Flexible N,N,N-chelates as supports for iron and cobalt chloride complexes; synthesis, structures, DFT calculations and ethylene oligomerisation studies

Article abstract of DOI:10.1039/b409827g

The aryl-substituted N-picolylethylenediamine and diethylenetriamine ligands, (ArNHCH₂CH₂){(2-C₅H ₄N)CH₂}NH and (ArNHCH₂CH₂) ₂NH (Ar = 2,6-Me₂C₆H

Full text of DOI:10.1039/b409827g

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F U L L P A P E R
Flexible N,N,N-chelates as supports for iron and cobalt chloride
complexes; synthesis, structures, DFT calculations and ethylene
oligomerisation studies
Richard Cowdell,a Christopher J. Davies,a Stephen J. Hilton,a Jean-Didier Maréchal,a,b
Gregory A. Solan,*a Owen Thomasa and John Fawcetta
a
Department of Chemistry, University of Leicester, University Road, Leicester,
UK LE1 7RH. E-mail: gas8@leicester.ac.uk
Department of Biochemistry, University of Leicester, University Road, Leicester,
b
UK LE1 7RH. E-mail: gas8@leicester.ac.uk
Received 30th June 2004, Accepted 9th August 2004
First published as an Advance Article on the web 27th August 2004
The aryl-substituted N-picolylethylenediamine and diethylenetriamine ligands, (ArNHCH2CH2){(2-C5H4N)CH2}NH
and (ArNHCH2CH2)2NH (Ar = 2,6-Me2C6H3, 2,4,6-Me3C6H2), have been prepared by employing palladium-catalysed
N–C(aryl) coupling reactions of the corresponding primary amines with aryl bromide. Treatment of MCl2 with
(ArNHCH2CH2){(2-C5H4N)CH2}NH affords [{(ArNHCH2CH2)((2-C5H4N)CH2)NH}CoCl2] (Ar = 2,6-Me2C6H3
1a; 2,4,6-Me3C6H2 1b) and [{(ArNHCH2CH2)((2-C5H4N)CH2)NH}FeCl2]n (n = 1, Ar = 2,6-Me2C6H3 2a; n = 2, 2,4,6-
Me3C6H2 2b) in high yield. The X-ray structures of 1a and 1b are isostructural and reveal the metal centres to adopt
distorted trigonal bipyramidal geometries with the N,N,N-chelates adopting fac-structures. A facial coordination
mode of the ligand is also observed in bimetallic 2b, however, in 2a the N,N,N-chelate adopts a mer-configuration
with the metal centre adopting a geometry best described as square pyramidal. Solution studies indicate that mer–fac
isomerisation is a facile process for these systems at room temperature. Quantum mechanical calculations (DFT)
have been performed on 1a and 2a, in which the ligands employed are identical, and show the fac- to be marginally
more stable than the mer-configuration for cobalt (1a) while for iron (2a) the converse is evident. Reaction of
(ArNHCH2CH2)2NH with CoCl2 gave the five-coordinate complexes [{(ArNHCH2CH2)2NH}CoCl2] (Ar = 2,6-
Me2C6H3 3a, 2,4,6-Me3C6H2 3b), in which the ligand adopts a mer-configuration; no reaction occurred with FeCl2. All
complexes 1–3 act as modest ethylene oligomerisation catalysts on activation with excess methylaluminoxane (MAO);
the iron systems giving linear a-olefins while the cobalt systems give mixtures of linear and branched products.
We have recently been attracted by the use of more flexible
1
Introduction
nitrogen donor ligands as potential supports for late transition
metal catalysts. One candidate for the role is the dipicolylamine
ligand (dpa, Fig. 1) which possess a saturated backbone but lacks
steric bulk and, as a result, has a propensity for formation of cata-
lytically undesirable complexes of the type [M(dpa)2]2+ (M = Fe,
Co).5 Herein, we report our efforts at modifying the dpa ligand ar-
chitecture by replacing one of the picolyl groups with a sterically
variable N-aryl-substituted ethylamine to furnish a new family
of ligands termed N-picolyen (B, Fig. 1). Cobalt(II) and iron(II)
chloride complexes containing B, and also A, are described as are
their application as precatalysts in olefin oligomerisation.
The application of tridentate nitrogen donor ligand
sets as supports for transition metal-based olefin
polymerisation catalysts has been the source of considerable
interest in recent years. Indeed, such ligands have found
prominence in both early and late transition metal catalysis. In
particular, diamido-donor ligands derived from aryl-substituted
dien ligands (A, Fig. 1) have proved compatible ligands for
preparing early transition metal catalysts (e.g., Zr and Hf).1 On
the other hand, the more rigid neutral bis(arylimino)pyridine
ligands have led the way for generating catalysts based on
iron,2,3 cobalt2,3 and vanadium centres.4 In common to both the
dianionic and neutral N,N,N-ligands, is the presence of N-aryl
substituents which can be readily modified with regard to both
their steric and electronic properties. Moreover, the nature of the
aryl substitution pattern may play a key role in influencing the
performance of the catalyst.
2
Results and discussion
(a) Synthesis of the ligands
The ligands [(ArNHCH2CH2){(2-C5H4N)CH2}NH] (Ar = 2,6-
Me2C6H3, 2,4,6-Me3C6H2) were synthesised in high yield by
a palladium catalysed N–C(aryl) coupling reaction of N-
picolyethylenediamine [prepared by treating 2-chloroethylamine
with excess 2-(aminomethyl)pyridine)] with one equivalent of
the corresponding aryl bromide (Scheme 1) using experimental
protocols established by Buchwald and Hartwig.6 A similar pal-
ladium catalysed coupling reaction was employed for the synthesis
of [(ArNHCH2CH2)2NH] (Ar = 2,6-Me2C6H3, 2,4,6-Me3C6H21b
)
by treating diethylenetriamine with either two equivalents of 2-
bromo-m-xylene or 2-bromomesitylene, respectively. All the new
ligands have been characterised by IR, 1H and 13C NMR spectros-
copy, mass spectrometry (FAB or ES) (see Experimental section).
(b) Synthesis of the complexes
(i) Reaction
of
MCl2
with
(ArNHCH2CH2){(2-
Fig. 1 Aryl-substituted dien (A), bis(imino)pyridine, dpa and N-
picolylen (B) ligands.
C5H4N)CH2}NH. The reaction of (ArNHCH2CH2){(2-
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0
3 2 3 1

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Scheme 1 Reagents and conditions: (i) NaOH, H2NCH2CH2Cl·HCl, EtOH, heat, 2 h; (ii) Ar–Br (Ar = 2,6-Me2C6H3, 2,4,6-Me3C6H2), NaOBut,
Pd2(dba)3, rac-BINAP, toluene, heat, 4 days.
Table 1 Spectroscopic and analytical data for the new complexes 1–3
Microanalysis (%)c
Compound
leffa/lB
v(N–H)b/cm−1
FAB mass spectrum
C
H
N
1a
1b
2a
2b
3a
3b
3.8
3.7
4.9
7.4
3.9
4.0
3213w
3136w
3171w
3125w
3156w
3335w
385 (M+), 350 (M+ − Cl), 314 (M+ − 2Cl)
399 (M+), 364 (M+ − Cl), 328 (M+ − 2Cl)
755 (2M+ − Cl), 347 (M+ − Cl), 311 (M+ − 2Cl)
755 (M+ − Cl), 395 (M+/2), 361 (M+/2 − Cl),
441 (M+), 405 (M+ − Cl), 370 (M+ − 2Cl)
469 (M+), 434 (M+ − Cl), 398 (M+ − 2Cl)
50.01 (49.87)
51.84 (51.80)
49.65 (50.26)
51.59 (51.52)
54.07 (54.42)
56.11 (56.29)
5.61 (5.45)
5.97 (5.90)
5.62 (5.50)
5.51 (5.81)
6.53 (6.58)
6.99 (7.04)
10.80 (10.91)
12.61 (12.70)
10.62 (10.99)
10.70 (10.61)
9.15 (9.52)
8.67 (8.96)
a Recorded on an Evans Balance at room temperature. b Recorded on a Perkin-Elmer Spectrum One FT-IR spectrometer on solid samples. c Calculated
values are shown in parentheses.
