Iron and cobalt complexes of tridentate N-donor ligands in ethylene polymerization: Efficient shielding of the active sites by simple phenyl groups

Article abstract of DOI:10.1002/ejic.200800374

Tridentate 2,6-bis[3(5)-pyrazolyl]pyridines and 2,6-bis(4-pyrimidinyl) pyridine were synthesized and characterized spectroscopically and by single-crystal X-ray structure analysis. The derived complexes with FeCl ₂ and CoCl₂ were investigated for their activity in the ethylene polymerization in the presence of methylalumoxane (MAO). Iron and cobalt catalysts bearing the ligand 2,6-bis[5-butyl-1-(4-nitrophenyl)pyrazol-3- yl]pyridine showed moderate catalytic activity and gave PE with high molecular weight, although the aryl substituents are not equipped with additional bulky side chains in the 2,6-positions to shield the metal centre. This can be explained by the geometric parameters of the pyrazole units, which provide efficient shielding of the active site, even with unsubstituted aryl groups. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800374

FULL PAPER
DOI: 10.1002/ejic.200800374
Iron and Cobalt Complexes of Tridentate N-Donor Ligands in Ethylene
Polymerization: Efficient Shielding of the Active Sites by Simple Phenyl
Groups
Dirk Zabel,[a] Anett Schubert,[a] Gotthelf Wolmershäuser,[a] Robert L. Jones Jr,[b][‡] and
Werner R. Thiel*[a]
Keywords: Polyethylene / Iron / Cobalt / Pyridine / Pyrazole
Tridentate 2,6-bis[3(5)-pyrazolyl]pyridines and 2,6-bis(4-pyr-
gave PE with high molecular weight, although the aryl sub-
imidinyl)pyridine were synthesized and characterized spec- stituents are not equipped with additional bulky side chains
troscopically and by single-crystal X-ray structure analysis.
The derived complexes with FeCl2 and CoCl2 were investi-
gated for their activity in the ethylene polymerization in the
presence of methylalumoxane (MAO). Iron and cobalt cata-
lysts bearing the ligand 2,6-bis[5-butyl-1-(4-nitrophenyl)pyr-
azol-3-yl]pyridine showed moderate catalytic activity and
in the 2,6-positions to shield the metal centre. This can be
explained by the geometric parameters of the pyrazole units,
which provide efficient shielding of the active site, even with
unsubstituted aryl groups.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
ium species or by β-hydrogen transfer, either to the catalyti-
cally active site or to the coordinated monomer.[3] The latter
two products can start the propagation of a new chain.
Obviously, these processes are strongly dependent on the
steric demand of the ligands coordinated to the active site.
For the 2,6-diiminopyridines aryl groups at the imine nitro-
gen atoms are required. These aryl substituents have to be
functionalized in the 2- and 6-positions with alkyl groups
to increase the steric demand of the whole ligand system.
Otherwise only oligomers can be obtained. Starting from
the basic structure of 2,6-diiminopyridine ligands, a series
of new catalysts were developed including novel ligand
structures.[5]
Introduction
At the end of the last century, Brookhart and Gibson
independently published the first members of a class of new
transition metal catalysts for ethylene polymerisation,[1] ob-
tained by coordination of iron or cobalt dichloride with 2,6-
diiminopyridines. After activation with methylaluminoxane
(MAO), these systems exhibit a high catalytic activity in the
polymerisation of ethylene, although their structures differ
fundamentally from the well-established metallocene cata-
lysts.[2]
The role of methylaluminoxane, which is required for the
activation of such 2,6-diiminopyridine complexes, is com-
parable to its function in traditional metallocene polymeri-
sation catalysis: it acts as a methylating agent and as a
Lewis acidic (carb)anion acceptor. This leads to the forma-
tion of a cationic 14e complex in the case of FeII, which is
discussed as the active species.[3] As outlined in the Cossee–
Arlmann mechanism,[4] the propagation of the polymer
chain can be described by a coordination of the olefin fol-
lowed by the insertion of the olefin into the metal–carbon
bond. The degree of polymerisation is determined by chain
propagation and chain termination reactions. Chain ter-
mination may either proceed by chain transfer onto alumin-
In this paper we describe the synthesis and the catalytic
activity in the ethylene polymerisation of N-aryl-function-
alized (2,6-dipyrazolylpyridine)iron(II) and -cobalt(II) com-
plexes.
Results and Discussion
Since the mid 1990s, we have been working on the appli-
cation of ligands containing pyrazolyl fragments in homo-
geneous catalysis. We were able to show that 2-[3(5)-pyraz-
olyl]pyridine and its N-alkylated congeners can replace the
well-known 2,2Ј-bipyridyl ligand and additionally provide
all the advantages of pyrazole chemistry such as (a) the pos-
sibility to introduce electron-donating and -withdrawing
substituents in the five-membered pyrazole ring, (b) the
possibility to introduce groups at various positions which
enhance the solubility of the catalysts, (c) a simple protocol
[a] Fachbereich Chemie, Technische Universität Kaiserslautern
Erwin-Schrödinger-Str. Geb. 54, 67663 Kaiserslautern, Ger-
many
Fax: +49-631-2054676
E-mail: thiel@chemie.uni-kl.de
[b] DSM PTG Part of of DSM Biomedical
2810 7th Street, Berkeley, California 94710, USA
[‡] Former address: BASELL Polyolefin GmbH
Industriepark Hoechst, G832, 65926 Frankfurt/Main, Germany for the generation of chiral ligands, and (d) a simple proto-
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Iron and Cobalt Complexes of Tridentate N-Donor Ligands
col for the heterogenization of these.[6] Aliphatic as well as
aromatic[7] substitution using the N1 atom as the nucleo-
philic centre provide access to further modified systems.
