Palladium-Catalyzed Ethylene/Methyl Acrylate Co-Oligomerization: The Effect of a New Nonsymmetrical α-Diimine with the 1,4-Diazabutadiene Skeleton

Article abstract of DOI:10.1002/cctc.201700504

Pd^II complexes with a nonsymmetrical bis(aryl-imino)diazabutadiene ligand (ArDAB) have been synthesized and characterized. The new ligand features one aryl ring substituted in the ortho positions with a methyl group and the other ring that bears a trifluoromethyl group on the meta positions, which leads to subtle steric and electronic differences at the two N donor atoms. This peculiar substitution makes the direct synthesis of the ligand unfeasible, and the relevant Pd^II complex, [Pd(CH₃)Cl(ArDAB)], is obtained directly through a template reaction. The corresponding cationic complexes with either acetonitrile or DMSO were synthesized and characterized. The X-ray crystal structure of a Pd complex with an α-diimine and DMSO is reported. The monocationic complexes were tested as precatalysts in ethylene/methyl acrylate co-oligomerization under mild reaction temperature and pressure conditions. A comparison of the catalytic behavior of the precatalysts with the corresponding nonsymmetrical aryl α-diimines with an acenaphthene skeleton indicated that the active species with the new ligand is more productive and leads to the formation of ethylene oligomers and ethylene/methyl acrylate co-oligomers.

Full text of DOI:10.1002/cctc.201700504

Accepted Article
Title: Pd-catalyzed ethylene/methyl acrylate cooligomerization:
the effect of a new nonsymmetric alfa-diimine with the 1,4-
diazabutadiene skeleton
Authors: Barbara Milani, Vera Rosar, Tiziano Montini, Gabriele
Balducci, Ennio Zangrando, and Paolo Fornasiero
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.201700504
Link to VoR: http://dx.doi.org/10.1002/cctc.201700504
A Journal of
www.chemcatchem.org

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
Pd-catalyzed ethylene/methyl acrylate cooligomerization: the
effect of a new nonsymmetric -diimine with the 1,4-
diazabutadiene skeleton
Vera Rosar,[a,b]* Tiziano Montini,[a,c] Gabriele Balducci,[a] Ennio Zangrando,[a] Paolo Fornasiero,[a,c]
Barbara Milani[a]*
Dedication
Abstract: Palladium(II) complexes with a nonsymmetric bis(aryl-
imino)diazabutadiene ligand (ArDAB) have been synthesized and
characterized. The new ligand is featured by one aryl ring
substituted in ortho positions with methyl groups and the other ring
bearing a trifluoromethyl group on the meta positions, leading to a
subtle steric and electronic difference on the two nitrogen-donor
atoms. This peculiar substitution makes the direct synthesis of the
ligand not feasible, and the relevant Pd(II) complex,
functionalized analogues, they exhibit advantageous surface
properties with respect to adhesion, toughness, printability,
paintability and compatibility with other materials.[2] Brookhart’s
discovery that palladium complexes efficiently catalyze the
homopolymerization of ethylene,[3] opened the possibility of their
application as catalysts for the synthesis of functionalized
polyolefins. The two main catalytic systems reported are both
based on palladium(II) complexes, and differ for the ancillary
ligand coordinated to the metal center, that is either a neutral -
diimine (N-N),[4] or an anionic phosphine-sulfonate derivative (P-
O).[5]
In the copolymerization of ethylene with methyl acrylate (MA),
the model reaction, both systems lead to real copolymers,
featured by remarkable differences in the macromolecule
structure. Copolymers are highly branched, amorphous
materials, with a content of MA up to 25% if produced with the -
diimine system,[4a] or linear, with a content of MA up to 52 %
when obtained with the phosphine-sulfonate system.[6]
During this year, highly active nickel catalysts have been
reported.[7]
[Pd(CH3)Cl(ArDAB)], is directly obtained through
a template
reaction. The corresponding cationic complexes with either
acetonitrile or dimethyl sulfoxide have been synthesized and
characterized. The X-ray crystal structure of a palladium complex
with an -diimine and dimethyl sulfoxide is reported. The
monocationic complexes have been tested as precatalysts in the
ethylene/methyl acrylate cooligomerization under mild reaction
conditions of temperature and pressure. The comparison with the
catalytic behavior of the precatalysts with the corresponding
nonsymmetric ArBIAN ligand indicated that the active species with
the currently investigated ligand is more productive, leading to the
formation of ethylene oligomers and ethylene/methyl acrylate
cooligomers.
In addition, to the two classes of ligands mentioned above,
palladium complexes having either bis(phosphine) monoxide[8]
or phosphine-phosphonic amides[9] or N-heterocyclic carbenes
have been reported to catalyze the copolymerization of ethylene
with polar vinyl monomers.[10]
Introduction
As far as catalysts based on the N-donor ligands are concerned,
aryl -diimines with either the acenaphthene (ArBIAN) or the
The catalytic polymerization of alkenes such as ethylene or
propylene is among the synthetic reactions performed on largest
scale today. By contrast, the insertion copolymerization of
ethylene with polar vinyl monomers for the direct synthesis of
functionalized polyolefins has been recognized as one of the
major unsolved problems in the polymer field.[1] Polymers
bearing polar functional groups are highly desirable materials,
due to their unique properties: compared to their non-
1,4-diaza-2,3-butadiene
(ArDAB)
skeleton
have
been
investigated (Figure 1), achieving an increase in productivity of
one order of magnitude when moving from the ArBIAN to the
ArDAB, regardless of the nature of the aromatic substituents.[4a,
4b, 11]
[a]
Dr. V. Rosar, Prof. E. Zangrando, Dr. G. Balducci, Dr. T. Montini,
Prof. Dr. P. Fornasiero, Prof. Dr. B. Milani
Department of Chemical and Pharmaceutical Sciences
University of Trieste
Figure 1. General structure of acenaphthene (ArBIAN) and 1,4-diaza-2,3-
butadiene (ArDAB) -diimines.
Via Licio Giorgieri 1, 34127 Trieste, Italy
Fax: (+39)0405583903
E-mail: milaniba@units.it
[b]
[c]
Dr. V. Rosar
The studies on palladium catalysts with aryl -diimines
encompass variation of the ligand skeleton,[12] further
enhancement of the steric hindrance[13] and the use of dinuclear
complexes.[14]
It is worth noting that all the ArDAB ligands applied in the
ethylene/MA copolymerization are symmetric molecules,
featured by the same aryl rings on the iminic nitrogen atoms.[2h,
Consorzio Interuniversitario per la Reattività Chimica e la Catalisi
CIRCC
Via Celso Ulpiani 27, 70126 Bari, Italy
Dr. T. Montini, Prof. Dr. P. Fornasiero,
ICCOM-CNR and INSTM Trieste
Via Licio Giorgieri 1, 34127 Trieste, Italy
Supporting information for this article contains details of crystal data
(CCDC 1530764-1530765), structure solution and refinements,
NMR spectra of complexes, of ethylene/MA cooligomers, and
GC/MS analyses, and is given via a link at the end of the document.
1
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
4c]
On the other hand, the reason of the peculiar behavior of the
phosphine-sulfonate catalysts is attributed to the different nature
of the two donor atoms, and to their capability to differentiate the
two coordination sites trans to them.[15] Therefore, we now report
the first nonsymmetric ArDAB ligand (Figure 2, ligand L1)
characterized by one aryl ring substituted on both ortho positions
with a methyl group and the other aryl having the CF3
substituent on the meta positions, resulting in a subtle electronic
and steric unbalance of the two N-donor atoms. The catalytic
behavior of the related Pd(II) complexes in the ethylene/MA
copolymerization is investigated and compared to that of the
compounds having the corresponding symmetric ligands (Figure
2, ligands L2 and L3) and the corresponding ArBIAN derivative
L4 (Figure 3).[16] Indeed, we have recently demonstrated that
palladium catalysts with nonsymmetric ArBIAN ligands are more
productive than those having the corresponding symmetric
derivatives in both the ethylene/MA cooligomerization[16] and the
CO/vinyl arene copolymerization.[17] Thus, according to
Brookhart’s results,[4a] a remarkable increase in the productivity
should be expected moving from the catalyst with L4 to that with
L1.