C5H4N)CH2}NH with MCl2 (M = Co, Fe) in n-BuOH at
elevated temperature gave complexes [{(ArNHCH2CH2)((2-
C5H4N)CH2)NH}CoCl2] (Ar = 2,6-Me2C6H3 1a, 2,4,6-Me3C6H2
1b) and [{(ArNHCH2CH2)((2-C5H4N)CH2)NH}FeCl2]n (n = 1,
Ar = 2,6-Me2C6H3 2a; n = 2, Ar = 2,4,6-Me3C6H2 2b) in high
yield (Scheme 2). All products have been characterised by FAB
mass spectrometry, magnetic susceptibility, IR spectroscopy and
by elemental analysis (see Table 1). In addition, crystals of 1a,
1b, 2a and 2b have been subject to single crystal X-ray diffrac-
tion studies.
[N(1)–Co(1)–N(3) 109.78(6)°, N(1)–Co(1)–Cl(1) 107.97(5)°,
N(3)–Co(1)–Cl(2) 95.27(5)°. The N,N,N-chelate adopts a fac
configuration with N(1) located 1.871(1) Å out of the plane
defined by N(3)–N(2)–Co(1). The aryl group is oriented such
that the ortho-methyl groups [C(15), C(16)] are positioned above
and the below the plane defined by N(3)–N(2)–Co(1) [torsion
angle: C(10)–C(9)–N(3)–Co(1) 46.4(1)°] with one ortho-methyl
[C(15)] pointing in a similar direction to the equatorial chloride
atom [Cl(1)]. The Co–N distances are far from equivalent
with the longest involving the aryl-substituted amine nitrogen
[Co(1)–N(3) 2.209(1) Å] and the shortest involving the pyridyl
nitrogen [Co(1)–N(1) 2.089(2) Å]; the shortness of the latter
can presumably be attributed to some dp–pp overlap between
metals and pyridyl nitrogen atoms. There is also a difference
observed for the Co–Cl distances with the equatorial chloride
being longer than the axial chloride [Co(1)–Cl(1) 2.360(1) Å vs.
Co(1)–Cl(2) 2.283(1) Å]. The Cl–Co–Cl angle at 103.09(2)° falls
below the range found in bis(imino)pyridine-containing cobalt
dichloride complexes7 but compares well with less rigid N,N,N-
chelated five-coordinate cobalt dichloride complexes.8 Due to
the centric nature of the space group, both R/R and S/S forms
are present for the two chiral centres at N(1) and N(2) in the
crystal of 1b (also 1a).
In the FAB mass spectrum of 1a and 1b molecular ion peaks
are observed along with fragmentation peaks corresponding
to the loss of chloride ligands; very minor peaks relating to
dimeric species are also evident. In the IR spectrum the m(N–H)
absorption bands are seen at ca. 3175 cm−1 and shifted to a
lower wavenumber than that in the corresponding free ligands.
The magnetic susceptibility measurements for 1a and 1b reveal
magnetic moments of ca. 3.75 lB (Evans balance at ambient
temperature) which are consistent with high spin configurations
possessing three unpaired electrons.
Golden coloured crystals of 2a and 2b suitable for the X-ray
determination were grown by layering an acetonitrile solution
of the corresponding complex with hexane at room temperature.
The structures of 2a and 2b are dissimilar and will be discussed
separately. The molecular structure of 2a is illustrated in Fig. 3;
selected bond distances and angles are listed in Table 2.
Scheme 2 Reagents and conditions: (i) n-BuOH, 90 °C; (ii) (ArNH-
CH2CH2){(2-C5H4N)CH2}NH (Ar = 2,6-Me2C6H3, 2,4,6-Me3C6H2),
n-BuOH, 90 °C; * refers to the site of chiral centre.
Dark blue single crystals of 1a and 1b suitable for the X-ray
determination were grown by layering an acetonitrile solution of
the corresponding complex with hexane at ambient temperature.
The structures of 1a and 1b are essentially the same and only
1b will be discussed in detail. A view of 1b is shown in Fig. 2;
selected bond distances and angles are listed for both 1a and 1b
in Table 2. The structure of 1b comprises a single cobalt atom
surrounded by a mesityl-substituted N-picolylethylenediamine
ligand and two monodentate chloride ligands. The geometry at
cobalt can be best described as distorted trigonal bipyramidal
with N(2) and Cl(2) defining the axial sites [N(2)–Co(1)–Cl(2)
171.10(5)°] and N(1), Cl(1) and N(3) the equatorial sites
The structure of 2a is based on an iron atom bound by a 2,6-
dimethylphenyl-substituted N-picolylethylenediamine ligand
and two monodentate chloride ligands. The geometry at iron
is distorted square pyramidal with N(1), N(2), N(3) and Cl(2)
3 2 3 2
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0

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Table 2 Selected bond distances (Å) and angles (°) for 1a, 1b and 2a
M = Co (1a)
M = Co (1b)
M = Fe (2a)
M(1)–N(1)
M(1)–N(2)
M(1)–N(3)
M(1)–Cl(1)
M(1)–Cl(2)
2.082(1)
2.188(1)
2.168(1)
2.347(1)
2.296(1)
2.089(2)
2.179(2)
2.209(2)
2.360(1)
2.283(1)
2.178(1)
2.185(1)
2.296(1)
2.398(1)
2.285(1)
Cl(1)–M(1)–N(1)
Cl(1)–M(1)–N(2)
Cl(1)–M(1)–N(3)
Cl(1)–M(1)–Cl(2)
Cl(2)–M(1)–N(1)
Cl(2)–M(1)–N(2)
Cl(2)–M(1)–N(3)
N(1)–M(1)–N(3)
N(1)–M(1)–N(2)
N(2)–M(1)–N(3)
105.79(4)
87.42(3)
141.63(4)
104.30(2)
98.71(4)
168.22(4)
91.95(3)
105.72(5)
76.64(5)
79.14(5)
107.97(5)
85.78(5)
134.59(5)
103.09(2)
98.69(5)
171.10(5)
95.27(5)
109.78(6)
77.49(7)
78.72(6)
101.16(4)
99.92(4)
84.72(4)
109.24(2)
98.19(4)
150.84(4)
104.46(4)
153.28(6)
75.56(6)
77.75(5)
Fig. 2 Molecular structure of 1b including the atom numbering
scheme. All hydrogen atoms except for H2 and H3 have been omitted
for clarity.
fall at the top end of the range found for related complexes.10
As expected, the Fe–Cl(terminal) bond distances [Fe(1)–Cl(2)
2.310(1) Å] are shorter than those seen for the bridging chlorides
but at the top end of the range observed in structurally related
complexes.10 The ClFe(l-Cl)2FeCl motif has been found in
a number of crystallographically characterised complexes
with the transannular FeFe separation in 2b [3.600(1) Å]
falling in the mid-range.10 Unlike in 1a, 1b and 2a, the relative
configuration of the chiral centres is distinct with both R/S and
S/R forms adopted within the structure of 2b.
