Electronically variable imino-phenanthrolinyl-cobalt complexes; synthesis, structures and ethylene oligomerisation studies

Article abstract of DOI:10.1016/j.jorganchem.2006.06.018

The 2-imino-1,10-phenanthroline ligands, 1,10-C₁₂H₇N₂-2-CR{double bond, long}N(2,6-i-Pr₂-4-R¹-C₆H₂) [R = R¹ = H (L1); R = H, R¹ = Br (L2); R = H, R¹ = CN (L3); R = H, R¹ = i-Pr (L4); R = Me, R¹ = H (L5); R = Me, R¹ = i-Pr (L6)], have been prepared in high yield from the condensation reaction of 1,10-C₁₂H₇N₂-2-CR{double bond, long}O (R = H, Me) with one equivalent of the corresponding 4-substituted 2,6-diisopropylaniline. The molecular structures of L2, L5 and L6 reveal the imino nitrogen atoms to adopt a transoid configuration with respect to the phenanthrolinyl nitrogen atoms. Treatment of Lx with one equivalent of CoCl₂ in n-BuOH at 90 °C gives the high spin complexes, (Lx)CoCl₂ [Lx = L1 (1a), L2 (1b), L3 (1c), L4 (1d), L5 (1e), L6 (1f)], in which the metal centres exhibit distorted square pyramidal geometries. Activation of 1a-1f with excess methylaluminoxane (MAO) gives catalysts that are modestly active for the oligomerisation of ethylene affording mainly linear α-olefins along with some degree of internal olefins. While the donor capability of the 4-position of the N-aryl group does not appear to affect the activity of the catalyst, it does have an influence on the ratio of α-olefins to internal olefins. Single crystal X-ray diffraction studies have been performed on L2, L5, L6, 1a, 1c and 1f.

Full text of DOI:10.1016/j.jorganchem.2006.06.018

Journal of Organometallic Chemistry 691 (2006) 4114–4123
www.elsevier.com/locate/jorganchem
Electronically variable imino-phenanthrolinyl-cobalt
complexes; synthesis, structures and ethylene oligomerisation studies
´ ´
Jeremie D.A. Pelletier, Yohan D.M. Champouret, Jesus Cadarso, Lucy Clowes,
*
Marcos Ganete, Kuldip Singh, Vakesan Thanarajasingham, Gregory A. Solan
˜
Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK
Received 23 May 2006; received in revised form 12 June 2006; accepted 12 June 2006
Available online 23 June 2006
Abstract
The 2-imino-1,10-phenanthroline ligands, 1,10-C12H7N2-2-CR@N(2,6-i-Pr2-4-R1-C6H2) [R = R1 = H (L1); R = H, R1 = Br (L2);
R = H, R1 = CN (L3); R = H, R1 = i-Pr (L4); R = Me, R1 = H (L5); R = Me, R1 = i-Pr (L6)], have been prepared in high yield from
the condensation reaction of 1,10-C12H7N2-2-CR@O (R = H, Me) with one equivalent of the corresponding 4-substituted 2,6-diisopro-
pylaniline. The molecular structures of L2, L5 and L6 reveal the imino nitrogen atoms to adopt a transoid configuration with respect to
the phenanthrolinyl nitrogen atoms. Treatment of Lx with one equivalent of CoCl2 in n-BuOH at 90 ꢀC gives the high spin complexes,
(Lx)CoCl2 [Lx = L1 (1a), L2 (1b), L3 (1c), L4 (1d), L5 (1e), L6 (1f)], in which the metal centres exhibit distorted square pyramidal geom-
etries. Activation of 1a–1f with excess methylaluminoxane (MAO) gives catalysts that are modestly active for the oligomerisation of eth-
ylene affording mainly linear a-olefins along with some degree of internal olefins. While the donor capability of the 4-position of the
N-aryl group does not appear to affect the activity of the catalyst, it does have an influence on the ratio of a-olefins to internal olefins.
Single crystal X-ray diffraction studies have been performed on L2, L5, L6, 1a, 1c and 1f.
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: Cobalt; Ethylene oligomerisation; Catalyst; Electronic variation; Imino-phenanthroline
1. Introduction
been reported. However, the level of performance exhibited
by the resultant catalytic systems has not, on the whole,
reached the high levels displayed by the parent bis(aryli-
mino)pyridine-iron or -cobalt prototypes. Nevertheless,
by appreciation of the steric and planar characteristics of
A, neutral tridentate ligands imparting high activities for
metal-mediated alkene oligomerisation and polymerisation
can be accessed [7,8]. For example, incorporation of a pyr-
idyl group in place of an imino unit in A to give arylimino-
bipyridine ligands (B, Fig. 1) has seen the development of a
highly active iron ethylene oligomerisation catalyst for the
synthesis of short chain a-olefins [8].
During the course of our study, Sun et al. reported the
use of unsymmetrical arylimino-phenanthrolinyl ligands
(C, Fig. 1) as supports for highly active iron catalysts for
ethylene oligomerisation [9]. Indeed, the performance of
these systems was shown, in a similar fashion to bis(aryli-
mino)pyridine-iron systems, to be related to both the steric
Since the initial discovery of iron and cobalt catalysts
that can deliver very high activities for ethylene polymeri-
sation [1], considerable research activity has been directed
towards the modification of the tridentate bis(aryli-
mino)pyridine supporting ligand frame (A, Fig. 1). In the
main, this has focused on varying the steric [2] and, more
recently, the electronic properties [3] of the N-aryl groups,
the results of which have allowed access to a highly versa-
tile family of catalysts capable of affording high molecular
weight polymers through to lower molecular weight oligo-
mers. More drastic modification in A such as replacement
of the central pyridine [4], one or both exterior imines [5]
or all three moieties [6] by alternative donor units, has also
*
Corresponding author. Tel.: +44 116 2522096.
E-mail address: gas8@leicester.ac.uk (G.A. Solan).
