Synthesis of new polydentate nitrogen ligands and their use in ethylene polymerization in conjunction with iron(II) and cobalt(II) bis-halides and methylaluminoxane

Article abstract of DOI:10.1021/om7005062

Original synthetic routes to polydentate nitrogen ligands combining in the same molecular structure either 2,6-bis(imino)pyridine and (imino)pyridine moieties or two 2,6-bis(imino)pyridine units are described. The tris-imino-bis-pyridine ligands (^Me<

Full text of DOI:10.1021/om7005062

Organometallics 2007, 26, 4639-4651
4639
Synthesis of New Polydentate Nitrogen Ligands and Their Use in
Ethylene Polymerization in Conjunction with Iron(II) and Cobalt(II)
Bis-halides and Methylaluminoxane
Pierluigi Barbaro,† Claudio Bianchini,*,† Giuliano Giambastiani,† Itzel Guerrero Rios,†
Andrea Meli,† Werner Oberhauser,† Anna M. Segarra,† Lorenzo Sorace,‡ and
Alessandro Toti†
Istituto di Chimica dei Composti Organometallici (ICCOM-CNR), Via Madonna del Piano 10,
50019 Sesto Fiorentino (Firenze), Italy, and Dipartimento di Chimica and UdR INSTM, UniVersita` di
Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino (Firenze), Italy
ReceiVed May 22, 2007
Original synthetic routes to polydentate nitrogen ligands combining in the same molecular structure
either 2,6-bis(imino)pyridine and (imino)pyridine moieties or two 2,6-bis(imino)pyridine units are
described. The tris-imino-bis-pyridine ligands (MeN5 and iPrN5) and the tetrakis-imino-bis-pyridine ligand
(iPrN6) react with FeCl2 and/or CoX2 (X ) Cl, Br) to give paramagnetic monometallic, homobimetallic,
or heterobimetallic complexes. These have been characterized, both in the solid state and in solution, by
a variety of techniques, including single-crystal X-ray diffraction analyses, magnetic susceptibility
1
determinations, IR, vis-NIR, H NMR, and X-band EPR spectroscopies. The combination of these
analytical tools has allowed us to unravel the geometrical and electronic structure of quite complicated
systems. Selected mono- and binuclear FeII and CoII complexes have been used as catalyst precursors in
toluene for the polymerization of ethylene to high-density polyethylene (HDPE) upon activation with
MAO. From fairly good to very good catalytic activities (up to 64.5 tons of PE (mol of M)-1 h-1) have
been observed. Of particular relevance is the dicobalt complex iPrN6Co2Cl4, which is more active than
any other known CoII catalyst for the polymerization of ethylene to HDPE.
The most relevant and studied application is certainly the
oligomerization and polymerization of ethylene, independently
discovered by Brookhart, Bennett, and Gibson in 1998.6,7 Since
then, five-coordinate 2,6-bis(arylimino)pyridine FeII and CoII
dihalides, activated by MAO, are currently used as catalyst
precursors to convert ethylene either to high-density polyeth-
ylene (HDPE) or to R-olefins with turnover frequencies (TOFs)
as high as several million moles of C2H4 converted (mol of
metal)-1 h-1 (Scheme 1a).9,10
Introduction
Remarkable advances in homogeneous catalysis have been
recently achieved with systems comprising late transition metals
and 2,6-bis(imino)pyridine ligands. Successful reactions span
from the epoxidation1 and cyclopropanation2 of olefins, to the
enantioselective reduction of prochiral ketones,3 to the hydro-
genation of olefins,4 to the dimerization of R-olefins,5 to the
oligomerization and polymerization of ethylene6,7 and propene.5,8
The advantages of 2,6-bis(arylimino)pyridine FeII and CoII
catalysts over other types of single-site Ziegler-Natta catalysts
for ethylene homopolymerization (e.g., metallocenes, con-
strained geometry early transition metal complexes) are mani-
fold, spanning from the ease of preparation and handling to the
use of low-cost metals with negligible environmental impact.9
Another intriguing feature of bis(imino)pyridine FeII and CoII
precursors is provided by the facile tuning of their polymeri-
zation activity by simple modifications of the ligand architecture
that can be adjusted so as to allow for the use of the cor-
responding catalysts in heterogeneous polymerization reac-
tions.10 It has been shown that the number, size, nature, and
regiochemistry of the substituents in the arylimino groups are
of crucial importance in controlling the polymerization activ-
ity.9,10 Moreover, due to the good compatibility with various
early and late metal copolymerization catalysts, 2,6-bis(arylimi-
no)pyridine FeII and CoII dihalides can be used as oligomer-
* To whom correspondence should be addressed. E-mail:
claudio.bianchini@iccom.cnr.it.
† ICCOM-CNR.
‡ Universita` di Firenze and UdR INSTM-Firenze.
(1) C¸ etinkaya, B.; C¸ etinkaya, E.; Brookhart, M.; White, P. S. J. Mol.
Catal. A 1999, 142, 101.
(2) Bianchini, C.; Lee H. M. Organometallics 2000, 19, 1833.
(3) De Matrin, S.; Zassinovich, G.; Mestroni, G. Inorg. Chim. Acta 1990,
174, 9.
(4) Knijnenburg, Q.; Horton, A. D.; van der Heijden, H.; Kooistra, T.
M.; Hettershield, D. G. H.; Smits, J. M. M.; de Bruin, B.; Budzelaar, P. H.
M.; Gal, A. W. Eur. J. Inorg. Chem. 2004, 1204.
(5) (a) Tellmann, K. P.; Gibson, V. C.; White, A. J. P.; Williams, D. J.
Organometallics 2005, 24, 280. (b) Small, B. L.; Schmidt, R. Chem.-Eur.
J. 2004, 10, 1014. (c) Small, B. L. Organometallics 2003, 22, 3178. (d)
Small, B. L.; Marcucci, A. J. Organometallics 2001, 20, 5738.
(6) (a) Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143.
(b) Britovsek, G. J. P.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.; Maddox,
P. J.; McTavish, S. J.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem.
Commun. 1998, 849. (c) Britovsek, G. J. P.; Mastroianni, S.; Solan, G. A.;
Baugh, S. P. D.; Redshaw, C.; Gibson, V. C.; White, A. J. P.; Williams, D.
J.; Elsegood, M. R. J. Chem.-Eur. J. 2000, 6, 2221.
(7) (a) Britovsek, G. J. P.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.;
Maddox, P. J.; Mastroianni, S.; McTavish, S. J.; Redshaw, C.; Solan, G.
A.; Stro¨mberg, S.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1999,
121, 8728. (b) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem.
Soc. 1998, 120, 4049. (c) Bennett, A. M. A. (DuPont) WO 98/27124, 1998.
(8) Small, B. L.; Brookhart, M. Macromolecules 1999, 32, 2120.
(9) (a) Britovsek, G. J. P.; Gibson, V. C.; Wass D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428. (b) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem.
ReV. 2000, 100, 1169.
(10) (a) Bianchini, C.; Giambastiani, G.; Guerrero Rios, I.; Mantovani,
G.; Meli, A.; Segarra, A. M. Coord. Chem. ReV. 2006, 250, 1391. (b)
Gibson, V. C.; Redshaw, C.; Solan, G. A. Chem. ReV. 2007, 107, 1745.
10.1021/om7005062 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/01/2007

4640 Organometallics, Vol. 26, No. 18, 2007
Barbaro et al.
Scheme 1
Scheme 2
ization catalysts in tandem catalytic systems for the production
of branched PE as well as in reactor blending processes to give
PE with controlled molecular weight distribution and rheology.10
The one-pot transformation of ethylene into mixtures of HDPE
and R-olefins with a Schulz-Flory distribution has also been
achieved with C1-symmetric 2,6-bis(imino)pyridine FeII di-
halides.11
The success of 2,6-bis(imino)pyridine ligands in ethylene
polymerization/oligomerization has also stimulated much re-
search aimed at developing late transition metal catalysts with
(imino)pyridine ligands. A number of (mono-imino)pyridine CoII
catalysts are already available for the oligomerization of ethylene
to R-olefins with TOFs as high as 1.5 × 106 mol of C2H4
converted (mol of metal)-1 h-1 as well as the production of
low-density polyethylene (LDPE) via tandem catalysis in
conjunction with metallocenes (Scheme 1b).12,13
Scheme 3
In light of the increasing number of publications and patents,
the search for new molecular architectures of either 2,6-bis-
(imino)pyridine or (imino)pyridine ligands seems to be endless,14
yet no example of ligands combining both structural motifs has
been reported so far. Likewise, the condensation of two 2,6-
bis(imino)pyridine units into a single molecule has never been
described as such, the only examples of dimerization of 2,6-
bis(imino)pyridine ligands being those reported by Gambarotta15
(Scheme 2a) and by Gibson14d (Scheme 2b).
In this paper, we report two original synthetic routes to ligands
that combine in the same molecular structure either 2,6-bis-
(imino)pyridine and (imino)pyridine moieties or two 2,6-bis-
(imino)pyridine units (Scheme 3).
We describe also the synthesis and characterization of several
FeII, CoII, and NiII monometallic and homo- and hetero-
bimetallic complexes with these new polydentate nitrogen
ligands, and finally, we provide some preliminary data on their
use, in combination with MAO, as catalysts for the polymeri-
zation of ethylene to HDPE.
techniques. Anhydrous benzene, toluene, THF, and Et2O were
obtained by means of an MBraun solvent purification system, while
CH2Cl2 and MeOH were distilled over CaH2 and Mg, respectively.
A 10 wt % solution of methylaluminoxane (MAO) in toluene (d )
0.88 g mL-1) was purchased from Aldrich. All the other reagents
and solvents were used as purchased from commercial suppliers.
Catalytic reactions were performed with a 500 mL stainless steel
reactor, constructed at the ICCOM-CNR (Firenze, Italy), equipped
with a magnetic drive stirrer and a Parr 4842 temperature and
pressure controller. The reactor was connected to an ethylene
reservoir to maintain a constant pressure throughout the catalytic
runs. Deuterated solvents for NMR measurements were dried over
4 Å molecular sieves. 1H and 13C{1H} NMR spectra were recorded
on Bruker ACP 200 (200.13 and 50.32 MHz, respectively) and
Bruker Avance DRX-400 (400.13 and 100.62 MHz, respectively)
spectrometers equipped with variable-temperature control units
accurate to (0.1 °C. Chemical shifts are reported in ppm (δ) relative
to TMS or referenced to the chemical shifts of residual solvent
resonances (1H and 13C). The number of protons attached to the
carbon nuclei was determined by means of both 13C{1H} DEPT
135 and J-modulated spin-echo NMR pulse programs. The
assignment of the signals was achieved with the aid of 1D spectra,
2D 1H COSY, 1H NOESY, and proton detected 1H-13C correlations
(HMQC) using nonspinning samples. 2D NMR spectra were
recorded with pulse sequences suitable for phase-sensitive repre-
sentations using TPPI. 1H NOESY measurements16 were recorded
with 1024 increments of size 2 K (with 8 scans each) covering the
full range in both dimensions and with mixing times of 800 and
Experimental Section
General Considerations. All manipulations and reactions were
carried out under an atmosphere of nitrogen using standard Schlenk
(11) Bianchini, C.; Giambastiani, G.; Guerrero Rios, I.; Meli, A.;
Passaglia, E.; Gragnoli, T. Organometallics. 2004, 23, 6087.
(12) (a) Bianchini, C.; Mantovani, G.; Meli, A.; Migliacci, F.; Laschi,
F. Organometallics 2003, 22, 2545. (b) Bianchini, C.; Giambastiani, G.;
Mantovani, G.; Meli, A.; Mimeau, D. J. Organomet. Chem. 2004, 689,
1356. (c) Bianchini, C.; Gatteschi, D.; Giambastiani, G.; Guerrero Rios, I.;
Ienco, A.; Laschi, F.; Mealli, C.; Meli, A.; Sorace, L.; Toti, A.; Vizza, F.
Organometallics. 2007, 26, 726.
(13) Bianchini, C.; Frediani, M.; Giambastiani, G.; Kaminsky, W.; Meli,
A.; Passaglia, E. Macromol. Rapid Commun. 2005, 26, 1218.
(14) (a) Wang, L.; Sun, W.-H.; Han, L.; Yang, H.; Hu, Y.; Jin, X. J.
Organomet. Chem. 2002, 658, 62. (b) Britovsek, G. J. P.; Baugh, S. P. D.;
Hoarau, O.; Gibson, V. C.; Wass D. F., White, A. J. P.; Williams, D. J.
Inorg. Chim. Acta 2003, 345, 279. (c) Liu, Jingyu; Li, Y.; Liu, Jingyao; Li,
Z. Macromolecules 2005, 38, 2559. (d) Gibson, V. C.; McTavish, S. J.;
Redshaw, C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Dalton Trans.
2003, 221. (e) Champouret, Y. D. M.; Mare´chal J.-D.; Dadhiwala, I.;
Fawcett, J.; Palmer, D.; Singh, K.; Solan G. A. Dalton Trans. 2006, 2350.
(15) Scott, J.; Gambarotta, S.; Korobkov, I.; Budzelaar, P. H. M. J. Am.
Chem. Soc. 2005, 127, 13019.
1
300 ms. H-13C HMQC correlations17 were recorded by use of
the standard sequence with decoupling during acquisition. Elemental
(16) (a) Sklener, V.; Miyashiro, H.; Zon, G.; Miles, H. T.; Bax, A. FEBS
Lett. 1986, 208, 94. (b) Jeener, J.; Meier, B. H.; Bachmann, P.; Ernst, R.
R. J. Chem. Phys. 1979, 71, 4546.
(17) Bax, A. A.; Griffey, R. H.; Hawkins, B. L. J. Magn. Reson. 1983,
55, 301.

