Side chain Co(i) polymers featuring acrylate functionalized neutral 18 electron CpCo(C4R4) (R = Ph, Me) units

Article abstract of DOI:10.1039/c1cc11076d

The synthesis of novel Co(i) polymers featuring CpCo(C₄R ₄) units are reported. The cyclopentadienyl ring on the CpCo(C ₄R₄) unit has been functionalized with acrylate or methacrylate groups. Acrylate derivative

Full text of DOI:10.1039/c1cc11076d

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2011, 47, 5301–5303
www.rsc.org/chemcomm
COMMUNICATION
Side chain Co(I) polymers featuring acrylate functionalized neutral 18
electron CpCo(C4R4) (R = Ph, Me) unitsw
Preeti Chadha and Paul J. Ragogna*
Received 23rd February 2011, Accepted 17th March 2011
DOI: 10.1039/c1cc11076d
The synthesis of novel Co(I) polymers featuring CpCo(C4R4)
units are reported. The cyclopentadienyl ring on the
CpCo(C4R4) unit has been functionalized with acrylate or
methacrylate groups. Acrylate derivatives of these compounds
were found to polymerize giving rise to the first example of
polymers containing neutral, 18 e cobaltoarenocenes in the
side chain.
The field of metallopolymers has quickly matured over the last
Scheme 1 Synthesis of the acrylate appended monomer 1d.w
decade due to the emerging applications of these materials in
various fields of science and technology.1 Polyferrocenyl-
The acrylate appended monomer 1d was obtained in a
silanes (PFS) are by far the most broadly developed and well
moderate yield by the in situ conversion of carboxylic acid
studied class of metallocene based polymers, which have found
1b to the acid chloride 1c and subsequent halide displacement
applications in areas such as ceramics,2 photonic crystal
with hydroxyethylacrylate (HEA) (Scheme 1). Compound 1b
displays,3 nanolithography,4 as well as precursors to electro-
was prepared from the hydrolysis of the ester 1a following a
active, magnetic or catalytically active nanostructures.5 The
literature procedure.11 The phenyl substituted (C4R4QC4Ph4)
cobaltocenium cation (CoCp2+) is isoelectronic with ferrocene
acrylate monomer 1d was comprehensively characterized using
and three recent reports of cobaltocenium containing polymers
NMR spectroscopy, FT-IR spectroscopy, mass spectrometry
have emerged, where one incorporates cobaltocenium in the
and elemental analysis.w
main chain of the polymer6 and the others incorporate it
Synthesis of the methyl derivative of 1d (C4R4QC4Me4)
in the side chain.7 Cyclopentadienyl-cobalt-cyclobutadiene
proved to be difficult since we were unable to hydrolyze the
(CpCoCb) is also isoelectronic with ferrocene and cobaltocenium
ester Cb*Co(C5H4CO2Me)12 (Cb*QC4Me4) into the corres-
and has different properties (cf. cobaltocenium) because it is
ponding carboxylic acid, partly due it’s lower stability towards
electronically neutral (e.g. excellent solubility in many solvents).
the comparatively harsh conditions required for the synthesis.
It also has the additional advantage that a wide variety of
An alternative approach was followed as to introduce the
substituents can be incorporated on the cyclobutadiene ring,
alcohol on the cyclopentadienyl ring prior to the installation of
which in turn, greatly influence the properties of the CpCoCb
the Cb*Co unit (Scheme 2). Lithium(1-carboxy-propan-3-
framework.8,9 Cobaltocenium, in comparison, is relatively
ol)cyclopentadiene was reacted with Cb*Co(CO)2I to generate
difficult to functionalize. Polymers containing these Co(I) units
the alcohol appended species 2a which was then treated with
have seen limited development wherein main chain Co(I)
methacryloyl and acryloyl chloride to obtain 2b and 2c
polymers have been primarily prepared by metallacycling
polymerization (MCP)10 of bisalkynes at a Co(I) centre.
However, side chain Co(I) polymers utilizing the CpCoCb
framework remain unreported. In this context, we have developed
methacrylate and acrylate functionalized cobaltoarenocenes
1d, 2b and 2c as the first representatives of this class of
compounds and studied their polymerization behaviour.
