Synthesis and structure of amine-bridged bis(phenolate) lanthanide complexes and their application in the polymerization of ε-caprolactone

Abstract

A series of lanthanide complexes 1–8 were afforded by the amine elimination reactions of amine-bridged bis(phenols) H2L1–3 [L1–3 = Et2NCH2CH2N{CH2–(2-O–C6H2–R2-3–R1-5)2, R1 = tBu, R2 = tBu (L1); R1 = Me, R2 = tBu (L2); R1 = Me, R2 = Me (L3)] and H2L4–6 [L4–6 = CH3CH2CH2N{CH2–(2-O–C6H2–R2-3–R1-5)}2, R1 = tBu, R2 = tBu (L4); R1 = Me, R2 = tBu (L5); R1 = Me, R2 = Me (L6)] with Ln[N(SiMe3)2]3 (Ln = La, Gd). The bis(phenolate) lanthanide amides L1–6La[N(SiMe3)2] (1–6) were given by the reactions of La[N(SiMe3)2]3 with H2L1–6 in 1:1 M ration in THF. The bis(phenolate) lanthanide complexes Ln2[L6]3 (Ln = La (7), Ln = Gd (8)) were given by the reactions of Ln[N(SiMe3)2]3(Ln = La, Ga) with H2L6 in 2:3 M ratio in THF. Complexes 3 and 8 have been characterized by X-ray crystal structural analysis. The structure of complexes 3 reveals that it has unsolvated centrosymmetric dimer, built around a central, planar La2O2 ring. Complex 8 possesses a THF-solvated unsymmetric dimer. The coordination geometry in complexes 3 and 8 around each of the lanthanide metal atoms can be described as a distorted octahedron. The catalytic properties of complexes 1–6 on the ring-opening polymerization of ε-caprolactone have been studied. The results show that lanthanide amides complexes 1–6 are efficient catalysts for the ring-opening polymerization of ε-caprolactone.