Palladium(ii) complexes with pentafluorophenyl ligands: Structures, C 6F5 fluxionality by 2D-NMR studies and pre-catalysts for the vinyl addition polymerization of norbornene

Article abstract of DOI:10.1039/b925674a

The palladium(ii) complex [Pd(C₆F₅)Cl(bpzm*)] (5) [bpzm* = bis(3,5-dimethylpyrazol-1-yl)methane] was characterized by ¹H,¹H-TOCSY, ¹H-NOE difference spectra, ¹H,¹⁹F-HOESY and ¹³C,¹H-HMBC 2D-NMR techniques. Chemical exchange of the methylene protons from ¹H, ¹H-NOESY cross peaks and exchange of the ortho- and meta-fluorine atoms, respectively, from ¹⁹F,¹⁹F-EXSY cross peaks indicates that the Pd-bpzm* chelate ring boat-to-boat inversion occurs at a rate slower than the NMR time scale together with a concomitant change of the C₆F₅ atom positions. The presence of three ¹⁹F-NMR signals for 2F_o:1F_p:2F_m of the C₆F₅ ligand for complexes [Pd(C₆F ₅)Cl(tmeda)] (1) and [Pd(C₆F₅)Cl(bipy)] (3) (tmeda = N,N,N′,N′-tetramethylethylenediamine; bipy = 2,2′-bipyridine) is interpreted as being due to identical hemi-spaces above and below an apparent symmetry plane coinciding with the Pd-coordination plane instead of free ring rotation. The molecular structures of 1, 3 and 5 from single-crystal studies suggest that the hindered C₆F₅ rotation is not limited to 5 but is also present in 1 and 3 due to ligand repulsion. Complexes [Pd(C₆F₅)Cl(tmeda)] (1), [Pd(C ₆F₅)OH(tmeda)] (2), [Pd(C₆F₅) Cl(bipy)] (3), [Pd(C₆F₅)OH(bipy)] (4) and [Pd(C ₆F₅)Cl(bpzm*)] (5) have been applied as pre-catalysts for the vinyl homopolymerization of norbornene in combination with the cocatalyst methylaluminoxane (MAO). Activities of more than 10⁶ g_polymer/(mol_Pd h) could be reached with these catalytic systems. Based on the spectrochemical series, pre-catalysts 1 and 2 with the pure σ-donor and more weakly bound aliphatic amine ligands showed higher polymerization activities than compounds 3-5 with modest π-accepting and stronger bound aromatic substituents. This is reasoned with a kinetic activation effect through a faster removal of the more weakly bound ligands upon reaction with MAO together with the chloro or hydroxo ligands to give the active, almost naked Pd²⁺ cations. For the activation mechanism, ¹H-, ¹³C- and ¹⁹F-NMR studies of the MAO activated complex 5 showed about 13% chlorine-to-methyl exchange for a molar Pd:Al ratio of 1:10. For 5:MAO at a Pd:Al ratio of 1:100 abstraction of C ₆F₅ takes place with a redox reaction giving Pd metal and C₆F₅-CH₃ in the absence of norbornene monomer.

Full text of DOI:10.1039/b925674a

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PAPER
www.rsc.org/dalton | Dalton Transactions
Palladium(II) complexes with pentafluorophenyl ligands: structures, C F5
6
fluxionality by 2D-NMR studies and pre-catalysts for the vinyl addition
polymerization of norbornene†
a
a
b
b
a
Frederik Blank, Harald Scherer, Jos e´ Ruiz,* Venancio Rodr ´ı guez and Christoph Janiak*
Received 7th December 2009, Accepted 4th February 2010
First published as an Advance Article on the web 5th March 2010
DOI: 10.1039/b925674a
The palladium(II) complex [Pd(C
was characterized by H, H-TOCSY, H-NOE difference spectra, H, F-HOESY and C, H-HMBC
6
F
5
)Cl(bpzm*)] (5) [bpzm* = bis(3,5-dimethylpyrazol-1-yl)methane]
1
1
1
1
19
13
1
1
1
2
D-NMR techniques. Chemical exchange of the methylene protons from H, H-NOESY cross peaks
1
9
19
and exchange of the ortho- and meta-fluorine atoms, respectively, from F, F-EXSY cross peaks
indicates that the Pd-bpzm* chelate ring boat-to-boat inversion occurs at a rate slower than the NMR
time scale together with a concomitant change of the C
6
F
5
atom positions. The presence of three
1
9
F-NMR signals for 2F
Pd(C
o
: 1F
p
: 2F
m
of the C
6
F
5
ligand for complexes [Pd(C )Cl(tmeda)] (1) and
6
F
5
[
6
F
5
)Cl(bipy)] (3) (tmeda = N,N,N¢,N¢-tetramethylethylenediamine; bipy = 2,2¢-bipyridine) is
interpreted as being due to identical hemi-spaces above and below an apparent symmetry plane
coinciding with the Pd-coordination plane instead of free ring rotation. The molecular structures of 1, 3
and 5 from single-crystal studies suggest that the hindered C
present in 1 and 3 due to ligand repulsion. Complexes [Pd(C
2), [Pd(C )Cl(bipy)] (3), [Pd(C )OH(bipy)] (4) and [Pd(C
6
F
5
rotation is not limited to 5 but is also
)Cl(tmeda)] (1), [Pd(C )OH(tmeda)]
)Cl(bpzm*)] (5) have been applied as
6
F
5
6
F
5
(
6
F
5
6
F
5
6
F
5
pre-catalysts for the vinyl homopolymerization of norbornene in combination with the cocatalyst
6
methylaluminoxane (MAO). Activities of more than 10 gpolymer/(molPd h) could be reached with these
catalytic systems. Based on the spectrochemical series, pre-catalysts 1 and 2 with the pure s-donor and
more weakly bound aliphatic amine ligands showed higher polymerization activities than compounds
3–5 with modest p-accepting and stronger bound aromatic substituents. This is reasoned with a kinetic
activation effect through a faster removal of the more weakly bound ligands upon reaction with MAO
2
+
together with the chloro or hydroxo ligands to give the active, almost “naked” Pd cations. For the
1
13
19
activation mechanism, H-, C- and F-NMR studies of the MAO activated complex 5 showed about
1
1
3% chlorine-to-methyl exchange for a molar Pd : Al ratio of 1 : 10. For 5 : MAO at a Pd : Al ratio of
: 100 abstraction of C takes place with a redox reaction giving Pd metal and C -CH in the
6
F
5
6
F
5
3
absence of norbornene monomer.
Introduction
Norbornene (NB, bicyclo[2.2.1]hept-2-ene) can be polymerized
by three different ways, each leading to its own polymer type
1–3
(
Scheme 1). The best known polymerization route of nor-
bornene is the ring-opening metathesis polymerization (ROMP),
which leads to a polynorbornene (PNB) still containing double
bonds in the polymer backbone.
In the vinyl or addition polymerization of NB, the bicyclic
structure of the monomer remains intact, and only the double
1,2,3,4
bond of the p component is opened.
