Reactivity of a Gallium(I) Carbenoid towards Silylated Isomers of the 2-Phosphaethynolate Ion

The reaction of a silylated phosphaketene, iPr3SiPCO, toward the gallium(I) carbenoid Ga(DippNacNac) (DippNacNac = HC[C(Me)N(Dipp)]2; Dipp = diisopropylphenyl) is described. The resultant product is a four-membered heterocycle which is generated via a transient phosphagallene (DippNacNac)Ga═PSiiPr3. This intermediate goes on to react with a further equivalent of iPr3SiPCO to generate the observed heterocycle. The mechanism of formation of this compound was probed by in situ NMR and IR measurements and is supported by Density Functional Theory (DFT) calculations. In order to determine whether the heterocyclic product can act as a masked phosphagallene, its reactivity toward carbon dioxide, iPr3SiPCO, white phosphorus and water was explored. In all cases, the reactions proceeded through cleavage of one of the Ga–P bonds of the four-membered heterocycle resulting in ring-expanded or ring-opened products.