Protonation of palladium(II)-allyl and palladium(0)-olefin complexes containing 2-pyridyldiphenylphosphine

Article abstract of DOI:10.1016/j.jorganchem.2008.09.063

The pendant nitrogen atom of the Ph₂PPy ligand in the Pd(II)-allyl complexes [PdCl(η³-2-CH₃-C₃H₄)(Ph₂PPy)] (1) and [Pd(η³-2-CH₃-C₃H₄)(Ph₂

Full text of DOI:10.1016/j.jorganchem.2008.09.063

Journal of Organometallic Chemistry 694 (2009) 131–136
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Journal of Organometallic Chemistry
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Note
Protonation of palladium(II)-allyl and palladium(0)-olefin complexes containing
2-pyridyldiphenylphosphine
a
a
a
b
A. Scrivanti a, , M. Bertoldini , V. Beghetto , U. Matteoli , A. Venzo
*
a Dipartimento di Chimica, Università di Venezia, Calle Larga S. Marta 2137, 30123 Venezia, Italy
b I.S.T.M., CNR, Via Marzolo 1, 35131 Padova, Italy
a r t i c l e i n f o
a b s t r a c t
g
3-2-CH3-
Article history:
The pendant nitrogen atom of the Ph2PPy ligand in the Pd(II)-allyl complexes [PdCl(
C3H4)(Ph2PPy)] (1) and [Pd(
3-2-CH3-C3H4)(Ph2PPy)2]BF4 (3) has been protonated with methanesulfonic
acid to afford the corresponding pyridinium salts [PdCl(
3-2-CH3-C3H4)(Ph2PPyH)](CH3SO3) (1a) and
Received 17 June 2008
Received in revised form 12 September
2008
Accepted 30 September 2008
Available online 8 October 2008
g
g
[Pd(g
3-2-CH3-C3H4)(Ph2PPyH)2](CH3SO3)2(BF4) (3a).
Protonation strongly influences the 1H and 13C NMR spectral parameters of the allyl moieties of 1a and
3a whose signals resonate at lower fields with respect to the parent species indicating that upon proton-
ation Ph2PPy becomes a weaker
becomes dynamic in 1a, the observed syn–syn and anti–anti exchange being due to deligation of the pro-
tonated phosphine from the metal centre. Treatment of complex 3 with diethylamine in the presence of
r-donor and a stronger P-acceptor. The allyl moiety, which in 1 is static,
Keywords:
Palladium
Palladium allyl complexes
Palladium olefin complexes
2-Pyridyldiphenylphosphine
Protonation
fumaronitrile gives the new Pd(0)-olefin complex [Pd(
characterized by elemental analysis and NMR spectroscopy. Low temperature protonation of 4 with
g
2-fumaronitrile)(PPh2Py)2] (4) which has been
methanesulfonic acid leads to the bis-protonated species [Pd(g
2-fumaronitrile)(Ph2PPyH)2](CH3SO3)2
(4a) which is stable only at temperatures <0 °C.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
R
R
CO, XH
R
+
Pd cat.
XOC
linear
COX
branched
The transition-metal catalyzed carbonylation of alkynes is an
important synthetic tool in the synthesis of intermediates and fine
chemicals [1–3]. Among the catalysts which promote the reaction,
the system formed by Pd(OAc)2 in combination with 2-pyridyldi-
phenylphosphine (Ph2PPy) and methanesulfonic acid is of particu-
lar interest since it provides very high activities accompanied by
almost complete chemoselectivity (no saturated product arising
from double carbonylation is formed) and regioselectivity (the
branched to linear isomer ratio is about 200:1) (Scheme 1) [4].
Even if it has been firmly established that the use of Ph2PPy as
the ligand in combination with a strong protic acid as the promoter
is essential to achieve high reaction rates [2,4], the mechanism of
the reaction and the reasons for the excellent selectivity are still
unclear, in particular as far as the role of the ligand and the acid
is concerned [5,6].
Pd cat. : Pd(OAc)2/Ph2PPy/CH3SO3H
R = alkyl, aryl
X = OH, OR', NR'2 ; branched:linear ~ 200:1
Scheme 1. Synthetic utility of the alkyne carbonylation.
ium into the coordination sphere of the metal [4,5]. The impor-
tance of bifunctional organometallic catalysts containing basic
sites in proton transfer processes has been recently reviewed
by Grotjahn [7].
The chemistry of Ph2PPy has been the subject of a large number
of investigations [8,9]. Faraone and co-workers have shown that
the pyridyl nitrogen atom of a P-bonded Ph2PPy can be protonated
by HPF6 [10]. However, to the best of our knowledge, there are no
studies dealing with the effects brought about by protonation on
the coordination ability of Ph2PPy.
It has been suggested that the very high reaction rate ob-
served using Ph2PPy is to attribute to the double role that this
ligand might play in catalysis, in fact: (i) since it is a P donor li-
gand it contributes to stabilize the catalytically active species,
and (ii) it provides a pendant nitrogen atom which could assist
the transport of the protons from the core of the reaction med-
Prompted by our interest in the use of this catalytic system in
fine chemistry [11] and in the mechanism of the reaction [5], we
have investigated the NMR behavior of some palladium allyl com-
plexes containing Ph2PPy in the presence of methanesulfonic acid.
