Unique syndio-selectivity in CO/styrene copolymerization reaction catalyzed by palladium complexes with 2-(2′-oxazolinyl)-1,10-phenanthrolines

Article abstract of DOI:10.1039/c2dt30157a

The reaction of the neutral Pd complex [Pd(CH₃)Cl(cod)] with the potentially terdentate 2-oxazolinyl phenanthroline ligands 1-3 affords the corresponding cationic dinuclear Pd-complexes 1a-3a, which can be isolated in the solid state in good yields. By treatment with AgPF₆ the complexes 1a-3a were converted into the corresponding hexafluorophosphate derivatives 1b-3b, where both the ligand units feature a terdentate coordination around the two Pd-centres with the phenanthroline fragment of each unit displaying a chelate coordination to one Pd-centre, while the corresponding oxazolinyl pendant acts as a bridging ligand towards the second Pd-centre. The persistence of this dimeric structure of 1b-3b in CD₂Cl₂ solution was confirmed by ¹⁵N-NMR experiments at natural abundance, which clearly show the binding to the metal of all of the nitrogen donors, as well as the overall C₂ symmetry of the compound. In consequence of the different strengths of the relevant ion-pair, the dimeric structure of the complex undergoes partial fragmentation in the case of the chloride derivatives 1a-3a, as evidenced from the ¹⁵N-NMR spectra. Complexes 1b-3b are active catalysts in styrene alternate carbonylation, where, under very mild conditions (30 °C and 1 atm of CO), they provide oligomers with 3-5 repetitive units as the exclusive or prevailing product. When traces of the CO/styrene polyketones are also formed, their ¹³C-NMR characterization shows that they are stereochemically homogeneous with a unique syndio-tacticity. This result implies that Pd-complexes able to induce a complete enantioface discrimination in the insertion step of the alkene during the catalytic cycle of the styrene alternate carbonylation have been produced for the first time.

Full text of DOI:10.1039/c2dt30157a

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PAPER
Unique syndio-selectivity in CO/styrene copolymerization reaction catalyzed
by palladium complexes with 2-(2′-oxazolinyl)-1,10-phenanthrolines†
a
b
a
a
b
Angelo Meduri, Daniela Cozzula,‡ Angela D’Amora,§ Ennio Zangrando, Serafino Gladiali and
a
Barbara Milani*
Received 20th January 2012, Accepted 12th April 2012
DOI: 10.1039/c2dt30157a
The reaction of the neutral Pd complex [Pd(CH )Cl(cod)] with the potentially terdentate 2-oxazolinyl
3
phenanthroline ligands 1–3 affords the corresponding cationic dinuclear Pd-complexes 1a–3a, which can
be isolated in the solid state in good yields. By treatment with AgPF the complexes 1a–3a were
6
converted into the corresponding hexafluorophosphate derivatives 1b–3b, where both the ligand units
feature a terdentate coordination around the two Pd-centres with the phenanthroline fragment of each
unit displaying a chelate coordination to one Pd-centre, while the corresponding oxazolinyl pendant acts
as a bridging ligand towards the second Pd-centre. The persistence of this dimeric structure of 1b–3b in
1
5
CD Cl solution was confirmed by N-NMR experiments at natural abundance, which clearly show the
2
2
binding to the metal of all of the nitrogen donors, as well as the overall C symmetry of the compound.
2
In consequence of the different strengths of the relevant ion-pair, the dimeric structure of the complex
undergoes partial fragmentation in the case of the chloride derivatives 1a–3a, as evidenced from the
1
5
N-NMR spectra. Complexes 1b–3b are active catalysts in styrene alternate carbonylation, where,
under very mild conditions (30 °C and 1 atm of CO), they provide oligomers with 3–5 repetitive units
as the exclusive or prevailing product. When traces of the CO/styrene polyketones are also formed,
1
3
their C-NMR characterization shows that they are stereochemically homogeneous with a unique syndio-
tacticity. This result implies that Pd-complexes able to induce a complete enantioface discrimination in the
insertion step of the alkene during the catalytic cycle of the styrene alternate carbonylation have been
produced for the first time.
homobidentate P-donor and N-donor ligands, as well as of
Introduction
19–22
heterobidentate phosphine–nitrogen (P–N)
or phosphine–
23–26
The synthesis of perfectly alternating carbon monoxide/alkene
copolymers has been the subject of intense research activity in
the last few decades.
phosphite (P–OP)
ligands have been utilized in the prep-
aration of active metal catalysts. From the data available in the
literature, P-donor derivatives are the catalysts of choice for the
copolymerization of aliphatic α-olefins, whereas Pd complexes
based on P–N or P–OP or N–N ligands turn out to be better
suited to the copolymerization of vinyl arenes; a process where
these catalysts enable the proper control of the reaction leading
to good yields of copolymer.
1
–7
Despite polyketones being withdrawn
8,9
from the market, Asian industrial development has continued.
Moreover, thanks to the presence of the carbonyl group, the
post-functionalization of the polyketone macromolecules is
possible with no degradation of the polymeric chain yielding
new polymeric materials.
Palladium complexes with bidentate chelating ligands are the
catalysts of choice for this process and a wide range of
1
0–18
The main issues of this process are the catalyst stability
and the control of the stereochemistry of the polymer. The cata-
lyst lifetime is strongly dependent on the relationship between
the rate of alkene insertion into the Pd–H intermediate and
that of Pd–H decomposition. Mild operative conditions (CO
pressure below 50 bar and reaction temperatures below 100 °C),
addition of suitable additives, such as an oxidizing agent,
usually 1,4-benzoquinone (BQ), and the presence of a Brønsted
acid provide the appropriate conditions for increasing the life-
time of the catalyst. When the copolymerization is run under
these conditions in a solvent of poor nucleophilicity, such as
trifluoroethanol, polymers of very high molecular weight can be
a
Dipartimento di Scienze Chimiche e Farmaceutiche, Università di
Trieste, Via Licio Giorgieri 1, 34127 Trieste, Italy. E-mail: milaniba@
units.it
b
Dipartimento di Chimica, Università di Sassari, Via Vienna 2, 07100
Sassari, Italy
†
Electronic supplementary information (ESI) available. CCDC reference
numbers 864728 and 864729. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c2dt30157a
‡
1
§
Current address: Leibniz Institute für Katalyse, A. Einstein Str. 29 a,
8059 Rostock, Germany.
Current address: Università di Napoli Federico II, Dipartimento di
27–29
Chimica Paolo Corradini, Via Cintia, 80126 Napoli, Italy.
obtained.
7474 | Dalton Trans., 2012, 41, 7474–7484
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The stereochemistry of these polyketones is basically dictated
by the symmetry of the ligand and, to a minor extent, by the
nature/position of the substituent(s) with respect to the donor
Results and discussion
Synthesis and characterization of Pd-complexes
30,31
centres.
ligands, such as 1,10-phenanthroline (phen) and 2,2′-bipyridine
As a general rule, C2v symmetry N–N chelating
ox
44
Ligands 1–3, N–N–N , are known compounds. They were
synthesized according to the procedure reported in the literature
by condensation of the methoxy imidate obtained from 2-cyano-
1,10-phenanthroline with the suitable enantiopure β-amino-
alcohol of (S)-configuration (1 and 2) or with (1S,2R)-(+)-
norephedrine (3) (Scheme 1). They have been isolated as crystal-
line solids and gave spectroscopic and elemental analysis data in
agreement with the expected structures.