Fig. 3 Molecular structure of 2a including the atom numbering
scheme. All hydrogen atoms except for H2 and H3 have been omitted
for clarity.
defining the square base and Cl(1) the apex. The N,N,N-chelate
adopts a mer-configuration with the N(1)–Fe(1)–N(3) angle
being 153.28(6)° and the deviation from planarity displayed by
the N(1)–N(2)–N(3)–Fe(1) plane minimal [max. deviation: Fe(1)
0.018 Å]. The secondary amine terminus of the ligand possesses
the aryl substituent which is inclined at an angle of 69.2(1)°
to the N(1)–N(2)–N(3)–Fe(1) plane with its ipso-carbon atom
[C(9)] sitting 0.733(1) Å out of the plane and on the same side
as Cl(2). The ortho-methyl groups of the aryl group sit above
and below the N(1)–N(2)–N(3)–Fe(1) plane [deviation from
plane: C(16) 2.923(1), C(15) 1.478(1) Å], with C(16) pointing
in a similar direction to Cl(1). There is a difference in the Fe–N
bond lengths with the distance to the pyridyl donor being the
shortest [Fe(1)–N(1) 2.178(1) Å] and to the arylamine the
longest [Fe(1)–N(3) 2.296(1) Å]. Similarly, the Fe–Cl distances
are asymmetric with the distance to the apical chloride the
longest [Fe(1)–Cl(1) 2.398(1) Å vs. Fe(1)–Cl(2) 2.285(1) Å]. The
Cl–Fe–Cl angle at 109.24(2)° falls in the lower end of the range
for the corresponding angle in related complexes.9 As with 1a
and 1b, both R/R and S/S forms of the complex are present
within the crystal of 2a.
The molecular structure of 2b is shown in Fig. 4; selected
bond distances and angles are listed in Table 3. The struc-
ture consists of a dimeric unit generated through a crystallo-
graphically imposed inversion centre. The iron centres are
bridged by two chloride ligands and bound terminally by a
chloride and a mesityl-substituted N-picolylen ligand to give
a pseudo-octahedral geometry at each metal centre. The two
N-picolylen ligands adopt facial bonding modes such that the
pyridyl and the aryl-substituted amine moieties are trans to the
bridging chlorides and the central amine trans to a terminal
chloride. At each metal centre the pyridyl nitrogen–iron
distance [Fe(1)–N(1) 2.168(2) Å] is the shortest of the three
Fe–N distances while the aryl-substituted amine–iron distance
the longest [Fe(1)–N(3) 2.334(2) Å]. The Fe–l-Cl distances are
similar [Fe(1)–Cl(1) 2.509(1), Fe(1)–Cl(1A) 2.546(1) Å] and
Fig. 4 Molecular structure of 2b including the atom numbering
scheme; the atoms labelled with a suffix are generated by symmetry (−x,
1 − y, −z). All hydrogen atoms except for H2 and H3 have been omitted
for clarity.
Despite the molecular structures of 2a and 2b being
monomeric and dimeric respectively, their FAB mass spectra are
similar. Both show peaks consistent with the loss of a chloride
ligands from a monomeric species, [(N-picolylen)FeCl2], along
with minor peaks attributable to chloride loss from dimeric
species, [(N-picolylen)FeCl2]2. In the IR spectrum the m(N–H)
absorption bands are seen at ca. 3150 cm−1 and shifted to a lower
wavenumber than that in the corresponding free ligands. The
magnetic susceptibility measurement for 2a gives a magnetic
moment of 4.9 lB (Evans balance at ambient temperature)
which is consistent with a high spin configuration possessing
four unpaired electrons. In dimeric 2b, a magnetic moment of
7.4 lB is observed which is consistent with two non-interacting
high spin metal centres. Indeed, cooling of 2b down to 50 K
shows little variation in the magnetic moment.11
Although the complexes are paramagnetic, 1H NMR
spectroscopy can be informative. Fig. 5 shows the room
temperature 1H NMR spectra (recorded in acetonitrile-d3)
of monomeric 2a and dimeric 2b. The spectra of 2a and 2b
show broad paramagnetically shifted peaks between −16.0 and
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0
3 2 3 3

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Table 3 Selected bond distances (Å) and angles (°) for 2b
postulated lability of the aryl-substituted arylamino arm is
given on inspection of the M–N distances in 2a and 2b, in which
the corresponding Fe–N distances are ca. 0.1 Å longer than
the other M–N distances. A related dissociation of an amino
group in a N,N,N-chelate has previously been observed in a five-
coordinate group 4 system.13
Fe(1)–N(1)
Fe(1)–N(2)
Fe(1)–N(3)
Fe(1)–Cl(1)
2.168(2)
2.218(2)
2.334(2)
2.509(1)
Fe(1)–Cl(2)
Fe(1)–Cl(1A)
Fe(1)Fe(1A)
2.310(1)
2.546(1)
3.600(1)
Cl(1)–Fe(1)–N(3)
Cl(1)–Fe(1)–Cl(2)
Cl(1)–Fe(1)–N(1)
Cl(1)–Fe(1)–Cl(1A)
Cl(1)–Fe(1)–N(2)
Cl(2)–Fe(1)–N(1)
Cl(2)–Fe(1)–N(3)
Cl(2)–Fe(1)–N(2)
81.06(6)
94.41(2)
162.93(6)
89.19(2)
87.88(5)
101.05(6)
98.84(5)
175.13(6)
Cl(2)–Fe(1)–Cl(1A)
N(3)–Fe(1)–N(1)
N(3)–Fe(1)–N(2)
N(3)–Fe(1)–Cl(1A)
N(1)–Fe(1)–N(2)
N(1)–Fe(1)–Cl(1A)
N(2)–Fe(1)–Cl(1A)
96.56(3)
103.43(7)
77.24(7)
162.33(5)
77.27(7)
81.94(5)
87.76(6)
The atoms labelled with
a suffix are generated by symmetry
(−x, 1 − y, −z).
131.0 ppm (Fig. 5). Some degree of assignment can be made
on comparison of the chemical shifts and relaxation times in
2a and 2b with the related iron(II) complexes [(fac-dpa)FeCl(l-
Cl)2ClFe(fac-dpa)] and [(tpa)FeCl2] (tpa = tripicolylamine) in
which the pyridyl (Ha, Hb and Hc) and methylene protons of the
picolyl group have characteristic chemical shifts.5,12 Typically,
Ha is observed most downfield (115–130 ppm) while Hc most
upfield (6–20 ppm). In between these signals are located the Hb
and CH2 signals. The aromatic signals have been assigned on the
basis of integration and by direct comparison between the two
spectra (mesityl vs. 2,6-dimethyphenyl). In particular, the para-
substituent of the aryl group can be informative with the Mep
in 2b appearing at d 15.7 while in 2a this is signal is absent but
replaced by Hp at d −5.4.
What is clear from the two spectra, despite the difference
in the solid-state structures, both behave similarly in solution
at room temperature. Scheme 3 shows a series of equilibria
that can explain the apparent dynamic behaviour of 2a and
2b. Dissociation of the arylamine arm of the ligand in mer-2a
could generate a four-coordinate iron complex containing a
pendant amine group. Inversion of the stereochemistry of the
pendant amine, some reorganisation of the ethyl unit, followed
by recoordination would generate the fac-coordinated species A.
As the bulky aryl group is now remote from the chloride ligands,
dimerisation can occur to give a fac-coordinated dimer (isolated
for 2b). On the other hand, recoordination following inversion
would generate the mer-species B, while recoordination without
inversion would generate fac-C. Notably C, although not
isolated with iron as the metal centre, has been structurally
characterised for cobalt (1a and 1b). Some support for the
Scheme 3 Aryl–amino nitrogen dissociation in 2a and recoordination
possibilities.
In order to probe the relative stabilities of the mer and fac
isomers for the cobalt and iron chloride complexes containing
aryl-substituted N-picolylen ligands, DFT (B3LYP) calculations
were undertaken. Geometry optimisations were carried out on
[{((2,6-Me2C6H3)NHCH2CH2)((2-C5H4N)CH2)NH}MCl2]
[M = Co (1a) or Fe (2a)] for both mer-RR and fac-RR
conformations taking into account the high spin state of all
species. All unpaired electrons are located on the metal centre:
four and three for the Fe and Co complexes, respectively.
Different electronic repartitions of the metals d orbitals have
been considered for both 1a and 2a and the lowest energetic ones
were selected for geometry optimisation.