* Corresponding author. Tel.: +39 0412348903; fax: +39 0412348967.
E-mail address: scrivanti@unive.it (A. Scrivanti).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.09.063

132
A. Scrivanti et al. / Journal of Organometallic Chemistry 694 (2009) 131–136
We were confident that the allyl moiety could withstand the pres-
ence of a strong protic acid [12] and behave as a reporter ligand
able to highlight the modifications caused by protonation on the
electronic properties of the phosphine and the metal centre. For in-
stance, it is well-know that the dynamic behavior of Pd-allyl com-
plexes is strongly affected by the electronic and steric properties of
the ancillary ligands [12,13]. In this connection, it is worth of note
that the reports dealing with palladium allyl complexes containing
Ph2PPy are rare [6a,9,14,15]. We employed palladium allyl com-
plexes in our investigations also because they are convenient start-
ing compounds for the synthesis of Pd(0)-alkene species via
reductive amination [6a,16–19]; accordingly we report herein de-
aromatic rings are AXX0 multiplets providing evidence that the li-
gands are firmly coordinated to palladium.
Other examples of palladium(0) complexes containing Ph2PPy
and alkenes or alkynes bearing electron-withdrawing substituents
have been previously reported by Edwards and co-workers [6a].
2.2. Protonation of 2-pyridyldiphenylphosphine
As preliminary investigation, we have fully assigned the 1H and
13C{1H} NMR spectra of the free phosphine by means of 2D NMR.
The data for the hydrogen and carbon atoms of the pyridyl moiety
are reported in Table 1 (the relevant numbering scheme is shown
in Fig. 1); the chemical shifts of 13C resonances of the phenyl rings
are reported in Section 4.
tails on the synthesis of the new Pd(0) complex [Pd(
rile)(Ph2PPy)2] and on its protonation.
g
2-fumaronit-
Addition of one equivalent of methanesulfonic acid to a dichlo-
romethane solution of 2-pyridyldiphenylphosphine followed by
dilution with diethyl ether affords the corresponding pyridinium
salt in almost quantitative yield. As observed for pyridine [22],
upon protonation the resonances of all the hydrogen atoms
belonging to the pyridyl moiety move to lower fields. The differ-
2. Results and discussion
2.1. Synthesis and characterization of the palladium complexes
The complexes 1 [10,14], 2 [15] and 3 [15] were prepared
according to the literature as outlined in Scheme 2. The hitherto
unreported Pd(0)-olefin complex 4 was obtained in good yield by
treating complex 3 with three equivalents of diethylamine in the
presence of fumaronitrile according to a well-know method for
the synthesis of zerovalent palladium olefin complexes [16,17].
Complex 4 was characterized by elemental analysis and multi-
nuclear NMR spectroscopy. As usual for this type of complexes in
the 1H NMR spectrum the protons of the coordinated fumaronitrile
appear as the AA0 part of an AA0XX0 multiplet centered at d 3.19
[17–19] which integrates in the correct ratio with the Ph2PPy pro-
tons (partially overlapping multiplets at d 7.1–7.5 and a doublet at
d 8.54). Owing to the chemical equivalence of the phosphorus
atoms of the ligands, the 31P{1H} NMR spectrum of 4 consists of
a singlet at d 27.6. In the 13C{1H} NMR spectrum the resonance of
the olefin carbons appears as the A part of a AXX0 spin system
(the X nuclei are the two phosphorus atoms of Ph2PPy) centered
at d 33.7 in keeping with the literature data for similar Pd(0)-
fumaronitrile complexes [20,21].
ences in the chemical shifts
in the order:
(see Table 1) in keeping with the behavior found for pyridine
[23]. In addition, it appears that also the resonances of the phenyl
D
d (
d(H-5Py) >
D
d = dprotonated ꢀ dunprotonated) are
D
d(H-4Py) ꢁ
D
D
d(H-6Py) > d(H-3Py)
D
ring protons are displaced to lower fields even if the single
Dd val-
ues were not evaluated. At room temperature in CD2Cl2 the N–H of
the pyridinium salt is a very broad featureless singlet centered at
ca. 14.0 d. On lowering the temperature at 195 K, the slow ex-
change temperature region is reached and the signal sharpens giv-
ing rise to an apparent triplet since JH-6Py–H-5Py ꢁ JH-6Py–NH
.