0022-328X/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.06.018

J.D.A. Pelletier et al. / Journal of Organometallic Chemistry 691 (2006) 4114–4123
4115
CR@N(2,6-i-Pr2-4-R1-C6H2) [R = R1 = H (L1); R = H,
R1 = Br (L2); R = H, R1 = CN (L3); R = H, R1 = i-Pr
(L4); R = Me, R1 = H (L5); R = Me, R1 = i-Pr (L6)] in
moderate to good yield (Scheme 1). In general, the aldim-
ine ligands L1–L4 required milder conditions while the ket-
imine ligands, L5 and L6, higher temperatures and longer
reaction times. The carbonyl-containing precursors are
not commercially available and were both synthesised from
2-cyano-1,10-phenanthroline [10] in a series of steps
(Scheme 2) using slight modifications of the literature pro-
cedures (see Section 4). In the case of 2-acetyl-1,10-phenan-
throline [9], an improved yield has been obtained by the
revised method. L1–L6 have been characterised by 1H
NMR, 13C NMR and IR spectroscopy along with Electro-
Spray (ES) mass spectrometry (see Section 4). In addition,
L2, L5 and L6 have been the subject of single crystal X-ray
diffraction studies.
Slow evaporation of ethanol solutions containing L2, L5
and L6 gave single crystals suitable for the X-ray determi-
nations. Compound L2 contains three unique molecules in
the asymmetric unit, compound L5 one and L6 has two
with only minor differences evident between unique mole-
cules in each (e.g., the relative inclination of the aryl sub-
stituents). The structures are essentially the same and
only the structure of L2 will be discussed in any detail.
The molecular structures of L2 and L5 are depicted in
Fig. 2; selected bonds lengths and angles for L2, L5 and
L6 (including the unique molecules) are shown in Table
1. This structure of L2 consists of a phenanthroline moiety
linked to an arylimino group at the 2-position with the
R
R
R
N
N
N
N
N
N
N
N
N
Ar
Ar
Ar
Ar
(A)
(B)
(C)
Fig. 1. Bis(imino)pyridine (A), imino-bipyridine (B) and imino-phenan-
throline (C); R = H or hydrodrocarbyl, Ar = aryl group.
and electronic properties of C. With a view to probing the
role of the metal centre in systems bound by C, we disclose
our results on the synthesis and catalytic evaluation of a
series of imino-phenanthrolinyl-cobalt(II) chloride com-
plexes. Specifically, we are concerned with the synthesis
and screening of [1,10-C12H7N2-2-CR@N(2,6-i-Pr2-4-R1-
C6H2)]CoCl2 [R = R1 = H (1a); R = H, R1 = Br (1b);
R = H, R1 = CN (1c); R = H, R1 = i-Pr (1d); R = Me,
R1 = H (1e); R = Me, R1 = i-Pr (1f)], in which the steric
bulk of the ortho-aryl substitution pattern has been kept
constant and the electronic properties of the para-substitu-
ent systematically varied for aldimine- and ketimine-based
ligand frames.
2. Results and discussion
2.1. Ligand synthesis
Treatment of 1,10-C12H7N2-2-CR@O (R = H, Me) with
one equivalent of 2,6-i-Pr2-4-1C6H2NH2 (R1 = H, Br, CN,
i-Pr) in ethanol at elevated temperature, in the presence of
a catalytic amount of acetic acid, afforded 1,10-C12H7N2-2-
1
R = R = H L1 (77%)
1
R = H, R = Br L2 (87%)
N
(i)
O
N
1
N
R = H, R = CN L3 (68%)
N
N
R
R
1
1
R = H, R = i-Pr L4 (60%)
R
1
R = Me, R = H L5 (70%)
1
R = H, Me
R = Me, R = i-Pr L6 (61%)
Scheme 1. Reagents and conditions: (i) 2,6-i-Pr2-4-R1-C6H2NH2 (R1 = H, Br, CN, i-Pr), EtOH, cat. H+, heat.
(ii)
(i)
(iii)
O
O
N
N
N
N
OMe
N
OH
N
CN
N
N
(iv), (v)
O
N
N
Scheme 2. Reagents and conditions: (i) cat. Na, MeOH, 90 ꢀC; (ii) NaBH4, EtOH, rt; (iii) SeO2, dioxane, 110 ꢀC; (iv) 2AlMe3, toluene, 70 ꢀC; and (v) H2O,
Na2EDTA.

4116
J.D.A. Pelletier et al. / Journal of Organometallic Chemistry 691 (2006) 4114–4123
Fig. 2. Molecular structures of L2 and L5. All the hydrogen atoms apart from H11 in L2 have been omitted for clarity.
Table 1
˚
Selected bond distances (A) and angles (ꢀ) for L2, L5 and L6
L2
L5
L6
Molecule A
Molecule B
Molecule C
Molecule A
Molecule B
Bond lengths
C(10)–C(11)
C(11)–N(3)
C(14)–N(3)
C(17)–Br(1)
C(11)–C(110)
1.466(5)
1.265(4)
1.433(4)
1.911(4)
–
1.466(4)
1.255(4)
1.426(4)
1.913(3)
–
1.475(5)
1.257(4)
1.430(4)
1.903(4)
–
1.491(2)
1.278(2)
1.423(2)
–
1.505(4)
1.292(4)
1.423(4)
–
1.496(4)
1.283(4)
1.425(4)
–
1.494(2)
1.496(4)
1.513(4)
Bond angles
C(11)–N(3)–C(14)
C(10)–C(11)–N(3)
118.2(4)
121.6(3)
120.5(3)
121.4(3)
116.7(3)
121.1(3)
121.7(1)
116.5(1)
121.5(3)
116.1(3)
121.5(3)
117.1(3)
imino nitrogen [N(3)] atom adopting a transoid configura-
tion with respect to the nitrogen donors of the phenanthro-
line unit [N(2),N(1)]. The imino-phenanthroline unit is
almost planar [tors. N(3)–C(11)–C(10)–N(2) 2.0ꢀ] with
the N-aryl groups essentially orthogonal to this plane.
ketimine-containing compounds L5 and L6, the MeC@N
protons were seen as singlets at ca. d 2.5 in their 1H
NMR spectra with the MeC@N carbon at ca. d 167 in their
13C NMR spectra.
˚
The short length of the N(3)–C(11) [1.265(4) A] bond is
2.2. Synthesis of complexes
consistent with double bond character and the C–Br dis-
˚
tance [C(17)–Br(1) 1.911(4) A] is typical of a single bond
between these elements.
Interaction of L1–L6 with one equivalent of cobalt
dichloride in n-butanol at 90 ꢀC for 1 h gave (Lx)CoCl2
[Lx = L1 (1a), L2 (1b), L3 (1c), L4 (1d), L5 (1e), L6 (1f)]
as green to red–brown solids in good yield (Scheme 3).
