Synthesis of a new polydentate ligand obtained by coupling 2,6-bis(imino)pyridine and (imino)pyridine moieties and its use in ethylene oligomerization in conjunction with iron(II) and cobalt(II) bis-halides

Article abstract of DOI:10.1021/om7006503

In this paper are described the synthesis, characterization, and coordinating properties of a new potentially pentadentate nitrogen ligand, ^CyAr2N₅, that combines in the same molecular structure 2,6-bis(imino)pyridine and (imino)pyridine moieties. This ligand reacts with 1 or 2 equiv of anhydrous MCl₂ (M = Fe, Co) to give paramagnetic mononuclear or homodinuclear complexes of the formula ^CyAr2N ₅MCl₂ and ^CyAr2N₅M ₂CL₄. In the dinuclear complexes, one metal center is five-coordinate, while the other is fourcoordinate. Ligand and metal complexes 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 determinations, IR, vis-NIR, ¹H NMR, and X-band EPR spectroscopies. On activation by methylaluminoxane (MAO) in toluene, the Fe ^II and Co^II complexes generate effective catalysts for the oligomerization of ethylene to a-olefins with productivities and Schulz-Flory parameters depending on the type and number of the coordinated metals. In an attempt to rationalize the surprisingly high activity of the Co^II precursors, and in particular that of the dinuclear derivative ^CyAr2N₅Co₂CL₄, which is 4 times higher than that of the mononuclear analogue ^CyAr2N ₅CoCl₂, a Co^II complex has been synthesized where the supporting ligand is sterically similar to ^CyAr2N ₅, yet it contains only the three nitrogen donor atoms of the 2,6-bis(imino)pyridine moiety. From this study, it is concluded that all five nitrogen atoms of ^CyAr2N₅ play an active role under catalytic conditions, even when the precursor contains a free (imino)pyridine moiety.

Full text of DOI:10.1021/om7006503

5066
Organometallics 2007, 26, 5066-5078
Synthesis of a New Polydentate Ligand Obtained by Coupling
2,6-Bis(imino)pyridine and (Imino)pyridine Moieties and Its Use in
Ethylene Oligomerization in Conjunction with Iron(II) and
Cobalt(II) Bis-halides
Claudio Bianchini,*,† Giuliano Giambastiani,*,† Itzel Guerrero Rios,† Andrea Meli,†
Werner Oberhauser,† 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 June 28, 2007
In this paper are described the synthesis, characterization, and coordinating properties of a new potentially
pentadentate nitrogen ligand, CyAr2N5, that combines in the same molecular structure 2,6-bis(imino)-
pyridine and (imino)pyridine moieties. This ligand reacts with 1 or 2 equiv of anhydrous MCl2 (M ) Fe,
Co) to give paramagnetic mononuclear or homodinuclear complexes of the formula CyAr2N5MCl2 and
CyAr2N5M2Cl4. In the dinuclear complexes, one metal center is five-coordinate, while the other is four-
coordinate. Ligand and metal complexes 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. On activation by methylalu-
minoxane (MAO) in toluene, the FeII and CoII complexes generate effective catalysts for the oligomerization
of ethylene to R-olefins with productivities and Schulz-Flory parameters depending on the type and
number of the coordinated metals. In an attempt to rationalize the surprisingly high activity of the CoII
precursors, and in particular that of the dinuclear derivative CyAr2N5Co2Cl4, which is 4 times higher than
that of the mononuclear analogue CyAr2N5CoCl2, a CoII complex has been synthesized where the supporting
ligand is sterically similar to CyAr2N5, yet it contains only the three nitrogen donor atoms of the 2,6-bis-
(imino)pyridine moiety. From this study, it is concluded that all five nitrogen atoms of CyAr2N5 play an
active role under catalytic conditions, even when the precursor contains a free (imino)pyridine moiety.
oligomerization of ethylene to R-olefins with a Schulz-Flory
distribution are shown in Scheme 1.
Introduction
The success of iron and cobalt bis-chloride catalysts supported
by either 2,6-bis(imino)pyridine1-3 or (imino)pyridine4,5 ligands
in ethylene oligomerization is stimulating much research aimed
at developing analogous catalytic systems with improved
productivity and selectivity. Some active precursors for the
The advantages of 2,6-bis(arylimino)pyridine or (imino)-
pyridine FeII and CoII catalysts over other types of early and
late transition metal systems for ethylene oligomerization are
manifold, spanning from the ease of preparation and handling,
to the use of cheap metals with reduced environmental impact.
Another intriguing feature of these catalyst precursors is
provided by the facile tuning of their activity by simple structural
modifications such as the number, size, nature, and regiochem-
istry of the substituents either in the pyridine ring or in the
arylimino groups.1,4 Moreover, due to the good compatibility
with other catalytic systems, 2,6-bis(arylimino)pyridine6 and
(imino)pyridine4c,7 FeII and CoII dihalides can be used as
oligomerization catalysts in tandem reactions for the production
of branched polyethylene (PE) as well as in reactor blending
processes to give PE with controlled molecular weight distribu-
tion and rheology.8
* To whom correspondence should be addressed. E-mail: claudio.
bianchini@iccom.cnr.it.
† ICCOM-CNR.
‡ Universita` di Firenze and UdR INSTM-Firenze.
(1) (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.
(2) (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.
(3) (a) Bianchini, C.; Mantovani, G.; Meli, A.; Migliacci, F.; Zanobini,
F.; Laschi, F.; Sommazzi, A. Eur. J. Inorg. Chem. 2003, 1620. (b) Bianchini,
C.; Giambastiani, G.; Guerrero Rios, I.; Meli, A.; Passaglia, E.; Gragnoli,
T. Organometallics 2004, 23, 6087.
(4) (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.; Frediani, M.; Giambastiani, G.; Kaminsky, W.;
Meli, A.; Passaglia, E. Macromol. Rapid Commun. 2005, 26, 1218. (d)
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.
(5) (a) 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. (b) Tang, X.; Sun, W.-H.; Gao, T.; Hou, J.; Chen, J.; Chen, W. J.
Organomet. Chem. 2005, 690, 1570.
(6) (a) Quijada, R.; Rojas, R.; Bazan, G.; Komon, Z. J. A.; Mauler, R.
S.; Galland, G. B. Macromolecules 2001, 34, 2411. (b) Wang, H.; Ma, Z.;
Ke, Y.; Hu, Y. Polym. Int. 2003, 52, 1546. (c) Zhang, Z.; Lu, Z.; Chen, S.;
Li, H.; Zhang, X.; Lu, Y.; Hu, Y. J. Mol. Catal. A 2005, 236, 87.
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10.1021/om7006503 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/25/2007

Synthesis of a New Polydentate Ligand
Organometallics, Vol. 26, No. 20, 2007 5067
Scheme 1
Scheme 2
Scheme 3
ane (MAO), convert ethylene into R-olefins with productivities
and Schulz-Flory parameters depending on the type and the
number of coordinated metals.
For these reasons, the search for new molecular architectures
of either 2,6-bis(imino)pyridine or (imino)pyridine ligands is a
topic of much current interest. Among the many possible
structural variations, great interest is being stirred up by the
incorporation of 2,6-bis(imino)pyridine and (imino)pyridine
moieties into the same molecular structure.1,5a,9,10 Such poly-
dentate nitrogen ligands are expected to generate polymetallic
catalysts with diverse applications in homogeneous catalysis,
with particular regard to ethylene oligomerization/polymeriza-
tion. Indeed, homo- or heteropolymetallic catalysts may (i)
produce unconventional mixtures of PEs and/or R-olefins, (ii)
exhibit increased activity due to favorable steric and electronic
metal-metal interactions, and (iii) produce tailored materials
via chain transfer from one metal to the other with or without
a shuttling agent.
The coupling of a 2,6-bis(imino)pyridyl moiety with an
(imino)pyridyl fragment has been recently described, and the
corresponding FeII and CoII mono- and dinuclear complexes
have been successfully used for the polymerization of ethylene
to high-density PE (Scheme 2).10
In this paper, we describe the synthetic route to a new
molecule, CyAr2N5 (Scheme 3), that combines in the same
molecular structure two ligands, each of which is independently
capable of generating an effective FeII or CoII catalyst for the
oligomerization of ethylene.3,4 The CyAr2N5 ligand differs from
any other previously described related molecule, for example
Ar3N5 shown in Scheme 3,10 for the position of the (imino)-
pyridine fragment with respect to the central imine group as
well as the presence of a cyclohexyl substituent on the latter
group. As it will be shown in this paper, CyAr2N5 allows for the
formation of mononuclear and dinuclear FeII and CoII bis-
chloride complexes that, upon activation with methylaluminox-
Experimental Section
General Considerations. All air- and/or water-sensitive reactions
were performed under either nitrogen or argon in flame-dried flasks
using standard Schlenk-type techniques. Anhydrous toluene, THF,
and Et2O were obtained by means of an MBraun solvent purification
systems, while CH2Cl2 and MeOH were distilled over CaH2 and
Mg, respectively. Solid MAO for polymerization was prepared by
removing toluene and AlMe3 under vacuum from a commercially
available MAO solution (10 wt % in toluene, Sigma-Aldrich). The
MAO solution was filtered on a D4 funnel and evaporated to
dryness at 50 °C under vacuum. The resulting white residue was
heated further to 50 °C under vacuum overnight. A stock solution
of MAO was prepared by dissolving solid MAO in toluene (100
mg mL-1). The solution was used within three weeks to avoid self-
condensation effects of the MAO. All the other reagents and
solvents were used as purchased from commercial suppliers. Solid
compounds were collected on sintered-glass frits and washed with
appropriate solvents before being dried in a stream of nitrogen.
Ethylene oligomerization reactions and reactions under high CO
pressure were performed in stainless steel reactors (500 and 100
mL for ethylene and CO, respectively), 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
1
measurements were dried over 4 Å molecular sieves. H 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 vari-
able-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 assignments 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
(8) De Souza, R. F.; Casagrande, O. L., Jr. Macromol. Rapid Commun.
2001, 22, 1293.
(9) (a) Wang, L.; Sun, W.-H.; Han, L.; Yang, H.; Hu, Y.; Jin, X. J.
Organomet. Chem. 2002, 658, 62. (b) Champouret, Y. D. M.; Mare´chal
J.-D.; Dadhiwala, I.; Fawcett, J.; Palmer, D.; Singh, K.; Solan G. A. Dalton
Trans. 2006, 2350. (c) Zhang, S.; Vystorop, I.; Tang, Z.; Sun, W.-H.
Organometallics 2007, 6 2456.
(10) Barbaro P.; Bianchini, C.; Giambastiani, G.; Guerrero Rios, I.; Meli,
A.; Oberhauser, W.; Segarra, A. M.; Sorace, L.; Toti, A. Organometallics,
in press.
1
phase-sensitive representations using TPPI. H NOESY measure-
ments11 were recorded with 1024 increments of size 2 K (with 8

