Dipyridylamine ligands - Synthesis, coordination chemistry of the group 10 metals and application of nickel complexes in ethylene oligomerization

Article abstract of DOI:10.1002/1099-0682(200109)2001:9<2421::AID-EJIC2421>3.0.CO;2-6

A great variety of 2,2′-bipyridylamines can be synthesized starting from primary amines or 2-aminopyridines (for instance, symmetrically and unsymmetrically substituted as well as chiral ligands) by palladium-catalyzed aryl amination. The reaction of such ligands with [PdCl₂(COD)] or [NiBr₂(DME)] (COD = cycloocta-1,5-diene; DME = 1,2-dimethoxyethane) led to the corresponding dichloro or dibromo complexes. The results of X-ray crystal structure analyses of selected compounds show that the ligands coordinate through the two pyridine N-atoms. Their palladium complexes have a slightly distorted planar coordination (in the case of nickel a distorted tetrahedral coordination), with N-M-N angles of 96.0(2)° (M = Ni) and 85.7° (averaged, M = Pd). The nickel complexes are highly active ethylene oligomerization catalysts if activated with Et₃Al₂Cl₃.

Full text of DOI:10.1002/1099-0682(200109)2001:9<2421::AID-EJIC2421>3.0.CO;2-6

FULL PAPER
Dipyridylamine Ligands ؊ Synthesis, Coordination Chemistry of the Group 10
Metals and Application of Nickel Complexes in Ethylene Oligomerization
Thomas Schareina,[a] Gerhard Hillebrand,[a] Hans Fuhrmann,[a] and Rhett Kempe*[a]
Keywords: N ligands / Nickel / Palladium / Polymerization / Catalysis
A great variety of 2,2Ј-bipyridylamines can be synthesized
starting from primary amines or 2-aminopyridines (for in-
selected compounds show that the ligands coordinate
through the two pyridine N-atoms. Their palladium com-
stance, symmetrically and unsymmetrically substituted as plexes have a slightly distorted planar coordination (in the
well as chiral ligands) by palladium-catalyzed aryl amin- case of nickel a distorted tetrahedral coordination), with
ation. The reaction of such ligands with [PdCl2(COD)] or
[NiBr2(DME)] (COD = cycloocta-1,5-diene; DME = 1,2-dime-
thoxyethane) led to the corresponding dichloro or dibromo
complexes. The results of X-ray crystal structure analyses of
N−M−N angles of 96.0(2)° (M = Ni) and 85.7° (averaged, M =
Pd). The nickel complexes are highly active ethylene oligo-
merization catalysts if activated with Et3Al2Cl3.
Introduction
2,2Ј-Bipyridylamines are accessible by sequential palla-
dium-catalyzed aryl amination reactions starting from a
primary amine[1,2] (Scheme 1, above). Such compounds
have three sites where coordination to a transition metal
may occur: the two pyridine moieties and the amine func-
tion. Since the amine N-atom can only bind in a strained
fashion together with one or two pyridyl units, such ligands
act as bidentate chelates with binding only to the pyridyls.
In contrast to the classical 2,2Ј-bipyridine type ligand,
which was described recently as the most widely used li-
gand,[3] six-membered rings are formed (Scheme 1, below).
Recently N-ligands have received much attention,[4] as bipy-
ridylamines might be an interesting alternative to diphos-
phane or diimine ligands, the latter of which has recently
attracted considerable interest in regard to its combination
with the group 10 metals as olefin polymerisation cata-
lysts.[5,6] Due to the great variety of substitution patterns
which can be easily established for the bipyridylamines
(variation of R, RЈ and RЈЈ, Scheme 1) it may be possible
to fine-tune transition metal complex reactivity. To the best
of our knowledge, work on applications of bipyridylamine
ligand complexes in olefin polymerization has not been
published yet.[6] The coordination chemistry of the simplest
member of the bipyridylamine group, the 2,2Ј-dipyridylam-
ine (commercially available), has been described in detail
for copper.[7] However, compounds of other transition
metals such as complexes of the chromium triad,[8] of rhod-
ium,[9] cobalt,[10] nickel,[11] palladium,[12] ruthenium,[13] and
cadmium[14] are much rarer. In this article we report on the
ligand synthesis and coordination chemical studies of novel
bipyridylamines, as well as some applications of the synthe-
sized nickel complexes in ethylene oligomerization.