Figure 4. The nonsymmetric DAB molecules of literature.[18,19]
Results and Discussion
Synthesis and characterization of ligands and Pd-
complexes.
Ligands L2, L3 (Figure 2) were synthesized according to
literature procedures,[3a, 20] based on the condensation reaction
of 2,3-butanedione with the proper aniline, and they were
obtained as white-yellow solids with average yields of 30 %.
Their characterization is in agreement with the one reported.
Ligands L2, L3 were reacted with [Pd(cod)(CH3)Cl] (cod = 1,5-
cis,cis-cyclooctadiene) to obtain the corresponding neutral
derivatives [Pd(CH3)Cl(ArDAB)] (2(Cl), 3(Cl); ArDAB = L2, L3)
following the standard procedure (Scheme 1).[21] Whereas 2(Cl)
is known from literature,[22] 3(Cl) is reported here for the first time
and it has been fully characterized through NMR spectroscopy
(Supporting Information). In analogy to what reported for the
corresponding complexes with L5 and L6, [Pd(CH3)Cl(ArBIAN)],
11(Cl) and 12(Cl), respectively,[16] even for 2(Cl) and 3(Cl) the
singlet of the methyl group bonded to palladium moves from
0.26 to 0.52 ppm, strongly supporting our hypothesis that this
signal is a good probe for the electron donor capability of the
ligand.[16, 23]
Figure 2. The studied -diimines L1-L3 and the related numbering scheme.
Figure 3. Ligands L4-L6.[16]
During the preparation of this manuscript, palladium catalysts for
the ethylene/MA copolymerization with five nonsymmetric ortho-
substituted ArDAB ligands have been reported. They are
characterized by one aryl ring bearing benzhydryl groups and
the other having various aliphatic or aromatic substituents of
increasing bulkiness (Figure 4a).[18] As far as other
nonsymmetric ArDAB molecules are concerned, when we
designed ligand L1, only three other examples were known, all
of them featured by iso-propyl groups on the ortho positions of
one aryl ring (Figure 4b).[19] Ligands L14 were used to obtain
nickel complexes that generated very active catalysts for
ethylene homopolymerization, whereas the coordination
chemistry to palladium(II) of ligands L15 was investigated, but
no catalytic studies were reported.
Scheme 1. Synthesis of the neutral and monocationic complexes 1-3(Cl), 4-
6(CH3CN), 7-9(CH3CN), with the corresponding numbering scheme.
As far as the synthesis of the nonsymmetric ArDAB molecules
reported up to now (Figure 4) is concerned, all of these ligands
share the presence of one aryl ring substituted in 2,6 positions
with highly encumbered groups. Their synthesis was based on
the isolation of the monoketoimine derived from the reaction of
2,3-butanedione with the hindered 2,6-disubstituted aniline,
which was then reacted with the other aniline.[18,19]
2
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
To obtain ligand L1, a similar approach was attempted (Scheme
2), but the isolation and purification of the relevant
monoketoimines L16 and L17 was unsuccessful, thus
hampering their use in the synthesis of ligand L1.
identified as the isomer with the Pd-CH3 moiety trans to the Pd-
N bond of the CF3-substituted aryl ring. For the sake of clarity,
this species is designated as the trans isomer. Only traces of the
cis species were observed. However, the presence of exchange
cross peaks between the two species indicated that, in solution
at room temperature, the two isomers are in equilibrium at slow
rate on the NMR timescale. The same strong preference for the
trans species was also found in the case of the palladium neutral
complex with the nonsymmetric ArBIAN ligand L4,
[Pd(CH3)Cl(L4)], 10(Cl),[16] suggesting that the preference for
one isomer over the other is not affected by the ligand skeleton.
Likewise in the case of the neutral palladium complexes with
ligands L7-L11 (Figure 4a) two isomers were observed in
solution, but no indication about the nature of the major species
was reported.[18]
Scheme 2. Synthetic approaches to obtain the monoketoimines L16 or L17.
The neutral complexes were converted into the cationic
precatalysts [Pd(CH3)(NCCH3)(ArDAB)][X] (X
=
PF6¯, 4-
Since the aim of our work was to obtain the palladium
derivative with ligand L1, [Pd(CH3)Cl(L1)], 1(Cl), a template
procedure was performed by reacting the in situ generated
monoketoimine L17 with 2,6-dimethylaniline in the presence of
6(CH3CN); X = SbF6¯, 7-9(CH3CN); ArDAB = L1-L3) according
to the protocol published for the PF6¯ derivatives, that resulted to
be valid also for the compounds with SbF6¯ (Scheme 1).[21]
Comparing the NMR spectra of the couples of complexes
4(CH3CN) - 7(CH3CN), 5(CH3CN) - 8(CH3CN) and 6(CH3CN) -
9(CH3CN), the same signals were observed, showing that the
nature of the counterion did not affect them; thus, only the
characterization of the hexafluorophosphate derivatives is
discussed. In the 1H NMR spectra sharp signals were present at
298 K, as generally observed for similar acetonitrile complexes
(Supporting Information).[11, 16, 21] For complex 4(CH3CN), both
cis and trans isomers were present, the major species being
identified by a NOESY experiment as the trans isomer. In
addition, the presence of exchange peaks for both the Pd-CH3
and the Pd-NCCH3 groups indicated that they were in slow
exchange on the NMR timescale at room temperature. The trans
to cis ratio was 6 : 1 regardless of the nature of the counterion,
while for the acetonitrile derivative with the analogous ArBIAN
ligand L4 it was 10 : 1.[16]
1
[Pd(cod)(CH3)Cl] as templating agent. The comparison of the H
NMR spectrum of the solid isolated from this synthesis with
those of the neutral complexes 2(Cl) and 3(Cl) indicated that the
solid contained a mixture of 2(Cl) and a new palladium complex
(Figure 5, left). In particular, the singlet of the Pd-CH3 of the new
complex resonated at 0.40 ppm, intermediate between those of
2(Cl) and 3(Cl). This trend, analogous to that found for the
neutral complexes with ligands L4 – L6,[16] identified the new
complex as 1(Cl). The comparison of the 19F NMR spectrum of
the crude solid with those of ligand L3 and complex 3(Cl)
indicated that none of these was present (Figure 5, right),
supporting the hypothesis that the solid contained 1(Cl).
Ar-CH3
DAB-CH3
Pd-CH3
The series of the monocationic complexes with ligand L1 was
(a)
(b)
(c)
(a)
(b)
(c)
extended
to
the
dimethyl
sulfoxide
derivative
Ar-CH3
[Pd(CH3)(dmso)(L1)][PF6], 4(dmso), synthesized according to
1
the procedure we developed.[11, 16] In the H NMR spectrum of
4(dmso) in CD2Cl2, broad signals were observed at room
DAB-CH3
Pd-CH3
temperature, and they became sharper with the decrease in
16]
temperature, as already observed for similar complexes.[11,
The decoalescence of all the methyl group signals was reached
at 233 K, showing the presence of both trans and cis isomers in
4 : 1 ratio. The presence of exchange peaks in the NOESY
spectrum at the decoalescence temperature indicated that the
two isomers were in slow exchange on the NMR timescale.
Pd-CH3
DAB-CH3
The chemical shift values of the carbon atoms of dmso methyl
groups in the 1H,13C-HSQC experiment unambiguously indicated
that dmso is S-bonded to palladium in both isomers, although
traces of the O-bonded species were observed. The S-
coordination of dmso was also confirmed by the IR spectrum in
solid state, which showed one band at 1128 cm-1. Both the
preference for the trans isomer and the S-bonded coordination
of dmso are analogous to what found for the corresponding
cationic complex with the ArBIAN L4.[16]
Figure 5. (left) 1H NMR spectra (aliphatic region) in CDCl3 at 298 K of: (a)
2(Cl); (b) crude product of the template reaction; (c) 3(Cl). (right) 19F NMR
spectra in CDCl3 at 298 K of: (a) L3; (b) crude product of the template
reaction; (c) 3(Cl).
