Monomethylaluminum and dimethylaluminum pyrrolylaldiminates for the ring-opening polymerization of rac-lactide: effects of ligand structure and coordination geometry
Tabthong, S; Nanok, T; Kongsaeree, P; Prabpai, S; Hormnirun, P
| HERO ID | 3539087 |
|---|---|
| In Press | No |
| Year | 2014 |
| Title | Monomethylaluminum and dimethylaluminum pyrrolylaldiminates for the ring-opening polymerization of rac-lactide: effects of ligand structure and coordination geometry |
| Authors | Tabthong, S; Nanok, T; Kongsaeree, P; Prabpai, S; Hormnirun, P |
| Journal | Dalton Transactions (Online) |
| Volume | 43 |
| Issue | 3 |
| Page Numbers | 1348-1359 |
| Abstract | Two series of aluminum alkyl complexes supported by pyrrolylaldiminate ligands, LAlMe2 (1a-7a) and L2AlMe (1b-7b), were successfully synthesized and characterized by NMR spectroscopy and elemental analysis. Reactions of trimethylaluminum with the corresponding pyrrolylaldiminate ligands in the molar ratios of 1 : 1 and 1 : 2 yielded dimethylaluminum pyrrolylaldiminates (1a-7a) and monomethylaluminum pyrrolylaldiminates (1b-7b), respectively, in good yields. The structure of 3b, determined by single-crystal X-ray diffraction, displayed a distorted trigonal bipyramidal geometry with the τ value of 0.65. Upon addition of 1 equivalent of benzyl alcohol, all complexes promoted the living ring-opening polymerization of rac-lactide with a good control over molecular weights and polydispersities. Complexes 6a and 7a were found to efficiently mediate the immortal polymerization in the presence of excess equivalents of benzyl alcohol (up to 5 equivalents), as evidenced by the narrow PDI values and the good agreement between the experimental M(n) values and monomer/benzyl alcohol ratios. The steric and electronic effects of the imine nitrogen substituents had a strong influence on the polymerization activities both in catalytic activity and polymer microstructure. The catalytic activity decreased as follows: 4-Me-C6H4 (3) > C6H5 (1) ≈ 4-F-C6H4 (2) ≈ 2-Me-C6H4 (5) > 4-OMe-C6H4 (4) ≫ 2-(t)Bu-C6H4 (6) > adamantyl (7). In comparison, the catalytic activity of the monomethylaluminum complex is slightly higher than that of the dimethylaluminum counterpart. The polymerization of rac-lactide by 6b yielded heterotactically enriched polylactide (P(r) = 0.60) whereas the isotactic-enriched polymer (P(m) = 0.74) was obtained from 7b. |
| Doi | 10.1039/c3dt52455h |
| Pmid | 24196719 |
| Wosid | WOS:000328654000048 |
| Is Certified Translation | No |
| Dupe Override | No |
| Comments | Scopus URL: https://www.scopus.com/inward/record.uri?eid=2-s2.0-84890503394&doi=10.1039%2fc3dt52455h&partnerID=40&md5=9347bab047d4eec408dfd1b52bf6d02c |
| Is Public | Yes |
| Language Text | English |