Enantiomers and Structural Isomers of Sodium and Palladium Complexes Bearing ortho-Bis(3,5-dimethylpyrazolylmethyl)phenolate: Fluxional Property and Highly Active Catalysts for Norbornene Polymerization

Article abstract of DOI:10.1021/acs.inorgchem.8b00744

2,6-Bis(3,5-dimethylpyrazoylmethyl)-4-methylphenol LH was readily synthesized by the reaction between 2,6-bis[(dimethylamino)methyl]-4-methylphenol and 3,5-dimethylpyrazole. The X-ray structure of the trisodium complex of LH showed the benzene-like planar

Full text of DOI:10.1021/acs.inorgchem.8b00744

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Enantiomers and Structural Isomers of Sodium and Palladium
Complexes Bearing ortho-Bis(3,5-
dimethylpyrazolylmethyl)phenolate: Fluxional Property and Highly
Active Catalysts for Norbornene Polymerization
Oishi Jana and Ganesan Mani*
Department of Chemistry, Indian Institute of Technology, Kharagpur, West Bengal 721 302, India
S
* Supporting Information
ABSTRACT: 2,6-Bis(3,5-dimethylpyrazoylmethyl)-4-methylphenol
LH was readily synthesized by the reaction between 2,6-bis-
[(dimethylamino)methyl]-4-methylphenol and 3,5-dimethylpyrazole.
The X-ray structure of the trisodium complex of LH showed the
benzene-like planar Na3O3 ring with alternative shorter (2.181−2.185
Å) and longer (2.244−2.263 Å) bonds. The reaction of anionic ligand
L with [PdCl2(COD)] yielded three Pd(II) complexes: [Pd-
{OC6 H2 (CH2 PzMe 2 )2 -2,6-Me-4-κN,O}2 ] (1), [PdCl{μ-
OC6H2(CH2PzMe2)2-2,6-Me-4-κN,O,N}]2 (2), and [PdCl2{μ-OC6H2(CH2PzMe2)2-2,6-Me-4-κN,O,N}2Pd] (3) (PzMe2 = 3,5-
dimethylpyrazole). Conversely, the neutral ligand LH reacts with [PdCl2(PhCN)2] to give the 20-membered palladacycle,
[Pd2Cl4{μ-HOC6H2(CH2PzMe2)2-2,6-Me-4-κN,N}2] (4). 2 and 3 are structural isomers and rigid molecules, whereas 1 and 4
1
are fluxional, as shown by their H NMR spectra. Hence, the dynamic behaviors of 1 and 4 were studied by variable-
1
temperature H NMR methods and are proposed to be interconversion processes: cis−trans for 1 and two chiral enantiomers
for 4. The structures of all complexes were determined by single crystal X-ray diffraction methods, which showed the presence
of two different conformations of LH (trans and semitrans) bound to metal atoms. In addition, complexes 2−4 were found to
be excellent precatalysts for the vinyl polymerization of norbornene in the presence of varying amount of MMAO and EtAlCl2
in toluene or CH2Cl2.Within a short period of time (1 min), almost all monomers are changed to polymers with one micromole
of precatalyst. The optimized conditions of 1000 molar excess of MMAO gave 1.20 × 108 g PNB mol−1 h−1 at room
temperature. These addition polymers are completely insoluble in several organic solvents and hence were only characterized by
1H, IR, powder XRD, and TGA methods.
presence of MAO and Et2AlCl cocatalysts.11 Recently, Li and
INTRODUCTION
■
co-workers have reported vinyl polymerization in air and water
One of the commercially important reactions is the polymer-
ization of norbornene, carried out by three different methods:
ring opening metathesis polymerization (ROMP), cationic or
using palladium complexes with the activity up to 109 g PNB
mol−1 h−1.12 Furthermore, the polymerization of norbornene
derivatives has been reported without a cocatalyst or activator
radical polymerization, and vinyl-polymerization.1 As ROMP
as well.13
attracted attention, the vinyl polymerization of norbornene has
also received a great deal of attention owing to its attractive
physical properties such as mechanical, heat resistivity,
transparency properties, high glass transition temperature,
low dielectric constant, and good solubility in organic solvents.
In addition, the vinyl norbornene polymer is used in making
cover layers for liquid-crystals displays and has a cost
Upon deprotonation with a base, 2,6-bis(3,5-dimethylpyr-
azoylmethyl)-4-methylphenol LH becomes monoanionic
tridentate ligand L containing a gap of four atoms between
the donor atoms. As 2,6-bis[(dimethylamino)methyl]-4-
methylphenol does,14 L can also readily bridge as well as
chelate metal atoms owing to the presence of two flexible
methylene groups on either side of the phenyl ring. The
reported synthesis of LH or its simple pyrazole analogue
advantage over related materials. Several metal complexes
such as Ti,2 Zr,3 Cr,4 Co,5 Ni,6 Pd,7 and Cu8 have been
involves multiple steps. In addition, its coordination chemistry
reported for the vinyl polymerization of norbornene. Most of
these complexes became highly active catalysts upon activation
by MAO, MMAO, boranes, and AgSbF6 salts. Among these,
has not been fully explored except few zinc,15 copper,16 and
cobalt17 complexes. Herein, we report the synthesis, X-ray
9
structures, and fluxional properties of the palladium complexes
of LH which was synthesized by a new method. We also report
Ni complexes have been shown to be impressively highly active
catalysts with activities up to 108 g PNB mol−1 h−1.10 Besides,
palladium complexes are also known for their very high
activities.7 Wang and co-workers have reported highly active
NHC-Pd complexes for addition polymerization in the
Received: March 20, 2018
© XXXX American Chemical Society
A
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a
Scheme 1. (a) Synthesis of 2,6-Bis(3,5-dimethylpyrazoylmethyl)-4-methylphenol LH and (b) Possible Conformations of LH
a
Conditions: (i) HCHO/Me2NH/H2O and (ii) 3,5-dimethylpyrazole/xylene/140 °C/12 h.
Scheme 2. Synthesis of the Trisodium, Mononuclear, and Binuclear Pd(II) Complexes of LH
a new trisodium complex of LH and the vinyl polymerization
of norbornene using three different palladium complexes in the
presence of MMAO or EtAlCl2 as a cocatalyst.
both the pyrazole rings situated above or below the phenyl ring
are termed as cis (I), one up and down as trans (II), and one
up and the other in the middle as semitrans (III). Interestingly,
two of these are observed in their palladium complex structures
(see below).
