Indium complexes supported by 1,omega-dithiaalkanediyl-bridged bis(phenolato) ligands: synthesis, structure, and controlled ring-opening polymerization of L-lactide.

Indium bis(phenolato) complexes [In(L)R(THF)(n)] (L = 1,4-dithiabutanediylbis(4,6-di-tert-butylphenolato) (etbbp), R = Cl, n = 0, 1; L = 1,3-dithiapropanediylbis(6-tert-butyl-4-methylphenolato) (mtbmp), R = Me, n = 1, 2; L = 1,4-dithiabutanediyl-bis(6-tert-butyl-4-methyl-phenolato) (etbmp), R = Me, n = 0, 3; L = etbbp, R = CH(2)SiMe(3), n = 0, 4; L = 1,4-dithiabutanediylbis{4,6-di(2-phenyl-2-propyl)phenolato} (etccp), R = CH(2)SiMe(3), n = 0, 5) were prepared from indium trichloride or from the corresponding tris(alkyl) complexes and 1 equiv of tetradentate 1,omega-dithiaalkanediyl-bridged bis(phenol) LH(2). The monomeric nature of the alkyl indium complexes was shown by X-ray diffraction studies of the complexes [In(mtbmp)Me(THF)] (2), [In(etbbp)(CH(2)SiMe(3))] (4), and [In(etccp)(CH(2)SiMe(3))] (5). Pseudo-octahedral configuration was found for 2, while square pyramidal structure was observed for 4 and 5. The isopropoxy complexes [In(L)(O(i)Pr)] (L = etbbp, 6; etccp, 7) were synthesized starting with indium tris(isopropoxide). Complex 6 crystallized as homochiral dimer of pseudo-octahedral fragments with bridging mu(2)-alkoxide ligands, but in solution two diastereomers were observed. The isopropoxy complexes efficiently initiated the ring-opening polymerization of L-lactide in toluene to give isotactic poly(L-lactides) with narrow molecular weight distribution (M(w)/M(n) = 1.03-1.18).