrans appeared at 0.9 ppm and Pcis at
34.9 ppm. The multiplicity of each phosphorus signal was
a doublet due to the coupling with the non-equivalent moi-
ety of the ligand. The 2JP–P for the isomer MI was 43.0 Hz,
while that for the isomer mI was 42.2 Hz. The phosphorus
signals for the secondary insertion products MII and mII
are probably overlapped with those of MI and mI (see
below).
1
1
mation afforded by H–31P correlation, H-TOCSY and
1H–13C correlation and by comparison with the data
obtained from the ethene insertion study into the acyl com-
Table 3
1
Relevant H NMR data (d ppm, CDCl3; T = 253 K) for the ethene insertion products of [PdC(O)CH3(3)(CH3CN)](OTf)
Ethene insertion
PdCHa
(ppm)
d
PdCHa
(ppm)
d
CHbC(O) d
(ppm)
CHbC(O) d
(ppm)
C(O)CH3
(ppm)
d
Ratioa
M0:m0
M0, Pd–CH2 bond trans to PPh2
m0, Pd–CH2 bond trans to P(4-CH3OC6H4)2
1.20
1.24
1.52
1.54
3.16
3.14
3.50
3.40
2.30
2.28
ca. 1:1
ca. 1:1
a
Ratio between the isomers calculated from the integration of the acyl groups in the 1H NMR spectrum.
Table 4
Relevant 31P NMR data (d ppm, CDCl3; T = 253 K) for the ethene insertion products of [PdC(O)CH3(3)(CH3CN)](OTf)
Ethene insertion
Ptrans d (ppm)
Pcis d (ppm)
2JP–P (Hz)
Ratioa M0:m0
M0, Pd–CH2 bond trans to PPh2
m0, Pd–CH2 bond trans to P(4-CH3OC6H4)2
0.9
3.2
34.6
32.0
41.5
43.0
ca. 1:1
ca. 1:1
Pcis and Ptrans describe the phosphorus atom cis and trans to the alkyl group, respectively.
a
Ratio between the isomers calculated from the integration of the acyl groups in the 1H NMR spectrum.

A. Leone, G. Consiglio / Journal of Organometallic Chemistry 691 (2006) 4204–4214
4207
Fig. 3. Detail of the 31P{1H} NMR spectrum (d ppm, CDCl3; T = 253 K) for the propene insertion products of [PdC(O)CH3(3)(CH3CN)](OTf). The alkyl
palladium complex, resulting from the decarbonylation of the in situ formed acyl complex [PdC(O)CH3(3)(CH3CN)](OTf), can be recognized (peaks
indicated with D = decarbonylation products). U = unidentified products.
The main pair of stereoisomers was characterized by
means of 1H–31P correlation spectroscopy. Three cross
peaks at about d 1.30, 1.60 and 3.00 ppm are detected.
The broad signals at ca. 1.30 and 1.60 ppm (the latter over-
lapped with the –CH3 residual peak of the non-inserted
propene) were assigned to methylene diastereotopic pro-
tons directly bound to the metal, CH2Pd (Ha), while that
at ca. 3.00 ppm described the methine group CHCH3
(Hb). For the same insertion mode, e.g., 1,2-insertion, the
protons of the two stereoisomers MI and mI appeared over-
the most straightforward way to identify the two pairs of
regioisomers. In the H NMR (Fig. 4) the methyl of the
1
acyl groups appeared now as doublets for the coupling of
2
the protons with the 13C of the labeled 13CO. The JH–C
ranged between 5.78 and 6.07 Hz.
The 1H–13C correlation displayed four different peaks in
the carbonyl region (238–241 ppm), corresponding to the
ketone groups of the formed stereoisomers. Each carbonyl
group appeared as a doublet for the coupling with the
phosphorus atom in position trans to the ketone group.