In the 13C{1H} NMR upon protonation the C-2Py and C-6Py res-
onances move to higher fields in contrast with the C-3Py, C-4Py
and C-5Py resonances which are shifted to lower fields similarly
to what found for pyridine [23]. Upon protonation also all the res-
onances of the carbon atoms belonging to the phenyl rings are
shifted to lower fields, the effect is in the order
(+3.2 ppm) ꢂ d(C3-Ph) (+0.9 ppm) ꢁ d(C4-Ph) (+0.7 ppm) >
d(C2-Ph) (+0.2 ppm). In the 31P{1H} NMR, addition of methane-
Dd(C1-Ph)
D
D
D
It is noteworthy that in the 13C{1H} NMR there are two well sep-
arate sets of resonances for the carbon atoms of the phenyl rings
according to the different spatial position they occupy with respect
to the Pd-fumaronitrile moiety. Furthermore, it is to point out that
the resonances of the ipso-, ortho- and meta- carbon atoms of the
sulfonic acid to 2-pyridyldiphenylphosphine displaces the reso-
nance of the phosphorus atom to higher fields (free ligand: d =
ꢀ3.5, protonated ligand: d = ꢀ6.5).
2.3. Protonation of complex 1
The protonations of complexes 1–4 were carried out in situ by
adding aliquots of methanesulfonic acid (up to an acid:phosphorus
molar ratio of 1:1) to NMR tubes containing 0.05–0.02 M solutions
of the palladium complexes in CD2Cl2.
Addition of one equivalent of acid to complex 1 leads to the cor-
responding pyridinium salt 1a. In fact, all the proton resonances of
the pyridyl moiety are shifted downfield in almost the same way as
in the protonation of the free ligand (see Table 1). The differences
Pd
Ph2P
N
N
AgBF4
- AgCl
2 BF4
1/2
Pd
PPh2
Cl
Pd
Ph2PyP
1
in the chemical shifts
D
d are in the order:
D
d(H-4Py) ꢁ
Dd(H-
5Py) > d(H-6Py) > d(H-3Py) in keeping with the behavior found
D
D
2
for pyridine and the free ligand.
In the 13C{1H} NMR spectrum, upon protonation the C-2Py and
C-6Py resonances are displaced to higher fields while the signals of
C-3Py, C-4Py and C-5Py move downfield (Table 1) again similarly
to that observed for pyridine and 2-pyridyldiphenylphosphine.
The allyl moiety, which in complex 1 is rigid, upon protonation
becomes dynamic [24], as indicated by the broad profiles of the rel-
evant proton resonances. On lowering the temperature, the allyl
resonances of 1a sharpen and a static spectrum is obtained at
253 K. 2D NMR experiments allow the definite assignment of the
low temperature spectrum as reported in Table 2 (for the number-
ing system see Fig. 1).
PPyPh2
CN
CN
NC
NC
BF4
PPyPh2
Pd
Pd
Et2NH
Ph2PyP
PPyPh2
Ph2PyP
3
4
Scheme 2. Synthesis of the palladium complexes used in protonation studies.

A. Scrivanti et al. / Journal of Organometallic Chemistry 694 (2009) 131–136
133
Table 1
Selected 1H and 13C NMR data for the protonation of complexes 1–4 and Ph2PPy.a
d(H-3Py) [
D
d]
d(H-4Py) [
D
d]
d(H-5Py) [
D
d]
d(H-6Py) [
D
d]
d(C-2Py) [
D
d]
d(C-3Py) [
D
d]
d(C-4Py) [
D
d]
d(C-5Py) [
D
d]
d(C-6Py) [Dd]
Ph2PPy
7.15
7.60
7.22
8.72
164.0
128.2
135.9
122.5b
150.5
Ph2PPyH+
7.27 [+0.12]
8.22 [+0.62]
7.82 [+0.60]
7.33
9.16 [+0.44]
8.76
160.1 [ꢀ3.9]
130.9 [+2.7]
144.5 [+8.6]
125.9 [+3.4]
145.0 [ꢀ5.5]
1
1a
3
3a
4
4a
7.4b
7.7b
157.7c
130.0c
135.9c
123.8c
150.2c
7.7b,d [ꢄ+0.3]
7.06
8.32d [ꢄ+0.6]
7.45
7.96d [+0.63]
7.20
9.24d [+0.48]
8.44
153.4c [ꢀ4.3]
156.9
131.4c [+1.4]
128.0
143.4c [+7.5]
136.6
127.0c [+3.2]
124.8
146.0c [ꢀ4.2]
150.6
7.6b [ꢄ+0.5]
8.17 [+0.72]
7.8b [ꢄ+0.6]
8.32 [ꢀ0.12]
152.3 [ꢀ4.6]
ꢄ129.8e [ꢄ+1.8]
142.6 [+6.0]
135.8
127.1 [+2.3]
123.5
147.4 [ꢀ3.2]
7.1b
7.5b
7.2b
8.54
159.7
ꢄ128.3e
150.4
7.5b,d [ꢄ+0.4]
8.11d [ꢄ+0.6]
7.67d [ꢄ+0.5]
8.61d [+0.07]
151.9f [ꢀ7.8]
129.9f [ꢄ+1.6]
145.3f [+9.5]
127.4f [+3.9]
145.5f [ꢀ4.9]
a
Spectra registered on CD2Cl2 solutions (0.01–0.04 M) at 298 K unless otherwise stated,
Resonance obscured by the phenyl protons and detected by COSY NMR.
