Telechelic poly(ε-caprolactones) with tethered mixed ligand ruthenium(II) chromophores

Article abstract of DOI:10.1139/v03-215

Well-characterized templates of polymer-forming ligands and their ruthenium tris(αα′-diimine) initiators were utilized to divergently ring open an ε-caprolactone monomer. The same polymers were also obtained through the synthesis of quinoline and bipyridine diimine ligands incorporating poly(ε-caprolactone) (PCL) chains. These polymers contain vacant molecular recognition sites, enabling subsequent chelation of these macroligands to metal precursors. Both methods provided telechelic (ε-caprolactone) ruthenium(II)-centered polyesters of various hierarchy. Solution properties and thermal behaviour of such polyesters are described.

Full text of DOI:10.1139/v03-215

5
95
Telechelic poly( -caprolactones) with tethered
mixed ligand ruthenium(II) chromophores
Abdiaziz A. Farah and William J. Pietro
Abstract: Well-characterized templates of polymer-forming ligands and their ruthenium tris(α,α′-diimine) initiators
were utilized to divergently ring open an ε-caprolactone monomer. The same polymers were also obtained through the
synthesis of quinoline and bipyridine diimine ligands incorporating poly(ε-caprolactone) (PCL) chains. These polymers
contain vacant molecular recognition sites, enabling subsequent chelation of these macroligands to metal precursors.
Both methods provided telechelic (ε-caprolactone) ruthenium(II)-centered polyesters of various hierarchy. Solution
properties and thermal behaviour of such polyesters are described.
Key words: redox polymers, poly(ε-caprolactone), telechelics, metal–polymer complexes, macroligands, ring-opening
polymerization (ROP).
Résumé : On a utilisé des gabarits bien caractérisés de ligands conduisant à la formation de polymères et leurs initia-
teurs ruthénium tris(α,α′-diimine) pour provoquer des ouvertures de cycle divergentes d’un monomère ε-caprolactone.
On a pu aussi obtenir les mêmes polymères en effectuant la synthèse de ligands quinoléine ou bipyridine diimine in-
corporant des chaînes poly(ε-caprolactone) (PCL). Ces polymères contiennent des sites vacants de reconnaissance molé-
culaire qui permettent d’effectuer une chélation subséquente de ces macroligands sur des précurseurs métalliques. Les
deux méthodes permettent d’obtenir des polyesters téléchéliques centrés sur le (ε-caprolactone)ruthénium(II). On décrit
les propriétés en solution et le comportement thermique de tels polyesters.
Mots clés : polymères redox, poly(ε-caprolactone), téléchéliques, complexes métal–polymère, macroligands, polymérisa-
tion par ouverture de cycle (POC).
[
Traduit par la Rédaction] Farah and Pietro 607
Introduction
elements becomes rather difficult if not impossible. Radical
or ionic chain polymerization of unsaturated monomers
proved to be possible only in some specific cases (3). Even
the apparently easier step-growth polymerizations were also
problematic because of the necessity of strict stoichiometric
balance and monomer purity. Consequently, only low-
molecular-weight products have been available in most
cases (4).
Progress in inorganic polymer chemistry became possible
when more specialized polymerization reactions were ap-
plied, such as ring-opening polymerization (ROP) (5) or
transition-metal-catalyzed processes (6). These techniques,
along with solubilizing side-chain moieties, provided a wide
range of inorganic macromolecules with valuable properties.
Four possible synthetic methods have been utilized for the
incorporation of metal complexes into polymeric structures:
binding via coordination site from a polymer-bound ligand
The design and the study of functional polymers contain-
ing metal centers in their structure remains an area of grow-
ing interest (1). Such materials exhibit attractive electrical,
electrochemical, magnetic, and optical properties associated
with the metal (2). Inorganic and organometallic polymers
are relatively underrepresented in the available literature
concerning polymeric functional materials. Hence, the syn-
thesis of analogous polymeric architecture with inorganic
fragments would expand the structural features and proper-
ties of the resulting inorganic–organic hybrid materials. New
applications in supramolecular chemistry and the need for
new materials are the driving forces for the development of
inorganic and organometallic polymeric systems. Owing to
the lack of appropriate organic–inorganic hybrid monomers,
along with poorly optimized reaction conditions that other-
wise would ensure homogeneous and quantitative conversion
of these monomers, the synthesis of long chains of inorganic
(
7); covalent attachment by reaction of a functionalized
complex with a functionalized polymer (8); homopolymeri-
zation of metal-containing monomers incorporating poly-
merizable groups; and copolymerization of a complex
bearing a polymerizable group with other selected mono-
mers (9). Recently, Fraser and co-workers (10) have ele-
gantly demonstrated that the combination of coordination
chemistry with controlled polymerization methodologies
would lead to a variety of functional materials. In contrast to
the conventional way of synthesizing functional polymeric
materials via post-polymer modification of end-reactive oli-
gomers and polymeric precursors (11), this synthetic ap-
Received 21 April 2003. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 6 May 2004.
1
2
A.A. Farah and W.J. Pietro. Department of Chemistry,
York University, 4700 Keele Street, Toronto, ON M3J 1P3,
Canada.
1Present address: National Research Council Canada (NRC),
Institute of Microstructural Science, Ottawa, ON K1A OR6,
Canada.
Corresponding author (e-mail: pietro@yorku.ca).
2
Can. J. Chem. 82: 595–607 (2004)
doi: 10.1139/V03-215
© 2004 NRC Canada

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Can. J. Chem. Vol. 82, 2004
proach provides polymers of controlled molecular weights
and, in particular, unique and well-defined spatial shapes.
Almost none of these characteristics are found in conven-
tional, mostly linear synthetic polymers. In turn, metal moi-
eties in well-defined microdomains in the polymer chain
allow the precise incorporation of functional groups, an in-
dispensable feature in developing specific material functions
with multi-dimensional environments.
Fig. 1. General structure of the telechelic ruthenium-centered
poly(ε-caprolactones).
In this contribution the synthesis and characterization of
telechelic linear and multi-dimensional poly(ε-caprolactones)
tagged with ruthenium(II)-centered chromophores of the
general structure in Fig. 1 will be described. These polyes-
ters have been prepared by two distinct approaches:
macroligand-chelation and metalloinitiation. Both methods
proceed under mild conditions and provide polymers with
controlled properties, i.e., molecular weight and molecular-
weight distributions.
Experimental
Methods and materials
All reagents were obtained from Aldrich Chemicals
Canada/Fluka and Alfa Aesar (Ward Hill, Mass). Reagent-
grade solvents were obtained from Caledon and BDH Inc.
Electrochemical solvents were freshly distilled over P O
2
5
under inert atmosphere, and electrolytes were twice recry-
stallized from absolute ethanol and dried in vacuum. All
chemicals and solvents were purified where necessary, ac-
cording to the conventional laboratory techniques (12), or
were used as received. cis-Ru(bpy) Cl ·xH O (bpy = bipyri-
corder or a computerized Cypress workstation was used for
all electrochemical studies. All electroanalytical solutions
2
2
2
dine) and metal complexes (5), (6), (7), (8), (9), and (10)
were obtained as described in refs. 13 and 14, respectively.
