Probing the effect of binding site and metal centre variation in pentadentate oligopyridylimine-bearing bimetallic (Fe2, Co 2, Ni2) ethylene oligomerisation catalysts

Article abstract of DOI:10.1002/ejic.200800650

The symmetrical and unsymmetrical pentaaza 2,6-oligopyridylimines, 6,6″-[(2,6-iPr₂C₆H₃)N=CMe]2-2,2′: 6′,2″-C₁₅H₉N₃ (L1) and 6-[(2,6-iPr₂C₆H₃)N=CMe]-2,2′:6′,

Full text of DOI:10.1002/ejic.200800650

FULL PAPER
DOI: 10.1002/ejic.200800650
Probing the Effect of Binding Site and Metal Centre Variation in Pentadentate
Oligopyridylimine-Bearing Bimetallic (Fe2, Co2, Ni2) Ethylene Oligomerisation
Catalysts
Andrew P. Armitage,[a] Yohan D. M. Champouret,[a] Hubert Grigoli,[a]
Jérémie D. A. Pelletier,[a] Kuldip Singh,[a] and Gregory A. Solan*[a]
Keywords: Bis(imino)terpyridine / Iminoquaterpyridine / Diiron / Dicobalt / Dinickel / C2 Oligomerisation / α-Olefins
The symmetrical and unsymmetrical pentaaza 2,6-
oligopyridylimines, 6,6ЈЈ-[(2,6-iPr2C6H3)N=CMe]2-2,2Ј:6Ј,2ЈЈ-
Unexpectedly during crystallisation of 6 from acetonitrile, the
salt [(L2)Ni2Br2(µ-Br)(NCMe)2]2[NiBr4] (7) was obtained as
the only crystalline product. On activation with MAO (meth-
ylaluminoxane), 4–6 show only low activities for ethylene
oligomerisation (6/MAO Ͼ 5/MAO) or are inactive (4/MAO).
On the other hand, 1–3 are considerably more active (3/MAO
Ͼ 2/MAO Ͼ 1/MAO) with the most productive system, di-
nickel-based 3/MAO (450 gmmol–1 h–1 bar–1), yielding
methyl-branched waxes composed of mostly internal unsatu-
ration along with lower levels of α-olefins; conversely the di-
iron (1/MAO) and dicobalt (2/MAO) systems give uniquely
linear α-olefins. For purposes of comparison the synthesis,
structure and catalytic activity of mono-nickel [(6-{(2,6-
iPr2C6H3)N=CMe}-2,2Ј-C10H7N2)NiBr2] (8) are also reported.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
C15H9N3
(L1)
and
6-[(2,6-iPr2C6H3)N=CMe]-
2,2Ј:6Ј,2ЈЈ:6ЈЈ,2ЈЈЈ-C20H13N4 (L2), have been prepared in good
yield using a combination of palladium(0)-mediated cross-
coupling and condensation strategies. Treatment of L1 or L2
with two equivalents of MX2 in nBuOH at elevated tempera-
tures affords the paramagnetic bimetallic complexes [(L1)-
M2X4] [M = Fe, X = Cl (1); M = Co, X = Cl (2a); M = Co, X =
Br (2b); M = Ni, X = Br (3)] and [(L2)M2X4] [M = Fe, X = Cl
(4); M = Co, X = Cl (5a); M = Co, X = Br (5b); M = Ni, X = Br
(6)] in high yield, respectively. The molecular structures of 2a
along with the acetonitrile adduct of 5b, [5b(NCMe)], have
been determined and reveal that L1 and L2 compartmen-
talise the MX2 units into mixed pyridylimine/dipyridylimine
(2a) and pyridylimine/terpyridine [5b(NCMe)] binding sites.
e.g., 2,6-bis(imino)pyridines and 2,2Ј-dipyridyl-6-imines (B,
in Figure 1), have also started to emerge as compatible sup-
ports for iron(II)- and cobalt(II)-mediated oligomerisa-
Introduction
The application of metal-based oligomerisation catalysts
to promote the conversion of ethylene- to olefinic-contain-
ing short/medium chain hydrocarbons continues to be the
subject of considerable interest to both the academic and
industrial communities.[1] In particular, the production of
α-olefins (range: C4–C20) represents an important industrial
process due, in large measure, to the use that the resultant
oligomers have in the manufacture of detergents, plasti-
cisers and linear low-density polyethylene (LLDPE). A vari-
ety of different catalysts are currently used commercially
to mediate this transformation but arguably the most well-
known within the late-transition-metal arena is the SHOP
catalyst, a neutral nickel(II)-based catalyst bearing a
monoanionic P,O-chelate.[2,3] More recently, cationic nickel
catalysts based on a variety of neutral N,N-ligands such as
2-pyridylimines (A in Figure 1) have afforded highly active
oligomerisation catalysts that can operate at more modest
temperatures and pressures than their SHOP-type predeces-
sors.[4] 2-Pyridylimines and their more extended relatives,
[a] Department of Chemistry, University of Leicester,
University Road, Leicester LE1 7RH, UK
E-mail: gas8@leicester.ac.uk
Figure 1. Pyridylimine (A), dipyridylimine (B), bis(imino)terpyrid-
ine (L1) and iminoquaterpyridine (L2).
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tions.[5–8] For example, the [(B)FeCl2]/MAO catalyst is (metal = Fe, Ni, Zn) in the manner desired.[10a] This work
highly active for the conversion of ethylene to 1-hexene and therefore begins by extending the range of L1ketimine-sup-
1-octene.[8] A general feature of these pyridylimine-based ported complexes to include dicobalt species and then ex-
family of catalysts is the presence of a bulky N-aryl group plores the potential of L2 (R = Me, Ar = 2,6-iPr2C6H3) to
(e.g., 2,6-iPr2C6H3), this is considered important in influ- promote bimetallic assembly. Full details of MAO-activated
encing the activity of the catalyst and in some cases the oligomerisations are reported for bimetallic precatalysts
Schulz–Flory parameter α.[7]
based on L1 and L2.
In recent years we have been interested in developing
even more extended pyridylimine ligands and have reported
a straightforward synthetic route to generate a range of
symmetrical and unsymmetrical 2,6-oligopyridylimines,
ArN=RC(C5H3N)mCR=NAr or C5H4(C5H3N)nCR=NAr
(m = 2–5 or n = 2,3; R = H or Me; Ar = 2,6-iPr2C6H3).[9]
Results and Discussion
1. Ligand Synthesis
Both ligands 6,6ЈЈ-[(2,6-iPr2C6H3)N=CMe]2-2,2Ј:6Ј,2ЈЈ-
Depending on a variety of properties including the chain C15H9N3
(L1)
and
6-[(2,6-iPr2C6H3)N=CMe]-
length, these ligand frames are capable of housing one or 2,2Ј:6Ј,2ЈЈ:6ЈЈ,2ЈЈЈ-C20H13N4 (L2) can be prepared in good
two metal centres furnishing complexes of general composi- yield by the acid-catalysed condensation reaction of the cor-
tion [(oligopyridylimine)MxXy] (x = 1, 2; y = 2, 4).[10] responding carbonyl compound with 2,6-diisopropylaniline
Herein we are concerned with exploring the ethylene oligo- (as reagent and solvent) at 160–200 °C for 30 min. The car-
merisation potential of diiron(II), dicobalt(II) and dinickel- bonyl precursors have been prepared in a series of steps
(II) catalysts bearing an oligopyridylimine that is capable of from 2-(2-methyl-1,3-dioxolan-2-yl)-6-tributylstannyl-pyr-
accommodating the closely located metals in two distinct idine (Scheme 1) using literature (L1)[9] or slightly modified
binding sites (e.g., N,N-bidentate and N,N,N-tridentate). procedures (L2).