Expanding the bidentate 2-[3(5)-pyrazolyl]pyridine sys-
tem by a further pyrazolyl substituent in the 6-position of
the pyridine ring gives tridentate ligands which are structur-
ally related to 2,2Ј:6Ј2ЈЈ-terpyridine, a ligand system that is
commonly used in coordination chemistry.[8] However,
2,2Ј:6Ј2ЈЈ-terpyridine was only rarely applied in catalysis,
probably due to solubility problems. By applying the syn-
thetic routes described for the synthesis of 2-[3(5)-pyrazolyl]-
pyridines and using 2,6-difunctionalized pyridines as the
starting materials, 2,6-bis[3(5)-pyrazolyl]pyridines are ac-
cessible. The structure of the resulting tridentate ligands is
closely related to the 2,6-diiminopyridine used for the syn-
thesis of post-metallocene olefin polymerisation catalysts
(Scheme 1). However, due to the five-membered pyrazole
rings, the bond angles in the ligand backbone are different
resulting in a different shielding of the active metal site (see
discussion below).
Scheme 2. Synthesis of the tridentate ligands 4 and 5.
Scheme 1. Structural comparison of 2,6-diiminopyridines and 2,6-
dipyrazolylpyridines.
The ligand synthesis starts from cheap 2,6-pyridinedi-
carboxylic acid (1) which is transformed into the corre-
sponding diester 2 in almost quantitative yield.[9] To en-
hance the solubility of the derived complexes, we generally
introduce alkyl chains in the ligand backbone. Condensa-
tion of 2 with n-butyl or tert-butyl methyl ketone under
Claisen conditions provides the tetraketones 3a,b. Due to
the dynamic equilibration between the 1,3-diketone form
and the oxo enol forms, the NMR spectra of the tetra-
ketones 3a,b are complex. 3a was transformed into the di-
pyrazolyl derivative 4a in high yield by ring closure with
hydrazine.[10] 3b[11] was treated with formamide in the pres-
ence of ammonium carbonate and sodium sulfate to give
the dipyrimidinyl derivative 5 in moderate yield (Scheme 2).
Experiments on the ring closure to pyrimidines with sub-
Figure 1. Molecular structure of 3b in the solid state. Selected dis-
tances [Å], angles [°] and dihedral angles [°]: O1–C5 1.303(4), C5–
C6 1.370(4), C6–C7 1.392(4), O2–C7 1.286(4), O3–C13 1.275(4),
C13–C14 1.391(4), C14–C15 1.367(4), O4–C15 1.310(4), O1–H1
1.22(5), H1···O2 1.32(4), O1···O2 2.475(3), O3–H3 1.23(3), H3···O4
1.38(3), O3···O4 2.504(3), C6–H6 0.93, H6···N1 2.50, C6···N1
stituents other than tert-butyl resulted in very poor yields 2.816(3), C14–H14 0.93, H14···N1 2.50, C14···N1 2.823(4), C9–H9
of the desired products.
The success of the syntheses was further confirmed by
an X-ray structure analysis. Single crystals of compound 3b
–172.0(3).
could be obtained by recrystallisation from ethanol. Fig-
0.93, H9···O2Ј 2.48, C9···O2Ј 3.305(4); O1–H1···O2 154(4), O3–
H3···O4 148(3), C6–H6···N1 100.00, C14–H14···N1 100.00, C9–
H9···O2Ј 148.00; C6–C7–C8–C9 –172.3(3), C11–C12–C13–C14
ure 1 presents the molecular structure of the tetraketone 3b
in the solid state.
is confirmed by a quite small variation of the corresponding
Although a series of transition metal complexes contain- C–C and C–O bond lengths, although the O–H distances
ing tetraketones with structures similar to 3b are differ significantly. At a first glance it is surprising that in
known,[11,12] this is the first structure determination of an one of the 1,3-diketo groups, the O–H bond belonging to
uncoordinated compound of this type. The 1,3-diketo moie- the oxygen atom in the 3-position is shorter than the O–H
ties are both found in the enol structure. The extended delo- bond belonging to the oxygen atom in the 1-position, while
calization of the negative charge over the whole diketo unit in the other 1,3-diketo group the situation is opposite. This
Eur. J. Inorg. Chem. 2008, 3648–3654
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D. Zabel, A. Schubert, G. Wolmershäuser, R. L. Jones Jr, W. R. Thiel
FULL PAPER
Scheme 3. Alkylation and arylation of 4a.
is due to the involvement of O2 in an intermolecular hydro-
gen bond, which gives rise to the formation of hydrogen-
bonded dimers in the solid state. These dimers undergo π-
interactions between the electron-rich diketonate group and
the electron-poor pyridine ring.
The dipyrazolyl derivative 4a shows a strong absorption
for the N–H vibration at 3184 cm–1 in the IR spectrum.
1H and 13C NMR spectra recorded in CDCl3 confirm the
presence of only one tautomer. The 1H NMR spectrum
(CDCl3) of the bright yellow dipyrimidinyl compound 5
shows one triplet at δ = 8.05 ppm and one doublet at δ =
8.59 ppm (3JHH = 7.8 Hz) for the protons of the pyridine
ring and two doublets at δ = 8.61 and 9.26 ppm with a small
5JHH coupling constant of 1.0 Hz for the pyrimidine ring
protons.
Further derivatization at the N–H group of 4a was per-
formed by nucleophilic substitution with either halogenoal-
kyl or -aryl substrates (Scheme 3). Deprotonation of the
pyrazole groups of 4a with NaH in THF solution generates
Figure 2. Molecular structure of 4d in the solid state (the hydrogen
atoms at the disordered butyl chains are omitted for clarity). Se-
lected dihedral angles [°]: N3–C7–C8–N4 –179.54(15), N4–C12–
C13–N5 –178.47(15), N3–N2–C26–C27 –66.2(2), N5–N6–C20–
C21 –61.3(2), O1–N1–C27–C26 141.37(18), O3–N7–C21–C20
–43.6(3).
