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

The reactivity of the phosphanyl-phosphagallene, [H2C{N(Dipp)}](2)PP=Ga(Nacnac) (Nacnac=HC[C(Me)N(Dipp)](2); Dipp=2,6-(Pr2C6H3)-Pr-i) 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 (E delta--H delta+), 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 (NH2Pr)-Pr-i and ammonia can react via a second, higher energy, pathway resulting in the hydroamination of the Ga=P bond. By contrast, with hydridic reagents (E delta+-H delta-), 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.