Functionalised dien ligands of the type (ArNHCH2CH 2)2NR [R = Me, (2-C5H4N)CH 2] and their complexes with iron and cobalt halides

Article abstract of DOI:10.1016/j.poly.2005.06.005

The alkylation of (ArHNCH₂CH₂)₂NH with RX [RX = MeI, (2-C₅H₄N)CH₂Cl] under basic conditions gives (ArHNCH₂CH₂)₂NMe (Ar = 2,6-Me₂C₆H₃ L1a, 2,4-Me₂C ₆H₃ L1b) and (ArHNCH₂CH₂) ₂{(2-C₅H₄N)CH₂}N (Ar = 2,4,6-Me ₃C₆H₂ L2a, 2,4-Me₂C ₆H₃ L2b) in moderate yield, respectively. Alternatively, L1a and L1b can be accessed by the arylation (with Ar-Br) of (H ₂NCH₂CH₂)₂NMe in the presence of a catalytic quantity of Pd₂(dba)₃. Treatment of L1 with CoCl₂ in n-BuOH gave high-spin [{(ArHNCH₂CH ₂)₂NMe}CoCl₂] (Ar = 2,6-Me₂C ₆H₃ 1a, 2,4-Me₂C₆H₃ 1b) in good yield; no reaction occurred with FeCl₂. The molecular structure of 1a reveals a distorted trigonal bipyramidal geometry with the L1a adopting a mer-configuration. Reaction of L2 with MCl₂ affords the cobalt and iron complexes, [{ArNHCH₂CH₂} ₂{(2-C₅H₄N)CH₂}NMCl₂] (M = Co, Ar = 2,4,6-Me₃C₆H₂ 2a, 2,4-Me ₂C₆H₃ 2b; M = Fe, Ar = 2,4,6-Me ₃C₆H₂ 3a, 2,4-Me₂C₆H ₃ 3b); the octahedral frameworks in 2a and 3a are found to be considerably distorted with one of the two M-N(mesityl-substituted) distances noticeably elongated [M-N 2.597(4)-2.795(2) ?]; no such inequivalence is observed in solution at room temperature. On activation with methylaluminoxane, complexes 1a and 1b display some activity for the oligomerisation of ethylene.

Full text of DOI:10.1016/j.poly.2005.06.005

Polyhedron 24 (2005) 2017–2026
www.elsevier.com/locate/poly
Functionalised dien ligands of the type
(ArNHCH2CH2)2NR [R = Me, (2-C5H4N)CH2] and their
complexes with iron and cobalt halides
*
Christopher J. Davies, Stephen J. Hilton, Gregory A. Solan ,
Wesley Stannard, John Fawcett
Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK
Received 24 April 2005; accepted 3 June 2005
Available online 19 July 2005
Abstract
The alkylation of (ArHNCH2CH2)2NH with RX [RX = MeI, (2-C5H4N)CH2Cl] under basic conditions gives (ArHNCH2CH2)2-
NMe (Ar = 2,6-Me2C6H3 L1a, 2,4-Me2C6H3 L1b) and (ArHNCH2CH2)2{(2-C5H4N)CH2}N (Ar = 2,4,6-Me3C6H2 L2a, 2,4-
Me2C6H3 L2b) in moderate yield, respectively. Alternatively, L1a and L1b can be accessed by the arylation (with Ar–Br) of
(H2NCH2CH2)2NMe in the presence of a catalytic quantity of Pd2(dba)3. Treatment of L1 with CoCl2 in n-BuOH gave high-spin
[{(ArHNCH2CH2)2NMe}CoCl2] (Ar = 2,6-Me2C6H3 1a, 2,4-Me2C6H3 1b) in good yield; no reaction occurred with FeCl2. The
molecular structure of 1a reveals a distorted trigonal bipyramidal geometry with the L1a adopting a mer-configuration. Reaction
of L2 with MCl2 affords the cobalt and iron complexes, [{ArNHCH2CH2}2{(2-C5H4N)CH2}NMCl2] (M = Co, Ar = 2,4,6-
Me3C6H2 2a, 2,4-Me2C6H3 2b; M = Fe, Ar = 2,4,6-Me3C6H2 3a, 2,4-Me2C6H3 3b); the octahedral frameworks in 2a and 3a are
found to be considerably distorted with one of the two M-N(mesityl-substituted) distances noticeably elongated [M-N 2.597(4)–
˚
2.795(2) A]; no such inequivalence is observed in solution at room temperature. On activation with methylaluminoxane, complexes
1a and 1b display some activity for the oligomerisation of ethylene.
ꢀ 2005 Published by Elsevier Ltd.
Keywords: Iron; Cobalt; Tridentate; Tetradentate; Nitrogen donor; Aryl-substituted
1. Introduction
tion and, in particular, towards the incorporation of
steric bulk has allowed access to a wide range of substi-
tuted dien compounds of the type, R2-dien (R = silyl [2],
aryl [3]) and R0R2-dien (R0 = R = silyl [2,4]; R0 = alkyl,
R = silyl [5]; R0 = vinyl, R = alkyl [6]; R0 = alkyl,
R = aryl [7]; R0 = picolyl, R = silyl [8]) (Fig. 1). In many
cases, ligand synthesis necessitates firstly the introduc-
tion of two R groups to the terminal nitrogen atoms
in dien to give R2-dien and then, in a second step, addi-
tion of R0 group at the central secondary amine to afford
R0R2-dien.
Dianionic ligands derived from functionalised diethy-
lenetriamines (dien) have been the subject of consider-
able interest in recent years due, in part, to the ability
of the tridentate diamido unit to act as an inert spectator
ligand for main group [1] and transition metals [2–8]
during a variety of chemical transformations. The ame-
nability of the dien manifold towards structural varia-
*
Corresponding author. Tel.: +44 116 252 2096; fax: +44 116 252
Recently, we have been interested in employing the
functionalised dien ligands as neutral supports for late
transition metals and have prepared a series of
3789.