Spectrum registered in CDCl3 at 298 K.
Spectrum registered in CD2Cl2 at 253 K.
Resonance obscured by phenyl carbons.
D
d = dprotonated ꢀ dunprotonated
.
b
c
d
e
f
Spectrum registered in CD2Cl2 at 233 K.
r
-donor ability of Ph2PPyH+ is
5Py
Most importantly, the reduced
4Py
3Py
6Py
C4
C2
decisive in determining the dynamic behavior of 1a observed at
room temperature. As a matter of fact, 1H NMR spin saturation
transfer experiments [26] show that the allyl dynamic is to be
attributed to a syn–syn, anti–anti exchange. The experiments were
carried out at 273 K since at this temperature the exchange is quite
slow and the 1H NMR spectrum displays four separate broad reso-
nances for the terminal allyl protons. Selective irradiation of the Ha
resonance at d 3.42 causes a strong decrease of the intensity of the
Hc signal at d 4.64 and the same behavior is observed for the Hb–Hd
proton pair. Such syn–syn and anti–anti exchange can be accounted
for by assuming reversible dissociation of the protonated ligand as
shown in Scheme 3.
Ha
Hc
N
C1
Hb
C3
Hd
2Py
P
1Ph
Pd
P
X
2Ph
4Ph
3Ph
Fig. 1. Numbering scheme for Ph2PPy and the allyl moiety.
By comparing the data of parent complex 1 and those of 1a it
appears that all the resonances of allyl protons move to lower
fields upon protonation indicating that -donor ability of 2-pyr-
r
idyldiphenylphosphine decreases upon protonation.
This hypothesis on the nature of the dynamic process is defini-
tively assessed by the results of two dimensional 31P–1H NMR cor-
relation experiments which definitely show that at room
temperature the protonated phosphine dissociates from the metal
centre.
It is worthy of note that the allyl protons on the carbon atom cis
to protonated Ph2PPy are more deshielded than the trans ones. A
similar effect has been previously described by Pörschke et al.
[25] who noticed that in a homologous series of [Pd(allyl)(PR3)X]
complexes on decreasing the donor ability of the X group, the allyl
resonances are displaced to lower fields the effect being larger for
the allyl protons in cis to the X group.
Hc
Ha
In the 13C{1H} NMR spectrum all the resonances of the allyl car-
bons of 1a appear deshielded with respect to the parent complex 1;
it is interesting to note that the effect is larger for the carbon atom
trans to the phosphine and the central carbon atom in contrast
with that found for the proton resonances.
Hc
Ha
Hb
Hd
Hb
Hd
Pd
Pd
PPh2
N
Cl
Ph2P
N
Cl
H
H
It should be noted that in complex 1a the N–H and the Pd–Cl
moieties are close together so that the existence of an intramolec-
ular N–Hꢃ ꢃ ꢃCl hydrogen bonding interaction cannot be ruled out;
½ [(η3-2-CH3-C3H4)PdCl]2
1a
1a
such interaction should decrease the
r-donor ability of the chlo-
+ Ph2PPyH+
ride and hence also affect to some extent the chemical shifts of
the allyl group.
Scheme 3. Dynamic behavior of complex 1a.
Table 2
NMR data for the allyl and the olefin moieties of complexes 1–4.a
Complex
d(CH3)
d]
d(Hb)
d]
d(Ha)
d]
d(Hd)
d]
d(CH)
d]
d(Hc)
d(C1)
d]
d(C2)
d]
d(C3)
d]
d(C4)
d]
d(=C)
[Dd]
[
D
[
D
[
D
[
D
[
D
[D
d]
[
D
[
D
[
D
[
D
1
1a
1.96
2.76
3.06
3.56
4.48
61.3b
62.3b
[+1.0]
76.9
80.6
[+3.7]
132.9b
134.6b
[+1.7]
138.2
140.0
[+1.8]
78.0b
79.6b
[+1.6]
76.9
80.6
[+3.7]
23.2b
23.2b
[0]
23.4
23.2
[ꢀ0.2]
2.03c
[+0.07]
1.89
3.08c
[+0.32]
3.21
3.43c
[+0.37]
3.82
3.70c
[+0.14]
3.21
4.62c
[+0.14]
3.82
3
3a
1.97
[+0.9]
3.90
[+0.69]
3.93
[+0.11]
3.90
[+0.69]
3.93
[+0.11]
4
4a
3.19
33.7
3.53c
[+0.34]
36.5d
[+2.8]
a
In CD2Cl2 at 298 K unless otherwise stated.
In CDCl3 at 298 K.
In CD2Cl2 at 253 K.
b
c
d
In CD2Cl2 at 233 K.

134
A. Scrivanti et al. / Journal of Organometallic Chemistry 694 (2009) 131–136
The 31P NMR spectrum of 1 consists of a singlet at d 26.0 [15]
which moves downfield to d 26.8 upon protonation; it is worth
noting that the d (+0.8, at 253 K) is much smaller and opposite
in sign to that observed in the protonation of the free ligand
d = ꢀ3.0).
central carbon resonance is a triplet at d 140.0 as found for the par-
ent complex 3 [15]. These data show that also the allyl carbon
atoms of 3a are significantly deshielded upon protonation. It is to
D
point out that the
Dd of the terminal carbons is much larger than
(D
that of the central carbon atoms (see Table 2) and that the overall
effect is larger than that observed in the protonation of complex 1.
