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Sterically constrained tricyclic phosphine: redox behaviour, reductive and oxidative cleavage of P–C bonds, generation of a dilithium phosphaindole as a promising synthon in phosphine chemistry.

Sterically constrained tricyclic phosphines with annulated five- and six-membered rings show fascinating chemical and redox reactivity as indicated by sophisticated in situ UV-vis CV and multi-pulse chronoamperometry. The data suggested a highly negative reduction potential with the reversible formation of a dianionic species. Accordingly, the constrained tricyclic phosphines react with two equivalents of Li/naphthalene by reductive cleavage of a P–C bond of one of the PC₄ heterocycles. The resulting dilithium compound represents a phosphaindole derivative with annulated aromatic C₆ and PC₄ rings. It is an interesting starting material for the synthesis of new heterocyclic molecules. More information can be found in the Edge article by W. Uhl and  J. J. Weigand  (DOI: 10.1039/D0SC06155G)