E-mail addresses: gas8@leicester.ac.uk, gas8@le.ac.uk (G.A. So-
lan).
0277-5387/$ - see front matter ꢀ 2005 Published by Elsevier Ltd.
doi:10.1016/j.poly.2005.06.005

2018
C.J. Davies et al. / Polyhedron 24 (2005) 2017–2026
R
To circumvent this problem, we have employed a
R
palladium catalysed N-C(aryl) coupling reaction of
N-methyldiethylenetriamine (prepared from N-methyld-
iethanolamine [10]) with two equivalents of the corre-
sponding aryl bromide using experimental conditions
established by Buchwald and Hartwig [11]. Following
work-up L1a and L1b could be isolated as the sole prod-
uct in high yield (Scheme 2).
NH2
NH2
NH
NH
NH
NH
R
R
NH
NH
NR'
R'R2-dien
dien
R2-dien
Fig. 1. Diethylenetriamine and derivatives (R or R0 = alkyl, aryl, silyl
or a combination).
The picolyl-substituted ligands, (ArHNCH2CH2)2-
{(2-C5H4N)CH2}N (Ar = 2,4,6-Me3C6H2 L2a [12],
2,4-Me2C6H3 L2b) could be prepared in modest yield
from (ArHNCH2CH2)2NH (Ar = 2,4,6-Me3C6H2, 2,4-
Me2C6H3) by treating them with 2-picolyl chloride
hydrochloride in acetonitrile at 55 ꢁC in the presence
of potassium carbonate (Scheme 1). Following purifica-
tion on an alumina column, L2a and L2b could be iso-
lated as yellow oils. All the new ligands have been
Ar2-dien-supported metal halide complexes. Notably,
the cobalt-containing examples exhibit, on activation
with methylaluminoxane (MAO), some activity for the
oligomerisation of ethylene [9]. In this article we are con-
cerned with derivatising the central amine in Ar2-dien
with an alkyl group or with a potential donor group,
2-pyridylmethyl (2-picolyl), and examining the resultant
coordination chemistry with divalent iron and cobalt
halide precursors.
1
characterised by IR, H and 13C NMR spectroscopy,
mass spectrometry (see Section 4).
2.2. Synthesis of the complexes
The reaction of L1a and L1b with CoCl2 in n-
butanol at elevated temperatures gave complexes
2. Results and discussion
[{(ArHNCH2CH2)2NMe}CoCl2]
(Ar = 2,6-Me2C6H3
2.1. Synthesis of the ligands
1a, 2,4-Me2C6H3 1b) in high yield (Scheme 3), respec-
tively. The corresponding reactions of L1 with FeCl2
in n-butanol at elevated temperature or with
FeCl2(THF)1.5 in tetrahydrofuran at ambient tempera-
ture gave only unreacted starting materials. Complexes
1a and 1b have been characterised by FAB mass spec-
trometry, infrared spectroscopy, magnetic susceptibility
and by elemental analysis (see Table 1). In addition, a
crystal of 1a has been the subject of a single crystal
X-ray diffraction study.
The ligands, (ArHNCH2CH2)2NMe (Ar = 2,6-
Me2C6H3 L1a, 2,4-Me2C6H3 L1b), could be prepared
in modest yield by treating (ArHNCH2CH2)2NH with
MeI under conditions established by Schrock et al. for
the preparation of (MesHNCH2CH2)2NMe [7a]. How-
ever, we have found this approach for the synthesis of
L1a and L1b to be hampered by the ready formation
of ammonium salts of the type ((ArHNCH2CH2)2-
NMe2)Iꢀ (Scheme 1).
Ar
Ar
NH
NH
NH
NH
Ar
Ar
(i)
+
-
NMe
I
NMe
L1a Ar = 2,6-Me C H
6 3
2
Ar
2
NH
NH
Ar
L1b Ar = 2,4-Me C H
2
6 3
NH
Ar
Ar
N
NH
NH
Ar
NH
NH
Ar
(ii)
N
N
+
N
N
-
Cl
L2a Ar = 2,4,6-Me C H
6 2
3
L2b Ar = 2,4-Me C H
2
6 3
Scheme 1. Reagents and conditions: (i) K2CO3, 0 ꢁC, MeI; (ii) K2CO3, 55 ꢁC, C5H4NCH2Cl Æ HCl.

C.J. Davies et al. / Polyhedron 24 (2005) 2017–2026
2019
Ar
OH
OH
NH2
NH
NH
Ar
(i), (ii), (iii)
(iv)
NH2
NMe
NMe
NMe
L1a Ar = 2,6-Me2C6H3 (75%)
L1b Ar = 2,4-Me2C6H3 (68%)
Scheme 2. Reagentsand conditions:(i) Phthalimide, heat [10]; (ii)H+; (iii)NaOH; (iv)Ar–Br, Pd2(dba)3 (0.5 mol%), rac-BINAP, NaOBut, toluene, heat.
Me
N
R1
R1
N
H
N
H
M
Cl
Cl
R2
R2
1a M = Co, R1 = Me, R2 = H
1b M = Co, R1 = H, R2 = Me
(i) or (ii, for M = Fe)
L1
(M = Fe)
No reaction
R1
R1
N
N
(i) or (ii, for 3a)
R2
N
H
M
N
H
L2
R2
Cl
Cl
2a M = Co, R1 = R2 = Me
2b M = Co, R1 = H, R2 = Me
3a M = Fe, R1 = R2 = Me
3b M = Fe, R1 = H, R2 = Me
Scheme 3. Reagents and conditions: (i) MCl2, n-BuOH, heat; (ii) FeCl2(THF)1.5, THF, room temperature.