To this end we have targeted the pentaaza members as po-
Crystals of L2 suitable for an X-ray determination were
tential supports for two MX2 units (X = Cl, Br); see Fig- grown from a concentrated nitromethane solution. A view
ure 1, bis(imino)terpyridine L1 and iminoquaterpyridine of L2 is shown in Figure 2; selected bond lengths and angles
L2. In a previous study we have shown that only the diket- are given in Table 1. The molecular structure consists of a
imine (R = Me) derivative of L1 (with Ar = 2,6-iPr2C6H3) chain of four 2,6-linked pyridine rings containing one 2,6-
can readily facilitate the assembly of the two metal centres diisopropylphenyl-substituted imino group as a chain-end.
Scheme 1. Reagents and conditions: (i) 6,6ЈЈ-dibromo-2,2Ј;6Ј,2ЈЈ-terpyridine (0.5 equiv.), Pd(PPh3)4 (8 mol-%), toluene, 90 °C, 72 h; (ii)
HCl (4 ), 60 °C, 12 h; (iii) 2,6-iPr2C6H3NH2 (xs.), 160–200 °C, cat. H+; (iv) 6-bromo-2,2Ј;6Ј,2ЈЈ-terpyridine (1 equiv.), Pd(PPh3)4 (6 mol-
%), toluene, 90 °C, 72 h.
Figure 2. Molecular structure of L2 including a partial atom numbering scheme. All hydrogen atoms have been omitted for clarity.
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Bimetallic Ethylene Oligomerisation Catalysts
A mutually transoid conformation of the nitrogen atoms is 2. Synthesis of Complexes
observed throughout the pyridine backbone which is also
Complexes [(L1)Co2X4] (X = Cl 2a; X = Br 2b) and
extended to the imino unit in a fashion akin to that ob-
served for other 2,6-oligopyridylimines[9,10] as well as 2,6-
oligopyridines.[11] Some twisting is evident within the back-
bone of L2 which is most notable with regard to the chain-
end pyridine and its nearest neighbour [torsion angle N(1)–
C(5)–C(6)–N(2) 167.80°]. The C(21)–N(5) bond length of
the chain-end imine group [1.277(2) Å] is consistent with
double bond character while the Nimine-aryl group is in-
clined essentially perpendicularly to this unit [torsion angle
C(21)–N(5)–C(23)–C(24) 92.3°]. Some intermolecular π–π
stacking of the pyridine groups (closest contact: 3.708 Å) is
also evident.
[(L2)M2X4] (M = Fe, X = Cl 4; M = Co, X = Cl 5a; M =
Co, X = Br 5b; M = Ni, X = Br 6) have been prepared in
high yield from the reaction of L1 or L2 with two equiva-
lents of MX2 in nBuOH using conditions previously em-
ployed for the formation of [(L1)M2X4] (M = Fe, X = Cl 1;
M = Ni, X = Br 3) (Scheme 2).[10a] Complex 6 has also been
prepared by treating L2 with (DME)NiBr2 in a 1:2 molar
ratio in dichloromethane at room temperature. The new
complexes 2a, 2b and 4–6 have been characterised by a
combination of FAB mass spectrometry, IR spectroscopy,
elemental analysis and by magnetic measurements (see
Table 2 and experimental section). In addition, crystals of
2a and the acetonitrile adduct of 5b have been the subject
of single-crystal X-ray diffraction studies.
Table 1. Selected bond lengths [Å] and angles [°] for L2.
Bond lengths
Crystals of 2a suitable for the X-ray determination were
grown from a concentrated acetonitrile solution. A view of
2a is shown in Figure 3; selected bond lengths and angles
are listed in Table 3. The molecular structure reveals a bi-
metallic complex in which the two metal centres are sup-
ported on the same L1 ligand frame and each bound ter-
minally by two chloride ligands. One of the metal centres
[Co(2)] occupies a bidentate pyridylimine pocket while the
other [Co(1)] a tridentate dipyridylimine cavity so as to gen-
C(5)–C(6)
1.493(2)
1.490(2)
1.491(2)
1.495(2)
C(21)–N(5)
C(21)–C(22)
N(5)–C(23)
1.277(2)
1.501(3)
1.426(2)
C(10)–C(11)
C(15)–C(16)
C(20)–C(21)
Bond angles
C(22)–C(21)–N(5)
C(21)–N(5)–C(23)
124.88(17)
120.55(16)
C(20)–C(21)–N(5) 117.34(17)
As with L1,[9,10a] the spectroscopic properties of L2 sup- erate a tetrahedral geometry at Co(2) and a distorted trigo-
port its formulation. In the ES mass spectrum of L2 a peak nal bipyramidal geometry at Co(1) [τ = 0.67].[12] Within the
corresponding to the protonated form of the molecular ion ligand frame the chelating pyridylimine and dipyridylimine
is evident while in its IR spectrum a υ(C=N)imine band at moieties are both nearly planar, with each of the planes
1634 cm–1 is clearly visible. The H NMR spectrum reveals being disposed orthogonally to one another [torsion angle
1
a singlet for the imino methyl group at δ = 2.28; the imino N(3)–C(18)–C(19)–N(4) 90.1°] with the result that the metal
carbon is seen at δ = 166.1 in the 13C NMR spectrum.
centres are located 5.336 Å apart. For Co(1) the two Co(1)–
Scheme 2. Reagents and conditions: (i) MX2 (2 equiv.) [MX2 = FeCl2, CoCl2, CoBr2, (DME)NiBr2], nBuOH, 110 °C, 20 min; (ii) (DME)-
NiBr2 (2 equiv.), CH2Cl2, room temp., 12 h; (iii) MeCN, heat.
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Table 2. Selected data for the new complexes 2, 4–6.
Complex Colour
v(C=N)
µeff
FAB mass spectrum
Microanalysis (%)[c]
[cm–1][a]
[µB][b]
C
H
N
2a
2b
4
blue
1594
1595
1596
1598
1595
1599
5.7
5.6
6.8
5.3
5.7
4.3
860 [M – Cl]+,
824 [M – 2Cl]+
993 [M – Br]+,
913 [M – 2Br]+
731 [M – Cl]+,
696 [M – 2Cl]+
736 [M – Cl]+,
699 [M – 2Cl]+
870 [M – Br]+,
789 [M – 2Br]+
867 [M – Br]+,
786 [M – 2Br]+
57.75
(57.67)
48.22
(48.11)
53.11
5.35
(5.51)
4.36
(4.57)
4.29
7.78
(7.82)
6.41
(6.53)
9.46
blue
dark purple
blue
(53.35)
52.20
(4.31)
4.34
(9.15)
9.04
5a
5b
6
(52.33)[d]
42.88
(4.39)[d]
3.30
(8.97)[d]
7.14
blue
(43.02)
41.58
(3.50)
3.42
(7.38)
7.31
pale orange
(41.70)[e]
(3.40)[e]
(7.08)[e]
[a] Recorded with a Perkin–Elmer Spectrum One FT-IR spectrometer on solid samples. [b] Recorded with an Evans Balance at room
temperature. [c] Calculated values shown in parentheses. [d] Value calculated with 0.5H2O. [e] Value calculated with 1/3CHCl3.
