Mechanism-Inspired Upgradation of Phosphonium-Containing Organoboron Catalysts for Epoxide-Involved Copolymerization and Homopolymerization

The dynamic Lewis multicore system (DLMCS) which integrates
the
Lewis acidic boron center(s) and an ammonium salt in one molecule
has shown good catalytic performance in polymer synthesis. Inspired
by the insightful intramolecular ammonium cation assisted mechanism,
herein, we communicated a superior organoboron system by replacing
a nitrogen atom with a phosphorus atom. The upgraded mono-, di-, and
trinuclear organoboron catalysts show significantly improved catalytic
performance and heat resistance for versatile epoxide-involved transformations,
including ring-opening copolymerization of epoxides and cyclic anhydrides,
copolymerization of CO2 and epoxides, and ring-opening
polymerization of epoxides. 11B NMR, single-crystal X-ray
diffraction, and DFT results imply that the replacing nitrogen with
phosphorus in an onium cation led to an effective epoxide activation
and nucleophilic attack of the counterion on the activated epoxide,
which remarkably shortened the initiation period and accelerated chain
expansion, resulting in the obvious improvement of the activity. The
upgraded phosphonium-containing organoboron system combined with the
mechanism study and insightful understanding would be instructive
in designing advanced metal-free catalysts.