Sodium aryloxides are well-known to have a diverse range of
structures such as squares, hexagonal, ladder, and cubic, fused
cubic depending upon the nature of ligand.20 In view of this,
LH was treated with NaH in toluene, and an interesting new
trinuclear sodium complex, 1, was isolated as crystals (Scheme
RESULTS AND DISCUSSION
■
Synthesis of LH and Its Na and Pd Complexes. As
illustrated in Scheme 1a, the synthesis of LH involves two steps
from phenol. Without making the quaternary ammonium salt
of 2,6-bis[(dimethylamino)methyl]-4-methylphenol, the dia-
mine was directly treated with 3,5-dimethylpyrazole in xylene
under reflux conditions followed by chromatographic separa-
tion to give ortho-bis(3,5-dimethylpyrazolylmethyl)phenol
ligand LH in good yield (66%). This method of synthesis is
similar to that of 2,5-bis(3,5-dimethylpyrazolylmethyl)-
pyrrole18 and 1,9-bis(3,5-dimethylpyrazolylmethyl)-
dipyrrolylmethane.19 LH can have three conformations based
on the orientation of the pyrazole ring about the phenyl ring
plane, as shown in Scheme 1b. The conformations in which
̅
2). It crystallizes in the triclinic space group P1, and the
asymmetric unit constitutes the whole molecule of 1 together
with 1.5 molecules of toluene as solvent of crystallization. The
molecular structure of the sodium salt is given in Figure 1
along with selected bond distances and angles. The 6-
membered Na2O3 ring structure is formed by three anionic
ligands L, each spanning two sodium atoms by the bis-
chelation mode, and the ring is an almost perfect planar with
alternative oxygen and sodium atoms. Each ligand adopts trans
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The ring Na−O−Na and O−Na−O angles are in the ranges
of 113.6−120.1° and 119.2−126.1°, respectively. The ring
contains an alternatively located shorter (2.181−2.185 Å) and
́
longer (2.244−2.263 Å) Na−O distances, as Kekule’s benzene
structure exhibits. The Cipso−O distances (1.295−1.314 Å) are
shorter than that (1.372(4) Å) found in the free ligand
structure.22 These bond lengths and angles indicate that the
phenoxy oxygen atoms undergone the hybridization change
from sp3 to sp2 and the oxygen π-electrons are delocalized in
the Na3O3 ring. The average Na−O distance is 2.217(3) Å,
which is slightly shorter than the distances, 2.2263(13),20c
2.29,20d and 2.328(2) Å,20e found in the analogous six-
membered sodium structures. In addition, there are three weak
bonding interactions of the type Na···Cipso (2.840, 2.888, and
2.909 Å) in the ring, which are slightly longer than those
reported for the analogous sodium structure.20c The geometry
around each sodium atom is a distorted tetrahedral formed by
two pyrazole nitrogens and two bridging oxygens with N−Na−
N angles (100.55(12)−103.76(14)°) being smaller than the
O−Na−O angles (119.28(12)−126.18(12)°). Interestingly,
the geometry around each ring oxygen atom is trigonal planar
and the sum of the angles around each oxygen atom (358.1,
355.1, and 357.3°) is close to 360°, indicating sp2 hybrid-
ization. The three-bladed turbine-like orientation of three
ligands about the Na3O3 ring is not rigid in solution, as shown
Figure 1. ORTEP diagram of the trinuclear sodium complex1.
Selected bond distances (Å) and angles (deg). All hydrogens are
omitted for clarity. O1−Na2 2.185(3), O1−Na1 2.244(3), O2−Na3
2.181(3), O2−Na2 2.263(3), O3−Na1 2.181(3), O3−Na3 2.252(3),
C13−O1 1.313(5), C32−O2 1.314(4), C51−O3 1.295(4), N1−Na1
2.380(3), N12−Na1 2.396(4), N4−Na2 2.406(4), N5−Na2
2.386(4), N8−Na3 2.399(4), N9−Na3 2.382(4), O3−Na1−O1
123.48(12), O3−Na1−N1 113.47(12), O3−Na1−N12 94.12(12),
O1−Na1−N1 98.35(12), O1−Na1−N12 125.45(13), N1−Na1−
N12 100.55(12). Na2−O1−Na1 120.14(13), Na3−O2−Na2
117.15(12), Na1−O3−Na3 113.65(13), O3−Na1−O1 123.48(12),
O1−Na2−O2 119.27(12), O2−Na3−O3 126.17(12).
1
by its H NMR spectrum which featured a broad singlet at δ
5.21 ppm for all the methylene protons, indicating the dynamic
behavior of molecule in solution.
As shown in Scheme 2, the reaction between deprotonated
ligand L and [PdCl2(COD)] in THF gave three Pd(II)
complexes 2−4, whereas the reaction of neutral ligand LH with
conformation II (Scheme 1b) and bridges two sodium atoms
with the bridged bonded phenoxy oxygen atom. This
orientation of L renders the Na2O3 ring with a three-bladed
wind-turbine-like structure and screw-type chirality. Both
enantiomers are present in the crystal lattice. This is similar
to the Li3O3 ring reported by van Koten and co-workers.21
1
Figure 2. Variable-temperature (VT) H NMR spectra (400 MHz) of 2 in CDCl3.
C
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1
[PdCl2(PhCN)2] afforded yet another binuclear Pd(II)
complex 5 in 46% yield. Crystals of 2−4 were formed together
from the reaction mixture upon crystallization and were
separated by handpicking as they have different crystal
morphology and colors with crystalline yields of 9, 18, and
17%, respectively. In addition, complex 2 was also obtained
from the reaction among LH, NaH, and [PdCl2(COD)] in
THF in 47% yield. Furthermore, the 1H NMR spectrum of the
residue obtained from the reaction between complex 5 and 2
equiv of NaH showed the formation of complex 3, a major
product. All complexes are characterized by both spectroscopic
and single crystal X-ray diffraction methods. The unforeseen
chelation and bridging mode of LH (μ2-κ2NO:κ1N) in 3 and 4
The room-temperature H NMR spectrum of 5 in CD2Cl2
featured broad resonances at δ 5.53, 6.00, and 6.86 ppm for the
diastereotopic methylene, pyrazole, and phenyl CH protons,
respectively. This indicates a dynamic process occurring in
1
solution and prompted us to investigate it by VT H NMR
method. As shown in Figure 4, the H NMR spectra were
1
recorded for every 10 °C decrease in temperature up to −70
°C. As the temperature is decreased, the above-mentioned
signals broadened, and four doublets for the methylene
protons and two singlets each for the pyrazole and phenyl
ring protons then appeared at −70 °C. The coalescence
temperature is −50 °C, after which two signals appeared for
the phenyl ring CH protons. This dynamic behavior is due to
the interconversion between the two enantiomers, as shown in
Figure 5, one of which is present in the asymmetric unit of the
crystal lattice. The X-ray structure of this complex showed that,
for a given ligand, the three ring planes, that is, two pyrazole
and one phenyl, are perpendicular to each other and molecule
possesses a C2 axis. In the interconversion process, one
enantiomer is changed to another by ring-flipping process in
which the two pyrazole rings swap their planes about the
phenyl ring plane, that is, the pyrazole ring lying above the
phenyl ring changes to the pyrazole ring lying middle to the
phenyl plane and vice versa. At room temperature, the rate of
pyrazole ring plane swapping is faster so that the diastereotopic
methylene HAHB are changed to HCHD protons and vice versa,
and they appear as a single broad resonance. At low
temperature (−70 °C), the plane swapping is arrested or
slowed down, and they give a well-resolved spectrum with the
average coupling constant J(HAHB) = 19 Hz for the methylene