The University of Western Ontario, 1151 Richmond St., N6A 5B7,
London, ON, Canada. E-mail: pragogna@uwo.ca;
Fax: +1 519-661-3022; Tel: +1 519-661-2111 ext 87048
w Electronic supplementary information (ESI) available: Extensive
experimental details for the synthesis of all compounds and full
characterization data. CCDC 812213. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c1cc11076d
Scheme 2 Synthesis of methyl substituted cyclobutadiene complexes
2a–2c.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 5301–5303 5301

View Article Online
Scheme
3 Polymerization of monomer (1d) via ATRP and
Fig. 1 Proton NMR spectra of monomer 1d and polymer A. %
denotes the vinylic protons and K denotes the CH2 protons in the
linker.
conventional free radical methods. Polymers A–C have the same
general structure, but vary in the number of units (n).
(see ESIw for X-ray structural details) respectively, by simple
halide displacement reaction.
Compounds 1d, 2b and 2c were then subjected to polymer-
ization conditions using two different methods: (a) atom
transfer radical polymerization (ATRP); and (b) conventional
free radical. The polymerization reactions were performed in
J-Young NMR tubes in C6D6 to monitor the progress of the
reaction by 1H NMR spectroscopy. Copper(I) bromide (CuBr)
was used as the catalyst, ethyl 2-bromoisobutyrate (EBiB) as
the initiator, and pentamethyldiethylenetriamine (Pmdeta) as
the ligand. The first attempt was made with 1 mol% of the
initiator (keeping the mol% of initiator : catalyst : ligand
constant) and no polymerization was observed in all cases.
Upon increasing to 10 mol%, the reaction was observed to
70% completion for 1d (giving polymer A, Scheme 3) and only
10% for 2c over a period of 4 d at 80 1C. Due to the low %
conversion of the methyl substituted polymer by this method,
no further investigations were pursued. Precipitation of green
solids, likely resulting from the oxidation of CuBr was
observed during the course of conversion, and accounts for
the cessation of the reaction.
Fig. 2 Proton NMR spectra of monomer 2c and polymer D. %
denotes the vinylic protons and K denotes the CH2 protons in the
linker.
MeOH in contrast to polymer D which was soluble. The
polymers were stored in open atmosphere and were found to
be air and moisture stable for upto 30 d. Proton NMR spectra
of the isolated polymer and monomer (Fig. 1 and 2), show the
disappearance of the vinylic protons and a general broadening
of the spectra. The appearance of broad peaks in the alkyl
region (1.5–2.5 ppm) of the polymer correspond to the
conversion of vinylic CHQCH2 group into the internal
CH–CH2– fragment. The disappearance of the alkene peak
at 1635 cmÀ1 in the FT-IR spectra of polymer A (Fig. S1,
ESIw) gave corroborating evidence to polymer formation.
Molecular weights and PDI’s of the polymers were determined
by size exclusion chromatography (SEC) (Table 1) which
indicates both low molecular weight and low PDI for polymer
A prepared by the ATRP method. Lower molecular weight for
A results from the use of more initiator which was necessary,
since a lower percentage resulted in sluggish reactivity. Polymers
B and C exhibit higher molecular weights (less mol% of
initiator used) and higher PDI values. The methyl substituted
polymer D had a lower molecular weight due to the higher
percentage of AIBN (9 mol%) that was required. The requirement
of more AIBN may be speculated due to the short lifetime of
the radical that is formed and propagates the chain during
The conventional free radical method was also tested using
azobisisobutyronitrile (AIBN). In the case of 1d, polymer-
ization proceeded with 1 mol% as well as 0.1 mol% AIBN.
