Y3+ and Nd3+ Complexes Coordinated by ansa-Bis(amidinate) Ligands. Synthesis, Structural Features, and Catalytic Performance in Ring-Opening Polymerization of rac-Lactide and ε-Caprolactone

The reaction of equimolar amounts of disodium derivative of ansa-bis(amidine) (L1Na2) (L1 = [C6H4-1,2-{NC(But)N(2,6-Me2C6H3)}2]2–) with [YCl2(N(SiMe3)2)] affords the tris(amidinate) complex Y{κ4-L1}{κ2-Lamd} (2) (Lamd = ((2,6-Me2C6H3N)2CBut)–). For the bulkier analogue the reactions of L2Na2 (L2 = [C6H4-1,2-{NC(But)N(2,6-Pri2C6H3)}2]2–) with [LnCl2(N(SiMe3)2)] (Ln = Y, Nd) led to the formation of ionic compounds [Na(DME)3][Nd{κ3-L2}{κ2-L2}] (3) and [Na(DME)3][Y{κ3-L2}2] (4) featuring different types of coordination of ansa-bis(amidinate) ligands. Complexes 2–4 proved to be efficient catalysts for rac-lactide polymerization. Complexes 3 and 4 in the presence of PriOH allow to perform controlled polymerization and obtaining PLAs with molecular weights close to the theoretical ones. Complexes 2–4 are also active in ε-caprolactone polymerization achieving full conversion of up to 500 equivalents of ε-CL in 1–10 min giving polycaprolactone samples characterized by high Mn (34.9–542.0 × 103) and somewhat broaden molecular weight distribution Mw/Mn = 1.31–2.61.