All the complexes have been characterised by FAB-mass
spectrometry, IR spectroscopy and by magnetic suscepti-
bility measurements (Table 2). In addition, 1a, 1c and 1f
have been the subject of single crystal X-ray diffraction
studies.
All the compounds (L1–L6) gave peaks corresponding
to their molecular ions in their mass spectra. In their infra-
red spectra, the absorption bands observed at ca.
1629 cmꢀ1 were consistent with the presence of a C@N
functionality. In the case of L3 a band at 2224 cmꢀ1, char-
1
acteristic of a t(C„N) stretch, was also evident. The H
NMR spectra for the aldimines L1–L4 showed singlets at
ca. d 8.75 for the CH@N proton while the CH@N carbon
was seen at ca. d 168 in their 13C NMR spectra. For the
Recrystallisation of 1a, 1c and 1f from hot acetonitrile
gave single crystals suitable for the X-ray determinations.
1
R = R = H 1a
(i)
R
1
R = H, R = Br 1b
N
Lx
1
R = H, R = CN 1c
N
N
Co
1
R = H, R = i-Pr 1d
1
1
Cl
Cl
R
R = Me, R = H 1e
1
R = Me, R = i-Pr 1f
Scheme 3. Reagents and conditions: (i) CoCl2, n-BuOH, heat.

J.D.A. Pelletier et al. / Journal of Organometallic Chemistry 691 (2006) 4114–4123
4117
Table 2
Selected characterisation data for the new complexes 1a–1f
Compound
Colour
v(C@N) (cmꢀ1 a
)
leff (BM)b
FAB mass spectrum
Microanalysis (%)c
C
H
N
1a
1b
1c
1d
1e
1f
a
Brown
1609
1612
1606
1611
1607
1615
4.3
3.9
4.1
4.0
4.2
4.0
461 [MꢀCl]+,
426 [Mꢀ2Cl]+
541 [MꢀCl]+,
504 [Mꢀ2Cl]+
486 [MꢀCl]+,
451 [Mꢀ2Cl]+
503 [MꢀCl]+,
468 [Mꢀ2Cl]+
475 [MꢀCl]+,
440 [Mꢀ2Cl]+
517 [MꢀCl]+,
481 [Mꢀ2Cl]+
60.51
(60.36)
52.41
(52.09)
59.99
(59.78)
62.03
(62.34)
60.95
(61.06)
62.72
5.21
(5.03)
4.49
(4.17)
4.71
(4.60)
5.66
(5.75)
5.11
(5.28)
6.05
8.61
(8.45)
7.31
(7.29)
10.81
(10.73)
7.65
(7.79)
8.05
Dark green
Olive green
Brown
Red–brown
Red–brown
(8.22)
7.77
(7.59)
(62.93)
(5.97)
Recorded on a Perkin–Elmer spectrum one FT-IR spectrometer on solid samples.
Recorded on an Evans Balance at room temperature.
Calculated values are shown in parentheses.
b
c
The molecular structures of 1a, 1c and 1f are shown in
Figs. 3–5, respectively; selected bonds and angles for all
structures are listed in Table 3.
The structures of 1a, 1c and 1f are similar and will be dis-
cussed together. In each structure, a single cobalt atom is
surrounded by an imino-phenanthroline ligand, L1 (for
1a), L3 (for 1c) and L6 (for 1f), along with two terminally
bound chloride ligands. The geometry of the five-coordinate
complexes can be best described as distorted square pyrami-
dal as indicated by the low values of their structural index
parameters [s = 0.18 (1a), 0.28 (1c), 0.03 (1f)] [11], with a
chloride ligand in each occupying an axial site. The Co–N
distances are inequivalent with the central Co(1)–N(2) dis-
˚
˚
tance being the shortest [2.0447(18) A (1a), 2.018(6) A
˚
(1c), 2.059(3) A (1f)], while the external cobalt nitrogen dis-
tances are longer with Co(1)–N(3)imine being the longest
˚
˚
˚
[2.2939(18) A (1a), 2.353(6) A (1c), 2.248(6) A (1f)]. The
reason for the asymmetry between the external metal nitro-
gen distances [N(1)imine vs. N(3)phen] is likely to be due to the
improved donor capability of a pyridine nitrogen over an
imine nitrogen [12], with the discrepancy most evident for
the aldimine-containing complexes 1a and 1c. Moreover
in the case of 1c, the discrepancy is the most significant,
probably due to the additional influence of the electron
Fig. 3. Molecular structure of (L1)CoCl2 (1a). All the hydrogen atoms
apart from H11 have been omitted for clarity.
Fig. 4. Molecular structure of (L3)CoCl2 (1c). All the hydrogen atoms apart from H11 have been omitted for clarity.

4118
J.D.A. Pelletier et al. / Journal of Organometallic Chemistry 691 (2006) 4114–4123
Fig. 5. Molecular structure of (L6)CoCl2 (1f). All the hydrogen atoms have been omitted for clarity.
Table 3
unpaired electrons (S = 3/2). The IR spectra for 1a–1f
show absorption bands between 1606 and 1615 cmꢀ1 which
correspond to the t(C@N) stretching frequencies for a
coordinated imine and are shifted by ca. 30 cmꢀ1 to lower
wavenumber in comparison with the free ligands. In the
case of 1c, the C„N band is seen at 2215 cmꢀ1 and is sim-
ilar in magnitude to that seen in free L3.