32
(bpy), result in the prevalence of syndiotactic polyketones,
while enantiopure C symmetry ligands, such as bisoxazolines
2
or diketimines, preferentially give rise to optically active isotactic
33–35
copolymers.
On the other hand, the stereoselectivity is
hardly predictable when C or C ligands, such as pyridine–
s
1
oxazolines or pyridine–imidazolines, are used in building up the
21,36–39
Pd catalyst.
In the course of our previous investigations on the CO/styrene
copolymerization, we have shown that in the case of phen or bpy
Ligands 1–3 were reacted at room temperature with [Pd(CH3)-
Cl(cod)] according to the well-established procedure reported in
the literature, based on the substitution reaction of the diolefin
ligands the absence of C symmetry in the chelating N-donors,
2
29,48–50
as determined by the presence of one single substituent onto the
heterocyclic scaffold, is the cause of some major effects on the
catalyst performance. While alkyl substitution in position 3 of
phenanthroline can result in one of the most efficient catalysts
ever reported for the production of polyketones of high molecu-
with the nitrogen-donor ligand (Scheme 2).
The products,
1a–3a, isolated as yellow solids, were characterized by multinuc-
lear NMR spectroscopy and mass spectrometry. For the sake of
clarity, their characterization will be discussed after that of the
corresponding hexafluorophosphate derivatives, 1b–3b, obtained
40,41
lar weight,
substitution at the carbon atom adjacent to the
by treatment of 1a–3a with AgPF in the presence of acetonitrile
6
nitrogen shifts the selectivity of the reaction towards the prefer-
ential formation of oligoketones featuring no more than 5 repeti-
tive units.
at room temperature in dichloromethane following the literature
procedure.
29,48–50
42,43
Single crystals suitable for X-ray analysis of 3b were obtained
upon addition of n-hexane to a dichloromethane solution of the
complex at low temperature (Fig. 1).
The X-ray structural characterization of 3b evidences the for-
mation of a dinuclear Pd complex arranged around a crystallo-
graphic two-fold axis where the metal ions exhibit a square
planar coordination geometry, being chelated by the phenanthro-
line ligand and coordinated by a methyl group and the oxazoline
We were intrigued as to whether this last result was conse-
quent to a mere effect of the steric congestion generated
by the presence of a substituent in close proximity to the
metal center or whether it could be related to the direct invol-
vement of this encumbering substituent in the binding to the
metal. We were well aware that participation of the vicinal
substituent to metal binding can occur either through cyclo-
metallation, as noticed in the case of 6-sec-butyl-2,2′-bipyri-
dine, or through hemilabile coordination of an oxygen donor,
as in the case of 6-(1′-methoxyethyl)-2,2′-bipyridine. It might
be speculated which way the presence of the vicinal substitu-
ent can affect the competition between the β-elimination
process leading to the termination of the growing chain and
the insertion reaction supporting the propagation of the
polymer chain.
N-donor of the symmetry related terdentate ligand. The coordi-
phen
nation distances are as expected, with Pd–N
bond lengths dif-
fering for the trans influence of the methyl group (Pd–N(1) =
ox
2.164(4), Pd–N(2) = 2.032(4) Å). The Pd–N and the Pd–CH3
are of 2.027(4) and 2.049(5) Å, respectively.
The coordination donor atoms show a slightly tetrahedral dis-
tortion from their mean plane with maximum deviations up to
0.42 Å. The coordination planes form a dihedral angle of
43.8(1)° with metals separated by 3.4256(8) Å. On the other
hand, the two phen moieties that embrace a solvent molecule
(Fig. 1b) make an angle of 57.84(8)°. Inside the complex the
centroids of the two oxazoline rings are at 3.44 Å, but no sig-
nificant π–π interaction between the aromatic rings is detected in
the crystal packing. The two PF6− anions are located on a two-
fold axis and in both cases are far apart from the metal centre.
Single crystals suitable for X-ray analysis were also obtained
for complex 3a. Although the crystal data are of lower accuracy,
the X-ray structural determination confirms a dinuclear entity
To solve this dilemma we have undertaken an investigation
on the catalytic performances in CO/styrene copolymerization
of preformed Pd complexes where the terdentate coordination
of a suitable bpy or phen derivative could be ensured by the
presence of a strong N-donor in close proximity to the chelat-
ing template. This prompted us to resume some 2-oxazolinyl-
phenanthroline (Scheme 1) derivatives that were prepared
several years ago by one of us and utilized with some
success in the enantioselective hydrosilylation of acetophenone
44
by Rh catalysts and in the cyclopropanation of styrene by
45
Cu catalysts. Here, we report on the coordination chemistry
of these ligands around the Pd center and on the behavior of
the relevant complexes in the styrene carbonylation reaction.
Pd–methyl complexes with terdentate nitrogen-donor ligands,
like 2,2′:6′,2′′-terpyridine (terpy), 2,6-bis(2-pyrimidyl)pyridine
and 2,6-bis(N-pyrazolyl)pyridine, were applied to study the
stepwise insertion of carbon monoxide and norbornadiene into
the Pd–methyl bond, but no data about any possible catalytic
activity in the corresponding copolymerization reaction was
(Fig. S1†). The complex, still of C symmetry, presents slight
2
modifications in the conformation of the ligand. Although the
coordination distances follow a trend similar to that of 3b, it is
worth noting the intermetallic separation of 3.039(4) Å (shorter
by ca. −0.4 Å with respect to 3b). This feature is hard to ascribe
to the different anions, to packing effects, or to the intercalation
of the solvent molecule in between the phen ligands, as observed
in the hexafluorophosphate complex, since here the phen moi-
eties form a dihedral angle that is even slightly larger (61.5(4)°).
The chloride anions are disordered in the unit cell and located in
46–48
reported.
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Scheme 1 The synthetic pathway for ligands 1–3 and their numbering scheme.
Scheme 2 The synthetic pathway for the Pd complexes 1a–3a, 1b–3b.
the presence, in solution, of one species only. No spectra vari-
ation is observed with time for at least one month, suggesting
the high stability of the dimeric structure in solution of non-
9
coordinating solvents. The resonance of H was recognized by
an NOE experiment performed upon irradiation of the singlet
assigned to the Pd–CH fragment. Starting from this resonance,
3
it was possible to attribute all the signals to protons by homo-
and heteronuclear COSY experiments. It is worth noting that the
9
4
3
signals of H , H and H are the most affected by the coordi-
nation to palladium (Table 1), their chemical shifts being remark-
ably different from those of the same signals in the free ligand
(
CIS = 1.00–0.33 ppm; CIS = coordination induced shift).
4
3
However, while the resonances of H and H are shifted in a
deshielding direction, that of H is remarkably upfield shifted.