Scheme 1 Schematic representation of the three different types of
polymerization of norbornene.
a
Institut f u¨ r Anorganische und Analytische Chemie, Universit a¨ t Freiburg,
Albertstr., 21, 79104, Freiburg, Germany. E-mail: janiak@uni-freiburg.de;
Fax: +49 761 2036147; Tel: +49 761 2036127
Vinyl PNB is of interest due to its good mechanical strength,
heat resistivity, and optical transparency, for example, for deep
ultraviolet photoresists, interlevel dielectrics in microelectronics
b
Departamento de Qu ´ı mica Inorg a´ nica, Facultad de Qu ´ı mica, Universidad de
Murcia, 30071, Murcia, Spain. E-mail: jruiz@um.es; Fax: +34 868 384148;
Tel: +34 868 887455
5,6
applications, or as a cover layer for liquid-crystal displays.
†
Electronic supplementary information (ESI) available: Packing diagrams
Films made from norbornene vinyl polymer are excellent in
transparency and heat resistance and have unchanged viscoelas-
tic and electric characteristics to high temperatures. Such a
and supramolecular interactions for 1, 3, 5, additional and enlarged NMR
spectra. CCDC reference numbers 757345–757347. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/b925674a
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7
◦
film is suitable for a condenser or an insulator. Furthermore,
Table 1 Selected bond lengths ( A˚ ) and angles ( ) for 1, 3 and 5
it shows a low water uptake, a small optical birefringence
and dielectric loss. The addition polymerization of substituted
8
Compound
1
3
5
norbornenes was adopted for the preparation of electroac-
tive polymers, in particular polymers designed as electro opti-
a
Pd–C–1
1.995(4)
2.122(3)
2.081(3)
2.302(1)
178.48(14)
93.14(14)
85.35(12)
88.24(11)
93.27(9)
178.62(9)
87.9(1)
2.010(2)
2.0768(18)
2.0368(17)
2.2757(5)
176.31(8)
97.74(8)
79.93(7)
87.56(6)
94.78(5)
174.70(5)
68.81(5)
1.996(3)
2.121(2)
2.029(2)
2.2963(6)
169.59(10)
91.12(10)
85.66(8)
90.08(8)
93.37(6)
178.31(6)
57.47(6)
b
Pd–N trans to C
Pd–N trans to Cl
9
c
cal materials. Bis(trifluoromethyl)carbinol-substituted polynor-
10
Pd–Cl
bornenes are promising materials for 157 nm photoresist resins.
C-1–Pd–N-trans
C-1–Pd–N-cis
N–Pd–N
The vinyl polymerization of NB uses catalytic systems based on
titanium, chromium, iron, cobalt, copper, with recent emphasis
1–3
on highly active nickel and palladium.
C-1–Pd–Cl
cis-N–Pd–Cl
trans-N–Pd–Cl
Dihedral angle
Some examples of palladium(II) complexes bearing N,N-
chelate ligands have been reported for the vinyl polymerization
1
,2,3,5,11,12
of norbornene.
At the same time, the pentafluorophenyl
C
6 5
(F )–PdClCipsoNN
1
9
group with the F nucleus is an excellent probe for molecular
dynamics and for pre-catalyst activation mechanism by F-
NMR spectroscopy. Generally, the species in MAO-activated
Ni- or Pd-complexes and initiation steps for norbornene
polymerization are not well known. For the better defined
co-catalytic system B(C or B(C /AlEt the activation
process of the pre-catalyst [Ph PCH C(O)CH [Pd Cl
was followed by multinuclear ( H, C, F, and P) NMR
investigations and points to the formation of molecular PdCl
which may represent the active species in the polymerization
a
C(arbon)1 (= Cipso of C
6 5
F group) is labeled as C-1 to avoid being misread
c
1
9
b
as Cl(chlorine). N1 in compounds 1 and 3, N2 in 5. N2 in compounds
1 and 3, N4 in 5.
13
1,2,3,14
6
F
5
)
3
6
F
5
)
3
3
3
13
2
3
31
]
2
2
6
]
1
19
2
15
31
19
process. Multinuclear ( P and F) NMR investigations
on [PdCl (dppe)] and [PdCl (dppp)] in combination with
B(C and B(C /AlEt suggest the formation of [Pd(L)]
cations (L = dppe, 1,2-bis(diphenylphosphino)ethane; dppp,
,3-bis(diphenylphosphino)propane) in the activation process.
E(C (L)] under
(E = B, Al) reacts with the pre-catalysts [MCl
abstraction of the two chloride atoms followed by the formation
2
2
2
+
6
F
5
)
3
6
F
5
)
3
3
1
6
F
5
)
3
2
2
+
of highly active “naked” Pd through a ligand redistribution of
2
+
2+
2+ 16
the unstable [Pd(dppe)] cation to yield [Pd(dppe)
2
]
and Pd .
1
19
H-NMR and F-NMR showed that the polynorbornene
obtained in the presence of ethylene with activator-free (h -
6
17
C
6
H
5
CH
The reaction of trans-[Pd(C
,4,6-trifluorophenyl,C Cl
with an excess of norbornene but no cocatalyst was moni-
3
)Ni(C
6
F
5
)
2
had the end-groups –CH=CH
)Br(AsRfPh ] (R
) and [Pd(C )(NCMe)(bipy)]BF
2
and –C
6
F
5
.
6
F
5
2
)
2
f
3,5-dichloro-
2
6
2
F
3
6
F
5
4
Scheme 2 Palladium(II)-C F pre-catalysts for the vinyl polymerization
6
5
of norbornene.
1
9
tored by F-NMR and signals from (NB)C–C
6
F indicated
5
that the polymerization process starts with the insertion of NB
a pentafluorophenyl and a hydroxo or chloro ligand. The
solid-state molecular structures of 1, 3 and 5 with their
slightly, chelate-induced distorted square-planar palladium co-
ordination are depicted in Fig. 1–3, respectively. Distances
18,19
into the Pd–C
6
F
5
bond.
From the cationic complex trans-
and norbornene (NB : Pd =
[
Pd(C
6
F
5
)(AsRfPh
2
)
2
(NCMe)]BF
4
1
0 : 1), the polymerization starts with the substitution of an
AsRfPh
norbornene into the Pd–C
NMR and F-NMR).
Here the palladium(II) complexes 1–5 (Scheme 2) with different
N,N-chelate ligands and the C group in combination with
2
ligand cis to the C
6
F
5
group followed by insertion of
and angles (Table 1) are as expected from a compari-
1
20
6
F
5
bond and the chain growth (by H-
son to the related complexes [Pd(C
[Pd(C )(CO Me)(tmeda)], [Pd(C
[{Pd(C )(4,4¢-Me -2,2¢-bipy)} (m-CO
Mecyt)(bpzm*)]ClO
6
5
F )(maleimidate)(tmeda)],
1
9
18
6
F
5
2
6
5
F )(SC(OMe)NPh)(tmeda)],
21
6
F
5
2
2
3
)],
and [Pd(C
6
5
F )(1-
22
6
F
5
4
.
either the chloro- or hydroxo-substituent were used for the vinyl-
homopolymerization of norbornene with MAO as activator. Com-
plex 5 was fully characterized by 1D- and 2D-NMR spectroscopy
and NMR experiments were performed with the MAO-activated
catalyst 5.