Cl bond lengths are alike [2.2558(19) vs. 2.268(2) Å], while Table 3. Selected bond lengths [Å] and angles [°] for 2a.
the Co(1)–N distances vary appreciably with the interior
Co(1)–N(2)pyridyl distance [2.027(5) Å] being shorter than
the exterior Co(1)–N(1)imine [2.219(6) Å] and Co(1)–
N(3)pyridyl [2.219(6) Å] ones. At Co(2), the two cobalt–ni-
Bond lengths
Co(1)–N(1)
Co(1)–N(2)
Co(1)–N(3)
2.219(6)
2.027(5)
2.219(6)
2.2558(19) C(7)–N(1)
2.268(2)
2.038(6)
Co(2)–N(5)
Co(2)–Cl(3)
Co(2)–Cl(4)
2.052(5)
2.212(2)
2.229(2)
1.281(8)
1.286(7)
5.336(5)
trogen and two cobalt-chloride distances show little varia- Co(1)–Cl(1)
Co(1)–Cl(2)
C(24)–N(5)
Co(1)···Co(2)
tion within each pair. On comparison with the free ligand
Co(2)–N(4)
L1,[10a] there is no marked variation in the C=N bond
Bond angles
lengths on coordination with the average value [1.284(8) Å]
in 2a consistent with double bond character being main-
tained. The structure of 2a closely resembles the diiron (1)
and dizinc analogues previously reported.[10a]
The FAB mass spectra for 2a and 2b show fragmentation
peaks corresponding to the loss of one or two halide groups
from the corresponding molecular ion peak. In their IR
N(1)–Co(1)–N(2) 75.2(2)
N(1)–Co(1)–N(3) 151.8(2)
Cl(1)–Co(1)–N(1) 96.78(15)
Cl(2)–Co(1)–N(1) 101.44(15) N(4)–Co(2)–Cl(4)
Cl(1)–Co(1)–Cl(2) 127.10(8) Cl(3)–Co(2)–Cl(4)
Cl(1)–Co(1)–N(2)
N(4)–Co(2)–N(5)
N(4)–Co(2)–Cl(3)
115.44(17)
77.0(2)
119.75(18)
103.73(17)
118.76(9)
spectra, the υ(C=N)imine bands are seen at ca. 1595 cm–1 of the individual metal centres).[13] A similar pair of non-
and shifted to lower wavenumber by ca. 47 cm–1 in com- interacting high-spin configurations has also been seen for
parison with the free ligand L1 and thus support the coor- the diiron(II) and dinickel(II) counterparts.[10a]
dination of both imine groups. Complexes 2a and 2b are
Crystals of 5b(NCMe) were grown by slow cooling of a
paramagnetic and display magnetic moments of ca. 5.7 µB warm acetonitrile solution containing the complex. A view
(Evans Balance at ambient temperature) which are consis- of 5b(NCMe) is depicted in Figure 4; selected bond lengths
tent with non-spin coupled CoII (S = 3/2)–CoII (S = 3/2) and angles are collected in Table 4. The molecular structure
systems (using µ2 = Σµi2, where µi is the magnetic moment of 5b(NCMe) reveals a bimetallic neutral cobalt complex in
Figure 3. Molecular structure of 2a including a partial atom-numbering scheme. All hydrogen atoms have been omitted for clarity.
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Bimetallic Ethylene Oligomerisation Catalysts
which one metal centre occupies the tridentate terpyridyl Table 4. Selected bond lengths [Å] and angles [°] for 5b(NCMe).
pocket in L2 while the other one a bidentate pyridylimine
cavity. The coordination spheres at both metal centres are
completed by two terminal bromide ligands with an ad-
ditional N-bound molecule of acetonitrile at Co(2). The
Bond lengths
Co(1)–Br(1)
Co(1)–Br(2)
Co(1)–N(1)
2.4196(18)
2.4505(19)
2.153(9)
2.035(8)
2.197(9)
2.4334(18)
2.4135(19)
2.176(9)
Co(2)–N(5)
Co(2)–N(6)
C(5)–C(6)
C(10)–C(11)
C(15)–C(16)
C(21)–N(5)
C(35)–N(6)
Co(1)···Co(2)
2.080(8)
2.180(11)
1.489(16)
1.450(15)
1.525(13)
1.271(13)
1.147(14)
5.556(9)
geometries at Co(1) and Co(2) can be best described as dis- Co(1)–N(2)
Co(1)–N(3)
torted trigonal bipyramidal with the deviation from ideality
Co(2)–Br(3)
being most significant at Co(1) [τ = 0.51 (Co(1)) vs. 0.65
Co(2)–Br(4)
(Co(2))].[12] Within the ligand frame the chelating terpyridyl
[torsion angle N(1)–C(5)–C(6)–N(2) 1.2°, N(2)–C(10)–
C(11)–N(3) 3.4°] and pyridylimine [torsion angle N(4)–
C(20)–C(21)–N(5) 5.8°] units are almost planar with the re-
spective planes inclined at an angle of 107.9° to one another
[torsion angle N(3)–C(15)–C(16)–N(4)]; the N-substituted
Co(2)–N(4)
Bond angles
N(1)–Co(1)–N(2)
76.9(4)
152.7(3)
91.8(3)
94.8(3)
N(4)–Co(2)–N(6) 167.1(3)
N(4)–Co(2)–Br(3) 99.5(2)
N(4)–Co(2)–Br(4) 91.8(2)
N(5)–Co(2)–Br(3) 128.4(2)
Br(3)–Co(2)–Br(4) 124.90(7)
N(1)–Co(1)–N(3)
N(1)–Co(1)–Br(1)
N(1)–Co(1)–Br(2)
aryl group is oriented at 111.8° [torsion angle C(21)–N(5)– Br(1)–Co(1)–Br(2) 122.16(7)
N(4)–Co(2)–N(5) 76.1(3)
C(23)–C(24)] with respect to the pyridylimine plane. With
regard to the Co(1) centre, the Co–Br distances are
asymmetric [Co(1)–Br(1) 2.4196(18) Å vs. Co(1)–Br(2)
2.4505(19) Å] as are the three Co(1)–Npyridyl distances with
the one involving the central pyridine, the shortest [Co(1)–
N(2) 2.035(8) Å vs. Co(1)–N(1) 2.153(9) and Co(1)–N(3)
2.197(9) Å]. At Co(2), the three Co–N bond lengths are also
inequivalent with the Co–Nacetonitrile bond being the longest
[Co(2)–N(6) 2.180(11) Å] while the Co–Br bond lengths
again show some slight variation [Co(2)–Br(3)
2.4334(18) Å, Co(2)–Br(4) 2.4135(19) Å]. The C(21)–
N(5)imine distance of 1.271(13) Å is comparable with the
corresponding length found in L2 [1.277(2) Å]. No intermo-
lecular interactions of note are apparent.
υ(C=N)imine stretches and corroborate imino group coordi-
nation in each case. All the complexes are paramagnetic
and exhibit magnetic moments of 6.8 µB (4), 5.3 µB (5a),
5.7 µB (5b) and 4.3 µB (6), their magnitudes being consistent
with non-spin coupled FeII (S = 2)–FeII (S = 2), CoII (S =
3/2)–CoII (S = 3/2) and NiII (S = 1)–NiII (S = 1) systems,
respectively.
Unlike with 2a and 5, recrystallisation of 6 from warm
acetonitrile gave on prolonged standing a few crystals of
salt [(L2)Ni2Br2(µ-Br)(NCMe)2]2[NiBr4] (7) as green blocks.