Scheme 1. Synthesis of bipyridylamines and the coordination mode
of these ligands in transition metal complexes (R, RЈ, RЈЈ ϭ alkyl,
aryl substituents; X ϭ Cl, Br; L ϭ additional ligands)
Results and Discussion
Ligand Syntheses
Palladium-catalyzed arylϪX activation (X ϭ I, Br or Cl)
reactions are an efficient tool for the synthesis of bi- and
triarylamines by CϪN bond formation.[1] If 2-X-pyridines
are used X can be Cl as the systems are activated, although
the formation of catalyst-deactivating palladium pyridine
complexes has to be avoided. In order to prevent this the
palladium catalyst has to be stabilized by chelating bisphos-
phane ligands.[1a] Reactions of 2-aminopyridines with one
or two equivalents of the corresponding 2-halopyridines
and 1.25 or 2.5 equiv. of sodium-tert-butoxide in the pres-
ence of 1 mol % 1,3-bis(diphenylphosphanyl)propane and
0.5 mol % Pd2dba3 in toluene at 80 °C leads, usually after
less than one hour, to a color change to yellow. After stir-
ring for an additional 12 hours, work up with dichlorome-
[a]
Institut für Organische Katalyseforschung (IfOK),
Buchbinderstraße 5Ϫ6, 18055 Rostock, Germany
Eur. J. Inorg. Chem. 2001, 2421Ϫ2426
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0909Ϫ2421 $ 17.50ϩ.50/0
2421

T. Schareina, G. Hillebrand, H. Fuhrmann, R. Kempe
FULL PAPER
thane, or ether, and water followed. The compounds were ideal tetrahedral angle, although still far from the ideal
purified by chromatography, distillation or crystallization. value.
Compound 1 was prepared from 2,6-diisopropylaniline,
compound 2 from 2-(benzylamino)-4-methylpyridine, com-
pound 3 from 2-(benzylamino)-6-methylpyridine, com-
pound 4 from 2-pyridylaniline and compound 5 from (S)-
1-phenylethylamine (Scheme 2).
Scheme 4. Synthesized Ni and Pd complexes, including numbering
Scheme 2. The bipyridylamine ligands used, including numbering
Group 10 Metal Complex Syntheses and Structures
The reaction of 1, 3 and 4 with [NiBr2(DME)] (DME ϭ
dimethoxyethane) gave rise to blue- or purple-colored crys-
talline materials (Scheme 3). The structures of all the syn-
thesized group 10 metal complexes are summarized in
Scheme 4. NMR investigation of 6, 8 and 9 gave rather
broad signals indicating the existence of d8 high-spin com-
˚
plexes. EPR spectra in dilute CH2Cl2 solutions could not
be recorded either at room or at lower temperatures. Single
crystals of 8 suitable for an X-ray crystal structure analysis
(Figure 1) could be grown from a CH2Cl2 solution; crystal-
lographic details are listed in Table 1. The coordination of
the nickel center is best described as tetrahedral as observed
for dibromodipyridylnickel(II) complexes[15] {dibromodi-
pyridylnickel(II) ϭ [NiBr2(dipy)]}. The NiϪNpyridine bond
Figure 1. Molecular structure of 7; selected bond lengths [A] and
angles [°]: N1ϪPd1 2.032(3), N2ϪPd1 2.012(3), Cl1ϪPd1
2.3033(11), Cl2ϪPd1 2.2980(10), N2ϪPd1ϪN1 84.82(11),
N2ϪPd1ϪCl2 91.80(8), N1ϪPd1ϪCl2 173.83(8), N2ϪPd1ϪCl1
170.54(8), N1ϪPd1ϪCl1 92.79(8), Cl2ϪPd1ϪCl1 91.36(4)
The reaction of 2 and 5 with [PdCl2(COD)] (COD ϭ
cycloocta-1,5-diene) gave rise to yellow crystalline materials
(Scheme 3). NMR investigation of 2 and 5 revealed a sharp
single signal set suggesting the existence of monomeric dia-
magnetic species in solution. The X-ray crystal structure
analyses of both compounds confirm these complexes to be
mononuclear in the solid state as well; crystallographic de-
tails are listed in Table 1. The coordination of the palladium
centers is best described as square planar, in contrast to
the nickel compounds but well in agreement with what was
observed previously for dipyridyldichloropalladium(II)
˚
lengths of 8 (mean ϭ 1.99 A) are well in accordance with
˚
those observed for (dipy)NiBr2 complexes (mean ϭ 2.00 A).