The influence of the nature of the ligands on the 13C NMR spec-
tra of a series of symmetrically substituted complexes of formula-
2.4. Protonation of complex 2
The dinuclear complex 2 was treated with methanesulfonic acid
to ascertain whether addition of a proton could break the palla-
dium–nitrogen bond and open the ring structure, but no proton-
tion [Pd(g
3-2-CH3-C3H4)L2] + (L = Clꢀ, amine, phosphine or
L2 = 1,5-cyclooctadiene) has been studied by Åkermark [27] who
concluded that the resonances of the terminal carbon atoms un-
dergo significant downfield displacements when the L ligands have
ation is observed even if complex
2 is treated with two
equivalent of methanesulfonic acid at room temperature. More-
over, when 2 is treated with a large excess of acid (four equiva-
lents) decomposition to ill-defined products occurs within 24–
36 h.
P
-acceptor character; accordingly, the above results suggest that
upon protonation not only Ph2PPy becomes a weaker -donor,
but also increases its -acceptor ability.
r
P
No dynamic behavior was detected for 3a. Indeed, even if upon
protonation at room temperature the resonances of the two type
of allylic protons become very close, they retain their own profiles
so that a syn–anti exchange of the allyl hydrogen atoms can be ruled
out; moreover, in the 1H and 13C NMR spectra of 3a all the reso-
nances relevant to the allyl moiety couple with the phosphorus
atoms of Ph2PPyH+, ruling out dissociation of the protonated ligand.
2.5. Protonation of complex 3
In spite of its cationic nature, complex 3 promptly reacts with
two equivalents of methanesulfonic acid to give the protonated
derivative 3a (Scheme 4).
Protonation of both pyridyl moieties is supported by the obser-
vation that in the 1H and 31P{1H} NMR spectra of 3a, registered
over a wide temperature range (from +25 to ꢀ85 °C), the two li-
gands appear chemically equivalent.
As observed for the free phosphine and complex 1, upon pro-
tonation the resonances of protons H-3Py, H-4Py and H-5Py move
to lower fields and the difference in the chemical shifts are in the
2.6. Protonation of complex 4
Treatment of complex 4 with two equivalents of methanesulf-
onic acid at ꢀ70 °C leads to the formation of the protonated com-
plex 4a (Scheme 5).
As it will be discussed below, 4a is not stable under ambient
conditions and it has been characterized by 1H, 13C and 31P NMR
spectroscopy at low temperature. Protonation occurs on both pyr-
idyl moieties as inferred from the observation that in the NMR
spectra both ligands appear chemically equivalent. In the 1H
NMR spectrum of 4a all the pyridyl signals resonate at fields lower
order
D
d(H-4Py) ꢁ
D
d(H-5Py) >
D
d(H-3Py); quite surprisingly, in
d = ꢀ0.12 ppm)
3a the H-6Py resonance is displaced upfield (
D
(see Table 1). Although we have no rationale for this finding, we
tentatively attribute this odd behavior to solvent effects; indeed,
it should be pointed out that in the 13C{1H} NMR spectrum the
C-3Py, C-4Py and C-5Py resonances move to low fields and the C-
6Py and C-2Py signals shift to higher fields similarly to that found
for 1a and Ph2PPyH+. It is interesting to note that some of the aro-
matic carbon resonances (see Section 4) display strong second or-
der character being coupled with two chemically, but not
magnetically equivalent phosphorus atoms.
than in the non-protonated parent compound, the greatest
Dd val-
ues being observed for H-4Py and for H-5Py (see Table 1). In the
13C{1H} NMR spectrum (recorded at 233 K) the resonances of C-
3Py, C-4Py and C-5Py move to lower fields and at the same time
C-2Py, C-6Py are displaced to higher fields as found for Ph2PPy, 1
and 3 (see Table 1). Moreover, as for 4, two different sets of signals
are detected for the phenyl rings of coordinated Ph2PPyH+.
In keeping with the chemical equivalence of the two phospho-
rus atoms the 31P{1H} NMR spectrum of 3a consists of a singlet
The fumaronitrile protons of 4a appear as an AA0XX0 multiplet
centered at d 3.53, about 0.4 d downfield of the corresponding sig-
nal in 4, indicating a significant decrease of the electron density at
the metal centre. Reduction of the electron density at the metal
centre is confirmed by the shift to lower fields of the resonance
at d 26.6. It is noteworthy that the
Dd value (+0.2) is much smaller
than that observed for the protonation of 1 and opposite in sign to
that observed for the protonation of the free phosphine.