The primary insertion products MI and mI gave two dou-
blets at d 238.4 and 238.6 ppm, respectively, while the sec-
ondary insertion products MII and mII were found at 240.0
1
lapped in the H NMR spectrum. From the cross peaks in
the 1H–31P correlation spectrum the major stereoisomer
resulting from the primary insertion of propene into the
acyl complex (MI) was identified. In MI the alkyl group
occupied the position trans to PPh2, as in the major isomer
of the acyl complex [PdC(O)CH3(3)(CH3CN)](OTf). From
3
and 240.2 ppm. The JC–P was in all the cases 8.0 Hz. The
1H–13C correlation (Fig. 5) showed the cross peak of the
methyne group PdCHCH3 (Ha) for MII and mII with the
carbonyl carbon at ca. 1.15 ppm (almost overlapped with
the methyl groups of the four isomers) and confirmed the
assignments of the alkyl protons that had been already
1
the H–31P correlation spectrum the identification of the
secondary insertion products MII and mII was not straight-
forward. On one hand the 31P{1H} NMR signals of MII
and mII were overlapped to those of the primary insertion
products, as MII and mII were present in small concentra-
tion in the system. On the other hand the chemical shifts
of their alkyl protons were slightly different from those of
1
observed from the H-TOCSY experiment.
Tables 5 and 6 summarize the most relevant NMR
parameters for the primary and secondary insertion prod-
ucts of [PdC(O)CH3(3)(CH3CN)](OTf). Table 7 reports
the important NMR parameters acquired through experi-
ments with labeled 13CO.
1
MI and mI. H-TOCSY correlation spectroscopy allowed
the identification of the two diastereotopic protons
CH2C(O)CH3 (Hb). One appeared as a multiplet at ca.
2.51 ppm, while the other overlapped with the signals of
the methine groups of MI and mI at ca. 3.00 ppm. All the
signals describing the alkyl groups of the five-membered
ring appeared quite broadened. Methylene and methyne
protons showed a cross peak with the methyl groups of
the diastereoisomeric complexes, which were found as
overlapped doublets in the region 1.04–1.16 ppm for the
four species.
The same kind of study was carried out for the acyl
complexes [PdC(O)CH3(PÙP0)(CH3CN)](OTf) (where
PÙP0 = 1, 2 and 4). In the case of 1, the parent C2v-symmet-
rical ligand, the acyl complex [PdC(O)CH3(1)(CH3C-
N)](OTf) exists as a single isomer. The 1H NMR
spectrum showed the acyl group as a broad singlet at d
1
2.22 ppm. From the H-TOCSY experiment of the inser-
tion product cross peaks at d 1.34, 1.58 and 3.04 ppm were
observed. From the comparison with the results obtained
for 3, the species formed corresponded to a primary inser-
tion product of the olefin. No secondary insertion product
was detected. The 31P{1H} NMR showed two doublets at d
3.15 and at 35.2 ppm, corresponding to Ptrans, and Pcis to
In a separate experiment the acyl complex was generated
from [PdCH3(3)(CH3CN)](OTf) by bubbling 13CO and was
subsequently treated with propene according to the
described procedure. This kind of experiment provided

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Fig. 4. Detail of the acyl groups region in the 1H NMR spectrum (d ppm, CDCl3; T = 253 K) for the propene insertion products of
[Pd13C(O)CH3(3)(CH3CN)](OTf) (MI: major isomer for primary insertion, MII: major isomer for secondary insertion). Free acetonitrile (indicated as
S, solvent molecule) is observed as a broad peak at ca. 2.16 ppm. The ratio MI:mI:MII:mII was obtained by deconvolution of the acyl group peaks.
ppm
237
238
239
240
241
242
3.0
2.5
2.0
1.5
1.0
0.5
0.0
ppm
1
Fig. 5. Detail of the H–13C correlation experiment (d ppm, CDCl3; T = 253 K) of the propene insertion products of [Pd13C(O)CH3(3)(CH3CN)](OTf).