After several attempts and a fine-tuning of the reaction
conditions, it was possible to obtain pure 1(Cl) from column
chromatography. The NMR characterization at room
temperature in CD2Cl2 solution revealed the presence of almost
exclusively one species that, by a NOESY experiment, was
For 1(Cl) and 4(dmso), single crystals suitable for X-ray
diffraction were obtained upon slow diffusion of n-hexane into a
3
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
dichloromethane solution of each complex at 277 K (Figure 6,
Supporting Information).
Ethylene/methyl
reaction
acrylate
cooligomerization
The synthesized monocationic complexes 4-6(CH3CN), 7-
9(CH3CN), 4(dmso) were tested as precatalysts for the
ethylene/methyl acrylate cooligomerization reaction (Scheme 3).
The catalytic tests were run in 2,2,2-trifluoroethanol (TFE) as
solvent, at T = 308 K and Pethylene = 2.5 bar, for 18 h. These
reaction conditions are the same applied for the catalytic tests
run on the palladium complexes with the analogous ArBIAN
ligands, allowing a direct comparison of the data.[16]
(a)
The isolated products were characterized by NMR
spectroscopy after removing the volatile fraction at reduced
pressure, while the presence of higher alkenes was determined
by GC/MS analysis on the reaction mixture before the workup.
(b)
Scheme 3. Ethylene/methyl acrylate cooligomerization.
Figure 6. ORTEP representation (ellipsoid probability at 50 %) of (a) 1(Cl);
and (b) one of the two independent cations of 4(dmso).
Table 1. Ethylene/methyl acrylate cooligomerization: effect of the ancillary
ligand.[a]
Precatalyst: [Pd(CH3)(NCCH3)(N-N')][PF6]
The structural analysis of 1(Cl) showed the presence of only
the trans isomer in the unit cell (Figure 6a), corresponding to the
almost exclusive species observed in solution. It is noteworthy
that the Pd-N bond distances found in 1(Cl) (Pd-N(1) 2.138(2) Å;
Pd-N(2) 2.042(2) Å) are remarkably shorter than those observed
in the analogue 10(Cl) (Pd-N(1) 2.201(4) Å; Pd-N(2) 2.063(4)
Å),[16] thus suggesting a stronger coordination of the ArDAB
ligand with respect to the ArBIAN one. This trend does not seem
to depend on the nature of the arylic substituents, since it is also
Run
1
N-N'
L1
Yield (g)
1.28
g P/g Pd[b]
544.6
mol % MA[c]
alkenes/esters[d]
C4-16
4.5
2.8
2
L2
2.90
1298.8
none
C4-8
3
L3
0.01
-
-
C5-7[e]
4[f]
5[f]
6[f]
[a]
L4
L5
L6
0.297
0.171
0.019
133.2
79.4
-
14.7
10.4
-
C4-16
none
C4-6
observed
for
corresponding
ArBIAN/ArDAB
dichlorido
complexes with isopropyl ortho disubstituted aryl rings (2.041(8)
Å vs 2.009(2) – 2.017(2) Å).[24]
In complex 1(Cl), the dihedral angles made by the aryl rings
with the coordination plane are both close to 90° (82.8(1)° and
89.8(1)°); this differs from the values found for complex 10(Cl),
where the CF3-substituted aryl ring is markedly bent towards the
Reaction conditions: nPd = 2.1∙10-5 mol, VTFE = 21 mL, VMA = 1.130 mL,
[b]
[MA]/[Pd] = 594, T = 308 K, Pethylene = 2.5 bar, t = 18 h;
isolated yield,
productivity as g P/g Pd = grams of product per gram of Pd; [c] calculated by 1H
NMR spectroscopy on isolated product; [d] deteremined by GC/MS; [e] traces of
methyl esters of pentenoic and eptenoic acids; [f] ref.[16] t = 24 h.
coordination plane (64.5(1)° and 80.1(1)°, respectively).[16]
A
similar situation is found for the corresponding palladium
complexes with the naphthyl-substituted ArDAB and ArBIAN
ligands (80.9(4)° - 86.9(1)° vs 83.4(4) - 69.3(1)).[11] This trend is
reasonably due to the enhanced out-of-plane steric hindrance of
the DAB skeleton with respect to the BIAN one.
A remarkable effect of the nitrogen-donor ligand on the
catalytic behavior was observed (Table 1). The most productive
catalyst was generated by 5(CH3CN) (1.3 kg P/g Pd; Table 1 run
2), which was more than two times as productive as 4(CH3CN)
(0.5 kg P/g Pd; Table 1 run 1). Comparing these data with those
reported for the corresponding catalysts with ligands L4-L6,[16]
and in agreement with literature,[4a, 11] moving from the ArBIAN to
the ArDAB derivatives (Table 1, runs 4 vs 1, 5 vs 2), a
remarkable increase in the productivity was observed. However,
in the case of the catalysts with the nonsymmetric ligands L4
and L1 (Table 1, runs 4 vs 1) the increase was not as
pronounced as that found for the catalysts with the symmetric
ligands L5 and L2 (Table 1, runs 5 vs 2). For both catalysts
The solid state structure of 4(dmso) is the first example
reported for a Pd(II) complex with dmso and an -diimine ligand
(Figure 6b). Only the trans isomer with S-bonded dmso is
present in the unit cell and it corresponds to the major species
observed in solution. Unlikely to the crystal structure of 1(Cl), in
this case, the CF3-substituted aryl ring is significantly rotated
towards the coordination plane (dihedral angles: 65.9 and 68.9°
in the two crystallographically independent molecules), while the
other arylic residue is almost normal to it.
obtained
from
5(CH3CN)
and
4(CH3CN)
negligible
4
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
decomposition to inactive palladium black was observed at the
end of the reaction time, in contrast to what found with the
catalysts having ligands L5 and L4 in 24 h.[16] Since the
decomposition pathway involves ligand dissociation, this
observation is in line with the stronger coordination of ArDAB
ligand with respect to that of the ArBIAN. Precatalyst 6(CH3CN)
did not produce appreciable amounts of cooligomers, yielding an
oil that contained mainly palladium derivatives and higher
alkenes. This can be related to the fast decomposition of the
catalyst to inactive palladium black, which formed already within
the first 30 min of reaction.
Precatalyst 4(CH3CN) showed
ethylene within the first 2 h of reaction with respect to both
precatalysts 5(CH3CN) and [Pd(CH3)(NCCH3)(L4)][PF6]
a greater absorption of
13(CH3CN), together with a remarkable evolution of volatile
products at the opening of the reactor at the end of the catalytic
run, suggesting that a considerable amount of ethylene was
converted into volatile alkenes, which are not the product of
interest and were not quantified (Figure S24). Therefore, as in
the case of the literature catalysts, the productivity of catalyst
with ligand L1 was evaluated on the basis of the isolated product
only (Table 1), and resulted to be in the range of the values very
recently reported for palladium catalysts with nonsymmetric
ArDAB that also were found to be less productive than the
catalyst with the corresponding symmetric ligand.[18]
Figure 7. 1H NMR spectrum in CDCl3 at 298 K of the catalytic product
obtained with 4(CH3CN).
The effect of reaction time was investigated in the range from
2 to 18 h. For 5(CH3CN) the increase in productivity with time
was almost linear, whereas for 4(CH3CN) it increased only in the
first 6 h, and afterward an asymptotic behavior was observed
(Figure 8). Since no formation of palladium black was evident,
this trend suggests that catalyst with ligand L1 might be
deactivated through a different pathway, probably generating
soluble inactive palladium species. The polar monomer
incorporation decreased with time, and the MA content in the
product was always higher for 4(CH3CN) with respect to
5(CH3CN) (Figure 8).
