Sustainable Polyesters and Polycarbonates via ROP and ROCOP Catalyzed by Alkyl In(III) Complexes Containing Chiral Amino Alcohol Ligand

ABSTRACT A new series of optically pure dimeric In(III) complexes ( 1 – 3 ) incorporating bidentate chiral amino alcohol ligands were synthesized and comprehensively characterized using multiple analytical techniques. Single‐crystal x‐ray diffraction confirmed that complexes ( S,S )‐ 1 and ( R,R )‐ 1 adopt distorted square‐pyramidal geometries at the indium centers, whereas complex 2 contains one pentacoordinate and one tetracoordinated indium site, although spectroscopic studies indicated the presence of monomeric In(III) species in solution. These complexes displayed excellent catalytic activity in the ring‐opening polymerization (ROP) of rac ‐lactide ( rac ‐LA), affording isotactic‐enriched polylactide (PLA) ( P m = 0.60–0.65), with stereoregularity influenced by the ligand architecture. The ROP is proposed to proceed via an alkyl‐initiated coordination–insertion mechanism. In the ROCOP of cyclohexene oxide (CHO) with CO 2 , complexes 1 – 3 also exhibited catalytic activity (TOF ≈ 453 h − 1 ), producing isotactic‐enriched poly(cyclohexene carbonate) with moderate number‐average molecular weights ( M n ≈ 85.3 Kg·mol − 1 ) and narrow dispersities ( Đ ≈ 1.10–1.31). Kinetic and mechanistic investigations revealed that ROCOP is initiated by the alkyl group bound to the In(III) center and proceeds via a coordination–insertion pathway.