The acyl carbonyl groups are visible as doublets in the 13C NMR spectrum.

A. Leone, G. Consiglio / Journal of Organometallic Chemistry 691 (2006) 4204–4214
4209
Table 5
1
Relevant H NMR parameters (d ppm, CDCl3; T = 253 K) of the 1,2- and 2,1-propene insertion products of [PdC(O)CH3(3)(CH3CN)](OTf)
Primary insertion
PdCHa
(ppm)
d
d
PdCHa
(ppm)
d
CHbCH3
(ppm)
d
CHbCH3
(ppm)
d
d
C(O)CH3
(ppm)
d
Ratioa
MI:mI
MI, Pd–CH2 bond trans to PPh2
mI, Pd–CH2 bond trans to P(4-CH3OC6H4)2
1.64
1.62
1.36
1.32
3.04
3.14
1.09
1.11
2.19
2.22
1.5:1
1.5:1
Secondary insertion
PdCHa
(ppm)
CHb
d
CHb
d
CHaCH3
(ppm)
C(O)CH3
(ppm)
d
Ratiob
MII: mII
(ppm)
(ppm)
MII
mII
1.18
Overl.c ca. 1.20
ca. 3
Overl. ca. 3
ca. 2.5
Overl. ca. 2.5–2.6
ca. 1.15
Overl. ca. 1.15
2.30
2.10
1:1
1:1
The signals of the secondary insertion products were in some cases overlapped.
a
Ratio MI:mI normalized to the concentration of mI, calculated from deconvolution of the acyl groups in 1H NMR.
MII:mII normalized to the concentration of mII, calculated from deconvolution of the acyl groups in 1H NMR.
Overlapping between MII and mII.
b
c
Table 6
Relevant 31P{1H} NMR parameters (d ppm, CDCl3; T = 253 K) of the 1,2- and 2,1-propene insertion products of [PdC(O)CH3(3)(CH3CN)](OTf)
Primary insertion
Ptrans d (ppm)
Pcis d (ppm)
2JP–P (Hz)
Ratioa MI:mI
MI
mI
3.0
0.6
32.3
34.9
43.0
42.2
1.5:1
1.5:1
Secondary insertion
Ptrans d (ppm)
Pcis d (ppm)
2JP–P (Hz)
Ratiob MII:mII
MII
mII
Overl.c ca. 1.0
Overl. ca. 3.0
Overl. ca. 32.0
Overl. ca. 35.0
n.o.d
n.o.
1:1
1:1
The signals of the secondary insertion products were in some cases overlapped. Pcis and Ptrans describe the phosphorus atom cis and trans to the alkyl
group, respectively.
a
Ratio MI:mI normalized to the concentration of mI, calculated from deconvolution of the acyl groups in 1H NMR.
b
MII:mII normalized to the concentration of mII, calculated from deconvolution of the acyl groups in 1H NMR.
c
Overlapping between MII and mII.
Not observed.
d
Table 7
Relevant 1H and 13C NMR data (d ppm, CDCl3; T: 253 K) for the acyl groups of the primary (MI and mI) and secondary (MII and mII) propene insertion
products of [Pd13C(O)CH3(3)(CH3CN)](OTf)
3
Primary insertion
1H NMR13C(O)CH3
d (ppm)
2JH–C
13C NMR13 C(O)CH3
d (ppm)
JC–P
Ratioa
MI:mI
Overall ratio primary:
secondary insertionb
(Hz)
(Hz)
MI
mI
2.19, d
2.22, d
6.07
6.07
238.4, d
238.6, d
8.0
8.0
1.5:1
5.9:1
3
Secondary insertion
1H NMR13C(O)CH3
d (ppm)
2JH–C
13C NMR13 C(O)CH3
d (ppm)
JC–P
Ratioc
MII: mII
(Hz)
(Hz)
MII
mII
2.30, d
2.10, d
5.78
6.07
240.1, d
240.2, d
8.0
8.0
1:1
Multiplicity of the signals is reported.
a
The ratio MI:mI is normalized with respect to the amount of mI and calculated from the deconvolution of the acyl groups in the 1H NMR spectrum.
