New aryl α-diimine palladium(II) catalysts in stereocontrolled CO/vinyl arene copolymerization

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pubs.acs.org/Organometallics

New Aryl α‑Diimine Palladium(II) Catalysts in Stereocontrolled

CO/Vinyl Arene Copolymerization

Carla Carfagna,*^,†Giuseppe Gatti,^†Paola Paoli,^‡Barbara Binotti,^†Francesco Fini,^†Alessandra Passeri,^†

Patrizia Rossi,^‡and Bartolo Gabriele^§

^†Dipartimento di Scienze Biomolecolari, Universita

^‡Dipartimento di Ingegneria Industriale, Universita

̀

di Urbino “Carlo Bo”, Piazza Rinascimento 6, 61029 Urbino, Italy

̀

di Firenze, Via S. Marta 3, 50139 Firenze, Italy

^§Dipartimento di Chimica e Tecnologie Chimiche, Universita

Italy

̀

della Calabria, Via P. Bucci, 12/C, 87036 Arcavacata di Rende (CS),

S

* Supporting Information

ABSTRACT: The eﬀect of the catalyst structure on the

stereoselectivity of CO/vinyl arene copolymerization has

been studied with the aim of developing catalytic systems able

to improve the yields while maintaining the high degree of

copolymer isotacticity previously obtained using achiral nitrogen

ligands. Aryl α-diimine ligands having extended aromatic rings

(Ar)₂DABMe₂, with Ar = 1-C₁₀H₇(e), 1-C₁₄H₉(f), 9-C₁₄H₉

(g), have been synthesized, and α-diimine coordination to

cationic methylpalladium complexes has been investigated in

solution, by means of NMR spectroscopy, and in the solid

state for [Pd(Me)(NCMe)((9-C₁₄H₉)₂DABMe₂)][PF₆] (2g).

The performance of these catalysts in CO/vinyl arene

copolymerization, under mild conditions, was analyzed in terms of productivity and degree of stereoregularity of the resulting

polyketones. In comparison with previous results, a remarkable enhancement in the yield of isotactic copolymer was observed

using the new achiral 9-anthryl α-diimine ligand g, conﬁrming that the ortho disubstitution and the extended aromatic rings play

key roles in obtaining good stereoselectivity and good productivity. To perform a structural analysis of the ﬁrst steps of the

CO/p-methylstyrene copolymerization, complex [Pd(Me)(CO)((9-C₁₄H₉)₂DABMe₂)][BAr′₄] (3g) was used as a starting point:

NMR investigation reveals the stereoselective formation of the oleﬁn/CO/oleﬁn insertion product (6g), which prevalently exists in

solution in only one diastereoisomeric form, thus justifying the observed high polymer isotacticity.

presence of bulky nitrogen ligands is crucial for blocking the axial

coordination sites on the metal toward incoming monomer,

retarding the chain transfer.¹Conversely, in CO/oleﬁn co-

polymerization the presence of large ortho substituents on the

aryl rings⁷is critical in determining the stereoselectivity of the

Pd(II) catalysts,^2b−das observed by some of us during recent

investigations on CO/vinyl arene copolymerization catalyzed

by the complexes [Pd(η¹,η²-C₈H₁₂OMe)((Ar)₂DABR₂)]X and

[Pd(Me)(NCMe)((Ar)₂DABR₂)]X bearing achiral α-diimine

ligands ((Ar)₂DABR₂≡ ArNC(R)C(R)NAr).^2a−c,8These

catalysts are able to produce atactic or stereoblock isotactic CO/

p-methylstyrene copolymers, depending on the aryl substituents,

through a “ligand assisted” chain-end control mechanism: both

the ligand and the growing chain cooperate in selecting the

enantioface and the direction of the incoming oleﬁn during the

copolymerization process.^2d,8This behavior is diﬀerent from

that observed with other achiral ligands (C_2vor C_ssymmetry),

which generally produce highly syndiotactic polyketones due to

1. INTRODUCTION

Late-transition-metal catalysts bearing nitrogen ligands have

found applications in several polymerization reactions. Within

these numerous kinds of complexes, palladium(II) catalysts

containing ortho-substituted aryl diimines appear to be rather

peculiar. Depending on the steric hindrance of the ortho sub-

stituents, they are excellent catalysts for homopolymerization of

oleﬁns¹or quite good catalysts for the alternating copolymeriza-

tion of aromatic oleﬁns with carbon monoxide.²The latter is

one of the best ways to eﬃciently synthesize polar function-

alized polymers through a coordination−insertion mechanism.³

The resulting polyketone possesses valuable properties:

mechanical and surface characteristics can be easily tuned,

and the polymer chain can be postfunctionalized, due to the

presence of the carbonyl group.⁴These characteristics, together

with the promising biocompatibility of produced materials,⁵

make the CO/oleﬁn copolymerization still an attractive research

ﬁeld.⁶Nevertheless, few examples of this process, using

α-diimine catalysts, have been reported.²The key role played

by the aryl-substituted α-diimine structure on the reactivity of

the metal complex is well-known. In oleﬁn polymerization, the

Received: September 4, 2013

A

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chain-end control,⁹while isotactic microstructures are commonly

obtained with optically active C₂-symmetric ligands that provide

an enantiomorphic site-control propagation.¹⁰The isotacticity

strongly increases using bulky groups in the phenyl ortho posi-

tions and in the ligand backbone. From a DFT study it appears

that the strong steric interactions between the substituents of

the backbone and those in the phenyl ortho positions constrain

the phenyl rings to arrange almost perpendicularly with respect

to the palladium mean coordination plane and parallel to each

other.⁸Reasonably, this aﬀects the coordination of the aromatic

oleﬁn and the stereochemistry of the resulting intermediate,

inducing high enantioface discrimination and the consequent

synthesis of isotactic copolymer. Unfortunately, moderate pro-

ductivities are generally observed, due to the crowded coordina-

tion sites of the catalysts as well as to the low catalyst stability

in the copolymerization medium. For example, the complex with

the methyl substituents in phenyl ortho positions and in the

ligand backbone (i.e., bearing the (2,6-Me₂Ph)₂DABMe₂ligand)

gives a copolymer characterized by a high degree of isotacticity

(ll = 74%) but with a modest productivity (about 0.7 (g of CP)

(g of Pd)⁻¹h⁻¹) in comparison with that of the atactic

copolymer obtained using the (4-MeOPh)₂DABMe₂ligand

(about 4 (g of CP) (g of Pd)⁻¹h⁻¹).^2dWith the main intention

of improving the performance of stereoselective CO/vinyl arene

copolymerization, our approach was to synthesize complexes in

which the structure of the nitrogen ligand, especially its ability to

shield the axial positions, allows the production of a stereoregular

isotactic polymer without suppressing the catalyst activity.

Ligands e−g, having two or three fused aromatic rings, were

synthesized and the catalytic properties of the corresponding

novel catalysts 2e−g were tested and compared with those of

complexes 2a−d (Scheme 1). Structural analysis was performed

(9-C₁₄H₉)NH₂, respectively; meanwhile ligand e was synthesized

according to literature methods.¹¹Recently the synthesis of a

series of α-diimine ligands with substituted naphthyl groups has

been reported.¹²Palladium(II) complexes 1e−g were obtained

from the reaction of [Pd(Me)(Cl)(COD)] (COD = 1,5-cyclo-

octadiene) with the α-diimine ligands e−g, in dichloromethane

at 25 °C (Scheme 1); the diene was substituted quantitatively by

the nitrogen ligand within a few hours. Complexes 1a−g react

with AgPF₆at 0 °C in a CH₂Cl₂/MeCN (5/1, v/v) mixture,

leading to the cationic acetonitrile compounds 2a−g with

satisfactory to excellent yield (60−98%) (Scheme 1). Structures

1

of all compounds were investigated in CD₂Cl₂or CDCl₃by H

and ¹³C NMR spectroscopy. The assignments of the ¹H and ¹³C

resonances were performed by following the scalar and dipolar

1

nuclear interactions in the H−COSY, H,¹³C-HSQC, H,¹³C-

HMBC, and ¹H-NOESY spectra (data are reported in the

Experimental Section).

The comparative analysis of the chemical shifts of the

Pd−Me protons in complexes 1a−g and 2a−g suggests

that the shielding eﬀect exerted by the π electrons of the

9-anthracenediimine ligand in 1g and 2g is more important

than that of the other ligands (Table 1).

Table 1. Chemical Shift Values (CDCl₃, 19 °C) of the

Pd−Me Resonance in Complexes Pd(Me)Cl((Ar)₂DABMe₂)

(1a−g) and [Pd(Me)(NCMe)((Ar)₂DABMe₂)]⁺[PF₆]⁻

(2a−g)

Ar

complex 1a−g δ (ppm) complex 2a−g

δ (ppm)

0.41

Ph

1a

1b

1c

1d

1e

1f

0.63

0.65

0.44

0.36

0.46

0.31

0.05

2a

2b

2c

2d

2e

2f

4-MeOPh

2,6-Me₂Ph

2,6-iPr₂Ph

1-C₁₀H₇

0.47

0.29

0.42

a

0.18, 0.19

0.07, 0.12

−0.03

Scheme 1. Synthesis of Complexes 2a−g from 1a−g

1-C₁₄H₉

9-C₁₄H₉

1g

2g

a

Two resonances are detected due to the presence in solution of two

conformational isomers (vide infra).

A plausible explanation could be found in the larger size of

the aromatic portion of ligand g, in comparison to a−e, and in

the symmetric placement of the aromatic rings above and below

the coordination plane in complexes 1g and 2g, diﬀerently from

what occurs in 1e,f and 2e,f. The almost perpendicular orienta-

tion of the aromatic rings with respect to the coordination

plane (see the X-ray structure of 2g; Figure 2) favors the

observed upﬁeld shift. For complexes 1e,f and 2e,f, the NMR

investigations indicated that the two possible conformational

diastereoisomers in which the nitrogen ligand adopts a C₂- or

a C_s-symmetric coordination geometry (Scheme 2: a and b,

C₂-conformational enantiomers; c and d, C_s-conformational

enantiomers), are simultaneously present in CD₂Cl₂(and

CDCl₃) solution at 19 °C, with an approximate equimolar ratio.

This ﬁnding agrees well with previously reported theoretical

results for the [PdCl₂(Ar-BIAN)] complex¹³(Ar-BIAN =

bis(1-naphthylimino)acenaphthene), where the syn and anti

isomers are almost isoenergetic. Besides ab initio calculations

performed on the e and f nitrogen ligands (Scheme 1) show

that the syn and anti conformers diﬀer by a maximum of ca.

1 kcal mol⁻¹, the anti isomer being more stable than the cor-

responding syn isomer, as expected.^12,13

for all compounds, as well as for the ﬁrst intermediates of the

stereoselective CO/p-methylstyrene copolymerization catalyzed

by complex 2g.

2. RESULTS AND DISCUSSION

2.1. Synthesis and Characterization of Ligands f and g

and Complexes 1e−g and 2a−g. Ligands (1-C₁₄H₉)₂-

DABMe₂(f) and (9-C₁₄H₉)₂DABMe₂(g) were synthesized

by condensation of 2,3-butanedione with (1-C₁₄H₉)NH₂and

The presence (in solution) of both C₂and C_sconformational

1

isomers generates split signals in both the H and ¹³C NMR

B

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From Table 2 it appears that in CH₂Cl₂the productivity in

CO/p-methylstyrene copolymer tends to diminish with an

increase in the size of the substituents in the ortho positions of

the aromatic rings of the ligand, in fact passing from catalysts

2a,b, in which the productivity is around 100 (g of CP) (g of

Pd)⁻¹(Table 2, entries 1 and 2), to the hemihindered 2e,f

(83 and 58 (g of CP) (g of Pd)⁻¹; Table 2, entries 7 and 9) and

the hindered 2c,d (52 and 0 (g of CP) (g of Pd)⁻¹; Table 2,

entries 3 and 6), a reduction in yields was observed. The only

catalyst that does not follow this trend is 2g, which, although it

has encumbered apical positions, is the most active, producing

130 (g of CP) (g of Pd)⁻¹(Table 2, entry 10). An increase in

CO pressure up to 5 bar results in a decrease of productivity

together with a signiﬁcant increase of M_w(weight-average

molecular weight) (Table 2, entry 10 vs entry 12). Formation

of inactive palladium metal was generally observed at the end

of the reaction (2a−c,f); meanwhile, with catalyst 2e it was

possible to prolong the reaction time up to 51 h, obtaining a

yield of 296 (g of CP) (g of Pd)⁻¹(Table 2, entry 8). With

styrene as comonomer instead of p-methylstyrene an increase

in yield and M_wwas achieved (see Table 4, entry 1, vs Table 2,

entry 10). In addition, considering that the capacity of the TFE

as solvent and BQ (1,4-benzoquinone) as oxidant was

previously observed to increase the yield of the CO/styrene

copolymerization catalyzed by analogous Pd complexes,^2f

reactions with catalysts 2c,e−g were also carried out in TFE

plus BQ. A beneﬁcial eﬀect was observed in all cases, and

mainly isotactic copolymer (vide infra) was produced. In

particular with catalysts 2g,c the yield in p-methylstyrene/CO

copolymer was more than doubled in TFE and BQ in

comparison to that in methylene chloride (Table 2, entry 10

vs entry 11 and entry 3 vs entry 5). Combining the use of

styrene as comonomer and TFE as solvent plus BQ, a sharp

increase in productivity was recorded with catalysts 2e−g,

giving up to 564 (g of CP) (g of Pd)⁻¹(Table 4, entry 3). In

agreement with the literature, the productivity is aﬀected by

four main factors: the structure of the nitrogen ligand and

therefore of the catalyst, the kind of oleﬁn comonomer, the

nature of the reaction solvent, and the presence of the oxidant.