9
Fig. 1 (a) An ORTEP drawing (40% probability ellipsoids) of the
complex cation of 3b with atom labelling scheme of the crystallographic
independent moiety (the same scheme is applied to 3a); (b) a perspective
Even the signal of the Pd–CH moiety, which falls in a range of
3
chemical shift of 0.31–0.07 ppm, is significantly upfield shifted
with respect to the usual chemical shift observed for this group
in mononuclear Pd complexes with bidentate nitrogen-donor
of the complex cation illustrating the C
anion position. Selected bond lengths [Å] and angles [°]: Pd–N(1) 2.164
4), Pd–N(2) 2.032(4), Pd–N(3′) 2.027(4), Pd–C(23) 2.049(5), N(1)–
Pd–N(2) 79.84(17), N(1)–Pd–N(3′) 99.85(16), N(2)–Pd–N(3′)
73.45(16), N(1)–Pd–C(23) 172.78(19), N(2)–Pd–C(23) 93.0(2), N(3′)–
2
symmetry and highlighting the
29,38,51
9
ligands.
The variations in chemical shifts for H and for
(
the Pd–CH are consistent with a palladium coordination geo-
3
metry in solution analogous to that observed in solid state, with
these two groups falling in the shielding cone of the phenanthro-
line moiety of the ligand bonded to the other Pd ion. The vari-
1
Pd–C(23) 87.2(2); non-bonding Pd⋯Pd′ interaction 3.4256(8). Primed
atoms at x, −y + 1, −z + 3/2.
4
3
ations in chemical shifts for H and H might be related to the
coordination of the oxazoline ring to the metal center that
enhances the difference between the two halves of the phenan-
throline skeleton.
channels running parallel to axis c and formed by the packing of
the complexes (Fig. S1†).
The coordination of the ligand as terdentate, bridging two Pd
ions, is retained in solution, as evidenced by NMR spectroscopy.
To substantiate the terdentate coordination mode of the ligand
1
15
PFG, { H, N}-HMBC NMR experiments were performed at
1
15
Indeed, the H NMR spectra of CD Cl solution of complexes
natural abundance of N isotope for the free ligands and the
2
2
1
b–3b, recorded at room temperature, show one set of signals at
two series of palladium complexes. The nuclear properties of
15
chemical shifts different from those of the same protons in the
free ligand. The number of signals and their integration indicate
N, i.e. its very low natural abundance and its rather low and
15
negative gyromagnetic ratio, render acquisition of N data
7476 | Dalton Trans., 2012, 41, 7474–7484
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1
a
Table 1 Relevant H NMR data for complexes 1a–3a, 1b–3b and free ligands 1–3
9
3
4
5′
4′
Ligand/compound
H
H
H
H
H
Pd–CH
3
1
9.19(dd)
8.97(d)
8.47(d)
8.39(d)
4.48(t)
.01(dd)
4.46(m)
4.73(dd)
5.54(dd)
5
1
a
8.32(d)
9.09(d)
8.58(m)
7.79(d)
5.57(dd)
5.92(dd)
1.26(s)
1.17(s)
8
.91(d)
5
4
.14(dd)
.89(dd)
1
2
2
b
8.27(m)
9.16(d)
8.94(t)
8.80(d)
8.32(m)
8.22(d)
9.06(d)
8.32(m)
5.16(t)
.61(t)
4.70(t)
.17(t)
4.77(dd)
4.23(m)
5.38(t)
0.07(s)
5
4.49(m)
4
a
8.56(m)
8.64(m)
4.64(m)
4.49(m)
1.21(s)
1.17(s)
9
.53(d)
4
.64(m)
5.27(t)
.69(t)
2
b
8.50(d)
8.54(d)
8.97(d)
4.31(m)
0.31(s)
4
3
3
9.18(d)
8.94(dd)
8.41(s)
8.31(d)
9.73(d)
8.74(m)
8.41(s)
8.61(m)
8.61(m)
9.04(d)
5.97(d)
6.23(m)
6.23(m)
6.60(d)
4.82(m)
4.90(m)
4.67(m)
4.86(m)
a
1.24(s)
1.26(s)
0.38(s)
8
.97(d)
3
b
8.53(d)
a
Measured at 500 MHz, in CD
2
Cl
2
at 298 K; δ in ppm; s = singlet, d = doublet, dd = double doublet, t = triplet, m = multiplet.
1
5
ox
ox
Table 2
N NMR chemical shifts for complexes 1a–3a, 1b–3b and
between N and CH of the sec-butyl group for 2 and N and
2
a
free ligands 1–3
the CH substituent for 3 (Table 2). Even for ligands 2 and 3, no
3
correlation was observed with the signal of the proton in position
4′ of the oxazoline ring, as well as no relationship between N
Ligand/
compound
1
1
0
1
ox
N
N
N
3
1
and H . Therefore, the exact chemical shift of N for the three
ligands remains unknown, even though, on the basis of literature
1
1
−73.3
n. o.
−134.7
n. o.
a
−149.9 (−76.6),
−117.0,
−117.6
−119.8
n. o.
−117.4
−121.0
n. o.
10
data, they should not be much different from that of N . The
−
150.5 (−77.2)
10
values of N range around −75 ppm and are in agreement with
those reported in the literature for the 1,10-phenanthroline and
its methyl substituted derivatives, 4,7-dimethyl-1,10-phenanthro-
line and 3,4,7,8-tetramethyl-1,10-phenanthroline.
values of N are around −135 ppm.
In the { H, N}-HMBC NMR spectra of complexes 1b–3b
clear cross peaks are present for all the nitrogen atoms (Fig. 2a,
S5 and S6†). In particular, for all of the complexes the corre-
lation between N and H now becomes evident and in the case
of 1b and 2b even the cross peak between N and Pd–CH is
1
2
2
2
3
3
b
−157.9 (−84.6)
−74.5
−185.4 (−50.7)
−139.6
n. o.
a
b
−149.7 (−75.2)
−158.0 (−83.5)
−75.4
−189.0 (−49.4)
49,52–54
The
−137.6
ox
a
−149.8 (−74.4)
−116.7
−191.5 (−53.9),
1
15
−
131.3 (+6.3)
3
b
−158.0 (−82.6)
−121.0
−187.0 (−49.4)
a
2 2
Measured at 50.60 MHz, in CD Cl at 298 K; δ in ppm; CIS values in
1
3
parenthesis. n. o. = not observed.
1
3
1
present, allowing assignment of the N chemical shift around
1
15
employing the PFG { H, N}-HMBC scheme the method of
choice, provided a suitable J( N, H) is present. The
−121.0 ppm and confirming their mutual trans position
n
15
1
15
10
N
(Table 2). For N , in addition to the expected cross peak with
9
8
chemical shifts were assigned on the basis of their cross peaks
with the signal of the closest proton to the nitrogen in the mole-
cule, that is H for N , H for N , and H for N . A first series
of experiments was run on ligand 1 at several input values of the
scalar coupling constant from 2 to 12 Hz (with increments of
H , the signal due to the long range coupling with H also
ox
5′
appears (Fig. 2). Finally, N gives a cross peak with H for
complexes 1b and 2b, plus additional signals with the Pd–CH3
fragment and with the two methylenic protons of the sec-butyl
substituent in 2b. For complex 3b, only the correlation peak
9
10
3
1
4′
ox
ox
1
4
Hz from one experiment to the other), establishing the value of
Hz as the most suitable for J( N, H) between N and H .
