Synthesis and Structural Studies of Lithium and Sodium Complexes with OOO-Tridentate Bis(phenolate) Ligands: Effective Catalysts for the Ring-Opening Polymerization of L-Lactide

A series of lithium and sodium complexes with OOO-tridentate bis(phenolate) ligands have been synthesized and fully characterized. The reaction of 2,2′-dihydroxy-3,3′,5,5′-tetrakis[(1-methyl-1-phenyl)ethyl]dibenzyl ether (L1-H2) with different ratios of nBuLi in toluene or tetrahydrofuran (THF) gave [Li2(L1-H)2] (1), [Li4L12] (2), and [Li2L1(THF)3] (3), respectively. Similarly, [Na(L1-H)(THF)] (4), [Na2(L1-H)]2 (5), and [Na4L12] (6) were prepared by the reaction of L1-H2 and NaN[Si(CH3)3]2 or sodium metal. In addition, the reaction of 2,2′-dihydroxy-3,3′,5,5′-tetra-tert-butyldibenzyl ether (L2-H2) with nBuLi in toluene or THF yields Li2(L2-H)2] (7) and [Li2(L2-H)2(THF)2] (8), respectively. Further treatment of 7 with 2 mol equiv of benzyl alcohol provides [Li2(L2-H)2(BnOH)2] (9). Complexes 1−4 and 6−9 have been structurally characterized by single-crystal X-ray analysis. The dinuclear nature of complexes 1 and 3 was confirmed from their molecular structure. Complexes 2 and 6 illustrate tetranuclear specie...