Analytical thin layer chromatography (TLC) was done on
commercially prepared silica gel 60F 254 coated plastic
sheets (Aldrich). Preparative TLC was performed on Aldrich
silica gel 60F 254 precoated glass plates. For column chro-
matography, high-purity grade (70–230 mesh, 60 Å) silica
gel and neutral standard grade (150 mesh, 58 Å) aluminum
oxide were used. Melting points (mp) were recorded using a
Laboratory Devices U.S.A. MEL-TEMP II and were uncor-
rected. Infrared spectra were recorded neat, as KBr pellets,
or as solution-casted films with a Mattson 3000 Fourier
were degassed with N or argon for 20 min prior to each ex-
2
periment. Molecular weights were determined by gel perme-
ation chromatography (GPC) with a Waters Associates 2690
separation module accessoried inline solvent degasser, a
high performance liquid chromatography (HPLC) pump, and
an autosampler. The separation module was equipped with a
Waters 410 differential refractometer as the concentration
detector and was connected in parallel. A Viscotek T60A
dual detector consisted of a right-angle laser light scattering
detector with a laser source of 670 nm and a four-capillary
differential viscometer. Software from Viscotek was used to
analyze the data. Columns from Polymer Laboratories with
1
13
2
4
5
transform infrared spectrophotometer. H and C NMR
spectra were obtained on a Bruker ARX 400-MHz nuclear
magnetic resonance spectrometer in an appropriate solvent,
using tetramethylsilane as an internal standard. Electronic
spectroscopy was performed using a Hewlett-Packard 8452
diode array spectrophotometer. Fluorimetry experiments
were conducted in a Shimadzu RF 551 fluorimeter or a
PerkinElmer LS-50B luminescence fluorimeter on argon or
pore sizes of 5 × 10 , 1 × 10 , and 1 × 10 Å were used with
THF as the eluent at a flow rate of 1.0 mL/min. Polystyrene
standards purchased from Aldrich and Viscotek were used
for calibration. Absolute molecular weights were determined
by low angle laser light scattering (LALLS) performed on a
Chromatix KMX-6 instrument at a wavelength of 632.8 nm
and a scattering angle of 6°–7°. Measurements were carried
out at room temperature with a metal cell 4.93 mm long.
Each solution was filtered three times through a MILEX fil-
ter with an average pore size of 0.2 µm before injection into
the cell. The refractive index increment (dn/dc) of the poly-
mer solution was obtained with a Chromatix KMX-16 dif-
ferential refractometer, operating at a wavelength of
632.8 nm. The instrument was calibrated with NaCl solu-
tions. A PerkinElmer DSC7 equipped with a TAC7 instru-
ment controller or TA instrument DSC 2920 was used to
study polymer thermal behavior. For differential scanning
calorimetry (DSC) experiments, the instruments were cali-
brated with melting transitions of decane and indium, and
N deaerated samples prior to recording. Electron impact
2
(
EI) mass spectrometry (positive mode) was carried out us-
ing a Kratos 902 mass spectrometer. Electrochemistry exper-
iments were performed in a conventional three-electrode cell
using a platinum working electrode, a platinum counter elec-
+
trode, and an Ag/Ag wire “quasi” reference electrode refer-
enced to the ferrocenium–ferrocene couple (15). The solvent
used was dimethylformamide (DMF), with tetrabutylammo-
nium hexafluorophosphate (TBAPF ) as the supporting elec-
6
trolyte. A Princeton Applied Research Corp. 174 Potentiostat
or an RDE3 potentiostat (Pine Instrument) with an x–y re-
©
2004 NRC Canada

Farah and Pietro
597
samples were heated under N atmosphere at a heating rate
of 10 °C/min. Reported thermal parameters were taken from
the second heating cycle if not otherwise indicated. The
removed by rotary evaporation, the residue was partially dis-
solved in 450 mL of ethyl acetate and filtered to remove the
insoluble fraction. The filtrate was extracted with 0.1 mol/L
Na CO (2 × 100 mL) and 0.3 mol/L Na S O (2 ×
2
glass transition (T ) value was the mid-point of the heat ca-
g
2
3
2
2
5
pacity change, whereas the melting point (T ) was the peak
100 mL). The combined aqueous extracts were adjusted to
pH 10 with Na CO , extracted with dichloromethane (3 ×
m
maximum. Thermogravimetric analyses (TGA) were also
obtained on the same instrument, TGA7, and the tempera-
ture was calibrated with the transitions of Perkalloy and
Nicoseal. Thermograms were obtained at a heating rate of
2
3
50 mL), and dried over Na SO . The solvent was removed
2
4
under reduced pressure, affording an off-white solid. Yield
2.8 g (50%); mp 130 to 131 °C (lit. (18) value mp 130.9–
131.7 °C).
2
0 °C/min under an N atmosphere.
2
–
1
IR (KBr pellets, ν in cm ) ν: 3061 (m, sharp, arom C-H
str), 2961 (s, sharp, aliph C-H str), 2093–1817 (m, sharp,
arom overtone bands), 1702 (s, sharp, C=O aldehyde str),
1593 (s, sharp, C=C ring str), 1350 (s, sharp, arom C-N str),
2
-(2-Pyridyl)-4-hydroxymethylquinoline (pq) ligand (1)
Lithium aluminum hydride (2.3 g, 52 mmol) was added
into 200 mL of anhydrous diethyl ether under nitrogen. To
this suspension was added 3.2 g (13 mmol) of 2-(2-pyridyl)-
1090–1031 (m, sharp, aliph C-H in-plane bend), 754 (s,
1
4
-methylcarbonylquinoline (16) in 20 mL of dry THF over a
sharp, arom out-of-plane bend). H NMR (DMSO-d , δ in
6
period of 30 min at room temperature. The reaction mixture
was allowed to reflux gently for 3 h and then cooled to room
temperature. The excess lithium aluminum hydride was de-
composed by gentle addition of 5% H SO , and the phases
ppm) δ: 10.18 (s, 1H, CHO), 8.93 (d, 1H, H6, J = 4.8 Hz),
8.76 (s, 1H, H3), 8.57 (d, 1H, H6′, J = 4.8 Hz), 8.23 (s, 1H,
H3′), 7.81 (d, 1H, H5, J = 4.8 Hz, J = 1.3 Hz), 7.30 (d, 1H,
1
3
H5′, J = 4.2 Hz), 2.47 (s, 3H, CH ). C NMR (DMSO-d , δ
2
4
3
6
were separated. The organic phase was washed with 5%
in ppm) δ: 193.46, 157.01, 154.15, 150.71, 149.28, 148.30,
142.68, 125.54, 121.40, 119.46, 20.73. EI-MS (m/z) (%):
198 (100), 170 (68), 169 (52).
NaHCO (3 × 30 mL) and water (2 × 30 mL) and then dried
3
over Na SO . After removal of the solvent, the desired prod-
2
4
uct was obtained as an orange crystalline solid. Yield 2.2 g
(
64%); mp 108 °C.
