Iron complexes bearing iminopyridine and aminopyridine ligands as catalysts for atom transfer radical polymerisation

Article abstract of DOI:10.1039/b303094f

A series of iron(II) complexes bearing iminopyridine and aminopyridine ligands with N-alkyl and N-aryl substituents has been synthesised. X-Ray crystal structures of n-propyl- and 2,6-diisopropylphenyl-iminopyridine derivatives reveal dinuclear structures

Full text of DOI:10.1039/b303094f

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Iron complexes bearing iminopyridine and aminopyridine ligands
as catalysts for atom transfer radical polymerisation
Vernon C. Gibson,*a Rachel K. O’Reilly,a Duncan F. Wass,b Andrew J. P. Whitea and
David J. Williamsa
a Department of Chemistry, Imperial College, Exhibition Road, South Kensington, London,
UK SW7 2AY. E-mail: v.gibson@imperial.ac.uk; Fax: 020 7594 5810; Tel: 020 7594 5830
b BP Chemicals, Sunbury Research Centre, Chertsey Road, Sunbury on Thames, Middlesex,
UK TW16 7LN. E-mail: WassDF@bp.com; Fax: 01932 775467; Tel: 01932 775247
Received 18th March 2003, Accepted 6th June 2003
First published as an Advance Article on the web 24th June 2003
A series of iron() complexes bearing iminopyridine and aminopyridine ligands with N-alkyl and N-aryl substituents
has been synthesised. X-Ray crystal structures of n-propyl- and 2,6-diisopropylphenyl-iminopyridine derivatives
reveal dinuclear structures with halide bridges; a derivative carrying a cyclododecyl imine substituent and an
α-methylpyridine unit is mononuclear. In studies of their atom transfer radical polymerisation behaviour, the
mononuclear iminopyridine derivative is found to catalyse the polymerisation of styrene and methyl methacrylate
while the dinuclear catalysts polymerise styrene only. The aminopyridine complexes are more efficient ATRP catalysts
for styrene polymerisation than their unsaturated iminopyridine relatives.
Introduction
Atom transfer radical polymerisation is an attractive technique
for the controlled synthesis of a wide variety of polystyrenic
and polyacrylic materials.1 By their nature, conventional free
radical polymerisations are difficult to control due to the
extremely reactive nature of radicals which causes irreversible
termination reactions. Thus, to produce a controlled radical
Scheme 1 Synthesis of complexes 1–6 where RЈ = H; R = n-propyl, 1;
c-C6H11, 2; c-C12H23, 3; R = 2,6 diisopropylphenyl, 4 and RЈ = Me;
polymerisation, the concentration of active radical chain ends
must be kept low. This can be achieved by establishing a fast
and dynamic equilibrium between growing and dormant
polymer chains using a metal-mediated halide exchange
process. Under these circumstances, a well-controlled, pseudo-
living polymerisation, affording good control over molecular
weight and molecular weight distributions, can be achieved.
Building on knowledge gained from metal mediated coupling
reactions involving organic radicals (the Kharasch reaction),2
Wang and Matyjaszewski3 and Sawamoto et al.4 showed that
copper- and ruthenium-based catalyst systems, respectively,
effect well-controlled polymerisations of styrene and methyl-
methacrylate. Since then, catalysts based on a number of other
metals have been reported, including systems based on Ru,5
Rh,6 Pd,7 Ni8 and Fe.9 Following the initial studies on Cu/bipy
systems, a variety of ligands have been investigated for copper,
including bi- and tri-dentate amines,10 aminopyridines,11 imino-
pyridines12 and tripodal ligands.13
R = n-propyl, 5; c-C12H23, 6.
stirring a solution of anhydrous FeCl2 with a slight excess of
the iminopyridine in tetrahydrofuran at 60 ЊC for 16 h.
After cooling, filtration and washing, 1–6 can be isolated as
microcrystalline, air-stable solids in excellent yields (typically
80–90%). 1–6 have been characterised by magnetic moment
measurements, infrared spectroscopy, mass spectrometry and
elemental analysis.
A single crystal X-ray analysis of 5 showed it to be the
centrosymmetric dimeric complex illustrated in Fig. 1. The
geometry at each iron centre is best described as distorted
trigonal bipyramidal, there being within the equatorial plane
a
noticeable enlargement of the Cl(1)–Fe–Cl(2Ј) angle
[137.54(4)Њ], and small contractions of the N(7)–Fe–Cl(2Ј) and
Some time ago, we disclosed a new family of four-coordinate
iron-based catalysts stabilised by α-diimine ligands,14 and found
that their catalytic behaviour was strongly influenced by the
nature of the imine substituents. In the case of alkylimines,
well-controlled polymerisations of both styrene and MMA
were found. However, for aryl substituents, rapid chain transfer
processes are competitive.15 With a view to obtaining a better
understanding of the steric and electronic factors influencing
the behaviour of four-coordinate iron ATRP catalysts contain-
ing N-donor ligands, we decided to extend our studies to readily
accessible imino- and amino-pyridine derivatives. In this
paper we report the synthesis of a family of imino- and amino-
pyridine complexes, their solution and solid-state structures
and their behaviour as ATRP catalysts.
Fig. 1 The molecular structure of 5. Selected bond lengths (Å) and
angles (Њ): Fe–Cl(1) 2.2890(10), Fe–Cl(2) 2.5246(9), Fe–Cl(2Ј)
2.4029(10), Fe–N(1) 2.219(3), Fe–N(7) 2.119(3), C(7)–N(7) 1.274(4);
Cl(1)–Fe–Cl(2) 96.41(4), Cl(1)–Fe–Cl(2Ј) 137.65(4), Cl(1)–Fe–N(1)
96.21(7), Cl(1)–Fe–N(7) 112.40(8), Cl(2)–Fe–Cl(2Ј) 83.79(3), Cl(2)–Fe–
N(1) 167.36(7), Cl(2)–Fe–N(7) 97.41(8), Cl(2Ј)–Fe–N(1) 87.28(7),
Cl(2Ј)–Fe–N(7) 109.53(8), N(1)–Fe–N(7) 77.16(10), Fe–Cl(2)–FeЈ
96.21(3). The transannular Fe ؒ ؒ ؒ Fe separation is 3.669(1) Å.
Results and discussion
(i) Synthesis and structural characterisation. The para-
magnetic complexes 1–6 (Scheme 1) are readily prepared by
D a l t o n T r a n s . , 2 0 0 3 , 2 8 2 4 – 2 8 3 0
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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N(7)–Fe–Cl(1) angles [109.53(8) and 112.40(8)Њ, respectively].