Synthesis of New Polydentate Nitrogen Ligands
Organometallics, Vol. 26, No. 18, 2007 4641
analyses were performed using a Carlo Erba model 1106 elemental
analyzer with an accepted tolerance of (0.4 unit on carbon (C),
hydrogen (H), and nitrogen (N). Melting points were ensued by
using a Stuart Scientific melting point apparatus SMP3. Conductiv-
ity measurement was obtained with an Orion model 990101
conductance cell connected to a model 101 conductivity meter. The
conductivity data18 were obtained at sample concentrations of ca.
10-3 M in 1,2-dichloroethane solution. Magnetic moments were
measured at 22 °C with a Cryogenic SQUID S600 magnetometer
at three different applied magnetic fields (0.5, 1, and 2 T). Raw
data were corrected for the diamagnetism of the sample holder,
measured in the same conditions, and for the intrinsic diamagnetism
of the sample, estimated through Pascal’s constants. Vis-NIR
spectra (range 25000-4550 cm-1) in both solid state (reflectance)
and CH2Cl2 solution (absorption) were recorded on a Perkin-Elmer
Lamda 9 spectrophotometer. Infrared spectra were recorded with
a Perkin-Elmer Spectrum BX FT-IR spectrophotometer. X-band
EPR spectra on both powder and frozen solution (CH2Cl2) samples
were recorded on a Bruker Elexsys E500 spectrometer equipped
cooled to room temperature and then treated with 5 mL of a 0.5 M
aqueous NaOH solution. The formed layers were separated. The
aqueous phase was washed with Et2O (2 × 5 mL), and the
combined organic extracts were dried over NaSO4. After removal
of the solvent under reduced pressure a white solid was obtained
in a pure form (yield >99%). Mp: 40-42 °C. 1H NMR (CDCl3):
δ 1.80 (s, 3H, Me), 3.95-4.20 (m, 4H, CH2), 7.49 (dd, J ) 7.7,
1.3 Hz, 1H, Py-Hm), 7.58-7.65 (m, 2H, Py-Hm/Hp). 13C{1H} NMR
(CDCl3): δ 25.6 (1C, Me), 65.6 (2C, CH2), 108.5 (1C, OCO), 118.9
(1C, Py-CHm), 128.1 (1C, Py-CHm), 139.6 (1C, Py-CHp), 142.5
(1C, Py-C-Br), 163.0 (1C, Py-C-CO). Anal. Calcd (%) for C9H10-
BrNO2 (244.09): C, 44.29; H, 4.13; N, 5.74. Found: C, 44.09; H,
4.22; N, 5.69.
Synthesis of Bis[3-(2-methyl-1,3dioxolan-2-yl)pyridin-2-yl]-
methanone. A solution of 6-bromo-2-(2′-methyl-1′,3′-dioxolan-2′-
yl)pyridine (2.64 g, 10.81 mmol) in 50 mL of THF at -78 °C was
treated dropwise with a 1.7 M solution of t-BuLi in n-pentane (6.67
mL, 11.35 mmol) over 15 min. After 30 min at -78 °C,
methylchloroformate (0.42 mL, 5.40 mmol) was added dropwise
over 10 min. The reaction mixture was stirred for an additional 1
h at -78 °C and then allowed to warm at room temperature
overnight. Brine was added, and the phases were separated. The
aqueous layer was extracted with 30 mL of Et2O and subsequently
with CH2Cl2 (2 × 25 mL). The combined organic layers were dried
over Na2SO4, and after removal of solvents under reduce pressure,
a pale yellow solid was obtained as the pure product (yield 91%).
Mp: 96-97 °C. IR (KBr): ν 1677 cm-1 (CdO). 1H NMR
(CDCl3): δ 1.73 (s, 6H, Me), 3.88-4.13 (m, 8H, CH2), 7.73 (dd,
J ) 7.7, 1.3 Hz, 2H, Py-Hm), 7.88 (dd, J ) 7.7, 7.6 Hz, 2H, Py-
Hp), 8.03 (dd, J ) 7.6, 1.3 Hz, 2H, Py-Hm) 13C{1H} NMR
(CDCl3): δ 25.5 (2C, Me), 65.7 (4C, CH2), 109.2 (2C, OCO), 122.6
(2C, Py-CH), 125.0 (2C, Py-CH), 137.7 (2C, Py-CHp), 154.9 (2C,
Py-C), 160.9 (2C, Py-C), 193.7 (2C, CdO). Anal. Calcd (%) for
C19H20N2O5 (356.38): C, 64.04; H, 5.66; N, 7.86. Found: C, 64.10;
H, 5.73; N, 7.78.
4
with a He continuous flow cryostat for operation at cryogenic
temperature (4-20 K). GC analyses were performed with a
Shimadzu GC-17 gas chromatograph equipped with a flame
ionization detector and a 30 m (0.25 mm i.d., 0.25 µm film
thickness) SPB-1 Supelco fused silica capillary column. GC/MS
analyses were performed on a Shimadzu QP 5000 apparatus
equipped with a column identical with that used for GC analysis.
DSC (differential scanning calorimetry) spectroscopic analyses were
obtained using a Perkin-Elmer DSC7 instrument at a heating rate
of 20 °C/min from 40 to 200 °C. Calibration of both temperature
and enthalpy was made with a standard sample of In and Zr. The
molecular weight (Mw) and molecular weight distribution (Mw/Mn)
of the polymers were evaluated by gel permeation chromatography
(GPC) with a Waters GPC 2000 system equipped with a set of
three columns, Styragel HT6, HT5, and HT3, and a refractive index
detector. The analyses were performed at 140 °C using 1,2,4-
trichlorobenzene as solvent with an elution time of 1 mL min-1
and standard polystyrene as the reference.
Synthesis of 1-[6-(6-Acetylpyridine-2-carbonyl)pyridin-2-yl]-
ethanone. Bis[3-(2-methyl-1,3dioxolan-2-yl)pyridin-2-yl]methanone
(1.50 g, 4.21 mmol) was suspended in 2 M HCl (15 mL) and stirred
at 80-85 °C for 2 h. The resulting mixture was then cooled in an
ice bath, diluted with iced water (15 mL), and neutralized with
solid NaHCO3 portionwise. A standard extractive workup with ethyl
acetate (EtOAc, 3 × 50 mL) gave, after removal of solvent, a crude,
slightly brown solid, which was purified by filtration on a silica
gel pad (EtOAc/petroleum ether, 95:5) to afford the expected
compound as pure, pale yellow crystals (yield >99%). Mp: 97-
Synthesis of 1-(6-Bromopyridin-2-yl)ethanone.19 To a stirred
solution of 2,6-dibromopyridine (7.11 g, 30.0 mmol) in Et2O (130
mL) at -78 °C was added a 1.7 M solution of t-BuLi in n-pentane
(18.8 mL, 30.0 mmol) within 10 min. After 30 min of stirring at
-78 °C, N,N-dimethylacetamide (3.1 mL, 33.0 mmol) was added
and stirring was maintained for a further 1.5 h. The resulting mixture
was allowed to warm at room temperature and treated with water
(30 mL). The formed layers were separated. The aqueous layer
was extracted with Et2O (3 × 30 mL), and the collected organic
layers were washed with water (2 × 30 mL). The organic phase
was dried over Na2SO4, and the solvent was removed under reduced
pressure to give a yellow crude oil, which solidified upon cooling
at -20 °C in petroleum ether. After 6 h, small, pale yellow crystals
were separated by filtration (yield 90%). Mp: 44 °C. IR (KBr): ν
1
99 °C. IR (KBr): ν 1697, 1686 cm-1 (CdO). H NMR (CDCl3):
δ 2.61 (s, 6H, C(O)Me), 8.07 (td, J ) 8.0, 7.6 Hz, 2H, Py-Hp),
8.25 (dd, J ) 8.0, 1.3, Hz, 2H, Py-Hm), 8.30 (dd, J ) 7.6, 1.3, Hz,
2H, Py-Hm). 13C{1H} NMR (CDCl3): δ 26.2 (2C, Me), 124.8 (2C,
Py-CH), 128.7 (2C, Py-CH), 138.3 (2C, Py-CHp), 153.3 (2C, Py-
C), 153.9 (2C, Py-C), 192.4 (1C, CdO), 200.1 (2C, C(O)Me). Anal.
Calcd (%) for C15H12N2O3 (268.27): C, 67.16; H, 4.51; N, 10.44.
Found: C, 67.12; H, 4.57; N, 10.37.
1
1695 cm-1(CdO). H NMR (CDCl3): δ 2.70 (s, 3H, C(O)Me),
7.68 (m, 2H, Py-Hm/Hp), 7.98 (dd, J ) 6.5, 2.1 Hz, 1H, Py-Hm).
13C{1H} NMR (CDCl3): δ 26.4 (1C, C(O)Me), 121.1 (1C, Py-
CH), 132.4 (1C, Py-CH), 139.8 (1C, Py-CH), 142.0 (1C, Py-C),
154.9 (1C, Py-C), 198.5 (1C, C(O)Me). Anal. Calcd (%) for C7H6-
BrNO (200.03): C, 42.03; H, 3.02; N, 7.00. Found: C, 42.09; H,
2.90; N, 7.02.
Synthesis of 6-Bromo-2-(2′-methyl-1′,3′-dioxolan-2′-yl)pyri-
dine.20 A solution of 1-(6-bromopyridin-2-yl)ethanone (1.0 g, 5
mmol), 1,2-ethanediol (0.34 mL, 6 mmol), and 4-toluenesulfonic
acid (0.1 g, 0.5 mmol) in benzene (15 mL) was heated at reflux
temperature for 24 h in a Dean-Stark apparatus. The mixture was
Synthesis of {6-[1-(2,6-Diisopropylphenylimino)ethyl]pyridin-
2-yl}-{6-[1-(2,6-diisopropylphenylimino)ethyl]pyridin-3-yl}-
methanone (MeN5). A mixture of 1-[6-(6-acetylpyridine-2-carbonyl)-
pyridin-2-yl]ethanone (0.52 g, 1.94 mmol) and 2,4,6-trimethylaniline
(1.8 mL, 1.73 g, 12.8 mmol) was dissolved in MeOH (20 mL)
containing a few drops of formic acid, and the resulting mixture
was heated to reflux of solvent for 3 days. The resulting yellow-
orange solution was cooled to -24 °C. After 2 days, yellow crystals
of the desired product were isolated by filtration (yield 92%). Mp:
1
180-181 °C. IR (KBr): ν 1643 cm-1 (CdN). H NMR (CDCl3):
(18) Geary, W. J. J. Coord. Chem. ReV. 1971, 7, 81. (b) Morassi, R.;
Sacconi, L. J. Chem. Soc. A 1971, 492.
(19) Bolm, C.; Ewald, M.; Schilingloff, G. Chem. Ber. 1992, 125, 1169.
(20) Constable, E. C.; Heirtzler, F.; Neuburger, N.; Zehnder, M. J. Am.
Chem. Soc. 1997, 119, 5606.
δ 1.84 (s, 3H, NdCMe), 1.93 (s, 6H, Ar-Meo), 1.94 (s, 3H, Nd
CMe), 1.99 (s, 6H, Ar-Meo), 2.09 (s, 6H, Ar-Meo), 2.19 (s, 3H,
Ar-Mep), 2.30 (s, 3H, Ar-Mep), 2.31 (s, 3H, Ar-Mep), 6.71 (s, 2H,
Ar-Hm), 6.88 (s, 2H, Ar-Hm), 6.90 (s, 2H, Ar-Hm), 7.54 (dd, J )