The NϪNiϪN angle in 8 [96.0(2)°] is significant larger than
that observed in [NiBr2(dipy)] complexes (mean ϭ 82.8°).
Thus it can be concluded that the bipyridylamine-type li-
gands may favor tetrahedral coordination, similar to bipyri-
dyl ligands, since the six-membered chelate is closer to the
complexes {dichlorodipyridylpalladium(II)
ϭ
[PdCl2-
(dipy)]}. A CSD[16] search for [PdCl2(dipy)] complexes re-
vealed ten hits with a mean of the PdϪN bond length of
2.029(18) and a mean of the NϪPdϪN bond angle of
˚
80.1(7)°. Similar PdϪN distances (mean ϭ 2.02 A) have
Scheme 3. Synthesis of the group 10 metal complexes (R, RЈ, RЈЈ ϭ
alkyl, aryl substituents; X ϭ Cl, Br; L ϭ additional ligands)
been found in 7 and 10 (Figure 2 and 3) The NϪPdϪN
2422
Eur. J. Inorg. Chem. 2001, 2421Ϫ2426

Nickel Complexes of Dipyridylamine Ligands as Ethylene Oligomerization Catalysts
Table 1. Details of the X-ray crystal structure analyses
FULL PAPER
Compound
7
8
10
Crystal system
Space group
triclinic
P1
monoclinic
P21/c
9.194(2)
19.609(4)
12.522(3)
Ϫ
98.75(3)
Ϫ
2231.3(9)
4
orthorhombic
P212121
10.434(2)
12.164(3)
14.856(3)
Ϫ
¯
˚
a, A
8.772(2)
10.721(2)
13.849(3)
77.53(2)
86.38(2)
80.88(2)
1255.1(5)
2
˚
b, A
˚
c, A
α, deg
β, deg
γ, deg
Ϫ
Ϫ
3
˚
V, A
1885.5(7)
4
Z
Crystal size, mm
ρcalcd, g cmϪ3
µ, cmϪ1 (Mo-Kα)
T, K
0.5 ϫ 0.3 ϫ 0.3
1.592
1.183
200(2)
1.97Ϫ24.13
3644
0.7 ϫ 0.3 ϫ 0.1
1.661
4.465
200(2)
1.95Ϫ24.22
6518
0.4 ϫ 0.4 ϫ 0.35
1.595
1.271
293(2)
2.39Ϫ24.29
8678
θ range, deg
No. of reflections
No. of reflections unique
No. of reflections obs.
[I Ͼ 2σ(I)]
3644
3063
3342
2096
2940
2854
No. of parameters
wR2 (all data)
R value [I Ͼ 2σ(I)]
325
0.073
0.029
262
0.119
0.047
234
0.090
0.030
˚
˚
Figure 2. Molecular structure of 8; selected bond lengths [A] and
angles [°]: N1ϪNi1 1.977(5), N2ϪNi1 1.997(6), Ni1ϪBr1
2.3699(13), Ni1ϪBr2 2.3898(12), N1ϪNi1ϪN2 96.0(2),
Figure 3. Molecular structure of 10; selected bond lengths [A] and
angles [°]: N2ϪPd1 2.025(4), N3ϪPd1 2.020(4), Cl1ϪPd1
2.2993(14),
Cl2ϪPd1
2.267(2),
N3ϪPd1ϪN2
86.5(2),
N1ϪNi1ϪBr1
105.1(2),
N2ϪNi1ϪBr1
107.8(2),
N3ϪPd1ϪCl2 174.47(12), N2ϪPd1ϪCl2 91.23(12), N3ϪPd1ϪCl1
91.85(12), N2ϪPd1ϪCl1 175.37(13), Cl2ϪPd1ϪCl1 90.77(6)
N1ϪNi1ϪBr2105.07(15), N2ϪNi1ϪBr2 107.5(2), Br1ϪNi1ϪBr2
130.04(5)
bond angle (mean ϭ 85.7°) differs by more than 5° and is
even 4.5° larger than the highest value observed in known
[PdCl2(dipy)] complexes.