5068 Organometallics, Vol. 26, No. 20, 2007
Bianchini et al.
scans each) covering the full range in both dimensions and 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
1
mixing times of 800 and 300 ms. H-13C HMQC correlations12
were recorded by use of the standard sequence with decoupling
during acquisition. Vis-NIR spectra (range 25 000-4550 cm-1
)
1
in both solid-state (reflectance) and CH2Cl2 solution (absorption)
were recorded on a Perkin-Elmer Lamda 9 spectrophotometer.
Infrared spectra were recorded on a Perkin-Elmer Spectrum BX
FT-IR spectrophotometer using samples mulled in Nujol between
KBr plates. 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 condi-
tions, and for the intrinsic diamagnetism of the sample, estimated
through Pascal’s constants. X-band EPR spectra of both powder
and frozen solution (CH2Cl2) samples were recorded on a Bruker
obtained in pure form (yield >99%). Mp: 40-42 °C. H NMR
(CDCl3): δ 1.80 (s, 3H, Me), 3.95-4.20 (m, 4H, CH2), 7.49 (dd,
J ) 7.7, 1.3, 1H, CH Ar), 7.58-7.65 (2H, m, CH Ar). 13C{1H}
NMR (CDCl3): δ 25.6 (1C, Me); 65.6 (2C, CH2); 108.5 (1C, C
Ar); 118.9 (1C, CH Ar); 128.1 (1C, CH Ar); 139.6 (1C, CH Ar);
142.5 (1C, CH Ar); 163.0 (1C, CH Ar). 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 2-Cyano-5-bromopyridine. To a solution of 2,5-
dibromopyridine (5.0 g, 21.1 mmol) in DMF (40 mL) were added
in sequence CuCN (1.5 g, 16.75 mmol) and NaCN (0.85 g, 17.34
mmol). The reaction mixture was stirred at reflux temperature for
4 h. After cooling to room temperature, water was added and the
reaction mixture was extracted three times with AcOEt (3 × 20
mL). The collected organic layers were dried over Na2SO4, filtered,
and evaporated under reduced pressure to give a pale yellow
semisolid material. Chromatographic purification over silica (AcOEt/
n-pentane, 5:95) gave a white solid in 82% yield. 1H NMR
(CDCl3): δ 7.59 (d, J ) 10.5 Hz, 1H), 8.00 (dd, J ) 10.5, 2.7 Hz,
1H), 8.79 (s, 1H). 13C{1H} NMR (CDCl3): δ 116.9 (1C, CtN),
125.4 (1C, CH), 129.6 (1C, CH), 132.4 (1C, CH), 140.1 (1C, CH),
152.9 (1C, CH). Anal. Calcd (%) for C6H3BrN2 (183.01): C, 39.38;
H, 1.65; N, 15.31. Found: C, 39.09; H, 1.5; N, 15.52.
4
Elexsys E500 spectrometer equipped with a He continuous flow
cryostat for operation at cryogenic temperature (4-20 K). Elemental
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 recorded on
a Stuart Scientific SMP3 apparatus. Conductivity measurement was
obtained with an ORION model 990101 conductance cell connected
to a model 101 conductivity meter. The conductivity data13 were
obtained at sample concentrations of ca. 10-3 M in 1,2-dicholoet-
hane solution. GC analyses of the reaction products were performed
on a Shimadzu GC-17 gas chromatograph equipped with a flame
ionization detector and a Supelco SPB-1 fused silica capillary
column (30 m length, 0.25 mm i.d., 0.25 µm film thickness) for
the C6-C20 fraction or a HP-PLOT Al2O3 KCl column (50 m
length, 0.53 mm i.d., 15 µm film thickness) for the C4-C6 fraction.
The GC/MS analyses were performed on a Shimadzu QP2010S
apparatus equipped with a column identical with that used for GC
analysis.
Synthesis of 5-Bromo-2-[(trimethylsilyl)ethynyl]pyridine. A
solution of 2,5-dibromopyridine (5.0 g, 21.1 mmol) and trimeth-
ylsilylacetylene (2.21 g, 22.5 mmol) in NEt3/MeCN (1:1, 40 mL)
at room temperature was treated with dichlorobis(triphenylphos-
phine)palladium(II) (PdCl2(PPh3)2, 298 mg, 0.425 mmol) and CuI
(81 mg, 0.425 mmol). After 1 h stirring the slurry solution formed
was concentrated. The salts formed were filtered off, and the
solution was evaporated under reduced pressure. The dark orange
oil obtained was purified by a chromatographic filtration over a
silica gel pad using n-hexane/AcOEt (97:3) as eluent, providing a
yellow oil. The oil was then dissolved in CH2Cl2 and treated with
activated carbon. Filtration over a Celite pad and evaporation of
the solvent afforded a colorless oil, which solidifies upon standing
Synthesis of 1-(6-Bromopyridin-2-yl)ethanone.14 To a stirred
solution of 2,6-dibromopyridine (7.11 g, 30.0 mmol) in Et2O (130
t
mL) at -78 °C was added dropwise a 1.7 M solution of BuLi
(18.8 mL, 30.0 mmol) in n-pentane over 10 min. After 30 min
stirring at -78 °C, N,N-dimethylacetamide (3.1 mL, 33.0 mmol)
was added and stirring maintained for 1.5 h. The resulting mixture
was allowed to warm to room temperature and treated with water
(30 mL). The formed layers were separated, and the organic phase
was washed with water (2 × 30 mL). The aqueous layer was
extracted with Et2O (3 × 30 mL). The combined organic layers
were dried over Na2SO4. Removal of the solvent under reduced
pressure gave a yellow oil that was dissolved in petroleum ether
and cooled to -20 °C. After 6 h, small pale yellow crystals were
separated by filtration (yield 90%). Mp: 44 °C. IR (KBr): ν 1695
1
at room temperature (96%). H NMR (CDCl3): δ 0.26 (s, 9H),
7.48 (d, J ) 8.5 Hz, 1H), 7.77 (dd, J ) 8.4, 2.1 Hz, 1H), 8.62 (d,
J ) 2.1 Hz, 1H). 13C{1H} NMR (DMSO-d6): δ -0.1, 96.1, 103.5,
120.7, 129.0, 139.8, 140.7, 151.2.
Synthesis of 1-(5-Bromo-2-pyridinyl)ethanone. A solution of
5-bromo-2-[(trimethylsilyl)ethynyl]pyridine (9.8 g, 38.5 mmol) in
acetone/H2O (8:1, 150 mL) at room temperature was treated with
Hg(OAc)2 (12.9 g, 40.4 mmol). After 15 min stirring, the reaction
was treated with H2SO4 (3 M, 38.8 mL) and heated to reflux for 1
h. The mixture was cooled in an ice bath, neutralized with 2 M
NaOH, and extracted with AcOEt. The combined organic layers
were dried (Na2SO4) and evaporated to dryness. The residue was
purified by silica gel chromatography (n-hexane/AcOEt, 97:3) to
provide the product as a white crystalline solid (yield 75%). IR
1
cm-1 (CdO). H NMR (CDCl3): δ 2.70 (s, 3H, C(O)Me), 7.68
(m, 2H, CH), 7.98 (dd, J ) 6.5, 2.1, 1H, CH). 13C{1H} NMR
(CDCl3): δ 26.4 (1C, C(O)Me), 121.1 (1C, CH), 132.4 (1C, CH),
139.8 (1C, CH), 142.0 (1C, C), 154.9 (1C, C), 198.5 (1C, C(O)-
Me). Anal. Calcd (%) for C7H6BrNO (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 (I).15 A solution of 1-(6-bromopyridin-2-yl)ethanone (1.0 g,
5 mmol), 1,2-ethanediol (0.34 mL, 6 mmol), and p-toluenesulfonic
acid monohydrate (PTSA, 0.1 g, 0.5 mmol) in 15 mL of distilled
benzene was heated for 24 h under reflux in a Dean-Stark apparatus.
The mixture was cooled to room temperature and then treated with
1
(KBr): ν 1697 cm-1 (CdO). H NMR (CDCl3): δ 2.69 (s, 3H,
Me), 7.92 (d, J ) 7.5 Hz, 1H, Py-Hm), 7.98 (dd, J ) 7.2, 2.1 Hz,
1H, Py-Hp), 8.73 (d, J ) 1.2, 1H, Py-Ho). 13C NMR (CDCl3): δ
26.1 (1C, C(O)Me), 123.2 (1C, CH), 125.6 (1C, C), 139.9 (1C,
CH), 150.5 (1C, CH), 152.1 (1C, C), 199.5 (1C, C(O)Me). Anal.
Calcd (%) for C7H6BrNO (200.03): C, 42.03; H, 3.02; N, 7.00.
Found: C, 42.09; H, 2.90; N, 7.02.
(11) (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.
Synthesis of 5-Bromo-2-(2-methyl-1,3-dioxolan-2-yl)pyridine
(II). To a solution of 1-(5-bromo-2-pyridinyl)ethanone (7.3 g, 36.6
mmol) and ethylene glycol (43.9 mmol) in 80 mL of distilled
benzene was added a catalytic amount of PTSA. The solution was
warmed to reflux temperature using a Dean-Stark apparatus. After
36 h the reaction was cooled to room temperature and 50 mL of
(12) Bax, A. A.; Griffey, R. H.; Hawkins, B. L. J. Magn. Reson. 1983,
55, 301.
(13) Geary, W. J. J. Coord. Chem. ReV. 1971, 7, 81. (b) Morassi, R.;
Sacconi, L. J. Chem. Soc. A 1971, 492.
(14) Bolm, C.; Ewald, M.; Schilingloff, G. Chem. Ber. 1992, 125, 1169.
(15) Constable, E. C.; Heirtzler, F.; Neuburger, N.; Zehnder, M. J. Am.
Chem. Soc. 1997, 119, 5606.