protons. In addition, this arrested pyrazole ring orientation
renders two different chemical environments for each phenyl
and pyrazole CH protons and four different environments for
the pyrazole methyl groups; hence, they all appear as singlets at
the −70 °C spectrum. Its activation energy barrier (ΔG⧧) was
calculated based on the phenyl proton resonances at δ 6.88 and
5.58 ppm at −70 °C which merge into a broad peak at the
coalescence temperature (Tc) −50 °C (223.15 K) is 24.7 kJ/
mol with Δν = 520 Hz and kc = 1154.9 s−1.23
The X-ray structure of complex 2 is given in Figure 6 along
with selected bond lengths and angles. It crystallizes in the
monoclinic centrosymmetric space group P21/c, and the
asymmetric unit constitutes a half molecule. The symmetry
generated molecule revealed that it consists of one palladium
atom coordinated by two ligands via its deprotonated phenolic
oxygen and pyrazole nitrogen atoms, forming two seven-
membered puckered chelate rings. The other pyrazole arm of
each ligand remains as a spectator. As a result, the molecule is
fluxional in solution. The geometry around the palladium atom
is a distorted square planar in which the phenoxy oxygens or
pyrazole nitrogens are trans bonded with the O1−Pd1−N1
and O1i−Pd1−O1 angles of 92.74(11) and 180.0°, respec-
tively. The N1−Pd1 bond distance of 2.009(3)Å falls within
the range of distances reported for complexes containing Pd−
Npyrazole bonds24,19 and is shorter than the Pd−NMe2 distance
(2.082(5) Å) found in [Pd(OC6H2(CH2NMe2)2-2,6-Me-
4)2].25 The O1−Pd1 bond distance of 2.0004(19) Å is close
to those found in palladium complexes containing Pd−O
bonds [1.974(11) and 1.989(10)Å,26 1.994(4) and 1.987(4)
Å],27 but it is slightly shorter than 2.021(4) Å found in
[Pd(OC6H2(CH2NMe2)2-2,6-Me-4)2].25
1
are shown by their H NMR spectra recorded in CDCl3. Two
AB quartets are observed for the two different diastereotopic
methylene groups with different coupling constants (for
example, J(HAHB) = 14.2 and 17.4 Hz for complex 3).
Furthermore, the unsymmetrical coordination mode of LH is
also indicated by the number of peaks appeared for the
pyrazole methyl, CH and phenyl CH protons. In addition,
their 13C NMR spectra showed 19 peaks for the 19 different
carbon atoms in the structure.
1
Conversely, the H NMR spectra of complex 2 and 5 in
CDCl3 displayed broad resonances for their methylene
protons, suggesting fluxional behaviors in solution. Complex
2 possesses two different pyrazole arms, coordinated and
spectator, but its room-temperature spectrum featured only
one broad singlet for the diastereotopic methylene protons as
well as for the phenyl protons. Hence, it was studied by VT
NMR method. As the temperature is decreased, a well resolved
complicated spectrum featuring AB quartets for the diaster-
eotopic methylene protons was obtained at −30 °C (Figure 2).
From the number (three) and integrated intensity of the
signals in the aromatic region, at least two complexes are in a
dynamic process. As the spectrum appears complicated, the
dynamic process could be the interconversion between the
trans (observed in the solid state) and cis structures through
the κ1O coordination mode of LH or dissociation-association
processes, as shown in Figure 3. Its activation energy barrier
(ΔG⧧) calculated based on the methylene proton resonances
at δ 5.15 and 4.74 ppm at −30 °C which merge into a broad
peak at the coalescence temperature (Tc) 0 °C (273.15 K) is
53.3 kJ/mol with Δν = 163.2 Hz and kc = 362.5 s−1.
Figure 3. Proposed dynamic process of 2 in CDCl3 solution:
Complex 3 crystallizes in the noncentrosymmetric ortho-
rhombic space group Aba2 and the asymmetric unit contains a
interconversion between the trans and cis complexes through the two
1
coordinate Pd(II) complex, as studied by VT H NMR method.
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1
Figure 4. VT H NMR spectra (400 MHz) of 5 in CD2Cl2.
1
Figure 5. Dynamic behavior of complex 5 in CD2Cl2 studied by VT H NMR method.
half molecule of 3 and a half molecule of water. The full
molecule was generated by C2 rotation and is given in Figure 7
along with selected bond distances and angles. The X-ray
structure revealed two Pd−Cl units bridged by two phenolate
ligands L. Each ligand renders one seven-membered chelate
ring formed by the coordination of one of the pyrazole
nitrogens and the phenolate oxygen atom, while it bridges the
other palladium atom via the other pyrazole nitrogen atom.
Thus, each ligand displays both bridging and chelating modes,
represented as μ2-κ2NO:κ1N. As a result, there are two seven-
and one 14-membered palladacycles in the structure and the
molecule exhibits a tub shape containing one water molecule
hydrogen bonded to the phenolate oxygen atoms. To maintain
a square planar geometry around each palladium atom, both
pyrazole arms are twisted and ligand assumes the trans
conformation II. The angle between the mean planes of the
pyrazole rings or the phenyl rings is 74.4 or 87.4°, respectively.
The twist angle between the palladium square plane and the
phenyl ring plane is 46.9°. In addition, the angle between the
two palladium square planes is 72.8°. This configuration is
Figure 6. X-ray structure of complex 2 with 50% probability
ellipsoids. All hydrogen atoms are omitted for clarity. Selected bond
distances (Å) and angles (deg): N1−Pd1 2.009(3), O1−Pd1
2.0004(19), C13−O1 1.337(4), N1−N2 1.366(4), O1−Pd1−N1
92.74(11), O1−Pd1−N1i 87.26(11), O1i−Pd1−O1 180.0, N1−
Pd1−N1i 180.0. Symmetry transformations used to generate
i
equivalent atoms: = −x + 2, −y, −z + 1.
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because of the different conformation adopted by L.
Interestingly, unlike the structure of 3, only one of the
pyrazole rings is above or below the phenyl ring plane, and the
other remains middle to the phenyl ring, that is, each ligand
adopted the semitrans conformation III. As a result, the mean
planes of phenyl and two pyrazole rings are approximately
perpendicular to each other. The coordination environment
around one palladium atom exhibits two seven-membered
chelate rings, whereas the other metal contains two pyrazole
nitrogens and two chlorine atoms in a trans fashion. Hence,
complexes 3 and 4 are structural isomers in which the metal
centers differ by the coordinated ligands. The two distorted
palladium square planes are almost perpendicular to each other
with the angle of 83.3°. At the bischelated palladium atom, the
N8−Pd1−N1 (pyrazole nitrogen) angle of 95.5(2)° is larger
the O1−Pd1−O2 (phenoxy oxygen) angle (88.08(18)°),
probably because of steric crowding caused by 3,5-
dimethylpyrazole rings. Conversely, the N−Pd−N angle at
the other palladium atom is almost linear, 176.1°. The Pd−
Figure 7. X-ray structure of complex 3 with 50% probability
ellipsoids. Most hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): N4−Pd1 2.009(4), N1−
Pd1i2.020(4), O3−Pd1 2.018(3), Cl1−Pd1 2.2846(12), N4−Pd1−
O3 90.19(18), N4−Pd1−N1i 177.89(16), O3−Pd1−N1i 88.68(17),
N4−Pd1−Cl(1) 92.24(13), N1i−Pd1−Cl1 88.92(12). Symmetry
transformations used to generate equivalent atoms: i = −x + 2, −y, z.