The overall ratio is normalized to the sum of the secondary insertion products MII + mII.
The ratio MII:mII is normalized with respect to the amount of mII and calculated from the deconvolution of the acyl groups in the 1H NMR spectrum.
b
c
2
the alkyl group, respectively. The coupling constant JP–P
d ca. 240.9 ppm corresponded to the secondary insertion
1
was 41.5 Hz. Table 8 reports the relevant NMR data for
this insertion study.
products (determined from H–13C correlation).
Deconvolution of the acyl peaks provided an estimation
Propene insertion in [Pd13C(O)CH3(4)(CH3CN)](OTf)
showed the formation of primary and secondary insertion
products. In the 1H NMR spectrum three acyl groups,
appearing as doublets for the coupling of protons with
13C, were identified in the region 2.20–2.35 ppm (Fig. 6).
From the 13C spectrum one primary insertion product
of the isomer distribution equal to MI:MII:mII ca. 8.9:1.4:1.
1
From the H–31P correlation spectrum the stereochemistry
of the primary insertion product MI was determined, corre-
sponding to the alkyl group trans to P(3-CF3C6H4)2. No
stereochemical information could be obtained for MII
and mII, as there were no cross peaks for these species.
The relevant 1H and 31P{1H} NMR are reported in Tables
9 and 10.
3
was identified (doublet at d 239.2 ppm, JC–P = 9 Hz, cou-
pling with the Ptrans to the alkyl group). The broad signal at

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A. Leone, G. Consiglio / Journal of Organometallic Chemistry 691 (2006) 4204–4214
Table 8
Relevant NMR data for the primary propene insertion product in [PdC(O)CH3(1)(CH3CN)](OTf) (d ppm, CDCl3; T = 253 K)
Primary insertion
1H NMR
PdCHa d (ppm)
1.34
PdCHa d (ppm)
1.58
CHbCH3 d (ppm)
3.04
CHbCH3 d (ppm)
C(O)CH3 d (ppm)
1.10
2.22
31P{1H} NMR
Ptrans d (ppm)
3.1
Pcis d (ppm)
35.2
2JP–P (Hz)
41.5
Pcis and Ptrans describe the phosphorus atom cis and trans to the alkyl group, respectively.
Fig. 6. Detail of the acyl groups region in the 1H NMR spectrum (d ppm, CDCl3; T = 253 K) for the propene insertion products of
[Pd13C(O)CH3(4)(CH3CN)](OTf) (MI: major isomer for primary insertion, MII: major isomer for secondary insertion). The acyl group for the species
mII appears as a shoulder at ca. 2.24 ppm. Free acetonitrile (indicated as S, solvent molecule) is observed as a broad peak at 2.06 ppm.
Table 9
1
Relevant H NMR parameters (d ppm, CDCl3; T = 253 K) of the 1,2- and 2,1-propene insertion products of [PdC(O)CH3(4)(CH3CN)](OTf)
Primary insertion
PdCHa
d
PdCHa
d
CHbCH3
d
CHbCH3
d
C(O)CH3
d
MI
(ppm)
(ppm)
(ppm)
(ppm)
(ppm)
MI, Pd–CH2 bond trans to P(3-CF3C6H4)2
1.71
1.41
3.00–3.11
1.06–1.15
2.21
1 isomer primary insertion
Secondary insertion
PdCHaCH3
(ppm)
d
CHb
(ppm)
d
CHb
(ppm)
d
CHaCH3
(ppm)
d
C(O)CH3
(ppm)
d
Ratioa
MII:mII
MII
mII
ca. 1.20–1.25
ca. 1.20–1.25
2.48–2.57
2.48–2.57
ca. 3.0
ca. 3.0
ca. 1.11
ca. 1.11
2.31
2.24
ca. 1.4:1
The signals of the secondary insertion products were in some cases overlapped.
a
The MII:mII was normalized to the concentration of mII, calculated from deconvolution of the acyl groups in the 1H NMR spectrum.
