N-Acyl-N,N-dipyridyl and N-acyl-N-pyridyl-N-quinoyl amine based palladium complexes. Synthesis, X-ray structures, heterogenization and use in Heck couplings

www.elsevier.nl/locate/jorganchem

Journal of Organometallic Chemistry 622 (2001) 6–18

N-Acyl-N,N-dipyridyl and N-acyl-N-pyridyl-N-quinoyl amine

based palladium complexes. Synthesis, X-ray structures,

heterogenization and use in Heck couplings

Josef Silberg ^a, Thomas Schareina ^c, Rhett Kempe* ^c,1, K. Wurst ^b,

Michael R. Buchmeiser* ^a,2

^aInstitut fu¨r Analytische Chemie und Radiochemie, Uni6ersita¨t Innsbruck, Innrain 52 a, A-6020 Innsbruck, Austria

^bInstitut fu¨r Allgemeine, Anorganische und Theoretische Chemie, Uni6ersita¨t Innsbruck, Innrain 52 a, A-6020 Innsbruck, Austria

^cInstitut fu¨r Organische Katalyseforschung an der Uni6ersita¨t Rostock e.V., Buchbinderstrasse 5-6, D-18055 Rostock, Germany

Received 11 July 2000; received in revised form 7 September 2000

Abstract

A series of homogeneous and heterogeneous palladium(II)-catalysts and their use in Heck-couplings is described. Starting from

four different amines, N-pyrid-2-yl-N-(3-methylpyrid-2-yl)amine (1), N-pyrid-2-yl-N-(6-methylpyrid-2-yl)amine (2), N-(6-

methylpyrid-2-yl)-N-(4-methylquinolin-2-yl)amine (3) and N-bis(6-methylpyrid-2-yl)amine (4), the corresponding acetyl- and

norbornene derivatives, N-pyrid-2-yl-N-(3-methylpyrid-2-yl) acetamide (5), N-pyrid-2-yl-N-(6-methylpyrid-2-yl) acetamide (6),

N-(6-methylpyrid-2-yl)-N-(4-methylquinolin-2-yl) acetamide (7), N-bis(6-methylpyrid-2-yl)acetamide (8) and N-pyrid-2-yl-N-(3-

methylpyrid-2-yl)-endo-norborn-2-ene-5-carbamide (9), N-pyrid-2-yl-N-(6-methylpyrid-2-yl)-endo-norborn-2-ene-5-carbamide (10)

and N-(6-methylpyrid-2-yl)-N-(4-methylquinolin-2-yl)-endo-norborn-2-ene-5-carbamide (11), respectively, have been prepared.

The acetyl derivatives 5–8 have been used for the preparation of the homogeneous Heck catalysts N-acetyl-N-pyrid-2-yl-N-(3-

methylpyrid-2-yl)amine palladium dichloride (13), N-acetyl-N-pyrid-2-yl-N-(6-methylpyrid-2-yl)amine palladium dichloride (14),

N-acetyl-N-(6-methylpyrid-2-yl)-N-(4-methylquinolin-2-yl)amine palladium dichloride (15) and N-acetyl-N-bis(6-methylpyrid-2-

yl)amine palladium dichloride (16). X-ray data were obtained for compounds 9, 11, 13 and 14. Polymer supports 17–19 were

prepared via ring-opening metathesis copolymerization of the norbornene derivatives 9–11 with 1,4,4a,5,8,8a-hexahydro-1,4,5,8-

exo-endo-dimethano-naphthalene (HDMN-6) and subsequently loaded with palladium(II) chloride. Both the homogeneous

catalysts 13–16 and the heterogeneous catalysts are active in the vinylation of aryl iodides and aryl bromides with turn-over

numbers (TONs) of up to 220 000. Comparably low yields (=34%) and TONs (=2100) are achieved in the tetrabutylammonium

bromide- (TBAB-) assisted vinylation of aryl chlorides as well as in the amination of aryl bromides. Structural data of compounds

9, 11, 13 and 14 were compared with those of the parent systems, N-acetyldipyridylamine palladiumdichloride (20) and the

poly(N,N-dipyrid-2-yl-endo-norborn-2-ene-5-carbamide)based resin (21), respectively. Thus, methyl-substitution leads to a signiﬁ-

cant perturbation of the almost perfect square planar coordination of Pd found in 20 resulting in lowered stabilities of the

Keywords: Palladium(II)-catalysts; Heck-couplings; Polymerizations; X-ray structures

1. Introduction

Palladium-mediated reactions such as polymeriza-

tions, C–C coupling reactions, aminations and hy-

drophosphorylations have attracted signiﬁcant interest

during the last years [1–8]. Nevertheless, ‘classical’

reactions such as the vinylation of aryl halides —

commonly called the Heck reaction — are still the

¹*Corresponding author. Tel.: +49-381-4669369; fax: +49-381-

4669369; e-mail: rhett.kempe@ifok.uni-rostock.de

²*Corresponding author. Tel.: +43-512-5075184; fax: +43-512-

5072677; e-mail: michael.r.buchmeiser@uibk.ac.at

PII: S0022-328X(00)00783-X

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

7

center of interest [6]. In view of the signiﬁcant progress

in homogeneous catalysis [9,10] including asymmetric

reactions [11–14], the demand for highly active and

stable heterogeneous systems [15–19] is still high. Only

few reports exist on the synthesis of heterogeneous

palladium catalysts, e.g. based on palladium-loaded

carbon or alumina, palladium-loaded porous glass, zeo-

lite- (NaY-type) entrapped Pd-complexes, palladium

colloids, Pd-grafted MCM-41 or triazene-functionalized

Merriﬁeld polymers [18–21]. Despite the high coupling

activity of systems that may be generated from phos-

phine- or aminophosphine-based ligands [22], these are

transformed easily into the corresponding phosphine

oxides. This reaction results in a slow but permanent

release of palladium (catalyst bleeding) which signiﬁ-

cantly restricts their industrial use. In order to circum-

vent this problem, more stable catalytic systems have

been elaborated for homogeneous catalysis [19,23–25]

including phospha-palladacyles [25,26], homoleptic

chelating N-heterocyclic carbene complexes [27,28] as

well as dipyridylamide based systems [29]. Ligands

solely based on nitrogen [30], e.g. dipyridyl amide-based

Heck coupling systems are relatively rare, yet turned

out to be suitable for the synthesis of highly tempera-

ture stable and active Heck catalysts [29]. If incorpo-

rated into suitable monomers, ring-opening metathesis

polymerization (ROMP) may be used for the prepara-

tion of well-deﬁned heterogeneous Heck systems based

on such ligands [29]. Generally speaking, heterogeneous

polymer supports prepared by this approach are char-

acterized by an exact knowledge about the chemical

structure of the corresponding catalytic sites. Based on

the encouraging results obtained with N-acyl-N,N-

dipyridylamine-based Pd-complexes, we extended this

type of N,N-ligands to other pyridine homologues. In

this contribution, the use of methyl-substituted

dipyridyl amide and pyridyl–quinoyl amide ligands for

homogeneous and heterogeneous Heck couplings as

well as the structural features that inﬂuence reactivity

will be presented.