25]
In agreement with Brookhart's system,[3a,
in the case of
catalysts with the symmetrically ortho-substituted ligands, L2
and L5, no higher alkenes were formed. For catalysts with the
nonsymmetric L1 and L4, the detected alkenes are from C4 to
C16 (Figure S25). Precatalyst 6(CH3CN), due to the lack of steric
hindrance on the ortho positions of the aryl rings of the ancillary
ligand,[3a, 4a, 25] produced C4 - C8 alkenes.
2000
1800
1600
1400
1200
1000
800
10
9
8
7
6
5
4
3
2
1
0
In all cases the formed alkenes are a complex mixture of
isomers, as the result of the chain walking mechanism.[3a] In the
case of catalyst with ligand L1, having one aryl ring substituted
on both ortho positions, longer alkenes were produced (Figure
S25). This result indicates that the associative displacement of
the produced alkene by the incoming monomer is slowed down
using the nonsymmetric ligand, as previously observed for the
ArBIAN analogue catalysts.[16]
The NMR analysis of the product of the catalytic runs (Figure
7), in agreement with the literature,[16] pointed out that 4(CH3CN)
led to the formation of a mixture of ethylene oligomers and
ethylene/MA cooligomers with a content of polar monomer
higher than that present when 5(CH3CN) was used. In the NMR
spectra, the signal centered at 5.4 ppm, due to vinylic protons,
indicates that the -hydrogen elimination is the termination
process. The ethylene/MA cooligomers obtained with
precatalysts 4(CH3CN) and 5(CH3CN) have a content of methyl
acrylate remarkably lower than that obtained with the
corresponding ArBIAN analogues L4 and L5, respectively (Table
1).[16] This trend, in contrast with that reported by Brookhart,[4a] is
in agreement with our previous findings: as the productivity of
the catalyst increased, a decrease in the polar monomer content
was observed, which was due not only to the different catalyst
nature, but also to the consumption of the polar monomer, and
to the corresponding decrease in its concentration with the
proceeding of the reaction, whereas the ethylene pressure was
kept constant.[11, 16]
600
400
200
0
0
2
4
6
8
10 12 14 16 18 20
t / h
Figure 8. Ethylene/MA cooligomerization: effect of the reaction time. Reaction
conditions: see Table 1. Filled symbols: productivity data; open symbols: mol%
MA. 4(CH3CN) (●,○); 5(CH3CN) (♦,◊).
The results from quantification of higher alkenes by GC/MS
analysis (Figure S26) evidenced that their concentration
progressively increased with the reaction time. Notably, the
chain length distribution expressed as weight fraction gradually
decreased as reaction time increased. A similar behavior was
5
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
previously reported for the analog ArBIAN derivatives,[16] and
was attributed to the competition between the formed short
alkenes and ethylene for the incorporation into the growing
polymer chain.
productivity and catalyst lifetime with respect to acetonitrile
becomes evident when catalyst decomposition is relevant.
Table 2. Ethylene/methyl acrylate cooligomerization: effect of the labile ligand
and reaction time.
The effect of [MA]/[Pd] ratio was studied for 4(CH3CN) and
5(CH3CN) by decreasing the amount of precatalyst. Both
complexes showed a slight increase in the productivity by
doubling the [MA]/[Pd] ratio from 600 to 1200, followed by an
almost negligible decrease for a further increase up to [MA]/[Pd]
= 2400 (Figure 9). The MA content slightly decreased upon
increasing the ratio of polar monomer to palladium, with
4(CH3CN) and 5(CH3CN) showing the same behavior, and
maintaining the trend of higher value of inserted MA for the
former with respect to the latter.
Precatalysts: [Pd(CH3)(S)(N-N')][PF6], 4(CH3CN), 4(dmso) [a]
Yield
(g)
g P/g
Pd[b]
mol %
MA[c]
alkenes/
esters[d]
Run
N-N'
S
t
1
2
L1
L1
L4
L4
L1
L1
L4
L4
CH3CN
CH3CN
CH3CN
CH3CN
dmso
18
48
24
48
18
48
24
48
1.28
1.27
544.6
570.1
133.2
141.7
511.6
549.0
233.5
349.3
4.5
5.2
C4-16
C4-14
C4-16
C4-16
C4-8
3[e]
4[e]
5
0.297
0.316
1.14
14.7
14.9
5.5
2000
1800
1600
1400
1200
1000
800
10
9
8
7
6
5
4
3
2
1
0
6
dmso
1.22
5.4
C4-16
C4-16
C4-16
7[e]
8[e]
[a]
dmso
0.521
0.779
12.5
10.5
dmso
Reaction conditions: nPd = 2.1∙10-5 mol, VTFE = 21 mL, VMA = 1.130 mL,
[b]
[MA]/[Pd] = 594, T = 308 K, Pethylene = 2.5 bar, t = 18 h;
isolated yield,
productivity as g P/g Pd = grams of product per gram of Pd; [c] calculated by 1H
NMR spectroscopy on isolated product; determined by GC/MS; ref.[16] t =
[d]
[e]
600
24 h.
400
The production of higher alkenes is also slightly lower for
precatalyst 4(dmso) with respect to 4(CH3CN), independently
from the reaction time considered (Figure S28). Notably, the
weight fraction distribution of the produced higher alkenes
increased to some extent using the precatalyst 4(dmso) as the
reaction time increased, while it is not affected for precatalyst
4(CH3CN) (Figure S28). This analysis suggests that dmso
remains, anyhow, in the second coordination sphere of
palladium, thus limiting the availability of the fourth coordination
site for the -H elimination to occur.
200
0
0
600
1200
1800
2400
3000
[MA]/[Pd]
Figure 9. Ethylene/MA cooligomerization: effect of MA to palladium ratio.
Reaction conditions: see Table 1. Filled symbols: productivity data; open
symbols: mol% MA. 4(CH3CN) (●,○); 5(CH3CN) (♦,◊).
The GC/MS analysis of the higher alkenes highlighted that the
amounts of C4-C16 products decreased as the [MA]/[Pd] ratio
increased (Figure S27). This is in agreement with the increased
productivity observed (Figure 9), considering that alkenes
compete with ethylene for the catalytic sites. Notably, the weight
fraction distribution of the produced alkenes showed only
marginal differences.
The effect of the counterion, hexafluorophosphate vs
hexafluoroantimonate,
was
initially
investigated
in
trifluoroethanol (Table 3). In agreement with the high dielectric
constant of the solvent, which disfavors the formation of ion
pairs,[26] only a slight increase in the productivity was observed
moving from the PF6- to the SbF6- precatalysts, regardless of the
nature of the ancillary ligand (Table 3, runs 1 vs 2, and 3 vs 4).
No influence on either catalyst stability or polar monomer
content was observed. In agreement with this, the
hexafluoroantimonate precatalyst produced slightly lower
amount of higher alkenes with lower weight fraction distribution
with respect to the hexafluorophosphate counterpart (Figure
S29).
When precatalyst 4(CH3CN) was tested at T = 318 K, in
analogy to the behavior of the corresponding catalyst with ligand
L4,[16] a decrease in the productivity was observed together with
the formation of inactive palladium black (Table S5).
Complex 4(dmso), having dmso in place of acetonitrile, was
also tested as precatalyst in the target reaction, showing a
productivity slightly lower than that of precatalyst 4(CH3CN),
even at longer reaction time (Table 2). This trend, in contrast to
what observed with precatalyst [Pd(CH3)(dmso)(L4)][PF6],[16] is
in agreement with the catalytic behavior reported by us for the
precatalysts with the naphthyl-substituted -diimines, for which
no positive effect of dmso with respect to acetonitrile was
observed.[11] Therefore, the present catalytic data support our
previous hypothesis that a beneficial influence of dmso on
To highlight any possible counterion effect, a series of
catalytic tests was performed in dichloromethane (Table 3).
