Amido rare-earth complexes supported by an ansa bis(amidinate) ligand with a rigid 1,8-naphthalene linker: synthesis, structures and catalytic activity in rac-lactide polymerization and hydrophosphonylation of carbonyl compounds

• Published in: New journal of chemistry 2015-01, Vol.39 (2), p.1083-1093
• Main Authors: Yakovenko, Marina V., Udilova, Natalia Yu, Glukhova, Tatyana A., Cherkasov, Anton V., Fukin, Georgy K., Trifonov, Alexander A.
• Format: Article
• Language: English
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/C4NJ01698J

A synthetic approach to rare-earth amido complexes coordinated by an ansa bis(amidinate) ligand with a 1,8-naphthalene linker was developed and allowed for the synthesis of a series of complexes [1,8-C 10 H 6 {NC( t Bu)N-2,6-Me 2 C 6 H 3 } 2 ]LnN(SiMe 3 ) 2 (THF) n (Ln = Y, n = 0 ( 2 ); Ln = Sm, n = 1 ( 3 ); Ln = Nd, n = 1 ( 4 )) in reasonable yields. Complexes 2–4 initiate ring-opening polymerization (ROP) of rac -lactide and enable complete conversion of 100–250 equiv. of monomer within 60–90 min at 25 °C. The obtained polylactides feature atactic structures and moderate molecular-weight distributions ( M w / M n = 1.30–2.12). The experimental M n values of the obtained polymers are found to be significantly higher than the calculated ones due to a slow initiation stage. Effective immortal ROP of lactide with 3–5 equiv. of isopropanol per metal center was performed using complexes 2–4 as the catalysts. The systems 2–4 /iPrOH exhibit higher activities in ROP and allow for complete conversion of 100–300 equiv. of rac -lactide to polymer within 30–60 min at 25 °C and provide a living polymerization mode and very narrow polydispersities ( M w / M n = 1.13–1.27). Complexes 2–4 as well as related borohydrides [1,8-C 10 H 6 {NC( t Bu)N-2,6-Me 2 C 6 H 3 } 2 ]Ln(BH 4 )(μ-BH 4 )Li(THF) 2 (Ln = Sm, Nd) catalyze hydrophosphonylation of aldehydes at room temperature with good reaction rates and hydrophosphonylation of benzylideneacetone at 65 °C.