As far as the allyl moiety is concerned, upon protonation the
anti protons (an AA0XX0 multiplet) undergo a considerable dis-
placement to lower fields: from d 3.21 (complex 3) to d 3.90 (com-
of the olefin carbon atoms (AXX0 multiplet at 36.5 d,
see Table 2). Hence, these data further highlight the weak
D
d = +2.8,
-donor
r
plex 3a),
D
d = 0.69; the syn protons (singlet) also move to lower
ability of Ph2PPyH+and its improved
P-acceptor character.
field ( d = 0.12), so that in 3a the resonances of the syn and the anti
D
Finally, it is to mention that the 31P NMR of 4a consists of a sin-
glet at d 26.4, thus it appears that, at variance with that found for
protons almost coincide (Table 2).
In the 13C{1H} NMR spectrum the two terminal carbon atoms of
the allyl moiety are chemically but not magnetically equivalent
and give rise to an AA0X resonance centered at d 80.6, while the
complexes 1a and 3a, the signal moves to lower fields (
on protonation.
As anticipated, 4a is not thermally stable and slowly decom-
poses on standing at temperatures above 0 °C. The process is slow
D
d = ꢀ0.2)
CN
CN
NC
NC
Pd
Pd
Pd
Pd
PPh2
N
PPh2
N
Ph2P
N
Ph2P
N
PPh2
N
PPh2
N
Ph2P
Ph2P
H
H
H
2 CH3SO3H
H
2 CH3SO3H
N
N
3
3a
4
4a
Scheme 4. Protonation of complex 3.
Scheme 5. Protonation of complex 4.

A. Scrivanti et al. / Journal of Organometallic Chemistry 694 (2009) 131–136
135
even at room temperature and in the early stages consists of a
‘‘clean” deligation of the olefin from the metal centre which can
be monitored recording the growth of the singlet due to uncoordi-
nated fumaronitrile at d 6.35 in the 1H NMR spectrum. Experiments
aimed to highlight the fate of the metal fragment were unsuccess-
ful and in particular it should be mentioned that no evidence sup-
porting the formation of palladium-hydride species [21,28] was
found. On standing the solutions of 4a darken, thus, it is likely that
at the end the decomposition leads to colloidal palladium.
(d, C-6Py, JPC = 11.8 Hz), 136.8 (d, C-1Ph, JPC = 10.7 Hz), 135.9 (d,
C-4Py, JPC = 3.0 Hz), 134.5 (d, C-2Ph, JPC = 20.0 Hz), 129.3 (s, C-
4Ph), 128.8 (d, C-3Ph, JPC = 7.1 Hz), 128.2 (d, C-3Py, JPC = 18.6 Hz),
122.5 (s, C-5Py).
4.2. [Ph2PPyH](CH3SO3)
To a solution of 2-pyridyldiphenylphosphine in dichlorometh-
ane (150 mg, 0.57 mmol in 20 mL) were added 37 lL (55 mg,
The poor stability of 4a is likely to be attributed to the reduced
0.57 mmol) of CH3SO3H under stirring. Addition of diethylether af-
fords the pyridinium salt as a white microcrystalline powder
(194 mg, 95% yield). Anal. Calc. for C18H18NO3PS: C, 60.16; H,
5.05. Found: C, 60.2; H, 5.1%.
r
-donor ability of Ph2PPyH+ and its improved
P-acceptor
character: since
P-back-donation from the metal is a key factor
in determining the stability of the fumaronitrile–palladium bond
[17,19,29], it is conceivable that ligand protonation leads to a
significant decrease of the electron density at the metal centre so
that the back-donation from the metal to the olefin decreases
and the palladium–fumaronitrile interaction is substantially
weakened.
1H NMR (CD2Cl2, 298 K): d 2.50 (s, 3H, CH3SO3), 7.3–7.6 (m,
11H, phenyl and H-3Py), 7.82 (m, 1H, H-5Py), 8.22 (m, 1H, H-
4Py), 9.18 (d, 1H, H-6Py, JH-5Py–H-6Py = 5.9 Hz), 14.0 (very br s,
1H, NH). 1H NMR (CD2Cl2, 195 K): d 2.34 (s, 3H, CH3SO3), 7.27
(m, 1H, H-3Py), 7.3–7.6 (m, 10H, phenyl), 7.82 (m, 1H, H-5Py),
8.22 (m, 1H, H-4Py), 9.11 (apparent t, 1H, H-6Py, JH-5Py–H-6Py
ꢁ
3. Conclusions
JNH–H-6Py ꢁ 5 Hz), 17.05 (br d, 1H, NH, JNH–H-6Py ꢁ 5 Hz). 31P {1H}
NMR (CD2Cl2, 298 K): d ꢀ6.5 (s). 13C {1H} NMR (CD2Cl2, 298 K):
d 160.1 (d, C-2Py, JPC = 31.6 Hz), 145.0 (d, C-6Py, JPC = 3.6 Hz),
144.5 (s, C-4Py), 134.7 (d, C-2Ph, JPC = 21.4 Hz), 131.4 (d, C-1Ph,
This study shows that the palladium allyl moiety is quite robust
and able to withstand the treatment with strong protic acids such
as the methanesulfonic acid. Thus, complexes 1 and 3 containing
the P monodentate 2-pyridyldiphenylphosphine are smoothly pro-
tonated at the pendant nitrogen atom forming the corresponding
species containing the 2-(diphenylphosphino)pyridinium ion act-
ing as a P monodentate ligand; these complexes appear stable even
under ordinary atmosphere at room temperature. The effects
brought about by the protonation on the 1H and 13C NMR
resonances of the allyl moieties of both 1 and 3 indicate that the
JPC = 8.8 Hz), 131.0 (s, C-4Ph), 130.9 (d, C-3Py, JPC
129.7 (d, C-3Ph, JPC= 8.2 Hz), 125.9 (s, C-5Py), 39.3 (s, CH3SO3).
