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

A series of calcium complexes containing oxalamidinate ligands is described. Reactions of oxalamidinate ligand precursors, [PhN[double bond, length as m-dash]C{NH(CH2)2OMe}–C{NH(CH2)2OMe}[double bond, length as m-dash]NPh] (1), [PhN[double bond, length as m-dash]C{NH(CH2)2NMe2}–C{NH(CH2)2NMe2}[double bond, length as m-dash]NPh] (2), [PhTriMeN[double bond, length as m-dash]C{NH(CH2)2OMe}–C{NH(CH2)2OMe}[double bond, length as m-dash]NPhTriMe] (3), [PhTriMeN[double bond, length as m-dash]C{NH(CH2)2SMe}–C{NH(CH2)2SMe}[double bond, length as m-dash]NPhTriMe] (4), [PhTriMeN[double bond, length as m-dash]C{NHCH2Py}–C{NHCH2Py}[double bond, length as m-dash]NPhTriMe] (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)(PhTriMeN)C{N(CH2)2OMe}–]2 (8), [Ca{N(SiMe3)2}(THF)(PhTriMeN)C{N(CH2)2SMe}–]2 (9), [Ca{N(SiMe3)2}(THF)(PhTriMeN)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