N
pyrazole bond distances are similar to those in complex 3 or 2,
rigid with the help of water molecule hydrogen bondings in the
and the Pd−O bond distances are slightly shorter than the
distance (2.018(3) Å) found in 3.
1
cavity, and as a result, its H NMR spectrum showed well
resolved peaks. The angle between the trans pyrazole nitrogen
atoms and the Cl−Pd−O angle are almost the same, 177.9(1)
and 177.5(1)°, respectively. The nonbonding Pd···Pd distance
is 5.44 Å. The structure contains two slightly different Pd−
Npyrazole distances: 2.009(4) and 2.020(4) Å; nevertheless,
these are very close to the Pd−N distances found in complex 2
and 4 and are in the range reported for other complexes.24 The
Pd−O bond distance of 2.018(3) Å is close to the Pd−O bond
in [Pd(OC6H2(CH2NMe2)2-2,6-Me-4)2]25 but is slightly
longer than that found in other palladium complexes.26,27
The X-ray structure of complex 4 is given in Figure 8 with
selected bond distances and angles. It crystallizes in the
centrosymmetric space group P21/c, and the asymmetric unit
consists of one full molecule and two dichloromethanes.
Although this binuclear palladium complex contains the same
metal to ligand ratio, bonding mode of L, and number of
palladacycles as those in complex 3, it is structurally different
̅
Complex 5 crystallizes in the triclinic space group P1, and
the asymmetric unit consists of two molecules of 5 held
together by hydrogen bondings of the type OH···Cl−Pd along
with one dichloromethane and four water molecules. The
hydrogen bonded dimeric structure is shown in Figure 9. Each
Figure 9. X-ray structure of complex 5 with 50% probability
ellipsoids. Most hydrogen atoms, CH2Cl2, and water are omitted
for clarity. Selected bond distances (Å) and angles (deg): N1−Pd1
1.999(5), N8−Pd1 2.020(5), N4−Pd2 2.024(4), N5−Pd21.996(5),
Cl1−Pd1 2.3223(16), Cl2−Pd1 2.2867(16), Cl3−Pd2 2.2946(17),
Cl4−Pd2 2.3143(16), Cl2−Pd1−Cl1 177.12(7), N1−Pd1−N8
178.0(2), N1−Pd1−Cl2 90.14(14), N8−Pd1−Cl2 90.40(15), N1−
Pd1−Cl1 87.68(14), N8−Pd1−Cl1 91.71(15), N5−Pd2−N4
174.5(2), N5−Pd2−Cl3 90.69(17), N4−Pd2−Cl3 90.66(14), N5−
Pd2−Cl4 87.38(17), N4−Pd2−Cl4 91.29(14), Cl3−Pd2−Cl4
178.06(6). Hydrogen bonding parameters: O1···Cl7 3.178(4), H1···
Cl7 2.40, O1−H1···Cl7160.0; O2···Cl63.178(5), H2···Cl6 2.38, O2−
H2···Cl6 164.6; O3···Cl13.145(5), H3A···Cl1 2.40, O3−H3A···Cl1
152.0; O4···Cl43.212(6), H4···Cl4 2.41, O4−H4···Cl4 166.5.
Figure 8. X-ray structure of complex 4 with 50% probability
ellipsoids. All hydrogen atoms and CH2Cl2 are omitted for clarity.
Selected bond distances (Å) and angles (deg): N1−Pd1 2.012(5),
N8−Pd1 2.007(5), O1−Pd1 1.981(4), O2−Pd1 2.006(4), N4−Pd2
2.018(5), Cl1−Pd2 2.2856(18), Cl2−Pd2 2.2964(18), N5−Pd2
1.999(5), N8−Pd1−N1 95.5(2), O1−Pd1−O2 88.08(18), O1−
Pd1−N1 90.08(19), O2−Pd1−N8 87.42(19), O1−Pd1−N8
170.6(2), O2−Pd1−N1 171.9(2), N5−Pd2−N4 176.1(2), Cl1−
Pd2−Cl2 177.14(6), N5−Pd2−Cl1 90.27(16), N4−Pd2−Cl1
89.98(15), N5−Pd2−Cl2 87.09(16), N4−Pd2−Cl2 92.72(15).
molecule consists of two “PdCl2” moieties bridged by two
neutral LH ligands via their pyrazole nitrogens, forming the 20-
membered palladacycle in which the two palladium square
planes are almost parallel to each other, as do the phenyl ring
planes. The aryl OH groups are pointed to the same direction
and involved in hydrogen bonding interactions to the adjacent
molecule. Each ligand adopts the “semitrans” conformation
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a
Table 1. Catalysis of Norbornene Polymerization by Complexes 3−5 with MMAO-12 as a Cocatalyst
b
c
entry
catalyst (μmol)
MMAO (mmol)
solvent (mL)
[NB]/[Cat]
[Al]/[Cat]
PNB (g)
yield (%)
activity
1
2
3
4
5
6
7
8
5 (1)
5 (1)
5 (2)
5 (2)
5 (3)
5 (1)
5 (1)
5 (1)
5 (1)
5 (1)
3 (1.1)
3 (1.1)
3 (1.1)
3 (1.1)
4 (1.1)
4 (1.1)
1
1
1
1
1
0.1
2
3
1
0.5
1
2
1
2
1
2
1
1
toluene (9)
toluene (19)
toluene (9)
toluene (19)
toluene (9)
toluene (9.9)
toluene (8)
toluene (7)
CH2Cl2 (9)
CH2Cl2 (9.5)
toluene (9)
toluene (8)
CH2Cl2 (9)
CH2Cl2 (8)
CH2Cl2 (9)
CH2Cl2 (8)
toluene (9)
toluene (9)
toluene (8.5)
toluene (9)
21240
21240
10620
10620
7080
21240
21240
21240
21240
21240
19309
19309
19309
19309
19309
19309
2124
1000
1000
500
500
333
1.43
1.35
1.638
1.33
1.32
71
67
82
66
66
8
93
95
∼100
20
30
73
66
95
49
96
8.6
8.61 × 107
8.12 × 107
4.91 × 107
4.00 × 107
2.64 × 107
0.96 × 106
1.12 × 108
1.15 × 108
1.20 × 108
2.46 × 107
3.09 × 107
8.20 × 107
7.53 × 107
1.06 × 108
5.50× 107
1.07× 108
5.20 × 105
3.42× 106
6.52 × 107
1.50× 107
100
0.16
1.87
2000
3000
1000
500
909
1818
909
1818
909
1818
100
1000
1000
1000
1.911
1.995
0.410
0.610
1.47
9
10
11
12
13
14
15
16
17
18
19
20
1.32
1.90
0.986
1.932
0.173
0.060
1.701
0.500
[PdCl2(COD)] (10)
[PdCl2(COD)] (1)
[PdCl2(PhCN)2] (1.56)
PdCl2 (1)
21240
13579
21240
3
85
25
1.56
1
a
b
In all cases, 2.0 g of norbornene was used, and the reactions were carried out at room temperature. Quantity of polymer after 1 min, except
c
entries 17 and 20 for which the reaction time is 2 min, and for entry 6, it is 10 min. Given in g PNB mol−1 h−1. The molecular weight of complex 3
or 4 is 930.58 g, and that of 5 is 1003.49 g without any solvent crystallization as supported by their CHN analyses.