˚
Selected bond distances (A) and angles (ꢀ) for 1a, 1c and 1f
1a
1c
1f
Bond lengths
Co(1)–N(1)
Co(1)–N(2)
Co(1)–N(3)
Co(1)–Cl(1)
Co(1)–Cl(2)
C(17)–C(26)
C(26)–N(4)
C(11)–C(11A)
2.2138(18)
2.0447(18)
2.2939(18)
2.2612(7)
2.2393(7)
–
2.189(6)
2.018(6)
2.353(6)
2.251(2)
2.247(2)
1.485(12)
1.103(11)
–
2.225(3)
2.059(3)
2.248(3)
2.2861(12)
2.2608(11)
1.520(5)
–
2.3. Screening for ethylene oligomerisation
–
–
1.495(5)
All the complexes were screened as precatalysts for olig-
omerisation of ethylene. Typically, a complex in toluene
was treated with 400 equivalents of methylaluminoxane
(MAO) at room temperature and ethylene (1 bar) gas
introduced over a period of 30 min. In all cases oligomeric
material (C6–C26) was afforded; the results of the tests are
collected in Table 4 (entries 1–6). Catalyst activities were
calculated from GC traces, using extrapolated values for
C4–C10. All the systems screened display only low activities
(2.0–5.2 g mmolꢀ1 hꢀ1 barꢀ1) for ethylene oligomerisation
when compared with their iron counterparts [9] and no dis-
Bond angles
N(1)–Co(1)–N(2)
N(1)–Co(1)–N(3)
N(1)–Co(1)–Cl(1)
N(1)–Co(1)–Cl(2)
N(2)–Co(1)–N(3)
N(2)–Co(1)–Cl(1)
N(2)–Co(1)–Cl(2)
N(3)–Co(1)–Cl(1)
N(3)–Co(1)–Cl(2)
Cl(2)–Co(1)–Cl(1)
75.95(7)
148.23(7)
94.64(5)
99.29(5)
73.67(7)
104.94(5)
137.49(5)
101.88(5)
96.81(5)
117.57(3)
77.7(3)
149.6(2)
75.65(11)
145.68(11)
99.12(8)
97.33(8)
73.14(11)
98.76(9)
147.44(9)
99.39(8)
101.25(8)
113.79(5)
94.91(18)
100.12(18)
72.3(2)
132.58(19)
122.61(19)
101.34(16)
96.19(16)
114.79(9)
withdrawing cyano group on the donor capability of the
imine nitrogen. In 1c the Co–Cl distances are essentially
the same while in 1a and 1f the Co–Cl(1) distance is
noticeably longer than the Co–Cl(2) distance [2.2612(7)
Table 4
Screening for ethylene oligomerisationa
Entry Pre-
Mass of
Activityꢀ1 a-Olefinc Internal
ꢀ1 barꢀ1
h )
ad
catalyst oligomerb (g mmol
(%)
olefinc(%)
˚
˚
(g)
vs. 2.2393(7) A (1a), 2.2861(12) vs. 2.2608(11) A (1f)]. As
expected the aryl groups in each structure adopt an orthog-
onal disposition with respect to the plane formed by the
imino-phenanthroline unit. The short length of the N(4)–
1
2
3
4
5
6
1a
1b
1c
1d
1e
1f
0.023
0.024
0.013
0.026
0.010
0.016
4.5
4.8
2.6
5.2
2.0
3.2
87
70
61
89
93
60
13
30
39
11
7
0.81
0.83
0.67
0.85
0.69
0.82
˚
C(23) [1.103(11) A] bond is consistent with triple bond char-
acter for the nitrile functionality in 1c. Inspection of the
packing diagram for 1a, 1c and 1f shows no evidence for
any short intermolecular distances.
The FAB mass spectrometric data for 1a–1f display
fragmentation peaks corresponding to the loss of one and
two chloride ions. The magnetic moments (measured on
an Evans balance at ambient temperature) for all the cobal-
t(II) complexes exhibit values at ca. 4.0 lb which are consis-
tent with high spin configurations possessing three
40
a
General conditions: 1 bar (100 kPa) ethylene Schlenk test carried out
in toluene (35 ml) at ambient temperature using 4.0 mmol MAO
(Al:Co = 400:1), 0.01 mmol precatalyst, over 30 min. Reactions were ter-
minated by addition of dilute HCl.
b
Mass of oligomer based on GC using a C17 standard.
Oligomerisation product percentages calculated via integration of the
c
1H NMR spectra.
d
Determined from GC; a = (rate of propagation)/((rate of propaga-
tion) + (rate of chain transfer)) = (moles of Cn+2)/(moles of Cn).

J.D.A. Pelletier et al. / Journal of Organometallic Chemistry 691 (2006) 4114–4123
4119
standard Schlenk techniques or in a nitrogen purged glove
box. Solvents were distilled under nitrogen from appropri-
ate drying agents and degassed prior to use [14]. The infra-
red spectra were recorded on a Perkin–Elmer spectrum
one FT-IR spectrometer on solid samples. 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, respectively. High res-
olution (HR) FAB mass spectra were recorded on Kratos
Concept spectrometer (xenon gas, 7 kV) with NBA as
matrix. 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 peak and coupling
constants are in Hertz (Hz). Magnetic Susceptibility studies
were performed using an Evans Balance (Johnson Matthey)
at room temperature. The magnetic moments were calcu-
lated following standard methods [15] and corrections for
underlying diamagnetism were applied to the data [16]. Oli-
gomer products were analysed by GC, using a Perkin–Elmer
Autosystem XL chromatograph equipped with a flame
ionisation detector and 30 m PE-5 column (0.25 mm thick-
ness), injector temperature 45 ꢀC and the following temper-
CH3
a
b
CH3
H3C
c
(α-olefins)
(internal olefins)
Fig. 6. Oligomeric products accessible using 1a–1f.
cernible trends in activity between aldimine- (1a–1d) and
ketimine-containing (1e, 1f) complexes are apparent. Fur-
thermore, the selectivity of these cobalt systems for linear
a-olefins (range: 60–93%) is much reduced in comparison
to the imino-phenanthroline-Fe systems with significant
levels of internal olefins evident (Fig. 6). No activity for
ethylene oligomerisation was reported using MAO alone
under these conditions.
For the aldimine-containing species 1a–1d (entries 1–4),
the degree of isomerisation seems to be related to the elec-
tronic properties of the para-aryl substituent with electron
withdrawing substituents (Br in 1b and CN in 1c) leading
to increased levels of internal olefins (entries 2 and 3). On
the other hand in the ketimine complexes (1e and 1f), the
para-isopropyl substituted species (1f) gives the highest
degree of isomerisation (entry 6). In all cases the catalysts
give a Schulz–Flory distribution of oligomers, with the
Schulz–Flory parameters a ranging form 0.67 to 0.85 [13].
The observation of solely oligomeric products using 1a–
1e is consistent with rapid chain transfer process as a result
of there being insufficient steric bulk to prevent associative
displacement of the growing oligomeric chain. Indeed, the
performance of 1a–1e can be compared to the less bulky
members of the bis(arylimino)pyridine-Co family of ethyl-
ene oligomerisation catalysts (e.g., aryl = 2-MePh) [2c].
ature programme: 45 ꢀC/7 min, 45–195 ꢀC/10 ꢀC minꢀ1
,
195 ꢀC/5 min, 195–225 ꢀC/10 ꢀC minꢀ1
, 225 ꢀC/5 min,
225–250 ꢀC/10 ꢀC minꢀ1, 250 ꢀC/22 min. Melting points
(m.p.) were measured on a Gallenkamp melting point appa-
ratus (model MFB-595) in open capillary tubes and were
uncorrected. Elemental analyses were performed at the
Science Technical Support Unit, London Metropolitan
University.
