Earth-abundant nickel-catalyzed carbonylative polymerization of olefins offers a cost-effective alternative to conventional precious palladium catalysis, but the homogeneous nature of this catalyst causes severe reactor fouling that precludes industrial application. Herein, we report the first heterogeneous nickel-catalyzed carbonylative polymerization based on immobilization of a phosphine-sulfonate nickel complex onto silica. The supported nickel catalyst exhibits high activity and enhanced thermal stability, enabling production of polyketones with markedly increased molecular weight while virtually eliminating fouling (as low as 3%), and affording a high bulk density of 0.23 g mL−1. Remarkably, it yields polyketones with exclusive α-phase and unique flower-like morphology composed of interstacked petals, in stark contrast to the disordered porous β-phase obtained with homogeneous catalysis. The system also tolerates carbonylative polymerization with propylene or 1-hexene while preserving morphological control. This work represents a pioneering study in heterogeneous nickel-catalyzed carbonylative polymerization of ethylene, thus establishing the industrial practicability of nickel-based polyketone resin and fiber products.
Isotactic poly(propylene oxide) (iPPO) is a semicrystalline polyether that has emerged as a high-strength, photodegradable material for marine applications. To improve the accessibility of iPPO, catalysts with higher activity and selectivity are required. Using rational catalyst design informed by computational insights, we developed a flexibly tethered, bimetallic chromium catalyst exhibiting high enantioselectivity (k rel ∼ 100) and unprecedented activity (TOF ∼ 50,000 h–1) for propylene oxide (PO) polymerization. Mechanistic studies reveal that high enantioselectivity originates from increased steric bulk at the ortho position of the salicylimine moiety, which increases steric repulsion between the alkoxide chain end and the ligand in the disfavored transition state. Furthermore, introducing geminal dimethyl groups that rigidify the flexible tether between the two ligand moieties significantly enhances catalyst activity by destabilizing the resting state during polymerization. The catalyst remains active at loadings as low as 0.5 ppm, enabling the synthesis of colorless, tough iPPO.
Bai-Hao Ren, Bryce M Lipinski, L. S. Morris et al.· Journal of the American Chem...· 0 citations