= 3.0 Hz),
4.3. [Pd(
g
3-2-CH3-C3H4)Cl(Ph2PPyH)](CH3SO3) (1a)
2.0
lL of CH3SO3H (2.9 mg, 0.03 mmol) were added to a CD2Cl2
solution of 1 (13.7 mg, 0.03 mmol) in CD2Cl2 (1 mL).
1H NMR (CD2Cl2, 253 K): d 2.03 (s, 3H, CH3), 2.51 (s, 3H,
CH3SO3), 3.08 (s, Hb anti), 3.43 (br s, Ha syn), 3.70 (d, Hd anti,
JHP = 10.2 Hz), 4.63 (m, Hc syn, JHP = 6.5 Hz), 7.5–7.7 (m, 11H, phe-
protonated phosphine is a poor
r-donor and an enhanced P-
acceptor. The scarce donor ability of the 2-(diphenylphos-
phino)pyridinium ligand is confirmed by the thermal unstability
of complex 4a. Finally, it should be remarked that the deligation
of fumaronitrile from the metal centre suggests a rationale for
the complete chemoselectivity observed in the catalytic alkyne
carbonylation: a second carbonylation does not occur probably be-
cause the formed acrylic acid derivative is unable to coordinate to
palladium.
nyl and H-3Py), 7.96 (m, 1H, H-5Py), 8.32 (m, 1H, H-4Py), 9.24
31
(m, H-6Py, JH-5Py–H-6Py = 3.3 Hz), 11.9 (br s, 1H, NH).
P{1H} NMR
(CD2Cl2, 253 K): d 26.8 (s). 13C NMR (CDCl3, 298 K): d 153.4 (d, C-
2Py, JCP = 33.5 Hz), 146.0 (d, C-6Py, JCP = 6.5 Hz), 143.4 (d, C-4Py,
JCP = 4.2 Hz), 134.6 (br d, C-2all, JCP = 3.0 Hz), 134.2 (d, C-2Ph,
JCP = 14.3 Hz), 131.9 (d, C-4Ph, JCP = 1.6 Hz), 131.4 (d, C-3Py,
JCP = 10.4 Hz), 129.4 (d, C-3Ph, JCP = 10.4 Hz), 128.0 (d, C-1Ph,
JCP = 41.7 Hz), 127.0 (s, C-5Py), 79.6 (br s, C-3all), 62.3 (br s, C-
1all), 39.1 (s, CH3SO3), 23.2 (s, C-4all).
4. Experimental
4.4. [Pd(
g
3-2-CH3-C3H4)(PPh2PyH)2](BF4)(CH3SO3)2 (3a)
1H, 13C{1H} and 31P{1H} NMR spectra were registered on a Bru-
ker Avance 300 spectrometer operating at 300.213, 75.44, and
100.015 MHz, respectively. 1H and 13C chemical shifts are re-
ported relative to TMS using solvent resonances as a secondary
reference. 31P chemical shifts are reported relative to external
85% H3PO4. All manipulations were performed under argon
atmosphere using standard Schlenk techniques. Solvents (Al-
drich) were purified according to standard literature methods
[30].
4.0
l
L of CH3SO3H (5.8 mg, 0.06 mmol) were added to a CD2Cl2
solution of 3 (23.3 mg, 0.03 mmol) in CD2Cl2 (1 mL).
1H NMR (CD2Cl2, 298 K): d 1.97 (s, 3H, CH3), 2.73 (6H, CH3SO3),
3.90 (m, 2H, Hb and Hd anti), 3.93 (br s, 2H, Ha and Hc syn), 7.3–7.7
(m, 26H, arom), 8.17 (t, 2H, H-4Py, JH-4Py–H-5Py ꢁ JH-4Py–H-
3Py = 7.7 Hz), 8.32 (d, 2H, H-6Py, JH-5Py–H-6Py = 4.4 Hz), 13.2 (br s,
2H, N-H). 31P{1H} NMR (CD2Cl2, 298 K): d 26.6 (s). 13C{1H} NMR
(CD2Cl2, 298 K): d 152.3 (AA0X0 m, 2C, C-2Py), 147.4 (AA0X m, 2C,
C-6Py), 142.6 (s, 2C, C-4Py), 140.0 (t, 1C, C-2all, JCP = 5.0 Hz),
134.4 (AA0X m, 8C, C-2Ph), 132.7 (s, 4C, C-4Ph), 129.9–129.7 (m,
10C, C-3Ph and C-3Py), 127.6 (AA0X m, 2C, C-1Ph), 127.1 (s, 2C,
C-5Py), 80.6 (AA0X m, 2C, C-1all and C-3all), 39.5 (s, 2C, CH3SO3),
23.2 (s, 1C, C-4all).