Optimised structures of the fac and mer complexes for 1a and
2a are depicted in Fig. 6; geometrical parameters are listed in
Table 4. Overall, experimental and theoretical structures for fac-
1a and mer-2a complexes are in good agreement. In particular,
the optimised values for the internal bond lengths and angles
of the tridentate ligand compare well with the experimental
Fig. 5 Paramagnetically shifted 1H NMR spectra for complexes 2a and 2b in acetonitrile-d3.
3 2 3 4
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0

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Table 4 Selected bond distances (Å) and angles (°) for fac-RR and mer-RR complexes of 1a and 2a
fac-RR Conformers
mer-RR Conformers
Experimental
M = Co (1a)
Optimised
M = Co (1a)
Optimised
M = Fe (2a)
Experimental
M = Fe (2a)
Optimised
M = Co (1a)
Optimised
M = Fe (2a)
M(1)–Cl(1)
M(1)–Cl(2)
M(1)–N(1)
M(1)–N(2)
M(1)–N(3)
2.347
2.296
2.082
2.188
2.168
2.34
2.33
2.19
2.25
2.26
2.35
2.34
2.23
2.30
2.35
2.398
2.285
2.178
2.185
2.296
2.37
2.30
2.18
2.23
2.27
2.41
2.29
2.24
2.23
2.37
Cl(1)–M(1)–N(1)
Cl(1)–M(1)–N(2)
Cl(1)–M(1)–N(3)
Cl(1)–M(1)–Cl(2)
Cl(2)–M(1)–N(1)
Cl(2)–M(1)–N(2)
Cl(2)–M(1)–N(3)
N(1)–M(1)–N(2)
N(2)–M(1)–N(3)
N(1)–M(1)–N(3)
105.8
87.4
141.6
104.3
98.7
168.2
91.9
76.6
108.8
84.1
125.4
118.3
95.0
157.3
90.1
74.7
106.9
84.3
130.9
121.8
95.7
153.8
86.8
73.5
101.2
99.9
84.7
109.2
98.2
150.8
104.5
75.6
104.1
90.0
90.3
119.2
96.3
150.8
102.5
73.7
95.0
92.6
84.6
130.2
95.4
137.1
106.0
75.0
79.1
105.7
76.4
114.4
74.8
108.8
77.7
153.3
76.7
146.9
77.2
152.2
ones (values not reported). The most important discussion
focused on the coordination sphere of the metal centre. The
optimised M–ligand bond lengths (especially the M–N ones)
are slightly longer that the experimental ones for both the fac-1a
and mer-2a, with discrepancies less than 0.1 Å; discrepancies of
this magnitude are sometimes observed with high spin systems
studied by B3LYP.14 Further comparison of the first coordina-
tion sphere of the metal atoms reveals that some reorganisation
of the ligands occurs between experimental and theoretical
structures. The most noticeable is the Cl(1)–M(1)–Cl(2) angle
withdiscrepanciesof 14°in 1a(computed118.3° vs. experimental
104.3°) to 20.9° in 2a (computed 130.2° vs. experimental
109.3°). Interestingly, the values of the Cl(1)–M(1)–Cl(2)
optimised angles are significantly closer to those observed in the
molecular structures of 3a and 3b (see later, 114.4 and 113.3°,
respectively). To further investigate the relevance of these struc-
tural differences, geometry optimisations of fac-1a and mer-
2a were carried out by fixing the Cl(1)–M(1)–Cl(2) angle to
their experimental values (104.3 and 109.3° respectively), and
optimising all the other geometrical variables. Comparison
between experimental, fully optimised and partially optimised
structures shows that the increase of the Cl(1)–M(1)–Cl(2) angle
is related to the rotation of the aryl group and the pyridine (to
a lesser extent) around their N–C bond. Analysis of the whole
unit cell of both crystals shows that significant p-stacking and
other ‘long distance’ contacts exist between monomers in the
crystals. The observed rearrangements in the optimised struc-
tures are therefore associated with the vacuum condition of the
calculations as compared to the packing environment of the
experimental system. This observation associated with the low
difference in potential energy between the partially optimised
and fully optimised structures of fac-1a and mer-2a (fully
optimised structures in both cases are 1.7 kcal mol−1 more stable
than the partially optimised ones) show that the discrepancies of
the Cl(1)–M(1)–Cl(2) angle are not physically significant.
Geometry optimisations of the non-experimentally
characterised structures fac-2a and mer-1a have been carried out
using B3LYP and lead to two stable structures. The optimised
fac-2a and mer-1a structures (Fig. 6) are in good agreement with
the data presented for fac-1a and mer-2a. In particular, the bond
lengths do not change significantly between the computed fac-
and mer-isomers (Table 4). With regard to the Cl(1)–M(1)–Cl(2)
angle, these optimised structures show the same tendency for
a more accentuated angle (121.8 and 119.2° for fac-2a and
mer-1a respectively) than the experimental fac-2a and mer-1a
conformers. Therefore, theoretical calculations lead to two
stable fac- and mer-conformers for both 1a and 2a.
Fig. 6 B3LYP optimised structures of mer and fac isomers of 1a and
2a.
equation DG0 = G0fac − G0mer. The differences of enthalpy are
also provided as indicative values. For the cobalt compound 1a,
DG0 = −1.04kcalmol−1 (DH0 = −0.84kcalmol−1),andfortheiron
compound 2a, DG0 = 2.41 kcal mol−1 (DH0 = 2.41 kcal mol−1).
Several points emerge; firstly, these results show that for
both cobalt and iron species, fac- and mer-conformations are
very close in energy. Secondly, for 1a, the fac-conformer is
approximately 1 kcal mol−1 more stable than the mer one, while
for 2a, the mer-conformer is approximately 2.5 kcal mol−1
more stable than the fac one. These results concur with the
experimental observations with fac-1a and mer-2a being the
most stable conformers.
In summary, the computed energetics in the gas phase for the
two isomers reproduce properly the nature of the most stable
isomer for both cobalt and iron in the crystalline state. Indeed,
the low energy difference between fac- and mer-structures for
both iron and cobalt would suggest an equilibrium to be likely
in solution which is confirmed by the 1H NMR studies of 2 (vide
supra). However, these calculations do not take into account
the possible mechanism involved in the transition from one
conformer to the other.
(ii) Reaction of CoCl2 with (ArNHCH2CH2)2NH.
The reaction of (ArNHCH2CH2)2NH with CoCl2
in n-BuOH at elevated temperature gave complexes
[{(ArNHCH2CH2)2NH}CoCl2] (Ar = 2,6-Me2C6H3 3a, 2,4,6-
Me3C6H2 3b) in high yield (Scheme 4). The corresponding
reactionsof (ArNHCH2CH2)2NHwithFeCl2 gaveonlyunreacted
starting materials. All products have been characterised by FAB
mass spectrometry, magnetic susceptibility and by elemental
analysis (Table 1). In addition, crystals of 3a and 3b have been
the subject of single crystal X-ray diffraction studies.
The difference in free Gibbs energy between fac- and mer-
conformers for both 1a and 2a has been calculated with the
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0
3 2 3 5

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Table 5 Selected bond distances (Å) and angles (°) for 3a and 3b
3a
3b
Co(1)–N(1)
Co(1)–N(2)
Co(1)–N(3)
Co(1)–Cl(1)
Co(1)–Cl(2)
2.219(3)
2.082(2)
2.243(2)
2.269(1)
2.350(1)
2.221(4)
2.066(4)
2.265(4)
2.2557(19)
2.3126(18)
Cl(1)–Co(1)–Cl(2)
Cl(2)–Co(1)–N(1)
Cl(2)–Co(1)–N(2)
Cl(2)–Co(1)–N(3)
N(1)–Co(1)–Cl(1)
N(1)–Co(1)–N(2)
N(1)–Co(1)–N(3)
N(2)–Co(1)–Cl(1)
N(2)–Co(1)–N(3)
N(3)–Co(1)–Cl(1)
114.91(4)
90.50(7)
99.76(7)
88.06(7)
98.82(7)
80.45(8)
160.08(7)
145.33(6)
80.23(8)
99.79(7)
113.29(7)
93.79(12)
102.01(14)
89.26(13)
100.51(13)
80.96(17)
160.00(16)
144.40(14)
79.07(17)
96.39(13)
Scheme 4 Reagents and conditions: (i) n-BuOH, 90 °C; (ii) (ArNH-
CH2CH2)2NH (Ar = 2,6-Me2C6H3, 2,4,6-Me3C6H2), n-BuOH, 90 °C.