(III) in which one of the pyrazole rings lies above the phenyl
ring and the molecule possesses a C2 axis, rendering both
palladium atoms to be in one environment. Both molecules in
the dimer represent one chiral enantiomer and the opposite
enantiomer is present in the crystal lattice. The average
distance between the two palladium atoms is 8.71 Å. The
geometry around each palladium atom is a distorted square
plane containing two trans pyrazole nitrogen and chloride
atoms with the average N−Pd−N and Cl−Pd−Cl angles of
176.1 and 177.5°, respectively. The Pd−N distances range
from 1.996(5) to 2.024(4) Å and are similar to those found in
previous complexes 3 and 4.
Vinyl Polymerization of Norborene. The vinyl polymer-
ization of norbornene was carried out with new complexes 3−
5, and the conditions and activities are summarized in Table 1.
When the reaction was carried out with 1 μmol of complex 5
and 1000 molar excess of MMAO in toluene, the yield of
polynorbornene is 71% in 1 min, and the activity is 8.61 × 107
g PNB mol−1 h−1. The yield of PNB is increased to 82% with
the increased catalyst loading of 2 μmol ([Al]/[Cat] = 500)
and then decreased with further increase in the catalyst loading
of 3 μmol ([Al]/[Cat] = 333). A poor yield and activity was
obtained with the aluminum to catalyst ratio of 100 (entry 6).
In addition, we also found that the activity is slightly decreased
under the relatively dilute conditions (entries 2 and 4).
Conversely, when the [Al]/[Cat] ratio is increased to 2000 or
3000, the yield of the polymer is significantly increased to
greater than 90% yields with the activity shoot up of 1.15 × 108
g PNB mol−1 h−1 in toluene (entry 7 and 8). It suggests that
MMAO plays an important role in stabilizing the active metal
center to give a greater yield and activity. This encouraged us
to carry out the polymerization in a different solvent to observe
the activity difference. Thus, when the reaction was carried out
in dichloromethane with the 1000 molar excess of aluminum,
an almost quantitative yield of PNB was obtained with activity
of 1.20 × 108 g PNB mol−1 h−1 (entry 9). However, the yield
and activity is decreased as the aluminum ratio is decreased to
500. Hence, entry 9 represents the optimized conditions for
the greater activity; it is one of the highly active palladium
catalysts reported to date. Furthermore, it suggests CH2Cl2 is a
better solvent than toluene. The same polymerization reactions
were also carried out with complex 3 and 4. The yield and
activity is increased, as the aluminum ratio is increased from
1000 to 2000 in dichloromethane or toluene (1.06 × 108 g
PNB mol−1 h−1, entry 14). This activity is comparable to that
of complex 5 in dichloromethane with the aluminum to
catalyst ratio of 1000, suggesting that complex 5 is a better
catalyst as compared to complex 3 or 4. Furthermore,
polymerizations were also carried out with precursors: PdCl2,
[PdCl2(COD)], and [PdCl2(PhCN)2]. Although all catalyze
the vinyl polymerization of norbornene in combination with
MMAO in toluene at room temperature, their activities are
different, as given in Table 1 (entries 17−20). While PdCl2 and
[PdCl2(COD)] activities are lower, [PdCl2(PhCN)2] activity
is almost equal to those given by complex 3, 4, or 5, suggesting
that similar type of active metal center is involved in the
polymerization reactions catalyzed by complex 3, 4, or 5.
Furthermore, catalysis reactions with 1000 molar excess of
MMAO in toluene at 50 or 100 °C did not give
polynorbornene precipitate, and the reaction mixture turned
to a black turbid suspension, indicating decomposition of the
catalyst at higher temperatures.
Polynorbornenes obtained from all these reactions are only
sparingly soluble in chlorobenzene. The 1H NMR spectrum of
polynorbornene in chlorobenzene-d5 showed two major broad
signals at δ = 1.17 and 2.30 ppm and no peak in the region
around 5.5 ppm. In addition, no stretching frequency was
observed in the range 1620−1680 cm−1 in the IR spectrum.
Hence, the polymers are formed by the vinyl addition of
norbornene, not ring opening. The TGA showed polymers are
stable up to 450 °C, a characteristic property of poly-
norbornene as reported in several cases. The X-ray diffraction
G
DOI: 10.1021/acs.inorgchem.8b00744
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 2. Norbornene Polymerizations with EtAlCl2 as a Cocatalyst
a
entry
catalyst (μmol)
EtAlCl2 (mmol)
solvent (mL)
time (min)
[NB]/[Cat]
[Al]/[Cat]
PNB (g)
yield (%)
activity
1
1
2
3
4
5
6
5 (1)
5 (1)
5 (1)
5 (1)
5 (1)
3 (1.1)
4 (1.1)
1
1
1
2
2
1
toluene (9.5)
toluene (9.5)
toluene (9.5)
toluene (9)
toluene (9)
toluene (9.5)
toluene (9.5)
1
2
3
1
3
1
1
21240
21240
21240
21240
21240
19309
19309
1000
1000
1000
2000
2000
909
0.907
1.716
1.87
1.31
1.89
45
86
93
65
94
5.46 × 107
5.16 × 107
3.75 × 107
7.88 × 107
3.79 × 107
1.09 × 108
1.13 × 108
1.998
2.233
100
111
b
1
909
a
b
Given in g PNB mol−1 h−1. Greater than 2 g probably because of water as shown by IR spectrum, which could not be removed at 80 °C under
vacuum.
pattern showed noncrystalline nature of the polymer and is
similar to the literature reports (see Supporting Informa-
tion).7c,f However, it is insoluble in THF, dichloromethane,
and CHCl3, which precluded us from characterization by GPC
method.
interconversions are studied by VT NMR methods, providing
insights into the structures in solutions. Importantly, all the
three binuclear palladium complexes 3−5 are precatalysts for
the vinyl polymerization of norbornene in combination with
MMAO and EtAlCl2 at room temperature. Almost all the
monomers are converted into polymers within a short period
of time 1 min, representing them as highly active catalysts.
