Indium Complexes Supported by 1,ω-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 = CH2SiMe3, n = 0, 4; L = 1,4-dithiabutanediylbis{4,6-di(2-phenyl-2-propyl)phenolato} (etccp), R = CH2SiMe3, n = 0, 5) were prepared from indium trichloride or from the corresponding tris(alkyl) complexes and 1 equiv of tetradentate 1,ω-dithiaalkanediyl-bridged bis(phenol) LH2. 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)(CH2SiMe3)] (4), and [In(etccp)(CH2SiMe3)] (5). Pseudo-octahedral configuration was found for 2, while square pyramidal structure was observed for 4 and 5. The isopropoxy complexes [In(L)(OiPr)] (L = etbbp, 6; etccp, 7) were synthesized starting with indium tris(isopropoxide). Complex 6 crystallized as homochiral dimer of pseudo-octahedral fragments with bridging μ2-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 (Mw/Mn = 1.03−1.18).