The differences in Pd–N distances, with trans-N–Pd–carbon
longer than trans-N–Pd–chlorine in 1, 3 and 5 are in agreement
with the higher trans influence of the C
6
5
F group, i.e. better
s-donor character compared to chlorine. While the solid-state
◦
structures of 3 and 5 show dihedral angles of less than 70 for
the C
6
5
F ring with the PdCl(Cipso)NN coordination plane, the
Results and discussion
most stable conformation in solution has the aryl ring roughly
23
perpendicular to this coordination plane.
Complex 1 crystallizes in the non-centrosymmetric space group
Molecular structures
24
Compounds 1–5 are molecular palladium(II) complexes with
a bidentate chelating aliphatic amine or bipyridine ligand,
Aba2 (now called Aea2). In the crystal the molecules of 1 are all
oriented with the tmeda side or C and Cl side, respectively, in
6
F
5
3
610 | Dalton Trans., 2010, 39, 3609–3619
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Fig. 1 Thermal ellipsoid plot (50% probability) of complex 1, also
showing the conformational racemic l/d disorder of the tmeda chelate
ring. Selected distances and angles in Table 1.
1
-1
Fig. 4 H-NMR spectrum of complex 5 in CD
2
Cl
2
(0.03 mol l ) at
room temperature (*CDHCl
H, H-TOCSY spectrum (Fig. 5), NOE difference spectra (Fig. 6(b) and
(c)) and the H, F-HOESY spectrum (Fig. S16 in ESI†).
2
). The peak assignment is based on the
1
1
1
19
6
Fig. 2 Thermal ellipsoid plot (50% probability) of complex 3. Selected
distances and angles in Table 1.
1
1
Fig. 5 H, H-TOCSY spectrum of 5 (mixing time: 0.2 s) in CD
(
2
Cl
2
-
1
0.03 mol l ) at RT. Rectangles of the same color emphasize the
small homonuclear coupling correlation of protons situated on the same
pyrazolyl ring.
Fig. 3 Thermal ellipsoid plot (50% probability) of complex 5. Selected
distances and angles in Table 1.
1
.75 and 2.31 ppm belong to the same pyrazole ring, likewise the
olefinic proton at d = 5.87 ppm and the methyl groups at 2.30 and
2
.44 ppm.
the same direction along the polar c axis (Fig. S1 in ESI†). This
25
In the 1D-NOE difference spectra (Fig. 6) the positions of
polar packing in the crystal of 1 occurs in domains with opposite
molecular orientations so that overall the crystal is a racemic
mixture. Packing diagrams for 1–3 together with supramolecular
the CH groups on the pyrazolyl rings can be identified. If the
3
methylene proton signal with the chemical shift of d = 7.21 ppm is
selectively irradiated, positive NOEs are found for the resonances
of the methyl groups at 2.30 and 2.31 ppm (Fig. 6(b)), which proves
that these methyl groups are directed to the side of the methylene
protons, whereas the methyl groups with the chemical shifts of d =
26
27
p-, C–H ◊ ◊ ◊ F/Cl- and C–F ◊ ◊ ◊ p-interactions are given in the
ESI (Fig. S1–S3).†
NMR spectroscopy
1.75 ppm and d = 2.44 ppm point into the direction of the other
An NMR study of 5 was carried out to assess the solution structure
in terms of ligand fluxionality. Understanding, for example, the
ligands. The strong negative signal at d = 6.02 ppm results from
chemical exchange of the methylene-bridge protons (see below).
The 1D-NOE difference experiment in Fig. 6(c) was used as a
duplicate test. Irradiation of the methyl group with the chemical
shift of d = 1.75 did not cause a positive NOE of the methylene
protons at 6.02 and 7.21 ppm, which confirms the large spatial
distance between this methyl group and the methylene protons.
So far, the question is still open, which pyrazolyl ring of the
bis(pyrazolyl) ligand is neighboring the pentafluorophenyl and
C
6
F ring rotation is important for the interpretation of the
5
13
1
reactivity and selectivity in catalysis. The H-NMR spectrum
of complex 5 (Fig. 4) was unequivocally assigned by 2D and NOE
techniques.
The H, H-TOCSY experiment (Fig. 5) allows correlations via
small homonuclear couplings and proves that the olefinic proton
with the chemical shift of d = 5.80 ppm and the methyl groups at
1
1
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1
13
a
Table 2 H- and C-NMR assignment of the bpzm* ligand in 5
1
b
13
b
H
d (ppm)
C
d (ppm)
C16–H
C11–H
C17–H
C10–H
C14–H
C8–H
3
3
3
3
1.75
2.30
2.31
2.44
5.80
5.87
6.02
7.21
C11
C17
C16
C10
C12
C8
C14
C9
C15
C13
C7
10.8
11.0
13.5
13.5
57.4
107.8
108.0
140.6
141.3
152.6
153.2
C12–H
C12–H
2
2
a/b
b/a
1
-1
Fig. 6 (a) H-NMR spectrum of complex 5 in CD
room temperature; (b) 1D-NOE difference spectrum (mixing time: 1.0 s)
with signal irradiation at 7.21 ppm (*CDHCl ); the positive NOE (red
2 2
Cl (0.03 mol l ) at
2
a
1
1
1
Based on the H-NMR spectrum (Fig. 4), H, H-TOCSY (Fig. 5), NOE
circle) indicates the spatial proximity; the strong negative signal at 6.02 ppm
a chemical exchange – see text; (c) NOE difference spectrum (mixing time:
1
19
difference spectra (Fig. 6b, c), H, F-HOESY (Fig. S16 in ESI†) and
13
1
b
1
13
C, H-HMBC spectrum (Fig. 7). The H and C atom numbering follows
the X-ray structure atom numbering in Fig. 3.
1
.0 s) with signal irradiation at 1.75 ppm; the positive NOE (green circle)
1
1
confirms the H, H-TOCSY result that the methyl group at 1.75 and the
olefinic proton at 5.80 ppm are situated on the same pyrazolyl ring.
the chlorine substituent, respectively. The answer is found in the
1
19
H, F-HOESY spectrum (Fig. S16 in ESI†). Only the methyl
resonance at 1.75 ppm shows NOE cross peaks to the ortho-
fluorine signals at -119.3 and -121.4 ppm and must therefore
belong to the methyl group in the neighborhood of the C
6
5
F group.
This is in good agreement with the highfield shift that is observed
for this methyl resonance in comparison with the other methyl
signals, because nuclei that are positioned above the plane of a
phenyl ring experience a shielding effect.
By this means all proton signals are unambiguously assigned as
recorded in Table 2.