The inﬂuence of the catalyst structure on the productivity

((g of CP) (g of Pd)⁻¹) is evident from the trend found in

Scheme 2. C₂and C_sConformational Isomers of Complex 2e

spectra of complexes 1e,f and 2e,f. For instance, two deﬁned

1

doublets for the H5 resonance are present in the H spectrum

2

of 2e, centered at 8.25 and 8.17 ppm (CDCl₃, 19 °C, J_HH

=

8.2 Hz), corresponding to two carbon signals at 123.8 and

123.4 ppm. Analogously, two singlets are observed at 0.18 and

0.19 ppm attributable to the Pd−Me protons of the two

isomers, which correspond to two ¹³C resonances at 4.43 and

4.37 ppm. Unfortunately, the overlapping of many resonances

precludes the unambiguous assignment of all signals.

2.2. CO/Vinyl Arene Copolymerization. Complexes 2a−

g were tested as catalysts in the copolymerization of CO with

p-methylstyrene (Table 2) or styrene (Table 4); reactions were

carried out for 27 h at room temperature (26 °C), under 1 atm

pressure of CO, in dichloromethane or TFE (TFE = 2,2,2-

triﬂuoroethanol) (Scheme 3, Tables 2 and 4).

Scheme 3. Copolymerization Reaction

a

Table 2. CO/p-Methylstyrene Copolymerization Results

c

triad (%)

b

d

entry

cat.

yield (g)

CP (%)

productivity ((g of CP) (g of Pd)⁻¹

)

ll

ul/lu

uu

n_l

10⁻³M_w(PDI)

1

2

3

2a

2b

2c

2d

2e

2f

0.480

0.450

0.200

0.355

0.535

0.096

0.448

1.160

0.221

0.495

1.080

0.608

78

94

101

114

52

30

25

71

69

71

49

53

26

29

26

21

22

3

2.2

2.0

6.5

5.8

6.5

7.5 (1.9)

10.5 (1.8)

9.2 (1.3)

15.4 (1.2)

6.6 (1.6)

96

e

4

96

91

2

f

5

87

125

3

6

7

<1

69

83

296

58

53

51

45

71

72

73

37

41

44

25

23

10

8

3.9

3.5

3.1

6.7

6.8

7.4

4.4 (1.6)

18.0 (3.2)

10.5 (1.4)

16.7 (1.2)

8.5 (1.6)

g

8

95

9

97

11

4

10

2g

>99

60

130

290

98

f

11

3

h

12

4

27.6 (1.8)

a

Reaction conditions: n_Pd= 0.035 mmol; volume of p-methylstyrene 2.8 mL (21 mmol, Pd/oleﬁn = 1/600); solvent CH₂Cl₂(2.8 mL); T = 26 °C;

b

c

P_CO= 1 atm; t = 27 h. Total yield of homopolymer (HP) and copolymer (CP). Evaluated from the intensities of the ¹³C NMR ipso carbon

d

e

f

g

atom resonances. PDI = M_w/M_n. Solvent 2,2,2-triﬂuoroethanol. Solvent 2,2,2-triﬂuoroethanol (2.8 mL); Pd/1,4-benzoquinone = 1/5. t = 51 h.

h

P_CO= 5 atm.

C

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CH₂Cl₂: 2g (130) > 2b (114) > 2a (101) > 2e (83) > 2f (58) >

2c (52) > 2d (0) (Table 2, entries 10, 2, 1, 7, 9, 3, and 6,

respectively), which seems related to the pK_avalues of the

anilines employed in the synthesis of the corresponding ligands

(except for 2d) (Table 3).¹⁴

ﬂuorinated alcohol;¹⁶however, a coordination of the CF₃

moiety of the alcohol to the metal center might play a role in

the stabilization process of the catalyst, as highlighted by the

X-ray structures of 4g,c (vide infra). Regarding the eﬀect of the

monomer, a greater productivity of styrene in comparison to

that of p-methylstyrene either in CH₂Cl₂(130 and 142 (g of

CP) (g of Pd)⁻¹; Table 2, entry 10, vs Table 4, entry 1) and in

TFE (290 and 495 (g of CP) (g of Pd)⁻¹; Table 2, entry 11, vs

Table 4, entry 2) was found, similarly to what was observed

with palladium catalysts bearing meta-substituted aryl-BIAN

ligands.^2fThis might be linked to an easier complexation of

styrene versus p-methylstyrene due to a higher π* acidity of the

former compound.

Table 3. Relationship between the pK_aValues of the Anilines

and the Productivities of the Corresponding Complexes

2a−g

productivity ((g of CP)

entry

aniline

pK_a

cat.

(g of Pd)⁻¹

)

1

2

3

4

5

6

7

9-C₁₄H₉NH₂

4-MeOC₆H₄NH₂

C₆H₅NH₂

6.34^15a

2g

2b

2a

2e

2f

130

114

101

83

5.29^14a,15b

4.58^14a,15b

4.11^15c

In general, moderate to good results in terms of M_w(weight-

average molecular weight) and polydispersity were achieved;

M_wranges from 4400 with catalyst 2e (Table 2, entry 7) to

35000 for catalyst 2f in TFE (Table 4, entry 4). We can identify

diﬀerent responses of M_wwith the variation of the reaction

conditions: for example, with TFE as the reaction medium an

increase of M_wwas detected (Table 2, compare entries 3 and 4),

meanwhile the presence of benzoquinone gives a decrease of M_w

and an increase of polydispersity (Table 2, entry 4 vs entry 5).^16a,e

Although an increase of CO pressure has a beneﬁcial eﬀect on the

M_wof the polymer, we could record a detrimental eﬀect regarding

the polydispersity (Table 2, compare entries 12 and 10).

2.3. Copolymer Stereochemistry. The polyketones were

1-C₁₀H₇

1-C₁₄H₉NH₂

2,6-Me₂C₆H₃NH₂3.89^15b

3.85^15a

58

2c

2d

52

2,6-iPr₂C₆H₃NH₂

4.41^14a

0

In fact, on analyzing the pK_avalue of anilines (Table 3),^14b,15

it appears that when the basicity of the anilines, and accordingly

the coordination ability of the ligands is decreased,¹⁴the pro-

ductivity of the corresponding catalysts diminishes (Table 3),

possibly due to a higher decomposition rate. Thus, the pro-

ductivity seems to be governed mainly by the catalyst stability,

which correlates with the binding strength of the ligand.

Therefore, catalyst 2g is the most active probably because of

the high basicity of the anthryl ligand, which tends to stabilize

the complex, dramatically reducing the deactivation rate.

However, a stabilizing eﬀect deriving from a π stacking interac-

tion between the three condensed aromatic rings of 2g and the

styrene in the oleﬁn insertion transition state cannot be ruled

out (vide infra). Conversely, the steric hindrance at the ortho

position, together with a lower basicity, causes a decrease of

the productivity of the process involving 2e,f,c (see Table 2,

entries 7, 9 and 3). The steric eﬀect is remarkable especially in

the reaction with complex 2d, which, despite a basicity almost

comparable to that of 2a for the corresponding anilines (4.41 vs

4.58), is not productive. In this case probably the isopropyl

groups block the copolymerization due to a diﬃcult access of

monomers to the catalytic center (Table 2, entry 6).¹⁴

Concerning the eﬀect of the solvent on the productivity,

while in dichloromethane catalysts 2a−g show a diﬀerent

performance, depending on the electronic and steric features,

in TFE catalysts 2e−g, with fused aromatic rings, have similar

rather high activities, reaching a plateau of productivity at

about 500 (g of CP) (g of Pd)⁻¹(Table 4). We attribute this

behavior to a stabilizing eﬀect of the TFE solvent that prolongs

the life of the catalysts 2e−g in the reaction medium. This extra

stabilization was previously ascribed to the higher acidity of the

1

characterized by means of H NMR (CDCl₃) and ¹³C NMR

spectroscopy (1,1,1,3,3,3-hexaﬂuoro-2-propanol/CDCl₃1/1

(v/v), 298 K), and their tacticity was evaluated by integrating

the ¹³C NMR resonances corresponding to the ipso carbon

atoms of the aryl groups. The microstructures of copolymers

range from atactic to isotactic even if achiral C_2vor C_snitrogen

ligands generally produce syndiotactic polyketones. Catalysts

2a (Ar = Ph) and 2b (Ar = 4-MeOPh) aﬀorded regioregular

p-methylstyrene/CO polyketones with an atactic micro-

structure^2a−c(Table 2, entries 1 and 2), while a slight pre-

valence of the ll triad is observed for the copolymers produced

by the hemihindered complexes 2e (Ar = 1-C₁₀H₇) and 2f

(Ar = 1-C₁₄H₉) (53% and 45% ll, Table 2, entries 7 and 9).

A remarkable increment of the isotactic component was instead

observed using complexes 2c (Ar = 2,6-MePh)^2a,c,dand 2g

(Ar = 9-C₁₄H₉), which produced a copolymer with a value for

the ll triad of 71% (Table 2, entries 3 and 10), in line with the

highest value found in previous work.^2cSimilarly, with styrene

as comonomer, prevailingly isotactic copolymer was obtained

with 2e (43% ll, Table 4, entry 3) and 2f (46% ll, Table 4,

entry 3), while 2g (Ar = 9-C₁₄H₉) gave an isotactic polyketone

with an ll value of 73% (Table 4, entry 2). As a result,

stereoregularity is mainly dictated by the catalyst regardless of

the nature of comonomer, solvent, and reaction conditions. As

triad distribution points out¹⁷(ll = 73%, ul/lu = 25%, uu = 2%)

a

Table 4. CO/Styrene Copolymerization Results

c

triad (%)

b

d

entry

cat.

yield (g)

CP (%)

productivity ((g of CP) (g of Pd)⁻¹

)

ll

ul/lu

uu

n_l

10⁻³M_w(PDI)

e

1

2g

2e

2f

0.530

1.846

2.100

1.757

>99

142

495

564

472

71

73

43

46

26

25

47

46

3

2

7.2

6.8

2.8

3.0

25.7 (1.2)

10.0 (1.5)

12.0 (2.0)

35.9 (1.4)

2

3

4

10

8

a

Reaction conditions: n_Pd= 0.035 mmol; volume of styrene 2.6 mL (21 mmol, Pd/oleﬁn = 1/600); solvent 2,2,2-triﬂuoroethanol (2.8 mL);

b

c

Pd/1,4-benzoquinone = 1/5; T = 26 °C; P_CO= 1 atm; t = 27 h. Total yield of homopolymer (HP) and copolymer (CP). Evaluated from the

d

e

intensities of the ¹³C NMR ipso carbon atom resonances. PDI = M_w/M_n. Solvent CH₂Cl₂, without 1,4-benzoquinone.

