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=C{NH(CH2)2OMe}-C{NH(CH2)2OMe}=NPh] (1), [PhN=C{NH(CH2)2NMe2}-C{NH(CH2)2NMe2}=NPh] (2), [Ph(TriMe)N=C{NH(CH2)2OMe}-C{NH(CH2)2OMe}=NPh(TriMe)] (3), [Ph(TriMe)N=C{NH(CH2)2SMe}-C{NH(CH2)2SMe}=NPh(TriMe)] (4), [Ph(TriMe)N=C{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(TriMe)N)C{N(CH2)2OMe}-]2 (8), [Ca{N(SiMe3)2}(THF)(Ph(TriMe)N)C{N(CH2)2SMe}-]2 (9), [Ca{N(SiMe3)2}(THF)(Ph(TriMe)N)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.