The reagents, trimethylaluminium (2.0 M in heptane),
MAO (10 wt% in toluene), ethylenediaminetetraacetic acid
disodium salt dihydrate, 2,6-diisopropylaniline, n-heptade-
cene and cobalt dichloride were purchased from Aldrich
Chemical Co., and used without further purification. The
compounds, 2,6-diisopropyl-4-bromo-aniline [17], 2,6-
diisopropyl-4-cyano-aniline [17], 2,4,6-triisopropylaniline
[18] and 2-cyano-1,10-phenanthroline [10], were prepared
according to previously reported procedures. All other
chemicals were obtained commercially and used without
further purification.
3. Conclusions
Full characterisation of a series of 4-substituted 2,6-iso-
propylphenylimino-phenanthroline ligands and their resul-
tant cobalt(II) chloride complexes has been achieved. All
the systems displayed low activity for ethylene oligomeri-
sation on treatment with excess MAO affording mainly lin-
ear a-olefins along with some degree of internal olefins. The
nature of the 4-position substitution pattern appears to
have little effect on the activity of the catalyst under these
conditions but does influence the a-olefin:internal olefin
ratio. It is notable that these systems are much less active
when compared with the recently reported imino-phen-
anthrolinyl-iron systems [9], a trend that is also apparent
for bis(imino)pyridine-iron over bis(imino)pyridine-cobalt
oligomerisation catalysts [2c].
4.2. Preparation of starting materials
4.2.1. Methyl 1,10-phenanthroline-2-carboxylate
The procedure was based on that described by Engber-
sen et al. [19]. Under an atmosphere of nitrogen 2-cyano-
1,10-phenanthroline (3.00 g, 0.014 mol) and a catalytic
amount of sodium (50 mg) in dry methanol (130 ml) was
stirred and heated to reflux for 0.5 h. The reaction mixture
was cooled to 0 ꢀC and made slightly acidic with 2% HCl
(ca. 100 ml) and stirred for a further 0.5 h. The solution
was neutralised with sodium hydrogencarbonate and the
methanol removed on the rotary evaporator. The aqueous
phase was extracted with chloroform (3 · 75 ml) and the
organic extracts combined and dried over magnesium sul-
phate. Following filtration, the solvent was removed under
4. Experimental
4.1. General
All reactions, unless otherwise stated, were carried out
under an atmosphere of dry, oxygen-free nitrogen, using

4120
J.D.A. Pelletier et al. / Journal of Organometallic Chemistry 691 (2006) 4114–4123
reduced pressure to afford methyl 1,10-phenanthroline-2-
carboxylate as a dark brown solid (2.14 g, 62%). M.p.
111–113 ꢀC [lit. [19] 110–112 ꢀC].
2,6-diisopropylaniline (0.19 ml, 1.01 mmol, 1.05 equiv.).
The suspension was allowed to warm to 50 ꢀC and one
drop of acetic acid introduced. After stirring at 50 ꢀC over-
night the solvent was removed on the rotary evaporator
and the residue taken up in chloroform (25 ml) and dried
over magnesium sulphate. Following filtration, all volatiles
were removed under reduced pressure to give L1 as a pale
yellow solid (77%, 0.27 g). M.p.: 194–196 ꢀC [lit. [9] 192–
194 ꢀC]. IR (cmꢀ1). ES mass spectrum, m/z 368 [M+H]+.
4.2.2. 2-Carbinol-1,10-phenanthroline
To a solution of methyl 1,10-phenanthroline-2-carbox-
ylate (2.50 g, 10.50 mmol) in absolute ethanol (150 ml)
was slowly added sodium borohydride (6.0 g, 0.158 mol,
15 equiv.) and the reaction mixture stirred at ambient tem-
perature for 2 days. Water (50 ml) was added carefully and
the resultant yellow solution neutralised (pH 7–8) with a
solution of dilute hydrochloric acid before being extracted
with chloroform (3 · 75 ml). The organic extracts were
combined and dried over magnesium sulphate. Following
filtration the solvent was removed under reduced pressure
to yield 2-carbinol-1,10-phenanthroline as a brown solid
4.3.2. 1,10-C12H7N2-CH@N(2,6-i-Pr2-4-Br-C6H2) (L2)
In a manner similar to that outlined for L1, L2 was pre-
pared as a pale orange solid (87%). Recrystallisation from
ethanol gave L2 as pale green plates. M.p.: 198–200 ꢀC. IR
(cmꢀ1) 2957, 2865, 1633 t(C@Nimine), 1589, 1553, 1492,
1452, 1393, 1318, 1184, 1081, 858, 788, 751. ES mass spec-
1
1
(2.01 g, 91%). The H NMR spectrum of the product was
trum, m/z 447 [M+H]+. H NMR (300 MHz, CDCl3): d
consistent with the literature report [20].
9.20 (d, J = 1.8, 1H, phen-H), 8.69 (s, 1H, CH@N), 8.60
(d, J = 8.5, 1H, phen-H), 8.32 (d, J = 8.2, 1H, phen-H),
8.24 (dd, J = 8.2, 1.5, 1H, phen-H), 7.79 (s, 2H, phen-H),
7.62 (dd, J = 8.2, 4.4, 1H, phen-H), 7.20 (s, 2H, Ar-H),
2.93 (sept, J = 6.7, 2H, CHMe2), 1.09 (d, J = 6.7, 12H,
CHMe2). 13C NMR (75 MHz, CDCl3): d 163.2, 153.2,
149.6, 148.5, 135.9, 135.5, 133.6, 128.8, 128.0, 127.4,
126.9, 125.4, 125.2, 124.7, 122.1, 120.4, 119.4, 21.2, 19.9.
Anal. Calcd. for C25H24BrN3: C, 67.28; H, 5.38; N, 9.42.
Found: C, 67.41; H, 5.70; N, 9.71%.