IR (KBr pellets, ν in cm ) ν: 3355 (s, broad, O-H str),
924 (m, sharp, arom C-H str), 2859 (m, sharp, aliph C-H
4
-Methyl-4′-hydroxymethyl-2,2′-bipyridine (4)
–
1
After 2.2 g (10 mmol) of (3) in 50 mL of ethanol were
2
cooled in an ice-bath while stirring for 20 min, 1.9 g
50 mmol) of NaBH dissolved in 20 mL of 0.2 mol/L
str), 1991–2058 (m, broad, arom overtone bands), 1602 (s,
sharp, C=C ring str), 1310 (s, sharp, arom C-N str), 1260 (w,
(
4
NaOH (aq) was added. The reaction mixture was left react-
sharp, C-O-C str), 1037 (s, broad, C-H in-plane bend), 745
ing under vigorous stirring for 4 h. Excess NaBH was de-
stroyed by treatment with dilute H SO , and most of the
ethanol was removed under reduced pressure. The remaining
white slurry was diluted with water and extracted with chlo-
roform (3 × 40 mL). The chloroform extracts were washed
with NaHCO (3 × 30 mL) and water (3 × 30 mL) and dried
with Na SO . The desired product was obtained following
removal of the solvent. Yield 1.6 g (78%); mp 122 °C.
4
1
(
s, sharp, arom C-H out-of-plane bend). H NMR (DMSO-
6
2
4
d , δ in ppm) δ: 9.08 (s, H3 of quinoline), 8.82 (d, H5 of
quinoline, J = 9.6 Hz), 8.79 (d, H12 of pyridine, J = 12 Hz),
8
.68 (d, H9 of pyridine, J = 8 Hz), 8.24 (d, H8 of quinoline,
J = 8 Hz), 7.89 (dd, H10 of pyridine, J = 8 Hz), 7.79 (dd,
H7 of quinoline, J = 7.5 Hz, J = 15 Hz), 7.67 (dd, H6 of
quinoline, J = 7.5 Hz, J = 15 Hz), 7.38 (dd, H11 of pyridine,
J = 8 Hz, J = 12 Hz), 5.23 (s, 2H, OCH ), 3.72 (br. 1H,
OH). EI-MS (m/z) (%): 236 (65), 205 (21), 178 (12).
3
2
4
–
1
2
IR (KBr pellets, ν in cm ) ν: 3470 (w, shoulder, O-H str),
3
185 (s, sharp, arom str), 2833 (s, sharp, aliph str), 2064 (w,
broad, arom overtone), 1586 (m, sharp, C=C ring str), 1454
(s, sharp, arom C-N str), 1247 (s, sharp, C-O str), 758 (s,
4
,4′-Dimethyl-2,2′-bipyridine (2)
1
4
,4′-Dimethyl-2,2′ bipyridine (2) was prepared following
sharp, C-H out-of-plane bend). H NMR (DMSO-d , δ in
6
the Sassi method (17), using 220 g (2.36 mol) of 4-picoline
and 10 g of 10 wt % palladium on activated carbon. Yield
ppm) δ: 8.50 (d, 1H, H6′, J = 3.4 Hz), 8.42 (d, 1H, H6, J =
5 Hz), 8.22 (s, 1H, H3′), 8.11 (s, 1H, H3), 7.20 (d, 1H, H5′,
J = 4.9 Hz), 7.07 (d, 1H, H5, J = 4.9 Hz), 4.69 (s, 1H,
8
1
.2 g (59%). (lit. (17) value 1.4 g/g of 10 wt % Pd–C). mp
1
3
74 °C (lit. (17) value mp 174–176 °C). IR (KBr pellets, ν
CH O), 2.37 (s, 1H, CH ). C NMR (DMSO-d , δ in ppm)
2 3 6
–
1
in cm ) ν: 3037 (s, sharp, arom C-H str), 2967 (m, sharp,
aliph C-H str), 2017–1677 (m, broad, arom overtone bands),
δ: 155.25, 152.74, 148.91, 148.88, 147.81, 124.82, 121.34,
121.27, 121.24, 117.87, 117.85, 61.85, 61.85, 20.68. EI-MS
(m/z) (%): 200 (85), 169 (54), 154 (36).
1
1
598 (s, sharp, C=C ring str), 1369 (s, sharp, arom C-N str),
119–1045 (m, sharp, aliph C-H in-plane bend), 725 (s,
1
sharp, arom C-H out-of-plane bend). H NMR (CDCl , δ in
3
Synthesis of ruthenium-centered polyesters via ring-
opening polymerization of ε-caprolactone with
ruthenium(II) metalloinitiators
ppm) δ: 8.54 (s, 2H, H6, J = 4.9 Hz), 8.23 (d, 2H, H3, J =
1
.7 Hz), 7.12 (d, 2H, H5, J = 4.7 Hz), 2.45 (s, 6H, CH ). EI-
3
MS (m/z) (%): 184 (100), 169 (14), 156 (11).
Ru(bpy) (bpyPCL)(PF ) (11)
2
6 2
4
-Methyl-2,2′-bipyridine-4′-carboxaldehyde (3)
Initiator (5) (91 mg, 0.11 mmol) and 2.3 g (18 mmol) of
A mixture of 5.27 g (28.6 mmol) of (2) and 3.48 g
ε-caprolactone were charged into an N -filled polymeriza-
2
(
31.4 mmol) of SeO in 1,4-dioxane was refluxed for 24 h
tion flask and immersed into a preheated oil at 110 °C for
2
with vigorous stirring and hot filtered. The filtrate was
cooled to room temperature, and the resulting light-brown
precipitate was filtered and discarded. After the solvent was
20 min before addition of a catalytic amount (0.60 µL) of
stannous octanoate (Sn(Oct) ). The polymerization reaction
2
mixture was then left reacting with stirring at 110 °C for
©
2004 NRC Canada

5
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Can. J. Chem. Vol. 82, 2004
2
4 h. The resulting viscous product was diluted with THF
str), 2095–2019 (m, broad, arom overtone bands), 1730 (s,
sharp, C=O ester str), 1595 (s, sharp, C=C ring str), 1471
(m, sharp, arom C-N str), 1100 (s, broad, C-O-C str), 842 (s,
sharp, arom out-of-plane bend). UV–vis (DMF) λmax:
while still warm and precipitated in cold MeOH. The poly-
mer was further purified by precipitation twice from THF
solution into MeOH. Yield 2.6 g (91%) of a red-orange
polymeric product.
–
1
–1
290 nm (ε = 47 100 (mol/L) cm ), 500 nm (ε = 8 900
–
1
–1
–1
1
IR (KBr pellets, ν in cm ) ν: 3442 (s, broad, OH str),
(mol/L) cm ). H NMR (DMSO-d , δ in ppm) δ: 4.03 (m,
6
2
944 (m, sharp, arom C-H str), 2863 (m, sharp, aliph C-H
broad, CH O of PCL), 2.39 (m, broad, OCCH of PCL),
2
2
str), 2195–1890 (m, broad, arom overtone bands), 1723 (s,
sharp, C=O ester str), 1592 (s, sharp, C=C ring str), 1471
1.69 (m, broad, CH of PCL), 1.31 (m, broad, CH of PCL).
2
2
GPC (LALLS): M : 19 150, M /M : 1.52.
w
w
n
(
m, sharp, arom C-N str), 1092 (s, broad, C-O-C str), 729 (s,
sharp, arom out-of-plane bend). UV–vis (DMF) λmax:
2
Ru(pqPCL) (bpy)(PF ) (18)
2
6 2
–
1
–1
86 nm (ε = 78 500 (mol/L) cm ), 456 nm (ε = 12 700
The two-dimensional (18) was synthesized by a similar
procedure to that described for (11), using 46 mg
(0.045 mmol) of (9), 1.5 g (13 mmol) of ε-caprolactone, and
–
1
–1
1
(
mol/L) cm ). H NMR (DMSO-d , δ in ppm) δ: 4.05 (m,
6
broad, CH O of PCL), 2.30 (m, broad, OCCH of PCL),
2
2
1
.64 (m, broad, CH of PCL), 1.39 (m, broad, CH of PCL).