tivation with chloroaluminum alkyls. The results of the oli-
gomerization experiments are summarized in Table 2. Re-
markably high activities are observed for all Ni complexes
when using Et3Al2Cl3 as a co-catalyst and CH2Cl2 as the
solvent. All nickel complexes show a high tendency towards
Ethylene Oligomerization Studies
Recently, considerable effort has been devoted to the syn- the formation of C4ϪC6 fraction products. Highly
thesis of hyperbranched oligomers from inexpensive mono- branched oligomers with a ratio of methyl protons (at δ ϭ
1
mers such as ethylene and propene.[17] Such materials are 0.87)/total alkyl protons (by H NMR integration) of 0.61
useful in the lubricant industry as base stocks and as pre- were obtained for the higher boiling fraction. An important
cursors to lubricant additives, especially since the demand quantity of these oligomeric products were saturated, as
for synthetic lubricants is rising.[18]
found by GC-IR studies. A low temperature and low ethyl-
Complexes 6, 8 and 9 were investigated with regard to ene pressure were used due to the high activity of the sys-
catalytic applications in ethylene oligomerization after ac- tems under the described conditions.
Eur. J. Inorg. Chem. 2001, 2421Ϫ2426
2423

T. Schareina, G. Hillebrand, H. Fuhrmann, R. Kempe
3 ϫ
10Ϫ5 mol) and sodium tert-butoxide (1.20 g,
FULL PAPER
Table 2. Oligomerization of ethylene with Ni complexes (5 ϫ 10Ϫ6
molNi, Al/Ni ϭ 600, activator Et3Al2Cl3, 200 mL of dichloro-
methane)
(28 mg,
12.5 mmol) were combined in a Schlenk vessel under argon. Tolu-
ene (20 mL) was then added and the mixture stirred at 80 °C for
120 h. After cooling, the resulting mixture was taken up with di-
ethyl ether and washed twice with a saturated aqueous sodium
chloride solution. The organic solution was dried over sodium sulf-
ate and the solvent removed in a rotary evaporator. The resulting
dark red oil was subjected to fast column chromatography over
silica gel (eluent: petroleum ether/ethyl acetate, 10:1 v/v) to remove
polar by-products. Recrystallization of the resulting semi-solid oil
from n-hexane yielded 0.82 g (37%) of colorless needles. Ϫ 1H
(C6D6): δ ϭ 7.95 (d, 2 H), 7.62 (d, 2 H), 7.45 (s, 2 H), 7.36 (m, 3
H), 7.29 (m, 2 H), 7.17 (m, 2 H), 3.57 (hept, J ϭ 6.7 Hz, 2 H), 2.19
(s, 6 H), 1.11 (d, J ϭ 6.7 Hz, 12 H). Ϫ 13C NMR(C6D6): δ ϭ 156.4,
148.7, 147.9, 144.5, 139.0, 129.3, 129.0, 125.9, 124.8, 124.2, 123.8,
116.9, 29.1, 24.1, 18.7. Ϫ C32H33N3 (459.62): calcd. C 83.62, H
7.24, N 9.14; found C 82.98, H 7.54, N 9.26.
Comp.
T
p
t
yield TON[a]
[°C] [bar] [min] [g]
Products [%]
C4ϪC6:C8Ϫ
C16:ϾC16
6
8
9
12
20
30
1.3
0.6
1.0
60[b]
60[c]
60[c]
58.8
85.1
83.6
420 000 57:18:25
608 000 68[d]:17:15
597 000 71[d]:23:6
[a]
[b]
TON ϭ turnover number [molethene/molcatalyst]. Ϫ
Thereafter
[c]
[d]
no gas uptake. Ϫ
Ͼ90% butenes.
Thereafter only marginal gas uptake. Ϫ
Conclusion
Synthesis of 2: 2-(Benzylamino)-4-methylpyridine (2.77 g,
14 mmol), 2-chloro-4-methyl-quinoline (2.5 g, 14.1 mmol), 1,3-
Several conclusions can be drawn from this study. Firstly,
palladium-catalyzed aryl amination is an efficient tool in bis(diphenylphosphanyl)propane (0.23 g, 0.56 mmol), dipalla-
diumtris(benzylideneacetone) (0.26 g, 0.28 mmol) and sodium tert-
butoxide (4.06 g, 42.2 mmol) were combined in a Schlenk vessel
under argon. Toluene (40 mL) was then added and the resulting
brown mixture stirred at 70 °C for 40 h. After cooling to room
temperature the solvent was evaporated in vacuo into a dry-ice-
cooled trap. The resulting slurry was taken up with diethyl ether
and the solution washed three times with a saturated aqueous so-
dium chloride solution. The organic solution was dried over mag-
nesium sulfate, and the solvent removed on a rotary evaporator.
