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Cited by 444

The DOI matches its Crossref record; 19 of the 19 references it cites were found in a registry or an index.

Molecular Design of Single-Site Metal Alkoxide Catalyst Precursors for Ring-Opening Polymerization Reactions Leading to Polyoxygenates. 1. Polylactide Formation by Achiral and Chiral Magnesium and Zinc Alkoxides, (η3-L)MOR, Where L = Trispyrazolyl- and Trisindazolylborate Ligands

Chisholm, Malcolm H., Eilerts, Nancy W., Huffman, John C., Iyer, Suri S., Pacold, Martha, Phomphrai, Khamphee·2000·Journal of the American Chemical Society
DOI 10.1021/ja002160g
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Abstract

Single-site achiral and chiral C 3 -symmetric complexes LMOR, where M = Mg and Zn, L = an η 3 -trispyrazolyl- or η 3 -trisindazolyl-borate ligand and R = Et, t Bu, Ph, or SiMe 3, have been synthesized and employed in the ring-opening polymerization of l -, rac -, and meso -lactide in CH 2 Cl 2 at 25 °C and below. The polymerization occurs by acyl cleavage and gives rise to polylactide, PLA, with PDI of 1.1−1.25 up to 90% conversion. Studies of the kinetics of polymerization reveal first order behavior in both lactide and metal catalyst. For L = tris(3- tert -butylpyrazolyl)borate, ( t Bupz) 3 BH, polymerization of ∼500 equiv of l -lactide proceeds to 90% conversion within 1 h and 6 d for the magnesium and zinc catalysts, respectively. The zinc complexes are, however, more tolerant to air and moisture and solid samples where R = SiMe 3 are persistent in air for several days. The rate of polymerization is also significantly influenced by the nature of the η 3 -L spectator ligand. Chiral C 3 -symmetric catalysts, where L = tris(indazolyl)borates derived from camphor and menthone, show only slight enantioselectivity in their polymerization of rac -lactide but do show significant diastereoselectivity in their ability to preferentially polymerize meso -lactide from a mixture of rac - and meso -lactide. The poly(mesolactide) shows a modest preference for syndiotactic junctions, RSRSRS . The molecular structures, deduced from single-crystal X-ray crystallography, are reported for η 3 -HB(3-Phpz) 3 MgEt(THF), [η 3 -HB((7 R )- i Pr-(4 R )-Me-4,5,6,7-tetrahydro-2H-indazolyl) 3 ]ZnMe and [η 3 -HB(3- t Bupz)(3,5-(CF 3 ) 2 pz) 2 ]ZnOSiMe 3 and serve as structural models for activated and ground-state configurations of the metal ions during the polymerization reaction. The molecular structure of meso -lactide is also reported. These results are compared with polymerizations of lactide by other coordinate catalysts.

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Metadata

Authors
Chisholm, M. H., Eilerts, N. W., Huffman, J. C., Iyer, S. S., Pacold, M., & Phomphrai, K.
Venue
Journal of the American Chemical Society
Publisher
American Chemical Society (ACS)
Published
2000-11-17
Volume
122
Issue
48
Pages
11845-11854
ISSN
  • 0002-7863 (ISSN-L)
  • 1520-5126
DOI
10.1021/ja002160g
OpenAlex
W2092337099
Cited by
444
References
19
FWCI
11.73
Type
journal article
Language
en
Open access
closed

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