The axial N(1)–Fe–Cl(2) angle exhibits a small non-linearity
[167.36(7)Њ] and the axial/equatorial N(1)–Fe–N(7) angle is, as
expected, substantially contracted [77.16(10)Њ] as a consequence
of the bite of the five-membered chelate ring. The iron
coordination distances are unexceptional, exhibiting an
expected lengthening of the axial bonds relative to their
equatorial counterparts. The chloride bridges are thus
asymmetric [Fe–Cl(2) 2.5246(9) Å, Fe–Cl(2Ј) 2.4029(10) Å].
The five-membered chelate ring is slightly folded about the
N(1) ؒ ؒ ؒ N(7) vector such that the iron atom lies 0.204 Å out of
the plane of the remaining four atoms which are coplanar
to within 0.012 Å. The molecules pack to form end-to-end
chains that extend in the crystallographic 011 direction
with π–π stacking of symmetry-related pyridyl rings with
centroid ؒ ؒ ؒ centroid and mean-interplanar separations of
3.75 and 3.35 Å, respectively. The most closely related structure
in the literature is that of bis(µ2-bromo)dibromo-bis(2,6-
bis(isopropyl)phenyl((6-methyl-2-pyridinyl)methylene)amine)-
dinickel()16 which has two independent centrosymmetric
dimers in the unit cell. In this latter structure the distortion
from trigonal bipyramidal geometry at the nickel centre is
greater with the pair of equatorial Ni–Br bonds subtending an
angle of ca. 144Њ; the chelate geometry is very similar to that
observed in 5.
By contrast, a structure determination of compound 6,
where the n-propylimine substituent has been replaced by
a cyclododecyl ring, reveals a monomeric complex with a
four-coordinate iron atom (Fig. 2). The geometry at the metal
is severely distorted tetrahedral, the N(1)–Fe–N(7) ligand bite
angle being 77.8(2)Њ [cf. 77.16(10) in 5]; the remaining angles
subtended at the iron centre are in the range 108.6(1)–117.8(1)Њ
and the coordination distances are unexceptional. The five-
membered chelate ring is slightly folded with the metal lying
0.15 Å out of the plane of the other four atoms (which are
coplanar to within 0.02 Å). Interestingly, the methine hydrogen
at the quaternary centre C(9) has exactly the same syn
relationship with respect to the imino hydrogen on C(7) as was
observed in the related bis(cyclohexylimino) species.14b The only
intermolecular feature of note is a weak C–H ؒ ؒ ؒ Cl inter-
action between this imino hydrogen and the Cl(2) chlorine
centre of a glide-related molecule [H ؒ ؒ ؒ Cl 2.77 Å, C–H ؒ ؒ ؒ Cl
163Њ] to form pseudo-polymer chains that propagate along the
crystallographic b direction.
Fig. 3 1H NMR spectrum of 6 in CDCl3 (* = CHCl3).
envisaged that the bulky 2,6-diisopropylphenyl substituent may
also favour a mononuclear structure. An X-ray structure
determination of 4, in which the pyridine α-methyl group is
absent, reveals a dimeric species with crystallographic inversion
symmetry (Fig. 4). In this complex, the geometry at the two iron
centres is probably best described as distorted square pyramidal
(cf. trigonal bipyramidal in 5), the four basal atoms [N(1), N(7),
Cl(2) and Cl(2Ј)] being coplanar to within 0.068 Å with the iron
atom lying 0.714 Å out of this plane. Consistent with this
change in coordination geometry, the Fe coordination distances
exhibit distinct differences from their counterparts in 5. Most
noticeable in particular is a reduction in ∆(Fe–Cl) within the
bridge from 0.12 Å in 5 to 0.06 Å in 4. The five-membered
chelate ring has a slightly folded geometry with the iron atom
lying 0.064 Å out of the plane of the remaining four atoms
which are coplanar to within 0.003 Å. The 2,6-diisopropyl-
phenyl ring is inclined almost orthogonally (ca. 87Њ) to the
chelate ring plane. The nickel analogue of 4 shows similar
structural features.17 The only intermolecular packing inter-
action of note is a weak C–H ؒ ؒ ؒ Cl interaction, analogous
to that seen in 6, between the imino hydrogen and the Cl(1)
chlorine centre of a glide-related molecule [C ؒ ؒ ؒ Cl 3.60 Å,
H ؒ ؒ ؒ Cl 2.76 Å, C–H ؒ ؒ ؒ Cl 149Њ] to form a pseudo-polymer
chain. It would appear that the α-methyl pyridine substituent
plays a crucial role in determining whether these iminopyridine
complexes are mononuclear or dinuclear in the solid state.
Cryoscopic solution molecular weight determinations show
that 1–5 retain aggregated structures in solution, whereas
complex 6 retains its monomeric structure.18
Fig. 2 The molecular structure of 6. Selected bond lengths (Å) and
angles (Њ): Fe–Cl(1) 2.2233(15), Fe–Cl(2) 2.2307(16), Fe–N(1) 2.145(4),
Fe–N(7) 2.111(4), C(7)–N(7) 1.277(6); N(7)–Fe–N(1) 77.82(16), N(7)–
Fe–Cl(1) 113.68(12), N(1)–Fe–Cl(1) 108.63(12), N(7)–Fe–Cl(2)
117.84(12), N(1)–Fe–Cl(2) 116.16(12), Cl(1)–Fe–Cl(2) 116.48(6).
Fig. 4 The molecular structure of 4. Selected bond lengths (Å) and
angles (Њ): Fe–N(1) 2.150(3), Fe–N(7) 2.227(2), Fe–Cl(1) 2.2649(11),
Fe–Cl(2) 2.4693(10), Fe–Cl(2Ј) 2.4056(11), C(7)–N(7) 1.272(4); N(1)–
Fe–N(7) 75.11(10), N(1)–Fe–Cl(1) 101.34(8), N(7)–Fe–Cl(1) 108.38(7),
N(1)–Fe–Cl(2Ј) 146.47(7), N(7)–Fe–Cl(2Ј) 90.53(7), Cl(1)–Fe–Cl(2Ј)
111.98(5), N(1)–Fe–Cl(2) 88.27(7), N(7)–Fe–Cl(2) 140.90(7), Cl(1)–Fe–
Cl(2) 109.49(4), Cl(2)–Fe–Cl(2Ј) 84.22(4), Fe–Cl(2)–FeЈ 95.78(3). The
transannular Fe ؒ ؒ ؒ Fe separation is 3.617(1) Å.
Although paramagnetic, 6 affords a reasonably sharp
1
contact-shifted H NMR spectrum (Fig. 3). Tentative assign-
ments have been made on the basis of integrated signal
intensities and the chemical shifts as an indication of proximity
to the paramagnetic iron centre.