However, for 2c 9 mol% AIBN was required to observe any
polymerization. Over a period of 3 d at 60 1C, 90% completion
was observed for the phenyl substituted polymers B and C
(Scheme 3) and only 65% completion for methyl substituted
polymer D (Scheme 2). It should be noted that no polymer-
ization was observed in the case of 2b under any of the above
conditions. This could be due to the low reactivity of the
methacrylate unit13 in the present system or possible chain
transfer processes involving the organometallic moiety. This is
however, in contrast with the analogous ferrocene compounds
reported by Tang et al. where the methacrylate species was
found to be more reactive towards polymerization.14
All polymers A–D were found to be soluble in common
organic solvents such as DCM, THF and benzene, allowing
for their easy characterization by standard methods; and
insoluble in n-pentane, Et2O and H2O. However, subtle
differences were observed in the physical properties of the
phenyl substituted polymers A–C which were insoluble in
c
5302 Chem. Commun., 2011, 47, 5301–5303
This journal is The Royal Society of Chemistry 2011

View Article Online
Table 1 Summary of the molecular weights and PDI of polymers A–D
Polymer
Method
Mol%
PDI
Mn/g molÀ1 (Â103)
n
% Yield (isolated)
A
B
C
D
ATRP
AIBN
AIBN
AIBN
10%
1.15
2.09
1.90
1.31
3.6
30.5
26.1
10.6
6
60
70
70
50
0.1%
1.0%
9.0%
49
42
28
n = average number of monomer units incorporated in the polymer based on Mn (absolute mol. wt.); Mol% = mol% of the initiator with respect
to the monomer 1d or 2c respectively.
polymerization, however, further studies are required in this
Notes and references
regard.
1 (a) G. R. Whittel, M. D. Hager, U. S. Schubert and I. Manners,
Nat. Mater., 2011, 10, 176–188; (b) J.-C. Eloi, L. Chabanne,
Thermogravimetric analysis (TGA) (Fig. S2, ESIw) of the
polymers revealed that the phenyl substituted polymers A–C
are stable upto 360 1C, whereas the methyl substituted
polymer D was found to be thermally less stable (Td = 235 1C)
(Fig. S2, ESIw). This can be attributed to the lower thermal
stability of the monomer 2c (Td = 214 1C) as compared to the
phenyl substituted monomer 1d (Td = 367 1C).
Differential Scanning Calorimetry (DSC) of monomer 1d
(Fig. S3, ESIw) showed a melting endotherm and an exotherm
for polymerization suggesting that the phenyl substituted
monomer is thermally polymerizable. No melting or polymer-
ization transition was observed in the DSC of monomer 2c.
Glass transition temperatures (Tg) of the polymers (Fig. S4,
ESIw), were determined from the DSC measurements and were
found to be in the range of 100 1C–130 1C for polymers A–C.
Thermal analysis of polymer D revealed a much lower Tg at 43
1C. This can be attributed to increased flexibility of the methyl
substituted polymer due to less steric bulk.
G. R. Whittel and I. Manners, Mater. Today, 2008, 11, 28–34.
2 M. Ginzburg, M. J. MacLachlan, S. M. Yang, N. Coombs,
T. W. Coyle, N. P. Raju, J. E. Greedan, R. H. Herber, G. A. Ozin
and I. Manners, J. Am. Chem. Soc., 2002, 124, 2625–2639.
3 (a) G. A. Ozin and A. C. Arsenault, Mater. Today, 2008, 11, 44–51;
(b) D. P. Puzzo, A. C. Arsenault, I. Manners and G. A. Ozin,
Angew. Chem., Int. Ed., 2009, 48, 943–947.
4 C. A. Ross, Y. S. Jung, V. P. Chuang, F. Ilievski, J. K. W. Yang,
I. Bita, E. L. Thomas, H. I. Smith, K. K. Berggren, G. J. Vancso
and J. Y. Cheng, J. Vac. Sci. Technol., B: Microelectron.
Nanometer Struct.–Process., Meas., Phenom., 2008, 26, 2489–2494.
5 (a) D. A. Rider, K. Liu, J.-C. Eloi, L. Vanderark, L. Yang,
J.-Y. Wang, D. Grozea, Z.-H. Lu, T. P. Russell and I. Manners,
ACS Nano, 2008, 2, 263–270; (b) I. Manners, J. Organomet. Chem.,
2011, 696, 1146–1149; (c) S. Lastella, Y. J. Jung, H. Yang,
R. Vajtai, P. M. Ajayan, C. Y. Ryu, D. A. Rider and
I. Manners, J. Mater. Chem., 2004, 14, 1791–1794;
(d) C. Hinderling, Y. Keles, T. Stockli, H. F. Knapp, T. de los
¨
Arcos, P. Oelhafen, I. Korczagin, M. A. Hempenius, G. J. Vancso,
R. Pugin and H. Heinzelmann, Adv. Mater., 2004, 16, 876–879.
6 U. F. J. Mayer, J. B. Gilroy, D. O’Hare and I. Manners, J. Am.
Chem. Soc., 2009, 131, 10382–10383.
