Contrasting E-H Bond Activation Pathways of a Phosphanyl-Phosphagallene

The reactivity of the phosphanyl-phosphagallene, [H₂ C{N(Dipp)}]₂ PP=Ga(Nacnac) (Nacnac=HC[C(Me)N(Dipp)]₂ ; Dipp=2,6-ⁱ Pr₂ C₆ H₃ ) towards a series of reagents possessing E-H bonds (primary amines, ammonia, water, phenylacetylene, phenylphosphine, and phenylsilane) is reported. Two contrasting reaction pathways are observed, determined by the polarity of the E-H bonds of the substrates. In the case of protic reagents (^δ- E-H^δ+ ), a frustrated Lewis pair type of mechanism is operational at room temperature, in which the gallium metal centre acts as a Lewis acid and the pendant phosphanyl moiety deprotonates the substrates. Interestingly, at elevated temperatures both NH₂ ⁱ Pr and ammonia can react via a second, higher energy, pathway resulting in the hydroamination of the Ga=P bond. By contrast, with hydridic reagents (^δ+ E-H^δ- ), such as phenylsilane, hydroelementation of the Ga=P bond is exclusively observed, in line with the polarisation of the Si-H and Ga=P bonds.