Synthesis of a New Polydentate Ligand
Organometallics, Vol. 26, No. 20, 2007 5069
H2O was added slowly. The phases were separated, and the aqueous
layer was extracted with 2 × 50 mL of Et2O. The combined organic
layers were dried over Na2SO4. The solvent was removed under
reduced pressure, and the white solid obtained was used without
mL), and neutralized portionwise with solid NaHCO3. A standard
extractive workup with AcOEt (3 × 50 mL) gave after removal of
solvent a crude, slightly brown solid, which was purified by
filtration over a silica gel pad (AcOEt/petroleum ether, 95:5) to
afford the expected compound as pure yellow crystals (yield 94%).
Mp: 98-99 °C. IR (KBr): ν 1701 cm-1 (CdO), ν 1664 cm-1
(CdO). 1H NMR (CDCl3): δ 2.68 (s, 3H, Me), 2.78 (s, 3H, Me),
8.12 (pseudo-t, J ) 7.57, 7.81, 1H, Py-Hp), 8.17 (d, J ) 8.09, 1H,
Py-Hm), 8.29 (d, J ) 7.82, 1H, Py-Hm), 8.40 (d, J ) 7.57, 1H,
Py-Hm), 8.59 (dd, J ) 8.06, 1.95, 1H, Py-Hp), 9.43 (d, J ) 1.95,
1H, Py-Ho). 13C{1H} NMR (CDCl3): δ 25.79 (1C, C(O)Me), 26.05
(1C, C(O)Me), 120.79 (1C, CH), 124.89 (1C, CH), 127.78 (1C,
CH), 134.21 (1C, C), 138.62 (1C, CH), 139.13 (1C, CH), 151.27
(1C, CH), 152.32 (1C, C), 152.52 (1C, C), 155.16 (1C, C), 190.62
(1C, CdO), 198.81 (1C, C(O)Me), 199.53 (1C, C(O)Me). Anal.
Calcd (%) for C15H12N2O3 (268.27): C, 67.16; H, 4.51; N, 10.44.
Found: C, 67.10; H, 4.60; N, 10.39.
1
further purification (yield 98%). H NMR (CD2Cl2): δ 1.70 (s,
3H, Me), 3.88 (m, 2H, CH2), 4.08 (m, 2H, CH2), 7.49 (d, J ) 8.3
Hz, 1H, Py-Hm), 7.86 (dd, J ) 8.3, 2.4 Hz, 1H, Py-Hp), 8.68 (d, J
) 2.1 Hz, 1H, Py-Ho). 13C{1H} NMR (CDCl3): δ 35.03 (1C, Me),
75.36 (2C, CH2), 118.63 (1C, C), 130.24 (1C, C), 131.37 (1C, CH),
149.28 (1C, CH), 160.60 (1C, CH), 170.05 (1C, C).
Synthesis of 6-(2-Methyl[1,3]dioxolan-2-yl)nicotinic Acid Pro-
pyl Ester (III). The reaction was carried out in a 200 mL stainless
steel reactor provided by magnetic stirring and a pressure controller.
The reactor was charged with a solution of II (2 g, 8.19 mmol)
and Pd(PPh3)2Cl2 (0.4 g, 0.57 mmol) in 40 mL of a mixture of
EtOH/NEt3 (7:3). It was stirred and warmed to 80 °C for 24 h under
a CO atmosphere (4 bar). The reactor was cooled to room
temperature and depressurized. The solution was concentrated under
reduced pressure, the resulting suspension was dissolved with CH2-
Cl2, and water was added. The phases were separated, and the
aqueous phase was extracted with CH2Cl2 (3 × 50 mL). The
combined organic layers were dried over Na2SO4, and the removal
of solvent under reduced pressure gave a crude orange oil, which
was purified by silica gel chromatography using n-hexane/AcOEt
(8:2, v/v) and 5% NEt3 as eluent, to provide a yellow oil (yield
96%). IR (KBr): ν 1695 cm-1 (CdO). 1H NMR (CD2Cl2): δ 1.42
(t, J ) 7.15 Hz, 3H, C(O)OCH2Me), 1.73 (s, 3H, Me), 3.89 (m,
2H, CH2), 4.10 (m, 2H, CH2), 4.42 (q, J ) 7.15 Hz, 2H, C(O)-
OCH2Me), 7.66 (dd, J ) 8.16, 0.74 Hz, 1H, Py-Hm), 8.31 (dd, J )
8.16, 2.11 Hz, 1H, Py-Hp), 9.19 (pseudo-t, J ) 2.11, 0.74 Hz, 1H,
Py-Ho). 13C{1H} NMR (CDCl3): δ 14.01 (1C, C(O)OCH2Me),
24.67 (1C, Me), 61.32 (C(O)OCH2Me), 65.01 (1C, CH2), 65.06
(1C, CH2), 108.43 (1C, C), 119.00 (1C, CH), 125.60 (1C, C), 137.45
(1C, CH), 150.37 (1C, CH), 164.93 (1C, C), 165.05 (1C, C(O)-
OCH2Me). Anal. Calcd (%) for C12H15NO4 (237.26): C, 60.75; H,
6.37; N, 5.90. Found: C, 60.80; H, 6.35; N, 5.94.
Synthesis of {6-[1-(2,6-Diisopropylphenylimino)ethyl]pyridin-
2-yl}{6-[1-(2,6-diisopropylphenylimino)ethyl]pyridin-3-yl}-
methanone (VI). A solution of V (1.0 g, 3.7 mmol), 2,6-
bis(isopropylphenyl)amine (2.8 mL, 14.9 mmol, 4 equiv), and a
few drops of formic acid in MeOH (30 mL) were refluxed for 28
h. The reaction mixture was cooled to room temperature under
stirring overnight to give a solid, which was filtered and washed
several times with cold MeOH. Recrystallization from boiling
MeOH gave a yellow solid in 82% yield. IR (KBr): ν 1669 cm-1
1
(CdO), ν 1639 cm-1 (CdN). H NMR (CD2Cl2): δ 1.20-1.15
(m, 24H, CHMe2), 2.24 (s, 3H, C(N-Ar)Me), 2.26 (s, 3H, C(N-
Ar)Me), 2.79-2.74 (m, 4H, CHMe2), 7.14-7.12 (m, 2H, CH-Ar),
7.21-7.19 (m, 4H, CH-Ar), 8.14 (pseudo-t, J ) 7.84, 7.80 Hz,
1H, Py-Hp), 8.34 (dd, 1H, J ) 7.80, 1.09 Hz, Py-Hm), 8.51 (d, J )
8.32 Hz, 1H, Py-Hm), 8.67 (dd, 1H, J ) 8.32, 1.98 Hz, Py-Hp),
8.68 (dd, 1H, J ) 7.84, 1.09 Hz, Py-Hm), 9.51 (d, J ) 1.98 Hz,
1H, Py-Ho). 13C NMR (CD2Cl2): δ 17.03 (1C, Me), 17.15 (1C,
Me), 22.51 (2C, Me), 22.95 (2C, Me), 22.97 (1C, Me), 28.25 (2C,
CH), 28.30 (2C, CH), 120.33 (1C, CH), 122.98 (1C, CH), 122.99
(1C, CH), 123.75 (1C, CH), 123.76 (1C, CH), 124.43 (1C, CH),
125.59 (1C, CH), 132.73 (1C, C), 135.59 (1C, CH), 135.63 (1C,
CH), 135.64 (1C, CH), 137.89 (1C, CH), 138.63 (1C, CH), 146.20
(1C, C), 146.31 (1C, C), 151.20 (1C, CH), 152.91 (1C, C), 155.34
(1C, C), 158.67 (1C, C), 166.28 (1C, CdN), 166.88 (1C, CdN),
191.37 (1C, CdO). Anal. Calcd (%) for C39H46N4O (586.82): C,
79.82; H, 7.90; N, 9.55. Found: C, 79.79; H, 7.94; N, 9.50.
Synthesis of [6-(2-Methyl[1,3]dioxolan-2-yl)pyridin-2-yl][6-
(2-methyl[1,3]dioxolan-2-yl)pyridin-3-yl]methanone (IV).
A
solution of I (2 g, 8.0 mmol) in 60 mL of THF was cooled to
t
-78 °C and treated dropwise with a 1.7 M solution of BuLi in
n-pentane (5.22 mL, 8.9 mmol). After 30 min a solution of III
(2.1 g, 8.9 mmol) in 10 mL of THF was added slowly at -78 °C
by cannula. After 1 h stirring, the mixture was allowed to warm to
room temperature. After standing overnight, 25 mL of H2O was
added portionwise. The phases were separated, and the aqueous
layer was extracted with 2 × 30 mL of Et2O. The combined organic
layers were dried over Na2SO4. The solvent was removed under
reduced pressure, and the yellow oil obtained was purified by silica
gel chromatography (n-hexane/AcOEt, 65:35 and 3% NEt3) to
provide a pure pale yellow oil (yield 83%). Mp: 94-96 °C. IR
Synthesis of (1-{6-[Cyclohexylimino(6-(2,6-diisopropylphe-
nylimino)ethylpyridin-3-yl)methyl]pyridin-2-yl}ethylidene)(2,6-
diisopropylphenyl)amine (CyAr2N5). A mixture of VI (0.5 g, 0.86
mmol) and cyclohexylamine (86.4 mmol, 1 mL) was heated at
100 °C without stirring for 24 h. The excess of cyclohexylamine
was removed under reduced pressure. The solid formed was
dissolved in CH2Cl2, cooled to 0 °C and cold MeOH was added to
induce crystallization. After 5 h at -20 °C, pale yellow crystals
separated, which were filtered and washed with cold MeOH (yield
75%). IR (KBr): ν 1646 cm-1 (CdN). 1H NMR (CD2Cl2): δ 1.17-
1.11 (m, 24H, CHMe2), 1.39-1.26 (m, 3H, Cy), 1.76-1.65 (m,
5H, Cy), 1.86-1.81 (m, 2H, Cy), 1.88 (s, 3H, C(N)Me), 2.22 (s,
3H, C(N)Me), 2.80-2.66 (m, 4H, CHMe2), 3.50-3.55 (m, 1H, CH
Cy), 7.19-7.08 (m, 6H, CH Ar), 7.79 (d, J ) 8.00 Hz, 1H, Py-
Hm), 7.95 (t, J ) 7.80 Hz, 1H, Py-Hp), 8.37 (d, J ) 7.80 Hz, 1H,
Py-Hm), 8.39 (d, J ) 7.80 Hz, 1H, Py-Hm), 8.45 (d, J ) 8.00 Hz,
1H, Py-Hp), 8.60 (s, 1H, Py-Ho). 13C{1H} NMR (CD2Cl2): δ
166.87, 166.85, 162.43, 156.20, 155.57, 154.77, 153.56, 148.67,
147.58, 146.45, 146.41, 136.98, 136.83, 136.71, 135.74, 135.72,
135.66, 135.44, 133.44, 124.34, 123.65, 123.53, 123.44, 122.98,
122.95, 122.87, 122.50, 121.21, 120.83, 120.52, 120.03, 61.90,
33.93, 28.23, 25.65, 24.16, 23.04, 22.90, 22.55, 22.50, 22.46, 17.04,
17.00, 16.48. Anal. Calcd (%) for C45H57N5 (667.98): C, 80.91;
H, 8.60; N, 10.48. Found: C, 80.88; H, 8.57; N, 10.53.
1
(KBr): ν 1675 cm-1 (CdO). H NMR (CD2Cl2): δ 1.77 (s, 3H,
Me), 1.78 (s, 3H, Me), 3.94 (m, 4H, CH2), 4.12 (m, 4H, CH2),
7.72 (dd, J ) 8.21, 0.55 Hz, 1H, Py-Hm), 7.84 (dd, J ) 7.81, 1.11
Hz, 1H, Py-Hm), 7.98 (pseudo-t, J ) 7.81, 7.71 Hz, 1H, Py-Hp),
8.09 (dd, J ) 7.72, 1.12 Hz, 1H, Py-Hm), 8.53 (dd, J ) 8.28, 1.95
Hz, 1H, Py-Hp), 9.39 (dd, J ) 1.85, 0.59 Hz, 1H, Py-Ho). 13C{1H}
NMR (CD2Cl2): δ 34.93 (1C, Me), 35.11 (1C, Me), 75.44 (1C,
CH2), 75.52 (1C, CH2), 118.75 (1C, CH), 118.84 (1C, CH), 129.09
(1C, CH), 132.96 (1C, CH), 133.86 (1C, CH), 141.53 (1C, C),
148.23 (1C, CH), 149.36 (1C, CH), 162.35 (1C, CH), 163.93 (1C,
C), 170.68 (1C, C), 174.73 (1C, C), 201.67 (1C, CdO). Anal. Calcd
(%) for C19H20N2O5 (356.38): C, 64.04; H, 5.66; N, 7.86. Found:
C, 63.59; H, 5.74; N, 7.80.
Synthesis of 1-[5-(6-Acetylpyridine-2-carbonyl)pyridin-2-yl]-
ethanone (V). A sample of IV (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 ice water (15

