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 [Li 2L1(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-H 2) with nBuLi in toluene or THF yields Li 2(L2-H)2] (7) and [Li2(L 2-H)2(THF)2] (8), respectively. Further treatment of 7 with 2 mol equiv of benzyl alcohol provides [Li 2(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 species; however, complex 4 shows a mononuclear feature. A p-π interaction exists from the phenyl ring of the 2-(methyl-1-phenylethyl) groups to the central metal in complexes 2, 4, and 6, which could effectively stabilize the metal center. Among them, complexes 1, 2, and 5-9 displayed efficient catalytic behavior for the ring-opening polymerization of L-lactide in the presence of benzyl alcohol. Experimental results indicate that among these alkali-metal complexes, the sodium compound 6 displays a rapid catalytic polymerization of L-lactide in "living" fashion, yielding poly(L-lactide) with a controlled molecular weight and narrow polydispersity indices for a wide range of monomer-to-initiator ratios.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry