Phosphagallenes (1 a/1 b) featuring double bonds between phosphorus and gallium were synthesized by reaction of (phosphanyl)phosphaketenes with the gallium carbenoid Ga(Nacnac) (Nacnac=HC[C(Me)N(2,6‐i‐Pr2C6H3)]2). The stability of these species is dependent on the saturation of the phosphanyl moiety. 1 a, which bears an unsaturated phosphanyl ring, rearranges in solution to yield a spirocyclic compound (2) which contains a P=P bond. The saturated variant 1 b is stable even at elevated temperatures. 1 b behaves as a frustrated Lewis pair capable of activation of H2 and forms a 1:1 adduct with CO2.
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.
Phosphagallenes (1 a/1 b) featuring double bonds between phosphorus and gallium were synthesized by reaction of (phosphanyl)phosphaketenes with the gallium carbenoid Ga(Nacnac) (Nacnac=HC[C(Me)N(2,6‐i‐Pr2C6H3)]2). The stability of these species is dependent on the saturation of the phosphanyl moiety. 1 a, which bears an unsaturated phosphanyl ring, rearranges in solution to yield a spirocyclic compound (2) which contains a P=P bond. The saturated variant 1 b is stable even at elevated temperatures. 1 b behaves as a frustrated Lewis pair capable of activation of H2 and forms a 1:1 adduct with CO2.
Research on using H-phosphonate diesters to introduce phosphorus functionality into molecules and polymers, some of which have medicinal applications, has recently attracted a lot of attention. Deuterium labelling to yield the corresponding D-phosphonate diesters, although desirable in order to help with the mechanistic elucidation of reactions containing H-phosphonate diesters, has been demonstrated to be a challenge. Deuterium exchange at Hphosphonate diesters using D 2 O, MeOD and ND 2 Bn has shown competitive behavior with hydrolysis, alcoholysis and aminolysis reactions, respectively. This facile substituent exchange for the addition of D 2 O and MeOD can be attributed to the similar energy required to eliminate ROH or H 2 O (ROD or HOD, R = iPr, Et, Me) from a pentavalent P(V) intermediate which is generated from axial delivery of an OD or OR group from D 2 O and MeOD, respectively. The trend in reaction rate for the exchange processes follows the order of R = Me > Et > iPr in (RO) 2 P(O)H and also depends on the nucleophilicity of the incoming group. Attempted synthesis of D-phosphonate diesters directly from PCl 3 and alcohols or via lithiation reactions further demonstrated just how sensitive the H/D-scrambling process is. These results have implications for the general reactivity of H-phosphonate diesters towards water, alcohol, and amines and their potential to selectively undergo substitution at either P-OR or P-H. Moreover, insight into the mechanism(s) of selective deuterium exchange, for example to give D-phosphonate diesters via the direct exchange of D for H, was illuminated through this research. at 101 MHz and are given in parts per million relative to CDCl 3 (δ = 77.0 ppm). Chemical shifts for 31 P NMR spectra are recorded at 161.97 MHz and given relative to external 85% phosphoric acid (δ = 0 ppm). Data are represented as follows: chemical shift, multiplicity (app = apparent, br = broad, s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet), coupling constants in Hertz (Hz), and integration.
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.
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