4.2.3. 2-Formyl-1,10-phenanthroline
A red suspension of 2-carbinol-1,10-phenanthroline
(2.00 g, 9.52 mmol) and selenium dioxide (2.11 g,
19.01 mmol, 2 equiv.) in dioxane (150 ml) were heated to
reflux for 2 h. Hot filtration through celite followed by
the washing of the celite cake with hot dioxane (100 ml)
afforded a red solution. The solvent was removed under
reduced pressure yielding 2-formyl-1,10-phenanthroline as
a red solid (1.41 g, 71% yield). M.p.: 150–153 ꢀC [lit. [21]
152–153 ꢀC]. IR (cmꢀ1): 1707 t(C@O). ES mass spectrum,
m/z 209 [M+H]+.
4.3.3. 1,10-C12H7N2-CH@N(2,6-i-Pr2-4-CN-C6H2) (L3)
In a manner similar to that outlined for L1, L3 was pre-
pared as a brick red solid (68%). IR (cmꢀ1) 2963, 2871,
2213 t(C„N), 1639 t(C@Nimine), 1559, 1492, 1462, 1383,
1165, 1093, 865, 768, 741. ES mass spectrum, m/z 393
[M+H]+. 1H NMR (300 MHz, CDCl3): d 9.20 (d,
J = 1.8, 1H, phen-H), 8.69 (s, 1H, CH@N), 8.60 (d,
J = 8.5, 1H, phen-H), 8.40 (d, J = 8.2, 1H, phen-H), 8.27
(dd, J = 8.2, 1.8, 1H, phen-H), 7.90 (s, 2H, phen-H), 7.66
(dd, J = 8.2, 4.4, 1H, phen-H), 7.20 (s, 2H, Ar-H), 2.94
(sept, J = 7.1, 2H, CHMe2), 1.12 (d, J = 6.7, 12H,
CHMe2). 13C NMR (75 MHz, CDCl3): d 163.3, 152.7,
151.3, 149.9, 144.8, 135.5, 131.1, 128.8, 128.4, 127.3,
126.4, 125.4, 125.3, 122.5, 121.9, 120.0, 119.3, 99.1, 27.8,
21.8. Anal. Calcd. for C26H24N4: C, 79.59; H, 5.38; N,
14.29. Found: C, 79.81; H, 5.74; N, 14.51%.
4.2.4. 2-Acetyl-1,10-phenanthroline
The procedure was similar to that described by Sun et al.
[9] but with some modifications made to the reaction condi-
tions and the work-up. Thus, 2-cyano-1,10-phenanthroline
(1.0 g, 4.87 mmol) was suspended in dry toluene (100 ml)
under an atmosphere of nitrogen. Trimethylaluminium
(5 ml, 10.00 mmol, 2 equiv.) was added dropwise at room
temperature and the reaction mixture stirred and heated
to 70 ꢀC overnight to give a dark green solution. On cooling
to room temperature, all volatiles were removed under
reduced pressure and chloroform introduced (30 ml). Water
(40 ml) was carefully added to the reaction and the mixture
stirred vigorously for 2 h. Following filtration, the organic
phase was separated and washed with a saturated solution
of the disodium salt of EDTA (2 · 30 ml) and then with
water (2 · 30 ml). After drying over anhydrous magnesium
sulphate the solvent was removed under reduced pressure to
give 2-acetyl-1,10-phenanthroline as a pale white solid
(80%, 0.87 g). M.p.: 151–153 ꢀC [lit. [9] 152–154 ꢀC]. IR
(cmꢀ1) 1694 t(C@O). ES mass spectrum, m/z 223 [M+H]+.
4.3.4. 1,10-C12H7N2-CH@N(2,4,6-i-Pr3-4-C6H2) (L4)
In a manner similar to that outlined for L1, L4 was pre-
pared as an orange solid (60%). M.p.: 191–193 ꢀC. IR
(cmꢀ1) 2958, 2867, 1635 t(C@Nimine), 1589, 1553, 1490,
1461, 1381, 1319, 1173, 1090, 875, 829, 764. ES mass spec-
1
trum, m/z 410 [M+H]+. H NMR (300 MHz, CDCl3): d
9.19 (dd, J = 4.4, 1.8, 1H, phen-H), 8.76 (s, 1H, CH@N),
8.65 (d, J = 8.5, 1H, phen-H), 8.33 (d, J = 9.0, 1H, phen-
H), 8.25 (dd, J = 8.2, 1.8, 1H, phen-H), 7.83 (s, 2H,
phen-H), 7.63 (dd, J = 7.9, 4.4, 1H, phen-H), 6.84 (s, 2H,
Ar-H), 3.0–2.7 (m, 3H, CHMe2), 1.3–1.1 (m, 18H,
CHMe2). 13C NMR (75 MHz, CDCl3): d 163.3, 154.9,
4.3. Preparation of ligands (L1–L6)
4.3.1. 1,10-C12H7N2-CH@N(2,6-i-Pr2-C6H3) (L1)
To
a
suspension of 2-formyl-1,10-phenanthroline
(0.200 g, 0.96 mmol) in absolute ethanol (2 ml) was added

J.D.A. Pelletier et al. / Journal of Organometallic Chemistry 691 (2006) 4114–4123
4121
150.6, 146.1, 146.0, 145.8, 144.5, 138.0, 136.8, 136.6, 129.8,
4.4.2. R = H, R1 = Br (1b)
129.0, 127.7, 126.5, 123.2, 120.9, 120.5, 34.1, 28.0, 24.2,
23.4. Anal. Calcd. for C28H31N3: C, 82.21; H, 7.58; N,
10.27. Found: C, 82.11; H, 7.77; N, 10.12%.
Employing the method outlined for 1a using anhydrous
cobalt dichloride (0.112 g, 0.862 mmol), n-butanol (5 ml)
and L2 (0.384 g, 0.862 mmol, 1 equiv.) gave 1b as a dark
green solid (0.397 g, 80%). IR (cmꢀ1) 2962, 1612, 1575,
1515, 1494, 1462, 1437, 1404, 1296, 864, 739.