Table 1
Spectroscopic and analytical data for the new complexes 1–3
Compound
l
eff(BM)a
v(N–H) (cmꢀ1 b
)
FAB mass spectrum
Microanalysis (%)c
C
H
N
1a
3.90
3286w
454 [M]+, 419 [M ꢀ Cl]+
55.65
(55.39)
7.02
(6.86)
9.11
(9.23)
1b
2a
4.01
3.80
3257w
3245w
454 [M]+, 419 [M ꢀ Cl]+
524 [M ꢀ Cl]+
60.13
(60.00)
58.59
6.94
(6.76)
6.11
10.14
(10.00)
10.30
2b
3a
3b
a
4.10
4.88
5.11
3190w
3209w
3233w
496 [M ꢀ Cl]+
521 [M ꢀ Cl]+
493 [M ꢀ Cl]+
(58.65)
60.11
(6.39)
6.79
(10.53)
10.09
(60.34)
59.12
(58.98)
(6.87)
6.51
(6.43)
(10.05)
10.81
(10.59)
Recorded on an Evans Balance at room temperature.
Recorded on a Perkin–Elmer Spectrum One FT-IR spectrometer on solid samples.
Calculated values are shown in parentheses.
b
c
Dark blue crystals of 1a suitable for the X-ray deter-
mination were grown by layering an acetonitrile solution
of the complex with hexane at ambient temperature. A
view of 1a is shown in Fig. 2; selected bond distances
and angles are listed in Table 2. The structure con-
sists of a cobalt centre surrounded by a tridentate

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C.J. Davies et al. / Polyhedron 24 (2005) 2017–2026
Fig. 2. Molecular structure of 1a including the atom numbering scheme. All hydrogen atoms except for H1 and H3 have been omitted for clarity.
˚
2.289(4) A]. The two Co–Cl bond distances are asym-
˚
metric with Co–Cl(2) being ca. 0.07 A longer than Co–
Table 2
˚
Selected bond distances (A) and angles (ꢁ) for 1a
Cl(1). The Cl(1)–Co(1)–Cl(2) bond angle of 118.72(6)ꢁ
falls in the mid-range for those found in related five-
coordinate cobalt(II) dichloride complexes [9,13].
Complex 1a has two chiral centres at N(1) and N(3)
and crystallises with the relative configuration being dis-
tinct. The structural features of 1a closely resemble those
observed for the related complexes [{(ArNHCH2CH2)2-
NH}CoCl2] (Ar = 2,6-Me2C6H3, 2,4, 6-Me3C6H2) [9].
The FAB mass spectrometric data for 1a and 1b re-
veal molecular ions peaks along with fragmentation
peaks corresponding to the loss of chloride ions; no
peaks are evident for dimeric species. In their IR spectra,
the t(N–H) absorption band is seen at ca. 3270 cmꢀ1
and is ca. 100 cmꢀ1 lower in wavenumber than in the
free-ligands (L1a and L1b). The room temperature mag-
netic susceptibility measurements (Evans Balance) for 1a
and 1b afforded magnetic moments of ca. 3.95 BM,
characteristic of high spin cobalt(II) configurations
(S = 3/2) containing three unpaired electrons. Attempts
to acquire assignable paramagnetically shifted 1H
NMR spectra in acetonitrile-d3 at room temperature
proved unsuccessful.
It is uncertain as to why a stable complex (under the
conditions employed) containing L1 cannot be isolated
with iron chloride. It is noteworthy that we have
also been similarly unsuccessful in isolating iron
complexes with the non-methylated counterpart of
L1, (ArHNCH2CH2)2NH [9]. Replacement of one
ArHNCH2CH2 arm in (ArHNCH2CH2)2NH with a
picolyl group has, however, afforded isolable complexes
with iron chloride [14]. It would appear that the p-accep-
tor capability of the pyridyl donor plays a key role in
complex stability.
Bond lengths
Co(1)–N(1)
Co(1)–N(2)
Co(1)–N(3)
Co(1)–Cl(1)
Co(1)–Cl(2)
2.274(4)
2.088(3)
2.289(4)
2.2472(16)
2.3136(15)
Bond angles
N(1)–Co(1)–N(2)
N(1)–Co(1)–N(3)
N(2)–Co(1)–N(3)
N(1)–Co(1)–Cl(1)
N(2)–Co(1)–Cl(1)
N(3)–Co(1)–Cl(1)
N(1)–Co(1)–Cl(2)
N(2)–Co(1)–Cl(2)
N(3)–Co(1)–Cl(2)
Cl(1)–Co(1)–Cl(2)
80.24(13)
156.94(12)
80.49(12)
100.49(10)
132.81(10)
101.88(9)
87.09(10)
108.46(10)
87.10(9)
118.72(6)
N,N,N-chelate and two terminal chloride ligands. The
geometry at the cobalt(II) centre may be best described
as distorted trigonal bipyramidal with the equatorial
plane defined by N(2), Cl(1) and Cl(2) [N(2)–Co(1)–
Cl(1) 132.81(10)ꢁ, N(2)–Co(1)–Cl(2) 108.46(10)ꢁ] and
the axial sites by N(1) and N(3) [N(1)–Co(1)–N(3)
156.94(12)ꢁ]. The N,N,N-chelate is bound in a meridio-
nal configuration and contains two five-membered che-
late rings, the bite angle for each being 80.24(13)ꢁ
[N(1)–Co(1)–N(2)] and 80.49(12)ꢁ [N(2)–Co(1)–N(3)].