0.46 µL of Sn(Oct) . Yield 0.81g (62%) of a dark-red poly-
2
2
2
GPC (LALLS): M : 28 130; M /M : 1.26.
meric product.
w
w
n
–
1
IR (KBr pellets, ν in cm ) ν: 3442 (s, broad, OH str),
2939 (m, sharp, arom C-H str), 2857 (m, sharp, aliph C-H
str), 2095–2019 (m, broad, arom overtone bands), 1721 (s,
sharp, C=O ester str), 1591 (s, sharp, C=C ring str), 1475
(m, sharp, arom C-N str), 1100 (s, broad, C-O-C str), 842 (s,
sharp, arom out-of-plane bend). UV–vis (DMF) λmax:
Ru(bpyPCL) (bpy)(PF ) (12)
2
6 2
The two-dimensional (12) polymer was synthesized by a
similar experimental procedure to that described above for
(
11), using 45 mg (0.047 mmol) of (6), 2.4 g (18 mmol) of
ε-caprolactone, and 0.63 µL of Sn(Oct) . Yield 1.6 g (52%)
of a red-orange polymeric product.
2
–
1
–1
300 nm (ε = 46 200 (mol/L) cm ), 486 nm (ε = 10 200
–
1
–1
–1
1
IR (KBr pellets, ν in cm ) ν: 3445 (s, broad, OH str),
(mol/L) cm ). H NMR (DMSO-d , δ in ppm) δ: 4.08 (m,
6
2
945 (m, sharp, arom C-H str), 2863 (m, sharp, aliph C-H
broad, CH O of PCL), 2.41 (m, broad, OCCH of PCL),
2
2
str), 2199–1891 (m, broad, arom overtone bands), 1721 (s,
sharp, C=O ester str), 1592 (s, sharp, C=C ring str), 1479
1.60 (m, broad, CH of PCL), 1.39 (m, broad, CH of PCL).
2
2
GPC (LALLS): M : 28 500, M /M : 1.51.
w
w
n
(
m, sharp, arom C-N str), 1090 (s, broad, C-O-C str), 743 (s,
sharp, arom out-of-plane bend). UV–vis (DMF) λmax:
2
Ru(pqPCL) (PF ) (19)
3
6 2
–
1
–1
89 nm (ε = 71 400 (mol/L) cm ), 452 nm (ε = 10 900
The three-dimensional (19) was synthesized by a similar
procedure to that described for (11), using 40 mg
(0.036 mmol) of (10), 1.5 g (13 mmol) of ε-caprolactone,
–
1
–1
1
(
mol/L) cm ). H NMR (DMSO-d , δ in ppm) δ: 4.06 (m,
6
broad, CH O of PCL), 2.37 (m, broad, OCCH of PCL),
2
2
1
.65 (m, broad, CH of PCL), 1.40 (m, broad, CH of PCL).
and 0.60 µL of Sn(Oct) . Yield 0.98 g (79%) of a dark-red
2
2
2
GPC (LALLS): M : 47 300, M /M : 1.37.
polymeric product.
w
w
n
–
1
IR (KBr pellets, ν in cm ) ν: 3449 (s, broad, OH str),
2951 (m, sharp, arom C-H str), 2857 (m, sharp, aliph C-H
str), 2095–2019 (m, broad, arom overtone bands), 1725 (s,
sharp, C=O ester str), 1594 (s, sharp, C=C ring str), 1471
(m, sharp, arom C-N str), 1100 (s, broad, C-O-C str), 842 (s,
sharp, arom out-of-plane bend). UV–vis (DMF) λmax:
Ru(bpyPCL) (PF ) (13)
3
6 2
The three-dimensional (13) was synthesized by a similar
procedure to that described for (11), using 60 mg
(
0
0.060 mmol) of (7), 2.5 g (22 mmol) of ε-caprolactone, and
.60 µL of Sn(Oct) . Yield 2.3 g (82%) of a red-orange poly-
2
–
1
–1
meric product.
311 nm (ε = 57 500 (mol/L) cm ), 480 nm (ε = 8 600
–
1
–1
–1
1
IR (KBr pellets, ν in cm ) ν: 3442 (s, broad, OH str),
(mol/L) cm ). H NMR (DMSO-d , δ in ppm) δ: 4.00 (m,
6
2
940 (m, sharp, arom C-H str), 2863 (m, sharp, aliph C-H
broad, CH O of PCL), 2.31 (m, broad, OCCH of PCL),
2
2
str), 2191–1898 (m, broad, arom overtone bands), 1719 (s,
sharp, C=O ester str), 1597 (s, sharp, C=C ring str), 1471
1.68 (m, broad, CH of PCL), 1.29 (m, broad, CH of PCL).
2
2
GPC (LALLS): M : 34 540, M /M : 1.47
w
w
n
(
m, sharp, arom C-N str), 1092 (s, broad, C-O-C str), 733 (s,
sharp, arom out-of-plane bend). UV–vis (DMF) λmax:
2
Synthesis of ruthenium-centered polyesters via
macroligand–chelation approach
–
1
–1
92 nm (ε = 79 300 (mol/L) cm ), 458 nm (ε = 12 800
–1 –1 1
(
mol/L) cm ). H NMR (DMSO-d , δ in ppm) δ: 4.03 (m,
6
broad, CH O of PCL), 2.31 (m, broad, OCCH of PCL),
bpyPCL macroligand (23)
2
2
1
.69 (m, broad, CH of PCL), 1.37 (m, broad, CH of PCL).
This macroligand was synthesized by a similar procedure
to that described for (11), using 0.52 g (3.2 mmol) of (4) ini-
tiator, 33 g (289 mmol) of ε-caprolactone, and 16 µL of
2
2
GPC (LALLS): M : 64 300, M /M : 1.45.
w
w
n
Ru(bpy) (pqPCL)(PF ) (17)
Sn(Oct) . Yield 35 g (94%) of a white polymeric product.
2
6 2
2
–
1
The one-dimensional (17) was synthesized by a similar
IR (KBr pellets, ν in cm ) ν: 3439 (s, broad, OH str),
2951 (m, sharp, arom C-H str), 2857 (m, sharp, aliph C-H
str), 2095–2019 (m, broad, arom overtone bands), 1719 (s,
sharp, C=O ester str), 1594 (s, sharp, C=C ring str), 1471
(m, sharp, arom C-N str), 1100 (s, broad, C-O-C str), 849 (s,
sharp, arom out-of-plane bend). H NMR (DMSO-d , δ in
ppm) δ: 8.65 (d, broad, H6′ of bpy), 8.53 (d, broad, H6 of
procedure to that described for (11), using 74 mg
(
0
0.070 mmol) of (8), 2.3 g (18 mmol) of ε-caprolactone, and
.54 µL of Sn(Oct) . Yield 1.1 g (82%) of a dark-red poly-
2
meric product.
