Benzoxazole phenoxide ligand supported group IV catalysts and their application for the ring‐opening polymerization of rac‐lactide and ε‐caprolactone
Open accessAbstract
Monomeric titanium [C 48 H 62 N 2 O 6 Ti] (1) and zirconium [C 48 H 62 N 2 O 6 Zr] (2) complexes were synthesized by combining the monoanionic salicylbenzoxazole pro‐ligand 2‐(5‐X‐benzoxazol‐2‐yl)‐6‐R 1‐4‐R 2‐phenol, LH (R 1, R 2, X = tBu, tBu, H, respectively) with Ti(OiPr)4 or Zr(OiPr)4∙(iPrOH) in a 2:1 stoichiometric ratio. Controlled hydrolysis of the monomeric Ti complex with deionized water yielded a new unusual hexanuclear titanium complex [C 126 H 144 N 6 O 21 Ti 6] (3). In addition, the cage formed in this complex 3 was surrounded by all‐oxygen and penta‐coordinated Ti(IV) atoms, which leads to an hexanuclear drum‐shaped Ti complex 3 with a trigonal‐bipyramidal geometry at the metal center. The catalytic activity of these complexes toward ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) and rac‐lactide (rac‐LA) was studied. All these complexes showed moderate to good catalytic activity without using any co‐catalyst additives. Single‐site zirconium alkoxide 2 showed the best catalytic activity and was able to convert 400 units of ε‐CL or rac‐LA into the polymer product in high yield (≥90%) within 1 hour under solvent‐free conditions. The obtained polymers showed good control in molecular weight (Mn = 46.2–6.3 kg/mol) and molecular weight distributions (MWD's = 1.37–1.15). The polymerization of rac‐LA by 2 yielded iso‐enriched polylactide (Pm = 0.60).
Integrity signals
Registry
Cites
Statistics
Claims the paper makes
0 of 2 cited sources checked · 0 supported · 0 flagged
- Findingown data
Mononuclear titanium and zirconium complexes 1 and 2 were synthesized by reacting the salicylbenzoxazole pro-ligand LH with Ti(OiPr)4 or Zr(OiPr)4·(iPrOH) in a 2:1 stoichiometric ratio.
“In the present work, we report the synthesis of mononuclear titanium and zirconium complexes (1 and 2) by combining the monoanionic salicylbenzoxazole pro-ligand 2-(5-X-benzoxazol-2-yl)-6-R 1 -4-R 2 -phenol, LH (R 1 , R 2 , X = t Bu, t Bu, H, respectively) with Ti(O i Pr) 4 or Zr(O i Pr) 4 Á( i PrOH) in a 2:1 stoichiometric ratio (Scheme 1).”
- Also stated in: § 4 | CONCLUSIONS · plain
“In summary, mononuclear Ti and Zr complexes were obtained by the reaction of the salicylbenzoxazole pro-ligand LH with Ti(O i Pr) 4 or Zr(O i Pr) 4 Á( i P r OH).”
Quote in the paperSubstantial claim- Rests on an assumption: The salicylbenzoxazole pro-ligand LH is monoanionic.
- Also stated in: § 4 | CONCLUSIONS · plain
- Findingown data
In complex 3, six bidentate benzoxazole phenoxy proligands are coordinated to the six Ti atoms through oxygen and nitrogen atoms.
“As shown in Figure 2A, six bidentate benzoxazole phenoxy proligands, are coordinated to the six Ti atoms through oxygen and nitrogen atoms.”
Quote in the paperNot a substantial claim - Findingreasoning
The mononuclear Ti (1) and Zr (2) alkoxy complexes exhibited good catalytic activity for ROP of ε-CL and rac-LA compared to hexanuclear Ti complex (3).
“The mononuclear Ti (1) and Zr (2) alkoxy complexes exhibited good catalytic activity compared to hexanuclear Ti complex (3).”
- Also stated in: § 4 | CONCLUSIONS · plain
“The ability of these complexes to catalyze the ROP of ε-CL and rac-LA was tested and the mononuclear Zr complex showed better activity as compared to the Ti complexes.”
Quote in the paperSubstantial claim - Also stated in: § 4 | CONCLUSIONS · plain
- Findingnone given
The same reaction of Zr(OiPr)4·(iPrOH) with controlled hydrolysis gave a reaction mixture with intractable products.
“The same reaction when carried out with Zr(O i Pr) 4 Á( i PrOH) gave a reaction mixture with intractable products.”