D

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(Table 4 entry 2) and due to the achiral nature of the catalyst,

junctions of the type ...RRRSSS... (...SSSRRR...) must be present

along the polymer chains. As previously reported for 2c, a

ligand-assisted chain-end control mechanism should be res-

ponsible for the production of isotactic copolymer with 2g.⁸

Using the relationship n_l= 1 + 2(ll)/(lu),¹⁸which takes into

account the intensities of the isotactic (ll) and heterotactic (ul)

triads, it was possible to calculate the average length of the

isotactic sequences n_l, assuming a Bernoulli propagation model,

commonly observed for copolymers obtained with these kinds

of Pd-complexes. The stereoblock length with catalysts 2c,g

was around 7 (n_l), while with the hemihindered complexes

this value was about 3.5 (Tables 2 and 4). The strong steric

interactions between the methyl groups of the DAB backbone

and the groups in the phenyl ortho positions constrain the

phenyl rings to arrange almost perpendicularly with respect to

the palladium mean coordination plane (vide infra).⁸This

catalyst geometry, together with the conformation of the growing

polymer chain, is able to select the same oleﬁn enantioface within

each stereoblock, producing isotactic copolymer. Since catalyst

2g gives, in term of stereoregularity, results similar to those for

2c, we attribute this behavior to an analogous disposition of the

N-aryl rings. In this regard, the two model complexes 5g′,c′,¹⁹

intermediates of the copolymerization process,^2d,8appear

similarly hindered in the region close to the metal reaction

center, as shown by their van der Waals surfaces, depicted in

Figure 1.

have optimized the copolymerization reaction under diﬀerent

conditions, achieving good results in terms of copolymer pro-

ductivity, stereoregularity, and M_w. In particular, in chlorinated

solvent we obtained good productivity, up to 130 (g of CP)

(g of Pd)⁻¹of stereoblock isotactic CO/p-methylstyrene poly-

ketone, with a tacticity of 71%, M_w= 16700, and good poly-

dispersity (1.2); meanwhile, by using ﬂuorinated ethanol we

attained excellent productivity, up to 500 (g of CP) (g of Pd)⁻¹

of CO/styrene copolymer with a tacticity of 73% (n_l= 7), M_w=

10000, and good polydispersity (1.5).

2.4. Mechanistic Studies: Synthesis and Character-

ization of Complexes 3g−6g. Initial steps of the co-

polymerization reaction were investigated to understand how

the steric arrangement of the catalyst, bearing the achiral

α-diimine g, is able to determine the stereoselective insertion of

the oleﬁn (Scheme 4). For this purpose, complex 3g was used,

Scheme 4. First Intermediates of Copolymerization

a

Reaction

Figure 1. van der Waals surfaces of the carbonylated species 5g′ (left,

red) and 5c′ (right, blue).

Finally, the next intermediate, having a structure similar to

that of 5g′ but with the styrene in place of CO,^2d,8was analyzed

by rigid potential energy surface scans performed along both

the N−Ar bonds (for details, see Computational Methods in

the Experimental Section). A comparative analysis, performed

for all analogous complexes with ligands a, c, f ,and g, shows

that the 9-anthryl derivative is by far the most rigid.

a

For clarity 1,1′-methyls are not depicted in complexes 4g−6g.

In conclusion, introducing a new set of achiral diaryl di-

azabutadiene ligands with extended fused aromatic rings, we

since it was previously observed that methyl acetonitrile Pd

complexes with α-diimine ligands led, under a CO atmosphere,

E

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to the corresponding methyl carbonyl derivatives that are the

real catalytic initiators (Scheme 4).²⁰In addition, the less co-

ordinating tetraarylborate counterion was chosen to favor alkene

insertion in the stoichiometric reactions.

reveals the formation of an equilibrium mixture between the

starting species 4g and the corresponding carbonylated product

5g (Scheme 4). The equilibrium ratio appears to be aﬀected

by the temperature, and the maximum conversion in 5g (60%)

was observed at −17 °C after 3 days under an atmospheric

pressure of CO. From the NMR analysis of 5g (for details, see

section 4.5.3 in the Experimental Section) some similarities

The insertion of p-methylstyrene in the Pd−acetyl bond,

derived from the methyl migration in 3g, leads to complex 4g,

having the p-methylstyrene unit coordinated in an η³-allyl

fashion. Complex 4g shows chemical shift values typical of

allyl systems (C22−C22′, 107.2 ppm; C20, 54.8 ppm; H20,

2.73 ppm (CDCl₃, 4 °C)) and a considerable shielding of the

H19a and H19b resonances (0.29 and 1.58 ppm, respectively)

due to the anisotropy eﬀects of the aryl rings of the nitrogen

ligand. The NMR characterization in CDCl₃allowed the

determination of the intramolecular structure of 4g (Scheme 4).

The assignment of the ¹H resonances of the allyl fragment of 4g

was made on the basis of the dipolar and scalar interactions

detected in the ¹H-NOESY and ¹H-COSY spectra, respectively,

and conﬁrmed with previous reported studies^2d(see section

4.5.2 in the Experimental Section).

1

with 4g can be recognized. H signals of protons H19a, H19b

and H20 (0.62, 2.23, and 3.92 ppm, respectively) appear strongly

shielded in comparison with those of the analogous complex

bearing the (iPr)₂DABMe₂ligand (2.67, 3.50, and 4.54 ppm,

respectively).^20aThis suggests that they are located in the

shielding cone of the aromatic rings of the N-anthryl ligand.

Furthermore, since the ¹³C resonance of C18 in 5g (202.7 ppm)

is notably diﬀerent from the typical value reported for a palladium

O-coordinated acetyl moiety (around 230 ppm),^10b,20,22a six-

membered chelate structure (with the acetyl linked to

palladium²³) was ruled out. In addition, both the NOE

interactions involving the growing chain and the nitrogen ligand

and the strong shielding eﬀect observed for H19a, H19b and H20

give evidence in favor of the open-chain structure of complex 5g

(Scheme 4). The structure of 5g in solution, depicted according

to the NMR evidence, is in agreement with the fully optimized

5g′¹⁹model (Figure 1) with the DFT method (see Computa-

tional Methods in the Experimental Section). Finally, the upﬁeld

1

A comparative analysis between the H NMR spectra of 4g

1

and 4c was made. Interestingly the upﬁeld shift of several H

resonances of the allyl fragment in 4g was more pronounced

than that observed for the analogous α-diimine complex

[Pd(η³-C₁₁H₁₃O)((2,6-MePh)₂DABMe₂)]⁺[BAr′₄]⁻(4c) bearing

the 2,6-dimethyl-substituted phenyl ring^2d(Table 5).

1

shift of the H resonances of the acetyl fragment in 5g is more

Table 5. Chemical Shifts (¹H NMR, δ ppm) of the Growing

pronounced than that observed for the analogous α-diimine

complex [Pd{C(O)CH(p-Me-C₆H₄)CH₂C(O)Me}((2,6-

Me₂Ph)₂DABMe₂)]⁺[BAr′₄]⁻(5c) bearing the 2,6-dimethyl-

substituted phenyl ring^2d(Table 5).

Chain in the Intermediate Complexes 4g,c^2dand 5g,c^2d

complex

a

b

c

4g

4c

Δδ

5g

5c

Δδ

The addition of p-methylstyrene to the equilibrium mixture

of 4g and 5g (40/60) in CD₂Cl₂under 1 atm of carbon

monoxide leads to the formation of the allyl intermediate 6g

as the major product (NMR yield 74%) (Scheme 4). NMR

investigation reveals that 6g exists prevalently as a single

diastereoisomeric form that should correspond to a RR (or SS)

conﬁguration, considering the isotacticity of the copolymer

obtained with the precatalyst 2g (Scheme 1). Similarly to 4g, in

6g the growing chain is coordinated in an η³-allyl fashion

involving one double bond of the aryl ring of the second

inserted oleﬁn (Scheme 4). For analogous complexes bearing

the (2,6-Me₂Ph)₂DABMe₂ligand c, a 25/75 mixture of the two

η³-allyl complexes 4c and 6c was obtained instead.^2dThis

diﬀerent behavior outlines that the reaction performed with

catalyst 2g is much more eﬃcient than that performed with 2c

and the process is eﬃciently driven toward the insertion of the

H25

0.92

5.80

6.11

2.8

1.79

6.54

6.33

3.17

1.12

2.31

1.89

0.87

0.74

0.22

0.37

0.82

0.68

0.56

2.06

6.91

6.77

3.92

0.62

2.23

1.61

2.22

7.14

7.01

4.20

1.67

2.72

1.92

0.16

0.23

0.24

0.28

1.05

0.49

0.31

H23/H23′

H22/H22′

H20

H19a

0.30

1.63

1.33

H19b

H17

a

b

Conditions: CDCl₃, 4 °C. Conditions: CD₂Cl₂, −17 °C.

c

Conditions: CDCl₃, 20 °C.

This could be reasonably ascribed to the larger size of the

magnetic anisotropy shielding cone on top of the anthryl moiety

in 4g in comparison to the phenyl ring in 4c. As a consequence,

for example, the H23/H23′ resonances are observed at

6.54 ppm in 4c and at 5.80 ppm in 4g, and protons H22/H22′

are found at 6.33 ppm in 4c and 6.11 ppm in 4g. As expected, the

value Δδ decreases on going from H25 to H23/H23′ and then to

H22/H22′ (Scheme 4): i.e., from the external side of the nitrogen

ligand toward the palladium center, moving away from the

shielding cone of the anthracene ring. The same occurs on going

1

new styrene unit. The analysis of the H-NOESY spectrum of

6g (see section 4.5.4 in the Experimental Section) depicts the

molecular structure illustrated in Scheme 4; moreover, due to

the presence of an aromatic ring in the growing chain H10, H8,

and H12 resonances were quite shielded in 6g (Table S3 in the

Supporting Information).

As a result of the magnetic anisotropy shielding cone in 6g,

we suppose the presence of π stacking interactions that stabilize

the 6g-like intermediates, increasing their population.²¹In

addition, a π stacking interaction could be responsible for lowering

the energy transition of the oleﬁn insertion reaction, driving the

copolymerization process toward higher productivity.²¹

2.5. Solid-State Molecular Structures of Complexes 2g

and 4g. The solid-state structure was obtained, by means of X-

ray single-crystal studies, for catalyst 2g and remarkably for

intermediate 4g, which proved to be stable enough to obtain

crystals. The molecular structure of the catalyst 2g is shown in

1

from H19a, H19b to H20. These H NMR upﬁeld shifts of 4g

relative to the signals for 4c could point toward a greater π

stacking interaction in the former between the η³-allylc moiety

and the N-aryl counterpart.²¹A π stacking interaction, between

the rings of the ligand and the styrene unit, could be present also

in the oleﬁn insertion transition states relative to intermediates 4g

and 6g, producing the stabilization needed for the productivity of

2g being greater than that of 2c.

The next step of the copolymerization process was

investigated by bubbling carbon monoxide into a CD₂Cl₂

solution of 4g for 10 min at −70 °C. The NMR analysis

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Figure 2. ORTEP 3 views of the complex cation of 2g (top left), the relative cation−anion positions in 2g (top right), and the complex cation of 4g

(bottom center). Hydrogen atoms have been omitted for sake of clarity. All atoms are drawn at 30% probability.

Figure 2 (selected bond lengths and angles are given in Table S2

in the Supporting Information).

The similarity between the interionic structures discussed

above (2g vs 7a in ref 2c) suggests that the anthracene units

and the o-dimethylphenyl moieties cause comparable steric

hindrance in the metal apical positions. As a consequence, for

2g,c a similar accessibility of the carbonyl moiety and then

of the monomers to the metal apical position should be

expected. Thus, the steric features of 2g must be balanced by

the already mentioned high basicity of the corresponding

diimine ligand and/or by a possible π stacking interaction

between the aromatic ring of the growing chain and the

anthracene ligand;²¹both eﬀects could signiﬁcantly trigger and

enhance the productivity.

In the complex cation of intermediate 4g, the palladium ion

is coordinated to the p-methylstyrene unit in a η³-allyl fashion,

involving the C(1a) (C(1b)), C(2a) (C(2b)), and C(8a)

(C(8b)) atoms (Figure 2). For the p-methylstyrene unit, which

appears disordered except for the acetyl group, the two models

a and b were found. The least-squares planes deﬁned by the

atoms of a and b are nearly coplanar. The three Pd−C bond

distances are signiﬁcantly diﬀerent in model a, while in b they

are comparable (Table S2 in the Supporting Information). The

resulting coordination geometry about the metal ion can be

conveniently described as distorted square planar (Table S2).

The four donor atoms (N(1), N(2), C(2a) (C(2b)) and

C(8a) (C(8b))) deﬁne a mean plane which is almost per-

pendicular both to the anthracene units (about 65 and 75° for

models a and b, respectively) and to the p-methylstyrene unit

(79.4(2) and 76.8(2)° for a and b, respectively) (Figure 2).