Cl) reactions are an efﬁcient tool for the synthesis of

amines via C–N-bonds formation [31,32]. If 2-X–

pyridines are used X can be Cl since the systems are

activated, but the formation of catalyst deactivating

palladium pyridine complexes has to be avoided. Thus,

the palladium catalyst has to be stabilized by chelating

bisphosphine ligands. Reactions of 2-aminopyridines

with one equivalent of the corresponding 2-halogen-

pyridine and 1.25 equivalents of sodium-tert-butylate in

the presence of 1 mol% bis-diphenylphosphinopropane

and 0.5 mol% Pd₂dba₃in toluene at 80°C leads usually

after less than 1 h to a color change to yellow. After

stirring additional 12 h, workup with dichloromethane

and water, the compounds were puriﬁed via chro-

matography or crystallization. The reactions are highly

selective, almost no formation of doubly arylated

amines has been found. Compound 1 was prepared

from 3-methylpyrid-2-yl-amine and 2-bromopyridine,

compound 2 from 6-methylpyrid-2-yl-amine and 2-bro-

mopyridine, compound 3 from 6-methylpyrid-2-yl-

amine and 2-chloro-4-methylquinoline and compound 4

from 6-methyl-2-yl-amine and 2-chloro-6-methyl-

pyridine (Fig. 1). All starting materials are commer-

cially available.

2.2. Homogeneous Heck catalysts

In order to obtain structural information about ge-

ometry and binding, homogeneous analogues were pre-

pared by reaction of the amines 1–4 with acetyl

chloride and acetic anhydride, respectively (Scheme 1).

Reaction of the resulting acetyl derivatives 5–8 with

H₂PdCl₄in methanol/water at pH 5 yields the corre-

sponding palladium complexes 13–16. Complexes 13

and 14 were characterized by X-ray analysis and show

the expected yet distorted square planar conformation

of the palladium center (Figs. 2 and 3). A summary of

the relevant structural data is given in Table 1. A

comparison between compounds 13 and 14, N-acetyl-

N,N-dipyrid-2-ylamine palladium dichloride (20) [29],

the free ligands 7, 9 (Figs. 4 and 5) and norborn-2-ene-

5-(N,N-dipyrid-2-yl)carbamide [33] reveals no signiﬁ-

cant differences between the angles deﬁned by

C3–N3–C8 (C_a–N3–C_a% , 115.5–119.4°). The same ap-

plies to the distances Pd–N1, which were found to lie in

the range of 142.2–144.4 pm. Nevertheless, the dihedral

angle deﬁned by PdN(1)N(2)–PdCl(1)Cl(2) turned out

2. Results and discussion

2.1. Synthesis of amines

Palladium-catalyzed aryl–X activation (X=I, Br or

Fig. 1. Structure of compounds 1–4.

8

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

Scheme 1. Synthesis of acetyl- and norbornene derivatives of compounds 1–4.

Fig. 2. X-ray structure of compound 13.

to be an appropriate probe for the steric situation at the

palladium. Thus, this angle is almost zero in the case of

compounds 20 or 13 (2.8(1) and 1.1(1)°, respectively),

yet is increased to 10.5(8)° in the case of compound 14.

Obviously, the steric repulsion between the methyl

group and one chlorine atom results in the formation of

such distorted square planar complexes. As might be

expected, this unfavorable change in conformation is

also reﬂected on the stability of the resulting Pd com-

plexes. While the high stability of 20 basically impedes

any quantitative NMR measurements, the dissociation

constants (K_D) for complexes 13–16 may be obtained

3-position (compounds 13 and support 17, respectively)

basically has no inﬂuence on the reactivity, the methyl

group in position six (compounds 14–16 and supports

18–19, respectively) drastically reduces the stability of

these catalytic systems. Consequently, coupling results

obtained with these compounds are similar to those of

Pd(OAc)₂(vide infra).

2.3. Heterogeneous Heck catalysts

Ring-opening metathesis polymerization (ROMP)

has been demonstrated to present a powerful tool in the

preparation of functionalized polymer supports [29,33–

40]. Even complex functionalities may be introduced

with high reproducibility and without any change in the

chemical nature, geometry and even chirality of the

corresponding functional group. The norborn-2-ene-

1

easily by H-NMR in dmso-d₆. Thus, K_Dincreases in

the order 13 (9×10⁻⁵)B14 (2.7×10⁻³)B16 (2.3×

10⁻²)B15 (4.8×10⁻²mol l⁻¹). The reactivity of

compounds 13–16 and supports 17–19, respectively

(Table 3) is directly related to these geometric and

thermodynamic features. While the methyl group in

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

9

Fig. 4. X-ray structure of compound 7.

Fig. 3. X-ray structure of compound 14.

derivatives 9–11 are conveniently prepared from nor-

born-2-ene-5-carboxylic chloride and the corresponding

amine (Scheme 1) and may be polymerized in a living

manner using the Schrock-catalyst Mo(N-2,6-i-Pr₂-

C₆H₃)(CHCMe₂Ph)(OCMe(CF₃)₂)₂. Similar procedures

for the synthesis of functional supports and subsequent

loading of the resin have been reported previously [29].

Brieﬂy, living polymers of compounds 9–11 were cross-

linked using DMNH-6 (Scheme 2, Table 2). As a

consequence of the polymerization order, the linear

polymer chains bearing the functional groups form

tentacles that are attached to the surface of the cross-

linked carrier. The use of a Mo-based system is essen-

tial, since Ru-based Grubbs systems generally fail to

polymerize such strongly chelating systems [41]. In con-

trast to the parent dipyridylamide-based ligands, signiﬁ-

cantly lowered Pd-loadings (0.03–0.05 mmol g⁻¹

,

Table 2) may be achieved. The palladium-loaded

chelating groups are located exclusively at the surface

of the particle [33,42], are easily accessible, diffusion

plays a minor role and coupling reactions may proceed

within the interphase [43,44].

Table 1

Selected X-ray data for compounds 9, 11, 13 and 14

9

11

13

14

Molecular formula

Formula weight

Crystal system

Space group

a (pm)

b (pm)

c (pm)

h (°)

C₁₉H₁₉N₃O

305.37

C₂₄H₂₃N₃O

369.45

C₁₃H₁₃Cl₂N₃OPd·C₄H₈O C₁₃H₁₃Cl₂N₃OPd

476.67

404.56

Orthorhombic

Pna2₁(no. 33)

1861.5(5)

1443.3(4)

602.2(4)

90

Monoclinic

P2₁/n (no. 14)

975.5(2)

1816.4(3)

1195.3(2)

90

Triclinic

Monoclinic

P2₁/c (no. 14)

1485.9(2)

1509.0(2)

1496.7(2)

90

(

P1 (no. 2)

778.63(2)

916.75(2)

1449.77(4)

88.005

i (°)

90

112.79(2)

90

1.9526(6)

4

76.030

71.236

0.94984(4)

2

117.95(1)

90

2.9645(7)

8

k (°)

V (nm³)

Z

1.6179(12)

4

T (K)

218.2

1.254

0.080

Colorless prism

1358

1.098

R₁=0.0400,

ꢀR₂=0.0984

293(2)

1.257

0.078

Colorless prism

2124

1.071

R₁=0.0435,

ꢀR₂=0.1019

213(2)

1.667

1.274

Yellow prism

3505

1.096

R₁=0.0266,

ꢀR₂=0.0735

218(2)

1.813

1.610

Light yellow prism

1967

D_calc(mg m⁻³

)

Absorption coefﬁcient (mm⁻¹

Color, habit

No. of reﬂections with I\2|(I)

Goodness-of-ﬁt on F²

R indices I\2|(I)

)

1.126

R₁=0.1057,

ꢀR²=0.2002

10

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

systems 17–19 between aryl iodides, bromides as well

as chlorides and styrene and ethyl acrylate, respectively.

A summary of the results is given in Table 3.