The resulting brown oil was purified by column chromatography
over silica gel (eluent: petroleum ether/ethyl acetate, 4:1 v/v). Yield:
4.38 g (91%) of a yellow oil, which didnЈt solidify even after drying
the preparation of a great variety of 2,2Ј-bipyridylamine li-
gands. Secondly, these compounds act as bidentate ligands
to stabilize group 10 metal complexes. Thirdly, the nickel
complexes are highly active ethylene oligomerization cata-
lysts if activated with Et3Al2Cl3.
Experimental Section
Materials and Procedures: All reagents were obtained commercially
and used as supplied. Column chromatography was performed on
silica gel 60 (0.063Ϫ0.200 mm) from Merck. All manipulations of
air-sensitive materials were performed with rigorous exclusion of
oxygen and moisture in dried Schlenk-type glassware on a dual
manifold Schlenk line, interfaced to a high-vacuum line, or in an
argon-filled glovebox (mBraun labmaster 130) with a high-capacity
recirculator (Ͻ1.5 ppm O2). Solvents (Aldrich) and NMR solvents
(Cambridge Isotope Laboratories all 99 atom% D) were freshly
distilled from sodium tetraethylaluminate.
1
in vacuum and prolonged standing. Ϫ H NMR (C6D6): δ ϭ 8.41
(d, 1 H), 8.24 (d, 1 H), 7.83 (d, 2 H), 7.70 (dd, 1 H), 7.56 (td, 1
H), 7.31 (s, 2 H), 7.29 (s, 1 H), 7.08 (s, 1 H), 6.50 (d, 1 H), 6.06 (s,
2 H, benzyl. CH2), 2.21 (d, J ϭ 7.0 Hz, 3 H, Lp-CH3), 1.91 (s, 3 H,
py-CH3). Ϫ 13C NMR (C6D6): δ ϭ 157.63, 155.72, 148.13, 147.90,
147.69, 143.93, 140.13, 135.64, 128.93, 128.38, 127.44, 126.37,
125.16, 123.38, 123.25, 118.83, 115.75, 115.43, 51.31, 20.29, 18.12.
Ϫ C23H21N3 (339.43): calcd. C 81.38, H 6.24, N 12.38; found C
81.32, H 6.21, N 12.15.
Physical Measurements: NMR spectra were recorded on
a
BRUKER ARX 400 instrument with a variable temperature unit.
1H and 13C chemical shifts were referenced to the solvent reson-
ances and reported relative to TMS. Elemental analysis were per-
formed with a Leco CHNS-932 elemental analyzer. X-ray diffrac-
tion data were collected on a STOE-IPDS diffractometer using
graphite monochromated Mo-Kα radiation. The crystals were
mounted in a cold nitrogen stream. The structure was solved by
direct methods (SHELXS-86)[19] and refined by full-matrix least-
squares techniques against F2 (SHELXL-93).[20] SCHAKAL was
used for structure representations.
Crystallographic data (excluding structure factors) for the struc-
tures reported in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publication
nos. CCDC-159116 (7), CCDC-159117 (8) and CCDC-159118 (10).
Copies of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: (internat.)
ϩ44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
Synthesis of 3: 2-(Benzylamino)-6-methylpyridine (1.49 g,
7.5 mmol), 2-chloro-4-methyl-quinoline (1.33 g, 7.5 mmol), 1,3-
bis(diphenylphosphanyl)propane (0.124 g, 0.30 mmol), dipalla-
diumtris(benzylideneacetone) (0.140 g, 0.153 mmol) and sodium
tert-butoxide (0.96 g, 10 mmol) were combined in a Schlenk vessel
under argon. Dry toluene (25 mL) was then added and the resulting
brown mixture stirred at 70 °C for 40 h. After cooling, the solvent
was removed on a rotary evaporator, the resulting slurry taken up
with diethyl ether and the solution washed three times with a satu-
rated aqueous sodium chloride solution. The organic solution was
dried over magnesium sulfate and the solvents evaporated. The re-
sulting brown oil was purified by fast column chromatography over
silica gel (eluent: petroleum ether/ethyl acetate, 5:1 v/v). Yield:
2.42 g (7.13 mmol, 95%) of a yellow highly viscous oil, which didnЈt
solidify even after drying in vacuum and prolonged standing. Ϫ 1H
NMR (C6D6): δ ϭ 2.00 (s, 3 H), 2.30 (s, 3 H), 5.53 (s, 2 H, benzyl.