A comparison with structurally related complexes deposited in

the CSD does not reveal any peculiar geometrical feature for

The metal center adopts the usual square-planar coordina-

tion. Bond lengths and angles featuring the metal environment

are in line with those of structural related complexes retrieved

in the Cambridge Structural Database (CSD version 5.34,

November 2012).²⁴

Because of their size and due to the presence of the methyl

groups on the back, both anthracene units are almost per-

pendicular with respect to the metal coordination mean plane

(dihedral angles of 75.7(1) and 86.5(1)°). As a consequence of

this arrangement, the four anthryl hydrogen atoms in 1- and

8- positions are facing each other, thus preventing the counterion

from locating near the metal center. In fact, the closest

counterion,²⁵as already found in the crystal lattice of similar

catalysts,^2c,26is located in the back, above the diimine carbons of

the nitrogen ligand (Figure 2), and weakly interacts with the

aromatic hydrogen atoms of the ligand. Interestingly the

interionic structure of 2g closely resembles that found in a

similar dimethyl ortho-substituted aryl α-diimine complex.^2cThe

horizontal distance between the Pd atom and the intercept of

the vertical distance which separates the P atom from the metal

coordination mean plane²⁷are roughly the same: 4.639(2) vs

4.723 Å (compare 2g with 7a in ref 2c), while in 2g the PF₆⁻ion

is slightly higher with respect to the metal coordination mean

plane (4.226(2) vs 3.994 Å). Finally, the next closest PF₆⁻ion

(related by the symmetry operation −x + 1, y − ¹/₂, −z + ¹/₂) is

also shown in Figure 2, together with selected distances involving

the phosphorus atoms in order to determine the position of both

the anions with respect to the metal complex.²⁷

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Figure 3. (left) Shape match between the cation and anion in the crystal lattice of 4g. (right) Closest cation−anion interaction in the crystal lattice of 4c.

the palladium complex. As shown in Figure 3, a good shape

match between the two ions occurs in the crystal lattice: the

closest BArF anion places a ﬂuorine atom in the metal apical

position 3.646(3) Å from the palladium cation. A longer Pd−F

distance (ca. 4.0 Å) was found in the crystal structure of the

analogous complex having the o-dimethyl substituted ligand 4c

(Figure 3, right).^2dThe unexpectedly short Pd−F distance in

4g could indicate the presence of an interaction between the

palladium and the ﬂuoro atom that stabilizes the crystal lattice

(Figure 3). A similar contact might occur between palladium

complexes and the ﬂuorinated alcohol in the copolymerization

reaction carried out in TFE. In particular, we suppose that a

Pd−F interaction might contribute to the catalyst stability, in

combination with the acidity of the alcohol,¹⁶increasing the

productivity in polyketones.¹⁶

To validate this hypothesis, a copolymerization reaction

with catalyst 2g was performed using α,α,α-triﬂuorotoluene as

solvent, giving a copolymer yield of 423 (g of CP) (g of Pd)⁻¹,

M_w= 24000 and a value for the ll triad of 75%; these data are

comparable to those achieved carrying out the reaction in TFE

(Table 4, entry 2).

transition states, and ﬂuoro−palladium interactions between

catalyst and ﬂuorinated alcohol, in combination with the alcohol

acidity, could reasonably be the origin for the high productivity

found with the new 9-anthryl catalyst.

4. EXPERIMENTAL SECTION

4.1. Materials and Methods. All manipulations were carried out

under a nitrogen atmosphere by using Schlenk techniques. Solvents

were dried by standard methods and freshly distilled under nitrogen.

p-Methylstyrene (Aldrich) was dried over calcium hydride and distilled

before use. Carbon monoxide (Cp grade 99.99%) was supplied by

Air Liquide. CP grade chemicals were used as received unless

otherwise stated. Chloroform-d and methylene chloride-d₂were

degassed and stored over 4 Å molecular sieves. Ligands a−d²⁸and

complexes 1a−c,^1,2d,291d,³⁰and 2b,c^2dwere synthesized according to

literature methods. NaBAr′₄(Ar′ = 3,5-(CF₃)₂C₆H₃) was synthesized

as previously reported.³¹Elemental analyses (C, H, N) were carried

out with a Fisons Instruments 1108 CHNS-O Elemental Analyzer.

Infrared spectra were measured in the range 4000−600 cm⁻¹on a

Nicolet FT-IR Avatar 360 spectrometer. NMR spectra were measured

on a Bruker Advance 200 spectrometer with a multinuclear 5 mm

probe head. ¹H and ¹³C NMR chemical shifts are relative to TMS and

were measured using the residual proton or carbon resonance of the

deuterated solvents.

3. CONCLUSION

In this paper we have shown the synthesis and coordination

chemistry of a series of cationic Pd(II) complexes, bearing new

α-diimine ligands with fused aromatic rings, and their applica-

tion in CO/vinyl arene copolymerization. Among all species,

the catalyst with the C_2v-symmetric 9-anthracenyl diimine

ligand (9-C₁₄H₉)₂DABMe₂(g) provides stereoblock isotactic

CO/p-methylstyrene and CO/styrene polyketones in yields

that are the highest reported for the stereoselective copolymeri-

zation of aromatic oleﬁns with carbon monoxide using achiral

nitrogen ligands. The structural analysis of the ﬁrst steps of the

CO/p-methylstyrene copolymerization revealed the stereo-

selective formation of the oleﬁn/CO/oleﬁn insertion product

(6g), which prevalently exists in solution in only one diastereo-

isomeric form, thus justifying the observed high polymer

isotacticity provided by complex 2g. Moreover, both analyzing

the copolymerization results and the structure of the ﬁrst

intermediates, we postulated that the donor capacity of the

ligand, a possible π stacking interaction in the oleﬁn insertion

4.2. Synthesis of Ligands e−g. 4.2.1. Synthesis of

(N,N′E,N,N′E)-N,N′-(Butane-2,3-diylidene)dinaphthalen-1-amine

(e).

Ligand e was synthesized according to literature methods.¹²¹H NMR

(200.13 MHz, CDCl₃, 19 °C): δ 7.86 (m, 4H; H8 and H5), 7.68

3

(d, J_H,H= 8.28 Hz, 2H; H10), 7.52 (m, 6H; H6, H7 and H11), 6.87

(d, 2H; H12), 2.33 ppm (s, 6H; H1). ¹³C NMR (50.32 MHz, CDCl₃,

19 °C): δ 169.1 (s; C2), 147.0 (s; C3), 134.1 (s; C9), 128.1 (s; C8),

126.3 (s; C7), 125.8 (s; C11), 125.7 (s; C6), 125.5 (s; C4), 124.1 (s;

C10), 123.4 (s; C5), 113.0 (s, C12), 16.0 ppm (s; C1). Anal. Calcd for

C₂₄H₂₀N₂(336.43): C, 85.68; H, 5.99; N, 8.33. Found: C, 85.73; H,

5.92; N, 8.37.

H

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4.2.2. Synthesis of (N,N′E,N,N′E)-N,N′-(Butane-2,3-diylidene)-

dianthracen-1-amine (f).

resulting solid was washed with diethyl ether (5 mL) and dried under

vacuum.

4.3.2. Synthesis of Pd(Me)Cl((1-C₁₀H₇)₂DABMe₂) (1e).

2,3-Butanedione (114 μL, 1.30 mmol) and 1 drop of formic acid were

added to a solution of (1-C₁₄H₉)NH₂(510 mg, 2.64 mmol) in

methanol (6 mL), and the mixture was stirred for 48 h at 25 °C.

The formed precipitate was collected by ﬁltration, washed with

methanol (2 × 10 mL), and dried under vacuum. The product was

than solubilized in hot toluene (10 mL), precipitated with cold

methanol, collected by ﬁltration, washed with methanol (2 × 10 mL),

and dried under vacuum. Ligand f was obtained as a brown powder

Reagents: (1-C₁₀H₇)₂DABMe₂ligand, 200 mg (0.59 mmol); [Pd-

(Me)(Cl)(COD)], 158 mg (0.59 mmol). Yield: 148 mg (0.30 mmol,

50%) of 1e as a red-orange powder. The NMR analysis indicated that

the two possible conformational isomers, in which the nitrogen ligand

adopts a C₂- or a C_s-symmetric coordination geometry, are simultaneously

present in CD₂Cl₂solution at 19 °C with an approximate equimolar

ratio. ¹H NMR (200.13 MHz, CDCl₃, 19 °C): δ 7.96 (br d, 2H; H8(C₂

and C_s) and H8′(C₂and C_s)), 7.93 (br d, 1H; H5′(C₂and C_s)), 7.90

(br d, 1H; H5(C₂and C_s)), 7.87 (br d, 1H; H10′) (C₂and C_s), 7.82 (br

d, 1H; H10(C₂and C_s)), 7.59 (m, 6H; H6, (C₂and C_s) H6′(C₂and

C_s), H7(C₂and C_s), H7′(C₂and C_s), H11(C₂and C_s) and H11′(C₂and

C_s)), 7.18 (br dd, 1H; H12(C₂and C_s)), 7.14 (br dd, 1H; H12′(C₂and

C_s)), 2.12 (s, 3H; H1(C₂and C_s)), 2.06 (br s, 3H; H1′(C₂and C_s)),

0.46 ppm (s, 3H; H13(C₂and C_s)). ¹³C NMR (50.32 MHz, CDCl₃,

19 °C) δ 175.7 (s; C2′(C₂and C_s)), 170.3 (s; C2(C₂and C_s)), 143.1,

143.0 (s; C3(C₂and C_s)), 142.7 (s; C3′(C₂and C_s)), 133.8 (s; C9(C₂

and C_s) and C9′(C₂and C_s)), 128.66, 128.63, 128.56, 128.50 (s; C8(C₂

and C_s) and C8′(C₂and C_s)), 127.5 (br s; C10′(C₂and C_s) and

C11(C₂and C_s)), 127.2, 127.1, 126.8, 126.7 125.2 (s; C6(C₂and C_s),

C6′(C₂and C_s), C7(C₂and C_s), and C7′(C₂and C_s)), 127.1 (s; C10(C₂

and C_s)), 126.5 (s; C11′(C₂and C_s)), 125.5 (s; C4(C₂and C_s) and

C4′(C₂and C_s))), 122.9, 122.8 (s; C5(C₂and C_s)), 122.3, 122.2 (s;

C5′(C₂and C_s)), 117.6 (s; C12′(C₂and C_s)), 117.1 (s, C12(C₂and

C_s)), 20.8 (s; C1′(C₂and C_s)), 19.8 (s; C1(C₂and C_s)), 2.8, 2.6 ppm

(s; C13(C₂and C_s)). Anal. Calcd for C₂₅H₂₃ClN₂Pd (493.33): C,

60.86; H, 4.70; N, 5.68. Found: C, 60.80; H, 4.66; N, 5.63.

1

(320 mg, 0.73 mmol; yield 56%). H NMR (200.13 MHz, CD₂Cl₂,

19 °C): δ 8.53 (s, 2H; H12), 8.47 (s, 2H; H5), 8.08 (m, 4H; H10

3

and H7), 7.89 (d, J_H,H= 7.2 Hz, 2H; H14), 7.55 (m, 6H; H15, H8

and H9), 6.89 (br d, 2H; H16), 2.45 ppm (s, 6H; H1). ¹³C NMR

(50.32 MHz, CD₂Cl₂, 19 °C): δ 169.4 (s; C2), 147.1 (s; C3), 132.3 (s;

C6 or C11 or C13), 131.9 (s; C6 or C11 or C13), 131.4 (s; C6 or C11

or C13), 128.4 (s; C7 or C10), 128.0 (s; C7 or C10), 126.3 (s; C12),

125.7 (s; C8 or C9), 125.5 (s; C8 or C9), 125.3 (s; C15), 125.0 (s;

C4), 124.3 (s; C14), 122.2 (s, C5), 111.4 (s; C16), 15.8 ppm (s; C1).

Anal. Calcd for C₃₂H₂₄N₂(436.55): C, 88.04; H, 5.54; N, 6.42. Found:

C, 88.09; H, 5.50; N, 6.47.

4.2.3. Synthesis of (N,N′E,N,N′E)-N,N′-(Butane-2,3-diylidene)-

dianthracen-9-amine (g).

4.3.3. Synthesis of Pd(Me)Cl((1-C₁₄H₉)₂DABMe₂) (1f).

9-Aminoanthracene (9-C₁₄H₉)NH₂was synthesized as follows:

palladium on charcoal (10%, 30 mg) was added to a solution of

9-nitroanthracene (300 mg, 1.34 mmol) in ethyl acetate (15 mL).