All dichloridoiron and -cobalt complexes were investi-
the corresponding pyrazolides which react with butyl or gated for activity in the ethylene polymerisation. It turned
benzyl bromide to give the alkylated derivatives 4b,c. Treat- out that exclusively 6eFe and 6eCo showed activity when
ment of 4a at 170 °C in dry DMSO with ortho- or para- treated in toluene with the olefin in the presence of a large
fluoronitrobenzene results in the formation of the arylated excess of MAO. All other iron and cobalt compounds were
ligands 4d,e. Single crystals of compound 4d could be ob- not active. This is not surprising for the alkyl-substituted
tained by recrystallization from ethanol. Figure 2 presents systems 6b,cFe and 6b,cCo and for 7Fe and 7Co since aryl
the molecular structure of the twofold nitroarylated dipyr- substituents are also required in the 2,6-diiminopyridine
azolyl derivative 4d in the solid state.
series for an efficient shielding of the metal centre. Whereas
Both n-butyl groups of 4d were found to be disordered the iron and cobalt complexes 6eFe and 6eCo with para-
in the solid state. Due to four weak N···C–H interactions, nitrophenyl substituents at the N1 atom of the pyrazole
the pyrazole rings are found in an almost coplanar arrange- rings are active catalysts, their ortho-nitrophenyl-bearing
ment with the pyridine ring. The o-nitrophenyl rings are congeners 6dFe and 6dCo are not active. There may be ste-
twisted by 66.2 and 61.3° against the pyrazole rings, and ric or electronic reasons for this behaviour. On the other
the nitro groups are twisted by 141.4 and 43.6° against the hand, it is unlikely, that a nitro substituent will remain un-
phenyl rings.
affected in the presence of highly alkylating (and thus re-
The N1-substituted ligands 4b–e and the dipyrimidinyl- ducing) MAO. This can generate amido (Ar–NR–) as well
pyridine derivative 5 were treated with anhydrous iron or as imido (Ar–N2–) groups, which would be located in close
cobalt dichloride in dry methanol to give the paramagnetic proximity to the reactive metal site in the case of 6dFe and
complexes 6b–eFe, 6b–eCo, 7Fe, and 7Co in good yields 6dCo. In the case of 6eFe and 6eCo, these strongly coordi-
(Scheme 4). They were characterized by elemental analysis, nating sites would only be able to bind to MAO. The reac-
MALDI-TOF mass spectrometry and IR spectroscopy (in tion conditions for the polymerization tests are summarized
the case of the nitro-substituted derivatives).
in Table 1.
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Iron and Cobalt Complexes of Tridentate N-Donor Ligands
aryl substituents much closer to the metal sites than it is
the case for 2,6-diiminopyridines. This is qualitatively dem-
onstrated in Figure 3, which shows the structures of a
(2,6-diiminopyridine)- and
a (2,6-dipyrazolylpyridine)-
dichloridozinc complex, calculated with the semiempirical
method PM3.[13]
Figure 3. Shielding of the metal site in {2,6-bis[(2,6-dimeth-
ylphenyl)imino]pyridine}dichloridozinc (top) and {2,6-bis[(1-
phenyl)pyrazol-3-yl]pyridine}dichloridozinc (bottom).
Scheme 4. Synthesis of iron and cobalt complexes.
Table 1. Summary of the polymerization experiments.
Catalyst Amount MAO/ p[C2H4] PE yield
Activity[a,b]
[mg]
catalyst [atm]
[g]
[kgPE mmol–1 h–1]
Conclusions
6eFe
6eFe
6eCo
6eCo
13.7
10
19
500
1000
500
1
10
1
0.1
12.7
0.0
0.02
0.44
0.00
0.58
Increasing of the shielding of the active sites of post-me-
tallocene polymerization catalysts can efficiently be
achieved by implying a five-membered ring like pyrazole
instead of an sp2-hybridized imine group or a six-membered
ring. This allows to use simple and cheap phenyl substitu-
ents. We are at the moment looking for other applications
of this principle in catalysis.
10
1000
10
16.6
[a] Reaction time 110 min. [b] T = 30 °C.
At an ethylene pressure of 10 bar, the reaction started
after a short induction period and had to be kept at 30 °C
by external cooling. At the end of the reaction, the polymer
was isolated by precipitation and analyzed by means of gel
permeation chromatography. The results are summarized in
Table 2.
Experimental Section
General Remarks: All manipulations were carried out under dini-
trogen. Only dry solvents were used. All commercially available
starting materials were used without further purification. Elemen-
tal analyses were carried out at the Departmernt of Chemistry (TU
Kaiserslautern). IR spectra were recorded with a Perkin–Elmer FT-
IR 1000 spectrometer. NMR spectra were recorded with a Bruker
Avance 400 spectrometer.
Table 2. Characteristic properties of the obtained polymers.
Catalyst Amount[a] p[C2H4] M.p.
Mw
Mn
Q
[mg]
[atm]
[°C] [g/mol] [g/mol]
6eFe
6eCo
10
10
10
10
134
135
524177 155089 3.38
485026 194428 2.49
2,6-Bis(1,3-dioxoheptyl)pyridine (3a) and 2,6-Bis(4,4-dimethyl-1,3-
dioxopentyl)pyridine (3b):[11] 2-Hexanone or pinacolone (40 mmol)
was added to a suspension of NaOEt (2.72 g, 40 mmol) and di-
methyl 2,6-pyridinedicarboxylate (4.46 g, 20 mmol) in dry THF
(100 mL). The mixture was heated to reflux for 3 h. After this time,
the solvent was removed under vacuum, the resulting sodium salt
was suspended in water, and the suspension was treated with HCl
until pH = 4. Extraction with CHCl3, drying of the solution with
Na2SO4, and removal of the solvent in vacuo yielded the crude
tetraketones in 70–80% yield as bright yellow solids, which were of
[a] Al/M = 1000:1.