Near quantitative yields and very high activities under mild
conditions such as low catalyst loading, relatively low [Al]/
[Pd] ratio, and room temperature are favorable attributes of
the polymerization reactions reported here. Homopolymeriza-
tion of norbornene and copolymerization with other olefins
using Ni(II) and Pd(II) complexes containing other ligand
systems are under progress.
The norbornene polymerization catalysis was also carried
out with EtAlCl2 as a cocatalyst. We applied the best
conditions of polymerization obtained with MMAO to
polymerize norbornene in combination with EtAlCl2, and
complex 3, 4, or 5, and the results are summarized in Table 2.
Complex 5 catalyzes the polymerization in the presence of
1000 or 2000 molar excess of EtAlCl2, and their yields increase
as time increases from 1 to 3 min (entry 1−4). The 1000
molar excess reaction in 3 min gave the maximum yield. In
contrast to this, the catalyzes reactions using either complex 3
or 4 afforded quantitative yields of polymers in the presence of
909 molar excess of EtAlCl2 in toluene in 1 min ,and their
activities are in the range of 108 g PNB mol−1 h−1 (entry 5 and
6), showing both complexes as highly active catalysts. In
addition, polymerization reactions using 3, 4, or 5 in the
presence of 400 or 1000 molar excess of AlMe3 gave no
precipitate.
In contrast to the powdery nature of polymers obtained with
MMAO, polymers obtained with EtAlCl2, in most cases are a
viscous oily film or gel-type precipitate which turned to one
piece of colorless almost transparent chunk upon hydrolysis
and air drying. In some cases, it appears similar to the MMAO
polymer. Again, the dried polymer is insoluble in solvents such
as CH2Cl2, CHCl3, toluene, THF, acetone, CH3CN, and
diethyl ether. The IR spectrum of this polymer showed a broad
band at 3422 cm−1, indicating the presence of OH groups. The
TGA of this polymer is different from that of MMAO polymers
in terms of mass changes. Decomposition occurs from 100 °C
onward and then appears to be similar to the mass change
profile of MMAO polymers. The polymer was again not
characterized by GPC method as it remains completely
insoluble in solvents mentioned above.
EXPERIMENTAL SECTION
■
General Procedure. All reactions were carried out under a
nitrogen atmosphere using standard Schlenk line techniques or
nitrogen-filled glovebox. Petroleum ether (bp 40−60 °C) and other
solvents were distilled under N2 atmosphere according to the standard
procedures. Norbornene, modified methylaluminoxane (MMAO-12,
7 wt % in toluene), EtAlCl2 (25 wt % in toluene), and Me3Al (2 M in
toluene) were purchased from Aldrich and used as received except
norbornene which was distilled over sodium under vacuum. Other
chemicals were obtained from commercial sources and used as
received. [PdCl2(COD)]28 and [PdCl2(PhCN)2]29 were synthesized
according to the reported procedures. 1H (400 MHz) and 13C (102.6
MHz) NMR spectra were recorded at room temperature. For 1H
NMR spectra, chemical shifts are referenced with respect to the
chemical shift of the residual protons present in the deuterated
solvents, and for 13C NMR spectra, the CDCl3 chemical shift was
used a reference. Chemical shifts are in parts per million, and coupling
constants are in Hz. FTIR and ATR spectra were recorded using
PerkinElmer Spectrum Rx. High-resolution mass spectra (ESI) were
recorded using the Xevo G2 Tof mass spectrometer (Waters).
Elemental analyses were carried out using a PerkinElmer 2400 CHN
analyzer. Thermogravimetric analysis (TGA) was recorded on a TG
209 F3 Tarsus (Netzsch) in which polymer samples were heated from
room temperature to 800 °C at a rate of 10.0 K per minute under a
nitrogen atmosphere.
Synthesis of 2,6-Bis(3,5-dimethylpyrazoylmethyl)-4-meth-
ylphenol LH. To a solution of 2,6-bis[(dimethylamino)methyl]-4-
methyl-phenol (5.00 g, 22.5 mmol) in xylene (50 mL) was added 3,5-
dimethylpyrazole (4.54 g, 47.2 mmol) and stirred for 12 h under
reflux conditions. The solvent was removed under vacuum, and the
resulting residue was loaded onto a silica gel column and eluted with
EtOAc/petroleum ether (v/v = 1:5). The solvents were removed
from the first fraction to give 4.80 g of LH (14.8 mmol, yield: 66%).
1H NMR (CDCl3, 400 MHz): δ 10.88 (s, 1H, phenyl−OH), 6.66 (s,
CONCLUSIONS
■
In conclusion, we have developed a new synthetic method for
the bis(pyrazolylmethyl)phenol ligand LH. In addition to the
mononuclear palladium complex containing the spectator
ligand, the unforeseen coordination mode of LH, μ2-
κ2NO:κ1N in 3 and 4, was also observed, proving its flexibility
in choosing the bonding modes: mono- and bischelation and
bridging. As a result, benzene-like enantiomers and structural
isomers containing trans and semitrans conformations of LH
were structurally characterized. Interestingly, while complexes
3 and 4 are stereochemically rigid, complex 5 with its simple
bridging mode of LH and complex 2 are fluxional and their
2H, phenyl−CH), 5.79 (s, 2H, pyrazole−CH), 5.13 (s, 4H, CH2),
2.24 (s, 6H, pyrazole−CH3), 2.22 (s, 6H, pyrazole−CH3), 2.15 (s,
3H, phenyl−CH3).