The reaction mixture was transferred into a steel autoclave which was

charged with H₂(3 atm) and stirred for 5.5 h at 20 °C. The mixture was

then ﬁltered under a nitrogen atmosphere, and the solvent was

evaporated under vacuum. 9-Aminoanthracene was obtained as a yellow

1

powder (242 mg, 1.25 mmol; yield 94%). H NMR (200.13 MHz,

CDCl₃, 19 °C): δ 7.98−7.90, 7.47−7.40 (m, 9H; aromatic protons),

4.87 ppm (br s, 2H; NH₂). Ligand g was synthesized as follows:

2,3-butanedione (85 μL, 0.97 mmol) and 1 drop of formic acid were

added to a solution of (9-C₁₄H₉)NH₂(374 mg, 1.94 mmol) in methanol

(1 mL), and the mixture was stirred overnight at 25 °C. The formed

precipitate was collected by ﬁltration, washed with cold methanol, and

dried under vacuum. Ligand g was obtained as an orange powder

Reagents: (1-C₁₄H₉)₂DABMe₂ligand, 100 mg (0.23 mmol); [Pd-

(Me)(Cl)(COD)], 56 mg (0.21 mmol). Yield: 83 mg (0.14 mmol,

67%) of 1f as a brown powder. The NMR analysis indicated that the

two possible conformational isomers, in which the nitrogen ligand adopts

a C₂- or a C_s-symmetric coordination geometry, are simultaneously

present in CD₂Cl₂solution at 19 °C with an approximate equimolar

1

(245 mg, 0.56 mmol; yield 58%). H NMR (200.13 MHz, CD₂Cl₂,

ratio. H NMR (200.13 MHz, CD₂Cl₂, 4 °C): δ 8.78−8.52 (m; 4H;

19 °C): δ 8.32 (s, 2H; H10), 8.10 (d, ³J_H,H= 5.1 Hz, 4H; H8), 7.91 (d,

³J_H,H= 4.3 Hz, 4H; H5), 7.56 (m, 8H; H6 and H7), 2.26 ppm (s, 6H;

H12(C₂and C_s), H12′(C₂and C_s), H5(C₂and C_s), H5′(C₂and C_s)),

8.32 (t, 1H; H7(C₂and C_s)), 8.20 (brt, 1H; H7′(C₂and C_s)), 8.08 (m,

4H; H10(C₂and C_s), H10′(C₂and C_s), H14(C₂and C_s) and H14′(C₂

and C_s)), 7.63 (m, 6H; H8(C₂and C_s), H8′(C₂and C_s), H9(C₂and C_s),

H9′(C₂and C_s), H15(C₂and C_s) and H15′(C₂and C_s)), 7.23 (m, 2H;

H16(C₂and C_s) and H16′(C₂and C_s)), 2.23, 2.15 (s, 6H; H1(C₂and

H1). ¹³C NMR (50.32 MHz, CD₂Cl₂, 18 °C): δ 170.8 (s; C2), 143.1 (s;

C3), 131.84 (s; C4), 128.4 (s; C8), 125.6 (s; C6 or C7), 125.2 (s; C7 or

C6), 123.5 (s; C5), 121.8 (s; C10), 119.7 (s; C9), 16.9 ppm (s; C1).

Anal. Calcd for C₃₂H₂₄N₂(436.55): C, 88.04; H, 5.54; N, 6.42. Found:

C, 88.00; H, 5.56; N, 6.45.

C_s) and H1′(C₂and C_s)), 0.28, 0.27 ppm (s, 3H; H17(C₂and C_s)). ¹³

C

4.3. Synthesis of Complexes 1e−g. 4.3.1. General Procedure

for the Synthesis of Complexes 1e−g. A solution of the appropriate

ligand in 5 mL of dichloromethane was added to a solution of

[Pd(Me)(Cl)(COD)] in 5 mL of the same solvent. The reaction

mixture was stirred overnight at 25 °C. The solvent was reduced up to

2 mL by evaporation under vacuum, and diethyl ether (30 mL) was

added to precipitate the desired compound. After ﬁltration, the

NMR (50.32 MHz, CD₂Cl₂, 19 °C) δ 176.84 (s; C2′(C₂and C_s) or

C2(C₂and C_s)), 171.59 (s; C2(C₂and C_s) or C2′(C₂and C_s)), 143.6

(br s; C3′(C₂and C_s) and C3(C₂and C_s)), 132.21, 132.09, 131.99,

131.67 (s; C11(C₂and C_s), C11′(C₂and C_s), C13(C₂and C_s), C13′(C₂

and C_s), C6(C₂and C_s), C6′(C₂and C_s), C4(C₂and C_s) and C4′(C₂

and C_s)), 128.43 (s; C7(C₂and C_s)), 128.11 (br s; C7′(C₂and C_s)),

127.42 (s; C12(C₂and C_s) or C12′(C₂and C_s)), 127.07 (br s; C12′(C₂

I

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and C_s) or C12(C₂and C_s)), 128.11, 127.7, 127.07 (br s; C10(C₂and

C_s), C10′(C₂and C_s), C14(C₂and C_s) and C14′(C₂and C_s)), 126.36,

126.00 (br s; C9(C₂and C_s), C9′(C₂and C_s), C15(C₂and C_s) and

C15′(C₂and C_s)), 124.31, 124.14 (s; C8(C₂and C_s) and C8′(C₂and

C_s)), 121.71, 121.00 (C5(C₂and C_s) and C5′(C₂and C_s)), 117.06,

115.86 (s; C16(C₂and C_s) and C16′(C₂and C_s)), 20.83, 19.75 (s;

C1(C₂and C_s) and C1′(C₂and C_s)), 1.23 ppm (s; C17(C₂and C_s)).

Anal. Calcd for C₃₃H₂₇ClN₂Pd (593.45): C, 66.79; H, 4.59; N, 4.72.

Found: C, 66.82; H, 4.60; N, 4.72.

4.4.3. Synthesis of [Pd(Me)(MeCN)((2,6-i-Pr₂Ph)₂DABMe₂)]⁺[PF₆]⁻

(2d).

Reagents: AgPF₆, 30.5 mg (0.11 mmol); 1d, 70 mg (0.11 mmol).

1

4.3.4. Synthesis of Pd(Me)Cl((9-C₁₄H₉)₂DABMe₂) (1g).

Yield: 61 mg (0.086 mmol, 78%) of 2d as a yellow powder. H NMR

(200.13 MHz, CD₂Cl₂, 19 °C): δ 7.32 (m, 6H; aromatic protons),

2.99 (sept, 4H; −CH(CH₃)₂), 2.35 (s, 6H; ligand backbone protons),

2

1.83 (s, 3H; Pd-NCCH₃), 1.38 (d, J_HH= 6.8 Hz, 3H; −CH(CH₃)₂),

1.33 (d, ²J_HH= 6.8 Hz, 3H; −CH(CH₃)₂), 1.28 (d, ²J_HH= 6.9 Hz, 3H;

−CH(CH₃)₂), 1.24 (d, ²J_HH= 6.9 Hz, 3H; −CH(CH₃)₂), 0.42 (s, 3H;

Pd-CH₃). ¹³C NMR (50.32 MHz, CDCl₃, 19 °C) 179.8, 174.6, 141.8,

141.2, 137.6, 137.2, 128.8, 128.2, 126.3, 125.6, 122,8, 30.5, 29.6,

24.2, 23.8, 23,5, 23.2, 21.8, 20.5, 7.2, 2.8. Anal. Calcd for

C₃₁H₄₆F₆N₃PPd (712.01): C, 52.29; H, 6.51; N, 5.90. Found: C,

52.22; H, 6.47; N, 5.86.

Reagents: (9-C₁₄H₉)₂DABMe₂ligand, 167 mg (0.38 mmol); [Pd-

(Me)(Cl)(COD)], 87 mg (0.32 mmol). Yield: 145 mg (0.24 mmol,

75%) of 1g as a brown powder. H NMR (200.13 MHz, CD₂Cl₂, 19

1

4.4.4. Synthesis of [Pd(Me)(MeCN)((1-C₁₀H₇)₂DABMe₂)]⁺[PF₆]⁻

(2e).

°C): δ 8.59 (s, 1H; H10 or H10′), 8.51 (s, 1H; H10′ or H10), 8.23−

8.12 (m, 8H; H8, H8′, H12, H12′, H5, H5′, H15 and H15′), 7.81−

7.60 (m, 8H; H7, H7′, H6, H6′, H13, H13′, H14 and H14′), 2.05 (s,

3H; H1), 1.98 (s, 3H; H1′), 0.05 ppm (s, 3H; H17); ¹³C NMR (50.32

MHz, CD₂Cl₂, 19 °C) δ 177.6 (s; C2′), 172.8 (s; C2), 144.8 (s; C3

and C3′), 131.1 (s; C4, C4′, C16 and C16′), 129.0 (s; C8′ or C12′ or

C8 or C12), 128.9 (s; C8′ or C12′ or C8 or C12), 128.8 (s; C8 or C12

or C8′ or C12′), 128.7 (s; C8 or C12 or C8′ or C12′), 127.5 (s; (C7

and C13) or (C7′ and C13′)), 126.6 (s; C10 or C10′), 126.4 (s; (C7′

and C13′) or (C7 and C13)), 126.1 (s; (C6 and C14) or (C6′ and

C14′)), 125.8 (s; (C6′ and C14′) or (C6 and C14), 125.5 (s; C10′ or

C10), 122.9 (s; (C5 and C15) or (C5′ and C15′)), 122.0 (s; (C5′ and

C15′) or (C5 and C15)), 115.9 (s; C9 and C9′ and C11 and C11′),

20.8 (s, C1′), 19.9 (s; C1), 0.81 (s; C17). Anal. Calcd for

C₃₃H₂₇ClN₂Pd (593.45): C, 66.79; H, 4.59; N, 4.72. Found: C,

66.84; H, 4.63; N, 4.74.

Reagents: AgPF₆, 50 mg (0.2 mmol); 1e, 90 mg (0.182 mmol). Yield:

114 mg (0.18 mmol, 98%) of 2e as a yellow-orange crystalline powder.

The NMR analysis indicated that the two possible conformational

isomers, in which the nitrogen ligand adopts a C₂- or a C_s-symmetric

coordination geometry, are simultaneously present in CD₂Cl₂solution

at 19 °C with an approximate equimolar ratio. ¹H NMR (200.13 MHz,

CDCl₃, 19 °C): δ 8.25 (d, ²J_HH= 8.2 Hz; H5(C₂) or H5(C_s)), 8.17 (d,

²J_HH= 8.2 Hz; H5(C_s) or H5(C₂)), 7.96 (m, 3H; H5′(C_sand C₂),

H8(C_sand C₂) and H8′(C_sand C₂)), 7.85 (d, 2H; H10(C_sand C₂)

and H10′(C_sand C₂)), 7.66 (m, 6H; H6(C_sand C₂), H6′(C_sand C₂),

H7(C_sand C₂), H7′(C_sand C₂), H11(C_sand C₂) and H11′(C_sand

C₂)), 7.45 (d, ²J_HH= 4.7 Hz; H12(C_sor C₂)), 7.41 (d, ²J_HH= 4.7 Hz;

4.4. Synthesis of Complexes 2a,d−g. 4.4.1. General Procedure

for the Synthesis of Complexes 2a,d−2g. AgPF₆was added to a

dichloromethane/acetonitrile (5/1) solution (6 mL) of 1a,d−g

cooled at 0 °C. The mixture was allowed to react for 2 h, during

which time AgCl precipitated. The mixture was ﬁltered through Celite,

and a solid was obtained after evaporation of the solvent under

vacuum. The solid gave the desired complex on treatment with hexane

(2 × 5 mL).