The ortho-methyl groups of the N-aryl substituents are
positioned above and below the plane defined by
N(1)–N(2)–N(3)–Co(1) [max. deviation from plane:
˚
Co(1) 0.170 A] with C2A and C12A pointing in a similar
direction to Cl(2). There is a difference in the Co–N
bond lengths with the central Co–N being shorter than
the terminal Co–N bond lengths [Co(1)–N(2)
Interaction of L2a or L2b with MCl2 in n-butanol at
elevated temperatures gave complexes [{ArNHCH2-
˚
˚
2.088(3) A versus Co(1)–N(1) 2.274(4) A, Co(1)–N(3)

C.J. Davies et al. / Polyhedron 24 (2005) 2017–2026
2021
Table 3
CH2}2{(2-C5H4N)CH2}NMCl2] (M = Co, Ar = 2,4,6-
Me3C6H2 2a, 2,4-Me2C6H3 2b; M = Fe, Ar = 2,4,6-
Me3C6H2 3a, 2,4-Me2C6H3 3b) in good yield.
Complexes 3a and 3b can also be prepared from the
reaction of FeCl2(THF)1.5 with L2 in tetrahydrofuran
at room temperature (Scheme 1). Complexes 2 and 3
have been characterised by FAB mass spectrometry,
infrared spectroscopy, magnetic susceptibility and by
elemental analysis (see Table 1). In addition, crystals
of 2a Æ CH2Cl2 and 3a Æ MeCN have been the subject
of a single crystal X-ray diffraction study.
˚
Selected bond distances (A) and angles (ꢁ) for 2a Æ CH2Cl2 and
3a Æ MeCN
2a Æ CH2Cl2
(M = Co)
3a Æ MeCN
(M = Fe)
Bond lengths
M(1)–N(1)
M(1)–N(2)
M(1)–N(3)
M(1) ꢁ ꢁ ꢁ N(4)
M(1)–Cl(1)
M(1)–Cl(2)
2.217(2)
2.117(2)
2.202(2)
2.795(2)
2.3219(8)
2.4238(8)
2.248(4)
2.165(5)
2.319(4)
2.597(4)
2.3215(17)
2.480(2)
Bond angles
Pale blue crystals of 2a Æ CH2Cl2 and golden crystals
of 3a Æ MeCN suitable for X-ray determinations were
grown by layering dichloromethane and acetonitrile
solutions of the complexes with hexane at ambient tem-
perature, respectively. The molecular structures of 2a
and 3a are essentially the same and only 3a will be dis-
cussed in any detail. A view of 3a is shown in Fig. 3; se-
lected bond distances and angles for both complexes are
listed in Table 3.
N(1)–M(1)–N(2)
N(1)–M(1)–N(3)
N(2)–M(1)–N(3)
N(1)–M(1)–Cl(1)
N(2)–M(1)–Cl(1)
N(3)–M(1)–Cl(1)
N(1)–M(1)–Cl(2)
N(2)–M(1)–Cl(2)
N(3)–M(1)–Cl(2)
Cl(1)–M(1)–Cl(2)
78.38(9)
80.45(8)
109.98(8)
172.95(6)
94.59(6)
101.65(7)
91.70(6)
160.27(6)
84.71(6)
95.19(3)
77.89(18)
78.13(15)
104.89(16)
170.73(13)
93.23(14)
101.90(12)
92.44(13)
166.94(14)
81.31(12)
96.73(6)
The structure of 3a consists of a single iron centre
bound by an N,N,N,N-chelate and two monodentate
chloride ligands to form a geometry that can be best de-
scribed as a distorted octahedral. The pyridyl donor
[N(2)] is trans to Cl(2) and the tertiary amine N(1) is
trans to Cl(1) leaving the mesityl-substituted amines lo-
cated mutually trans. There is considerable variation in
the Fe–N bond lengths with the distance to the pyridyl
idyl donor, due to geometry constraints within the
ligand framework, is inclined more towards one aryl-
amine than the other with the result than an ortho-
methyl group [C(28)] hinders efficient coordination of
N(4). Unfortunately, single crystals of 2b and 3b, which
lack one o-Me group per aryl ring, could not be grown
in order to demonstrate this steric effect. Notably, in
[{(ArNHCH2CH2){(2-C5H4N)CH2}2N}FeCl2] (Ar = 2,
4-Me2C6H3, 2,6-Me3C6H2) effective coordination of
the aryl-amine arm occurs for the 2,4-Me2Ph derivative
but not for the 2,6-Me2Ph derivative [14]. The two
Fe–Cl bond distances are asymmetric with Fe–Cl(2)
˚
donor being the shortest [Fe(1)–N(2) 2.165(5) A] fol-
lowed by the distance to the tertiary amine [Fe(1)–
˚
N(1) 2.248(4) A]. Despite the same substitution pattern
˚
on N(3) and N(4), the Fe–N(4) [2.597(4) A] bond dis-
tance is significantly longer than that for Fe–N(3)
˚
˚
[2.319(4) A] and ca. 0.3 A longer than that found for
the corresponding distance in related ferrous complexes
[9,14]. Indeed in 2a this asymmetry is even more
˚
being ca. 0.16 A longer than Fe–Cl(1), presumably as
˚
dramatic [Co(1)–N(4) 2.795(2) A vs. Co(1)–N(3)
a consequence of the trans-coordinated pyridyl group.
The IR spectra of 2a and 3a both show broad
t(NH) absorption bands at ca. 3200 cmꢀ1 which, in
comparison with the free ligand L1a, are shifted to
˚
2.202(2) A] to the point where a weak interaction offers
a more suitable description. The origin of the elongation
of the M(1)–N(4) distance is likely to be steric; the pyr-
Fig. 3. Molecular structure of 3a including the atom numbering scheme. All hydrogen atoms except for H3 and H4 have been omitted for clarity.