1
3
1
The corresponding C shifts (Table 2) are derived by the J
1
3
1
1
cross peaks from the C, H-HMBC spectrum (Fig. 7). The J cross
peaks are distinguished from long-range correlations by their large
1
splitting due to the large J coupling constants. The quaternary
2
3
4
carbon resonances are identified by the J, J and J long range
correlations in the same spectrum. The olefinic CH resonance at
2
13
5
1
.80 ppm shows two J cross peaks to the C signals at 141.3 and
52.6 ppm, which therefore belong to the same pyrazolyl ring as
1
3
2
this CH group. These two C signals can be distinguished by the J
correlations from the attached methyl groups, which show that the
resonance at 152.6 ppm belongs to the carbon atom attached to the
methyl group with the proton resonance at 1.75 ppm. Whereas the
signal at 141.3 ppm belongs to the carbon atom that is bound to
the methyl group with the proton shift at 2.31 ppm. Analogously,
the resonance at 140.6 ppm belongs to the carbon atom attached
to the methyl group with the proton resonance at 2.30 ppm and the
signal at 153.2 ppm can be attributed to the carbon atom bound
to the methyl group with the proton resonance of 2.44 ppm. The
1
3
1
2 2
Cl
(0.03 mol l-1)
Fig. 7
C, H-HMBC spectrum of complex 5 in CD
at room temperature. The cross peaks represent the coupling constants
J( H, C) in red rectangles, J( H, C) in green rectangles, J( H, C) in
blue rectangles and J( H, C) in violet rectangles. Due to low sample
concentration a good quality C-NMR spectrum could not be measured
1
1
13
2
1
13
3
1
13
4
1
13
13
separately (see enlarged and more detailed Fig. S4 in ESI†).
1
3
peaks to the same C resonance in the aliphatic region at 57.4 ppm
(see enlarged and more detailed Fig. S4 in ESI†).
1
9
The F-NMR spectrum of 5 shows five signals for the C
6
F
5
1
methylene bridge proton signals (6.02 and 7.21 ppm) show J cross
ligand (Fig. 8, Table 3). The signals at -119.3 and -121.4 ppm can
3
612 | Dalton Trans., 2010, 39, 3609–3619
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19
13
Table 3
F-NMR and C-NMR assignment for the C
6
F
5
ligand in 5
structure (Fig. 9). The methyl group in the 3-position of the cis-
positioned pyrazolyl ring blocks the rotation of the C
6
5
F ring.
a
19
13
Atom
F d (ppm)
C d (ppm)
b
b
b
o-F5–C6
o-F1–C2
p-F3–C4
m-F4–C5
m-F2–C3
ipso-C–1
-119.3/-121.4
148.3/146.8
-161.7
137.7
135.6/135.1
b
-164.5/-165.0
106.0
a
The F and C atom numbering follows the X-ray structure atom numbering
b
in Fig. 3. A more specific assignment in the ortho and meta region to the
individual atoms was not possible.
Fig. 9 Space-filling representation of complex 5 to illustrate the hindered
rotation of the C group around the Pd–Cipso bond. The C plane
6
F
5
6 5
F
is tilted to the PdCl(Cipso)NN coordination plane in the solid state
◦
(
interplanar angle 57.47(6) ).
1
9
19
The F, F-EXSY spectrum (Fig. S9 in ESI†), however, displays
cross peaks between the two ortho-F resonances, as well as between
the two meta-F resonances. The cross peaks are in phase with the
diagonal peaks, which indicates that they result from chemical
exchange.
This exchange could be explained by a very slow rotation (slower
than the NMR time scale) of the pentafluorophenyl ring or a slow
flip with an exchange of the hemi-spaces. At the same time there
is a chemical exchange between the methylene bridge protons of
the bpzm* ligand observed in the 1D-NOE difference spectrum
1
9
-1
Fig. 8
F-NMR spectrum of 5 in CD
2 2
Cl (0.03 mol l ) at RT. Identically
colored arrows indicate which o- and m-F are neighbors from the cross
peaks of a F, F-COSY experiment (see Fig. S5 in ESI†).
19
19
1
1
be attributed to the ortho-fluorine atoms, the signal at -161.7 ppm
to the para-fluorine atom and the signals at -164.5 and -165.0 ppm
represent the meta-fluorine atoms of the C
(Fig. 6(b)) and confirmed by a 2D H, H-NOESY experiment
(Fig. S10 in ESI†). The cross peaks between the resonances of the
two methylene protons are in phase with the diagonal peaks, which
again indicates that they result from chemical exchange due to a
slow fluxional process. For this exchange, the following mechanism
seems to be the most reasonable: a slow boat-to-boat inversion
(Scheme 3) of the Pd-bpzm* chelate ring is typical for this type
6
F ligand because of
5
13
19
19
their chemical shifts. This assignment is confirmed by the F, F-
COSY spectrum (Fig. S5 in ESI†), where the signals at -119.3 ppm
and -121.4 ppm in contrast to the other resonances show only
one intensive cross peak. Based on this cross peak, the meta-
F atom with the resonance at -164.5 ppm is identified as the
neighbor of the ortho-F atom at -119.3 ppm and the meta-F atom
at -165.0 ppm is the neighbor of the ortho-F atom at -121.4 ppm.
This interpretation is possible because the absolute value of the
28
of complexes. There is a concerted flip of the pentafluorophenyl
group as a consequence of such a boat-to-boat inversion, which
causes a simultaneous exchange of the chemical environment of
the fluorine atoms and the methylene protons (Fig. 10). Given the
fact, that almost no line broadening is observed in the line shape
of the ortho- and meta-fluorine resonances at room temperature,
3
19
19
5
19
19
J( F, F) coupling constant is dominating the J( F, F) coupling
constant (see Table S1 in ESI†), so that the corresponding cross
1
9
19
13
peaks of the F, F-COSY spectrum display significantly different
intensities.
this process has to be slow (or “frozen”) on the NMR timescale.
The finding of a slow (“frozen”) boat-to-boat inversion
The chemical shifts of the carbon atoms (Table 3) of the
and hindered C
with the previous interpretations (observations) in the cationic
complex [Pd(C )(1-Mecyt)(bpzm*)]ClO (in acetone-d , 1-
6
F
5
ring rotation in 5 (in CD
2
Cl ) contrasts
2
1
9
13
pentafluorophenyl substituent were identified by a F, C-HSQC
spectrum (see Fig. S6 in ESI†). However, the spatial positions
of the different ortho-fluorine and meta-fluorine atoms were
not identified. The remaining quaternary ipso-carbon atom was
6
F
5
4
6
22
Mecyt = 1-methylcytosine) and in the neutral complexes
i
21
[Pd(C
6
F
5
)(CO
2
R)(bpzm*)] (R = Me, Et, Pr) (in CDCl
3
). There,
1
9
13
determined by a F-decoupled C-NMR experiment (see Fig. S7
in ESI†).
the boat-to-boat inversion was also frozen (two doublets for the
two diastereotopic methylene protons Ha, Hb) but the C
“rotation” noted as “unhindered” (because of only three
resonances). In Pd(C )(CO
6
F
5
ring
F
1
9
19
The presence of five signals in the F-NMR spectrum of 5
1
9
(
Fig. 8, see Fig. S8 for F-NMR of 5 in acetone-d
6
in ESI†)
6
F
5
2
R)(bpzm*)] the o-F resonance was
21
indicates the absence of fast rotation of the C substituent
6
F
5
broad.
