B(C6F5)3-based Lewis pair-catalyzed acrylate polymerization: Lewis base effects on pairing interactions

Acrylate polymerizations catalyzed by Lewis pairs (LP) composed of B(C6F5)3 and various Lewis bases (phosphines, amines, and an N-heterocyclic carbene) in dichloromethane were investigated using two procedures based on different monomer/catalyst addition sequences. In procedure 1, Lewis bases were added to B(C6F5)3-activated n-butyl acrylate (nBA), and the polymerization proceeded quantitatively using all Lewis bases at a wide temperature range (−60 °C to 30 °C). A low nucleophilic Lewis base Et3N also initiated the polymerization even at −60 °C. However, t-butyl acrylate was not polymerized, as LP promoted its conversion into acrylic acid and isobutene. In procedure 2, nBA was added to interacting LPs; the type of Lewis base significantly affected the polymerization results. Specifically, polymerization was not observed when 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and PnBu3 were applied; however, similar to the reaction in procedure 1, PPh3, PtBu3, and 1,4-diazabicyclo[2.2.2]octane (DABCO) initiated nBA polymerization. The pairing interactions between LBs/B(C6F5)3 (PPh3, Et3N, DBU, and DABCO) were investigated using the shift of 19F nuclear magnetic resonance signals, demonstrating that weak interacting LPs efficiently initiated the polymerizations in procedure 2.