Quote in the paperNot a substantial claim - Findingown data
In complex 3, nine oxygen atoms (as oxides) are coordinated to the six Ti atoms forming a drum-like architecture by means of oxo bridges.
“Further, nine oxygen atoms (belonging to water molecules present in the environment) as oxides are also coordinated to the six Ti atoms forming a drum-like architecture by means of oxo bridges (Figure 3).”
Quote in the paperNot a substantial claim
- Findingown data
Complex 2 is a single-site zirconium alkoxide complex.
“In addition, single-site zirconium alkoxide complex 2 showed good control in polymer stereoselectivity and produced isotactic rich PLA.”
Quote in the paperSubstantial claim - Findingnone given
The Ti mono and hexanuclear complexes produced atactic polymers.
“However the Ti mono and hexanuclear complexes produced atactic polymers.”
Quote in the paperSubstantial claim - Findingown data
Controlled hydrolysis of mononuclear Ti complex 1 with 2 equivalents of deionized water yields hexanuclear titanium complex 3.
“Controlled hydrolysis of complex 1 using 2 equivalents of deionized water in dry toluene and THF (v/v 1:1) mixture yields the rare type of hexanuclear titanium complex, 3 (Scheme 2).”
- Also stated in: § 4 | CONCLUSIONS · plain
“Controlled hydrolysis of complex 1 using 2 equivalent of deionized water in dry THF yielded the hexanuclear titanium complex, 3.”
Quote in the paperSubstantial claim - Also stated in: § 4 | CONCLUSIONS · plain
- Findingown data
EI-MS positive ion peak near m/z 833.5 confirmed the presence of mononuclear species 1.
“EI-MS spectrometry was also applied, the positive ion peak near at m/z 833.5 further confirmed the presence of mononuclear species 1.”
Quote in the paperNot a substantial claim - Findingown data
In complex 2, the Zr atom is bonded to six atoms-a nitrogen and an oxygen atom each from two benzoxazole phenoxy pro-ligands and oxygen atoms from two isopropoxide moieties-resulting in a hexa-coordinated octahedral geometry.
“The Zr atom is bonded to six atoms-a nitrogen and an oxygen atom each from two benzoxazole phenoxy pro-ligands and oxygen atoms from two isopropoxide moieties, resulting in a hexa-coordinated octahedral geometry (Figure 1) around the metal center.”
Quote in the paperNot a substantial claim - Findingown data
The mononuclear Zr complex 2 showed better catalytic activity than the Ti complexes (1 and 3) for ROP of ε-CL and rac-LA.
“The ability of these complexes to catalyze the ROP of ε-CL and rac-LA was tested and the mononuclear Zr complex showed better activity as compared to the Ti complexes.”
Quote in the paperSubstantial claim - Findingown data
Each Ti atom in complex 3 is coordinated to five atoms-oxygen and nitrogen atoms of the bidentate benzoxazole phenoxy pro-ligand and three oxide ions-resulting in a five-coordinated trigonal bipyramidal geometry.
“Each Ti atom is coordinated to five atoms-oxygen and nitrogen atoms of the bidentate benzoxazole phenoxy pro-ligand and three oxide ions, which results in a five-coordinated trigonal bipyramidal geometry around the metal ion.”
Quote in the paperNot a substantial claim - Findingown data
Active catalyst 2 was able to convert 400 ε-CL or rac-LA units into product in high yield (≥90%) within 1 hour under solvent-free conditions.
“active catalyst 2 was able to convert 400 ε-CL or rac-LA units into the product in high yield (≥90%) within 1 hour under solvent-free conditions.”
Quote in the paperSubstantial claim - Findingown data
The Ti...Ti distances between metal centers at the base and lid of the drum of complex 3 approximate 3.4 Å.
“The Ti…Ti distances between the metal centers at the base (Ti1…Ti2/Ti2…Ti6/Ti1…Ti6) and lid (Ti3…Ti4/Ti4…Ti5/Ti3…Ti5) of the drum approximate 3.4 Å.”
Quote in the paperNot a substantial claim - Findingown data
Complex 3 has a drum-shaped hexanuclear Ti6 cluster core.
“A significant feature in the structure is the drumshaped hexanuclear Ti 6 IV cluster located in the core of the molecule.”
- Also stated in: § 2.2 | Crystal structures of complexes 2 and 3 · plain
“Further, nine oxygen atoms (belonging to water molecules present in the environment) as oxides are also coordinated to the six Ti atoms forming a drum-like architecture by means of oxo bridges (Figure 3).”