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C.J. Davies et al. / Polyhedron 24 (2005) 2017–2026
lower wavenumber by ca. 100 cmꢀ1 (Table 1). Similar
shifts in wavenumber are observed for 2b and 3b.
The room temperature magnetic susceptibility measure-
ments for 2 and 3 indicate high spin behaviour with the
iron(II) complexes (2) displaying magnetic moments of
ca. 5.0 BM (consistent with four unpaired electrons)
and ca. 3.9 BM for the cobalt(II) complexes (consistent
with three unpaired electrons).
internal olefins, vinylidenes and trisubstituted olefins.
In contrast, 2 and 3 show scarcely any activity; it
would seem likely that the additional nitrogen donor
in the supporting ligand makes the metal centre too
electron rich.
3. Conclusions
Solution state studies performed on complexes 2a and
3a in acetonitrile-d3 at room temperature support their
In conclusion, a series of new aryl-substituted dien li-
gands (L1 and L2) containing a central tertiary amine
have been prepared and fully characterised. Tetraden-
tate coordination is possible for L2 in iron(II) and co-
balt(II) complexes; the effect of steric bulk on efficient
coordination is apparent. Coordination of L1 as a
tridentate ligand has only been observed in cobalt(II)
halide complexes. The L1-supported cobalt systems
show some activity as precatalysts for ethylene
oligomerisation.
1
paramagnetic nature with broad shifted H NMR spec-
tra in the range of ꢀ10.0 to 130.0 ppm (see Section 4).
Interpretation of the paramagnetic 1H NMR spectra
can be achieved by comparison of chemical shifts and
relaxation times (T1) to related metal(II) complexes such
as [{(ArNHCH2CH2}{(C5H4N)CH2}NH}MCl2] (M =
Fe, Co) [9] and to previously reported polypyridyl meta-
l(II) systems [15–17].
For 2a the protons of the coordinated pyridyl arm
display characteristic chemical shifts and relaxation
0
times [Ha, d = 97.0; Hb/Hb , d = 50.3/46.8 (T1 = 10.1
and 16.4 ms); Hc, d = 0.3 (T1 = 31.0 ms)]. The methylene
protons are not observed, possibly as a consequence of
the significant broadening of the spectrum. The aro-
matic region can be assigned as: Ar–Hm at d = 9.3
(T1 = 39.4 ms), ArMep at d = 11.5 (T1 = 135 ms) and Ar-
Meo at d = ꢀ4.8 (T1 = 2.8 ms). For 3a the Ha of the
coordinated pyridyl arm is shifted downfield the most
4. Experimental
4.1. 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 [18]. The infrared spec-
tra were recorded as Nujol mulls between 0.5 mm NaCl
plates or on a Perkin–Elmer 1600 series or in the solid
state using a Perkin–Elmer spectrum one FT-IR spec-
trometer The ES and the FAB mass spectra were re-
0
at d = 128.6, whilst Hb/b appear as sharp signals at
d = 53.6 and 52.1 (T1 = 13.1 and 11.1 ms) and Hc is
the most upfield at d = 18.2 (T1 = 42.3 ms). The methy-
lene protons are exceedingly broad and shifted down-
field at d ꢂ 115 and 35. The aromatic region can be
assigned as: ArMep at d = 13.3 (T1 = 40.5 ms), Ar–Hm
at d = 12.0 (T1 = 150 ms) and ArMeo at d = 8.7
(T1 = 3.1 ms).
It is noteworthy that, despite the inequivalence of the
aryl-amine arms in 2a and 3a in the solid state, their
behaviour in solution at ambient temperature reveals
signals (albeit rather broad) consistent with one type
of aryl group environment. Scheme 4 illustrates a series
of equilibria that could account for the apparent C2
symmetry in solution.
corded using
spectrometer and a Kratos Concept spectrometer with
methanol or NBA as the matrix respectively. H and
a
micromass Quattra LC mass
1
13C NMR spectra were recorded on a Bruker ARX spec-
trometer (250 or 300 MHz); chemical shifts (ppm) are
referred to the residual protic solvent peaks; relaxation
times (T1) are in seconds. Magnetic susceptibility studies
were performed using an Evans Balance (Johnson Mat-
they) at room temperature. The magnetic moment was
calculated following standard methods [19] and correc-
tions for underlying diamagnetism were applied to data
[20]. Elemental analyses were performed at the Depart-
ment of Chemistry, University of North London by
Dr S. Boyer.
Complexes 1a and 1b, on activation with MAO (300
eq.; conditions, 1 bar ethylene, room temperature, in
toluene), are modest catalysts for the oligomerisation
of ethylene, (ca. 45 g mmol/h/bar) giving a broad range
of linear and branched products including a-olefins,
N
N
N
N
N
N
N
H
M
N
H
N
H
N
H
M
N
H
M
N
H
Cl
Cl
Cl
Cl
Cl
Cl
Scheme 4. Possible interconversion occurring in solution for 2a or 3a.

C.J. Davies et al. / Polyhedron 24 (2005) 2017–2026
2023
The reagents, 2-picolyl chloride hydrochloride, so-
4.3. Synthesis of L2
dium t-butoxide, the aryl halides and the metal dichlo-
rides were purchased from Aldrich Chemical Co. and
used without further purification. rac-BINAP was pur-
chased from Strem Chemical Co. The compounds,
Pd2(dba)3 [21], (H2NCH2CH2)2NMe [10], FeCl2(THF)1.5
[22] and (ArNHCH2CH2)2NH (Ar = 2,4,6-Me3C6H2 [3],
2,4-Me2C6H3 [23]) were prepared according to previously
reported procedures. All other chemicals were obtained
commercially and used without further purification.