between N and the methyl group in position 4′ is observed. It
2
15
1
10
9
should be noted that even for complexes 1b–3b, as it is for the
ox
In addition, with this value of coupling constant, the cross peak
between N and H , due to J( N, H), was evidenced as well
as a very weak cross peak between the signals of N and that of
free ligand, no signal deriving from the relationship between N
1
0
8
3
15
1
4′
and H is evident.
ox
1
15
The { H, N}-HMBC NMR data are in agreement with the
coordination of the ligand in a terdentate fashion; the three nitro-
gen atoms have a chemical shift remarkably different with
respect to that of the free ligand. In particular, the CIS value is
approximately of −80 ppm for N , −50 ppm for N and, on
the basis of the literature data, it can be estimated at between
1
the phenyl protons at 7.39 ppm. No cross peak between N and
3
ox
4′
H
and between N and H was observed at any applied
n
15
1
J( N, H) values (Table 2 and Figs S2–S4†).
n
15
1
10
ox
The J( N, H) value of 4 Hz was subsequently used for all
of the other experiments. For ligands 2 and 3, the clear corre-
lation between N and H was observed, together with that
49
1
0
9
1
−40 and −50 ppm for N , thus confirming that the CIS value of
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1
15
2 2
Fig. 2 { H, N}-HMBC NMR spectra of complexes (a) 2b and (b) 3a recorded in CD Cl at 298 K.
the N atom trans to the Pd–CH fragment is smaller than that of
the N atom trans to another N.
corresponds to the same species obtained for complexes 1b–3b,
the other is due to the free ligand (Figs 3, S9 and S10†), plus a
singlet at 0.94 ppm, common to the spectra of all the three com-
plexes. The ratio between the free and the coordinated ligand
varies both with the nature of the ligand and with time. In the
spectrum recorded after 5 min from dissolution, the relative
amount of free ligand is 87%, 72% and 42% for 1a, 2a and 3a,
respectively. Following the reaction with time the intensity of the
signals of free ligand increases together with that of the singlet at
0.94 ppm, reaching an equilibrium within 5 h. For example, the
evolution of 3a, which is the lowest in decomposing, yields 57%
of free ligand in this period of time.
3
8
4
When the solids isolated from the reaction of ligands 1–3 with
1
[
Pd(CH )Cl(cod)] are dissolved in CD Cl , the related H NMR
3
2
2
spectra present two series of signals for all the protons, included
two singlets for the Pd–CH fragment. The ratio between the
3
two series of signals is approximately 1 : 1 for all complexes
1
a–3a. Most of the signals appear at frequencies different from
those of the free ligand, while one of the two peaks assigned to
4′
5′
H and H have chemical shifts very similar to those of the free
ligand (Table 1). NOE experiments performed upon independent
irradiation of the two singlets of the Pd–CH fragment reveals
3
9
their spatial relationship with H . These spectral features indicate
No variation with time is observed for the dmso solutions of
the hexafluorophosphate derivatives.
These results confirm that the solids isolated from the direct
that the species in solution is neither that obtained from dissolu-
tion of complexes 1b–3b nor just a mononuclear compound che-
lating the Pd ion via the nitrogen atoms of the phenanthroline
part of the ligand. Nevertheless, as discussed above, the X-ray
analysis of single crystals obtained upon addition of n-hexane to
the CD Cl solution analyzed by NMR of complex 3a shows in
reaction of ligands with [Pd(CH )Cl(cod)] are the same dinuclear
3
species observed for the hexafluorophosphate derivatives, but
with the chloride, a coordinating anion, as counterion. Indeed,
ESI-MS spectra of both series of complexes show analogous
molecular peaks and fragmentation patterns (Figs S11–S13†).
The behavior in solution of complexes 1a–3a varies depend-
ing on the solvent. In CD Cl , where the strength of the ion-pair
2
2
solid state a dimeric structure analogous to that observed for
complex 3b (Fig. S1†).
To gain more information about the structure in solution of
2
2
1
15
complexes 1a–3a, { H, N}-HMBC NMR spectra were recorded
is high, a chloride coordinates to palladium leading to a partial
cleavage of the bridge and to the formation of a dinuclear
1
0
1
(
Figs 2b, S7 and S8†). The cross peaks for N and N clearly
ox
indicate their coordination to palladium (Table 2), whereas for
species that has only one molecule of N–N–N ligand bridging
ox
N
in the spectrum of complex 3a two signals are evident: one
at −191.5 ppm with a CIS value of −53.9 ppm and the other at
131.3 ppm with a CIS value of +6.3 ppm (Fig. 2b). This
the two Pd ions and the other chelating one Pd via the nitrogen
atoms of the phenanthroline skeleton (Scheme 3a). In dmso-d6,
where the strength of the ion-pair is lower, the dinuclear structure
is retained. However, due to the coordinating nature of both
solvent and anion the complete cleavage of the complex is
observed with time, leading to the free ligand and to [Pd(CH3)-
Cl(dmso-d ) ], while no formation of palladium black is
−
suggests that one oxazoline ring is coordinated to the metal,
while the other one is not bonded to Pd.
The different behavior in solution for the two series of com-
plexes, a and b, might be due to the different counterion, which
is reflected in a different strength of the related ion-pair. To prove
this hypothesis, spectra of the two series of complexes (and of
6
2
observed (Scheme 3b).
The coordination chemistry of the present terdentate ligands is
different from that reported in literature for terpy and more
the free ligands) were recorded in dmso-d at room temperature.
6
46,48
While the spectra of complexes 1b–3b show only one set of
signals, the analysis of which confirms the dinuclear structure
observed both in solid state and in CD Cl solution, the spectra
flexible non-symmetric N–N–N ligands.
When these ligands
were reacted with [Pd(CH )Cl(cod)], different isomers were
3
formed with the ligand bonded to Pd both in a bidentate and ter-
dentate fashion depending on the ligand itself, on the counterion
2
2
of complexes 1a–3a present two sets of resonances; one
7478 | Dalton Trans., 2012, 41, 7474–7484
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1
Fig. 3 H NMR spectra in dmso-d
6
3 6 2
at room temperature of (a) 3b (•), (b) 3a, (c) 3 (∇); (*) signal of [Pd(CH )Cl(dmso-d ) ].
Scheme 3 Behavior in solution of complexes 1a–3a.
4
3
and on the solvent. However, it has to be pointed out that in all
cases only mononuclear species were detected. Thus, the present
results support the conclusion reported in the literature, that the
minute differences in the donating properties of the three nitro-
gen atoms play a subtle, but decisive part in the formation of
various isomers and in the choice between bidentate and terden-
for complexes containing 6-substituted-2,2′-bipyridines, that is
2,2,2-trifluoroethanol (TFE) as solvent, atmospheric CO
pressure, T = 303 K and [BQ]/[Pd] = 40. The reaction product
consists of a yellow/brown oil that according to the ESI-MS and
1
H NMR characterization is recognized as CO/styrene oligo-
ketones with a number of repetitive units ranging from 3 to 5,
analogous to those obtained with Pd-(6-substituted-2,2′-bipyri-
dines) catalysts.
48
tate coordination.
All tested complexes generate active catalysts for the carbony-
lation reaction leading to different productivities depending on
the ligand nature (Table 3).