2.4.1. Aryliodides

A comparison of the data reveals no signiﬁcant dif-

ferences between the four different homogenous cata-

lysts 13–16 (Table 3). In terms of the maximum

achievable TONs, similar numbers (66 000–80 000) are

obtained. Heterogenization requires a careful choice of

the solvent, since it inﬂuences strongly the chemistry at

the interphase [43,45]. Despite these similar results that

are obtained with compounds 13–16, some interesting

data may be deduced from the kinetics that have been

recorded for the corresponding heterogeneous systems

17–19. Generally speaking DMAc/NBu₃turned out to

be the best system for this type of coupling, resulting in

almost quantitative yields (91–96%) and acceptable

TONs (32 000). Interestingly, the use of sodium/potas-

sium carbonate did not give comparable results. Tetra-

butylammonium bromide (TBAB) is known to promote

Pd-mediated couplings [46] and may additionally be

used as a non-aqueous ionic solvent [47–49]. Conse-

Fig. 5. X-ray structure of compound 9.

2.4. Heck couplings

Heck couplings were carried out with compounds

13–16 as well as with the corresponding heterogeneous

Scheme 2. Preparation and loading of polymer supports (e.g. resin 19).

Table 2

Summary of cross-linked polymers

Resin

Monomer

Cross-linker

mg

Initiator

mg

Yield

mg

Nitrogen

%

Pd-loading

mmol g⁻¹

No.

mg

mmol

%

mmol g⁻¹

17

18

19

9

10

11

120

74

109

0.39

0.24

0.30

480

296

438

3.03

1.87

2.77

17.8

11.0

16.4

0.023

0.014

0.021

320

368

286

53

98

52

2.90

2.71

4.15

2.1

1.9

3.0

0.03

0.05

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

11

Table 3

Summary of Heck-couplings ^a

No.

Ar–X

H₂CꢀCHR

Product

Catalyst

Pd

(mol%)

Solvent

Yield

(%)

TON×10⁻³

1

2

3

4

5

6

7

8

9

Iodobenzene

Iodobenzene/TBAB

Iodobenzene

Bromobenzene

Styrene

Ethyl acrylate

Styrene

trans-Stilbene

Ethyl cinnamate

trans-Stilbene

13

14

15

16

17

18

19

21

17

18

19

21

17

18

19

13

14

15

17

18

21

17

18

19

21

13

14

15

17

18

19

21

17

18

19

21

17

18

19

21

17

18

19

21

0.001

0.003

0.0008

0.003

0.0014

0.001

0.002

0.0004

0.0006

0.002

0.004

0.0005

0.0004

0.002

0.0014

0.003

0.007

0.02

DMF ^b

66

80

75

80.0

75.0

75.8

31.9

33.6

32.2

111.0

28.0

28.4

30.5

93.2

54.2

45.0

52.9

49.3

213.2

223.0

218.1

175.1

2.5

14.4

12.8

40.0

10.3

20.1

19.8

67.6

63.8

62.0

157.7

22.2

23.9

12.3

34.4

0

DMAC ^b67

DMAC ^b91

DMAC ^b96

DMAC ^b92

DMAC ^b99

DMAC ^b80

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

DMF ^b

DMAC ^b

81

87

98

47

39

45

97

87

91

89

75

6

trans-Stilbene

DMAC ^b35

DMAC ^b31

DMAC ^c90

Bromobenzene

4-Bromobenzonitrile

4-Bromo-1-ﬂuorobenzene

Chlorobenzene/TBAB

4-Chloroacetophenone/TBAB

Bromobenzene/KO-t-Bu

4-cyano-trans-Stilbene

4-ﬂuoro-trans-Stilbene

trans-Stilbene

4-acetyl-trans-Stilbene

DMF ^b

45

88

87

36

34

33

83

DMAC ^b38

DMAC ^b41

DMAC ^b21

DMAC ^c58

Styrene

DMAC ^c

0

23.6

1.1

2.1

1.2

6.1

4.7

3.8

DMAC ^c89

DMAC ^b18

DMAC ^b34

DMAC ^b20

DMAC ^c95

0.02

0.014

0.003

0.017

Styrene

N-methylaniline N-methyldiphenylamine 18

N-methylaniline N-methyldiphenylamine 21

THF ^d

14

45

d

^aTBAB=tetrabutylammonium bromide. Yields were determined by ¹H-NMR. Heck-couplings were carried out at T=140°C, t=90 h.

^btri-n-Butylamine.

^cK₂CO₃/Na₂CO₃.

^dKO-t-Bu/NaO-t-Bu (1:1), reﬂux.

quently, its inﬂuence on the reactivity was investigated.

Interestingly, signiﬁcantly different kinetics were ob-

served for 17–19 in DMF (Fig. 6), these differences

basically vanished in the case of DMF/TBAB (Fig. 7)

or pure DMAc. Nevertheless, such drastic changes in

kinetics as found for the parent dipyridyl syste

[29] were not observed. Finally, as expected, rather

high TONs (\200 000) are obtained with electron

deﬁcient vinyl compounds such as ethyl acrylate

(Table 3). In summary, these results are comparable

12

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

comparatively results in terms of TONs (4700 for 18 vs.

3800 for 21) are obtained in the Pd-mediated arylation

of arylamines. As expected, chlorobenzene may not be

coupled even if TBAB is used. Finally, even activated

arylchlorides such as 4-chloroacetophenone in the pres-

ence of TBAB give lower yields (18–34%) compared to

the parent system 21 (95%) [29].

with those obtained with the parent, unsubstituted sys-

tem 21 [29].

2.4.2. Arylbromides and arylchlorides

In contrast to aryliodides, the successful coupling of

arylbromides and in particular arylchlorides requires

the presence of a stabilizing ligand. Consequently, such

couplings may be used as a probe for the effectiveness

of a coupling system. In the present system, changing

from aryliodides to the less reactive aryl bromides leads

to lower coupling yields and TONs both in the homo-

geneous and heterogeneous case. Thus, coupling yields

for bromobenzene and the more activated 4-ﬂuoro- and

4-cyano-substituted analogues were in the range of

33–41%, TONs of 21 000–68 000 were achieved. For

comparison, the use of the parent heterogeneous system

21 resulted in signiﬁcantly elevated coupling yields (58–

90%) and TONs (34 000–160 000) [29]. Interestingly,

2.4.3. Acti6e species

Neutral or anionic palladium(0) species are widely

accepted to represent the active species in phosphane-

based Heck couplings [50,51]. They are generated by a

redox-reaction [52], e.g. via oxidation of a phosphine to

the corresponding phosphine oxide [53,54]. Recently,

Arai et al. proposed that Pd(0) that leached into a

suitable solvent from a support essentially catalyzes the

reaction. Both the base and the solvent inﬂuence the

kinetics of the reaction, yet do not affect the overall

rate of the reaction much. Based on the comparably

large dissociation constants (K_D) of the Pd-complexes

13–16 (vide supra) and on the observed coupling activ-

ities in the current systems we believe that such dis-

solved Pd species may play a certain role in the present

systems. Consequently, these differ from the parent,

unsubstituted dipyridylamide-based system, which was

found to form stable Pd-complexes and is highly active

in the homogeneous and heterogeneous coupling of aryl

halides, including aryl chlorides. To provide some data

for this hypothesis, heterogeneous supports were

checked for their initial and ﬁnal Pd-content prior to

and after an iodobenzene/styrene coupling reaction by

means of ICP-OES. No change in the Pd-content was

detected within experimental error (10%). This indi-

cates, that (at least major amounts) of the Pd are still

on the carrier. The organic reaction mixture was not

found to be active in a consecutive coupling reaction.

Nevertheless, in contrast to the parent heterogeneous

dipyridyl system, the coupling activity of such a sup-

port was drastically diminished. This suggests that the

polymer supported palladium exists in form of rather

large, free Pd-clusters and not in form of ligated, well-

deﬁned organometallic compounds. So far, this hypoth-

esis is in accordance with the reports of Arai et al., who

found that dissolved Pd-species may ‘reprecipitate’ onto

a support [55,56].