(a) L2a, Ar = 2,4,6-Me3C6H2: An oven dried
Schlenk flask was charged with [{(2,4,6-Me3C6H2)-
HNCH2CH2}2NH] (0.50 g, 1.54 mmol), 2-picolyl chlo-
ride hydrochloride (0.380 g, 2.31 mmol), K2CO3
(0.457 g, 4.62 mmol) and acetonitrile (40 ml). The reac-
tion mixture was heated to 55 ꢁC and stirred for a per-
iod of three days. After cooling to room temperature,
the solution was filtered and the solvent removed under
reduced pressure to afford an oily residue. The residue
was dissolved in diethyl ether (30 ml) and washed with
water (3 · 30 ml). The organic phases were combined
and concentrated on a rotary evaporator to give a
brown oil. The crude product was purified via alumina
column chromatography employing ethyl acetate and
hexane (1:4) as the eluting solvents to give {(2,4,6-
Me3C6H2)NHCH2-CH2}2{(2-C5H4N)CH2}N (L2a) as
4.2. Synthesis of L1
(a) L1a, Ar = 2,6-Me2C6H3: An oven-dried Schlenk
flask equipped with a magnetic stir bar was evacu-
ated and backfilled with nitrogen. The flask was charged
with (H2NCH2CH2)2NMe (1.20 g, 10.3 mmol), 2-bro-
mo-m-xylene (2.74 ml, 3.81 g, 20.6 mmol), Pd2(dba)3
(0.047 g, 0.052 mmol, 0.005 eq.), rac-BINAP (0.096 g,
0.155 mmol, 0.015 eq.), NaOBut (2.97 g, 30.9 mmol)
and toluene (40 ml). The reaction mixture was heated
at reflux and stirred for a period of 4 days. After cooling
to room temperature, the solvent was removed under re-
duced pressure to afford an oily residue. The residue was
dissolved in diethyl ether (30 ml) and washed with water
(3 · 30 ml) and saturated NaCl solution (3 · 30 ml). The
organic layer was separated and dried over MgSO4.
The solvent was removed under reduced pressure and
the residue left under vacuum at 50 ꢁC for 24 h to give
[{(2,6-Me2C6H3)HNCH2CH2}2NMe] (L1a) as a viscous
oil. Yield: 75% (2.50 g, 7.73 mmol). Compound L1a: ES
mass spectrum, m/z 326 (M+ + H). IR (cmꢀ1): 3357
(NH, medium). NMR (CDCl3, 293 K): 1H NMR, d
a
yellow oil. Yield: 31% (0.202 g, 0.48 mmol).
Compound L2a: ES mass spectrum: m/z 431
[M + H]+. IR (cmꢀ1): 3356 (N–H, medium), 1590
(C = Npyridine). NMR (CDCl3, 293 K): 1H NMR,
d 8.45 (dd, 1H, 3J(HH) 5.0, 4J(HH) 1.0, PyCH),
7.55 (dt, 1H, 3J(HH) 7.0, 4J(HH) 1.8, PyCH), 7.39
(d, 1H, 3J(HH) 7.9, PyCH), 7.07 (m, 1H, PyCH),
6.70 (s, 4H, ArCH), 3.80 (s, 2H, PyCH2), 3.22 (br s,
2H, N–H), 3.0 (t, 4H, CH2), 2.74 (t, 4H, 3J(HH)
6.0, CH2) and 2.13 (s, 18H, Me). 13C NMR (1H com-
posite pulse decoupled): d 159.4 (s, C, Py), 149.2
(s, C, Py), 143.7 (s, C, Ar), 136.4 (s, C, Py), 130.9
(s, C, Ar), 129.4 (s, C, Ar), 129.3 (s, C, Ar), 123.0
(s, C, Py), 122.1 (s, C, Py), 60.5 (s, PyCH2), 55.1
(s, CH2), 46.1 (s, CH2), 20.6 (s, Mep) and 18.5
(s, Meo).
3
6.90 (d, 4H, J(HH) 7.2, Ar-Hm), 6.74 (t, 2H, Ar-Hp),
3
(b) L2b, Ar = 2,4-Me2C6H3: Using the same proce-
dure and molar quantities of reagents as above in
4.3(a) employing [{(2,4-Me2C6H3)HNCH2CH2}2NH]
(0.49 g, 1.54 mmol), 2-picolyl chloride hydrochloride
0.380 g, 2.31 mmol), K2CO3 (0.457 g, 4.62 mmol)
gave {(2,4-Me3C6H3)NHCH2CH2}2{(2-C5H4N)CH2}-
3.03 (t, 4H, J(HH) 6.0, CH2), 2.55 (t, 4H, CH2), 2.21
(s, 12H, Meo) and 2.19 (s, 3H, N–Me). 13C (1H compos-
ite pulse decoupled), d 146.9 (s, C, Ar), 129.3 (s, C, Ar),
129.2 (s, C, Ar), 121.8 (s, C, Ar), 58.7 (s, CH2), 46.1 (s,
CH2), 41.7 (s, N–Me) and 19.1 (s, Meo).
(b) L1b, Ar = 2,4-Me2C6H3: Using the same proce-
dure and molar quantities of reagents as above in
4.2(a) employing 4-bromo-m-xylene (2.78 cm3, 3.81 g,
20.6 mmol) as the aryl bromide, [{(2,4-Me2C6H3)-
HNCH2CH2}2NMe] (L1b) was isolated as a viscous
red oil. Yield: 68% (2.27 g, 6.97 mmol). Compound
L1b: ES mass spectrum, m/z 326 (M+ + H). IR (cmꢀ1):
3347 (NH, medium). NMR (CDCl3, 293 K): 1H
N (L2b) as a yellow oil. Yield: 29% (0.184 g,
0.47 mmol). Compound L2b: ES mass spectrum: m/z
403 [M + H]+. IR (cmꢀ1): 3371 (N–H, medium).