The molecular structure of 7 reveals two independent di-
nickel cationic units (cations A and B) that are charge bal-
anced by a tetrahedral nickel tetrabromide dianion. The cat-
ions A and B are similar and show only minor structural
differences; only the structure of cation A will be discussed
in any detail. A perspective view of A is depicted in Figure 5
while selected bond lengths and angles for both cations are
Figure 4. Molecular structure of 5b(NCMe) including a partial
atom numbering scheme. All hydrogen atoms have been omitted
for clarity.
In the FAB mass spectra of 4–6, fragmentation peaks
corresponding to the loss of one or two halide ions from
the corresponding molecular ion peak are evident. Their IR
Figure 5. Molecular structure of one of the cationic units (A) in 7
including a partial atom numbering scheme. All hydrogen atoms
spectra show bands at ca. 1595 cm–1 corresponding to the have been omitted for clarity.
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G. A. Solan et al.
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listed in Table 5. The structure of the cationic unit com- At each metal centre the Ni–Br(2)bridging distance is longer
prises a Ni(1)(µ-Br)Ni(2) core in which Ni(1) fills the pyr- than the corresponding Ni–Brterminal one [Ni(1)–Br(2)
idylimine pocket in L2 and Ni(2) the terpyridine pocket. 2.4839(12) vs. Ni(1)–Br(1) 2.4093(13) Å; Ni(2)–Br(2)
Each nickel centre is further coordinated by a monodentate 2.5868(12) vs. Ni(2)–Br(3) 2.5359(12) Å] while, in general,
bromide and a molecule of acetonitrile to complete a dis- the Ni(1)–Br distances are shorter than the Ni(2)–Br ones.
torted trigonal bipyramidal geometry [τ = 0.59][12] at Ni(1) Both acetonitrile molecules adopt sites trans to a pyridine
and an octahedral geometry at Ni(2). At Ni(2) the two bro- nitrogen atom [N(7)–Ni(2)–N(4) 171.2(2)°, N(6)–Ni(1)–
mide ligands are disposed trans to one another while at N(2) 170.7(2)°]. In comparison with 5b(NCMe) the effect
Ni(1) they fill the equatorial belt of the trigonal bipyramid. of the bridging bromide ligand is to compress the metal–
metal distance [4.134(5) (7) vs. 5.556(9) Å (5b(NCMe))] and
also to reduce the inclination between adjacent terpyridine
and pyridylimine planes [torsion angle N(3)–C(20)–C(19)–
N(2) 71.5° vs. 107.9 ((5b)NCMe)]. No significant inter
anion-cation interactions are evident.
The isolation of 7 during the attempted crystallisation of
6 was unexpected. It is uncertain whether 7 arises through
partial decomposition of 6 during thermal treatment with
acetonitrile or is a minor impurity in samples of 6. Never-
theless, crystalline 7 could only be obtained in low yield.
Table 5. Selected bond lengths [Å] and angles [°] for 7.
Cation A
Cation B
Bond lengths
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–N(6)
Ni(1)–Br(1)
Ni(1)–Br(2)
Ni(2)–N(3)
Ni(2)–N(4)
Ni(2)–N(5)
2.034(5)
2.099(5)
2.043(6)
2.4093(13)
2.4839(12)
2.135(5)
2.002(5)
2.105(5)
2.029(5)
2.109(5)
2.050(6)
2.4130(13)
2.5208(12)
2.151(5)
2.000(5)
2.116(5)
2.050(5)
2.6251(13)
2.5291(12)
4.149(5)
Ni(2)–N(7)
2.061(5)
Ni(2)–Br(2)
Ni(2)–Br(3)
Ni(1)···Ni(2)
range Ni–Br (dianion)
2.5868(12)
2.5359(12)
4.134(5)
3. Ethylene Oligomerisation
The bimetallic complexes 1–6 have all been screened as
precatalysts for oligomerisation (or polymerisation) of eth-
ylene; the results are collected in Table 6 (Entries 1–6). Typ-
ically, a complex in toluene was activated with 600 equiv.
(300 per metal centre) of methylaluminoxane (MAO) at
room temperature and ethylene (1 bar) gas then introduced
over a period of 30 min. All the systems, except for iron-
containing 4/MAO (Entry 4; which was inactive), showed
low to high activities for ethylene oligomerisation affording
hydrocarbon-based materials that were readily soluble in
toluene (and chloroform). No evidence for higher molecular
weight polymeric materials could be detected under these
experimental conditions.
2.3745(13)–2.3956(14)
Bond angles
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(6)
N(1)–Ni(1)–Br(1)
N(1)–Ni(1)–Br(2)
N(2)–Ni(1)–N(6)
N(2)–Ni(1)–Br(1)
N(2)–Ni(1)–Br(2)
Br(1)–Ni(1)–Br(2)
N(3)–Ni(2)–N(4)
N(3)–Ni(2)–N(5)
N(3)–Ni(2)–N(7)
N(3)–Ni(2)–Br(2)
N(3)–Ni(2)–Br(3)
N(4)–Ni(2)–N(5)
N(4)–Ni(2)–N(7)
N(4)–Ni(2)–Br(2)
N(4)–Ni(2)–Br(3)
N(5)–Ni(2)–N(7)
N(5)–Ni(2)–Br(2)
N(5)–Ni(2)–Br(3)
Br(2)–Ni(2)–Br(3)
79.6(2)
91.1(2)
79.0(2)
92.2(2)
115.43(16)
109.41(16)
170.7(2)
93.26(14)
95.57(14)
135.15(4)
78.2(2)
156.64(19)
110.12(19)
85.56(13)
89.35(13)
78.6(2)
171.2(2)
91.71(14)
93.46(14)
93.0(2)
93.08(15)
94.11(15)
171.85(4)
113.71(15)
112.04(15)
171.1(2)
92.72(14)
96.76(14)
134.24(4)
77.6(2)
155.74(19)
110.1(2)
91.92(14)
91.92(14)
78.2(2)
171.0(2)
91.15(15)
96.69(15)
93.95(19)
95.59(14)
91.63(14)
170.28(4)
The most active systems were found using L1 as the sup-
porting ligand with dinickel-based 3/MAO (Entry 3) giving
the highest productivity (450 gmmol–1 h–1 bar–1). Inspection
1
of the vinylic region of the H NMR spectrum of the re-
sulting wax reveals the presence of a mixture of alkene-con-
taining compounds composed of mostly internal olefins
(63%), α-olefins (25%), along with lower levels of tri-substi-
tuted (8%) and vinylidenes (4%) (Figure 6). In addition, the
Table 6. Catalytic evaluation of 1–6 for ethylene oligomerisation.[a]
Entry
Pre-catalyst
Mass of oligomer[b] Activity
Olefinic product[c] (%)
α[d]
[g]
[gmmol–1 h–1 bar–1]
α-olefin
internal vinylidene
tri-substituted
1
2
3
4
5
6
1
2a
3
4
5a
6
0.05
1.05
2.25
0
0.04
0.26
10
210
450
0
8
52
99.0
98.8
22.4
–
24.5
50.9
1.0
1.2
52.1
–
63.2
34.6
–
–
4.5
–
3.9
4.7
–
–
21.0
–
8.4
9.8
0.58
0.78
[e]
[e]
[e]
[e]
[a] General conditions: 1 bar ethylene Schlenk test carried out in toluene (40 mL) at ambient temperature using 6.0 mmol MAO (Al/M
= 300:1), 0.01 mmol precatalyst, over 30 min. Reactions were terminated by addition of dilute HCl. [b] Mass of oligomer based on GC
using a C17 standard. [c] Product percentages calculated via integration of their 1H NMR spectra. [d] Determined from GC; α = (rate of
propagation)/[(rate of propagation) + (rate of chain transfer)] = (mol of Cn+2)/(mol of Cn). [e] Not measured.
