To B-E or not to B-E? Developing New Boranes and Boration Reactions

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The addition of boron-element (B-E, where E = H, B, Si, etc) bonds to unsaturated compounds constitutes a family of remarkably important reactions in organic synthesis for the production of new compounds for the pharmaceutical and agricultural industries. Reactions of B-E where E is a heavier main group elements (E = silicon, germanium, etc) usually result in organodimetalloid compounds which are highly versatile building blocks that are otherwise difficult to synthesize. Given the intensity of interest in this area it is somewhat surprising that relatively little is known about the analogous addition chemistry of compounds containing single B-E bonds where E is either sulfur (S), selenium (Se), or phosphorus (P). To address this limitation in boron chemistry, this proposal will focus on expanding the scope and chemistry of relatively unknown B-E (E = P, S, Se) compounds. For instance, we have recently reported a new phosphinoboronate ester (Ph2PBpin, pin = pinacolato) that can be used as a platform for the synthesis of a wide range of new compounds. Likewise, we have prepared new starting materials containing discrete B-S and B-Se bonds and propose to further investigate their addition chemistry. The first project in this study will be to generate additional B-E (E = P, S, Se) compounds, where we can electronically and sterically vary the groups on the boron atom and/or the main group element. A variety of substrates will be examined in addition reactions to assess the efficacy of these simple new boron-main group compounds. New reagents will also be investigated for their ability to react with aldehydes (and ketones) already containing a phosphide (PR2) or sulfide group (SR). The resulting products will be examined for their potential to add to metals that can be used as catalysts. We have also found that Ph2PBpin adds to phenylacetylene (PhCCH) in the presence of a metal catalyst to give an unusual 1,1-addition product. We will expand the scope of this reaction by varying the alkynes and the catalysts to see if we can generate different products. The 1,1-addition products in these reactions will subsequently be investigated as ambiphilic (containing a donor and acceptor group) ligands for transition metals. Finally, while significant advances have been made in catalytic boration chemistry, the full potential of these reagents in organic synthesis is not yet close to being realized. Finally, we propose to investigate these new B-E species for their use in the borylformylation of alkynes. The related hydroformylation is one of the most important catalytic reactions in industry today. The last project may be challenging but it has the potential to generate novel chemical reactions. As always, this work will be used to attract, and train, the next generation of Wild Toad (the name of our group) researchers who will hopefully make a considerable impact in Canadian science, technology, medicine and education.