5070 Organometallics, Vol. 26, No. 20, 2007
Bianchini et al.
Synthesis of Methyl 4-(1-Phenylprop-1-en-2-yl)benzoate (X).15
A suspension of benzyltriphenylphosphonium chloride (2.43 g, 5.61
mmol) in THF (30 mL) at -5 °C was treated under stirring with
nBuLi (1.6 M in hexane, 3.7 mL, 5.92 mmol). When the ylide was
formed, an intense red color appeared. The ylide was transferred
via cannula under N2 atmosphere to a separate vessel containing a
cooled solution (0 °C) of methyl-4-acetylbenzoate (1 g, 5.61 mmol)
in 20 mL of dry and degassed THF. After 30 min stirring, the
mixture was warmed to 50 °C and stirred overnight. Afterward, it
was cooled to room temperature and treated with water (40 mL).
The resulting phases were separated, and the acqueous layer was
extracted with Et2O (3 × 30 mL). The collected organic phases
were dried over Na2SO4, and after removal of solvent, a yellow
crude solid was obtained. The crude material was purified by flash
chromatography (silica, hexane/EtOAc (95:5)) to afford a white
solid as a mixture of two inseparable diastereoisomers in 45(E):
55(Z) ratio (yield 55%). IR (KBr): ν 1718 cm-1 (CdO); 1601 cm-1
Me), 2.38 (d, 3 H(Z), J ) 1.0 Hz, Me), 2.67 (s, 3 H(E), Me), 2.74
(s, 3 H(Z), Me), 6.65 (bs, 1 H(E), CH), 7.03 (2 H, Ar), 7.07 (bs, 1
H(Z), CH), 7.14 (3 H, Ar), 7.38 (2 H, Ar), 7.44 (5 H, Ar), 7.74 (3
H, Ar), 8.11 (4 H, Ar), 8.26 (5 H, Ar). 13C{1H} NMR (CDCl3):
(selected data) δ 17.05, 25.54, 25.59. 26.23, 123.62, 125.57, 126.43,
126.91, 127.60, 127.87, 127.93, 128.09, 128.25, 129.01, 129.21,
129.68, 131.28, 131.34, 138.26, 134.47, 134.51, 136.44, 137.32,
137.81, 137.85, 147.25, 148.48, 152.06, 152.11, 154.19, 154.35,
191.76 (1 C, CdO), 192.04 (1 C, CdO), 199.19 (1 C, CdO),
199.23 (1 C, CdO). Anal. Calcd (%) for C23H19NO2 (341.4): C,
80.92; H, 5.61; N, 4.10. Found: C, 80.93; H, 5.60; N, 4.12.
Synthesis of (6-(1-(2,6-Diisopropylphenylimino)ethyl)pyridin-
2-yl)(4-((Z)-1-phenylprop-1-en-2-yl)phenyl)methanone (XIII). A
solution of XII (0.2 g, 0.6 mmol) and 2,6-diisopropylaniline (0.22
mL, 1.2 mmol) in dry nBuOH (1.5 mL) was treated with a catalytic
amount of formic acid and warmed to 65 °C overnight. The excess
of solvent and aniline were removed under reduced pressure, gently
warming the mixture. The remaining oil was dissolved in hot MeOH
and precipitated with n-pentane. The precipitate was filtered and
recrystallized from MeOH to afford yellow pale microcrystals of
the Z-isomer (yield 34%). IR (CH2Cl2): ν 1659 cm-1 (CdO); 1647
cm-1 (CdN); 1601 cm-1 (CdC). 1H NMR (CD2Cl2): δ 1.17 (d, 6
H, J ) 6.9 Hz, CHMe2), 1.19 (d, 6 H, J ) 6.9 Hz, CHMe2), 2.22
(s, 3 H, Me), 2.36 (d, 3 H, J ) 1.3 Hz, Me), 2.78 (sept, 2 H, J )
6.9 Hz, CHMe2), 7.04 (d, 1 H, J ) 1.3 Hz, CH), 7.12 (1 H, Ar),
7.20 (2 H, Ar), 7.43 (5 H, Ar), 7.71 (2 H, Ar), 8.09 (t, 1 H, J ) 7.8
Hz, Py-Hp), 8.20 (dd, 1 H, J ) 7.8, 1.1 Hz, Py-Hm), 8.28 (2 H,
Ar), 8.61 (dd, 1 H, J ) 7.8, 1.1 Hz, Py-Hm). 13C{1H} NMR
(CDCl3): (selected data) δ 16.96 (1 C, Me); 17.01 (1 C, Me), 22.51
(1 C, Me), 22.96 (1 C, Me), 28.27 (1 C, Me), 122.97 (CH Ar),
123.57 (CH Ar), 123.67 (CH Ar), 125.47 (CH Ar), 125.53 (CH
Ar), 126.84 (CH Ar), 127.98 (CH Ar), 128.20 (CH Ar), 128.95
(CH Ar), 129.16 (CH Ar), 129.53 (CH Ar), 131.33 (CH Ar), 134.88
(C), 135.68 (CH Ar), 136.50 (C), 137.56 (CH Ar), 137.88 (C),
146.31 (C), 148.28 (C), 154.09 (C), 155.07 (C), 166. 60 (CN),
192.19 (CO). Anal. Calcd (%) for C35H36N2O (500.67): C, 83.96;
H, 7.25; N, 5.60. Found: C, 83.94; H, 7.23; N, 5.63.
1
(CdC). H NMR (CD2Cl2): δ 2.24 (d, 3 H(E), J ) 1.5 Hz, Me),
2.33 (d, 3 H(Z), J ) 1.3 Hz, Me), 3.91 (s, 3 H(E), Me), 3.93 (s, 3
H(Z), Me), 6.59 (d, 1 H(E), J ) 1.5 Hz, CH), 6.98 (d, 1 H(Z), J )
1.3 Hz, CH), 6.95 (2 H, Ar), 7.12 (2 H, Ar), 7.29 (2 H, Ar), 7.42
(5 H, Ar), 7.64 (3 H, Ar), 7.95 (2 H, Ar), 8.04 (2 H, Ar). 13C{1H}
NMR (CD2Cl2): (selected data) δ 166.71, 148.37, 147.16, 137.87,
137.24, 136.46, 129.59, 129.50, 129.34, 129.17, 128.94, 128.80,
128.72, 128.37, 128.21, 127.90, 127.57, 126.83, 126.36, 125.88,
51.92, 26.37, 17.07. Anal. Calcd (%) for C17H16O2 (252.31): C,
80.93; H, 6.39. Found: C, 81.03; H, 6.41.
Synthesis of (6-(2-Methyl-1,3-dioxolan-2-yl)pyridin-2-yl)(4-
(1-phenylprop-1-en-2-yl)phenyl)methanone (XI). A solution of
6-bromo-2-(2′-methyl-1′,3′-dioxolan-2′-yl)pyridine (0.87 g, 3.6
mmol) in 25 mL of THF at -78 °C was treated dropwise with
t
2.34 mL of a 1.7 M solution of BuLi in n-pentane. After 30 min
stirring, the mixture was warmed to -55 °C and a solution of X (1
g, 4 mmol) in 15 mL of THF was added via cannula portionwise.
After 30 min stirring, the resulting solution was allowed to warm
to room temperature and then stirred for a further 2 h. Water (50
mL) was added, the phases were separated, and the acqueous layer
was extracted with Et2O (3 × 50 mL). The collected organic phases
were dried over Na2SO4, and after removal of solvent a yellow
crude oil was obtained. The product was purified by flash
chromatography (silica, hexane/EtOAc (4:1, v/v) + 3% (v/v) NEt3)
to afford a mixture of inseparable diastereoisomers (45(E):55(Z)
ratio) as a yellow oil (yield 51%). IR (CH2Cl2): ν 1661 cm-1 (Cd
O); 1601 cm-1 (CdC). 1H NMR (CD2Cl2): δ 1.74 (s, 3 H(E), Me),
1.79 (s, 3 H(Z), Me), 2.29 (s, 3 H(E), Me), 2.37 (s, 3 H(Z), Me),
4.02 (m, 8 H, CH2), 6.63 (s, 1 H(E), CH), 7.03 (2 H, Ar), 7.04 (bs,
1 H(Z), CH), 7.14 (3 H, Ar), 7.34 (2 H, Ar), 7.44 (5 H, Ar), 7.70
(2 H, Ar), 7.78 (2 H, Ar), 7.96 (4 H, Ar), 8.06 (2 H, Ar), 8.18 (2H,
Ar). 13C{1H} NMR (CD2Cl2): (selected data) δ 24.54 (1 C, C(C)-
Me), 26.35 (1 C, Me), 65.14 (4 C, CH2), 108.43, 121.92, 123.51,
123.54, 126.38, 127.95, 128.21, 129.00, 131.33, 134.76, 137.04,
137.64, 137.90, 147.05, 154.65, 159.94, 192.66 (1 C, CdO). Anal.
Calcd (%) for C25H23NO3 (385.46): C, 77.90; H, 6.01; N, 3.63.
Found: C, 77.92; H, 5.98, N, 3.50.
Synthesis of (E)-N-(1-(6-((E)-(cyclohexylimino)(4-((E)-1-phe-
nylprop-1-en-2-yl)phenyl)methyl)pyridin-2-yl)ethylidene)-2,6-di-
isopropylbenzenamine (CyArN3H). A mixture of XIII (0.12 g, 0.24
mmol) and cyclohexylamine (0.28 mL, 2.41 mmol) was heated at
100 °C for 40 h without stirring. The excess of cyclohexylamine
was removed under reduced pressure, and the remaining oil was
crystallized from n-pentane/MeOH (40:60, v/v) to afford the ligand
as pale yellow crystals (yield 30%). IR (CH2Cl2): ν 1647 cm-1
1
(CdN); 1601 cm-1 (CdC). H NMR (CD2Cl2): δ 1.11 (d, 12 H,
J ) 6.6 Hz, CHMe2), 1.29 (m, 3 H, Cy), 1.66 (m, 5 H, Cy), 1.80
(m, 2 H, Cy), 2.15 (s, 3 H, CH(C)Me), 2.33 (s, 3 H, C(N)Me),
2.70 (sept, 2 H, J ) 6.6 Hz, CHMe2), 3.51 (m, 1 H, Cy), 6.97
(s, 1 H, CH(C)Me), 7.07 (1 H, Ar), 7.14 (2 H, Ar), 7.30 (2 H,
Ar), 7,41 (5 H, Ar), 7.64 (2 H, Ar), 7.90 (t, 1 H, J ) 7.8 Hz, Py-
Hp), 8.29 (d, 1 H, J ) 7.8 Hz, Py-Hm), 8.35 (d, 1 H, J ) 7.8 Hz,
Py-Hm). 13C{1H} NMR (CD2Cl2): (selected data) δ 16.48, 17.07,
22.56, 22.90, 23.06, 24.31, 25.74, 28.19, 33.97, 61.66, 120.03,
120.55, 122.98, 123.35, 123.61, 125.34, 126.82, 128.14, 128.32,
129.13, 135.66, 135.79, 136.68. Anal. Calcd (%) for C41H47N3
(581.83): C, 84.64; H, 8.14; N, 7.22. Found: C, 84.62; H, 8.15;
N, 7.23.
Synthesis of CyAr2N5FeCl2. A suspension of FeCl2 (0.21 mmol)
in THF (3 mL) was transferred by a cannula into a stirred solution
of CyAr2N5 (0.23 mmol) in THF (5 mL) at room temperature. A
blue solution formed immediately. After stirring the solution
overnight, the solvent was partially evaporated, leading to the
precipitation of the product as a blue solid, which was filtered on
a sintered-glass frit, washed with n-pentane, and dried under a
stream of nitrogen (yield 82%). IR (KBr): ν 1640 cm-1 (CdN), ν
1617 cm-1 (CdN). µeff: 5.10 µB (22 °C). Electronic spectra:
Synthesis of 1-(6-(4-(1-Phenylprop-1-en-2-yl)benzoyl)pyridin-
2-yl)ethanone (XII). A solution of XI (0.4 g, 1 mmol) in acetone/
water (15:1, v/v; 16 mL) was treated with PTSA (0.04 g, 0.21
mmol) and refluxed for 40 h. The solution was cooled to room
temperature and neutralized with a saturated solution of K2CO3.
Then 10 mL of water was added and the phases were sepparated.
The aqueous phase was extracted with Et2O (2 × 15 mL), and the
collected organic layers were dried over Na2SO4. After solvent
removal the resulting yellow, crude oil was isolated and purified
over a silica gel pad (hexane/EtOAc, 85:15) to give a mixture of
inseparable diastereoisomers (45(E):55(Z) ratio) as a pale yellow
oil (yield 95%). IR (CH2Cl2): ν 1701, 1661 cm-1 (CdO); 1601
1
cm-1 (CdC). H NMR (CD2Cl2): δ 2.30 (d, 3 H(E), J ) 1.3 Hz,