CH2), 6.34 (d, 1 H), 6.79 (d, 1 H), 6.9 (t, 1 H), 6.95 (t, 1 H), 7.05
(m, 1 H), 7.07 (m, 1 H), 7.10 (m, 4 H), 7.33 (dt, 1 H), 7.48 (dd, 1
H), 7.59 (m, 2 H), 8.01 (m, 1 H). Ϫ 13C NMR (C6D6): δ ϭ 157.9,
157.4, 156.4, 148.6, 144.5, 140.9, 137.7, 129.6, 129.1, 128.2, 127.1,
Synthesis of the Ligands
Synthesis of 1: 2,6-Diisopropylaniline (0.89 g, 5.0 mmol), 2-chloro-
lepidine (1.78 g, 10.0 mmol), 1,3-bis(diphenylphosphanyl)propane
(25 mg,
6
ϫ
10Ϫ5 mol), dipalladiumtris(benzylideneacetone) 125.8, 124.1, 124.0, 117.3, 116.1, 112.9, 51.8, 24.7, 18.8. Ϫ
2424
Eur. J. Inorg. Chem. 2001, 2421Ϫ2426

Nickel Complexes of Dipyridylamine Ligands as Ethylene Oligomerization Catalysts
C23H21N3 (339.43): calcd. C 81.38, H 6.24, N 12.38; found C 81.05, cuum treatment: the X-ray analysis showed dichloromethane,
FULL PAPER
H 6.00, N 12.31.
whereas the elemental analysis of the material from the second run
showed none. Ϫ H (CD2Cl2): δ ϭ 9.37 (d, J ϭ 8.4 Hz, 1 H), 8.60
1
Synthesis of 4: 2-Pyridylaniline (1.702 g, 10 mmol), 2-chloro-4-
methylquinoline (1.78 g, 10 mmol), 1,3-bis(diphenylphosphanyl)-
propane (0.165 g, 0.40 mmol), dipalladiumtris(benzylideneacetone)
(0.18 g, 0.20 mmol) and sodium tert-butoxide (1.35 g, 14 mmol)
were combined in a Schlenk vessel under argon. Toluene (30 mL)
was then added and the dark green mixture stirred at 70 °C for
54 h. Workup as for 3, but with dichloromethane solvent. The raw
product was isolated as a dark brown solid, which was recrystal-
(d, J ϭ 7.4 Hz, 1 H), 7.90 (d, 2 H), 7.81 (m, 2 H), 7.57 (dt, J ϭ
1.5, J ϭ 8.4 Hz, 1 H), 7.43 (t, J ϭ 7.4 Hz, 2 H), 7.31 (br. t, J ϭ
7.5 Hz, 1 H), 7.16 (s, 1 H), 7.03 (m, 2 H), 5.45 (m, 2 H, NϪCH2),
2.66 (s, 3 H), 2.36 (s, 3 H). Ϫ C23H21Cl2N3Pd (516.76): calcd. C
49.51, H 3.79, N 7.53; found C 49.50, H 3.81, N 7.59. Ϫ 13C NMR
(CD2Cl2): δ ϭ 151.8, 150.3, 149.8, 144.5, 133.1, 130.1, 129.7, 128.5,
127.5, 126.8, 126.0, 125.6, 122.2, 121.8, 114.9, 113.0, 53.9, 28.7,
18.5.