The catalysts do not exhibit excellent activities, at least
when the PE pressure of 10 atm is taken into account. How-
ever, the molecular masses which were reached are quite
interesting because there are no sterically demanding
groups in the 2- and 6-positions of the aryl substituents at
the pyrazole ring. In our case two simple aryl rings allow
efficient shielding of the catalytically active site to prevent
chain termination reactions. We assign this to the internal
sufficient purity for the following transformations. 3a: IR (KBr): ν
˜
angles of the five-membered pyrazole rings which bring the = 3103 (w), 2957 (s), 2931 (s), 2871 (m), 1711 (s), 1696 (s), 1608
Eur. J. Inorg. Chem. 2008, 3648–3654
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D. Zabel, A. Schubert, G. Wolmershäuser, R. L. Jones Jr, W. R. Thiel
FULL PAPER
(s), 1574 (s), 1444 (m), 1408 (m), 1320 (m), 1238 (m), 1149 (m), 2.61 (t, 4 H, CCH2), 1.84 (q, 4 H, CH2), 1.72 (q, 4 H, CH2), 1.45
1080 (m), 994 (m), 942 (m), 809 (m), 748 (m), 612 (m) cm–1. 1H
(sext, 4 H, CH2), 1.37 (sext, 4 H, CH2), 0.94 (m, 12 H, CH3) ppm.
NMR (400 MHz, CDCl3, 25 °C): δ = 15.77 (br., 2 H, =COH), 8.17 13C{1H} NMR (100.6 MHz, CDCl3, 25 °C): δ = 152.0 (5-Cpz),
(d, 3JHH = 7.8 Hz, 2 H, 3,5-Hpy), 7.97 (t, 1 H, 4-Hpy), 6.87 (s, 2 H, 150.5 (2,6-Cpy), 143.8 (3-Cpz), 136.5 (4-Cpy), 117.80 (3,5-Cpy),
=CH), 2.53 (t, 4 H, CH2), 1.71 (q, 4 H, CH2), 1.43 (sext, 4 H, 102.77 (4-Cpz), 48.8 (NCH2), 32.4 (CCH2), 30.5 (CH2), 25.1 (CH2),
CH2), 0.96 (t, 6 H, CH3) ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 22.2 (CH2), 19.8 (CH2), 13.6 (CH3), 13.5 (CH3) ppm. C27H41N5
25 °C): δ = 198.1 (C=O), 180.8 (COH), 152.2 (2,6-Cpy), 138.2 (4- (435.66): calcd. C 74.44, H 9.49, N 16.08; found C 73.17, H 9.79,
Cpy), 124.3 (3,5-Cpy), 96.8 (=CH), 39.3 (CH2), 27.9 (CH2), 22.6
N 14.51. 4c: IR (KBr): ν = 3064 (w), 3031 (w), 2955 (s), 2928 (s),
˜
(CH2), 13.9 (CH3) ppm. C19H25NO4 (331.37): calcd. C 68.86, H
7.60, N 4.23; found C 69.04, H 7.36, N 4.31. The spectroscopic
data for 3b is in complete agreement with the data given in ref.[11]
2855 (m), 1594 (w), 1573 (m), 1546 (w), 1498 (m), 1455 (m), 1402
(m), 1380 (m), 1355 (m), 1316 (m), 1254 (m), 1192 (m), 1151 (w),
1078 (w), 1030 (w), 1003 (w), 991 (w), 959 (w), 803 (m), 726 (m),
695 (m), 580 (w), 456 (w) cm–1. 1H NMR (400 MHz, CDCl3,
2,6-Bis(5-butylpyrazol-3-yl)pyridine (4a): This compound was syn-
3
25 °C): δ = 7.94 (d, JHH = 7.7 Hz, 2 H, 3,5-Hpy), 7.76 (t, 1 H, 4-
thesized according to a published procedure[10] and obtained as a
H
py), 7.31 (m, 6 H, m-Hph, p-Hph), 7.13 (d, 3JHH = 7.1 Hz, 4 H, o-
colourless solid in 78% yield. Mp. 193 °C. IR (KBr): ν = 3184 (s),
˜
Hph), 6.94 (s, 2 H, 4-Hpz), 5.41 (s, 4 H, CH2Ph), 2.56 (t, 4 H, CH2),
1.64 (quint, 4 H, CH2), 1.38 (sext, 4 H, CH2), 0.91 (t, 6 H, CH3)
ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 25 °C): δ = 152.1 (5-
Cpz), 151.1 (2,6-Cpy), 144.9 (3-Cpz), 137.3 (1-Cph), 129.8 (4-Cpy),
128.7, 126.56 (o-Cph, m-Cph), 127.49 (4-Cph), 118.4 (3,5-Cpy), 103.9
(4-Cpz), 53.2 (CH2Ph), 30.45 (CH2), 25.4 (CH2), 22.3 (CH2), 13.8
(CH3) ppm. C33H37N5 (503.66): calcd. C 78.69, H 7.40, N 13.91;
found C 78.58, H 7.20, N 13.02.
3131 (s), 3106 (s), 2927 (s), 2858 (s), 1654 (m), 1599 (m), 1575 (s),
1505 (m), 1463 (s), 1398 (m), 1338 (m), 1297 (m), 1248 (m), 1169
(m), 1152 (m), 1094 (m), 1031 (m), 1010 (m), 963 (w), 811 (s), 792
(s), 769 (s), 727 (w), 646 (w) cm–1. 1H NMR (400 MHz, CDCl3,
3
25 °C): δ = 9.8 (br., 2 H, NH), 7.69 (t, JHH = 7.8 Hz, 1 H, 4-Hpy),
7.52 (d, 2 H, 3,5-Hpy), 6.54 (s, 2 H, 4-Hpz), 2.70 (t, 4 H, CH2), 1.67
(q, 4 H, CH2), 1.39 (sext, 4 H, CH2), 0.92 (t, 6 H, CH3) ppm.
13C{1H} NMR (100.6 MHz, CDCl3, 25 °C): δ = 152.4 (5-Cpz),
148.8 (2,6-Cpy), 144.8 (3-Cpz), 137.2 (4-Cpy), 118.1 (3,5-Cpy), 101.6
(4-Cpz), 31.7 (CH2), 27.3 (CH2), 22.5 (CH2), 13.9 (CH3) ppm.
C19H25N5 (323.43): calcd. C 70.21, H 7.57, N 21.67; found C 70.56,
H 7.79, N 21.65.