Synthesis of a New Polydentate Ligand
Organometallics, Vol. 26, No. 20, 2007 5071
Table 1. Crystallographic Data
VI‚0.8CH2Cl2
CyAr2N5
empirical formula
fw
C
39.80H47.60Cl1.60N4O
C45H57N5
667.96
654.74
temperature [K]
wavelength [Å]
cryst syst, space group
a [Å]
b [Å]
c [Å]
180(2)
0.71073
triclinic, P1h
11.613(5)
12.353(5)
14.453(5)
180(2)
0.71073
monoclinic, C2/c
31.166(5)
11.873(5)
25.816(5)
R [deg]
74.867(5)
77.213(5)
71.924(5)
1880.3(13)
2, 1.156
â [deg]
120.733(5)
γ [deg]
V [Å3]
8211(4)
8, 1.081
0.063
2896
Z, Dc [g m-3
]
absorp coeff [mm-1
F(000)
]
0.179
699
cryst size [mm]
θ range for data collection [deg]
limiting indices
0.30 × 0.20 × 0.20
4.22-36.25
-14 e h e 16
-20 e k e 15
-23 e l e 17
15524/6675
1.066
0.30 × 0.20 × 0.20
4.36-32.12
-45 e h e 33
0 e k e 17
0 e l e 37
8429/8429
1.211
no. of reflns collected/unique
GOF on F2
no. of data/restraints/params
final R indices [I > 2σ(I)]
R indices (all data)
6675/0/434
R1 ) 0.0717, wR2 ) 0.1847
R1 ) 0.1007, wR2 ) 0.2022
0.443 and -0.323
8429/0/461
R1 ) 0.0948, wR2 ) 0.2475
R1 ) 0.1813, wR2 ) 0.3015
0.487 and -0.298
largest diff peak and hole [e Å-3
]
(reflectance) 13 900, 4900sh cm-1; (absorption) 14 100 (ꢀ 700),
4850 (ꢀ 36) cm-1. Anal. Calcd (%) for C45H57Cl2FeN5 (794.73):
C, 68.01; H, 7.23; Fe, 7.03; N, 8.81. Found: C, 68.04; H, 7.20;
Fe, 7.05; N, 8.78.
15 350, 10 400, 8100, 5800 cm-1; (absorption) 16 500sh, 14 900
(ꢀ 129), 10 600 (ꢀ 74), 7800 (ꢀ 100), 5600 (ꢀ 90) cm-1. Anal. Calcd
(%) for C41H47Cl2CoN3 (711.68): C, 69.20; H, 6.66; Co, 8.28; N,
5.90. Found: C, 68.78; H, 6.59; Co, 8.18; N, 5.84.
Synthesis of CyAr2N5Fe2Cl4. Employing a procedure analogous
to that described above, except using FeCl2 (0.46 mmol), gave the
product as a blue solid in 80% yield. IR (KBr): ν 1617 cm-1 (Cd
N). µeff: 6.82 µB (22 °C). Electronic spectra: (reflectance) 13 900,
11 900sh, 5000sh cm-1. Anal. Calcd (%) for C45H57Cl4Fe2N5
(921.49): C, 58.65; H, 6.23; Fe, 12.12; N, 7.60. Found: C, 58.68;
H, 6.20; Cl, 15.42; Fe, 12.10; N, 7.63.
Synthesis of CyAr2N5CoCl2. Addition of a suspension of CoCl2
(0.21 mmol) in THF (3 mL) to a stirred solution of the ligand
CyAr2N5 (0.23 mmol) in a 5:1 mixture of Et2O/THF (15 mL) at room
temperature gave immediately a dark brown solution. After 30 min,
the precipitation of a small crop of product as a green solid occurred.
The mixture was allowed to stand overnight and then was
concentrated to small volume under vacuum. The product was
filtered on a sintered-glass frit, washed with Et2O, and dried under
a stream of nitrogen (yield 84%). IR (KBr): ν 1637 cm-1 (CdN),
ν 1616 cm-1 (CdN). µeff: 4.75 µB (22 °C). Electronic spectra:
(reflectance) 16 600sh, 15 150, 10 300, 7700, 5050sh cm-1; (ab-
sorption) 16400sh, 14 800 (ꢀ 109), 10 950 (ꢀ 10), 7750 (ꢀ 15),
5050sh cm-1. Anal. Calcd (%) for C45H57Cl2CoN5 (797.82): C,
67.75; H, 7.20; Co, 7.39; N, 8.78. Found: C, 67.78; H, 7.19; Co,
7.41; N, 8.81.
General Procedure for Ethylene Oligomerization. A 500 mL
stainless steel reactor was heated at 60 °C under vacuum overnight
and then cooled to room temperature under a nitrogen atmosphere.
The solid precatalyst (12 µmol) was charged into the reactor, which
was sealed and placed under vacuum. An appropriate solution of
MAO (1440 equiv/M), prepared by adding a stock toluene solution
of solid MAO in toluene (100 mg mL-1) into toluene, was
introduced into the reactor by suction. The reaction mixture was
stirred at room temperature for about 1 min. The reactor was then
pressurized with ethylene to 4 bar and stirred at 1500 rpm. Ethylene
was continuously fed to maintain the reactor pressure at the desired
value. The temperature inside the reactor increased due to the
exothermicity of the reaction and reached a maximum value within
5-7 min. After 15 min, the reaction was stopped by cooling the
reactor to -20 °C, depressurizing, and introducing 2 mL of acidic
MeOH (5% HCl). Depending on the oligomerization products, two
different procedures were followed. For reactions yielding mixtures
of R-olefins, n-heptane was injected into the reactor as the GC
internal standard and the reactor contents were stirred for 10 min.
The solution was analyzed by GC and GC/MS. The moles of the
C6 and C8 fractions were determined by GC using calibration
curves with standard toluene solutions containing concentrations
of 1-hexene and 1-octene as close as possible to those in the sample
under analysis. Schulz-Flory R constants were determined by the
molar ratio of the couple C8/C6. The moles of C4 were calculated
by the Schulz-Flory R constant and the moles of C6 by the formula
moles(C4) ) moles(C6)/R, whereas the moles of the oligomers in
the C10-C34 range were calculated by the Schulz-Flory R
constant and the moles of C8 by the formula moles(Ci) ) moles-
(C8) × Ri-8/2. The total moles of converted ethylene was obtained
by the formula moles(C2H4) ) ∑moles(Ci) × i/2 with i ) 4-34;
therefore, the TOFs were obtained. For reactions yielding exclu-
sively butenes, the reactor contents, after cooling to -50 °C, were
transferred into a flask immersed in a bath at -50 °C. Oligomers
were distilled over a Vigreux column (70 °C), condensed into a
cooling trap (-196 °C) containing isobutane as the GC internal
standard, and analyzed by GC.4
Synthesis of CyAr2N5Co2Cl4. Employing an analogous procedure
to that described above except using CoCl2 (0.46 mmol) gave the
product as a brown solid in 88% yield. IR (KBr): ν 1617 cm-1
(CdN). µeff: 6.33 µB (22 °C). Electronic spectra: (reflectance)
18 000sh, 16 600sh, 15 150, 10 900, 8500sh, 7200, 5050sh cm-1
.
Anal. Calcd (%) for C45H57Cl4Co2N5 (927.66): C, 58.26; H, 6.19;
Co, 12.71; N, 7.55. Found: C, 58.29; H, 6.21; Co, 12.74; N, 7.59.
Synthesis of CyArN3HCoCl2. The solid ligand CyArN3 (0.07
H
mmol) was added in one portion to a solution of CoCl2 (0.07 mmol)
in THF (3 mL) at room temperature. The resulting green solution
was stirred at room temperature for 2 h. Bubbling n-pentane vapors
overnight led to the precipitation of green microcrystals, which were
filtered on a sintered-glass frit, washed with Et2O, and dried under
a stream of nitrogen (yield 84%). IR (KBr): ν 1595 cm-1 (CdN).
µeff: 4.80 µB (22 °C). Electronic spectra: (reflectance) 16 800sh,