Styrene carbonylation reaction
Complexes 1b–3b are tested as precatalysts in styrene carbonyla-
tion under reaction conditions analogous to those reported by us
It is worth noting that whereas for all of the catalysts the
major product of the catalytic reaction is the CO/styrene
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ox
a
Table 3 CO/styrene oligomerization; effect of the ligand nature. Precatalyst: [{Pd(CH
3
2 6 2
)(N–N–N )} ][PF ] 1b–3b
ox
b
g OM g−1 Pd
c
g PK g−1 Pd
g P g−1 Pdd
e
Run
N–N–N
Yield (OM , mg)
Yield (PK , mg)
TON
1
2
3
1
2
3
306.0
506.2
368.6
226.7
375.0
273.0
54.3
16.2
0
40.2
12.0
0
266.9
387.0
273.0
215.0
311.0
219.7
a
−5
Reaction conditions: nPd = 1.27 × 10 mol, styrene V = 10 mL, TFE V = 20 mL, PCO = 1 bar, T = 303 K, t = 24 h, [BQ]/[Pd] = 40, [styrene]/[Pd] =
b
c
d
−1
e
6
800. OM = oligoketone. PK = polyketone. g P g Pd = grams of product (OM + PK) per gram of palladium. TON = nRU/nPd (nRU = mol of
repetitive units inserted calculated by dividing the total mass of the product (OM+PK) by the molar mass of the repetitive unit).
ratio (Fig. 4). A macroscopic effect of BQ is related to the cata-
lyst stability; considerable formation of palladium metal is
observed in the absence of BQ, while no decomposition to palla-
dium black is evident for all the three catalysts carrying out the
reaction at [BQ]/[Pd] = 40 for 24 h. By using precatalyst 3b cata-
lytic experiments were performed at 16, 48 and 72 h (Fig. S14†).
A linear relationship between productivity and reaction time was
found up to 24 h of reactions, afterward the catalyst starts to
deactivate.
It is well-known from the literature that in CO/alkene copoly-
merization benzoquinone is very important to retain catalyst
activity, as evidenced by the linear relationship between the rate
of CO consumption and the [BQ]/[Pd] ratio, accompanied by no
36,55
effect on the reaction rate.
Indeed, in the copolymerization
process its role is well-understood regarding the oxidation of
Fig. 4 CO/styrene oligomerization; effect of [BQ]/[Pd]. Precatalyst:
Pd(0) to Pd(II) with the concomitant formation of hydro-
ox
[{Pd(CH
3
)(N–N–N )}
2
][PF
6
]
2
1b–3b. Reaction conditions: see
2,27,51,56
quinone.
The resulting Pd species is a Pd–alkoxy inter-
Table 1.
mediate and the corresponding carbo–alkoxy group was found as
one end group of the polymeric chains. On the other hand, in the
present investigation no ester group is observed at the end of the
oligoketone chains and there is no linear relationship between
productivity and [BQ]/[Pd] ratio (Fig. 4). Analogous experimen-
tal data were obtained by us in the CO/styrene oligomerization
oligoketone, in the case of complexes with ligands 1 and 2 traces
of the corresponding polyketone are also obtained. This rep-
resents a remarkable difference with respect to the catalytic
system based on 1,10-phenanthroline or on its alkyl substituted
derivatives that yielded the syndiotactic copolymer with produc-
43
catalyzed by Pd complexes with 6-substituted-2,2′-bipyridines
and in the styrene dimerization catalyzed by dinuclear Pd deriva-
−1
tivities in the order of 4 kg PK g Pd with Mw values up to
57
3
9
36 000 (M /M = 3.3) and with a content of uu triad up to
6%. In general, the obtained productivity values are higher
tives with terdentate P–N–N ligands. All of these findings
suggest that the role played by BQ in these catalytic systems is
apparently different from that exerted in the most common CO/
styrene copolymerization. In particular, it seems that benzoqui-
none not only increases the catalyst lifetime, but it might modify
the position of the equilibria involved in the formation of the
active species rendering available for the catalysis a higher
amount of palladium centres. However, the catalytic data do not
allow making any speculation and/or hypothesis on its specific
role.
w
n
2
9
than those reported for the catalysts with the 6-substituted-2,2′-
bipyridines, the only system reported up to now for the synthesis
4
3
of CO/styrene oligoketones. The most productive species is
that with ligand 2 that has the sec-butyl group in position 4′ and
no substituent in position 5′, while the complexes with the other
two ligands show similar productivities. This trend of pro-
ductivity is related to the nature of the substituents on the oxazo-
line ring and, in agreement with the data reported in the literature
2
1,36
for palladium complexes with pyridine–oxazolines,
the
The polyketones obtained with precatalysts 1b and 2b were
13
highest productivity is obtained with the ligand substituted in
position 4′ only. This suggests that the presence of a group in
position 5′, even though quite far from the metal center, has a
negative effect on the catalyst performances. This last result may
be indicative of the fact that in the catalytic active species the
oxazoline nitrogen donor is not involved in the coordination at
the metal centre, but rather that it acts as a mere chiral substituent
in the proximity of the coordination site.
analyzed by C NMR spectroscopy to characterize their stereo-
chemistry, recording the spectra in 1,1,1,3,3,3-hexafluoro-2-pro-
panol (HFIP) at room temperature. In the region of the ipso
carbon atom only the signal due to the uu triad is present, indi-
cating that the polyketone has a fully syndiotactic microstructure
(Fig. 5). This result represents the first time that the CO/styrene
polyketone with a content of uu triad higher than 99.0% is
obtained, the highest values reported up to now were of 96% and
97% obtained with a Pd–tetrafluoro substituted phenanthroline
1
,4-Benzoquinone is recognized as an essential component of
29
58
the catalytic system. Indeed, when it is not present the pro-
ductivity is very low and it increases on increasing the [BQ]/[Pd]
complex
and with a Pd–dipyridophenazine derivative,
respectively. Small signals that do not correspond to ul, lu and ll
7480 | Dalton Trans., 2012, 41, 7474–7484
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1
Fig. 6 H NMR spectra in CDCl
3
of oligoketones synthesized with (a)
1
3
43
Fig. 5
C NMR spectra in HFIP + CDCl
3
of polyketones synthesized
3 3 3 6
[Pd(CH )(CH CN)(bpy–OCH )][PF ] and (b) 1b.
with (a) [Pd(CH
carbon atom.
3 3 6
)(CH CN)(phen)][PF ] and (b) 1b. Region of the ipso
already applied by us to investigate the reactivity with carbon
monoxide of mononuclear Pd–CH complexes with one or two
3
molecules of bidentate N-donor ligands bonded to the Pd center.
In those cases, the reactivity of the precatalysts with carbon mon-
oxide was promptly evidenced by their complete transformation
into the Pd–acetyl–carbonyl intermediate within 10 minutes
38,43,51
from the treatment with CO.
On the other hand, a very
similar behavior was already observed for binuclear Pd-com-
56
plexes derived from a bisoxazoline ligand. Also, in that case it
was observed that the binuclear derivative was either completely
unreactive (in CD Cl ) or very poorly reactive (in CD Cl –TFE)
2
2
2
2
towards CO-insertion despite the fact that it displayed a fair cata-
lytic activity in the copolymerization reaction.
In addition, even the Pd–methyl complexes with the terdentate
terpy and the other N–N–N ligands reacted with CO under
similar mild conditions to yield the corresponding Pd–acetyl
l l
Chart 1 Possible CO/styrene oligoketone end groups (A and B are
not observed).