Fumaronitrile and methanesulfonic acid were high purity com-
mercial products (Aldrich) and were used as received. Commercial
Ph2PPy (Aldrich) was recrystallized from methanol. [Pd(
C3H4)Cl]2 [31], [PdCl(
3-2-CH3-C3H4)(Ph2PPy)] [9,14], [Pd2(
CH3-C3H4)2( -Ph2PPy)2](BF4)2 [15] and [Pd(
3-2-CH3-C3H4)
g
3-2-CH3-
3-2-
g
g
l
g
(Ph2PPy)2](BF4) [15] were prepared according to literature
methods.
4.5. [Pd(g
2-fumaronitrile)(PPh2Py)2] (4)
4.1. Ph2PPy
To a solution of 3 (332 mg, 0.43 mmol) in dichloromethane
(20 mL) were added first 39 mg (0.50 mmol) of fumaronitrile then
135 lL (95 mg, 1.25 mmol) of diethylamine dissolved in 10 mL of
dichloromethane. After stirring for 1 h the solution was extracted
1H NMR (CD2Cl2, 298 K): d 7.15 (m, 1H, H-3Py), 7.22 (m, 1H, H-
5Py), 7.3–7.4 (m, 10H, phenyl), 7.60 (H-4Py), 8.71 (d, 1H, H-6Py, JH-
5Py–H-6Py = 5.0 Hz). 31P {1H} NMR (CD2Cl2, 298 K): d ꢀ3.5 (s). 13C
{1H} NMR (CD2Cl2, 298 K): d 164.0 (d, C-2Py, JPC = 3.8 Hz), 150.5
with water (2 ꢅ 20 mL), dried over MgSO4 and filtered. The clear

136
A. Scrivanti et al. / Journal of Organometallic Chemistry 694 (2009) 131–136
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dichloromethane solution was concentrated to small volume under
reduced pressure. Addition of n-hexane afforded 4 as a yellow solid
(230 mg, 75% yield). Anal. Calc. for C38H30N4P2Pd: C, 64.19; H, 4.25.
Found: C, 64.1; H, 4.3%.
(b) A. Dervisi, P.G. Edwards, P.D. Newman, R.P. Tooze, S.J. Coles, M.B.
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1H NMR (CD2Cl2, 298 K): d 3.19 (AA0XX0 m, 2H, @CH), 7.13–7.19
(m, 4H, H-1Py and H-2Py), 7.20–7.55 (m, 20H, arom), 8.54 (d, 2H,
H-6Py, JH-5Py–H-6Py = 4.4 Hz). 31P{1H} NMR (CD2Cl2, 298 K): d 27.6
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d 159.7 (d, 2C, C-2Py,
JPC = 57.6 Hz), 150.4 (AXX0 m, 2C, C-6Py), 135.8 (AXX0 m, 2C, C-
4Py), 134.7 (AXX0 m, 4C, C-2Ph), 134.0 (AXX0 m, 4C, C-2Ph), 133.9
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CD2Cl2 (1 mL) was treated with 3.3
0.05 mmol).
ll of CH3SO3H (4.9 mg,
1H NMR (CD2Cl2, 253 K): d 2.53 (s, 6H, CH3SO3), 3.53 (AA0XX0 m,
@CH), 7.16–7.62 (m, 22H, phenyl and H-3Py), 7.67 (m, 2H, H-5Py),
8.11 (m, 2H, H-4Py), 8.61 (br s, 2H, H-6Py), 10.7 (br s, 2H, NH).
31P{1H} NMR (CD2Cl2, 253 K): d 26.4 (s). 13C{1H} NMR (CD2Cl2,
233 K): d 151.9 (d, 2C, C-2Py), 145.5 (AXX0 m, 2C, C-6Py), 145.3
(AXX0 m, 2C, C-4Py), 135.1 (d, 4C, C-2Ph, JPC = 17.0 Hz), 132.7 (d,
4C, C-2Ph, JPC = 15.5 Hz), 132.3 (s, 2C, C-4Ph), 131.7 (s, 2C, C-4Ph),
129.9 (s, 2C, C-3Py), 129.60 (d, 4C, C-3Ph, JPC = 4.6 Hz), 129.46 (d,
4C, C-3Ph, JPC = 4.9 Hz), 128.0 (d, 2C, C-1Ph, JPC = 37.6 Hz), 127.4
(s, 2C, C-5Py), 126.2 (d, 2C, C-1Ph, JPC = 37.6 Hz), 119.34 (s, 1C,
CN), 119.29 (s, 1C, CN), 38.8 (s, 2C, CH3SO3), 36.5 (br AXX0 m, 2C,
C@C).
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