To quote from ref. 13: “It is very unlikely that C
around theM–Cipso bond together with the inequivalence of the two
6
5
F rings
hemi-spaces above and below the coordination plane determined
flanked in square-planar complexes with donor atoms of the
size of chlorine or bigger are “freely rotating” and if rotation
is clearly observed, a dissociative mechanism should be taken into
by the other ligands for a near perpendicular position of the C
6
F
5
13
ring to this plane. The hindered rotation of the C
6
5
F group
in 5 becomes understandable with a space-filling drawing of the
account”. In complexes [Pd(C
6
F
5
)X(SPPy
2
Ph)] (X = Cl, Br, I) the
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1
9
The F-NMR spectra of both 1 and 3 exhibit three signals for
: 1F : 2F of the C ligand (Fig. S11 and S12 in ESI†). The
related complexes [Pd(C
2F
o
p
m
6
F
5
6
F
5
)(1-Mecyt)(tmeda)]ClO
4
(in acetone-
22
21
20
d
6
), [Pd(C
6
F
5
)(CO
2
Me)(NN)] and [Pd(C
6
F )(imidate)(NN)]
5
(
NN = 2,2¢-bipy and tmeda) (in CDCl
resonances (in the ratio 2 : 1 : 2) for the o-, p- and m-fluorine atoms,
respectively. However, [Pd(C )(1-Mecyt)(bipy)]ClO (in DMSO-
) shows a hindered rotation of the C ring with two separate
3
) also exhibit three
6
F
5
4
d
6
6
F
5
22
signals observed each for the o- and m-F-atoms. In accordance
with the space-filling diagrams of the X-ray structures of 1 and 3
(
Fig. 11, 12) we argue that a free rotation of the C
6
5
F group is not
necessary to yield only three resonances. An apparent symmetry
plane coinciding with the coordination plane of the complex as
in 1 and 3 will produce the same effect as a rotation in the
30–32
spectra.
If the hemi-spaces above and below the coordination
plane, which is set by the other ligands, are equivalent, so will the
13
o- and m-F-atoms. Or a dissociative mechanism: cytosine and
methylcytosine (1-Mecyt) ligands on the other hand are known to
easily dissociate in Pt and Pd complexes where free cytosine (in
acetone-d
two molecules (in methanol-d
Otherwise, the unsymmetrical 1-Mecyt ligand will render the hemi-
6
) and an intermolecular exchange of cytosine between
33
4
) could by observed by NMR.
spaces inequivalent for the C
not occur.
6
5
F group if such a dissociation does
Fig. 10 Inversion-symmetry (1 - x, 1 - y, 1 - z) related molecules of 5
based on the boat-to-boat inversion of the chelate ring which also induces
a concerted flip of C F ring plane so that the ortho- and meta-F atoms,
6 5
respectively (arbitrarily labeled as 2–6) exchange their positions without a
ring rotation.
Fig. 11 Space-filling representation of complex 1. The conformational
racemic l/d disorder of the tmeda chelate ring creates a pseudo-mirror
planes which passes through the C
meta-F positions, respectively, equivalent even if the rotation is blocked
by the tmeda methyl groups. Already in the solid state he C ring
6 5
F ring and renders the two ortho- and
6
F
5
plane is almost perpendicular to the PdCl(Cipso)NN coordination plane
◦
(
interplanar angle 87.9(1) ).
Scheme
Pd(C
or [Pd(C
3
Boat-to-boat inversion of the bpzm* ligand in
[
6
F
5
)L(bpzm*)] complexes, like 5, [Pd(C
6
F
5
)(1-Mecyt)(bpzm*)]ClO
4
i
21,22
6
F
5
)(CO
2
R)(bpzm*)] (R = Me, Et, Pr).
aryl rotation is very slow in CDCl
3
but very fast in polar solvents
such acetone, suggesting that halide dissociation takes place with
29
the energy compensated by ion solvation. Thus, we propose a
6 5
Fig. 12 Space-filling representation of complex 3. The C F plane
dissociative mechanism for the C
Mecyt)(bpzm*)]ClO and [Pd(C
Et, Pr), in view of the steric situation in a square-planar complex
with the Pd(C )(bpzm*) moiety, where the methyl group of the
bpzm* ligand blocks the C ring rotation.
6
F
F
5
ring rotation in [Pd(C
6
F )(1-
5
is tilted to the PdCl(Cipso)NN coordination plane in the solid state
)(CO
2
R)(bpzm*)] (R = Me,
◦
4
6
5
(
interplanar angle 68.81(5) ). However, a perpendicular orientation is
i
feasible in solution which then renders the two ortho- and meta-F positions,
respectively, equivalent in view of the identical hemi-spaces. A full rotation
may still be blocked by the C–H groups of the bipy ligand.
6
F
5
6
F
5
3
614 | Dalton Trans., 2010, 39, 3609–3619
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Table 4 Results of the NB polymerization with 1–5/MAO
Activity (gPNB
Catalyst Time/sec Polymer yield/g Conversion (%) molPd h)
/
6
6
6
6
6
5
6
5
6
5
1
1
2
2
3
3
4
4
5
5
/MAO 30
/MAO 60
/MAO 30
/MAO 60
/MAO 30
/MAO 60
/MAO 30
/MAO 60
/MAO 30
/MAO 60
0.31
0.44
0.34
0.47
0.13
0.16
0.15
0.16
0.10
0.13
31
44
34
47
13
16
15
16
10
13
3.51 ¥ 10
2.46 ¥ 10
3.79 ¥ 10
2.66 ¥ 10
1.48 ¥ 10
8.78 ¥ 10
1.70 ¥ 10
9.08 ¥ 10
1.14 ¥ 10
7.36 ¥ 10
Fig. 14 Norbornene monomer conversions with 1–5/MAO for different
polymerization times.
2 2
Conditions: room temperature, toluene–CH Cl solution, total volume
1
0.0 mL, 1.0 g (10.6 mmol) of NB, 10.6 mmol Pd complex, molar ratio
Pd : NB = 1 : 1000, Pd : Al = 1 : 100.
The polymerization activities differ over a range from 7.36 ¥
0 gPNB/molPd h (5/MAO) to 3.79 ¥ 10 gPNB/molPd h (2/MAO).
5
6
1,2
1
As expected, the activities obtained after a polymerization time of
30 s are higher than the activities for a time of 60 s (Fig. 13) while
polymer yields or conversions increased with longer reaction times
Norbornene polymerization
The results of the vinyl homopolymerization of NB with the
pre-catalysts 1–5 are summarized in Table 4 and Fig. 13 and
(
Fig. 14).
The palladium complexes 1 and 2 with the aliphatic N,N-
1
4. Reaction times of 30 or 60 s were chosen intentionally. The
chelating N,N,N¢,N¢-tetramethylethylenediamine ligand showed
markedly higher activities than compounds 3–5 with aromatic
N,N-chelating ligands. For 1/MAO and 2/MAO the monomer
conversions exceeded 40% within one minute of reaction time,
whereas the catalytic systems 3–5/MAO produced PNB in a range
of 13 to 16% monomer conversion under the same conditions
polymerization was stopped after this time by the addition of
MeOH/HCl. Such short reaction times with conversions still
below 50% allow for a better differentiation or comparison of
catalyst activities. The catalysts are longer living. Yet, the reac-
tion mixture becomes more viscous with time and concomitant
monomer conversion which leads to a lower reaction rate through
the decrease of the diffusion rate of NB monomer to the active
center. The NB polymerization is truly homogeneous only at the
very beginning. With PNB formation the active complex becomes
more and more embedded in the polymer matrix which represents
a transfer to a heterogeneous phase, that is, a heterogeneous active
(
Fig. 14). This must be attributed to the electronic effects of the
aromatic substituents since the steric demand for 3 and 4 is not
seen as higher than those of 1 and 2. In the literature electron-
withdrawing ligands or substituents are usually viewed as activity
35–42
enhancing in complexes activated for NB polymerization.