4642 Organometallics, Vol. 26, No. 18, 2007
Barbaro et al.
1
7.7, 0.8 Hz, 1H, Py-Hm), 7.74 (t, J ) 7.9 Hz, 1H, Py-Hp), 8.02 (t,
J ) 7.8 Hz, 1H, Py-Hp), 8.17 (dd, J ) 7.9, 0.8 Hz, 1H, Py-Hm),
8.51 (dd, J ) 8.0, 0.9 Hz, 1H, Py-Hm), 8.64 (dd, J ) 7.9, 0.8 Hz,
1H, Py-Hm). 13C{1H} NMR (CDCl3): δ 16.50 (1C, NdCMe), 16.61
(1C, NdCMe), 18.03 (1C, Ar-p-Me), 18.14 (2C, Ar-Meo), 18.26
(2C, Ar-Meo), 18.84 (2C, Ar-Meo), 21.03 (1C, Ar-Mep), 21.08 (1C,
Ar-Mep), 122.54 (1C, Py-CHm), 122.75 (1C, Py-CHm), 123.44 (1C,
Ar-Cp), 123.56 (1C, Ar-Cp), 123.61 (1C, Ar-Cp), 124.33 (1C, Py-
CHm), 126.13 (1C, Py-CHm), 128.46 (2C, Ar-CHm), 128.93 (2C,
Ar-CHm), 128.93 (2C, Ar-CHm), 135.22 (2C, Ar-Co), 135.66 (1C,
Py-CHp), 135.98 (2C, Ar-Co), 136.13 (2C, Ar-Co), 137.66 (1C, Py-
CHp), 146.75 (1C, Ar-Ci), 146.79 (1C, Ar-Ci), 146.82 (1C, Ar-Ci),
152.51 (1C, NdCMe), 155.42 (1C, Py-C), 155.53 (1C, Py-C),
155.71 (1C, Py-C), 155.77 (1C, Py-C), 164.48 (1C, NdCMe),
164.89 (1C, NdCMe). Anal. Calcd (%) for C42H45N5 (619.84): C,
81.38; H, 7.32; N, 11.30. Found: C, 81.52; H, 7.26; N, 11.41.
Synthesis of {6-[1-(2,6-Diisopropylphenylimino)ethyl]pyridin-
2-yl}-{6-[1-(2,6-diisopropylphenylimino)ethyl]pyridin-3-yl}-
methanone (iPrN5). A mixture of 1-{6-[(6-acetyl-2-pyridinyl)-
carbonyl]-2-pyridinyl}-1-ethanone (0.77 g, 2.87 mmol) and 2,6-
diisopropylaniline (tech. 90%, 3.0 mL, 14.4 mmol) in MeOH (20
mL) containing a few drops of formic acid was heated to reflux of
solvent for 72 h. The resulting yellow-orange solution was cooled
to -24 °C. After 2 days, yellow crystals of the desired product
were isolated by filtration (yield 84%). Mp: 194-195 °C. IR
(KBr): ν 1705 cm-1 (CdO). H NMR (CDCl3): δ 2.85 (s, 12H,
C(O)Me), 8.56 (s, 4H, Py-Hm). Anal. Calcd (%) for C18H26N2O4
(324.33): C, 66.66; H, 4.97; N, 8.64. Found: C, 66.51; H, 4.92;
N, 8.55.
Synthesis of 2,6,2′,6′-(2,6-Diisopropylphenyl)ethylideneamine-
[4,4′]bipyridinyl (iPrN6). A suspension of 1-(6,2′,6′-triacetyl[4,4′]-
bipyridinyl-2-yl)ethanone (300 mg, 0.925 mmol) in n-BuOH (6 mL)
was treated with 2,6-diisopropylaniline (2.62 mL, 13.87 mmol) and
a catalytic amount of formic acid (0.06 mL, 1.6 mmol), then
refluxed for 20 h. After that time, the reaction mixture was cooled
at 4 °C overnight and a yellow solid separated. The resulting pure,
yellow crystalline product was filtered and washed several times
with cold MeOH (yield 91%). IR (KBr): ν 1646 cm-1 (CdN). 1H
NMR (CD2Cl2): δ 1.16 (d, J ) 6.8, 24H, CHMeMe), 1.20 (d, J )
6.9, 24H, CHMeMe), 2.34 (s, 12H, NdCMe), 2.82 (sept, J ) 6.8,
8H, CHMe2), 7.12 (t, J ) 7.4, 4H, Ar-Hp), 7.21 (d, J ) 7.4, 8H,
Ar-Hm), 8.85 (s, 4H, Py-Hm). 13C{1H} NMR (CD2Cl2): δ 17.00
(4C, NdCMe), 22.5 (8C, CHMeMe), 23.08 (8C, CHMeMe), 28.30
(8C, CHMe2), 120.58 (4C, Py-CHm), 122.95 (8C, Ar-CHm), 123.62
(4C, Ar-CHp), 135.75 (8C, Ar-Co), 146.36 (4C, Ar-Ci), 147.63 (2C,
Py-Cp), 156.10 (4C, Py-Co), 166.78 (4C, NCMe). Anal. Calcd (%)
for C66H84N6 (961.43): C, 82.45; H, 8.81; N, 8.74. Found: C, 82.37;
H, 8.76; N, 8.81.
Synthesis of MeN5FeCl2. A suspension of FeCl2 (16 mg, 0.124
mmol) in THF (4 mL) was added dropwise to a yellow solution of
MeN5 (77 mg, 0.124 mmol) in diethyl ether (Et2O, 20 mL) at room
temperature. The resulting dark solution was maintained under
stirring for 12 h at room temperature. During this time the product
precipitated as a green powder. Further precipitation was obtained
by concentration to small volume under a stream of nitrogen and
addition of Et2O (20 mL). The complex was isolated by decantation,
washed with a 1:1 mixture of Et2O/n-pentane, and dried under
vacuum (yield 90%). IR (KBr): ν 1641, 1617 cm-1 (CdN). µeff:
5.36 µB (22 °C). Electronic spectra: (reflectance) 13 800, 4900sh
cm-1; (absorption) 14 000 (ꢀ 1000), 4900 (ꢀ 25) cm-1. Anal. Calcd
(%) for C42H45Cl2FeN5 (746.61): C, 67.57; H, 6.08; Fe, 7.48; N,
9.38. Found: C, 67.60; H, 6.12; Fe, 7.50; N, 9.33.
Synthesis of MeN5Fe2Cl4. A suspension of FeCl2 (31 mg, 0.248
mmol) in THF (4 mL) was added to a stirred solution of MeN5 (77
mg, 0.124 mmol) in CH2Cl2 (10 mL) at room temperature. Standing
overnight the resulting dark solution produced the product as dark
brown powder. The complex was isolated by decantation, washed
with n-pentane, and dried under vacuum (yield 70%). IR (KBr): ν
1617 cm-1 (CdN). µeff: 7.04 µB (22 °C). Electronic spectra:
(reflectance) 13 800, 4900 cm-1. Anal. Calcd (%) for C42H45Cl4-
Fe2N5 (873.36): C, 57.76; H, 5.19; Fe, 12.79; N, 8.02. Found: C,
57.74; H, 5.21; Fe, 12.80; N, 8.00.
Synthesis of iPrN5CoCl2. Dropwise addition of CoCl2 (16 mg,
0.124 mmol) in THF (3 mL) to iPrN5 (92 mg, 0.124 mmol) in Et2O
(30 mL) at room temperature yielded a dark brown solution. After
10 min the precipitation of a small crop of the product as a brown
solid occurred. The mixture was allowed to stand overnight under
stirring. The product was collected by decantation, washed with
small portions of Et2O and n-pentane, and dried under vacuum
(yield 84%). IR (KBr): ν 1648, 1615 cm-1 (CdN). µeff: 4.55 µB
(22 °C). Electronic spectra: (reflectance) 17 850sh, 15 050, 11 800,
8350, 6700 cm-1; (absorption) 17 900sh, 14 600 (ꢀ 102), 11 800
(ꢀ 10), 8350 (ꢀ 15), 6900 (ꢀ 25) cm-1. Anal. Calcd (%) for C51H63-
Cl2CoN5 (875.93): C, 69.93; H, 7.25; N, 8.00. Found: C, 69.90;
H, 7.28; N, 7.95.
1
(KBr): ν 1646 cm-1 (CdN). H NMR (CDCl3): δ 1.00 (d, J )
6.8 Hz, 6H, CHMeMe), 1.13 (d, J ) 7.0 Hz, 6H, CHMeMe), 1.14
(d, J ) 7.0 Hz, 6H, CHMeMe), 1.18 (d, J ) 6.9 Hz, 6H, CHMeMe),
1.22 (d, J ) 6.9 Hz, 6H, CHMeMe), 1.25 (d, J ) 6.8 Hz, 6H,
CHMeMe), 1.79 (s, 3H, NdCMe), 2.04 (s, 3H, NdCMe), 2.66
(spt, J ) 6.8 Hz, 2H, CHMe2), 2.79 (spt, J ) 6.8 Hz, 2H, CHMe2),
3.04 (spt, J ) 6.8 Hz, 2H, CHMe2), 7.01 (m, 1H, Ar-Hp), 7.06 (m,
2H, Ar-Hm), 7.12 (m, 1H, Ar-Hp), 7.18 (m, 2H, Ar-Hm), 7.19 (m,
1H, Ar-Hp), 7.22 (m, 2H, Ar-Hm), 7.59 (d, J ) 7.7 Hz, 1H, Py-
Hm), 7.78 (t, J ) 7.9 Hz, 1H, Py-Hp), 8.06 (t, J ) 7.8 Hz, 1H,
Py-Hp), 8.26 (d, J ) 7.8 Hz, 1H, Py-Hm), 8.57 (d, J ) 7.8 Hz, 1H,
Py-Hm), 8.66 (d, J ) 7.7 Hz, 1H, Py-Hm). 13C{1H} NMR (CDCl3):
δ 17.35 (1C, NdCMe), 17.72 (1C, NdCMe), 22.37 (2C, CHMeMe),
23.30 (2C, CHMeMe), 23.33 (2C, CHMeMe), 23.55 (2C, CHMeMe),
23.65 (2C, CHMeMe), 24.08 (2C, CHMeMe), 28.65 (2C, CHMe2),
28.77 (2C, CHMe2), 28.97 (2C, CHMe2), 121.11 (1C, Py-CHm),
122.46 (1C, Py-CHm), 122.97 (2C, Ar-CHm), 123.35 (2C, Ar-CHm),
123.42 (2C, Ar-CHm), 123.87 (1C, Ar-CHp), 123.94 (1C, Ar-CHp),
124.06 (1C, Ar-CHp), 124.84 (1C, Py-CHm), 126.90 (1C, Py-CHm),
135.42 (2C, Ar-o-C), 136.01 (1C, Py-CHp), 136.11 (2C, Ar-o-C),
136.18 (2C, Ar-o-C), 137.66 (1C, Py-CHp), 146.79 (2C, Ar-ipso-
C), 146.94 (1C, Ar-ipso-C), 152.45 (1C, NdCMe), 155.27 (1C,
Py-C), 155.32 (1C, Py-C), 155.50 (1C, Py-C), 155.52 (1C, Py-C),
167.20 (1C, NdCMe), 167.83 (1C, NdCMe). Anal. Calcd (%) for
C51H63N5 (746.08): C, 82.10; H, 8.51; N, 9.39. Found: C, 82.03;
H, 6.44; N, 9.48.
Synthesis of 1-(6,2′,6′-Triacetyl[4,4′]bipyridinyl-2-yl)etha-
none.21 To a suspension of 4,4′-bipyridyl (5 g, 33 mmol) in acetic
acid (30 mL) cooled in an ice bath were added FeSO4·7H2O (20
g), acetaldehyde (20 mL), and H2SO4 (1.6 mL) in sequence. The
slurry was treated dropwise under vigorous stirring at 0 °C with
t-BuOOH (20 mL, 220 mmol). Within 20 min the reaction mixture
turned to an orange solution with exothermicity. After 3 h the
reaction mixture was warmed to room temperature and stirred 1 h
further. During this time a white precipitate was formed. The
suspension was poured onto ice (200 g), and after dissolution the
remaining solid was separated by filtration. A standard extractive
procedure with CH2Cl2 (3 × 50 mL) achieved, after removal of
solvent under reduced pressure, a white solid. The desired product
was purified by flash chromatography (CH2Cl2/n-pentane/EtOAc,
70:25:5), providing a white solid (yield 12%). Mp: 262 °C. IR
Synthesis of MeN5CoCl2. Employing an analogous procedure to
that described above, but using the ligand MeN5 (77 mg, 0.124
mmol), gave MeN5CoCl2 as a brown solid in 82% yield. IR (KBr):
ν 1642, 1617 cm-1 (CdN). µeff: 4.68 µB (22 °C). Electronic
spectra: (reflectance) 18 200sh, 15 000, 11 500, 8300, 7050 cm-1
;
(absorption) 18 300sh, 14 650 (ꢀ 110), 11 600 (ꢀ 8), 8300 (ꢀ 18),
1
(21) Citterio, A.; Arnoldi, A.; Macr`ı, C. Chim. Ind. 1978, 60, 14.
6900 (ꢀ 30) cm-1. H NMR (CD2Cl2, all peaks appear as broad

