Trapping an Elusive Phosphanyl-Phosphaalumene

We describe our efforts to access a compound with an Al=P double bond by reaction of Al(Nacnac) towards [H₂CN(Dipp)]₂P(PCO) (Nacnac=HC[C(Me)N(Dipp)]₂; Dipp=2,6-ⁱPr₂C₆H₃). Our observations are consistent with the formation of a transient phosphanyl-phosphaalumene at low temperatures (-70 °C), however this species was found to readily undergo intramolecular C-H activation of the β-diketiminato ligand upon warming to room temperature. The reactivity of the transient complex toward small molecules including dihydrogen, carbon dioxide, phosphaketenes, amines and silanes could be explored at low temperatures, showcasing that the target compound can react as both a frustrated Lewis pair (via the pendant phosphanyl moiety) or in hydroelementation reactions of the Al=P bond. The elusive target molecule could be trapped by addition of a Lewis base (tetrahydrofuran) affording an isolable molecular species that reacts in an analogous fashion to the base-free compound.