1
Propene insertion in [PdC(O)CH3(2)(CH3CN)](OTf)
afforded only one primary insertion product. The alkyl
group occupied the position trans to the P(3-CF3C6H4)2,
as in the case of the major isomer observed upon CO inser-
tion into the palladium-alkyl group. The presence of the
only primary insertion product was quite remarkable, as
secondary insertion always took place in the case of the
other Cs-symmetrical diphosphine ligands 3 and 4. Assign-
ments of the resonances were achieved by means of H-
TOCSY experiments. Tables 11–13 report the main
NMR data for the obtained insertion product.
3. Discussion
The insertion of ethene and propene in palladium(II)
acyl complexes modified with Cs-symmetrical diphosphine

A. Leone, G. Consiglio / Journal of Organometallic Chemistry 691 (2006) 4204–4214
4211
Table 10
Relevant 31P{1H} NMR parameters (d ppm, CDCl3; T = 253 K) of the 1,2- and 2,1-propene insertion products of [PdC(O)CH3(4)(CH3CN)](OTf)
Primary insertion
Ptrans d (ppm)
4.4
Pcis d (ppm)
32.4
2JP–P (Hz)
MI
MI, Pd–CH2 bond trans to P(3-CF3C6H4)2
41.5
1 isomer primary insertion
RatioaMII:mII
Secondary insertion
Ptrans d (ppm)
Pcis d (ppm)
2JP–P(Hz)
MII
mII
n.o.b
n.o.
n.o.
n.o.
n.o.
n.o.
ca. 1.4:1
The signals of the secondary insertion products were too broad to be observed. Pcis and Ptrans describe the phosphorus atom cis and trans to the alkyl
group, respectively.
a
The ratio MII:mII was normalized to the concentration of mII, calculated from deconvolution of the acyl groups in the 1H NMR spectrum.
Not observed.
b
Table 11
1
Relevant H NMR parameters (d ppm, CDCl3; T = 253 K) of the 1,2-propene insertion product of [PdC(O)CH3(2)(CH3CN)](OTf)
Primary insertion
PdCHa
PdCHa
CHbCH3
CHbCH3
C(O)CH3
MI
MI, Pd–CH2 bond trans to P(3-CF3C6H4)2
1.74
1.46
3.09
1.13
2.24
1 isomer observed
Table 12
Relevant 31P{1H} NMR parameters (d ppm, CDCl3; T = 253 K) of the 1,2-propene insertion product of [PdC(O)CH3(2)(CH3CN)](OTf)
Primary insertion
Ptrans d (ppm)
Pcis d (ppm)
2JP–P (Hz)
MI
MI, Pd–CH2 bond trans to P(3-CF3C6H4)2
4.7
35.1
41.5
1 isomer primary insertion
Pcis and Ptrans describe the phosphorus atom cis and trans to the alkyl group, respectively.
ligands did not display in general any selectivity, with the
exception of 2 in the case of propene insertion. Upon eth-
ene insertion the complexes containing 2 and 3 formed the
two possible stereoisomers in ratio 1:1, in contrast to
what observed with CO insertion into the corresponding
palladium-methyl complexes. 2 and 3 are quite different
under the electronic point of view. Having in common
the PPh2 moiety, 3 is more basic than 2. One can con-
clude that the electronic nature of the ligand is not play-
ing a relevant role for the stereoselectivity of the insertion,
when the case of ethene is considered. Remarkably, the
1:1 ratio between the insertion products M and m differs
from the initial stereoisomer distribution observed for the
acetyl palladium complexes of 2 and 3, which was 1.8:1
and 1.5:1, respectively [44]. This fact might indicate that
the isomeric composition of the complexes reflects their
relative thermodynamic stability. However, we have no
reliable thermodynamic and kinetic data on this aspect.
