Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity

Understanding how to moderate and improve catalytic activity is critical to improving degradable polymer production. Here, di- and monozinc catalysts, coordinated by bis(imino)diphenylamido ligands, show remarkable activities and allow determination of the factors controlling performance. In most cases, the dizinc catalysts significantly outperform the monozinc analogs. Further, for the best dizinc catalyst, the ligand conformation controls activity: the catalyst with folded ligand conformation shows turnover frequency (TOF) values up to 60 000 h(-1) (0.1 mol% loading, 298 K, [LA]=1M), whilst that with a planar conformation is much slower, under similar conditions (TOF=30 h(-1)). Dizinc catalysts also perform very well under immortal conditions, showing improved control, and are able to tolerate loadings as low as 0.002 mol% whilst conserving high activity (TOF= 12500 h(-1)).