Christopher "Kit" Cummins
Massachusetts Institute of Technology
Phosphorus-Element Bond-Forming Reactions: Application to Strained Molecules and Multiple Bonds
Phosphinidene group transfer to olefins is an ideal route to three-membered rings containing phosphorus (phosphiranes), these being versatile building blocks in organophosphorus chemistry. To be described is a catalytic version of this reaction, with a simple iron organometallic complex as the catalyst or precatalyst. Styrenes undergo the phosphiranation reaction in good yield, and the resulting phosphiranes are stable enough to be purified by distillation. Keeping in mind the notion of a phosphinidenoid key intermediate, with a role analogous to that of a carbenoid in cyclopropanation, we designed a route to tri-tert-butyl phosphatetrahedrane. The strain of this molecule will be put into a context of the full series of mixed phosphorus-carbon tetrahedranes. Some of its ring-opening and ensuing cycloaddition reactions will be described. All of the described chemistry benefits from the use of anthracene as a benign, neutral leaving group. We recently extended this methodology to the synthesis of a PN molecular precursor. PN is a triply bonded diatomic molecule that is metastable due to a strong propensity to polymerize, and was the first phosphorus-containing molecule detected in the interstellar medium. Our PN molecular precursor is shown to decompose explosively upon mild heating as a solid, and it has a thirty minute half life in solution at room temperature. The new molecular precursor is also a PN transfer reagent, as it undergoes reaction with an organometallic iron complex cation to install a PN ligand, to be compared with the corresponding dinitrogen complex of the same system.