The trans influence of the methyl group in the palladium
methyl complexes and that of the alkyl group in the eth-
ene insertion products are similar. Therefore, other fac-
tors, such as the coordination of the ketone oxygen to
the metal center, should play a role in the stabilization
of these species.
[PdC(O)CH3(2)(CH3CN)](OTf) gave exclusively primary
insertion. 3 formed the four possible products upon inser-
tion. 4 afforded one primary insertion product, as well as
the two products derived from secondary insertion. The
relative ratio primary:secondary insertion for each acyl
complex was obtained by deconvolution of the peaks of
the acyl groups in the 1H NMR spectrum. For 3 the overall
ratio between primary and secondary insertion products
was 5.9:1, while for 4 was 3.7:1. 2 and 1 afforded efficient
regiocontrol as no 2,1-insertion products were observed.
Among the systems investigated, primary and secondary
insertion were more competitive in [PdC(O)CH3(4)-
(CH3CN)](OTf).
The stereochemical control for the propene insertion in
this kind of systems is reflected in the formation of one or
two isomers for each insertion mode. Each regioisomer
existed as a mixture of two different stereoisomers, where
the alkyl group was trans to each non-equivalent phospho-
rus moiety. 3 afforded two stereoisomers for each insertion
mode. The relative ratio MI:mI was 1.5:1, while the relative
ratio MII:mII was 1:1. For 4 one stereoisomer was identified
upon primary insertion, but the secondary insertion affor-
ded the two isomers MII and mII (MII:mII ca. 1.4:1).
Regarding the stereocontrol, 2 was the most efficient sys-
tem of the series, as only one product was found upon pri-
mary insertion of propene. The C2v-symmetry of 1 did not
give rise to any stereocontrol issue. Apart from the total
stereoselectivity of 2, the stereocontrol achieved for each
insertion mode was more efficient in 3, with one prevailing
product for each insertion mode. The results obtained can
be summarized as follows.
In addition to the stereochemical control, regiochemical
control must be taken into account in the case of propene
insertion. Primary and secondary insertions were competi-
tive, although the primary mode was prevailing in all the
cases investigated. The ligand 1, the only C2v-symmetrical
term of the series, inserted propene only according to a pri-
mary mode. Among the Cs-symmetrical terms, only

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A. Leone, G. Consiglio / Journal of Organometallic Chemistry 691 (2006) 4204–4214
Table 13
1H and 13C NMR data (d ppm, CDCl3; T: 253 K) for the acyl groups of the primary (MI and mI) and secondary (MII and mII) propene insertion products
of [Pd13C(O)CH3(PÙP0)(CH3CN)](OTf) (PÙP0 = 2, 4)
PP2
1H NMR13C(O)CH3
(ppm)
d
2JH–C
13C NMR 13C(O)CH3 d (ppm)
3JC–P (Hz)
Ratio MI:mI
Overall ratio primary:
secondary insertion
(Hz)
Primary insertion
MI
2.24, d
5.20
239.6, broad
n.o.a
Only MI observed
Ratio MI:mI
Only MI observed
PP4
1H NMR 13C(O)CH3 d (ppm)
2JH–C (Hz)
13C NMR 13C(O)CH3 d (ppm)
3JC–P (Hz)
Overall ratio primary:
secondary insertionb
Primary insertion
MI
2.21, d
5.20
239.2, d
9.0
Only MI observed
Ratioc MII:mII
3.7:1
1H NMR 13C(O)CH3 d (ppm)
2JH–C (Hz)
13C NMR 13C(O)CH3 d (ppm)
3JC–P (Hz)
Secondary insertion
MII
mII
2.31
2.24
5.78
6.35
240.9, broad
240.9, broad
n.o.
n.o.
ca. 1.4:1
ca. 1.4:1
Multiplicity of the signals is reported.
a
Not observed.
b
The overall ratio is normalized to the sum of the secondary insertion products MII + mII and calculated from the deconvolution of the acyl groups in
the 1H NMR spectrum.
c
The ratio MII:mII is normalized with respect to the amount of mII and calculated from the deconvolution of the acyl groups in the 1H NMR spectrum.