lized from absolute ethanol. Yield: 1.57 g (5.04 mmol, 50%) of yel-
1
low crystalline needles. Ϫ H (C6D6): δ ϭ 1.98 (d, 3 H, CH3), 6.64 Synthesis of 8: A solution of 3 (0.34 g, 1 mmol) in 10 mL of dichloro-
(m, 1 H), 6.93 (m, 2 H), 7.0Ϫ7.1 (m, 6 H), 7.18 (m, 2 H), 7.24 methane was added to [NiBr2(DME)] (0.31 g, 1 mmol) in a
(ddd, 1 H), 7.48 (dd, 1 H), 7.89 (dd, 1 H), 8.15 (m, 1 H). Ϫ 13C Schlenk vessel, resulting in a purple solution. After 4 days at room
(C6D6): δ ϭ 157.7, 156.1, 147.6, 147.2, 144.7, 143.8, 135.9, 128.7,
128.4, 128.2, 127.7, 125.1, 124.8, 123.4, 122.7, 117.2, 116.9, 116.8,
temperature the solution was filtered and the remaining solid
washed with three 5 mL portions of dichloromethane. The wash-
17.5. Ϫ C21H17N3 (311.38): calcd. C 81.00, H 5.50, N 13.49, found ings were added to the filtrate. The combined solution was layered
C 81.00, H 5.74, N 13.27.
with 15 mL of diethyl ether and kept for one week at room temper-
ature. The solvent was then removed from the resulting purple pris-
matic crystals, which were washed with two 10 mL portions of di-
ethyl ether. Yield: 0.32 g (0.57 mmol, 57%). Ϫ 1H (CDCl3): δ ϭ (all
broad singlets due to the paramagnetism of the Ni) 11.16 (0.3 H),
10.50 (0.8 H), 7.17 (3 H), 7.02 (1 H), 6.88 (2 H), 6.17/6.02 (4 H),
2.59 (1 H), 1.40 (1 H), 0.00 (12 H). Ϫ C23H21Br2N3Ni (557.93):
calcd. C 49.51, H 3.79, Br 28.64, N 7.53; found C 49.50, H 3.81,
Br 28.45, N 7.59.
Synthesis of 5: 2-Bromopyridine (2.53 g, 16.0 mmol), (S)-1-phenyl-
ethylamine (0.97 g, 8.00 mmol), Pd2(DBA)3 (0.18 g, 0.20 mmol,
4 mol %
Pd),
1,3-bis(diphenylphosphanyl)propane
(0.16 g,
0.39 mmol), sodium tert-butoxide (1.34 g, 13.9 mmol) and 50 mL
of toluene were combined in a Schlenk vessel. The mixture was
stirred at 70 °C for 36 h. After cooling to room temperature the
solvent was evaporated in vacuo into a dry-ice-cooled trap. Ether
(50 mL) and water (50 mL) were added to the reaction mixture and,
after separation, the organic phase was extracted twice with a satu- Synthesis of 9: [NiBr2(DME)] (0.30 g, 0.9 mmol) was suspended in
rated aqueous sodium chloride solution. The solution was dried 5 mL of THF and a warm solution of 4 (0.28 g, 0.9 mmol) in 5 mL
over magnesium sulfate and the solvent removed on the rotary of THF was added in four portions with a syringe. A purple solid
evaporator. Vacuum distillation at 150 °C/0.1 mbar yielded 1.85 g
precipitated after 5 min. The next day, filtration yielded a purple,
microcrystalline solid, which was dried in vacuo. The yield was not
(84%) of a colorless oil. Ϫ 1H NMR (C6D6): δ ϭ 1.47 (d, J ϭ
6.7 Hz, 3 H, CH3), 4.64 (quint, J ϭ 6.7 Hz, 1 H, CH), 6.08Ϫ6.12 determined. For recrystallisation, a small amount was dissolved in
(m, 2 H), 6.43Ϫ6.47 (m, 2 H), 7.13Ϫ7.17 (m, 2 H), 7.20Ϫ7.31 (m, 5 mL hot dichloromethane, cooled to room temperature and
5 H), 7.80Ϫ8.00 (m, 2 H). Ϫ 13C NMR (C6D6): δ ϭ 24.3 (CH3), layered with 3 mL of diethyl ether. Again, only a microcrystalline
54.6 (CH), 107.2, 117.3, 117.9, 127.8, 128.7, 137.9, 145.2, 148.8, powder was obtained.1H (CDCl3): δ ϭ (all broad due to the para-
156.2. Ϫ C18H17N3 (275.35): calcd. C 78.52, H 6.22, N 15.26; found magnetism of the Ni) 12.4 (br. s, 2 H), 8.8 (s, 1 H), 8.35 (d, 1 H),
C 78.37, H 6.45, N 15.31.