Synthesis of New Polydentate Nitrogen Ligands
Organometallics, Vol. 26, No. 18, 2007 4643
singlets): six-coordinate species δ 62.64 (1H), 60.59 (1H), 17.44
(6H), 14.28 (6H), 11.31 (3H), 10.92 (3H), 8.21 (3H), 7.68 (1H),
6.9 (2+1H), 2.41 (3H), 2.05 (2+1H), 1.95 (2H), -2.98 (3H), -3.38
(6H), -8.95 (1H). Anal. Calcd (%) for C42H45Cl2CoN5 (749.69):
C, 67.36; H, 6.06; Co, 7.88; N, 9.36. Found: C, 65.95; H, 5.93;
Co, 6.65; N, 10.45.
(154 mg, 0.248 mmol) in Et2O (30 mL) under stirring at room
temperature. Within a few minutes the solid dissolved, giving an
orange solution. After 16 h, the formed orange precipitate was
collected by decantation, washed with small portions of Et2O and
n-pentane, and dried under vacuum (yield 85%). IR (KBr): ν 1618
cm-1 (CdN). µeff: 2.85 µB (22 °C). Electronic spectra: (reflectance)
22 600sh, 12 500, 8100 cm-1; (absorption) 22 600 (ꢀ 80), 13 300
(ꢀ 24), 8200 (ꢀ 28) cm-1. Anal. Calcd (%) for C43H49Cl2NiN5
(838.35): C, 60.17; H, 5.41; Ni, 7.00; N, 8.35. Found: C, 60.11;
H, 5.35; Ni, 6.91; N, 8.24.
Synthesis of iPrN6Co2Cl4. A mixture of CoCl2 (13 mg, 0.104
mmol) and iPrN6 (50 mg, 0.052 mmol) in THF (3 mL) was stirred
overnight at room temperature. The formed light brown precipitate
was filtered on a sintered-glass frit, washed with Et2O, and dried
in a stream of nitrogen (yield 87%). IR (KBr): ν 1594 cm-1 (Cd
N). µeff: 6.45 µB (22 °C). Electronic spectra: (reflectance) 18 200sh,
14 500, 11 100, 8000, 6600 cm-1; (absorption) 18 100sh, 14 200
(ꢀ 80), 11 100 (ꢀ 10), 8000 (ꢀ 28), 6600 (ꢀ 28) cm-1. Anal. Calcd
(%) for C66H84Cl4Co2N6 (1221.11): C, 64.92; H, 6.93; N, 6.88.
Found: C, 64.88; H, 6.98; N, 6.90.
Synthesis of iPrN6Fe2Cl4. A mixture of FeCl2 (13 mg, 0.104
mmol) and iPrN6 (50 mg, 0.052 mmol) in THF (3 mL) was stirred
overnight at room temperature. The formed green precipitate was
filtered on a sintered-glass frit, washed with Et2O, and dried in a
stream of nitrogen (yield 85%). IR (KBr): ν 1596 cm-1 (CdN).
µeff: 7.27 µB (22 °C). Electronic spectra: (reflectance) 13 400, 5200
cm-1; (absorption) 13 200 (ꢀ 1000), 5200 (ꢀ 24) cm-1. Anal. Calcd
(%) for C66H84Cl4Fe2N6 (1214.94): C, 64.92; H, 6.93; N, 6.88.
Found: C, 64.92; H, 6.91; N, 6.89.
Synthesis of MeN5CoBr2. Employing an analogous procedure
to that described above, but using CoBr2 (27 mg, 0.124 mmol),
gave the product as a orange solid in 80% yield. IR (KBr): ν 1617
cm-1 (CdN); (CH2Cl2): ν 1642, 1617 cm-1 (CdN). µeff: 4.74 µB
(22 °C). Electronic spectra: (reflectance) 17 800sh, 9900 cm-1
;
(absorption) 17 900sh, 14 600 (ꢀ 90), 10 500 (ꢀ 24), 8200 (ꢀ 21),
1
6900 (ꢀ 28) cm-1. H NMR (CD2Cl2, all peaks appear as broad
singlets): 114.10 (1H), 111.95 (1H), 70.15 (1H), 66.01 (1H), 49.85
(1H), 43.90 (1H), 43.75 (1H), 28.85 (6H), 23.45 (6H), 22.21 (3H),
19.96 (3H), 15.80 (3H), 14.04 (3H), 12.11 (3H), 9.45 (1H), 9.21
(2H), 8.89 (1H), 6.99 (2H), 6.48 (2H), 6.11 (1H), 3.45 (3H), 2.11
(2H), 1.9 (3+3+2H), 1.5 (2+1H), 1.18 (6H), 0.8 (3+3H), 0.28
(6H), -1.38 (1H), -23.21 (6H), -25.85 (6H). Anal. Calcd (%)
for C42H45Br2CoN5 (838.59): C, 60.28; H, 5.42; Co, 7.05; N, 8.37.
Found: C, 60.40; H, 5.80; Co, 6.93; N, 8.21.
Synthesis of MeN5Co2Cl4. Dropwise addition of a solution of
MeN5 (77 mg, 0.124 mmol) in THF (2 mL) to a stirred solution of
CoCl2 (32 mg, 0.248 mmol) in THF (6 mL) at 60 °C yielded a
green solution. After 7 h, the solution was cooled to room
temperature, and the green solid was collected by decantation,
washed with small portions of Et2O and n-pentane, and dried under
vacuum (yield 82%). IR (KBr): ν 1617 cm-1 (CdN). µeff: 6.36
µB (22 °C). Electronic spectra: (reflectance) 17 250, 15 000, 11 300,
9050, 8200, 7000 cm-1. Anal. Calcd (%) for C42H45Cl4Co2N5
(879.53): C, 57.36; H, 5.16; Co, 13.40; N, 7.96. Found: C, 57.40;
H, 5.19; Co, 13.43; N, 7.88.
General Procedure for Ethylene Polymerization. A 500 mL
stainless steel reactor was heated to 60 °C under vacuum overnight
and then cooled to room temperature under a nitrogen atmosphere.
Synthesis of MeN5Co2Br4. A solution of CoBr2 (14 mg, 0.062
mmol) in THF (2 mL) was added to a stirred suspension of
MeN5CoBr2 (52 mg, 0.062) in THF (2 mL) at room temperature. A
green solution immediately formed, from which a small amount of
a green solid separated after a few minutes. After 8 h, the product
was collected by decantation, washed with small portions of Et2O
and n-pentane, and dried under vacuum (yield 90%). IR (KBr): ν
1617 cm-1 (CdN). µeff: 6.42 µB (22 °C). Electronic spectra:
(reflectance) 16 400, 14 450, 11 100, 8950, 8400, 6600 cm-1. Anal.
Calcd (%) for C42H45Br4Co2N5 (1057.34): C, 47.71; H, 4.29; Co,
11.15; N, 6.62. Found: C, 47.69; H, 4.27; Co, 11.12; N, 6.64.
Monometallic Catalyst Precursors. Procedure A. The solid
precatalyst (12 µmol) was charged into the reactor, which was sealed
and placed under vacuum. A toluene solution of MAO (3600 µmol),
prepared by diluting 2.4 mL of a standard solution of MAO (10 wt
% in toluene) in 97.6 mL of toluene, was then introduced into the
reactor by suction.
Procedure B. A solution (1.2 mL) of MAO in toluene (1800
µmol) was diluted with 96.3 mL of toluene, and the resultant
solution was introduced by suction into the reactor previously
evacuated by a vacuum pump. The system was pressurized with
ethylene to the desired pressure and stirred for 5 min. The ethylene
pressure was then released slowly, and 2.5 mL of a precatalyst
solution, prepared by dissolving the solid precatalyst (12 µmol) in
50 mL of toluene, was syringed into the reactor.
MeN5CoFeCl4. A suspension of FeCl2 (8 mg, 0.062 mmol) in
THF (4 mL) was added to a solution of MeN5CoCl2 (46 mg, 0.062)
in CH2Cl2 (20 mL) at room temperature to yield immediately a
dark solution, which was stirred for 24 h. The formed green-brown
product was collected by decantation, washed with small portions
of Et2O and n-pentane, and dried under vacuum (yield 90%). IR
(KBr): ν 1620 cm-1 (CdN). µeff: 6.82 µB (22 °C). Electronic
Procedure C. A solution (2.4 mL) of MAO in toluene (3600
µmol) was diluted with 96.6 mL of toluene, and the resultant
solution was introduced by suction into the reactor previously
evacuated by a vacuum pump. The system was pressurized with
ethylene to the desired pressure and stirred for 5 min. The ethylene
pressure was then released slowly, and 1.0 mL of a precatalyst
solution, prepared by dissolving the solid precatalyst (12 µmol) in
50 mL of toluene, was syringed into the reactor.
spectra: (reflectance) 18 200sh, 15 000, 11 000, 8250, 7000 cm-1
.
Anal. Calcd (%) for C42H45Cl4CoFeN5 (876.44): C, 57.56; H, 5.18;
Co, 6.72; Fe, 6.37; N, 7.99. Found: C, 57.41; H, 5.14; Co, 6.65;
Fe, 6.28; N, 7.97.
MeN5CoNiBr2Cl2. A suspension of NiBr2‚MeOCH2CH2OMe (19
mg, 0.062 mmol) in THF (3 mL) was added to a solution of
MeN5CoCl2 (46 mg, 0.062) in CH2Cl2 (20 mL) at room temperature.
After 24 h, the formed light green product was collected by
decantation, washed with small portions of Et2O and n-pentane,
and dried under vacuum (yield 90%). IR (KBr): ν 1617 cm-1 (Cd
N). µeff: 5.74 µB (22 °C). Electronic spectra: (reflectance) 15 650,
14 800, 11 900, 8300, 7050sh, 6000 cm-1. Anal. Calcd (%) for
C42H45Br2Cl2CoN5Ni (968.19): C, 52.10; H, 4.68; Co, 6.09; N,
7.23; Ni 6.06. Found: C, 52.01; H, 4.61; Co, 5.99; N, 7.18; Ni
6.00.
Bimetallic Catalyst Precursors. Procedure A′. The solid
precatalyst (6-12 µmol) was charged into the reactor, which was
sealed and placed under vacuum. A toluene solution of MAO
(3600-7200 µmol), prepared by diluting 2.4-4.8 mL of a standard
solution of MAO (10 wt % in toluene) in 97.6-95.2 mL of toluene,
was then introduced into the reactor by suction.
Procedure B′. A solution (2.4 mL) of MAO in toluene (3600
µmol) was diluted with 92.6 mL of toluene, and the resultant
solution was introduced by suction into the reactor previously
evacuated by a vacuum pump. The system was pressurized with
ethylene to the desired pressure and stirred for 5 min. The ethylene
pressure was then released slowly, and 5 mL of a precatalyst
Synthesis of MeN5NiBr2. A solid sample of NiBr2‚MeOCH2CH2-
OMe (77 mg, 0.248 mmol) was added to a yellow solution of MeN5