4602
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Bimetallic Ethylene Oligomerisation Catalysts
13C NMR spectrum of these oligomeric products indicates
the presence of mainly methyl branches, along with very
low levels of longer chain branches (e.g., ethyl and pro-
pyl).[13] Examination of the GC spectrum confirms the
broad product distribution with multiple peaks found in ad-
dition to those corresponding to the linear α-olefins (in the
range C8–C26). The observed production of methyl-
branched materials is similar to that obtained using the
highly active monometallic pyridylimine-nickel family of
catalysts (e.g., [(2-{(2,6-iPr2C6H3)N=CMe}C5H4N)NiBr2]/
MAO), in which a chain-walking mechanism has been
used to account for the observed isomerisation/
branching,[1g,1h,15] although the material obtained here is of
lower molecular weight. In order to additionally compare
the performance of 3/MAO against a potential monometal-
lic dipyridylimine-nickel catalyst (see B in Figure 1), we
have prepared (see experimental section) and screened a
genuine sample of [(6-{(2,6-iPr2C6H3)N=CMe}-2,2Ј-
C10H7N2)NiBr2] (8). The molecular structure of 8 is shown
in Figure 7; selected bond lengths and angles are collected
in Table 7. The structure reveals the expected features with
the single nickel centre bound by a tridentate dipyridylimine
ligand and two bromide ligands to complete a distorted tri-
gonal-bipyramidal geometry (τ = 0.63;[12] cf. 0.67 for the
dipyridylimine-CoCl2 moiety in 2a). Solutions of 8/MAO in
toluene, however, show only low activity for ethylene oligo-
Figure 7. Molecular structure of 8 including a partial atom-num-
bering scheme. All hydrogen atoms have been omitted for clarity.
Table 7. Selected bond lengths [Å] and angles [°] for 8.
Ni(1)–Br(1)
Ni(1)–Br(2)
Ni(1)–N(1)
N(1)–Ni(1)–N(2) 77.71(12)
N(1)–Ni(1)–N(3) 151.12(11)
N(1)–Ni(1)–Br(1) 94.81(8)
2.4555(6)
2.3520(6)
2.103(3)
Ni(1)–N(2)
Ni(1)–N(3)
C(11)–N(3)
N(1)–Ni(1)–Br(2) 96.72(8)
Br(1)–Ni(1)–Br(2) 113.21(2)
1.978(3)
2.147(3)
1.286(4)
merisation with an olefinic product distribution comparable propagation/(rate of propagation + rate of chain transfer)
to that seen with 3/MAO. It would, therefore, be possible = (mol of Cn+2)/(mol of Cn)][18] for Entry 2 being higher
to conclude based on the evidence above that the main (0.78) than for Entry 1 (0.58) consistent with a higher prob-
propagation/termination pathway is occurring at the pyr- ability of chain propagation and the observed broader
idylimine-Ni centre within L1 in 3/MAO. However, this range of α-olefins. No saturated hydrocarbon was produced
conclusion should be viewed with some caution as 6-or- in either Entry, which indicates the absence of chain trans-
ganyl-substituted pyridylimine-nickel catalysts[16] in general fer to aluminium as a termination mechanism.[19] Interest-
show much lower activities than their unsubstituted coun- ingly, catalytic evaluation of the monometallic pyridylimine
terparts.[4] Moreover, we have reported that dinickel cata- and
dipyridylimine
precursors
[(2-{(2,6-iPr2C6H3)-
lysts in which the central pyridine ring in L1 has been re- N=CMe}C5H4N)CoCl2] and [(6-{(2,6-iPr2C6H3)N=CMe}-
placed by 1,3-phenyl group displays an order of magnitude 2,2Ј-C10H7N2)CoCl2] using MAO as co-catalyst have been
drop in activity.[17]
previously reported to be inactive for ethylene oligomeris-
ation using conditions similar to those employed in this
work.[4a,4b,4e] The explanation for the significant activity of
2a/MAO for α-olefin production is unclear but it may be
connected to the observation made by Bianchini and co-
workers that the presence of a 6-substituted organyl group
(with hemilabile donor properties) in monometallic pyr-
idylimine-Co catalysts is important for oligomerisation ac-
tivity.[5b] Significantly, we have shown previously that the
central pyridine ligand in the dizinc analogue of 2a, [(L1)-
Zn2Cl4], is labile and can interchange between metal centre
coordination on the NMR timescale.[10a] It is therefore pos-
sible that a similar hemilability of the central pyridine in the
Figure 6. Types of olefinic products accessible in Entries 1–6.
In contrast to 3/MAO, dicobalt and diiron systems bear- 2a/MAO is operational and contributes to the performance
ing L1, 2a/MAO (Entry 2) and 1/MAO (Entry 1), are more characteristics observed.
selective and generate even-numbered linear α-olefins
Catalysts systems based on L2 display much lower activi-
[Ͼ 98%; range: C6–C20,ՆC20 0.28% (Entry 1), range: C6– ties than their L1 counterparts with dinickel-containing
C28,ՆC20 29% (Entry 2)] with the dicobalt system giving 6/MAO (Entry 6) displaying the highest activity
the higher of the activities (210 gmmol–1 h–1 bar–1 vs. (52 gmmol–1 h–1 bar–1) of the series followed by 5a/MAO
10 gmmol–1.h–1.bar–1). Both catalysts afford Schulz–Flory (Entry 5). As with 3/MAO, 6/MAO affords a mixture of α-
distributions for the α-olefins, with the α value [rate of olefins and internal olefins as the major oligomeric prod-
Eur. J. Inorg. Chem. 2008, 4597–4607
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4603

G. A. Solan et al.
FULL PAPER
The metal dihalides, MAO (10 wt.-% in toluene) and (DME)NiBr2
(DME = 1,2-dimethoxyethane) were purchased from Aldrich
Chemical Co. and used without further purification while 2,6-diiso-
propylaniline was distilled prior to use. The compounds tetrakis-
(triphenylphosphane)palladium(0),[26] 2-(2-methyl-1,3-dioxolan-2-
yl)-6-(tributylstannyl)pyridine,[9] 6-bromo-2,2Ј:6Ј,2ЈЈ-terpyridine,[27]
ucts. The superior catalytic activities of L1-based systems
over the L2 systems is likely due to the presence of steric
bulk at both ends of the pyridyl chain rather than one end,
thereby limiting more effectively β-hydrogen elimination
during termination. Notably, monometallic iron, cobalt and
nickel catalysts bearing terpyridine ligands also show either
very low catalytic activities or are inactive.[20–22]
L1,[9,10a] 1,[10a] 3[10a] and 6-[(2,6-iPr2C6H3)N=CMe]-2,2Ј-
[5b]
C10H7N2
were prepared according to previously reported pro-
cedures. All other chemicals were obtained commercially and used
without further purification.
Conclusions
Synthesis of L2 (two-step procedure). (a) Preparation of 6-Acetyl-
The pentaaza 2,6-oligopyridylimine-type ligands, bis-
(imino)terpyridine (L1) and iminoquaterpyridine (L2), have
been synthesised and successfully employed as scaffolds for
supporting two metal(II) centres [metal = iron (1,4), cobalt
(2,5) and nickel (3,6)]. As representative examples, the mo-
lecular structures of dicobalt complexes of both ligand
types have been determined and indicate that the metal
centres occupy inequivalent binding domains with the metal
centres separated by 5.336(5)–5.556(9) Å. Upon activation
with MAO, the L1-supported precatalysts (1,2,3) display
modest to good activities for the oligomerisation of ethylene
with the dinickel system, 3/MAO, displaying the highest.