Since replacement of the 1Њ n-propyl substituent by the much
larger 2Њ cyclododecyl unit led to a mononuclear complex, we
(ii) Styrene polymerisation. The use of 1–6 in the bulk
polymerisation of styrene initiated by 1-phenylethyl chloride
(1-PECl) has been monitored at 120 ЊC under an inert
D a l t o n T r a n s . , 2 0 0 3 , 2 8 2 4 – 2 8 3 0
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Table 1 Styrene polymerisation data for complexes 1–6a
Table 2 MMA polymerisation results for 6a
Catalyst
kobs/hϪ1
Mn,th
Mn
Mw/Mn
TosCl
EBrB
MBPA
1
2
3
4
5
6
0.06
0.05
0.05
–
0.06
0.17
19000
17200
17400
19400
19200
21000
18400
18000
19000
5000
18600
23300
1.34
1.41
1.32
1.79
1.39
1.34
Mn
Mn,th
Mw/Mn
23600
20000
1.49
25200
20000
1.62
24500
20000
1.64
b
a MMA polymerisations (200 equiv.) at 80 ЊC in 10% v/v toluene, for
32 h.
a Polymerisation performed over 24 h. b Non-linear kinetics.
polymerisation markedly (cf. for 6: kobs(1-PEBr) = 0.04 hϪ1 vs.
kobs(1-PECl) = 0.17 hϪ1).
atmosphere. The experimentally determined rate constants are
given in Table 1 along with molecular weights and molecular
weight distributions at ca. 100% conversion. Semilogarithmic
plots of ln([M]o/[M]) vs. time were found to be linear in the
cases of 1, 2, 3, 5 and 6, indicating that the radical con-
centration is constant throughout the polymerisation runs.
Typical plots for catalysts 3 and 6 are shown in Fig. 5.
Overall, styrene polymerisations using the iminopyridine
complexes 1, 2, 3 and 5 are quite well controlled, though ca. five
times slower than their diimine analogues (cf. 2, kobs = 0.05 hϪ1
;
iron()diimines, kobs ca. 0.25 hϪ1).14b For the mononuclear
derivative 6, polymerisations are considerably faster than for 1,
2, 3 and 5 but still slower than for its α-diimine analogues. Thus,
whereas pyridylimine ligands on copper do not slow down the
rate of polymerisation,20 on iron significantly slower rates are
found.
In the case of 4, the semilogarithmic plot of ln([M]o/[M]) vs.
time was non-linear: Mn did not increase linearly over time and
did not agree with theoretical molecular weights. (Mn,th
=
16800, Mn = 4700 and Mw/Mn = 1.79). Such behaviour is
reminiscent of α-diimine derivatives bearing aryl substituents
and has been shown to be attributable to competitive chain
transfer processes.15
The trichloride analogue of 6, complex 7, was synthesised by
an analogous procedure to that shown in Scheme 1, except iron
trichloride was employed. The product was washed with diethyl
ether to afford 7 as a microcrystalline, paramagnetic solid
in 84% yield. Both solid-state and solution studies indicate
that this complex exists as a mononuclear species.21 7 was tested
for the reverse ATRP of styrene (200 equiv., bulk) initiated by
azobisisobutyronitrile (AIBN) at 110 ЊC. The semilogarithmic
plot of ln([M]o/[M]) vs. time is linear with a kobs of 0.19 hϪ1
indicating a constant radical concentration throughout the
polymerisation. The molecular weight (Mn) increases linearly
with time and agrees with calculated molecular weights (Fig. 7).
The polydispersities (Mw/Mn) are slightly higher than
those obtained using 6, a common feature of reverse ATRP
polymerisations.22
Fig. 5 Plot of ln([M]0/[M]) vs. time for 3 (᭹) and 6 (᭺). ([catalyst]0 =
5.0 × 10Ϫ4 M, [PECl]0 = 5.0 × 10Ϫ4 M, [St]0 = 0.1 M).
The molecular weights (Mn) of the resultant polystyrene
samples increase linearly with time and are in good agreement
with calculated molecular weights. Polydispersities (Mw/Mn) are
slightly higher (typically ca. 1.4) than for previously reported
iron() diimine complexes.14b 1H NMR spectroscopic analysis
of the resultant polystyrene samples show the presence of the
halide capping group (ClCH(Ph)CH2–, δ 4.5 ppm) which is also
supported by halide microanalysis.19
Complex 6 affords a significantly faster polymerisation rate
than the dimeric complex, 3 [kobs(3) = 0.05 hϪ1, kobs(6) = 0.17
h
Ϫ1], possibly a consequence of the need to cleave the halide
bridges prior to halogen atom transfer. Molecular weights (Mn)
increase linearly with conversion and with monomer to initiator
ratio; a plot of Mn vs. monomer:initiator ratio for catalyst 6 is
shown in Fig. 6.
Fig. 7 Plot of molecular weight with Mw/Mn in parentheses vs. time
for 7 ([7]0 = 5.0 × 10Ϫ4 M, [AIBN]0 = 3.125 × 10Ϫ4 M, [St]0 = 0.1 M).
Fig. 6 Plot of molecular weight vs. M0/I0 for 6 with Mw/Mn in
parentheses ([6]0 = 1.0 × 10Ϫ3 M, [PECl]0 = 1.0 × 10Ϫ3 M, [St]0 = 0.05,
0.1, 0.2, 0.3 and 0.4 M).
(iii) Methyl methacrylate (MMA) polymerisation. Complexes
1–6 were tested as catalysts for the ATRP of MMA under
various conditions using a range of different initiators.
However, all of these complexes, with the exception of mono-
nuclear 6, were found to be ineffective catalysts for MMA. For
6, promising polymerisation results were obtained using
sulfonylhalide (tosyl chloride), α-bromoester (ethyl 2-bromo-
isobutyrate) or phenylacetate (methyl-α-bromophenylacetate)
initiators. The results are summarised in Table 2 which shows
fairly good agreement between Mn(obs) and Mn,th though
molecular weight distributions are quite broad. The tacticity of
For comparative purposes, styrene polymerisations were
also investigated using 6 and an aryl sulfonyl halide initiator
(phenoxy disulfonyl chloride, PDSC). These proceeded in a
similarly well-controlled manner (Mw/Mn
= 1.33) with
a polymerisation rate close to that reported using 1-PECl as
initiator (kobs(PDSC) = 0.19 hϪ1 vs. kobs(1-PECl) = 0.17 hϪ1).
The other alkyl complexes also gave comparable polymerisation
results when either 1-PECl or PDSC were used as initiators.