4644 Organometallics, Vol. 26, No. 18, 2007
Table 1. Crystallographic Data for iPrN5CoCl2 and MeN5CoBr2
iPrN5CoCl2
C51H63Cl2CoN5
Barbaro et al.
MeN5CoBr2
C42H45Br2CoN5
empirical formula
fw
875.89
838.58
temperature [K]
wavelenght [Å]
cryst syst, space group
a [Å]
b [Å]
c [Å]
203(2)
0.71073
triclinic, P1h
9.8615(9)
10.8452(8)
25.9804(19)
89.473(6)
87.860(7)
78.520(7)
2721.1(4)
2, 1.069
0.448
930
213(2)
0.71073
monoclinic, P21/n
8.5871(7)
27.3894(14)
16.7052(13)
R [deg]
â [deg]
101.091(6)
γ [deg]
V [Å3]
3855.6(5)
4, 1.445
2.554
1716
Z, Dc [g m-3
]
absorp coeff [mm-1
F(000)
]
cryst size [mm]
θ range for data collection [deg]
limiting indices
0.30 × 0.20 × 0.10
3.98-25.25
-7 e h< e 11
-12< e k< e 13
-27< e l< e 31
15 510/9088
0.967
0.20 × 0.15 × 0.10
3.83-29.98
-12< e h< e 11
-31< e k< e 30
-21< e l< e 21
29 744/8892
1.031
no. of reflns collected/unique
GOF on F2
no. of data/restraints/params
final R indices [I > 2σ(I)]
R indices (all data)
9088/0/532
R1 ) 0.0905, wR2 ) 0.1870
R1 ) 0.1703, wR2 ) 0.2253
0.437 and -0.486
8892/0/463
R1 ) 0.0853, wR2 ) 0.1075
R1 ) 0.2222, wR2 ) 0.1475
0.717 and -0.397
largest diff peak and hole [e Å-3
]
Scheme 4a
solution, prepared by dissolving the solid precatalyst (6 µmol) in
50 mL of toluene, was syringed into the reactor.
Procedure C′. A solution (1.2 mL) of MAO in toluene (1800
µmol) was diluted with 96.3 mL of toluene, and the resultant
solution was introduced by suction into the reactor previously
evacuated by a vacuum pump. The system was pressurized with
ethylene to the desired pressure and stirred for 5 min. The ethylene
pressure was then released slowly, and 2.5 mL of a precatalyst
solution, prepared by dissolving the solid precatalyst (6 µmol) in
50 mL of toluene, was syringed into the reactor.
Procedure D′. A solution (2.4 mL) of MAO in toluene (3600
µmol) was diluted with 96.6 mL of toluene, and the resultant
solution was introduced by suction into the reactor previously
evacuated by a vacuum pump. The system was pressurized with
ethylene to the desired pressure and stirred for 5 min. The ethylene
pressure was then released slowly, and 1.0 mL of a precatalyst
solution, prepared by dissolving the solid precatalyst (6 µmol) in
50 mL of toluene, was syringed into the reactor.
on F2 were carried out with anisotropic thermal parameters for all
non-hydrogen atoms, which were included using a riding model
with isotropic U values depending on the Ueq of the adjacent carbon
atoms.
Results and Discussion
Irrespective of the procedure, the reactor was immediately
pressurized with ethylene to the desired pressure (4/5 bar) and stirred
at 1500 rpm. Ethylene was continuously fed to maintain the reactor
pressure at the desired value. The temperature inside the reactor in-
creased solely from the exothermicity of the reaction and reached
a maximum value within a few minutes. After 15 min, the reaction
was terminated by cooling the reactor to -20 °C, venting off the vola-
tiles, and introducing 2 mL of acidic MeOH (5% HCl v/v). The
solid products were filtered off, washed with cold toluene and MeOH,
and dried in a vacuum oven at 50 °C. The filtrates were analyzed
by GC and GC/MS for detecting the presence of oligomers.
X-ray Diffraction Data. Crystallographic data of iPrN5CoCl2
and MeN5CoBr2 are reported in Table 1. X-ray diffraction intensity
data were collected on an Oxford Diffraction CCD diffractometer
with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å)
using ω-scans. Cell refinement, data reduction, and empirical
absorption correction were carried out with the Oxford diffraction
software and SADABS.22 All structure determination calculations
were performed with the WINGX package23 with SIR-97,24
SHELXL-97,25 and ORTEP-3 programs.26 Final refinements based
Tris-imino-Bis-pyridine Ligands. The synthetic protocol
developed to synthesize the tris-imino-bis-pyridine ligands with
either 2,4,6-Me3C6H2 (MeN5) or 2,6-i-Pr2C6H3 (iPrN5) groups at
the imine nitrogen atoms is shown in Scheme 4. 2,6-Dibro-
mopyridine was monolithiated with t-BuLi, then treated with
N,N-dimethylacetamide to give 1-(6-bromopyridin-2-yl)etha-
none. After the ketone group in the latter compound was
protected as O,O-ketal, the coupling of two pyridine rings was
achieved by lithiation of the bromoketal, followed by reaction
with methylchloroformate. The deprotection of the carbonyl
group under acidic conditions gave the triketone 1-[6-(6-
acetylpyridine-2-carbonyl)pyridin-2-yl]ethanone, which was ul-
timately converted into the desired N5 ligand by formic acid-
catalyzed condensation with the appropriate aniline in MeOH.
Overall yields of 74-67% were consistently obtained.
Tetrakis-imino-Bis-pyridine Ligands. The stepwise proce-
dure developed to synthesize the tetrakis-imino-bis-pyridine
(24) Altomare, A.; Burla, M. C.; Cavalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Gagliardi, A.; Moliterni, G. G.; Polidori, G.; Spagna, R. J.
Appl. Crystallogr. 1999, 32, 115.
(22) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Corrections; University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(23) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(25) Sheldrick, G. M. SHELX-97; Univeristy of Go¨ttingen, 1997.
(26) Burnett, M. N.; Johnson, C. K. ORTEP-3, Report ORNL-6895; Oak
Ridge National Laboratory: Oak Ridge, TN, 1996.

Synthesis of New Polydentate Nitrogen Ligands
Organometallics, Vol. 26, No. 18, 2007 4645
Scheme 5a
Scheme 6
Figure 1. ORTEP drawing of compound iPrN5CoCl2. Hydrogen
atoms are omitted for clarity. Thermal ellipsoids are shown at the
30% probability level.
Table 2. Selected Bond Distances [Å] and Angles [deg] for
iPrN5CoCl2 and MeN5CoBr2
iPrN5CoCl2
MeN5CoBr2
Co(1)-Cl(1)
2.240(2)
2.301(2)
Co(1)-Cl(2)
Co(1)-Br(1)
2.558(1)
2.733(1)
2.146(5)
2.102(5)
2.089(6)
2.147(5)
Co(1)-Br(2)
Co(1)-N(1)
2.179(5)
2.045(5)
2.282(5)
Co(1)-N(2)
Co(1)-N(3)
ligand iPrN6 is shown in Scheme 5. The tetra-acetyl-bis(pyridine)
intermediate was obtained by a radical reaction involving the
treatment of 4,4′-bipyridine with t-BuOOH, followed by addition
of acetaldehyde.21 The plain condensation of the resulting
tetraketone with 2,6-diisopropylaniline gave the desired iPrN6
ligand. The overall yield was rather low due to the low
regioselectivity of the radical reaction.
Co(1)-N(4)
N(1)-C(13)
1.288(8)
1.290(7)
1.273(7)
118.13(8)
N(1)-C(11)
1.276(8)
1.288(8)
1.276(8)
N(3)-C(20)
N(4)-C(23)
N(5)-C(38)
N(5)-C(17)
Cl(1)-Co(1)-Cl(2)
Br(1)-Co(1)-Br(2)
N(1)-Co(1)-N(2)
N(1)-Co(1)-N(3)
N(2)-Co(1)-N(3)
N(3)-Co(1)-N(4)
165.25(4)
77.4(2)
169.9(2)
92.5(2)
Monometallic FeII, CoII, and NiII Complexes with the iPrN5
and MeN5 Ligands. The monometallic FeII, CoII, and NiII
complexes with either iPrN5 or MeN5 were isolated as crystalline
materials in excellent yields by mixing equimolar amounts of
the anhydrous metal dihalides with the appropriate ligand in
THF/Et2O at room temperature. Scheme 6 shows the structures
of the isolated complexes as ascertained by single-crystal X-ray
analyses or inferred by spectroscopic methods.
All compounds are air-stable in the solid state and in
deaerated solutions of polar solvents such as THF, CH2Cl2, and
1,2-dichloroethane. In the last solvent they behave as nonelec-
trolytes. All the complexes have been characterized by elemental
analysis, magnetic and spectrophotometric measurements, and
IR, 1H NMR, and X-band EPR spectroscopies. Also, the
molecular structures of iPrN5CoCl2 and MeN5CoBr2 have been
determined by single-crystal X-ray diffraction analyses.
Brown crystals of iPrN5CoCl2 suitable for an X-ray diffraction
study were obtained by recrystallization from warm n-butanol.
An ORTEP drawing of the molecule contained in the asym-
metric unit is shown in Figure 1, while selected bond lengths
and angles are reported in Table 2.
The coordination geometry of the cobalt atom can be best
described as a distorted square pyramid with the basal plane
defined by the N(1), N(2) N(3), and Cl(1) atoms and the Cl(2)
atom occupying the apical position.7a,27 The deviation of the
metal center from the coordination plane, defined by N(1), N(2),
and N(3), is 0.4803(49) Å, which is comparable to that found
for the analogous symmetrical complex iPrN3CoCl2 (iPrN3 )
2,6-(2,6-i-Pr2C6H3NdCMe)2C5H3N).7a The basal halogen atom
Cl(1) deviates by 0.1196 (123) Å from the coordination plane
75.1(2)
143.6(2)
73.5(2)
78.0(2)
Intramolecular Short Contact Distances [Å]
Br(1)‚‚‚H(13)
Br(1)‚‚‚H(10B)
Br(2)‚‚‚H(24B)
C(5)‚‚‚H(36)
H(31C)‚‚‚H(40A)
H(7B)‚‚‚H(9C)
2.833
2.880
2.993
2.367
2.312
2.335
and is typically sandwiched by the two substituted phenyl rings,
which are practically orthogonal to the N3 plane (81.08(32)°
(plane with C(1) as ipso atom) and 85.98(38)° (plane with C(21)
as ipso atom)). The apical atom Cl(2) shows a deviation from
the N3 coordination plane of 2.7257(38) Å, with a Co-Cl(2)
bond length of 2.301(2) Å, which is significantly longer than
the basal Co-Cl(1) distance.7a Due to the asymmetry of the
molecule, the Co-N(imine) bonds Co(1)-N(1) and Co(1)-
N(3) (2.179(5) and 2.282(5) Å, respectively) are significantly
different from each other, while the C-N(imine) bond lengths
(N(1)-C(13) and N(3)-C(20) of 1.288(8) and 1.290(7) Å,
respectively) are typical for coordinated imine groups and
comparable to each other within the standard deviation.7a,27 The
free pyridine ring is coplanar neither with the coordination plane
(27) (a) Kooistra, T. M.; Hekking, K. F. W.; Knijnenburg, Q.; de Bruin,
B.; Budzelaar, P. H. M.; de Gelder, R.; Smits, J. M. M.; Gal, A. W. Eur.
J. Inorg. Chem. 2003, 648. (b) Bianchini, C.; Mantovani, G.; Meli, A.;
Migliacci, F.; Zanobini, F.; Laschi, F.; Sommazzi, A. Eur. J. Inorg. Chem.
2003, 1620. (c) Kleigrewe, N.; Steffen, W.; Blo¨mker, T. G.; Kehr, G.;
Fro¨hlich, R.; Wibbeling, B.; Erker, G.; Wasilke, J. C.; Wu, G.; Bazan, G.
C. J. Am. Chem. Soc. 2005, 127, 13955.