Synthesis of [NaOC6H2(CH2PzMe2)2-2,6-Me-4]3 1. NaH (0.025
g, 60% in mineral oil, 0.625 mmol) was taken in a 250 mL Schlenk
H
DOI: 10.1021/acs.inorgchem.8b00744
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
flask, washed with petroleum ether (3 × 5 mL), and then dried under
vacuum. To the resulting NaH powder was added toluene (30 mL)
followed by LH (0.150 g, 0.462 mmol) at room temperature. The
solution was stirred for 12 h and layered with petroleum ether (50
mL). Colorless crystals of complex 1 were formed over a period of 3
days at room temperature. Crystals were separated and dried under
pyrazole−CH), 5.07 (dd, 4H, J(HAHB) = 18.6, CH2), 2.89 (s, 6H,
pyrazole−CH3), 2.38 (s, 6H, pyrazole−CH3), 2.07 (s, 6H, pyrazole−
CH3), 2.06 (s, 6H, phenyl−CH3). 13C NMR (CDCl3, 102.6 MHz): δ
161.2, 149.4, 149.0, 143.6, 142.0, 128.8, 126.7, 126.4, 122.0, 117.5,
107.6, 107.0, 53.1, 52.3, 20.8, 15.1, 13.5, 12.1, 12.0. FTIR (KBr,
cm−1): 3129 (vw), 3089 (vw), 2918 (m), 2865 (m), 2663 (vw), 2553
(vw), 1610 (w), 1557 (s), 1464 (vs), 1424 (s), 1395 (s), 1312 (m),
1292 (m), 1226 (s), 1156 (m), 1066 (w), 1037 (w), 944 (w), 864
(w), 804 (m), 735 (m), 658 (vw), 608 (vw), 569 (w), 539 (vw), 508
(w), 442 (w). HRMS (+ESI): m/z calcd for [M + H+] C38H47
1
vacuum (0.070 g, 0.059 mmol). Yield: 38%. H NMR (C6D6, 400
MHz): δ 6.95 (s, 6H, phenyl−CH), 5.52 (s, 6H, pyrazole−CH), 5.21
(br s, 12H, CH2), 2.25 (s, 9H, phenyl−CH3), 1.96 (s, 18H, pyrazole−
CH3), 1.68 (s, 18H, pyrazole−CH3). 13C NMR (C6D6, 102.6 MHz):
δ 147.1, 138.8, 131.5, 128.1, 126.0, 104.7, 49.2, 20.7, 12.6, 11.4. FTIR
(Nujol, cm−1): 2924 (vs), 2855 (vs) 2729 (w), 1611 (w), 1549 (m),
1354 (m), 1335 (m), 1311 (m), 1255 (m), 1158 (w), 1118 (vw),
1034 (w), 983 (w), 919 (vw), 872 (vw), 825 (w), 806 (w), 785 (w),
768 (m), 722 (m), 629 (vw), 596 (vw), 562 (w), 544 (w), 504 (vw),
475 (w), 460 (w).
+
Cl2N8O2Pd2 929.1263, found 929.1298. Anal. Calcd for
C38H46Cl2N8O2Pd2: C, 49.05; H, 4.98; N, 12.04. Found: C, 49.33;
H, 5.06, N, 12.56.
Synthesis of [Pd{OC6H2(CH2PzMe2)2-2,6-Me-4-κN,O}2] 2. To a
solution of LH (0.113 g, 0.348 mmol) in dry THF was added NaH
(0.015 g, 60% in mineral oil, 0.37 mmol), and the solution was stirred
for 1 h at room temperature. To this [PdCl2(COD)] (0.050 g, 0.175
mmol) was added and stirred for 1 h at room temperature. Then, the
solvent was removed, and the resulting orange residue was dissolved
in dichloromethane (30 mL) and layered with petroleum ether (60
mL). Dark red crystals of complex 2 were obtained over a period of 7
days. The crystals were separated and dried under vacuum (0.062 g,
0.082 mmol, yield: 47%). The identity of 2 synthesized by this
method was confirmed by comparing the1H NMR spectrum with that
of crystals obtained from the above reaction.
Synthesis of [Pd{OC6H2(CH2PzMe2)2-2,6-Me-4-κN,O}2] 2,
[PdCl{μ-OC6H2(CH2PzMe2)2-2,6-Me-4-κN,O,N}]2 3, and [PdCl2{μ-
OC6H2(CH2PzMe2)2-2,6-Me-4-κN,O,N}2Pd] 4. To a solution of LH
(0.108 g, 0.333 mmol) in THF (30 mL) was added n-BuLi (0.22 mL,
0.352 mmol, 1.6 M in hexane) at −114 °C. The solution was allowed
to come to room temperature, and then [PdCl2(COD)](0.050 g,
0.175 mmol) was added and stirred for 12 h at room temperature.
The solvent was removed under vacuum and the resulting reddish
brown residue was dissolved in dichloromethane (30 mL), filtered,
and then layered with petroleum ether (60 mL). A dark red colored
sphere shaped crystals of complex 2, yellow colored prism shaped
crystals of complex 3, and yellow colored needle shaped crystals of
complex 4 were formed in the same flask over a period of 10 days and
separated by hand picking. All crystals were washed with petroleum
ether and dried under vacuum: 2 (0.012 g, 0.016 mmol, yield: 9%), 3
(0.015 g, 0.016 mmol, yield: 18%), and 4 (0.014 g, 0.015 mmol, yield:
17%).
Synthesis of [Pd2Cl4{μ-HOC6H2(CH2PzMe2)2-2,6-Me-4-κN,N}2]
5. To a solution of LH (0.042 g, 0.13 mmol) in dichloromethane (30
mL) was added [PdCl2(PhCN)2] (0.050 g, 0.13 mmol). The solution
was stirred for 12 h at room temperature and the color of the solution
is changed to a yellow-orange. The solution was layered with
petroleum ether (60 mL) and yellow colored crystals of complex 5
were formed over a period of 7 days, which were separated and dried
1
under vacuum (0.030 g, 0.030 mmol). Yield: 46%. Mp > 200 °C. H
[Pd{OC6H2(CH2PzMe2)2-2,6-Me-4-κN,O}2] 2. Mp > 200 °C. 1H
NMR: (CDCl3, 400 MHz): δ 6.71 (s, phenyl−CH), 6.04 (br s,
phenyl−CH), 5.78 (s, pyrazole−CH), 5.75 (s, pyrazole−CH), 4.87
(br s, CH2), 2.51 (br s, phenyl−CH3), 2.34 (s, pyrazole−CH3), 2.20
(s, pyrazole−CH3), 2.04 (s, pyrazole−CH3), 2.02 (s, pyrazole −CH3).
13C NMR (CDCl3, 102.6 MHz): δ 161.0, 149.9, 147.2, 140.5, 139.6,
129.3, 128.6, 128.2, 122.8, 118.9, 107.6, 104.8, 51.5, 49.0, 20.5, 13.80,
13.76, 11.7, 10.9. FTIR (KBr, cm−1): 3432 (br), 3124 (vw), 3086
(vw), 2922 (m), 2859 (w), 1613 (m), 1554 (m), 1457 (vs), 1428 (s),
1389 (w), 1341 (w), 1308 (s), 1259 (s), 1162 (m), 1069 (w), 1032
(w), 973 (w), 869 (w), 802 (m), 769 (m), 705 (w), 660 (vw), 616
(vw), 568 (w), 522 (w), 434 (vw). HRMS (+ESI): m/z calcd for [M
+ H+] C38H47N8O2Pd+ 753.2851, found 753.2911. Anal. Calcd for
C38H46N8O2Pd: C, 60.59; H, 6.16; N, 14.88. Found: C, 60.42; H,
6.27, N, 14.56.
NMR (CDCl3, 400 MHz): δ 6.83 (s, 4H, phenyl−CH), 6.20 (s, 2H,
OH), 5.93 (s, 4H, pyrazole−CH), 5.57 (br s, 8H, CH2), 2.88 (s, 12H,
pyrazole−CH3), 2.32 (s, 6H, phenyl−CH3), 2.03 (s, 12H, pyrazole−
CH3). 13C NMR (CDCl3, 102.6 MHz): δ 150.9, 149.9, 144.8, 131.0,
130.3, 122.2, 108.6, 50.6, 20.7, 15.3, 12.6. FTIR (KBr, cm−1): 3341
(br vs), 3136 (m), 2960 (m), 2919 (m), 2863 (m), 1616 (w), 1557
(s), 1477 (vs), 1421 (vs), 1401 (s), 1315 (s), 1291 (m), 1253 (w),
1211 (s), 1147 (m), 1066 (w), 1038 (m), 993 (w), 963 (w), 924 (w),
864 (m), 795 (m), 703 (w), 658 (w), 626 (w), 567 (w), 459 (w).