Changing the initiator to a bromo derivative, 1-PEBr, slows the
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Table 3 Redox potentials (E1/2) and peak separation (∆Ep) for 1–9
E1/2/mV
∆Ep/mV
1
2
3
4
5
6
7
8
9
1200
1100
1100
840
1100
1100
Ϫ10
1100
890
190
180
190
240
190
100
140
130
230
Ferrocene/ferrocenium couple E1/2 = 450 mV and ∆Ep = 110 mV.
Fig. 8 Cyclic voltammetry trace for 6: start potential: Ϫ1500 mV, end
potential: Ϫ1500 mV, sweep rate: 250 mV sϪ1
the resultant PMMA was found to be consistent with the
syndio-rich atactic form (mm : rm : rr ca. 3 : 33 : 64) which is
typical of PMMA synthesised using conventional radical
polymerisation methods.23
.
other characterisation techniques. For example, it is possible
that one arm of the bidentate donor could dissociate in solu-
tion and, under those circumstances, a direct comparison of
α-diimines and iminopyridines may not be valid. Alternatively,
acetonitrile, the solvent in which the CV measurements are
conducted, may bind to the iron centres substantially altering
the coordination geometry. We were surprised that complexes
with such high E1/2 values could function so efficiently as ATRP
catalysts, possibly indicating that their catalytic behaviour is
driven by exceptionally high halogenophilicities.
As for their α-dimine analogues, ∆Ep values seem to provide a
useful indicator of catalytic performance. For the dinuclear
alkylimino complexes 1, 2, 3 and 5, ∆Ep is ca. 180–190 mV while
for the arylimino derivative 4 this value is raised to 240 mV. The
higher ∆Ep for the latter, as for its related diimine relatives,
appears to correlate with chain transfer behaviour.14b,15 It is
only for the mononuclear complex 6 that ∆Ep, at 100 mV, is low
and comparable to its α-diimine analogues, and where the best
control is found. For the pyridylamino complexes 8 and 9, high
E1/2 values are again observed, and a similar difference in ∆Ep
values are seen for the alkyl vs. aryl derivatives (130 mV for 8 vs.
230 mV for 9). Consistently, the alkyl derivative, 8, affords
reasonably well-behaved ATRP, while the aryl catalyst, 9, gives
rise to chain transfer.
(iv) Aminopyridine complexes. It has been shown that satur-
ated nitrogen donor ligands can improve the control and
efficiency in copper ATRP systems due to their increased
reducing power.24 Thus, the study was extended to include
saturated aminopyridine analogues. These complexes were
synthesised using analogous procedures to those described
for their iminopyridine counterparts (Scheme 2). Solution
molecular weight determinations on the cyclohexyl and
2,6-diisopropylphenyl derivatives 8 and 9 are consistent with
aggregated structures25 possibly related to their iminopyridine
analogues. Attempts to grow crystals of these complexes were
unsuccessful.
Scheme 2 Synthesis of complexes 8 and 9 where R = c-C6H11, 8 and
R = 2,6 diisopropylphenyl, 9.
Styrene polymerisations using 8 and 9 were performed under
similar conditions to their iminopyridine analogues. 8 behaved
similarly to its unsaturated counterpart, 2, although the
Conclusion
polymerisation was significantly faster (cf. kobs(8) = 0.16 hϪ1
;
A series of iron() complexes containing iminopyridine and
aminopyridine ligands has been synthesised and evaluated in
atom transfer radical polymerisation. These ligands, even for
relatively bulky N-substituents, are generally found to stabilise
binuclear species in solution and the solid state and, as a con-
sequence, are found to be relatively slow ATRP catalysts. It
proved possible to isolate a mononuclear derivative by employ-
ing a bulky imine substituent along with an α-methyl substi-
tuent on the pyridyl ring, and here relatively fast and well con-
trolled polymerisations of styrene and MMA are observed.
Expectedly, the trichloride analogue of 6 (complex 7) was found
to be an effective reverse ATRP catalyst. A notable feature of
these systems, which is also found in their α-diimine relatives, is
the differing ATRP behaviour of catalysts bearing alkyl vs. aryl
substituents. The former, with their relatively low ∆Ep values,
facilitate well-controlled ATRP, while the latter, with higher
∆Ep values, favour chain transfer. Overall, these iminopyridine
complexes appear to be better suited to the ATRP of styrene
rather than MMA.
kobs(2) = 0.08 hϪ1) and some loss of control was observed. (cf. 8;
Mw/Mn = 1.52; 2; Mw/Mn = 1.41) Polymerisations using 9, as for
the unsaturated aryl derivative 4, were found to be uncontrolled
and non-living in character (Mn,th = 16400, Mn = 5000 and
Mw/Mn = 1.72).
(v) Cyclic voltammetry. In order to obtain a better under-
standing of the differing behaviour of these complexes as
ATRP catalysts, the redox potentials (E1/2) and reversibility
(∆Ep) of 1–9 (Table 3) were probed using cyclic voltammetry
(CV). Although CV measurements are not performed under
conditions that mimic precisely the conditions of the ATRP
experiments, they can provide an indication of the efficiency of
ATRP catalysis and, in certain cases, the propensity for chain
transfer. A typical trace, for complex 6, is shown in Fig. 8. The
main feature, at ca. 1.1 V, is attributed to the reversible Fe()/
Fe() couple relevant to ATRP catalysis; a second weaker
feature at ca. Ϫ1.0 V is assigned to an irreversible Fe()/Fe()
couple.
All of the divalent alkylimine complexes 1, 2, 3, 6, 7 and 9
possess surprisingly high E1/2 values (typically ca. 1000 mV)
compared to their α-diimine relatives where E1/2 values lie in the
range Ϫ20 to Ϫ130 mV.14b This is unexpected given the lower
π-acceptor capacity of iminopyridine ligands26 and may
indicate more complex solution behaviour than revealed by
Experimental
General considerations
All manipulations were carried out under a nitrogen atmos-
phere using Schlenk vacuum-line techniques and glove boxes.
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All starting materials and initiators were purchased from
Aldrich Chemical Co and used as supplied without further
purification unless otherwise stated. All reaction solvents were
dried by prolonged reflux over appropriate drying agents and
were degassed immediately prior to use. Styrene (>98%) was
purified by vacuum distillation and then stored in an inert
atmosphere over molecular sieves at Ϫ15 ЊC. MMA was stirred
over CaH2 for 24 h and then freshly distilled before use. 1-Phe-
nylethylchloride, 1-PECl was prepared according to a literature
preparation and purified by column chromatography.27 AIBN
was recrystallised twice from diethyl ether and stored at Ϫ30 ЊC.