On the other hand, the less sterically bulky L2-supported
precatalysts (4,5,6) show significantly lower activities. In ge-
neral the nickel systems afford a broad range of methyl-
branched materials containing a variety of olefinic end
groups, while the cobalt systems form either linear α-olefins
(with L1) or a mixture of olefinic types (with L2); the only
active iron system, 1/MAO, displays low activity and yields
uniquely linear α-olefins.
2,2Ј:6Ј,2ЈЈ:6ЈЈ,2ЈЈЈ-quaterpyridine: 6-Bromo-2,2Ј:6Ј,2ЈЈ-terpyridine
(1.50 g,
4.82 mmol),
2-(nBu3Sn)-6-[C(Me)CH2CH2O]-C5H3N
(2.410 g, 5.30 mmol, 1.1 equiv.) and tetrakis(triphenylphosphane)-
palladium(0) (0.334 g, 0.29 mmol, 0.06 equiv.) were loaded in a
Schlenk vessel under nitrogen and the contents stirred in dry tolu-
ene (30 mL) for 72 h at 90 °C. After removal of the solvent under
reduced pressure, ethanol was introduced to precipitate the acetal
protected form of 6-acetyl-2,2Ј:6Ј,2ЈЈ:6ЈЈ,2ЈЈЈ-quaterpyridine which
was then filtered and dried. The collected solid with then treated
with 4  HCl (20 mL), stirred overnight at 60 °C and, on cooling
to room temperature, carefully neutralised with 2  NaHCO3. The
organic phase was extracted with CHCl3 (3ϫ30 mL) and washed
with water (3ϫ30 mL), brine (1ϫ40 mL) and dried with magne-
sium sulfate. Following filtration, the solvent was removed under
reduced pressure and the crude product crystallised from ethanol
at – 30 °C. The resulting precipitate was collected by filtration to
afford 6-acetyl-2,2Ј:6Ј,2ЈЈ:6ЈЈ,2ЈЈЈ-quaterpyridine as a white solid.
Yield 1.270 g, 75%; m.p. 215–217 °C. 1H NMR (300 MHz,
CDCl3): δ = 2.81 (s, 3 H, CH3C=O), 7.2–7.3 (m, 1 H, Py-H), 7.82
3
4
(dd, JH,H = 7.9, JH,H = 1.7 Hz, 1 H, Py-H), 7.9–8.0 (m, 4 H, Py-
3
4
H), 8.43 (dd, JH,H = 7.9, JH,H = 0.9 Hz, 1 H, Py-H), 8.54 (dd,
3JH,H = 7.9, JH,H = 1.7 Hz, 1 H, Py-H), 8.5–8.7 (m, 4 H, Py-H),
4
8.80 (dd, 3JH,H = 7.6, JH,H = 1.2 Hz, 1 H, Py-H) . 13C{1H} NMR
4
(75 MHz, CDCl3): δ = 25.9 (CH3C=O), 121.1 (Py), 121.5 (Py),
123.9 (Py), 124.4 (Py), 136.9 (Py), 137.8 (Py), 137.9 (Py), 149.2
Experimental Section
(Py), 154.5 (Py), 155.5 (Py), 200.4 (CH C=O) ppm. IR: ν = 1697
˜
3
General Remarks: All reactions, unless otherwise stated, were car-
ried out under dry, oxygen-free nitrogen, using standard Schlenk
techniques or in a nitrogen-purged glove box. Solvents were dis-
tilled under nitrogen from appropriate drying agents and degassed
prior to use.[23] The infrared spectra were recorded with a Perkin–
Elmer Spectrum One FT-IR spectrometer on solid samples. The
ES (Electrospray) and the FAB (Fast atom bombardment) mass
spectra were recorded using a micromass Quattra LC mass spec-
trometer and a Kratos Concept spectrometer with dichloromethane
or NBA as the matrix, respectively. High-resolution FAB mass
spectra were recorded with Kratos Concept spectrometer (xenon
gas, 7 kV) with NBA as the matrix. Oligomer products were ana-
lysed by GC, using a Perkin–Elmer Autosystem XL chromatograph
equipped with a flame ionisation detector and 30 m PE-5 column
(0.25 mm thickness), injector temperature 45 °C and the following
temperature programme: 45 °C/7 min, 45–195 °C/10 °Cmin–1,
195 °C/5 min, 195–225 °C/10 °Cmin–1, 225 °C/5 min, 225–250 °C/
10 °Cmin–1, 250 °C/22 min. 1H and 13C NMR spectra were re-
corded with a Bruker ARX spectrometer (300 MHz) at ambient
temperature unless otherwise stated; chemical shifts (ppm) are re-
ferred to the residual protic solvent peaks and chemical shifts are
in Hertz [Hz]. Magnetic susceptibility studies were performed using
an Evans Balance (Johnson Matthey) at room temperature. The
magnetic moment data were calculated following standard meth-
ods[24] and corrections for underlying diamagnetism were applied
to the data.[25] Elemental analyses were performed at the Science
Technical Support Unit, London Metropolitan University.
(C=O), 1562, 1426, 1352, 1267, 1109, 1075, 992, 804, 775, 740 cm–1.
ESMS: m/z = 353 [M + H]+. HRMS (FAB): calcd for C22H17N4O
[M + H]+ 353.14024; found 353.14016.
(b) Preparation of L2: 6-Acetyl-2,2Ј:6Ј,2ЈЈ:6ЈЈ,2ЈЈЈ-quaterpyridine
(1.50 g, 4.44 mmol) was suspended in an excess of 2,6-diisopro-
pylaniline (7.86 g, 44.40 mmol, 10 equiv.) and stirred for 15 min at
160 °C on a heating mantle. A catalytic amount of formic acid was
added, and the reaction mixture was stirred for an additional
20 min at temperatures between 160–200 °C. Following removal of
the excess 2,6-diisopropylaniline under reduced pressure (130 °C,
0.5 Torr), the resulting brown residue was stirred in ethanol at
room temperature and the resultant precipitate filtered and washed
with ethanol. The residue was crystallised from a dichloromethane/
hexane (1:9) mixture at room temperature and the resulting precipi-
tate filtered, washed with hexane and dried under reduced pressure
to afford L2 as a pale yellow solid. Yield 0.629 g, 60%. Recrystalli-
sation by slow cooling of a warm nitromethane solution of L2 gave
clear needles; m.p. Ͼ 260 °C. 1H NMR (300 MHz, CDCl3): δ =
3
1.10 [d, JH-H = 6.7 Hz, 12 H, CH(Me)2], 2.28 (s, 3 H, CH3C=N),
2.71 [sept, 2 H, CH(Me)2], 7.0–7.2 (m, 3 H, Ar-H), 7.2–7.3 (m, 1
3
3
H, Py-H), 7.8–7.9 (m, 1 H, Py-H), 7.91 (dd, JH-H = 7.9, JH-H
=
3
7.9 Hz, 2 H, Py-H), 8.35 (d, JH-H = 7.9 Hz, 1 H, Py-H), 8.42 (d,
3JH-H = 7.9 Hz, 1 H, Py-H), 8.53 (d, JH-H = 7.9 Hz, 1 H, Py-H),
3
3
8.59 (d, JH-H = 7.9 Hz, 1 H, Py-H), 8.67 (m, 2 H, Py-H) ppm.