4.3.5. 1,10-C12H7N2-CMe@N(2,6-i-Pr2-C6H3) (L5)
To a suspension of 2-acetyl-1,10-phenanthroline (0.50 g,
2.25 mmol) in absolute ethanol (2 ml) was added 2,6-diiso-
propylaniline (0.46 ml, 2.47 mmol, 1.05 equiv.). The sus-
pension was heated to reflux and one drop of acetic acid
introduced. After stirring at reflux overnight the solvent
was removed on the rotary evaporator and the residue
taken up in chloroform (25 ml) and dried over magnesium
sulphate. Following filtration, all volatiles were removed
under reduce pressure to give L5 as a pale yellow solid
(70%, 0.62 g). Recrystallisation from ethanol gave L5 as
yellow blocks. M.p.: 191–193 ꢀC [lit. [9] 196–198 ꢀC]. ES
mass spectrum, m/z 382 [M+H]+.
4.4.3. R = H, R1 = CN (1c)
Employing the method outlined for 1a using anhydrous
cobalt dichloride (0.112 g, 0.862 mmol), n-butanol (5 ml)
and L3 (0.338 g, 0.862 mmol, 1 equiv.) gave 1c as an olive
green solid (0.293 g, 65%). Recrystallisation of 1c from ace-
tonitrile afforded crystals suitable for a single crystal X-ray
diffraction study. IR (cmꢀ1) 2965, 2215 t(C„N), 1606,
1517, 1494, 1464, 1442, 1407, 1297, 868, 743.
4.4.4. R = H, R1 = i-Pr (1d)
Employing the method outlined for 1a using anhydrous
cobalt dichloride (0.078 g, 0.60 mmol), n-butanol (10 ml)
and L4 (0.245 g, 0.60 mmol, 1 equiv.) gave 1d as a brown
solid (0.193 g, 60%). IR (cmꢀ1) 3061, 2960, 2868, 1611,
1579, 1513, 1493, 1458, 1402, 1381, 1318, 1170, 1119,
1071, 865, 796, 742.
4.3.6. 1,10-C12H7N2-CMe@N(2,4,6-i-Pr3-C6H2) (L6)
In a manner similar to that outlined for L5, L6 was pre-
pared as a brick red solid (92%). Recrystallisation from
ethanol gave L6 as yellow blocks. M.p.: 186–188 ꢀC. IR
(cmꢀ1) 3254, 2958, 2067, 1652, 1587, 1552, 1490, 1461,
1362, 1317, 1177, 1116, 874, 834, 785, 751. ES mass spec-
4.4.5. R = Me, R1 = H (1e)
Employing the method outlined for 1a using anhydrous
cobalt dichloride (0.102 g, 0.79 mmol), n-butanol (10 ml)
and L5 (0.300 g, 0.79 mmol, 1 equiv.) gave 1e as a red–
brown solid (0.280 g, 70%). IR (cmꢀ1) 2969, 1607, 1582,
1511, 1466, 1407, 1373, 1287, 1206, 1192, 1146, 1088,
873, 833, 784, 741, 657.
1
trum, m/z 424 [M+H]+. H NMR (250 MHz, CDCl3): d
9.21 (d, J = 3.0, 1H, phen-H), 8.74 (d, J = 8.5, 1H, phen-
H), 8.29 (m, 2H, phen-H), 7.80 (s, 2H, phen-H), 7.61 (m,
1H, phen-H), 6.95 (s, 2H, Ar-H), 2.87 (app. sept, J = 6.8,
3H, CHMe2), 2.53 (s, 3H, CMe@N), 1.19 (m, 18H,
CHMe2). 13C NMR (75 MHz, CDCl3): d 167.8, 156.1,
150.6, 146.7, 146.3, 136.4, 135.7, 129.6, 129.0, 127.5,
126.5, 123.7, 123.4, 123.0, 122.8, 120.4, 118.5, 28.3, 26.1,
23.0, 18.4, 17.6. HRMS (FAB): Anal. Calcd. for
C29H33N3 [M+H]+ 424.27527, found 424.27520.
4.4.6. R = Me, R1 = i-Pr (1f)
Employing the method outlined for 1a using anhydrous
cobalt dichloride (0.100 g, 0.77 mmol), n-butanol (9 ml)
and L6 (0.326 g, 0.77 mmol, 1 equiv.) gave 1f as a red–brown
solid (0.26 g, 61%). Recrystallisation of 1f from hot acetoni-
trile afforded crystals suitable for a single crystal X-ray dif-
fraction study. IR (cmꢀ1) 2960, 1615, 1582, 1511, 1469,
1407, 1371, 1285, 1211, 1180, 1151, 869, 835, 788, 741, 658.
4.4. Preparation of [1,10-C12H7N2-CR@N(2,6-i-Pr2-4-R1-
C6H2)]CoCl2 (1)
4.4.1. R = R1 = H (1a)
4.5. General screening for ethylene oligomerisation
An oven dried Schlenk vessel equipped with magnetic
stirrer was evacuated and backfilled with nitrogen. The
vessel was charged with anhydrous cobalt dichloride
(0.048 g, 0.369 mmol) and suspended in n-BuOH (5 ml)
and the contents stirred at 90 ꢀC until the cobalt salt
had completely dissolved. L1 (0.136 g, 0.369 mmol,
1 equiv.) was added and the mixture heated to 90 ꢀC
for 1 h. On cooling to ambient temperature, hexane
was added to induce precipitation of the product. Fol-
lowing filtration, washing with hexane and drying under
reduced pressure, 1a (0.120 g, 65%) was isolated as a
brown solid. Recrystallisation of 1a from acetonitrile
afforded crystals suitable for a single crystal X-ray dif-
fraction study. IR (cmꢀ1) 2963, 1609, 1573, 1515, 1462,
1436, 1404, 1172, 1118, 856, 811, 736.