2,6-Bis[5-butyl-1-(2-nitrophenyl)pyrazol-3-yl]pyridine (4d) and 2,6-
Bis[5-butyl-1-(4-nitrophenyl)pyrazol-3-yl]pyridine (4e): A mixture of
4a (4.00 g, 12.4 mmol), K2CO3 (10.00 g, 70 mmol), 1-fluoro-2-
nitrobenzene or 1-fluoro-4-nitrobenzene (4.23 g, 30.0 mmol), and
DMSO (150 mL) was heated to 170 °C for 4 h. After pouring on
ice, addition of HCl until pH = 3, and warming to room temp., the
crude products could be separated by filtration. They were washed
with water and dried at 50 °C under vacuum. The crude products
were purified by column chromatography (SiO2), first by elution of
residual 1-fluoronitrobenzene with pentane followed by elution of
the product with diethyl ether/acetone (1:1). Yields: 4.30 g (61%)
of 4d, dark brown solid; 4.60 g (65%) of 4e, yellow solid. 4d: Mp.
2,6-Bis(6-tert-butylpyrimidin-4-yl)pyridine (5): A mixture of com-
pound 3b (5.10 g,15.4 mmol), Na2SO4 (6.50 g, 45.8 mmol), (NH4)2-
CO3 (5.00 g, 52.0 mmol), and formamide (10 g, 222 mmol) was
heated to 180 °C for 12 h. After cooling of the mixture to room
temp., it was treated with 1  NaOH (100 mL) to hydrolyze excess
formamide. The crude product was extracted with diethyl ether, the
organic solution was dried with CaCl2, and the solvent was re-
moved in vacuo. Purification by flash chromatography (Al2O3; hex-
ane/ethyl acetate, 4:1) yielded 1.17 g (22%) of 5 as a bright yellow
164 °C. IR (KBr): ν = 2962 (m), 2933 (m), 2860 (m), 1608 (m),
˜
1587 (m), 1572 (m), 1535 [s, ν(NO2)], 1494 (s), 1456 (m), 1398 (w),
1376 (s), 1358 [s, ν(NO2)], 1301 (m), 1253 (m), 1196 (w), 1152 (m),
1138 (m), 1102 (w), 1039 (w), 1019 (w), 957 (m), 852 (m), 814 (m),
780 (m), 750 (m), 703 (m), 645 (w) cm–1. 1H NMR (400 MHz,
CDCl3, 25 °C): δ = 8.06 (dd, 3JHH = 8.1, 4JHH = 1.2 Hz, 2 H, Hph),
solid. IR (KBr): ν = 2961 (s), 2864 (m), 1599 (m), 1576 (s), 1528
˜
(s), 1478 (w), 1447 (w), 1392 (w), 1355 (m), 1314 (w), 1254 (m),
1078 (w), 992 (w), 899 (m), 863 (m), 822 (m), 786 (m), 741 (m), 667
1
(m), 634 (m), 545 (w), 475 (m) cm–1. H NMR (400 MHz, CDCl3,
5
25 °C): δ = 9.26 (d, JHH = 1.0 Hz, 2 H, 2-Hpm), 8.61 (d, 2 H, 5-
3
7.92 (d, JHH = 7.8 Hz, 2 H, 3,5-Hpy), 7.75 (m, 3 H, 4-Hpy, Hph),
3
Hpm), 8.59 (d, JHH = 7.8 Hz, 2 H, 3,5-Hpy), 8.05 (t, 1 H, 4-Hpy),
3
4
3
7.64 (dt, JHH = 7.8, JHH = 1.2 Hz, 2 H, Hph), 7.59 (dd, JHH
=
1.47 (s, 18 H, tBu) ppm. 13C{1H} NMR (100.6 MHz, CDCl3,
25 °C): δ = 179.0 (4-Cpm), 162.5 (6-Cpm), 158.4 (2-Cpm), 154.1 (2,6-
Cpy), 138.5 (4-Cpy), 123.1 (3,5-Cpy), 112.7 (5-Cpm), 37.9 [C(CH3)3],
29.5 [C(CH3)3] ppm. C21H25N5 (347.44): calcd. C 72.39, H 7.51, N
18.67; found C 72.59, H 7.25, N 20.16.
4
7.8, JHH = 1.2 Hz, 2 H, Hph), 7.23 (s, 2 H, 4-Hpz), 2.59 (t, 4 H,
CH2), 1.68 (q, 4 H, CH2), 1.39 (sext, 4 H, CH2), 0.89 (t, 6 H, CH3)
ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 25 °C): δ = 153.3 (5-
Cpz), 151.3 (2,6-Cpy), 146.8, 146.7, 137.4, 133.4, 133.3, 129.8, 129.8,
125.4, 119.51, 105.1 (4-Cpz), 30.7 (CH2), 25.70 (CH2), 22.35 (CH2),
2,6-Bis(1,5-dibutylpyrazol-3-yl)pyridine (4b) and 2,6-Bis(1-benzyl-5- 13.79 (CH3) ppm. C31H31N7O4 (565.60): calcd. C 65.83, H 5.52, N
butylpyrazol-3-yl)pyridine (4c): NaH (0.74 g, 31 mmol) was sus-
pended in dry THF (150 mL). Solid 4a (4.85 g, 15 mmol) was
added slowly, and the resulting mixture was stirred at room temp.
until the evolution of H2 had ceased. Then of either butyl or benzyl
bromide (33 mmol) was added, and the solution was heated under
reflux for 8 h. After filtration of NaBr, the solvent was removed in
vacuo, and the crude product was purified by column chromatog-
raphy (4b: SiO2; ethyl acetate; 4c: Al2O3; hexane/ethyl acetate, 1:1).