2

H12(C₂or C_s)), 7.37 (d, J_HH= 7.5 Hz; H12′(C_sor C₂)), 7.30 (d,

²J_HH= 7.5 Hz; H12′(C₂or C_s)), 2.42 (s, 3H; H1(C_sand C₂)), 2.28,

2.29 (s, 3H; H1′(C_sand C₂)), 1.338, 1.331 (s, 3H; NCCH₃(C_sand

C₂)), 0.18, 0.19 ppm (s, 3H; H13(C_sand C₂)). ¹³C NMR (50.32 MHz,

CDCl₃, 19 °C) δ 182.78, 182.68 (s; C2′(C_sand C₂)), 173.94, 173.81

(s; C2(C_sand C₂)), 142.02, 141.88, 141.83 (s; C3(C_sand C₂) and

C3′(C_sand C₂)), 133.63, 133.57 (s; C9(C_sand C₂) and C9′(C_sand

C₂)), 128.62, 128.30, 128.07, 127.76 (s; C8(C_sand C₂) and C8′(C_s

and C₂)), 127.76, 127.19 (s; C10(C_sand C₂) and C10′(C_sand C₂)),

127.19 (br s; C7(C_sand C₂), C7′(C_sand C₂), C6(C_sand C₂) and

C6′(C_sand C₂)), 125.94, 125.79, 125.48, 125.20, 125.20, 125.11 (s;

C4(C_sand C₂), C4′(C_sand C₂), C11(C_sand C₂) and C11′(C_sand

C₂)), 123.75, 123.39 (s; C5(C_sand C₂)), 122.54, 122.03 (s; C5′(C_s

and C₂)), 120.82 (br s; CH₃CN(C_sand C₂)), 118.49, 118.17 (s;

C12′(C_sand C₂)), 117.43, 117.23 (s; C12(C_sand C₂)), 21.08 (s;

C1′(C_sand C₂)), 19.57 (s; C1(C_sand C₂)), 4.43, 4.37 (s; C13(C_sand

C₂)), 1.33 ppm (br s; CH₃CN(C_sand C₂)). Anal. Calcd for

C₂₇H₂₆F₆N₃PPd (643.91): C, 50.36; H, 4.07; N, 6.53. Found: C,

50.40; H, 4.10; N, 6.55.

4.4.2. Synthesis of [Pd(Me)(MeCN)(Ph₂DABMe₂)]⁺[PF₆]⁻(2a).

Reagents: AgPF₆, 55 mg (0.22 mmol); 1a, 80 mg (0.20 mmol). Yield:

65 mg (0.12 mmol, 60%) of 2a as a yellow powder. ¹H NMR (200.13

MHz, CDCl₃, 19 °C): δ 7.47, 7.33, 7.13, 6.99 (10H; aromatic

protons), 2.32, 2.26 (3H each; ligand backbone protons), 1.92 (s, 3H;

Pd-NCCH₃), 0.41 (s, 3H; Pd-CH₃). ¹³C NMR (50.32 MHz, CDCl₃,

19 °C) 180.7, 171.6, 132.9, 132.7, 130.6, 130.4, 128.8, 128.5, 122.1,

21.5, 19.7, 6.2, 3.0. Anal. Calcd for C₁₉H₂₂F₆N₃PPd (543.78): C,

41.97; H, 4.08; N, 7.73. Found: C, 41.92; H, 4.03; N, 7.77.

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4.4.5. Synthesis of [Pd(Me)(MeCN)((1-C₁₄H₉)₂DABMe₂)]⁺[PF₆]⁻

(2f).

Reagents: AgPF₆, 33 mg (0.13 mmol); 1f, 70 mg (0.118 mmol). Yield:

58 mg (0.078 mmol, 66%) of 2f as a brown powder. The NMR

analysis indicated that the two possible conformational isomers, in

which the nitrogen ligand adopts a C₂- or a C_s-symmetric coordination

geometry, are simultaneously present in CD₂Cl₂solution at 19 °C

with an approximate equimolar ratio. ¹H NMR (200.13 MHz, CD₂Cl₂,

19 °C): δ 8.78, 8.59, 8.53 (s, 2H; H5(C₂and C_s) and H5′(C₂and C_s)),

8.50 (m, 2H; H12(C₂and C_s) and H12′(C₂and C_s)), 8.38 (br d, 2H;

H7(C₂and C_s) and H7′(C₂and C_s)), 7.99−7.92 (mbr, 4H; H10(C₂

and C_s), H10′(C₂and C_s), H14(C₂and C_s) and H14′(C₂and C_s)),

7.65−7.21 (m, 8H; H8(C₂and C_s), H8′(C₂and C_s), H9(C₂and C_s),

H9′, H16(C₂and C_s), H16′(C₂and C_s), H15(C₂and C_s) and H15′(C₂

and C_s)), 2.41, 2.40, 2.28 (s, 6H; H1(C₂and C_s) and H1′(C₂and C_s)),

1.02 (br s, 3H; NCCH₃(C₂and C_s)), 0.12, 0.07 ppm (s, 3H; H17(C₂

and C_s)). ¹³C NMR (50.32 MHz, CDCl₃, 19 °C) δ 183.06, 182.94 (s;

C2(C₂and C_s) or C2′(C₂and C_s)), 174.17, 173.94 (s; C2′(C₂and C_s)

or C2(C₂and C_s)), 142.16, 142.01, 141.8 (s; C3(C₂and C_s) and

C3′(C₂and C_s)), 132.48−131.78 (br; C11(C₂and C_s), C11′(C₂and

C_s), C13(C₂and C_s), C13′(C₂and C_s), C6(C₂and C_s) and C6′(C₂and

C_s)), 130.93 (br s; C4(C₂and C_s) and C4′(C₂and C_s)), 129.30, 129.03

(s; C7(C₂and C_s) and C7′(C₂and C_s)), 128.22, 128.15, 128.04,

127.96, 127.72, 127.49, 127.29, 126.86, 126.70, 126.60, 126.43, 126.23

(s; C8(C₂and C_s), C8′(C₂and C_s), C10(C₂and C_s), C10′(C₂and C_s),

C14(C₂and C_s), C14′(C₂and C_s), C12(C₂and C_s), C12′(C₂and C_s)

and [(C15′(C₂and C_s) and C15(C₂and C_s)) or (C9′(C₂and C_s) and

C9(C₂and C_s))], 124.95, 124.84, 124.36, 124.16 (s; (C9(C₂and C_s)

and C9′(C₂and C_s)) or (C15(C₂and C_s) and C15′(C₂and C_s)),

122.78, 122.51, 121.41, 121.14 (s; C5(C₂and C_s) and C5′(C₂and

C_s)), 120.19 (br s; CH₃CN(C₂and C_s)), 117.82, 117.68, 116.36 (s;

C16(C₂and C_s) and C16′(C₂and C_s)), 21.10, 19.59, 19.48 (s; C1(C₂

and C_s) and C1′(C₂and C_s)), 4.53, 4.33 (s; C17(C₂and C_s)), 1.17

ppm (br s; CH₃CN). Anal. Calcd for C₃₅H₃₀F₆N₃PPd (744.00): C,

56.50; H, 4.06; N, 5.65. Found: C, 56.55; H, 4.08; N, 5.65.

C14′) or (C6 and C12)), 127.45 (s; C10′), 126.77 (s; C10), 126.36

(s; (C7 and C13) or (C7′ and C13′)), 126.30 (s; (C7′ and C13′) or

(C7 and C13)), 122.56 (s; C5 and C15), 122.19 (s; (C9 and C11) or

(C9′ and C11′)), 121.67 (s; C5′ and C15′), 121.56 (s; (C9′ and

C11′) or (C9 and C11)), 120.98 (s; NCCH₃), 21.30 (s; C1′), 20.37

(s; C1), 4.15 (s; C17), 1.49 ppm (s; NCCH₃). Anal. Calcd for

C₃₅H₃₀F₆N₃PPd (744.00): C, 56.50; H, 4.06; N, 5.65. Found: C,

56.56; H, 4.10; N, 5.65.

Intramolecular Structures of Complexes 1e−g and 2e−g,

Determined by NMR Experiments. The Pd−Me resonance (H17, in

1e−g and 2e−g) was used as the starting point for the assignment

of the protons of complexes 1g and 2g, because its chemical shift is

known from previous studies and it is well separated from other

resonances (H17 in 1g is at 0.05 ppm (CD₂Cl₂, 19 °C) and in 2g at

−0.03 ppm (CDCl₃, 19 °C)).

4.4.6. Synthesis of [Pd(Me)(MeCN)((9-C₁₄H₉)₂DABMe₂)]⁺[PF₆]⁻

(2g).

Signals of the nitrogen ligand were essentially assigned on the basis

of intramolecular dipolar interactions detected in the ¹H-NOESY

spectrum. The H17 protons strongly interact with the aromatic H5′

and H15′ protons, which give interactions with CH₃(1′), allowing

assignment of the ligand backbone resonances CH₃(1′) and CH₃(1).

1

The other protons were then assigned from either the H-COSY or

1

¹H-NOESY spectra, while their carbons were identiﬁed by H,¹³C-

HSQC and ¹H,¹³C-HMBC spectra. Also in the case of complexes 1e,f

and 2e,f the Pd−Me resonance was helpful to assign aromatic protons.

In compounds 1e and 2e H13 showed a strong NOE contact with

H12′ and H5′. The interactions of the latter with CH₃(1′) allow

discrimination between CH₃(1′) and CH₃(1). At the same time,

CH₃(1) interacts both with H12 and H5 of the other half of the ligand.

H5−H5′ and H12−H12′ are well separated in the ¹H NMR spectrum

(for example, in 1e: H5′, 7.93; H5, 7.90; H12, 7.18; H12′, 7.14 ppm

(CDCl₃, 19 °C)). Similarly, in 1f and 2f NOE interactions of Pd−Me

protons with H5′ and H16′ and those of CH₃(1) with H5 and

Reagents: AgPF₆, 37.4 mg (0.148 mmol); 1g, 80 mg (0.135 mmol).

Yield: 97 mg (0.13 mmol, 96%) of 2g as a brown-violet powder. H

1

NMR (200.13 MHz, CD₂Cl₂, 4 °C): δ 8.64 (s, 1H; H10′), 8.62 (s, 1H;

H10), 8.22 (br d, 6H; H8, H12, H8′, H12′,H5 and H15), 8.11 (br d,

2H; H5′ and H15′), 7.83 (m, 4H; H6, H14, H6′ and H14′), 7.71 (m,

4H; H7, H13, H7′ and H13′), 2.32 (s, 3H; H1), 2.23 (s, 3H; H1′),

1.16 (s, 3H; NCCH₃), 0.03 ppm (s, 3H; H17). ¹³C NMR (50.32 MHz,

CD₂Cl₂, 4 °C): δ 183.98 (s; C2′), 175.51 (s; C2), 136.19 (s; C3),

135.89 (s; C3′), 131.20 (s; (C4 and C16) or (C4′ and C16′)), 130.97

(s; (C4′ and C16′) or (C4 and C16)), 129.12 (s; (C8 and C12) or

(C8′ and C12′)), 128.96 (s; (C8′ and C12′) or (C8 and C12)),

128.11 (s; (C6 and C14) or (C6′ and C14′)), 127.79 (s; (C6′ and

1

H16 deﬁne the structures of complexes, and the remaining H and

¹³C resonances were then assigned following scalar and dipolar

interactions.

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4.5. Synthesis and Characterization of the First Intermediates

3g−6g in the CO/p-Methylstyrene Copolymerization Reaction.

4.5.1. Synthesis of [Pd(Me)(CO)((9-C₁₄H₉)₂DABMe₂)]⁺[BAr′₄]⁻(3g).

C8), 129.6 (s, 2C; (C12′ or C8′) and (C12 or C8)), 129.2 (s; C8′ or

C12′), 128.8 (q, ²J_C,F= 27.0 Hz; Ar′-C_m), 128.7, 128.5, 128.3, 127.6 (s;

4C; C6, C6′, C14 and C14′), 127.2 (s; C10), 127.0 (s; C7 or C13),

1

126.5 (s, 4C; C10′, C7′, C14′ and (C13 or C7)), 124.2 (q, J_C,F

=

272.7 Hz; CF₃), 121.18 (s; C9 or C9′ or C11 or C11′), 120.94 (s;

C15), 120.88 (s; C15′ or C5′), 120.7, 120.6, 120.3 (s, 3C; C9 and/or

C9′ and/or C11 and/or C11′), 120.0 (s; C5), 119.7 (s; C5′ or C15′),

117.6 (s; Ar′-C_p), 115.7 (s; C21), 107.2 (br; C22 and C22′), 54.8 (s;

C20), 41.0 (s; C19), 29.0 (s; C17), 20.9 (s; C25), 20.3 (s; C1), 20.0

(s; C1′). Anal. Calcd for C₇₅H₄₉F₂₄N₂OBPd (1567.40): C, 57.47; H,

3.15; N, 1.79. Found: C, 57.60; H, 3.22; N, 1.91.

A 60 mg (0.101 mmol) sample of 1g and a 93.4 mg (0.105 mmol)

sample of NaBAr′₄were dissolved at 0 °C in dichloromethane (4 mL)

previously saturated with CO. The reaction mixture was ﬁltered

through Celite to remove NaCl. The solvent was evaporated under

vacuum, and the resulting oil was washed with hexane (3 × 5 mL).