NMR (CDCl3, 293 K):1H NMR, d 8.61 (dd, 1H,
3J(HH) 5.8, 4J(HH) 1.1, PyCH), 7.51 (dt, 1H,
3J(HH) 7.0, 4J(HH) 1.8, PyCH), 7.46 (d, 1H,3J(HH)
7.9, PyCH), 7.05 (m, 1H, PyCH), 6.90 (m, 4H, Ar–
H), 6.45 (d, 2H, 3J(HH) 8.1, Ar–H), 3.86 (s, 2H,
PyCH2), 3.55 (m, 4H, CH2), 3.20 (m, 4H, CH2),
2.12 (s, 6H, Mep) and 2.00 (s, 6H, Meo). 13C NMR
(1H composite pulse decoupled), d 160.2 (s, C, Py),
149.5 (s, C, Py), 143.9 (s, C, Ar), 136.4 (s, C, Py),
131.3 (s, C, Ar), 127.7 (s, C, Ar), 126.4 (s, C, Ar),
122.8 (s, C, Ar), 122.5 (s, C, Py), 122.3 (s, C, Py),
110.5 (s, C, Ar), 59.9 (s, PyCH2), 48.7 (s, CH2),
44.2 (s, CH2), 20.7 (s, Mep) and 17.9 (s, Meo).
3
NMR, d 6.82 (m, 4H, Ar–H), 6.45 (d, 2H, J(HH) 8.1,
Ar–H), 3.20 (t, 4H, 3J(HH) 6.0, CH2), 2.71 (t, 4H,
CH2), 2.14 (s, 6H, Meo), 2.05 (s, 6H, Mep) and 2.10 (s,
3H, N–Me). 13C (1H composite pulse decoupled), d
144.6 (s, C, Ar), 131.3 (s, C, Ar), 127.7 (s, C, Ar),
126.4 (s, Ar), 122.8 (s, C, Ar), 110.5 (s, C, Ar), 48.7 (s,
CH2), 44.2 (s, CH2), 41.8 (s, N-Me), 20.7 (s, Mep) and
17.9 (s, Meo).

2024
C.J. Davies et al. / Polyhedron 24 (2005) 2017–2026
4.4. Synthesis of (1)
and backfilled with nitrogen. The flask was charged with
FeCl2(THF)1.5 (0.108 g, 0.47 mmol) in THF (10 ml) and
a solution of L2a (0.200 g, 0.47 mmol) in THF (5 ml)
was introduced to form a yellow solution. After being
stirred at room temperature for 24 h, the reaction mix-
ture was concentrated and hexane added to induce pre-
cipitation of the product. The suspension was stirred
overnight, filtered, washed with hexane (2 · 30 ml) and
dried under reduced pressure to give [{(2,4,6-
Me2C6H2)NHCH2CH2)}2{(2-C5H4N)CH2}N}FeCl2]
(3a) as a pale yellow solid. Layering of an acetonitrile
solution of 3a with hexane gave 3a as golden crystals
suitable for a single crystal X-ray structure determina-
(a) 1a, Ar = 2,6-Me2C6H3: An oven-dried Schlenk
flask equipped with a magnetic stir bar was evacuated
and backfilled with nitrogen. The flask was charged with
CoCl2 (0.040 g, 0.32 mmol) in n-BuOH (5 ml) at 90 ꢁC
and a solution of L1a (0.105 g, 0.32 mmol) in n-BuOH
was introduced 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 concen-
trated and hexane added to induce precipitation of the
product. The suspension was stirred overnight, filtered,
washed with hexane (2 · 30 ml) and dried under reduced
pressure to give [{((2,6-Me2C6H3)NHCH2CH2)}2N-
Me}CoCl2] (1a) as a pale blue solid. Layering of an ace-
tonitrile solution of 1a with hexane gave 1a as pale blue
crystals suitable for a single crystal X-ray structure
determination. Yield: 75% (0.110 g, 0.24 mmol).
1
tion. Yield: 80% (0.212 g, 0.38 mmol). H NMR (aceto-
nitrile-d3, 293 K): d 128.6 (Ha), 115.0 (very broad, CH2),
0
0
53.6 (13.1 ms, Hb or Hb ), 52.1 (11.1 ms, Hb or Hb ), 35.0
(very broad, CH2), 18.2 (42.3 ms, Hc) 13.3 (40.5 ms, Ar–
Mep), 12.0 (150.0 ms, Ar–Hm), and 8.7 (3.1 ms, ArMeo).
(b) 3b, Ar = 2,4-Me2C6H3: An oven-dried Schlenk
flask equipped with a magnetic stir bar was evacuated
and backfilled with nitrogen. The flask was charged with
FeCl2 (0.019 g, 0.15 mmol) in n-BuOH (5 ml) and the
reaction stirred at 90 ꢁC until dissolution. L2b
(0.063 g, 0.15 mmol) in n-BuOH (2 ml) was added and
the reaction mixture stirred at 90 ꢁC for 20 min. Follow-
ing concentration of the reaction mixture hexane was
added to induce precipitation of the product. The sus-
pension was stirred overnight, filtered, washed with
hexane (2 · 30 ml) and dried under reduced pressure
to afford [{(2,4-Me2C6H3)NHCH2CH2)}2{(2-C5H4N)-
CH2}N}FeCl2] (2a) as a pale yellow solid. Yield: 65%
(0.053 g, 0.10 mmol).
(b) 1b, Ar = 2,4-Me2C6H3: Using the sameprocedure and
molar quantities of reagents as above in 4.4(a) employing
L1b (0.104 g, 0.32 mmol) and CoCl2 (0.042 g, 0.32 mmol),
gave [{((2,4-Me2C6H3)NHCH2CH2)}2NMe CoCl2] (1b) as
a pale blue solid. Yield: 71% (0.103 g, 0.23 mmol).