5072 Organometallics, Vol. 26, No. 20, 2007
Bianchini et al.
Scheme 4
Scheme 5
X-ray Diffraction Data. Crystallographic data of VI·0.8CH2Cl2
and CyAr2N5 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. Details of data collection, refinement, and crystal data
are listed in Table 1. Cell refinement, data reduction, and empirical
absorption corrections were carried out with the Oxford diffraction
software and SADABS.16 All structure determination calculations
were performed with the WINGX package17 using SIR-97,18
SHELXL-97,19 and ORTEP-3 programs.20 Final refinements based
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
Synthesis and Characterization of the CyAr2N5 Ligand.
Scheme 4 illustrates the stepwise procedure developed to prepare
the desired CyAr2N5 ligand in good yield. Since this synthesis
work has not been technically trivial and may be useful to design
other molecular architectures containing pyridine and imine
groups, a description of the most relevant reaction steps is given
in the following.
tion of the acetyl group of 2-acetyl-6-bromopyridine as ethyl-
enedioxy ketal was achieved in benzene by reaction with ethane-
1,2-diol in the presence of a catalytic amount of PTSA using a
Dean-Stark apparatus.15,22
Two different strategies, summarized in Scheme 5, have been
developed to prepare the ethylenedioxy ketal of 2-acetyl-5-
bromo pyridine II.
The regioselective cyanation of 2,5-dibromopyridine, followed
by reductive alkylation with MeMgBr (path A),23 gave only
modest yields of the desired 2-ketone-5-bromopyridine, due to
the low selectivity of the reductive alkylation step. A much
The ethylenedioxy ketal building block I was straightfor-
wardly synthesized by lithiation of 2,6-dibromopyridine with a
t
slight excess of BuLi in ether at -78 °C, followed by mono-
acetylation with N,N-dimethylacetamide (DMAc).21 The protec-
(16) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Corrections; University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(17) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(18) 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.
(19) Sheldrick, G. M. SHELX-97; University of Go¨ttingen, 1997.
(20) Burnett, M. N.; Johnson, C. K. ORTEP-3, Report ORNL-6895; Oak
Ridge National Laboratory: Oak Ridge, TN, 1996.
(21) (a) Parks, J. E.; Wagner, B. E.; Holm, R. H. J. Organomet. Chem.
1973, 56, 53. (b) Bolm, C.; Ewald, M.; Felder, M.; Schlingloff, G. Chem.
Ber. 1992, 125, 1169. (c) Peterson, M. A.; Mitchell, J. R. J. Org. Chem.
1997, 62, 8237.
(22) Kocien´ski, P. J. Protecting Groups, 3rd ed.; George Thieme
Verlag: New York, 2004; p 49.

Synthesis of a New Polydentate Ligand
Organometallics, Vol. 26, No. 20, 2007 5073
Table 2. Selected Bond Lengths (Å) and Angles (deg) for the
Two Ligands
higher yield was obtained by transformation of 2,5-dibromopy-
ridine into the 5-bromo-2-trimethylsilyl acetylene derivative via
a regioselective Sonogashira protocol,24,25 followed by a mer-
cury(II)-catalyzed hydrolysis.25,26 2-Ketone-5-bromopyridine
was finally protected in the O,O-ketal form via the acid-
catalyzed dioxolanation method15,22 to give II in 98% yield
(overall yield 71%).
VI‚0.8CH2Cl2
CyAr2N5
C(13)-N(1)
1.280(3)
1.262(4)
1.269(4)
C(20)-N(3)
C(26)-N(4)
C(32)-N(5)
C(1)-N(1)-C(13)
C(20)-N(3)-C(21)
C(32)-N(5)-C(34)
C(28)-N(4)-C(26)
1.281(3)
121.7(2)
1.273(4)
123.6(3)
120.2(3)
121.1(3)
After several attempts to couple the two pyridine rings of I
and II via formyl derivatives (Vide infra), the target bis-
(pyridine)ketone IV was best obtained by coupling the lithium
salt of I with the ethyl ester building block III, in turn prepared
by methoxycarbonylation of II.27 Acid hydrolysis of IV gave
the tris(ketone) bis(pyridine) intermediate V in almost quantita-
tive yield, which was transformed into the bis(iminodipyridine)-
ketone VI by formic acid-catalyzed condensation with 2,6-
diisopropylaniline in refluxing MeOH. Notably, the central
ketone group of V remained intact even by treatment with a
large excess of 2,6-diisopropylaniline, irrespective of the solvent
and the reaction temperature.3 Likewise, aniline and other
anilines such as 2,6-dimethylaniline did not react with VI
even when used as solvents at reflux temperature. In contrast,
a selective reaction occurred with neat cyclohexylamine at
100 °C to give the desired CyAr2N5 ligand in 75% yield.
Apparently, the attack by primary amines at the central CdO
group of VI is primarily governed by electronic factors rather
than by steric factors, which is consistent with the nonsterically
congested structure of VI in the solid state, provided this is
maintained in solution.
120.4(2)
with the nearest pyridine unit of 72.37(0.35)° and 75.45(0.27)°,
respectively. The three CdN bond lengths are comparable to
each other and are in the typical range for imine groups.28
Prior to the synthetic procedure reported in Scheme 4, the
ketal-protected tris(ketone) IV was prepared by an alternative
method involving the reaction of the formyl derivative VII with
the lithium salt derived from II (Scheme 6). This protocol was
soon abandoned due to its low yield. Nevertheless, it is worth
commenting upon, as it opens the door to a different building
block, namely, the dipyridine methane derivative IX, which may
be useful to synthesize poly(imino)pyridine structures.
Indeed, the direct coupling of the lithiated form of II with
the formyl VII produced a chromatographically separable
mixture of IX and of the ketal-protected tris(ketone) IV, due to
disproportionation of the benzydryl intermediate VIII.29
Synthesis and Characterization of the Mono- and Di-
nuclear Complexes with CyAr2N5. The mono- and dinuclear
complexes with the ligand CyAr2N5 were prepared in good yields
by the reaction of the ligand with 1 or 2 equiv of the appropriate
anhydrous FeII or CoII dihalide in THF at room temperature
(Scheme 7).
All the mononuclear complexes are sparingly soluble in
aromatic hydrocarbons, while they dissolve fairly well in organic
solvents such as THF, CH2Cl2, and 1,2-dichloroethane. In the
last solvent they behave as nonelectrolytes. All compounds are
fairly air-stable in the solid state, whereas they decompose in
solution unless protected by a nitrogen or argon atmosphere.
Magnetic data at room temperature and relevant IR and vis-
NIR absorptions (range 25 000-4550 cm-1) for each complex
are reported in the Experimental Section.
The IR spectra of the mononuclear compounds are identical
both in the solid state and in solution and show two ν(CdN)
bands, one for the coordinated CdN groups at ca. 1617 cm-1
and another for the uncoordinated CdN group at ca. 1640 cm-1
(ν(CdN) in the free ligand falls at 1646 cm-1), which indicates
that not all of the imine nitrogen atoms of the ligand are engaged
in bonding a metal center.5a,9b,30
The mononuclear complexes exhibit high-spin electronic
configurations with µeff values of 5.10 and 4.75 µB at room
temperature for CyAr2N5FeCl2 and CyAr2N5CoCl2, respectively.
These data are comparable to those reported for other iron(II)
and cobalt(II) complexes with quintuplet and quartet ground
states, respectively.10
Yellow needles of VI·0.8CH2Cl2, suited for a single-crystal
X-ray analysis, were obtained from a CH2Cl2 solution of the
bis(iminopyridine)ketone VI on standing at -5 °C for 3 days.
An ORTEP drawing of the molecule is shown in Figure 1, while
crystallographic data and selected bond distances and angles
are given in Tables 1 and 2, respectively.
The two pyridine units attached to the central carbonyl carbon
atom C(20) are not coplanar, as put in evidence by torsion angles
with the CdO unit of 29.47(0.52)° (pyridine ring with N(2))
and of 34.88(0.39)° (pyridine ring with N(3)), respectively. The
hydrogen atom H(17) shows an intramolecular distance of 2.676
i
Å to the pyridine nitrogen atom N(3). Both Pr rings bearing
the ipso carbon atoms C(1) and C(28) exhibit a torsion angle
with the nearest pyridine unit of 61.44(0.24)° and 89.92(0.24)°,
respectively.
Well-shaped pale yellow crystals of the ligand CyAr2N5 were
obtained by recrystallization of the crude product from a CH2-
Cl2/MeOH mixture at 0 °C. An ORTEP drawing of the molecule
of CyAr2N5 in the asymmetric unit is shown in Figure 2, while
crystallographic data and selected bond distances and angles
are given in Tables 1 and 2, respectively.
The two pyridine units attached through the C(18) and C(27)
carbon atoms to the central imine fragment (C(20)-N(3)) are
not coplanar, the latter group showing a torsion angle of 80.66-
i
(0.41)° and of 10.21(0.37)°, respectively. Both Pr rings with
the ipso carbon atoms C(1) and C(34) exhibit torsion angles
(23) Jo, Y. W.; Im, W. B.; Rhee, J. K.; Shim, M. J.; Kim, W. B.; Choi,
E. C. Bioorg. Med. Chem. 2004, 12, 5909.
(28) (a) Pelascini, F.; Wesolek, M.; Peruch, F.; Lutz, P. J. Eur. J. Inorg.
Chem. 2006, 4309. (b) Bart, S. C.; Chlopek, K.; Bill, E.; Bouwkamp, M.
W.; Lobkovsky, E.; Neese, F.; Wieghardt, K.; Chirik, P. J. J. Am. Chem.
Soc. 2006, 128, 13901.
(29) (a) Bisaro, F.; Prestat, G.; Vitale, M.; Poli, G. Synlett 2002, 11,
1823. (b) Gautert, P.; El-Ghammarti, S.; Legrand, A.; Couturier, D.; Rigo,
B. Synth. Commun. 1996, 26, 707. (c) Balfe, M. P.; Kenyon, J.; Thain, E.
M. J. Chem. Soc. 1952, 790. (d) Burton, H.; Cheesman, G. W. H. J. Chem.
Soc. 1953, 986. (e) Bartlett, P.; McCollum, J. D. J. Am. Chem. Soc. 1956,
78, 1441.
(24) Tilley, J. W.; Zawoiski, S. J. Org. Chem. 1988, 53, 386.
(25) Matulenko, M. A.; Lee, C. H.; Jiang, M.; Frey, R. R.; Cowart, M.
D.; Bayburt, E. K.; Di Domenico, S., Jr.; Gfesser, G. A.; Gomtsyan, A.;
Zheng, G. Z.; Mc Kie, J. A.; Stewart, A. O.; Yu, H.; Kohlhaas, K. L.;
Alexander, K. M.; McGaraughty, S.; Wismer, C. T.; Mikusa, J.; Marsh, K.
C.; Snyder, R. D.; Diehl, M. S.; Kowaluk, E. A.; Jarvisa, M. F.; Bhagwata,
S. S. Bioorg. Med. Chem. 2005, 13, 3705.
(26) Reed, M. W.; Moore, H. W. J. Org. Chem. 1988, 53, 4166.
(27) Mameri, S.; Charbonniere, L. J.; Ziessel, R. F. Synthesis 2003, 17,
2713.
(30) Britovsek, G. J. P.; Gibson, V. C.; Spitzmesser, S. K., Tellmann,
K. P.; White, A. J. P.; Williams, D. J. Dalton Trans. 2002, 1159.