A 119.5 mg (0.08 mmol, yield 81%) sample of 3g was collected as a

Intramolecular Structure of Complex 4g Determined by NMR

Experiments. The assignment of the ¹H resonances of the allyl

fragment of 4g was made on the basis of the dipolar and scalar interac-

1

tions detected in the H-NOESY and H-COSY spectra, respectively,

and conﬁrmed by previously reported studies.^2dThe starting point was

H17, the aliphatic signals integrating for three protons at 1.33 ppm

,which shows long-range correlation with the CO singlets at 202.7

(C18) ppm in the ¹H−¹³C HMBC spectrum. The remaining

resonances were individuated following the interactions H17−H19a/

H19b, H19a−H19b, H19a/H19b−H20, H20−H22/H22′, H22/

H22′−H23/H23′ ,and H23/H23′−H25. In the aromatic region of

1

violet powder. H NMR (200.13 MHz, CDCl₃, −20 °C): δ 8.67 (s,

1H; H10′), 8.65 (s, 1H, H10), 8.23 (m, 4H; H8, H8′, H12 and H12′),

H87 (br d, 2H; H5 and H15), 7.71 (s, 10H; H5′, H15′ and Ar′-H_o),

7.64 (m, 8H; H7, H7′, H13, H13′, H6, H6′, H14 and H14′), 7.49 (s,

4H; Ar′-H_p), 2.30 (s, 3H; H1′), 2.27 (s, 3H; H1), 0.40 ppm (s, 3H;

H17). ¹³C NMR (50.32 MHz, CDCl₃, −20 °C): δ 186.5 (s; C2), 177.3

1

(s; C2′), 173.7 (s; CO), 161.5 (q, J (C,B) = 49.5 Hz; Ar′-C_i), 136.7

(s; C3), 134.8 (s; Ar′-C_o), 132.7 (s; C3′), 131.1 (s; (C4 and C16) or

(C4′ and C16′)), 130.9 (s; (C4′ and C16′) or (C4 and C16)), 130.1

(s; (C8 and C12) or (C8′ and C12′)), 129.9 (s; C8′ and C12′) or (C8

and C12)), 129.0 (s; (C6, C14, C6′ and C14′) or (C7, C13, C7′ and

1

the H NMR spectrum, the only two singlets were ascribable to

H10 and H10′ protons. Due to the NOE interactions of H17 with

H10 and of H25 with H10′, it was possible to discriminate between

the two signals, and so, the halves of the nitrogen ligand (n and n′)

were diﬀerentiated. The overlap of most aromatic resonances

makes diﬃcult the assignment of other signals starting from H10,

H10′ and following the scalar or dipolar interactions. Despite this,

the following assignments were made: (i) H8′ was identiﬁed

thanks to its NOE contacts with both H10′ and H25; (ii) H12′ was

assigned due to its interactions with H10′, H22/H22′, and H23/

H23′; (iii) H15′ was deﬁned from its NOE contact with H22/

H22′; (iv) H8 and H12 were assigned on the base of their

interactions with H10 and H17; (v) H15 was assigned from the

interaction with H20.

2

C13′) C10 and C10′), 128.6 (q, J_C,F= 27.0 Hz; Ar′-C_m), 126.6 (s;

(C7, C13, C7′ and C13′) or (C6, C14, C6′ and C14′)), 124.2 (q,

¹J_C,F= 267.7 Hz; CF₃), 121.9 (s; C9′ and C11′), 120.6 (s; C9, C11, C5

and C15), 120.1 (s; C5′ and C15′), 117.6 (s; Ar′-C_p), 21.9 (s; C1′),

20.6 (s; C1), 8.3 ppm (s; C17). Anal. Calcd for C₆₆H₃₉F₂₄N₂OBPd

(1449.22): C, 54.70; H, 2.71; N, 1.93. Found: C, 54.77; H, 2.80;

N, 1.94.

4.5.2. Synthesis of [Pd(η³-C₁₁H₁₃O)((9-C₁₄H₉)₂DABMe₂)]⁺[BAr′₄]⁻(4g).

The similar intensities of the NOE interactions H1−H5, H1−

H15 and of H1′−H5′, H1′−H15′ suggest the nearly perpendicular

placement of the halves of the N-anthryl ligand with respect to the

square-planar coordination plane of the complex, as observed in the

solid state (Figure 2). Following the NOE connectivity, from H15′

and H15 it was possible to assign H1′ and H1 signals, of methyl

groups of the DAB backbone, and consequently H5′ and H5. Both

H15′−H22/H22′ and H5′−H22/H22′ contacts were detected

in the ¹H-NOESY spectrum; however, the stronger intensity of

the former conﬁrms the rather inclined orientation of the

p-methylstyrene ring with respect to the n′ half of the 9-anthryl

ligand, delineating a solution structure essentially similar to that

determined in the solid state by means of X-ray analysis (Figure 2).

Other main observations that allow us to deﬁne the intramolecular

structure of 4g were the following: (i) a stronger intensity of the

H5′−H23/H23′ contact is detected relative to the H5′−H22/H22′

contact; (ii) H25 interacts with H10′ and H8′ with approximately

the same intensity; (iii) H23/H23′ preferentially interacts with

H10′, H12′, and H5′; (iv) H22/H22′ preferentially interacts with

H15′, H12′, and H15; (v) H20 interacts almost exclusively with

H15; (vi) H19a weakly interacts with H10 and H5; (vii) H19b

weakly interacts with H5; (viii) H17 interacts with H10 and, weakly,

with H8 and/or H12.

A 82.3 mg (0.056 mmol) sample of 3g was dissolved in di-

chloromethane (5 mL) at 0 °C; then p-methylstyrene (7.5 μL,

0.056 mmol) was added. After 1 h the solution was ﬁltered trough

Celite and the solvent was evaporated under vacuum. The resulting oil

was washed with hexane (2 × 3 mL) to yield complex 4g (83 mg,

1

0.053 mmol, yield 95%) as a red-brown powder. H NMR (200.13

MHz, CDCl₃, 4 °C): δ 8.70 (s, 1H; H10), 8.68 (s, 1H; H10′), 8.33 (br

d, 1H; H15), 8.29 (br d, 2H; H8 and H12), 8.28 (br d, 1H; H12′),

8.19 (d, ³J_H,H= 8.4 Hz, 1H; H8′), 8.07 (d, ³J_H,H= 8.6 Hz, 1H; H15′),

7.89−7.58 (m, 18H; Ar′-H_o, Ar′-H_p, H6, H14, H14′, H7, H13, H13′),

7.70 (brt, 1H; H7′), 7.66 (br d, 1H; H5), 7.50 (brt, 1H; H6′), 7.18 (d,

³J_H,H= 8.6 Hz, 1H; H5′), 6.11 (br d, 2H; H22 and H22′), 5.80 (d, 2H;

3

H23 and H23′), 2.80 (dd, J_H,H= 4.2 Hz and J_H,H= 9.5 Hz, 1H;

3

H20), 2.24 (s, 3H; H1′), 2.14 (s, 3H; H1), 1.63 (dd, J_H,H= 9.4 Hz

2

and J_H,H= 18.5 Hz, 1H; H19b), 1.33 (s, 3H; H17), 0.92 (s, 3H;

H25), 0.30 (dd, J_H,H= 4.3 Hz and J_H,H= 18.8 Hz, 1H; H19a). ¹³C

NMR (50.32 MHz, CDCl₃, 4 °C) δ 202.7 (s; C18), 178.8 (s; C2),

176.5 (s; C2′), 161.5 (q, ¹J_C,B= 49.7 Hz; Ar′-C_i), 142.0 (s; C24), 137.2

(s; C3), 136.5 (s; C3′), 134.8 (s; Ar′-C_o), 133.6 (s; C23 and C23′),

131.4, 131.2, 130.9 (s; 4C; C4, C4′, C16 and C16′), 129.7 (s; C12 or

3

2

L

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4.5.3. Synthesis of [Pd{C(O)CH(4-Me-C₆H₄)CH₂C(O)CH₃}((9-

p-Methylstyrene (3.5 μL, 0.027 mmol) was added to the CD₂Cl₂

equilibrium mixture of 4g and 5g (40/60) in an NMR tube. Then

carbon monoxide was bubbled through the solution for 5 min at

−20 °C. The mixture was allowed to react for 9 days at −18 °C under

1 atm of CO. The solvent was evaporated under vacuum, and the

resulting oil was washed with hexane (2 × 3 mL). The NMR analysis

indicates the formation of complex 6g as the major product (74%),

together with other unidentiﬁed species. ¹H NMR (200.13 MHz,

CD₂Cl₂, 4 °C): δ 8.68 (s, 1H; H10′), 8.32 (s, 1H; H10), 8.30 (d,

³J_H,H= 8.8 Hz, 1H; H12′), 8.23 (d, ³J_H,H= 8.4 Hz, 1H; H15), 8.18 (d,

³J_H,H= 8.4 Hz, 1H; H8′), 8.07 (d, ³J_H,H= 8.6 Hz, 1H; H15′), 7.98 (d,

³J_H,H= 8.4 Hz, 1H; H8), 7.80 (br d, 1H; H12), 7.78−7.62 (m, 17H;

H6, H13, H13′, H14, Ar′-H_oand Ar′-H_p), 7.66 (br d, 1H; H5), 7.63

(brt, 1H; H7′), 7.61 (br t, 1H; H7′), 7.56 (br t, 1H; H6′), 7.14 (d,

³J_H,H= 8.5 Hz, 1H; H5′) 7.12 (br d, 2H; H23, H23′), 6.52 (br d, 2H;

H22 and H22′), 6.19 (br, 2H; H30 and H30′), 5.83 (br, 2H; H31 and

H31′), 3.16 (dd, 1H; H20), 3.08 (m, 1H; H19a), 2.50 (br s, 3H;

H25), 2.45 (dd, 1H; H28), 2.41 (m, 1H; H19b), 2.21 (s, 3H; H1),

2.13 (s, 3H; H1′), 1.95 (m, 1H; H27b), 1.93 (s, 3H; H17), 0.93 (s,

3H; H33), 0.21 (dd, 1H; H27a). ¹³C NMR (50.32 MHz, CD₂Cl₂,

4 °C) δ 207.2 (s; C18), 204.6 (s; C26), 178.7 (s; C2), 176.5 (s; C2′),

161.7 (q, ¹J_C,B= 49.8 Hz; Ar′-C_i), 141.9 (s; C32), 137.4 (s; C3), 137.3

(s; C21), 136.6 (s; C3′), 134.8 (s; Ar′-C₀), 133.5 (s; C31 and C31′),

132.7 (s; C24), 131.3, 130.9, 130.6 (s; C4, C4′, C16 and C16′), 129.6

(s; C23 and C23′), 129.5 (s; C8′), 129.4 (s; C8), 129.3 (C12′), 128.8

(q, ²J_C,F= 27.0 Hz; Ar′-C_m), 128.7, 126.5 (s; C7, C13, C7′, C13′, C6,

C14, C14′ and C10′), 128.2 (s; C12), 127.4 (s; C22, C22′, C10 and

C6′), 124.2 (q, ¹J_C,F= 272.7 Hz; CF₃), 121.8 (s, C9 or C9′ or C11 or

C11′), 121.1 (s; C15′), 121.0 (s; C15), 120.8 (s, C9 or C9′ or C11 or

C11′), 120.4 (s, C9 or C9′ or C11 or C11′), 120.3 (s; C5), 119.9 (s;

C5′), 117.5 (s; Ar′-C_p), 116.9 (s, C9 or C9′ or C11 or C11′), 55.5 (s;

C28), 51.5 (s; C20), 47.6 (s; C19), 40.1 (s; C27), 29.1 (s; C17), 21.0

(s; C25), 20.7 (s; C33), 20.4 (s; C1), 20.2 (s; C1′).

C₁₄H₉)₂DABMe₂)]⁺[BAr′₄]⁻(5g).