Dark blue single crystals of 3a and 3b suitable for the X-ray
determination were grown by layering a acetonitrile solution of
the corresponding complex with hexane. The structures of 3a
and 3b are essentially the same and only 3a will be discussed in
detail. A view of 3a is shown in Fig. 7; selected bond distances
and angles are listed for both 3a and 3b in Table 5. The structure
of 3a consists of a cobalt atom surrounded by a single chelating
tridentate 2,6-dimethylphenyl-substituted dien ligand and two
monodentate chloride ligands. The five-coordinate geometry
can be best described as distorted trigonal bipyramidal with
N(3) and N(1) forming the axial sites and N(1), Cl(1) and
Cl(2) the equatorial sites. The dien ligand adopts, unlike in 1a
and 1b, a mer configuration with the N(1)–Co(1)–N(3) angle
being 160.08(7)° and the deviation from planarity displayed
by the N(1)–N(2)–N(3)–Co(1) plane minimal [max. deviation:
Co(1) 0.063 Å]. Each terminal nitrogen atom of the dien ligand
possesses an aryl substituent which are positioned mutually
cis with both ipso-carbon atoms [C(11) and C(1)] ca. 0.68 Å
below the N(1)–N(2)–N(3)–Co(1) plane and on the same
side as Cl(1). The ortho-methyl groups of each aryl group sit
above and below the N(1)–N(2)–N(3)–Co(1) plane [deviation
of o-Me groups from plane: C(6A) 1.341(1), C(16A) 1.799(1),
C(2A) 2.885(1), C(12A) 2.919(1) Å] with the two located above
[C(6A) and C(16A)] pointing in a similar direction to Cl(2).
There is a difference in the Co–N bond lengths with the central
N–Co distance being noticeably shorter than the terminal N–Co
bond lengths [Co(1)–N(2) 2.082(2) Å vs. Co(1)–N(1) 2.219(3),
Co(1)–N(3) 2.243(2) Å]. There is also a difference observed for
the Co–Cl distances with that involving Cl(2) being longer than
that to Cl(1) [Co(1)–Cl(2) 2.350(1) Å vs. Co(1)–Cl(1) 2.269(1) Å].
The Cl–Co–Cl angle at 114.91(4)° falls in the same range as those
observed for the bis(imino)pyridine-containing cobalt dichloride
complexes.7 As with the N-picolylen-systems (1 and 2), 3 also
has two chiral centres, in this case located on the termini of the
N,N,N-chelate at N(1) and N(3). Both 3a and 3b crystallise with
the relative configurations of the chiral centres being distinct.
The FAB mass spectrum of 3a and 3b both display molecular
ion peaks and peaks corresponding to the loss of chloride
ligands; no evidence for dimerised products is observed.
In the IR spectrum the m(N–H) absorption bands are seen
at ca. 3250 cm−1 and shifted to a lower wavenumber than that
in the corresponding free ligands. The magnetic susceptibility
measurements for 3a and 3b reveal magnetic moments of ca. 3.95
lB (Evans balance at ambient temperature) which are indicative
of high spin configurations possessing three unpaired electrons.
The 1H NMR spectra of 3a and 3b exhibit characteristic broad
and paramagnetically shifted peaks but afforded no informative
information with respect to peak assignment.
No DFT calculations were performed on the relative stability
of the mer- and possible fac-isomers for 3, but it is likely that the
observed mer isomer is preferred on steric grounds. Similarly,
a mer structure is observed in the related diamido complex
[{(ArNCH2CH2)2NMe}ZrMe2] (Ar = 2,4,6-Me3C6H2); forma-
tion of the alkyl cation notably leads to a facially coordinated
species.1
(c) Ethylene oligomerisation
Allthecomplexesweretestedforoligomerisation/polymerisation
activity by treating them with 400 equivalents of MAO in toluene
under an ethylene pressure (1 bar) and ambient temperature. In
all cases oligomeric material was afforded; the results of the
tests are shown in Table 6. The most active systems contain
cobalt as the metal centre (1 and 3) with entry 1 the highest at
59 g mmol−1 h−1 bar−1. The iron systems (entries 2 and 3) display
much lower activities when compared to the corresponding
cobalt complexes and are ca. 5000 times less active than most
productive bis(imino)pyridine iron oligomerisation catalysts
(under similar conditions).2,3
The nature of the oligomeric material does show some
differences from that obtained using bis(imino)pyridine
catalysts. While the iron-based systems behave similarly giving
greater than 95% linear a-olefins (C6–C26), the cobalt systems
give mixtures of linear and branched products (C6–C26). Indeed,
extensive isomerisation is evident with terminal and internal
olefins present along with vinylidenes, R1R2CCH2, and small
amounts of trisubstituted alkenes, R1R2CCHR3 (Fig. 8).
For both the iron and cobalt systems a coordinative-insertion
mechanism seems likely followed by a b-H elimination. To
explain the branched components of the oligomers, insertion
of a terminal olefin into a Co–R bond seems likely, followed
by b-H elimination. For both the iron systems the oligomeric
distribution is found to follow a Schulz–Flory distribution for
both 2a and 2b with the Schulz–Flory parameter a in both cases
being around 0.8.15
The observation that 1 and 2 result in oligomeric materials is
consistent with a rapid chain transfer process as a consequence
of there being insufficient steric bulk to prevent associative
displacement of the growing oligomeric chain. Indeed iron
complexes containing sterically bulky 2-iminobipyridine
ligands afford only short-chain oligomeric products.16 However,
for 3 which possess 2,6-substituted groups on both sides of the
Fig. 7 Molecular structure of 3a including the atom numbering
scheme. All hydrogen atoms except for H1, H2 and H3 have been
omitted for clarity.
3 2 3 6
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0

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Table 6 Ethylene oligomerisation with the iron(II) and cobalt(II) catalysts
Entrya
Pre-catalyst
Yieldb (%)
Activity/g mmol−1 h−1 bar−1
Internal
External
Branchedc (%)
Av. chain
olefinc (%)
olefinc (%)
length,c Cn
1
2
3
4
5
6
1a
1b
2a
2b
3a
3b
0.295
0.131
0.020
0.025
0.206
0.198
59
26
4
5
41
40
63.6
59.7
1.0
0.7
61.5
62.2
25.5
29.9
98.5
99.3
27.3
27.7
10.9
10.4
0.5
—
11.2
10.1
12.7
11.7
6.5
6.87
11.3
10.6
a General conditions: 1 bar ethylene Schlenk test carried out in toluene (40 cm3) at ambient temperature, using 4.0 mmol MAO (Al:M = 400:1),
0.01 mmol precatalyst, over 30 min. Reactions terminated by addition of dilute HCl. b Yield calculated based on GC using a C17 internal standard.
1
c Oligomerisation product percentages and average chain length, Cn calculated via integration of H NMR spectra.
The reagents, 2-(aminomethyl)pyridine, diethylenetriamine,
sodium tert-butoxide, the aryl halides, MAO (10% wt solution
in toluene) and the metal dichlorides were purchased from
Aldrich Chemical Co. and used without further purification.
rac-BINAP was purchased from Strem Chemical Co. Ethylene
gas (Grade 3.5) was supplied from BOC. The compounds,
Pd2(dba)3,20 and {(2,4,6-Me3C6H2)NHCH2CH2}2NH1b were
prepared according to previously reported procedures. All
other chemicals were obtained commercially and used without
further purification.