FeCl2(THF)1.5 was synthesised as described in the literature.28
The ligands used to synthesise 1 and 4 were prepared as
described in the literature.12b,29
a large excess of MgSO4 (5 g). The suspension was stirred for
2 h and then filtered. The MgSO4 was thoroughly washed with
diethyl ether and then the filtrate was reduced in volume to yield
a pale yellow oil. This was purified by vacuum distillation at 130
ЊC and 5 mmHg to produce a yellow oil. Yield 17.32 g, 92%.
Found: C, 76.7; H, 8.6; N, 15.0. C12H16N2 requires C, 76.6; H,
8.6; N. 14.9%; IR/cmϪ1: 1648s, ν(C᎐N); δH (CDCl3) 8.41 (1H, s,
᎐
CH), 8.20 (1H, s, N᎐CH), 7.77 (1H, d, J(HH) 4 Hz, CH), 7.47
᎐
(1H, t, J(HH) 8 Hz, CH), 7.04 (1H, m, CH), 3.07 (1H, q, J(HH)
4 Hz, CH), 1.59 (4H, m, 2CH2), 1.42 (6H, m, 3CH2); δC (CDCl3)
159.3 (1C, s, N᎐CH), 154.8 (1C, s, C), 149.1 (1C, s, CH), 136.3
᎐
(1C, s, CH), 124.2 (1C, s, CH), 121.1 (1C, s, CH), 69.4 (1C, s,
CH), 34.0 (4C, s, 4CH2), 25.4 (4C, s, 4CH2), 24.5 (1C, s, CH2);
MS (ϩCI) (m/z): 189 [M ϩ H]ϩ
Characterisation
Dichloro(N-cyclohexylimino-2-pyridyl)iron(II), 2. The same
procedure was employed as for 1. After drying a purple micro-
crystalline solid, 2, was isolated. Yield 5.42 g, 86%. Found: C,
45.7; H, 5.1; N, 8.9; Cl, 23.4. C12H16N2FeCl2 requires C, 45.8; H,
NMR spectra were recorded on a Bruker AC 250 MHz
instrument. Chemical shifts are reported as δ (in ppm) and
referenced to residual proton impurity present in the NMR
solvent. Magnetic moments were determined using the Evans
NMR method in dichloromethane spiked with cyclohexane.30
Mass spectra were recorded on a Micromass GC 8000 Autospec
mass spectrometer. IR spectra were recorded on a Perkin-Elmer
1710 FTIR instrument using NaCl plates. Microanalyses
(C, H and N) were carried out by Dr S. Boyer at London
Metropolitian University, London. Halide microanalyses was
performed by Dr G. A. Maxwell at University College London.
GPC chromatograms were recorded on a Knauer differential
refractometer connected to a Gynotek HPLC pump (model
300) and two 10 µm columns (PSS) at a flow rate of 1.00 cm3
minϪ1 using CHCl3 as the eluent. The columns were calibrated
against polystyrene standards with molecular weights ranging
from 1560 to 128000 and polymethylmethacrylate standards
ranging from 2400 to 174000. Analysis was performed using
Version 3.0 of the Conventional Calibration module of the
Viscotek SEC3 software package. Cyclic voltammetry (CV) was
performed using a MacLab potentiostat operated by EChem
1.3.2. software. The working electrode and reference electrode
were purchased from Bioanalytical (ref: MF-2013 and RE-5B)
Solution molecular weights were determined by melting point
depression of bromoform31 by means of a TC Ltd platinum
5.1; N. 8.9; Cl, 22.5%; IR/cmϪ1: 1594m, ν(C᎐N); MS (ϩFAB)
᎐
(m/z): [2LFeCl]ϩ = 467, [LFeCl2]ϩ = 314. µeff = 3.19 µB.
N-Cyclododecylimino-2-pyridine. N-Cyclododecylimino-2-
pyridine was prepared as described for N-cyclohexylimino-2-
pyridine. On reduction of the filtrate a pale yellow solid
resulted. This was purified by recrystallisation from ethanol to
produce a pale yellow solid. Yield 24.78 g, 91%. Found: C, 79.6;
H, 10.4; N, 10.1. C18H28N2 requires C, 79.4; H, 10.4; N. 10.3%;
IR/cmϪ1: 1646s, ν(C᎐N); δ (CDCl3) 8.62 (1H, d, J(HH) 5 Hz,
᎐
H
CH), 8.37 (1C, s, N᎐CH), 7.70 (1H, t, J(HH) 6 Hz, CH), 7.28
᎐
(1H, m, CH), 3.47 (1H, s, CH), 1.84 (4H, m, 2CH2), 1.39 (18H,
m, 9CH2); δC (CDCl ) 159.9 (1C, s, N᎐CH), 154.9 (1C, s, C),
᎐
3
149.3 (1C, s, CH), 136.5 (1C, s, CH), 124.5 (1C, s, CH), 121.3
(1C, s, CH), 66.8 (1C, s, CH), 31.2 (2C, s, 2CH2), 24.3 (1C, s,
CH3), 23.6 (8C, m, CH2), 21.6 (1C, s, CH2); MS (ϩCI) (m/z):
273 [M ϩ H]ϩ
Dichloro(N-cyclododecylimino-2-pyridyl)iron(II), 3. The same
complexation procedure was employed as for 1. After drying 3
was isolated as a pale pink microcrystalline solid. Yield 7.10 g,
89%. Found: C, 39.5; H, 4.4; N, 10.1; Cl, 17.8. C18H28N2FeCl2
requires C, 39.3; H, 4.4; N. 10.2; Cl, 17.8%; IR/cmϪ1: 1594m,
resistance thermometer mounted coaxially in
a vacuum
ν(C᎐N); MS (ϩFAB) (m/z): [2LFeCl]ϩ = 635, [LFeCl]ϩ = 363.
᎐
jacketed cell containing a solution of approximately 0.02 M
concentration and cooled in an ice-bath. The thermometer was
connected to an Autotherm II instrument interfaced to an
PC-486 running the Mettler Toledo Balance Link software
programme (Version 3.01). Cooling curves were collected over
45 minutes and temperature was sampled every 30 s.
µeff = 3.25 µB.
Dichloro(N-2,6-diisopropylphenylimino-2-pyridyl)iron(II), 4.
The same procedure was employed as for 1. After drying a
purple microcrystalline solid 4 was isolated. Yield 6.45 g, 82%.
Found: C, 55.0; H, 5.6; N, 7.1; Cl 16.3. C18H22N2FeCl2 requires
C, 55.0; H, 5.6; N. 7.1; Cl 18.0%; IR/cmϪ1: 1560m, ν(C᎐N);
᎐
Preparations
MS (ϩFAB) (m/z): [2LFeCl]ϩ = 623, [LFeCl]ϩ = 357. µeff
3.50 µB.