Quote in the paperNot a substantial claim - Also stated in: § 2.2 | Crystal structures of complexes 2 and 3 · plain
- Findingcitation
The best reactivity of Zr complex 2 is comparable with previously reported other zirconium active catalysts for ROP of ε-CL and rac-LA.
“The best reactivity of the Zr complex 2 (Table 1, entries 2-5 and 8-11) is comparable with the previously reported other zirconium active catalysts for ROP of ε-CL and rac-LA.23,[25][26][27]31,32,34”
Quote in the paperSubstantial claim0 of 1 sources checked- cites 23,[25][26][27]31,32,34
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
- Findingown data
MALDI-TOF mass spectrum of 3 indicates that it is hexanuclear.
“The MALDI-TOF mass spectrum of 3 indicates that it is hexanuclear.”
Quote in the paperNot a substantial claim - Study design and conductown data
The formation of desired mononuclear species 1 was confirmed by elemental analysis.
“The formation of the desired mononuclear species 1 was confirmed by elemental analysis.”
Quote in the paperNot a substantial claim - Interpretationreasoning
The oxide ions in complex 3 originate from reaction of water with iso-propoxides of complex 1.
“The origin of the oxide ions can be attributed by the reaction of water with iso-propoxides of complex 1, which leads to oxide ions in the system.”
Quote in the paperNot a substantial claim - Interpretationreasoning
The higher catalytic activity of mononuclear Ti and Zr complexes compared to hexanuclear Ti complex 3 is attributed to the higher nucleophilic nature of the iso-propoxide at the metal site compared to the benzoxazole phenoxy ligand, which is responsible for the ring-opening step.
“This can be attributed due to the higher nucleophilic nature of the iso-propoxideat the metal site in comparison to the benzoxazole phenoxy ligand, which is responsible for the ring-opening step in ε-CL or rac-LA.”
Quote in the paperSubstantial claim - Interpretationnone given
The coordinated sterically bulky benzoxazole phenoxy ligand suitably regulates the Lewis acidity at the large size Zr center for activating the monomers.
“In addition, the coordinated sterically bulky benzoxazole phenoxy ligand suitably regulates the Lewis acidity at the large size Zr center for activating the monomers.”
Quote in the paperSubstantial claim - Interpretationreasoning
A good match between the Lewis acidity of the Zr metal site and iso-propoxide nucleophilicity at the metal center is crucial for achieving good control in polymer stereoselectivity.
“Hence, it is inferred that the good match between the Lewis acidity of Zr metal site and iso-propoxide nucleophilicity at the metal center are crucial for achieving good control in polymer stereoselectivity.”
Quote in the paperSubstantial claim - Interpretationown data
The ROP of ε-CL and rac-LA catalyzed by complexes 1, 2, and 3 proceeds by a coordination-insertion mechanism.
“From this analysis, as depicted in Scheme 4 we concluded that the expected coordination-insertion mechanism operated during the ROP.”
Quote in the paperSubstantial claim - Study design and conductown data
The structures of complexes 2 and 3 are confirmed with single crystal X-ray analysis.
“In addition, the structures of complexes 2 and 3 are confirmed with single crystal X-ray analysis.”
Quote in the paperNot a substantial claim
- May combine two claims. 8
- Classified as probably not a substantial claim. 2
May combine two claims.
Findingown dataComplex 3 crystallizes in the monoclinic space group P2_1/c with one molecule of the complex in the asymmetric unit.
“Complex 3, C 126 H 144 N 6 O 21 Ti 6 : Structure solution from single crystal X-ray diffraction data revealed that 3 crystallizes in the monoclinic space group P2 1 /c, with one molecule of the complex in the As”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
Findingown dataThe height of the drum in complex 3 is 3.376 Å.
“The height of the drum (measured as the distance between the centroids of the irregular hexagons Ti1-O20-Ti6-O21-Ti2-O13 and Ti3-O15-Ti4-O17-Ti5-O18) is 3.376 Å.”
Quote in the paperNot a substantial claimMay combine two claims.
Findingown dataEnd-group analysis of PCLs and PLAs indicated that iso-propoxy group was the initiating group for catalysts 1 and 2, and ligand phenoxide was the initiating group for catalyst 3.
“The end-group analysis of these polymer chains (PCLs and PLAs) indicated that iso-propoxy group was the initiating group for catalysts 1, 2 and ligand phenoxide was as an initiating group for catalyst 3, which was confirmed by 1 H NMR as well as MALDI-TOF spectrum (Figures 2, 4, and S10).”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataThe obtained polymers showed good control in molecular weight (Mn = 46.2-6.3 kg/mol) and molecular weight distributions (MWD = 1.37-1.15).