The basic system 3 inserted the olefin with a preference
toward primary over secondary insertion, but was less
efficient in the regiochemical control. 2 and 4, containing
the more acid moiety P(3-CF3C6H4)2, displayed a higher
selectivity for the primary insertion over the secondary.
Total regio- and stereocontrol was achieved with 2. 4 affor-
ded one primary insertion products and a mixture of the
two secondary insertion products in comparable amount
(MII:mII ca. 1.4:1).
As far as the complexes modified with Cs-symmetrical
ligands are concerned, the insertion products have different
stability and their distributions can be explained in terms
of trans influence control, as in the case of CO insertion
into metal-alkyl complexes [21]. 2 afforded one primary
insertion product with the alkyl group trans to the P(3-
CF3C6H4)2. The same stereochemical control was observed
for the only primary insertion product identified for 4.
Also in the case of 3 the main primary insertion product
MI presented the alkyl group trans to the more acidic moi-
ety PPh2.
Steric reasons may explain the prevalence of primary to
secondary insertion for all the systems investigated. In the
secondary insertion the methyl group of propene under-
goes stronger steric repulsion due to aryl substituents of
the phosphorus, while in the primary insertion it is
exposed to a less hindered environment. The overall prod-
uct distribution suggests that an isomerization pathway is
very likely for each insertion mode. The major isomer in
the palladium acyl complex presents the acyl group trans
to the more electron-withdrawing moiety of the ligand.
Upon propene insertion, the primary insertion product
MI presents the alkyl group trans to the more electron-
withdrawing moiety in the case of 2 and 4 (PdCH2 trans
to P(3-CF3C6H4)2), where only one stereoisomer is
formed, and in the case of 3 (PdCH2 trans to PPh2),
where two stereoisomers in ratio 1.5:1 are observed. For
3 and 4 the ratio between the secondary insertion
products is 1:1 and ca. 1.4:1, respectively. The ratios of
the isomers and the competition primary/secondary inser-
tion indicate a combination of electronic and steric effects
in the regio- and stereocontrol of propene insertion.
Conversely, the stereocontrol in ethene insertion appears
to be driven by steric factors, as the closely equimolar
distribution of the products is formed with the more
electron-rich ligand 3, as well as with the more elec-
tronic-withdrawing system 2.
Propene insertion into a palladium acyl complex modi-
fied with a phosphine-imine ligand has been recently
reported [21]. Upon treatment with propene, two products
were formed in ratio 1:1. Although not explicitly men-
tioned in the work reported, propene insertion into the pal-
ladium imine phosphine complex should lead to a good
stereochemical control, with the formation of only one
kind of stereoisomer (i.e., the product with the alkyl group
trans to the imine and cis to the phosphine), but displayed
no regiochemical control as the two modes were equally
accessible. The systems investigated in this work displayed
a higher degree of regiocontrol with the prevalence of pri-
mary over secondary insertion.
In comparison with propene insertion into Pd complexes
containing BINAPHOS, an efficient stereocontrol was
achieved, with the preferential location of the alkyl group
trans to the more electron-withdrawing moiety of the
ligand. Regiocontrol was sometimes not so high (case of
the ligands 3 and 4) with a maximum overall ratio primary:
secondary insertion of 3.7:1 (systems containing 4).