Fig. 6. Time proﬁle for the formation of trans-stilbene in DMF

(T=140°C). (A) Using 18; (B) using 19, (C) using 17.

3. Experimental

3.1. General details

NMR data were obtained in the indicated solvent at

30°C on a Bruker AM 300 and 400, unless stated

otherwise and are listed in parts per million downﬁeld

from tetramethylsilane for proton and carbon. Cou-

pling constants are given in Hertz. IR-spectra were

Fig. 7. Time proﬁle for the formation of trans-stilbene in DMF/

TBAB (T=140°C). (A) Using 19; (B) using 18, (C) using 17.

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

13

recorded on a Nicolet FT-IR. Further instrumentation

for GPC and ICP-OES experiments, is described else-

where [33]. Purchased starting materials were used with-

out any further puriﬁcation. Reagent grade

tetrahydrofuran and toluene were distilled from sodium

benzophenone ketyl under nitrogen. endo-Norborn-2-

ene-5-carboxylic acid chloride [33] and Mo(N-2,6-

Method B: 300–370 mg of the corresponding amine

were dissolved in 4 ml of acetic anhydride. The solution

was stirred at 110°C for 4 h. For work-up, 50 ml of

saturated aqueous sodium bicarbonate solution was

added and the mixture was stirred until no more carbon

dioxide developed. The alkaline solution was extracted

with diethyl ether. The combined organic layers were

dried over sodium sulfate and the solvent was removed

in vacuo. The oily product was puriﬁed by column

chromatography (silica G-60, 2.5×25 cm, diethyl

ether) and repeated crystallization from diethyl ether.

Me₂C₆H₃)(CHCMe₂Ph)(OCMe(CF₃)₂)₂

[57]

were

synthesized as described in the literature. Polymeriza-

tions were carried out in a nitrogen-mediated dry-box

(Braun, Germany). Column chromatography was per-

formed on silica gel 60 (0.063–0.200 mm) from Merck.

3.2. Preparation of amines

3.3.1. N-Pyrid-2-yl-N-(3-methylpyrid-2-yl)amine (1)

Compound 1 was prepared from 3-methylpyrid-2-yl-

amine (1.62 g, 15 mmol) and 2-bromopyridine (1.46 ml,

2.37 g, 15 mmol). Chromatography of the crude

product over silica gel (eluent: petroleum ether (b.p.

40–60°C)/ethyl acetate 2:1) gave a yellow viscous oil,

which did not solidify even after prolonged standing, in

All operations are performed under argon. In a

Schlenk vessel, 15 mmol of a 2-aminopyridine and one

molar equivalent of a 2-halogenpyridine (2-bromopy-

ridine, 2-chlorolepidine or 2-chloro-6-methylpyridine)

are mixed with 62 mg (1 mol%) bis-diphenylphos-

phinopropane, 69 mg (0.5 mol%) dipalladium-tris(ben-

zylideneacetone) Pd₂dba₃and 1.80 g (1.25 equivalents)

sodium-t-butylate. To this mixture 15 ml of dry toluene

is added and heated to 80°C with stirring. For reasons

of safety, pressure should be released after reaching this

temperature by brieﬂy opening the Schlenk valve. After

1 h, usually earlier, the contents of the Schlenk turns

yellow and a solid precipitates. The reaction mixture is

stirred over night for completion and cooled to room

temperature. Depending on the viscosity of the mixture

the solvent is removed in a rotary evaporator or con-

densed into a dry ice trap under vacuum. For work up,

dichloromethane and water are added to the reaction

mixture, the organic phase is washed once with water,

the aqueous phase re-extracted once with a small

amount of dichloromethane. The combined organic

phase is dried over sodium sulfate and the solvents

evaporated to yield the crude product, which is puriﬁed

by the method given in detail below.

1

2.66 g (95%) yield. H-NMR (C₆D₆): l 8.94 (d, 1H,

J=8.4); 8.31 (m, 1H); 8.20 (d, 1H, J=4.9); 7.36 (m,

1H); 7.24 (s, broad, 1H, NH); 6.81 (m, 1H); 6.57 (m,

1H); 6.44 (dd, 1H, J=7.2, J=4.9); 1.57 (s, 3H, Ar–

CH₃). ¹³C-NMR (C₆D₆): l 154.9; 153.5; 148.5; 145.6;

138.0; 137.8; 119.0; 117.3; 116.2; 113.1; 16.8 (Ar–CH₃).

Elemental Anal. Calc. for C₁₁H₁₁N₃(M_w=185.23 g

mol⁻¹): C, 71.33; H, 5.99; N, 22.69. Found: C, 71.70;

H, 6.15; N, 22.42%.

3.3.2. N-Pyrid-2-yl-N-(6-methylpyrid-2-yl)amine (2)

Compound 2 was prepared from 6-methylpyrid-2-yl-

amine (1.62 g, 15 mmol) and 2-bromopyridine (1.46 ml,

2.37 g, 15 mmol). Chromatography of the crude

product over silica gel (eluent: petroleum ether (b.p.

40–60°C)/ethyl acetate 3:1) gave a yellow viscous oil,

which did not solidify even after prolonged standing, in

2.67 g (96%) yield. MS (CI, 70eV): 185 (60) [M⁺]; 184

(100) [M⁺−H]; 170 (3) [M⁺−CH₃]; 78 (15). ¹H-NMR

(C₆D₆): l 8.27 (m, 1H); 7.60 (s, broad, 1H, NH); 7.39

(m, 1H); 7.26 (d, 1H, J=8.2); 7.13 (m, 2H) 6.46

(d×d×d, 1H, J₁=1.2, J₂=5.2, J₃=7.5); 6.42 (d, 1H,

J=7.4), 2.40 (s, 3H, Ar–CH₃). ¹³C-NMR (C₆D₆): l

157.0; 155.1; 154.3; 148.3; 138.1; 137.6; 116.3; 115.7;

112.1; 109.1; 24.6 (Ar–CH₃). Elemental Anal. Calc. for

C₁₁H₁₁N₃(M_w=185.23 g mol⁻¹): C, 71.33; H, 5.99; N,

22.69. Found: C, 71.21; H, 6.19; N, 21.98%.

3.3. Preparation of acetyl deri6ati6es

Method A: the reaction was performed under an

argon atmosphere by standard Schlenk techniques. A

solution of the corresponding amine in 15 ml dry

methylene chloride was cooled to −40°C. Acetyl chlo-

ride was added to the well-stirred solution. The mixture

was slowly warmed to room temperature, and stirred

for an additional 19 h. For work up, the mixture was

extracted with saturated aqueous sodium bicarbonate

solution (until the aqueous layer was alkaline). The

organic layers were dried over sodium sulfate, and the

solvent was removed in vacuo. The formerly oily

product was puriﬁed by repeated crystallization from

diethyl ether.