7.97 (m, 2 H), 7.7 (m, 7 H), 7.54 (m, 1 H), 6.83 (br. s, 2 H), 6.65
(br. s, 5 H), 6.53 (s, 1 H), 2.67 (s, 3 H). Ϫ C21H17Br2N3Ni (Mw
529.88 g/mol): calcd. C 47.60, H 3.23, Br 30.16, N 7.93; found C
47.45, H 3.21, Br 29.39, N 7.74.
ϭ
Synthesis of the Metal Complexes
Synthesis of 6: [NiBr2(DME)] (0.23 g, 0.74 mmol) was suspended
in 5 mL dichloromethane. A solution of 1 (0.34 g, 0.76 mmol) in
5 mL dichloromethane was then added, the color of the solution Synthesis of 10: [PdCl2(COD)] (0.13 g, 0.47 mmol) was added to a
changing to a deep purple. After standing overnight the solution
was filtered and the grey residue washed with 10 mL of dichloro-
methane. 10 mL of toluene was then added to the solution and the
solution of 5 (0.14 g, 0.50 mmol) in 30 mL of dichloromethane. The
mixture was stored at Ϫ78 °C for crystallization. Filtration yielded
0.13 g (61%) of orange crystals. Ϫ H NMR (C6D6): δ ϭ 1.73 (d,
1
solvents were evaporated until about 8 mL of toluene remained. J ϭ 6.4 Hz, 3 H, CH3), 5.44 (q, J ϭ 6.4 Hz, 1 H, CH), 6.88Ϫ6.94
After some days of standing crops of purple crystals precipitated,
and these were separated and washed with 5 mL of toluene. Yield:
0.31 g (54%). Ϫ 1H NMR (CDCl3): δ ϭ 12.70 (br. s), 7.25Ϫ7.40
(m, 2 H), 7.15Ϫ7.19 (m, 2 H), 7.25Ϫ7.29 (m, 3 H), 7.43Ϫ7.49 (m,
1 H), 7.53Ϫ7.58 (m, 2 H), 7.78Ϫ7.85 (m, 1 H), 8.64Ϫ8.85 (m, 2
H). Ϫ 13C NMR (C6D6): δ ϭ 22.6 (CH3), 59.7 (CH), 118.3, 119.0,
(m), 7.13Ϫ7.22 (m), 2.98 (s), 2.37 (s), 1.46 (s), 1.16 (d). Ϫ 13C NMR 120.2, 120.8, 126.5, 127.3, 128.5, 138.7, 139.7, 140.2, 150.3, 151.2,
(CDCl3): δ ϭ 142.9, 133.6, 129.5, 128.7, 125.8, 123.4, 121.9, 116.8,
151.6, 152.5. Ϫ C18H17Cl2N3Pd (452.68): calcd. C 62.14, H 5.05,
24.7. The NMR spectra obtained were rather broad due to the N 7.51; found C 62.08, H 5.21, N 7.33.
paramagnetism of the Ni. Ϫ C39H41Br2N3Ni (5·toluene: 770.26):
calcd. C 60.81, H 5.37, N 5.46; found C 61.17, H 5.21, N 5.42.
Polymerization Studies: The oligomerization of ethylene (99.95%)
was carried out in a batch process using a 1-L glass autoclave fitted
with a gas inlet, dosing device, pressure gauge, and a magnetically
Synthesis of 7: Compound 2 (0.125 g, 0.37 mmol) was dissolved
in 3 mL of dichloromethane and added to [PdCl2(COD)] (0.105 g, driven and continuously regulated paddle stirrer with a hollow
0.37 mmol, 1 equiv.) in a Schlenk vessel. After a week orange crys- shaft (0 to 800 rpm). The solvent, dichloromethane, was dried by
tals separated from the solution, and these were used directly for standard methods and distilled under argon. Et3Al2Cl3 was used
an X-ray analysis. In a separate run, the solvent was removed with
a syringe under argon, the crystals were washed twice with 1 mL
as supplied (Aldrich). 5 ϫ 10Ϫ3 mmol of the Ni complexes were
dissolved in 200 mL of dichloromethane and introduced under in-
portions of diethyl ether and dried in vacuum to yield 0.11 g (49%) ert conditions into the autoclave. After the temperature of the mix-
of product. The crystals appeared to lose dichloromethane on va-
ture had been adjusted and Et3Al2Cl3 had been added as a cocata-
2425
Eur. J. Inorg. Chem. 2001, 2421Ϫ2426

T. Schareina, G. Hillebrand, H. Fuhrmann, R. Kempe
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