46,47
derivatives.
It should be noted, however, that for practical
reasons all of the NMR experiments are performed at a Pd-con-
centration that is at least two orders of magnitude higher than in
the catalytic runs. As a result of this difference, in the catalytic
conditions the equilibrium between di- and mono-nuclear Pd-
complexes shall be shifted in such a way as to build up a fair
concentration of mononuclear species that promptly reacts with
CO according to the established mechanism. Thus, binuclear Pd-
complexes may be viewed as a resting state of the catalyst.
Notably, the presence of a third N-donor centre in the proximity
of the metal can be helpful in stabilizing coordinatively unsatu-
rated intermediates in the catalytic cycle. This may eventually
results in a positive effect exerted by this type of ligand towards
the catalyst.
triads are present in the region between 135.4–135.7 ppm. They
might be assigned to ennades of higher order than three.
1
9,43,59
1
In agreement with the literature,
the H NMR spectra of
the oligoketones synthesized with precatalysts 1b–3b allow us to
characterize their end groups as the vinyl function deriving from
β-hydrogen elimination on the Pd–alkyl bond and the 2,5-diphe-
nyl pentyl-3-one originated by the insertion of styrene into the
Pd–H bond. For the latter end group the like (A ) and the unlike
l
(
A ) diastereoisomers, differing for the relative configuration of
u
the two stereogenic centres, might form (Chart 1). It is straight-
forward to note that, as evidenced by the presence of the doublet
at 1.48 ppm, only the unlike diastereoisomer is observed, thus
indicating that the enantioface discrimination that leads to the
fully syndiotactic polyketone is very efficient since the insertion
of the first two styrene units (Fig. 6).
Conclusion
Attempts to gain some insights into the possible mechanism
for the activation of precatalyst were made by reacting a CD Cl
The coordination chemistry to palladium of three terdentate
N-donor ligands featured by a phenanthroline skeleton substi-
tuted in position 2 by an oxazoline ring was investigated in
detail. These ligands show the tendency to bridge two metal
ions, leading to dinuclear complexes where the phenanthroline
nitrogen atoms chelate one Pd ion, while the oxazoline nitrogen
donor is bonded to the other metal ion. The stability in solution
of the resulting cationic complexes is related to the nature of the
2
2
1
3
solution of complex 1b with CO in the NMR tube, at 298 K.
No reaction was observed over a period of time of 12 h. Another
in situ experiment in the NMR tube was performed by treating a
CD Cl solution of complex 1b with 2 eq. of BQ, 2 μL of TFE
2
1
2
3
and CO, in order to mimic the overall catalytic system. Again,
1
no variation was evident in the H NMR spectra. The protocol
followed in the present work to perform these studies was
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ox
counterion: with hexafluorophosphate the complexes are stable
both in CD Cl and in dmso-d , whereas in the case of chloride
a different behavior is observed depending on the solvent. In
dichloromethane a partial cleavage of the dinuclear species is
observed as a consequence of the coordination of the anion,
3 2 2
[{Pd(CH )(N–N–N )} ][Cl] (1a–3a)
2
2
6
General synthesis. To a stirred solution of [Pd(CH )Cl(cod)]
3
(
0.3 mmol) in CH Cl (2 mL), a solution of the ligand (1.1 eq.)
2
2
in CH Cl (3 mL) was added. After 1 h at room temperature the
2
2
reaction mixture was concentrated and the product precipitated
as a yellow solid upon addition of diethyl ether or petroleum
ether, bp 40–60 °C.
while in dmso-d the dimeric species is detected immediately
6
after dissolution, followed by the complete dissociation of
the N-donor ligand and the formation of the solvated species,
[
Pd(CH )Cl(dmso-d ) ].
The hexafluorophosphate derivatives generate active catalysts
[{Pd(CH )(1)} ][Cl] (1a). Yield: 67%.
δH (500 MHz; CD Cl ) 9.09 (1H, d, H ), 8.97 (1H, d, H ),
2 2
3
6 2
3
2
2
3
9
9
7
4
3
for styrene carbonylation under mild reaction conditions leading
to higher productivities than those reported by us for Pd com-
plexes with 2,2′-bipyridines substituted in position 6 with an
alkyl group. In addition to the CO/styrene oligoketones, traces of
the corresponding polyketones are also obtained. Their NMR
characterization reveals that the copolymers have a fully syndio-
tactic microstructure.
Even though from the experimental data it is not possible to
gain an insight into the mechanism involved in the activation
step of the precatalyst and into the nature of the active species,
this is the first time ever that a CO/vinyl arene copolymer with a
fully syndiotactic microstructure has been obtained.
8.91 (1H, d, H ), 8.60–8.55 (3H, m, H , H ), 8.32 (1H, d, H ),
5,6
5,6
8.08–7.93 (2H, dd, H ), 8.02 (2H, s, H ), 7.90–7.82 (3H, m,
H , Ar–H), 7.79 (1H, d, H ), 7.52–7.30 (9H, m, Ar–H, Ar–H),
5.92 (1H, dd, H ), 5.57 (1H, dd, H ), 5.14 (1H, dd, H ), 4.89
(1H, dd, H ), 4.73 (1H, dd, H ), 4.46 (1H, dd, H ), 1.26 (3H, s,
8
4
4
′
4′
5′
5
′
5′
5′
Pd–CH ), 1.17 (3H, s, Pd–CH ).
3
3
9
9
δ (125.68 MHz; CD Cl ) 149.10 (C ), 148.81 (C ), 138.43
C
2
2
4
7
4
8
3
5
(C , C ), 138.27 (C ), 130.66 (C ), 129.0 (C , C ), 128.5 (C or
Ar
C ), 128.5 (C ), 127.8 (C , C ), 127.8 (C or C ), 127.3 (C ),
125.5 (C ), 77.5 (C ), 76.3 (C ), 72.8 (C ), 71.31 (C ), 1.8
6
5,6
5
6
3
Ar
Ar
5′
8
5′
4′
4′
(Pd–CH ), 1.3 (Pd–CH ).
3
3
10
10
δ (50.65 MHz; CD Cl ) −150.5 (N ), −149.9 (N ), −117.6
N
2
2
1
1
(
N ), −117.0 (N ).
m/z 446 (%, M ), 431 (M − CH ).
+
3
Experimental
[
{Pd(CH )(2)} ][Cl] (2a). Yield: 73%.
3 2 2
Materials and methods
3
9
δH (500 MHz; CD Cl ) 9.53 (1H, d, H ), 8.94 (2H, t, H ),
.64 (1H, m, H ), 8.56 (2H, m, H ), 8.22 (1H, d, H ),
.07–8.00 (4H, m, H ), 7.86 (1H, dd, H ), 4.77 (1H, dd, H ),
.64 (2H, m, H ), 4.49 (1H, m, H ), 4.23 (1H, m, H ), 2.32
2H, m, CH ), 1.85 (2H, m, CH and CH), 1.76 (1H, m, CH),
.56 (1H, m, CH ), 1.21 (3H, s, Pd–CH ), 1.17 (3H, s, Pd–
2 3
CH ), 1.01 (9H, m, CH ), 0.94 (3H, m, CH ).