=
Dichloro(N-propylimino-2-pyridyl)iron(II), 1. To a stirred
suspension of FeCl2 (2.54 g, 0.02 mol) in tetrahydrofuran (20
ml) at 60 ЊC was added dropwise a solution of N-propylimino-
2-pyridine12b (3.11 g, 0.021 mol) in tetrahydrofuran (15 ml).
This suspension was stirred overnight at 60 ЊC and then allowed
to cool and filtered. The residue was washed with tetrahydro-
furan (3 × 10 ml). The purple microcrystalline solid, 1, was
dried overnight in vacuo. Yield 4.67 g, 85%. Found: C, 39.5; H,
4.4; N, 10.1; Cl, 25.2. C9H12N2FeCl2 requires C, 39.3; H, 4.4; N.
2-(N-Propylimino)-6-methylpyridine. To a stirred solution of
6-methyl-2-pyridinecarbaldehyde (4.5 g, 0.037 mol) in 30 ml
diethyl ether was added n-propylamine (2.25 g, 0.038 mol)
dropwise. The solution was stirred at room temperature for 10
min prior to the addition of a large excess of MgSO4 (10 g). The
suspension was stirred for 2 h and then filtered. The MgSO4 was
thoroughly washed with diethyl ether and then the filtrate was
reduced in volume to yield a pale yellow oil. This was purified
by vacuum distillation at 110 ЊC and 5 mmHg to produce a
yellow oil. Yield 5.52 g, 92%. Found: C, 74.6; H, 8.7; N, 17.6.
C10H14N2 requires C, 74.0; H, 8.7; N. 17.3%; IR/cmϪ1: 1650s,
10.2; Cl, 25.8%; λmax/cmϪ1 (C᎐N) 1671s; MS (ϩFAB) (m/z):
᎐
[2(LFeCl2) Ϫ Cl]ϩ = 513, [2LFeCl2]ϩ = 387, [2LFe]ϩ = 352,
[LFeCl]ϩ = 239. µeff = 3.24 µB.
N-Cyclohexylimino-2-pyridine.
N-Cyclohexylimino-2-pyr-
modification of literature
ν(C᎐N); δ (CDCl ) 8.15 (1H, s, N᎐CH), 7.39 (1H, t, J(HH) 8
᎐ ᎐
H 3
idine29 was prepared by
a
a
Hz, CH), 7.59 (1H, d, J(HH) 8 Hz, CH), 6.93 (1H, d, J(HH) 8
Hz, CH), 3.40 (2H, t, J(HH) 7 Hz, CH2), 2.37 (3H, s, CH3), 1.54
(2H, st, J(HH) 7 Hz, CH2), 0.75 (3H, t, J(HH) 7 Hz, CH3) δC
method.12b To a stirred solution of 2-pyridinecarbaldehyde
(10.71 g, 0.1 mol) in 30 ml diethyl ether at 0 ЊC was added
cyclohexylamine (13.86 g, 0.14 mol) dropwise. The solution was
stirred at room temperature for 15 min prior to the addition of
(CDCl ) 161.8 (1C, s, N᎐CH), 157.8 (1C, s, C), 153.9 (1C, s,
᎐
3
C(CH3)), 136.4 (1C, s, CH), 124.0 (1C, s, CH), 118.0 (1C, s,
D a l t o n T r a n s . , 2 0 0 3 , 2 8 2 4 – 2 8 3 0
2828

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CH), 63.1 (1C, s, CH2), 24.1 (1C, s, C(CH3)), 23.7 (1C, s, CH2),
toluene (20 ml) at 80 ЊC was added dropwise a solution of
11.67 (1C, s, CH3); MS (ϩCI) (m/z): 163 [M ϩ H]ϩ
N-cyclohexylamino-2-pyridine (2.10 g, 0.011 mol) in toluene
(15 ml). This suspension was stirred overnight at 80 ЊC and then
allowed to cool and then filtered. The residue was washed with
toluene (3 × 10 ml). The pale yellow microcrystalline solid 8 was
dried overnight in vacuo. Yield 2.35 g, 74%. Found: C, 45.9; H,
5.6; N, 8.6; Cl 24.3. for C12H18N2FeCl2 requires C, 45.5; H, 5.7;
N. 8.8; Cl 22.4%; IR/cmϪ1 2941w ν(NH); MS (ϩFAB) (m/z):
7: [2LFeCl2]ϩ = 507, [LFeCl2]ϩ = 316, [LFeCl]ϩ = 281. µeff = 3.01
µB.
Dichloro[2-(N-propylimino)-6-methylpyridyl]iron(II), 5.
A
similar procedure was employed as for 1. After drying a 5 was
isolated as a red microcrystalline solid. Yield 4.97 g, 86%.
Found: C, 41.4; H, 4.8; N, 9.7; Cl 25.9. C10H14N2FeCl2 requires
C, 41.6; H, 4.9; N, 9.7; Cl 24.5%; IR/cmϪ1: 1591m, ν(C᎐N); MS
᎐
(ϩFAB) (m/z): [2LFeCl]ϩ = 415, [LFeCl2]ϩ = 288, [LFeCl]ϩ
253. µeff = 3.39 µB.
=
N-2,6-Diisopropylphenylamino-2-pyridine.
N-2,6-Diiso-
2-(N-Cyclododecylimino)-6-methylpyridine.