Fig. 8 Types of oligomeric product obtained using cobalt catalysts
(1a, 1b, 3a and 3b).
3.2 Synthesis of (H2NCH2CH2){(2-C5H4N)CH2}NH
molecule it might be expected that polymeric material would
The preparation was carried out based on a modification
of the literature report.21 2-Chloroethylamine monohydro-
chloride (12.0 g, 0.103 mol) was added in portions to an ice-
cooled solution of sodium hydroxide (51.5 cm3, 2 M NaOH,
0.103 mol). This was repeated and the contents of the two
flasks (0.206 mol) combined. The free 2-chloroethylamine
was then added dropwise to a rapidly stirred solution of 2-
(aminomethyl)pyridine (44.0 g, 0.407 mol) in absolute ethanol
(50 cm3) and refluxed for 2 h. The volatiles were removed by ro-
tary evaporation, the residue poured onto crushed ice and ex-
cess KOH pellets added. The dark orange–brown solution was
extracted with CHCl3 (3 × 100 cm3). The combined extracts
were dried over MgSO4, filtered and taken to dryness to give an
oily residue. Distillation of the residue under reduced pressure
(3.0 × 10−1 mmHg) gave unreacted 2-(aminomethyl)pyridine
(44 °C) as the first fraction followed by (H2NCH2CH2){(2-
C5H4N)CH2}NH (9.1 g, 26%) (84 °C) as a pale yellow liquid.
FAB mass spectrum, m/z 151 (M+). NMR (CDCl3, 293 K):
1H, d 8.7–7.0 (m, 4H, Py-H), 3.9 (s, 2H, PyCH2, 2H), 2.87 (m,
2H, CH2), 2.78 (s, 2H, CH2) and 1.6 (s, br, 3H, NH). 13C (1H
composite pulse decoupled), d 159.8 (s, C, Py), 149.0 (s, C, Py),
136.2 (s, C, Py), 122.2 (s, C, Py), 121.9 (s, C, Py), 55.2 (s, CH2),
50.8 (s, CH2) and 41.7 (s, CH2).
result; the explanation for this observation is unclear.
(d) Conclusions
A series of iron and cobalt chloride complexes (1, 2) contain-
ing aryl-substituted N-picolylen ligands have been prepared
and fully characterised. Both the experimental results and
calculations indicate that fac- and mer-structures are possible
for this ligand type with the energy difference between each
minimal. Moreover, interconversion between structures in
solution has been shown to be a facile process. Application
of 1 and 2 along with the aryl-substituted dien cobalt comp-
lexes (3) as catalysts for the oligomerisation of ethylene has
been demonstrated. While only modest activities result, both
linear and branched oligomeric materials are accessible. The
conformation of the tridentate nitrogen donor ligands in the
catalytically active species is uncertain and will be the subject
of further studies.
3
Experimental
3.1 General
All reactions were carried out under an atmosphere of dry,
oxygen-free nitrogen, using standard Schlenk techniques or
in a nitrogen purged glove box. Solvents were distilled under
nitrogen from appropriate drying agents and degassed prior
to use.17 The infrared spectra were recorded as Nujol mulls
between 0.5 mm NaCl plates on a Perkin Elmer 1600 series
or in the solid state using a Perkin Elmer Spectrun One FT-IR
spectrometer. The ES and the FAB mass spectra were recorded
using a micromass Quattra LC mass spectrometer and a Kratos
Concept spectrometer with methanol or NBA as the matrix re-
spectively. 1H and 13C NMR spectra were recorded on a Bruker
ARX spectrometer 250 or 300 MHz; chemical shifts (ppm) are
referred to the residual protic solvent peaks; relaxation times
(s1) are in milliseconds. GC mass spectrometry measurements
were obtained using a Perkin Elmer Autosystem XL chromato-
gram and a Perkin Elmer Turbo Mass Spectrometer. Magnetic
susceptibility studies were performed using an Evans Balance
(Johnson Matthey) at room temperature. The magnetic moment
was calculated following standard methods18 and corrections
for underlying diamagnetism were applied to data.19 Elemental
analyses were performed at the Department of Chemistry, Uni-
versity of North London by Dr S. Boyer.
3.3 Synthesis of (ArNHCH2CH2){(2-C5H4N)CH2}NH
(i) (Ar = 2,6-Me2C6H3). A Schlenk flask was charged
with (H2NCH2CH2){(2-C5H4N)CH2}NH (1.00 g, 6.62 mmol),
2-bromo-m-xylene (0.88 cm3, 1.23 g, 6.62 mmol), Pd2(dba)3
(0.030 g, 0.033 mmol, 0.005 equiv.), rac-BINAP (0.062 g,
0.099 mmol, 0.015 equiv.), NaOBut (1.91 g, 19.9 mmol, 3 equiv.)
and toluene (40 cm3). The reaction mixture was heated to
100 °C and stirred for a period of 4 days. After cooling to room
temperature, the solvent was removed under reduced pressure
to afford an oily residue. The residue was dissolved in diethyl
ether (30 cm3) and washed with water (3 × 30 cm3) and satu-
rated sodium chloride solution (3 × 30 cm3). The organic layer
was separated and dried over magnesium sulfate. The volatiles
were removed under reduced pressure and the residue left
under vacuum at 70 °C for 24 h to give 1.30 g (77%) of {(2,6-
Me2C6H3)HNCH2CH2}{(2-C5H4N)CH2}NH as a viscous oil.
ES mass spectrum, m/z 256 (M+ + H). NMR (CDCl3, 293 K):
1H, d 8.5–7.0 (m, 4H, Py-H), 6.88 (m, 2H, Ar-H), 6.70 (m, 1H,
Ar-H), 3.85 (s, 2H, PyCH2, 2H), 3.02 (t, 2H, 3J(HH) 5.7, CH2),
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0
3 2 3 7

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2.77 (t, 2H, CH2) and 2.20 (s, 6H, Meo). 13C (1H composite pulse
decoupled), d 160.3 (s, C, Py), 149.7 (s, C, Py), 146.8 (s, C, Ar),
136.9 (s, C, Py), 129.7 (s, C, Ar), 129.2 (s, C, Ar), 122.6 (s, C, Py),
122.4 (s, C, Py), 121.9 (s, C, Ar), 55.4 (s, CH2), 50.0 (s, CH2), 48.4
(s, CH2) and 19.0 (s, Meo).
ArMep), 12.5 (45.3 ms, Ar-CHm), −3.0 (52.6 ms, Hc), −11.8
(2.2 ms, ArMeo).
3.6 Synthesis of [{(ArNHCH2CH2)((2-C5H4N)CH2)NH}-
FeCl2]n (2)
(i) (n = 1,
Ar = 2,6-Me2C6H3).