Yields: 4.20 g (64%) of 4b, bright brown solid; 3.20 g (41%) of 4c,
17.34; found C 65.73, H 5.65, N 17.33. 4e: Mp. 214 °C. IR (KBr):
ν = 2954 (m), 2932 (m), 2871 (m), 1596 (s), 1574 (m), 1520 [s,
˜
ν(NO2)], 1497 (s), 1452 (m), 1378 (m), 1339 [s, ν(NO2)], 1259 (m),
1198 (m), 1153 (m), 1131 (m), 1109 (m), 1082 (m), 1025 (m), 1008
(m), 955 (w), 853 (m), 802 (m), 788 (m), 750 (m), 730 (w), 689 (w),
644 (w), 534 (w) cm–1. 1H NMR (400 MHz, CDCl3, 25 °C): δ =
3
8.38 (m, 4 H, m-Hph), 8.05 (d, JHH = 7.7 Hz, 2 H, 3,5-Hpy), 7.85
(t, 1 H, 4-Hpy), 7.77 (m, 4 H, o-Hph), 7.21 (s, 2 H, 4-Hpz), 2.81 (t,
4 H, CH2), 1.74 (q, 4 H, CH2), 1.42 (sext, 4 H, CH2), 0.93 (t, 6 H,
colourless oil. 4b: IR (KBr): ν = 2957 (s), 2931 (s), 2871 (s), 1594 CH3) ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 25 °C): δ = 152.9
˜
(m), 1573 (m), 1545 (m), 1503 (m), 1464 (m), 1402 (m), 1381 (m), (5-Cpz), 151.2 (2,6-Cpy), 146.6 (3-Cpz), 146.1, 145.2 (i-Cph, p-Cph),
1346 (m), 1315 (m), 1283 (m), 1254 (m), 1194 (m), 1151 (w), 1078 137.9 (4-Cpy), 125.1 (m-Cph), 124.9 (o-Cph), 119.9 (3,5-Cpy), 106.8
1
(m), 991 (w), 960 (m), 800 (m), 743 (m), 649 (w) cm–1. H NMR
(4-Cpz), 31.1 (CH2), 26.8 (CH2), 22.5 (CH2), 13.9 (CH3) ppm.
3
(400 MHz, CDCl3, 25 °C): δ = 7.81 (d, JHH = 7.7 Hz, 2 H, 3,5- C31H31N7O4 (565.60): calcd. C 65.83, H 5.52, N 17.34; found C
Hpy), 7.67 (t, 1 H, 4-Hpy), 6.77 (s, 2 H, 4-Hpz), 4.06 (t, 4 H, NCH2),
3652
65.55, H 5.30, N 16.98.
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3648–3654

Iron and Cobalt Complexes of Tridentate N-Donor Ligands
Synthesis of the Dichloridoiron and -cobalt Complexes 6b–eFe, 6b–
eCo, 7Fe, and 7Co: FeCl2 or CoCl2 (1 equiv., ca. 1.00 g) was added
to a solution of the tridentate ligand 4b–e or 5 (1 equiv.) in dry and
degassed methanol (50 mL). The solution was heated to reflux for
4 h. After cooling to room temp., about 80% of the solvent was
removed in vacuo, and the precipitated products were isolated by
filtration and dried in vacuo.
was solved by direct methods.[15] The hydrogen atoms were local-
ized geometrically, a riding model was taken for refinement.[16]
CCDC-692307 (3b) and CCDC-692308 (4d) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Table 3. Crystal data and structural refinement for compounds 3b
and 4d.
[2,6-Bis(1,5-dibutylpyrazol-3-yl)pyridine]dichloridoiron(II) (6bFe):
Yield: 33%, orange yellow solid. MALDI-TOF MS: m/z (%) =
561.17 (23) [M]+, 526.25 (100) [M – Cl]+. C27H41Cl2FeN5 (562.41):
calcd. C 57.66, H 7.35, N 12.45; found C 57.74, H 7.31, N 12.59.
3b
4d
Empirical formula
Formula mass
Crystal size [mm]3
Scan mode
Crystal system
Space group
T [K]
C19H25NO4
331.40
C31H31N7O4
565.63
[2,6-Bis(1,5-dibutylpyrazol-3-yl)pyridine]dichloridocobalt(II) (6bCo):
Yield: 52%, green solid. MALDI-TOF MS: m/z (%) = 529.19 (100)
[M – Cl]+. C27H41Cl2CoN5 (565.50): calcd. C 57.35, H 7.31, N
12.38; found C 56.70, H 7.08, N 12.28.
0.42ϫ0.32ϫ0.09
Φ-oscillation
monoclinic
P21/n (no. 14)
293(2)
0.45ϫ0.38ϫ0.27
Φ-oscillation
triclinic
¯
P1 (no. 2)
193(2)
[2,6-Bis(1-benzyl-5-butylpyrazol-3-yl)pyridine]dichloridoiron(II) (6cFe):
Yield: 67%, bright brown solid. MALDI-TOF MS: m/z (%) =
594.11 (100) [M – Cl]+. C33H37Cl2FeN5 (630.40): calcd. C 62.87, H
5.92, N 11.10; found C 62.75, H 6.04, N 10.96.
a [Å]
b [Å]
c [Å]
α [°]
15.698(3)
6.2374(6)
19.935(3)
90
100.235(19)
90
1920.9(5)
4
1.146
9.5267(8)
10.8174(9)
15.0455(13)
105.179(10)
97.332(10)
98.290(10)
1458.4(2)
2
β [°]
[2,6-Bis(1-benzyl-5-butylpyrazol-3-yl)pyridine]dichloridocobalt(II)
(6cCo): Yield: 58 %, green solid. MALDI-TOF MS: m/z (%) =
597.29 (100) [M – Cl]+. C33H37Cl2CoN5 (633.49): calcd. C 62.56,
H 5.89, N 11.11; found C 62.71, H 5.70, N 11.10.
γ [°]
V [Å3]
Z
ρcalcd. [gcm–1]
1.288
0.088
µ [mm–1]
0.080
{2,6-Bis[5-butyl-1-(2-nitrophenyl)pyrazol-3-yl]pyridine}dichlorido-
F(000)
712
596
iron(II) (6dFe): Yield: 72%, bright brown solid. IR (KBr): ν = 1531
˜
θmin–θmax [°]
h, k, l
2.1 to 24.0
2.7 to 26.7
(s), 1342 [s, 2 ν(NO2)] cm–1. MALDI-TOF MS: m/z (%) = 690.99
(100) [M]+, 656.05 (90) [M – Cl]+, 566.22 (16) [M – FeCl2]+.