–
1
1
IR (KBr pellets, ν in cm ) ν: 3440 (s, broad, OH str),
6
2
951 (m, sharp, arom C-H str), 2857 (m, sharp, aliph C-H
©
2004 NRC Canada

Farah and Pietro
599
–
1
–1
bpy), 8.36 (s, broad, H3′ of bpy), 8.23 (s, broad, H3 of bpy),
290 nm (ε = 73 500 (mol/L) cm ), 456 nm (ε = 9 800
–
1
–1
1
7
.13–7.18 (d, broad, H5′ & H5 of bpy), 5.20 (s, broad, CH O
(mol/L) cm ). H NMR (DMSO-d , δ in ppm) δ: 7.58–
8.60 (m, broad, bpy ArH), 5.31 (s, broad CH O of bpy),
2
6
of bpy), 4.05 (m, broad, CH O of PCL), 2.30 (m, broad,
2
2
OCCH of PCL), 1.64 (m, broad, CH of PCL), 1.39 (m,
4.06 (m, broad, CH O of PCL), 2.33 (m, broad, OCCH of
2
2
2
2
broad, CH of PCL). GPC (LALLS): M : 27 900, M /M :
PCL), 1.69 (m, broad, CH of PCL), 1.45 (m, broad, CH of
2
w
w
n
2
2
1
.27.
PCL). GPC (LALLS): M : 29 870, M /M : 1.31.
w
w
n
Ru(bpy) (bpyPCL)(PF ) (14)
Ru(bpyPCL) (PF ) (16)
2
6 2
3
6 2
cis-Ru(bpy) Cl (50 mg, 0.11 mmol) was dissolved in
This three-dimensional (16) polymer was obtained from
2
2
2
0 mL of methanol; 43 mg (0.25 mmol) of AgNO were
40 mg (0.082 mmol) of RuCl ·xH O and 6.9 g (0.33 mmol)
3
3
2
of (23) macroligand polymer in 30 mL of acetonitrile–DME
(20:80 volume fraction), using the procedure described for
(14). Yield 5.1 g (61%).
IR (KBr pellets, ν in cm ) ν: 3455 (s, broad, OH str),
2942 (m, sharp, arom C-H str), 2866 (m, sharp, aliph C-H
str), 2195–1890 (m, broad, arom overtone bands), 1729 (s,
sharp, C=O ester str), 1602 (s, sharp, C=C ring str), 1471
(m, sharp, arom C-N str), 1098 (s, broad, C-O-C str), 756 (s,
–
1
sharp, arom out-of-plane bend). UV–vis (DMF) λ : 286
max
–
1
–1
–1
–1
(ε = 78 400 (mol/L) cm ), 456 (ε = 12 700 (mol/L) cm ).
1
H NMR (DMSO-d , δ in ppm) δ: 7.52–8.67 (m, broad, bpy
6
ArH), 5.28 (s, broad CH O of bpy), 4.08 (m, broad, CH O
2
2
of PCL), 2.31 (m, broad, OCCH of PCL), 1.65 (m, broad,
2
CH of PCL), 1.42 (m, broad, CH of PCL). GPC (LALLS):
2
2
M : 53 370, M /M : 1.37.
w
w
n
pqPCL macroligand (24)
str), 2195–1890 (m, broad, arom overtone bands), 1719 (s,
sharp, C=O ester str), 1592 (s, sharp, C=C ring str), 1471
This macroligand polymer was synthesized by a similar
procedure to that described for (23), using 0.59 g (2.5 mmol)
of (1) initiator, 35 g (306 mmol) of ε-caprolactone, and
(
m, sharp, arom C-N str), 1092 (s, broad, C-O-C str), 729 (s,
sharp, arom out-of-plane bend). UV–vis (DMF) λmax:
2
(
8
4
17 µL of Sn(Oct) . Yield 23 g (66%) of a white polymeric
2
–
1
–1
88 nm (ε = 79 600 (mol/L) cm ), 456 nm (ε = 12 900
product.
–
1
–1
1
–1
mol/L) cm ). H NMR (DMSO-d , δ in ppm) δ: 7.63–
IR (KBr pellets, ν in cm ) ν: 3356 (s, broad, O-H str),
6
.66 (m, broad, bpy ArH), 5.33 (s, broad, CH O of bpy),
2928 (m, sharp, arom C-H str), 2860 (m, sharp, aliph C-H
str), 1991–2058 (m, broad, arom overtone bands), 1726 (s,
sharp, C=O ester str), 1609 (s, sharp, C=C ring str), 1315 (s,
sharp, arom C-N str), 1260 (w, sharp, C-O-C str), 1037 (s,
2
.06 (m, broad, CH O of PCL), 2.37 (m, broad, OCCH of
2
2
PCL), 1.69 (m, broad, CH of PCL), 1.41 (m, broad, CH of
2
2
PCL). GPC (LALLS): M : 28 430, M /M : 1.29.
w
w
n
broad, C-H in-plane bend), 749 (s, sharp, arom C-H out-of-
1
Ru(bpyPCL) (bpy)(PF ) (15)
plane bend). H NMR (DMSO-d , δ in ppm) δ: 9.05 (s,
2
6 2
6
RuCl ·xH O (30 mg, 0.062 mmol), 3.5 g (0.13 mmol) of
broad, H3 of quinoline), 7.35–8.80 (m, complex, quinoline
3
2
(
23) macroligand polymer, and 2.1 g (50 mmol) of lithium
& bpy ArH), 5.27 (s, broad CH O of quinoline), 4.07 (m,
2
chloride were dissolved in 30 mL of acetonitrile–DME (1:1)
and refluxed overnight while stirring. The resulting intense
dark-blue reaction product was evaporated to dryness, then
dissolved in 10 mL of acetonitrile–DME (1:1) and reacted
broad, CH O of PCL), 2.32 (m, broad, OCCH of PCL),
2
2
1.65 (m, broad, CH of PCL), 1.43 (m, broad, CH of PCL).
2
2
GPC (LALLS): M : 19 800, M /M : 1.54.
w
w
n
with 54 mg (0.32 mmol) of AgNO under vigorous stirring
for 6 h at room temperature. After filtering out the white
Ru(bpy) (pqPCL)(PF ) (20)
3
2
6 2
The one-dimensional polymer (20) was synthesized by a
similar procedure to that described for (14), using 45 mg
(0.093 mmol) of cis-Ru(bpy) Cl , 40 mg (0.23 mmol) of
AgCl precipitate through
a
Celite pad, 9.67 mg
(
0.063 mmol) of 2,2′-bipyridine was added to the filtrate and
2
2
refluxed for 16 h. The desired polymer was then isolated
from the reaction mixture by addition to a cold methanolic
potassium hexafluorophosphate solution and filtered. It was
further purified by column chromatography on silica and
eluted with methylene chloride. Yield 2.7 g (70%) of an or-
ange-red polymer.
AgNO , and 2.7 g (0.091 mmol) of (24) macroligand poly-
3
mer. Yield 1.7 g (90%) of a dark-red polymeric product.
