ACCEPTED MANUSCRIPT
1H NMR data, an intramolecular C=O···H interaction of 2.238 Å
Bryce, D. L.; Lelj, F.; MacLachlan, M. J., J. Am. Chem. Soc. 2010, 132,
3893–3908.
is observed, which is shorter than the sum of the van der Waals
radii for hydrogen (rVDW = 1.2 Å) and oxygen (rVDW = 1.50 Å). 2
displays three coordination domains for zinc. In the first domain,
two zinc ions show tetra-coordinated O2(THF)ZnEt fragments in a
very distorted tetrahedral environment, where three O atoms two
comes from the ligand carbonyls and the third comes from THF.
A second domain shows two zinc ions in highly distorted tetrahe-
dral O3ZnEt fragments, but in this case two O atoms are provided
by phenoxide substituents and one O comes from a carbonyl
substituent. The third domain shows two penta-coordinated
ON2(THF)Zn fragments in a distorted tbp coordination geometry
(χ = 0.58); where two O atoms are provided by two phenoxides
and one O by THF, the two N atoms come from the amide sub-
stituents. The Zn‒C (1.940(7)-1.969(6) Å), Zn‒N (1.990(4)-
2.084(4) Å) and Zn‒O (1.941(4)-2.215 Å) bond lengths are in the
range of Zn8 species and other complexes, vide supra.
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Two important factors can be identified on the process Zn8 →
Zn6: one factor is the increasing of coordination number of two
zinc ions on addition of THF to 1 (tetrahedral to tbp), and the
other factor is the isomerization of the bis-oxamidate ligand from
the trans to the cis-conformer. It is very well known that cis-
conformation of bis-oxamidates favors low nuclearity complexes
due to the easy access of metallic centers to the four donor atoms
(N2O2) available on the ligand.28
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2985.
Both complexes were moderately active for the ROP of rac-
lactide, however good polymer conversions are achieved by using
iPrOH and BnOH with 1 and 2. Polymerization experiments were
carried out with a 100:1 monomer:initiator and results are given in
Supporting Information Table S3. The low performance of 1 and
2 could be attributed to the low polarity of the Zn‒C bond and the
lipophilic nature of the cages. Spacefill X-ray models of 1 and 2
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2711.
t
(Figure S6) show that in both complexes the Bu and Et substitu-
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K., J. Am. Chem. Soc. 2008, 130, 2944-2945.
ents project outward the core of the aggregates precluding easy
access of LA to the metallic centers, which in combination with
long reaction times favor transesterification of PLA chains. An
additional factor operating in the differences observed in Mn,calcd
and Mn,exptl is the formation of lower nuclearity species, upon
coordination of LA. To improve the performance of catalysts,
iPrOH and BnOH were used to obtain derivatives with polar
Zn‒OR bonds. The best results were obtained with BnOH (entries
3 and 8 in Table S3).
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Mashima, K., Chemistry - A European Journal 2010, 16, 11567-11571.
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M. n.; Martin, E.; Benet-Buchholz, J.; Kleij, A. W., Inorg. Chem. 2011,
50, 7934-7936.
(19) Maegawa, Y.; Ohshima, T.; Hayashi, Y.; Agura, K.; Iwasaki, T.;
Mashima, K., ACS Catalysis 2011, 1, 1178-1182.
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Ohshima, T.; Okuda, J.; Mashima, K., Catalysis Science & Technology
2012, 2, 509, (b) nselmo, .; Bocokić, V.; ecortes, .; Escudero-Adán,
E. C.; Benet-Buchholz, J.; Reek, J. N. H.; Kleij, A. W., Polyhedron 2012,
32, 49-53, (c) Taherimehr, M.; Decortes, A.; Al-Amsyar, S. M.;
Lueangchaichaweng, W.; Whiteoak, C. J.; Escudero-Adán, E. C.; Kleij, A.
W.; Pescarmona, P. P., Catalysis Science & Technology 2012, 2, 2231.
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Ikeda, C.; Sato, S., Chem. Lett. 2006, 35, 1070-1071, (b) Nabeshima, T.,
Bull. Chem. Soc. Jpn. 2010, 83, 969-991, (c) Frischmann, P. D.;
MacLachlan, M. J., Chem. Soc. Rev. 2013, 42, 871-890.
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J., Inorg. Chem. 2008, 47, 101-112.
ASSOCIATED CONTENT
Supporting Information
Experimental details; NMR spectra of 1 and 2 and alkoxide de-
rivatives; details of X-ray single crystal studies for 1 and 2 and
CCDC reference numbers 1057248-1057249 (2 and 1, respective-
ly). This material is available free of charge via the Internet at
(23) mene - re , V. .; Camacho-Camacho, C.; i ado-
Rodr gue , M.; Nöth, H.; Contreras, R., J. Organomet. Chem. 2000, 614–
615, 283-293.
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Güizado-Rodriguez, M.; Wrackmeyer*, B., J. Organomet. Chem. 2000,
604, 229-233, (b) Jiménez-Pérez, V. M.; Camacho-Camacho, C.; Ramos-
Organillo, Á.; Ramírez-Trejo, R.; Peña-Hueso, A.; Contreras, R.; Flores-
Parra, A., J. Organomet. Chem. 2007, 692, 5549-5554.
ACKNOWLEDGMENTS
Financial support from CONACyT (Grant No. 155247) is
acknowledged. NMR measurements are gratefully acknowledged
to B.D. from CIQ-UAEM.
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