Regardless of the ancillary ligand, moving from trifluoroethanol
to dichloromethane resulted in a significant decrease in the
productivity, with the exception of precatalyst 8(CH3CN), that in
both solvents generated the most productive catalyst and in
dichloromethane a productivity value of more than 1.7 kg P/g Pd
was achieved (Table 3, run 6). The ethylene/MA cooligomers
produced in dichloromethane have a slightly higher content of
6
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
inserted polar monomer than those obtained in the fluorinated
alcohol. As observed in TFE, also in dichloromethane the
productivity of the catalysts with the nonsymmetric ligand L1
was remarkably lower than that of the active species with the
symmetric derivative L2 (Table 3, runs 7 and 8 vs 5 and 6). In
addition, whereas no formation of palladium black was observed
for the catalyst having ligand L2, remarkable decomposition to
inactive palladium metal was evident for catalysts with ligand L1,
in agreement with the known positive effect of the fluorinated
alcohol.[27]
Table 3. Ethylene/methyl acrylate cooligomerization reaction: effect of the counterion X and of the solvent.
Precatalyst: [Pd(CH3)(CH3CN)(N-N')][X].[a]
alkenes/
esters[d]
Run
Precat.
X
Solvent
Yield (g)
g P/g Pd[b]
mol % MA[c]
-
1
2
3
4
5
6
7
8
5(CH3CN)
8(CH3CN)
4(CH3CN)
7(CH3CN)
5(CH3CN)
8(CH3CN)
4(CH3CN)
7(CH3CN)
PF6
TFE
TFE
2.90
2.92
1.28
1.31
1.26
3.89
0.140
0.500
1298.8
1310.1
544.6
588.0
566.7
1744.7
62.5
2.8
2.6
4.5
5.3
3.7
3.5
8.9
9.3
none
none
C4-16
C4-16
-
-
-
-
SbF6
-
PF6
TFE
SbF6
TFE
-
PF6
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
none
none
C4-16
C4-16
SbF6
-
PF6
SbF6
224.4
[a] Reaction conditions: nPd = 2.1∙10-5 mol, Vsolvent = 21 mL, VMA = 1.130 mL, [MA]/[Pd] = 594, T = 308 K, Pethylene = 2.5 bar, t = 18 h; [b] isolated yield, productivity as
g P/g Pd = grams of product per gram of Pd; [c] calculated by 1H NMR spectroscopy on isolated product; [d] determined by GC/MS.
It is noteworthy that in dichloromethane, regardless of the
represents the first X-ray analysis of a palladium complex with
an -diimine and dimethyl sulfoxide.
-
-
nature of the ancillary ligand, moving from PF6 to SbF6 , an
increase of roughly three times in productivity was achieved,
without any decrease in the content of polar monomer inserted
(Table 3, runs 5 vs 6 and 7 vs 8). In dichloromethane, even the
production of higher alkenes is affected by the nature of the
In addition, the corresponding symmetric ligands L2, L3 were
synthesized according to literature procedures, and used to
obtain the relevant palladium neutral and monocationic
acetonitrile derivatives.
-
-
counterion: it remarkably decreases moving from PF6 to SbF6 .
These data confirm the formation of ion pair in the chlorinated
solvent, and suggest that the larger, and less coordinating,
hexafluoroantimonate[28] is located further away from palladium
favoring the formation of longer chains and resulting in the
observed higher yield in the isolated product, than that obtained
with the hexafluorophosphate derivative.
All the monocationic complexes were tested as precatalysts
for the ethylene/MA cooligomerization reaction under mild
conditions of temperature and ethylene pressure, and in TFE as
solvent. The complex with the meta-substituted symmetric ligand
was found to be inactive, while the other derivatives led to a
mixture of ethylene/MA cooligomers and ethylene oligomers.
Differently with what previously observed for catalysts with
nonsymmetric ArBIAN ligands,[16] for the ArDAB precatalysts
under investigation the active species with the nonsymmetric
ArDAB L1 was found to be less productive than that with the
symmetric ligand L2.
Conclusions
The nonsymmetric ArDAB ligand L1, characterized by one
aryl ring substituted in ortho positions with the methyl group and
the other ring bearing a trifluoromethyl group on the meta
positions, was tailored. In contrast to the few other
nonsymmetric ArDAB molecules reported in the literature, the
direct synthesis of L1 was not possible. Therefore, the relevant
neutral palladium complex [Pd(L1)(CH3)Cl], 1(Cl), was directly
synthesized by using [Pd(cod)(CH3)Cl] as templating agent.
1(Cl) was transformed in the monocationic complexes
[Pd(CH3)(L1)(L)][X] (L = CH3CN, dmso; X = PF6¯, SbF6¯). The
neutral and monocationic complexes were characterized both in
solid state and solution. In particular, the crystal structure of
[Pd(CH3)(L1)(dmso)][PF6] was solved pointing out that dmso is
S-bonded to palladium, and that the Pd-CH3 fragment is trans to
the Pd-N bond of CF3-substituted aryl ring of the ligand. This
Comparing the catalytic behavior of the ArDAB precatalysts
with that reported for the corresponding ArBIAN derivatives
pointed out that moving from the BIAN to the DAB skeleton an
increase in productivity was observed, in agreement with
literature, but for the catalyst with the nonsymmetric ligand L1
the increase was not as pronounced as that observed for that
with symmetric methyl-substituted derivative L2. The produced
ethylene/MA cooligomers have a content of polar monomer
remarkably lower than that present in the cooligomers obtained
with ArBIAN derivatives.
The effect of several parameters, such as the labile ligand,
acetonitrile vs dimethyl sulfoxide, the reaction time, the polar
monomer to palladium ratio, the solvent, the counterion, was
investigated in detail and compared to what we previously found
with the corresponding ArBIAN catalysts.[16] In particular, the use
7
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
[Pd(CH3)Cl(ArDAB)] (2(Cl), 3(Cl)). To
a
stirred solution of
of different solvents remarkably points out the positive effect of
trifluoroethanol with respect to dichloromethane. As already
observed for the CO/vinyl arene copolymerization, also in the
ethylene/polar monomer copolymerization the reaction medium
plays a fundamental role in determining the catalytic behavior of
the complexes and thus each comparison, even with the data
reported in the literature, has to be carefully made.
[Pd(cod)(CH3)Cl] (0.38 mmol) in 1 mL of CH2Cl2, a solution of 1.1 equiv
of the desired ligand in CH2Cl2 (2 mL for L2, 6 mL for L3) was added.
After the established reaction time (2.5 h for 2(Cl), 5 h for 3(Cl)) at room
temperature, the reaction mixture was concentrated and the product
precipitated upon addition of cold diethyl ether.
2(Cl). Yield 91 %. Found C = 56.70, H = 6.16, N = 6.34. Calc. % for
C21H27N2ClPd: C = 56.14, H = 6.06, N = 6.23.
1H NMR (500 MHz, CD2Cl2, 298 K) δ = 7.22 – 7.08 (m, 6H, Ar-H), 2.22 (s,
1
4
12H, Ar-CH3), 2.00 (s, 3H, CH3 ), 1.96 (s, 3H, CH3 ), 0.26 (s, 3H, Pd-
CH3). 13C NMR (125.68 MHz, CD2Cl2, 298 K) δ = 128.85 – 126.52 (CAr),
19.73 (C4), 18.90 (C1), 18.11 (Ar-CH3), 0.66 (Pd-CH3).
Experimental Section
3(Cl). Yield 51 %. Found C = 38.16, H = 2.28, N = 4.23. Calc. % for
C21H15N2ClF12Pd: C = 37.92, H = 2.27, N = 4.21.
Materials and methods. All complex manipulations were performed
using standard Schlenk techniques under argon. Anhydrous
dichloromethane was obtained by distilling it over CaH2 and under argon.