3.3.3. N-(6-Methylpyrid-2-yl)-N-(4-methylquinolin-

2-yl)amine (3)

Compound 3 was prepared from 6-methylpyrid-2-yl-

amine (1.62 g, 15 mmol) and 2-chloro-4-methylquino-

line (2.67 g, 15 mmol). The crude product was dissolved

in a minimum amount of dichloromethane, layering

14

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

with the double amount of n-pentane and standing for

a few days yields yellow blocky crystals in 2.59 g (69%)

yield. The yield can be improved by treating the mother

liquor again in the same way or by chromatography of

the crude product over silica gel (eluent: petroleum

ether (b.p. 40–60°C)/ethyl acetate 1:1). ¹H-NMR

(CDCl₃): l 8.25 (d, 1H, J=8.3); 7.84 (m, 2H); 7.58 (m,

2H); 7.50 (s, 1H, NH); 7.34 (m, 1H); 7.00 (s, 1H); 6.76

(d, 1H, J=7.5); 2.60 (s, 3H, quin-CH₃); 2.46 (s, 3H,

py-CH₃). ¹³C-NMR (CDCl₃): l 157.0; 153.4; 153.0;

147.6; 146.0; 138.8; 136.1; 129.8; 128.1; 125.2; 124.0;

123.8; 117.0; 114.1; 109.8; 24.6; 19.3. Elemental Anal.

Calc. for C₁₆H₁₅N₃(M_w=249.31 g mol⁻¹): C, 77.08;

H, 6.06; N, 16.85. Found: C, 77.01; H, 6.05; N, 16.73%.

70% yield (147 mg). IR (KBr, cm⁻¹): 3109m, 3053m,

3001m, 2928m, 1688vs (w_CꢀO), 1587s, 1575s, 1457s,

1433s, 1365s, 1305s, 1272s, 1219s, 1150s, 1098m,

1021m, 993m, 807m, 779s, 625m, 554m, 525m, 410m;

¹H-NMR (CDCl₃): l 8.40 (m, broad, 1H), 7.62 (m,

3H), 7.08 (m, 3H), 2.49 (s, 3H, Ar–CH₃), 2.12 (s, 3H,

CH₃CO); ¹³C-NMR (CDCl₃): l 170.9 (CO), 158.4,

154.6, 154.0, 148.6, 138.3, 137.8, 121.8, 121.5, 119.4,

24.6 (CH₃CO), 24.2 (Ar–CH₃). Elemental Anal. Calc.

for C₁₃H₁₃N₃O (M_w=227.27 g mol⁻¹): C, 68.71; H,

5.77; N, 18.49. Found: C, 68.53; H, 5.75; N, 18.40%.

3.3.7. N-(6-Methylpyrid-2-yl)-N-(4-methylquinolin-

2-yl) acetamide (7)

Compound 7 was prepared according to method B

from N-(6-methylpyrid-2-yl)-N-(4-methylquinolin-2-yl)

amine (370 mg, 1.5 mmol) in 72% yield (309 mg). IR

3.3.4. N-bis(6-Methylpyrid-2-yl)amine (4)

Compound 4 was prepared from 6-methylpyrid-2-yl-

amine (1.62 g, 15 mmol) and 2-chloro-6-methylpyridine

(1.64 ml, 1.91 g, 15 mmol). The crude oily product

solidiﬁes on standing over night. Melting in vacuum (1

mbar) and cooling gives after resolidiﬁcation a brown-

ish solid, 2.99 g (quantitative), which is sufﬁciently pure

for further work. For elemental analysis an analytical

sample was puriﬁed by chromatography over silica gel

(eluent: petroleum ether (b.p. 40–60°C)/ethyl acetate

2:1). ¹H-NMR l (C₆D₆, Bruker 400MHz): 8.25 (s,

broad, 1H, NH); 7.37 (d, 2H, J=8.3); 7.14 (t, 2H,

J=7.5); 6.42 (d, 2H, J=7.1); 2.40 (s, 6H, CH₃). ¹³C-

NMR (C₆D₆): l 156.7; 154.4; 137.8; 115.3; 108.8; 24.3.

Elemental Anal. Calc. for C₁₂H₁₃N₃(M_w=199.25 g

mol⁻¹): C, 72.33; H, 6.58; N, 21.09. Found C, 72.10;

H, 6.62; N, 20.88%.

1

(KBr, cm⁻¹): H-NMR (CDCl₃): l 7.95 (m, 2H), 7.65

(m, 2H), 7.54 (m, 1H), 7.34 (s, 1H), 7.25 (d, 1H,

J=7.9), 7.08 (d, 1H, J=7.5), 2.68 (s, 3H, quin-CH₃),

2.50 (s, 3H, py-CH₃), 2.24 (s, 3H, CH₃CO). ¹³C-NMR

(CDCl₃): l 171.4 (CO), 158.3, 153.9, 153.7, 146.9,

146.4, 138.2, 129.6, 129.3, 126.9, 126.3, 123.6, 121.7,

120.4, 119.3, 24.7 (CH₃CO), 24.2 (py-CH₃), 18.8 (quin-

CH₃).

3.3.8. N,N-Bis-(6-methylpyrid-2-yl) acetamide (8)

Compound 8 was prepared according to method B

from bis-(6-methylpyrid-2-yl) amine (327 mg, 1.6

mmol) in 90% yield (358 mg). IR (KBr, cm⁻¹): 1688vs

(w_CꢀO), 1594s, 1566s, 1457s, 1364s, 1304s, 11261m,

1169m, 1032m, 1001m, 820m, 789m, 746m, 654m,

1

629m, 558m, 546m, 407m. H-NMR (CDCl₃): l 7.59

3.3.5. N-Pyrid-2-yl-N-(3-methylpyrid-2-yl) acetamide

(5)

(d×d, 2H, J₁=7.9, J₂=7.5), 7.19 (d, 2H, J=7.9),

7.02 (d, 2H, J=7.5), 2.47 (s, 6H, Ar–CH₃), 2.14 (s, 3H,

CH₃CO). ¹³C-NMR (CDCl₃): l 171.0 (CO), 158.1,

154.0, 138.1, 121.4, 118.9, 24.5 (CH₃CO), 24.2 (Ar–

CH₃). Elemental Anal. Calc. for C₁₄H₁₅N₃O (M_w=

241.29 g mol⁻¹): C, 69.69; H, 6.27; N, 17.41; found: C,

69.35, H, 6.13, N, 17.35%.

Compound 5 was prepared according to method A

from acetyl chloride (1 ml, 14 mmol) and N-pyrid-2-yl-

N-(3-methylpyrid-2-yl)amine (460 mg, 2.5 mmol) in

36% yield (100 mg). IR (KBr, cm⁻¹): 3066w, 2985w,

2954w, 1692vs (w_CꢀO),1576s, 1466s, 1438s, 1370s, 1328s,

1302vs, 1264s, 1156s, 1123m, 1023m, 1007m, 985w,

816m, 780s, 743m, 656m, 602s, 525m. ¹H-NMR

(CDCl₃): l 8.41 (m, 1H), 8.28 (d, broad, 1H, J=4.5),

7.68 (m, 3H), 7.25 (m, 1H), 7.04 (m, 1H), 2.20 (s, 3H,

Ar–CH₃), 2.03 (s, 3H, CH₃CO). ¹³C-NMR (CDCl₃): l

170.6 (CO), 153.8, 148.2, 147.3, 140.0, 137.7, 132.2,

123.7, 120.6, 119.5, 24.3 (CH₃CO), 17.5 (CH₃Ar). Ele-

mental Anal. Calc. for C₁₃H₁₃N₃O (M_w=227.27 g

mol⁻¹): C, 68.71; H, 5.77; N, 18.49. Found: C, 68.95;

H, 5.76; N, 18.47%.

3.4. Preparation of homogenous Pd-catalysts

A solution of sodium hydroxide (15%) was added to

a solution of palladium(II) chloride in conc. hydrochlo-

ric acid (1 ml) to adjust to a pH of roughly 5. A

solution of the corresponding acetyl-derivative in

methanol (3 ml) was added to the well-stirred solution.

A yellow crystalline solid formed which was ﬁltered off,

washed with methanol and diethyl ether and dried in

vacuo.