C31H31Cl2FeN7O4 (692.34): calcd. C 53.78, H 4.51, N 14.16; found
C 53.53, H 4.38, N 13.81.
–17/17, –6/6 –22/22 –12/12, –13/13 –19/19
Total data
Unique data
Observed data [IϾ2.0σ(I)]
Nref, Npar
R (all data)
wR2 (all data)
R [IϾ2.0σ(I)]
wR2 [IϾ2.0σ(I)]
GooF
14517
2942
1269
2942, 229
0.1136
0.1328
0.0533
0.1179
0.859
15595
5706
4123
5706, 457
0.0698
0.1468
0.0503
0.1343
1.043
{2,6-Bis[5-butyl-1-(2-nitrophenyl)pyrazol-3-yl]pyridine}dichlorido-
cobalt(II) (6dCo): Yield: 67%, green solid. IR (KBr): ν = 1531 (s),
˜
1342 [s, 2 ν(NO2)] cm–1. MALDI-TOF MS: m/z (%) = 658.81 (100)
[M – Cl]+, 563.89 (10) [M – CoCl2]+. C31H31Cl2CoN7O4 (695.47):
calcd. C 53.59, H 4.50, N 14.12; found C 53.68, H 4.54, N 13.93.
Min/max residual density [eA–3] 0.160/–0.134
–0.212/0.188
{2,6-Bis[5-butyl-1-(4-nitrophenyl)pyrazol-3-yl]pyridine}dichlorido-
iron(II) (6eFe): Yield: 65%, bright brown solid. IR (KBr): ν = 1528
˜
(s), 1344 [s, 2 ν(NO2)] cm–1. MALDI-TOF MS: m/z (%) = 656.31
(100) [M – Cl]+, 642.43 (25) [M – Cl – CH3]+, 629.32 (25) [M –
Cl – 2 CH3]+, 566.43 (29) [M – FeCl2]+, 535.33 (38) [M – FeCl2 –
2 CH3]+. C31H31Cl2FeN7O4 (692.38): calcd. C 53.78, H 4.51, N
14.16; found C 53.67, H 4.59, N 14.15.
Acknowledgments
The authors wish to thank the Deutsche Forschungsgemeinschaft
for financial support of this work and the analytical and polymeri-
zation laboratories at Basell Polyolefin GmbH for their help in the
evaluation of the polymers.
{2,6-Bis[5-butyl-1-(4-nitrophenyl)pyrazol-3-yl]pyridine}dichlorido-
cobalt(II) (6eCo): Yield: 76%, green solid. IR (KBr): ν = 1526 (s),
˜
1344 [s, 2 ν(NO2)] cm–1. MALDI-TOF MS: m/z (%) = 659.44 (100)
[M – Cl]+, 643.43 (34) [M – Cl – CH3]+, 630.43 (44) [M – Cl – 2
CH3]+, 566.53 (14) [M – CoCl2]+. C31H31Cl2CoN7O4 (695.43):
calcd. C 53.54, H 4.49, N 14.09; found C 53.68, H 4.61, N 14.16.
[1] a) B. L. Small, M. Brookhart, A. M. A. Bennet, J. Am. Chem.
Soc. 1998, 120, 4049–4050; b) B. L. Small, M. Broohart, J. Am.
Chem. Soc. 1998, 120, 7143–7144; c) B. L. Small, M. Broohart,
Macromolecules 1999, 32, 2120–2130; d) E. L. Dias, M. Brook-
hart, P. S. White, Organometallics 2000, 19, 4995–5004; e)
G. J. P. Britovsek, V. C. Gibson, B. S. Kimberley, P. J. Maddox,
S. J. McTavish, G. A. Solan, A. J. P. White, D. J. Williams,
Chem. Commun. 1998, 849–850; f) G. K. B. Glentsmith, V. C.
Gibson, P. B. Hitcock, B. S. Kimberley, C. W. Rees, Chem.
Commun. 2002, 1498–1499; g) V. C. Gibson, K. P. Tellmann,
M. J. Humphries, D. F. Wass, Chem. Commun. 2002, 2316–
2317.
[2,6-Bis(6-tert-butylpyrimidin-4-yl)pyridine]dichoridoiron(II) (7Fe):
Yield: 87%, dark blue solid. MALDI-TOF MS: m/z (%) = 473.25
(100) [M]+, 438.29 (90) [M – Cl]+. C21H25Cl2FeN5 (474.22): calcd.
C 53.19, H 5.31, N 14.95; found C 52.19, H 5.32, N 14.12.
[2,6-Bis(6-tert-butylpyrimidin-4-yl)pyridine]dichloridocobalt(II) (7Co):
Yield: 89%, bright green solid. MALDI-TOF MS: m/z (%) =
441.27 (100) [M]+. C21H25Cl2CoN5 (477.30): calcd. C 52.85, H
5.28, N 14.67; found C 52.76, H 5.33, N 14.42.
[2] a) G. P. P. Britovsek, V. C. Gibson, D. F. Wass, Angew. Chem.
1999, 111, 448–468; Angew. Chem. Int. Ed. 1999, 38, 428–447;
b) P. Margl, L. Deng, T. Ziegler, Organometallics 1999, 18,
5701–5708.
X-ray Structure Analyses of Compounds 3b and 4d: The crystal data
of compounds 3b and 4d were obtained with a Stoe IPDS dif-
fractometer with Mo-Kα radiation (λ = 0.71073 Å).[14] Table 3 sum-
marizes the crystallographic and refinement data. The structure
[3] a) S. Mecking, Angew. Chem. 2001, 113, 550–557; Angew.
Chem. Int. Ed. 2001, 40, 534–540; b) D. V. Khoroshun, D. G.
Eur. J. Inorg. Chem. 2008, 3648–3654
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3653

D. Zabel, A. Schubert, G. Wolmershäuser, R. L. Jones Jr, W. R. Thiel
FULL PAPER
Musaev, T. Vreven, K. Morokuma, Organometallics 2001, 20,
2007–2026; c) L. Deng, P. Margl, T. Ziegler, J. Am. Chem. Soc.
