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isolated solid by vacuum (10 Torr) at room temperature for
half an hour, before use for the next catalytic run.
tem, 1þ2L1 can be recovered from the reaction solution by a
simple precipitation step and reused for consecutive catalytic
runs.
Instruments and Characterization
UV–vis spectra were recorded on a Varian-Cary 4000 UV–vis
spectrophotometer, using HPLC-grade CHCl3 solutions with a
concentration of 3 mg/mL. The measurement was performed
in a quartz cuvette with a 10 mm optical path length.
ACKNOWLEDGMENT
The present research was performed in the framework of the
PRIN-2008 project (no. 200898KCKY) entitled: Inorganic nano-
hybrides based on bio-polyesters from renewable resources,
which was financed by the Ministero dell ‘Istruzione, dell’ Uni-
(GPC)-analyses were performed with a GPC system, equipped
with a Waters Binary HPLC 1525 pump; a manual injector
with a six-way valve and a 200 lL loop; three in-series con-
nected Shodex KF-802.5; KF-803 and KF-804 columns (length:
300 mm each; inner diameter: 8.0 mm; 24,500 theoretical
plates; exclusion limit for PS: up to 400,000 g/mol); a RI de-
tector (Waters, mod. 2414). HPLC-grade THF with a water
content of maximal 0.1 vol % was used as eluent at a constant
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versita e della Ricerca.
REFERENCES AND NOTES
1 Stahl, S. S. Angew. Chem. Int. Ed. Engl. 2004, 43, 3400–3420.
2 Nishimura, T.; Onoue, T.; Ohe, K.; Uemura, S. J. Org. Chem.
1999, 64, 6750–6755.
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flux of 1 mL/min, keeping the columns at 30 C by a thermo-
3 Komano, T.; Iwasawa, T.; Tokunaga, M.; Obora, Y.; Tsuji, Y.
Org. Lett. 2005, 7, 4677–4679.
stat. The GPC system was calibrated using polystyrene (PS) as
standard. It is important to note at this point, that Mn values
for PLA-based materials determined by PS-based GPC-calibra-
tion curves are overestimated, due to the different hydrody-
namic volume of PLA and PS of the same molar mass.
4 Bettucci, L.; Bianchini, C.; Filippi, J.; Lavacchi, A.; Ober-
hauser, W. Eur. J. Inorg. Chem. 2011, 1797–1805.
5 Iwasawa, T.; Tokunaga, M.; Obora, Y.; Tsuji, Y. J. Am. Chem.
Soc. 2004, 126, 6554–6555.
6 Ye, X.; Johnson, M. D.; Diao, T.; Yates, M. H.; Stahl, S. S.
Green Chem. 2010, 12, 1180–1186.
XRPD spectra were acquired on a X’Pert PRO (PANalytical)
powder diffractometer in a 2H range from 5 to 80ꢀ with a
step size of 0.1050ꢀ, using Cu Ka radiation (1.541874 Å).
7 Kakiuchi, N.; Maeda, Y.; Nishimura, T.; Uemura, S. J. Org.
Chem. 2001, 66, 6620–6625.
(GC)-analyses were performed with a Shimadzu 2010 gas
chromatograph equipped with a flame ionization detector
and a 30 m (0.25 mm i.d., 0.25 lm film thickness) VF-
WAXms capillary column, using n-decane as internal stand-
ard. (GC-MS)-analyses were performed with a Shimadzu QP
5000 apparatus, equipped with a 30 m (0.32 mm i.d., 0.50
lm film thickness) CP-WAX 52 CB WCOT-fused silica column.
8 Giachi, G.; Frediani, M.; Oberhauser W.; Passaglia, E.
J. Polym. Sci. Part A: Polym. Chem. 2011, 49, 4708–4713.
9 Bergbreiter, D. E.; Tian, J.; Hongfa, C. Chem. Rev. 2009, 109,
530–582.
10 Lu, J.; Toy, P. H. Chem. Rev. 2009, 109, 815–838.
11 Benaglia, M.; Puglisi, A.; Cozzi, F. Chem. Rev. 2003, 103,
3401–3429.
12 Dickerson, T. J.; Reed, N. N.; Janda, K. D. Chem. Rev. 2002,
102, 3325–3344.
(ICP-MS)-analyses were performed on a Thermo ICP-MS
XSeries 2.
13 Bergbreiter, D. E. Chem. Rev. 2002, 102, 3345–3384.
14 Osburn, P. L.; Bergbreiter, D. E. Prog. Polym. Sci. 2001, 26,
2015–2081.
CONCLUSIONS
The macroligands L1 and L2, bearing an end-capping 4-pyri-
dinemethylene unit, were obtained by a Sn(Oct)2-catalyzed
ROP reaction of l-lactide and e-caprolactone, respectively.
Both macroligands coordinated trans to each other to
Pd(OAc)2 yielding the corresponding homoleptic macrocom-
plexes 1 and 2. Unlike L2, L1 showed, under real aerobic oxi-
dative catalytic conditions, high stability against polymer
chain degradation. From a screening of the catalytic perform-
ance of 1 and 2 versus a reference system [i.e., trans-
[Pd(OAc)2(4-EtPy)2] (4-EtPy ¼ 4-ethylpyridine)] emerged
that: (i) 1 is superior to 2 concerning substrate conversion,
which might be rationalized by a polymer chain flexibility-
driven substrate migration toward the palladium center; (ii)
the addition of two molequivalents of L1 to 1-catalyzed reac-
tions (i.e., 1þ2L1) led to a catalytic system that showed a
superior stability against Pd-black formation compared to
the analogous reference system, due to an efficient polymer
chain-assisted separation of the metal centers from each
other, avoiding thus agglomeration of Pd-centers in the
course of the catalytic reaction; (iii) unlike the reference sys-
15 Bergbreiter, D. E. J. Polym. Sci. Part. A: Polym. Chem. 2001,
39, 2351–2363.
16 Toy, P. H.; Janda, K. D. Acc. Chem. Res. 2000, 33, 546–554.
17 Wentworth, P. J.; Janda, K. D. Chem. Commun. 1999,
1917–1924.
18 Bergbreiter, D. E. Catalysis Today 1998, 42, 389–297.
19 Ferreira, P.; Hayes, W.; Phillips, E.; Rippon, D.; Tsang, S. C.
Green Chem. 2004, 6, 310–312.
20 Dijksman, A.; Arends, I. W. C. E.; Sheldon, R. A. Chem.
Commun. 2000, 271–272.
21 Chung, C. W. Y.; Toy, P.
H J. Comb. Chem. 2007, 9,
115–120.
22 Pozzi, G.; Cavazzini, M.; Quici, S.; Benaglia, M.; Dell’ Anna,
G. Org. Lett. 2004, 6, 441–443.
23 Tanyeli, C.; Gumusꢀ, A. Tetrahedron Lett. 2003, 44,
¨
¨
1639–1642.
24 Hamamoto, H.; Suzuki, Y.; Yamada, Y. M. A.; Tabata, H.;
Takahashi, H.; Ikegami, S. Angew. Chem. Int. Ed. Engl. 2005,
44, 4536–4538.
25 Nlate, S.; Astruc, D.; Neumann, R. Adv. Synth. Catal. 2004,
346, 1445–1448.
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