13C{1H} NMR (75 MHz, CDCl3): δ = 16.3 (s, CH3C=N), 21.9
(CH3), 22.2 (CH3), 27.3 (CH), 120.1 (Py), 120.2 (Py), 121.0 (Py),
4604
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Bimetallic Ethylene Oligomerisation Catalysts
122.0 (Py), 122.5 (Ar), 122.8 (Ar), 134.8 (Py), 135.9 (Py), 136.3
(Ar), 136.7 (Py), 136.9 (Py), 148.1 (Py), 154.2 (Py), 154.4 (Py),
(s), 778 (s), 769 (s) and 659 cm–1 (m); (see Table 2 for further char-
acterisation).
154.6 (Py), 166.1 (C=N) ppm. IR: ν = 2950, 1634 (C=N), 1562,
˜
(d) M = Ni, X = Br (6): Using an analogous procedure to that
described for 4 employing (DME)NiBr2 (0.148 g, 0.480 mmol) and
L2 (0.123 g, 0.240 mmol, 0.5 equiv.) gave [(L2)Ni2Br4] (6) as a pale
orange powder. Yield 0.090 g, 44%. Recrystallisation from chloro-
1425, 1362, 1292, 1269, 1188, 1111, 1080, 991, 807, 759, 684 cm–1.
ESMS: m/z = 512 [M + H]+. HRMS (FAB): Calcd. for C34H34N5
[M + H]+ 512.28142, found 512.28155.
Synthesis of [(L1)Co2X4] (2). (a) X = Cl (2a): An oven-dried
Schlenk flask equipped with a magnetic stir bar was evacuated and
backfilled with nitrogen. The flask was charged with anhydrous
CoCl2 (0.041 g, 0.315 mmol) in nBuOH (10 mL) and the contents
stirred at 110 °C until the salt had completely dissolved. L1
(0.100 g, 0.157 mmol, 0.5 equiv.) was added and the reaction mix-
ture stirred at 110 °C for a further 20 min. After cooling to room
temperature, the suspension was concentrated and hexane added
to induce precipitation of the product. The solid was filtered,
washed with hexane and dried overnight under reduced pressure
to afford [(L1)Co2Cl4] (2a) as a blue solid. Yield 0.099 g, 70%.
Recrystallisation from warm acetonitrile gave 2a as blue blocks. IR:
form afforded 6 as an orange microcrystalline powder. IR: ν = 2970
˜
(m), 2949 (w), 1599 [m, υ(C=N)], 1575 (m), 1568 (s), 1464 (s), 1445
(m), 1379 (w), 1322 (w), 1254 (m), 1243 (m), 1196 (s), 1159 (s),
1013 (m), 821 (m), 802 (s), 786 (s), 749 (s), 755 (m) and 697 cm–1
(s); (see Table 2 for further characterisation).
Alternative Synthesis of [(L2)Ni2Br4] (6): A mixture of L2 (0.100 g,
0.196 mmol) and (DME)NiBr2 (0.121 g, 0.391 mmol, 2 equiv.) were
added to a Schlenk flask and dry dichloromethane (10 mL) intro-
duced at 0 °C under nitrogen. The stirred reaction mixture was
warmed to room temperature and stirring continued for a further
12 h to give a pale orange precipitate. The precipitate was filtered
and washed with dichloromethane (20 mL) to yield 6 as a pale
orange solid. Yield 0.176 g, 95%. See Table 2 for further characteri-
sation.
ν = 2959 (m), 2870 (w), 1594 [s, υ(C=N)imine], 1575 (m), 1459 (s),
˜
1430 (m), 1368 (m), 1322 (w), 1244 (m), 1194 (m), 1113 (m), 1011
(m), 936 (w), 825 (m), 795 (s), 750 (s) and 660 cm–1 (m); (see Table 2
for further characterisation).
Reaction of 6 with NCMe: A Schlenk flask was charged with 6
(0.176 g, 0.186 mmol), acetonitrile (10 mL) and the contents heated
to reflux with stirring for 0.5 h. The resulting fine suspension
(0.050 g of orange solid material) was filtered and the pale green
filtrate concentrated to half volume and left to stand. After four
days at room temperature green blocks of [(L2)Ni2Br2(µ-
(b) X = Br, (2b): Using an analogous procedure to that described
in 2a employing CoBr2 (0.036 g, 0.164 mmol) and L1 (0.052 g,
0.082 mmol, 0.5 equiv.) gave [(L1)Co2Br4] (2b) as a blue solid. Yield
0.141 g, 80%. Recrystallisation from warm acetonitrile gave 2b as
a blue-green microcrystalline powder. IR: ν = 2960 (m), 2873 (w),
˜
Br)(NCMe) ] [NiBr ] (7) were formed. Yield 0.020 g, 9%. IR: ν =
˜
2 2
4
1595 [s, υ(C=N)imine], 1574 (m), 1459 (s), 1429 (m), 1367 (m), 1323
(w), 1246 (m), 1195 (m), 1113 (m), 1011 (m), 824 (m), 796 (s), 751
(s) and 601 cm–1 (m); (see Table 2 for further characterisation).
Synthesis of [(L2)M2X4] (4–6). (a) M = Fe, X = Cl (4): An oven- [M/2 – 1/2 NiBr4 – 2 MeCN]+, 788 [M/2 – 1/2 NiBr4 – 2 MeCN –
2962 (m), 2283 [w, υ(CϵN)], 1600 [m, υ(C=N)], 1577 (m), 1461 (s),
1443 (m), 1366 (w), 1323 (w), 1251 (m), 1196 (m), 1006 (m), 821
(m), 783 (s), 755 (m) and 697 (s) cm–1. Positive FABMS: m/z = 868
dried Schlenk flask equipped with a magnetic stir bar was evacu-
ated and backfilled with nitrogen. The flask was charged with an-
hydrous FeCl2 (0.061 g, 0.480 mmol) in nBuOH (10 mL) and the
contents stirred at 110 °C until the iron salt had completely dis-
solved. L2 (0.123 g, 0.240 mmol, 0.5 equiv.) was added and the re-
action mixture stirred at 110 °C for a further 20 min. After cooling
to room temperature, the suspension was concentrated and hexane
added to induce precipitation of the product. The solid was filtered,
washed with hexane and dried overnight under reduced pressure to
afford [(L2)Fe2Cl4] (4) as a black-purple powder. Yield 0.112 g,
55%. Recrystallisation from warm acetonitrile gave 4 as a dark
Br]+, 708 [M/2 – 1/2 NiBr4 – 2 MeCN – 2 Br]+. Negative FABMS:
m/z = 298 [NiBr3]–.
Synthesis of [(6-{(2,6-iPr2C6H3)N=CMe}-2,2Ј-C10H7N2)NiBr2] (8):
An oven-dried Schlenk flask equipped with a magnetic stir bar was
evacuated and backfilled with nitrogen. The flask was charged with
(DME)NiBr2 (0.121 g, 0.391 mmol) in nBuOH (10 mL) and the
contents stirred at 110 °C until the nickel complex had partially
dissolved.
