Enhancement on Alternating Copolymerization of Carbon Monoxide and Styrene by Dibenzobarrelene-Based α‑Diimine Palladium Catalysts

CO/styrene
copolymerization by α-diimine palladium catalysts
is a promising method for direct synthesis of polyketones. The effect
of the catalyst backbone structure on CO/styrene copolymerization
has been studied with the aim of developing robust α-diimine
palladium catalysts able to improve the polymerization productivity
and controllability. Dibenzobarrelene derived α-diimine palladium
catalysts without o-aryl substituents were designed
and synthesized for CO/styrene alternating copolymerization. Introduction
of the rigid and bulky dibenzobarrelene backbone enhanced the thermal
stability and the productivity of palladium catalyst. The dibenzobarrelene
ligand backbone also improved the polymerization controllability,
and living CO/styrene copolymerizations were achieved at 15 °C
using α-diimine palladium catalysts in CH2Cl2. The steric hindrance of backbone and the π–π
stacking between the dibenzobarrelene backbone and the aniline played
crucial roles in stereocontrol and productivity.