1999, 121, 6479–6487.
Thiel, J. Organomet. Chem. 2001, 621, 153–157; h) M. Jia,
W. R. Thiel, Chem. Commun. 2002, 2392–2393.
K. Rößler, T. Kluge, A. Schubert, Y. Sun, E. Herdtweck, W. R.
Thiel, Z. Naturforsch., Teil B 2004, 59, 1253–1264.
a) H. Nishiyama, T. Shimada, H. Itoh, H. Sugiyama, Y. Mo-
toyama, Chem. Commun. 1997, 1863–1864; b) Y. Ura, H. Tsu-
jita, K. Wada, T. Kondo, T. Mitsudo, J. Org. Chem. 2005, 70,
6623–6628.
C. Reichardt, A. Blum, K. Harms, G. Schäfer, Liebigs Ann./
Recueil 1997, 707–720.
A.-K. Pleier, H. Glas, M. Grosche, P. Sirsch, W. R. Thiel, Syn-
thesis 2001, 55–62.
R. W. Saalfrank, N. Löw, S. Trummer, G. M. Sheldrick, M. Te-
ichert, D. Stalke, Eur. J. Inorg. Chem. 1998, 559–563.
[7]
[8]
[4] a) P. Cossee, J. Catal. 1964, 3, 80–88; b) E. J. Arlman, P. Cossee,
J. Catal. 1964, 3, 99–104; c) I. Silanes, J. M. Ugalde, Organome-
tallics 2005, 24, 3233–3246.
[5] a) W.-H. Sun, X. Tang, T. Gao, B. Wu, W. Zhang, H. Ma,
Organometallics 2004, 23, 5037–5047; b) C. Bianchini, G. Gi-
ambastiani, I. R. Guerrero, A. Meli, E. Passaglia, T. Gragnoli,
Organometallics 2004, 23, 6087–6089; c) T. M. Kooistra, Q.
Knijnenburg, J. M. M. Budzelaar, A. W. Gal, Angew. Chem.
2001, 113, 4855–4858; Angew. Chem. Int. Ed. 2001, 40, 4719–
4722; d) Y. Chen, R. Chen, C. Qian, X. Dong, J. Sun, Organo-
metallics 2003, 22, 4312–4321; e) K. P. Tellmann, V. C. Gibson,
A. J. P. White, D. J. Williams, Organometallics 2005, 24, 280–
286; f) W.-H. Sun, S. Jie, S. Zhang, W. Zhang, Y. Song, H. Ma,
Organometallics 2006, 25, 666–677; g) M. W. Bouwkamp, E. L.
Lobkovsky, P. J. Chirik, J. Am. Chem. Soc. 2005, 127, 9660–
9661; h) F. A. R. Kaul, G. T. Puchta, G. D. Frey, E. Herdtweck,
W. A. Herrmann, Organometallics 2007, 26, 988–999; i) C. Bi-
anchini, D. Gatteschi, G. Giambastiani, I. G. Rios, A. Ienco,
F. Laschi, C. Mealli, A. Meli, L. Sorace, A. Toti, F. Vizza,
Organometallics 2007, 26, 726–739; j) V. C. Gibson, N. J. Long,
P. J. Oxford, A. J. P. White, D. J. Williams, Organometallics
2006, 25, 1932–1939; k) J. Cámpora, A. M. Naz, P. Palma, E.
Álvarez, Organometallics 2005, 24, 4878–4881; l) W. Zhang, W.-
H. Sun, S. Zhang, J. Hou, K. Wedeking, S. Schulz, R. Fröhlich,
H. Song, Organometallics 2006, 25, 1961–1969.
[9]
[10]
[11]
[12] a) T. Shiga, T. Nakanishi, M. Ohba, H. Okawa, Polyhedron
2005, 24, 2732–2736; b) R. W. Saalfrank, V. Seitz, D. L.
Caulder, K. N. Raymond, M. Teichert, D. Stalke, Eur. J. Inorg.
Chem. 1998, 1313–1317; c) T. Shiga, M. Ohba, H. Okawa, In-
org. Chem. 2004, 43, 4435–4446; d) R. W. Saalfrank, A. Dresel,
V. Seitz, S. Trummer, F. Hampel, M. Teichert, D. Stalke, C.
Stadler, J. Daub, V. Schünemann, A. X. Trautwein, Chem. Eur.
J. 1997, 3, 2058–2062; e) T. Shiga, M. Ohba, H. Okawa, Inorg.
Chem. Commun. 2003, 6, 15–18; f) R. W. Saalfrank, V. Seitz,
F. W. Heinemann, C. Göbel, R. Herbst-Irmer, J. Chem. Soc.,
Dalton Trans. 2001, 599–603.
[13] J. J. P. Stewart, J. Comput. Chem. 1989, 10, 209–220.
[14] IPDS software: IPDS Operating System, version 2.8., Stoe &
Cie. GmbH, Darmstadt, Germany, 1997.
[15] SIR92: A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagli-
ardi, M. C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr.
1994, 27, 435–436.
[6] a) W. R. Thiel, M. Angstl, T. Priermeier, Chem. Ber. 1994, 127,
2373–2377; b) W. R. Thiel, M. Angstl, N. Hansen, J. Mol. Ca-
tal. A 1995, 103, 5–10; c) M. Barz, E. Herdtweck, W. R. Thiel,
Tetrahedron: Asymmetry 1996, 7, 1717–1722; d) W. R. Thiel, J.
Eppinger, Chem. Eur. J. 1997, 3, 696–705; e) H. Glas, E.
Herdtweck, G. R. J. Artus, W. R. Thiel, Inorg. Chem. 1998, 37,
3644–3646; f) A. Hroch, G. Gemmecker, W. R. Thiel, Eur. J.
Inorg. Chem. 2000, 3, 1107–1114; g) H. Glas, M. Barz, W. R.
[16] G. M. Sheldrick, SHELXL-97, University of Göttingen,
Göttingen, Germany, 1998.
Received: April 11, 2008
Published Online: July 4, 2008
3654
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3648–3654