Deuterated solvents (Cambridge Isotope Laboratories, Inc. (CIL)) were
stored as recommended by CIL. Ethylene (purity ≥ 99.9 %) supplied by
SIAD and methyl acrylate (99.9%, with 0.02% of hydroquinone
monomethyl ether) supplied by Aldrich were used as received. TFE, and
all the other reagents and solvents were purchased from Sigma-Aldrich
and used without further purification for synthetic, spectroscopic and
catalytic purposes. Ligands L2, L3 were synthesized according to
literature procedures.[3a, 20] [Pd(OAc)2] was a donation from BASF Italia
and used as received. [Pd(cod)Cl2], [Pd(cod)(CH3)Cl] were synthesized
according to literature procedures.[21] NMR spectra of ligands, complexes
and catalytic products were recorded on a Varian 500 spectrometer at
the following frequencies: 500 MHz (1H), 125.68 MHz (13C) and 470 MHz
(19F). The resonances are reported in ppm (δ) and referenced to the
residual solvent peak versus Si(CH3)4: CDCl3 at δ 7.26 (1H) and δ 77.0
(13C), CD2Cl2 at δ 5.32 (1H) and δ 54.0 (13C). NMR experiments were
performed employing the automatic software parameters. In the case of
NOESY experiments a mixing time of 500 ms was used. IR spectra were
recorded in Nujol on a Perkin Elmer System 2000 FT-IR. Elemental
analyses were performed in the analytical laboratories of the Department
of Chemistry of the University of Bologna. GC/MS analysis were
performed with an Agilent GC 7890 instrument using a DB-225ms
column (J&W, 60 m, 0.25 mm ID, 0.25 μm film) and He as carrier
coupled with a 5975 MSD. Before analysis, samples were diluted with
methanol and nonane was added as internal standard.
1H NMR (500 MHz, CD2Cl2, 298 K) δ = 7.92 (s, 1H, H8), 7.87 (s, 1H, H8ꞌ),
1
7.54 (s, 2H, H6,10), 7.50 (s, 2H, H6ꞌ,10ꞌ), 2.26 (s, 3H, CH3 ), 2.14 (s, 3H,
4
CH3 ), 0.52 (s, 3H, Pd-CH3). 13C NMR (125.68 MHz, CD2Cl2, 298 K) δ =
4
122.29 (C6,10), 122.09 (C6',10'), 121.07 (C8), 120.94 (C8'), 21.10 (CH3 ),
1
19.75 (CH3 ), 2.46 (Pd-CH3). 19F NMR (470 MHz, CD2Cl2, 298 K) δ = -
63.22, -63.35 (CF3).
Synthesis of the monocationic Pd-complexes
-
-
[Pd(CH3)(NCCH3)(ArDAB)][X] (X = PF6 , 4-6(CH3CN); X = SbF6 , 7-
9(CH3CN)). To stirred solution of the neutral complex
a
[Pd(CH3)Cl(ArDAB)] (1-3(Cl)) (0.10 mmol) in 5 mL CH2Cl2, a solution of
1.15 equiv of AgX (AgPF6 for 4-6(CH3CN), AgSbF6 for 7-9(CH3CN)) in 1
mL of anhydrous acetonitrile was added. The reaction mixture was
protected from light and stirred at room temperature for 45 min, then it
was filtered over Celite®, concentrated and precipitated upon addition of
cold diethyl ether.
4(CH3CN). Yield 82 %. Found C = 38.80, H = 3.40, N = 5.61. Calc. % for
¯
C23H24N3F12PdP: C = 39.03, H = 3.42, N = 5.94. IR:  = 843 cm-1 (PF6 ).
7(CH3CN). Yield 91 %. Found C = 34.71, H = 3.29, N = 5.01. Calc. % for
C23H24N3F12PdSb: C = 34.59, H = 3.03, N = 5.26. IR:  = 663 cm-1
¯
(SbF6 ).
1H NMR (500 MHz, CD2Cl2, 298 K), cis : trans = 1 : 6. trans isomer δ =
7.93 (s, 1H, H8'), 7.77 (s, 2H, H6',10'), 7.20 (s, 3H, H7,8,9), 2.41 (s, 3H,
4
1
CH3 ), 2.21 (s, 6H, Ar-CH3), 2.18 (s, 3H, CH3 ), 2.04 (s, 3H, Pd-NCCH3),
0.47 (s, 3H, Pd-CH3); cis isomer δ = 7.93 (s, 1H, H8'), 7.61 (s, 2H, H6',10'),
7.20 (s, 3H, H7,8,9), 2.35 (s, 3H, CH3 ), 2.30 (s, 6H, Ar-CH3), 2.22 (s, 3H,
4
1
CH3 ), 1.89 (s, 3H, Pd-NCCH3), 0.43 (s, 3H, Pd-CH3). 13C-NMR (125.68
MHz, CD2Cl2, 298 K), trans isomer δ = 129.00 (C7,8,9), 122.91 (C6',10'),
Synthesis of neutral Pd-complexes
121.77 (C8'), 20.31 (CH3 ), 20.26 (CH3 ), 18.04 (Ar-CH3), 5.85 (Pd-CH3),
1
4
[Pd(CH3)Cl(L1)] 1(Cl). To a stirred solution of 2,3-butanedione (3.0
mmol) in 5 mL of methanol with a catalytic amount of formic acid at 303 K,
1 equiv of 3,5-bis(trifluoromethyl)aniline (3.0 mmol) was added dropwise.
The solution was stirred at 303 K for 1 h, then a 1H NMR spectrum of the
reaction mixture was recorded to determine the amount of
monoketoimine L17 formed and to check that no traces of L3 were
3.00 (Pd-NCCH3).
5(CH3CN). Yield 92 %. Found C = 45.48, H = 5.24, N = 6.86. Calc. % for
C23H30N3F6PdP: C = 46.05, H = 5.04, N = 7.00. IR:  = 842 cm-1 (PF6¯).
8(CH3CN). Yield 79 %. Found C = 40.66, H = 4.51, N = 6.07. Calc. % for
C23H30N3F6PdSb: C = 40.00, H = 4.38, N = 6.08. IR:  = 657 cm-1 (SbF6¯).
1H NMR (500 MHz, CD2Cl2, 298 K) δ = 7.24 – 7.17 (m, 6H, Ar-H), 2.28 (s,
present. To this reaction mixture,
[Pd(cod)(CH3)Cl] and 1.2 equiv of 2,6-dimethylaniline in
a
suspension of 0.8 equiv of
mL of
1
2
6H, Ar-CH3), 2.21 (s, 3H, CH3 ), 2.20 (s, 6H, Ar'-CH3), 2.19 (s, 12H,
4
CH3 ), 1.83 (s, 3H, Pd-NCCH3), 0.35 (Pd-CH3). 13C NMR (125.68 MHz,
methanol were added. After 2 h at 303 K, the solvent was removed and
the resulting oil was treated with diethyl ether (0.5 mL) and cold n-hexane
(1 mL) until the incipient precipitation of a yellow solid. After 56 h at room
temperature, the formed solid was filtered and washed thoroughly with n-
hexane. The solid, containing complexes 2(Cl) and 1(Cl), was purified
through flash chromatography on silica with chloroform/n-hexane 1 : 1,
and the polarity was gradually varied by increasing the amount of
chloroform. The desired complex was eluted second as a bright orange
band, and was recovered after removing the solvent by precipitation with
diethyl ether (yield 23 %).
CD2Cl2, 298 K) δ = 128.76 (C8) , 127.59 (CAr), 17.76 (Ar-CH3), 18.65
1
4
(CH3 ), 17.71 (Ar'-CH3), 19.97 (CH3 ), 2.11 (Pd-NCCH3), 4.31 (Pd-CH3).
6(CH3CN). Yield 82 %. Found C = 33.76, H = 2.46, N = 4.98. Calc. % for
C23H18N3F18PdP: C = 33.86, H = 2.22, N = 5.15. IR:  = 837 cm-1 (PF6¯).