“The obtained polymers showed good control in molecular weight (M n = 46.2-6.3 kg/mol) and molecular weight distributions (MWD's = 1.37-1.15).”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataGood control over the ROP process was observed, affording PCLs and PLAs with good match between observed and calculated molecular weights and good to moderate molecular weight distributions.
“Good control over the ROP process was observed, affording PCLs and PLAs with good match between the observed (M n(expt ) as determined by GPC) and calculated molecular weights (M n(calcd) ), as F I G U R E 2 MALDI-TOF spectrum of the crude product obtained from a reaction between rac-LA and 2 in 100:1 ratio at 140 C well as good to moderate molecular weight distributions (M w /”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataComplex 2 crystallizes in the triclinic space group P-1 with one molecule in the asymmetric unit.
“Complex 2 crystallized in the triclinic space group P-1, with one molecule in the asymmetric unit (Figure 1).”
Quote in the paperNot a substantial claimMay combine two claims.
Findingown dataComplex 2 showed good control in polymer stereoselectivity and produced isotactic rich polymers.
“After screening all the three complexes, we observed that complex 2, that is, mononuclear Zr complex showed good control in polymer stereoselectivity and produced isotactic rich polymers, which was confirmed from homonuclear decoupled H 1 NMR spectrum (Figure 5).”
- Also stated in: § 4 | CONCLUSIONS · plain
“In addition, single-site zirconium alkoxide complex 2 showed good control in polymer stereoselectivity and produced isotactic rich PLA.”
Quote in the paperSubstantial claim- Also stated in: § 4 | CONCLUSIONS · plain
May combine two claims.
Study design and conductown dataCrystals of complex 1 showed very weak diffraction, so its structure was confirmed through NMR, EI-MS and elemental analysis.
“Since the crystals of complex 1 showed very weak diffraction, we have confirmed the structure through NMR, EI-MS and elemental analysis.”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
InterpretationcitationThe coordination sphere of complex 3 resembles a structure reported by Tshuva and co-workers.
“This coordination sphere resemblance to a structure reported by Tshuva and co-workers, where the combination of the pro-ligand 1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-imidazolidine with Ti(IV) resulted in the formation of a dimer.47”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [47] 47. Manna CM, Shavit M, Tshuva EY. Structural characterization of din- uclear Ti(IV) complexes of rigid tetradentate dianionic diamine bis(phenolato) ligands; effect of steric bulk on coordination features. J Organomet Chem. 2008;693:3947-3950. source
May combine two claims.
Study design and conductown dataThe molecular structures of hexanuclear Ti complex 3 and mononuclear Zr complex 2 were confirmed by single-crystal X-ray crystallography.
“The molecular structures of the hexanuclear Ti complex 3 and the mononuclear Zr complex 2 were confirmed by single-crystal X-ray crystallography.”
- Also stated in: § 2.1 | Synthesis of Ti and Zr complexes 1, 2, and 3 · plain
“In addition, the structures of complexes 2 and 3 are confirmed with single crystal X-ray analysis.”
Quote in the paperNot a substantial claim- Also stated in: § 2.1 | Synthesis of Ti and Zr complexes 1, 2, and 3 · plain
The paper relies on this without support.
The salicylbenzoxazole pro-ligand LH is monoanionic.
“monoanionic salicylbenzoxazole pro-ligand 2-(5-X-benzoxazol-2-yl)-6-R 1 -4-R 2 -phenol, LH”
The paper relies on this without support.
Hexanuclear titanium complexes are rarely applied for ring-opening polymerization.
“Notably, while significant mono or dinuclear Ti complexes for ROP have been reported, hexanuclear titanium complexes are so far very rarely applied.”
Self-check
Percentages, sums and reported differences re-computed from the paper’s own numbers.
Each contradiction between two passages listed here was confirmed by an independent check.
Dry Ti-alkoxide reaction is assigned two different products
MinorThe crystal-structure section says reacting Ti(O i Pr) 4 with the pro-ligand in dry toluene forms hexanuclear complex 3. Elsewhere, that reaction forms mononuclear complex 1, which is subsequently hydrolyzed to obtain 3.
“The metal precursors Ti(O i Pr) 4 and Zr(O i Pr) 4 Á( i PrOH) were reacted in turn with benzoxazole phenoxy pro-ligand at room temperature in dry toluene resulting in the formation of the hexanuclear Ti cluster 3 and the mononuclear Zr complex 2, respectively.”
