Transition-metal-free approaches to poly(aminoboranes) and poly(phosphinoboranes): mechanisms, advances, and future directions

Abstract

Poly(aminoboranes) and poly(phosphinoboranes) have been of interest as inorganic analogues of poly(olefins) as early as the mid-20th century. However, their synthesis was only realised about 15 and 25 years ago, respectively. Initially, poly(aminoboranes) and poly(phosphinoboranes) were accessed via transition-metal-catalysed dehydropolymerisation of amine- and phosphine-borane adducts. Despite the many advances made using this method, limitations remained, particularly in the conditions required for dehydropolymerisation and in the design of effective catalysts for producing materials with controlled molar mass and specific polymer architectures. Accordingly, new routes to these materials were sought through the synthesis of reactive aminoboranes or phosphinoboranes generated in situ for subsequent polymerisation. In doing so, materials that were previously inaccessible by metal-mediated dehydropolymerisation were unlocked. Mechanistically, there are fundamental differences between the transition-metal-catalysed approaches and transition-metal-free reactions with reactive monomers, and it is the understanding and research of these new mechanisms that are the foundation for the development of new polymer syntheses that allow for new polymer designs. This review article discusses the new design principles and polymer synthetic concepts.