+
HRMS (+ESI): m/z calcd for [M − Cl]+ C38H48Cl3N8O2Pd2
965.1035, found 965.0999. Anal. Calcd for C38H48Cl4N8O2Pd2: C,
45.48; H, 4.82; N, 11.17. Found: C, 45.28; H, 4.71; N, 11.07.
General Procedure for Norbornene Polymerization. In a
typical norbornene polymerization reaction, 0.001 g (∼1 μmol) of
crystals of precatalyst (3, 4, or 5) was taken in a 100 mL Schlenk flask
and dissolved in toluene. Then, 2.0 g of freshly distilled solid
norbornene was added. To this mixture was quickly added MMAO-12
(7 wt % in toluene) with stirring at room temperature. Total volume
of the solvent is 10 mL. Precipitate is formed within 30 s and it could
not be stirred. The reaction was stopped after 1 min starting from the
time at which the MMAO addition is complete by adding MeOH/
HCl (v/v = 10/1 mL) mixture. The precipitate was filtered, washed
with MeOH several times, and then dried in an oven at 100 °C for 6 h
followed by drying under vacuum at 80 °C. In the case of EtAlCl2 (25
wt % in toluene) as cocatalyst, a thick oily material is formed which
became colorless, very soft, gel-like precipitate and dried under
vacuum at 80 °C. After drying, it became a very hard one piece of
chunk.
[PdCl{μ-OC6H2(CH2PzMe2)2-2,6-Me-4-κN,O,N}]2 3. Mp > 200 °C.
1H NMR: (CDCl3, 400 MHz): δ 7.32 (d, 2H, J(HAHB) = 17.2, CH2),
6.87 (d, 2H, J(HAHB) = 14, CH2), 6.72 (s, 2H, phenyl−CH), 6.54 (s,
2H, phenyl−CH), 5.92 (s, 2H, pyrazole−CH), 5.52 (s, 2H, pyrazole−
CH), 5.24 (d, 2H, J(HAHB) = 17.6, CH2), 4.82 (d, 2H, J(HAHB) =
14.4, CH2), 2.73 (s, 6H, pyrazole−CH3), 2.42 (s, 6H, pyrazole−
CH3), 2.19 (s, 6H, pyrazole−CH3), 2.06 (s, 6H, pyrazole−CH3),0.95
(s, 6H, phenyl−CH3). 13C NMR (CDCl3, 102.6 MHz): δ 161.6,
153.9, 152.3, 144.3, 142.0, 129.2, 128.9, 127.0, 125.1, 123.0, 108.2,
107.3, 50.6, 49.5, 20.6, 15.9, 13.4, 12.0. FTIR (KBr, cm−1): 3433 (m),
2984 (w), 2919 (m), 2859 (w), 1654 (w), 1612 (w), 1552 (m), 1466
(vs), 1421 (s), 1400 (s), 1351 (m), 1315 (s), 1269 (s), 1206 (m),
1164 (m), 1608 (w), 1036 (w), 984 (w), 934 (vw), 871 (w), 812
(m), 775 (m), 734 (w), 695 (w), 657 (w), 580 (w), 550 (w), 503
(w), 432 (w). HRMS (+ESI): m/z calcd for [M + H+]C38H47
Cl2N8O2Pd2+: 929.1263, found 929.1235. Anal. Calcd for
C38H46Cl2N8O2Pd2: C, 49.05; H, 4.98; N, 12.04. Found: C, 49.33;
H, 5.06, N, 12.16.
Control Experiment with EtAlCl2. To a toluene solution (10
mL) of norbornene (2.00 g, 21.24 mmol) was quickly added EtAlCl2
(0.55 mL, 1 mmol, 25 wt % in toluene) with stirring at room
temperature. No precipitate or viscous oily materials formed up to 7
min. To this clear solution was then added complex 5 (0.001 g, 1
μmol), and precipitate began to form within 30 s. This confirms that
complex 5 is required for polymerization, and it is the precatalyst.
X-ray Crystallography. Suitable single crystals of 1−5 were
grown from the solvents mentioned in their respective synthetic
[PdCl2{μ-OC6H2(CH2PzMe2)2-2,6-Me-4-κN,O,N}2Pd] 4. Mp > 200
1
°C. H NMR: (CDCl3, 400 MHz): δ 7.94 (d, 2H, J(HAHB) = 15.6,
CH2), 7.15 (d, 2H, J(HAHB) = 18.8, CH2), 6.79 (s, 2H, phenyl−CH),
5.92 (s, 2H, phenyl−CH), 5.80 (s, 2H, pyrazole−CH), 5.79 (s, 2H,
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procedures. Single crystal X-ray diffraction data collections were
performed using Bruker APEX-II or D8 Venture APEX3 CCD
diffractometer with graphite monochromated Mo Kα radiation (λ =
0.71073 Å). The space group for every structure was obtained by
XPREP program. The structures were then solved by SIR-9230 or
SHELXT31 available in WinGX, which successfully located most of
the non-hydrogen atoms. Subsequently, least-squares refinements
were carried out on F2 using SHELXL-2018/1 (Sheldrick, 2018)32 to
locate the remaining non-hydrogen atoms. Non-hydrogen atoms were
refined with anisotropic displacement parameters. All hydrogen atoms
were fixed in calculated positions. In the crystal structure of 1, 1.5
toluene molecules are present in the crystal lattice. One of them is
disordered over two positions with occupancy factor of 60 and 40%,
and the other toluene has 0.5 occupancy. All of them were refined
with DFIX, SADI, and RIGU restraints. In the case of structure (5)2·
(H2O)4·CH2Cl2, all lattice water molecules have been treated as a
diffuse contribution to the overall scattering without specific atom
positions by SQUEEZE/PLATON.33 The refinement data for all the
structures are given in Table 3.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b00744.
■
S
NMR, IR, TGA, powder XRD (PDF)
Accession Codes
CCDC 1831191−1831195 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: gmani@chem.iitkgp.ac.in. Phone: +91 3222 282320.
Fax: +91 3222 282252.
■
ORCID
Ganesan Mani: 0000-0002-0782-6484
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are thankful to the DST and CSIR (New Delhi, India) for
financial support, and DST FIST Level-II grant (No. SR/FST/
CSII-026/2013) for 500 MHz NMR machine. We are also
thankful to Prof. M. C. Das, Department of Chemistry, IIT-
Kharagpur, for TGA and to Vasudevan Subramaniyan for
completing one of the X-ray structures.
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