Arylamide-Ligated Scandium Bis(alkyl) Complexes in the Ring-Opening Polymerization of Trimethylene Carbonate: Comparing the Reactivity of Mono- Versus Dinuclear Complexes

Abstract Compared with mononuclear catalysts, dinuclear catalysts often exhibit synergistic effects between their two metal centers, offering unique advantages in enhancing catalytic performance. In this work, an alkyl elimination strategy was employed to synthesize novel arylamido mono- and dinuclear scandium bis(alkyl) complexes. The phenyl-bridged arylamido ancillary ligands (2,6-iPr2C6H3)NH(C6H4)NH(C6H3-2,6-iPr2) (HL1) and [4,4′-(2,6-iPr2C6H3NH)2][C6H4]2 (HL2) were reacted with Sc(CH2SiMe3)3(THF)2 in a 1:2 molar ratio in THF, yielding the corresponding dinuclear complexes [1,4-(2,6-iPr2C6H3N)2(C6H4)][Sc(CH2SiMe3)3(THF)]2 (1) and [4,4′-(2,6-iPr2C6H3N)2(C6H4)2][Sc(CH2SiMe3)2(THF)2]2 (2). To investigate the differences in polymerization performance between mononuclear and dinuclear complexes, the mononuclear arylamido scandium bis(alkyl) complex [(2,6-iPr2C6H3)N(C6H5)]Sc(CH2SiMe3)2(THF) (3) was prepared by reacting (2,6-iPr2C6H3)NH(C6H5) (HL3) with Sc(CH2SiMe3)3(THF)2 in a 1:1 molar ratio in hexane. All complexes were characterized by NMR spectroscopy and elemental analysis. Furthermore, the molecular structures of complexes 1 and 2 were unambiguously determined by single-crystal X-ray diffraction. All complexes were able to initiate the ring-opening polymerization (ROP) of trimethylene carbonate (TMC) with high activity under mild conditions. Compared to the mononuclear complex 3, complex 1 displayed a distinct dinuclear synergistic effect on TMC polymerization. Complex 1 enabled the ROP of TMC in a molecular-weight-controllable manner, allowing for the synthesis of high-molecular-weight PTMC (Mn > 105 g/mol) by tuning the monomer-to-initiator molar ratio.