3.3.6. N-Pyrid-2-yl-N-(6-methylpyrid-2-yl) acetamide

(6)

Compound 6 was prepared according to method A

from acetyl chloride (1 ml, 14 mmol) and N-pyrid-2-yl-

N-(6-methylpyrid-2-yl) amine (340 mg, 1.8 mmol) in

3.4.1. N-Acetyl-N-pyrid-2-yl-N-(3-methylpyrid-

2-yl)amine palladium dichloride (13)

Compound 13 was synthesized from 5 (62 mg, 0.27

mmol) and palladium(II) chloride (48 mg, 0.27 mmol)

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

15

in 58% yield (64 mg). IR (KBr, cm⁻¹): 3099w, 2962w,

in 90% yield (63 mg). IR (KBr, cm⁻¹): 1711 (w_CꢀO),

1606s, 1565m, 1467s, 1371s, 1296s, 1262s, 1248s,

1167m, 1096m, 1032m, 951m, 866m, 808m, 754m,

2913w, 1700vs (w_CꢀO), 1603s, 1461, 1372s, 1302s, 1279s,

1

1229m, 1135m, 1040m, 1023m, 795s, 595m; H-NMR

1

(DMSO-d₆): l 8.82 (d, 1H, J 0 5.3), 8.62 (d, 1H,

J=5.6), 8.29 (m, 2H), 8.11 (d, 1H, J=7.5), 7.72 (m,

1H), 7.59 (m, 1H), 2.41 (s, 3H, Ar–CH₃), 2.28 (s, 3H,

CH₃CO); ¹³C-NMR (DMSO-d₆): l 168.3 (CO), 153.3,

150.5, 148.5, 146.9, 143.4, 143.3, 135.1, 126.3, 126.1,

125.6, 22.6 (CH₃CO), 17.0 (Ar–CH₃). Elemental Anal.

Calc. for C₁₃H₁₃N₃OPdCl₂(M_w=404.59 g mol⁻¹): C,

38.59; H, 3.24; N, 10.39. Found: C, 38.79; H, 3.27; N,

10.26%. Single crystals suitable for X-ray analysis were

obtained by crystallization from methylene chloride/

THF.

626m, 607m. H-NMR (DMSO-d₆): l 8.11 (d×d, 2H,

J₁=7.9, J₂=7.9), 8.03–7.86 (s, broad, 2H), 7.55 (d,

broad, 2H, J=7.1), 3.07 (s, 6H, Ar–CH₃), 2.41 (s, 3H,

COCH₃). ¹³C-NMR (DMSO-d₆): l 168.3 (CO), 162.0,

133.7, 126.1, 122.3, 26.1 (Ar–CH₃), 23.0 (COCH₃).

Elemental Anal. Calc. for C₁₄H₁₅N₃OPdCl₂(M_w=

418.62g mol⁻¹): C, 40.17, H, 3.61, N, 10.04. Found: C,

40.09, H, 3.56, N, 9.89%.

3.5. Preparation of norbornene-based monomers

Reactions were performed under an argon atmo-

sphere by standard Schlenk techniques. A solution of

the corresponding amine in 10 ml of dry methylene

chloride was cooled to −40°C. endo-Norborn-2-ene-5-

carboxylic acid chloride was added to the well-stirred

solution. The mixture was warmed slowly to room

temperature and stirred for additional 18 h. For work

up, 20 ml of saturated aqueous sodium bicarbonate

solution were added and the mixture was stirred until

no more carbon dioxide was developed. The alkaline

solution was extracted with methylene chloride. The

combined organic layers were dried over sodium sul-

fate, and the solvent was removed in vacuo. The re-

maining brown residue was dissolved in diethyl ether

and the product was isolated by column chromatogra-

phy (silica G-60, 2.5×25 cm, diethyl ether) and

puriﬁed by repeated crystallization from diethyl ether.

3.4.2. N-Acetyl-N-pyrid-2-yl-N-(6-methylpyrid-

2-yl)amine palladium dichloride (14)

Compound 14 was synthesized from 6 (57 mg, 0.32

mmol) and palladium(II) chloride (56.8 mg, 0.32 mmol)

in 89% yield (115 mg). IR (KBr, cm⁻¹): 3073w, 2925m,

1712vs (w_CꢀO), 1604s, 1572m, 1469vs, 1444m, 1371s,

1283s, 1252s, 1168m, 1158m, 1035m, 803m, 774m,

757m, 670m, 615m, 602m, 558m. ¹H-NMR (DMSO-

d₆): l 8.65 (d, 1H, J=5.7), 8.25 (m, 1H, J=7.5), 8.16

(m, 1H), 7.93 (m, broad, 2H), 7.65 (m, 1H), 7.55 (d,

1H, J=8.3), 3.11 (s, 3H, Ar–CH₃), 2.36 (s, 3H,

CH₃CO). ¹³C-NMR (DMSO-d₆): l 168.4 (CO), 162.3,

152.7, 148.7, 148.5, 142.3, 141.9, 126.3, 125.6, 125.3,

122.4, 26.5 (Ar–CH₃), 22.8 (CH₃CO). Elemental Anal.

Calc. for C₁₃H₁₃N₃OPdCl₂(M_w=404.59 g mol⁻¹): C,

38.59; H, 3.24; N, 10.39. Found: C, 38.36; H, 3.19; N,

10.17%. Single crystals suitable for X-ray analysis were

obtained by crystallization from methylene chloride/

THF.

3.5.1. N-Pyrid-2-yl-N-(3-methylpyrid-2-yl)-

endo-norborn-2-ene-5-carbamide (9)

Compound 9 was prepared from 1 (377 mg, 2.0

mmol) and norborn-2-ene carboxylic chloride (1 ml, 7

mol) in 80% yield (251 mg). IR (KBr, cm⁻¹): 3050m,

2979m, 2932m, 2864m, 1680vs (w_CꢀO), 1572s, 1434s,

1357s, 1310s, 1248s, 1204s, 1119m, 1025m, 990m, 794m,

768m, 768s, 712s, 641m. ¹H-NMR (CDCl₃): l 8.44

(d×d, 1H, J₁=4.9, J₂=1.5), 8.29 (d (broad), 1H,

J=4.9), 7.63 (m, 3H), 7.23 (m, 1H), 7.03 (m, 1H), 6.21

(d×d, 1H, J₁=5.7, J₂=3.0, H₂), 6.11 (d×d, 1H,

J₁=5.7, J₂=3.0, H₃), 3.11 (m (broad), 2H, H_4,5), 2.80

(s (broad), 1H, H₁), 2.16 (s, 3H, CH₃), 1.50 (m (broad),

2H, H_6a,b), 1.29 (m, 1H, H_7a), 1.04 (d (broad), 1H,

J=8.3, H_7b). ¹³C-NMR (CDCl₃): l 174.9 (CO), 154.3,

153.8, 148.3, 147.1, 139.8, 137.4, 137.1, 132.6, 132.2,

123.4, 120.5, 120.4, 49.6, 45.9, 44.4, 42.7, 30.4, 17.8

(CH₃). Elemental Anal. Calc. for C₁₉H₁₉N₃O (M_w=

305.38 g mol⁻¹): C, 74.73; H, 6.27; N, 13.76. Found: C,

74.59; H, 6.31; N, 13.79%. Single crystals suitable for

X-ray analysis may be obtained by crystallization from

diethyl ether.