4. Conclusions
Insertion of ethene was investigated for the systems 2
and 3. Irrespective of the electronic character, the insertion
afforded the equimolar mixture of the two stereoisomers in

A. Leone, G. Consiglio / Journal of Organometallic Chemistry 691 (2006) 4204–4214
4213
both cases. This suggests that electronic factors are not so
crucial for the insertion of ethene in this kind of complexes.
Steric factors have been proposed to play the major role in
the reactivity toward olefins [45].
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.
Propene insertion into the stereoisomeric mixture of the
acyl complexes modified with Cs-symmetric diphosphine
ligands 2–4 and the parent ligand 1 were investigated. 1,
the reference compound, formed one primary insertion
product. Among the Cs-symmetric ligands investigated, 2
displayed the higher stereo- and regioselectivity. Upon pro-
pene insertion only one stereoisomer was formed, bearing
the alkyl group trans to the P(3-CF3C6H4)2 moiety, which
corresponded to a primary insertion product. In the case of
4, three products resulted from propene insertion. The
ratio between 1,2- and 2,1-insertion products was 3.7:1.
The species afforded by primary insertion bore the alkyl
group trans to the more acid moiety P(3-CF3C6H4)2. The
secondary insertion products were found in ratio ca.
1.4:1, but could not be completely characterized by
NMR. For 3 four products were formed. The primary
insertion and the secondary insertion products were
formed in an overall ratio of 5.9:1. The two primary inser-
tion products were formed in a ratio 1.5:1. The main ste-
reoisomer of the primary insertion products, MI, had the
alkyl group trans to the more acidic moiety PPh2 of the
ligand. The 2,1-insertion products, which were formed in
a ratio 1:1, could not be fully characterized by NMR.
The stereoisomeric distribution can be rationalized to some
extent by trans influence concept. The alkyl group with
high trans influence receives better thermodynamic stabil-
ization by locating trans to the less electron donating moi-
ety of the ligand, as already observed for the CO insertion
studies in the palladium-alkyl complexes [44].
NMR probe temperature was measured by means of a
thermocouple. Standard pulse sequences were employed
1
1
for 13C–1H, 31P–1H, H-TOCSY and H-NOESY correla-
tion studies. 1H-TOCSY spectra were recorded using a
1
0.2 s mixing time. H-NOESY spectra were recorded using
a 0.8 s mixing time.
5.2. Olefin insertion study
From a 20–25 mg of the complex [PdCH3(PÙP0)-
(CH3CN)](OTf) (PÙP = 1–4) in CDCl3, the acyl complex
was generated in situ by bubbling CO or 13CO for 5–
10 min at ꢀ60 °C. The temperature of the solution was
raised from ꢀ60 °C to ꢀ20 °C and 25–28 equivalents of
the olefin (ethene, propene) were introduced into the
NMR tube by means of a gastight syringe. The sample
was inserted into a precooled (ꢀ20 °C) NMR probe and
the spectra were acquired at that temperature. Attempts
to isolate the insertion products resulted in the decomposi-
tion of the adducts and formation of Pd(0). Deconvolution
of the NMR spectra was performed using the Bruker soft-
ware WINNMR.
Carbon monoxide (purity grade 4.7) was purchased
from Pan Gas. 13CO (13C, 99%) was purchased from
Cambridge Isotope Laboratories. Propene (purity grade
2.8) and ethene (purity grade 3.5) were purchased from
Linde.
The high regio- and stereocontrol observed in the copo-
lymerization experiments suggest that isomerization path-
ways may take place at some point of the catalytic cycle.
Contributions of the growing polymer chain may influence
and differentiate the stability of the intermediates, lowering
the energy of some defined reaction pathways. Only one
intermediate may then be effective in controlling the stereo-
and regioselectivity of the copolymerization.
Acknowledgement
We thank Dr. Heinz Ruegger (Laboratory of Inorganic
Chemistry, ETH Zurich) for the support in the NMR mea-
¨
surements and for a lot of helpful discussions.
¨
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