Aromatic nitrogen ligands are stronger and electron-withdrawing
ligands in the spectrochemical series than aliphatic amine ligands
due to their modest p-accepting character whereas aliphatic
amines are pure s-donor ligands. Hence, our activity order is
counterintuitive. Therefore, we argue here with a kinetic activation
effect. Previous work has shown that upon borane or MAO
34
complex form, and this leads to a diffusion-controlled reaction.
The reaction rate is then controlled by the rate of diffusion of
the monomer through the polymer matrix to the enclosed active
center and can no longer be compared in terms of steric or
electronic ligand effects, for example. In a diffusion-controlled
regime all catalysts with a faster, albeit still different insertion
rate, will show the same activity due to the more rapid monomer
insertion over diffusion under these conditions. In order to
obtain meaningful different catalytic activities the polymerization
conditions have to be chosen such as to avoid a diffusion-
controlled process. Therefore, we ensured short reaction times with
2
+
activation all ligands can be lost to give a “naked” Pd as the
16
active species. Hence, more weakly bound ligands which will
be removed faster will lead more quickly to the active palladium
+
dications. Based on dissociation energies for M –L (L = NH
3
,
pyridine) the aliphatic diamine ligands are bound more weakly
to a metal atom than the aromatic pyridine ligands by about
0 kJ mol . We are not aware of any similar comparison between
34
monomer conversions of less than 50%.
-
1 43
2
aliphatic and aromatic dinitrogen ligands. There is no significant
effect of the chloro vs. hydroxo ligand on the polymerization
activity as shown by a comparison of catalysts 1/MAO vs. 2/MAO
and 3/MAO vs. 4/MAO. Complexes with the hydroxo ligands
appear to be, if any, only very slightly more active. The often
encountered insolubility of the obtained PNBs made a further
characterization of the polymer molar mass and mass distribution
1
,2,3
by gel permeation chromatography impossible.
1
9
F solid-state NMR-experiments were attempted with the
PNBs obtained by the catalytic systems 1–5/MAO to try to get
information on the polymer start group, for a better understanding
of the mechanism of the norbornene polymerization, whose
1
9
Fig. 13 Polymerization activities of MAO activated pre-catalysts 1–5 for
different reaction times.
initiation step is of high interest. However, no signals in the F-
spectra could be detected. This could be attributed to the fact,
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that the PNBs were of too high molecular weight to determine the
end-group by NMR or that the C ligand is not the start group,
that is, the first insertion does not occur into the Pd–C bond
see below).
rophenyl group still bound to a palladium atom (Fig. 16(b) and
enlarged version in Fig. S15(a),(b) in ESI†). The integrals of the
fluorine resonances provide the same ratio of 1 : 6.7 (new complex
6
F
5
6
F
5
1
(
to 5) as the integrals in the H-NMR spectrum. There is, however,
only one signal, each, of the ortho- and meta-F atoms of the C
6
F
5
Pre-catalyst activation
ligand in the methylated complex, albeit significantly broadened.
Complex 5 was chosen for an NMR study to elucidate the
activation mechanism with MAO at two different molecular
Pd : Al ratios of 1 : 10 and 1 : 100. At a Pd : Al ratio of 1 : 10 the
1
H-NMR spectrum is dominated by the signals of the unchanged
complex 5, which are slightly shifted compared to the resonances
of pure 5 mainly due to the different solvent (toluene-d
8
versus
CD Cl ). In addition, less intense resonances are found for a
2
2
complete second set of signals of the bpzm* ligand (Fig. 15(a)).
At 0.43 ppm another resonance appears with an integral identical
to the integrals of the CH groups of this second bpzm* set. If
3
this signal is selectively irradiated, a positive NOE is found for the
methyl group on the bis(3,5-dimethylpyrazol-1-yl)methane ligand
with the chemical shift d = 2.18 ppm (Fig. 15(b)).
19
Fig. 16 (a) F-NMR spectrum of the unactivated complex 5 in CD
(
2
Cl
L = Cl) (0.03 mol l ) at room temperature. (b) F-NMR spectrum
of 5/MAO (L = CH ) (molecular Pd : Al ratio of 1 : 10), see also Fig.
S15(a),(b) in ESI† for an enlarged version. (c) F-NMR spectrum of
2
-1
19
3
19
5
/MAO (molecular Pd : Al ratio of 1 : 100).
In Table 5, the chemical shifts of the methylated complex
1
3
from 5/MAO with Pd : Al = 1 : 10 are summarized. The
C
1
3
1
resonances are derived from the C, H-HMBC spectrum for
1
Fig. 15 (a) Methyl region of the H-NMR spectrum of the MAO activated
5/MAO (Fig. S13 in ESI†).
complex 5 with a molecular Pd : Al ratio of 1 : 10 (in a 1 : 1 mixture
1
of CD
2
Cl
2
and toluene-d
8
as a 0.03 mol l- solution in Pd, RT). Cyan
1
13
19
Table 5 H-, C- and F-NMR assignment of the methylated complex
a
rectangles highlight the newly formed bpzm* signal set, the red rectangle
in 5/MAO at a molar Pd : Al ratio of 1 : 10
the new methyl resonance. There is signal overlap at 1.60 ppm for 5 and its
1
b
13 b,c
19
b
methylated form [Pd(C
6
F
5
)CH
3
(bpzm*)]. (b) 1D NOE-difference spectrum
H
d (ppm)
C
d (ppm)
F
d (ppm)
of 5/MAO with signal irradiation at 0.43 ppm and the positive NOE (red
circle).
Pd–CH
3
0.43
1.60
Pd-CH
C11
C17
C16
C10
C12
C8
C14
C15
C9
3
–13.0
10.3
10.6
13.6
14.0
F1,F5
F3
F2,F4
114.1
163.8
165.0
d
C16–H
C11–H
3
3
1.84
1.88
2.18
5.37
5.54
5.32
6.76
1
3
1
In a C, H-correlation (Fig. S13 in ESI†) the resonance of the
C17–H3
corresponding C atom is identified at -13 ppm. This strongly
C10–H
C14–H
C8–H
3
56.8
suggests that the new resonance at 0.43 ppm belongs to a CH
group directly bound to a Pd atom that is still coordinated by a
bpzm* ligand. This Pd–CH group is then neighboring the CH
3
107.8
108.0
140.3
141.0
151.8
152.7
C12–H
2
a/b
3
3
C12–H b/a
2
group of the pyrazolyl ring with the proton resonance at 2.18 ppm.