3.4.3. N-Acetyl-N-(6-methylpyrid-2-yl)-N-

(4-methylquinolin-2-yl)amine palladium dichloride (15)

Compound 15 was synthesized from 7 (105 mg, 0.36

mmol) and palladium(II) chloride (64 mg, 0.36 mmol)

in 83% yield (146 mg). IR (KBr, cm⁻¹): 1707vs (w_CꢀO),

1594s, 1565s, 1512m, 1469s, 1414m, 1367s, 1341s,

1311m, 1278m, 1251m, 1171m, 1033m, 982m, 798m,

1

762s, 634m, 607m. H-NMR (DMSO-d₆): l 9.04 (d (b),

1H, J=8.7), 7.99 (m, 4H), 7.75 (m, 2H), 7.49 (d (b),

1H, J=7.9), 3.10 (s, 3H, py-CH₃), 2.81 (s, 3H, quin-

CH₃), 2.49 (s, 3H, CH₃CO). ¹³C-NMR (DMSO-d₆): l

168.4 (CO), 162.0, 149.9, 148.4, 144.4, 141.9, 131.2,

128.7, 127.8, 126.4 (2 C), 124.7, 124.1, 122.2, 26.3

(py-CH₃), 23.3 (CH₃CO), 18.2 (quin -CH₃).

3.4.4. N-Acetyl-N,N-bis(6-methylpyrid-2-yl)amine

palladium dichloride (16)

Compound 16 was synthesized from 8 (29.5 mg, 0.17

mmol) and palladium(II) chloride (40.0 mg, 0.17 mmol)

16

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

3.5.2. N-Pyrid-2-yl-N-(6-methylpyrid-2-yl)-

diethyl ether, ﬁltered off and dried in vacuo. The ob-

endo-norborn-2-ene-5-carbamide (10)

tained yields were \80%.

Compound 10 was prepared from 2 (500 mg, 2.7

mmol) and norborn-2-ene carboxylic chloride (0.4 ml, 4

mol) in 38% yield (157 mg). IR (KBr, cm⁻¹): 3063m,

2979m, 2938w, 2872m, 1673vs (w_CꢀO), 1657s, 1589s,

1574s, 1565s, 1455s, 1432s, 1377s, 1338s, 1313s, 1264s,

1223s, 1153s, 1093m, 996m, 910m, 836m, 790s, 760s,

3.6.1. Poly-9

M_w=6400, PDI=1.16; ¹H-NMR (CDCl₃): l 8.33

(broad, 1H), 8.25 (broad, 1H), 7.66 (broad, 1H),

7.57(broad, 2H), 7.18 (broad, 1H), 7.66 (d, broad, 1H,

J=7.5), 5.62 (broad, 1H), 5.40 (broad, 1H), 4.13 (m),

4.04 (s) (Cp), 2.79 (broad, 1H), 2.61 (broad, 2H), 2.06

(broad, 3H), 1.89 (broad, 2H), 1.46 (broad, 1H), 1.26

(d, J=6.8) (CHCMe₂Ph) (90% cis). ¹³C-NMR

(CDCl₃): l 175.1 (CO), 154.1, 148.2, 146.9, 139.9,

137.5, 134.3, 132.0, 130.2, 127.8, 126.3, 123.3, 122.7,

120.8, 69.0 (Cp), 47.7, 41.8, 40.5, 37.4, 27.9, 18.0 (CH₃).

1

714s, 695m. H-NMR (CDCl₃): l 8.41 (m, 1H), 7.66

(m, 2H), 7.50 (d (broad), 1H, J=8.3), 7.11 (m, 3H),

6.22 (d×d, 1H, J₁=5.7, J₂=3.0, H₂), 6.13 (d×d,

J₁=5.7, J₂=3.0, H₃), 3.26 (m, 1H, H₅), 2.94 (s

(broad), 1H, H₄), 2.82 (s (broad), 1H, H₁), 2.51 (s, 3H,

CH₃), 1.54 (m, 2H, H_6a,b), 1.30 (m, 1H, H_7a), 1.08 (m,

1H, J=8.3, H_7b). ¹³C-NMR (CDCl₃): l 175.1 (CO),

158.3, 155.0, 154.1, 148.6, 138.0, 137.5, 137.0, 132.6,

122.0, 121.5, 121.2, 119.8, 49.6, 46.1, 44.4, 42.8, 30.9,

24.3 (CH₃). Elemental Anal. Calc. for C₁₉H₁₉N₃O

(M_w=305.38 g mol⁻¹): C, 74.73; H, 6.27; N, 13.76.

Found: C, 74.60; H, 6.24; N, 13.79%.

3.6.2. Poly-10

M_w=7500, PDI=1.19; ¹H-NMR (CDCl₃): l 8.34

(broad, 1H), 7.58 (m, broad, 3H), 7.57(broad, 2H), 7.01

(m, broad, 1H), 5.54 (broad, 1H), 5.40 (broad, 1H),

4.13 (m), 4.02 (s) (Cp), 3.10 (broad, 1H), 2.76 (broad,

1H), 2.54 (broad, 1H), 2.40 (broad, 3H), 1.92 (broad,

2H), 1.81 (broad, 1H), 1.37 (broad, 1H), 1.26 (d, J=

6.8) (CHCMe₂Ph) (80% cis). ¹³C-NMR (CDCl₃): l

174.8(CO), 158.2, 154.8, 154.1, 148.6, 138.2, 137.6,

133.9, 130.6, 122.2, 121.6, 119.8, 47.6, 41.8, 37.8, 37.4,

27.9, 24.3 (CH₃).

3.5.3. N-(6-Methylpyrid-2-yl)-N-(4-methylquinolin-

2-yl)-endo-norborn-2-ene-5-carbamide (11)

Compound 11 was prepared from 3 (500 mg, 2.0

mmol) and norborn-2-ene carboxylic chloride (2.0 ml,

13 mol) in 60% yield (220 mg). IR (KBr, cm⁻¹):

3072m, 2966m, 2931m, 2854m, 1673vs (w_CꢀO), 1595s,

1569s, 1509s, 1455s, 1343s, 1278s, 1245s, 1220s, 1187m,

3.6.3. Poly-11

M_w=14300, PDI=1.38; H-NMR (CDCl₃): l 7.85

1

1016m, 837m, 769s, 719s, 616w. H-NMR (CDCl₃): l

(broad, 1H), 7.72 (m, broad, 1H), 7.53(broad, 1H), 7.44

(broad, 2H), 7.44 (m, broad, 3H), 5.58 (broad, 1H),

5.41 (broad, 1H), 4.02 (s) (Cp), 3.27 (broad, 1H), 2.75

(broad, 1H), 2.55 (s, broad, 3H) (CH₃), 2.31 (s, broad,

3H) (CH₃), 2.00 (broad, 2H), 1.79 (broad, 2H), 1.32

(broad, 1H), 1.25 (d, J=6.8) (CHCMe₂Ph) (80% cis).

¹³C-NMR (CDCl₃): l 175.3 (CO), 158.0, 154.0, 146.9,

146.0, 138.0, 137.5, 134.1, 130.7, 129.4, 129.1, 126.9,

126.1, 123.7, 121.4, 120.8, 119.8, 47.9, 41.8, 40.2, 37.4,

24.2(CH₃), 18.9(CH₃).