In summary, we have synthesized a series of functionalized
CpCo(C4R4) complexes bearing a methacrylate or acrylate
moiety on the Cp ring. The acrylate-appended monomers (1d
and 2c) were found to polymerize using radical polymerization
methods. These polymers represent the first example
of the incorporation of such unique organometallic species
into a poly(acrylate) architecture and furthermore, attains a
100% incorporation of the Co(I) subunit in the resulting
material. The reactivity of the monomer was found to be
influenced by the variation of substituents on the remotely
located C4R4 ring (away from the polymerization site). The
thermal properties of the polymer could also be varied by
changing the R substituents. Future efforts aim at incorporating
7 (a) L. Ren, C. G. Hardy and C. Tang, J. Am. Chem. Soc., 2010,
132, 8874–8875; (b) L. Ren, C. G. Hardy, S. Tang, D. B. Doxie,
N. Hamidi and C. Tang, Macromolecules, 2010, 43, 9304–9310.
8 U. H. F. Bunz, Top. Curr. Chem., 1999, 201, 131–160.
9 (a) J. Jiao, G. J. Long, F. Grandjean, A. M. Beatty and
T. P. Fehler, J. Am. Chem. Soc., 2003, 125, 7522–7523;
(b) P. D. Byrne, D. Lee, P. Muller and T. M. Swager, Synth.
¨
Met., 2006, 156, 784–791; (c) S. Sasaki, Y. Tanabe and
M.
Yoshifuji,
Chem.
Commun.,
2002,
1876–1877;
(d) A. Goswami, Y. Nie, T. Oeser and W. Siebert, Eur. J. Inorg.
Chem., 2006, 566–572; (e) A. Goswami, C.-J. Maier, H. Pritzkow
and W. Siebert, J. Organomet. Chem., 2005, 690, 3251–3259.
10 (a) H. Nishihara, M. Kurashina and M. Murata, Macromol.
Symp., 2003, 196, 27–38; (b) M. Kurashina and H. Nishihara,
Macromol. Symp., 2004, 209, 141–162; (c) I. L. Rozhanskii,
I. Tomita and T. Endo, Macromolecules, 1996, 29, 1934–1938;
(d) Y. Sawada, I. Tomita and T. Endo, Polym. Bull., 1999, 43,
electron withdrawing
R groups, studying their effects,
165–170; (e) W. Steffen, B. Kohler, M. Altmann, U. Scherf,
¨
standardizing living polymerization methods for these species,
and developing Co(I) block copolymers and studying their self
assembly.
K. Stitzer, H.-C. Z. Loye and U. H. F. Bunz, Chem.–Eur. J.,
2001, 7, 117–126.
11 C. E. Anderson, L. E. Overman, C. J. Richards, M. P. Watson and
N. White, Org. Synth., 2007, 84, 139.
12 P. O’Donohue, S. A. Brusey, C. M. Seward, Y. Ortin,
We thank the Natural Sciences and Engineering Research
Council (NSERC) of Canada, the Canada Foundation for
Innovation (CFI) and The University of Western Ontario
for generous financial support. We also thank Ali Nazemi
and Dr E. Gillies (UWO) for the GPC analysis of the
polymers; Jacquelyn Price and Caleb Martin for X-ray data
collection.
B. C. Molloy, H. Muller-Bunz, A. R. Manning and
¨
M. J. McGlinchey, J. Organomet. Chem., 2009, 694, 2536.
13 A. D. Pomogailo and V. S. Savost’yanov, Synthesis and
Polymerization of Metal-containing Monomers, CRC Press, Boca
Raton, 1994.
14 C. G. Hardy, L. Ren, T. C. Tamboue and C. Tang, J. Polym. Sci.,
Part A: Polym. Chem., 2011, 49, 1409–1420.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 5301–5303 5303