5074 Organometallics, Vol. 26, No. 20, 2007
Bianchini et al.
Figure 1. ORTEP drawing of VI·0.8CH2Cl2. Hydrogen atoms and solvent molecules are omitted for clarity. Thermal ellipsoids are shown
at the 30% probability level.
Scheme 6
Figure 2. ORTEP drawing of CyAr2N5. Hydrogen atoms are omitted
for clarity. Thermal ellipsoids are shown at the 30% probability
components with an energy difference of ca. 3000 cm-1 is
level.
indicative of a high distortion in these complexes. The other
two bands are due to transitions from the fundamental state 4A2′-
The electronic spectra of the mononuclear complexes show
bands that are typical of the N3MCl2 chromophores (M ) Fe,
Co) in five-coordinate structures with an intermediate geometry
(F) to the states originating from splitting of the 4P term (4A2′-
(P) and 4E′′(P)). The absorption spectrum of CyAr2N5FeCl2
between a square pyramid and a trigonal bipyramid.3a,30-32The
reflectance spectra of the solids closely resemble those of the
complexes in solution. Accordingly, no significant change in
the stereochemistry of the complexes should occur on going
from solid state to solution. The absorption spectrum of
CyAr2N5CoCl2 consists of five bands at 5050sh, 7750 (ꢀ 15),
10 950 (ꢀ 10), 14 800 (ꢀ 109), and 16 400sh cm-1. The first
three bands are assignable to transitions between states origi-
displays, in the visible region, a broad and strong absorption (ꢀ
700) at 14 100 cm-1, which is probably due to a ligand to metal
charge transfer.10-30 However, in the NIR region, the spectrum
seems to contain also a low-intensity band (ꢀ 36) at 4850 cm-1
.
Generally, high-spin five-coordinate FeII complexes with an N3-
Cl2 donor atom set show two low-intensity absorption bands,
one, in the 10 000-7000 cm-1 region, attributed to the spin-
5
allowed d-d transition from the quintet ground state E′′ to
the excited state 5A1′, and another below ca. 5000 cm-1 for the
4
nating from splitting of the F term of the d7 configuration in
5
5E′′ f E′ transition.3a,10,30-32 It is very likely that the latter
the field of D3h symmetry. The first band is assignable to a
4A2′(F) f 4E′′(F) transition and the other two to the two
components of the 4A2′(F) f 4E′(F) transition in a field of lower
symmetry. The fact that the latter transition is split into two
transition is responsible for the band observed at 4850 cm-1
,
whereas the transition 5E′′ f 5A1′ could be masked by the broad
absorption centered at 14 100 cm-1, which covers spectral
frequencies up to 8500 cm-1
.
(31) (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.
(32) (a) Morassi, R.; Bertini, I.; Sacconi, L. Coord. Chem. ReV. 1973,
11, 343. (b) Ciampolini, M.; Gelsomini, J. Inorg. Chem. 1967, 6, 1821.
Useful information for assigning the solution structure of the
mononuclear complexes was obtained by 1H NMR spectroscopy.
1
The H NMR spectra have been acquired in CD2Cl2 solutions
at 22 °C, and the data obtained are collected in Table 3. All

Synthesis of a New Polydentate Ligand
Organometallics, Vol. 26, No. 20, 2007 5075
Scheme 7
Table 3. 1H NMR Assignments for Iron(II) and Cobalt(II) Complexes with CyArN3 and CyAr2N5 (CD2Cl2, 22 °C, 400.13 MHz)
CyAr2N5CoCl2
CyAr2N3CoCl2
CyAr2N5FeCl2
CyArN3FeCl2
position
Py-Hm
δ
int
δ
int
δ
int
δ
int
Coordinated Portion
1,1
109.35
107.58
34.54
1,1
108.18, 103.73
80.92 70.20
1,1
89.11 68.55
1,1
Py-Hp
1
25.92
1
52.44
1
35.97
1
NdCMe
-5.84
-11.12
-14.81
-19.72
-20.20
-71.41
-74.61
2.12
-10.83
174.81
15.53
-84.79
-85.61
3
3,3
-4.63, -15.41
3,3
6,6
-25.41
3
6,6
-12.79 -33.57
3,3
6,6
iPr-Me
-12.14, -17.81
1.24 -5.23
3.08 -5.38
3,3
1,1
iPr-CH
-73.80
2
-26.06
2
-14.94
2
Ar-Hm
Ar-Hp
Cy
Cy
Cy
Cy
Cy
Cy
Cy
2
1
1
1
1
1
1.15
2
1
1
1
2
1
2
2
2
2.85
-1.10
2
1
20.69
-1.70
1.28
-2.99
-4.72
-6.74
-7.85
-29.10
-37.18
2
1
1
2
1
1
2
2
2
-12.69
143.42
17.63
4.10
0.25
-3.72
-14.75
-71.05
Uncoordinated Portion
NdCMe
0.45
2.12
3
6,6
-3.41
2.41 1.24
3
6,6
iPr-Me
-1.25
Unassigned Peaks
6.79
1
1
1
2
2
1
2
1
1
3
19.44
18.71
12.28
2.41
1.95
4.33
19.77
15.45
-1.10
-2.71
-2.91
-6.95
-7.68
-14.10
-18.12
-29.30
1
1
1
2
2
1
1
1
2
1
1
1
1
1
1
1
-7.74
-12.74
3.84
7.32
6.22
4.52
-0.58
-6.61
-16.77
1
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. All resonances appear as broad singlets,
and their assignment has been carried out on the basis of their
relative intensities and line-widths (correlated to the proximity
to the paramagnetic metal center), COSY experiments, and a
comparison with analogous FeII and CoII complexes with the
2-(arylimino)-6(cyclohexylimino)pyridine ligand 2-(2,6-iPr2-
C6H3NdCMe)-6-(cyclo-C6H11NdCMe)C5H3N (CyArN3) (Scheme
1).3a
7). The H NMR spectrum of the complex also shows four
different methyl signals and two different methine signals for
the CHMe2 group, as expected for the hindered rotation of the
iPr-substituted aryl of the coordinated imino nitrogen.10 In
contrast, the H NMR spectrum of CyAr2N5FeCl2 shows two
methyl signals and one methine signal for the coordinated imine
moiety, which suggests a less rigid structure in solution for this
iron derivative.
1
Unlike the mononuclear complexes, which are fairly soluble
in chlorinated solvents, the dinuclear complexes dissolve only
in very polar solvent like DMF, with decomposition however.
For this reason, the dinuclear complexes have been exclusively
characterized by solid-state techniques. The IR spectra contain
In line with the presence of a five-coordinate metal center in
CyAr2N5CoCl2, 12 proton resonances are assigned to the
coordinated bis(imino)pyridine portion of the ligand (Scheme

5076 Organometallics, Vol. 26, No. 20, 2007
Bianchini et al.
Figure 3. (a) Solid-state (upper trace) and CH2Cl2 solution (lower trace) EPR spectra of CyAr2N5CoCl2 at 5 K. (b) Variable-temperature
solid-state EPR spectra of CyAr2N5Co2Cl4.
only one ν(CdN) absorption, at 1617 cm-1, consistent with the
coordination of all nitrogen atoms.
) 0.85 (parallel type). Notably, the temperature dependence of
the spectra is compatible with the presence of two different
paramagnetic centers, as both the transition occurring close to
zero field and that around g ) 0.85 decreased in intensity on
increasing the temperature from 5 to 15 K. Conversely, the
perpendicular type transition at ca. g ) 1.13 was not signifi-
cantly affected by the temperature variation. The two sets of
transitions can then be reasonably attributed to two CoII ions in
different coordination environments, hence with different re-
laxation behavior as well as different g patterns. Finally, we
note that the spectra of the mono- and dinuclear complexes
CyAr2N5CoCl2 and CyAr2N5Co2Cl4 do not contain any signals in
coincident positions. This suggests that the addition of a second
cobalt ion to CyAr2N5CoCl2 affects somehow the coordination
environment of the first cobalt center, likely by increasing the
degree of distortion from the idealized geometries.
The magnetic properties and the spectral parameters of the
dinuclear complexes are strongly indicative of the presence of
two high-spin metal centers in either square-pyramidal or
tetrahedral geometry (µeff values of 6.82 and 6.33 µB in
CyAr2N5Fe2Cl4 and CyAr2N5Co2Cl4, respectively). Since µeff
values of 7.6 and 6.7 µB are expected for noninteracting high-
spin couples of FeII and CoII ions, respectively,9b,33 one may
reasonably conclude that the metal centers behave almost as
separated entities with negligible magnetic interaction.
The reflectance spectrum of the dinuclear iron complex
CyAr2N5Fe2Cl4 shows no additional absorption with respect to
the mononuclear parent, which is likely due to the fact that
tetrahedral N2FeX2 chromophores exhibit only one spin-allowed
d-d transition observable beyond the low-energy limit of our
spectrophotometer (4550 cm-1). The reflectance spectrum of
CyAr2N5Co2Cl4 is more complex than that of its mononuclear
congener CyAr2N5CoCl2 and exhibits additional absorptions at
ca. 18 000 cm-1 and in the region 10 000-7000 cm-1, which
are typical of a N2CoX2 chromophore in a tetrahedral
environment.4d
Synthesis and Characterization of the CyArN3H Ligand and
of Its Mononuclear Complex CyArN3HCoCl2. Scheme 8 il-
lustrates the stepwise procedure developed to prepare the
CyArN3 ligand, which is sterically comparable to CyAr2N5, yet
H
with only three nitrogen donor atoms like CyArN3. The reasons
H
that prompted us to synthesize CyArN3 will be accounted for
The EPR spectra of CyAr2N5CoCl2 and CyAr2N5Co2Cl4 were
recorded at 5 K due to the fast spin-lattice relaxation time,
which makes high-spin CoII centers detectable only at very low
temperature.34 As for the FeII complexes, the large zero field
splitting of their integer ground state (S ) 2) makes them EPR
silent in the X-band even at the lowest temperature attained.
CyAr2N5CoCl2 shows a typical EPR spectrum for an effective
Seff ) 1/2 spin Hamiltonian with a rhombic g factor, g1 ) 5.9,
g2 ) 2.02, g3 ) 0.96 (Figure 3a). This pattern is in agreement
with the literature data for CoII centers in a distorted square-
pyramidal geometry35 and, in particular, with the pattern
exhibited by bis(imino)pyridine CoII complexes.10 Interestingly,
a similar rhombic pattern of g values was observed for the frozen
CH2Cl2 solution spectrum (g1 ) 6.6, g2 ) 1.7, g3 ) 1.06) that
shows a hyperfine structure for the low-field signal. The
observed differences in the g factors between the solid-state and
frozen solution spectra can be reasonably attributed to differ-
ences in the intermolecular interactions of the two phases.
A fairly different EPR spectrum was obtained for the
dinuclear complex CyAr2N5Co2Cl4 (Figure 3b), as three different
transitions were actually observed: the first close to zero field,
the second at g ) 1.14 (perpendicular type), and the third at g
in a following section dealing with our efforts to correlate
catalytic activity and ligand structure.
The 4-vinyl benzoate X, straightforwardly prepared in fairly
good yield as a mixture of two inseparable diasteroisomers via
a Wittig protocol,36 was reacted with the lithiated form of
2-ethylenedioxy ketal-6-bromopyridine to afford the intermedi-
ate XI as a mixture of E/Z isomers. The deprotection of the
ethylenedioxy ketal XI, followed by an acid-catalyzed imination
with 2,6-diisopropylaniline, gave the monoimine-monoketone
XIII, which was recrystallized from hot methanol in its Z, pure
form. On reaction in hot cyclohexylamine, XIII was converted
H
to the target CyArN3 ligand. It is noteworthy that, besides
exhibiting similar steric properties, CyAr2N5 and CyArN3 share
H
a similar network of single and double bonds, which should
contribute to make a comparison of the catalytic performance
of their CoII complexes as reliable as possible.
The cobalt complex CyArN3HCoCl2 was finally prepared by
the reaction of the CyArN3H with 1 equiv of anhydrous CoCl2 in
THF at room temperature (Scheme 8). Like all its congeners
described in this paper, CyArN3HCoCl2 is fairly air-stable in the
solid state, whereas it decomposes in solution unless protected
by an inert atmosphere. The complex shows a good solubility
in organic solvents such as THF, CH2Cl2, and 1,2-dichloroet-
hane. In the latter solvent it behaves as a nonelectrolyte. Since
the magnetic data and the relevant IR and vis-NIR absorptions
of CyArN3HCoCl2 are fully comparable to those of the five-
(33) Gerli, A.; Hagen, K. S.; Marzilli, L. G. Inorg. Chem. 1991, 30,
4673.
(34) Abragam, A.; Bleaney, B. Electron Paramagnetic Resonance of
Transition Ions; Dover: New York, 1986.
(35) Bencini, A.; Gatteschi, D. In Transition Metal Chemistry; Figgis,
B. N., Melson, G., Eds.; Marcel Dekker: New York, 1982; Vol. 8.
(36) Nakamura, Y.; Yamazaki, T.; Nishimura, J. Org. Lett. 2005, 7, 3259.