9(CH3CN). Yield 37 %. Found C = 30.76, H = 1.78, N = 4.72. Calc. % for
C23H18N3F18PdSb: C = 30.47, H = 2.00, N = 4.64. IR:  = 658 cm-1
(SbF6¯).
1H NMR (500 MHz, CD2Cl2, 298 K) δ = 7.93 (s, 2H, H8,8ꞌ), 7.71 (s, 2H,
1
4
H10,10'), 7.59 (s, 2H, H6,6ꞌ), 2,37 (s, 3H, CH3 ), 2.30 (s, 3H, CH3 ), 2.03 (s,
3H, Pd-NCCH3), 0.53 (s, 3H, Pd-CH3). 13C NMR (125.68 MHz, CD2Cl2,
1(Cl). Found
C = 44.96, H = 3.63, N = 4.96. Calc. % for
298 K) δ = 121.82 (C8,8ꞌ), 122.33 (C10,10'), 122.52 (C6,6ꞌ), 20.01 (CH3 ),
1
C21H21N2Pd1F6Cl1: C = 45.26, H = 3.80, N = 5.03.
1H NMR (500 MHz, CD2Cl2, 298 K) δ = 7.85 (s, 1H, H8'), 7.59 (s, 2H,
21.89 (CH3 ), 2.87 (Pd-NCCH3), 6.40 (Pd-CH3). 19F NMR (470 MHz,
4
4
H6',10'), 7.21-7.15 (m, 3H, H7,8,9), 2.24 (s, 3H, CH3 ), 2.21 (s, 3H, Ar-CH3),
CD2Cl2, 298 K) δ = -63.21, -63.42 (CF3).
1
1.99 (s, 3H, CH3 ), 0.40 (s, 3H, Pd-CH3). 13C-NMR (125.68 MHz, CD2Cl2,
298 K) δ = 128.88-127.28 (C7,8,9), 123.29 (C6',10'), 121.04 (C8'), 20.17
[Pd(CH3)(dmso)(L1)][PF6] 4(dmso). To a stirred solution of the neutral
complex [Pd(CH3)Cl(L1)] (1(Cl)) (0.13 mmol) in 7 mL CH2Cl2, 2 equiv of
anhydrous dimethyl sulfoxide (18.5 μL) and a suspension of 1.15
equivalents of AgPF6 (0.15 mmol) in 1 mL of CH2Cl2 were added. The
4
1
(CH3 ), 19.90 (CH3 ), 18.13 (Ar-CH3), 1.33 (Pd-CH3). 19F NMR (470 MHz,
CD2Cl2, 25°C) δ = -63.17 (CF3).
8
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
reaction mixture was protected from light and stirred at room temperature
for 30 min, then it was filtered over Celite®, concentrated and precipitated
upon addition of cold n-hexane after 2-3 h at 277 K.
every 15 min. Afterward the valve to connect the reactor with the
ethylene tank was open in order to keep constant the ethylene pressure
for the whole remaining reaction time. After the proper time, the reactor
was cooled to room temperature and vented. An aliquot (200 μL) of the
reaction mixture was withdrawn and diluted in CH3OH (1 mL) for GC/MS
analysis. The reaction mixture was poured in a 50 mL round flask,
together with the dichloromethane (3 x 1 mL) used to wash the glass
vessel. Volatiles were removed under reduced pressure and the residual
gum or oil was dried at constant weight and analyzed by NMR
spectroscopy.
4(dmso). Yield 88 %. Found C = 37.00, H = 3.91, N = 3.61. Calc. % for
C23H27N2F12Pd1P1O1S1: C = 37.09, H = 3.65, N = 3.76. IR:  = 843 cm-1
¯
(PF6 ),  = 1128 cm-1 (S=O, S-bonded dmso).
1H NMR (500 MHz, CD2Cl2, 233 K) trans : cis = 4 : 1. trans isomer δ =
7.85 (s, 1H, H8'), 7.66 (s, 2H, H6',10'), 7.19 (s broad, 3H, H7,8,9), 2.91 (s, 6H,
Pd-SO(CH3)2), 2.33 (s, 3H, CH34 or 1), 2.24 (s, 3H, CH31 or 4), 2.17 (s, 6H,
Ar-CH3), 0.14 (s, 3H, Pd-CH3); cis isomer δ = 7.94 (s, 1H, H8'), 7.68 (s,
2H, H6',10'), 7.19 (s broad, 3H, H7,8,9), 2.69 (s, 6H, Pd-SO(CH3)2), 2.40 (s,
3H, CH34 or 1), 2.24 (s, 6H, Ar-CH3), 2.17 (s, 3H, CH31 or 4), 0.41 (s, 3H,
Pd-CH3).
Acknowledgements
13C-NMR (125.68 MHz, CD2Cl2, 233 K) trans isomer δ = 128.52 (C7,8,9),
4
122.08 (C6',10'), 121.11 (C8'), 44.85 (Pd-SO(CH3)2), 20.71 (CH3 ), 20.29 –
1
This work was financially supported by Università degli Studi di
Trieste – Finanziamento di Ateneo per progetti di ricerca
scientifica – FRA2015. BASF Italia is acknowledged for a
generous donation of [Pd(OAc)2]. Dr. Nicola Demitri and the staff
of the Elettra Synchrotron in Trieste are gratefully acknowledged
for assistance in collecting X-ray data. CIRCC is thanked for a
fellowship to V.R.. P.F. and T.M. acknowledge INSTM
Consortium and ICCOM-CNR for financial support.
17.86 (CH3 ), 17.99 (Ar-CH3), 9.37 (Pd-CH3); cis isomer δ = 128.52
(C7,8,9), 122.08 (C6',10'), 121.88 (C8'), 44.27 (Pd-SO(CH3)2), 22.13 (CH34,1),
20.29 – 17.86 (Ar-CH3), 14.56 (Pd-CH3).
Ethylene/methyl acrylate Cooligomerization Reactions. All catalytic
experiments were carried out in a Büchi “tinyclave” reactor equipped with
an interchangeable 50 mL glass vessel. The vessel was loaded with the
desired complex (21 μmol), TFE (21 mL) or distilled CH2Cl2 (22 mL) and
methyl acrylate (1.13 mL). The reactor was then placed in a preheated oil
bath, connected to the ethylene tank, ethylene was bubbled for 10 min,
then the reactor was pressurized. The reaction mixture was stirred at
constant temperature. During the first 2 h the ethylene consumption was
monitored by keeping the reactor closed and recharging the ethylene
Keywords: palladium • homogeneous catalysis •
copolymerization • polar monomer • N ligands
9
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
Text for Table of Contents
Author(s), Corresponding Author(s)*
Pd(II) complexes with a new
Page No. – Page No.
nonsymmetric ArDAB, were studied
as precatalysts in the ethylene/MA
cooligomerization. The comparison
with the corresponding ArBIAN
analogues pointed out that the ArDAB
derivatives were more productive.
Title
10
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
References
[1]
J. A. Gladysz, Z. T. Ball, G. Bertrand, S. A. Blum, V. M. Dong, R. Dorta, F. E. Hahn, M. G.
Humphrey, W. D. Jones, J. Klosin, I. Manners, T. J. Marks, J. M. Mayer, B. Rieger, J. C. Ritter,
A. P. Sattelberger, J. M. Schomaker, V. W.-W. Yam, Organometallics 2012, 31, 1-18.
a) A. Nakamura, S. Ito, K. Nozaki, Chem. Rev. 2009, 109, 5215-5244; b) A. Berkefeld, S.
Mecking, Angew. Chem. Int. Ed. 2008, 47, 2538-2542; c) A. Sen, S. Borkar, J. Organomet.
Chem. 2007, 692, 3291-3299; d) J.-Y. Dong, Y. Hu, Coord. Chem. Rev. 2006, 250, 47-65; e) L.
