Contrasting E−H Bond Activation Pathways of a Phosphanyl‐Phosphagallene

Abstract

The reactivity of the phosphanyl‐phosphagallene, [H2C{N(Dipp)}]2PP=Ga(Nacnac) (Nacnac=HC[C(Me)N(Dipp)]2; Dipp=2,6‐iPr2C6H3) 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−Hδ+), 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 NH2iPr 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−Hδ−), 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.

Thermoneutral N−H Bond Activation of Ammonia by a Geometrically Constrained Phosphine

“…[3j,n] Main group species offer an attractive alternative to precious metals due to their higher crustal abundance, lower toxicity (in most cases) and reduced tendency to form unreactive ammonia adducts. While numerous examples of oxidative addition of N À H bonds to main group species have been reported over the last decade, [4][5][6][7] NÀH bond splitting of ammonia still poses a significant challenge and reversible activation of this indispensable nitrogen feedstock close to thermoneutrality remains unprecedented in all of molecular chemistry.…”

“…B(C 6 F 5 ) 3 , C 6 D 6 , 16 h, 258C; Molecular structure of 3 (B) and 4 (C) in the solid state (thermal ellipsoids set at the 50 % probability level); hydrogen atoms omitted for clarity. Selected bond lengths [] and angles [8]: 3 P1-N1 1.667(2), P1-N2 1.700(2), P1-S1 2.1263(10), P1-Se1 2.0643(7); N1-P1-N2 93.05(12), N1-P1-S1 115.74(9), N2-P1-S1 95.59(9); 4 P1-N1 1.6793(16), P1-N2 1.7126(15), P1-S1 2.1181(6), P1-B1 2.0823(19); N1-P1-N2 93.80(8), N1-P1-S1 116.62(6), N2-P1-S1 93.35(5) [9].…”