2-(N-Cyclo-
propylphenylamino-2-pyridine was prepared as described for
N-cyclohexylamino-2-pyridine. On reduction of the filtrate a
white solid resulted. Yield 9.77 g, 91%. Found: C, 80.5; H, 9.1;
N, 10.3. C18H24N2 requires C, 80.5; H, 9.0; N. 10.4%; IR/cmϪ1
3358w ν(NH); δH (CDCl3) 8.64 (1H, d, J(HH) 6 Hz, CH), 7.66
(1H, d of t, J(HH) 6 and 2 Hz, CH), 7.32 (1C, d, J(HH) 7 Hz,
CH), 7.21 (1C, d of t, J(HH) 6 and 2 Hz, CH), 7.12 (3H, m,
3CH), 4.21 (2H, s, CH2), 4.09 (1H, br s, NH), 3.39 (2H, sp,
J(HH) 7 Hz, 2CH), 1.26 (12H, d, J(HH) 7 Hz, 4CH3);
δC (CDCl3) 159.0 (1C, s, C), 149.4 (1C, s, CH), 143.1 (1C, s, C),
142.7 (1C, s, C), 136.5 (1C, s, CH), 123.9 (2H, s, 2CH), 123.6
(1H, s, CH), 122.2 (1C, s, CH), 122.0 (1C, s, CH), 56.8 (1C, s,
CH2), 27.7 (2C, s, CH), 24.3 (4C, s, 4CH3); MS (ϩCI) (m/z): 268
[M ϩ H]ϩ
dodecylimino)-6-methylpyridine was prepared as described
for 2-(N-propylimino)-6-methylpyridine. On reduction of the
filtrate a yellow solid resulted. This was purified by recrystallis-
ation from diethyl ether to produce a pale yellow solid. Yield
10.17 g, 96%. Found: C, 79.6; H, 10.5; N, 9.8. C19H30N2 requires
C, 79.7; H, 10.6; N. 9.8%; IR/cmϪ1: 1646m, ν(C᎐N); δ (CDCl )
᎐
H
3
8.34 (1H, s, N᎐CH), 7.79 (1H, d, J(HH) 8 Hz, CH), 7.57 (1H, t,
᎐
J(HH) 8 Hz, CH), 7.12 (1H, d, J(HH) 8 Hz, CH) 3.45 (1H, m,
CH), 2.55 (3H, s, CH3), 1.82 (4H, m, 2CH2), 1.36 (18H, br m,
c-C11H22); δC (CDCl ) 160.3 (1C, s, N᎐CH), 157.9 (1C, s, C),
᎐
3
154.3 (1C, s, C(CH3)), 136.7 (1C, s, CH), 124.1 (1C, s, CH),
118.1 (1C, s, CH), 66.7 (1C, s, CH), 31.2 (2C, s, 2CH2), 24.3 (1C,
s, CH3), 23.4 (8C, m, CH2), 21.6 (1C, s, CH2); MS (ϩCI) (m/z):
287 [M ϩ H]ϩ
Dichloro(N-2,6-diisopropylphenylamino-2-pyridyl)iron(II), 9.
The same complexation procedure was employed as for 8. After
drying an off-white microcrystalline solid 9 was isolated. Yield
2.85 g, 72%. Found: C, 54.6; H, 6.2; N, 7.0; Cl 17.9. for
C18H24N2FeCl2 requires C, 54.7; H, 6.1; N. 7.1; Cl 17.9%; MS
(ϩFAB) (m/z): [2LFeCl]ϩ = 627, [LFeCl2]ϩ = 394. µeff = 3.19 µB.
[2-(N-Cyclododecylimino)-6-methylpyridyl]dichloroiron(II), 6.
A similar procedure was employed as for 1. After drying 6 was
obtained as a bright pink microcrystalline solid. Yield 7.11 g,
86%. Found: C, 55.2; H, 7.3; N, 6.7; Cl 17.2. for C19H30N2FeCl2
requires C, 55.2; H, 7.3; N. 6.8; Cl 17.2%; IR/cmϪ1: 1595m,
ν(C᎐N); MS (ϪCI) (m/z): [LFeCl ]Ϫ = 412, [LFeCl]Ϫ = 377.
᎐
2
µeff = 5.07 µB.
Polymerisation procedure
Trichloro(N-cyclododecylimino-2-pyridyl)iron(III), 7. To
a
Normal ATRP reactions were performed under nitrogen, in a
15 cm3 glass ampoule fitted with a Teflon stopcock. The
ampoule was equipped with a magnetic stirrer bar and the
following were placed in it in the order, monomer, initiator
solvent and catalyst. The ampoules were transferred to a
preheated oil bath, at 120 ЊC (St) and 80 ЊC (MMA). After
magnetic stirring for the allotted period of time an aliquot (0.1
ml) was removed and quenched by addition of THF (1 ml).
Conversion was determined by integration of monomer vs.
polymer backbone resonances in the 1H NMR spectrum of the
crude product (in CDCl3). The polymer was purified by pre-
cipitating from a rapidly stirred acidified (5%) methanol
solution. For reverse ATRP experiments all conditions were
identical with the exception that the polymerisation temper-
ature was 110 ЊC.
stirred suspension of FeCl3 (2.54 g. 0.02 mol) in tetra-
hydrofuran (20 ml) was added dropwise a solution of
N-cyclohexylimino-2-pyridine (6.02 g, 0.021 mol) in tetra-
hydofuran (15 ml). This suspension was heated to 60 ЊC, stirred
overnight and then filtered. The residue was washed with
diethyl ether (3 × 10 ml). Complex 7 was isolated as a
orange–yellow microcrystalline solid and was dried overnight
in vacuo. Yield 7.53 g, 84%. Found: C, 49.9; H, 6.6; N, 6.3; Cl
23.9. for C19H30N2FeCl3 requires C, 50.8; H, 6.7; N. 6.3; Cl
23.7%; IR/cmϪ1: 1596w, ν(C᎐N); MS (ϪCI) (m/z): [LFeCl ]Ϫ
=
᎐
2
412. µeff = 4.69 µB.
N-Cyclohexylamino-2-pyridine. N-Cyclohexylamino-2-pyr-
idine was prepared by reduction of N-cyclohexylamino-2-
pyridine. To
a stirred solution of N-cyclohexylamino-2-
pyridine (8.0 g, 0.04 mol) in methanol (30 ml) was added excess
NaBH4 (6.47 g, 0.17 mol). The reaction was stirred overnight,
and then water was added to remove any excess NaBH4. The
product was extracted into dichloromethane and washed with
water and dried over Na2SO4. The solvent was removed to
afford a white solid. Yield 6.77 g, 89%. Found: C, 75.1; H, 9.3;
N, 14.1. C12H18N2 requires C, 75.7; H, 9.5; N. 14.7%; IR/cmϪ1
3302w ν(NH); δH (CDCl3) 8.34 (1H, d, J(HH) 4 Hz, CH), 7.42
(1H, t, J(HH) 5 Hz, CH), 7.11 (1H, d, J(HH) 4 Hz, CH), 6.93
(1H, t, J(HH) 5 Hz, CH), 3.74 (2H, s, CH2), 2.44 (1H, br s,
NH), 2.30 (1H, q, J(HH) 5 Hz, CH), 1.54 (4H, m, 2CH2), 1.37
(6H, m, 3CH2); δC (CDCl3) 159.9 (1C, s, C), 149.0 (1C, s, CH),
136.3 (1C, s, CH), 122.2 (1C, s, CH), 121.7 (1C, s, CH), 56.4
(1C, s, CH2), 52.1 (1C, s, CH2), 33.3 (4C, s, 4CH2), 26.0 (4C, s,
4CH2), 24.8 (1C, s, CH2); MS (ϩCI) (m/z): 381 [2M ϩ H]ϩ, 191
[M ϩ H]ϩ
Cyclic voltammetry
CV analyses were performed in acetonitrile (10 cm3), under a
nitrogen atmosphere, using a platinum (0.05 mm wire) counter
and working electrode and a Ag/AgCl reference electrode with
[nBu4N][PF6] (0.1 M) as a supporting electrolyte. The ferro-
cene()/() couple (E1/2 = 450 mV and ∆Ep = 110 mV) was used
as a benchmarked redox couple. In all cases, the reversibility
was confirmed by altering the scan rate. This resulted in no
changes to the aniodic or cathodic peak positions.
