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

摘要

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-C10H6{NC(tBu)N-2,6-Me2C6H3}(2)]LnN(SiMe3)(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 degrees 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 degrees 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-C10H6{NC(tBu)N-2,6-Me2C6H3}(2)]Ln(BH4)(mu-BH4)Li(THF)(2) (Ln = Sm, Nd) catalyze hydrophosphonylation of aldehydes at room temperature with good reaction rates and hydrophosphonylation of benzylideneacetone at 65 degrees C.