Sulfonamide-Supported Group 4 Catalysts for the Ring-Opening Polymerization of ε-Caprolactone and <i>rac</i>-Lactide

Abstract

Reaction of RCH2N(CH2CH2NHSO2Tol)2 (R = 2-NC5H4 (8, H2Lpy) or MeOCH2 (9, H2LOMe)) with Ti(NMe2)4 at room temperature afforded Ti(Lpy)(NMe2)2 (10) or Ti(LOMe)(NMe2)2 (11), respectively, which contain tetradentate bis(sulfonamide)amine ligands. The corresponding reactions with Ti(OiPr)4 or Zr(OiPr)4·HOiPr required more forcing conditions to form the homologous bis(isopropoxide) analogues, M(LR)(OiPr)2 (M = Ti, R = py (12) or OMe (14); M = Zr, R = py (13) or OMe (15)). Reaction of Ti(NMe2)2(OiPr)2 with H2LR formed 12 or 14 under milder conditions. The X-ray structures of 10−15 have been determined revealing Cs symmetric, 6-coordinate complexes except for 13 which is 7-coordinate with one κ2(N,O) bound sulfonamide donor. Compounds 10− 15 are all catalysts for the ring-opening polymerization (ROP) of ε-caprolactone, with the isopropoxide compounds being the fastest and best controlled, especially in the case of zirconium. In addition, Zr(LOMe)(OiPr) 2 (15) was an efficient catalyst for the well-controlled ROP of rac-lactide both in toluene at 100 °C and in the melt at 130 °C, giving atactic poly(rac-lactide). The polymerization rates and control achieved for 13 and 15 are comparable to those of the well-established bis(phenolate)amine-supported Group 4 systems reported recently