“Controlled hydrolysis of complex 1 using 2 equivalents of deionized water in dry toluene and THF (v/v 1:1) mixture yields the rare type of hexanuclear titanium complex, 3 (Scheme 2).”
Reported rac-LA reaction temperatures differ
MinorThe Table 1 conditions specify 130 C for rac-LA, whereas the experimental procedure says those reactions were carried out at 140 C.
“a Reaction conditions: Unless otherwise noted, [M] 0 /[Cat.]0 = 200:1, 130 C for rac-LA and 100 C for ε-CL, solvent-free.”
“However, the reactions were carried out at 140 C in a Schlenk tube as described below.”
The claimed one-hour conversion conflicts with the 400:1 experiments
MinorThe statement says catalyst 2 reached at least 90% conversion for both monomers at a 400:1 ratio within one hour. Table 1 reports 1.8 hours for ε-CL and 4.4 hours for rac-LA at that ratio.
“active catalyst 2 was able to convert 400 ε-CL or rac-LA units into the product in high yield (≥90%) within 1 hour under solvent-free conditions.”
“5 2 ε-CL 400 1.8 96 43.8 46.2 1.17 6 3 ε-CL 200 5 55 12.6 8.1 1.35 7 1 rac-LA 200 5 80 23.1 16.3 1.28 8 2 rac-LA 100 1 98 14.1 10.1 1.15 9 2 rac-LA 200 1.8 95 27.3 23.7 1.19 10 2 rac-LA 300 3.1 95 41.0 38.1 1.17 11 2 rac-LA 400 4.4 92 53.0 44.5 1.21”
Quenching at complete consumption conflicts with measured conversions
MinorThe table note says polymerization times were measured by quenching when all monomer had been consumed, but the table lists conversions below 100%, including 51% for entry 12.
“b Time of polymerization measured by quenching the polymerization reaction when all monomer was found consumed.”
“12 3 rac-LA 200 10 51 14.7 6.3 1.37”
Cites
Structure validation in chemical crystallography
Spek, A. L. (2009) · Acta Crystallographica Section D Biological Crystallography · doi:10.1107/s090744490804362x · Cited by 15,452 · see citing works
Designing materials for biology and medicine
Langer, R., & Tirrell, D. A. (2004) · Nature · doi:10.1038/nature02388 · Cited by 3,198 · see citing works
Sustainable polymers from renewable resources
Zhu, Y., Romain, C., & Williams, C. K. (2016) · Nature · doi:10.1038/nature21001 · Cited by 2,762 · see citing works
Controlled Ring-Opening Polymerization of Lactide and Glycolide
Dechy-Cabaret, O., Martin-Vaca, B., & Bourissou, D. (2004) · Chemical Reviews · doi:10.1021/cr040002s · Cited by 2,257 · see citing works
Polymerization of Lactide with Zinc and Magnesium β-Diiminate Complexes: Stereocontrol and Mechanism
Chamberlain, B. M., Cheng, M., Moore, D. R., Ovitt, T. M., Lobkovsky, E. B., & Coates, G. W. (2001) · Journal of the American Chemical Society · doi:10.1021/ja003851f · Cited by 1,207 · see citing works
Catalysis as an Enabling Science for Sustainable Polymers
Zhang, X., Fevre, M., Jones, G. O., & Waymouth, R. M. (2018) · Chemical Reviews · doi:10.1021/acs.chemrev.7b00329 · Cited by 936 · see citing works
Polymerization of lactide and related cyclic esters by discrete metal complexes
O'Keefe, B. J., Hillmyer, M. A., & Tolman, W. B. (2001) · Journal of the Chemical Society, Dalton Transactions · doi:10.1039/b104197p · Cited by 825 · see citing works
WU, J., YU, T., CHEN, C., & LIN, C. (2006) · Coordination Chemistry Reviews · doi:10.1016/j.ccr.2005.07.010 · Cited by 779 · see citing works
Biocompatible Initiators for Lactide Polymerization
Platel, R., Hodgson, L., & Williams, C. (2008) · Polymer Reviews · doi:10.1080/15583720701834166 · Cited by 706 · see citing works
Kricheldorf, H. R., Berl, M., & Scharnagl, N. (1988) · Macromolecules · doi:10.1021/ma00180a002 · Cited by 597 · see citing works
Biodegradable polymers as non-viral carriers for plasmid DNA delivery