The fact, that one pyrazolyl methyl group of the new set is still
upfield shifted (1.60 ppm) as in 5 (1.75 ppm) leads to the conclusion
C7
C13
a
1
Based on the H-NMR spectrum (cf. Fig. 15(a) – full range as Fig. S14
that the C
6
5
F substituent remained bound to Pd and it is the
13
1
19
in ESI†), C, H-HMBC spectrum (Fig. S13 in ESI†) and the F-NMR
spectrum (Fig. 16(b)). The spectra were recorded in a 1 : 1 mixture of
chlorine which is replaced by the entering methyl group. According
to the proton integrals the ratio between the methylated complex
and complex 5 is 1 : 6.7, amounting to 13% chlorine-to-methyl
exchange (see Fig. S14 with integrals in ESI†).
-1
b
CD
2
Cl
2
and toluene-d
8
as a 0.03 mol l solution with respect to Pd. The
F and C atom numbering follows the X-ray structure atom numbering in
c
13
6 5
Fig. 3. An assignment of the C resonances for C1-C6 of the C F ligand
d
was not undertaken. There is signal overlap at 1.60 ppm for 5 and its
methylated form.
1
9
Consistent with the proton NMR, the F-NMR spectrum also
shows the signals of 5 and the resonances of a second pentafluo-
3
616 | Dalton Trans., 2010, 39, 3609–3619
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A molecular Pd : Al ratio of 1 : 100 for 5/MAO led to an
General polymerization procedure
The palladium complexes/pre-catalysts (1.06 ¥ 10 mmol) were
immediate dark palladium metal precipitate in the NMR tube,
-
2
2
+
probably due to formation of “naked” Pd from complete ligand
2
+
dissolved in 4 ml of CH
2
Cl
2
to give a light-yellow colored clear
abstraction and subsequent reduction of reactive Pd in the
-
3
-1
16
19
solution (cPd = 2.65 ¥ 10 mmol ml ). A 25 ml Schlenk-flask
was charged with the NB/toluene solution (1.5 ml, 10.6 mmol
NB) and an additional 3.8 ml of toluene. Then, the MAO solution
absence of the stabilizing norbornene monomer. In the F-
NMR spectrum no signals of a Pd-bound pentafluorophenyl
ligand could be found anymore. Instead, the resonances of the
(0.7 ml) was added to reach a total reaction volume of 10 ml. After
corresponding oxidation product pentafluorotoluene, C
were almost exclusively detected (Fig. 16(c)).
6
F
5
-CH
3
1
min of stirring the pre-catalyst/dichloromethane solution was
added via syringe to start the polymerization. The polymerizations
were run at room temperature. The activity did not lead to a
significant warming of the reaction mixture; hence, no cooling
bath was necessary. After 30 or 60 s the polymerization was
stopped by the addition of a methanol/concentrated HCl mixture
(10 : 1, 30 ml). The precipitated polymer was filtered, washed
with methanol, and dried in vacuo for 6 h. Each polymerization
experiment was performed twice to ensure reproducibility. The
vinyl type polymerization of norbornene was ensured by infrared
spectroscopy of the polymers which showed no absorption bands
Conclusions
Complex [Pd(C
NMR spectroscopy in terms of complete peak assignment by
various 1D and 2D H-, C- and F-NMR techniques. The
bpzm* boat-to-boat inversion occurs at a rate slower than the
NMR time scale together with a concomitant change of the
6
F )Cl(bpzm*)], 5 was fully characterized by
5
1
13
19
C
6
F atom positions (no ring rotation). The presence of only
5
1
9
-1
three F NMR signals for complexes [Pd(C
6
F
5
)Cl(tmeda)], 1
in the region of 1640 cm , which otherwise would indicate the
and [Pd(C )Cl(bipy)], 3 is interpreted as being due to the
6
F
5
presence of double bonds.
identical hemi-spaces above and below an apparent symmetry
plane coinciding with the Pd-coordination plane instead of free
ring rotation. X-Ray structures of 1, 3 and 5 agree to the
hindered ring rotation due to ligand repulsion. Five palladium(II)
pre-catalysts with N,N-chelating ligands and chloro vs. hydroxo
substituents could be activated with MAO towards the vinyl
X-Ray crystallography†
A suitable single crystal of 1, 3 or 5 was carefully selected
under a polarizing microscope. Data Collection: Bruker Smart
˚
Apex diffractometer Mo Ka radiation (l = 0.71073 A), graphite
monochromator, double-pass method w-scan, temperature 100(2)
polymerization of NB and showed activities of more than
45
6
K. Data collection with SMART, cell refinement and data
1
0 gPNB/molPd h. The complexes with the aliphatic N,N-chelating
4
5
reduction with SAINT, experimental absorption correction with
ligand N,N,N¢,N¢-tetramethylethylenediamine gave significantly
higher catalytic activities than the Pd complexes bearing aromatic
N,N-chelating substituents. This behavior is reasoned by faster
MAO activation through a more rapid ligand abstraction of
the more weakly bound aliphatic N,N-ligand together with the
46
SADABS. Structure Analysis and Refinement: the structures
were solved by direct methods (SHELXS-97); refinement was
2
done by full-matrix least squares on F using the SHELXL-
47
9
7 program suite. All non-hydrogen positions were refined
2
+
with anisotropic displacement parameters. Hydrogen atoms were
positioned geometrically and refined using riding models with
chloro or hydroxo ligands to give the active, almost “naked” Pd
1
13
19
cations. Furthermore, H-, C- and F-NMR studies of the MAO
activated complex 5 showed a chlorine-to-methyl exchange for a
molar Pd : Al ratio of 1 : 10. At a Pd : Al ratio of 1 : 100 for 5/MAO
U
iso(H) = 1.2 Ueq(CH, CH
2
) and Uiso(H) = 1.5 Ueq(CH
3
).
In the structure of 1 the ethylene moiety of the tmeda ligand
was refined with equally occupied split positions for the l and d
no Pd-bound C
pentafluorotoluene, C
6
F
5
could be detected any more but only the species
-CH . Also, an immediate formation of
conformers as in the previously reported 173 K structure (Refcode
6
F
5
3
24
MAGPIU). The structure of 1 was refined in a twin-refinement
with a BASF-scale factor to a near racemic twin. An attempted
solution and refinement in the super-group Cmca (Cmce) did
not give satisfactory results but gave two positions for each
ligand around the Pd atom on the special position (0 y z). The
metallic palladium occurred.
Experimental
All work involving air-and/or moisture-sensitive compounds
was carried out with standard vacuum, Schlenk, or dry-box
techniques. IR spectra were recorded on a Nicolet Magna-IR 760
Spectrometer. MAO (10% solution in toluene, Witco) was used as
received. Toluene and dichloromethane were dried under argon
with an MBraun SPS-800 system. The drying agent for toluene
48
program PLATON also did not suggest a space group change
but confirmed the present non-centrosymmetric space group Aba2
24
(
now called Aea2) as in MAGPIU. The three largest residual
˚
Fourier peaks (2.28, 1.96 and 0.64) are all found within 0.83 A
˚
of the Pd atom in 1. The deepest hole (-0.44) is 1.23 A from
the Pd atom. Crystal data and details on the structure refinement
was activated Al
oxygen scavenger. Al
2
O
3
in addition to a copper-catalyst used as an
alone was used as the drying agent for
49
are given in Table 6. Graphics were drawn with DIAMOND,
2
O
3
analyses on the supramolecular p-, C–H ◊ ◊ ◊ F/Cl- and C–F ◊ ◊ ◊ p-
dichloromethane. After the drying process the water content was
determined by a Karl-Fischer titration, which showed a water
mass of 0.0008% for toluene and 0.0004% for dichloromethane.