Crystallography
Crystal data for 4. C36H44N4Cl4Fe2, M = 786.3, monoclinic,
P21/n (no. 14), a = 9.805(2), b = 14.496(2), c = 14.204(2) Å, β =
107.35(2)Њ, V = 1927.0(6) Å3, Z = 2 (Ci symmetry), Dc = 1.355 g
cmϪ3, µ(Mo-Kα) = 1.06 mmϪ1, T = 203 K, red–brown blocks;
3157 independent measured reflections, F 2 refinement, R1
=
Dichloro(N-cyclohexylamino-2-pyridyl)iron(II), 8. To
stirred suspension of FeCl2(THF)1.5 (2.35 g. 0.01 mol) in
a
0.041, wR2 = 0.093, 2448 independent observed absorption
corrected reflections [|Fo| > 4σ(|Fo|), 2θ ≤ 50Њ], 208 parameters.
D a l t o n T r a n s . , 2 0 0 3 , 2 8 2 4 – 2 8 3 0
2829

View Article Online
¯
Macromolecules, 1999, 32, 3820; (d ) Y. Kotani, M. Kamigaito and
Crystal data for 5. C20H28N4Cl4Fe2, M = 578.0, triclinic, P1
M. Sawamoto, Macromolecules, 1999, 32, 6877; (e) M. Teodrescu,
S. G. Gaynor and K. Matyjaszewski, Macromolecules, 2000, 33,
2335; ( f ) Y. Kotani, M. Kamigaito and M. Sawamoto,
Macromolecules, 2000, 33, 3543; (g) B. Göbelt and
K. Matyjaszewski, Macromol. Chem. Phys., 2000, 201, 1619; (h)
J. Louis and R. H. Grubbs, Chem. Commun., 2000, 1479.
10 (a) J. Xia and K. Matyjaszewski, Macromolecules, 1997, 30, 7697; (b)
J. Xia, S. G. Gaynor and K. Matyjaszewski, Macromolecules, 1998,
31, 5968; (c) B. Yu and E. Rustenstein, J. Polym. Sci., Part A: Polym.
Chem., 1999, 37, 4191; (d ) Y. Shen, S. Zhu, F. Zeng and R. Pelton,
Macromol. Chem. Phys., 2000, 201, 7999; (e) X. Wan and S. Ying,
J. Polym. Sci., 2000, 75, 802.
(no. 2), a = 7.943(1), b = 8.337(1), c = 10.505(1) Å, α = 107.01(1),
β = 108.41(1), γ = 97.02(1)Њ, V = 613.3(1) Å3, Z = 1 (Ci
symmetry), Dc = 1.565 g cmϪ3, µ(Mo-Kα) = 1.63 mmϪ1, T = 293
K, orange–red blocks; 2116 independent measured reflections,
F 2 refinement, R1 = 0.035, wR2 = 0.071, 1653 independent
observed absorption corrected reflections [|Fo| > 4σ(|Fo|), 2θ ≤
50Њ], 145 parameters.
Crystal data for 6. C19H30N2Cl2Fe, M = 413.2, orthorhombic,
Pbca (no. 61), a = 8.177(1), b = 13.524(2), c = 37.608(6) Å, V =
4159(1) Å3, Z = 8, Dc = 1.320 g cmϪ3, µ(Mo-Kα) = 0.99 mmϪ1, T
= 203 K, orange platy blocks; 3401 independent measured
reflections, F 2 refinement, R1 = 0.052, wR2 = 0.093, 1886
independent observed absorption corrected reflections [|Fo| >
4σ(|Fo|), 2θ ≤ 50Њ], 218 parameters.
11 (a) J. Xia and K. Matyjaszewski, Macromolecules, 1999, 32, 2434; (b)
B. Göbelt and K. Matyjaszewski, Macromol. Chem. Phys., 2000,
201, 1619.
12 (a) D. M. Haddleton, C. B. Jasieczek, M. J. Hannon and
A. J. Shooter, Macromolecules, 1997, 30, 2190; (b) A. J. Shooter,
Ph. D. Thesis, University of Warwick, 1997; (c) D. M. Haddleton,
D. J. Duncalf, D. Kukuli, M. C. Crossman, S. G. Jackson,
S. A. F. Bon, A. J. Clark and A. J. Shooter, Eur. J. Inorg. Chem.,
1998, 1799; (d ) G. M. DiRenzo, M. Messerschmidt and
R. Mulhaupt, Macromol. Rapid Commun., 1998, 19, 381; (e)
A. J. Amass, C. A. Wyres, E. Colclough and I. M. Hohn, Polymer,
1999, 41, 1697.
CCDC reference numbers 206397–206399.
See http://www.rsc.org/suppdata/dt/b3/b303094f/ for crystal-
lographic data in CIF or other electronic format.
13 J. Queffelec, S. G. Gaynor and K. Matyjaszewski, Macromolecules,
2000, 33, 8629.
14 (a) V. C. Gibson and D. F. Wass, PCT Int. Appl., WO 9958578, 1999;
(b) V. C. Gibson, R. K. O’Reilly, W. Reed, D. F. Wass, A. J. P. White
and D. J. Williams, Chem. Commun., 2002, 1850.
15 V. C. Gibson, R. K. O’Reilly, D. F. Wass, A. J. P. White and
D. J. Williams, Macromolecules., 2003, 36, 2591.
Acknowledgements
BP Chemicals Ltd is thanked for financial support (R. K. O’R.).
Prof. F. G. N. Cloke and Dr G. K. B. Clentsmith are thanked for
assistance with cryoscopic molecular weight determinations.
16 T. V. Laine, I. Piironen, K. Lappalainen, M. Klinga, E. Aitola and
M. Leskelä, J. Organomet. Chem., 2000, 606, 112.
17 T. V. Laine, M. Klinga and M. Leskelä, Eur. J. Inorg. Chem., 1999,
959.
18 Solution MW determinations: 1: RMM, found (calc.) = 906 (275), 2:
RMM, found (calc.) =1054 (315), 3: RMM, found (calc.) 1102 (399),
4: RMM, found (calc.) = 1097 (393), 5: RMM, found (calc.) = 853
(289) and 6: RMM, found (calc.) = 454 (413).
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