Luten, J., van Nostrum, C. F., Smedt, S. C. D., & Hennink, W. E. (2007) · Journal of Controlled Release · doi:10.1016/j.jconrel.2007.10.028 · Cited by 471 · see citing works
Complexes of Mg, Ca and Zn as homogeneous catalysts for lactide polymerization
Wheaton, C. A., Hayes, P. G., & Ireland, B. J. (2009) · Dalton Transactions · doi:10.1039/b819107g · Cited by 438 · see citing works
Controlled Ring-Opening Polymerization: Polymers with designed Macromolecular Architecture
Stridsberg, K. M., Ryner, M., & Albertsson, A.-C. (2002) · Advances in Polymer Science · doi:10.1007/3-540-45734-8_2 · Cited by 375 · see citing works
Chmura, A. J., Davidson, M. G., Jones, M. D., Lunn, M. D., Mahon, M. F., Johnson, A. F., Khunkamchoo, P., Roberts, S. L., & Wong, S. S. F. (2006) · Macromolecules · doi:10.1021/ma061028j · Cited by 277 · see citing works
Gendler, S., Segal, S., Goldberg, I., Goldschmidt, Z., & Kol, M. (2006) · Inorganic Chemistry · doi:10.1021/ic052120j · Cited by 240 · see citing works
Thomas, A., Müller, S. S., & Frey, H. (2014) · Biomacromolecules · doi:10.1021/bm5002608 · Cited by 236 · see citing works
Stereosequenced crystalline polyhydroxyalkanoates from diastereomeric monomer mixtures
Tang, X., Westlie, A. H., Watson, E. M., & Chen, E. Y. ‐. (2019) · Science · doi:10.1126/science.aax8466 · Cited by 228 · see citing works
Perumal, G., Pappuru, S., Chakraborty, D., Nandkumar, A. M., Chand, D. K., & Doble, M. (2017) · Materials Science and Engineering C · doi:10.1016/j.msec.2017.03.200 · Cited by 209 · see citing works
Self-citationHigh-performance pan-tactic polythioesters with intrinsic crystallinity and chemical recyclability
Shi, C., McGraw, M. L., Li, Z., Cavallo, L., Falivene, L., & Chen, E. Y. ‐. (2020) · Science Advances · doi:10.1126/sciadv.abc0495 · Cited by 208 · see citing works
Mechanism of ε-Caprolactone polymerization by Aluminum Alkoxides
Ouhadi, T., Stevens, C. V., & Teyssié, P. (1975) · Die Makromolekulare Chemie · doi:10.1002/macp.1975.020011975112 · Cited by 147 · see citing works
Li, H., Shakaroun, R. M., Guillaume, S. M., & Carpentier, J. (2020) · Chemistry – A European Journal · doi:10.1002/chem.201904108 · Cited by 132 · see citing works
Takeuchi, D., Nakamura, T., & Aida, T. (2000) · Macromolecules · doi:10.1021/ma991441+ · Cited by 124 · see citing works
Cayuela, J., Bounor-Legaré, V., Cassagnau, P., & Michel, A. (2006) · Macromolecules · doi:10.1021/ma051272v · Cited by 110 · see citing works
Chmura, A. J., Davidson, M. G., Jones, M. D., Lunn, M. D., & Mahon, M. F. (2006) · Dalton Trans. · doi:10.1039/b513345a · Cited by 108 · see citing works
Sulfonamide-Supported Aluminum Catalysts for the Ring-Opening Polymerization ofrac-Lactide
Schwarz, A. D., Chu, Z., & Mountford, P. (2010) · Organometallics · doi:10.1021/om901070g · Cited by 97 · see citing works
Schwarz, A. D., Thompson, A. L., & Mountford, P. (2009) · Inorganic Chemistry · doi:10.1021/ic901524s · Cited by 91 · see citing works
Drug Delivery Interfaces in the 21st Century: From Science Fiction Ideas to Viable Technologies
Chertok, B., Webber, M. J., Succi, M. D., & Langer, R. (2013) · Molecular Pharmaceutics · doi:10.1021/mp4003283 · Cited by 90 · see citing works
Chuck, C. J., Davidson, M. G., Jones, M. D., Kociok-Köhn, G. I., Lunn, M. D., & Wu, S. G. (2006) · Inorganic Chemistry · doi:10.1021/ic060969+ · Cited by 90 · see citing works
Saha, T. K., Ramkumar, V., & Chakraborty, D. (2011) · Inorganic Chemistry · doi:10.1021/ic1025262 · Cited by 86 · see citing works
Self-citationTitanium and Zirconium Complexes for Polymerization of Propylene and Cyclic Esters
