Phosphine–borane dehydrocoupling

Polymers, also referred to as plastics, have improved products in virtually every field. They are ubiquitous, found in items as varied as food packaging, transportation components, consumer electronics and biomedical devices.

The phosphine–borane dehydrogenation (or dehydrocoupling) reaction could be a route to exciting new polymer-based products. These materials are expected to include those that are elastomeric, fire retardant or scratch resistant. EU-funded scientists working on the project DEHYDROCOUPLE have elucidated important mechanistic pathways to spur exploitation.

Dehydrocoupling involves the coupling of two or more amine–borane addition products (adducts) accompanied by the release of molecular hydrogen. It is catalysed by a transition metal. Scientists studied all the steps and their chemistry through synthesis and investigation of catalytic species, reactants, intermediates and products.

Synthesis and study of a number of molecular fragments provided important insight into likely intermediates in the reaction. Of particular importance, the team identified the catalytic species involved in the first published report of the reaction using a rhodium-based catalyst. Scientists described the active species, product distributions and a suggested catalytic cycle in a published peer-reviewed article.

Building on this finding, researchers studied the detailed mechanistic pathway for the entire phosphine–borane dehydrocoupling reaction involving another phosphine–borane and a different rhodium-based catalyst. They identified for the first time the detailed thermodynamic and kinetic parameters, including the rate-limiting process and turnover-limiting process for catalysis.

The experiments, providing for the first time data on the phosphine–borane bond-forming events critical to dehydrocoupling of phosphine–boranes, were published in another peer-reviewed scientific journal. Final work on the rates of reaction produced new data currently being prepared for publication.

Along the way, the grant has supported career advancement of supported researchers through training, opportunities for mentorship, and presentations at meetings and conferences.

DEHYDROCOUPLE has made an important contribution to the vitally important field of polymers with detailed work on reactions leading to promising new compounds.