4646 Organometallics, Vol. 26, No. 18, 2007
Barbaro et al.
deviation of the four coordinating nitrogen atoms from the latter
plane ranges from 0.0530(26) to 0.0626(30) Å. Both pyridine
rings are not coplanar, showing a torsion angle of 36.36(1.23)°,
which triggers also a deviation of the free imine nitrogen atom
(N(5)) from the coordination plane in the direction of Br(1).
The apical Co-Br bond lengths are significantly different from
each other (2.558(1) and 2.733(1) Å), while the Co-N(imine)
distances (2.146(5) and 2.147(5) Å) are significantly longer than
the Co-N(pyridine) distances (2.102(5) and 2.089(6) Å). The
mesityl groups attached to the N(1) and N(4) atoms are nearly
coplanar, showing torsion angles with the best coordination
plane of 77.26(21)° (plane with C(25) as ipso-atom) and of
72.76(20)° (plane with C(1) as ipso-atom). Short intramolecular
contacts have been detected in the crystal structure, which might
also contribute to build up the overall structural conformation.
Unlike iPrN5CoCl2, MeN5CoBr2 is featured by different solid-
state and solution IR spectra (see Figure 2S in the Supporting
Information). The solution spectrum of MeN5CoBr2 contains two
bands at 1617 and 1642 cm-1, which are characteristic of bonded
and free imine groups, respectively, whereas the solid-state
spectrum shows only the absorption band at 1617 cm-1 due to
the coordinated imine.14b,e,28 This behavior could be indicative
either of a change in the cobalt coordination geometry on going
from six-coordination (solid state) to five-coordination (solution)
or, more likely, of an equilibrium between five- and six-
coordinate species. Indirect support for this hypothesis is
provided by the intensities of the solution ν(CdN) bands, which
are opposite those of the corresponding bands of iPrN5CoCl2
(see Figure 1S, trace d).
Figure 2. ORTEP drawing of compound MeN5CoBr2. Hydrogen
atoms are omitted for clarity. Thermal ellipsoids are shown at the
30% probability level.
(N1-N3) nor with the uncoordinated imine group, showing
dihedral angles of 65.73(0.35)° and 26.85(76)°, respectively.
Consistent with the X-ray crystal structure determination, the
IR spectra of iPrN5CoCl2 are identical both in the solid state
and in solution and contain two ν(CdN) bands, one for the
coordinated imine groups at 1615 cm-1 and one, more intense,
for the free imine group at 1648 cm-1, which indicates that not
all of the nitrogen atoms of the potentially pentadendate ligand
iPrN5 are involved in the coordination to the metal center.14b,e,28
Details of the IR spectra are reported in the Supporting
Information (Figure 1S).
The magnetic and spectrophotometric data of iPrN5CoCl2,
obtained both in the solid state and in solution, are fully
consistent with an N3Cl2 donor atom set and a coordination
geometry closer to a distorted square pyramid than to a trigonal
bipyramid.29,30 The magnetic susceptibility measurements of
iPrN5CoCl2 gave magnetic moments of 4.55 µB at room
temperature, as expected for a high-spin electronic configuration
with three unpaired electrons. The reflectance and absorption
vis-NIR spectra (25 000-4550 cm-1) are similar to each other.
The absorption spectrum consists of five bands at 6900 (ꢀ 25),
The occurrence of an equilibrium between five- and six-
coordinate species in solution is also suggested by the spectro-
photometric measurements. Indeed, in agreement with the
octahedral geometry adopted in the solid state, the reflectance
spectrum of MeN5CoBr2 shows two spin-allowed transitions at
4
9900 and 17 800sh cm-1, which are assignable to the T1g(F)
f 4T2g(F) and 4T1g(F) f 4T1g(P) transitions, respectively. Due
to the low intensity and vicinity to the highest energy transition,
the two-electron transition 4T1g(F) f 4A2g(F) is not observed.29a,32a
Unlike the spectrum in the solid state, the absorbance spectrum
closely resembles that of the five-coordinate CoII complex
iPrN5CoCl2. However, the spectrum of MeN5CoBr2 displays also
an extra absorption at ca. 10 000 cm-1, which suggests the
contemporaneous presence of six-coordinate CoII centers. On
the other hand, the presence of two distinct CoII species in
8350 (ꢀ 15), 11 800 (ꢀ 10), 14 600 (ꢀ 102), and 17 900sh cm-1
,
which is in agreement with the spectra of several other five-
coordinate CoII (d7 configuration) complexes with geometry
intermediate between C4V and D3h.29,30 Strong support for a
distorted square-pyramidal structure for iPrN5CoCl2 has been
also provided by the solid-state and frozen solution EPR spectra
(see below).
Orange crystals of MeN5CoBr2 suitable for an X-ray diffrac-
tion study were obtained by slow diffusion of toluene into a
CHCl3 solution of the complex. An ORTEP drawing of the
molecule contained in the asymmetric unit is shown in Figure
2, while selected bond lengths and angles are reported in Table
2.
The coordination geometry around the cobalt atom can be
described as a distorted octahedron. Four nitrogen atoms,
namely, the two imine nitrogen atoms N(1) and N(4) and the
two pyridine nitrogen atoms N(2) and N(3), occupy the
equatorial positions, while two axially coordinating bromides,
with a Br(1)-Co(1)-Br(2) coordination angle of 165.25(4)°,
complete the coordination sphere.31 The metal center deviates
from the coordination plane defined by the atoms N(1)-N(4),
by 0.0720(31) Å in the direction of Br(1).31a Furthermore, the
1
solution is also supported by the H NMR and X-band EPR
spectra (see below).
On the basis of an in-depth spectroscopic analysis (IR, H
1
NMR, EPR) as well as a comparison with the corresponding
characteristics of MeN5CoBr2 and iPrN5CoCl2, the complex
MeN5CoCl2 is assigned a five-coordinate structure in the solid
state, most likely a distorted trigonal bipyramid, while this
complex apparently exists in solution as a mixture of five- and
six-coordinate species (see the EPR study reported below).
Like the analogous cobalt derivative, the iron complex
MeN5FeCl2 is featured by a µeff of 5.36 µB at room temperature,
consistent with a high-spin electronic configuration. The
electronic spectra are very close to those reported for related
(31) (a) Hierso, J. C.; Bouwman, E.; Ellis, D. D.; Cabero, M. P.; Reedijk,
J.; Spek, A. L. Dalton Trans. 2001, 197. (b) Zangrando, E.; Trani, M.;
Strabon, E.; Carfagna, C.; Milani, B.; Mestroni, G. Eur. J. Inorg. Chem.
2003, 2683.
(32) (a) Carlin, R. L. In Transition Metal Chemistry; Carlin, R. L., Ed.;
Marcel Dekker: New York, 1965; Vol. 1. (b) Sacconi, L. In Transition
Metal Chemistry; Carlin, R. L., Ed.; Marcel Dekker: New York, 1968;
Vol. 4.
(28) Britovsek, G. J. P.; Gibson, V. C.; Spitzmesser, S. K., Tellmann,
K. P.; White, A. J. P.; Williams, D. J. Dalton Trans. 2002, 1159.
(29) (a) Sacconi, L.; Morassi, R.; Midollini, S. J. Chem. Soc. A 1968,
1510. (b) Sacconi, L.; Bertini, I.; Morassi, R. Inorg. Chem. 1967, 6, 1548.
(c) Ciampolini, M.; Speroni, G. P. Inorg. Chem. 1966, 5, 45.
(30) (a) Morassi, R.; Bertini, I.; Sacconi, L. Coord. Chem. ReV. 1973,
11, 343. (b) Ciampolini, M.; Gelsomini, J. Inorg. Chem. 1967, 6, 1821.

Synthesis of New Polydentate Nitrogen Ligands
Organometallics, Vol. 26, No. 18, 2007 4647
Scheme 7
overnight. All complexes are relatively air-stable in the solid
state. Unlike the monometallic complexes, which are fairly
soluble in chlorinated solvents, the bimetallic complexes dissolve
only in very polar solvent like DMF, where, however, a color
change occurs with formation of other species. For this reason,
the bimetallic complexes have been exclusively characterized
by solid-state techniques.
The IR spectra of the bimetallic compounds show a ν(CdN)
absorption at ca. 1617 cm-1, consistent with the coordination
of all nitrogen atoms.
The reflectance spectra of the bimetallic complexes MeN5Fe2Cl4
and MeN5CoFeCl4 show no significant deviations as compared
to the mononuclear parents MeN5FeCl2 and MeN5CoCl2 due to
the fact that tetrahedral FeN2X2 chromophores exhibit only one
spin-allowed d-d transition detectable only beyond the low-
energy limit of our spectrophotometer (4550 cm-1).33 Unlike
MeN5Fe2Cl4, the spectra of the bimetallic complexes MeN5Co2X4
(X ) Cl, Br) are very complex. In particular, absorptions at ca.
8500, 9500, and 17 500 cm-1, assignable to the d-d transitions
of CoN2X2 chromophores in a tetrahedral environment,12 are
superimposed on the typical bands of high-spin five-coordinate
CoII ions.29 The reflectance spectrum of the hetero-bimetallic
complex MeN5CoNiBr2Cl2 shows additional bands at 15650 and
6000 cm-1, as compared to the parent cobalt complex, which
are ascribed to the presence of a tetrahedral NiN2X2 chro-
mophore in the complex molecule.
Like the vis-NIR spectra, the magnetic moments of the
bimetallic complexes are indicative of the presence of two high-
spin metal centers in either square-pyramidal or tetrahedral
geometry. Indeed, the bimetallic complexes exhibit overall µeff
values of 7.04 µB (Fe/Fe), 6.42-6.36 µB (Co/Co), 6.82 µB (Co/
Fe), and 5.74 µB (Co/Ni), which are in line with the values
calculated for metal ion couples of the same type (7.6, 6.7, 7.1,
and 6.0 µB, respectively).14e,34
five-coordinate bis(imino)pyridine iron complexes.27b,28-30 In
particular, the absorption spectrum displays, in the visible region,
a broad and strong absorption (ꢀ 1000) at 14 000 cm-1, which
is probably due to a ligand-to-metal charge transfer. However,
in the NIR region, the spectrum seems to contain also a low-
intensity band (ꢀ 25) at 4900 cm-1. Generally, high-spin five-
coordinate FeII complexes with an N3Cl2 donor atom set show
two low-intensity absorption bands, one, in the 10 000-7000
cm-1 region, attributed to the spin-allowed d-d transition from
the quintet ground state 5E′′ to the excited state 5A1′ and another
5
5
below ca. 5000 cm-1 for the transition E′′ f E′. It is very
likely that the latter transition is responsible for the band
observed at 4900 cm-1, whereas the transition 5E′′ f 5A1′ could
be masked by the broad absorption centered at 14 000 cm-1
,
which covers frequencies up to 8000 cm-1. The diffuse
reflectance spectrum of solid MeN5FeCl2 closely resembles that
of the complex in solution, thus indicating no significant change
in the stereochemistry of the complex on going from solid state
to solution. Also, the IR spectra of MeN5FeCl2 are identical both
in the solid state and in solution and contain the two charac-
teristic ν(CdN) bands for coordinated and uncoordinated imine
groups at 1617 and 1641 cm-1, respectively. Further information
on the five-coordinate solution structure of MeN5FeCl2 has been
Bimetallic FeII and CoII Complexes with the iPrN6 Ligand.
As previously anticipated, the formation of bimetallic complexes
with the ligand iPrN6 occurs under any ligand/metal ion ratio.
The complexes iPrN6Fe2Cl4 and iPrN6Co2Cl4 were prepared in
good yield by mixing 2 equiv of the anhydrous metal dichlorides
to the ligand in THF at room temperature. On standing
overnight, crystalline solids precipitated in good yield.
The IR spectra of these bimetallic compounds are identical
both in the solid state and in solution and show a ν(CdN)
absorption at 1594 cm-1, which reflects the coordination of all
nitrogen atoms to the metal centers (i.e., see the IR spectrum
of iPrN3CoCl2 reported in Figure 1S, trace b).
1
obtained by H NMR spectroscopy in CD2Cl2 (see below).
Like MeN5CoBr2 in the solid state, the nickel derivative
MeN5NiBr2 exhibits a six-coordinate metal center, which reflects
the tendency of NiII to form stable 20e- octahedral complexes.
The IR spectra are identical both in the solid state and in solution
and exhibit only the absorption band due to the coordinated
imine (1618 cm-1). The absorption spectrum shows a band at
8200 (ꢀ 28) cm-1 and two bands at 13 300 (ꢀ 24) and 22 600 (ꢀ
80) cm-1. The last band appears as a shoulder over a much
stronger absorption band, probably due to charge transfer. These
bands are assigned to the transitions from the fundamental state
The spectrophotometric and magnetic characterization of the
bimetallic iPrN6 complexes is unambiguously indicative of the
presence of two high-spin metal centers in five-coordinate
coordination geometries. In particular, the reflectance and
absorption spectra are similar to each other and almost identical
to those of the corresponding monometallic complexes with the
iPrN3 and iPrN5 ligands. iPrN6Fe2Cl4 and iPrN6Co2Cl4 exhibit
overall µeff values of 7.27 µB and 6.45 µB, respectively. These
values are comparable to those observed for the bimetallic N5
complexes, yet they are slightly smaller than those expected
for two noninteracting high-spin FeII or CoII centers (7.6 or 6.7
µB).14e,34
3
3
3
3A2g(F) to the excited states T2g(F), T1g(F), and T1g(P),
respectively.29a,b,32b The µeff of 2.85 µB at room temperature falls
in the expected range for octahedral nickel(II) complexes.
In the case of the ligand iPrN6, the kinetic preference for
bimetallic species even under metal ion deficiency precluded
the synthesis of monometallic complexes in analytically pure
form (see below).
Homo- and Hetero-bimetallic Complexes with the MeN5
Ligand. The homo- and hetero-bimetallic complexes MeN5Fe2Cl4,
MeN5Co2Cl4, MeN5Co2Br4, MeN5CoFeCl4, and MeN5CoNiBr2Cl2
(Scheme 7) were prepared in good yields by mixing equimo-
lecular amounts of the anhydrous metal dihalide (metal ) Fe,
Co, Ni) in THF with the appropriate monometallic complex in
CH2Cl2. The homo-bimetallic complexes were alternatively
prepared by adding 2 equiv of anhydrous FeII or CoII dihalide
to a solution of the ligand. Crystalline compounds in analytically
pure form were obtained from the reaction mixtures on standing
1H NMR Characterization of Mono- and Homo-bimetallic
FeII and CoII Complexes. Useful information for assigning the
(33) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 4th
ed.; John Wiley & Sons: New York, 1980; p 756.
(34) Gerli, A.; Hagen, K. S.; Marzilli, L. G. Inorg. Chem. 1991, 30,
4673.