Gornshtein, F., Kapon, M., Botoshansky, M., & Eisen, M. S. (2007) · Organometallics · doi:10.1021/om060723c · Cited by 77 · see citing works
Huang, B.-H., Tsai, C.-Y., Chen, C.-T., & Ko, B.-T. (2016) · Dalton Transactions · doi:10.1039/c6dt03384a · Cited by 75 · see citing works
Li, C.-Y., Yu, C.-J., & Ko, B.-T. (2013) · Organometallics · doi:10.1021/om300962k · Cited by 67 · see citing works
Advances in urea and thiourea catalyzed ring opening polymerization: A brief overview
Jain, I., & Malik, P. (2020) · European Polymer Journal · doi:10.1016/j.eurpolymj.2020.109791 · Cited by 56 · see citing works
Mandal, M., & Chakraborty, D. (2015) · Journal of Polymer Science Part A Polymer Chemistry · doi:10.1002/pola.27918 · Cited by 50 · see citing works
Self-citationPappuru, S., Chokkapu, E. R., Chakraborty, D., & Ramkumar, V. (2013) · Dalton Transactions · doi:10.1039/c3dt52065j · Cited by 47 · see citing works
Self-citationHsieh, K., Lee, W., Hsueh, L., Lee, H. M., & Huang, J. (2006) · European Journal of Inorganic Chemistry · doi:10.1002/ejic.200500679 · Cited by 46 · see citing works
Duparc, V. H., Shakaroun, R. M., Slawinski, M., Carpentier, J., & Guillaume, S. M. (2020) · European Polymer Journal · doi:10.1016/j.eurpolymj.2020.109858 · Cited by 45 · see citing works
Gupta, P. K., Pappuru, S., Gupta, S., Patra, B., Chakraborty, D., & Verma, R. S. (2019) · Materials Science and Engineering: C · doi:10.1016/j.msec.2019.03.041 · Cited by 44 · see citing works
Self-citationChuang, H.-J., & Ko, B.-T. (2015) · Dalton Transactions · doi:10.1039/c4dt02774d · Cited by 38 · see citing works
Pappuru, S., Chakraborty, D., Sundar, J. V., Roymuhury, S. K., Ramkumar, V., Subramanian, V., & Chand, D. K. (2016) · Polymer · doi:10.1016/j.polymer.2016.08.007 · Cited by 36 · see citing works
Self-citationYuntawattana, N., McGuire, T. M., Durr, C. B., Buchard, A., & Williams, C. K. (2020) · Catalysis Science & Technology · doi:10.1039/d0cy01484b · Cited by 35 · see citing works
Saha, T., Rajashekhar, B., Gowda, R. R., Ramkumar, V., & Chakraborty, D. (2010) · Dalton Transactions · doi:10.1039/c002875d · Cited by 35 · see citing works
Self-citationRoymuhury, S. K., Chakraborty, D., & Ramkumar, V. (2015) · Dalton Transactions · doi:10.1039/c5dt01092f · Cited by 34 · see citing works
Self-citationChakraborty, D., Mandal, D., Ramkumar, V., Subramanian, V., & Vijaya Sundar, J. (2015) · Polymer · doi:10.1016/j.polymer.2014.10.074 · Cited by 33 · see citing works
Self-citationGupta, P. K., Tripathi, S. K., Pappuru, S., Chabattula, S. C., Govarthanan, K., Gupta, S., Biswal, B. K., Chakraborty, D., & Verma, R. S. (2020) · Materials Science and Engineering: C · doi:10.1016/j.msec.2019.110285 · Cited by 29 · see citing works
Self-citationShi, X.-C., & Jin, G.-X. (2012) · Organometallics · doi:10.1021/om3007568 · Cited by 27 · see citing works
Kummari, A., Pappuru, S., Gupta, P. K., Chakraborty, D., & Verma, R. S. (2019) · Materials Today Communications · doi:10.1016/j.mtcomm.2019.02.007 · Cited by 27 · see citing works
Self-citationJeong Go, M., Min Lee, J., Mun Lee, K., Hwa Oh, C., Park, K. H., Kim, S. H., Kim, M., Park, H.-R., Park, M. H., Kim, Y., et al. (2014) · Polyhedron · doi:10.1016/j.poly.2013.09.017 · Cited by 25 · see citing works
Shi, X.-C., & Jin, G.-X. (2011) · Dalton Transactions · doi:10.1039/c1dt10851d · Cited by 23 · see citing works
Manna, C. M., Shavit, M., & Tshuva, E. Y. (2008) · Journal of Organometallic Chemistry · doi:10.1016/j.jorganchem.2008.09.056 · Cited by 19 · see citing works
Gupta, P. K., Gupta, S., Pappuru, S., Chabattula, S. C., Chakraborty, D., & Verma, R. S. (2019) · Journal of Drug Delivery Science and Technology · doi:10.1016/j.jddst.2019.02.022 · Cited by 12 · see citing works