6-[(2,6-iPr2C6H3)N=CMe]-2,2Ј-C10H7N2
(0.140 g,
0.391 mmol, 1 equiv.) was added and the reaction mixture stirred
at 110 °C for a further 20 min. After cooling to room temperature,
the suspension was concentrated and hexane added to induce pre-
cipitation of the product. The solid was filtered, washed with hex-
ane and dried overnight under reduced pressure to afford [(6-{(2,6-
iPr2C6H3)N=CMe}-2,2Ј-C10H7N2)NiBr2] (8) as a red powder.
Yield 0.124 g, 55%. Recrystallisation from warm acetonitrile gave
8 as dark red blocks. FAB mass spectrum, m/z 497 [M – Br]+, 417
purple microcrystalline powder. IR: ν = 2961 (m), 2930 (w), 1598
˜
[m, υ(C=N)], 1569 (m), 1460 (m), 1440 (m), 1370 (s), 1310 (w),
1263 (s), 1197 (s), 1101 (m), 1030 (m), 829 (m), 795 (s), 774 (s), 693
(m) and 655 (s); (see Table 2 for further characterisation) cm–1.
(b) M = Co, X = Cl (5a): Using an analogous procedure to that
described for 4 employing CoCl2 (0.062 g, 0.480 mmol) and L2
(0.123 g, 0.240 mmol, 0.5 equiv.) gave [(L2)Co2Cl4] (5a) as a blue
powder. Yield 0.126 g, 68%. Recrystallisation from warm acetoni-
trile solution afforded 5a(NCMe) as a blue microcrystalline pow-
[M – 2Br]+. IR: ν = 1596 [υ(C=N)imine] cm–1. µeff = 2.8 BM at
˜
293 K. C24H27Br2N3Ni: calcd. C 50.04, H 4.69, N 7.30; found C
49.95, H 4.51, N 7.66.
General Screening for Ethylene Oligomerisation: An oven-dried
200 mL Schlenk vessel equipped with magnetic stir bar was evacu-
ated and backfilled with nitrogen. The vessel was charged with the
precatalyst (0.01 mmol) and dissolved or suspended in toluene
(40 mL). MAO (6.0 mmol, 300 equiv./metal centre) was introduced
and the reaction mixture left to stir for 5 min. resulting in a colour
change of the solution. The vessel was purged with ethylene and
the contents magnetically stirred under 1 bar ethylene pressure 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
(5 mL). The organic phase was separated and dried with magne-
sium sulfate and filtered. Quantitative GC analysis was performed
der. IR: ν = 2962 (m), 2928 (w), 1598 [m, υ(C=N)], 1588 (s), 1574
˜
(m), 1455 (m), 1428 (m), 1383 (m), 1367 (s), 1316 (w), 1253 (s),
1200 (s), 1101 (m), 1023 (m), 820 (m), 796 (s), 775 (s), 750 (s), 693
(m) and 655 cm–1 (s); (see Table 2 for further characterisation).
(c) M = Co, X = Br (5b): Using an analogous procedure to that
described for 4 employing CoBr2 (0.105 g, 0.480 mmol) and L2
(0.123 g, 0.240 mmol, 0.5 equiv.) gave [(L2)Co2Br4] (5b) as a blue
powder. Yield 0.090 g, 42%. Recrystallisation from hot acetonitrile
solution gave 5b(NCMe) as blue blocks. IR: ν = 2961 (m), 2938
˜
(w), 1595 [s, υ(C=N)], 1588 (s), 1574 (m), 1488 (m), 1458 (m), 1396
(w), 1316 (w), 1251 (m), 1194 (s), 1186 (s), 1010 (m), 829 (m), 786
Eur. J. Inorg. Chem. 2008, 4597–4607
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4605

G. A. Solan et al.
FULL PAPER
Table 8. Crystallographic and data processing parameters for L2, 2a, 5b(NCMe), 7 and 8.
Complex
L2
2a
5b(NCMe)
7
8
Formula
M
C34H33N5
511.65
0.08ϫ0.03ϫ0.01 0.21ϫ0.19ϫ0.02
C43H49Cl4Co2N5·MeCN C36H36Br4Co2N6·2MeCN C38H39Br5Ni2.5N7·10MeCN C24H27Br2N3Ni
936.59
1072.32
0.23ϫ0.16ϫ0.04
150(2)
monoclinic
P21/c
1345.36
576.02
Crystal size [mm]3
Temperature [K]
Crystal system
Space group
a [Å]
0.38ϫ0.20ϫ0.12
150(2)
0.28ϫ0.26ϫ0.04
150(2)
monoclinic
C2/c
150(2)
150(2)
monoclinic
P21/c
triclinic
triclinic
¯
¯
P1
P1
6.4213(7)
11.1354(12)
19.629(2)
97.3630(1)
92.906(2)
102.1910(10)
1356.2(3)
2
17.012(4)
18.325(4)
15.685(4)
90
110.634(4)
90
16.136(5)
17.538(6)
17.152(5)
90
113.153(5)
90
16.852(4)
18.486(4)
19.344(4)
84.739(4)
76.443(4)
64.805(4)
5301(2)
4
31.086(3)
9.8651(8)
15.6922(12)
90
111.555(2)
90
b [Å]
c [Å]
α [°]
β [°]
γ [°]
V [Å3]
4576.1(17)
4
4463(2)
4
4475.7(6)
8
Z
Dc [Mgm–3]
F(000)
1.253
544
0.075
1.359
1944
1.596
2128
1.686
2684
1.710
2320
µ(Mo-Kα) [mm–1]
0.996
4.362
4.697
4.455
Reflections collected 10471
32333
33947
41314
15823
Independent reflec-
tions
Rint
Restraints/
parameters
Final R indices
[IϾ2σ(I)]
All data
4734
8048
8436
20522
0.0641
0/960
3949
0.0405
0/357
0.1889
0/525
0.1430
0/495
0.0505
0/276
R1 = 0.0501,
wR2 = 0.1258
R1 = 0.0791,
wR2 = 0.1411
R1 = 0.0568,
wR2 = 0.0856
R1 = 0.1723,
wR2 = 0.1073
0.658
R1 = 0.0759,
wR2 = 0.1699
R1 = 0.1607,
wR2 = 0.1961
0.961
R1 = 0.0494,
wR2 = 0.1017
R1 = 0.1050,
wR2 = 0.1096
0.765
R1 = 0.0371,
wR2 = 0.0903
R1 = 0.0457,
wR2 = 0.0930
0.964
Goodness of fit on F2 1.015
(all data)
Data in common: graphite-monochromated Mo-Kα radiation, λ = 0.71073 Å; R1 = Σ||Fo| – |Fc||/Σ|Fo|, wR2 = [Σw(Fo2 – Fc2)2/Σw(Fo2)2]1/2, w–1
= [σ2(Fo)2 + (aP)2], P = [max(Fo2,0) + 2(Fc2)]/3, where a is a constant adjusted by the program; goodness of fit: [Σ(Fo2 – Fc )2/(n – p)]1/2 where
2
n is the number of reflections and p the number of parameters.
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by taking an aliquot of the solution containing a weighed amount
of a standard (n-heptadecene). For analysis of the oligomers by 1H
NMR spectroscopy, the solvent was removed on the rotary evapo-
rator and the residue dissolved in CDCl3.
Crystallographic Studies: Data for L2, 2a, 5b(NCMe), 7 and 8 were
collected with a Bruker APEX 2000 CCD diffractometer. Details
of data collection, refinement and crystal data are listed in Table 8.
The data were corrected for Lorentz and polarisation effects and
empirical absorption corrections applied. Structure solution by di-
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Received: June 27, 2008
Published Online: September 2, 2008
Eur. J. Inorg. Chem. 2008, 4597–4607
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4607