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polymer 8, but the green solution did not change color with
time, which indicates that the AuI species is fully stabilized in
15 (Scheme 3), as also shown by IR (Table S3 in the Supporting
Information). Indeed, the IR spectrum of this green solution
(Figure S53 in the Supporting Information) indicated that the
NÀH band returned to its original position at 3447 cmÀ1 as ob-
served before supramolecular interaction, which signifies that
the NÀH···OÀCO bond of 14 was then disrupted in 15 (Table S3
in the Supporting Information). To confirm the structure of par-
amagnetic polymer 15, related diamagnetic complex 19,
formed from the reaction between [AuCl(SC4H8)] and 13, was
synthesized. The 1H, 13C, and mass spectroscopy data of 19
modeling the coordination mode of Au in 15 indicate that 19
is oligomeric, with both the carboxylate and the central tria-
zole nitrogen atom coordinated to AuI, as shown by the IR and
NMR spectra and the Au-containing fragments observed in the
MALDI-TOF MS at 413.3 and 629.5 Da (Supporting Information
p. S35 and Figures S55–S59).[23]
down these reduction processes and consequently provides
the possibility of identifying intermediates and the formation
of large polymer-embedded nanoparticles. This is illustrated
with a rare isolation of AuI intermediates in the course of Au
nanoparticle formation. Moreover, additional control becomes
possible in the supramolecular variation of the PMF polymer
connected to a hanging triazole ligand that traps AuI, even if
further NaBH4 reduction to form Au nanoparticles remains pos-
sible. In conclusion, supramolecular redox engineering of
redox-robust nanomaterials becomes a promising method to
control their formation, reactivity, and physical properties for
future nanodevices.
Experimental Section
General data
For general data including solvents, apparatuses, compounds, reac-
tions, spectroscopy, CV, and SEC, see the Supporting Information.
To obtain AuNPs by reduction of AuI in 15, it was necessary
to add the strong reductant NaBH4. The addition of this re-
agent led to the formation of a purple solution characterized
by using UV/Vis (Figure S56 in the Supporting Information, SPB
at l=531 nm), and the core size of the AuNPs is (11Æ2) nm as
determined by TEM (Figure S57 in the Supporting Information).
After addition of NaBH4 to 15, the PMFium polymer was re-
duced to the PMF polymer, which was verified by using CV
and IR spectroscopy (Figures S58 and S59 in the Supporting In-
formation), in which the carbonyl bond was unaltered. The sta-
bilization of AuI in this case is thus due to the presence of the
triazole ligand. Electron density provided by this ligand upon
coordination to AuI makes the AuI species more electron rich
and thus more difficult to reduce, so that the slow reduction
of AuI to AuNPs observed in the absence of this ligand is no
longer observed in its presence.
N-[11’-PMF-formamido-3’,6’,9’-trioxaundecyl]-cis-5-norbor-
nene-exo-2, 3-dicarboximide monomer (5)
Oxalyl chloride (0.25 mL, 2.85 mmol) was added dropwise to a solu-
tion of PMF carboxylic acid (0.17 g, 0.57 mmol) in dry CH2Cl2
(30 mL) at 08C under nitrogen and the mixture was stirred over-
night at 208C, then dried in vacuo. The residual yellow-brown solid
of crude chlorocarbonyl-PMF was dissolved in dry CH2Cl2 (5.0 mL)
and added dropwise to a solution of 4 (0.19 g, 0.57 mmol) and trie-
thylamine (0.8 mL, 5.7 mmol) in CH2Cl2 (10 mL). The obtained mix-
ture was stirred overnight at 208C under nitrogen, then washed
with 10% K2CO3 solution (50 mL) and distilled water (250 mL).
The collected organic solution was dried over anhydrous Na2SO4,
filtered, and the solvent was removed in vacuo. The product was
purified by using column chromatography with CH2Cl2/MeOH (1:10
v/v) as the eluent and obtained as a red-brown sticky oil (yield:
0.30 g, 85.4%). 1H NMR (300 MHz, CDCl3, 258C, TMS): d=1.31 (d,
J=9.8 Hz, 1H; CH2 bridge), 1.43 (d, J=9.8 Hz, 1H; CH2 bridge),
1.78 (s, 15H; 5CH3), 2.62 (d, J=1.2 Hz, 2H; COCH), 3.21 (t, J=
3.2 Hz, 2H; =CHCH), 3.53–3.67 (m, 16H; 4CH2CH2), 3.83 (t, J=
3.8 Hz, 2H; sub. Cp; Cp=h5-C5H5), 4.1 (t, J=3.8 Hz, 2H; sub. Cp),
6.1 (t, J=9.2 Hz, 1H; NHCO), 6.23 ppm (t, J=3.7 Hz, 2H; CH=CH);
13C NMR (75 MHz, CDCl3, 258C, TMS): d=177.96 (CON), 169.20
(CONH), 137.81 (CH=CH), 81.08 (Cp*; Cp*=h5-C5Me5), 74.37 (sub.
Cp), 70.57, 70.20, 69.88 (CH2 and sub. Cp), 66.92 (CH2NH), 47.78
(CO-CH), 45.26 (=CH-CH), 42.69 (CH2-bridge), 39.18 (CH2-NCO),
37.74 (-CH2CH2-NCO), 10.52 ppm (CH3); MS ESI: m/z calcd for
C33H44N2O6Fe: 620.6; found: 643.2 [M+Na]+.
Conclusion
Pentamethylation of a ferrocene Cp ring fully stabilizes the oxi-
dized green d5 FeIII polymers so that they become robust in
aerobic solutions, even with the electron-withdrawing amido
group that serves as a linker. The pentamethylferrocene poly-
mers add to the short list of redox-robust iron sandwich com-
plexes with useful electron-transfer properties,[24,25] but they
are also the first polymer series to contain a stabilizing perme-
thylated ring. This ring permethylation not only ensures com-
plete air stability of the oxidized polymers, which is essential
for further redox engineering, but also accelerates polymeri-
zation and modifies the solubility and adsorption properties of
the polymers. Given the low polymer dispersities obtained
with the third-generation Grubbs ruthenium polymerization
catalysts, this new very robust FeIII/FeII redox couple provides
well-defined nanomaterials with extended redox-engineering
possibilities. These properties have been exemplified here with
the formation/encapsulation of Ag and Au nanoparticles in
which the nanoparticle size can be modulated. The reduction
of AgI and AuIII to zero-valent metals by electron transfer
rather than hydride transfer (traditionally with NaBH4) slows
General procedure for the synthesis of poly-N-[3-(3’,6’,9’-tri-
oxaundecyl-11’-PMF-formamido)]-cis-5-norbornene-exo-2, 3-
dicarboximide (6) via ROMP
The desired amount of 1 was first dissolved in a minimum amount
of dry CH2Cl2 in a small Schlenk flask. Then, a known amount of
monomer 5 in dry CH2Cl2 (1 mL per 100 mg of monomer 5) was
added to the catalyst solution with vigorous stirring under nitro-
gen. The obtained reaction mixture was stirred vigorously for
10 min at 208C, and then quenched with ethyl vinyl ether (EVE;
0.2 mL). The yellow solid polymers 6 were purified by precipitation
in MeOH five times and dried in vacuo until a constant weight was
attained. 1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.20–7.39 (m,
Chem. Eur. J. 2015, 21, 18177 – 18186
18184
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Gu, Haibin