Self-citationTakeuchi, D., Nakamura, T., & Aida, T. (2000) · Macromolecules · doi:10.1021/ma991441
Chuck, C. J., Davidson, M. G., Jones, M. D., Kociok-Köhn, G., Lunn, M. D., & Wu, S. (2006) · Inorganic Chemistry · doi:10.1021/ic060969
Controlled Ring‐Opening Polymerization of Lactide and Glycolide
Dechy‐Cabaret, O., Martin‐Vaca, B., & Bourissou, D. (2005) · ChemInform · doi:10.1002/chin.200514262
Li, H., Shakaroun, R. M., Guillaume, S. M., et al. (2020) · Chemistry – A European Journal · doi:10.1002/chem.202080167
Flagged first, then by citations
Cited by
Sorted by citations
Nakornkhet, C., Nanok, T., Wattanathana, W., Chuawong, P., & Hormnirun, P. (2022) · Inorganic Chemistry · doi:10.1021/acs.inorgchem.2c00577 · Cited by 15 · see citing works
Schubert, U., & Stöger, B. (2024) · Chemistry - A European Journal · doi:10.1002/chem.202400744 · Cited by 9 · see citing works
Flores-Romero, V., Leblanc, J. H., Chen, Z., & Lavoie, G. G. (2024) · RSC Advances · doi:10.1039/d4ra05146g · Cited by 5 · see citing works
Khononov, M., Liu, H., Fridman, N., Tamm, M., & Eisen, M. S. (2022) · Catalysts · doi:10.3390/catal12101201 · Cited by 3 · see citing works
Kumar, H., Naithani, K., Bhalerao, P., et al. (2023) · Tetrahedron Letters · doi:10.1016/j.tetlet.2023.154514 · Cited by 2 · see citing works
Comprehensive review on 2-Aminobenzazoles: Synthesis, metal complexes and biological applications
Abdel‐Megid, M., Fouad, R., Adly, O. M. I., Ibrahim, M. A., Farag, A. A. M., Raza, N., & Yousef, T. A. (2026) · Inorganic Chemistry Communications · doi:10.1016/j.inoche.2026.116568 · Cited by 1 · see citing works
Robust Y and Lu TrenSal catalysts for ring-opening polymerisation
Fazekas, E., Etcheverry-Berríos, Á., Nichol, G. S., Piligkos, S., Brechin, E. K., & Garden, J. A. (2024) · Polyhedron · doi:10.1016/j.poly.2024.117308 · Cited by 1 · see citing works
Sharma, H., Pandya, C., Mathivathanan, L., Sinha, A., Sivaramakrishna, A., & Pathak, M. (2025) · ChemPlusChem · doi:10.1002/cplu.202400716 · Cited by 1 · see citing works
- Authors
- Pappuru, S., Ramkumar, V., & Chakraborty, D.
- Affiliations
- Indian Institute of Technology Madras (IN)
- Corresponding author
- Chakraborty, Debashis
- Venue
- Polymers for Advanced Technologies
- Publisher
- Wiley
- Published
- 2021-04-26
- Volume
- 32
- Issue
- 9
- Pages
- 3392-3401
- ISSN
- 1042-7147 (ISSN-L)
- 1099-1581
- OpenAlex
- W3158433890
- Cited by
- 9
- References
- 46
- Citations by year
- 2026: 1 · 2025: 2 · 2024: 3 · 2023: 1 · 2022: 2
- FWCI
- 0.39
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- Polymers for Advanced Technologies (publishedVersion)
- Funders
- University Grants Commission (/2018)
- Israel Science Foundation
- Topics
- Physical Sciences › Materials Science › Biomaterials › biodegradable polymer synthesis and properties
- Physical Sciences › Chemistry › Organic Chemistry › Organometallic Complex Synthesis and Catalysis
- Physical Sciences › Chemical Engineering › Process Chemistry and Technology › Carbon dioxide utilization in catalysis
- Keywords
- titanium alkoxide complexes, ring-opening polymerization, ε-caprolactone, rac-lactide, polylactic acid, solvent-free polymerization, trigonal bipyramidal coordination, molecular weight control
About these checks
Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-11.
Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-11.
Statistics and arithmetic are recomputed, not judged.
Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.
What counts as a claim ›How we measure confidence ›How we check this ›
Are you an author, or do you see a problem with this page? Request a review