4648 Organometallics, Vol. 26, No. 18, 2007
Barbaro et al.
Table 3. 1H NMR Assignments for (Imino)pyridine Iron and Cobalt Complexes (CD2Cl2, 22 °C, 400.13 MHz)a
MeN3CoCl2
MeN5CoCl2 (five-coord species)
MeN3FeCl2
MeN5FeCl2
position
δ
int
δ
int
δ
int
δ
int
Py-Hm
Py-Hp
NdCMe
Ar-Meo
Ar-Hm
Ar-Mep
111.02
2
1
6
12
4
110.81, 108.73 [44.33, 41.76]
34.12 [4.40]
1,1,1,1
1,1
3,3
6,6,6
2,2,2
3,3,3
83.7
40.1
-20.5
12.9
15.6
21.7
2
1
6
12
4
87.98, 78.91 [9.08, 3.10]
40.98 [2.28]
-2.89 [2.05]
12.93 12.23 [1.23]
17.14 13.94 [6.59]
23.31 21.61 [0.38]
1,1,1,1
1,1
3,3
6,6,6
2,2,2
3,3,3
36.28
-0.58
-26.74
6.40
-0.33 [3.79]
-26.20, -28.63 [1.17]
6.58 6.33 [2.94]
17.00
6
17.20, 14.57 [2.09]
6
a δ between square brackets denotes the uncoordinated (imino)pyridine hydrogens
Table 4. 1H NMR Assignments for (Imino)pyridine Cobalt
center in a distorted square-pyramidal coordination, the 1H NMR
spectrum (Figure 3Sb) can be rationalized by assuming the
occurrence of a fast rearrangement of the iPrN5 ligand around
CoCl2 so as to form a five-coordinate complex using either
possible 2,6-bis(imino)pyridine moiety. According to this
interpretation, this process would be averaged on the 1H NMR
time scale, whereas the other spectroscopic techniques, having
faster time scales, would allow one to have a snapshot of the
five-coordinate metal center and of the free (imino)pyridyl
moiety.
Complexes (CD2Cl2, 22 °C, 400.13 MHz)
iPrN3CoCl2
iPrN5CoCl2
position
δ
int
δ
int
Py-Hm
Py-Hp
NdCMe
i-Pr-Me
116.47
49.39
4.36
2
1
6
122.10 118.05
50.01
6.50
2,2
2
6
-17.54, -18.74
12,12
-18.7,0-20.27,
-20.41, -22.68
-95.20-96.80
9.26-9.39
12,6,6,12
i-Pr-CH
Ar-Hm
Ar-Hp
-84.44
10.00
-8.78
4
4
2
4,2
4,2
1,2
The 1H NMR spectrum of MeN5CoCl2 is more complex than
the previous ones and may be interpreted only by assuming the
formation in solution of two equilibrating CoII species, each of
which is featured by a specific set of NMR resonances (Table
3). A 17-peak set can be assigned to a five-coordinate species
of the type of iron analogue MeN5FeCl2. These resonances are
also similar to those observed for the 2,6-bis(imino)pyridine
complex MeN3CoCl2 (Table 3). A second set of resonances (see
Experimental Section) can be tentatively assigned to another
species where the CoII center is octahedrally coordinated. This
interpretation is consistent with the IR and electronic spectra
as well as the frozen solution EPR spectrum at 5 K (see below).
-7.49-8.46
solution structure of some monometallic and bimetallic com-
plexes with the MeN5, iPrN5, and iPrN6 ligands has been obtained
by 1H NMR spectroscopy. Unfortunately, the very low solubility
of the bimetallic complexes with the N5 ligands in either
hydrocarbon or chlorinated solvents precluded their NMR
1
characterization. The H NMR spectra have been acquired in
CD2Cl2 solutions at 22 °C, and the data obtained are collected
in Tables 3, 4, and 5. All protons have been found to resonate
at remarkably different chemical shifts as compared to the
corresponding protons in the free ligands, which is consistent
with the paramagnetic nature of the metal complexes. Consis-
tently, all resonances appear as broad singlets and their
assignment has been made on the basis of the relative intensities
and line widths (correlated to the proximity to the paramagnetic
metal center) as well as by comparison with structurally related
paramagnetic FeII and CoII complexes.7a,27b,28,35 For comparative
purposes, NMR data relative to the 2,6-bis(imino)pyridine
complexes iPrN3FeCl2, MeN3FeCl2, iPrN3CoCl2, and MeN3CoCl2
are reported in the tables (MeN3 ) 2,6-(2,4,6-Me3C6H2Nd
CMe)2C5H3N).
1
It is noteworthy that the H NMR spectrum of the bromide
derivative MeN5CoBr2 is practically identical with that of
MeN5CoCl2, except for the low-field shift of all resonances due
to replacement of chloride by bromide (see Experimental
Section).
The 1H NMR spectra of iPrN6Fe2Cl4 and iPrN6Co2Cl4 (Table
5) are easily rationalized, as they closely resemble those of the
mononuclear 2,6-bis(imino)pyridine analogues, except for the
absence of the p-hydrogen atoms of the two pyridine rings,
which have been sacrificed to couple the two moieties.
EPR Characterization of Mono- and Homo-bimetallic CoII
Complexes. In agreement with the fast spin-lattice relaxation
time expected for systems containing high-spin CoII centers,
all the complexes reported in this paper were EPR-silent at room
temperature. The EPR behavior of the CoII complexes was
therefore analyzed at very low temperature. The results obtained
in the solid state (Figure 3a) and in frozen CH2Cl2 solution
(Figure 3b) at 4 K are summarized in Table 6. As for the FeII
complexes, their quintuplet ground state and large zero-field
splitting (ZFS) make them EPR-silent even at 4 K.
Overall, the proton chemical shifts of MeN5FeCl2 follow the
trend previously reported for the 2,6-bis(imino)pyridine complex
MeN3FeCl2 (Table 3). In line with the presence of a single, five-
coordinate FeII center, seven proton resonances (δ between
square brackets), out of the total 17 signals observed, are easily
assigned to the uncoordinated (imino)pyridine portion of the
ligand (Figure 3Sa).
Notably, the spectrum of iPrN5CoCl2 (Figure 3Sb) contains
only 14 paramagnetically shifted peaks, instead of the 20 peaks
expected for a structure involving a CoII ion bonded to the three
nitrogen atoms of the 2,6-bis(imino)pyridine part of the iPrN5
ligand, with the (imino)pyridine moiety free from coordination
(Table 4). Consistent with the hindered rotation of the i-Pr-
1
substitued aryl rings around the N-Caryl bond, the H NMR
spectrum of iPrN5CoCl2 shows four different signals for the
CHMe2 protons.
Since the IR, vis-NIR, and EPR (see below) characterization
of iPrN5CoCl2 solutions is unambiguously indicative of a CoII
(35) (a) Gibson, V. C.; Long, N. J.; Oxford, P. J.; White, A. J. P.;
Williams, D. J. Organometallics 2006, 25, 1932. (b) Britovsek, G. J. P.;
England, J.; Spitzmesser, S. K.; White, A. J. P.; Williams, D. J. Dalton
Trans. 2005, 945.
Figure 3. X-Band (9.37 GHz) EPR spectra of CoII complexes at
4 K in the solid-state sample (a) and in frozen CH2Cl2 solution
(b).

Synthesis of New Polydentate Nitrogen Ligands
Table 5. 1H NMR Assignments for (Imino)pyridine Iron and Cobalt Complexes (CD2Cl2, 22 °C, 400.13 MHz)
iPrN6Fe2Cl4 iPrN3FeCl2 iPrN6Co2Cl4 iPrN3CoCl2
Organometallics, Vol. 26, No. 18, 2007 4649
position
δ
int
δ
int
δ
int
δ
int
Py-Hm
Py-Hp
93.50
4
81.7
81.1
-37.1
-5.3, -6.3
-22.4
14.9
2
1
6
133.35
11.34
-13.45, -16.11
-75.78
12.57
4
116.47
49.39
4.36
-17.54, -18.74
-84.44
10.00
2
1
6
NdCMe
i-Pr-Me
i-Pr-CH
Ar-Hm
Ar-Hp
-51.98
12
24,24
8
8
4
12
24,24
8
8
4
-4.56, -5.43
-44.00
12,12
12,12
4
4
2
4
4
2
16.40
-11.55
-10.9
-7.04
-8.78
Table 6. Relevant EPR Parameters of CoII Complexes with
iPrN5, MeN5, and iPrN6
that a similar pattern is exhibited by the solid-state spectrum of
the octahedral MeN5CoBr2 complex (Figure 3a). One may
therefore conclude that also MeN5CoCl2 can exist as an
octahedral complex in solution. On the other hand, the remaining
signals in the spectrum of MeN5CoCl2, at g1 ) 7.3, g2 ) 3.1, g3
) 2.1, can be safely attributed to a five-coordinate species with
a distorted square-pyramidal structure and in lower concentra-
tion.
As for the binuclear complexes iPrN6Co2Cl4 and MeN5Co2Cl4,
their EPR spectra in the solid state are characterized by very
broad lines that do not allow one to assign the g factors to the
different transitions (Figure 3a). As for MeN5Co2Cl4, the
presence of two different chromophores, namely, a CoII ion in
a four-coordinate site and a CoII ion in a five-coordinate site,
may apparently contribute to originate several unresolved
transitions.
A better resolved spectrum was obtained for iPrN6Co2Cl4 after
dissolution in CH2Cl2 solution. The spectrum can be interpreted
in terms of an effective Seff ) 1/2 with a rhombic g pattern (g1
) 5.4, g2 ) 2.2, g3 ) 1.2), while the presence of only one
series of signals indicates that the two CoII centers are
coordinatively equivalent. A comparison of the solution and
solid-state spectra shows that the dissolution of iPrN6Co2Cl4 in
CH2Cl2 has the only effect of sharpening the signals with no
major change in the distorted square-pyramidal structure of each
metal center.
solid
gy
CH2Cl2 solution
complex
gx
gz
gx
gy
gz
iPrN5CoCl2
MeN5CoCl2
7.5
1.2
0.9
7.45
4.4a
7.3b
1.35
4.4a
3.1b
1.35
2.4a
2.1b
S ) 3/2 with ZFS
MeN5CoBr2
MeN5Co2Cl4
iPrN6Co2Cl4
2.4
c
c
4.4
c
c
4.4
c
c
insoluble
5.4
2.2
1.2
b
a Attributed to six-coordinate species. Attributed to five-coordinate
c
species. Not assignable.
The powder EPR spectrum of iPrN5CoCl2 shows a typical
pattern for an effective Seff ) 1/2 spin Hamiltonian with a
strongly anisotropic g factor. Clear evidence of hyperfine
structure is observed for the parallel transition, occurring around
g1 ) 7.5, but not for the partially split perpendicular transition
(g2 ) 1.2, g3 ) 0.9). The observed g pattern is consistent with
a CoII center in a distorted square-pyramidal geometry,36 as
determined by the X-ray structure analysis (Figure 1). A closely
similar pattern is shown by the frozen solution spectrum, with
g| ) 7.45 and g ) 1.35, the small differences in the g factors
being attributable to the different packing effects in the solid
state and in the frozen solution. The EPR study therefore
confirms that iPrN5CoCl2 does not change primary structure on
going from the solid state to solution.
A different solid-state spectrum is shown by the MeN5
derivative MeN5CoCl2: the four broad transitions observed can
be interpreted only by assuming an S ) 3/2 system with small
ZFS. In such a situation, there are EPR transitions not only
within the ground Kramers doublet but also between the two
doublets with MS ) (3/2 and MS ) (1/2. Given that
MeN5CoCl2 is five-coordinate, as indicated by the IR and vis-
NIR spectra (Vide infra), the EPR spectrum suggests a coordina-
tion geometry somewhat different from that of iPrN5CoCl2. A
small value of the ZFS can be indicative of a trigonal
bipyramidal structure affected by the so-called tetrahedral
distortion.37 It may be useful to recall at this point that the size
of the ortho-alkyl substituents on the N-aryl rings can control
the overall geometry of the RN3MCl2 complexes (M ) Fe, Co;
R ) i-Pr, Me), with the larger i-Pr substituents favoring the
square-pyramidal coordination and the smaller methyl groups
favoring the trigonal-bipramydal geometry.7a
Polymerization of Ethylene Catalyzed by Mono- and
Bimetallic Complexes Stabilized by the N5 and N6 Ligands.
The mono- and bimetallic complexes with the ligands iPrN5,
MeN5 (Table 7), and iPrN6 (Tables 8 and 9) were tested in toluene
as catalyst precursors for the polymerization of ethylene under
standard experimental conditions.
Upon activation by MAO, the monometallic FeII and CoII
complexes with the iPrN5 and MeN5 ligands formed active
catalysts for the polymerization of ethylene, exhibiting com-
parable activities. Irrespective of the catalyst precursor, high-
density polyethylene (HDPE) with no branching was invariably
obtained. The weight average molecular weights (Mw) and the
polydispersities (Mw/Mn) were typical for this kind of material
produced by FeII and CoII bis(imino)pyridine catalysts.10
Irrespective of the metal, the activities of the monometallic
N5 catalysts were significantly higher than those of the corre-
sponding bimetallic derivatives, yet lower than those obtained
with the classic RN3FeCl2 and RN3CoCl2 precursors under
comparable conditions (Table 7). This decrease in productivity
may originate for various reasons, for example the capability
of the N5 ligands to wrap the metal center with four nitrogen
atoms (Scheme 6), leading to partial formation of catalytically
inactive species on treatment with MAO. A role may also be
played by the free (imino)pyridine moiety in the five-coordinate
complexes that, besides subtracting some activator, may interact
with MAO or with the residual AlMe3, leading to less active
structures.39
Interestingly, on dissolution in CH2Cl2, the EPR spectrum
of MeN5CoCl2 changes completely (Figure 3b). Two series of
partially hyperfine-split signals are evident with a predominance
in intensity of a g pattern typical for axially distorted, six-
coordinate CoII centers (g ) 4.4, g| ) 2.4).38 It is worth noticing
(36) Bencini, A.; Gatteschi, D. In Transition Metal Chemistry; Figgis,
B. N, Melson, G., Eds.; Marcel Dekker: New York, 1982; Vol. 8.
(37) (a) Banci, L.; Bencini, A.; Benelli, C.; Gatteschi, D.; Zanchini, C.
Struct. Bonding 1982, 52, 37. (b) Jime´nez, H. R.; Salgado, J.; Moratal, J.
M.; Morgenstern-Badarau I. Inorg. Chem. 1996, 35, 2737.
(38) Abragam, A.; Pryce, M. H. L. Proc. R. Soc. A 1951, 206, 173.