–
1
IR (KBr pellets, ν in cm ) ν: 3356 (s, broad, O-H str),
2928 (m, sharp, arom C-H str), 2860 (m, sharp, aliph C-H
str), 1991–2058 (m, broad, arom overtone bands), 1726 (s,
sharp, C=O ester str), 1609 (s, sharp, C=C ring str), 1315 (s,
sharp, arom C-N str), 1260 (w, sharp, C-O-C str), 1037 (s,
broad, C-H in-plane bend), 749 (s, sharp, arom C-H out-of-
–
1
IR (KBr pellets, ν in cm ) ν: 3449 (s, broad, OH str),
2
945 (m, sharp, arom C-H str), 2866 (m, sharp, aliph C-H
plane bend). UV–vis (DMF) λ : 290 nm (ε = 41 200
max
–
1
–1
–1
–1
1
(mol/L) cm ), 496 nm (ε = 8 900 (mol/L) cm ). H
NMR (DMSO-d , δ in ppm) δ: 8.87 (s, broad, H3 of
6
quinoline), 7.35–8.97 (m, complex, quinoline & bpy ArH),
©
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00
Can. J. Chem. Vol. 82, 2004
Scheme 1. Synthesis of macroligands (23) and (24) via ring-opening polymerization of (ε-caprolactone) monomer.
5
.27 (s, broad CH O of quinoline), 4.07 (m, broad, CH O of
str), 1991–2058 (m, broad, arom overtone bands), 1715 (s,
sharp, C=O ester str), 1617 (s, sharp, C=C ring str), 1322 (s,
sharp, arom C-N str), 1260 (w, sharp, C-O-C str), 1037 (s,
broad, C-H in-plane bend), 762 (s, sharp, arom C-H out-of-
2
2
PCL), 2.32 (m, broad, OCCH of PCL), 1.65 (m, broad, CH
of PCL), 1.43 (m, broad, CH of PCL). GPC (LALLS): M :
2
2
2
2
w
0 120, M /M : 1.58.
w n
plane bend). UV–vis (DMF) λ : 298 nm (ε = 51 300
max
–
1
–1
–1
–1
1
Ru(pqPCL) (bpy)(PF ) (21)
The two-dimensional polymer (21) was obtained by a
similar procedure to that described for (14), using 35 mg
(mol/L) cm ), 496 nm (ε = 9 700 (mol/L) cm ). H
2
6 2
NMR (DMSO-d , δ in ppm) δ: 8.83 (s, broad, H3 of
6
quinoline), 7.35–8.80 (m, complex, quinoline & bpy ArH),
5
.23 (s, broad CH O of quinoline), 4.01 (m, broad, CH O of
(
0.072 mmol) of RuCl ·xH O, 5.1 g (0.18 mmol) of (24)
2
2
3
2
PCL), 2.29 (m, broad, OCCH of PCL), 1.65 (m, broad, CH2
macroligand polymer, 2.1 g (50 mmol) of lithium chloride,
2
of PCL), 1.41 (m, broad, CH of PCL). GPC (LALLS): M :
3
2
1 mg (0.18 mmol) of AgNO , and 11 mg (0.071 mmol) of
,2′-bipyridine. Yield 1.2 g (79%) of a dark-red polymeric
2
w
3
2
9 780, M /M : 1.67.
w n
product.
–
1
IR (KBr pellets, ν in cm ) ν: 3356 (s, broad, O-H str),
Results and discussion
2
928 (m, sharp, arom C-H str), 2860 (m, sharp, aliph C-H
str), 1991–2058 (m, broad, arom overtone bands), 1726 (s,
sharp, C=O ester str), 1609 (s, sharp, C=C ring str), 1315 (s,
sharp, arom C-N str), 1260 (w, sharp, C-O-C str), 1037 (s,
broad, C-H in-plane bend), 749 (s, sharp, arom C-H out-of-
Macroligand synthesis
Polymeric macroligands (23) and (24) of controlled
molecular weight, bearing end-reactive functional groups,
were prepared by insertion–coordination ring-opening poly-
merization of ε-caprolactone with high yield (19). The
polymerization was initiated by 2-(2-pyridyl)-4-hydroxy-
methylquinoline ligand (1) and 4-methyl-4′-hydroxymethyl-
plane bend). UV–vis (DMF) λ : 294 nm (ε = 39 700
max
–
1
–1
–1
–1
1
(
mol/L) cm ), 494 nm (ε = 8 900 (mol/L) cm ). H
NMR (DMSO-d , δ in ppm) δ: 8.85 (s, broad, H3 of
6
quinoline), 7.35–8.80 (m, complex, quinoline & bpy ArH),
2
,2′-bipyridine (4) in the presence of stannous octanoate
5
.27 (s, broad CH O of quinoline), 4.05 (m, broad, CH O of
2
2
(Sn(Oct) ) as a catalyst, as shown in Scheme 1. As expected,
2
PCL), 2.31 (m, broad, OCCH of PCL), 1.64 (m, broad, CH
2
2
the resulting polymeric macroligands possess one chain ter-
minated with a hydroxy group, active in post-polymerization
reactions originating from the (ε-caprolactone) ring-opening
polymerization reaction (19), and another terminus end-
capped with an α,α′-diimine ligand, providing a free coordi-
nation site originating from the initiators. This synthetic ap-
proach has a notable advantage over the other conventional
methods of synthesizing telechelic polymers, as it provides
macromers with two distinct end functional groups per poly-
meric chain.
of PCL), 1.43 (m, broad, CH of PCL). GPC (LALLS): M :
2
w
2
0 840, M /M : 1.62.
w n
Ru(pqPCL) (PF ) (22)
3
6 2
The three-dimensional polymer (22) was synthesized by a
similar procedure to that described for (16), using 25 mg
(
0.052 mmol) of RuCl ·xH O and 4.7 g (0.17 mmol) of (24)
3 2
macroligand polymer. Yield 1.1 g (69%) of a dark-red poly-
meric product.
–
1
IR (KBr pellets, ν in cm ) ν: 3338 (s, broad, O-H str),
928 (m, sharp, arom C-H str), 2860 (m, sharp, aliph C-H
GPC, thermal, and electronic absorption data of these
macroligands are collected in Table 1. UV–vis spectra of
2
©
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Farah and Pietro
601
Table 1. Summary of data of macroligands (23) and (24) and their Ru(II)-containing polyesters obtained via macroligand–chelation.
MWa
(g/mol)
Polydispersity
index
Tmb
(°C)
∆Hfb
(J/g)
Tdecc
(°C)
Absorbance
(λ/nm)
Emissiond
(λ/nm)
Ch.
eff.
e
Polymer
(
(
(
(
(
(
(
(
14)
15)
16)
20)
21)
22)
23)
24)
a
28 430
29 870
53 370
20 120
20 840
29 782
27 900
19 800
1.29
1.31
1.37
1.58
1.62
1.67
1.27
1.54
62
62
63
62
63
67
61
62
97
101
89
311
321
327
294
307
311
275
281
456
456
456
496
494
496
292
340
600
605
610
670
97
76
92
74
73
78
94
f
105
112
84
—
f
—
87
Determined using LALLS–triple detector.
DSC traces from second heating cycle.
b
c
Thermogravimetric analysis (TGA); Tdec = decomposition temperature.
In CHCl degassed samples.
d
3
e
f
2+
2+
Ch. eff. = estimated chelation efficiency; for example: εMLCT(16) /εMLCT([Ru(bpy) ] ). For εMLCT and λ values, refer to Experimental section.
3
max
Non-emissive at room temperature.
1
Fig. 2. H NMR of macroligand (23) in CDCl .