S. Boffa, B. M. Novak, Chem. Rev. 2000, 100, 1479-1494; f) S. Ito, K. Nozaki, Chem. Rec. 2010,
10, 315-325; g) Y. Chen, L. Wang, H. Yu, Y. Zhao, R. Sun, G. Jing, J. Huang, H. Khalid, N. M.
Abbasi, M. Akram, Prog. Polym. Sci. 2015, 45, 23-43; h) L. Guo, S. Dai, X. Sui, C. Chen, ACS
Catal. 2016, 6, 428-441.
[2]
[3]
[4]
a) L. K. Johnson, C. M. Killian, M. Brookhart, J. Am. Chem. Soc. 1995, 117, 6414-6415; b) S. D.
Ittel, L. K. Johnson, M. Brookhart, Chem. Rev. 2000, 100, 1169-1204.
a) L. K. Johnson, S. Mecking, M. Brookhart, J. Am. Chem. Soc. 1996, 118, 267-268; b) S.
Mecking, L. K. Johnson, L. Wang, M. Brookhart, J. Am. Chem. Soc. 1998, 120, 888-899; c) L.
Guo, C. Chen, Sci. China Chem. 2015, 58, 1663-1673.
[5]
[6]
E. Drent, R. van Dijk, R. van Ginkel, B. van Oort, R. I. Pugh, Chem. Commun. 2002, 744-745.
a) B. P. Carrow, K. Nozaki, Macromolecules 2014, 47, 2541-2555; b) A. Nakamura, T. M. J.
Anselment, J. Claverie, B. Goodall, R. F. Jordan, S. Mecking, B. Rieger, A. Sen, P. Van
Leeuwen, K. Nozaki, Acc. Chem. Res. 2013, 46, 1438-1449.
[7]
[8]
[9]
a) M. Chen, C. Chen, ACS Catal. 2017, 7, 1308-1312; b) B. S. Xin, N. Sato, A. Tanna, Y. Oishi,
Y. Konishi, F. Shimizu, J. Am. Chem. Soc. 2017, 139, 3611-3614.
a) B. P. Carrow, K. Nozaki, J. Am. Chem. Soc. 2012, 134, 8802-8805; b) Y. Mitsushige, B. P.
Carrow, S. Ito, K. Nozaki, Chem. Sci. 2016, 7, 737-744.
X. Sui, S. Dai, C. Chen, ACS Catal. 2015, 5, 5932-5937.
[10] a) R. Nakano, K. Nozaki, J. Am. Chem. Soc. 2015, 137, 10934-10937; b) W. Tao, S. Akita, R.
Nakano, S. Ito, Y. Hoshimoto, S. Ogoshi, K. Nozaki, Chem. Commun. 2017, 53, 2630-2633.
[11] V. Rosar, A. Meduri, T. Montini, F. Fini, C. Carfagna, P. Fornasiero, G. Balducci, E. Zangrando,
B. Milani, ChemCatChem 2014, 6, 2403-2418.
[12] a) L. Guo, H. Gao, Q. Guan, H. Hu, J. Deng, J. Liu, F. Liu, Q. Wu, Organometallics 2012, 31,
6054-6062; b) W. Zou, C. Chen, Organometallics 2016, 35, 1794-1801.
[13] a) K. E. Allen, J. Campos, O. Daugulis, M. Brookhart, ACS Catal. 2015, 5, 456-464; b) S. Dai,
X. Sui, C. Chen, Angew. Chem. Int. Ed. 2015, 54, 9948-9953.
[14] S. Takano, D. Takeuchi, K. Osakada, N. Akamatsu, A. Shishido, Angew. Chem. Int. Ed. 2014,
53, 9246-9250.
[15] a) S. Noda, A. Nakamura, T. Kochi, L. W. Chung, K. Morokuma, K. Nozaki, J. Am. Chem. Soc.
2009, 131, 14088-14100; b) R. Nakano, L. W. Chung, Y. Watanabe, Y. Okuno, Y. Okumura, S.
Ito, K. Morokuma, K. Nozaki, ACS Catal. 2016, 6, 6101-6113; c) A. Haras, G. D. W. Anderson,
A. Michalak, B. Rieger, T. Ziegler, Organometallics 2006, 25, 4491-4497.
[16] A. Meduri, T. Montini, F. Ragaini, P. Fornasiero, E. Zangrando, B. Milani, ChemCatChem 2013,
5, 1170-1183.
[17] a) A. Scarel, M. R. Axet, F. Amoroso, F. Ragaini, C. J. Elsevier, A. Holuigue, C. Carfagna, L.
Mosca, B. Milani, Organometallics 2008, 27, 1486-1494; b) F. Amoroso, E. Zangrando, C.
Carfagna, C. Muller, D. Vogt, M. Hagar, F. Ragaini, B. Milani, Dalton Trans. 2013, 42, 14583-
14602.
[18] S. Dai, S. Zhou, W. Zhang, C. Chen, Macromolecules 2016, 49, 8855-8862.
[19] a) G. A. Abakumov, V. K. Cherkasov, N. O. Druzhkov, T. N. Kocherova, A. S. Shavyrin, Russ.
Chem. Bull., Int. Ed. 2011, 60, 112-117; b) M. Schmid, R. Eberhardt, J. Kukral, B. Rieger, Z.
Naturforsch. b 2002, 57, 1141-1146; c) F. Zhai, R. F. Jordan, Organometallics 2014, 33, 7176-
7192.
11
This article is protected by copyright. All rights reserved.

10.1002/cctc.201700504
ChemCatChem
FULL PAPER
[20] a) L. Johansson, O. B. Ryan, M. Tilset, J. Am. Chem. Soc. 1999, 121, 1974-1975; b) H. tom
Dieck, M. Svobada, T. Z. Greiser, Z. Naturforsch. b 1981, 36, 823-832.
[21] a) J. Durand, E. Zangrando, M. Stener, G. Fronzoni, C. Carfagna, B. Binotti, P. C. J. Kamer, C.
Muller, M. Caporali, P. W. N. M. van Leeuwen, D. Vogt, B. Milani, Chem. Eur. J. 2006, 12,
7639-7651; b) R. E. Rülke, J. M. Ernsting, A. L. Spek, C. J. Elsevier, P. W. N. M. Van Leeuwen,
K. Vrieze, Inorg. Chem. 1993, 32, 5769-5778.
[22] a) C. Hinderling, P. Chen, Int. J. Mass Spec. 2000, 195–196, 377-383; b) R. Lepski, A. Lüning,
K. Stirnat, A. Klein, J. Organomet. Chem. 2014, 751, 821-825.
[23] V. Rosar, D. Dedeic, T. Nobile, F. Fini, G. Balducci, E. Alessio, C. Carfagna, B. Milani, Dalton
Trans. 2016, 45, 14609-14619.
[24] a) E. K. Cope-Eatough, F. S. Mair, R. G. Pritchard, J. E. Warren, R. J. Woods, Polyhedron 2003,
22, 1447-1454; b) D. N. Coventry, A. S. Batsanov, A. E. Goeta, J. A. K. Howard, T. B. Marder,
Polyhedron 2004, 23, 2789-2795.
[25] D. J. Tempel, L. K. Johnson, R. L. Huff, P. S. White, M. Brookhart, J. Am. Chem. Soc. 2000,
122, 6686-6700.
[26] H. C. Eckstrom, J. E. Berger, L. R. Dawson, J. Phys. Chem. 1960, 64, 1458-1461.
[27] a) B. Milani, A. Anzilutti, L. Vicentini, A. Sessanta o Santi, E. Zangrando, S. Geremia, G.
Mestroni, Organometallics 1997, 16, 5064-5075; b) A. Scarel, J. Durand, D. Franchi, E.
Zangrando, G. Mestroni, B. Milani, S. Gladiali, C. Carfagna, B. Binotti, S. Bronco, T. Gragnoli,
J. Organomet. Chem. 2005, 690, 2106-2120.
[28] I. Krossing, I. Raabe, Angew. Chem. Int. Ed. 2004, 43, 2066-2090.
12
This article is protected by copyright. All rights reserved.