4650 Organometallics, Vol. 26, No. 18, 2007
Table 7. Ethylene Polymerization with Mono- and Bimetallic Precursors of N5 Ligandsa
Barbaro et al.
c
M amount
(µmol)
MAO amount
PE
amount (g)
TOFb
Mw
∆Hd
(J/g)
c
run
precatalyst
(µmol)
Ti (°C)
∆T (°C)
(×10-5
)
(kg mol-1
)
Mw/Mn
Tmd (°C)
1
2
3
4
5
6
7
8
MeN3CoCl2
12
12
12
12
24
24
24
24
12
12
24
3600
3600
3600
3600
7200
7200
7200
7200
3600
3600
7200
27
26
27
22
25
24
27
26
27
26
29
35
10
27
24
19
25
12
14
45
21
18
13.5
5.2
9.4
7.2
7.6
8.8
5.7
5.3
18.2
9.2
1.60
0.61
1.12
0.85
0.45
0.52
0.34
0.31
2.16
1.09
0.63
iPrN5CoCl2
751
314
4.1
14.0
140.9
139.1
139.2
201.0
MeN5CoCl2
MeN5CoBr2
MeN5Co2Cl4
MeN5Co2Br4
MeN5CoNiCl2Br2
MeN5CoFeCl4
MeN3FeCl2
439
14.6
143.0
164.3
9
10
11
MeN5FeCl2
378
12.0
139.3
199.5
MeN5Fe2Cl4
10.6
a Reaction conditions: 500 mL stainless steel reactor; precatalyst, 12 µmol; MAO/M, ratio 300; toluene, 100 mL; ethylene, 4 bar; 15 min, 1500 rpm.
c
d
bTOF expressed as mol C2H4 converted (mol metal)-1 h-1; average values calculated for 4 runs. Detected by GPC at 140 °C. Detected by DSC.
Table 8. Ethylene Polymerization with iPrN6Fe2Cl4 Precursorsa
precatalyst
amount
(µmol)
MAO
Fe amount amount
c
c
Al/Fe
ratio
Ti
∆T
PE
TOFb
Mw
Tm
(°C)
∆Hd
run
precatalyst
(µmol)
(µmol)
(°C) (°C) amount (g) (×10-5
)
(kg mol-1
413
)
Mw/Mn
(J/g)
c
1
2
3
4
5
6
7
iPrN6Fe2Cl4
iPrN6Fe2Cl4
iPrN6Fe2Cl4
iPrN6Fe2Cl4
iPrN3FeCl2
iPrN3FeCl2
iPrN3FeCl2
6
12
3600
3600
1800
3600
3600
1800
3600
300
3000
3000
15000
300
3000
23
27
23
23
22
22
22
44
37
7
8
51
5
14.2
6.3
3.4
3.9
19.1
3.3
1.69
7.49
8.17
22.99
2.27
7.87
15.0
139.9 200.5
0.6
0.3
0.12
12
0.6
0.24
1.2
0.6
0.24
12
0.6
0.24
15 000
2
4.0
23.76
b
a Reaction conditions: 500 mL stainless steel reactor; toluene, 100 mL; ethylene, 5 bar; 15 min; 1500 rpm. TOF expressed as mol C2H4 converted (mol
c
d
metal)-1 h-1; average values calculated for 4 runs. Detected by GPC at 140 °C. Detected by DSC.
Table 9. Ethylene Polymerization with iPrN6Co2Cl4 Precursorsa
precatalyst
amount
(µmol)
MAO
amount
(µmol)
PE
amount
(g)
c
c
Co amount
(µmol)
Al/Fe
ratio
Ti
(°C)
∆T
TOFb
Mw
Tm
∆Hd
c
run
precatalyst
(°C)
(×10-5
)
(kg mol-1
485
)
Mw/Mn
(°C)
(J/g)
1
2
3
4
iPrN6Co2Cl4
iPrN6Co2Cl4
iPrN3CoCl2
iPrN3CoCl2
6
0.6
12
12
1.2
12
3600
3600
3600
3600
300
3000
300
26
25
24
25
38
30
15
27
16.1
7.1
10.4
4.5
1.81
8.50
1.24
5.35
10.1
142.9
190.5
1.2
1.2
3000
b
a Reaction conditions: 500 mL stainless steel reactor; toluene, 100 mL; ethylene, 5 bar; 15 min; 1500 rpm. TOF expressed as mol C2H4 converted (mol
c
d
metal)-1 h-1; average values calculated for 4 runs. Detected by GPC at 140 °C. Detected by DSC.
Scheme 8
In contrast, the productivity of the FeII catalyst iPrN6Fe2Cl4
was practically identical to that of the congener iPrN3FeCl2,
provided a double proportion of the latter is used (Table 8).
Apparently, the coupling of two bis(imino)pyridine moieties via
the pyridine C4 carbon atom does not influence the catalytic
activity of the FeII centers.
Unlike iPrN6Fe2Cl4, the dicobalt congener iPrN6Co2Cl4 was
significantly more active than the classic bis(imino)pyridine
spin CoII center antiferromagnetically coupled to a ligand radical
anion; that is, the reduction of high-spin CoX2L to low-spin
CoXL (L ) 2,6-bis(imino)pyridine ligand) would occur at the
ligand rather than at the metal (Scheme 8).42 Within this context,
yet on a pure speculative basis, the surprisingly high polymer-
ization activity of iPrN6Co2Cl4/MAO may be related to the
creation of cobalt centers with a favorable electronic structure.
catalyst iPrN3CoCl2 (Table 9). This finding is certainly intriguing
and worthy of further investigation. At the present stage, we
can only emphasize the fact that the two cobalt centers may
electronically interact in a conjugated structure such as that of
the iPrN6 ligand. In actuality, the electronic delocalization seems
to play a significant role in ethylene polymerization by
RN3CoCl2/MAO catalysis. It has been demonstrated by several
authors that the action of MAO on the precursors RN3CoCl2 is
quite complex, involving not only the replacement of chloride
with methyl and the creation of a coordination vacancy but also,
at an initial stage, the formation of diamagnetic square-planar
complexes.40,41 Some authors describe these diamagnetic com-
pounds as containing CoI centers, while other authors propose
that the singlet ground state may be due to a square-planar, low-
Conclusions
New penta- and hexadentate nitrogen ligands have been
synthesized either by coupling 2,6-bis(imino)pyridine and
(40) (a) Humphries, M. J.; Tellmann, K. P.; Gibson, V. C.; White, A. J.
P.; Williams, D. J. Organometallics 2005, 24, 2039. (b) Gibson, V. C.;
Humphries, M. J.; Tellmann, K. P.; Wass, D. F.; White, A. J. P.; Williams,
D. J. Chem. Commun. 2001, 2252.
(39) (a) Knijnenburg, Q.; Smits, J. M. M.; Budzelaar, P. H. M.
Organometallics 2006, 25, 1036. (b) Bruce, M.; Gibson, V. C.; Redshaw,
C.; Solan, G. A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998,
2523.
(41) Kooistra, T. M.; Knijnenburg, Q.; Smits, J. M. M.; Horton, A. D.;
Budzelaar, P. H. M.; Gal, A. W. Angew. Chem., Int. Ed. 2001, 40, 4719.
(42) Knijnenburg, Q.; Hettershield, D.; Kooistra, T. M.; Budzelaar, P.
H. M. Eur. J. Inorg. Chem. 2004, 1204.

Synthesis of New Polydentate Nitrogen Ligands
Organometallics, Vol. 26, No. 18, 2007 4651
(imino)pyridine molecules or by homocoupling 2,6-bis(imino)-
pyridine molecules. The presence of five or six nitrogen donor
atoms allows these ligands to coordinate either one or two FeII
or CoII bis-halides. In the bimetallic systems with the N5 ligands,
one metal is five-coordinate, generally in a square-pyramidal
geometry, and the other is tetrahedrally coordinated. In the
monometallic N5 complexes, depending on the halide (Cl, Br)
and on the size of the substituents on the N-aryl rings, either
five- or six-coordinate monometallic complexes are formed,
which shows that these ligands maintain a high degree of
structural flexibility notwithstanding the extensive conjugation
provided by uninterrupted sequences of C-C and C-N double
bonds.
ever reported. The good results obtained in the polymerization
of ethylene and the proved, facile structural modification of the
(imino)pyridine moiety forecast the use of these N5 and N6
ligands in other homogeneously catalyzed reactions.
Acknowledgment. Thanks are due to the European Com-
munity (STREP project no. 516972-NANOHYBRID; Network
of Excellence no. NMP3-CT-2005-0011730-IDECAT), Min-
istero dell’Istruzione, dell’Universita` e della Ricerca (FIRB
project no. RBNE03R78E-NANOPACK), and Firenze-HY-
DROLAB project for financial support. L.S. acknowledges Prof.
D. Gatteschi for useful suggestions and the financial support
of Ente Cassa di Risparmio di Firenze.
Effective catalysts for the polymerization of ethylene to
HDPE are generated by activating the bis-chloride precursors
with MAO in toluene. Of particular relevance is the very good
productivity (more than 1.8 × 105 mol C2H4 converted (mol
cobalt)-1 h-1) exhibited by the dicobalt complex iPrN6Co2Cl4,
which is more active than any other CoII polymerization catalyst
Supporting Information Available: Text and tables giving
crystallographic data for compounds iPrN5CoCl2 and MeN5CoBr2.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM7005062