Subsequently, the solvents were stored under argon prior to use.
Norbornene (Acros) was purified by distillation under argon and
48
interactions with PLATON for Windows.
NMR spectroscopy
NMR spectra of 1 and 3 were measured on a Bruker 300 MHz
spectrometer. The 1D and 2D-NMR experiments with 5 were
performed on a Bruker Avance II 400 WB spectrometer (400 MHz
-
1
used as a 7.07 mol l solution in toluene. The palladium complexes
44
21
1
and 3, 2, 4 and 5 were prepared as reported previously.
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Table 6 Crystal data and structure refinement for 1, 3 and 5
Compound
1 (cf. ref. 24)
3
5
Empirical formula
M/g mol-
C
425.12
12
H
16ClF
5
N
2
Pd
C
465.09
16
H
8
ClF
5
N
2
Pd
C
513.19
0.17 ¥ 0.16 ¥ 0.05
Prism, colorless
3.58–54.30
±9; -21, 22; ±19
Monoclinic
P2 /c
7.1660(3)
17.2246(6)
15.2372(6)
96.7630(10)
1867.66(13)
4
1.825
1016
1.195
0.9427/0.8227
20 956
17 5 4
H16ClF N Pd
1
Crystal size/mm
0.27 ¥ 0.17 ¥ 0.03
Plate, pale-yellow
4.05–56.20
±16; -25, 26; ±15
Orthorhombic
Aba2 (Aea2)
12.5450(7)
19.9097(8)
11.9976(8)
90
2996.6(3)
8
1.885
1680
1.464
0.32 ¥ 0.08 ¥ 0.08
Needle, pale-yellow
3.20–56.44
±9; -21, 22; ±33
Orthorhombic
Pbca
7.0364(3)
16.9602(7)
25.4701(11)
90
3039.6(2)
8
2.033
1808
1.454
Crystal appearance
◦
2
q range/
h; k; l range
Crystal system
Space group
a/A˚
1
b/A˚
c/A˚
◦
b/
V/A˚
3
Z
D
c
/g cm-
3
F(000)-
1
m/mm
Max/min transmission
Reflections collected
Indep. reflections
0.9574/0.6933
16 309
3408 (0.0558)
3266
0.8926/0.6534
32 576
3596 (0.0260)
3357
4116 (Rint = 0.0279)
Obs. reflect [I > 2s(I)]
3846
Parameters refined
209
226
253
a
˚
-3
Max./min. Dr /e A
2.279/-0.439
0.0326/0.0753
0.0344/0.0763
1.081
0.0493/0.0000
0.45(3)
0.478/-0.329
0.0284/0.0606
0.0257/0.0619
1.114
0.0285/3.5253
—
0.736/-0.705
0.0293/0.0728
0.0319/0.0744
1.067
0.0356/3.4764
—
b
R
R
1
, wR
, wR
2
[I > 2s(I)]
b
1
2
(all reflect.)
2
c
Goodness-of-fit on F
d
Weight scheme w; a/b
Flack parameter
e
f
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a
b
2
2
2
2
2
1/2
c
2
2
2
Largest difference peak and hole. R
1
= [ (ꢀF
o
| - |F
c
ꢀ)/ |F
o
|]; wR
2
= [ [w(F
o
- F
c
) ]/ [w(F
o
) ]] . Goodness-of-fit = [ [w(F
o
- F
c
) ]/(n -
1
/2
d
2
2
2
2
2
e
50 f
p)]
.
w = 1/[s (F
o
) + (aP) + bP] where P = (max(F
o
or 0) + 2F
c
)/3. BASF-scale factor, absolute structure parameter. See comment in X-ray
crystallography section.
1
19
for H, 376.54 MHz for F) in regular NMR tubes with a screw
cap to ensure an inert atmosphere. The NMR tube was filled in a
Schlenk tube under argon atmosphere. For the measurements with
heteronuclear through-space NOE connectivities between non-
bonded nuclei. The H, H-NOESY was performed with spectral
1
1
widths of 3.24 kHz in both dimensions and a 256·2k data matrix
1
9
19
the pure pre-catalyst 5 (15.4 mg, 0.03 mmol) dichloromethane-d
CD Cl , 1 ml) was used as the solvent. The procedure for the
MAO activated complex was as follows: a 10% MAO solution in
toluene (0.21 ml, 0.30 mmol Al) was placed in a Schlenk flask and
the toluene was removed under reduced pressure. After complete
evaporation it was replaced by toluene-d
total volume of 1 ml, which is suitable for NMR measurements.
For a molecular Pd : Al ratio of 1 : 10 compound 5 (15.4 mg,
.03 mmol) was dissolved in dichloromethane-d
2
collecting 24 scans for each time increment. The F, F-EXSY
(exchange spectroscopy) was performed with spectral widths of
22.7 kHz for both dimensions collecting a 256·2k data matrix with
(
2
2
1
19
8 scans for each time increment. The H, F-HOESY was detected
1
9
with a spectral width of 3.0 kHz in f2 ( F) and 3.2 kHz in f1
1
8
(0.5 ml) to ensure a
( H) using a data matrix of 256·2k and accumulating 72 scans for
each time increment. The heteronuclear multiple bond correlation
55
(HMBC ) allows to obtain a 2D heteronuclear chemical shift
1
0
2
(0.5 ml), then,
correlation map between long-range coupled H and heteronuclei.
the MAO/toluene-d solution was added. For a molecular Pd : Al
8
The delay 1/(2 J) was optimized to a value of 62.5 ms (8 Hz). The
1
ratio of 1 : 100 the procedure was the same except for use of the
tenfold amount of the 10% MAO solution in toluene (2.1 ml).
In this case a black precipitate appeared immediately. With total
spectrum was detected with a spectral width of 3.2 kHz in f2 ( H)
1
3
and 19.1 kHz in f1 ( C) and a data matrix of 512·2k collecting 16
scans for each time increment.
51
correlation spectroscopy (TOCSY ) coherence transfer is possible
between all coupled nuclei in a spin system, even if they are
not directly coupled. The TOCSY spectrum was acquired with
Acknowledgements
spectral widths of 3.2 kHz in both dimensions and a 256·1k (t
1
·t
2
)
This work was supported by the Ministerio de Ciencia y
Tecnolog ´ı a (Project CTQ2008-02178/BQU), Spain.
data matrix collecting 8 scans for each time increment. In the
52
1
D nuclear overhauser effect (NOE) difference spectroscopy the
intensity change of a certain resonance upon the irradiation of
another spin can be related to the distance between the two nuclei.
The spectra were detected using the DPFGSENOE experiment.
The 2D nuclear or heteronuclear overhauser enhancement spec-
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54
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3
618 | Dalton Trans., 2010, 39, 3609–3619
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Dalton Trans., 2010, 39, 3609–3619 | 3619