High‐Activity Organocatalysts for Polyether Synthesis via Intramolecular Ammonium Cation Assisted S_N2 Ring‐Opening Polymerization

Abstract

This manuscript describes a kind of bifunctional organocatalyst with unprecedented reactivity for the synthesis of polyethers via ring‐opening polymerization (ROP) of epoxides under mild conditions. The bifunctional catalyst incorporates two 9‐borabicyclo[3.3.1]nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site. The catalyst could be easily prepared in two steps from commercially available stocks on up to kilogram scale with ≈100 % yield. The organoboron catalyst mediated ROP of epoxides displays living behavior with low catalyst loading (5 ppm) and enables the synthesis of polyethers with molecular weights of over a million grams per mole (>106 g mol−1). Based on the investigations on crystal structure of catalyst, MALDI‐TOF, and 11B NMR spectroscopy, an intramolecular ammonium cation assisted SN2 mechanism is proposed and verified by DFT calculations.

Scalable, Durable, and Recyclable Metal‐Free Catalysts for Highly Efficient Conversion of CO2 to Cyclic Carbonates

“…The synthetic procedure of our bifunctional organoboron catalysts 1 a , 1 b , and 1 c are presented in Figure 1 A, wherein two‐step synthetic process with a nearly quantitative yield is applied [17, 18] . The reaction of amine and alkyl halide (or alkenyl halide) generated allyl‐containing quaternary ammonium salts, which sequentially produced the target catalysts 1 a , 1 b , and 1 c through the hydroboration reaction with borabicyclo[3.3.1]nonane (9‐BBN) via regioselective anti ‐Markovnikov syn ‐addition.…”

“…An efficiency of 5.0 kg CO 2 ‐polymer g −1 catalyst was achieved, which is the highest record achieved to date in all of homogeneous organic and metallic catalysts for the CHO/CO 2 coupling reaction. Interestingly, by adding one more alkylborane center into the catalyst structure, the binuclear boron compounds show unprecedented activity for ring‐opening polymerization of epoxides [18] . In addition, the synthetic procedure for these catalysts is extremely simple and efficient, the scalable preparation of these catalysts could be performed on a kilogram scale with nearly quantitative yield via two steps using commercially available stocks.…”

Scalable, Durable, and Recyclable Metal‐Free Catalysts for Highly Efficient Conversion of CO2 to Cyclic Carbonates

“…Thesynthetic procedure of our bifunctional organoboron catalysts 1a, 1b,and 1c are presented in Figure 1A,wherein two-step synthetic process with an early quantitative yield is applied. [17,18] Ther eaction of amine and alkyl halide (or alkenyl halide) generated allyl-containing quaternary ammonium salts,w hich sequentially produced the target catalysts 1a, 1b,a nd 1c through the hydroboration reaction with borabicyclo [3.3.1]nonane (9-BBN) via regioselective anti-Markovnikov syn-addition. Benefited from the simple operation and nearly quantitative yield, the catalysts can be prepared on > 1kgs cale as exemplified by 1c in Figure S1.…”

Organo-catalyzed/initiated ring opening co-polymerization of cyclic anhydrides and epoxides: an emerging story

“…36 DMAP (Figure 2), 37 N-heterocyclic olefins, 38 ammoniums, 39 organoboranes 40 ammonium functionalyzed boranes, 41 and NHCs 42 are also known to polymerize epoxides in a controlled manner. Figure 5 shows the monomers and organocatalytic/initiator systems for the ROCOP of cyclic anhydrides and epoxides discussed in this review.…”