2
2
4
7,4
3
8
8
4
(
1
[
Pd(OAc) ] was a gift from Engelhard Italia and was used as
2
5,6
8
5′
received. All of the solvents were purchased from Sigma-Aldrich
and used without further purification for synthetic, spectroscopic
and catalytic purposes, with the only exception being the
dichloromethane used for the synthesis of complexes, which was
4
′,5′
4′
5′
2 2
purified through distillation over CaH under argon atmosphere
3
3
3
2
9
4,7
δ
(125.68 MHz; CD Cl ) 148.8 (C ), 138.3 (C ), 137.7
2 2
and used freshly distilled. Carbon monoxide (CP grade 99.9%)
was supplied by SIAD. NMR spectra of ligands, complexes and
C
4
3
3
5
6
5
6
(
1
(
(
C ), 129.3 (C ), 127.0 (C ), 128.7 (C or C ), 128.8 (C or C ),
8
5′
5′
5′
4′
13
25.4 (C ), 75.5 (C ), 74.9 (C ), 74.6 (C ), 66.9 (C ), 66.6
their reactivity with CO were recorded on a Varian 500 spec-
trometer at 298 K and at the following frequencies: 500 MHz
4
′
C ), 43.9 (CH ), 44.7 (CH ), 45.1 (CH ), 25.9 (CH), 23.8
2 2 2
1
13
15
CH ), 22.5 (CH ), 1.9 (Pd–CH ), 1.10 (Pd–CH ).
δ (50.65 MHz; CD Cl ) −149.7 (N ), −117.4 (N ).
m/z 426 (%, M ), 411 (M − CH ).
(
H), 125.68 MHz ( C), 50.65 MHz ( N); the resonances were
3
3
3
3
10
1
referenced to the solvent peak versus TMS: CDCl at δ 7.26
N
2
2
3
+
1
13
1
13
(
H) and δ 77.0 ( C), CD Cl at δ 5.32 ( H) and 54.0 ( C),
3
2
2
1
13
dmso-d at δ 2.50 ( H). C NMR spectra of polyketones were
6
[{Pd(CH )(3)} ][Cl] (3a). Yield: 85%.
δH (500 MHz; CD Cl ) 9.73 (1H, d, H ), 8.97 (1H, d, H ),
3
2
2
recorded in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) with a
3
9
2
2
small amount of CDCl for locking purposes at 125.68 MHz and
9
4
3
8.94 (1H, dd, H ), 8.64–8.57 (2H, m, H ), 8.57–8.54 (2H, m,
1
5
referenced at δ 77.0. Chemical shifts of N NMR spectra
referred to CH NO as the external standard. IR spectra of com-
7
3
5,6
H ), 8.31 (1H, d, H ), 8.07–7.97 (4H, m, H ), 7.88–7.83 (2H,
8
5′
3
2
m, H ), 7.38–7.27 (10H, m, Ar–H), 6.27–6.19 (2H, m, H ),
.90 (1H, m, H ), 4.67 (1H, m, H ), 1.26 (3H, s, Pd–CH ), 1.24
3
3H, s, Pd–CH ), 0.92–0.88 (6H, m, CH ).
plexes 1b–3b were recorded in Nujol on a Perkin Elmer System
000 FT-IR. Mass spectra of complexes and catalytic products
4′
4′
4
(
2
3 3
were run by ESI-ion trap on a Bruker-Esquire 4000.
9
4,7
δ
(125.68 MHz; CD Cl ) 149.0 (C ), 138.5 (C ), 129.1
2 2
C
3
5,6
3
(
(
C ), 128.6 (C ), 127.9 (C ), 127.2 (C ), 126.8 (C ), 125.6
Ar
5′
Ar
8
5′
4′
4′
C ), 86.3 (C ), 85.6 (C ), 66.7 (C ), 66.3 (C ), 17.8 (CH ),
Synthesis of ligands 1–3
3
1
.8 (Pd–CH ), 1.3 (Pd–CH ).
3 3
10
1
Ligands 1–3 were prepared following the procedure reported in
the literature.
δ (50.65 MHz; CD Cl ) −149.8 (N ), −116.7 (N ), −191.5
N
ox
2
2
44
ox
(N ), −131.3 (N ).
+
m/z 460 (%, M ), 445 (M − CH ).
3
Synthesis of Pd complexes
[
{Pd(CH
3 2 6 2
)(N–N–N)} ][PF ] (1b–3b)
All syntheses were performed using standard vacuum-line and
Schlenk techniques under argon atmosphere and at room temp-
erature, according to the published procedures.
General synthesis. To a stirred solution of [{Pd(CH )(N–N–
3
2
9,48–50
ox
ox
N )} ][Cl] (N–N–N = 1–3) (0.15 mmol) in CH Cl (3 mL),
2 2 2 2
7482 | Dalton Trans., 2012, 41, 7474–7484
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5
′
4′
a solution of AgPF (1.1 eq.) in acetonitrile (2 mL) was added.
6.91 (1H, d, H ), 4.89 (1H, m, H ), 0.98 (3H, d, –CH ), 0.20
6
3
After 1 h at room temperature the reaction mixture was filtrated
over Celite®, concentrated and the product precipitated as a
yellow solid upon addition of diethyl ether or petroleum ether,
bp 40–60 °C.
(3H, s, Pd–CH3).
IR (Nujol mull): ν /cm− 842br and 556br (PF −).
1
max
6
+
m/z 460 (%, M ), 445 (M − CH ).
3
[
{Pd(CH )(1)} ][PF ] (1b). Yield: 75%.
3 2 6 2
Oligo- and polymerization reactions
4
3
δH (500 MHz; CD Cl ) 9.06 (1H, d, H ), 8.80 (1H, m, H ),
2
2
7
5,6
9
8
.63 (1H, d, H ), 8.29–8.21 (3H, m, H , H ), 7.76 (1H, dd,
All experiments were carried out at atmospheric CO pressure in
a three-necked, thermostated, 75 mL glass reactor equipped with
a magnetic stirrer and connected to a temperature controller.
After establishment of the reaction temperature, the precatalyst,
1,4-benzoquinone, styrene and TFE were placed inside. CO was
bubbled through the solution for 10 min; afterwards, a 4 L
balloon previously filled with CO was connected to the reactor.
The system was stirred at the same temperature for 24 h remain-
ing as a yellow solution. The reaction mixture was then poured
into methanol (100 mL) and stirred for 1 h at room temperature.
The solid, if any was formed, was filtered off and washed with
methanol. The filtrate was brought to dryness yielding a yellow-
brown oil. The products (solid and oil) were dried under vacuum
to constant weight.
8
5′
H ), 7.18–7.00 (5H, m, Ar–H), 5.61 (1H, t, H ), 5.38 (1H, t,
4′
5′
H ), 5.16 (1H, t, H ), 0.07 (3H, s, Pd–CH ).
3
9
4
δ (125.68 MHz; CD Cl ) 150.29 (C ), 141.34 (C ), 140.36
C
2
6
2
7
5
(
(
7
C ), 130.83 (C or C ), 129.90 (C ), 129.67 (C ), 128.52
Ar Ar
8
5
6
3
5′
C ), 127.89 (C or C ), 126.90 (C ), 126.88 (C ), 78.30 (C ),
Ar
4
′
3.76 (C ), 7.37 (Pd–CH ).
