Ligand Variations in New Sulfonamide-Supported Group 4 Ring-Opening Polymerization Catalysts

The synthesis, structures, and ring-opening polymerization (ROP) capability of a wide range of sulfonamide-supported group 4 amide, alkyl, and alkoxide complexes, varying in sulfonamide N-substituent, metal, coordination number, and geometry, are reported. Reaction of Ti(NMe2)4 or Ti(NMe2)2(OiPr)2 with MeOCH2CH2N(CH2CH2NHSO2Me)2 (12, H2N2MsNOMe) or PhCH2N(CH2CH2NHSO2R)2 (R = Tol (10, H2N2TsNPh) or Me (11, H2N2MsNPh)) afforded Ti(N2MsNOMe)(NMe2)2 (18), Ti(N2TsNPh)(NMe2)2 (19), Ti(N2MsNPh)(NMe2)2 (20), Ti(N2MsNOMe)(OiPr)2 (21), Ti(N2TsNPh)(OiPr)2 (22), Ti(N2MsNPh)(OiPr)2 (23), and Ti(N2TsNPh)(OiPr)(NMe2) (24). Reaction of N(CH2CH2NHSO2R)3 (R = Tol (13, H3N3TsN), Me (14, H3N3MsN), or ArF (15, H3N3ArFN, ArF = 3,5-C6H3(CF3)2)) with Zr(CH2SiMe3)4 formed Zr(N3RN)(CH2SiMe3) (R = Ts (30), Ms (31), or ArF (32)). Reaction of 15 with Zr(NMe2)4 gave Zr(N3ArFN)(NMe2) (33). Complexes 19, 21, 24, 30, 32, and 33 were crystallographically characterized. Monomeric six- or five-coordinate structures were found for the titanium complexes 19, 21, and 24, whereas the zirconium alkyls 30 and 32 were dimeric in the solid state with terminal and bridging κ2(N,O)-bound sulfonamides. Complexes 18−24 and 30−33, the previously reported Ti(CyN2R)(OiPr)2 (25 or 26; CyN2R = 1,2-C6H10(NSO2Tol)2 or 1,2-C6H10(NSO2Mes)2), and in situ generated isopropoxide initiators derived from 30−32 were investigated for the ROP of ε-caprolactone (ε-CL). The four-coordinate 25 was the most active, forming poly(ε-CL) with a relatively narrow PDI and well-controlled Mn. Compounds 22, 23, 25, and 26 and isopropoxides generated in situ from 30−32 were all active for the ROP of rac-lactide. Of these, the initiators based on Zr(N3RN)(CH2SiMe3) (30−32) with iPrOH co-initiator gave good activities and excellent PDIs (1.08−1.11) and agreement between measured and predicted Mn.