Diphosphorus is a high-temperature molecule having an electronic structure featuring a pair of reactive π bonds. In general, compounds that contain phosphorus-phosphorus π bonds are not isolable unless the reactive functional group is protected by sterically demanding blocking groups. Therefore, to access the chemistry of P2 under mild conditions, one must have a method for generating it “on demand” from some kind of precursor that can be activated by a convenient stimulus. The stable molecular form of the element phosphorus consists of tetrahedral P4 units, termed white phosphorus, and it has been suggested that UV irradiation of P4 can lead to photo-cracking into P2 units, an attractive process for generating diphosphorus that is thermally forbidden according to the Woodward-Hoffmann rules. The presentation will recount some examples from the literature indicating that diphosphorus may indeed be generated upon P4 irradiation. Our own investigations aimed at photochemical incorporation of P2 units into organic molecules will be described and contrasted with results obtained thermally using an anthracene-based P2 precursor. Finally, a quantum chemical investigation of P4 photochemistry will be discussed as revealing a plausible pathway for production of diphosphorus molecules following initial promotion of P4 to its first singlet excited state.

Irradiation of white phosphorus as a means to access the chemistry of diphosphorus

256th National Meeting (2018)

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