3
ox
10
δ (50.65 MHz; CD Cl ) −185.4 (N ), −157.9 (N ), −119.8
N
2
2
1
(
N ).
4
3,7
δ (500 MHz; dmso-d ) 9.38 (1H, d, H ), 8.91 (2H, m, H ),
.46 (2H, d, H ), 8.33 (1H, d, H ), 7.83 (1H, dd, H ), 7.21
2H, d, Ar–H), 7.12 (3H, m, Ar–H), 5.77 (1H, t, H ), 5.40 (1H,
H
6
5,6
9
8
8
(
5
′
4
′
5′
t, H ), 5.22 (1H, t, H ), −0.13 (3H, s, Pd–CH ).
3
IR (Nujol mull): νmax/cm 841br and 556br (PF6−).
−1
+
m/z 446 (%, M ), 431 (M − CH ).
3
[
{Pd(CH
3 2 6 2
)(2)} ][PF ] (2b). Yield: 69%.
X-ray crystallography
4
7
δH (500 MHz; CD Cl ) 8.97 (1H, d, H ), 8.74 (1H, d, H ),
.54 (1H, d, H ), 8.50 (1H, d, H ), 8.29 (2H, q, H ), 7.90 (1H,
2
2
3
9
5,6
8
Due to the small crystal dimensions, diffraction data of 3b were
collected at 100(2) K at the XRD1 diffraction beamline of
Elettra Synchrotron, Trieste (Italy), wavelength radiation λ =
1.0000 Å. Collection data of 3a were performed by using a
Brucker Kappa CCD imaging plate mounted on a Nonius FR591
rotating anode (λ = 1.5418 Å). Cell refinement, indexing and
8
5′
5′
dd, H ), 5.27 (1H, t, H ), 4.69 (1H, t, H ), 4.35–4.26 (1H, m,
4′
H ), 2.24–2.17 (1H, m, –CH –CH–), 1.89–1.77 (1H, m, –CH –
2
2
CH–), 1.66–1.59 (1H, m, –CH –CH–), 0.66 (3H, d, –CH–
CH ) ), 0.62 (3H, d, –CH–(CH ) ), 0.31 (3H, s, Pd–CH ).
2
(
3 2 3 2 3
9
C
4
δ (125.68 MHz; CD Cl ) 150.70 (C ), 141.27 (C ), 140.61
2
2
7
5
6
5
6
8
60
(
(
C ), 130.94 (C or C ), 128.00 (C or C ), 127.06 (C ), 126.60
scaling of the data sets were carried out using Mosflm and
3
5′
4′
60
C ), 77.18 (C ), 67.67 (C ), 46.12 (–CH –CH–), 25.80 (–CH –
Scala. The structure was solved by direct methods and sub-
2
2
6
1
CH–), 22.50 (–(CH ) ), 21.60 (–(CH ) ), 6.46 (Pd–CH ).
δN (50.65 MHz; CD Cl ) −189.0 (N ), −158.0 (N ),
121.0 (N ).
δH (500 MHz; dmso-d ) 9.29 (1H, d, H ), 8.99 (1H, d, H ),
.65 (1H, d, H ), 8.53 (1H, d, H ), 8.50 (2H, s, H ), 7.95 (1H,
dd, H ), 5.55 (1H, t, H ), 4.69 (1H, m, H ), 4.22 (1H, m, H ),
.12 (1H, m, –CH –CH–), 1.88 (1H, m, –CH –CH–), 1.63 (1H,
m, –CH –CH–), 0.57 (6H, d, –CH–(CH ) ), 0.16 (3H, s, Pd–
sequent Fourier analyses and refined by the full-matrix least-
3
2
3 2
3
ox
10
2
61
squares method based on F with all observed reflections. The
enantiomorphic space group (P6 22 vs. P6 22) could not be
properly fixed being the Flack parameter of 0.48(2), indicative of
2
2
1
−
1
5
4
7
6
3
9
5,6
−
8
a possible twinned crystal. Beside the PF
two-fold axis, a CH Cl lattice molecule was detected on the
Fourier map. All of the calculations were performed using the
6
anions located on a
8
5′
5′
4′
2
2
2
2
2
62
WinGX System, Ver. 1.80.05.
2
3 2
CH3).
IR (Nujol mull): νmax/cm− 845br and 557br (PF6−).
1
Crystal data of 3b. CH Cl : C H Cl F N O P Pd , M =
2
2
47 42
2
12
6
2
2
2
+
m/z 426 (%, M ), 411 (M − CH ).
1296.51, hexagonal, space group P6 22 (No. 178), a = 14.1900
1
3
3
(
11), c = 42.200(4) Å, V = 7358.8(10) Å , Z = 6, ρ
= 1.755 g
calcd
[
{Pd(CH
3
)(3)}
2
][PF
6
]
2
(3b). Yield: 65%.
−3
cm , F(000) = 3876. Final R = 0.0283, wR = 0.0709, S =
2
4
δ
(500 MHz; CD Cl ) 9.04 (1H, d, H ), 8.78–8.69 (2H, m,
H
2
2
1
.058 for 336 parameters and 82 509 reflections, 2120 unique
3
,7
9
5,6
8
H
7
4
), 8.53 (1H, d, H ), 8.31 (2H, s, H ), 7.90 (1H, dd, H ),
[
R(int) = 0.0228], of which 2113 with I > 2σ(I), max. positive
5
′
.57–7.45 (3H, m, Ar–H), 7.39 (2H, d, Ar–H), 6.60 (1H, d, H ),
.86 (1H, dq, H ), 1.12 (3H, d, –CH ), 0.38 (3H, s, Pd–CH ).
−3
and negative peaks in ΔF map 0.354, −0.348 e Å
Crystal data of 3a are reported as ESI.†
.
4
′
3
3
9
4
δ (125.68 MHz; CD Cl ) 150.65 (C ), 141.20 (C ), 140.59
C
2
2
7
5
6
5
6
(
(
(
C ), 130.89 (C or C ), 129.72 (C ), 127.80 (C or C ), 126.93
Ar
8
3
5′
4′
C ), 126.81 (C ), 126.38 (C ), 87.91 (C ), 68.50 (C ), 19.26
Ar
Acknowledgements
–CH ), 6.62 (Pd–CH ).
δN (50.65 MHz; CD Cl ) −187.0 (N ), −158.0 (N ),
3
3
ox
10
Collaborative research was carried out by S. G. and B. M. in the
framework of the COST D40 project of EU. This work was sup-
ported by MIUR (PRIN N° 2007HMTJWP_002). Engelhard
Italia is gratefully acknowledged for a generous gift of [Pd-
2
2
1
−
121.0 (N ).
δ (500 MHz; dmso-d ) 9.34 (1H, d, H ), 8.99 (1H, d, H or
4
3
H
6
7
3
7
9
H ), 8.94 (1H, d, H or H ), 8.58 (1H, d, H ), 8.53 (1H, dd,
5
,6
8
H
), 7.96 (1H, t, H ), 7.56 (4H, s, Ar–H), 7.48 (1H, s, Ar–H),
(AcO) ]. Fondazione CRTrieste is also gratefully acknowledged
2
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 7474–7484 | 7483

View Online
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7484 | Dalton Trans., 2012, 41, 7474–7484
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