Calcium complexes containing oxalamidinate ligands as catalysts for ε-caprolactone polymerization

Abstract

A series of calcium complexes containing oxalamidinate ligands is described. Reactions of oxalamidinate ligand precursors, [PhNC{NH(CH₂)₂OMe}–C{NH(CH₂)₂OMe}NPh] (1), [PhNC{NH(CH₂)₂NMe₂}–C{NH(CH₂)₂NMe₂}NPh] (2), [Ph^TriMeNC{NH(CH₂)₂OMe}–C{NH(CH₂)₂OMe}NPh^TriMe] (3), [Ph^TriMeNC{NH(CH₂)₂SMe}–C{NH(CH₂)₂SMe}NPh^TriMe] (4), [Ph^TriMeNC{NHCH₂Py}–C{NHCH₂Py}NPh^TriMe] (5), with two molar equivalents of Ca[N(SiMe₃)₂]₂(THF)₂ gave calcium oxalamidinate complexes, [Ca{N(SiMe₃)₂}(THF)(PhN)C{N(CH₂)₂OMe}–]₂ (6), [Ca{N(SiMe₃)₂}(THF)(PhN)C{N(CH₂)₂NMe₂}–]₂ (7), [Ca{N(SiMe₃)₂}(THF)(Ph^TriMeN)C{N(CH₂)₂OMe}–]₂ (8), [Ca{N(SiMe₃)₂}(THF)(Ph^TriMeN)C{N(CH₂)₂SMe}–]₂ (9), [Ca{N(SiMe₃)₂}(THF)(Ph^TriMeN)C{NCH₂Py}–]₂ (10), respectively. The molecular structure of complex 7 was further characterized by the single crystal X-ray diffraction technique. The catalytic activities of complexes 6–10 toward the ring opening polymerization of ε-caprolactone were studied. Complex 8 exhibited excellent activity for the polymerization of ε-caprolactone with controlled molecular weights and polydispersities.