Chiral diboranes as catalysts for the stereoselective organopolymerization of epoxides

Abstract

It is demonstrated that stereoselective polymerization of epoxides, long a domain of metal-based compounds, can also be achieved via the application of organocatalysts. A simple two-step synthesis starting from widely...

Rational Optimization of Bifunctional Organoboron Catalysts for Versatile Polyethers via Ring-Opening Polymerization of Epoxides

“…Though polyethers are extensively used, their synthetic processes still suffer from low catalytic efficiency, high consumption of energy, and metal residue contamination (Figure S1). The involved catalysts are mainly based on alkali metal derivatives (commonly potassium hydroxide), double metal cyanide complexes, and the Vandenberg catalyst. − In the past decades, organocatalysts have started to attract interest in organic and polymeric chemistry, as they are readily available and free of metal contaminants. − To date, a number of organocatalysts for polyether synthesis have been developed, such as tris­(perfluorophenyl)­borane, , triethylborane/Lewis base systems, phosphazenes, , and N-heterocycles. , Although great achievements have been made, searching for organic or metal-free catalysts that have combined advantages of cost-effectiveness, high reliability, and remarkable performances remains a subject of study.…”

Tailoring Rate and Temperature-Dependent Fracture of Polyether Networks with Organoaluminum Catalysts

“…More recently, Lynd and co-workers synthesized chelates of trialkylaluminum (AlR 3 ) with dialkylaminoethanol to attain control over the kinetics of polymerization, enabling synthesis of polyethers of narrow dispersity, well-defined molecular weight, and tailored end-group functionality. However, it is worth noting that Naumann, 7,8 Deffieux, 9 Coates, 10,11 and others 12 have attained similar control using a range of catalysts.…”

Borane catalysis for epoxide (co)polymerization

“…Indeed, using polycaprolactone or polylactide macroinitiators, it is possible to introduce blocks of it -PPO with high precision by the action of 11 or 12 (excess of borane functionalities relative to the organobase). 66 Such “polyester-first” strategies and related approaches are considered to be of great benefit for the preparation of tacticity-tuned polymeric additives and, as outlined above, cannot be realized by conventional means.…”

“…65 Chiral diborane catalysts now offer a first glimpse of what might be possible by using organocatalytic approaches. 66 While selectivity is still inferior to the best bimetallic catalysts, it is especially the combination of controlled polymerization, functional group tolerance and stereoselectivity which might render this strategy useful for future applications.…”

“…Also in 2022, the group of Naumann described organoboron catalysts for the stereoselective polymerization of rac-PO. 66 Inspired by the polymerization mechanism for epoxide homopolymerization (see above and Scheme 25), involving two equivalents of Et 3 B, and by the work of Du on chiral diboranes for hydrogenation reactions, 159 axially chiral backbones were used as linker structures. Starting from the well-available diol compounds (i.e., 1,1′-bi-2-naphthol, BINOL), a simple sequence of etherification followed by hydroboration yielded the corresponding diboranes 11 and 12.…”