An oven dried 200 ml Schlenk vessel equipped with
magnetic stir bar was evacuated and backfilled with nitro-
gen. The vessel was charged with the precatalyst
(0.01 mmol) and dissolved or suspended in toluene
(35 ml). MAO (2.10 ml, 4.0 mmol) was introduced and
the reaction mixture left to stir for 5 min. 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 over magne-
sium sulphate and filtered. Quantitative GC analysis was
performed by taking an aliquot of the solution containing
a weighted amount of a standard (n-heptadecene). For

Table 5
Crystallographic and data processing parameters for L2, L5, L6, 1a, 1c and 1f
Complex
L2
L5
L6
1a
1c
1f
Formula
M
Crystal size (mm3)
Temperature (K)
Crystal system
Space group
C
25H24BrN3
C26H28N3 Æ CH3CH2OH
427.57
0.29 · 0.21 · 0.16
150(2)
Triclinic
P-1
8.2035(15)
11.747(2)
13.004(2)
82.296(3)
73.587(3)
85.972(3)
1190.5(4)
2
C29H33N3
423.58
0.22 · 0.14 · 0.11
150(2)
Monoclinic
P2(1)/c
17.966(6)
20.715(7)
13.640(5)
90
105.130(7)
90
4900(3)
8
1.148
1824
C25H25Cl2CoN3
497.31
0.28 · 0.19 · 0.15
150(2)
Orthorhombic
Pbca
14.863(2)
15.957(2)
19.182(3)
90
C26H24Cl2CoN4
522.32
0.33 · 0.21 · 0.09
150(2)
Monoclimic
P2(1)
9.457(3)
13.843(4)
9.736(3)
90
94.597(5)
90
1270.4(6)
2
1.365
538
0.907
C29H33Cl2CoN3
553.41
0.20 · 0.18 · 0.07
150(2)
Triclinic
P-1
8.200(2)
9.399(3)
19.369(5)
87.602(5)
78.408(5)
71.459(5)
1385.9(6)
2
446.38
0.24 · 0.18 · 0.08
150(2)
Monoclinic
C2/c
34.646(5)
9.5442(15)
43.782(7)
90
108.448(3)
90
13733(4)
24
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
90
90
3
˚
U (A )
4549.4(11)
8
1.452
2056
1.007
Z
Dc (Mg mꢀ3
F(000)
)
1.295
5220
1.811
1.193
460
0.073
1.326
578
0.834
l (Mo Ka) (mmꢀ1
)
0.067
Reflections collected
Independent reflections
Rint
51960
13489
0.0584
0/796
8698
4171
0.0380
0/267
35320
8640
0.1536
0/591
31159
4009
0.0455
0/284
9179
4450
0.0720
1/302
10941
5372
0.0711
0/323
Restraints/parameters
Final R indices (I > 2r(I))
All data
R1 = 0.0500
wR2 = 0.0974
R1 = 0.1112
wR2 = 0.1067
0.793
R1 = 0.0468
wR2 = 0.1166
R1 = 0.0645
wR2 = 0.1229
1.006
R1 = 0.0610
wR2 = 0.0869
R1 = 0.1710
wR2 = 0.1122
0.812
R1 = 0.0326
wR2 = 0.0742
R1 = 0.0456
wR2 = 0.0781
R1 = 0.0700
wR2 = 0.01392
R1 = 0.1046
wR2 = 0.1517
0.901
R1 = 0.0624
wR2 = 0.1235
R1 = 0.0880
wR2 = 0.1329
0.986
Goodness-of-fit on F2 (all data)
0.968
P
P
P
P
2
2 1=2
2
2
2
Data in common: graphite-monochromated Mo Ka radiation, k = 0.71073 A; R1 = ||Fo| ꢀ |Fc||/ |Fo|, wR2 ¼ ½ wðF 2o ꢀ F c2Þ = wðF 2oÞ ꢁ , wꢀ1 = [r (Fo) + (aP) ], P ¼ ½maxðF o2; 0Þ þ 2ðF c2Þꢁ=3,
˚
P
1=2
where a is a constant adjusted by the program; goodness-of-fit ¼ ½ ðF 2o ꢀ F c2Þ2=ðn ꢀ pÞꢁ where n is the number of reflections and p is the number of parameters.

J.D.A. Pelletier et al. / Journal of Organometallic Chemistry 691 (2006) 4114–4123
4123
1
(e) Z. Zhang, S. Chen, X. Zhang, H. Li, Y. Ke, Y. Lu, Y. Hu, J.
Mol. Cat. A 230 (2005) 1;
(f) V.C. Gibson, N.J. Long, P.J. Oxford, A.J.P. White, D.J. Williams,
Organometallics 35 (2006) 1932.
analysis of the oligomers by H NMR spectroscopy, the
solvent was removed on the rotary evaporator and the res-
idue dissolved in CDCl3.
[4] See for example (a) D.M. Dawson, D.A. Walker, M. Thornton-Pett,
M. Bochmann, J. Chem. Soc. Dalton Trans. (2000) 459;
(b) G.J.P. Britovsek, V.C. Gibson, O.D. Hoarau, S.K. Spitzmesser,
A.J.P. White, D.J. Williams, Inorg. Chem. 42 (2003) 3454;
(c) V.C. Gibson, S.K. Spitzmesser, A.J.P. White, D.J. Williams,
J. Chem. Soc. Dalton Trans. (2003) 2718;
4.6. Crystallography
Data for L2, L5, L6, 1a, 1c and 1f were collected on a
Bruker APEX 2000 CCD diffractometer. Details of data col-
lection, refinement and crystal data are listed in Table 5. The
data were corrected for Lorentz and polarisation effects and
empirical absorption corrections applied. Structure solution
by direct methods and structure refinement on F2 employed
SHELXTL version 6.10 [22]. Hydrogen atoms were included in
(d) S. Matsui, M. Nitabaru, K. Tsuru, T. Fujita, Y. Suzuki, Y.
Takagi, H. Tanaka (Mitsui Chemicals Inc., Japan). PCT Int. Appl.
WO9954364, 1999 [Chem. Abstr. 131 (1999) 310946];
(e) L. Wang, W.-H. Sun, L. Han, Z. Li, Y. Hu, C. He, C. Yan, J.
Organomet. Chem. 650 (2002) 59.
[5] See for example (a) G.J.P. Britovsek, V.C. Gibson, S. Mastroianni,
C. Redshaw, G.A. Solan, A.J.P. White, D.J. Williams, Eur. J. Inorg.
Chem. (2001) 431;
˚
calculated positions (C–H = 0.96 A) riding on the bonded
atom with isotropic displacement parameters set to
1.5Ueq(C) for methyl H atoms and 1.2 Ueq(C) for all other
H atoms. All non-H atoms were refined with anisotropic dis-
placement parameters. Disordered solvent was omitted
using the SQUEEZE option in platon for L2 and L5.
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5. Supplementary material
Chem. 628 (2002) 2839.
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC No. 608572–608577 for compounds L2, L5,
L6, 1a, 1c and 1f, respectively. Copies of this information
may be obtained free of charge from The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44 1223
336033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
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Acknowledgements
We thank the University of Leicester and ExxonMobil
(to JDAP) for financial assistance.
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imines/pyridines see: (a) M. Brockmann, H. tom Dieck, J. Klaus,
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