Synthesis of a New Polydentate Ligand
Organometallics, Vol. 26, No. 20, 2007 5077
Scheme 8
Table 4. Ethylene Oligomerization with CyAr2N5 and CyArN3
Iron(II) and Cobalt(II) Catalyst Precursorsa
coordinate CyAr2N5 congener (see Experimental Section), no
further comment is given here.
R-olefin
Ethylene Oligomerization Catalyzed by Mono- and Di-
nuclear Precursors with the CyAr2N5 Ligand. The mono- and
dinuclear CoII and FeII complexes with CyAr2N5 have been
scrutinized as catalyst precursors for the oligomerization of
ethylene in toluene under standard experimental conditions,
using MAO as activator.1,37 No attempt of optimizing the
catalytic performance was carried out, this study being es-
sentially concerned with a preliminary screening of the potential
of CyAr2N5 metal complexes in homogeneous catalysis. Com-
parative reactions were performed with known oligomerization
FeII and CoII catalysts modified with the more conventional 2,6-
bis(imino)pyridine ligand CyArN3 (Scheme 1). Table 4 reports
the experimental conditions and the results obtained.
Upon activation by MAO, all CoII and FeII complexes with
the CyAr2N5 ligand gave R-olefins with a Schulz-Flory distribu-
tion (Table 4). Irrespective of the supporting ligand, the chain
length of the oligomers showed a clear dependence on the nature
of the metal center, as C4-C14 R-olefins (R ) 0.18-0.12) were
produced with the CoII catalysts, whereas the FeII derivatives
gave a broader oligomer distribution (R ) 0.71-0.63). The
ability of the FeII precursors to produce higher molecular weight
oligomers as compared to CoII analogues is typical of systems
supported by 2,6-bis(imino)pyridine ligands where one nitrogen
atom bears an aryl substituent and the other a cyclohexyl
substituent.3a Unlike classical 2,6-bis(imino)pyridine ligands,
∆T oligomers TOFb,c
selectivityb
(%)
run
precatalyst
(°C)
(g)
(×10-4
)
Rd
1
2
3
4
5
6
7
CyArN3CoCl2
CyArN3HCoCl2
CyA2rN5CoCl2
CyAr2N5Co2Cl4
CyArN3FeCl2
CyAr2N5FeCl2
CyAr2N5Fe2Cl4
1
1
0.1
0.1
0.1
0.1
2.9
6.1
6.5
6.3
6.7
e
e
96
96
98
96
96
98
99
5
2.5
0.18
0.12
0.74
0.63
0.71
17
17
13
29
10.2
5.5
5.3
11.2
a Reaction conditions: precatalyst, 12 µmol; MAO, 1440 equiv/M; C2H4
pressure, 4 bar; toluene, 100 mL; initial temperature, 25 °C; reaction time,
15 min; stirring, 1500 rpm. b Determined by GC. c In units of mol of C2H4
converted (mol of M)-1 h-1. Average values over at least three reactions.
d Schulz-Flory parameter, R ) rate of propagation (rate of propagation +
rate of chain transfer)-1 ) mol of Cn+2 (mol of Cn)-1 e Not determined.
.
Almost exclusively butenes produced.
CyAr2N5 forms FeII and CoII oligomerization catalysts with
comparable activities.1,2 Unexpectedly, however, it turned out
that the catalyst generated by CyAr2N5CoCl2 was more than 1
order of magnitude more active than that supported by the ligand
CyArN3.3a More surprisingly, the activity of the mononuclear
precursor CyAr2N5CoCl2 was 4 times lower than that of the
dinuclear analogue CyAr2N5Co2Cl4 (2.5 vs 10.4 g, entries 3, 4).
This result cannot be simply related to the presence of a double
proportion of metal in the latter precursor, as one may suggest
to explain the activity of the FeII catalyst CyAr2N5Fe2Cl2, which
actually gives twice as much R-olefins than its mononuclear
(37) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391.

5078 Organometallics, Vol. 26, No. 20, 2007
Bianchini et al.
analogue CyAr2N5FeCl2 (entries 6, 7) and is also as active as its
2,6-bis(imino)pyridine counterpart CyArN3FeCl2 (entries 5, 6).
In an attempt to address the superior activity of CyAr2N5CoCl2,
some oligomerization reactions were carried out in the presence
of the precursor CyArN3HCoCl2 containing a ligand sterically
comparable to CyAr2N5, yet with only three nitrogen donor atoms
as in CyArN3. Indeed, we thought that a comparison between
the catalytic activity of CoCl2 modified with either CyArN3 or
more than the FeII ones. Perhaps an accurate analysis of the
products formed by the reaction of the precursors with MAO
might contribute to unravel these questions. Studies in this
direction are in progress in our laboratory.
Conclusions
A new potentially pentadentate ligand, CyAr2N5, has been
synthesized through a protocol that will allow one to prepare
many other structurally similar molecules for use in organo-
metallic chemistry and homogeneous catalysis.
This ligand joins 2,6-bis(imino)pyridyl and (imino)pyridyl
moieties and, as such, can accommodate one or two metal
centers with different coordination geometries. Moreover, the
geometry of CyAr2N5, with the second pyridine ring linked in
the 3-position, makes very unlikely the formation of octahedral
mononuclear complexes, as it has been found to occur for
analogous Ar3N5 derivatives (Scheme 3).10
In the present work, CyAr2N5 has been used to prepare mono-
and homodinuclear FeII and CoII bis-chloride complexes that
have been characterized by a variety of analytical and spectro-
scopic techniques. On activation by MAO in toluene, FeCl2 and
CoCl2 modified with CyAr2N5 generate effective catalysts for
the oligomerization of ethylene to R-olefins with productivities
and Schulz-Flory parameters depending on the type and number
of coordinated metals. In particular, unlike separate 2,6-bis-
(imino)pyridine and (imino)pyridine ligands, their coupling, as
in CyAr2N5, results in comparably active FeII and CoII catalysts,
with the latter yielding shorter oligomers. A model study has
allowed us to rule out any significant role of steric effects in
increasing the catalytic activity of the mononuclear CoII complex
CyAr2N5CoCl2 versus its 2,6-bis(imino)pyridine counterpart,
while no rationale has been reached to explain why the dinuclear
derivative CyAr2N5Co2Cl4 is 4 times more active than its
mononuclear analogue CyAr2N5CoCl2.
H
CyArN3 would have been useful to assess whether a group of
the same size as that borne by the (cyclohexyl)imine carbon
atom in CyAr2N5 might account for so large an increase in
productivity. Indeed, steric interactions between the R and R′
substituents on the RCdNR′ moiety of 2,6-bis(imino)pyridine
ligands are crucial to control the chain-transfer rate of ethylene
oligomerization/polymerization reactions by late transition metal
complexes.1-4
Under the experimental conditions reported in Table 4,
CyArN3HCoCl2 generated a poorly active oligomerization cata-
lyst, comparable to CyArN3CoCl2 (entries 1, 2). In light of this
result, we are inclined to rule out any merely steric role of the
uncoordinated (imino)pyridyl group to account for the greater
catalytic activity of CyAr2N5CoCl2 versus CyArN3CoCl2. This
means that the two additional nitrogen atoms in CyAr2N5 may
play a substantial role once the precursor is activated by MAO.
These nitrogen atoms may interact with the metal center, leading
to more active species, or generate more active forms of the
activator. Indeed, the possible reactions of MAO with the FeII
and CoII complexes of the type described in this paper are
manifold, spanning from the formation of square-planar CoII
methyl compounds, either diamagnetic CoI or paramagnetic low-
spin CoII species,4,38 to adducts where the residual AlMe3 or
MAO itself reacts with the nitrogen atoms or is able to alkylate
and even reduce the CdN bonds,39 to species where the
π-electrons of the CdN-aryl rings interact with the metal
center.40 In the absence of an in-depth investigation, any of these
options is equally possible. Likewise, we have no reliable
explanation for the largely superior activity of the dinuclear
analogue CyAr2N5Co2Cl4 as compared to the mononuclear
derivative CyAr2N5CoCl2 as well as for the fact that the ligand
CyAr2N5 increases the catalytic activity of the CoII derivatives
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 discussion on the EPR spectra and the
financial support of Ente Cassa di Risparmio di Firenze.
(38) (a) Humphries, M. J.; Tellmann, K. P.; Gibson, V. C.; White, A. J.
P.; Williams, D. J. Organometallics 2005, 24, 2039. (b) Knijnenburg, Q.;
Hetterscheid, D.; Kooistra, T. M.; Budzelaar, P. H. M. Eur. J. Inorg. Chem.
2004, 1204.
(39) (a) Bruce, M.; Gibson, V. C.; Redshaw, C.; Solan, G. A.; White,
A. J. P.; Williams, D. J. Chem. Commun. 1998, 849. (b) Gibson, V. C.;
Redshaw, C.; White, A. J. P.; Williams, D. J. J. Organomet. Chem. 1998,
550, 453. (c) Milione, S.; Cavallo, G.; Tedesco, C.; Grassi, A. Dalton Trans.
2002, 1839. (d) Knijnenburg, Q.; Smits, J. M. M.; Budzelaar, P. H. M.
Organometallics 2006, 25, 1036.
Supporting Information Available: Text and tables giving
crystallographic data for VI·0.8CH2Cl2 and CyAr2N5. This material
is available free of charge via the Internet at http://pubs.acs.org.
(40) Archer, A. M.; Bouwkamp, M. W.; Cortez, M.-P.; Lobkovsky, E.;
Chirik, P. J. Organometallics 2006, 25, 4269.
OM7006503