3
(
23) and (24) macroligands clearly revealed the presence of
gration between the bipyridine and quinoline ligand signals
and the methylene units of the macroligand were approxi-
mately 1:1, suggesting that ligands (1) and (4) were the sole
π–π* transitions typical of polypyridyl chromophores in the
polymer chain. H NMR analysis of these macroligands
(
1
1
macroligand (23), for example, is shown in Fig. 2) revealed
polymerization initiators. Although H NMR spectroscopy
well-resolved characteristic signals of the bipyridine units,
as well as those of poly(ε-caprolactone). The ratios of inte-
has previously been utilized in determining the molecular
weight of similar polymers with low monomer loading
©
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02
Can. J. Chem. Vol. 82, 2004
Scheme 2. Synthesis of functionalized quinoline ligand based Ru(II) metal-centered polyesters.
(
10b), in our samples it would be difficult and inaccurate be-
with a well-defined transition-metal locus at the end of the
polymer chain. The second approach, termed macroligand–
chelation, involves the synthesis of polymeric macroligands
that are subsequently chelated to metal ions or complex pre-
cursors through standard inorganic reactions. In the latter
method, the reaction medium is modified to provide fully
compatible reaction conditions between the metal precursors
and the polymeric macroligands. With controlled experimen-
tal reaction settings and the use of an increasing number of
polymeric macroligands, both methods generate linear and
cause of their relatively high molecular weight.
Metal complexes of polymeric ligands
The design and synthesis of our metal-containing polyes-
ters was based principally on two different approaches
(
Schemes 2 and 3). The first, a metalloinitiation approach,
uses appropriately functionalized heteroleptic Ru(II)
complexes for the ring-opening polymerization of ε-
caprolactone, producing multi-functional macromolecules
©
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Farah and Pietro
603
Scheme 3. Synthesis of functionalized bipyridine ligand based Ru(II) metal-centered polyesters.
multi-dimensional ruthenium-centered polyesters. In the
metalloinitiation approach, mixed ligand ruthenium(II) com-
plexes (5), (6), (7), (8), (9), and (10), bearing peripheral OH
groups, were utilized as initiating sites for further ring-
opening polymerization of ε-caprolactone, employing simi-
lar procedures as those described in the preparation of the
macroligands. Thus, metal complexes of polymeric ligands
method, chains propagate divergently outward and away
from the congested metal center and can consequently pro-
vide materials of relatively high molecular weight. Very of-
ten the purification of the resulting polymeric metal complex
is facile, as polymeric products can be separated from
unreacted monomers by precipitation or by column chroma-
tography. Metal complexes must be soluble in the polymer-
ization conditions and be thermally stable so they do not
decompose during the polymerization process. Ru(II)
(
11), (12), (13), (17), (18), and (19) were obtained in high
yield in a one-pot synthesis, as red-orange products. In this
©
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Can. J. Chem. Vol. 82, 2004
Table 2. Summary of data of Ru(II)-containing polyesters obtained via metalloinitiation.
MWb
(g/mol)
Polydispersity
index
Tmc
(°C)
∆H c
Tdecd
(°C)
Absorbance
(λ/nm)
Emissione
(λ/nm)
f
Polymer
[M]/[I]a
(J/g)
(
(
(
(
(
(
11)
12)
13)
17)
18)
19)
a
175
370
365
250
290
290
28 130
47 000
64 300
19 150
28 500
34 540
1.26
1.37
1.45
1.52
1.51
1.47
62
64
67
59
61
63
92
97
107
89
95
102
317
329
333
289
307
317
456
456
454
490
494
498
600
608
610
670
—f
—f
Monomer to initiator loading.
b
Determined using LALLS–triple detector.
c
DSC traces from second heating cycle.
d
Thermogravimetric analysis (TGA).
e
f
In CHCl degassed samples.
3
Non-emissive at room temperature.
tris(bipyridine) complex initiators have been reported to be
stable in various polymerization reactions (20). In our hands,
bulk polymerization of ε-caprolactone with the aforemen-
tioned complexes under the conditions of our study provided
homogenous monomer–metal complex initiator solutions
with no evident metal residue upon reaction completion.
subsequently reacted with 2,2′-bipyridine to produce the de-
sired red-orange bis-ligated metal complexes of polymeric
ligands. In the case of tris-ligated metal complexes of poly-
meric ligands (16) and (22), RuCl ·xH O was reacted with
3 equiv. of (23) and (24) macroligands in polar reaction me-
dium for a longer time.
3
2
The macroligand–chelation approach is conceptually an
extension of normal chelation reactions of small molecules
and metal ion precursors in standard inorganic reactions
Summaries of molecular weight, thermal, electronic ab-
sorption, and emission analysis data for the ruthenium-
centered polyesters prepared via macroligand–chelation and
via metalloinitiation are presented in Tables 1 and 2, respec-
tively. The presence of the ruthenium chromophore in the
(
21). However, it is generally difficult to extrapolate chemis-
try from inorganic–organic synthesis to polymer reactions
because the kinetics are usually different for each case.
Polymer chain entanglement always limits the collision be-
tween active coordination sites in the polymer and metal
ions. In the case of high-molecular-weight polymeric
macroligands, additional reaction parameters have to be
taken into account (22). The reaction medium must be capa-
ble of efficiently solubilizing both the metal ion precursors
and the polymeric macroligand undergoing the substitution.
More importantly, the solvent has to facilitate ligand substi-
tution by solvating leaving groups or by providing labile
metal ion solvent-coordinated intermediates, making the
metal center sites prone to facile coordination. Macroligand
solution phenomena, such as chain conformation and aggre-
gation, have to be considered as well (23). Thus, in employ-
ing the macroligand–chelation method to prepare the mono-
ligated metal complexes of polymeric ligands (14) and (20),
cis-Ru(bpy) Cl was first dehalogenated with AgNO in
1
polymer chain was verified by H NMR spectroscopy and
electrochemical and UV–vis emission analysis. Metal-to-
ligand charge-transfer (MLCT) bands around 460 nm, char-
2
+
2+
acteristic of [Ru(bpy) ] , and at 490 nm for [Ru(pqX) ]
3
3
(X = hydroxymethyl functionality) cores were observed. An
emission band around 600–610 nm (excitation 400 nm) for
2
+
all [Ru(bpy) ] -containing polymers was observed. For
3
mixed quinoline ligand based ruthenium-centered polymers,
mono-ligated metal complexes of polymeric ligands (17) and
(20) were emissive at 670 nm (excitation 400 nm), while the
rest of the series were either weakly emissive or not
emissive at all. Molar absorptivities (ε) of the MLCT bands
for all the polymers obtained via macroligand–chelation
were determined using known masses and absolute molecu-
lar weights of the polymers. From these determinations, the
estimated chelation efficiencies relative to the corresponding
ruthenium complexes presented in Table 1 were obtained
(24) to account for factors that might influence substitution
reactions of macroligands of different molecular weights.
