P₂ acts like acetylene when it binds a single metal center

Since phosphorus is directly downstairs from nitrogen on the periodic table, chemists often consider diphosphorus to be a heavier analogue of dinitrogen. But when it binds in metal clusters, P₂ tends to act more like carbon-based acetylene. Researchers now have an explanation for why this happens. Joshua Figueroa and team at the University of California San Diego, the University of Rochester, and the Ohio State University have captured the crystal structure (shown) of a single iron atom bound to a P₂ ligand. The structure reveals that the ligand binds the metal from its side, as acetylene does, forming a triangle among the three atoms. This contrasts with just one of the two atoms binding the metal from the end, as N₂ would do (Science, 2022 DOI: 10.1126/science.abn7100). By studying this crystal structure, the team found that P₂ is electronically similar to double-bonded C complexes in how it binds to a single iron atom. N₂’s end-on binding means that a lone electron pair from only one of the two N atoms associates with the metal. Through orbital analysis of the crystal structure, the team showed that the pi bonding electrons of P₂ interact with the metal center instead, so that both P atoms participate in bonding with Fe. Figueroa presented this work March 22 in a session of the Inorganic Chemistry Division at ACS Spring 2022, a meeting of the American Chemical Society.