A
solution
of
(ii) (Ar = 2,4,6-Me3C6H2). Using the same procedure
and molar quantities of reagents as above in 3.3(i) but with
2-bromomesitylene (1.00 cm3, 1.32 g, 6.62 mmol) as the aryl
bromide, {(2,4,6-Me3C6H2)HNCH2CH2}{(2-C5H4N)CH2}NH
(1.43 g, 80%) was isolated as a red oil. ES mass spectrum, m/z
{(2,6-Me2C6H3)HNCH2CH2}{(2-C5H4N)CH2}NH (0.100 g,
0.39 mmol) in n-butanol was introduced dropwise to a solution
of FeCl2 (0.050 g, 0.39 mmol) in n-butanol (5 cm3) at 90 °C to
form a yellowish green solution. After being stirred at 90 °C for
1 h, the reaction was allowed to cool to room temperature. The
reaction mixture was concentrated and hexane added to induce
precipitation of the product as a yellow solid. The suspension
was stirred overnight, filtered, washed with hexane (2 × 30 cm3)
and dried under reduced pressure to afford 0.115 g (77%) of 2a
as a yellow–brown powder. Layering of an acetonitrile solution
of 2a with hexane gave golden crystals on prolonged stand-
1
270 (M+ + H). NMR (CDCl3, 293 K): H, d 8.5–7.1 (m, 4H,
Py-H), 6.72 (s, 2H, Ar-H), 3.86 (s, 2H, PyCH2), 2.98 (t, 2H,
3J(HH) 6.0, CH2), 2.89 (t, 2H, CH2), 2.29 (s, 6H, Meo) and 2.21
(s, 3H, Mep). 13C (1H composite pulse decoupled), d 160.3 (s, C,
Py), 149.7 (s, C, Py), 144.1 (s, C, Ar), 136.7 (s, C, Py), 131.4 (s, C,
Py), 130.0 (s, C, Ar), 129.4 (s, C, Ar), 122.6 (s, C, Py), 122.4 (s,
C, Ar), 55.5 (s, CH2), 50.0 (s, CH2), 48.7 (s, CH2), 20.9 (s, Mep)
and 18.8 (s, Meo).
1
ing. H NMR (acetonitrile-d3, 293 K): d 130.4 (poor data set,
65.6 ms, Ha), 124.1 (3.8 ms, NH), 104.9 (0.96 ms, CH2), 80.9
(0.73 ms, CH2), 62.9 (0.9 ms, CH2), 58.8 (16.4 ms, Hb), 57.4
(14.6 ms, Hb), 15.8 (37.1 ms, Hc), 12.3 (34.2 ms, Ar-CHm), 6.6
(2.0 ms, ArMeo), −5.4 (poor data set, 143 ms, Ar-CHp), −15.0
(15.3 ms, NH).
3.4 Synthesis of {(2,6-Me2C6H3)NHCH2CH2}2NH
A Schlenk flask was charged with (H2NCH2CH2)2NH (1.06 g,
10.3 mmol), 2-bromo-m-xylene (2.74 cm3, 3.81 g, 20.6 mmol),
Pd2(dba)3 (0.047 g, 0.052 mmol, 0.005 equiv.), rac-BINAP
(0.096 g, 0.155 mmol, 0.015 equiv.), NaOBut (2.97 g, 30.9 mmol)
and toluene (40 cm3). The reaction mixture was heated to
100 °C and stirred for a period of 4 days. After cooling to
room temperature, the solvent was removed under reduced
pressure to afford an oily residue. The residue was dissolved in
diethyl ether (30 cm3) and washed with water (3 × 30 cm3) and
saturated sodium chloride solution (3 × 30 cm3). The organic
layer was separated and dried over magnesium sulfate. The
solvent was removed under reduced pressure and the residue
left under vacuum at 70 °C for 24 h to give 2.46 g (77%) of
{(2,6-Me2C6H3)HNCH2CH2}2NH as a viscous oil. ES mass
spectrum, m/z 312 (M+ + H). IR (cm−1): 3358 (NH, medium).
NMR (CDCl3, 293 K): 1H NMR (CDCl3): d 6.89 (d, 4H, 3J(HH)
7.3, Ar-Hm), 6.72 (t, 2H, Ar-Hp), 3.00 (t, 4H, 3J(HH) 6.0, CH2),
2.76 (t, 4H, CH2) and 2.22 (s, 12H, Meo). 13C (1H composite pulse
decoupled), d 146.4 (s, C, Ar), 129.4 (s, C, Ar), 128.9 (s, C, Ar),
121.8 (s, C, Ar), 50.1 (s, CH2), 48.3 (s, CH2) and 18.7 (s, Meo).
(ii) (n = 2, Ar = 2,4,6-Me3C6H2). Using the same procedure
and molar quantities of reagents as above in 3.6(i) using {(2,4,6-
Me3C6H2)HNCH2CH2}{(2-C5H4N)CH2}NH and FeCl2, gave
0.107 g (80%) of 2b as a yellow–brown powder. Layering of
an acetonitrile solution of 2b with hexane gave golden crys-
1
tals on prolonged standing. H NMR (acetonitrile-d3, 293 K):
d 129.6 (0.9 ms, Ha), 120.0 (1.9 ms, NH), 108.1 (1.7 ms, CH2),
82.4 (1.1 ms, CH2), 63.9 (0.7 ms, CH2), 58.6 (13.2 ms, Hb), 56.6
(11.2 ms, Hb), 16.8 (90.3 ms, Hc), 15.7 (29.1 ms, ArMep), 11.6
(27.8 ms, Ar-CHm), 7.4 (2.5 ms, ArMeo), −12.7 (4.0 ms, NH).
3.7 Synthesis of [{(ArNHCH2CH2)2NH}CoCl2] (3)
(i) Ar = 2,6-Me2C6H3.
A solution of {(2,6-Me2C6H3)-
HNCH2CH2}2NH (0.100 g, 0.32 mmol) in n-butanol was
added dropwise to a solution of CoCl2 (0.042 g, 0.32 mmol) in
n-butanol (5 cm3) at 90 °C to yield a green solution. After being
stirred at 90 °C for 1 h, the reaction was allowed to cool to room
temperature. The reaction mixture was concentrated and hex-
ane added to induce precipitation of the product as a pale blue
solid. The suspension was stirred overnight, filtered, washed
with hexane (2 × 30 cm3) and dried under reduced pressure to
afford 0.121 g (80%) of 3a as a pale blue solid. Layering of an
acetonitrile solution of 3a with hexane gave pale blue crystals of
on prolonged standing.
3.5 Synthesis of [{(ArNHCH2CH2)((2-C5H4N)CH2)-
NH}CoCl2] (1)
(i) (Ar = 2,6-Me2C6H3). A solution of {(2,6-Me2C6H3)-
HNCH2CH2}{(2-C5H4N)CH2}NH (0.100 g, 0.39 mmol) in
n-butanol was introduced dropwise to a solution of CoCl2
(0.051 g, 0.39 mmol) in n-butanol (5 cm3) at 90 °C to form
a green solution. After being stirred at 90 °C for 1 h, the reaction
was allowed to cool to room temperature. The reaction mixture
was concentrated and hexane added to induce precipitation of
the product as a pale blue solid. The suspension was stirred
overnight, filtered, washed with hexane (2 × 30 cm3) and dried
under reduced pressure to afford 0.121 g (80%) of 1a as a pale
blue powder. Layering of an acetonitrile solution of 1a with
(ii) Ar = 2,4,6-Me3C6H2. Using the same procedure and
molar quantities of reagents as above in 3.7(i) using {(2,4,6-
Me3C6H2)HNCH2CH2}2NH and CoCl2, gave 0.112 g (75%) of 3b
as a pale blue powder. Layering of an acetonitrile solution of 3b
with hexane gave pale blue crystals of on prolonged standing.
1
3.8 Ethylene oligomerisation
hexane gave blue crystals of 1a on prolonged standing. H
NMR (acetonitrile-d3): d 113.8 (4.1 ms, Ha), 110.1 (1.0 ms, NH),
97.0 (0.8 ms, CH2), 87.3 (1.1 ms, CH2), 45.7 (15.9 ms, Hb), 42.5
(25.9 ms, Hb), 13.5 (2.9 ms, CH2), 11.8 (43.2 ms, Ar-CHm), −3.6
(poor data set, 52.8 ms, Hc), −9.1 (Ar-CHp), −14.1 (poor data
set, 5.3 ms, ArMeo), −40.0 (NH).
The precatalyst (1–3) (0.01 mmol) was added to a Schlenk tube,
dissolved or suspended in toluene (40 ml) and MAO (4.0 mmol,
400 equiv.) introduced. The tube was purged with ethylene and
the contents stirred under 1 bar ethylene at room temperature for
the duration of the test. After 0.5 h the test was terminated by the
addition of dilute aqueous hydrogen chloride. The organic phase
was separated, analysed by GC and then the solvent removed by
distillation and the residue analysed by NMR spectroscopy.