2
2
3
methanol. After solvent removal, the resulting solvent-
2
+
coordinated species [Ru(bpy) (MeOH) ] was reacted with
2
2
polymeric macroligands (23) and (24) in an acetonitrile–
DME (1:1 volume fraction) mixed solvent medium to gener-
ate the desired polymers after column chromatography. The
bis-ligated metal complexes of polymeric ligands (15) and
An overlay GPC trace of the tris-ligated metal complex of
polymeric ligand (16) and the macroligand (23) from which
it originated is shown in Fig. 3. As predicted, there was an
increase in molecular weight for the formation of the metal-
centered polymeric ligand (16), albeit lower than the theoret-
ical calculated value. An increase in polydispersity index
(PDI) of the target polymers and the existence of a shoulder
in the GPC traces were also evident for the series of ruthe-
nium-centered polymeric ligands, indicating the existence of
small amounts of unreacted macroligands in our polymers.
Although a small amount of uncomplexed macroligand does
not affect the bulk properties of polymeric metal complexes
or their usefulness in practical application, it can be removed
(
21) and also the tris-ligated metal complexes of polymeric
ligands (16) and (22) were obtained with controlled combi-
nation of the metal source and the appropriate mole ratio of
macroligands (23) and (24) in a polar reaction medium. For
samples (15) and (21), for example, RuCl ·xH O was heated
3
2
with 2 equiv. of the desired macroligand in the presence of
lithium chloride to prevent total substitution of the ligands
around the coordination sphere of the metal center. This has
provided dark, intense blue halogenated reaction intermedi-
ates of type [Ru(23) Cl ] or [Ru(24) Cl ]. These intermedi-
1
by iterative column chromatography. In the H NMR analy-
2
2
2
2
ate species were then dehalogenated in situ with AgNO and
sis of our polymers, the presence of characteristic signals of
3
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Farah and Pietro
605
Fig. 3. GPC traces of macroligand (23) and ruthenium-centered
tris-ligated polyester (16).
Fig. 4. Cyclic voltammogram of ruthenium-centered polyester
(14) in acetonitrile–N , 0.1 mol/L TBAPF , scan rate 100 mV/s,
2
6
Pt disc.
Table 3. Half-wave potentials for ruthenium-centered polymers
obtained via macroligand approach.
Polymer
E1/2(ox)a
Ecath(red)b
Ecath(red)b
(
(
(
(
(
(
14)
15)
16)
20)
21)
22)
a
1.26
1.26
1.29
1.31
1.30
1.33
–1.25
–1.33
–1.31
–1.32
–1.30
–1.21
–1.54
–1.59
–1.60
–1.62
–1.60
–1.68
II
Half-wave potential for Ru oxidation.
b
the metal-complex core was observed, along with capro-
lactone resonances, for all polymers obtained via the
macroligand approach. For polymers obtained via metallo-
initiation, the situation was different. Only caprolactone
peaks were observable in the H NMR spectra. Similar ob-
servations were previously reported by McAlvin and Fraser
Irreversible cathodic ligand reductions, all vs. SCE. Solutions were 0.1
mol/L in TBAPF , in acetonitrile, at room temperature.
6
onset of their thermal decomposition was high, as demon-
strated in Fig. 6 for polyester (16), and varied from 275 to
1
3
50 °C. Moreover, the onset of decomposition temperature,
(
25) using hexafunctional tris(bipyridine) metalloinitiators
as well as the apparent enthalpy of melting, increased
slightly with the number of macroligands present around the
metal center. This occurred with concomitant increase of
molecular weight of the resulting polymeric metal com-
plexes. This observation could be related to an increase of
crystallinity of the metal-centered polymers due to the in-
creasing content of semicrystalline poly(ε-caprolactone)
macroligands coordinated to the metal ion.
for cationic polymerization of 2-ethyl-2-oxazolines.
The cyclic voltammogram of polymeric metal complex
(
14) is depicted in Fig. 4 as a representative example of the
electrochemical behaviour of these series of polyesters.
Half-wave potentials (E ) in acetonitrile for all polymers
1
/2
obtained via the macroligand approach are collected in Ta-
ble 3. For all metal-centered polymers, one reversible oxida-
tion and two irreversible reduction waves were observed.
Within each series, these electrochemical processes occur at
nearly the same potential, regardless of the polymer
dimensionality. Electrode passivation due to polymer film
formation was also observed in equilibrium scans.
Concluding remarks
Mixed ligand ruthenium-centered poly(ε-caprolactones) of
various dimensionality were synthesized and characterized.
These materials were obtained by preparing linear polymers
with binding sites by ring-opening polymerization of ε-
caprolactone, by using bpy or quinoline ligand initiators fol-
lowed by chelation to metal ions. The same polymers were
also obtained from ring-opening polymerization of ε-
caprolactone via metal complexes with initiator sites in their
ligand periphery. Both strategies produced polymers of rela-
tively high molecular weight, possessing good filming prop-
erties and high thermal stability.
The macroligands and the ruthenium-centered polyesters
were also analyzed by differential scanning calorimetry
(
DSC) and thermogravimetric analysis (TGA). There were
no substantial differences in the melting points for the
macroligands and the ruthenium-centered polyesters, regard-
less of molecular weight increase and polymer dimension-
ality or the metal presence in the polymer chain. As a typical
example, an overlay DSC thermogram of macroligand (23)
and the tris-ligated metal complex polymeric ligand (16) is
shown in Fig. 5. Thermogravimetric analyses (TGA) of
these series of ruthenium-centered polyesters show that they
Selective end functionalization of macroligands, with the
coordination site of the diimine ligands remaining intact, and
the possibility for further functionalization of the metal-
possess a high thermal stability under N atmosphere. The
2
©
2004 NRC Canada

6
06
Can. J. Chem. Vol. 82, 2004
Fig. 5. DSC thermogram of macroligand (23) and the tris-ligated ruthenium-centered polyester (16).
Fig. 6. TGA thermogram of ruthenium-centered tris-ligated polyester (16).
centered polyesters both merit further studies. They could
potentially provide a wide of range of functionalized macro-
molecules of tailored properties. In turn, these polymers
with luminescent chromophores in a well-defined location in
the polymer chain have fulfilled our primary investigation in
designing a new class of organic polymers with polypyridyl
ruthenium(II) luminophores, a basis of transition-metal-
mediated electroluminescent devices. A full account of such
©
2004 NRC Canada

Farah and Pietro
607
an investigation will be the subject of a forthcoming publi-
cation.
Mlekuz, D. Zargarian, N.J. Taylor, and T.B. Marder. J. Chem.
Soc. Chem. Commun. 188 (1991).
7
8
. A.A. Farah and W.J. Pietro. Polym. Bull. 43, 135 (1999).
. A.A. Farah, J.G.C. Veinot, M. Najman, and W.J. Pietro. J.
Macromol. Sci. Pure Appl. Chem. A37(11), 1507 (2000).
. D.A. Friesen, T. Kajita, E. Danielson, and T.J. Meyer. Inorg.
Chem. 37, 2756 (1998).
Acknowledgements
9
We express our gratitude to Dr. I. Manners and his re-
search groups for GPC assistance. The Natural Sciences and
Engineering Research Council of Canada (NSERC) is also
acknowledged for financial support.
1
1
0. (a) C.L. Fraser and A.P. Smith. J. Polym. Sci. Polym. Chem.
3
8, 4707 (2000); (b) P.S. Corbin, M.P Webb, J.E. McAlvin,
and C.L Fraser. Biomacromolecules, 2, 223 (2001); (c) J.E.
Collins and C.L. Fraser. Macromolecules, 31, 6715 (1998);
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©
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