Complex 4g (42 mg, 0.027 mmol) was dissolved in CD₂Cl₂(0.5 mL)

in an NMR tube. Carbon monoxide was bubbled through the solution

for 10 min at −70 °C, resulting in the formation of an equilibrium

mixture of compounds 4g and 5g. The equilibrium ratios appear to be

strongly aﬀected by temperature, and the highest conversion in

compound 5g (60%) was observed at −17 °C in 3 days under 1 atm of

CO. ¹H NMR (200.13 MHz, CD₂Cl₃, −17 °C): δ 8.69 (br s, 2H; H10,

H10′), 8.31−8.19 (m, 3H; H8′, H12, H12′), 8.21 (m, 1H; H8), 8.02−

7.78 (m, 3H; H13, H14, H15), 8.02−7.58 (m, 21H; H5, H5′, H6, H6′,

H7, H7′, H13′, H14′, H15′, Ar′-H_o, Ar′-H_p), 6.91 (d, 2H; H23 and

H23′), 6.77 (d, 2H; H22 and H22′), 3.92 (dd, 1H; H20), 2.39 (s, 3H;

H1 or H1′), 2.23 (m, 1H; H19b), 2.20 (s, 3H; H1′ or H1), 2.06 (s,

3H; H25), 1.61 (s, 3H; H17), 0.62 (dd, 1H; H19a). ¹³C NMR (50.32

MHz, CD₂Cl₃, −17 °C): δ 210.1 (s; C26), 202.7 (s; C18), 169.6 (s;

C27), 179.5, 173.9 (s; C2 and C2′), 161.7 (q, ¹J_C,B= 49.8 Hz; Ar′-C_i),

134.8 (s; Ar′-C₀), 131.4−120.8 (aromatic carbons and Ar′-C_m), 130.2

1

(br s; C23 and C23′), 129.7 (br; C22 and C22′), 124.0 (q, J_C,F

=

272.5 Hz; CF₃), 117.5 (s; Ar′-C_p), 60.0 (br s; C20), 44.2 (s; C19), 29.2

(s; C17), 21.4 (s; C1 or C1′), 20.7 (s; C25), 20.4 (s; C1′ or C1).

Intramolecular Structure of Complex 5g Determined by NMR

Intramolecular Structure of Complex 6g Determined by NMR

1

Experiments. The analysis of the H-NOESY spectrum of 6g depicts

1

Experiments. The assignment of the H resonances of the growing

the molecular structure illustrated above. Starting from H27a (a

doublet of doublets at 0.21 ppm, separated from other signals in the

polymer chain of 5g was made starting from the H20 resonance, since

it is well identiﬁed at around 4 ppm, in analogy with previous results,^2d

1

¹H NMR spectrum), the H and ¹³C resonances of the allyl systems

1

were assigned on the basis of the ¹H−¹H and ¹H−¹³C NMR correlations.

In the aromatic region of the ¹H spectrum, the only singlets were

ascribable to the H10 and H10′ protons. The NOE interactions of H33

with H10′ and that of H25 with H10 allow discrimination between the

two signals and, then, between the halves of the 9-anthryl ligand. H10′

interacts with H8′ and H12′ and a selective NOE interaction is observed

between H33 and H8′. Similarly, H10 shows dipolar interactions with

H8 and H12, and the H8−H25 contact leads to assignment of the two

aromatic doublets. H15′ shows a NOE interaction with the H30/H30′

resonance, while H5′ interacts preferentially with the H31/H31′

resonance, and H1′ and H1 were assigned through the interactions

with H15′ and H5′ (Scheme 4). Following the NOE connectivity, from

H1 it was possible to individuate H15 and H5, which were discriminated

thanks to the selective H15−H28 interaction. The dipolar interactions in

6g, involving the second p-methylstyrene unit and the N-anthryl moiety,

are the same as those observed for 4g, although with lower intensity. The

position of the aryl ring of the ﬁrst inserted oleﬁn was deduced from the

following observations: (i) H25 interacts with H10 and H8; (ii) H23/

H23′ interact with H10 and H8 and, weakly, with H12 and H5; (iii)

H22/H22′ interact with H10, H15, and H12.

and it is the only −CH− aliphatic signal in the H NMR spectrum.

The other proton resonances H19a and H19b were easily recognized,

due to their direct correlation with the only −CH₂− carbon of the ¹³

C

NMR spectrum. As observed in 4g, the H22/H22′ protons (as well as

H23/H23′) give a single broad doublet because of the free rotation of

the p-methylstyrene aryl around the C20−C21 single bond. Following

the dipolar interactions in the ¹H-NOESY spectrum and the scalar

interactions in the ¹H−¹³C HSQC and ¹H−¹³C HMBC spectra, most of

the proton and carbon resonances of the acetyl moiety were deﬁned. Due

to the presence in solution of both 4g and 5g and to the overlap of most

aromatic signals, NOE interactions cannot be addressed to describe the

intramolecular structure of 5g. However, similarly to previous ﬁndings^2d

the preferred conformation of the growing chain was assumed to be that

reported for 5g, as conﬁrmed from the following NMR evidence: (i) the

absence of dipolar interactions involving H25 and the anthracenyl

protons of the nitrogen ligand; (ii) the weak NOE contacts between

H22/H22′, H23/H23′, H20 and the N-anthryl protons H15, H14, and

H13; (iii) the interactions of H19a and H17 with H8.

4.5.4. Synthesis of [Pd(η³-C₂₁H₂₂O₂)((9-C₁₄H₉)₂DABMe₂)]⁺[BAr′₄]⁻

(6g).

4.6. General Procedures for Copolymerization Processes.

4.6.1. CO/Vinyl Arene Copolymerization in CH₂Cl₂under 1 atm

of CO. In a typical copolymerization reaction, the Pd(II) complex

(0.035 mmol) was dissolved in dichloromethane (2.8 mL) at 17 °C

under a nitrogen atmosphere. The solution was transferred into a

thermostated Schlenk ﬂask equipped with a carbon monoxide gas

line and a tank for the CO. Then 21 mmol of the vinyl arene

(p-methylstyrene, 2.8 mL; styrene, 2.6 mL) was added (oleﬁn/

palladium molar ratio 600/1). The solution was allowed to react for

27 h (or 51 h) at 26 °C. The resulting gray polymer was precipitated

with methanol and washed with methanol. To remove metallic

palladium, the polymer was dissolved in chloroform, ﬁltered through

M

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Celite, precipitated with methanol, washed with methanol, and dried

under vacuum. When mixtures of copolymer and poly(p-methylstyrene)

were obtained from the reaction, diethyl ether was added to the mixture

in order to extract the homopolymer. The resulting suspension was

stirred vigorously for several hours and the ether solution was decanted

Fourier map. In this case the ﬂuorine atoms were reﬁned isotropically

with the occupancy factor set to 0.5. In both the crystal structures all

of the other non-hydrogen atoms were given anisotropic displacement

parameters, and all of the other hydrogen atoms were input at

calculated positions and reﬁned by using a riding model, with isotropic

thermal parameters varying in accord with those of the bound atoms.

Geometrical calculations were performed by PARST97,³⁵and

molecular plots were produced by the program ORTEP3.³⁶Crystallo-

graphic data and reﬁnement parameters for 2g and 4g are reported in

Table S1 in the Supporting Information.

4.9. Computational Methods. The Gaussian 09 (revision

C.01)³⁷package was used. Metal complexes 5c′ and 5g′¹⁹were fully

optimized by using the density functional theory (DFT) method by

means of Becke’s three-parameter hybrid method using the LYP

correlation functional.³⁸The eﬀective core potential of Hay and

Wadt³⁹was used for the palladium atom, and the 6-31G*⁴⁰basis set

was used for the remaining atomic species. The same model chemistry

was used for the rigid potential energy surface scans performed on the

postulated intermediates, resulting from the coordination of a second

styrene unit to the carbonylated products 5a′,c′,f′,g′. For the starting

geometries of all the species modeled above, see ref 8. For the nitrogen

ligands e and f the full optimization was performed at the HF-SCF

level of theory, with the basis set 6-311G**.⁴¹The starting geometries

of these latter species were based on X-ray diﬀraction data of analogous

species. In all cases the reliability of all the found stationary points

(minima on the potential energy surface) was assessed by evaluating

the vibrational frequencies.

1

oﬀ of the powder. H and ¹³C NMR spectroscopic data are consistent

with the isolation of atactic copolymer when catalysts 2a,b,e,f were

used^2c,for predominantly isotactic polyketone when catalysts 2c,g were

employed.^2c

4.6.2. CO/Vinyl Arene Copolymerization in 2,2,2-Triﬂuoroetha-

nol. In a typical copolymerization reaction, the Pd(II) complex

(0.035 mmol) was dissolved in 2,2,2-triﬂuoroethanol (2.8 mL) at

17 °C under a nitrogen atmosphere. The solution was transferred into

a thermostated Schlenk ﬂask containing 1,4-benzoquinone (19 mg,

0.175 mmol), equipped with a carbon monoxide gas line and a tank for

the CO. Then 21 mmol of the vinyl arene (p-methylstyrene, 2.8 mL;

styrene, 2.6 mL) was added (oleﬁn/palladium molar ratio 600/1).

The solution was allowed to react for 27 h at 26 °C. The resulting gray

polymer was precipitated with methanol and washed with methanol.

To remove metallic palladium, the polymer was dissolved in chloroform,

ﬁltered through Celite, precipitated with methanol, washed with

methanol, and dried under vacuum.

4.6.3. CO/p-Methylstyrene Copolymerization in CH₂Cl₂under 5

atm of CO. The Pd(II) complex (0.035 mmol) was dissolved in

methylene chloride (2.8 mL) at 17 °C under a nitrogen atmosphere.

The solution was transferred into a thermostated steel autoclave

equipped with a magnetic stirring bar and a carbon monoxide gas line.

Then p-methylstyrene (2.8 mL, 21 mmol) was introduced into the

autoclave (oleﬁn/palladium molar ratio 600/1). The nitrogen

atmosphere was replaced by carbon monoxide, and the autoclave was

charged with CO at 5 atm. The polymerization was allowed to run for

27 h at 26 °C. The run was terminated by venting the reactor vessel

and pouring the polymerization mixture into methanol. The resulting

gray polymer was washed with methanol. To remove metallic

palladium, the polymer was dissolved in chloroform, ﬁltered through

Celite, precipitated with methanol, washed with methanol, and dried

under vacuum.

4.7. Molecular Weight Measurements. The weight-average

molecular weights (M_w) of copolymers and molecular weight

distributions (PDI = M_w/M_n) were determined by gel permeation

chromatography versus polystyrene standards. The analyses were

recorded on a Knauer HPLC (K-501 Pump, K-2501 UV detector)

with a Plgel 5 μm 10⁴Å GPC column and chloroform as solvent (ﬂow

rate 0.6 mL min⁻¹). CO/styrene samples were prepared as follows:

2 mg of the copolymer was solubilized in 120 μL of 1,1,1,3,3,3-

hexaﬂuoro-2-propanol (HFIP) and chloroform was added up to 10 mL;

however, CO/p-methylstyrene copolymers were directly soluble in

chloroform. The statistical calculations were performed with the Bruker

Chromstar software program.

4.8. X-ray Crystallographic Structure Determinations for 2g

and 4g. Single crystals suitable for X-ray diﬀraction were obtained by

slow diﬀusion of hexane into a solution of the complex in dichloro-

methane with several drops of methanol at −30 °C. Diﬀraction data

for compound 2g and 4g were collected on an Oxford Diﬀraction

Xcalibur3 diﬀractometer equipped with a CCD area detector and Mo

Kα radiation (λ = 0.71073 Å). Data collections were carried out at

150 K by means of the program Crysalis CCD,⁸and data were reduced

with the program Crysalis RED.³²The absorption correction was

applied through the routine ABSPACK in the Crysalis RED program.

The structures were solved with the direct methods of the SIR2004³³

package and reﬁned by full-matrix least squares against F²with the

program SHELX97.³⁴In the crystal lattice of 2g, additional electron

density peaks were modeled as disordered acetonitrile and methanol

crystallization molecules, with site occupation factor 0.5 and isotropic

temperature factor (the hydrogen atoms were not introduced). In 4g,

the η³fragment appears disordered, except for the acetyl group. Two

models for the CH₂CH(p-Me-C₆H₄) moiety were found, each (a and

b) with occupancy factor 0.5. In the η³fragment all of the atoms were

reﬁned isotropically and the hydrogen atoms were not introduced.

Also for a −CF₃grouping two models were found in the diﬀerence

ASSOCIATED CONTENT

* Supporting Information

■

S

A CIF ﬁle giving crystallographic data for 2g and tables giving

crystal data and bond distances and angles for 2g and 4g and

Cartesian coordinates of the calculated structures. This material

is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

Corresponding Author

*C.C.: tel, (+39) 0722 303312; fax, (+39) 0722 303311; e-mail,

carla.carfagna@uniurb.it.

■

Author Contributions

The manuscript was written through contributions of all

authors. All authors have given approval to the ﬁnal version of

the manuscript.

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

This work was supported by the Ministero dell’Universita

Ricerca (PRIN no. 2008A7P7YJ). The CRIST (Centro di

Cristallograﬁa Strutturale), University of Florence, where the

X-ray measurements were performed, is gratefully acknowledged.

■

̀

e della

REFERENCES

■

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New aryl α-diimine palladium(II) catalysts in stereocontrolled CO/vinyl arene copolymerization

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