(ii) (Ar = 2,4,6-Me3C6H2). Using the same procedure and
molar quantities of reagents as above in 3.5(i) using {(2,4,6-
Me3C6H2)HNCH2CH2}{(2-C5H4N)CH2}NH and CoCl2, gave
0.117 g (75%) of 1b as a pale blue powder. Layering of an
acetonitrile solution of 1b with hexane gave blue crystals on pro-
longed standing. 1H NMR (acetonitrile-d3): d 116.7 (9.3 ms, Ha),
104.6 (1.5 ms, NH), 90.1 (0.8 ms, CH2), 86.9 (0.9 ms, CH2), 46.6
(15.0 ms, Hb), 44.0 (23.2 ms, Hb), 16.4 (poor data set, 135.4 ms,
3.9 Density functional calculations
Quantum mechanical calculations have been carried out using
the Gaussian 98 package of programs.22 The density functional
theory (DFT) was applied, in particular the functional Becke’s
3 2 3 8
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0

View Article Online
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0
3 2 3 9

View Article Online
7 Cl–Co–Cl range (for [bis(imino)pyridine]CoCl2 complexes):
112.9–120.1°; (a) see refs. 2a and 3b; (b) T. M. Kooistra,
K. F. W. Hekking, Q. Knijnenburg, B. de Bruin, P. H. M. Budzelaar,
R. de Gelder, J. M. M. Smits and A. W. Gal, Eur. J. Inorg. Chem.,
2003, 648; (c) Y. Chen, C. Qian and J. Sun, Organometallics, 2003,
22, 1231; (d) C. Bianchini, G. Mantovani, A. Meli, F. Migliacci,
F. Zanobini, F. Laschi and A. Sommazzi, Eur. J. Inorg. Chem., 2003,
1620.
8 Cl–Co–Cl range (general): 101.8–134.4°; (a) see ref. 7b;
(b) N. di Vaira and P. L. Orioli, Inorg. Chem., 1969, 8, 2729;
(c) Z. Dori, R. Eisenberg and H. B. Gray, Inorg. Chem., 1967, 6, 483;
(d) M. Gerloch, J. Chem. Soc. A, 1966, 1317; (e) S. J. Shieh, C.-C.
Chou, G.-H. Lee, C.-C. Wang and S.-M. Peng, Angew. Chem., Int.
Ed. Engl., 1997, 36, 56; (f) S.-C. Sheu, M.-J. Tien, M.-C. Cheng,
T.-I. Ho, S. M. Peng and Y.-C. Lin, J. Chem. Soc., Dalton Trans.,
1995, 3503.
three-parameter hybrid exchange method combined with LYP
correlation functional (B3LYP).23 The method was used in its
unrestricted implementation.
The quasi-relativistic effective core potential (ECP)
LANL2DZ was used for the metal atoms (Co and Fe).24 The
basis set for both atoms is the valence double-f contraction
associated to this ECP.22,24 The valence double-f with polarisa-
tion 6–31G(d)25,26 basis was used for N and Cl and the valence
double-f 6–31G for C and H.25 In all cases, the spin contamina-
tion, evaluated from the computed value of S2, was found to be
small.
3.10 Crystallography
Data for 1a, 1b, 2a and 2b were collected on a Bruker APEX
2000 CCD diffractometer, data for 3a and 3b were collected on a
Bruker P4 diffractometer. Details of data collection, refinement
and crystal data are listed in Table 7. The data were corrected
for Lorentz and polarisation effects and empirical absorption
corrections applied. Structure solution by Patterson methods
and structure refinement on F2 employed SHELXTL version
6.10.27,28 Hydrogen atoms were included in calculated positions
(C–H = 0.96 Å) riding on the bonded atom with isotropic
displacement parameters set to 1.5Ueq(C) for methyl H atoms
and 1.2Ueq(C) for all other H atoms. All non H atoms were
refined with anisotropic displacement parameters.
9 Cl–Fe–Cl range (for [bis(imino)pyridine]FeCl2 complexes):
106.9–118.3°; (a) see refs. 2, 3 and 7c; (b) Y. Chen, R. Chen, C. Qian,
Y. Dang and J. Sun, Organometallics, 2003, 22, 4312.
10 (a) M. Ito, Y. Takita, K. Sakai and T. Tubomura, Chem. Lett.,
1998, 1185; (b) E. S. Raper, A. Miller, T. Glowiak and M. Kubiak,
Transition Met. Chem., 1989, 14, 319; (c) D. A. Handley, P. B.
Hitchcock, T.-H. Lee and G. J. Leigh, Inorg. Chim. Acta, 2001, 314,
14; (d) S. Kasselouri, A. Garoufis, S. P. Perlepes, F. Lutz, R. Bau,
S. Gourbatsis and N. Hadjiliadis, Polyhedron, 1998, 17, 1281;
(e) V. C. Gibson, R. K. O’Reilly, D. F. Wass, A. J. P. White and
D. J. Williams, Dalton Trans., 2003, 2824.
11 C. J. Davies, A. Harrison and G. A. Solan, unpublished results.
12 D. Mandon, A. Machkour, S. Goetz and R. Welter, Inorg. Chem.,
2002, 41, 5364.
13 H. C. S. Clark, F. G. N. Cloke, P. B. Hitchcock, J. B. Love and
A. P. Wainwright, J. Organomet. Chem., 1995, 501, 333.
14 J. D. Maréchal, G. Barea, F. Maseras, A. Llenos, L. Mouawad and
D. Perahia, J. Comput. Chem., 1999, 21, 283.
CCDC reference numbers 243370–243375.
Seehttp://www.rsc.org/suppdata/dt/b4/b409827g/forcrystallo-
graphic data in CIF or other electronic format.
15 (a) P. J. Flory, J. Am. Chem. Soc., 1940, 62, 1561; (b) G. V. Schulz, Z.
Phys. Chem., B, 1935, 30, 379; (c) G. V. Schulz, Z. Phys. Chem., B,
1939, 43, 25.
16 G. J. P. Britovsek, S. P. D. Baugh, O. Hoarau, V. C. Gibson,
D. F. Wass, A. J. P. White and D. J. Williams, Inorg. Chim. Acta,
2003, 345, 279.
17 W. L. F. Armarego and D. D. Perrin, Purification of Laboratory
Chemicals, Butterworth–Heinemann, 4th edn., 1996.
18 F. E. Mabbs and D. J. Machin, Magnetism and Transition Metal
Complexes, Chapman and Hall, London, 1973.
Acknowledgements
We thank the EPSRC (to C. J. D.), ExxonMobil (to C. J. D.) and
the Nuffield Foundation for an Undergraduate Summer Bursary
(to S. J. H.) for financial assistance. Financial and equipment
support from the Department of Chemistry at the University
of Leicester and the Royal Society are gratefully acknowledged.
Johnson Matthey PLC are thanked for their loan of palladium
chloride. Finally, Dr Feliu Maseras (ICIQ) and Professor
Michael Sutcliffe (Leicester) are sincerely acknowledged for
their valuable advice.
19 C. J. O’Connor, Prog. Inorg. Chem., 1982, 29, 203; Handbook of
Chemistry and Physics, ed. R. C. Weast, CRC Press, Boca Raton,
FL, 70th edn., 1990, p. E134.
20 T. Ukai, H. Kawazura, Y. Ishii, J. J. Bonnett and J. A. Ibers, J.
Organomet. Chem., 1974, 65, 253.
21 G. Riggio, W. H. Hopff, A. A. Hofmann and P. G. Waser, Helv.
Chim. Acta., 1980, 63, 488.
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3 2 4 0
D a l t o n T r a n s . , 2 0 0 4 , 3 2 3 1 – 3 2 4 0