7.92 (m, 2H), 7.61 (m, 2H), 7.51 (m, 1H), 7.26 (d

(broad), 1H, J=8.3), 7.19 (d (broad), 1H, J=7.9), 7.03

(d (broad), 1H, J=7.5), 6.22 (d×d, 1H, J₁=5.7,

J₂=3.0, H₂), 6.15 (d×d, J₁=5.7, J₂=3.0, H₃), 3.42

(m, 1H, H₅), 3.01 (s (broad), 1H, H₄), 2.79 (s (broad),

1H, H₁), 2.66 (s, 3H, CH₃), 2.47 (s, 3H, CH₃), 1.54 (m,

2H, H_6a,b), 1.28 (m, 1H, H_7a), 1.06 (m, 1H, J=7.9,

H_7b). ¹³C-NMR (CDCl₃): l 175.7 (CO), 158.1, 154.0,

146.9, 145.8, 137.8, 137.0, 132.7, 129.6, 129.1, 126.8,

126.0, 123.5, 121.3, 120.7, 119.7, 49.6, 46.2, 44.5, 42.8,

31.0, 24.2 (CH₃), 18.8 (CH₃). Elemental Anal. Calc. for

C₂₄H₂₃N₃O (M_w=369.47 g mol⁻¹): C, 78.02; H, 6.27;

N, 11.37. Found: C, 77.86; H, 6.31; N, 11.28%. Single

crystals suitable for X-ray analysis may be obtained by

crystallization from diethyl ether.

3.7. Preparation of the resins

Resins were synthesized according to a previously

published procedure [29,33].

3.6. Preparation of linear polymers

3.8. Loading of heterogeneous Pd-catalysts

The corresponding monomer (20 mg) was dissolved

in dry methylene chloride. The initiator (Mo(N-2,6-i-

Pr₂C₆H₃)(CHCMe₂Ph)(OCMe(CF₃)₂)₂, 3 mg, 3.9 mmol,

dissolved in 1 ml of methylene chloride) was added to

the well-stirred solution. After stirring for 3 h, ferrocene

carboxaldehyde (about tenfold excess based on initia-

tor) was added, and stirring was continued for 1 h.

Finally, the polymer was precipitated by an excess of

Water (5 ml) was added to a solution of palladiu-

m(II) chloride (1.5-fold excess based on the total

amount of ligand attached to the support) in conc.

hydrochloric acid (1 ml). A solution of sodium hydrox-

ide (15%) was carefully added to adjust to a pH of 5.

After addition of ca. 5 ml of methanol, the cross-linked

polymer was added and the suspension was stirred for

20 h. The resin was ﬁltered off, washed with water and

J. Silberg et al. / Journal of Organometallic Chemistry 622 (2001) 6–18

17

dried in vacuo. The actual amount of palladium(II)

sorbed onto the resin was determined by ICP-OES.

tized Mo–Ka radiation (u=71.073 pm). Intensities were

measured via ꢀ-scans and corrected for Lorentz and

polarization effects. Compounds 13 and 14 were mea-

sured on a Nonius Kappa CCD area-detector diffrac-

tometer (u=71.073 pm) with the CCD detector placed

36 mm from the crystal via a mixture of 2 (13) or 1.3°

(14) and ꢀ-scans. The raw data were processed with

the program ^DENZO-SMN[58] to obtain conventional

3.9. Heck-couplings/aminations

Unless stated otherwise, couplings were carried out at

T=140°C on a 2–4-g scale in the solvent indicated in

Table 3. Solvents and reagents were used as purchased.

The educts were dissolved in 10–30 ml of solvent and the

base (tri-n-butylamine, K₂CO₃, Na₂CO₃) as well as the

catalyst were added. For aminations, the aryl halide and

the amine were dissolved in dry THF, the base as well

as the catalyst were added. Reactions were carried out

at 65°C. The reaction time was 90 h throughout. Reac-

tion times as well as a summary of the experiments

including the corresponding scales and molar ratios are

given in Table 3. Yields were determined from the educts:

data. Structures were solved by direct methods (SHELXS

-

86) [59] and reﬁned by full matrix least-squares against

F²

(SHELXL-93) [60]. The function minimized was

ꢀ[w(F²_o−F²_c)²] with the weight deﬁned as w⁻¹

=

[|²(F_o²)+(xP)²+yP] and P=(F_o²+2F²_c)/3. All non-hy-

drogen atoms were reﬁned with anisotropic displacement

parameters. All hydrogen atoms were located by differ-

ence Fourier methods, but in the reﬁnement they were

generated geometrically and reﬁned with isotropic dis-

placement parameters 1.2 times and 1.5 (for the methyl-

group) higher than U_eqof the attached carbon atoms. In

compound 11, the norborn-2-enyl-group was distorted in

ratio 0.7:0.3 by replacement of the enantiomeric group

at the same position; for 13, the solvent molecules (THF)

were disordered in three, partially overlaying positions in

the ratio 0.6:0.2:0.2. Single crystals of 14 were character-

ized by high mosaicity and had two molecules in the

asymmetric unit. The well-ordered molecule was used to

discuss bond distances and angles. The second molecule

was disordered 1:1 by the position of the methyl group

in a way that each pyridyl-group had half a methyl-

group. The carbon atom at this disordered position had

to be reﬁned isotropically. The relevant crystallographic

data are summarized in Table 1.

1

product ratio that was determined by H-NMR-spec-

troscopy via integration of the o-H signals of the stilbene

derivative and the aryliodide, respectively. For work-up,

the reaction mixture was poured on water, acidiﬁed with

hydrochloric acid (2 N) and extracted with diethyl ether

(4×50 ml). The combined organic phases were dried

over sodium sulfate. Finally, the solvent and (where

applicable) the reactants were evaporated in vacuo. The

coupling products were isolated by ﬂash chromatogra-

phy (silica G-60, 4×30 cm, pentane:diethyl ether=

90:10) and repeated crystallization. Purity of the

1

corresponding crops was determined by H-NMR.

3.10. Time proﬁles for the formation of trans-stilbene

(A) Standard procedure: a mixture of iodobenzene (1.5

g), styrene (0.77 g), Bu₃N (3 ml) and the Pd catalyst

(0.0027 mol% Pd(II) based on styrene) in dimethyl

formamide (DMF) was stirred at 140°C. The time-depen-

dent yield was calculated from the educt:product ratio

4. Summary

A series of methyl-substituted pyridyl and quinoyl-

based ligands have been synthesized. Heterogeneous

catalytic systems have been prepared therefrom via

ring-opening metathesis precipitation polymerization.

Subsequent loading with palladium(II) resulted in poly-

mer-immobilized palladium catalysts. The high afﬁnity

of the dipyridyl amides for Pd was found to be reduced

by the presence of additional methyl groups which leads

to a less favorable distorted square planar ligand sphere

around Pd. Consequently, compared to the parent

dipyridylamide-based supports, Pd-loadings of the

methyl-substituted pyridyl and quinoyl-based supports

were lowered by almost a factor of 10. Nevertheless, these

systems may still be used in Heck-type couplings of

aryliodides and bromides as well as for the amination of

arylbromides.

1

which was determined by H-NMR spectroscopy. (B)

Tetrabutylammonium bromide (Bu₄NBr, 0.5 g) was

added to the standard mixture. (C) Reaction was per-

formed in dimethyl acetamide (DMAC).

3.11. Dissociation constants

Values for K_D(equilibrium constant for dissociation,

deﬁned as L₂PdCl₂L₂+PdCl₂) were determined by

NMR spectroscopy in dmso-d₆via integration of the

signals for the methyl groups of the complex and the free

ligand and comparison with an internal standard

(Me₄Si).

3.12. X-ray measurement and structure determination

of compounds 9, 11, 13, 14

5. Supplementary material

Data for compounds 9 and 11 were collected on a

Bruker P4 diffractometer with graphite-monochroma-

Crystallographic data for the structural analysis have

been deposited with the Cambridge Crystallographic

18

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Article Doi

N-Acyl-N,N-dipyridyl and N-acyl-N-pyridyl-N-quinoyl amine based palladium complexes. Synthesis, X-ray structures, heterogenization and use in Heck couplings

DOI: 10.1016/S0022-328X(00)00783-X

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