Christopher Cummins, Massachusetts Institute of Technology

Henry Dreyfus Professor of Chemistry

Massachusetts Institute of Technology

Phi Lambda Upsilon Chemistry Honorary and C. Eugene Bennett Department of Chemistry

New Chemistry for Phosphorus Sustainability (March 20, 4:30 pm, 208 Clark Hall)

Abstract: Phosphorus, a chemical element essential for life, is presently obtained from mining operations as the mineral apatite, which contains phosphorus in its fully oxidized form referred to as “phosphate”. This raw material is a key feedstock for the fertilizer industry, underpinning global agriculture. At the same time, more than 75% of world reserves are concentrated in one place: Morocco. Agricultural runoff following precipitation events leads to phosphorus pollution of marine ecosystems, generating blooms of marine algae that choke off oxygen from other marine life. Industrialized nations have increasingly stringent regulations requiring waste water discharged into the environment to be below government mandated phosphate concentrations. This mandate for phosphate removal from waste waters represents a potentially new and valuable input stream of phosphate for the fertilizer industry, an alternative to using raw materials from an extractive industry. At the same time, the economically important phosphorus chemicals industry uses a legacy starting point of phosphate reduction to toxic, pyrophoric elemental “white” phosphorus. Paradoxically, this is followed by oxidation, often using environmentally hazardous chlorine, before finally arriving at value-added chemicals that usually contain no chlorine. This wasteful and energy intensive approach stands to be improved. New chemistry for connecting the dots between phosphate and value-added chemicals will be described, with the objective to make white phosphorus obsolete and disrupt the phosphorus chemicals industry. We will show how this might be interfaced with new developments in biotechnology to make possible the use of phosphate alternatives in agriculture, thereby mitigating or eliminating the problem of marine algae blooms (eutrophication).

Synthons for Reactive Intermediates and Group Transfer Reactions: Phosphinidenes and PN (March 21, 4:30 pm, 208 Clark Hall)

Abstract: Three-membered ring compounds are valuable building blocks in synthetic chemistry. Epoxides, aziridines, and cyclopropanes are available from alkenes via transition-metal catalyzed oxygen atom, nitrene group, or carbene transfer reactions. Each of these iconic alkene functionalization reactions requires a source of the oxygen, nitrene, or carbene, such as respectively iodosylbenzene, organic azides, or diazoalkanes. To date, the lack of a similar reaction for phosphinidene transfer to alkenes to afford the corresponding three-membered ring PC₂ compounds, phosphiranes, can be ascribed to the absence of a suitable phosphinidene source. In the present work we show that RPA (A = C₁₄H₁₀ or anthracene) compounds are suitable phosphinidene sources for a reaction that can be catalyzed by the simple Fp₂ dimer, where Fp = CpFe(CO)₂. The Fp-catalyzed reaction is successful for styrenic olefins, or ones possessing electron-withdrawing substituents. Another catalytic reaction has been discovered that leverages the highly strained phosphatetrahedrane P(Ct-Bu)₃ as the phosphinidene source. The latter reaction, which is nickel-catalyzed, proceeds at room temperature and is successful for unactivated alkenes, including ethylene. Time permitting, the synthesis and reactivity of a PN synthon, azidophosphine N₃PA, will be discussed.