4.5. Synthesis of (2)
(a) 2a, Ar = 2,4,6-Me3C6H2: An oven-dried Schlenk
flask equipped with a magnetic stir bar was evacuated
and backfilled with nitrogen. The flask was charged with
CoCl2 (0.020 g, 0.15 mmol) in n-BuOH (5 ml) and the
reaction stirred at 90 ꢁC until dissolution. L2a (0.065 g,
0.15 mmol) in n-BuOH (2 ml) was added and the reaction
mixture stirred at 90 ꢁC for 20 min. Following concentra-
tion of the reaction mixture hexane was added to induce
precipitation of the product. The suspension was stirred
overnight, filtered, washed with hexane (2 · 30 ml) and
dried under reduced pressure to afford [{(2,4,6-Me2C6H2)-
NHCH2CH2)}2{(2- C5H4N)CH2}N}CoCl2] (2a) as a pale
blue solid. Layering of a acetonitrile solution of 2a with
hexane gave pale blue crystals suitable for a single crystal
X-ray diffraction study. Yield: 81% (0.068 g, 0.12 mmol).
1H NMR (acetonitrile-d3, 293 K): d 97.0 (Ha), 50.3 (10.1
4.7. Ethylene oligomerisation
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 stir-
red 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.
0
0
ms, Hb or Hb ), 46.8 (16.4 ms, Hb or Hb ), 11.5 (135 ms,
ArMep), 9.3 (39.4 ms, Ar–Hm), 0.31 (31.0 ms, Hc) and
ꢀ4.8 (2.8 ms, ArMeo).
(b) 2b, Ar = 2,4-Me2C6H3: Using the same procedure
and molar quantities of reagents as above in 4.5(a)
employing L2b (0.061 g, 0.15 mmol) and CoCl2
(0.020 g, 0.15 mmol), gave [{(2,4-Me2C6H3)-NHCH2-
CH2)}2{(2-C5H4N)CH2}N}CoCl2] (2b) as a pale blue
solid. Yield: 65% (0.052 g, 0.10 mmol).
4.8. Crystallography
Data for 1a and 3a were collected on a Bruker P4 dif-
fractometer while that for 2a on a Bruker APEX 2000
CCD diffractometer. Details of data collection, refine-
ment and crystal data are listed in Table 4. The data
were corrected for Lorentz and polarisation effects and
empirical absorption corrections applied. Structure solu-
tion by Patterson methods and structure refinement on
F2 employed SHELXTL version 6.10 [24,25]. Hydrogen
4.6. Synthesis of (3)
(a) 3a, Ar = 2,4,6-Me2C6H2: An oven-dried Schlenk
flask equipped with a magnetic stir bar was evacuated

C.J. Davies et al. / Polyhedron 24 (2005) 2017–2026
2025
Table 4
Crystallographic and data processing parameters for complexes 1a, 2a and 3a
Complex
1a
2a
3a
Formula
M
C21H31Cl2CoN3
455.32
C28H38Cl2CoN4 Æ CH2Cl2
645.38
C28H38Cl2FeN4 Æ CH3CN
596.41
Crystal size (mm)
Temperature (K)
Crystal system
Space group
Lattice parameters
0.52 · 0.33 · 0.14
200(2)
0.11 · 0.18 · 0.32
150(2)
triclinic
0.15 · 0.03 · 0.03
120(2)
triclinic
monoclinic
P2(1)/c
ꢀ
ꢀ
P1
P1
˚
a (A)
12.727(8)
13.796(8)
13.816(8)
90
7.3225(12)
15.150(3)
15.669(3)
114.669(3)
99.627(3)
97.162(3)
1520.2(4)
2
7.4106(15)
15.244(3)
15.311(3)
115.74(3)
97.86(3)
99.89(3)
1490.7(5)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
112.66(4)
90
3
˚
U (A )
2239(2)
4
Z
Dc (Mg mꢀ3
F(000)
l(Mo Ka) (mmꢀ1
Reflections collected
Independent reflections
Rint
)
1.351
956
1.410
674
1.333
632
)
1.016
4814
4377
0.942
9555
0.713
10326
4362
0.0241
349/0
5606
0.1691
343/0
0.0489
249/0
Parameters/restraints
Final R indices
I > 2r(I)
R1 = 0.0555,
wR2 = 0.1220
R1 = 0.0906,
wR2 = 0.1399
1.019
R1 = 0.0318,
wR2 = 0.0746
R1 = 0.0463,
wR2 = 0.0789
0.961
R1 = 0.0607,
wR2 = 0.0945
R1 = 0.2275,
wR2 = 0.1298
All data
Goodness of fit on F2 (all data)
0.870
P
P
P
P
2
2 1=2
2
2
2
˚
Data in common: graphite-monochromated Mo Ka radiation, k = 0.71073 A; R1 = iFoj ꢀ jFci/ jFoj, wR2 ¼ ½ wðF o ꢀ F c Þ = wðF o Þ ꢃ
,
1=2
P
2
2
wꢀ1 ¼ ½r2ðF oÞ þ ðaPÞ ꢃ; P ¼ ½maxðF o2; 0Þ þ 2ðF c Þꢃ=3, where a is a constant adjusted by the program; goodness of fit ¼ ½ ðF o ꢀ F c Þ2=ðn ꢀ pÞꢃ
2
2
2
where n is the number of reflections and p the number of parameters.
atoms were included in calculated positions (C–H =
˚
0.96 A) riding on the bonded atom with isotropic dis-
placement parameters set to 1.5 Ueq(C) for methyl H
atoms and 1.2 Ueq(C) for all other H atoms. All non-
H atoms were refined with anisotropic displacement
parameters.
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.
References
5. Supplementary data
´
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´
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